JP2019021412A - Electric vehicle - Google Patents

Abstract

To circumvent excessive restriction of regeneration of a motor generator, while restraining precipitation of metallic lithium in the negative electrode of lithium ion battery.SOLUTION: A vehicle includes a motor generator (MG), a lithium ion battery (main battery), an auxiliary battery, a DC/DC converter, and an ECU. The ECU limits regenerative amount of the MG when the charging current of the main battery exceeds an allowable charging current Ilim. The allowable charging current Ilim is the maximum value of charging current capable of restraining precipitation of metallic lithium in the negative electrode of the main battery, and is increased when being discharged electrically from the main battery. When the charging current is not exceeding the allowable charging current Ilim, and the difference of the charging current and the allowable charging current Ilim is less than a threshold level, the ECU performs instant discharge for discharging from the main battery to the auxiliary battery, by controlling a DC/DC converter.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to an electric vehicle including a lithium ion battery.

  WO 2010/005079 pamphlet (Patent Document 1) discloses a hybrid vehicle including a motor generator mechanically connected to drive wheels, a lithium ion battery electrically connected to the motor generator, and a control device. Is disclosed. In this hybrid vehicle, the regeneration amount of the motor generator is limited in order to suppress the deposition of metallic lithium on the negative electrode of the lithium ion battery. Specifically, the control device mounted on the hybrid vehicle allows the maximum charging current that can suppress the deposition of metallic lithium at the negative electrode of the lithium ion battery based on the history of the input / output current of the lithium ion battery. Calculated as current. When the charging current of the lithium ion battery exceeds the allowable charging current, the control device limits the regeneration amount of the motor generator and reduces the charging current to less than the allowable charging current. Thereby, precipitation of metallic lithium in the negative electrode of the lithium ion battery is suppressed.

International Publication No. 2010/005079 Pamphlet

  However, in the hybrid vehicle disclosed in Patent Document 1, there is a possibility that the regenerative power of the motor generator cannot be sufficiently recovered. That is, for example, when the vehicle travels on a long downhill, the motor generator is in a regenerative state for a long period of time, but in order to suppress the deposition of metallic lithium while continuing charging during this period, the allowable charging current There is a concern that the size needs to be reduced to a considerably small value, and as a result, the regeneration of the motor generator is excessively limited, and the regenerative power of the motor generator cannot be sufficiently recovered.

  The present disclosure has been made in order to solve the above-described problem, and an object of the present disclosure is to avoid excessive limitation of regeneration of the motor generator while suppressing deposition of metallic lithium in the negative electrode of the lithium ion battery. It is.

  An electric vehicle according to the present disclosure includes a motor generator mechanically connected to drive wheels, a lithium ion battery electrically connected to the motor generator, and an auxiliary battery that stores electric power for operating an auxiliary machine of the electric vehicle. And a conversion device that performs voltage conversion between the lithium ion battery and the auxiliary battery, and limiting the regeneration amount of the motor generator when the charging current of the lithium ion battery exceeds the allowable charging current. And a control device configured as described above. The allowable charging current is a maximum value of the charging current that can suppress the deposition of metallic lithium on the negative electrode of the lithium ion battery, and is a value that is increased when the lithium ion battery is discharged. The control device controls the conversion device when the magnitude of the charging current does not exceed the magnitude of the allowable charging current and the difference between the magnitude of the charging current and the magnitude of the allowable charging current is less than a threshold value. As a result, the lithium ion battery is temporarily discharged to the auxiliary battery.

  According to the above configuration, the magnitude of the charging current does not exceed the allowable charging current (that is, the amount of regeneration of the motor generator is not limited), and the charging current and the allowable charging current are When the difference is less than the threshold value, the lithium ion battery is temporarily discharged to the auxiliary battery. This discharge increases the amount of allowable charging current (maximum value of charging current that can suppress the deposition of metallic lithium) before limiting the amount of motor generator regeneration. The magnitude of the charging current can be prevented from exceeding. As a result, it is possible to avoid excessive limitation of regeneration of the motor generator while suppressing deposition of metallic lithium on the negative electrode of the lithium ion battery.

1 is a diagram schematically showing a configuration of a vehicle. It is a figure which shows an example of the change of the request | requirement current IBreq and the allowable charging current Ilim in the case where instantaneous discharge is performed. It is a figure which shows an example of the change of the request | requirement current IBreq and the allowable charging current Ilim when instantaneous discharge and MG regeneration limitation are performed. It is a flowchart which shows an example of the process sequence of ECU.

  Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Vehicle configuration]
FIG. 1 is a diagram schematically showing a configuration of a vehicle 1 according to the present embodiment. Hereinafter, a case where the vehicle 1 is a hybrid vehicle will be described. However, the vehicle 1 according to the present embodiment is not limited to a hybrid vehicle, and can be applied to all electric vehicles (such as an electric vehicle) equipped with a lithium ion battery. is there.

  The vehicle 1 includes a main battery 10, a monitoring unit 20, a power control unit (PCU) 30, motor generators (MG) 41 and 42, an engine 50, a power split device 60, A drive shaft 70, a drive wheel 80, an auxiliary battery 90, a DC / DC converter 91, and an electronic control unit (ECU: Electronic Control Unit) 100 are provided.

  The engine 50 generates a driving force for rotating the crankshaft by combustion energy generated when the air-fuel mixture is burned. The MGs 41 and 42 function as both a generator and an electric motor.

  The MG 41 mainly operates as a generator that generates electricity using a part of the output of the engine 50 transmitted through the power split device 60. The electric power generated by the MG 41 is supplied to the MG 42 or the main battery 10 through the PCU 30.

  MG42 is driven by at least one of the power supplied from main battery 10 and the generated power of MG41. The driving force of the MG 42 is transmitted to the driving shaft 70. Further, when the vehicle 1 is decelerated, the MG 42 performs regenerative power generation by being driven by the rotational force of the drive wheels 80. The electric power generated by the MGs 41 and 42 is supplied to the main battery 10 through the PCU 30.

  Main battery 10 stores electric power for driving MGs 41 and 42. Main battery 10 is a lithium ion secondary battery, and includes a plurality of cells connected in series. The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. Voltage sensor 21 detects a voltage between terminals of main battery 10 (hereinafter also referred to as “voltage VB”). Current sensor 22 detects a charging / discharging current (hereinafter also referred to as “current IB”) of main battery 10. The temperature sensor 23 detects the temperature of the main battery 10 (hereinafter also referred to as “temperature TB”). Each sensor outputs a signal indicating the detection result to ECU 100. The output of the current sensor 22 shows a negative value when the main battery 10 is charged, and shows a positive value when the main battery 10 is discharged.

  PCU 30 is configured to perform bidirectional power conversion between main battery 10 and MGs 41 and 42 in accordance with a switching command from ECU 100. The PCU 30 is configured to be able to control the states of the MGs 41 and 42 separately. For example, the PCU 30 can place the MG 42 in a power running state while the MG 41 is in a power generation state.

  The auxiliary battery 90 stores electric power for operating the auxiliary machine mounted on the vehicle 1 and supplies electric power to each auxiliary machine as necessary. Note that the auxiliary machines include all electric devices that operate at a low voltage (for example, about 12 V), such as the ECU 100, headlights, and audio. The output voltage of auxiliary battery 90 is adjusted to the operating voltage of the auxiliary machine (for example, about 12V as described above), and is lower than the output voltage of main battery 10 (for example, about 200V).

  The auxiliary battery 90 is provided with a voltage sensor 92 and a current sensor 93. Voltage sensor 92 detects the voltage between terminals of auxiliary battery 90. Current sensor 93 detects a charge / discharge current of auxiliary battery 90. Each sensor outputs a signal indicating the detection result to ECU 100. ECU 100 calculates SOC (State Of Charge) of auxiliary battery 90 from the detection results of voltage sensor 92 and current sensor 93.

  DC / DC converter 91 is provided between auxiliary battery 90 and main battery 10. The DC / DC converter 91 is configured to step down the output voltage of the main battery 10 and supply it to the auxiliary battery 90.

  The ECU 100 is configured to include a CPU (Central Processing Unit), an input / output interface, and a memory (all not shown). ECU 100 controls engine 50, PCU 30, DC / DC converter 91, and the like based on signals from the sensors and information stored in the memory.

  For example, ECU 100 calculates a current required for main battery 10 (hereinafter also referred to as “request current IBreq”) based on the vehicle speed, the amount of accelerator operation by the user, and the like. ECU 100 controls engine 50, PCU 30, DC / DC converter 91, and the like so that current IB of main battery 10 becomes required current IBreq.

  In the present embodiment, when the required current IBreq is a positive value, it means that “discharge” is required, and when it is a negative value, “charge” is required. Means. For example, when the required current IBreq is a negative value, the charging required for the main battery 10 becomes smaller as the value including the sign of the required current IBreq is smaller, that is, as the magnitude (absolute value) of the required current IBreq is larger. This means that the current is large.

[Inhibition of metallic lithium deposition on the negative electrode of the main battery]
As described above, in the present embodiment, a lithium ion secondary battery is employed as the main battery 10. In lithium ion secondary batteries, it is known that when charging continues, the potential of the negative electrode decreases, and when the potential of the negative electrode decreases to a certain reference potential (for example, about 0 V), metallic lithium is deposited on the surface of the negative electrode. ing. When metallic lithium is deposited on the negative electrode, the performance of the lithium ion secondary battery is degraded.

  Therefore, ECU 100 according to the present embodiment limits the electric power input to main battery 10 in order to suppress the deposition of metallic lithium on the negative electrode of main battery 10. Specifically, ECU 100 performs the following processing.

  The ECU 100 first calculates the allowable charging current Ilim of the main battery 10 based on the charge / discharge history of the main battery 10. The allowable charging current Ilim is a charging current that is set as the maximum current that can suppress the deposition of metallic lithium on the negative electrode of the main battery 10.

  When the required current IBreq is a negative value (that is, when charging the main battery 10 is required), the ECU 100 determines that the required current IBreq exceeds the allowable charging current Ilim. In this case, the magnitude of the requested current IBreq is limited to be less than the magnitude of the allowable charging current Ilim. As a result, the amount of regeneration of MG42 is limited, and the actual current IB magnitude (charge current magnitude) becomes less than the allowable charge current Ilim magnitude. Thereby, the deposition of metallic lithium in the negative electrode of main battery 10 is suppressed. Hereinafter, the above-described series of processes performed for suppressing the precipitation of metallic lithium is also referred to as “MG regeneration restriction”.

  The allowable charging current Ilim is calculated based on the charging / discharging history of the main battery 10 as described above. Specifically, when the main battery 10 is charged, the ECU 100 decreases the allowable charging current Ilim as the amount of power charged in the main battery 10 (a value obtained by accumulating charging power by the charging duration time) increases. Value. Further, when the main battery 10 is discharged, the ECU 100 sets the allowable charging current Ilim to a larger value as the amount of power discharged to the main battery 10 (a value obtained by integrating the discharged power by the discharge duration time) is larger. .

[Instantaneous discharge]
As described above, when the required current IBreq is a negative value, the ECU 100 according to the present embodiment increases the required current IBreq when the required current IBreq exceeds the allowable charge current Ilim. By performing “MG regeneration limitation” that limits the length to less than the allowable charging current Ilim, deposition of metallic lithium on the negative electrode of the main battery 10 is suppressed.

  However, as described above, the allowable charging current Ilim has a smaller value as the amount of power charged in the main battery 10 is larger. For example, when the vehicle 1 travels on a long downhill, a large charging power is required. Since the allowable charging current Ilim continues to last for a long period of time and continues to decrease toward zero, the allowable charging current Ilim has a very small value. As a result, the regeneration of the MG 42 is excessively limited, and a problem that the regenerative energy cannot be sufficiently recovered may occur.

  Therefore, when required current IBreq is a negative value (that is, when charging of main battery 10 is required), ECU 100 according to the present embodiment has a magnitude of required current IBreq of allowable charging current Ilim. When the magnitude does not exceed (that is, the MG regeneration limit is not performed) and the difference between the magnitude of the required current IBreq and the allowable charging current Ilim is less than the threshold (that is, the required current IBreq is When close to the allowable charging current Ilim), by controlling the DC / DC converter 91, “instantaneous discharge” is performed in which the main battery 10 is instantaneously discharged to the auxiliary battery 90.

  Specifically, ECU 100 performs instantaneous discharge by setting required current IBreq to a large positive value (for example, a value exceeding 100 amperes) for a predetermined short time (for example, about 0.5 seconds). . After the instantaneous discharge is performed, ECU 100 returns the required current IBreq to a value based on the vehicle speed and the accelerator operation amount.

  FIG. 2 is a diagram showing an example of changes in required current IBreq and allowable charging current Ilim when instantaneous discharge is performed by ECU 100. In FIG. 2, the horizontal axis represents time, the upper part of the vertical axis represents the current value, and the lower part of the vertical axis represents the SOC of the auxiliary battery 90 (hereinafter also referred to as “auxiliary SOC”). As described above, when the current is a positive value, it means “discharge”, and when the current is a negative value, it means “charge”.

  In the example illustrated in FIG. 2, the state where the required current IBreq is a negative value continues immediately before time t1, and the main battery 10 is continuously charged. As a result, the allowable charging current Ilim continues to decrease toward zero, and the allowable charging current Ilim approaches the required current IBreq.

  When the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Ilim becomes less than the threshold value at time t1, the ECU 100 sets the required current IBreq to a large positive value for a short time. Perform “instant discharge”. By this instantaneous discharge, the magnitude (absolute value) of the allowable charging current Ilim can be increased before the MG regeneration limit is performed. Therefore, even if the required current IBreq is returned to a negative value based on the vehicle speed and the accelerator operation amount after the instantaneous discharge, it is possible to avoid that the required current IBreq exceeds the allowable charging current Ilim. As a result, it is possible to avoid excessive limitation of regeneration of the MG 42 while suppressing deposition of metallic lithium on the negative electrode of the main battery 10.

  When instantaneous discharge is performed at time t1, auxiliary machine SOC increases from predetermined value S0 to predetermined value S1. That is, the electric power output from the main battery 10 by the instantaneous discharge is not wasted but stored in the auxiliary battery 90.

  Thereafter, charging continues again, and when the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Ilim becomes less than the threshold value at time t2, the ECU 100 performs “instantaneous discharge” again. As a result, the magnitude (absolute value) of the allowable charging current Ilim is increased. Thereby, the excessive restriction | limiting of regeneration of MG42 can be avoided, suppressing precipitation of metallic lithium in a negative electrode.

  When instantaneous discharge is performed at time t2, auxiliary machine SOC increases from predetermined value S1 to predetermined value S2. Note that the predetermined value S2 is a value that is less than the upper limit value Smax of the auxiliary SOC, so that the auxiliary battery 90 is not overcharged.

  FIG. 3 is a diagram showing an example of changes in required current IBreq and allowable charging current Ilim when instantaneous discharge and MG regeneration restriction are performed by ECU 100. Also in FIG. 3, as in FIG. 2, the horizontal axis represents time, the upper part of the vertical axis represents the current value, and the lower part of the vertical axis represents the auxiliary SOC.

  In the example shown in FIG. 3, at time t11, the ECU 100 performs “instantaneous discharge” as the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Ilim becomes less than the threshold value. As a result, the magnitude (absolute value) of the allowable charging current Ilim is increased. Thereby, it is avoided that the magnitude of the required current IBreq exceeds the magnitude of the allowable charging current Ilim.

  As the instantaneous discharge is performed at time t11, the auxiliary SOC increases from the predetermined value S11 to a value close to the upper limit value Smax.

  At the subsequent time t12, the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Ilim again becomes less than the threshold value, but the auxiliary machine SOC has increased to a value close to the upper limit value Smax. (A state close to a fully charged state). If “instantaneous discharge” is performed in such a state, the auxiliary battery 90 may be overcharged.

  Therefore, even if the difference between the magnitude of required current IBreq and the magnitude of allowable charging current Ilim becomes less than the threshold at time t12, ECU 100 has a value close to upper limit value Smax (exceeds reference value Sth). Value), instantaneous discharge is not performed. As a result, when the magnitude of the allowable charging current Ilim further decreases and the magnitude of the required current IBreq exceeds the magnitude of the allowable charging current Ilim, the ECU 100 determines the magnitude of the required current IBreq as the allowable charging current Ilim. "MG regeneration restriction" is performed to limit the size to less than the size of the. Therefore, although the regeneration amount of MG42 is limited, precipitation of metallic lithium on the negative electrode of main battery 10 can be suppressed while suppressing auxiliary battery 90 from being overcharged.

  FIG. 4 is a flowchart illustrating an example of a processing procedure of the ECU 100. This flowchart is repeatedly executed at a predetermined cycle.

  First, the ECU 100 calculates a required current IBreq based on the vehicle speed, the amount of accelerator operation by the user, and the like (step S10).

  Next, ECU 100 calculates allowable charging current Ilim based on the charging / discharging history of main battery 10 (step S12). Specifically, as described above, when the main battery 10 is charged, the ECU 100 increases the allowable charging current Ilim as the amount of power charged in the main battery 10 (a value obtained by integrating the charging power with the charging duration time) increases. Reduce the size of. Further, when the main battery 10 is discharged, the ECU 100 sets the allowable charging current Ilim to a larger value as the amount of power discharged to the main battery 10 (a value obtained by integrating the discharged power by the discharge duration time) is larger. .

  Next, the ECU 100 determines whether or not the required current IBreq is a negative value (step S14). If requested current IBreq is not a negative value (NO in step S14), ECU 100 skips the subsequent processing and shifts the processing to return.

  If the required current IBreq is a negative value (YES in step S14), the ECU 100 determines whether the required current IBreq (= | IBreq |) exceeds the allowable charging current Ilim (= | Ilim |). It is determined whether or not (step S16).

  When the magnitude of request current IBreq exceeds the magnitude of allowable charging current Ilim (YES in step S16), ECU 100 performs the above-described MG regeneration limitation (step S20). Specifically, ECU 100 limits the magnitude of request current IBreq to be less than the magnitude of allowable charging current Ilim.

  On the other hand, when the magnitude of requested current IBreq does not exceed the magnitude of allowable charging current Ilim (NO in step S16), ECU 100 determines that the difference between the magnitude of required current IBreq and the magnitude of allowable charging current Ilim is a threshold value. It is determined whether it is less than (step S22).

  When the difference between the magnitude of required current IBreq and the magnitude of allowable charging current Ilim is equal to or greater than the threshold value (NO in step S22), ECU 100 skips the subsequent processing and shifts the processing to return.

  When the difference between the magnitude of requested current IBreq and the magnitude of allowable charging current Ilim is less than the threshold value (YES in step S22), ECU 100 determines whether or not auxiliary machine SOC exceeds reference value Sth ( Step S24). This determination is for determining whether or not the auxiliary SOC exceeds the upper limit value Smax by one instantaneous discharge. Therefore, reference value Sth is determined in advance based on a value obtained by subtracting the increase amount of auxiliary SOC from one instantaneous discharge from upper limit value Smax.

  If auxiliary machine SOC does not exceed reference value Sth (NO in step S24), ECU 100 performs the instantaneous discharge described above (step S26). Specifically, ECU 100 instantaneously discharges main battery 10 to auxiliary battery 90 by controlling DC / DC converter 91. As a result, the magnitude (absolute value) of the allowable charging current Ilim is increased. Therefore, it is difficult for the required current IBreq to exceed the allowable charging current Ilim. As a result, it is possible to avoid excessive limitation of regeneration of the MG 42 while suppressing deposition of metallic lithium on the negative electrode of the main battery 10.

  On the other hand, when auxiliary machine SOC exceeds reference value Sth (YES in step S24), ECU 100 proceeds to the return without performing “instantaneous discharge” in step S26. As a result, the auxiliary battery 90 is prevented from being overcharged by instantaneous discharge. Then, in the next cycle, when the magnitude of requested current IBreq exceeds the magnitude of allowable charging current Ilim (YES in step S16), MG regeneration restriction is performed (step S20). Precipitation of metallic lithium in the negative electrode is suppressed.

  As described above, when required current IBreq is a negative value (that is, when charging main battery 10 is required), ECU 100 according to the present embodiment has a required current IBreq of an allowable charge. When the magnitude of the current Ilim is not exceeded (that is, the MG regeneration limit is not performed) and the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Ilim is less than the threshold value (ie, the demand When the current IBreq is close to the allowable charging current Ilim), by controlling the DC / DC converter 91, “instantaneous discharge” for instantaneously discharging from the main battery 10 to the auxiliary battery 90 is performed. By this instantaneous discharge, before the MG regeneration limit is performed, the magnitude (absolute value) of the allowable charging current Ilim is increased to prevent the required current IBreq from exceeding the allowable charging current Ilim. be able to. As a result, it is possible to avoid excessive limitation of regeneration of the MG 42 while suppressing deposition of metallic lithium on the negative electrode of the main battery 10.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 10 Main battery, 20 Monitoring unit, 21,92 Voltage sensor, 22,93 Current sensor, 23 Temperature sensor, 30 PCU, 41,42 MG, 50 Engine, 60 Power split device, 70 Drive shaft, 80 Drive wheel , 90 Auxiliary battery, 91 DC / DC converter, 100 ECU.

Claims (1)

An electric vehicle,
A motor generator mechanically connected to the drive wheels;
A lithium ion battery electrically connected to the motor generator;
An auxiliary battery for storing electric power for operating the auxiliary machine of the electric vehicle;
A converter for performing voltage conversion between the lithium ion battery and the auxiliary battery;
A controller configured to limit the amount of regeneration of the motor generator when the magnitude of the charging current of the lithium ion battery exceeds the magnitude of the allowable charging current, and
The allowable charging current is a maximum value of a charging current capable of suppressing deposition of metallic lithium on the negative electrode of the lithium ion battery, and is a value that is increased when discharged from the lithium ion battery,
The control device, when the magnitude of the charging current does not exceed the magnitude of the allowable charging current, and the difference between the magnitude of the charging current and the magnitude of the allowable charging current is less than a threshold value, An electric vehicle that temporarily discharges the lithium ion battery to the auxiliary battery by controlling the converter.

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