JP6874648B2 - Battery system - Google Patents

Description

The present invention relates to limiting discharge due to deterioration of battery systems, especially batteries.

An electric vehicle (EV) is equipped with a large-capacity battery and runs by driving a motor with electric power from the battery. Then, when the capacity of the battery decreases, the battery is charged by the electric power supplied from the outside. Further, during traveling, charging is performed by the regenerative power of the motor.

Here, it is known that the battery deteriorates due to use, and particularly when the battery is continuously charged and discharged with a large current, high-rate deterioration occurs and the battery deteriorates significantly. Therefore, it has been proposed to calculate a deterioration index from the charge / discharge state of the battery, limit the charge / discharge of the battery when the deterioration index exceeds a predetermined value, and suppress an increase in the amount of deterioration due to high-rate deterioration. For example, in Patent Document 1, in a hybrid vehicle (HV), when the deterioration index becomes high due to continuous discharge, the engine generates electricity to suppress the increase in the deterioration index.

The calculation of the deterioration index is also described in Patent Documents 2 and 3.

Japanese Unexamined Patent Publication No. 2012-218599 Japanese Unexamined Patent Publication No. 2017-91602 Japanese Unexamined Patent Publication No. 2009-123245

Here, unlike hybrid vehicles, electric vehicles are not equipped with an engine. Further, even in a plug-in hybrid vehicle, the driving of the engine may be prohibited and the vehicle may run as an electric vehicle. In such an electric vehicle, a large current is likely to be discharged while the vehicle is running, and the high rate deterioration of the battery is likely to proceed as compared with the hybrid vehicle. Further, it is not possible to suppress high-rate deterioration by using an engine as in Patent Document 1. Therefore, it is conceivable that the deterioration index becomes more than a predetermined value and the vehicle cannot run.

The present invention is a battery system that limits the output to the limit value W1 when the deterioration index ΣD of the battery exceeds the limit limit value ΣDmax for discharge, and limits the output to the limit value W2 that is stricter than the limit value W1. _{The time Time2 at which the increase amount ΔΣD IB2} of the deterioration index when discharged at the usable current IB2 becomes the deterioration index difference value ΔΣD obtained by subtracting the current deterioration index ΣD from the limit limit value ΣDmax is calculated, and the usable current IB2 is used. The decrease amount ΔSOC2 of the charge capacity of the battery when discharged for the time Time2 was calculated, and the limit start SOC corresponding to the calculated decrease amount ΔSOC2 was determined, and the current SOC was equal to or less than the determined limit start SOC. In this case, the output power is limited to the limit value W2.

_{Further, the time Time1 at which the increase amount ΔΣD IB1} of the deterioration index when discharged at the usable current IB1 without the output limit becomes the deterioration index difference value ΔΣD is calculated, and when the battery is discharged at the usable current IB1, the battery is discharged. When the time Time3 for power shortage is calculated and the time Time1 is equal to or longer than the time Time3, the control for limiting the output power to the limit value W2 may not be performed.

According to the present invention, it is possible to suppress an increase in the deterioration index during running and to prevent the vehicle from becoming incapable of running.

It is a block diagram which shows the structure of the vehicle which mounted the battery system which concerns on embodiment. It is a flowchart which shows the process of discharge control in a battery system. It is a timing chart which shows the state of SOC, deterioration index, and output power limitation in a battery system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described herein.

"overall structure"
FIG. 1 shows a vehicle 10 equipped with a battery system according to an embodiment of the present invention. The vehicle 10 is equipped with a battery 12. The battery 12 is a rechargeable secondary battery such as a nickel hydrogen secondary battery or a lithium ion secondary battery. An inverter 16 is connected to the battery 12 via a converter 14. The converter 14 includes, for example, two switching elements and a reactor, and by switching the switching elements, the output voltage of the battery 12 is boosted to a predetermined voltage and supplied to the inverter 16. The converter 14 can also be stepped down. A motor generator (MG) 18 is connected to the inverter 16, and the motor generator 18 is driven by an alternating current from the inverter 16. The inverter 16 has, for example, three arms in which two switching elements are connected in series between the positive and negative bus, and the midpoint of each arm is connected to the coil of each phase of the motor generator 18. Then, by controlling the switching of the switching element, a desired three-phase alternating current is supplied to the stator coil of the motor generator 18 to drive the motor generator 18. By controlling the switching element, the motor generator 18 can be put into a regenerative state, and the battery 12 can be charged with the obtained regenerative power.

The output shaft of the motor generator 18 is connected to the wheels 22 via a power transmission mechanism 20 including a differential gear or the like, and the wheels 22 are rotated by the output of the motor generator 18 to drive the vehicle 10.

Further, an AC charging device 30 is connected to the battery 12. The AC charging device 30 includes a rectifier circuit, and an AC connector 32 is connected to the AC charging device 30. Therefore, the battery 12 can be charged by connecting a commercial AC power source (100V, 200V) to the AC connector 32 via a charging cable. A DC connector 36 is connected to the battery 12 via a DC charging device 34. Therefore, the battery 12 can be charged by connecting the DC quick charger to the DC connector 36 via the charging cable.

Further, the vehicle 10 has a control device 40, which has a vehicle ECU (Electronic Control Unit) 42, a motor ECU 44, and a battery ECU 46, and controls various operations of the vehicle.

A signal indicating a driver's request is input to the vehicle ECU 42 from an accelerator pedal, a brake pedal, a shift lever, or the like. Further, a signal indicating the state of the vehicle, such as a signal indicating the traveling speed from the vehicle speed sensor, is also input to the vehicle ECU 42. Further, the motor ECU 44 and the battery ECU 46 are connected to the vehicle ECU 42, and signals indicating the states of the motor generator 18, the battery 12, and the like are also supplied from these. Then, the vehicle ECU 42 supplies a control signal such as an output torque command to the motor ECU 44 and a charge control command to the battery ECU 46 so as to perform driving suitable for the driver's request and the state of the vehicle 10 from these signals. And so on.

The motor ECU 44 controls the operation of the motor generator 18 via the converter 14 and the inverter 16. For example, the converter 14 is controlled based on the output torque command to control the input voltage of the inverter 16 to the target voltage. Further, the inverter 16 is controlled based on the output torque command to control the output torque of the motor generator 18. The motor ECU 44 is supplied with the detection values of the sensor indicating the operating state of the motor generator 18 and the rotation angle sensor of the rotor.

The battery 12 is provided with a current sensor for detecting the battery current, a voltage sensor for detecting the battery voltage, and a temperature sensor for detecting the battery temperature. The signal detected by each sensor is supplied to the battery ECU 46. The battery ECU 46 calculates the remaining capacity (SOC) of the battery 12 based on the supplied signal, supplies the signal indicating the SOC to the vehicle ECU 42, and controls the charging of the battery 12 with reference to the battery temperature.

"Driving discharge control"
The vehicle ECU 42 controls the discharge of the battery 12 via the battery ECU 46 and the motor ECU 44. In particular, the battery ECU 46 receives the supply of the SOC, temperature, and charge / discharge current of the battery 12, and constantly calculates the deterioration index ΣD due to the high rate deterioration of the battery 12. The deterioration index ΣD is the accumulation of the deterioration (damage) D detected for each control loop Δt, and can be calculated by adopting a known method described in Patent Documents 1 to 3 and the like.

Then, the vehicle ECU 42 controls the discharge by the battery 12 according to the deterioration index (current deterioration index) ΣD calculated by the battery ECU 46 and the SOC of the battery 12. This will be described with reference to FIGS. 2 and 3.

First, it is determined whether the SOC is currently equal to or lower than a predetermined value, or the deterioration index (cumulative value of damage due to high rate deterioration) ΣD is equal to or higher than a predetermined value (S11). If the determination in S11 is NO, it is not necessary to limit the discharge, and the process for that time is terminated.

If the determination in S11 is YES, the usable current IB1 is calculated (S12). This usable current IB1 is a current value that can be output by the current battery 12, and can be obtained by a known method from the current SOC and the battery temperature. It is also preferable to calculate using a map. _{Next, the deteriorated DIB1} is calculated from the current SOC, the battery temperature, and the usable current IB1 (S13). This deterioration D is also calculated by a method as described in Patent Documents 1 to 3. Since the deteriorated _{DI IB1} is calculated using the usable current IB1 instead of the current current, it can be used as an _{appropriate deteriorated DI IB1 for predicting future deterioration.} The current deterioration index ΣD is calculated as usual using the current current.

Then, based on the current deterioration index ΣD, the time Time 1 until the limit limit value ΣDmax of the deterioration index that limits Wout to almost 0 (limit value W1) is reached is calculated (S14). The calculation of Time 1 is shown by a chain double-dashed line in FIG. That is, the value of the limit limits ΣDmax degradation index by dividing the deterioration index difference ΔΣD obtained by subtracting the current deterioration index ΣD in deterioration D _IB1 in the current available current IB1, the increase ΔΣD The time Time 1 at which deterioration occurs is calculated.

Next, the time Time3 is calculated from the current SOC, the full charge capacity FCC, and the usable current IB1 (S15). The battery capacity of the battery 12 can be calculated by multiplying the full charge capacity by the current SOC, and the time Time3 can be calculated by dividing this by the usable current IB1. This corresponds to the time until the SOC of the battery 12 runs out of power when the battery continues to be discharged at the usable current IB1. When the power shortage SOC is set to a value higher than 0%, the time obtained by dividing the battery capacity of the power shortage SOC by the usable current IB1 may be subtracted from Time3.

Then, it is determined whether there is a possibility that the Wout is restricted by the time of power shortage (Time1 <Time3) (S16). That is, when the discharge of the usable current IB1 is continued, it is determined whether the deterioration index ΣD reaches the limit limit value ΣDmax before the SOC reaches the power shortage. The value of Wout when there is no limit is set to the limit value W1.

If the determination in S16 is NO, the deterioration index ΣD does not reach the limit limit value ΣDmax during traveling, so the process ends. If YES in the determination of S16, the usable current IB2 corresponding to the limit value W2 (Wout = W2) after the limit and the deterioration _DIB2 per unit time (control loop Δt) from the current SOC and the current battery temperature are obtained. Calculate (S17). Here, the usable current IB2 is a current value required for traveling the vehicle, and a value determined by the required power of the vehicle may be adopted. Further, the usable current IB2 may be obtained by dividing the limit value W2 by the open circuit voltage CCV of the battery 12.

Then, when continuing the discharge at usable current IB2, the cumulative DerutashigumaD _IB2 deterioration _{D IB2,} calculated from the current degradation index .SIGMA.D, the equal time Time2 to increase ΔΣ up to the limit limits ΣDmax (S18). This may be calculated by time Time2 = (ΔΣD / D _{IB2) Δt.} The usable current IB2 has a smaller current amount than the usable current IB1, and the Time2 has a longer time than the Time1.

Then, for the period of the obtained time Time2, the SOC reduction amount ΔSOC2 when discharged at the usable current IB2 is calculated (S19). Here, ΔSOC2 = (currently SOC / FCC-IB2 / Time2) / FCC. Then, the restriction start SOC (t2) is calculated (S20). This calculation is performed with the restriction start SOC (t2) = power shortage SOC + ΔSOC2.

Then, it is determined whether or not the SOC is currently SOC (t2) or less (S21). If the determination in S21 is NO, the process is terminated because there is no need to limit the output. On the other hand, if the determination in S21 is YES, the output power limit Wout is limited to W2, and the output limit is implemented (S22). At this time, it is notified by a display or the like that the output is restricted.

In this way, when the deterioration index is about to reach the limit limit value ΣDmax during traveling, the output is limited in order to secure the traveling until the power shortage. Therefore, it is possible to prevent the deterioration index from reaching the limit limit value during traveling and becoming unable to travel.

FIG. 3 shows the states of SOC, deterioration index ΣD, and output power limit Wout during traveling. The thick line shows the embodiment, and the dotted line shows the comparative example. This battery system is installed in an electric vehicle, and is not charged except for regeneration while driving, and the SOC gradually decreases. On the other hand, the deterioration index ΣD of high rate deterioration due to charging gradually increases due to the discharge of a large current during traveling.

According to this embodiment, when the SOC becomes SOC (t2), Wout is set to a limited value W2 (battery current is limited to usable current IB2). As a result, it is possible to prevent the deterioration index ΣD from reaching the limit limit value ΣDmax before the power shortage, resulting in inability to travel. In the comparative example, when the deterioration index ΣD reaches ΣDmax, Wout is restricted and the vehicle cannot run.

10 vehicles, 12 batteries, 14 converters, 16 inverters, 18 motor generators, 22 wheels, 30 AC charging devices, 32, 36 connectors, 34 DC charging devices, 40 control devices, 42 vehicle ECUs, 44 motor ECUs, 46 battery ECUs.

Claims (1)

A battery system that limits the output to the limit value W1 when the battery deterioration index ΣD exceeds the limit limit value ΣDmax for discharge.
Deterioration index difference in which the amount of increase in the deterioration index when discharging with the usable current IB2 when the output is limited to the limit value W2, which is stricter than the limit value W1, ΔΣD _IB2 is the limit limit value ΣDmax minus the current deterioration index ΣD. Calculate the time Time2 that becomes the value ΔΣD, and calculate
The decrease amount ΔSOC2 of the charge capacity of the battery when discharged for the time Time2 at the usable current IB2 is calculated, and the limit start SOC corresponding to the calculated decrease amount ΔSOC2 is determined.
When the current SOC is less than or equal to the determined limit start SOC, the output power is limited to the limit value W2.
Battery system.

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