JP6798437B2 - Electric vehicle - Google Patents

Description

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

International Publication No. 2010/005079 (Patent Document 1) describes a hybrid vehicle including a motor generator mechanically connected to a drive wheel, a lithium ion battery electrically connected to the motor generator, and a control device. Is disclosed. In this hybrid vehicle, the amount of regeneration of the motor generator is limited in order to suppress the precipitation of metallic lithium in the negative electrode of the lithium ion battery. Specifically, the control device mounted on the hybrid vehicle allows the maximum value of the charging current capable of suppressing the precipitation of metallic lithium in 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. Then, when the charging current of the lithium ion battery exceeds the allowable charging current, the control device limits the amount of regeneration of the motor generator to reduce the charging current to less than the allowable charging current. As a result, precipitation of metallic lithium on 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 precipitation of metallic lithium while continuing charging during this period, the allowable charging current is It is necessary to reduce the size to a considerably small value, and as a result, there is a concern that 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 to solve the above-mentioned problems, and an object of the present disclosure is to avoid excessive limitation of regeneration of a motor generator while suppressing precipitation of metallic lithium in the negative electrode of a lithium ion battery. Is.

The electric vehicle according to the present disclosure includes a motor generator mechanically connected to a drive wheel, a lithium ion battery electrically connected to the motor generator, and an auxiliary battery for storing electric power for operating an auxiliary machine of the electric vehicle. And a converter that converts voltage between the lithium-ion battery and the auxiliary battery, and 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. It is equipped with a control device configured in. The permissible charging current is the maximum value of the charging current that can suppress the precipitation 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 the threshold value. This temporarily discharges the lithium-ion battery to the auxiliary battery.

According to the above configuration, the magnitude of the charging current does not exceed the magnitude of the allowable charging current (that is, the amount of regeneration of the motor generator is not limited), and the magnitude of the charging current and the magnitude of the allowable charging current If the difference is less than the threshold, the lithium-ion battery is temporarily discharged to the auxiliary battery. By this discharge, before limiting the amount of regeneration of the motor generator, the magnitude of the allowable charging current (the maximum value of the charging current that can suppress the precipitation of metallic lithium) is increased, and the magnitude of the charging current is allowed. It is possible not to exceed the magnitude of the charging current. As a result, it is possible to avoid excessive limitation of regeneration of the motor generator while suppressing precipitation of metallic lithium in the negative electrode of the lithium ion battery.

It is a figure which shows the structure of the vehicle schematicly. It is a figure which shows an example of the change of required current IBreq and permissible charge current Ilim when instantaneous discharge is performed. It is a figure which shows an example of the change of the required current IBreq and the permissible charge current Ilim when instantaneous discharge and MG regeneration limitation are performed. It is a flowchart which shows an example of the processing procedure of the ECU.

Hereinafter, embodiments 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.

[Vehicle configuration]
FIG. 1 is a diagram schematically showing a configuration of a vehicle 1 according to the present embodiment. Hereinafter, the case where the vehicle 1 is a hybrid vehicle will be described, but the vehicle 1 according to the present embodiment is not limited to the hybrid vehicle, and can be applied to all electric vehicles (electric vehicles, etc.) 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: Power Control Unit) 30, motor generators (MG: Motor Generator) 41 and 42, an engine 50, a power dividing device 60, and the like. It includes a drive shaft 70, drive wheels 80, an auxiliary battery 90, a DC / DC converter 91, and an electronic control unit (ECU) 100.

The engine 50 generates a driving force for rotating the crankshaft by the 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 by using a part of the output of the engine 50 transmitted through the power dividing 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.

The MG 42 is driven by at least one of the power supplied by the main battery 10 and the power generated by the MG 41. The driving force of the MG 42 is transmitted to the drive shaft 70. Further, when the vehicle 1 is decelerated, the MG 42 is driven by the rotational force of the drive wheels 80 to generate regenerative power generation. The generated power of the MGs 41 and 42 is supplied to the main battery 10 through the PCU30.

The main battery 10 stores electric power for driving the MGs 41 and 42. The 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. The voltage sensor 21 detects the voltage between the terminals of the main battery 10 (hereinafter, also referred to as “voltage VB”). The current sensor 22 detects the charge / discharge current of the main battery 10 (hereinafter, also referred to as “current IB”). 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 the 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.

The PCU 30 is configured to perform bidirectional power conversion between the main battery 10 and the MGs 41 and 42 in accordance with a switching command from the ECU 100. The PCU 30 is configured so that the states of the MGs 41 and 42 can be controlled separately. For example, the MG41 can be put into a power generation state and the MG42 can be put into a power running state.

The auxiliary battery 90 stores electric power for operating the auxiliary equipment mounted on the vehicle 1, and supplies electric power to each auxiliary equipment as needed. The auxiliary machine includes all electric devices such as the ECU 100, headlights, and audio that operate at a low voltage (for example, about 12 V). The output voltage of the 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 the main battery 10 (for example, about 200V).

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

The DC / DC converter 91 is provided between the auxiliary battery 90 and the main battery 10. The DC / DC converter 91 is configured so that the output voltage of the main battery 10 can be stepped down and supplied to the auxiliary battery 90.

The ECU 100 includes a CPU (Central Processing Unit), an input / output interface, and a memory (none of which are shown). The ECU 100 controls the engine 50, the PCU 30, the DC / DC converter 91, and the like based on the signals from each sensor and the information stored in the memory.

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

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. Shall mean. For example, when the required current IBreq is a negative value, the smaller the value including the sign of the required current IBreq, that is, the larger the magnitude (absolute value) of the required current IBreq, the more charging required for the main battery 10. It means that the current is large.

[Suppression of precipitation of metallic lithium in the negative electrode of the main battery]
As described above, in the present embodiment, a lithium ion secondary battery is adopted as the main battery 10. In a lithium ion secondary battery, it is known that when charging is continued, 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 precipitates 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 deteriorates.

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

First, the ECU 100 calculates the allowable charge current Illim of the main battery 10 based on the charge / discharge history of the main battery 10. The permissible charging current Illim is a charging current set as a maximum current capable of suppressing the precipitation of metallic lithium on the negative electrode of the main battery 10.

Then, when the required current IBreq is a negative value (that is, when the main battery 10 is required to be charged), the ECU 100 determines that the magnitude of the required current IBreq exceeds the magnitude of the allowable charging current Illim. The size of the required current IBreq is limited to less than the size of the allowable charging current Illim. As a result, the amount of regeneration of MG42 is limited, and the actual magnitude of the current IB (magnitude of the charging current) becomes less than the magnitude of the allowable charging current Illim. As a result, precipitation of metallic lithium at the negative electrode of the main battery 10 is suppressed. Hereinafter, the above-mentioned series of treatments performed to suppress the precipitation of metallic lithium will also be referred to as "MG regeneration restriction".

The allowable charging current Illim is calculated based on the charge / discharge history of the main battery 10 as described above. Specifically, when the main battery 10 is charged, the ECU 100 reduces the size of the allowable charging current Illim as the amount of power charged to the main battery 10 (the value obtained by integrating the charging power with the charging duration) increases. Make it a value. Further, when the ECU 100 is discharged from the main battery 10, the larger the amount of power discharged to the main battery 10 (the value obtained by integrating the discharge power with the discharge duration), the larger the value of the allowable charging current Illim. ..

[Instantaneous discharge]
As described above, in the ECU 100 according to the present embodiment, when the required current IBreq is a negative value and the magnitude of the required current IBreq exceeds the magnitude of the allowable charging current Illim, the required current IBreq is large. By performing "MG regeneration limitation" that limits the current to less than the allowable charge current Illim, precipitation of metallic lithium in the negative electrode of the main battery 10 is suppressed.

However, as described above, the magnitude of the allowable charging current Illim becomes smaller as the amount of electric power charged to the main battery 10 increases. Therefore, for example, when the vehicle 1 travels on a long downhill, a large charging electric power is generated. Since the magnitude of the permissible charge current Illim continues to decrease toward 0 for a long period of time, the magnitude of the permissible charge current Illim becomes a very small value. As a result, the regeneration of MG 42 is too limited, which may cause a problem that the regenerative energy cannot be sufficiently recovered.

Therefore, in the ECU 100 according to the present embodiment, when the required current IBreq is a negative value (that is, when the main battery 10 is required to be charged), the magnitude of the required current IBreq is the allowable charging current Illim. When the magnitude is not exceeded (that is, the MG regeneration limit is not applied) and the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Illim is less than the threshold value (that is, the required current IBreq is By controlling the DC / DC converter 91 (when the allowable charging current is close to Illim), "instantaneous discharge" is performed in which the main battery 10 is instantaneously discharged to the auxiliary battery 90.

Specifically, the ECU 100 performs instantaneous discharge by setting the 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, the 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 the required current IBreq and the allowable charging current Illim when instantaneous discharge is performed by the ECU 100. In FIG. 2, the horizontal axis represents time, the upper vertical axis represents the current value, and the lower vertical axis represents the SOC of the auxiliary battery 90 (hereinafter, also referred to as “auxiliary SOC”). As described above, when the current has a positive value, it means "discharge", and when the current has a negative value, it means "charge".

In the example shown in FIG. 2, immediately before the time t1, the required current IBreq continues to be a negative value, and the main battery 10 is continuously charged. As a result, the magnitude of the allowable charging current Illim continues to decrease toward 0, and the allowable charging current Illim approaches the required current IBreq.

Then, at time t1, when the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Illim becomes less than the threshold value, the ECU 100 sets the required current IBreq to a large positive value for a short period of time. Perform "instantaneous discharge". By this instantaneous discharge, the magnitude (absolute value) of the allowable charging current Ilim can be increased before the MG regeneration limitation is performed. Therefore, even if the required current IBreq is returned to a negative value based on the vehicle speed and the accelerator operating amount after the instantaneous discharge, it is possible to prevent the required current IBreq from exceeding the allowable charging current Illim. As a result, it is possible to avoid excessive restriction on the regeneration of MG 42 while suppressing the precipitation of metallic lithium on the negative electrode of the main battery 10.

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

After that, charging continues again, and when the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Illim 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 Illim is increased. This makes it possible to avoid excessive restriction on the regeneration of MG42 while suppressing the precipitation of metallic lithium on the negative electrode.

By performing the instantaneous discharge at the time t2, the auxiliary machine SOC increases from the predetermined value S1 to the predetermined value S2. Since the predetermined value S2 is a value less than the upper limit value Smax of the auxiliary machine SOC, overcharging of the auxiliary machine battery 90 does not occur.

FIG. 3 is a diagram showing an example of changes in the required current IBreq and the allowable charging current Illim when the ECU 100 performs instantaneous discharge and MG regeneration limitation. In FIG. 3, as in FIG. 2, the horizontal axis shows the time, the upper part of the vertical axis shows the current value, and the lower part of the vertical axis shows the auxiliary machine SOC.

In the example shown in FIG. 3, at time t11, the ECU 100 performs "instantaneous discharge" when the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Illim becomes less than the threshold value. As a result, the magnitude (absolute value) of the allowable charging current Illim is increased. This prevents the magnitude of the required current IBreq from exceeding the magnitude of the allowable charging current Illim.

By performing the instantaneous discharge at the 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 Illim is again below the threshold value, but the auxiliary SOC increases 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, there is a concern that the auxiliary battery 90 will be in an overcharged state.

Therefore, in the ECU 100, even if the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Illim becomes less than the threshold value at time t12, the auxiliary machine SOC exceeds the upper limit value Smax (exceeds the reference value Sth). Since it is a value), instantaneous discharge is not performed. As a result, when the magnitude of the allowable charging current Illim is further reduced and the magnitude of the required current IBreq exceeds the magnitude of the allowable charging current Illim, the ECU 100 determines the magnitude of the required current IBreq to be the allowable charging current Illim. "MG regeneration restriction" is performed to limit the size to less than the size of. Therefore, although the regenerative amount of the MG 42 is limited, it is possible to suppress the precipitation of metallic lithium in the negative electrode of the main battery 10 while suppressing the auxiliary battery 90 from being overcharged.

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

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

Next, the ECU 100 calculates the allowable charging current Illim based on the charge / discharge history of the main battery 10 (step S12). Specifically, as described above, when the main battery 10 is charged, the ECU 100 determines that the larger the amount of power charged to the main battery 10 (the value obtained by integrating the charging power with the charging duration), the more the allowable charging current Illim. Set the size of to a small value. Further, when the ECU 100 is discharged from the main battery 10, the larger the amount of power discharged to the main battery 10 (the value obtained by integrating the discharge power with the discharge duration), the larger the value of the allowable charging current Illim. ..

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

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

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

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

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

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

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

On the other hand, when the auxiliary machine SOC exceeds the reference value Sth (YES in step S24), the ECU 100 shifts the process to the return without performing the “instantaneous discharge” in step S26. As a result, it is possible to prevent the auxiliary battery 90 from being overcharged due to instantaneous discharge. Then, in the next cycle, when the magnitude of the required current IBreq exceeds the magnitude of the allowable charging current Lilim (YES in step S16), the MG regeneration limitation is performed (step S20), so that the main battery 10 Precipitation of metallic lithium on the negative electrode is suppressed.

As described above, in the ECU 100 according to the present embodiment, when the required current IBreq is a negative value (that is, when the main battery 10 is required to be charged), the magnitude of the required current IBreq is the allowable charging. When the magnitude of the current Illim is not exceeded (that is, MG regeneration limitation is not performed), and the difference between the magnitude of the required current IBreq and the magnitude of the allowable charging current Illim is less than the threshold value (that is, the requirement). When the current IBreq is close to the permissible charging current Illim), the DC / DC converter 91 is controlled to perform "instantaneous discharge" in which the main battery 10 is instantaneously discharged to the auxiliary battery 90. By this instantaneous discharge, the magnitude (absolute value) of the allowable charging current Illim is increased before the MG regeneration limitation is performed to prevent the magnitude of the required current IBreq from exceeding the magnitude of the allowable charging current Illim. be able to. As a result, it is possible to avoid excessive restriction on the regeneration of MG 42 while suppressing the precipitation of metallic lithium on the negative electrode of the main battery 10.

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

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 splitting device, 70 drive shaft, 80 drive wheels , 90 auxiliary battery, 91 DC / DC converter, 100 ECU.

Claims (1)

It ’s an electric vehicle,
A motor generator that is mechanically connected to the drive wheels,
A lithium-ion battery that is electrically connected to the motor generator
An auxiliary battery that stores electric power to operate the auxiliary equipment of the electric vehicle, and
A converter that performs voltage conversion between the lithium-ion battery and the auxiliary battery,
A control device 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 is provided.
The permissible charging current is the maximum value of the charging current capable of suppressing the precipitation 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.
In 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 the threshold value. An electric vehicle that temporarily discharges the lithium ion battery to the auxiliary battery by controlling the conversion device.

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