JP6790551B2 - Power system for electric vehicles - Google Patents

Description

This specification discloses a power supply system for an electric vehicle. The term "electric vehicle" as used herein includes a hybrid vehicle having both a traction motor and an engine.

Patent Document 1 discloses a power supply system including a main battery, a converter, a sub-battery, and a plurality of auxiliary machines. The converter converts the DC power of the main battery into a lower voltage DC power. The sub-battery is charged by the converted DC power. Auxiliary equipment is a general term for equipment (low-voltage equipment) that operates on the output power of the sub-battery (that is, DC power after conversion by the converter). Auxiliary equipment includes, for example, room lamps, navigation systems, car audio and the like.

In the power supply system of Patent Document 1, the converter can perform normal operation and power saving operation. In the power saving operation, the voltage of the converted DC power is lower than that in the normal operation. As a result, the auxiliary equipment operates at a low voltage, and power consumption is suppressed.

Japanese Unexamined Patent Publication No. 2014-166028

The power supply system of an electric vehicle has a power control unit (so-called PCU) for operating a traveling motor. The power control unit converts the DC power of the main battery into AC power and supplies it to the traveling motor. In this type of power control unit, an internal element (for example, a switching element) generates heat. Therefore, the power supply system has a cooling structure for cooling the power control unit by circulating the refrigerant. The pump for circulating the refrigerant is operated by the output power of the sub-battery. That is, the pump is a kind of auxiliary machine. Generally, the control unit of a pump adjusts the output of a pump by controlling the amount of electricity supplied to the pump. The amount of energization to the pump is adjusted by repeating energization and disconnection of the output power of the sub-battery at a constant rate periodically. In the present specification, the ratio of energization and interruption of electric power supplied to the pump is referred to as a duty ratio. By adjusting the duty ratio appropriately, the pump can be operated with high efficiency.

When the converter can perform normal operation and power saving operation as in Patent Document 1, the voltage of the converted DC power (that is, the output voltage of the sub-battery) becomes low in the power saving operation. Therefore, the voltage applied to the pump during the power saving operation becomes low. Therefore, it is necessary to increase the due diligence ratio to compensate for the low voltage so that sufficient cooling performance can be obtained during power saving operation. On the other hand, when the duty ratio is increased, the electric power supplied to the pump during normal operation (when the output voltage of the sub-battery is high) becomes larger than necessary, and the loss generated by the pump becomes large. Therefore, the present specification provides a technique capable of obtaining sufficient cooling performance and operating the pump with high efficiency in both normal operation and power saving operation.

It is a power supply system for an electric vehicle, and has a main battery, a power control unit, a traveling motor, a converter, a sub-battery, a plurality of auxiliary machines, and a pump control unit. The power control unit converts the DC power of the main battery into AC power. The traveling motor is operated by the AC power. The converter converts the DC power of the main battery into a lower voltage DC power. The sub-battery is charged by the converted DC power. The plurality of auxiliary machines are operated by the DC power after conversion. The plurality of auxiliary machines include a pump that circulates a refrigerant that cools the power control unit. The pump control unit controls the pump so that the period in which the converted DC power is supplied to the pump and the period in which the DC power is not supplied are alternately repeated. The converter executes a normal operation of controlling the voltage of the DC power after conversion to a first voltage and a power saving operation of controlling the voltage of the DC power after conversion to a second voltage lower than the first voltage. It is possible. During the power saving operation, the pump control unit increases the ratio of the period during which the converted DC power is supplied to the pump as compared with the normal operation.

In this power supply system, the pump control unit controls the pump so that the period in which the converted DC power is supplied to the pump and the period in which the converted DC power is not supplied are alternately repeated. As described above, the ratio of the period during which the converted DC power is supplied to the pump is called the duty ratio. The pump control unit has a higher duty ratio during power saving operation than during normal operation. That is, during the power saving operation, the voltage applied to the pump is lower than during the normal operation, while the duty ratio is higher than during the normal operation. By changing the duty ratio between the normal operation and the power saving operation in this way, the difference between the power supplied to the pump during the normal operation and the power supplied to the pump during the power saving operation becomes small. Therefore, it is possible to operate the pump under conditions in which sufficient cooling performance can be obtained and operation can be performed with high efficiency in both normal operation and power saving operation.

Schematic of the power supply system. The graph which shows the voltage V2 at the time of a normal operation. The graph which shows the voltage V2 at the time of power saving operation. A flowchart showing the processing performed by the power supply system. Graph of each value when switching from normal operation to power saving operation.

The power supply system 8 of the embodiment shown in FIG. 1 is mounted on a hybrid vehicle. The hybrid vehicle includes an engine 61, a motor 1 (MG1), and a motor 2 (MG2), and can travel by the power of these. When a motor is used, the hybrid vehicle drives the motor 2 by the electric power supplied from the main battery 4, and rotates the drive wheels (not shown) by the power of the motor 2. When traveling using the engine 61, the hybrid vehicle uses the motor 1 as a starter motor to start the engine 61. Then, in the hybrid vehicle, a part of the power generated by the engine 61 is transmitted to the drive wheels by the power distribution mechanism 62, while the remaining power is transmitted to the motor 1 to generate electricity in the motor 1. The electric power generated by the motor 1 can be supplied to the motor 2 and used for rotation of the drive wheels, or can be charged to the main battery 4.

When the running hybrid vehicle decelerates, the motor 1 or the motor 2 can regenerate power generation, and the generated power can be used to charge the main battery 4. In this way, the motor 1 and the motor 2 also function as generators. In that sense, the motor 1 and the motor 2 can be referred to as a "motor generator". “MG1” in FIG. 1 represents a motor 1 (motor generator 1), and “MG2” represents a motor 2 (motor generator 2).

The power supply system 8 includes a main battery 4, a sub-battery 22, a power control unit (PCU) 12, and a DC-DC converter (DDC) 30. Hereinafter, the power control unit 12 is referred to as a PCU 12, and the DC-DC converter 30 is referred to as a DDC 30.

The main battery 4 is a secondary battery (rechargeable battery) such as a nickel hydrogen battery or a lithium ion battery. In this embodiment, the voltage of the main battery 4 is about 300 V (volt). The main battery 4 is connected to the PCU 12 via a pair of main power lines 10.

The PCU 12 is connected between the main battery 4 and the MG1 and MG2. The PCU 12 converts the DC power (DC power supplied from the main battery 4) between the pair of main power lines 10 into three-phase AC power, and supplies the three-phase AC power to MG1 and MG2. Further, the PCU 12 can also convert the three-phase AC power supplied from MG1 and MG2 into DC power and supply the DC power between the pair of main power lines 10. The PCU 12 includes a converter (CNV) 16 and an inverter (INV) 17.

The converter 16 boosts the voltage of DC power between the pair of main power lines 10, and supplies the boosted voltage to the inverter 17. The inverter 17 converts the DC power supplied from the converter 16 into three-phase AC power, and supplies the converted three-phase AC power to MG1 and MG2. Further, the inverter 17 can also convert the three-phase AC power generated by MG1 and MG2 into DC power and supply the DC power to the converter 16. The converter 16 can also step down the voltage of the DC power supplied from the inverter 17 and apply the stepped down voltage between the pair of main power lines 10.

Further, the PCU 12 has a cooling water channel 46 for circulating cooling water. When the pump 40 described later operates, the cooling water circulates in the cooling water channel 46. When the PCU 12 operates, the converter 16 and the inverter 17 (more specifically, switching elements inside them) generate heat. The cooling water in the cooling water channel 46 cools the converter 16 and the inverter 17.

An SMR 20 is provided on the main power line 10. The SMR 20 switches between the connected state and the disconnected state between the main battery 4 and the PCU 12. When the SMR 20 is turned on, the main battery 4 is electrically connected to the PCU 12. When the SMR 20 is turned off, the main battery 4 is cut off from the PCU 12. The SMR 20 is off while the vehicle main switch (ignition switch) (not shown) is off. When the vehicle main switch is switched from off to on, the SMR 20 is turned on and the main battery 4 and the PCU 12 are connected. When the main battery 4 and the PCU 12 are connected, the MG1 and the MG2 can be supplied with electric power, that is, they can run.

The sub-battery 22 is typically a secondary battery (rechargeable battery) composed of a lead-acid battery. The output voltage of the sub-battery 22 is lower than the output voltage of the main battery 4. In this embodiment, the voltage of the sub-battery 22 is about 13.6V. The sub-battery 22 is connected between the pair of sub-power lines 24. The conductive body of the vehicle may also serve as the negative electrode wire of the sub power line 24.

The DDC 30 is connected between the positive electrode and the negative electrode of the main battery 4 (that is, between the main power lines 10 on the main battery 4 side of the SMR 20). The DDC 30 is also connected to the pair of sub power lines 24. The DDC 30 can perform a step-down operation in which the voltage between the positive electrode and the negative electrode of the main battery 4 is stepped down and the step-down voltage is applied between the pair of sub power lines 24. When the DDC 30 performs a step-down operation, the sub-battery 22 can be charged with the power of the main battery 4. The DDC 30 controls the voltage V1 (voltage after step-down) applied between the pair of sub power lines 24 to a predetermined voltage. The output voltage of the sub-battery 22 becomes equal to the voltage V1. The DDC 30 can perform normal operation and power saving operation based on a command from a control device (not shown). In normal operation, the DDC 30 controls the voltage V1 to a high voltage V1H (13.6V in this embodiment). In the power saving operation, the DDC 30 controls the voltage V1 to a low voltage V1L (in this embodiment, a voltage in the range of 12.5 to 13.5 V). That is, in the power saving operation, the output voltage V1 of the sub-battery 22 is lower than in the normal operation. Power saving operation includes system error (communication error, etc.), battery temperature abnormality (high or low temperature), low battery capacity, vehicle stop (parking or neutral), increased electrical load (tail lamp on, blower Hi, etc.) Is executed in the case of.

The sub-battery 22 is connected to the auxiliary machine (AUX) 26 via a pair of sub-power lines 24. Further, the sub-battery 22 is connected to the pump 40 via a pair of sub-power lines 24, a pump control unit 42, and a pair of pump wirings 44.

Auxiliary equipment 26 is a general term for equipment (low-voltage equipment) that operates at the output voltage V1 of the sub-battery 22. In FIG. 2, the auxiliary machine 26 is represented by one rectangle, and the auxiliary machine 26 includes a plurality of low-voltage devices such as a room lamp, a navigation system, and a car audio system. When the DDC 30 is performing the power saving operation, the voltage V1 supplied to the auxiliary machine 26 becomes low, and the power consumption in the auxiliary machine 26 is suppressed.

The pump 40 is interposed in the cooling water channel 46 and circulates the cooling water in the cooling water channel 46. The pump 40 is connected to the pump control unit 42 via the pump wiring 44. A pair of sub power lines 24 are connected to the pump control unit 42. The pump control unit 42 has a state in which the sub power line 24 is electrically connected to the pump wiring 44 (hereinafter referred to as an on state) and a state in which the sub power line 24 is electrically disconnected from the pump wiring 44 (hereinafter referred to as an on state). It switches to the off state). When the pump control unit 42 is in the ON state, the output voltage V1 of the sub-battery 22 is applied to the pump 40. When the pump control unit 42 is in the off state, the output voltage V1 of the sub-battery 22 is not applied to the pump 40. The pump 40 is operated by electric power from the sub-battery 22. That is, the pump 40 is a kind of auxiliary machine. The pump control unit 42 operates so that an on-state period (hereinafter, referred to as an on-period) and an off-state period (hereinafter, referred to as an off-period) are alternately repeated. Further, in the following, the ratio of the length of the on period is referred to as a duty ratio. When the length of the on period is T1 and the length of the off period is T2, the duty ratio D is represented by D = T1 / (T1 + T2).

The power supplied to the pump 40 changes depending on the output voltage V1 and the duty ratio D of the sub-battery 22. The larger the electric power supplied to the pump 40, the faster the circulation speed of the cooling water. The faster the circulation speed of the cooling water, the higher the cooling performance. However, when the circulation speed of the cooling water becomes higher than a constant speed, the cooling performance is hardly improved any more. If the circulation speed of the cooling water is too fast, the cooling performance will not be improved, but the power consumption of the pump 40 will be high. Therefore, it is preferable that the electric power supplied to the pump 40 is set so that the power consumption of the pump 40 does not become excessively high while sufficient cooling performance can be obtained. In the power supply system 8 of the present embodiment, the pump control unit 42 changes the duty ratio D to efficiently operate the pump 40.

FIG. 2 shows the voltage V2 applied to the pump 40 during normal operation. Further, FIG. 3 shows a voltage V2 applied to the pump 40 during the power saving operation. In FIGS. 2 and 3, the voltage V2 in the on period T1 is shown to coincide with the voltage V1, but the voltage V2 applied to the pump 40 is higher than the voltage V1 due to the voltage drop due to the wiring resistance or the like. May be slightly lower.

During normal operation, the pump control unit 42 controls the voltage V2 (voltage of the pump wiring 44) applied to the pump 40 as shown in FIG. As shown in FIG. 2, the pump control unit 42 operates so that the on period T1 and the off period T2 are alternately repeated. During the on period T1, a voltage having substantially the same magnitude as the output voltage V1 of the sub-battery 22 is applied to the pump 40. In normal operation, the output voltage V1 is a high voltage V1H. During the off period T2, the voltage applied to the pump 40 is substantially zero. The duty ratio D (= T1 / (T1 + T2)) during normal operation is set to a value at which the pump 40 operates with high efficiency and sufficient cooling performance can be obtained when the output voltage V1 is the high voltage V1H. ..

During the power saving operation, the pump control unit 42 controls the voltage V2 as shown in FIG. As shown in FIG. 3, the output voltage V1 is a low voltage V1L during the power saving operation. Further, during the power saving operation, the pump control unit 42 lengthens the on period T1 and shortens the off period T2 as compared with the normal operation. That is, the pump control unit 42 has a higher duty ratio D during the power saving operation than during the normal operation. As described above, during the power saving operation, the voltage V2 in the on period T1 becomes the low voltage V1L, while the duty ratio D becomes high. Therefore, the power supplied to the pump 40 during the power saving operation is substantially equal to the power supplied to the pump 40 during the normal operation. That is, the duty ratio D during the power saving operation is set to a value at which the pump 40 operates with high efficiency and sufficient cooling performance can be obtained when the output voltage V1 is the low voltage V1L.

FIG. 4 is a flowchart showing the operation of the pump control unit 42. In step S2, it is determined whether or not the power saving operation is being executed. When the power saving operation is not being executed, the pump control unit 42 operates at a low duty ratio in step S4. That is, the voltage V2 having the waveform shown in FIG. 2 is applied to the pump 40. Further, when the power saving operation is being executed, the pump control unit 42 operates at a high duty ratio in step S6. That is, the voltage V2 having the waveform shown in FIG. 3 is applied to the pump 40. By repeatedly executing the flowchart of FIG. 4, the duty ratio is appropriately switched. As a result, the pump 40 operates with high efficiency within a range in which sufficient cooling performance can be obtained.

FIG. 5 schematically shows a change in each value when switching from the normal operation to the power saving operation. The symbol V1 indicates the voltage, the symbol D indicates the duty ratio, the symbol n indicates the rotation speed n of the pump 40, the symbol Q indicates the flow rate of the cooling water, and the symbol t indicates the temperature of the cooling water. FIG. 5 is a schematic graph in which different physical quantities are mixed in one graph in order to make it easier to understand changes in each physical quantity.

When switching from the normal operation to the power saving operation, the output voltage V1 of the sub-battery 22 is switched from the high voltage V1H to the low voltage V1L. At the same time, the duty ratio D switches from the low value DL to the high value DH. In this way, even if the output voltage V1 of the sub-battery 22 decreases, the duty ratio D increases substantially at the same time, so that the power supplied to the pump 40 does not change much. Therefore, when switching from the normal operation to the power saving operation, the rotation speed n of the pump 40 hardly changes, and therefore the flow rate Q of the cooling water hardly changes. Therefore, the temperature t of the cooling water (more specifically, the temperature of the cooling water inside the PCU 12) does not change much when switching from the normal operation to the power saving operation. In this way, the cooling performance hardly changes when switching from the normal operation to the power saving operation.

As described above, in the power supply system 8 of the present embodiment, the duty ratio D is higher during the power saving operation than during the normal operation. As a result, the pump 40 can be operated with high efficiency and the PCU 12 can be sufficiently cooled in both the normal operation and the power saving operation.

The pump control unit 42 adjusts the output of the pump 40 according to the temperature of the PCU 12. The output of the pump 40 can be adjusted by the duty ratio D described above. The pump control unit 42 increases the duty ratio D as the temperature of the PCU 12 increases. The pump control unit 42 raises the duty ratio D when the output target of the pump 40 is maximum during the power saving operation rather than during the normal operation. In other words, the pump control unit 42 increases the ratio of the period during which the DC power is supplied to the pump 40 when the output target of the pump is maximum during the power saving operation rather than during the normal operation.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above. The technical elements described herein or in the drawings exhibit their technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques illustrated in the present specification or drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

1, 2: Motor 4: Main battery 8: Power supply system 10: Main power line 12: Power control unit 16: Converter 17: Inverter 22: Sub battery 24: Sub power line 26: Auxiliary machine 30: DC-DC converter 40: Pump 42 : Pump control unit 44: Pump wiring 46: Cooling water channel 61: Engine 62: Power distribution mechanism

Claims (1)

A power supply system for electric vehicles
With the main battery
A power control unit that converts the DC power of the main battery into AC power,
The traveling motor operated by the AC power and
A converter that converts the DC power of the main battery into a lower voltage DC power,
The sub-battery charged by the converted DC power and
A plurality of auxiliary machines that are operated by the converted DC power, and include a plurality of auxiliary machines that include a pump that circulates a refrigerant that cools the power control unit.
A pump control unit that controls the pump so that the period in which the converted DC power is supplied to the pump and the period in which the DC power is not supplied are alternately repeated.
Have,
The converter executes a normal operation of controlling the voltage of the DC power after conversion to a first voltage and a power saving operation of controlling the voltage of the DC power after conversion to a second voltage lower than the first voltage. It is possible and
The pump control unit determines whether the normal operation is being executed or the power saving operation is being executed, and when it is determined that the power saving operation is being executed, it is more than when it is determined that the normal operation is being executed. Increase the ratio of the period during which the converted DC power is supplied to the pump.
Power system.

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