JP2006158173A - Motor drive unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable motor driving device which is small in size and low in cost without a capacitor current limiting device as a main power source.
A control device 30 performs voltage control such that a voltage Vc between terminals of a capacitor C1 is substantially the same as a DC voltage Vb of a battery B at a timing before starting the vehicle system. When the inter-terminal voltage Vc falls below the lower limit value of the voltage range in which no inrush current occurs, the engine ENG is started using the battery B, and then the target engine speed is determined to drive the engine ENG. Then, motor generator MG1 is driven in the regeneration mode with the driving force of engine ENG, and capacitor C1 is charged with the regenerative power. On the other hand, when the inter-terminal voltage Vc exceeds the upper limit value of the voltage range, the boost converter 12 is driven and controlled to boost the voltage Vm across the capacitor C2 to the inter-terminal voltage Vc, and then the system relays SRC1 and SRC2 are turned on.
[Selection] Figure 1

Description

  The present invention relates to a motor drive device that drives a motor, and more particularly to a motor drive device that includes a secondary battery and a capacitor as a power source.

  Recently, hybrid vehicles and electric vehicles have attracted attention as environmentally friendly vehicles. A hybrid vehicle is a vehicle that uses a DC power source, an inverter, and a motor driven by the inverter as a power source in addition to a conventional engine. In other words, a power source is obtained by driving the engine, a DC voltage from a DC power source is converted into an AC voltage by an inverter, and a motor is rotated by the converted AC voltage to obtain a power source.

  An electric vehicle is a vehicle that uses a DC power source, an inverter, and a motor driven by the inverter as a power source.

  In such a hybrid vehicle or electric vehicle, in order to improve energy efficiency while driving the vehicle appropriately, power corresponding to the load on the motor is supplied and energy can be efficiently recovered during regeneration. Desired.

  In order to meet such a demand, for example, Patent Document 1 includes a battery and a large-capacity capacitor (electric double layer capacitor) as a power supply device, and mainly charges the capacitor during regeneration, and the battery during normal operation. Disclosed is a vehicle energy regeneration system characterized by charging only.

  FIG. 6 is a diagram showing an outline of the vehicle energy regeneration system disclosed in Patent Document 1. As shown in FIG.

  Referring to FIG. 6, three-phase AC machine 101 operates as a generator during regeneration and operates as an electric motor during power running. When operating as a generator, the generated voltage can be adjusted by adjusting the field current with the voltage regulator 103.

  The inverter 104 is constituted by, for example, a three-phase bridge of power MOSFETs, and each MOSFET is provided with a diode in parallel. During regeneration, the three-phase alternating current generated by the three-phase alternating current machine 101 is full-wave rectified by a diode connected in parallel to each MOSFET and charged in the electric double layer capacitor 113. Further, during power running, the inverter control circuit 105 adjusts the conduction timing of each MOSFET, thereby converting the direct current fed from the electric double layer capacitor 113 into a three-phase alternating current and driving the three-phase alternating current machine 101. . At the time of power running, while the voltage of the electric double layer capacitor 113 is higher than the voltage of the battery 114, the electric double layer capacitor 113 supplies power to the three-phase alternating current machine 101. Power is supplied from the battery 114.

  During normal operation, the voltage regulator 103 adjusts the generated voltage of the three-phase alternator 101 to a value suitable for charging the battery 114, and the thyristor 110 is turned on by the thyristor firing circuit 111 to charge the battery 114. Do.

  In addition, when the electric double layer capacitor 113 is fully charged during regeneration, the discharge resistor 107 is operated to operate the chopper 108 and flow current, consume the generated power as heat, and maintain the retarder function. Is.

  The diode 115 is for preventing an overvoltage from being applied to the battery 114 when the voltage of the electric double layer capacitor 113 is higher than the voltage of the battery 114. Although not shown, a key switch contact is provided in series with the diode 115. This serves to prevent the battery 114 from being discharged via the electric double layer capacitor 113 and the diode 115 when the internal combustion engine 102 is stopped for a long time.

According to such a configuration, the electric double layer capacitor 113 is mainly responsible for regeneration and power running, and energy regeneration efficiency can be increased. Further, since the battery 114 is used as an auxiliary, it is not exposed to rapid charge / discharge, and the life deterioration is suppressed.
JP-A-6-113407 JP 2001-218381 A JP 2002-213272 A JP 2000-278807 A JP 2003-199203 A

  Here, in the electric double layer capacitor 113, the stored energy is proportional to the square of the voltage of the capacitor. That is, when the electric double layer capacitor 113 is used as a DC power source, the voltage of the capacitor decreases as the energy consumption increases. When the overdischarge state is reached, the voltage of the electric double layer capacitor 113 becomes almost zero.

  Therefore, in the above vehicle energy regeneration system, when the electric double layer capacitor 113 is in an overdischarged state and the voltage of the capacitor reaches a substantially zero state, the electric double layer is caused by a voltage difference with the battery 114 connected in parallel. An excessive current may flow into the capacitor 113. In particular, when an excessive current flows instantaneously through the electric double layer capacitor 113, the inside of the capacitor is heated and eventually explodes.

  On the other hand, when the electric double layer capacitor 113 is in a fully charged state and the voltage of the capacitor becomes higher than the voltage of the battery, an overvoltage may be applied to the battery 114.

  Therefore, in order to avoid these inrush currents and overvoltages, it is necessary to install a current limiting device for limiting the charge / discharge current of the electric double layer capacitor 113. For example, a resistance or a reactor is applied as the current limiting device. In the system shown in FIG. 6, a diode is provided as means for protecting the battery from overvoltage.

  However, in a vehicle energy system using a large-capacity capacitor as a main power source, the output density of the capacitor itself is high, so that a large current-limiting device with a large impedance is required. For this reason, the problem that the apparatus scale and cost of the whole system increase arises.

  Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to eliminate the need for a current limiting device for a capacitor serving as a main power source, and to reduce the size and cost of a highly reliable motor driving device. Is to provide.

  According to an aspect of the present invention, a motor driving device includes a secondary battery, a capacitor connected in parallel to the secondary battery, a driving circuit that drives the motor by receiving power from the secondary battery and the capacitor, Voltage control means for controlling the voltage across the terminals of the capacitor so as to be substantially the same as the DC voltage of the secondary battery before driving the motor; The voltage control means charges the capacitor with the counter electromotive voltage of the motor when the voltage between the terminals of the capacitor is lower than the DC voltage of the secondary battery.

  Preferably, the motor is a motor that starts the internal combustion engine. When the voltage control means receives a start instruction for the internal combustion engine, it supplies power from the secondary battery to the drive circuit to drive the motor in the power running mode, and after the internal combustion engine is started, the internal combustion engine is rotated at a predetermined rotational speed. Then, a counter electromotive voltage corresponding to a predetermined rotational speed is generated in the motor.

  Preferably, the voltage control means further includes a rotational speed determination means for determining the rotational speed of the internal combustion engine. The rotation speed determination means determines the rotation speed so that the back electromotive voltage of the motor becomes a charging voltage necessary for the voltage across the capacitor to reach substantially the same voltage as the DC voltage of the secondary battery.

  Preferably, the motor drive device further includes a voltage conversion circuit that converts a DC voltage between the secondary battery and the drive circuit. The capacitor is disposed between the voltage conversion circuit and the drive circuit, and is charged by the converted DC voltage. The voltage control means receives a relay connected between the drive circuit and the capacitor, a target voltage determination means for determining a target voltage of the output voltage of the voltage conversion circuit, and a target voltage determined by the target voltage determination means Voltage conversion control means for controlling the voltage conversion circuit so that the output voltage becomes the target voltage. The target voltage determining means determines, as the target voltage, a voltage that is substantially the same as the terminal voltage of the capacitor in response to the voltage between the terminals of the capacitor being higher than the DC voltage of the secondary battery. The voltage control means turns on the relay in response to the output voltage reaching the target voltage.

  Preferably, the voltage control means determines whether or not the voltage difference between the voltage between the terminals of the capacitor and the DC voltage of the secondary battery is within a voltage range in which a DC current generated by the voltage difference is not more than a predetermined allowable value. And a means for determining that the voltage difference between the terminals of the capacitor and the DC voltage of the secondary battery are substantially the same when the determination means determines that the voltage difference is within the voltage range.

  According to another aspect of the present invention, a motor driving device drives a motor by receiving power from a secondary battery, a capacitor connected in parallel to the secondary battery, and either the secondary battery or the capacitor. A drive circuit and voltage control means for controlling the voltage across the capacitor so as to be substantially the same as the DC voltage of the secondary battery before the motor is stopped. The voltage control means discharges the capacitor and charges the secondary battery when the voltage between the terminals of the capacitor exceeds the DC voltage of the secondary battery.

  Preferably, the motor drive device further includes a voltage conversion circuit that converts a DC voltage between the secondary battery and the drive circuit. The capacitor is disposed between the voltage conversion circuit and the drive circuit, and is charged by the converted DC voltage. The voltage control means controls the voltage conversion circuit so that the converted DC voltage becomes the target voltage by receiving the target voltage determined by the target voltage determining means and the target voltage determining means for determining the target voltage of the converted DC voltage. Voltage conversion control means. When receiving a motor drive stop instruction, the target voltage determining means determines, as the target voltage, a voltage that is substantially the same as the DC voltage of the secondary battery in response to the voltage across the capacitor exceeding the DC voltage of the secondary battery. . The voltage conversion control means charges the secondary battery with the electric power generated by the step-down operation.

  Preferably, the voltage conversion control unit charges the secondary battery with the power generated by the step-down operation within a range of power that can be input to the secondary battery.

  Preferably, the voltage conversion control means charges the secondary battery with the electric power generated by the step-down operation in response to the electric power generated by the step-down operation exceeding the power that can be input to the secondary battery, and supplies it to the drive circuit. Supply.

  Preferably, the voltage control means determines whether or not the voltage difference between the voltage between the terminals of the capacitor and the DC voltage of the secondary battery is within a voltage range in which a DC current generated by the voltage difference is not more than a predetermined allowable value. And a means for determining that the voltage difference between the terminals of the capacitor and the DC voltage of the secondary battery are substantially the same when the determination means determines that the voltage difference is within the voltage range.

  According to another aspect of the present invention, a motor driving device drives a motor by receiving power from a secondary battery, a capacitor connected in parallel to the secondary battery, and either the secondary battery or the capacitor. A drive circuit; and voltage control means for controlling the voltage between the terminals of the capacitor so that the voltage between the terminals of the capacitor becomes a target voltage capable of supplying power from the capacitor to the drive circuit. The motor is a motor that starts the internal combustion engine. When the voltage between the terminals of the capacitor is lower than the target voltage, the voltage control means supplies power from the secondary battery to the drive circuit to drive the motor in the power running mode, and drives the internal combustion engine after starting the internal combustion engine. The electric power generated by the motor by the force is charged in the capacitor.

  Preferably, when the voltage control means determines that the charged amount of the secondary battery is smaller than a predetermined threshold when the voltage between the terminals of the capacitor is lower than the target voltage, the voltage control means switches from the secondary battery to the drive circuit. Electric power is supplied to drive the motor in the power running mode.

  Preferably, the predetermined threshold value is set such that electric power supplied from the secondary battery to the drive circuit for driving the motor by the power running motor is secured.

  According to an aspect of the present invention, the current limiting device is provided by controlling the voltage between the terminals of the capacitor so as to eliminate the voltage difference from the power supply voltage of the secondary battery at the timing before starting the vehicle system. Therefore, an inrush current due to the capacitor can be prevented, and a small and low-cost highly reliable motor driving device can be realized.

  Further, according to another aspect of the present invention, the voltage between the terminals of the capacitor is controlled so as to eliminate the voltage difference from the power supply voltage of the secondary battery at the timing before the stop of the vehicle system. Without providing a device, it is possible to realize a small and low-cost highly reliable motor driving device.

  According to another aspect of the present invention, the capacitor is charged with electric power generated by the motor by the driving force of the internal combustion engine after the internal combustion engine is started. Therefore, it is possible to suppress excessive power from being taken out from the secondary battery, and it is possible to protect the secondary battery from overcurrent. Furthermore, a rapid decrease in the amount of electricity stored in the secondary battery can be suppressed. In addition, the vehicle can be stably accelerated regardless of the amount of electric power stored in the capacitor, and the reliability can be improved.

  Furthermore, if the power required for driving the motor in the power running mode is secured to the secondary battery and the capacitor is charged from the secondary battery, the internal combustion engine is reliably started by the power of the secondary battery. The capacitor can be charged.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

[Embodiment 1]
FIG. 1 is a schematic block diagram of a motor drive device 100 according to the first embodiment of the present invention.

  Referring to FIG. 1, motor drive device 100 includes a battery B, a boost converter 12, a capacitor C1, a capacitor C2, inverters 13 and 15, voltage sensors 17 to 19, current sensors 14 and 16, System relays SRB1 to SRB3, SRC1, SRC2, a resistor R1, and a control device 30 are provided.

  The engine ENG generates driving force using combustion energy of fuel such as gasoline as a source. The driving force generated by the engine ENG is divided into two paths by the power split mechanism 50, as indicated by the thick oblique lines in FIG. One is a path that transmits to a drive shaft that drives a wheel via a reduction gear (not shown). The other is a path for transmission to motor generator MG1.

  Although motor generators MG1 and MG2 can function as both a generator and an electric motor, as will be described below, motor generator MG1 mainly operates as a generator, and motor generator MG2 mainly operates as an electric motor.

  Specifically, motor generator MG1 is a three-phase AC rotating machine, and is used as a starter that starts engine ENG during acceleration. At this time, motor generator MG1 receives the supply of electric power from battery B, drives it as an electric motor, cranks engine ENG, and starts it.

  Further, after engine ENG is started, motor generator MG1 is rotated by the driving force of engine ENG transmitted via power split mechanism 50 to generate electric power.

  The electric power generated by motor generator MG1 is properly used depending on the driving state of the vehicle and the energy stored in capacitor C1. For example, during normal traveling or sudden acceleration, the electric power generated by motor generator MG1 becomes electric power for driving motor generator MG2 as it is. On the other hand, when the stored energy of capacitor C1 is lower than a predetermined value, the power generated by motor generator MG1 is converted from AC power to DC power by inverter 13 and stored in capacitor C1.

  Motor generator MG2 is a three-phase AC rotating machine, and is driven by at least one of electric power stored in capacitor C1 and electric power generated by motor generator MG1. The driving force of motor generator MG2 is transmitted to the drive shaft of the wheel via the speed reducer. Thus, motor generator MG2 assists engine ENG to cause the vehicle to travel, or causes the vehicle to travel only by its own driving force.

  Further, at the time of regenerative braking of the vehicle, motor generator MG2 is rotated by a wheel via a speed reducer and operates as a generator. At this time, the regenerative power generated by motor generator MG2 is charged to capacitor C1 via inverter 15.

  The battery B is a secondary battery such as a nickel metal hydride battery or a lithium ion battery.

  Voltage sensor 17 detects DC voltage Vb output from battery B, and outputs the detected DC voltage Vb to control device 30.

  System relay SRB 1 and resistor R 1 are connected in series between the positive electrode of battery B and boost converter 12. System relay SRB2 is connected in parallel to system relay SRB1 and resistor R1 between the positive electrode of battery B and boost converter 12. System relay SRB 3 is connected between the negative electrode of battery B and boost converter 12.

  System relays SRB1 to SRB3 are turned on / off by a signal SEB from control device 30. More specifically, system relays SR1 to SR3 are turned on by an H (logic high) level signal SEB from control device 30, and are turned off by an L (logic low) level signal SEB from control device 30.

  Boost converter 12 boosts DC voltage Vb supplied from battery B to a boosted voltage having an arbitrary level and supplies the boosted voltage to capacitor C1. More specifically, when boost converter 12 receives signal PWC from control device 30, boost converter 12 supplies a DC voltage boosted according to signal PWC to capacitor C1. In addition, when boost converter 12 receives signal PWC from control device 30, boost converter 12 steps down the DC voltage supplied from capacitor C 1 and supplies it to battery B.

  Capacitor C1 is formed of, for example, an electric double layer capacitor, and is connected in parallel with battery B through boost converter 12. Boost converter 12 and capacitor C1 are electrically coupled / separated by system relays SRC1, SRC2.

  System relay SRC1 is connected between boost converter 12 and the positive electrode of capacitor C1. System relay SRC2 is connected between boost converter 12 and the negative electrode of capacitor C1.

  System relays SRC1 and SRC2 are turned on / off by a signal SEC from control device 30. More specifically, system relays SRC1 and SRC2 are turned on by an H level signal SEC from control device 30 and turned off by an L level signal SEC from control device 30.

  The voltage sensor 19 detects the voltage Vc across the capacitor C1 and outputs the detected voltage Vc to the control device 30.

  Capacitor C2 smoothes the DC voltage boosted by boost converter 12, and supplies the smoothed DC voltage to inverters 13 and 15.

  Voltage sensor 18 detects voltage Vm across capacitor C2 (corresponding to the input voltage of inverters 13 and 15) and outputs the detected voltage Vm to control device 30.

  The inverter 13 is a three-phase inverter. When a DC voltage is supplied from the capacitor C1 via the capacitor C2, the inverter 13 converts the DC voltage into a three-phase AC voltage on the basis of the control signal PWM1 from the control device 30, and the motor generator MG1 is driven. Thereby, motor generator MG1 is driven to generate torque specified by torque command value TR1. Further, inverter 13 converts the AC voltage generated by motor generator MG1 into a DC voltage based on signal PWM1 from control device 30 during regenerative braking of the hybrid vehicle equipped with motor drive device 100, and the converted DC A voltage is supplied to the capacitor C1 via the capacitor C2.

  Similarly, the inverter 15 is also a three-phase inverter. When a DC voltage is supplied from the capacitor C1 through the capacitor C2, the inverter 15 converts the DC voltage into a three-phase AC voltage based on the control signal PWM2 from the control device 30, and converts the motor into a motor. Generator MG2 is driven. Thereby, motor generator MG2 is driven so as to generate torque specified by torque command value TR2. Inverter 15 converts the AC voltage generated by motor generator MG2 into a DC voltage based on signal PWM2 from control device 30 during regenerative braking of the hybrid vehicle equipped with motor drive device 100, and the converted DC A voltage is supplied to the capacitor C1 via the capacitor C2.

  Note that regenerative braking here refers to braking with regenerative power generation when the driver driving the hybrid vehicle performs a foot brake operation or turning off the accelerator pedal while driving, although the foot brake is not operated. This includes decelerating (or stopping acceleration) the vehicle speed while generating regenerative power.

  Current sensor 14 detects motor current MCRT1 flowing through motor generator MG1, and outputs the detected motor current MCRT1 to control device 30.

  Current sensor 16 detects motor current MCRT2 flowing through motor generator MG2, and outputs the detected motor current MCRT2 to control device 30.

  Control device 30 receives torque command values TR1, TR2, motor rotation speeds MRN1, MRN2, ignition key IG and electric power that can be input to battery B (hereinafter referred to as battery input WIN) from an external ECU (Electrical Control Unit) (not shown). The voltage sensor 17 receives the DC voltage Vb, the voltage sensor 19 receives the terminal voltage Vc of the capacitor C1, the voltage sensor 18 receives the input voltage Vm, the current sensor 14 receives the motor current MCRT1, and the current sensor 16 receives Motor current MCRT2 is received.

  Control device 30 controls switching of an NPN transistor (not shown) of inverter 13 when inverter 13 drives motor generator MG1 based on input voltage Vm of inverter 13, torque command value TR1 and motor current MCRT1. The signal PWM1 is generated, and the generated signal PWM1 is output to the inverter 13.

  Control device 30 also controls switching of an NPN transistor (not shown) of inverter 15 when inverter 15 drives motor generator MG2 based on input voltage Vm of inverter 15, torque command value TR2 and motor current MCRT2. Signal PWM2 is generated, and the generated signal PWM2 is output to the inverter 15.

  Furthermore, when inverter 13 drives motor generator MG1, control device 30 determines NPN of boost converter 12 based on DC voltage Vb of battery B, input voltage Vm of inverter 13, torque command value TR1, and motor rotational speed MRN1. A signal PWC for switching control of a transistor (not shown) is generated, and the generated signal PWC is output to boost converter 12.

  When inverter 15 drives motor generator MG2, control device 30 determines NPN of boost converter 12 based on DC voltage Vb of battery B, input voltage Vm of inverter 15, torque command value TR2, and motor rotational speed MRN2. A signal PWC for switching control of a transistor (not shown) is generated, and the generated signal PWC is output to boost converter 12.

  Further, control device 30 generates an AC voltage generated by motor generator MG2 based on input voltage Vm of inverter 15, torque command value TR2 and motor current MCRT2 during regenerative braking of the hybrid vehicle on which motor drive device 100 is mounted. A signal PWM2 for conversion to a DC voltage is generated, and the generated signal PWM2 is output to the inverter 15. In this case, the NPN transistor (not shown) of the inverter 15 is switching-controlled by the signal PWM2. Thereby, inverter 15 converts the AC voltage generated by motor generator MG2 into a DC voltage and supplies it to capacitor C1.

  As described above, motor drive device 100 according to the present invention mainly uses the power stored in capacitor C1 as the power necessary for driving motor generators MG1 and MG2 in the powering mode. Further, the electric power generated when motor generators MG1 and MG2 are driven in the regeneration mode is mainly charged in capacitor C1. In particular, since a large-capacity electric double layer capacitor is employed for the capacitor C1 serving as the main power source, high energy regeneration efficiency can be maintained even with a rapid regenerative current.

  On the other hand, when the electric double layer capacitor is mounted, the above-described inrush current or overvoltage may occur, which may damage the battery B, the inverters 13 and 15, the boost converter 12, and the like. Further, in system relays SRC1 and SRC2, there is a possibility that welding occurs between the contacts.

  Therefore, the motor driving apparatus 100 according to the present invention is characterized by including voltage control means for the capacitor C1 described below as means for avoiding inrush current and overvoltage due to the capacitor C1. According to this, the installation of a current limiting device which has been conventionally required becomes unnecessary, and a small, low-cost and highly reliable motor driving device can be realized.

  Specifically, motor drive device 100 according to the present invention eliminates a voltage difference between terminal voltage Vc of capacitor C1 and DC voltage Vb of battery B either when the vehicle system is started or stopped. Voltage control is executed. Hereinafter, these voltage controls will be described in detail.

(1) Voltage control when starting the vehicle system First, voltage control performed when starting the vehicle system will be described. When the vehicle system is activated, the capacitor C1 may be in an overdischarged state, and an excessive current is caused by the voltage difference between the terminal voltage of the capacitor C1 (Vc is almost zero voltage) and the DC voltage Vb of the battery. May flow into On the other hand, if the inter-terminal voltage of the capacitor C1 is higher than the DC voltage Vb of the battery B, an overvoltage can be applied to the inverters 13 and 15 immediately after startup. Furthermore, there is a risk that the contacts of the system relays SRC1 and SRC2 are welded by this overcurrent.

  Therefore, when the vehicle system is started, voltage control is performed so that the voltage Vc between the terminals of the capacitor C1 is substantially the same as the DC voltage Vb level of the battery Vb in response to the ignition key IG being turned on. The system is configured to perform normal system startup.

  FIG. 2 is a flowchart for illustrating voltage control when the vehicle system is activated according to the embodiment of the present invention. The following voltage control is executed by the control device 30 that controls the entire motor drive device 100.

  Referring to FIG. 2, first, in response to ignition key IG being turned on (step S10), control device 30 outputs H-level signal SEB to system relays SRB1 to SRB3 on the battery B side. Then, system relays SRB1 to SRB3 are turned on (step S11).

  At this time, if the high-voltage battery B is suddenly connected to the load, a large current (inrush current) may flow instantaneously. Therefore, at the start of power supply, system relays SRB1 to SRB3 are turned on / off in a procedure that prevents an inrush current by resistor R1 provided in system relay SRB1. Specifically, first, system relay SRB1 and system relay SRB3 are turned on simultaneously. Thereby, system relay SRB1 supplies the direct current from battery B to boost converter 12 via resistor R1. Subsequently, system relay SRB2 is turned on with system relays SRB1 and SRB3 being turned on. System SRB2 directly supplies DC current from battery B to boost converter 12. Finally, only system relay SRB1 is turned off.

  Next, when receiving the voltage Vc between the terminals of the capacitor C1 from the voltage sensor 18, the control device 30 performs the system relay on the capacitor C1 side according to the following three procedures based on the voltage level of the voltage Vc between the terminals. SRC1 and SRC2 are turned on, and the capacitor C1 is connected to the motor driving apparatus 100.

  Specifically, control device 30 determines whether or not voltage Vc between terminals of capacitor C1 is within a voltage range that does not cause an inrush current when capacitor C1 is connected.

  This is because when the capacitor C1 is suddenly connected when the capacitor C1 is in an overcharged state or an overdischarged state, an excessive inrush current flows through the capacitor C1 due to a voltage difference from the battery B. . This inrush current may cause welding between the contact points of the system relays SRC1 and SRC2. Accordingly, the voltage range serving as a determination criterion at this time is such that the voltage difference between the inter-terminal voltage Vc of the capacitor C1 and the DC voltage Vb of the battery B is within a predetermined range that does not generate an inrush current exceeding an allowable value. It is predetermined.

  Specifically, first, control device 30 determines whether or not terminal voltage Vc of capacitor C1 is larger than a lower limit value (hereinafter referred to as lower limit value Vmin) of the voltage range (step S12). ).

  In step S12, when controller 30 determines that terminal voltage Vc of capacitor C1 is lower than or equal to lower limit value Vmin, controller 30 performs the charging operation of capacitor C1 according to the flowchart of FIG. This charging operation will be described in detail later.

  On the other hand, if it is determined in step S12 that the inter-terminal voltage Vc of the capacitor C1 is larger than the lower limit value Vmin, the control device 30 continues to set the inter-terminal voltage Vc to the upper limit value (hereinafter referred to as the upper limit value Vmax) of the voltage range. Or less) (step S13).

  At this time, if it is determined that the inter-terminal voltage Vc of the capacitor C1 is smaller than the upper limit value Vmax, that is, if the inter-terminal voltage Vc is determined to be within the voltage range, the control device 30 outputs an H level signal SEC. System relays SRC1 and SRC2 are turned on (step S14). When the capacitor C1 is connected, the motor driving apparatus 100 enters an RDY state in which system activation can be started (step S15), and thereafter, normal system activation operation is executed.

  On the other hand, in step S13, when control device 30 determines that voltage Vc between terminals of capacitor C1 is equal to or higher than upper limit value Vmax, prior to connection of capacitor C1, voltage Vm across capacitor C2 (the output of boost converter 12). Step-up operation is performed by controlling the boost converter 12 so that the voltage Vc corresponds to the voltage Vc between the terminals of the capacitor C1 (step S16).

  Specifically, when control device 30 receives voltage Vm across capacitor C2 from voltage sensor 18, control device 30 determines target voltage Vdc_com of boost converter 12 so that voltage Vm becomes voltage Vc between terminals of capacitor C1.

  Further, the control device 30 is based on the determined target voltage (Vdc_com = Vc), the DC voltage Vb, and the output voltage Vm. A signal PWC for boosting the DC voltage Vb to the output voltage Vm is generated so that the output voltage Vm becomes the target voltage, and the generated signal PWC is output to the boost converter 12. Thereby, boost converter 12 converts DC voltage Vb into output voltage Vm so that output voltage Vm becomes target voltage Vdc_com.

  The control device 30 continues the above boosting operation until the voltage difference between the output voltage Vm and the inter-terminal voltage Vc of the capacitor C1 is equal to or less than a predetermined voltage range V1. Finally, the control device 30 confirms that the voltage difference between the output voltage Vm and the inter-terminal voltage Vc has been reduced to V1 or less (step S17), and outputs the H level signal SEC to output the system relay SRC1. , SRC2 is turned on (step S18). When the capacitor C1 is connected, the motor driving apparatus 100 enters an RDY state in which system activation can be started (step S19), and thereafter, normal system activation operation is performed.

  FIG. 3 is a flowchart for illustrating voltage control at the time of starting the vehicle system according to the embodiment of the present invention.

  Referring to FIG. 3, when controller 30 determines in step S12 of FIG. 2 that terminal voltage Vc of capacitor C1 is lower than or equal to lower limit value Vmin, control device 30 drives engine ENG according to the following steps S20 to S28. Along with this, the capacitor C1 is charged by the back electromotive voltage generated in the motor generator MG1. The counter electromotive voltage is generally represented by the product of the rotational angular velocity of the rotor and the magnetic flux of the permanent magnet. Therefore, the counter electromotive voltage generated increases in proportion to the rotational angular velocity of motor generator MG1, that is, the engine speed.

  Specifically, first, motor generator MG1 is used as a starter for starting engine ENG. At this time, a command (torque command value TR1) for driving motor generator MG1 is given from external ECU to control device 30 so that the rotational speed of engine ENG is set to the idle rotational speed.

  Control device 30 generates signal PWM1 based on torque command value TR1, motor current MCRT1 and voltage Vm, and outputs the generated signal PWM1 to inverter 13.

  Inverter 13 converts the DC voltage from boost converter 12 into an AC voltage according to signal PWM1, and drives motor generator MG1 to output the torque specified by torque command value TR1. Motor generator MG1 is supplied as electric power from battery B and is driven as an electric motor, and cranks engine ENG via power split mechanism 50 to start it (step S20).

  After the engine ENG is started, when the start of the engine ENG is completed in response to the engine speed reaching a predetermined idle speed (step S21), the control device 30 outputs an L level signal SEB, and the battery The system relays SRB2 and SRB3 on the B side are turned off (step S22). Thereby, the battery B is electrically disconnected from the motor drive device 100.

  Here, when startup of engine ENG is completed, motor generator MG1 is rotated by the driving force of engine ENG transmitted through power split mechanism 50. At this time, a counter electromotive voltage proportional to the engine speed is generated in motor generator MG1. In the present invention, capacitor C1 is charged with a back electromotive voltage generated in motor generator MG1.

  Specifically, first, the controller 30 determines whether or not the input voltage Vm of the inverter 13 is lower than a predetermined voltage level V2 prior to the charging operation to the capacitor C1 (step S23). The predetermined voltage level V2 at this time is a voltage level that can prevent the occurrence of an inrush current due to the voltage difference between the terminal voltage Vc and the input voltage Vm when the system relays SRC1 and SRC2 are turned on and the capacitor C1 is connected. And This is because the input voltage Vm is boosted to a high voltage level by starting the engine ENG in step S20.

  If it is determined in step S23 that the input voltage Vm of inverter 13 is lower than predetermined voltage V2, control device 30 outputs H level signal SEC and turns on system relays SRC1 and SRC2 (step S24). .

  On the other hand, when it is determined in step S23 that the input voltage Vm of the inverter 13 is equal to or higher than the predetermined voltage V2, the control device 30 consumes the energy accumulated in the capacitor C2 and changes the input voltage Vm to the predetermined voltage V2. The voltage is reduced to the voltage V2 level (step S28). As a specific method of this energy consumption, an on-duty of an upper NPN transistor (not shown) of the inverter 15 is increased, and a path through which energy flows from the capacitor C2 to the motor generator MG2 via the inverter 15 is provided. Can be mentioned.

  Next, when system relays SRC1 and SRC2 are turned on and capacitor C1 is connected to motor drive device 100, the back electromotive voltage generated in motor generator MG1 by the driving force of engine ENG is charged in capacitor C1.

  Specifically, control device 30 determines a target rotational speed of engine ENG for generating a desired counter electromotive voltage in motor generator MG1 (step S25). The desired counter electromotive voltage is obtained from the amount of power that must be supplied to the capacitor C1 in order to set the inter-terminal voltage Vc of the capacitor C1 and the input voltage Vm of the inverter 13 to substantially the same voltage level. In step S25, the control device 30 stores the correlation between the engine speed and the counter electromotive voltage as a map in advance, and selects the engine speed corresponding to the desired counter electromotive voltage from the map. Also good.

  The back electromotive voltage generated in motor generator MG1 is converted from AC power to DC power in inverter 13 and stored in capacitor C1. As a result, the terminal voltage Vc of the capacitor C1 increases.

  The control device 30 continues the above charging operation of the capacitor C1 until the voltage difference between the input voltage Vm of the inverter 13 and the terminal voltage Vc of the capacitor C1 becomes equal to or less than a predetermined voltage range V1. Finally, the control device 30 confirms that the voltage difference between the output voltage Vm and the inter-terminal voltage Vc has been reduced to V1 or less (step S26), and the motor drive device 100 can start system startup. The RDY state is set (step S27). The motor drive device 100 executes a normal system startup operation in response to being in the RDY state.

  As described above, according to the motor drive device 100 of the present invention, it is confirmed that the voltage difference between the terminal voltage Vc of the capacitor C1 and the DC voltage Vb of the battery B has been eliminated when the vehicle system is started. Therefore, inrush current due to the capacitor C1 can be prevented without using a current limiting device. Therefore, a highly reliable motor drive device can be realized in a small size and at low cost.

(2) Voltage control when the vehicle system is stopped Next, voltage control performed when the vehicle system is stopped will be described. As shown below, if the capacitor C1 is in a fully charged state when the vehicle system is stopped, an excessive discharge current may flow out of the capacitor C1 when the capacitor C1 is connected when the vehicle system is started next time. Therefore, the discharging operation of the capacitor C1 is performed so that the inter-terminal voltage Vc of the capacitor C1 becomes substantially the same voltage level as the DC voltage Vb of the battery B.

  FIG. 4 is a flowchart for illustrating voltage control performed when the vehicle system is stopped according to the embodiment of the present invention. The following voltage control is executed by the control device 30.

  Referring to FIG. 4, when control device 30 receives the ignition key IG from the external ECU being turned off (step S01), control device 30 charges battery B from capacitor C1 based on terminal-to-terminal voltage Vc of capacitor C1. The amount of electric power to be used (hereinafter also referred to as charge amount α) is obtained (step S02). Specifically, the charge amount α is expressed as shown in Equation (1).

α = 1/2 · C (Vc ² −Vdc_com ² ) (1)
Here, C is the capacitance of the capacitor C1, Vc is the voltage across the capacitor C1 when the vehicle is stopped, and Vdc_com is the voltage across the terminal of the capacitor C1 after discharging, and indicates the target voltage of the boost converter 12.

Here, since the target voltage Vdc_com of the boost converter 12 is finally determined to be the DC voltage Vb of the battery B, the equation (1) is
α = 1/2 · C (Vc ² −Vb ² ) (2)
Is converted as follows.

  Next, control device 30 determines whether or not all of charge amount α can be input to battery B (step S03). It is known that battery B generally varies in the amount of power that can be input (corresponding to battery input WIN) depending on the battery temperature and SOC (State of Charge). When control device 30 receives battery input WIN from the external ECU, control device 30 determines the magnitude relationship between charge amount α and battery input WIN described above, and drives and controls boost converter 12 and inverter 13 according to the determination result.

  Specifically, when it is determined in step S03 that battery input WIN is larger than charge amount α, that is, when it is determined that all of charge amount α can be input to battery B, control device 30 includes boost converter 12. Is controlled to discharge from the capacitor C1 to the battery B (step S04). Specifically, control device 30 turns on / off an NPN transistor (not shown) of boost converter 12 based on DC voltage Vb, output voltage Vm (equivalent to voltage Vc between terminals of capacitor C1), and target voltage Vdc_com. Signal PWC is generated and output to boost converter 12. Boost converter 12 steps down output voltage Vm to DC voltage Vb to charge battery B.

  On the other hand, when it is determined in step S03 that battery input WIN is smaller than charge amount α, that is, when it is determined that all of charge amount α cannot be input to battery B, control device 30 drives boost converter 12. At the same time, the inverter 13 is driven and controlled, and the motor generator MG1 consumes the excess (step S05). Specifically, control device 30 supplies direct-current power to inverter 13 in parallel with the discharging operation to battery B in step S04 described above. At this time, by increasing the on-duty of the NPN transistor on the upper side of the inverter 13, a current path is formed from the capacitor C1 to the motor generator MG1 via the inverter 13, and the stored energy of the capacitor C1 is consumed.

  The drive control of the boost converter 12 or the drive control of the boost converter 12 and the inverter 13 is continued until the inter-terminal voltage Vc of the capacitor C1 is stepped down to a predetermined voltage Vx or less. The predetermined voltage Vx is equal to the direct current voltage Vb of the battery B plus the decrease ΔVc of the inter-terminal voltage Vc due to self-discharge of the capacitor C1.

  The control device 30 confirms that the inter-terminal voltage Vc of the capacitor C1 is equal to or lower than the predetermined voltage Vx (step S06), outputs an L level signal SEB, and outputs the system relay SRB2, battery B side. SRB3 is turned off (step S07).

  Subsequently, control device 30 outputs L level signal SEC and turns off system relays SRC1 and SRC2 (step S08). In this way, battery B and capacitor C1 are electrically disconnected from motor drive device 100. Finally, the control device 30 executes a normal battery system stop sequence to stop the vehicle system (step S09).

  As described above, according to the first embodiment of the present invention, when the vehicle system is stopped, the voltage difference between the terminal voltage Vc of the capacitor C1 and the DC voltage Vb of the battery B is eliminated, whereby the inrush current caused by the capacitor C1. A current-limiting device for suppressing this is not necessary. As a result, the reliability of the motor drive device can be improved with a small and low-cost device configuration.

[Embodiment 2]
As described above, motor drive device 100 according to the present invention drives motor generators MG1 and MG2 using capacitor C1 connected in parallel to battery B as a main power source. In particular, by adopting a large-capacity electric double layer capacitor as the capacitor C1, it is possible to maintain high energy regeneration efficiency even with a rapid regenerative current.

  However, when the engine ENG is in a stopped state, such as when the vehicle is stopped, if the stored energy of the capacitor C1 does not satisfy the predetermined power required to accelerate the vehicle, the charging operation of the capacitor C1 is accompanied. As described below, an overcurrent may flow through the battery B.

  Specifically, when the vehicle is stopped, when the energy stored in capacitor C1 is less than the predetermined power required for acceleration of the vehicle, if engine ENG is in an operating state, motor generator MG1 generates electric power with the driving force of engine ENG. Then, the generated electric power is stored in the capacitor C1 via the inverter 13.

  On the other hand, when engine ENG is in a stopped state, motor generator MG1 does not generate electric power, and thus capacitor C1 is charged with the supply of electric power from battery B. At this time, in the battery B, the SOC is lowered by supplying power to the capacitor C1. When SOC falls below a predetermined threshold value set in advance, engine ENG is started to charge battery B. When engine ENG is started, motor generator MG1 is rotated by the driving force of engine ENG to generate electric power. Electric power generated by motor generator MG1 is converted from AC power to DC power by inverter 13 and stored in battery B.

  Here, in starting engine ENG, as described above, motor generator MG1 is supplied with electric power from battery B and is driven as an electric motor, and engine ENG is cranked to start. At this time, excessive electric power is taken out from the battery B to start the engine ENG, so that an overcurrent flows through the battery B. As a result, the battery B may be damaged.

  Therefore, when charging the capacitor C1 when the vehicle is stopped, the motor drive device according to the present embodiment is first supplied with power from the battery B so that no overcurrent flows through the battery B. The engine ENG is activated, and the capacitor C1 is charged with the electric power generated by the motor generator MG1 using the driving force of the engine after activation. Hereinafter, the charge control of the capacitor C1 will be described in detail. Since the motor drive device according to the present embodiment has the same configuration as motor drive device 100 in FIG. 1, detailed description will not be repeated.

  FIG. 5 is a flowchart for illustrating charging control of capacitor C1 according to the second embodiment of the present invention.

  Referring to FIG. 5, when control device 30 receives voltage Vc between terminals of capacitor C1 from voltage sensor 18, it determines whether or not voltage Vc between terminals of capacitor C1 is smaller than a predetermined threshold value Va. (Step S30). The predetermined threshold value Va corresponds to the lower limit value of the terminal voltage Vc of the capacitor C1 when the stored energy of the capacitor C1 satisfies the electric power necessary for acceleration of the vehicle.

  If it is determined in step S30 that terminal voltage Vc of capacitor C1 is equal to or higher than threshold value Va, control device 30 does not perform charging operation of capacitor C1. Therefore, the electric power stored in the capacitor C1 is used for accelerating the vehicle.

  On the other hand, when it is determined in step S30 that terminal voltage Vc of capacitor C1 is lower than threshold value Va, control device 30 performs the charging operation of capacitor C1 according to the flowchart after step S31.

  Specifically, first, the control device 30 determines whether or not the vehicle is stopped (step S31). This determination is made, for example, by determining whether or not the vehicle speed is zero based on the vehicle speed detected by a vehicle speed sensor (not shown) by control device 30 in FIG.

  When it is determined in step S31 that the vehicle speed is not 0 and the vehicle is in a traveling state, the control device 30 determines whether or not the engine ENG has been started (step S36). When it is determined in step S36 that the engine ENG has been started, the control device 30 converts the power generated by the motor generator MG1 by the driving force of the engine ENG from AC power to DC power by the inverter 13. Is supplied to the capacitor C1 (step S37). When the inter-terminal voltage Vc of the capacitor C1 becomes equal to or higher than the threshold value Va (step S38), the control device 30 stops the charging operation of the capacitor C1.

  On the other hand, if it is determined in step S31 that the vehicle speed is 0 and the vehicle is in a stopped state, control device 30 subsequently determines whether or not engine ENG is in a stopped state (step S32). At this time, if the rotational speed of engine ENG is 0, control device 30 determines that engine ENG is in a stopped state.

  On the other hand, when it is determined in step S32 that the engine ENG is not at 0 and the engine ENG is in the operating state, the control device 30 proceeds to step S36 and determines whether or not the engine ENG has been started. Judging. At this time, if it is determined that startup of engine ENG has been completed, control device 30 charges capacitor C1 with the electric power generated by motor generator MG1 in accordance with steps S37 and S38 as described above.

  Returning again to step S32, when it is determined that engine ENG is in the stopped state, control device 30 determines whether or not the SOC of battery B is smaller than a predetermined SOC lower limit value SOC_min (step S33). Here, predetermined SOC lower limit value SOC_min is set in advance so that electric power supplied from battery B is secured to motor generator MG1 serving as a starter when engine ENG is started.

  When it is determined in step S33 that the SOC of battery B is equal to or higher than the SOC lower limit value SOC_min, control device 30 charges capacitor C1 using the power of battery B (step S37). Specifically, control device 30 drives and controls boost converter 12 to perform charging operation from battery B to capacitor C1. Based on DC voltage Vb, output voltage Vm (equivalent to inter-terminal voltage Vc of capacitor C1), and target voltage Vdc_com (equivalent to threshold value Va), controller 30 controls NPN transistor (not shown) of boost converter 12. Is generated and output to boost converter 12. Boost converter 12 boosts output voltage Vm to threshold value Va and charges capacitor C1. When the inter-terminal voltage Vc of the capacitor C1 becomes equal to or higher than the threshold value Va (step S38), the control device 30 stops the charging operation of the capacitor C1.

  On the other hand, when it is determined in step S33 that the SOC of battery B is smaller than SOC lower limit SOC_min, control device 30 determines that activation of engine ENG is requested (step S34), and starts engine ENG (step S34). Step S35).

  Engine ENG is activated by using motor generator MG1 as a starter for starting engine ENG. Motor generator MG1 is supplied with electric power from battery B and is driven as an electric motor, and cranks engine ENG via power split mechanism 50 to start it.

  After the engine ENG is started, the engine generator MG1 is transmitted via the power split mechanism 50 when the start of the engine ENG is completed in response to the rotation speed of the engine ENG reaching a predetermined idle speed (step S36). The engine ENG is rotated by the driving force to generate power. The electric power generated by motor generator MG1 is converted from AC power to DC power by inverter 13 and stored in capacitor C1 (step S37). When the inter-terminal voltage Vc of the capacitor C1 becomes equal to or higher than the threshold value Va (step S38), the control device 30 stops the charging operation of the capacitor C1.

  As described above, according to the second embodiment of the present invention, when the vehicle is stopped, the capacitor C1 is connected to the capacitor C1 by the electric power generated by the motor generator MG1 by the driving force of the engine ENG after the engine ENG is started. It will be charged. According to this, excessive electric power is not taken out from the battery B, and an overcurrent is prevented from flowing into the battery B. Furthermore, a rapid decrease in the SOC of the battery B is suppressed. As a result, the motor drive device can be more reliably protected.

  In addition, the vehicle can be stably accelerated regardless of the amount of electric power stored in the capacitor C1, and the reliability can be improved.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention 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.

  The present invention can be applied to a motor drive device mounted on a hybrid vehicle.

1 is a schematic block diagram of a motor drive device according to a first embodiment of the present invention. It is a flowchart for demonstrating the voltage control at the time of vehicle system starting by Embodiment 1 of this invention. It is a flowchart for demonstrating the voltage control at the time of vehicle system starting by Embodiment 1 of this invention. It is a flowchart for demonstrating the voltage control performed at the time of the vehicle system stop by Embodiment 1 of this invention. It is a flowchart for demonstrating the charge control of the capacitor by Embodiment 2 of this invention. It is a figure which shows the outline | summary of the vehicle energy regeneration system disclosed by patent document 1. FIG.

Explanation of symbols

  12,119 step-up converter, 13,15,104 inverter, 14,16 current sensor, 17-19 voltage sensor, 30 control device, 50 power split mechanism, 100 motor drive device, 101 three-phase AC machine, 102 internal combustion engine, 103 Voltage regulator, 105 Inverter control circuit, 106 Diode, 107 Discharge resistor, 108 Chopper, 109 Chopper control circuit, 110 Thyristor, 111 Thyristor firing circuit, 112 Total control unit, 113 Electric double layer capacitor, 114, B battery, 115 Diode, 116 Key switch contact, 120 converter control circuit, C1 capacitor, C2 capacitor, ENG engine, MG1, MG2 motor generator, SRB1-SRB3, SRC1, SRC2 system relay.

Claims (13)

A secondary battery,
A capacitor connected in parallel to the secondary battery;
A drive circuit that drives the motor by receiving power from the secondary battery and the capacitor;
Voltage control means for controlling the terminal voltage of the capacitor so as to be substantially the same as the DC voltage of the secondary battery before starting the driving of the motor;
The voltage control means charges the capacitor with a counter electromotive voltage of the motor when a voltage between terminals of the capacitor is lower than a DC voltage of the secondary battery. The motor is a motor for starting an internal combustion engine;
When the voltage control means receives an instruction to start the internal combustion engine, it supplies electric power from the secondary battery to the drive circuit to drive the motor in a power running mode, and after the internal combustion engine is started, the internal combustion engine The motor drive device according to claim 1, wherein a counter electromotive voltage corresponding to the predetermined rotation number is generated in the motor. The voltage control means further includes a rotational speed determining means for determining the rotational speed of the internal combustion engine,
The rotation speed determining means determines the rotation speed so that the back electromotive voltage of the motor becomes a charging voltage necessary for the voltage across the capacitor to reach substantially the same voltage as the DC voltage of the secondary battery. The motor drive device according to claim 2. A voltage conversion circuit for converting a DC voltage between the secondary battery and the drive circuit;
The capacitor is disposed between the voltage conversion circuit and the drive circuit, and is charged by the converted DC voltage,
The voltage control means includes
A relay connected between the drive circuit and the capacitor;
Target voltage determining means for determining a target voltage of the output voltage of the voltage conversion circuit;
Voltage conversion control means for receiving the target voltage determined by the target voltage determination means and controlling the voltage conversion circuit so that the output voltage becomes the target voltage,
The target voltage determining means determines, as the target voltage, a voltage substantially equal to the terminal voltage of the capacitor in response to the voltage between the terminals of the capacitor being higher than the DC voltage of the secondary battery.
4. The motor drive device according to claim 1, wherein the voltage control unit turns on the relay in response to the output voltage reaching the target voltage. 5. The voltage control means determines whether the voltage difference between the terminal voltage of the capacitor and the DC voltage of the secondary battery is within a voltage range in which a DC current generated by the voltage difference is not more than a predetermined allowable value. A determination means,
2. The determination unit determines that the voltage across the capacitor and the DC voltage of the secondary battery are substantially the same in response to the determination that the voltage difference is within the voltage range. The motor drive device according to claim 1. A secondary battery,
A capacitor connected in parallel to the secondary battery;
A drive circuit that drives the motor by receiving power from either the secondary battery or the capacitor;
Voltage control means for controlling the terminal voltage of the capacitor so as to be substantially the same as the DC voltage of the secondary battery before the motor is stopped.
The voltage control means discharges the capacitor and charges the secondary battery when the voltage between the terminals of the capacitor exceeds the DC voltage of the secondary battery. A voltage conversion circuit for converting a DC voltage between the secondary battery and the drive circuit;
The capacitor is disposed between the voltage conversion circuit and the drive circuit, and is charged by the converted DC voltage,
The voltage control means includes
Target voltage determining means for determining a target voltage of the converted DC voltage;
Voltage conversion control means for receiving the target voltage determined by the target voltage determination means and controlling the voltage conversion circuit so that the converted DC voltage becomes a target voltage;
When the target voltage determining means receives the instruction to stop driving the motor, the target voltage determining means generates a voltage substantially equal to the DC voltage of the secondary battery in response to the voltage across the capacitors exceeding the DC voltage of the secondary battery. Determined as the target voltage,
The motor drive device according to claim 6, wherein the voltage conversion control unit charges the secondary battery with electric power generated by the step-down operation.   The motor drive device according to claim 7, wherein the voltage conversion control unit charges the secondary battery with electric power generated by the step-down operation within a range of electric power that can be input to the secondary battery.   The voltage conversion control means charges the secondary battery with the power generated by the step-down operation in response to the power generated by the step-down operation exceeding the power that can be input to the secondary battery. The motor drive device according to claim 8, wherein the motor drive device is supplied to a drive circuit. The voltage control means determines whether the voltage difference between the terminal voltage of the capacitor and the DC voltage of the secondary battery is within a voltage range in which a DC current generated by the voltage difference is not more than a predetermined allowable value. A determination means,
The determination means determines that the voltage across the capacitor and the DC voltage of the secondary battery are substantially the same in response to the determination that the voltage difference is within the voltage range. The motor drive device according to claim 9. A secondary battery,
A capacitor connected in parallel to the secondary battery;
A drive circuit that drives the motor by receiving power from either the secondary battery or the capacitor;
Voltage control means for controlling the inter-terminal voltage of the capacitor so that the inter-terminal voltage of the capacitor becomes a target voltage capable of supplying power from the capacitor to the drive circuit;
The motor is a motor for starting an internal combustion engine;
When the voltage between the terminals of the capacitor is lower than the target voltage, the voltage control means supplies power from the secondary battery to the drive circuit to drive the motor in a power running mode, thereby starting the internal combustion engine And a motor driving device configured to charge the capacitor with electric power generated by the motor by the driving force of the internal combustion engine.   When the voltage control means determines that the charged amount of the secondary battery is smaller than a predetermined threshold when the voltage between the terminals of the capacitor is lower than the target voltage, the voltage control means The motor drive device according to claim 11, wherein power is supplied to a drive circuit to drive the motor in a power running mode.   The motor driving device according to claim 12, wherein the predetermined threshold value is set such that electric power supplied from the secondary battery to the driving circuit is secured to drive the motor with a power running motor. .

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