JP6657820B2 - Vehicle power supply - Google Patents

Description

  The present invention relates to a power supply device mounted on a vehicle such as an electric vehicle (EV) or a plug-in hybrid electric vehicle (PHEV).

  A vehicle such as an electric vehicle is equipped with a power supply device for driving a motor. BACKGROUND ART In a power supply device, electric energy is constantly transferred between a power storage device (for example, a battery) and a motor (in other words, a generator). Due to the structure of the vehicle, the motor is arranged near the front and rear wheels to increase the transmission efficiency of the driving force. On the other hand, the battery is large in size, and its performance and life are easily affected by the temperature. Since the motor and the battery are arranged apart from each other, a connecting member (for example, a wire harness) that connects the both in a circuit (a transmission path of electric energy) becomes long. Therefore, in the circuit, the resistance is increased by the length of the wire harness, so that the energy loss during transmission increases.

The energy loss during transmission in the circuit is proportional to the square of the current (W = I ² · R). For this reason, when transmitting the same amount of energy, increasing the voltage reduces the energy loss compared to increasing the current. Therefore, a method has been considered in which the voltage is increased using a voltage variable device (for example, a DC / DC converter) and the current is reduced to reduce energy loss during transmission (see Patent Document 1).

  On the other hand, when increasing the voltage, it is necessary to increase the withstand voltage of the entire circuit accordingly. For example, it is necessary to increase the withstand voltage of elements in various devices constituting a circuit and to extend the internal insulation distance. For this reason, there has been a problem that the cost and size of the device are increased. In addition, although the energy loss on the circuit can be reduced by using the voltage variable device, the energy loss in the voltage variable device itself due to the voltage conversion occurs.

  When an inductive load such as a motor operates, an inrush current is generated. As a result, a large current change occurs instantaneously in the circuit, so that the influence of the resistance on the circuit increases, and the energy loss increases. Particularly, in a power supply device that regenerates electric energy generated by a motor during deceleration, the regenerated electric energy is lost as heat energy due to the resistance of a wire harness connected to the battery and the resistance inside the battery. Therefore, at the time of regeneration, the effect of the resistance on the energy loss is further increased.

Japanese Patent No. 4960407

As a measure to mitigate energy loss due to a wire harness or the like on a circuit without using a device with energy loss such as a voltage variable device, a method of providing a second power storage device such as a capacitor between a battery and a motor is known. No. For example, a capacitor is generally smaller in size than various devices constituting a circuit, and thus can be arranged near a motor. For this reason, the wire harness connecting between the motor and the capacitor may be short, and the resistance (R ₀ ) between the two can be reduced. The internal resistance of the capacitor is smaller than that of the battery. Therefore, when supplying electric energy to the motor from the capacitor, energy loss can be suppressed as compared with supplying electric energy from the battery.

According to such a resistance characteristic, even when an inrush current is generated by an inductive load such as a motor, energy loss can be reduced because the resistance (R ₀ ) between the motor and the capacitor itself is small. it can.

Further, the capacitor can be arranged in the circuit closer to the motor than the battery. Therefore, the resistance (R ₀ ) between the motor and the capacitor can be made smaller than the resistance (R ₁ ) between the battery and the motor. Therefore, electric energy is supplied to the motor from the capacitor in preference to the battery. At this time, energy loss can be suppressed as compared with the case where energy is supplied from the battery to the motor.

However, when the potential of the capacitor becomes lower than the potential of the battery due to the supply of the electrical energy, the electrical energy is transferred (charged) from the battery to the capacitor until the potential of the capacitor becomes the same as that of the battery. As a result, energy loss occurs in the resistance (R ₂ ) between the battery and the capacitor.

In addition, when a capacitor and a battery are electrically connected in parallel and are always in the same potential state, the capacitor cannot be charged with electric energy. For example, even when the electric energy generated by the motor is regenerated at the time of deceleration of the vehicle, the capacitor cannot be charged with the electric energy at the time of regeneration. As described above, even when the battery is charged with electric energy at the time of regeneration in a state where the capacitor and the battery have the same potential, the current of the circuit greatly changes at the moment when the motor (generator) operates. For this reason, the effect of the resistance (R ₁ ) between the battery and the motor (generator) increases, and the energy loss also increases. In addition, if the battery is fully charged and is charged with electric energy during regeneration, the battery is overcharged, which adversely affects the life of the battery. Therefore, when the battery is fully charged, electric energy cannot be regenerated. That is, there is a possibility that the regenerative braking cannot be sufficiently maintained.

  In the power supply device described in Patent Document 1, although a capacitor is used, a voltage variable device for boosting is arranged between the capacitor and the motor, and the electric energy is boosted and supplied to the motor. For this reason, energy loss occurs in the voltage variable device itself, so that the characteristic that the internal resistance of the capacitor is small is not directly and fully utilized.

  Therefore, the present invention aims to reduce the energy loss due to circuit resistance when supplying electric energy to the motor, reduce the load on the power storage device (for example, deterioration of the battery), and improve the sustainability of the regenerative brake. A possible vehicle power supply is provided.

A power supply device for a vehicle according to the present invention includes a first power storage device, a second power storage device capable of charging and discharging more rapidly than the first power storage device, and a voltage variable for controlling a voltage of the second power storage device to rise and fall Determining a device, a motor that operates by receiving electric energy from at least one of the first power storage device and the second power storage device, and a traveling state of the vehicle and a charged state of the first power storage device and the second power storage device. And a determination device for performing the determination. The + side of the second power storage device is directly connected to the + side of the first power storage device , and the − side is connected to the + side of the first power storage device via a voltage variable device. The voltage variable device increases a potential on the negative side of the second power storage device and reduces a potential difference between the positive side and the second state based on the traveling state and the charging state determined by the determining device; The voltage of the second power storage device is shifted to a second state in which the potential on the negative side of the power storage device is reduced to increase the potential difference with the positive side.

  For example, the determination device determines whether the vehicle is traveling on a downhill. When the vehicle is traveling on a downhill, the voltage variable device immediately reduces the negative potential of the second power storage device based on the state of charge of the first power storage device, and switches the second power storage device to the second power storage device. State. On the other hand, when the vehicle is not traveling on a downhill, the voltage variable device gradually increases the negative potential of the second power storage device based on the state of charge of the second power storage device, and causes the second power storage device to perform the second power storage operation. The device is caused to transition to the first state, or the potential on the minus side of the second power storage device is gradually reduced to cause the second power storage device to transition to the second state.

As an example, when the vehicle is traveling on a downhill, the voltage variable device sets the amount of decrease in the potential of the second power storage device per unit time per unit time to a lower limit value, and sets the potential of the negative power to the second power storage device. Lower. The lower limit value is set in advance based on the amount of current flowing between the first power storage device and the second power storage device. On the other hand, if the vehicle is not running on a downhill, the voltage varying device, the second power storage devices - than raising limit value increase amount per unit time on the side of the potential set in the small range - Instead of raising the side potential, or the second power storage devices - than the decrease threshold the amount of decrease per unit time on the side of the potential is set to the small extent - to lower the side of the potential ing. The rising limit value is set in advance based on the amount of current flowing between the second power storage device and the motor.

  Further, for example, when the motor is started, the determination device determines whether or not the stored electric energy of the second power storage device is zero. When the stored electric energy of the second power storage device is zero, the voltage variable device gradually lowers the negative potential of the second power storage device to cause the second power storage device to transition to the second state. .

  After the second power storage device has transitioned to the second state, the determination device determines whether the stored electric energy of the second power storage device is fully charged. When the second power storage device is fully charged, the voltage variable device gradually increases the negative potential of the second power storage device and causes the second power storage device to transition to the first state.

When transitioning the second power storage device to the first state, the voltage varying device, the second power storage device - in the range of small than raising limit value increase amount per unit time on the side of the potential Thus, the negative potential is increased. The rising limit value is set in advance based on the amount of current flowing between the second power storage device and the motor.

  Note that the second power storage device is provided on a circuit of the power supply device closer to the motor than the first power storage device.

  According to the power supply device for a vehicle of the present invention, it is possible to reduce the energy loss due to the circuit resistance when supplying electric energy to the motor, and to reduce the load on the power storage device (for example, deterioration of the battery). Further, for example, it is possible to improve the sustainability of the regenerative brake during traveling on a downhill.

FIG. 1 is a block diagram showing a schematic configuration of a vehicle power supply device according to an embodiment of the present invention. FIG. 2 is a control flowchart of the power supply device of the vehicle according to the embodiment of the present invention (from the start of traveling of the vehicle to before traveling downhill). FIG. 3 is a control flowchart of the power supply device of the vehicle according to the embodiment of the present invention (from the start of traveling downhill to after traveling).

  Hereinafter, a power supply device for a vehicle (hereinafter, simply referred to as a power supply device) according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. The power supply device of the present embodiment controls a power storage device mounted on a vehicle to supply electric energy to a motor for driving wheels, and moves (charges) electric energy generated by the motor during regeneration to the power storage device. . As the vehicle, any vehicle such as an electric vehicle (EV) or a plug-in hybrid electric vehicle (PHEV) that can run with a motor supplied with electric energy from a battery is applied.

  FIG. 1 is a block diagram of the power supply device 1. As shown in FIG. 1, the power supply device 1 includes two power storage devices 2 (a first power storage device 21 and a second power storage device 22), a voltage variable device 3, a motor 4, and an inverter 5. It is configured. The power storage device 2, the voltage variable device 3, the motor 4, and the inverter 5 are connected by a connection member (for example, a wire harness), and form a circuit 6 together with the connection member.

  The first power storage device 21 is configured by, for example, arranging a plurality of flat batteries (secondary batteries). In the assembly of these batteries, electric wires are attached to the electrode rows and wired in series. As the secondary battery, a lithium ion battery can be used, but is not limited thereto.

  The second power storage device 22 is configured to be able to charge and discharge more rapidly than the first power storage device 21. In the present embodiment, a capacitor is applied as the second power storage device 22 to the first power storage device 21 which is a battery assembly. The capacitor is, for example, an electric double layer capacitor, has a lower internal resistance than a battery, and has a potential difference (V1−V2; hereinafter) between a positive potential (hereinafter, referred to as V1) and a negative potential (hereinafter, referred to as V2). Electric energy can be stored according to the voltage of the second power storage device 22 as appropriate). However, other types of capacitors, large-capacity capacitors, and the like may be used as long as charging and discharging can be performed more rapidly than the first power storage device 21.

  The voltage variable device 3 controls the voltage of the second power storage device 22, specifically, the negative potential (V2). In the present embodiment, a DC / DC converter is applied as the voltage variable device 3. In this case, voltage variable device 3 causes the voltage of second power storage device 22 to transition between the first state and the second state. In the first state, V2 of second power storage device 22 is increased to reduce the potential difference from V1. In the first state, the storable electric energy (hereinafter, referred to as energy capacity) of second power storage device 22 decreases. On the other hand, in the second state, V2 of the second power storage device 22 is reduced to increase the potential difference from V1. In the second state, the energy capacity of second power storage device 22 increases.

  The motor 4 operates by receiving electric energy from the first power storage device 21 or the second power storage device 22. However, motor 4 may be operated by receiving electric energy from at least one of first power storage device 21 and second power storage device 22. Therefore, a mode in which motor 4 operates by receiving electric energy from both power storage devices 21 and 22 is also conceivable. For example, the motor 4 is a three-phase AC induction motor that operates with three-phase AC current supplied from the inverter 5. The activated motor 4 drives the drive wheels of the vehicle.

  Inverter 5 is interposed between first power storage device 21 and second power storage device 22 and motor 4, and connects power storage devices 21 and 22 and motor 4. For example, the inverter 5 converts the electric energy, specifically a DC current, stored in the first power storage device 21 and the second power storage device 22 into a three-phase AC current, and converts the three-phase AC current into the motor 4. To supply.

  In addition, the power supply device 1 includes a determination device 7 that determines a traveling state of the vehicle and a charging state of the power storage device 2. The determination device 7 includes various sensors and radars, and based on detected values such as the vehicle speed and acceleration, the depression angles of an accelerator pedal and a brake pedal, the inclination angle of the vehicle body, and the rotation speed of the motor 4, the running of the vehicle is performed. The state is determined, and the state of charge of the power storage device 2 is determined based on detected values such as the voltage and the amount of charge of the power storage device 2. For example, it is determined whether or not the vehicle is traveling on a slope by using an acceleration sensor or a brake sensor, or whether or not the power storage device 2 is fully charged by using a voltmeter or a charge meter.

  As described above, in the power supply device 1, the determination result of the determination device 7 is provided to the voltage variable device 3, and the voltage variable device 3 controls the raising and lowering of V2 of the second power storage device 22 based on the provided determination result. . The determination result may be given to an engine control unit (ECU) or a separately provided control device, and the voltage variable device 3 may be controlled by these.

  In the circuit 6, the second power storage device 22 has the + side connected in parallel with the first power storage device 21 and the − side connected in series to the voltage variable device 3. Therefore, transfer (charge / discharge) of electric energy between the first power storage device 21 and the second power storage device 22 is directly possible. For example, when the first power storage device 21 is in a fully charged state, when the minus potential (V2) of the second power storage device 22 is approximated from the potential of the first power storage device 21 to the ground (GND) potential, Since the energy capacity of the second power storage device 22 increases, electric energy can be directly transferred (charged) from the first power storage device 21 to the second power storage device 22. At this time, electric energy is lost during movement due to the resistance of the wire harness connecting the first power storage device 21 and the second power storage device 22. As a result, a free space larger than the charge amount of the second power storage device 22 can be secured in the first power storage device 21. The resistance (circuit resistance between the two power storage devices 21 and 22) R of the wire harness connecting the first power storage device 21 and the second power storage device 22 is constant.

  Further, second power storage device 22 is arranged on circuit 6 closer to motor 4 than first power storage device 21. Therefore, the wire harness connecting motor 4 and second power storage device 22 is shorter than the wire harness connecting motor 4 and first power storage device 21. Therefore, the resistance between motor 4 and second power storage device 22 is smaller than the resistance between motor 4 and first power storage device 21. Therefore, electric energy can be supplied from second power storage device 22 to motor 4 with higher priority than first power storage device 21.

  FIG. 2 and FIG. 3 show a flow of control performed by the power supply device 1. Hereinafter, the control by the power supply device 1 and its operation will be described in accordance with the flowcharts shown in FIGS. FIG. 2 is a control flow diagram from when the vehicle starts traveling to before traveling downhill, and FIG. 3 is a control flow diagram from when the vehicle starts traveling downhill until after traveling. .

  For example, when the ignition key is turned on and the motor 4 is started, as shown in FIG. 2, the determination device 7 determines whether or not the electric energy stored in the second power storage device 22 is zero. (S201). Note that the threshold value may be a predetermined remaining amount before the stored electric energy of the second power storage device 22 becomes zero instead of zero. When the electric energy stored in the second power storage device 22 is zero, V2 of the second power storage device 22 is gradually reduced by the voltage variable device 3 (S202).

  By gradually lowering V2 of second power storage device 22, the potential difference from V1 increases accordingly, and the energy capacity of second power storage device 22 gradually increases. Thereby, electric energy is transferred (charged) from the first power storage device 21 to the second power storage device 22 (S203). At that time, the voltage variable device 3 sets the amount of decrease per unit time within a range sufficiently smaller than the decrease limit value (δV / dt), and gradually decreases V2 without abruptly decreasing. . If the amount of current flowing from the first power storage device 21 to the second power storage device 22 becomes too large, the heat generation of the first power storage device 21 increases, which causes deterioration. Therefore, the amount of current flowing from the first power storage device 21 to the second power storage device 22 is suppressed, and the lower limit value is set as a potential difference value that does not cause deterioration due to heat generation of the first power storage device 21. . Further, by setting the lower limit value, the energy capacity of the second power storage device 22 gradually increases, so that the electric energy moves with a small amount of current, and the energy loss due to the wire harness during the movement is suppressed. Can be.

  In this state, the determination device 7 determines whether or not the second power storage device 22 is fully charged (S204). If the battery is not fully charged, charging of second power storage device 22 is continued. In this case, the second power storage device 22 may not be fully charged, but may have a smaller charge amount as the threshold.

  When the second power storage device 22 is fully charged, electric energy is supplied from the second power storage device 22 to the motor 4. In addition, also when it is determined in S201 that the electric energy stored in the second power storage device 22 is not zero, the electric energy is supplied to the motor 4 from the second power storage device 22 in the same manner. Accordingly, V1 of second power storage device 22 decreases.

  Therefore, in order to suppress a decrease in V1 of the second power storage device 22, V2 is increased by the voltage variable device 3 (S205), and electric energy is supplied from the second power storage device 22 to the motor 4 (S206). Thus, V1 of second power storage device 22 is maintained at approximately the same level as the + potential of first power storage device 21. Therefore, the transfer (charging) of electric energy from the first power storage device 21 to the second power storage device 22 is suppressed, and the continuous supply (discharge) of electric energy from the second power storage device 22 to the motor 4 is possible. Becomes At that time, the voltage variable device 3 sets the amount of increase per unit time within a range sufficiently smaller than the increase limit value (δV / dt), and gradually increases V2 without abrupt increase. . The rising limit value is set as a value of the potential difference that suppresses the amount of current flowing from second power storage device 22 to motor 4 and does not cause deterioration due to heat generation of second power storage device 22.

  Meanwhile, the determination device 7 determines whether or not the stored electric energy of the second power storage device 22 is zero (S207), and the electric energy from the second power storage device 22 to the motor 4 until the stored electric energy becomes zero. Supply is continued. When the stored electric energy of the second power storage device 22 becomes zero, electric energy is supplied from the first power storage device 21 to the motor 4 instead of the second power storage device 22 (S208).

  Next, as shown in FIG. 3, the determination device 7 determines whether the vehicle is traveling on a downhill (S209). When the vehicle is traveling on a downhill, the motor 4 generates electric energy (hereinafter, referred to as regenerative energy) at the time of deceleration, and uses the regenerative brake. At this point, the stored electric energy of the second power storage device 22 is zero, and the regenerative energy is moved (charged) to the second power storage device 22 (S210). Since the second power storage device 22 is arranged closer to the motor 4 than the first power storage device 21, the second power storage device 22 efficiently regenerates energy while suppressing energy loss due to the wire harness. Can be charged.

  Then, the regenerative energy is charged into the second power storage device 22, and the determination device 7 determines whether the first power storage device 21 is fully charged (S211). When the first power storage device 21 is not fully charged, the first power storage device 21 has a remaining amount of storable electric energy, and is in a state where regenerative energy can be charged. Therefore, the determination device 7 determines whether or not the regenerative energy is zero (S212). If the regenerative energy is not zero, the regenerative energy is moved (charged) to the first power storage device 21 (S213). Thereby, regenerative energy can be charged to first power storage device 21 without waste. The charging of the regenerative energy to the first power storage device 21 is continued until the first power storage device 21 is fully charged or the regenerative energy becomes zero (S211 and S212). When the regenerative energy becomes zero before the first power storage device 21 is fully charged (S212), it is assumed that the vehicle has gone downhill, and the subsequent control (S216 to S219) is performed (details will be described later). ).

  When the first power storage device 21 is fully charged, V2 of the second power storage device 22 is immediately reduced by the voltage variable device 3 (S214). Immediately lowering V2 of the second power storage device 22 causes a potential difference from V1 to increase, thereby increasing the energy capacity of the second power storage device 22 at a stretch. Thereby, the electric energy is immediately transferred (charged) from the first power storage device 21 to the second power storage device 22 (S215). At this time, the voltage variable device 3 sets the amount of decrease per unit time to the decrease limit value (δV / dt) to decrease V2, and brings the potential difference from V1 close to approximately V1 (V1−V2 ≒ V1). ). Therefore, electric energy is transferred from the first power storage device 21 to the second power storage device 22 with a large amount of current, so that the energy loss due to the wire harness connecting the power storage devices 21 and 22 can be increased. This allows the first power storage device 21 to immediately have a free space larger than the amount of movement (charging amount) to the second power storage device 22. Thereafter, it is again determined by the determination device 7 whether the vehicle is traveling on a downhill (S209). If the vehicle is traveling on a downhill, steps S210 to S215 are repeated.

  By causing the first power storage device 21 to have a free space while the vehicle is traveling downhill, regenerative energy can be moved (charged) to the first power storage device 21. As a result, regenerative energy at the time of deceleration can be prevented from being wasted, and the regenerative braking can be more sustained.

  On the other hand, when the vehicle is not traveling on a downhill (S209), that is, when the vehicle is traveling on a flat road or an uphill, the determination device determines whether or not the second power storage device 22 is fully charged. 7 (S216). When the second power storage device 22 is fully charged (specifically, when the second power storage device 22 is fully charged and the vehicle goes downhill), the second power storage device 22 Energy is supplied to the motor 4. Accordingly, the electric energy is supplied from the second power storage device 22 to the motor 4 (S218) while the voltage V2 of the second power storage device 22 is gradually increased by the voltage variable device 3 (S217). Thus, the vehicle can be smoothly accelerated. By supplying the electric energy during acceleration from the second power storage device 22, the load (deterioration) of the first power storage device 21 can be reduced.

  Meanwhile, the determination device 7 determines whether or not the stored electric energy of the second power storage device 22 is zero (S219), and the electric energy from the second power storage device 22 to the motor 4 until the stored electric energy becomes zero. Supply is continued. When the stored electric energy of the second power storage device 22 becomes zero, electric energy is supplied from the first power storage device 21 to the motor 4 instead of the second power storage device 22 (similar to S208).

  When the second power storage device 22 is not fully charged (specifically, when the vehicle has not traveled downhill from the start, or before the second power storage device 22 is fully charged, (Corresponding to a case where the vehicle has passed through a slope) (S216), in preparation for acceleration, V2 of second power storage device 22 is gradually reduced by voltage variable device 3, and the energy capacity is gradually increased (similar to S202). Thereafter, the control from S203 is repeated.

  As described above, according to power supply device 1 of the present embodiment, reduction of energy loss due to circuit resistance when electric energy is supplied to motor 4 and load on power storage device 2 (for example, deterioration of first power storage device 21) Can be reduced. Further, it is possible to improve the regenerative braking sustainability when the vehicle is traveling on a downhill.

  As described above, the embodiments of the present invention have been described. However, the above-described embodiments have been presented as examples, and are not intended to limit the scope of the invention. Such a novel embodiment can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  DESCRIPTION OF SYMBOLS 1 ... Power supply device, 2 ... Power storage device, 3 ... Voltage variable device, 4 ... Motor, 5 ... Inverter, 6 ... Circuit, 7 ... Judgment device, 21 ... First power storage device, 22 ... Second power storage device, R ... resistance between the first power storage device and the second power storage device, V1 ... potential on the + side of the second power storage device, V2 ... potential on the-side of the second power storage device.

Claims (8)

A first power storage device;
A second power storage device capable of more rapid charging and discharging than the first power storage device,
A voltage variable device that controls the voltage of the second power storage device up and down;
A motor that operates by receiving electric energy from at least one of the first power storage device and the second power storage device;
A determination device that determines a traveling state of the vehicle and a charged state of the first power storage device and the second power storage device,
The second power storage device has a positive side directly connected to the positive side of the first power storage device, a negative side connected to the positive side of the first power storage device via the voltage variable device,
The first voltage varying device increases a potential on the negative side of the second power storage device and reduces a potential difference between the positive side and the second power storage device based on the traveling state and the charging state determined by the determination device. A power supply device for a vehicle, wherein the voltage of the second power storage device is transited to a state and a second state in which the potential on the negative side of the second power storage device is reduced to increase the potential difference between the second power storage device and the + side. The determination device determines whether the vehicle is traveling downhill,
The voltage variable device,
When the vehicle is traveling on a downhill, the potential on the negative side of the second power storage device is immediately reduced based on the state of charge, and the second power storage device is shifted to the second state. ,
When the vehicle is not traveling on a downhill, the potential on the negative side of the second power storage device is gradually increased based on the state of charge, and the second power storage device transitions to the first state. The power supply device for a vehicle according to claim 1, wherein the second power storage device is caused to transition to the second state by gradually lowering a negative potential of the second power storage device. When the vehicle is traveling downhill,
The voltage variable device sets the amount of decrease per unit time of the negative potential of the second power storage device to a lower limit value to reduce the negative potential,
The power supply device for a vehicle according to claim 2, wherein the lower limit value is set in advance based on an amount of current flowing between the first power storage device and the second power storage device. If the vehicle is not traveling downhill,
The voltage variable device sets the amount of increase per unit time of the negative potential of the second power storage device within a range smaller than a rising limit value to increase the negative potential, or The amount of decrease in the potential of the second power storage device on the negative side per unit time is set within a range smaller than the lower limit value to reduce the potential on the negative side,
The rising limit value is set in advance based on the amount of current flowing between the second power storage device and the motor, and the lower limit value is set between the first power storage device and the second power storage device. The power supply device for a vehicle according to claim 2, wherein the power supply device is set in advance based on an amount of current flowing therebetween. When the motor is started, the determination device determines whether or not stored electric energy of the second power storage device is zero,
When the stored electric energy of the second power storage device is zero, the voltage variable device gradually lowers the negative potential of the second power storage device, and causes the second power storage device to be in the second state. The power supply device for a vehicle according to claim 1. The determination device determines whether or not the stored electric energy of the second power storage device is fully charged after the second power storage device has transitioned to the second state,
When the second power storage device is fully charged, the voltage variable device gradually increases the negative potential of the second power storage device, and transitions the second power storage device to the first state. The power supply device for a vehicle according to claim 4. The voltage variable device is configured such that, when the second power storage device is caused to transition to the first state, the amount of increase in the potential of the negative side of the second power storage device per unit time is within a range smaller than a rising limit value. To raise the negative potential,
The power supply device for a vehicle according to claim 6, wherein the rising limit value is set in advance based on an amount of current flowing between the second power storage device and the motor. The power supply device for a vehicle according to any one of claims 1 to 7, wherein the second power storage device is disposed on a circuit of the power supply device closer to the motor than the first power storage device.

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