FR3123155A3 - Intelligent battery pack for energy-efficient and connected mobility - Google Patents
Intelligent battery pack for energy-efficient and connected mobility Download PDFInfo
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- FR3123155A3 FR3123155A3 FR2204877A FR2204877A FR3123155A3 FR 3123155 A3 FR3123155 A3 FR 3123155A3 FR 2204877 A FR2204877 A FR 2204877A FR 2204877 A FR2204877 A FR 2204877A FR 3123155 A3 FR3123155 A3 FR 3123155A3
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- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
- B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
- B60L58/18—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules
- B60L58/22—Balancing the charge of battery modules
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L50/00—Electric propulsion with power supplied within the vehicle
- B60L50/50—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells
- B60L50/60—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells using power supplied by batteries
- B60L50/64—Constructional details of batteries specially adapted for electric vehicles
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
- B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
- B60L58/24—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries for controlling the temperature of batteries
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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- H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/60—Heating or cooling; Temperature control
- H01M10/62—Heating or cooling; Temperature control specially adapted for specific applications
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- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
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- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- General Chemical & Material Sciences (AREA)
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Abstract
Un bloc-batterie intelligent pour une mobilité écoénergétique et connectée pour un système de propulsion électrique d’un véhicule électrique comprenant : un microcontrôleur multicœurs lockstep couplé à une alimentation électrique sûre ; un bloc-batterie comprenant des modules de cellule ; des relais configurés pour commuter des connexions de contacteur ; un système de gestion thermique de batterie ; et un module de communication à courte/longue portée. Le bloc-batterie intelligent est conçu pour surveiller des tensions de cellule pour : réaliser un équilibrage de tension de cellule ; et/ou réaliser des mesures de tension en circuit ouvert pour un réétalonnage d’état de charge. Le bloc-batterie intelligent est conçu pour surveiller la circulation de courant pour : éviter l’emballement thermique causé par une circulation de courant au-dessus des limites opérationnelles ; et/ou effectuer un comptage ampères/heures pour une estimation d’état de charge. Le bloc-batterie intelligent étant conçu en outre pour : surveiller la tension et la température dans différents modes de fonctionnement de véhicule pour protéger la cellule contre la dégradation ; mesurer le courant de batterie et la tension de bloc et calculer l’état de charge ; commander le contacteur de batterie ; et fournir un mécanisme d’équilibrage des cellules. A smart battery pack for energy-efficient and connected mobility for an electric vehicle electric propulsion system comprising: a multi-core lockstep microcontroller coupled to a safe power supply; a battery pack including cell modules; relays configured to switch contactor connections; a battery thermal management system; and a short/long range communication module. The smart battery pack is designed to monitor cell voltages to: perform cell voltage balancing; and/or perform open circuit voltage measurements for state of charge recalibration. The Intelligent Battery Pack is designed to monitor current flow to: prevent thermal runaway caused by current flow above operational limits; and/or perform Amp-Hour metering for a state of charge estimate. The smart battery pack being further designed to: monitor voltage and temperature in various vehicle operating modes to protect the cell from degradation; measure battery current and block voltage and calculate state of charge; control the battery contactor; and provide a cell balancing mechanism.
Description
The present invention relates, in general, to the automotive field and the powertrain domain, in particular to energy efficient and connected vehicles, specifically electric propulsion vehicles,i.e.having electric motor.The present invention relates, in general, to the automotive field and the powertrain domain, in particular to energy efficient and connected vehicles, specifically electric propulsion vehicles, ie having electric motor.
The present invention may be advantageously applied in any type of road vehicle, either used for transporting people, such as e-scooters, e-motorbikes, cars, buses, campers,etcetera, or for transporting wares, such as industrial vehicles (trucks, tractor trailer,etcetera) or light or medium-heavy commercial vehicles (such as vans,etcetera).The present invention may be advantageously applied in any type of road vehicle, either used for transporting people, such as e-scooters, e-motorbikes, cars, buses, campers, etcetera , or for transporting wares, such as industrial vehicles (trucks, tractor trailer, etcetera ) or light or medium-heavy commercial vehicles (such as vans, etcetera ).
Furthermore, the present invention may be advantageously applied for industrial applications enabling second life applications.Furthermore, the present invention may be advantageously applied for industrial applications enabling second life applications.
State of the ArtState of the Art
As is known, large-scale electrification of road transportation sector is crucial to mitigate the environmental impact in the urban areas. However, high manufacturing cost of battery packs and consequently EVs (Electric Vehicles) has been identified as a major block.As is known, large-scale electrification of road transportation sector is crucial to mitigate the environmental impact in the urban areas. However, high manufacturing cost of battery packs and consequently EVs (Electric Vehicles) has been identified as a major block.
It is known that thermal management system design and battery packaging design have the largest effect on modularity of battery packs. Hence, implementing modular architectures would make the battery packs easily scalable, thus allowing OEMs (Original Equipment Manufacturers) to target cross-platform technologies and justify bulk production of battery packs.It is known that thermal management system design and battery packaging design have the largest effect on modularity of battery packs. Hence, implementing modular architectures would make the battery packs easily scalable, thus allowing OEMs (Original Equipment Manufacturers) to target cross-platform technologies and justify bulk production of battery packs.
In order to improve the operative dependability of the battery pack, active balancing structures and advanced state-of-health based optimization algorithm should be developed. More generally the switch array of the battery pack must be able to isolate a failed cell and be dynamically reconfigurable. The implementation of modern wireless communication technologies between cells and the main battery monitoring systems allows getting rid of the wiring harness that reduces the reliability and the scalability of the battery pack.In order to improve the operative dependability of the battery pack, active balancing structures and advanced state-of-health based optimization algorithm should be developed. More generally the switch array of the battery pack must be able to isolate a failed cell and be dynamically reconfigurable. The implementation of modern wireless communication technologies between cells and the main battery monitoring systems allows getting rid of the wiring harness that reduces the reliability and the scalability of the battery pack.
In addition to manufacturing costs, safe operation of Li-ion traction batteries in electric cars is one of the main requirements for a broad acceptance of this technology. Safety critical factors such as over-temperature conditions must be reliably monitored and captured. Increasingly strict safety regulations in the automotive sector imply rising challenges to both car manufacturers and battery system suppliers and hence resilient, reliable yet inexpensive methods for battery state diagnosis are necessary to address these topics.In addition to manufacturing costs, safe operation of Li-ion traction batteries in electric cars is one of the main requirements for a broad acceptance of this technology. Safety critical factors such as over-temperature conditions must be reliably monitored and captured. Increasingly strict safety regulations in the automotive sector imply rising challenges to both car manufacturers and battery system suppliers and hence resilient, reliable yet inexpensive methods for battery state diagnosis are necessary to address these topics.
Object and Summary of the InventionObject and Summary of the Invention
In view of the foregoing, the Applicant has felt the need to improve current electric vehicles, thereby arriving at the present invention.In view of the foregoing, the Applicant has felt the need to improve current electric vehicles, thereby arriving at the present invention.
According to the present invention, a smart battery pack for energy efficient and connected mobility is provided, according to the appended set of claims.According to the present invention, a smart battery pack for energy efficient and connected mobility is provided, according to the appended set of claims.
Brief Description of the DrawingsBrief Description of the Drawings
Description of the Preferred Embodiments of the InventionDescription of the Preferred Embodiments of the Invention
The present invention will now be described in detail with reference to the attached figures to allow a skilled person to make and use it. Various modifications to the embodiments described will be immediately apparent to skilled person and the generic principles described can be applied to other embodiments and applications without thereby departing from the scope of the present invention, as defined in the attached claims. Therefore, the present invention should not be considered limited to the embodiments described and illustrated herein, but should be accorded the broadest scope of protection consistent with the described and claimed features.The present invention will now be described in detail with reference to the attached figures to allow a skilled person to make and use it. Various modifications to the embodiments described will be immediately apparent to skilled person and the generic principles described can be applied to other embodiments and applications without thereby departing from the scope of the present invention, as defined in the attached claims. Therefore, the present invention should not be considered limited to the embodiments described and illustrated herein, but should be granted the broadest scope of protection consistent with the described and claimed features.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning commonly used by persons of ordinary experience in the field pertaining to the present invention. In the event of a conflict, this description, including the definitions provided, will be binding. Furthermore, the examples are provided for illustrative purposes only and as such should not be regarded as limiting.Unless otherwise defined, all technical and scientific terms used herein have the same meaning commonly used by persons of ordinary experience in the field pertaining to the present invention. In the event of a conflict, this description, including the definitions provided, will be binding. Furthermore, the examples are provided for illustrative purposes only and as such should not be regarded as limiting.
In particular, the block diagrams included in the attached figures and described below are not intended as a representation of the structural characteristics, or constructive limitations, but must be interpreted as a representation of functional characteristics,i.e.intrinsic properties of the devices and defined by the effects obtained or functional limitations and which can be implemented in different ways, therefore in order to protect the functionality of the same (possibility of functioning).In particular, the block diagrams included in the attached figures and described below are not intended as a representation of the structural characteristics, or constructive limitations, but must be interpreted as a representation of functional characteristics, ie intrinsic properties of the devices and defined by the effects obtained or functional limitations and which can be implemented in different ways, therefore in order to protect the functionality of the same (possibility of functioning).
In order to facilitate the understanding of the embodiments described herein, reference will be made to some specific embodiments and a specific language will be used to describe them. The terminology used herein has the purpose of describing only particular embodiments, and is not intended to limit the scope of the present invention.In order to facilitate the understanding of the embodiments described herein, reference will be made to some specific embodiments and a specific language will be used to describe them. The terminology used herein has the purpose of describing only particular embodiments, and is not intended to limit the scope of the present invention.
The proposed approach is an innovative method based on Electrochemical Impedance Spectroscopy (EIS) which can be successfully integrated into a battery management system because it requires very limited HW (hardware) resources and processing capabilities, thus overcoming the main issues which prevented so far the large diffusion of the EIS methodology in the automotive. Consequently, the state of health of the battery pack can be estimated and prognostic monitoring can be implemented.The proposed approach is an innovative method based on Electrochemical Impedance Spectroscopy (EIS) which can be successfully integrated into a battery management system because it requires very limited HW (hardware) resources and processing capabilities, thus overcoming the main issues which prevented so far the large dissemination of the EIS methodology in the automotive. Consequently, the state of health of the battery pack can be estimated and prognostic monitoring can be implemented.
Due to the presence of high voltage Li-ion batteries, the hazards involved in the vehicle such as electric shock, thermal event and toxic gas release are typical threads. Here functional safety plays a very important role to design a battery pack and mitigate those hazards to make it a trouble free system.Due to the presence of high voltage Li-ion batteries, the hazards involved in the vehicle such as electric shock, thermal event and toxic gas release are typical threads. Here functional safety plays a very important role to design a battery pack and mitigate those hazards to make it a trouble free system.
Finally, the capability of the battery pack to communicate both short and long range is the ultimate essence of its smartness, since it allows to share the most relevant data regarding the status of the battery remotely and being easily located in the case of the rapidly growing battery swapping business model.Finally, the capability of the battery pack to communicate both short and long range is the ultimate essence of its smartness, since it allows to share the most relevant data regarding the status of the battery remotely and being easily located in the case of the rapidly growing battery swapping business model.
The novelty of the present invention lies in providing an unprecedented functional integration level in a very compact smart battery pack, as summarized herein below:The novelty of the present invention lies in providing an unprecedented functional integration level in a very compact smart battery pack, as summarized herein below:
- safety architecture based on multi-core lockstep microcontroller and safe power supply (Safety Element out of Context - SEooC);safety architecture based on multi-core lockstep microcontroller and safe power supply (Safety Element out of Context - SEooC);
- real-time diagnosis and safety mechanisms to prevent critical failures;real-time diagnosis and safety mechanisms to prevent critical failures;
- real-time prognostic and health monitoring functionality based on artificial intelligence technique;real-time prognostic and health monitoring functionality based on artificial intelligence technique;
- remaining time until the end of useful life estimation based on artificial intelligence technique;remaining time until the end of useful life estimation based on artificial intelligence technique;
- safe and redundant control of the high voltage contactors;safe and redundant control of the high voltage contactors;
- dynamic reconfigurable architecture for active balancing and failed cells isolation based on array of switches;dynamic reconfigurable architecture for active balancing and failed cells isolation based on array of switches;
- wireless communication between cells;wireless communication between cells;
- innovative solution to implement EIS with reduced HW/SW (software) resources;innovative solution to implement EIS with reduced HW/SW (software) resources;
- integrated GPS module for system localization; andintegrated GPS module for system localization; and
- integrated module for short and long range communication.integrated module for short and long range communication.
The proposed Smart Battery Pack (SBP) relies on smart cell modules, being able to control the insertion of the cell, perform a distributed monitoring of both the State Of Charge (SOC) and the State Of Health (SOH) and record useful data at a cell level. The main controller is designed to collect the states of each cell and perform the balancing algorithm. Communication ensures the data exchange between the individual slaves and the master (the main controller) and provides the control signals for the cells.The proposed Smart Battery Pack (SBP) relies on smart cell modules, being able to control the insertion of the cell, perform a distributed monitoring of both the State Of Charge (SOC) and the State Of Health (SOH) and record useful data at at cell level. The main controller is designed to collect the states of each cell and perform the balancing algorithm. Communication ensures the data exchange between the individual slaves and the master (the main controller) and provides the control signals for the cells.
This solution allows for complexity reduction, simplified manufacturing, easier maintenance, and more environmentally friendly recycling due to the absence of huge amounts of cables needed for communication. Furthermore, the proposed solution is easy to scale up and it can boost second-life battery applications, such as Renewable Energy Storage Systems (RESS). It is widely known that in EV applications batteries that reach 80% of the nominal capacity are considered to be at the end of life; however, these batteries can be adopted in applications where the size of the battery pack is not so important. Moreover, thanks to the recorded data at a cell level, an easier management of the battery pack composed by second-life batteries is achieved.This solution allows for complexity reduction, simplified manufacturing, easier maintenance, and more environmentally friendly recycling due to the absence of huge amounts of cables needed for communication. Furthermore, the proposed solution is easy to scale up and it can boost second-life battery applications, such as Renewable Energy Storage Systems (RESS). It is widely known that in EV applications batteries that reach 80% of the nominal capacity are considered to be at the end of life; however, these batteries can be adopted in applications where the size of the battery pack is not so important. Moreover, thanks to the recorded data at a cell level, an easier management of the battery pack composed by second-life batteries is achieved.
The integration of the abovementioned features into a single package, hosting the different electronic control modules, will guarantee a safe behavior of the system in case of faults and will be able to provide remotely details about the health status/localization both for improved maintenance and battery swapping business model.The integration of the abovementioned features into a single package, hosting the different electronic control modules, will guarantee a safe behavior of the system in case of faults and will be able to provide remotely details about the health status/localization both for improved maintenance and battery business model swapping.
The development of specific interfaces allows for a high level of scalability of the proposed architecture. This makes possible to generate a complete family of smart battery packs for electro-mobility, by simply integrating the sub-units to use, without changing the architecture.The development of specific interfaces allows for a high level of scalability of the proposed architecture. This makes possible to generate a complete family of smart battery packs for electro-mobility, by simply integrating the sub-units to use, without changing the architecture.
The system architecture, currently available at the time of filing the patent, is shown in
The SBP is designed to perform different functions, such as electrical management, safety management, communication, improving battery usage efficiency and lifetime. These tasks are distributed among different sub-modules of the SBP, clearly shown in the block diagram.The SBP is designed to perform different functions, such as electrical management, safety management, communication, improving battery usage efficiency and lifetime. These tasks are distributed among different sub-modules of the SBP, clearly shown in the block diagram.
The SBP is based on a sort of modular/master-slave architecture: Battery Measurement Modules (BMMs) are separated from the main PCB (e.g.main microcontroller, power supply, communication,etcetera) and are placed close to the battery modules, thus reducing the wiring complexity. The BMMs then transfer the cell parameter measurements to the main PCB via a communication interface. Thus, in contrast to the centralized BMS (Battery Management System) topology, the main PCB of the present SBP is connected indirectly to the individual cells in a modular arrangement.The SBP is based on a sort of modular/master-slave architecture: Battery Measurement Modules (BMMs) are separated from the main PCB ( eg main microcontroller, power supply, communication, etcetera ) and are placed close to the battery modules, thus reducing the wiring complexity. The BMMs then transfer the cell parameter measurements to the main PCB via a communication interface. Thus, in contrast to the centralized BMS (Battery Management System) topology, the main PCB of the present SBP is indirectly connected to the individual cells in a modular arrangement.
As shown in
Furthermore, the present SBP is designed such that cell balancing is homogenizing the series-connected cell voltages in the battery pack. Cells in a battery pack could age differently compared to one another. An aged cell would reach minimum or maximum limits of operation earlier than a less-aged cell for discharging or charging respectively. In the presence of unevenly aged cells in a battery pack, the useable capacity of the whole battery pack is reduced. The SBP monitors the voltage across all the cells in the battery pack. The SBP detects and reacts to monitored cell-voltages crossing the minimum or maximum operational limits specified by the cell manufacturer. Additionally, monitoring cell-voltages would support the SBP to perform other functionalities, such as:Furthermore, the present SBP is designed such that cell balancing is homogenizing the series-connected cell voltages in the battery pack. Cells in a battery pack could age differently compared to one another. An aged cell would reach minimum or maximum limits of operation earlier than a less-aged cell for discharging or charging respectively. In the presence of unevenly aged cells in a battery pack, the useable capacity of the whole battery pack is reduced. The SBP monitors the voltage across all the cells in the battery pack. The SBP detects and reacts to monitored cell-voltages crossing the minimum or maximum operational limits specified by the cell manufacturer. Additionally, monitoring cell-voltages would support the SBP to perform other functionalities, such as:
- perform cell voltage balancing; andperform cell voltage balancing; and
- perform Open-Circuit Voltage (OCV) measurements for SOC (System-on-a-Chip) recalibration.perform Open-Circuit Voltage (OCV) measurements for SOC (System-on-a-Chip) recalibration.
If cells are not operated under specified cell voltage limits, this could lead to cell degradation and accelerated aging. The SBP integrates a dynamically configurable array of power switches in order to implement the energy balancing of the cells and to isolate failed cells.If cells are not operated under specified cell voltage limits, this could lead to cell degradation and accelerated aging. The SBP integrates aally dynamic configurable array of power switches in order to implement the energy balancing of the cells and to isolate failed cells.
In addition, since wireless communication represents a significant breakthrough that offers the potential for improved reliability, lower cost and reduced wiring complexity for large multi-cell battery stacks. In particular each cell module is interconnected via a wireless connection instead of a wired technology (e.g.CAN or an isoSPI twisted pair). SmartMesh networking offers a truly redundant interconnect system through its use of both path and frequency diversity to route wireless messages around obstacles and to mitigate interference. The wireless mesh network enables the flexible placement of battery modules, and makes possible the installation of sensors in locations previously unsuitable for a wiring harness.In addition, since wireless communication represents a significant breakthrough that offers the potential for improved reliability, lower cost and reduced wiring complexity for large multi-cell battery stacks. In particular each cell module is interconnected via a wireless connection instead of a wired technology ( eg CAN or an isoSPI twisted pair). SmartMesh networking offers a truly redundant interconnect system through its use of both path and frequency diversity to route wireless messages around obstacles and to mitigate interference. The wireless mesh network enables the flexible placement of battery modules, and makes possible the installation of sensors in locations previously unsuitable for a wiring harness.
Furthermore, monitoring the status and controlling the switching of the high voltage battery pack contactors is one of the critical tasks of the SBP, failure of which may lead to electric shock or other safety hazards. For safety reasons, the battery pack should completely disconnect itself to external charge and discharge electrical connections, in case of battery safety parameters are violated. The switching of contactors connection with load shall be achieved through relays which should be of ‘normally-open’ type. This is because, if the SBP contactor switching losses power due to any failure, then the contactor terminals are automatically de-energized, and the pack is disconnected from the load. Reverse-polarity connection can occur in circumstances such as installation of a new battery, reconnection of the original battery after repairs etc. The BMS according to the present invention is designed to be able to detect a reverse polarity connection whenever the battery contactors are closed, before supplying the connected load.Furthermore, monitoring the status and controlling the switching of the high voltage battery pack contactors is one of the critical tasks of the SBP, failure of which may lead to electric shock or other safety hazards. For safety reasons, the battery pack should completely disconnect itself to external charge and discharge electrical connections, in case of battery safety parameters are violated. The switching of contactors connection with load shall be achieved through relays which should be of ‘normally-open’ type. This is because, if the SBP contactor switching power losses due to any failure, then the contactor terminals are automatically de-energized, and the pack is disconnected from the load. Reverse-polarity connection can occur in circumstances such as installation of a new battery, reconnection of the original battery after repairs etc. The BMS according to the present invention is designed to be able to detect a reverse polarity connection whenever the battery contactors are closed, before supplying the connected load.
The SBP is designed to continuously monitor the temperatures of critical points of the cells. According to the size of the system, the battery pack could be provided with a thermal management system: in this case the SBP can either actuate thermal management system control or send a ‘cooling/ heating’ request to the concerned system. This can help the cells to be operated within the allowed cell temperature limits stated in the cell data sheet, and avoid thermal runaway.The SBP is designed to continuously monitor the temperatures of critical points of the cells. According to the size of the system, the battery pack could be provided with a thermal management system: in this case the SBP can either actuate thermal management system control or send a ‘cooling/ heating’ request to the concerned system. This can help the cells to be operated within the allowed cell temperature limits stated in the cell data sheet, and avoid thermal runaway.
The SBP is configured to monitor the current flowing through the battery pack and the voltage across it. The SBP detects and reacts to the charging or discharging current flowing through the cells crossing the maximum operational limits specified by the cell manufacturer. Additionally, monitoring the current flow would support the SBP to perform other functionalities such as,The SBP is configured to monitor the current flowing through the battery pack and the voltage across it. The SBP detects and reacts to the charging or discharging current flowing through the cells crossing the maximum operational limits specified by the cell manufacturer. Additionally, monitoring the current flow would support the SBP to perform other functionalities such as,
- avoiding thermal runaway caused by current flow above operational limits; andavoiding thermal runaway caused by current flow above operational limits; and
- ampere/hour counting for SOC estimation.ampere/hour counting for SOC estimation.
The SBP further integrates a short/long range communication module to communicate both to nomadic devices and to remote service center. Consequently, the SBP can be easily located, also thanks to the integrated GPS module, and can provide details about SOH, SOC and, more generally, data useful for system maintenance. Concerning wired communication, the SBP is compliant with the recommended protocols, such as BraodR-Reach, CAN/CAN FD, isoSPI.The SBP further integrates a short/long range communication module to communicate both to nomadic devices and to remote service center. Consequently, the SBP can be easily located, also thanks to the integrated GPS module, and can provide details about SOH, SOC and, more generally, data useful for system maintenance. Concerning wired communication, the SBP is compliant with the recommended protocols, such as BraodR-Reach, CAN/CAN FD, isoSPI.
In addition, the SBP accomplishes several tasks which are relevant from the functional safety viewpoint:In addition, the SBP accomplishes several tasks which are relevant from the functional safety viewpoint:
- monitor the voltage and temperature in different vehicle operating mode and take necessary action to protect the cell from the degradation;monitor the voltage and temperature in different vehicle operating mode and take necessary action to protect the cell from the degradation;
- measure battery current and pack voltage and calculate SOC;measure battery current and pack voltage and calculate SOC;
- control the battery contactor based on different condition (e.g.isolation failure, low SOC, etcetera); andcontrol the battery contactor based on different condition ( eg isolation failure, low SOC, etcetera); and
- provide cell balancing mechanism to equate all the cell in same voltage level.provide cell balancing mechanism to equate all the cell in same voltage level.
In the following, a method for state of health estimation in automotive battery packs is described.In the following, a method for state of health estimation in automotive battery packs is described.
The battery packs of hybrid and electric vehicles (HEV and EV respectively) are made of a series of low-voltage battery elements, in order to reach the desired target voltage. Each battery element can be an elementary battery cell, or several battery cells connected in parallel to provide the desired current capability. For the sake of simplicity, in the following a battery pack composed byNelementary battery cells connected in series will be considered.The battery packs of hybrid and electric vehicles (HEV and EV respectively) are made of a series of low-voltage battery elements, in order to reach the desired target voltage. Each battery element can be an elementary battery cell, or several battery cells connected in parallel to provide the desired current capability. For the sake of simplicity, in the following a battery pack composed by N elementary battery cells connected in series will be considered.
The battery pack is still the most critical element in HEVs/EVs, mainly due to:The battery pack is still the most critical element in HEVs/EVs, mainly due to:
- the asSOCiated cost;the associated cost;
- the limitation in terms of range; andthe limitation in terms of range; and
- the reliability and life-time.the reliability and life-time.
It is worthy to note that either the degradation or the failure of a single battery cell will drastically affect the functionality of the entire battery pack. Therefore it is vital to identify as soon as possible, well before a failure happens, if any degradation of the single battery cells would take place. Consequently, it can be safely replaced at service while the car it is still functional. The same information may be used to assess the remaining driving range.It is worthy to note that either the degradation or the failure of a single battery cell will drastically affect the functionality of the entire battery pack. Therefore it is vital to identify as soon as possible, well before a failure happens, if any degradation of the single battery cells would take place. Consequently, it can be safely replaced at service while the car it is still functional. The same information may be used to assess the remaining driving range.
Several techniques can be found in literature to assess the State of Heath (SoH) of a battery pack; in particular, techniques based on EIS (Electrochemical Impedance Spectroscopy) can be used to analyse the drift of the impedance curve of the battery cells as they are wearing out and approaching to failure. The main disadvantages of the EIS techniques are related to their relevant asSOCiated costs, both for the generation of the stimulus, which must be provided to the battery pack, and for the signal acquisition and data processing of the cell’s electric parameters.Several techniques can be found in the literature to assess the State of Heath (SoH) of a battery pack; in particular, techniques based on EIS (Electrochemical Impedance Spectroscopy) can be used to analyze the drift of the impedance curve of the battery cells as they are wearing out and approaching to failure. The main disadvantages of the EIS techniques are related to their relevant asSOCIated costs, both for the generation of the stimulus, which must be provided to the battery pack, and for the signal acquisition and data processing of the cell's electric parameters.
A simpler and cost-effective method, that will be described hereafter, arises from a careful observation of electrical parameter both in faulty cells and other ones which are approaching failures. In fact, what is initially affected, under the above mentioned conditions, is the real part of the impedance’s cell in the low frequency range with particular respect to DC condition. Therefore, an accurate measurement of the resistance in DC (DCR) of each cell of the pack, is an effective and easy way to assess its SoH. It is well known that, for an healthy battery cell, its DCR has a strong dependency on cell temperature, State of Charge (SOC), and aging of the cell itself; instead a battery cell with a bad SoH (i.e.damaged or approaching to failure) will exhibit an abnormal DCR:A simpler and cost-effective method, that will be described hereafter, arises from a careful observation of electrical parameter both in faulty cells and other ones which are approaching failures. In fact, what is initially affected, under the above mentioned conditions, is the real part of the impedance's cell in the low frequency range with particular respect to DC condition. Therefore, an accurate measurement of the resistance in DC (DCR) of each cell of the pack, is an effective and easy way to assess its SoH. It is well known that, for a healthy battery cell, its DCR has a strong dependency on cell temperature, State of Charge (SOC), and aging of the cell itself; instead a battery cell with a bad SoH ( ie damaged or approaching to failure) will exhibit an abnormal DCR:
where T is temperature and Ncyclesis an effective index for aging (i.e.equivalent complete charge/discharge cycles).where T is temperature and N cycles is an effective index for aging ( ie equivalent complete charge/discharge cycles).
It is noted that the SoH estimation system is particularly useful when it is installed in the electric/hybrid vehicle, to allow an almost continuous monitoring of the battery health status. Therefore, the system shall be small in size, light in weight, cost effective, reliable, energy efficient and shall satisfy all automotive requirements. Unlike other techniques found in literature, the proposed methodology allows to satisfy all the above mentioned requirements.It is noted that the SoH estimation system is particularly useful when it is installed in the electric/hybrid vehicle, to allow an almost continuous monitoring of the battery health status. Therefore, the system shall be small in size, light in weight, cost effective, reliable, energy efficient and shall satisfy all automotive requirements. Unlike other techniques found in literature, the proposed methodology allows to satisfy all the above mentioned requirements.
Another important novelty, resulting from the proposed methodology, is the capability to assess SoH while the car is running unlike other methods which can be used only when the vehicle is turned off. Then the main advantage is the capability to detect the onset of parametric drift and potential failures in the shortest possible time.Another important novelty, resulting from the proposed methodology, is the capability to assess SoH while the car is running unlike other methods which can be used only when the vehicle is turned off. Then the main advantage is the capability to detect the onset of parametric drift and potential failures in the shortest possible time.
The DCR of a battery cell can be measured driving a constant current step of defined amplitude ΔI into the cell (in charge or discharge direction) and measuring the resulting voltage variation ΔV at the cell terminals after a predefined amount of time (e.g.the typical order of magnitude could be between 5 s and 10 s to reach the steady state). The DCR can be easily calculated as the ratio between the voltage and current variations:The DCR of a battery cell can be measured driving a constant current step of defined amplitude ΔI into the cell (in charge or discharge direction) and measuring the resulting voltage variation ΔV at the cell terminals after a predefined amount of time ( eg the typical order of magnitude could be between 5 s and 10 s to reach the steady state). The DCR can be easily calculated as the ratio between the voltage and current variations:
DCR = ΔV/ΔIDCR = ΔV/ΔI
Since the nominal DCR values of typical automotive battery cell is in the range of few mΩ (e.g. from 1mΩ to 10mΩ), a proper HW shall be provided in order to measure accurately the very small ΔV voltage variations (few mV or less) that can be obtained forcing a relatively small current step into the battery cell. An implementation of the measurement HW will be described in the following paragraphs.Since the nominal DCR values of typical automotive battery cell is in the range of few mΩ (e.g. from 1mΩ to 10mΩ), a proper HW shall be provided in order to measure accurately the very small ΔV voltage variations (few mV or less) that can be obtained forcing a relatively small current step into the battery cell. An implementation of the HW measurement will be described in the following paragraphs.
Regarding the SoH, different methods can be adopted to estimate the SoH of the battery cells from DCR measurementsRegarding the SoH, different methods can be adopted to estimate the SoH of the battery cells from DCR measurements
According to a first method, SoH can be estimated comparing the actual DCR measurement to the characterization DCR data for the specific type of battery cells adopted in the pack, in the same operating conditions. DCR characterization data are usually available in table form, at different SOC, different temperatures, and different aging, but only for healthy battery cells (apart from the effect of aging, since characterization data shall be measured in steady state condition only, thus wherein all electrical and chemical transients shall be extinguished before measuring the characterization data). A deviation of the measured DCR of a specific battery cell from the reference resistance value is an indication that the cell itself is approaching a failure, and therefore its SoH can be assessed. This technique requires the availability of a big amount of characterization data, usually obtained by means of a large measurement campaign at different SOCs, temperatures and aging conditions.According to a first method, SoH can be estimated comparing the actual DCR measurement to the characterization DCR data for the specific type of battery cells adopted in the pack, in the same operating conditions. DCR characterization data are usually available in table form, at different SOC, different temperatures, and different aging, but only for healthy battery cells (apart from the effect of aging, since characterization data shall be measured in steady state condition only, thus including all electrical and chemical transients shall be extinguished before measuring the characterization data). A deviation of the measured DCR of a specific battery cell from the reference resistance value is an indication that the cell itself is approaching a failure, and therefore its SoH can be assessed. This technique requires the availability of a large amount of characterization data, usually obtained by means of a large measurement campaign at different SOCs, temperatures and aging conditions.
For the best accuracy, DCR measurements shall be done only in steady state conditions, after some relaxation time after vehicle stop, when all chemical reactions and thermal transient are settle down. Moreover, a “small” current step shall be used to measure DCR, in order to avoid altering the chemical equilibrium of the battery cell. This aspect is particularly important in order to prevent major chemical transient phenomena, while operating the battery in a “linear” region (i.e.in such operating conditions that the battery cell can be represented by a linear model). It is further pointed out that an accurate measurement of the ΔV is rather critical for a proper DCR estimation and SoH assessment, due to the small ΔV (e.g.in the range of 100µV to 10mV) produced by the current flow into the battery DCR (e.g.in the range of 100mA to 1A).For the best accuracy, DCR measurements shall be done only in steady state conditions, after some relaxation time after vehicle stop, when all chemical reactions and thermal transient are settle down. Moreover, a “small” current step shall be used to measure DCR, in order to avoid altering the chemical equilibrium of the battery cell. This aspect is particularly important in order to prevent major chemical transient phenomena, while operating the battery in a “linear” region ( ie in such operating conditions that the battery cell can be represented by a linear model). It is further pointed out that an accurate measurement of the ΔV is rather critical for a proper DCR estimation and SoH assessment, due to the small ΔV ( eg in the range of 100µV to 10mV) produced by the current flow into the battery DCR ( eg in the range of 100mA to 1A).
According to a second method, it is noted that a battery pack is normally composed by a quite large number of battery cells connected in series. In practice, apart from the effects of aging, this architecture affects all the cells of the pack in the same way: just one or few cells can be weaker and approach to failure earlier than the other cells. If the DCR of all the battery cells of the pack is measured at the same time under the same conditions, the cells that reveal an abnormal DCR, usually higher, can be easily identified. Moreover, the deviation from the average DCR of the cell is an indication of a degraded SoH.According to a second method, it is noted that a battery pack is normally composed by a quite large number of battery cells connected in series. In practice, apart from the effects of aging, this architecture affects all the cells of the pack in the same way: just one or few cells can be weaker and approach to failure earlier than the other cells. If the DCR of all the battery cells of the pack is measured at the same time under the same conditions, the cells that reveal an abnormal DCR, usually higher, can be easily identified. Moreover, the deviation from the average DCR of the cell is an indication of a degraded SoH.
The clear advantage of this methodology is that it does not require a large, complex and costly characterization campaign, at the cost of not being able to assess an absolute figure for the SoH of each cell. The proposed methodology provides a relative indication compared to the “average SoH” of the cells constituting the battery pack. The approach is about monitoring on a “cell group” level and then updating all the different parameters and each charge event. The update process relies on artificial intelligence based algorithms to actually learn and adjust while it evolves, using a deep learning approach. Nevertheless, this is more than enough to identify the cells which are drifting and approaching to failures; then the battery control system will inform the driver thus allowing the further replacement of the faulty cells. Since this method is based only on the direct comparison of DCR between battery cells which are operating exactly under the same conditions (i.e.temperature, current cycles, aging and various stresses), there is no real need to measure the resistance only in steady state conditions. Hence the system does not need to wait for the relaxation time before running the measurements. In fact, transients will equally affect the measured DCR values of the different cells: the values measured before all transients are extinguished will not be directly compared with DCR characterization data (that shall be obtained in steady state conditions), but are useful for a relative comparison with the other cells in the pack to identify, as soon as possible, any potential outliers.The clear advantage of this methodology is that it does not require a large, complex and costly characterization campaign, at the cost of not being able to assess an absolute figure for the SoH of each cell. The proposed methodology provides a relative indication compared to the “average SoH” of the cells constituting the battery pack. The approach is about monitoring on a “cell group” level and then updating all the different parameters and each charge event. The update process relies on artificial intelligence based algorithms to actually learn and adjust while it evolves, using a deep learning approach. Nevertheless, this is more than enough to identify the cells which are drifting and approaching to failures; then the battery control system will inform the driver thus allowing the further replacement of the faulty cells. Since this method is based only on the direct comparison of DCR between battery cells which are operating exactly under the same conditions ( ie temperature, current cycles, aging and various stresses), there is no real need to measure the resistance only in steady state conditions . Hence the system does not need to wait for the relaxation time before running the measurements. In fact, transients will equally affect the measured DCR values of the different cells: the values measured before all transients are extinguished will not be directly compared with DCR characterization data (that shall be obtained in steady state conditions), but are useful for a relative comparison with the other cells in the pack to identify, as soon as possible, any potential outliers.
Therefore, this method does not need to be executed only when the vehicle is stopped and turned off, as in the previous case, but can be also run during the vehicle trip. In particular the measurement will be performed whenever the battery is in “idle” condition and no current is either sourced or sunk. Please note that DCR measurements, mentioned above, rely on imposing a small current step on the battery cells, which shall not be “disturbed” by any other current flowing in the battery during normal operation.Therefore, this method does not need to be executed only when the vehicle is stopped and turned off, as in the previous case, but can be also run during the vehicle trip. In particular the measurement will be performed whenever the battery is in “idle” condition and no current is either sourced or sunk. Please note that DCR measurements, mentioned above, rely on imposing a small current step on the battery cells, which shall not be “disturbed” by any other current flowing in the battery during normal operation.
As an extension of this concept, the DCR measurement can be performed also during the normal operation of the battery, exploiting the operating current that is sourced from (or sunk by) the battery pack. Each time a current step, or a current variation, is operated on the battery, a voltage variation will occur, enabling the calculation of the DCR in that specific operating conditions. Since the DCR measurements will occur during transients, the resulting values will strongly depend not only on the current levels that are operated on the battery, but also to their past history. Anyway, as soon as all the cells will “see” exactly the same current excitation in the same operating and environmental condition, the acquired DCR values will be useful for relative comparison to find any possible outliers.As an extension of this concept, the DCR measurement can be performed also during the normal operation of the battery, exploiting the operating current that is sourced from (or sunk by) the battery pack. Each time a current step, or a current variation, is operated on the battery, a voltage variation will occur, enabling the calculation of the DCR in that specific operating conditions. Since the DCR measurements will occur during transients, the resulting values will strongly depend not only on the current levels that are operated on the battery, but also on their past history. Anyway, as soon as all the cells will “see” exactly the same current excitation in the same operating and environmental condition, the acquired DCR values will be useful for relative comparison to find any possible outliers.
It is noted that, in this case, the SoH may be assessed several times during a trip, by exploiting the current variations on the battery whenever the car is either accelerating or recovering energy during regenerative braking. An additional advantage would be that the operating current variations could easily reach very high values, producing a larger voltage variation on the cell resistance. The clear advantage is that the higher voltage drop the more accurate the measurement. On the contrary, measurements accomplished in such operating conditions are subject to switching noise, due to traction inverter and DC/DC converter operations, which shall be properly rejected. Moreover, a very strict requirement on the synchronization of current and cells voltage acquisitions shall be guaranteed, in order to allow the proper comparison of the DCR values measured during transients.It is noted that, in this case, the SoH may be assessed several times during a trip, by exploiting the current variations on the battery whenever the car is either accelerating or recovering energy during regenerative braking. An additional advantage would be that the operating current variations could easily reach very high values, producing a larger voltage variation on the cell resistance. The clear advantage is that the higher voltage drop the more accurate the measurement. On the contrary, measurements accomplished in such operating conditions are subject to switching noise, due to traction inverter and DC/DC converter operations, which shall be properly rejected. Moreover, a very strict requirement on the synchronization of current and cells voltage acquisitions shall be guaranteed, in order to allow the proper comparison of the DCR values measured during transients.
An efficient and cost effective solution for the HW circuit enabling the DCR measurement will be described hereafter.An efficient and cost effective solution for the HW circuit enabling the DCR measurement will be described hereafter.
Automotive high voltage battery systems are usually organized in several modules connected in series, each of them composed by a certain number of cells connected in series. In low voltage battery systems, a single module usually constitutes the battery pack. A dedicated electronic circuit, usually based on a “Battery Monitoring and Balancing Integrated Circuit (IC)”, manages each battery module. Typical automotive battery modules are composed by a limited amount of cells, depending on the cell nominal voltage and the silicon technology in which the Monitoring IC is implemented. The main functions of this IC are the following:Automotive high voltage battery systems are usually organized in several modules connected in series, each of them composed by a certain number of cells connected in series. In low voltage battery systems, a single module usually constitutes the battery pack. A dedicated electronic circuit, usually based on a “Battery Monitoring and Balancing Integrated Circuit (IC)”, manages each battery module. Typical automotive battery modules are composed by a limited amount of cells, depending on the cell nominal voltage and the silicon technology in which the Monitoring IC is implemented. The main functions of this IC are the following:
- measurement of the battery cells voltage: please note that this is the complete voltage developed at each cell’s terminals, including the OCV (Open Circuit Voltage) plus the voltage drop caused by the operating current on the DCR;measurement of the battery cells voltage: please note that this is the complete voltage developed at each cell’s terminals, including the OCV (Open Circuit Voltage) plus the voltage drop caused by the operating current on the DCR;
- measurement of the battery cell temperature: several temperature sensors are provided in each module, to cover any temperature variations between the cells inside the module itself;measurement of the battery cell temperature: several temperature sensors are provided in each module, to cover any temperature variations between the cells inside the module itself;
- optionally, module current measurement;optionally, module current measurement;
- communication of all the measured data to a Battery Management System (BMS), via a proper physical communication interface; andcommunication of all the measured data to a Battery Management System (BMS), via a proper physical communication interface; and
- cell balancing (e.g.passive, active):cell balancing ( eg passive, active):
- in case of passive balancing, the cells which have a higher charge will be discharged connecting a resistor in parallel, until all the cells are equalized (i.e.they have the same charge, equal to the charge of the weakest cell in the pack); andin case of passive balancing, the cells which have a higher charge will be discharged connecting a resistor in parallel, until all the cells are equalized ( ie they have the same charge, equal to the charge of the weakest cell in the pack); and
- in case of active balancing, the cells which have a higher charge will be discharged with switching techniques over the cells with lower charge, which are charged accordingly, until all the cells are equalized. This technique shall be more efficient, but it is by far more complex and costly: therefore, the majority of the automotive systems use passive balancing.in case of active balancing, the cells which have a higher charge will be discharged with switching techniques over the cells with lower charge, which are charged accordingly, until all the cells are equalized. This technique shall be more efficient, but it is by far more complex and costly: therefore, the majority of the automotive systems use passive balancing.
It is noted that that the cell voltage measurements, and the optional current measurement, are usually loosely synchronized (e.g. started on a trigger and performed sequentially).It is noted that the cell voltage measurements, and the optional current measurement, are usually loosely synchronized (e.g. started on a trigger and performed sequentially).
Since the “Battery Monitoring and Balancing IC” is connected to each cells battery terminal, and includes the ADC to perform the battery cells voltage measurements, the most cost effective solution for DCR measurements is to integrate the proper circuitry in the Monitoring IC.Since the “Battery Monitoring and Balancing IC” is connected to each cells battery terminal, and includes the ADC to perform the battery cells voltage measurements, the most cost effective solution for DCR measurements is to integrate the proper circuitry in the Monitoring IC.
The monitoring IC has also the capability to communicate all the measured data, including the DCR parameters, to the Battery Management System (BMS), which will be responsible for all processing tasks and the evaluation of the SoH.The monitoring IC has also the capability to communicate all the measured data, including the DCR parameters, to the Battery Management System (BMS), which will be responsible for all processing tasks and the evaluation of the SoH.
To allow precise differential voltage measurements (i.e.the ΔV caused by the ΔI forced in the DCR) on top of the OCV of the battery cell, an additional differential amplifier and a Digital Analogue Converter (ADC) are required, as shown below in the
The DCR measurement procedure is now described in the following, assuming all the battery cells are processed in parallel in the same way:The DCR measurement procedure is now described in the following, assuming all the battery cells are processed in parallel in the same way:
- zero current is applied to the battery module;zero current is applied to the battery module;
- the analogue MUX is set to select the upper signal (Cell voltage);the analog MUX is set to select the upper signal (Cell voltage);
- the OCV is sampled by the ADC, and the measured value is communicated to the BMS (please note that communication signals have to be level-shifted);the OCV is sampled by the ADC, and the measured value is communicated to the BMS (please note that communication signals have to be level-shifted);
- the OCV value is programmed in the DAC, and the corresponding analogue voltage is provided at its output to the differential amplifier negative terminal;the OCV value is programmed in the DAC, and the corresponding analog voltage is provided at its output to the differential amplifier negative terminal;
- the differential amplifier provides at its output, amplified by the proper gain, the difference between the present cell voltage and previously measured OCV. Please note that at this point the amplifier output voltage should theoretically be 0V, but it will be equal to the offset voltage resulting from the DAC offset and the differential amplifier input offset (both multiplied by the differential gain of the amplifier);the differential amplifier provides at its output, amplified by the proper gain, the difference between the present cell voltage and previously measured OCV. Please note that at this point the amplifier output voltage should theoretically be 0V, but it will be equal to the offset voltage resulting from the DAC offset and the differential amplifier input offset (both multiplied by the differential gain of the amplifier);
- the ADC samples the output of the differential amplifier (voltage V1), and the measured value is communicated to the BMS: this measurement will be useful for digital offset cancelation;the ADC samples the output of the differential amplifier (voltage V1), and the measured value is communicated to the BMS: this measurement will be useful for digital offset cancellation;
- a current step is applied to the battery pack, causing a voltage variation at each battery cell terminal;a current step is applied to the battery pack, causing a voltage variation at each battery cell terminal;
- The differential amplifier provides at its output, amplified by the proper gain, the difference ΔV between the new cell voltage and the previously measured OCV;The differential amplifier provides at its output, amplified by the proper gain, the difference ΔV between the new cell voltage and the previously measured OCV;
- after a pre-defined delay, the ADC samples the output of the differential amplifier (voltage V2) and the measured value is communicated to the BMS. Please note that the gain of the differential amplifier will be selected in order to use the full dynamic range of the ADC during V2 measurement, optimizing the resolution of the measurement. Optionally, a dedicated ADC channel of the Monitoring IC measures in parallel the battery current value, and the measured value is communicated to the BMS. This step is useful only in case the battery current is unknown (e.g.it is not under the BMS control); andafter a pre-defined delay, the ADC samples the output of the differential amplifier (voltage V2) and the measured value is communicated to the BMS. Please note that the gain of the differential amplifier will be selected in order to use the full dynamic range of the ADC during V2 measurement, optimizing the resolution of the measurement. Optionally, a dedicated ADC channel of the Monitoring IC measures in parallel the battery current value, and the measured value is communicated to the BMS. This step is useful only in case the battery current is unknown ( eg it is not under the BMS control); and
- the BMS will calculate the ΔV caused by the current step, as ΔV = (V2 – V1)/Ad while the DCR is simply calculated as DRC = ΔV/ΔI.the BMS will calculate the ΔV caused by the current step, as ΔV = (V2 – V1)/Ad while the DCR is simply calculated as DRC = ΔV/ΔI.
The abovementioned procedure can also be easily adjusted in the case the DCR measurement is performed during normal operation, and there is already some current flowing in the battery pack at the beginning of the procedure.The abovementioned procedure can also be easily adjusted in the case the DCR measurement is performed during normal operation, and there is already some current flowing in the battery pack at the beginning of the procedure.
The current step needed for DCR measurement can be generated using the passive balancing circuit already available on the “Battery Monitoring and Balancing” electronic circuit. Enabling the passive balancing switch, a resistor is connected in parallel to the each cell, thus allowing the current flow from the cell to the resistor. The balancing current is, in this case, relatively small, and will be activated only for the duration of the measurement. Therefore the battery cell will be discharged only by a negligible amount during the DCR measurement process.The current step needed for DCR measurement can be generated using the passive balancing circuit already available on the “Battery Monitoring and Balancing” electronic circuit. Enabling the passive balancing switch, a resistor is connected in parallel to the each cell, thus allowing the current flow from the cell to the resistor. The balancing current is, in this case, relatively small, and will be activated only for the duration of the measurement. Therefore the battery cell will be discharged only by a negligible amount during the DCR measurement process.
During the balancing process the ADC acquires the cell voltage and communicate the results to the BMS: since the value of the balancing resistor is known, the BMS can easily calculate the current value, without any need to perform an additional current measurement.During the balancing process the ADC acquires the cell voltage and communicates the results to the BMS: since the value of the balancing resistor is known, the BMS can easily calculate the current value, without any need to perform an additional current measurement.
In case active balancing is performed, the active balancing circuit shall be adapted in order to provide a current step to the battery cells in the module. In this case, higher current values can be easily obtained. Since a great variety of active balancing circuits, operating with different principles, are available on the market, the details of the generation of the current step have to be investigated on a case by case basis.In case active balancing is performed, the active balancing circuit shall be adapted in order to provide a current step to the battery cells in the module. In this case, higher current values can be easily obtained. Since a great variety of active balancing circuits, operating with different principles, are available on the market, the details of the generation of the current step have to be investigated on a case by case basis.
In the following, a method for the measurement of the properties of a battery cell based on Electrochemical Impedance Spectroscopy is described.In the following, a method for the measurement of the properties of a battery cell based on Electrochemical Impedance Spectroscopy is described.
The electrochemical impedance spectroscopy (EIS) methodology measures dielectric properties of a medium as a function of the frequency. In particular, as applied to the battery cells, the goal of the EIS is to compute the impedance parameters thus being able to assess the State of Health (SoH) of the cells as a function of the impedance.The electrochemical impedance spectroscopy (EIS) methodology measures dielectric properties of a medium as a function of the frequency. In particular, as applied to the battery cells, the goal of the EIS is to compute the impedance parameters thus being able to assess the State of Health (SoH) of the cells as a function of the impedance.
The EIS algorithm injects a known current stimulus into the battery cell, reading the resulting voltage. The response waveform from the battery is the contribution of several components which makes the signal processing, needed to extract the proper information, rather complex.The EIS algorithm injects a known current stimulus into the battery cell, reading the resulting voltage. The response waveform from the battery is the contribution of several components which makes the signal processing, needed to extract the proper information, rather complex.
Hence the effectiveness of the EIS approach on automotive embedded platform relies on different attributes such as calculation performances, real time capabilities, accuracy of the sensing circuit and signal generation.Hence the effectiveness of the EIS approach on automotive embedded platform relies on different attributes such as calculation performances, real time capabilities, accuracy of the sensing circuit and signal generation.
The proposed method is based on the proper downscaling of the EIS algorithm, thus allowing its execution through simple real time calculations. This approach will overcome some of the inherent drawbacks affecting algorithms based on FFT computations, such as:The proposed method is based on the proper downscaling of the EIS algorithm, thus allowing its execution through simple real time calculations. This approach will overcome some of the inherent drawbacks affecting algorithms based on FFT computations, such as:
- “leakage” effects at the beginning/end of the measurement window; and“leakage” effects at the beginning/end of the measurement window; and
- large amount of data to be elaborated from FFT results.large amount of data to be elaborated from FFT results.
Furthermore, a particular attention has been devoted to the cost effective implementation of the EIS algorithm into an integrated circuit. Hence, the proposed HW architecture based on heterodyne modulation has the advantage of being easily integrated into the next generation of smart driver for cell-balancing: this will provide a very cost effective solution and could be considered the first attempt to embed EIS on practical automotive solutions. The same holds for the EIS real time signal processing running on a standard automotive microcontroller with limited HW resources unlike the actual solution based either on DSP or high end microprocessor which are not suitable for automotive applications.Furthermore, a particular attention has been devoted to the cost effective implementation of the EIS algorithm into an integrated circuit. Hence, the proposed HW architecture based on heterodyne modulation has the advantage of being easily integrated into the next generation of smart driver for cell-balancing: this will provide a very cost effective solution and could be considered the first attempt to embed EIS on practical automotive solutions. The same holds for the EIS real time signal processing running on a standard automotive microcontroller with limited HW resources unlike the actual solution based either on DSP or high end microprocessor which are not suitable for automotive applications.
In order to successfully determine the EIS spectrum, it is necessary to take into account certain inherent problems in the method and the component under test and, thus, make certain theoretical assumptions.In order to successfully determine the EIS spectrum, it is necessary to take into account certain inherent problems in the method and the component under test and, thus, make certain theoretical assumptions.
The EIS analysis is based on the following prerequisites:The EIS analysis is based on the following prerequisites:
- the system must be linear;the system must be linear;
- the system parameters should not vary over time; andthe system parameters should not vary over time; and
- the system must be Single Input Single Output (SISO).the system must be Single Input Single Output (SISO).
The battery cell is not generally satisfying these requirements: therefore, additional assumptions must be identified. First, the characteristic of a battery cell is not linear and then a linearization process is necessary to calculate the impedance. So, in normal EIS practice, a small AC signal is applied to the cell, in order to restrict the test into a pseudo-linear segment of the cell's current versus voltage curve.The battery cell is not generally satisfying these requirements: therefore, additional assumptions must be identified. First, the characteristic of a battery cell is not linear and then a linearization process is necessary to calculate the impedance. So, in normal EIS practice, a small AC signal is applied to the cell, in order to restrict the test into a pseudo-linear segment of the cell's current versus voltage curve.
The differential impedance ratio, which represents the EIS, is defined as:The differential impedance ratio, which represents the EIS, is defined as:
For the sake of simplicity the linearization will applied to the “zero current” point, so that the voltage will correspond with the Open Circuit Voltage (OCV).For the sake of simplicity the linearization will be applied to the “zero current” point, so that the voltage will correspond with the Open Circuit Voltage (OCV).
Then, the battery cell parameters are not constant. Generally, even with open battery terminals (i.e.zero current), the battery voltage varies over time depending on its previous history. Hence a “relaxation time”, depending on the temperature (ion mobility), must be respected in order to reach the electrochemical balance conditions in the battery.Then, the battery cell parameters are not constant. Generally, even with open battery terminals ( ie zero current), the battery voltage varies over time depending on its previous history. Hence a “relaxation time”, depending on the temperature (ion mobility), must be respected in order to reach the electrochemical balance conditions in the battery.
Finally, the voltage in a battery does not depend exclusively on the current flowing through it, but also on other parameters such temperature and State of Charge (SOC). During each EIS measurement, these parameters must remain constants, in order not to influence the output voltage. In general, it must be guaranteed that the battery OCV does not vary within the range of the test, otherwise this variation will influence the impedance spectrum computation.Finally, the voltage in a battery does not depend exclusively on the current flowing through it, but also on other parameters such temperature and State of Charge (SOC). During each EIS measurement, these parameters must remain constant, in order not to influence the output voltage. In general, it must be guaranteed that the battery OCV does not vary within the range of the test, otherwise this variation will influence the impedance spectrum computation.
Based on the assumptions above mentioned, the stimulus signal needed for the EIS test shall have the following characteristics:Based on the assumptions above mentioned, the stimulus signal needed for the EIS test shall have the following characteristics:
- the spectrum of the stimulus shall adequately cover the whole frequency range that has to be analysed (typically from 0.01 Hz to 1 kHz); andthe spectrum of the stimulus shall adequately cover the whole frequency range that has to be analyzed (typically from 0.01 Hz to 1 kHz); and
- the signal amplitude shall be “small enough” to avoid triggering any nonlinear response in the battery.the signal amplitude shall be “small enough” to avoid triggering any nonlinear response in the battery.
As a drawback, the smaller is the signal amplitude, the worse is the signal to noise ratio; for this reason a dedicated HW circuit is needed to obtain a good resolution of the acquired signal. In particular, the proposed solution is designed to:As a drawback, the smaller is the signal amplitude, the worse is the signal to noise ratio; for this reason a dedicated HW circuit is needed to obtain a good resolution of the acquired signal. In particular, the proposed solution is designed to:
- amplify and adequately filter the signal, due to the small signal amplitude;amplify and adequately filter the signal, due to the small signal amplitude;
- remove the OCV voltage, which is not useful for EIS measurements; andremove the OCV voltage, which is not useful for EIS measurements; and
- read each voltage value through a differential amplifier.read each voltage value through a differential amplifier.
In particular, the OCV must be measured before applying the stimulus signal, and then removed through the dedicated Digital to Analog Converter (DAC).In particular, the OCV must be measured before applying the stimulus signal, and then removed through the dedicated Digital to Analog Converter (DAC).
The current stimulus is the sum of sinusoidal current waveforms with predefined frequencies and current amplitude values:The current stimulus is the sum of sinusoidal current waveforms with predefined frequencies and current amplitude values:
An example is shown in
The EIS algorithm (schematically shown in
The response waveform from the cells is the combination of different values: 1) the voltage across the cells, 2) a DC offset, 3) some harmonic distortion components, and 4) some noise components generated by the cell. Nevertheless, the element of the measured signal which needs to be analysed is the one at the same frequency of the waveform generator. All the spurious components of the measured signal need to be rejected so that accurate measurements of the signal originated at the generator frequency can be made. Then the measured system output is multiplied by both the sine and cosine of the test frequency ω (
The abovementioned process is known as “correlation”.The abovementioned process is known as “correlation”.
Harmonics are rejected by the correlation process, and noise is rejected by averaging the signal over a number of cycles; the averaging asSOCiated with the correlation frequency response analyser acts as a band pass filter with a center frequency ω. As the average time T increases the bandwidth of the filter becomes narrower, thus the corrupting influence of wide band noise is increasingly filtered out as the correlation time is increased.Harmonics are rejected by the correlation process, and noise is rejected by averaging the signal over a number of cycles; the averaging asSOCIated with the correlation frequency response analyzer acts as a band pass filter with a center frequency ω. As the average time T increases the bandwidth of the filter becomes narrower, thus the corrupting influence of wide band noise is increasingly filtered out as the correlation time is increased.
Averaging over a complete cycle reduces measurement errors asSOCiated with offsets on the system output; the performed simulations demonstrates an effective rejection of all frequencies above 0.1 Hz while acquiring over a time window of three complete periods (
The result of the correlation process is made up of two components one of which is referred to as theReal(or in phase) component, the other is theImaginary(or quadrature) component. By performing simple mathematical operations on these raw measurement results, it is possible to obtain the magnitude and phase of the impedance.The result of the correlation process is made up of two components one of which is referred to as the Real (or in phase) component, the other is the Imaginary (or quadrature) component. By performing simple mathematical operations on these raw measurement results, it is possible to obtain the magnitude and phase of the impedance.
Hereinafter, the EIS software implementation is described.Hereafter, the EIS software implementation is described.
The EIS software, whose architecture is schematically shown in
- Basic Software LayerBasic Software Layer
- OCV removal: generates the signals needed to remove the OCV from the measured cell voltage; OCV shall be measured before applying the stimulus signal, and then canceled through a dedicated DAC signal;OCV removal: generates the signals needed to remove the OCV from the measured cell voltage; OCV shall be measured before applying the stimulus signal, and then canceled through a dedicated DAC signal;
- EIS Command Generator: its purpose is to generate the EIS Command signal (voltage reference) representing the current stimulus to be forced into the battery pack;EIS Command Generator: its purpose is to generate the EIS Command signal (voltage reference) representing the current stimulus to be forced into the battery pack;
- Cell voltages - both DC and AC (useful EIS signal) - for each battery cell; andCell voltages - both DC and AC (useful EIS signal) - for each battery cell; and
- EIS current flowing in the battery module/pack,EIS current flowing in the battery module/pack,
- Application Software LayerApplication Software Layer
- Data Processing System for the calculation of the EIS spectrum.Data Processing System for the calculation of the EIS spectrum.
The application SW layer implements the EIS algorithm, as described in the sections above; the flowchart in
The correctness of the EIS algorithm has been validated through several tests run under different working conditions.The correctness of the EIS algorithm has been validated through several tests run under different working conditions.
The effect of the external current amplifier (the transconductance amplifier) has been analysed, determining the effects on the impedance calculation of the introduced amplification and the (potential) phase shift. The results, as shown in
The final result of the impedance measurement are shown in
The EIS HW implementation is made of several subsystems, briefly described below and in the following block diagram in
- EIS Command Generator: its purpose is to generate the proper EIS Command signal (voltage reference) representing the current stimulus to be forced into the battery pack;EIS Command Generator: its purpose is to generate the proper EIS Command signal (voltage reference) representing the current stimulus to be forced into the battery pack;
- Power Current Driver amplifying the EIS command signal and providing the EIS current stimulus to the battery cells;Power Current Driver amplifying the EIS command signal and providing the EIS current stimulus to the battery cells;
- Battery Module/Pack, representing the load whose impedance has to be measuredBattery Module/Pack, representing the load whose impedance has to be measured
-
EIS Signals Acquisition Sub-system, for the coherent measurement of:
- Cell voltages - both DC and AC (useful EIS signal) - for each battery cell; and
- EIS current flowing in the battery module/pack; and
- Cell voltages - both DC and AC (useful EIS signal) - for each battery cell; and
- EIS current flowing in the battery module/pack; and
- Data Processing System for the calculation of the EIS spectrum based on automotive microcontroller.Data Processing System for the calculation of the EIS spectrum based on automotive microcontroller.
The heterodyne approach with coherent demodulation has been selected for EIS implementation: the impedance is evaluated only at N discrete frequency values, and therefore, the most efficient solution is to stimulate the battery under test providing energy only at the frequencies of interest. A proper stimulus is the sum of sine waves, one for each frequency value that has to be evaluated. The number N of frequency values should in any case be limited to achieve a good signal-to-noise ratio during the measurements.The heterodyne approach with coherent demodulation has been selected for EIS implementation: the impedance is evaluated only at N discrete frequency values, and therefore, the most efficient solution is to stimulate the battery under test providing energy only at the frequencies of interest. A proper stimulus is the sum of sine waves, one for each frequency value that has to be evaluated. The number N of frequency values should in any case be limited to achieve a good signal-to-noise ratio during the measurements.
The system is designed to measure the impedance in a broad frequency range and several aspects must be evaluated in order to:The system is designed to measure the impedance in a broad frequency range and several aspects must be evaluated in order to:
- maximize the rejection among different frequencies (or minimize the cross coupling between them when calculating the convolution), the frequency vector shall be chosen so that the single frequencies are integer multiples of the lowest frequency.maximize the rejection among different frequencies (or minimize the cross coupling between them when calculating the convolution), the frequency vector shall be chosen so that the single frequencies are integer multiples of the lowest frequency.
- minimize border effects, the acquisition time - and therefore the duration of the current stimulus - shall include an integer number of periods for any frequencies in the vector. This may be easily achieved selecting an acquisition time which is an integer multiple of the period of the lowest frequency in the vector.minimize border effects, the acquisition time - and therefore the duration of the current stimulus - shall include an integer number of periods for any frequencies in the vector. This may be easily achieved selecting an acquisition time which is an integer multiple of the period of the lowest frequency in the vector.
- achieve a good rejection among different frequencies, a long acquisition time shall be adopted: a minimum of 2 periods at the lowest frequency is requested.achieve a good rejection among different frequencies, a long acquisition time shall be adopted: a minimum of 2 periods at the lowest frequency is requested.
- limit the number of frequency in the vector, to maintain an adequate energy level asSOCiated to each frequency value, and in particular a good signal/noise ratio. The peak value of the current forced in the battery shall be limited to prevent non-linearity issues.limit the number of frequency in the vector, to maintain an adequate energy level associated to each frequency value, and in particular a good signal/noise ratio. The peak value of the current forced in the battery shall be limited to prevent non-linearity issues.
An EIS command signal is generated by the EIS HW Platform (EHP) and provided to an external current amplifier. The command provided by the EHP is a voltage signal in the range 0V to 5V and with a 2.5V offset. Please note that the current stimulus to be applied to the battery cells shall not have any DC offset and it shall be removed by the current amplifier. The EIS command signal, is obtained through a PWM signal generated by the microcontroller which is then filtered by a Bessel low-pass filter. A Bessel filter is required to avoid any signal distortion due to different phase delays at various frequencies. The overall error on the EIS command signal due to quantization and residual PWM ripple is designed to be lower than 1 LSB at the current sense ADC input of the microcontroller. The complete chain is radiometric since it uses the same supply voltage of the microcontroller peripheral and the ADC voltage reference, thus virtually removing any error on the 5V supply, while the overall offset shall be cancelled adjusting the duty cycle of the PWM until the current sense measurement is equal to zero.An EIS command signal is generated by the EIS HW Platform (EHP) and provided to an external current amplifier. The command provided by the EHP is a voltage signal in the range 0V to 5V and with a 2.5V offset. Please note that the current stimulus to be applied to the battery cells shall not have any DC offset and it shall be removed by the current amplifier. The EIS command signal, is obtained through a PWM signal generated by the microcontroller which is then filtered by a Bessel low-pass filter. A Bessel filter is required to avoid any signal distortion due to different phase delays at various frequencies. The overall error on the EIS command signal due to quantization and residual PWM ripple is designed to be lower than 1 LSB at the current sense ADC input of the microcontroller. The complete chain is radiometric since it uses the same supply voltage of the microcontroller peripheral and the ADC voltage reference, thus virtually removing any error on the 5V supply, while the overall offset shall be canceled adjusting the duty cycle of the PWM until the current sense measurement is equal to zero.
In order to compute the EIS algorithm, both voltage and current values shall be acquired for each of the battery cells under test.In order to compute the EIS algorithm, both voltage and current values shall be acquired for each of the battery cells under test.
Regarding the voltage acquisition, schematically shown in
The voltages of the individual cells can be measured through differential instrumentation amplifiers, but in order to reduce the cost of the automotive application, a simpler differential stage based on the classical operational amplifier with four matched resistors could be used as well: this could be done under the assumption the effect of the impedances of the generator could be considered negligible.The voltages of the individual cells can be measured through differential instrumentation amplifiers, but in order to reduce the cost of the automotive application, a simpler differential stage based on the classical operational amplifier with four matched resistors could be used as well: this could be done under the assumption the effect of the impedances of the generator could be considered negligible.
The cell voltage signal useful for EIS calculation is the AC value only, which is resulting from the EIS current stimulus: therefore, the DC cell voltage shall be completely removed. Since the EIS stimulus is a purely “small” AC signal that should not trigger any non-linear effects, the DC cell voltage during the EIS measurements is assumed to be equal to the Open Circuit Voltage (OCV) of the cells, and it shall be measured immediately before the EIS measurements are performed. Since it is assumed that the OCV does not change during the EIS measurements, the OCV is measured exactly in the same conditions as during the EIS measurements, in particular at the same temperature, SOC and SoH, and relaxation of the battery cells.The cell voltage signal useful for EIS calculation is the AC value only, which is resulting from the EIS current stimulus: therefore, the DC cell voltage shall be completely removed. Since the EIS stimulus is a purely “small” AC signal that should not trigger any non-linear effects, the DC cell voltage during the EIS measurements is assumed to be equal to the Open Circuit Voltage (OCV) of the cells, and it shall be measured immediately before the EIS measurements are performed. Since it is assumed that the OCV does not change during the EIS measurements, the OCV is measured exactly in the same conditions as during the EIS measurements, in particular at the same temperature, SOC and SoH, and relaxation of the battery cells.
A second difference amplifier stage is then implemented in the EIS expansion board to subtract the OCV from the cell voltage signal.A second difference amplifier stage is then implemented in the EIS expansion board to subtract the OCV from the cell voltage signal.
Offset voltage (OCV) generatorOffset voltage (OCV) generator
The offset voltageVoffwhich is subtracted from the cell voltageVcellto remove the OCV is generated by a DAC, implemented through a simple low pass filter, and according to the equation (where DC OffComp is the Duty Cycle ofOffCompsignal):The offset voltage Voff which is subtracted from the cell voltage Vcell to remove the OCV is generated by a DAC, implemented through a simple low pass filter, and according to the equation (where DC OffComp is the Duty Cycle of OffComp signal):
An offset compensation routine shall be run before performing any EIS measurement to cancel any DC voltages caused by both the OCV of the battery cells and the various offsets which are affecting the operational amplifiers in the acquisition chain (mainly the common mode voltage of the differential amplifiers, and all the input bias and offset voltages of the OpAmps).An offset compensation routine shall be run before performing any EIS measurement to cancel any DC voltages caused by both the OCV of the battery cells and the various offsets which are affecting the operational amplifiers in the acquisition chain (mainly the common mode voltage of the differential amplifiers , and all the input bias and offset voltages of the OpAmps).
To speed up the offset compensation routine, a precise OCV measurement may be performed right before the EIS measurements. The Duty Cycle of theOffCompsignal will be pre-set at the value corresponding to the OCV measurement, speeding up the offset compensation procedure since the major term of the offset voltage would already be known.To speed up the offset compensation routine, a precise OCV measurement may be performed right before the EIS measurements. The Duty Cycle of the OffComp signal will be pre-set at the value corresponding to the OCV measurement, speeding up the offset compensation procedure since the major term of the offset voltage would already be known.
The EIS voltage signal, as treated by the differential stages, shall be filtered before being sent to the A/D Converter of the automotive microcontroller (anti-aliasing filter). A Bessel type, low pass, 4thorder, active filter shall be adopted, to minimize the distortion of the signal due to different phase shifts at different frequencies. Moreover, since the Bessel filter provides a linear phase shift versus frequency, the phase shift at each frequency may be easily calculated and compensated. As a drawback, a higher sampling frequency shall be selected, due to the low selectivity of the Bessel filter.The EIS voltage signal, as treated by the differential stages, shall be filtered before being sent to the A/D Converter of the automotive microcontroller (anti-aliasing filter). A Bessel type, low pass, 4 th order, active filter shall be adopted, to minimize the distortion of the signal due to different phase shifts at different frequencies. Moreover, since the Bessel filter provides a linear phase shift versus frequency, the phase shift at each frequency can be easily calculated and compensated. As a drawback, a higher sampling frequency shall be selected, due to the low selectivity of the Bessel filter.
The anti-aliasing filters for current measurement must have the same characteristics above mentioned for voltage measurement, to avoid (at least theoretically) any difference in magnitude and phase between voltage and current. In fact, if the same transfer function is applied to both voltage and current signals, their ratio is not altered and therefore the impedance calculation is correct. Therefore, a 4th order low-pass Bessel filter has been implemented for each current sense.The anti-aliasing filters for current measurement must have the same characteristics above mentioned for voltage measurement, to avoid (at least theoretically) any difference in magnitude and phase between voltage and current. In fact, if the same transfer function is applied to both voltage and current signals, their ratio is not altered and therefore the impedance calculation is correct. Therefore, a 4th order low-pass Bessel filter has been implemented for each current sense.
The experimental activity run on battery cells has shown a correlation between the cell core temperature and the impedance obtained through the EIS algorithm. The expected accuracy could be in the range of +/-5°C which could be appropriate when used for the early detection of thermal runaway, which is a catastrophic behaviour affecting Li-Ion battery technology under stress condition.The experimental activity run on battery cells has shown a correlation between the cell core temperature and the impedance obtained through the EIS algorithm. The expected accuracy could be in the range of +/-5°C which could be appropriate when used for the early detection of thermal runaway, which is a catastrophic behavior affecting Li-Ion battery technology under stress condition.
Claims (8)
wherein the electric propulsion system comprises either a single multiphase electric motor to provide drive torque to drive wheels of the electric vehicle through a powertrain or a plurality of three-phase electric motors integrated into respective drive wheels of the electric vehicle;
the smart battery pack comprises:
- multicore lockstep microcontroller coupled with a safe power supply to comply with safety requirements;
- battery pack comprising cell modules, each cell module being interconnected via a wireless connection;
- relays configured to switch contactor connections;
- a battery thermal management system; and
- a short/long range communication module to communicate both to nomadic devices and to remote service centers,
the smart battery pack being designed to monitor cell-voltages to perform at least one of the following functionalities:
- perform cell voltage balancing; and/or
- perform Open-Circuit Voltage measurements for State Of Charge recalibration.
- avoid thermal runaway caused by current flow above operational limits; and/or
- ampere/hour counting for State Of Charge estimation.
- monitor the voltage and temperature in different vehicle operating mode and take necessary action to protect the cell from the degradation;
- measure battery current and pack voltage and calculate the State Of Charge;
- control the battery contactor based on different condition; and
- provide cell balancing mechanism to equate all the cell in same voltage level.
wherein the electric propulsion system comprises either a single multiphase electric motor to provide drive torque to drive wheels of the electric vehicle through a powertrain or a plurality of three-phase electric motors integrated into respective drive wheels of the electric vehicle;
the smart battery pack includes:
- multicore lockstep microcontroller coupled with a safe power supply to comply with safety requirements;
- battery pack comprising cell modules, each cell module being interconnected via a wireless connection;
- relays configured to switch contactor connections;
- a battery thermal management system; and
- a short/long range communication module to communicate both to nomadic devices and to remote service centers,
the smart battery pack being designed to monitor cell-voltages to perform at least one of the following functionalities:
- perform cell voltage balancing; and/or
- perform Open-Circuit Voltage measurements for State Of Charge recalibration.
- avoid thermal runaway caused by current flow above operational limits; and/or
- ampere/hour counting for State Of Charge estimation.
- monitor the voltage and temperature in different vehicle operating mode and take necessary action to protect the cell from the degradation;
- measure battery current and pack voltage and calculate the State Of Charge;
- control the battery contactor based on different condition; and
- provide cell balancing mechanism to equate all the cell in same voltage level.
wherein the smart battery pack is designed to measure resistance in DC of each cell of the battery pack by driving a constant current step of defined amplitude into each cell and measure the resulting voltage variation at each cell terminals after a predefined amount of time. Smart battery pack for energy efficient and connected mobility for an electric propulsion system of an electric vehicle according to claim 1 and further designed to estimate a State of Health of the battery pack by measuring the resistance in DC of each cell of the battery pack,
wherein the smart battery pack is designed to measure resistance in DC of each cell of the battery pack by driving a constant current step of defined amplitude into each cell and measure the resulting voltage variation at each cell terminals after a predefined amount of time.
- measurement of the battery cells voltage;
- measurement of the battery cell temperature;
- current measurement of a module comprising several battery cells;
- communication of all the measured data to a Battery Management System (BMS) via a proper physical communication interface; and/or
- cell balancing, wherein:
- in case of passive balancing, the cells which have a higher charge will be discharged connecting a resistor in parallel, until all the cells are equalized;
- in case of active balancing, the cells which have a higher charge will be discharged with switching techniques over the cells with lower charge, which are charged accordingly, until all the cells are equalized.
- measurement of the battery cells voltage;
- measurement of the battery cell temperature;
- current measurement of a module comprising several battery cells;
- communication of all the measured data to a Battery Management System (BMS) via a proper physical communication interface; and/or
- cell balancing, in which:
- in case of passive balancing, the cells which have a higher charge will be discharged connecting a resistor in parallel, until all the cells are equalized;
- in case of active balancing, the cells which have a higher charge will be discharged with switching techniques over the cells with lower charge, which are charged accordingly, until all the cells are equalized.
- an EIS Command Generator designed to generate an EIS Command signal representing the current stimulus to be injected into the battery pack;
- a Power Current Driver designed to amplify the EIS command signal and provide the EIS current stimulus to the battery cells;
- an EIS Signals Acquisition Sub-system, for the coherent measurement of:
- Cell voltages for each battery cell; and
- EIS current flowing in the battery pack; and
- Data Processing System for the calculation of the EIS spectrum.
- an EIS Command Generator designed to generate an EIS Command signal representing the current stimulus to be injected into the battery pack;
- a Power Current Driver designed to amplify the EIS command signal and provide the EIS current stimulus to the battery cells;
- an EIS Signals Acquisition Sub-system, for the coherent measurement of:
- Cell voltages for each battery cell; and
- EIS current flowing in the battery pack; and
- Data Processing System for the calculation of the EIS spectrum.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP21175026.0 | 2021-05-20 | ||
| EP21175026 | 2021-05-20 | ||
| IT102022000010349 | 2022-05-18 | ||
| IT202200010349 | 2022-05-18 |
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| Publication Number | Publication Date |
|---|---|
| FR3123155A3 true FR3123155A3 (en) | 2022-11-25 |
| FR3123155B3 FR3123155B3 (en) | 2023-08-25 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| FR2204877A Active FR3123155B3 (en) | 2021-05-20 | 2022-05-20 | Smart battery pack for energy-efficient and connected mobility |
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| Country | Link |
|---|---|
| DE (1) | DE202022001227U1 (en) |
| FR (1) | FR3123155B3 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116691442A (en) * | 2023-08-04 | 2023-09-05 | 合肥力高动力科技有限公司 | Fault monitoring method and system for battery management system in battery charging equipment |
-
2022
- 2022-05-20 FR FR2204877A patent/FR3123155B3/en active Active
- 2022-05-20 DE DE202022001227.6U patent/DE202022001227U1/en active Active
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116691442A (en) * | 2023-08-04 | 2023-09-05 | 合肥力高动力科技有限公司 | Fault monitoring method and system for battery management system in battery charging equipment |
| CN116691442B (en) * | 2023-08-04 | 2023-10-13 | 合肥力高动力科技有限公司 | Fault monitoring method and system for battery management system in battery charging equipment |
Also Published As
| Publication number | Publication date |
|---|---|
| FR3123155B3 (en) | 2023-08-25 |
| DE202022001227U1 (en) | 2022-10-28 |
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