CN115663973A

CN115663973A - Active equalization circuit and method for battery pack

Info

Publication number: CN115663973A
Application number: CN202211452470.2A
Authority: CN
Inventors: 王君; 袁明祥
Original assignee: Hangzhou Xieneng Technology Co ltd
Current assignee: Hangzhou Xieneng Technology Co ltd
Priority date: 2022-11-21
Filing date: 2022-11-21
Publication date: 2023-01-31

Abstract

The invention provides an active equalization circuit and method for a battery pack. Wherein, this active equalizer circuit's equalizer module includes: the battery pack comprises a plurality of balancing units, each balancing unit is connected with a corresponding group of adjacent batteries in the battery pack, and the balancing units are used for gating energy transmission paths of the balancing units through switch control signals under the condition of energy imbalance between the adjacent batteries and performing energy transfer between the adjacent batteries so as to achieve energy balance between the adjacent batteries. Therefore, the switching of the energy path can be realized by utilizing the balanced topology structure under the control of the switch control signal, the energy can be directly transferred to the battery with lower energy from the battery with higher energy, the energy transfer between adjacent batteries is realized, the phenomenon of over-charge and over-discharge of each single battery in the charging and discharging process is ensured, the unbalanced problem of the series battery pack is solved, and the balanced efficiency and the upper limit of the working voltage of the battery pack are improved.

Description

Active equalization circuit and method for battery pack

Technical Field

The disclosure relates to the technical field of battery management, in particular to an active equalization circuit and method for a battery pack.

Background

With the development of new energy industry, battery systems are widely applied in the fields of automobiles and energy storage. In order to increase the battery capacity, the number of series-parallel connection of the batteries is increasing, but the inconsistency of the cell voltages in the battery system can seriously affect the battery capacity and the service life of the battery pack. According to the barrel effect, the battery pack is obviously inferior to the monomer performance in the aspects of cycle life, capacity utilization rate and the like. Along with the recycling of the battery pack, the inconsistency of the monomers is aggravated, the grouping characteristic of the lithium ion battery is further worsened, and the overcharge and overdischarge conditions of a few monomers are easy to occur, so that the performance of the battery pack is greatly attenuated, even serious accidents such as combustion and explosion can occur under extreme conditions, and great obstruction is caused to the application and popularization of the lithium ion battery.

The battery pack is subjected to balance control, namely, in the recycling process, the monomer energy in the battery pack is timely balanced in an energy consumption or transfer mode, so that the probability of overcharge and overdischarge of the monomer is reduced, and the adverse effect of the discharge depth difference on the battery pack is eliminated. Specifically, when the voltage of a certain battery is too low, the energy of the connected power supply is transferred to the battery, otherwise, the energy with the too high voltage of the battery is transferred to the power supply, so that the real-time balance during charging and discharging is completely realized, and the potential of each battery is exerted. Each battery can be fully charged during charging, and each battery can be placed to the lowest limit during discharging, so that the capacity of each battery of the battery pack can be fully exerted. Therefore, the overall energy utilization rate of the battery pack is improved, and the cycle life of the battery can be prolonged.

Fig. 1 is a schematic diagram of a conventional battery management system, in which each balancing module can control two adjacent batteries, specifically: the balancing module A1 controls the battery BAT1 and the battery BAT2, the balancing module A2 controls the battery BAT3 and the battery BAT2, the balancing module A3 controls the battery BAT4 and the battery BAT3 \8230, and so on, the balancing module An-1 controls the battery BATn and the battery BATn-1, the balancing modules A1, A2 and An-1 are controlled to be turned on and off through a Micro Control Unit (MCU), and An active balancing chip controls An internal switching tube to realize energy transfer.

Disclosure of Invention

The active equalization circuit and method for the battery pack can solve the problems that in the prior art, the number of equalization devices is large and the cost is high in series battery pack equalization topology.

In one aspect the present invention provides an active equalization circuit for a battery pack, the battery pack comprising a plurality of cells connected in series, the active equalization circuit comprising:

a plurality of equalizing units, each equalizing unit being connected to a respective set of adjacent cells of the plurality of cells,

the balancing unit is used for gating an energy transmission path of the balancing unit through a switch control signal under the condition of energy imbalance between the adjacent batteries, and energy transfer is carried out between the adjacent batteries so as to achieve energy balance between the adjacent batteries.

Preferably, the plurality of equalization units respectively include:

a plurality of energy storage elements, and energy transfer between the adjacent cells using a charging and discharging process of the plurality of energy storage elements.

Preferably, the active equalization circuit works in a half-bridge mode, and at least can complete energy transfer between the nth battery and the (n + 1) th battery;

the active equalization circuit works in a CUK mode and can at least complete energy transfer between the (2 x n) th battery and the (2 x n + 3) th battery, wherein n is a positive odd number.

Preferably, the plurality of energy storage elements comprises:

the first inductor, the first capacitor, the second capacitor and the third inductor are sequentially connected in series between a middle node of the first battery and the second battery and a middle node of the fifth battery and the sixth battery; and

and the second inductor is connected between an intermediate node of the third battery and the fourth battery and an intermediate node of the first capacitor and the second capacitor.

Preferably, the plurality of equalizing units respectively comprise a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube and a sixth switching tube which are sequentially connected in series between the first battery and the sixth battery,

the middle node of the first switching tube and the second switching tube is connected with the middle node of the first inductor and the first capacitor, the middle node of the second switching tube and the third switching tube is connected with the middle node of the second battery and the third battery, the middle node of the third switching tube and the fourth switching tube is connected with the middle node of the second inductor and the first capacitor, the middle node of the fourth switching tube and the fifth switching tube is connected with the middle node of the fourth battery and the fifth battery, and the middle node of the fifth switching tube and the sixth switching tube is connected with the middle node of the second capacitor and the third inductor.

Preferably, the active equalization circuit works in a half-bridge mode, and controls the conduction states of the first switching tube and the second switching tube according to the battery voltage of the first battery.

Preferably, when the battery voltage of the first battery is greater than the voltage threshold of the second battery, the first battery charges the second battery by controlling the conduction states of the first switch tube and the second switch tube in a first time period and a second time period which are continuous.

Preferably, in the first time period, the first switch tube is turned on and the second switch tube is turned off, the first battery charges the first inductor,

in the second time period, the first switch tube is turned off and the second switch tube is turned on, and the first inductor charges the second battery.

Preferably, when the battery voltage of the first battery is smaller than the voltage threshold of the second battery, the conducting states of the first switch tube and the second switch tube are controlled in a third period and a fourth period which are continuous, and the second battery charges the first battery.

Preferably, in the third time period, the first switch tube is turned off and the second switch tube is turned on, the second battery charges the first inductor,

in the fourth time period, the first switch tube is turned on and the second switch tube is turned off, and the first inductor charges the first battery.

Preferably, the energy of the third battery, the fourth battery and the fifth battery is in reactive circulation in the second inductor, the third inductor, the first capacitor and the second capacitor.

Preferably, the active equalization circuit operates in a CUK mode, and controls the conduction states of the second switching tube and the fifth switching tube according to the battery voltage of the second battery.

Preferably, when the battery voltage of the second battery is greater than the voltage threshold of the fifth battery, the second battery charges the fifth battery by controlling the conduction states of the second switching tube and the fifth switching tube in a first period and a second period which are consecutive.

Preferably, in the first time period, the second switch tube is turned on and the fifth switch tube is turned off, the second battery charges the first inductor, and the first capacitor and the second capacitor charge the third inductor,

in the second time period, the second switch tube is turned off, the fifth switch tube is turned on, the third inductor charges the fifth battery, and the first inductor charges the first capacitor and the second capacitor.

Preferably, when the battery voltage of the second battery is smaller than the voltage threshold of the fifth battery, the on-state of the second switching tube and the fifth switching tube is controlled in a third period and a fourth period which are consecutive, and the fifth battery charges the second battery.

Preferably, in the third time period, the second switch tube is turned off and the fifth switch tube is turned on, the fifth battery charges the third inductor, and the first capacitor and the second capacitor charge the first inductor,

in the fourth time period, the second switch tube is turned on and the fifth switch tube is turned off, the first inductor charges the second battery, and the third inductor charges the first capacitor and the second capacitor.

In another aspect, the present invention further provides an active equalization method for a battery pack, where the battery pack includes a plurality of batteries connected in series, and adjacent batteries in the plurality of batteries are connected to corresponding equalization units, the active equalization method includes:

detecting a cell voltage of a target cell among the adjacent cells;

judging the energy unbalance situation of the adjacent batteries according to the battery voltage; and

under the condition of energy imbalance between the adjacent batteries, the energy transmission path of the balancing unit is gated through a switch control signal, and energy transfer is carried out between the adjacent batteries so as to achieve energy balance between the adjacent batteries.

Preferably, the step of determining the energy imbalance condition of the adjacent battery according to the battery voltage comprises:

comparing the cell voltage of the target cell to voltage thresholds of remaining ones of the neighboring cells; and

confirming that an energy imbalance condition exists when the cell voltage of the target cell is greater than or less than the voltage threshold.

Preferably, after the step of determining the energy imbalance condition of the adjacent battery according to the battery voltage, the active balancing method further includes:

the active equalization circuit is selected to operate in a half-bridge mode or a CUK mode,

wherein, when the active equalization circuit is selected to operate in a half-bridge mode, the step of transferring energy between the adjacent batteries comprises:

energy transfer between two adjacent batteries is performed by adopting a charging and discharging process of an energy storage element, the energy storage element comprises a first inductor connected between the two adjacent batteries,

and selecting the active equalization circuit to work in a CUK mode, and performing energy transfer between the adjacent batteries comprises the following steps:

the energy transfer is carried out between the adjacent batteries by adopting the charging and discharging processes of a plurality of energy storage elements, and the plurality of energy storage elements comprise a first inductor, a first capacitor, a second capacitor and a third inductor which are sequentially connected in series between the middle node of the first battery and the second battery and the middle node of the fifth battery and the sixth battery.

Preferably, the target battery is a first battery, the active balancing circuit is selected to operate in a half-bridge mode, and the step of transferring energy between the adjacent batteries comprises:

when the battery voltage of the first battery is greater than the voltage threshold of the second battery,

and in a first time period, controlling the first battery to charge the first inductor, and in a second time period, controlling the first inductor to charge the second battery.

when the battery voltage of the first battery is less than the voltage threshold of the second battery,

and in a third time period, controlling the second battery to charge the first inductor, and in a fourth time period, controlling the first inductor to charge the first battery.

Preferably, the target battery is a second battery, the active equalization circuit is selected to operate in the CUK mode, and the step of performing energy transfer between the adjacent batteries includes:

when the battery voltage of the second battery is greater than the voltage threshold of the fifth battery,

in a first time period, controlling the second battery to charge the first inductor and controlling the first capacitor and the second capacitor to charge the third inductor,

and in a second time period, controlling the third inductor to charge the fifth battery, and controlling the first inductor to charge the first capacitor and the second capacitor.

when the battery voltage of the second battery is less than the voltage threshold of the fifth battery,

in a third time period, controlling the fifth battery to charge the third inductor and controlling the first capacitor and the second capacitor to charge the first inductor,

and in a fourth time period, controlling the first inductor to charge the second battery, and controlling the third inductor to charge the first capacitor and the second capacitor.

The beneficial effects of the invention are: the invention provides an active equalization circuit and method for a battery pack, wherein the battery pack comprises a plurality of batteries which are connected in series, and the active equalization circuit comprises: the battery pack comprises a plurality of balancing units, each balancing unit is connected with a corresponding group of adjacent batteries in the plurality of batteries, and the balancing units are used for gating energy transmission paths of the balancing units through switch control signals under the condition of energy imbalance between the adjacent batteries, so that energy transfer is carried out between the adjacent batteries, and energy balance between the adjacent batteries is achieved. Therefore, under different working modes, the switching of the energy path is realized by utilizing the balanced topological structure under the control of the switch control signal, and the energy can be directly transferred from the battery with higher energy to the battery with lower energy.

The half-bridge mode is suitable for energy transfer based on a topology structure of a minimum balance unit (connecting two batteries), and can realize energy transfer between adjacent batteries; the CUK mode is suitable for energy transfer between any even-numbered (2 x n) battery and any odd-numbered (2 x n + 3) battery, and based on the common element connection design of adjacent minimum balancing units, the energy transfer between nonadjacent batteries can be realized, the phenomenon of over-charge and over-discharge of each single battery in the charging and discharging processes is ensured, the problem of unbalance of the series battery pack is solved, and the service life of the battery pack is prolonged.

Furthermore, the frequency and the duty ratio of the switch control signal can be controlled, so that the inductance-capacitance circuit works in a quasi-resonance state, the current of the inductance-capacitance series circuit is zero when the switch is switched on or off every time, zero current switching is realized, and the switching loss of the equalizing circuit is greatly reduced.

Meanwhile, the active equalization circuit provided by the disclosure has no limitation on the number of the battery strings, can greatly improve the upper limit of the working voltage of the battery pack, has a simple topological structure, has a small working number of modules, and can effectively improve the equalization efficiency.

In addition, based on the topological structure of the minimum equalizing unit (connecting two batteries) and the common inductance connecting design of the adjacent minimum equalizing units, the active equalizing circuit provided by the disclosure has the advantages of high module integration, few equalizing devices and low cost.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure with reference to the accompanying drawings.

Fig. 1 is a schematic diagram illustrating a partial structure of an equalizing circuit in a conventional battery system;

fig. 2 illustrates a schematic topology of an active equalization circuit provided by an embodiment of the present disclosure;

fig. 3a and 3b are schematic diagrams illustrating operation of the active equalization circuit of fig. 2 in a first time period and a second time period of energy transfer in a half-bridge mode, respectively;

fig. 3c and 3d are schematic diagrams illustrating operation of the active equalization circuit of fig. 2 in a third period and a fourth period of energy transfer in a half bridge mode, respectively;

fig. 4a and 4b are schematic diagrams illustrating operation of the active equalization circuit shown in fig. 2 during a first time period and a second time period of CUK mode energy uploading, respectively;

FIGS. 4c and 4d are schematic diagrams illustrating operation of the active equalization circuit of FIG. 2 during a third time period and a fourth time period, respectively, of CUK mode energy transfer;

fig. 5 is a schematic structural diagram of a battery management system provided in an embodiment of the present disclosure;

fig. 6 illustrates a flowchart of an active balancing method in a battery management system according to an embodiment of the present disclosure;

fig. 7 is a schematic diagram illustrating a model application of the active equalization method shown in fig. 6 applied to the active equalization circuit shown in fig. 2.

Detailed Description

To facilitate an understanding of the present disclosure, the present disclosure will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present disclosure are set forth in the accompanying drawings. This disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure.

In order to improve the inconsistency of the battery pack in the prior art and improve the overall performance of the battery pack, the equalization control is required. The existing lithium ion battery pack balance control method can be divided into two categories, namely an energy dissipation type method and an energy non-dissipation type method according to the energy consumption condition of a circuit in a balance process; the dissipation type is that a shunt resistor is connected in parallel outside each single battery, the energy of the battery module with higher residual capacity is consumed through the resistor by controlling the corresponding switch device, the method wastes the energy, a large amount of heat is generated in the balancing process, and the load of battery thermal management is increased. The non-dissipative type achieves energy transfer through a DC-DC circuit external to the battery.

The balance function is classified into charge balance, discharge balance, and dynamic balance. The charge equalization refers to equalization in the charging process, generally, equalization is started when the voltage of a battery pack monomer reaches a set value, and overcharge is prevented by reducing charge current; the discharge balance refers to balance in a discharge process, and prevents over-discharge by supplementing energy to the battery cells with low residual energy; the dynamic equalization mode combines the advantages of charge equalization and discharge equalization, and means equalization of the battery pack in the whole charge and discharge process. The balancing device can be divided into topologies such as a switched capacitor type, a switched inductor type, a transformer type, a DC-DC converter type and the like.

The traditional switched capacitor equalization circuit is simple in structure and control method. However, the problems of large loss, low equalization efficiency, low equalization speed and the like of hard switches exist. And the equalization device is more, the equalization circuit is larger in size and high in cost. And the equalization current of the equalization circuit based on LC quasi-resonance is limited by the battery voltage difference at two ends of the LC, and along with the reduction of the battery voltage difference, the equalization current of the LC quasi-resonance circuit is sharply reduced, and the equalization speed is greatly reduced.

Based on this, the embodiment of the invention provides an active equalization circuit and method for a battery pack, so as to solve the problems of high power loss, many equalization devices, low equalization efficiency and high cost of a series battery pack equalization topology in the prior art.

The present disclosure is described in detail below with reference to the accompanying drawings.

Fig. 2 shows a schematic topology of an active equalization circuit provided in an embodiment of the present disclosure.

Referring to fig. 2, in one aspect the present disclosure provides an active equalization circuit 100 for a battery pack 200, the active equalization circuit 100 comprising: a plurality of equalizing units (not shown), each of which is connected to a corresponding group of adjacent cells in the battery pack 200, wherein the battery pack 200 includes a plurality of cells connected in series, as shown in fig. 2, for example, six strings of cells; batteries BAT1, BAT2, BAT3, BAT4, BAT5, BAT6 connected in sequence from bottom to top. The plurality of equalizing units respectively include: a plurality of energy storage elements, and the equalizing unit performs energy transfer between the adjacent cells using a charging and discharging process of the plurality of energy storage elements. Referring to fig. 2, the active equalization circuit 100 includes switching tubes Q1, Q2, Q3, Q4, Q5, and Q6, and a plurality of energy storage elements as described above, where the plurality of energy storage elements include power inductors L1, L2, and L3, and energy storage capacitors C1 and C2, when the battery pack 200 needs to be maintained in equalization, a Micro Control Unit (MCU) provided by a battery management system (not shown) in this embodiment) will execute an equalization operation strategy, and send a switch Control signal to a driver (not shown) that needs to operate, and the corresponding driver controls on/off of the switching tube connected to the Micro Control Unit to perform energy transfer, so as to implement energy transfer of the entire battery management system.

In this embodiment, the active equalization is a dynamic equalization, and is completed by matching the connection design of the equalization unit and the adjacent equalization unit, and the equalization unit can select a corresponding working mode according to the working requirement, for example: the active equalization circuit 100 works in a half-bridge mode, and at least can complete energy transfer between the nth battery and the (n + 1) th battery (such as batteries BAT1 and BAT 2); the active balancing circuit 100 operates in the CUK mode, and at least completes energy transfer between the (2 x n) th cell and the (2 x n + 3) th cell (for example, the cells BAT2 and BAT 5) to complete energy balancing between adjacent single cells connected by the balancing unit, wherein n is a positive odd number. When the difference of the battery power in the battery pack 200 is large enough to meet the operation requirement of the active equalization circuit, each equalization unit starts to operate. When the battery difference in the battery pack 200 is smaller than the set value, the active equalization circuit 100 stops working, and the equalization operation ends. The switching devices in all active equalization circuits 100 respond to the switching control signals (e.g., EN 1-EN 6, provided by the battery management system, in this embodiment, the circuits thereof are not provided), and the transfer of energy is controlled by controlling the on/off of the switching devices Q1-Q6, so as to realize the equalization of the battery pack 200.

In the present embodiment, the topology of the system basically has no limitation on the number of series connections of the single batteries, and the single batteries can be infinitely cascaded upwards, so that the upper limit of the operating voltage of the battery pack 200 can be greatly increased.

In this embodiment, the active equalization circuit 100 includes a plurality of equalization units connected in series in sequence, each equalization unit manages at least two adjacent batteries connected thereto, which is different from the equalization circuit in the prior art shown in fig. 1, and the active equalization circuit has a simple topology structure, highly integrated modules, high equalization efficiency, few equalization devices, a small circuit volume, and a greatly reduced cost.

The balancing unit can be used for selecting a balancing topological structure under the control of a switch control signal under different working modes under the condition of energy imbalance between a group of adjacent batteries, so that the switching of an energy path is realized, the energy transmission path of the balancing unit is gated through the switch control signal, the energy is transferred from the battery with higher energy to the battery with lower energy, and the voltage balance of the batteries between at least two adjacent batteries is realized.

In this embodiment, an example of a balancing unit connected to a group of adjacent batteries BAT1 to BAT6 in the active balancing circuit 100 shown in fig. 2 is selected, the balancing unit includes a switching tube Q1, a switching tube Q2, a switching tube Q3, a switching tube Q4, a switching tube Q5, and a switching tube Q6 which are sequentially connected in series between the batteries BAT1 and BAT6, and control ends of the switching tubes Q1 to Q6 are sequentially connected to the switching control signals EN1 to EN6.

A plurality of energy storage elements in the balancing unit comprise an inductor L1, an inductor L2, a capacitor C1, a capacitor C2 and an inductor L3, the inductor L1, the capacitor C2 and the inductor L3 are sequentially connected in series between an intermediate node of the battery BAT1 and the battery BAT2 and an intermediate node of the battery BAT5 and the battery BAT6, and the inductor L2 is connected between an intermediate node of the battery BAT3 and the battery BAT4 and an intermediate node of the capacitor C1 and the capacitor C2.

The middle node of the switching tube Q1 and the switching tube Q2 is connected with the middle node of the inductor L1 and the middle node of the capacitor C1, the middle node of the switching tube Q2 and the switching tube Q3 is connected with the middle node of the battery BAT2 and the battery BAT3, the middle node of the switching tube Q3 and the switching tube Q4 is connected with the middle node of the inductor L2 and the middle node of the capacitor C1, the middle node of the switching tube Q4 and the switching tube Q5 is connected with the middle node of the battery BAT4 and the battery BAT5, and the middle node of the switching tube Q5 and the switching tube Q6 is connected with the middle node of the capacitor C2 and the middle node of the inductor L3.

The active equalization circuit 100 may select its equalization unit to operate in different modes of operation: the half-bridge mode is suitable for energy transfer based on a topology structure of a minimum equalization unit (connecting two batteries), and can realize energy transfer between adjacent batteries; the CUK mode is suitable for energy transfer between any other even-numbered (2 x n) battery and odd-numbered (2 x n + 3) battery, and based on the common element connection design of the adjacent minimum balancing units, the energy transfer between non-adjacent batteries can be realized, so that the phenomenon of over-charge and over-discharge of each single battery is avoided in the charging and discharging processes, the problem of unbalance of the series battery pack is solved, and the service life of the battery pack is prolonged.

Fig. 3a and 3b show operation diagrams of the active equalization circuit in fig. 2 during a first time period and a second time period of energy up-transfer in a half-bridge mode, respectively, fig. 3c and 3d show operation diagrams of the active equalization circuit in fig. 2 during a third time period and a fourth time period of energy down-transfer in a half-bridge mode, respectively, fig. 4a and 4b show operation diagrams of the active equalization circuit in fig. 2 during a first time period and a second time period of energy up-transfer in a CUK mode, respectively, and fig. 4c and 4d show operation diagrams of the active equalization circuit in fig. 2 during a third time period and a fourth time period of energy up-transfer in a CUK mode, respectively.

In this embodiment, the active equalization circuit 100 operates in a half-bridge mode, and can control the on-state of the switching tube Q1 and the switching tube Q2 according to the battery voltage of the battery BAT 1.

Specifically, in one embodiment, when the battery voltage of the battery BAT1 is higher than the battery voltage of the battery BAT2, the active equalization operation is performed to upload energy, and in response to the switch control signals EN1 to EN6, the on-state of the switch tube Q1 and the switch tube Q2 is controlled in the first and second continuous time periods, so that the energy of the battery BAT1 is charged to the battery BAT2, and the first and second battery voltages are equalized.

As shown in fig. 3a, in a first period of time, the switching tube Q1 is in a conducting state, the switching tube Q2 is in a disconnecting state, the switching tubes Q3 to Q6 are all in a disconnecting state, and energy of the battery BAT1 is stored in the inductor L1 through a loop; as shown in fig. 3b, in the second time period, the switching tube Q1 is turned off and the switching tube Q2 is turned on, the battery BAT2 is charged by the energy in the inductor L1, and the battery BAT2 is charged by the battery BAT1, and in the process, the energy of the battery BAT3, the battery BAT4, and the battery BAT5 performs a reactive cycle in the inductor L2, the inductor L3, the capacitor C1, and the capacitor C2.

In another embodiment, in a state where the battery voltage of the battery BAT1 is lower than the battery voltage of the battery BAT2, the on-state of the switching tube Q1 and the switching tube Q2 is controlled in response to the switching control signals EN1 to EN6 in the continuous third period and fourth period, so that the energy of the battery BAT2 is transferred to the battery BAT1, and the first battery voltage and the second battery voltage are balanced.

As shown in fig. 3c, in a third time period, the switching tube Q1 is in an off state, the switching tube Q2 is in an on state, the switching tubes Q3 to Q6 are all in an off state, and the energy of the battery BAT2 is stored in the inductor L1 through a loop; as shown in fig. 3d, in the fourth time period, the switching tube Q1 is turned on, and the switching tube Q2 is turned off, so that the battery BAT1 is charged by the energy in the inductor L1, and the battery BAT1 is charged by the battery BAT2, and in this process, the energy of the battery BAT3, the battery BAT4, and the battery BAT5 does a reactive cycle in the inductor L2, the inductor L3, the capacitor C1, and the capacitor C2.

In this embodiment, the active equalization circuit 100 can also selectively operate in the CUK mode, and can control the on-state of the switching tube Q2 and the switching tube Q5 according to the battery voltage of the battery BAT 2.

Specifically, in one embodiment, when the voltage of the battery BAT2 is higher than the fifth battery voltage of the battery BAT5, the active equalization operation is performed to upload energy, and in response to the switch control signals EN1 to EN6, the on-state of the switch tube Q2 and the switch tube Q5 is controlled in the continuous first time period and second time period, so that the energy of the battery BAT2 is charged to the battery BAT5, and the energy equalization between the non-adjacent batteries is achieved.

As shown in fig. 4a, in a first period of time, the switching tube Q2 is in an on state, the switching tube Q5 is in an off state, and the other switching tubes Q1, Q3, Q4 and Q6 are all in off states, the energy of the battery BAT2 is stored in the inductor L1 through a loop, and the energy of the capacitor C1 and the capacitor C2 is stored in the inductor L3 through a communication path formed by the battery BAT5, the battery BAT4, the battery BAT3 and the switching tube Q2; as shown in fig. 4b, in the second time period, the switching tube Q2 is turned off and the switching tube Q5 is turned on, the energy of the inductor L3 charges the battery BAT5 through the switching tube Q5, and the energy stored in the inductor L1 charges the energy storage capacitors C1 and C2 through a communication path formed by the battery BAT2, the battery BAT3, the battery BAT4 and the switching tube Q5.

In another embodiment, in a state that the battery voltage of the battery BAT2 is lower than the battery voltage of the battery BAT5, the on-off states of the switching tube Q2 and the switching tube Q5 are controlled in response to the switching control signals EN1 to EN6 in the continuous third time period and the continuous fourth time period, so that the energy of the battery BAT5 charges the battery BAT2, and energy balance between non-adjacent batteries is achieved.

As shown in fig. 4C, in the third time period, the switching tube Q2 is in an off state, the switching tube Q5 is in an on state, and the other switching tubes Q1, Q3, Q4 and Q6 are all in off states, the energy of the battery BAT5 is stored in the inductor L3 through the switching tube Q5, and simultaneously the energy storage capacitors C1 and C2 store the energy in the inductor L1 through a communication path formed by the switching tube Q5, the battery BAT4, the battery BAT3 and the battery BAT 2; as shown in fig. 4d, in the fourth time period, the switching tube Q2 is turned on, and the switching tube Q5 is turned off, so that the battery BAT2 is charged by the energy of the inductor L1 through the switching tube Q2, and the energy stored in the inductor L3 charges the energy storage capacitor C1 and the capacitor C2, thereby completing the energy transfer from the battery BAT5 to the battery BAT 2.

In some embodiments, in response to the aforementioned switch control signal, the switching tube Q1 and the switching tube Q2 are both characterized by a high level in a conducting state and a low level in an off state, or the switching tube Q1 and the switching tube Q2 are both characterized by a low level in a conducting state and a high level in an off state.

Therefore, the active equalization circuit 100 provided by the embodiment of the present disclosure can realize energy transfer between a group of adjacent batteries, which is specifically shown in that energy transfer is realized between the adjacent batteries in the above-mentioned half-bridge mode, and energy transfer is realized between non-adjacent batteries in the CUK mode, so as to ensure that each single battery does not have overcharge and overdischarge phenomena in the charging and discharging processes, improve the problem of unbalance of the series battery pack, and prolong the service life of the battery pack.

Further, taking the equalizing units connected to the batteries BAT1 to BAT6 in the active equalizing circuit 100 shown in fig. 2 as an example, in the above embodiment, through a new topology structure design, elements far less than the equalizing topology structure in the prior art are adopted to achieve energy equalization among the group of batteries, and are connected in series to form the active equalizing circuit 100, compared with the structure shown in fig. 1, the unique connection design is simple in topology structure, high in module integration, capable of effectively improving equalization efficiency, few in equalizing devices, small in circuit size, and capable of greatly saving cost.

In this embodiment, the battery cells BAT1 to BAT6 are secondary batteries, and may be any one of the following lithium ion batteries, lead acid batteries, super capacitors, or nickel metal hydride batteries.

In this embodiment, the balancing unit in the active balancing circuit 100 adopts an inductance-capacitance energy storage balancing topology, a physical model of the balancing unit is a buck-boost topology structure, and a single battery voltage inconsistency index or an SOC inconsistency index can be used as a balancing variable.

The embodiment of the disclosure adopts a new active balancing topology circuit to ensure that the single battery in the battery pack does not have overcharge and overdischarge in the charging and discharging processes, so as to improve the unbalanced phenomenon of the battery pack in series, improve the available capacity of the battery pack, reduce the maintenance and replacement period of the battery pack in series, prolong the service life of the battery pack, and reduce the operation cost of the battery pack in the application scenes of hybrid electric vehicles, energy storage power stations and the like.

Further, in some other embodiments, the active balancing circuit 100 manages m batteries connected in series in sequence, BAT1 to BAT, where m is a positive integer divisible by 2, and the balancing unit is configured to achieve battery voltage balancing between m adjacent batteries.

Furthermore, the topological structure of the active equalization circuit in the disclosure can control the frequency and duty ratio of signals through the control switch, so that the inductance-capacitance circuit works in a quasi-resonance state, and when the switch is switched on or off each time, the current of the inductance-capacitance series circuit is zero, zero-point current switching is realized, the switching loss of the equalization circuit is greatly reduced, the number of energy storage devices is small, the circuit size is small, the equalization speed is high, and the active equalization circuit is suitable for a battery management system of an energy storage device in an electric vehicle or an energy storage power station.

Fig. 5 shows a schematic structural diagram of a battery management system provided in an embodiment of the present disclosure.

Referring to fig. 5, another aspect of the present disclosure provides a battery management system 300, which includes at least: the battery pack 200 includes the active equalization circuit 100, the drivers 1 to 6, and a Micro Control Unit (MCU) as described above. The equalizing units in the active equalizing circuit 100 are the same as those in the previous embodiment, and the battery pack 200 formed by connecting 6 single batteries in series shown in fig. 2 is taken as an example for description, and the structure and the operation principle thereof are not described in detail. Control pins of the switching tubes Q1 to Q6 in the active equalization circuit 100 are respectively connected to the corresponding drivers 1 to 6, and input pins of the drivers are connected to corresponding I/O pins of the MCU.

When the battery pack 200 needs to be balanced and maintained, the MCU executes a balancing operation strategy, sends the switch control signals EN 1-EN 6 to the drivers 1-6 needing to be operated, and controls the on-off of the switch tube (for example, the driver 1 provides the switch control signal EN1 to the switch tube Q1 to control the on-off of the switch tube Q1, and the others are similar) through the corresponding driver to perform energy transfer, so that the energy transfer of the whole battery management system is realized.

Under the condition of energy imbalance between adjacent batteries, the balancing unit can select a corresponding working mode and gate an energy transmission path of the balancing unit by using a switch control signal, so that energy transfer is carried out between the at least two adjacent batteries, and the voltage balance of the batteries between the adjacent batteries is achieved.

In the active equalization circuit 100 in this embodiment, the connection design of the equalization unit of the Buck-Boost equalization topology structure and the adjacent equalization unit is used to cooperate to complete the active equalization operation of the active equalization circuit 100, the active equalization circuit 100 is controlled to operate in the BUK mode to realize energy transfer between nonadjacent even-numbered (2 × n) batteries and odd-numbered (2 × n + 3) batteries, the active equalization circuit 100 is controlled to operate in the half-bridge mode to realize energy transfer between adjacent nth batteries and (n + 1) th batteries, and when the battery electric quantity difference in the battery pack is large to meet the operation requirement of the equalization circuit, each equalization unit starts to operate. When the battery difference in the battery pack 200 is smaller than a set value, the active equalization circuit stops working, and the equalization operation is finished. The switching tubes in all the active equalization circuits 100 are controlled by the switching control signals, and the transfer of energy is controlled by controlling the on-off of each switching tube, so that the equalization of the battery pack is realized. The problems of over-charge and over-discharge of each single battery in the charging and discharging processes are avoided, and the unbalance of the series battery packs is solved.

The structure can realize the balance between the adjacent single batteries/nonadjacent single batteries, can exchange energy with the batteries which are far away from each other, obviously shortens the balance time, has simple topological structure and less module working quantity, and can greatly improve the balance efficiency.

Meanwhile, the battery management system 300 provided by the present disclosure has no limitation on the number of battery strings, and can greatly improve the upper limit of the operating voltage of the battery pack.

It should be understood that the battery management system 300 has other module structures, such as a detection circuit for detecting the battery voltage of each battery of the battery pack 200, a control circuit for generating a switch control signal with a logic time sequence based on the MCU chip control command, and an isolation transformer connected between the high voltage region and the low voltage region, and therefore the module structures and circuit principles thereof are well known in the prior art, and therefore are not shown or described herein again, but are not intended to limit the present disclosure.

Fig. 6 shows a schematic flow diagram of an active equalization method in a battery management system according to an embodiment of the present disclosure, and fig. 7 shows a schematic model application diagram of the active equalization method shown in fig. 6 applied to the active equalization circuit shown in fig. 2. For example, the active equalization method described below is executed in the active equalization circuit shown in fig. 2, specifically:

in step S01, a cell voltage of a target cell among the adjacent cells is detected.

As described above, the battery pack includes a plurality of batteries BAT1 to BAT6 connected in series, and adjacent batteries among the plurality of batteries are connected to the corresponding equalizing units. In this step, the cell voltage of the target cell among the adjacent cells is detected.

In step S02, the energy imbalance condition of the adjacent battery is determined according to the battery voltage.

In which the cell voltage of the target cell is compared with the voltage thresholds of the remaining cells of the adjacent cells; and confirming that an energy imbalance condition exists when the battery voltage of the target battery is greater than or less than the voltage threshold.

In step S03, under the condition of energy imbalance between the adjacent batteries, the energy transmission path of the balancing unit is gated by a switch control signal, and energy transfer is performed between the adjacent batteries, so as to achieve energy balance between the adjacent batteries.

Referring to fig. 7, in this embodiment, after the step of determining the energy imbalance condition of the adjacent battery according to the battery voltage, the active balancing method further includes:

energy transfer between the two adjacent batteries is performed by adopting a charging and discharging process of an energy storage element, the energy storage element comprises a first inductor connected between the two adjacent batteries,

In some embodiments, the target battery is a battery BAT1, the active equalization circuit is selected to operate in a half-bridge mode, and the step of transferring energy between the adjacent batteries includes:

when the battery voltage of battery BAT1 is greater than the voltage threshold of battery BAT2,

in a first time period, controlling a battery BAT1 to charge an inductor L1, and in a second time period, controlling the inductor L1 to charge a battery BAT 2.

In other embodiments, the target battery is a battery BAT1, the active balancing circuit is selected to operate in a half-bridge mode, and the step of transferring energy between the adjacent batteries includes:

when the battery voltage of battery BAT1 is less than the voltage threshold of battery BAT2,

in a third time period, controlling the battery BAT2 to charge the inductor L1, and in a fourth time period, controlling the inductor L1 to charge the battery BAT 1.

In some embodiments, the target battery is a battery BAT2, the active equalization circuit is selected to operate in a CUK mode, and the step of transferring energy between the adjacent batteries includes:

when the battery voltage of battery BAT2 is greater than the voltage threshold of battery BAT5,

in the first time period, battery BAT2 is controlled to charge inductor L1, and capacitor C1 and capacitor C2 are controlled to charge inductor L3,

in the second time period, the inductor L3 is controlled to charge the battery BAT5, and the inductor L1 is controlled to charge the capacitor C1 and the capacitor C2.

In other embodiments, the target battery is a battery BAT2, the active balancing circuit is selected to operate in the CUK mode, and the step of transferring energy between the adjacent batteries includes:

when the battery voltage of battery BAT2 is less than the voltage threshold of battery BAT5,

in the third time period, the battery BAT5 is controlled to charge the inductor L3, and the capacitor C1 and the capacitor C2 are controlled to charge the inductor L1,

in the fourth period, the inductor L1 is controlled to charge the battery BAT2, and the inductor L3 is controlled to charge the capacitor C1 and the capacitor C2.

In this embodiment, the active equalization method is applied to the active equalization circuit 100 shown in fig. 2, and by using the topology structure of the equalization unit and the common element connection design of the adjacent equalization units, a corresponding operating mode can be selected under the condition of energy imbalance between the adjacent batteries/non-adjacent batteries, and the topology structure is equalized under the control of the switch control signal, so as to implement switching of energy paths, and directly transfer energy from the battery with higher energy to the battery with lower energy, so that energy transfer is performed between the adjacent batteries/non-adjacent batteries, and the battery voltage equalization between the adjacent batteries/non-adjacent batteries is achieved. The switching loss of the active equalization circuit is reduced, the phenomenon of unbalance of the series battery pack is improved, the equalization efficiency is improved, and the service life of the battery pack is prolonged.

In the present embodiment, the half-bridge mode is suitable for energy transfer based on a minimum balance unit (connecting two batteries) topology, and energy transfer between adjacent batteries can be realized; the CUK mode is suitable for energy transfer between any even-numbered (2 x n) battery and any odd-numbered (2 x n + 3) battery, wherein n is a positive odd number, based on the topological structure of the balancing units and the connection design of the adjacent balancing units, the energy transfer between a plurality of adjacent batteries can be realized, the phenomenon of overcharge and overdischarge of each single battery in the charging and discharging processes is guaranteed, and the problem of unbalance of the series battery pack is solved.

It should be noted that in the description of the present disclosure, it is to be understood that the terms "upper", "lower", "inner", and the like, indicate an orientation or positional relationship for convenience in describing the present disclosure and simplifying the description, but do not indicate or imply that the referenced components or elements must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure.

Further, in this document, the contained terms "include", "contain" or any other variation thereof are intended to cover a non-exclusive inclusion, so that a process, a method, an article or an apparatus including a series of elements includes not only those elements but also other elements not explicitly listed or inherent to such process, method, article or apparatus. Without further limitation, an element defined by the phrases "comprising a," "8230," "8230," or "comprising" does not exclude the presence of additional like elements in a process, method, article, or apparatus that comprises the element.

Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present disclosure, and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention as herein taught are within the scope of the present disclosure.

Claims

1. An active equalization circuit for a battery pack, the battery pack including a plurality of cells connected in series, the active equalization circuit comprising:

2. The active equalization circuit of claim 1 wherein the plurality of equalization units each comprise:

3. The active equalization circuit according to claim 2, wherein the active equalization circuit operates in a half-bridge mode, and at least energy transfer between the nth cell and the (n + 1) th cell is accomplished;

4. The active equalization circuit of claim 3 wherein the plurality of energy storage elements comprises:

5. The active equalization circuit of claim 4 wherein the plurality of equalization units respectively comprise a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube and a sixth switching tube connected in series in sequence between the first battery and the sixth battery,

6. The active equalization circuit of claim 5 wherein the active equalization circuit operates in a half-bridge mode to control the conduction states of the first and second switching tubes according to the cell voltage of the first cell.

7. The active equalization circuit of claim 6 wherein when the cell voltage of the first cell is greater than the voltage threshold of the second cell, the first cell charges the second cell by controlling the conduction states of the first and second switching tubes for successive first and second time periods.

8. The active equalization circuit of claim 7 wherein during the first time period, the first switch is on and the second switch is off, the first battery charges the first inductor,

in the second time period, the first switch tube is turned off, the second switch tube is turned on, and the first inductor charges the second battery.

9. The active equalization circuit of claim 6 wherein the conductive states of the first and second switching tubes are controlled during successive third and fourth time periods when the cell voltage of the first cell is less than the voltage threshold of the second cell, the second cell charging the first cell.

10. The active equalization circuit of claim 9 wherein during the third time period the first switching transistor is off and the second switching transistor is on, the second battery charging the first inductor,

11. The active balancing circuit according to claim 8 or 10, wherein the energy of the third battery, the fourth battery and the fifth battery does a reactive cycle in the second inductor, the third inductor, the first capacitor and the second capacitor.

12. The active equalization circuit of claim 5 wherein the active equalization circuit operates in a CUK mode and controls the conduction states of the second switching tube and the fifth switching tube according to the battery voltage of the second battery.

13. The active equalization circuit of claim 12 wherein the second battery charges the fifth battery by controlling the conduction states of the second and fifth switching tubes for successive first and second time periods when the battery voltage of the second battery is greater than the voltage threshold of the fifth battery.

14. The active equalization circuit of claim 13 wherein during the first time period, the second switch is on and the fifth switch is off, the second battery charges the first inductor, and the first and second capacitors charge the third inductor,

15. The active equalization circuit of claim 12 wherein the on-state of the second and fifth switching transistors is controlled for successive third and fourth periods of time when the cell voltage of the second cell is less than the voltage threshold of the fifth cell, the fifth cell charging the second cell.

16. The active equalization circuit of claim 15 wherein during the third time period the second switching transistor is off and the fifth switching transistor is on, the fifth battery charges the third inductor, and the first and second capacitors charge the first inductor,

in the fourth time period, the second switching tube is turned on and the fifth switching tube is turned off, the first inductor charges the second battery, and the third inductor charges the first capacitor and the second capacitor.

17. An active equalization method for a battery pack including a plurality of cells connected in series, adjacent ones of the plurality of cells being connected with a respective equalization unit, the active equalization method comprising:

detecting a cell voltage of a target cell among the adjacent cells;

under the condition of energy imbalance between the adjacent batteries, an energy transmission path of the balancing unit is gated through a switch control signal, and energy transfer is carried out between the adjacent batteries so as to achieve energy balance between the adjacent batteries.

18. The active balancing method of claim 17, wherein the step of determining the energy imbalance condition of the neighboring cells according to the cell voltages comprises:

confirming that an energy imbalance condition exists when a battery voltage of the target battery is greater than or less than the voltage threshold.

19. The active balancing method as claimed in claim 18, wherein after the step of determining the energy imbalance condition of the neighboring cell according to the cell voltage, the active balancing method further comprises:

the energy transfer between adjacent batteries is performed by adopting the charging and discharging processes of a plurality of energy storage elements, and the plurality of energy storage elements comprise a first inductor, a first capacitor, a second capacitor and a third inductor which are sequentially connected in series between the middle node of the first battery and the second battery and the middle node of the fifth battery and the sixth battery.

20. The active balancing method of claim 19, wherein the target cell is a first cell, the active balancing circuit is selected to operate in a half-bridge mode, and the step of transferring energy between the adjacent cells comprises:

21. The active balancing method of claim 19, wherein the target cell is a first cell, the active balancing circuit is selected to operate in a half-bridge mode, and the step of transferring energy between the adjacent cells comprises:

in a third time period, the second battery is controlled to charge the first inductor, and in a fourth time period, the first inductor is controlled to charge the first battery.

22. The active balancing method of claim 19, wherein the target battery is a second battery, the active balancing circuit is selected to operate in a CUK mode, and the step of transferring energy between the adjacent batteries comprises:

23. The active balancing method of claim 19, wherein the target battery is a second battery, the active balancing circuit is selected to operate in the CUK mode, and the step of transferring energy between the adjacent batteries comprises: