JP2021158709A - Battery system - Google Patents

Abstract

To reduce the number of execution times of a process for reusing a battery module in a battery system which can be mounted in a vehicle.SOLUTION: A battery system 1 can be mounted in a vehicle 100 including an auxiliary machine load 70 and a PCU 60 for driving. The battery system 1 includes: a battery pack 10 which has a plurality of battery modules 11 to 16; the PCU 60 which converts power of the battery pack 10; a changeover circuit 30; and an ECU 50 which controls the changeover circuit 30. The changeover circuit 30 is electrically connected between the battery pack 10 and the PCU 60 and is configured so that each of the plurality of battery modules 11 to 16 can be assigned to one of power supply to the PCU 60 and power supply to the auxiliary machine load 70. The ECU 50 controls the changeover circuit 30 so as to assign the most deteriorated battery module of the plurality of battery modules 11 to 16 to power supply to the auxiliary machine load 70.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to battery systems, and more specifically to vehicle-mountable battery systems.

In recent years, many vehicles are equipped with battery systems. In general, a battery module included in an in-vehicle battery system deteriorates with the passage of time or with an increase in mileage. Therefore, a system for reusing a deteriorated battery module has been proposed (see, for example, Japanese Patent Application Laid-Open No. 2012-109260: Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-109260 Japanese Unexamined Patent Publication No. 2014-011060

Patent Document 1 describes that when the battery module is reused, the battery module is removed from the vehicle, and the battery module is disassembled and reconstructed. However, such a process is costly and time consuming. Therefore, it is desirable to reduce the number of times these steps are performed as much as possible.

The present disclosure has been made in order to solve such a problem, and the purpose of the present disclosure is to provide a technology capable of reducing the number of steps for reusing a battery module in a battery system that can be mounted on a vehicle. To provide.

A battery system according to an aspect of the present disclosure can be mounted on a vehicle including an auxiliary machine and a power converter for driving. The battery system includes an assembled battery including a plurality of battery modules, a power conversion device for converting the electric power of the assembled battery, a switching device, and a control device for controlling the switching device. The switching device is electrically connected between the assembled battery and the power conversion device, and each of the plurality of battery modules can be assigned to either power supply to the power conversion device or power supply to the auxiliary machine. It is configured in. The control device controls the switching device so as to allocate the most deteriorated battery module among the plurality of battery modules for power supply to the auxiliary machine.

According to the above configuration, the most degraded battery module is allocated for powering the auxiliary equipment. Normally, the load applied to the battery module when power is supplied to the auxiliary machine is smaller than the load applied to the battery module when the vehicle is driven. Therefore, by allocating as described above, the load on the most deteriorated battery module is reduced. As a result, the rate of deterioration of the most deteriorated battery module can be slowed down. As a result, it is possible to extend the period until all battery modules including the most deteriorated battery module are reused, and it is possible to reduce the number of times the reuse process is performed.

According to the present disclosure, in a battery system that can be mounted on a vehicle, the number of steps for reusing the battery module can be reduced.

It is a block diagram which shows schematic the whole structure of the vehicle in this embodiment. It is a circuit block diagram which shows an example of the structure of a PCU and a switching circuit. It is a flowchart which shows the switching control in this embodiment.

Hereinafter, the present embodiment will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

In the following, a configuration in which the battery system according to the present disclosure is mounted on a hybrid vehicle will be described as an example. However, the battery system according to the present disclosure can also be mounted on other types of vehicles (electric vehicles, plug-in hybrid vehicles, fuel cell vehicles, etc.).

[Embodiment]
<Vehicle configuration>
FIG. 1 is a block diagram schematically showing an overall configuration of a vehicle according to the present embodiment. With reference to FIG. 1, vehicle 100 is a hybrid vehicle and includes a battery system 1. The battery system 1 includes an assembled battery 10, a battery sensor group 20, a switching circuit 30, a system main relay (SMR) 40, and an ECU 50. In addition to the battery system 1, the vehicle 100 includes a power control unit (PCU: Power Control Unit) 60, an auxiliary load 70, a first motor generator (MG: Motor Generator) 81, a second motor generator 82, and the like. It includes an engine 83, a power dividing device 91, a drive shaft 92, and drive wheels 93.

The assembled battery 10 stores electric power for driving the first motor generator 81 and the second motor generator 82, and supplies electric power for driving the vehicle 100 to the first motor generator 81 and the second motor generator 82 through the PCU 60. Further, the assembled battery 10 is charged by receiving the generated power through the PCU 60 at the time of power generation of the first motor generator 81 and the second motor generator 82.

The assembled battery 10 includes a plurality of battery modules. Each of the plurality of battery modules includes a plurality of cells connected in series and / or in parallel. Each cell is a secondary battery, and in this embodiment, it is a lithium ion battery. Various known materials can be used as materials for the positive electrode, the negative electrode, the separator, the electrolytic solution, and the like of the lithium ion battery. The configuration of the assembled battery 10 will be described with reference to FIG.

The battery sensor group 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects the voltage of each cell contained in the assembled battery 10. As a result, the voltage of each battery module is calculated. The current sensor 22 detects the current IB charged and discharged in the assembled battery 10 (each battery module). The temperature sensor 23 detects the temperature TB of the assembled battery 10. Each sensor outputs the detection result to the ECU 50.

The switching circuit (switching device) 30 is electrically connected between the assembled battery 10 and the PCU 60. The configuration of the switching circuit 30 will be described in detail with reference to FIG.

The SMR 40 is electrically connected to a power line (high voltage power line PLH) connecting the assembled battery 10 (switching circuit 30 in this example) and the PCU 60. The SMR 40 switches between electrical connection and disconnection between the PCU 60 and the assembled battery 10 in response to a control command from the ECU 50.

The assembled battery 10, the battery sensor group 20, the switching circuit 30, and the SMR 40 may be packaged into one package to form a battery pack.

The ECU 50 includes a processor 51 such as a CPU (Central Processing Unit), a memory 52 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port (not shown) for inputting / outputting various signals. And include. The ECU 50 executes traveling control of the vehicle 100 based on a signal received from each sensor of the battery sensor group 20 and a program and a map stored in the memory 52. Further, the ECU 50 monitors the state of the assembled battery 10. As an example of the main monitoring process executed by the ECU 50, there is "switching control" in which the deterioration state of each battery module included in the assembled battery 10 is estimated and the switching circuit 30 is controlled based on the estimation result. The switching control will be described later.

The ECU 50 corresponds to the "control device" according to the present disclosure. In this embodiment, in order to avoid complication of the description, a configuration in which the ECU 50 is integrated into one will be described as an example. However, the ECU 50 may be divided into a plurality of ECUs (battery ECU, engine ECU, HVECU, etc.) according to the function.

The PCU 60 receives bidirectional power between the assembled battery 10 and the first motor generator 81 and the second motor generator 82, or between the first motor generator 81 and the second motor generator 82, in accordance with a control command from the ECU 50. Perform the conversion. The PCU 60 corresponds to the "power conversion device" according to the present disclosure.

Although the auxiliary load 70 is not shown, for example, lamps (headlamps, fog lamps, cornering signal lamps, corner lamps, etc.), air conditioners, audio systems, car navigation systems, ABS (Antilock Brake System), oil pumps, etc. Includes meters, defogers, wipers, actuators for driving power windows, etc. Auxiliary load 70 may further include by-wire systems such as electric power steering, accelerators and brakes.

Each of the first motor generator 81 and the second motor generator 82 is an AC rotating electric machine, for example, a three-phase AC synchronous electric machine in which a permanent magnet is embedded in a rotor.

The first motor generator 81 is mainly used as a generator driven by the engine 83 via the power dividing device 91. The electric power generated by the first motor generator 81 is supplied to the second motor generator 82 or the assembled battery 10 via the PCU 60. The first motor generator 81 can also crank the engine 83.

The second motor generator 82 mainly operates as an electric motor and drives the drive wheels 93. The second motor generator 82 is driven by receiving at least one of the electric power from the assembled battery 10 and the electric power generated by the first motor generator 81, and the driving force of the second motor generator 82 is transmitted to the drive shaft (output shaft) 92. NS. On the other hand, when the vehicle 100 is braking or the acceleration is reduced on a downward slope, the second motor generator 82 operates as a generator to generate regenerative power generation. The electric power generated by the second motor generator 82 is supplied to the assembled battery 10 via the PCU 60.

The engine 83 outputs power by converting the combustion energy generated when the air-fuel mixture is burned into the kinetic energy of movers such as pistons and rotors.

The power splitting device 91 is, for example, a planetary gear device. Although neither is shown, the power splitting device 91 includes a sun gear, a ring gear, a pinion gear, and a carrier. The carrier is connected to the engine 83. The sun gear is connected to the first motor generator 81. The ring gear is connected to the second motor generator 82 and the drive wheels 93 via the drive shaft 92. The pinion gear meshes with the sun gear and the ring gear. The carrier holds the pinion gear so that it can rotate and revolve.

<Switching circuit configuration>
FIG. 2 is a circuit block diagram showing an example of the configuration of the PCU 60 and the switching circuit 30. In FIG. 2, the SMR 40 is not shown in order to avoid complicating the drawings.

With reference to FIG. 2, the assembled battery 10 includes six battery modules 11-16 in this example. However, the number of battery modules is merely an example and can be changed as appropriate. The battery modules 11 to 16 are connected in parallel with each other.

The PCU 60 includes a high-voltage converter 61, an inverter 62, and an auxiliary converter 63. The switching circuit 30 includes switches 313-1316 and 3213-226.

The high voltage converter 61 is electrically connected to the high voltage power line PLH. The voltage of the DC power transmitted through the high-voltage power line PLH is, for example, several hundred V. The high-voltage converter 61 is a bidirectional converter, and boosts the DC power supplied from the assembled battery 10 and supplies it to the inverter 62, or lowers the DC power supplied from the inverter 62 and supplies it to the assembled battery 10. do.

The inverter 62 converts the DC power from the high-voltage converter 61 into AC power, and uses the AC power to drive the first motor generator 81 and the second motor generator 82. The inverter 62 may be divided into an inverter for driving the first motor generator 81 and an inverter for driving the second motor generator 82 (neither of them is shown). At the time of power generation of the first motor generator 81, the inverter 62 converts the AC power from the first motor generator 81 into DC power and supplies it to the high voltage converter 61. Further, when the second motor generator 82 is regenerated, the inverter 62 converts the AC power from the second motor generator 82 into DC power and supplies it to the high voltage converter 61.

The auxiliary converter 63 is electrically connected to the high voltage converter 61 and also electrically connected to the low voltage power line PLL. The voltage of the power transmitted through the low voltage power line PLL is, for example, about 12V. The auxiliary load 70 is also electrically connected to the low voltage power line PLL. Although not shown, an auxiliary battery (lead-acid battery or the like) is also electrically connected to the low-voltage power line PLL. The auxiliary converter 63 is configured so that the voltage level of DC power can be adjusted between the high-voltage converter 61 and the low-voltage power line PLL.

Each of the switches 31 to 316 and 321 to 326 is a power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor). One end of each of the switches 31 to 316 is electrically connected to the high voltage power line PLH. The other end of the switches 31 to 316 is electrically connected to the battery modules 11 to 16, respectively. Each end of the switches 321 to 326 is electrically connected to the low voltage power line PLL. The other end of the switches 321 to 326 are electrically connected to the battery modules 11 to 16, respectively.

The switch 311 and the switch 321 are selectively turned on / off in response to a control command from the ECU 50. That is, when one of the switches 311, 321 is on, the other is off. As a result, the battery module 11 is electrically connected to only one of the high-voltage power line PLL and the low-voltage power line PLL.

Similarly, the switch 312 and the switch 322 are selectively turned on / off in response to a control command from the ECU 50. As a result, the battery module 12 is electrically connected to only one of the high-voltage power line PLL and the low-voltage power line PLL. Since the control of the remaining switches 313 to 316 and 323 to 326 is the same, the description will not be repeated.

When the voltage of each of the battery modules 11 is higher than the voltage of the low-voltage power line PLL (for example, 12V), a buck converter (not shown) may be provided between the switches 321 to 326 and the low-voltage power line PLL. ..

<Progress of high rate deterioration>
In general, when the salt concentration of the electrolytic solution of a lithium ion battery is biased as the lithium ion battery is charged and discharged, the internal resistance of the lithium ion battery increases. The increase in internal resistance due to such a bias in salt concentration is referred to as "high rate deterioration" to distinguish it from the aged deterioration of the materials constituting the lithium ion battery. The degree of progress of high-rate deterioration is quantified using the evaluation value ΣD. The calculation method of the evaluation value ΣD will be described in detail later.

When the high-rate deterioration of any of the battery modules 11 to 16 progresses, it is conceivable to remove the deteriorated battery module from the vehicle 100 and disassemble / reconstruct (or replace) the deteriorated battery module. However, such a process is costly and time consuming.

Therefore, in the present embodiment, the switching circuit 30 configured as described above is used to supply power to the auxiliary load 70 from the battery modules 11 to 16 in which the highest rate deterioration is progressing. Used for. In the example shown in FIG. 2, since the high rate deterioration of the battery module 16 is most advanced, the battery module 16 is electrically connected to the low voltage power line PLL by turning off the switch 316 and turning on the switch 326. Will be done. As a result, the battery module 16 is allocated for supplying power to the auxiliary load 70.

In many cases, the battery load required for the operation of the auxiliary load is smaller than the battery load required for driving the vehicle. Therefore, according to FIG. 2, the load applied to the battery module 16 is reduced by connecting to the low voltage power line PLL. Then, the progress of the high rate deterioration in the battery module 16 may be slowed down, or the progress state of the high rate deterioration may be recovered (that is, the bias of the salt concentration of the electrolytic solution may be alleviated). As a result, the life of the battery module 16 is extended, and the period until the battery modules 11 to 16 are disassembled / reconstructed (or replaced) can be extended.

<Switching control flow>
FIG. 3 is a flowchart showing switching control in the present embodiment. This flowchart is repeatedly executed every time a predetermined condition is satisfied or a predetermined period elapses. Each step is realized by software processing by the ECU 50, but may be realized by hardware (electric circuit) manufactured in the ECU 50. Hereinafter, the step is abbreviated as S. In the initial state before the start of execution of this flowchart, it is assumed that all the battery modules 11 to 16 are used for driving the vehicle 100. In this case, the power supply source to the auxiliary load 70 is an auxiliary battery (not shown).

With reference to FIG. 3, in S1, the ECU 50 estimates the deterioration states of all the battery modules 11 to 16. More specifically, the ECU 50 calculates the evaluation value ΣD of the high rate deterioration for each of the battery modules 11 to 16. This calculation method will be described below.

The ECU 50 calculates the damage amount D due to the bias of the salt concentration for each of the battery modules 11 to 16 based on the input / output current IB and the energization time thereof. The damage amount D is calculated in a predetermined period Δt based on, for example, the following equation (1).
D (N) = D (N-1) -α x Δt x D (N-1) + (β / C) x IB x Δt
... (1)

Here, D (N) indicates the current calculated value of the damage amount D, and D (N-1) indicates the previously calculated value of the damage amount D calculated before the cycle Δt. For D (N-1), the value at the time of the previous calculation is stored, and the value is read out at the time of the current calculation.

The second term α × Δt × D (N-1) on the right side in the formula (1) is a reduction term of the damage amount D, and indicates a component when the bias of the salt concentration is alleviated. α is a forgetting coefficient, which corresponds to the diffusion rate of ions in the electrolytic solution. The higher the diffusion rate, the larger the forgetting coefficient α. The value of α × Δt is set to be a value from 0 to 1. The decrease term of the damage amount D becomes larger as the forgetting coefficient α is larger (that is, the higher the ion diffusion rate is) and the longer the period Δt is.

The forgetting coefficient α may depend on the SOC (State Of Charge) and temperature of the battery modules 11 to 16. By obtaining the correspondence between the forgetting coefficient α and the SOC and the temperature in advance by an experiment or the like and storing it in the memory 52, the forgetting coefficient α can be set based on the SOC and the temperature at the time of calculation. If the temperatures of the battery modules 11 to 16 are the same, the forgetting coefficient α is set to a larger value as the SOC is higher, and if the SOCs of the battery modules 11 to 16 are the same, the value is set to a larger value as the temperature is higher. obtain.

The third term (β / C) × IB × Δt on the right side in the formula (1) is an increase term of the damage amount D, and indicates a component when a bias in salt concentration occurs. β is the current coefficient and C is the limit threshold. The increase term of the damage amount D becomes larger as the current IB is larger and the period Δt is longer.

The current coefficient β and the limit threshold C can also depend on the SOC and temperature of the battery modules 11 to 16. By obtaining the correspondence between each of the current coefficient β and the limit threshold value C and the SOC and the temperature in advance by experiments or the like and storing them in the memory 52, the current coefficient β and the limit are based on the SOC and the temperature at the time of calculation. The threshold value C can be set. If the temperatures of the battery modules 11 to 16 are the same, the higher the SOC is set to a larger value, and if the temperatures of the battery modules 11 to 16 are the same, the higher the temperature is, the larger the value is set. obtain.

In this way, by expressing the occurrence and mitigation of the salt concentration bias by the above increase and decrease terms and calculating the current damage amount D, the change (increase / decrease) in the salt concentration bias, which is considered to be the cause of the high rate deterioration. ) Can be properly grasped.

Further, the ECU 50 calculates an evaluation value ΣD indicating the degree of high rate deterioration of the battery modules 11 to 16. The evaluation value ΣD can be calculated, for example, based on the following equation (2) for integrating the damage amount D described above.
ΣD (N) = γ × ΣD (N-1) + η × D (N) ・ ・ ・ (2)

Here, ΣD (N) indicates the currently calculated value of the evaluation value, and ΣD (N-1) indicates the previously calculated value of the evaluation value calculated before the period Δt. γ is the attenuation coefficient and η is the correction coefficient. The ΣD (N-1) is stored in the memory 52 at the time of the previous calculation, and is read from the memory 52 at the time of the current calculation. γ and η are also stored in the memory 52 in advance, and are read from the memory 52 at the time of this calculation.

The attenuation coefficient γ is set to a value smaller than 1. Since the bias of salt concentration is alleviated by the diffusion of ions over time, when calculating the current evaluation value ΣD (N), it is noted that the previous evaluation value ΣD (N-1) has decreased. It is something to consider. The correction coefficient η is set as appropriate.

In this way, the evaluation value ΣD is calculated by integrating the amount of damage based on the energization time of the current IB and the current IB of each battery module 11 to 16. When the battery modules 11 to 16 are overcharged, the evaluation value ΣD increases in the negative direction (negative value) due to the increase in the bias of the salt concentration according to the overcharge. On the other hand, when the battery modules 11 to 16 are used in an excessively discharged state, the evaluation value ΣD increases in the positive direction (positive value) due to an increase in the bias of the salt concentration according to the excessively discharged state.

In S2, the ECU 50 determines whether or not the battery modules 11 to 16 include a battery module in which the high rate deterioration has progressed more than a predetermined degree, based on the estimation result in S1. Specifically, the ECU 50 determines whether or not the absolute value of the evaluation value ΣD (N) exceeds a predetermined threshold value TH in at least one battery module 11 to 16.

When the absolute value of the evaluation values ΣD (N) of all the battery modules 11 to 16 is less than the threshold value TH (NO in S2), the ECU 50 skips the following processing and returns the processing to the main routine. In this case, all battery modules 11-16 are still used to drive the vehicle 100.

On the other hand, in one or more battery modules of the battery modules 11 to 16, when the absolute value of the evaluation value ΣD (N) is equal to or higher than the threshold value TH (YES in S2), the ECU 50 advances the process to S3.

In S3, the ECU 50 identifies the battery module in which the highest rate deterioration has progressed from the battery modules 11 to 16. Specifically, the ECU 50 identifies the battery module having the largest absolute value of the evaluation value ΣD (N). In the example shown in FIG. 2, the battery module 16 is specified as the battery module in which the high rate deterioration has progressed most.

In S4, the ECU 50 allocates the battery module specified in S3 for power supply to the auxiliary load 70. Specifically, in the ECU 50, the battery module (for example, the battery module 16) is electrically connected to the low voltage power line PLL, and the remaining battery modules (battery modules 11 to 15) are electrically connected to the high voltage power line PLH. The on / off of the switches 31 to 316 and 321 to 326 is controlled so as to be performed.

As described above, in the present embodiment, by switching the connection between the high-voltage power line PLH / low-voltage power line PLL of the battery modules 11 to 16 using the switching circuit 30, the battery module in which the highest rate deterioration has progressed is the auxiliary machine. It is assigned to power the load 70. Since a large current is not normally required for the operation of the auxiliary load 70, the bias of the salt concentration in the battery module can be alleviated while the battery module is used for the auxiliary load 70. That is, the degree of deterioration of the battery module in which the highest rate deterioration has progressed can be recovered with the passage of time. This extends the life of the battery module with the highest rate of deterioration. Therefore, the steps of removing, disassembling / reconstructing, and replacing the battery modules 11 to 16 can be postponed, and the number of such steps can be reduced.

In the present embodiment, the configuration in which each battery module 11 to 16 is composed of a lithium ion battery has been described as an example, but the type of the secondary battery is not limited to this. Other types of secondary batteries can also be used in the battery system 1 as long as the progress of deterioration can be suppressed by reducing the load (avoiding charging / discharging with a large current).

Further, in the example shown in FIG. 3, it is explained that the auxiliary battery (shown) initially supplies power to the low-voltage power line PLL, and when the high-rate deterioration progresses to some extent, the battery module also starts supplying power to the low-voltage power line PLL. bottom. However, power may be supplied from the battery module to the low-voltage power line PLL from the beginning. In this case, it is not necessary to provide an auxiliary battery.

Further, the number of battery modules that supply power to the low-voltage power line PLL is not limited to one (only the battery module in which the highest rate deterioration has progressed). If the drive power supply capacity of the vehicle 100 (the magnitude of the instantaneous charge / discharge power and the battery capacity capable of traveling a long distance) can be secured, power is supplied to the low-voltage power line PLL from two or more battery modules. May be good.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present disclosure is shown by the scope of claims rather than the description of the embodiment described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 Battery system, 10 sets of batteries, 11-16 battery modules, 20 battery sensor group, 21 voltage sensor, 22 current sensor, 23 temperature sensor, 30 switching circuit, 313-1316, 321-326 switches, 40 SMR, 50 ECU, 51 Processor, 52 Memory, 60 PCU, 61 High Voltage Converter, 62 Inverter, 63 Auxiliary Converter, 70 Auxiliary Load, 81 1st Motor Generator, 82 2nd Motor Generator, 83 Engine, 91 Power Splitter, 92 Drive Shaft , 93 drive wheels, 100 vehicles.

Claims (1)

A battery system that can be mounted on a vehicle, including an auxiliary machine and a power conversion device for driving.
Assembled batteries including multiple battery modules and
By switching the electrical connection between the assembled battery and the power conversion device, each of the plurality of battery modules is used for supplying power to the power conversion device or for supplying power to the auxiliary device. A switching device configured to be assignable to
A control device for controlling the switching device is provided.
The control device is a battery system that controls the switching device so as to allocate the most deteriorated battery module among the plurality of battery modules for power supply to the auxiliary machine.

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