Power control device

The present power control device includes an inverter, a step-up/down converter, a first capacitor, a second capacitor, and a control device. The step-up/down converter includes an upper arm and a lower arm that are switching elements, and a reactor that has a first end and a second end, the first end being connected to the first capacitor, and the second end being connected between the upper arm and the lower arm. The control device is configured to fix the lower arm in an off state and control the upper arm such that the upper arm switches at a predetermined duty ratio.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 U.S.C. § 119 to Japanese Application No. 2019-181832 filed Oct. 2, 2019, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a power control device.

Description of Related Art

In PCT International Publication No. WO. 2011/089723, a power control device that is mounted in a vehicle, converts DC power from a battery into AC power to supply the AC power to a motor generator, and converts AC power generated by the motor generator into DC power to supply the DC power to the battery is disclosed.

The power control device described above includes a step-up/down converter, a first capacitor, a second capacitor, and a motor electronic control unit (ECU). The step-up/down converter includes two switching elements serving as an upper arm and a lower arm and a reactor, and is provided between a battery and an inverter.

The first capacitor is a smoothing capacitor provided between the battery and the step-up/down converter (on a primary side). The second capacitor is a smoothing capacitor that is provided between the step-up/down converter and the inverter (on a secondary side). The motor ECU controls the upper arm and the lower arm.

Incidentally, when a vehicle stops due to a collision of the vehicle, it is necessary to disconnect a power control device from the battery and promptly consume the residual charge of a second capacitor. Therefore, the motor ECU described above performs control for alternately turning on an upper arm and a lower arm of the step-up/down converter and executes discharge control for discharging the residual charge of the second capacitor.

SUMMARY OF THE INVENTION

However, the residual charge of the second capacitor may flow into the first capacitor and a voltage on the primary side may become an overvoltage due to the discharge control in the power control device described above. As a result, the operation of the step-up/down converter may stop from a viewpoint of device protection in the power control device described above. Therefore, the present inventor has thought about controlling each of the first capacitor and the second capacitor at a predetermined duty ratio such that the voltage on the primary side is maintained at a target value to prevent the voltage on the primary side from becoming an overvoltage. However, in this case, since the power stepped-up by the step-up/down converter may be supplied from the primary side to the secondary side, there is a possibility that a voltage on the secondary side will become an overvoltage. As a result, the residual charge of the second capacitor cannot be discharged.

The present invention has been made in view of such circumstances, and an object thereof is to provide a power control device capable of suppressing voltages on the primary side and the secondary side from becoming an overvoltage, and discharging residual charge of the second capacitor.

(1) One aspect of the present invention is a power control device of a vehicle that has an electric motor, a first DC power supply, and a second DC power supply includes: an inverter configured to drive the electric motor; a step-up/down converter configured to perform a step-up operation of stepping up power from the first DC power supply and supplying the power to the inverter and a step-down operation of stepping down power from the inverter and supplying the power to the first DC power supply; a first capacitor that is provided between the first DC power supply and the step-up/down converter; a second capacitor that is provided between the step-up/down converter and the inverter; and a control device configured to execute discharge control for discharging residual charge of the second capacitor when power is supplied from the second DC power supply and a collision of the vehicle has occurred, wherein the step-up/down converter includes: an upper arm and a lower arm that are switching elements; and a reactor that has a first end and a second end, the first end being connected to the first capacitor, and the second end being connected between the upper arm and the lower arm, and wherein the control device is configured to fix the lower arm in an off state and control the upper arm such that the upper arm switches at a predetermined duty ratio, as the discharge control.

(2) In the power control device of (1) described above, an auxiliary device of the vehicle may be connected between the first DC power supply and the step-up/down converter.

(3) The power control device of (1) or (2) described above may further include a backup power supply configured to supply power stored in the first capacitor to the control device when a power supply from the second DC power supply to the control device is stopped.

(4) The power control device of any one of (1) to (3) described above may be configured as follows to further include a voltage sensor configured to measure an inter-terminal voltage of the first capacitor, in which the control device is configured to calculate a predetermined duty ratio on the basis of the inter-terminal voltage measured by the voltage sensor and a first target value that is a target value of the inter-terminal voltage.

(5) The power control device of (4) described above may be configured as follows to further include a current sensor configured to measure a current flowing through the reactor, in which the control device is configured to calculate a second target value that is a target value of the current on the basis of a difference between the inter-terminal voltage measured by the voltage sensor and the first target value, and calculate the predetermined duty ratio such that the current measured by the current sensor becomes the second target value.

As described above, according to each aspect of the present invention described above, it is possible to provide a power control device capable of suppressing voltages on a primary side and a secondary side from becoming over-voltages, and discharging the residual charge of the second capacitor.

DETAILED DESCRIPTION OF THE INVENTION

A power control device according to an embodiment of the present invention will be described using the drawings in the following description.FIG. 1is a block diagram which shows a configuration of a vehicle A that includes a power control device according to the embodiment. Note that the vehicle A shown inFIG. 1is, for example, a hybrid vehicle or an electric vehicle.

As shown inFIG. 1, the vehicle A includes a battery BT, a motor generator MG, and a power control device1.

The battery BT is, for example, a rechargeable secondary battery such as a lithium ion battery.

The motor generator MG is an AC rotating electric machine. For example, the motor generator MG is used as a generator driven by an engine (not shown) of the vehicle A and is also used as an electric motor for starting the engine. The motor generator mainly operates as an electric motor and drives wheels (not shown) of the vehicle A. On the other hand, when the vehicle A is being braked or the acceleration on a downward slope is being reduced, the motor generator MG operates as a generator and regenerates generated power (hereinafter, referred to as “regenerative power”) to the power control device1.

The power control device1converts DC power from the battery BT into AC power and supplies the AC power to a motor generator MG. In addition, the power control device1also converts regenerative power, which is AC power generated by the motor generator MG, into DC power, and supplies it to the battery BT.

When a collision of the vehicle A has occurred, the power control device1executes discharge control for discharging residual charge of a smoothing capacitor (at least residual charge of the second capacitor6) provided in the power control device1.

Hereinafter, a schematic configuration of the power control device1according to the present embodiment will be described.

The power control device1according to the present embodiment includes a contactor2, a first capacitor3, a step-up/down converter4, an auxiliary device5, a second capacitor6, a first voltage sensor7, a second voltage sensor8, an inverter9, a control power supply10, a diode11, a backup power supply12, a current sensor13, and a motor electronic control unit (ECU)15. Note that the motor ECU15is an example of a “control device” of the present invention.

The contactor2connects the battery BT and the step-up/down converter4or releases a connection between the battery BT and the step-up/down converter4under control of the external ECU14.

The first capacitor3is a smoothing capacitor provided on the primary side (a battery BT side) of the step-up/down converter4. That is, the first capacitor3is provided between the battery BT and the step-up/down converter4.

The step-up/down converter4includes a reactor L, switching elements T1and T2connected in series, and diodes D1and D2connected in parallel in a direction opposite to the switching elements T1and T2.

The reactor L has a first end and a second end. The first end of the reactor L is connected to the contactor2and the first capacitor3. The second end of the reactor L is connected between a switching element T1(an upper arm) and a switching element T2(a lower arm). Note that an insulated gate bipolar transistor (IGBT) or a field effective transistor (FET) can be used as the switching elements T1and T2.

The step-up/down converter4performs a step-up operation that steps up power from the battery BT (the first DC power supply) and supplies it to the inverter9or performs a step-down operation that steps down power from the inverter9and supplies it to the battery BT by turning on or off the switching elements T1and T2under control of the motor ECU15.

The auxiliary device5is connected to the primary side of the step-up/down converter4. That is, the auxiliary device5is connected between the contactor2and the first end of the reactor L. When the contactor2is open (in an open state) and the connection between the battery BT and the step-up/down converter4is released, the auxiliary device5operates by using power stored in the first capacitor3as an operation source.

The second capacitor6is a smoothing capacitor provided on the secondary side (the inverter9side) of the step-up/down converter4. That is, the second capacitor6is provided between the step-up/down converter4and the inverter9.

The first voltage sensor7is a sensor that is attached between both terminals of the first capacitor3, and measures a voltage value Vc1between both terminals of the second capacitor6(hereinafter, referred to as an “inter-terminal voltage value Vc1”). The first voltage sensor7outputs the measured inter-terminal voltage value Vc1to the motor ECU15.

The second voltage sensor8is a sensor that is attached between both terminals of the second capacitor6, and measures a voltage value Vc2between both terminals of the second capacitor6(hereinafter, referred to as an “inter-terminal voltage value Vc2”). The second voltage sensor8outputs the measured inter-terminal voltage value Vc2to the motor ECU15.

The inverter9rotationally drives the motor generator MG of the vehicle A. The inverter9converts the DC power supplied from the step-up/down converter4into AC power and supplies the AC power to the motor generator MG. In addition, the inverter9also converts the regenerative power regenerated from the motor generator MG into DC power and supplies the DC power to the step-up/down converter4. Note that the inverter9may be controlled by the motor ECU15.

The control power supply10(a second DC power supply) is a DC power supply that supplies power to the motor ECU15via a power supply line L. Specifically, the control power supply10is a power supply of the motor ECU15and supplies a control voltage, which is an operation source of the motor ECU15, to the motor ECU15. Note that a secondary battery such as a nickel hydrogen battery or a lithium ion battery can be used as the control power supply10. In addition, an electric double layer capacitor can be used as the control power supply10instead of the secondary battery.

The diode11has an anode connected to a positive terminal of the control power supply10and a cathode connected to the motor ECU15. This diode11is a diode for preventing a backflow.

The backup power supply12is a backup power supply of the control power supply10. The backup power supply12generates a backup voltage Va that is a voltage at which the motor ECU15can operate and supplies the backup voltage Va to the motor ECU15using power stored in the first capacitor3. For example, the backup power supply12supplies the power stored in the first capacitor3as an operation power of the motor ECU15. For example, the backup power supply12may include a DCDC converter. Note that the backup power supply12constantly supplies the backup voltage Va to the motor ECU15.

The current sensor13measures a current value IL flowing through a reactor L, and outputs the measured current value IL to the motor ECU15.

The external ECU14performs charge/discharge control of the battery BT and control of the contactor2. Specifically, when an abnormality of the vehicle A (for example, a battery abnormality, a collision of the vehicle A, or the like) has occurred, or when ignition is turned off, the external ECU14controls the contactor2to release the connection between the battery BT and the step-up/down converter4, and outputs a discharge command signal to the motor ECU15. For example, the external ECU14may detect the collision of the vehicle A according to a collision detection signal from a collision detection device (for example, a supplemental restraint system) mounted in the vehicle A.

The motor ECU15controls a rotation of the motor generator MG by controlling driving of the step-up/down converter4and the inverter9. The motor ECU15controls a step-up operation and a step-down operation of the step-up/down converter4by controlling switching of each of the switching elements T1and T2of the step-up/down converter4. In addition, the motor ECU15receives a discharge command signal output from the external ECU14and starts discharge control for rapidly discharging electric charges stored in at least the second capacitor6when the collision of the vehicle A has occurred.

This discharge control is control for causing the step-up/down converter4to operate only in the step-down operation to discharge the electric charges stored in at least the second capacitor6among the first capacitor3and second capacitor6by fixing the switching element T2(the lower arm) to be in an off state and controlling the switching of the switching element T1(the upper arm) at a predetermined duty ratio D.

Note that a power supply of this motor ECU15is the control power supply10and the backup power supply12. The motor ECU15may also be configured by a microprocessor such as a central processing unit (CPU) or a micro-processing unit (MPU), a micro controller such as a memory control unit (MCU), or the like.

In the following description, a functional unit for performing the discharge control of the control unit21according to the present embodiment will be described usingFIG. 2.FIG. 2is a block diagram that shows the functional unit for performing the discharge control of the control unit21according to the present embodiment.

The control unit21includes a duty generation unit30and a drive control unit40.

The duty generation unit30includes a first deviation device31, a first PI controller32, a second deviation device33, a second PI controller34, and a calculator35.

The first deviation device31acquires the inter-terminal voltage value Vc1measured by the first voltage sensor7from the first voltage sensor7. In addition, the first deviation device31reads a target voltage value VM(a first target value) stored in a storage unit (for example, a non-volatile memory) of the motor ECU15. This target voltage value VMis a target value of the inter-terminal voltage of the first capacitor3. Then, the first deviation device31calculates a difference ΔV between the inter-terminal voltage value Vc1acquired from the first voltage sensor7and the read first target value VM1. Then, the first deviation device31outputs the calculated difference ΔV to the first PI controller32.

The first PI controller32calculates a target current value IM(a second target value) that is a target value of a current IL flowing through the reactor L by the first deviation device31applying proportional-integral (PI) control to the calculated difference ΔV. Then, the first PI controller32outputs the calculated target current value IMto the second deviation device33.

The second deviation device33acquires the current IL measured by the current sensor13from the current sensor13. In addition, the second deviation device33acquires the target current value IMfrom the first PI controller32. Then, the second deviation device33calculates a difference ΔI between the current IL measured by the current sensor13and the target current value IM. Then, the second deviation device33outputs the calculated difference ΔI to the second PI controller34.

The second PI controller34calculates a command value such that the current IL flowing through the reactor L becomes the target current value IMby applying PI control to the difference ΔI calculated by the second deviation device33. Then, the second PI controller34outputs the calculated command value to the calculator35.

The calculator35calculates a duty ratio D according to a command value from the second PI controller34, and generates a pulse width modulation (PWM) signal of this duty ratio D. That is, the calculator35calculates the duty ratio D such that the current IL measured by the current sensor13becomes the target current value IM.

The drive control unit40controls the switching of the switching element T1at the duty ratio D calculated by the calculator35by outputting the PWM signal generated by the calculator35to a control terminal of the switching element T1(the upper arm).

Next, a flow of discharge control of the power control device1according to the present embodiment will be described usingFIG. 3.FIG. 3is a diagram which shows the discharge control of the power control device1according to the present embodiment.

As an initial condition, the power control device1acquires power from the battery BT via the contactor2in a closed state. The motor ECU15controls the switching of each of the switching element T1and the switching element T2at the same duty ratio. As a result, the step-up/down converter4rotationally drives the motor generator MG by stepping up the power from the battery BT and supplying this stepped-up power to the inverter9. In this case, power is stored in the first capacitor3using the power from the battery BT. Power is stored in the second capacitor6by the power stepped-up by the step-up/down converter4. Here, the control power supply10supplies power to the motor ECU15via the diode11. The backup power supply12steps-down the power from the first capacitor3and supply it to the motor ECU15.

As shown inFIG. 3, it is assumed that the collision of the vehicle A has first occurred at a time t1. In this case, the collision detection device50detects the collision of the vehicle A and performs control such that the contactor2is in an open state at a time t2after a predetermined time has elapsed from the time t1to release the connection between the battery BT and the step-up/down converter4. As a result, the supply of power from the battery BT to the step-up/down converter4is stopped.

Here, if the connection between the battery BT and the step-up/down converter4is released, power is supplied from the first capacitor3to the auxiliary device5and the backup power supply12. However, when the motor generator MG is in a rotating state, the regenerative power generated in the motor generator MG is stepped-down by the step-up/down converter4and supplied to the first capacitor3. Therefore, the inter-terminal voltage value Vc1of the first capacitor3may gradually increase from the time t2.

If the motor ECU15receives a discharge command signal from the external ECU14at a time t3, the motor ECU15fixes the switching element T2(the lower arm) to be in an off state, and executes discharge control for controlling the switching of the switching element T1(the upper arm) at the duty ratio D such that the current IL measured by the current sensor13becomes the target current value IM. As a result, the inter-terminal voltage value Vc1of the first capacitor3is maintained at the target voltage value VMlower than an overvoltage value Vo, and the step-up operation by the step-up/down converter4is limited. This suppresses over-voltages on the primary side and the secondary side.

Note that a transfer of electric charges from the second capacitor6to the first capacitor3is not performed when the inter-terminal voltage value Vc1of the second capacitor6exceeds the target voltage value VM. In this case, power is supplied from the first capacitor3to the auxiliary device5and the backup power supply12, and the inter-terminal voltage value Vc1of the first capacitor3is decreased. Note that the control unit21may drive the inverter9and discharge a part of the power stored in the second capacitor6to the motor generator MG (hereinafter, referred to as “motor load discharge”) via the inverter9. In addition, when the inter-terminal voltage value Vc1is higher than an inter-terminal voltage value Vc2due to this motor load discharge, power is discharged from the first capacitor3to the motor generator MG via the diode D1.

If the inter-terminal voltage value Vc1of the first capacitor3falls below the target voltage value VMat a time t4, electric charges of the second capacitor6move to the first capacitor3. As a result, the inter-terminal voltage value Vc2of the second capacitor6decreases while the inter-terminal voltage value Vc1of the first capacitor3is maintained at the target voltage value VM. Then, at a time t5, electric charges move from the first capacitor3to the second capacitor6if the inter-terminal voltage value Vc1is larger than the inter-terminal voltage value Vc2, and electric charges move from the second capacitor6to the first capacitor3if the inter-terminal voltage value Vc2is larger than the inter-terminal voltage value Vc1. Therefore, the inter-terminal voltage value Vc1and the inter-terminal voltage value Vc2gradually decrease after the time t5, and the electric charges stored in the first capacitor3and the second capacitor6are discharged. Then, when the inter-terminal voltage value Vc1and the inter-terminal voltage value Vc2fall to a predetermined value Vp at time t6, the motor ECU15may stop the discharge control. Moreover, the control unit21may stop the discharge control when the discharge command signal from the external ECU14disappears.

As described above, although one embodiment of the present invention has been described above in detail with reference to the drawings, a specific configuration is not limited to this embodiment, and a design and the like are included within a range not departing from the gist of the invention. Therefore, for example, a modified example to be described below can also be adopted.

Modified Example

The power control device1of the embodiment described above may not include a control power supply10and a diode11in the configuration.

As described above, the motor ECU15fixes the switching element T2(the lower arm) to be in the off state and controls the switching of the switching element T1(the upper arm) at the predetermined duty ratio D, as the discharge control.

According to such a configuration, it is possible to suppress voltages on the primary side and the secondary side from becoming over-voltages and discharge the residual charge of the second capacitor.

In addition, the auxiliary device5may be connected to the primary side of the step-up/down converter4described above. With such a configuration, it is possible to suppress a voltage on the primary side from becoming an overvoltage due to electric charges of the first capacitor3being discharged. As a result, the discharge control can be executed without stopping an operation of the step-up/down converter4from a viewpoint of device protection.

Note that all or a part of the motor ECU15described above may also be realized by a computer. In this case, the computer may include a processor such as a central processing unit (CPU) and a graphics processing unit (GPU), and a computer-readable recording medium. Then, a program for realizing all or a part of functions of the motor ECU15using a computer is recorded in the computer-readable recording medium, and the program recorded in the recording medium may be realized by causing the processor to read and execute it. Here, the “computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disc, a ROM, or a CD-ROM, a storage device such as a hard disk embedded in a computer system. Furthermore, the “computer-readable recording medium” may include a medium that dynamically holds a program for a short time, like a communication line in the case of transmitting the program via a network such as the Internet or a communication line such as a telephone line, and a medium that holds the program for a certain period of time, like a volatile memory inside the computer system that serves as a server or a client in this case. In addition, the program may be a program for realizing a part of the functions described above, or furthermore, may be a program that can realize the functions described above in combination with a program already recorded in the computer system, and may be a program realized by using a programmable logic device such as a field programmable gate array (FPGA).

According to the present invention, it is possible to provide a power control device capable of suppressing voltages on the primary side and the secondary side from becoming over-voltages and discharging residual charge of the second capacitor. Therefore, there is high industrial applicability.

EXPLANATION OF REFERENCES