JP6753332B2 - Battery system - Google Patents

Description

The present disclosure relates to a battery system, and more particularly to a battery system including an assembled battery configured to be mountable on a vehicle equipped with an electric motor and including a plurality of secondary batteries connected in parallel.

In recent years, vehicles equipped with electric motors such as hybrid vehicles and electric vehicles have become widespread. These vehicles are capable of "EV traveling" in which they travel only by the vehicle driving force from the electric motor. In addition, these vehicles are equipped with an assembled battery configured to include a plurality of secondary batteries connected in parallel. Various techniques for protecting this assembled battery have been proposed (for example, Japanese Patent Application Laid-Open No. 2009-216448 (Patent Document 1)).

JP-A-2009-216448

Generally, in an assembled battery composed of a plurality of secondary batteries connected in parallel (hereinafter, each secondary battery is also referred to as a "cell"), a current sensor is provided at an input / output terminal of the assembled battery and assembled. The current (total current) input to and from the battery is detected. In such an assembled battery, current variation can occur among a plurality of cells connected in parallel. Therefore, a current larger than the average current calculated from the value detected by the current sensor may flow to a specific cell, and the current flowing through the cell may exceed a predetermined limit.

Therefore, in preparation for such a case, it is conceivable to estimate the maximum current among the currents flowing through the plurality of cells connected in parallel and control the charging / discharging of the assembled battery based on the maximum current. For example, when the maximum current exceeds the first reference value when charging the assembled battery, the control upper limit value of the charging power to the assembled battery (compared to the case where the maximum current is below the first reference value) Win), which will be described later, can be suppressed. Further, when the maximum current exceeds the second reference value when the assembled battery is discharged, the control upper limit value of the discharge power to the assembled battery (compared to the case where the maximum current is lower than the second reference value) Wout), which will be described later, can be restricted (suppressed).

If the estimation accuracy of the maximum current is low, a situation may occur in which the control upper limit values of the charging power and the discharging power cannot be appropriately suppressed. As a result, it may not be possible to properly protect the assembled battery. Or conversely, there is a possibility that the protection of the assembled battery becomes excessive and the assembled battery cannot be fully utilized. Therefore, it is required to estimate the maximum current with high accuracy.

The present disclosure has been made to solve the above problems, and an object thereof is to provide a plurality of cells in a battery system including an assembled battery including a plurality of cells (secondary batteries) connected in parallel. It is to improve the estimation accuracy of the maximum current among the currents flowing through.

A battery system according to certain aspects of the present disclosure is configured to be mountable on a vehicle equipped with an electric motor. The battery system includes an assembled battery including a plurality of secondary batteries connected in parallel, and a control device. The control device estimates the current variation between the plurality of secondary batteries caused by the resistance variation among the plurality of secondary batteries, and uses the estimated current variation to disperse and flow in the plurality of secondary batteries. It is configured to estimate the maximum current. The control device circulates between a plurality of secondary batteries due to the OCV (Open Circuit Voltage) difference between the plurality of secondary batteries when the EV running in which the vehicle travels is continued for a predetermined period only by the vehicle driving force from the electric motor. The circulating current that flows so as to be calculated is calculated, and the maximum current is estimated using the calculated circulating current and the current variation.

According to the above configuration, the maximum current among the currents distributed and flowing in a plurality of cells connected in parallel is estimated (detailed estimation method will be described later). Therefore, according to this battery system, it is possible to prevent the current flowing through the cell from exceeding a predetermined limit by referring to the estimated maximum current.

According to the present disclosure, it is possible to improve the estimation accuracy of the maximum current in a battery system including an assembled battery including a plurality of secondary batteries connected in parallel.

It is a figure which shows schematic the whole structure of the vehicle which mounted the battery system which concerns on embodiment of this disclosure. It is a figure which shows an example of the detailed structure of an assembled battery. It is a figure which showed the calculation model used for the estimation of the current flowing through a cell. It is a figure for demonstrating the circulating current. It is a figure which shows the typical example (an example of a simulation condition) of the current IB flowing through the assembled battery at the time of HV mode selection and EV mode selection. FIG. 5 is a diagram showing an example (simulation result) of the OCV difference between when the HV mode is selected and when the EV mode is selected, which occurs when the current IB shown in FIG. 5 flows. It is a flowchart for demonstrating the maximum current estimation processing in this embodiment. It is a flowchart explaining the OCV difference calculation process executed in S30 of FIG.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. It should be noted that the same or corresponding parts in the drawings are designated by the same reference numerals and description thereof will not be repeated.

[Embodiment]
<Battery system configuration>
FIG. 1 is a diagram schematically showing an overall configuration of a vehicle 1 equipped with a battery system according to an embodiment of the present disclosure. In the following, a case where the vehicle 1 is a hybrid vehicle will be typically described, but the battery system according to the present disclosure can be applied not only to the hybrid vehicle but also to all vehicles equipped with an assembled battery.

With reference to FIG. 1, the vehicle 1 includes a battery system 2, a power control unit (PCU) 30, motor generators 41 and 42, an engine 50, a power dividing device 60, and a drive shaft 70. , The drive wheel 80 is provided. The battery system 2 includes an assembled battery 10, a monitoring unit 20, and an electronic control unit (ECU) 100.

The engine 50 is an internal combustion engine that outputs power by converting the combustion energy generated when a mixture of air and fuel is burned into the kinetic energy of movers such as pistons and rotors.

The power splitting device 60 includes, for example, a planetary gear mechanism having three rotation axes of a sun gear, a carrier, and a ring gear. The power dividing device 60 divides the power output from the engine 50 into a power for driving the motor generator 41 and a power for driving the drive wheels 80.

Each of the motor generators 41 and 42 is an AC rotating electric machine, for example, a three-phase AC synchronous motor in which a permanent magnet is embedded in a rotor.

The motor generator 41 is mainly used as a generator driven by the engine 50 via the power dividing device 60. The electric power generated by the motor generator 41 is supplied to the motor generator 42 or the assembled battery 10 via the PCU 30.

The motor generator 42 mainly operates as an electric motor and drives the drive wheels 80. The motor generator 42 is driven by receiving at least one of the electric power from the assembled battery 10 and the electric power generated by the motor generator 41, and the driving force of the motor generator 42 is transmitted to the drive shaft 70. On the other hand, when the vehicle is braking or the acceleration is reduced on a downward slope, the motor generator 42 operates as a generator to generate regenerative power generation. The electric power generated by the motor generator 42 is supplied to the assembled battery 10 via the PCU 30.

The assembled battery 10 is configured to include a plurality of cells (secondary batteries) connected in parallel (detailed configuration will be described later). The assembled battery 10 stores electric power for driving the motor generators 41 and 42, and supplies electric power to the motor generators 41 and 42 through the PCU 50. Further, the assembled battery 10 is charged by receiving the generated power through the PCU 30 when the motor generators 41 and 42 generate power.

The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects the voltage VB of a plurality of cells connected in parallel in the assembled battery 10. The current sensor 22 detects the current IB input / output to / from the assembled battery 10. The temperature sensor 23 detects the temperature TB for each cell. A plurality of temperature sensors 23 (a number smaller than the number of cells) may be provided with respect to the assembled battery 10, and the temperature may be detected using a plurality of (for example, several) adjacent cells as monitoring units.

The PCU 30 executes bidirectional power conversion between the assembled battery 10 and the motor generators 41 and 42 according to the control signal from the ECU 100. The PCU 30 is configured so that the states of the motor generators 41 and 42 can be controlled separately. For example, the motor generator 42 can be put into a power running state while the motor generator 41 is in a regenerative state (power generation state). The PCU 30 includes, for example, two inverters provided corresponding to the motor generators 41 and 42, and a converter (neither shown) that boosts the DC voltage supplied to each inverter to a voltage higher than the output voltage of the assembled battery 10. Consists of including.

The ECU 100 includes a CPU (Central Processing Unit) 100A, a memory (more specifically, a ROM (Read Only Memory) and a RAM (Random Access Memory)) 100B, and an input / output port (shown) for inputting / outputting various signals. ) And is included. The ECU 100 controls the charging / discharging of the assembled battery 10 by controlling the engine 50 and the PCU 30 based on the signal received from each sensor and the program and the map stored in the memory 100B.

FIG. 2 is a diagram showing an example of a detailed configuration of the assembled battery 10. In the assembled battery 10, a plurality of cells are connected in parallel to form a block (or module), and a plurality of blocks are connected in series to form the assembled battery 10. Specifically, the assembled battery 10 includes M blocks 101 to 10M connected in series. Each of blocks 101-10M contains N cells connected in parallel. Note that M and N are natural numbers of 2 or more.

The voltage sensor 211 detects the voltage of the block 101. That is, the voltage sensor 211 detects the voltage VB1 of the N cells constituting the block 101. The same applies to the voltage sensors 212 to 21M.

The current sensor 22 detects the current IB flowing through each block 101 to 10M. That is, the current sensor 22 detects the total current flowing through the N cells of each block.

In the assembled battery 10 configured to include the plurality of cells connected in parallel as described above, there is a possibility that current variation may occur among the plurality of cells connected in parallel. Therefore, for N cells connected in parallel in each block, a current larger than the average current of the N cells calculated from the value detected by the current sensor 22 flows to a specific cell, and the current flowing through the cells is predetermined. May exceed the limit.

In preparation for such a case, the ECU 100 estimates the maximum current among the currents flowing through the plurality of cells connected in parallel, and controls the charging / discharging of the assembled battery 10 based on the maximum current. More specifically, in the ECU 100, when the maximum current exceeds the first reference value when charging the assembled battery 10, the assembled battery 10 is compared with the case where the maximum current is lower than the first reference value. Suppresses the control upper limit Win of the charging power to. Further, in the ECU 100, when the maximum current exceeds the second reference value when the assembled battery 10 is discharged, the discharge power to the assembled battery 10 is compared with the case where the maximum current is below the second reference value. The control upper limit value Wout of is suppressed.

When the estimation accuracy of the maximum current is low, a situation may occur in which the control upper limit value Win of the charge power and the control upper limit value Wout of the discharge power cannot be appropriately suppressed. As a result, it may not be possible to properly protect the assembled battery 10. Or conversely, there is a possibility that the assembled battery 10 is excessively protected and the assembled battery cannot be fully utilized. Therefore, it is required to estimate the maximum current with high accuracy. Therefore, in the present embodiment, the current is estimated as follows.

<Maximum current and circulating current>
FIG. 3 is a diagram showing a calculation model used for estimating the current flowing through the cell. In FIG. 3, the block 10K (K is any of 1 to M) will be typically described. In this embodiment, a two-parallel model is used in which one cell in which the current is most concentrated among the N cells connected in parallel and the cell in which the remaining (N-1) cells are combined are used. The resistance of the cell in which the current is most concentrated (that is, the minimum resistance) is represented by Rmin, and the combined resistance of the remaining cells is represented by Rt.

Hereinafter, the cell in which the current is most concentrated (that is, the cell in which the maximum current flows among the currents distributed in N cells) is also referred to as a "maximum current cell", and the current flowing in the maximum current cell is referred to as Imax. Further, each (N-1) cell other than the maximum current cell is also referred to as a "standard cell", and the current flowing through each standard cell is referred to as Ityp. In this calculation model, it is assumed that no current variation occurs between standard cells. Therefore, the current flowing through (N-1) standard cells is represented as Ityp × (N-1).

In the assembled battery 10 (block 10K), a current can flow so as to circulate in a closed loop composed of a maximum current cell and a standard cell. This current is also referred to as "circulating current".

FIG. 4 is a diagram for explaining the circulating current. In the assembled battery 10, when an OCV difference occurs between the maximum current cell and (N-1) standard cells, a circulating current Ic flows in the direction shown in FIG. 4, for example, according to the OCV difference. The details of the calculation method of the circulating current Ic will be described later.

<Running mode>
The vehicle 1 has an HV mode and an EV mode as traveling modes. The HV mode is a traveling mode in which the engine 50 is driven and the engine 50, the assembled battery 10 and the motor generator 42 are used as power sources for traveling. On the other hand, the EV mode is a traveling mode in which the engine 50 is stopped and electric traveling (EV traveling) is performed by using the assembled battery 10 and the motor generator 42 as power sources. The HV mode and the EV mode are selected, for example, by the user operating a mode selection switch (not shown). The mode of the current IB flowing through the assembled battery 10 may differ greatly depending on the traveling mode of the vehicle 1 as described below.

FIG. 5 is a diagram showing a typical example (an example of simulation conditions) of the current IB flowing through the assembled battery 10 when the HV mode is selected and when the EV mode is selected. FIG. 5A shows an example of the current IB when the HV mode is selected, and FIG. 5B shows an example of the current IB when the EV mode is selected. The horizontal axis shows the elapsed time. The vertical axis shows the current IB. The positive direction is the discharge direction of the assembled battery 10, and the negative direction is the charging direction of the assembled battery 10.

FIG. 6 is a diagram showing an example (simulation result) of the OCV difference between when the HV mode is selected and when the EV mode is selected, which occurs when the current IB shown in FIG. 5 flows. In FIG. 6, the horizontal axis indicates the elapsed time. The vertical axis indicates the OCV difference (hereinafter, also referred to as “ΔOCV”) between the maximum current cell and the standard cell included in the assembled battery 10 (block 10K). ΔOCV is calculated by the following formula (1) using OCVmax, which is the OCV of the maximum current cell, and OCVtype, which is the OCV of the standard cell.
ΔOCV = OCVmax-OCVtype ... (1)

As shown in FIG. 5A, in general, in the HV mode, the charge / discharge direction of the assembled battery 10 is intermittently switched. In such a case, ΔOCV is unlikely to occur (see FIG. 6). Therefore, the influence of the circulating current Ic in the HV mode is relatively small. On the other hand, in the EV mode, as shown in FIG. 5B, the assembled battery 10 is often continuously discharged, and the assembled battery 10 is likely to be over-discharged. Therefore, an OCV difference between cells is likely to occur (see FIG. 6). As a result, the influence of the circulating current Ic may be relatively large.

<Maximum current estimation flow>
Therefore, in the present embodiment, when the EV mode of the vehicle 1 is continued for a predetermined period (when the EV running is continued for a predetermined period T), the circulating current Ic is calculated and the calculated circulating current Ic is calculated. The "maximum current estimation process" for estimating the maximum current Imax is executed.

FIG. 7 is a flowchart for explaining the maximum current estimation process in the present embodiment. This flowchart is called from the main routine (not shown) every time a predetermined calculation cycle elapses, and is executed by the ECU 100 shown in FIG. 1 for each block constituting the assembled battery 10. Further, each step (hereinafter abbreviated as "S") included in this flowchart is basically realized by software processing by the ECU 100, but is realized by dedicated hardware (electric circuit) manufactured in the ECU 100. You may.

In S10, the ECU 100 estimates the current variation between cells caused by the resistance variation between cells. As an example, in this embodiment, the current increase gain G indicating the current increase (= maximum current / average current) of the maximum current with respect to the average current due to the resistance variation between cells is calculated.

The current increase gain G can be calculated as follows. That is, for example, the minimum temperature Tmin of the N cells connected in parallel, the temperature difference between the cells (difference between the maximum temperature Tmax and the minimum temperature Tmin) ΔT, and the resistance between the cells due to the maximum temperature difference ΔT. The relationship with the current increase gain G based on the variation is obtained in advance by experiments or the like. This relationship can be prepared, for example, by measuring the ratio of the maximum current to the average current (maximum current / average current) by an experiment or the like. Alternatively, the ratio (Rt / Rmin) of the combined resistance Rt to the minimum resistance Rmin may be measured by an experiment or the like. By preparing this relationship as a map or a table and storing it in the memory 100B, the current increase gain G can be calculated based on the cell temperature detected by the temperature sensor 23. When the temperature sensor 23 is provided so as to detect the temperature using a plurality of (for example, several) adjacent cells as a monitoring unit, the minimum temperature Tmin of the temperature sensor 23 and the temperature difference ΔT are used. ..

In S20, the ECU 100 determines whether or not the EV mode of the vehicle 1 has continued for a predetermined period T. The predetermined period T is a period in which the ΔOCV between the maximum current cell and the standard cell increases to some extent so that the circulating current Ic becomes so large that it cannot be ignored, and is predetermined by experiment or simulation. The predetermined period T is, for example, about several minutes to several minutes. When the EV mode continues for a predetermined period T (YES in S20), the process proceeds to S30. In S30, the ECU 100 executes the “OCV difference calculation process” for calculating the ΔOCV between the maximum current cell and the standard cell.

FIG. 8 is a flowchart illustrating the OCV difference calculation process executed in S30 of FIG. In the following, the current calculation cycle will be the i (i is a natural number of 2 or more) th cycle.

With reference to FIG. 8, in S31, the ECU 100 uses Imax (i-1), which is an estimated value of the maximum current Imax calculated in S80 of FIG. 7 in the previous calculation cycle, to SOC of the maximum current cell. The SOCmax indicating (State Of Charge) is calculated. Specifically, SOCmax is calculated by adding or subtracting the amount of increase or decrease in the capacity of the cell obtained by multiplying Imax (i-1) by the calculation cycle Δt to the previously calculated value of SOCmax.

Then, the ECU 100 calculates OCVmax indicating the OCV of the maximum current cell from the calculated SOCmax (S32). Specifically, the OCV max can be calculated based on the SOC max calculated in S31 by using a map or the like prepared in advance showing the relationship between the SOC and the OCV in each cell constituting the assembled battery 10.

Next, the ECU 100 calculates the SOCtype indicating the SOC of the standard cell by using the Type (i-1) which is the calculated value of the current Ityp calculated in S90 of FIG. 7 in the previous calculation cycle (S33). Specifically, SOCtype is calculated by adding or subtracting the amount of increase or decrease in capacity obtained by multiplying Itype (i-1) by the calculation cycle Δt to the previously calculated value of SOCtype.

Then, the ECU 100 calculates an OCV type indicating the OCV of the standard cell from the calculated SOCtype (S34). Specifically, the OCV type can be calculated based on the SOCtype calculated in S33 by using the above-mentioned map or the like showing the relationship between the SOC and the OCV.

Next, the ECU 100 calculates ΔOCV, which is the OCV difference between the maximum current cell and the standard cell, by subtracting the OCV type of the standard cell calculated in S34 from the OCV max of the maximum current cell calculated in S32. (S35).

Returning to FIG. 7, in S40, the ECU 100 indicates a closed loop resistance composed of the maximum current cell and the standard cell in order to calculate the circulating current Ic generated between the maximum current cell and the standard cell. Is calculated. The circulation resistance Rc is expressed by the following equation (2) using the resistance Rmin of the maximum current cell and the combined resistance Rt of (N-1) standard cells.
Rc = Rmin + Rt ・ ・ ・ (2)

In the formula (2), the resistance Rmin is the previously calculated value (Imax (i-1)) of the current Imax, which is an estimated value of the current flowing in the maximum current cell, and the voltage detection value of the cell (block including the cell). It is calculated from (see S80 described later). Further, the combined resistance Rt is calculated from the previously calculated value (Itype (i-1)) of the current Ityp, which is an estimated value of the current flowing through the standard cell, and the voltage detection value of the cell (the block including the cell). (See S90 below).

In S50, the ECU 100 calculates the circulating current Ic. The circulating current Ic is obtained by dividing ΔOCV, which is the OCV difference calculated in S30, by the circulating resistance Rc calculated in S40.

The ECU 100 may calculate the circulating current Ic from the temperature of the assembled battery 10 and ΔOCV instead of the combined resistance Rt and ΔOCV. More specifically, when the protection of the assembled battery 10 is emphasized, it is desirable to estimate the circulating current Ic to a large extent and thereby suppress the charging / discharging of the assembled battery 10 as severely as possible. The higher the temperature of the assembled battery 10, the lower the circulation resistance Rc, and therefore the larger the circulation current Ic. Therefore, the relationship between the temperature of the assembled battery 10, ΔOCV, and the circulating current Ic is measured in advance by an experiment or the like, and stored in the memory 100B as a map. Then, the circulating current Ic can be calculated from the maximum temperature detected by the temperature sensor 23 (the maximum value among the temperatures measured by the plurality of temperature sensors 23) and ΔOCV. However, instead of the maximum temperature of the assembled battery 10, for example, the average temperature of the assembled battery 10 (the average value of the temperatures measured by the plurality of temperature sensors 23) may be used. After calculating the circulating current Ic, the ECU 100 advances the process to S70.

On the other hand, when the EV mode is not continued for the predetermined period T (NO in S20), the ECU 100 sets the circulating current Ic to 0 (zero), assuming that the circulating current Ic is still small and negligible (NO). S60). Instead of 0, a fixed value slightly smaller than 0 may be set as the circulating current Ic.

In S70, the ECU 100 calculates an average current Iave indicating the average of the currents flowing through all the cells (maximum current cell and (N-1) standard cells). The average current Iave is calculated by the following formula (3). The IB is a current (total current) detected by the current sensor 22.
Iave = IB / N ... (3)

In S80, the ECU 100 calculates the current Imax (i), which is an estimated value of the current flowing through the maximum current cell, by the following equation (4).
Imax (i) = Iave × G + Ic ・ ・ ・ (4)

On the right side of the equation (4), Iave × G is a current value obtained by multiplying the average current Iave by the current increase gain G calculated in S10, and is the amount of current increase due to resistance variation between cells. The current considered is shown. That is, Iave × G corresponds to the “current variation” according to the present disclosure. Ic is the circulating current calculated in S50.

The ECU 100 further calculates the current Imax (i), which is an estimated value of the current flowing through each standard cell, from the current Imax (i) calculated in S70 by the following formula (5) (S90). This current Ityp is used in the OCV difference calculation process (S30) in the next calculation cycle.
Itype (i) = (IB-Imax (i)) / (N-1) ... (5)

As described above, according to the present embodiment, when the EV mode in which the influence of the circulating current Ic flowing so as to circulate between the cells becomes remarkable continues for a predetermined period T, the current generated due to the resistance variation between the cells. The maximum current Imax of the currents distributed and flowing in a plurality of cells connected in parallel is estimated by using not only the variation (the term of Iave × G in the above equation (4)) but also the circulating current Ic. Thereby, the estimation accuracy of the maximum current Imax can be improved. Therefore, by referring to the maximum current estimated with high accuracy in this way, it is possible to prevent the current flowing through the cell from exceeding a predetermined limit. Further, the control upper limit value Win of the charge power of the assembled battery 10 and the control upper limit value Wout of the discharge power can be appropriately controlled.

The embodiments disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of the present disclosure is indicated 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 vehicle, 2 battery system, 10 sets of batteries, 101-10M block, 20 monitoring unit, 21,21 to 21M voltage sensor, 22 current sensor, 23 temperature sensor, 30 PCU, 41,42 motor generator, 50 engine, 60 power Divider, 70 drive shaft, 80 drive wheels, 100 ECU, 100A CPU, 100B memory.

Claims (2)

A battery system that can be mounted on a vehicle equipped with an electric motor.
An assembled battery composed of a plurality of secondary batteries connected in parallel, and
A temperature sensor that detects the temperature of the plurality of secondary batteries, and
Before SL includes a plurality of a controller configured to estimate the maximum current of the current flowing dispersed in the secondary battery,
The control device is
By using a pre-determined relationship between the temperature difference between the plurality of secondary batteries and the resistance variation between the plurality of secondary batteries, the plurality of two batteries are based on the temperature detected by the temperature sensor. Estimate the current variation between the next batteries and
When the EV running in which the vehicle runs is continued for a predetermined period only by the vehicle driving force from the electric motor.
The OCV (Open Circuit Voltage) difference between the plurality of secondary batteries is calculated based on the maximum current flowing through the secondary battery having the lowest resistance among the plurality of secondary batteries and the current flowing through the other secondary batteries. And
From the calculated OCV difference , the circulating current flowing so as to circulate between the plurality of secondary batteries is calculated.
A battery system that estimates the maximum current using the calculated circulating current and the current variation. The control device is
By using the relationship between the SOC and OCV of the plurality of secondary batteries, the first OCV is calculated from the amount of increase / decrease in the capacity of the secondary battery through which the maximum current flows, and the other secondary batteries Calculate the second OCV from the amount of increase / decrease in capacity,
The battery system according to claim 1, wherein the OCV difference is calculated by subtracting the second OCV from the first OCV.

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