GB2556129A

GB2556129A - Systems and methods for monitoring isolation in high voltage systems

Info

Publication number: GB2556129A
Application number: GB1701562.9A
Authority: GB
Inventors: Puttagowramma Renukaradhva Nagaraj; Ramesh Latha; Naikodi Allabaksh; Selvam Kandasamy Ezhil
Original assignee: Mahindra Electric Mobility Ltd
Current assignee: Mahindra Electric Mobility Ltd
Priority date: 2016-11-18
Filing date: 2017-01-31
Publication date: 2018-05-23
Anticipated expiration: 2037-01-31
Also published as: GB2556129B; GB201701562D0; CN108072792A

Abstract

Monitoring isolation in at least one High Voltage (HV) system present in an Electric Vehicle (EV) by calculating a leakage ratio as Vpack/Vi, wherein Vpack is the voltage of a vehicle battery and Vi is input voltage to a differential amplifier. A leakage resistance is determined using the calculated leakage ratio, and the leakage current as Vpack/leakage resistance. At least one action is performed if the leakage current has crossed pre-defined thresholds. The system comprises a series resistor chain having two high value resistances and two low value resistances, a power supply 602, a differential amplifier 603, an ADC (Analog to Digital Converter) 604, an isolator 605, and a controller 606. The high value resistances are connected to the positive and negative terminals of a battery 601. The low value resistances are connected across inverting and non-inverting inputs of the differential amplifier and a junction of the low value resistances is connected to chassis of the EV. The differential amplifier monitors voltage difference between the inverting and non-inverting inputs. The ADC 604 converts the voltage difference into digital form and the isolator isolates digital data from output of the ADC.

Description

(54) Title of the Invention: Systems and methods for monitoring isolation in high voltage systems Abstract Title: Monitoring isolation in a high voltage system in an electric vehicle (57) Monitoring isolation in at least one High Voltage (HV) system present in an Electric Vehicle (EV) by calculating a leakage ratio as Vpack/Vi, wherein Vpack is the voltage of a vehicle battery and Vi is input voltage to a differential amplifier. A leakage resistance is determined using the calculated leakage ratio, and the leakage current as Vpack/ leakage resistance. At least one action is performed if the leakage current has crossed pre-defined thresholds. The system comprises a series resistor chain having two high value resistances and two low value resistances, a power supply 602, a differential amplifier 603, an ADC (Analog to Digital Converter) 604, an isolator 605, and a controller 606. The high value resistances are connected to the positive and negative terminals of a battery 601. The low value resistances are connected across inverting and non-inverting inputs of the differential amplifier and a junction of the low value resistances is connected to chassis of the EV. The differential amplifier monitors voltage difference between the inverting and non-inverting inputs. The ADC 604 converts the voltage difference into digital form and the isolator isolates digital data from output of the ADC.

600 s

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FIG. 2

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-fPropulsion Battery chassis

FIG. 3

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FIG. 5

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FIG. 7 “Systems and methods for monitoring isolation in high voltage systems”

FIELD OF INVENTION [001] This invention relates to high voltage systems, and more particularly to monitoring isolation in high voltage systems.

BACKGROUND OF INVENTION [002] Currently, due to a growing environmental consciousness in society, use of vehicles powered by non-gasoline sources, such as electric vehicles (EV). The EV requires a high voltage battery pack to provide energy to modules present in the EV (such as a traction control unit to drive an A.C motor, a DC-DC converter to supply low voltage typically 12V to source ECUs, and so on). The high voltage (HV) battery pack can operate at voltages as high as 600V. In a typical electric vehicle environment, characterized by a low skin resistance (wet skin likely) and a contact with conductive bodies, the security extra low voltage level is 25 V for AC and 60 V for DC. The voltages used on EVs are thus potentially dangerous and measures should be taken to prevent electrocution through direct or indirect contact. For example, during the charging process, there may be potential issues such as high voltage leakage. In a scenario, a malfunction in the on-board charger can make a direct or indirect connection of one of its high voltage power supply lines to the chassis of the EV causing isolation failure. The HV battery pack serves as power and grounding lines for the HV systems. The HV systems are electrically connected in parallel to the vehicle chassis and hence float on the chassis. Therefore, an electrical resistance barrier has to be maintained between HV systems and chassis to ensure safety for the user and service personnel.

[003] Current isolation monitoring solutions can be complex and expensive, using switches, optical couplers and additional power sources for detecting isolation faults. Existing solutions may not continuously monitor the leakage current, the time will be spent on turning the switching elements, additional power supply units and so on. If the fault is intermittent, the existing system may fail to detect. Existing solutions also use separate fault detection circuits to measure DC and AC leakage currents.

OBJECT OF INVENTION [004] The principal object of this invention is to provide methods and systems for monitoring isolation in high voltage systems present in Electric Vehicles (EVs).

[005] Another object of the invention is to provide methods and systems for identifying leakage current in high voltage systems present in Electric Vehicles (EVs).

BRIEF DESCRIPTION OF FIGURES [006] This invention is illustrated in the accompanying drawings, through out which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[007] FIGs. 1-5 depict example methods for measuring isolation between the HV modules and the chassis of the EV, according to embodiments as disclosed herein;

[008] FIG. 6 depicts a system for monitoring isolation between the HV battery pack lines and the EV chassis, according to embodiments as disclosed herein; and [009] FIG. 7 is a flowchart depicting a process of monitoring isolation between the

HV battery pack lines and the EV chassis, according to embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION [0010] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0011] The embodiments herein disclose provide methods and systems for monitoring isolation in high voltage (HV) systems present in Electric Vehicles (EVs). Referring now to the drawings, and more particularly to FIGS. 1 through 7, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0012] The electric vehicle (EV) as referred to herein can be a car, a van, a twowheeler, a three-wheeler, a truck, a bus, a farm vehicle, a heavy vehicle, a kart-like vehicle, a racing car, or any other vehicle capable of being powered by electrical energy stored in an on-board energy storage means (such as batteries, super capacitors, rechargeable traction batteries, electric double-layer capacitors or flywheel energy storage, and so on). The EV can be powered only by electrical energy or can comprise of another means of power (as in a hybrid vehicle), such as a petrol/diesel engine, and so on.

[0013] Isolation can be defined as an electrical resistance barrier that exists between the HV (High Voltage) modules and a chassis of the EV.

[0014] Electronic Control Units (ECUs), which control HV functions, typically use a lower voltage level (for example, 12 Volts). To protect the vehicle, an isolation barrier has to be between the HV system components and the chassis. The isolation barrier can be an electrical resistance barrier. According to the FMVSS-305 standard, Electric-powered vehicles: electrolyte spillage and electrical shock protection specified by Japan Automobile Standards Internationalization Center (JASIC), it is necessary to have a minimum isolation resistance of 500Ω/νο1ΐ between the HV system and chassis. The vehicle chassis must be continually monitored for loss of isolation to ensure occupant safety anytime the vehicle systems are operational.

[0015] Consider that the voltmeter used for measurement herein measures direct current values and has an internal resistance of at least 10ΜΩ. The propulsion battery voltage (Vb) is measured as depicted in FIG. 1. Before any vehicle impact test, Vb should be equal to or greater than the nominal operating voltage as specified by the vehicle manufacturer. The voltage (VI) between the negative side of the propulsion battery and the vehicle chassis is measured as shown in FIG. 2. The voltage (V2) between the positive side of the propulsion battery and the vehicle chassis is measured as shown in FIG. 3.

[0016] If VI is greater than or equal to V2, a known resistance (Ro) is inserted between the negative side of the propulsion battery and the vehicle chassis. With the Ro installed, the voltage (VI¹) between the negative side of the propulsion battery and the vehicle chassis is measured, as depicted in FIG. 4. The electrical isolation (Ri Ω) is measured, according to the following formula:

Ri=Ro(l+V2/Vl)[(Vl-Vl’)/Vl’] Ω [0017] This electrical isolation value divided by the nominal operating voltage of the battery (in volts) must be equal to or greater than 500.

[0018] If V2 is greater than VI, a known resistance (Ro) is inserted between the positive side of the propulsion battery and the vehicle chassis. With Ro present, the voltage (V2¹) between the positive side of the propulsion battery and the vehicle chassis is measured, as shown in FIG. 5. The electrical isolation (Ri Ω) is calculated according to the following formula:

Ri = Ro(l+Vl/V2)[(V2-V2’)/V2’] Ω [0019] The electrical isolation value divided by the nominal operating voltage of the battery (in volts) must be equal to or greater than 500.

[0020] FIG. 6 depicts a system for monitoring isolation between the HV battery pack lines and the EV chassis. The system 600 comprises of a series resistor chain connected to the HV battery 601. The system 600, as depicted, further comprises of a power supply 602, a differential amplifier 603, an ADC (Analog to Digital Controller) 604, an isolator 605, and a controller 606.

[0021] The series resistor chain comprises of high value resistances RI and R2 (which can be in the mega ohms range) and low value resistances R3 and R4 (which can be in the kilo ohms range). RI and R2 can be connected to the positive and negative terminals of the HV battery 601 respectively, through battery contacts K1 and K2 respectively. R3 and R4 are connected across the inverting and non-inverting inputs of the differential amplifier 603. The R3-R4 junction is connected to the chassis of the EV. The differential amplifier 603 can continuously monitor the voltage difference between its non-inverting and inverting inputs. In an embodiment herein, the differential amplifier 603 comprises of an operational amplifier. The ADC 604 can convert the read difference voltage from the differential amplifier 603 into equivalent digital form. The power supply 602 can be used to source the power to the ADC 604 and the HV side of the isolator 605. The isolator 605 can pass the data to the low voltage section, while isolating the digital data. The controller 606 can process the read voltage in digital format. The controller 606 can read the input voltage ‘Vi’ from the differential amplifier 603, where Vi is the difference voltage measured by the differential amplifier 603 and calculate the leakage ratio by using the following formula:

Leakage ratio = Vpack/Vi

Where Vpack is the vehicle’s pack voltage of the battery 601. The controller 606 can determine the equivalent leakage resistance using the look up table method. The look up table method comprises of the controller 606 comparing the computed leakage ratio to a table (comprising of leakage ratios and corresponding leakage resistances) present in a memory (wherein the memory can be internal to the controller 606 or external to the controller 606). The controller 606 can control the battery contacts K1 and K2.

[0022] FIG. 7 is a flowchart depicting a process of monitoring isolation between the HV battery pack lines and the EV chassis. The controller 606 calculates (701) the leakage ratio by using the following formula:

Leakage ratio = Vpack/Vi [0023] The controller 606 determines (702) the equivalent leakage resistance using the look up table method. The look up table method comprises of the controller 606 comparing the computed leakage ratio to the table (comprising of leakage ratios and corresponding leakage resistances) present in a memory. The controller 606 determines (703) the leakage current using the following formula:

Leakage current = Vpack/ Leakage resistance [0024] The controller 606 checks (704) if the leakage current has crossed pre-defined thresholds. The manufacturer of the EV or any other authorized person/entity can define the pre-defined thresholds. A first threshold can be a positive threshold value, wherein the controller 606 checks if the resistance between the positive terminal of the battery and the chassis reduces below the positive threshold value. A second threshold can be a negative threshold value, wherein the controller 606 checks if the resistance between the negative terminal of the battery and the chassis reduces below the negative threshold value. In an embodiment herein, the threshold values can depend on the minimum isolation/leakage resistance of 500Q/volt. In an example herein, if the vehicle leakage resistance reduces below 500Q/volt during the failure condition, the controller 606 can determine that it as a failure condition. If the leakage current has exceeded the pre-defined threshold, the controller 606 performs (705) at least one action such as providing an alert, disconnecting the HV battery and so on. The alert can be in form of at least one of a visual and/or audio alert, such as a glowing indication, a chime/alarm, and so on. The alert can also be in the form of an error code, such as a Diagnostic trouble code (DTC). The controller 606 can disconnect the HV battery by disconnecting the battery contacts K1 and K2. The alert can be a service alert on the cluster, wherein the controller 606 can provide instructions to drive the vehicle to a nearby service station to get the failure rectified. Once after the failure part or connection in the vehicle is identified and corrected at the service station, the controller 606 reads the leakage current of the vehicle and if the reading is within in the acceptable limits, the vehicle allows the battery to be connected back by the service personnel. Depending upon the severity of the failure, the battery will be disconnected. The various actions in method 700 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 7 may be omitted.

[0025] Embodiments disclosed herein disclose low cost differential methods and systems to determine the leakage with isolated monitoring architecture. Embodiments disclosed herein have a less complex design, as compared to existing solutions. Embodiments disclosed herein can monitor isolation status continuously. Embodiments disclosed herein do not require any additional variable power source and switching element.

[0026] The embodiment disclosed herein describes methods and systems for monitoring isolation in HV systems present in EVs. Therefore, it is understood that the scope of the protection is extended to such a program and in addition to a computer readable means having a message therein, such computer readable storage means contain program code means for implementation of one or more steps of the method, when the program runs on a server or mobile device or any suitable programmable device. The method is implemented in a preferred embodiment through or together with a software program written in e.g. Very high speed integrated circuit Hardware Description Fanguage (VHDF) another programming language, or implemented by one or more VHDF or several software modules being executed on at least one hardware device. The hardware device can be any kind of portable device that can be programmed. The device may also include means which could be e.g. hardware means like e.g. an ASIC, or a combination of hardware and software means, e.g. an ASIC and an FPGA, or at least one microprocessor and at least one memory with software modules located therein. The method embodiments described herein could be implemented partly in hardware and partly in software. Alternatively, the invention may be implemented on different hardware devices, e.g. using a plurality of CPUs.

[0027] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

STATEMENT OF CLAIMS

Claims

We claim:

1. A system (600) for monitoring isolation in at least one High Voltage (HV) system present in an Electric Vehicle (EV), the system comprising a series resistor chain comprising of two high value resistances and two low value resistances, a power supply (602) a differential amplifier (603), an ADC (Analog to Digital Controller) (604), an isolator (605), and a controller (606), wherein the high value resistances are connected to the positive and negative terminals of a battery (601) present in the EV;

the low value resistances are connected across inverting and non-inverting inputs of the differential amplifier (603) and a junction of the low value resistances is connected to chassis of the EV;

the differential amplifier (603) monitors voltage difference between the inverting and non-inverting inputs;

the ADC (604) converts the voltage difference into digital form;

the isolator (605) isolating digital data from output of the ADC (604); and the controller (606) configured for calculating leakage ratio as Vpack/Vi, wherein Vpack is the voltage of the battery (601) and Vi is input voltage to the differential amplifier (603);

determining leakage resistance using the calculated leakage ratio;

determining leakage current as Vpack/leakage resistance; and performing at least one action, if the leakage current has crossed pre-defined thresholds.

2. The system, as claimed in claim 1, wherein the at least one action can comprise of providing an alert by the controller (606) to the user; and disconnecting the battery (601) by the controller (606) using a plurality of battery contacts.

3. The system, as claimed in claim 2, wherein the controller (606) is further configured for reconnecting the battery (601), if the leakage current is within the pre-defined thresholds.

4. A vehicle comprising a system (600) for monitoring isolation in at least one High Voltage (HV) system present in the vehicle, the system comprising a series resistor chain comprising of two high value resistances and two low value resistances, a power supply (602) a differential amplifier (603), an ADC (Analog to Digital Controller) (604), an isolator (605), and a controller (606), wherein the high value resistances are connected to the positive and negative terminals of a battery (601) present in the vehicle;

the low value resistances are connected across inverting and non-inverting inputs of the differential amplifier (603) and a junction of the low value resistances is connected to chassis of the vehicle;

the ADC (604) converts the voltage difference into digital form;

determining leakage resistance using the calculated leakage ratio;

5. The vehicle, as claimed in claim 4, wherein the at least one action can comprise of providing an alert by the controller (606) to the user; and disconnecting the battery (601) by the controller (606) using a plurality of battery contacts.

6. The vehicle, as claimed in claim 5, wherein the controller (606) is further configured for reconnecting the battery (601), if the leakage current is within the pre-defined thresholds.

7. A method for monitoring isolation in at least one High Voltage (HV) system present in an Electric Vehicle (EV), the method comprising calculating leakage ratio as Vpack/Vi by the controller (606), wherein Vpack is voltage of a battery (601) present in the EV and Vi is input voltage to a differential amplifier (603);

determining leakage resistance by the controller (606) using the calculated leakage ratio; determining leakage current by the controller (606) as Vpack/leakage resistance; and performing at least one action by the controller (606), if the leakage current has crossed pre-defined thresholds.

8. The method, as claimed in claim 7, wherein the at least one action can comprise of providing an alert by the controller (606) to the user; and disconnecting the battery (601) by the controller (606) using a plurality of battery contacts.

9. The method, as claimed in claim 8, wherein the controller (606) is further configured for reconnecting the battery (601), if the leakage current is within the pre-defined thresholds.

Intellectual

Property

Office

Application No: Claims searched:

GB1701562.9

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