Backup power supply system and moving vehicle

A backup power supply system supplies power to one or more loads in a situation where a power supply has caused a failure. The backup power supply system includes a plurality of power storage devices and a switching unit. The plurality of power storage devices are charged by the power supply. The switching unit switches electrical connection between the plurality of power storage devices to either a first state where the plurality of power storage devices are connected to the power supply in parallel or a second state where the plurality of power storage devices are connected to each other in series. The switching unit switches the electrical connection to the first state while the plurality of power storage devices are being charged and switches the electrical connection to the second state when the power supply has caused the failure.

CROSS-REFERENCE OF RELATED APPLICATIONS

The application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2021/018832, filed on May 18, 2021, which in turn claims the benefit of Japanese Patent Application No. 2020-131111, filed on Jul. 31, 2020, the entire disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to a backup power supply system and a moving vehicle. More particularly, the present disclosure relates to a backup power supply system for supplying power to one or more loads when a power supply has caused a failure and a moving vehicle including such a backup power supply system.

BACKGROUND ART

A boosting power supply circuit (voltage transformer circuit) of Patent Literature 1 supplies, when power stops being supplied from a battery, power from a lithium-ion battery (power storage device) as a backup power supply to various types of loads. The boosting power supply circuit boosts a DC voltage supplied from the lithium-ion battery and supplies the voltage thus boosted to the various types of loads.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2020-5481 A

SUMMARY OF INVENTION

The boosting power supply circuit boosts the output voltage of the lithium-ion battery and supplies the voltage thus boosted at a time to the various types of loads. Thus, the boosting power supply circuit needs to boost the voltage adaptively to a load having a higher minimum guaranteed operating voltage than any other one of the various types of loads and supply the voltage thus boosted at a time. This makes the voltage and current to be processed inside the boosting power supply circuit so high and so large that the noise generated inside the boosting power supply circuit may increase significantly.

It is therefore an object of the present disclosure to provide a backup power supply system and a moving vehicle, both of which are configured to reduce the noise to be generated.

A backup power supply system according to an aspect of the present disclosure supplies power to one or more loads in a situation where a power supply has caused a failure. The backup power supply system includes a plurality of power storage devices and a switching unit. The plurality of power storage devices are charged by the power supply. The switching unit switches electrical connection between the plurality of power storage devices to either a first state where the plurality of power storage devices are connected to the power supply in parallel or a second state where the plurality of power storage devices are connected to each other in series. The switching unit switches the electrical connection to the first state while the plurality of power storage devices are being charged and switches the electrical connection to the second state when the power supply has caused the failure.

A moving vehicle according to another aspect of the present disclosure includes the backup power supply system described above and a moving vehicle body. The moving vehicle body is equipped with the backup power supply system and the one or more loads.

The present disclosure achieves the advantage of enabling reducing the noise to be generated.

DESCRIPTION OF EMBODIMENTS

Embodiment

A backup power supply system1according to an exemplary embodiment will be described with reference to the accompanying drawings. Note that the embodiment to be described below is only an exemplary one of various embodiments of the present disclosure and should not be construed as limiting. Rather, the exemplary embodiment may be readily modified in various manners depending on a design choice or any other factor without departing from a true spirit and scope of the present disclosure.

As shown inFIG.1, the backup power supply system1may be installed in, for example, a vehicle9(refer toFIG.2). If the power supply2(such as a battery) has caused a failure, the backup power supply system1supplies power from a plurality of power storage devices C1to one or more loads3(e.g., a plurality of loads in this embodiment). This allows the one or more loads3to operate continuously with the power supplied from the plurality of power storage devices C1even if the power supply2has caused a failure. As used herein, the expression “the power supply2causes a failure” refers to a situation where the supply of power from the power supply2to the loads3is discontinued due to a failure, deterioration, or disconnection of the power supply2.

The backup power supply system1according to this embodiment includes the plurality of power storage devices C1and a switching unit12. The plurality of power storage devices C1are charged by the power supply2. The switching unit12switches electrical connection between the plurality of power storage devices C1to either a first state where the plurality of power storage devices C1are connected to the power supply2in parallel or a second state where the plurality of power storage devices C1are connected to each other in series. The switching unit12switches the electrical connection to the first state while the plurality of power storage devices C1are being charged and switches the electrical connection to the second state when the power supply2has caused a failure.

When charged, the plurality of power storage devices C1are connected to the power supply2in parallel. This allows the plurality of power storage devices C1to be charged with a lower voltage than in a situation where the plurality of power storage devices C1are connected to each other in series. Thus, there is no need for a charger circuit for charging the plurality of power storage devices C1to boost the voltage of the power supply2to a higher voltage, thus reducing the chances of the switching operation by the charger circuit generating noise and/or heat. In addition, in a situation where the power supply2has caused a failure, the plurality of power storage devices C1are connected to each other in series. This allows the plurality of power storage devices C1to output a higher voltage than in a situation where the plurality of power storage devices C1are connected to each other in parallel. Thus, there is no need for a voltage transformer circuit for transforming the output voltage of the plurality of power storage devices C1into a voltage required for the load3to boost the output voltage of the plurality of power storage devices C1to a higher voltage, thus reducing the chances of the switching operation by the voltage transformer circuit generating noise and/or heat. Consequently, the present disclosure enables providing a backup power supply system1with ability to reduce the noise to be generated and providing a backup power supply system1with ability to reduce the heat to be generated.

In addition, the backup power supply system1according to this embodiment is installed in a vehicle9including the power supply2and the plurality of loads3. That is to say, the vehicle9(moving vehicle) includes the backup power supply system1and a moving vehicle body91. The moving vehicle body91is equipped with the backup power supply system1and the one or more loads3. In the following description of embodiments, a situation where the backup power supply system1is installed in a vehicle9will be described as an example. However, this is only an example and should not be construed as limiting. Alternatively, the backup power supply system1may also be installed in any other suitable type of moving vehicle (such as an aircraft, a watercraft, or a railway train).

In this embodiment, there are a plurality of loads3to be supplied with power by the backup power supply system1in a situation where the power supply2has caused a failure. The plurality of loads3includes a first load31including an actuator and a second load32serving as a control system for controlling the actuator.

The first load31is a power system load3including an actuator. The first load31is a load3that satisfies a condition that the load3has greater power consumption (i.e., requires a larger operating current) than the second load32(hereinafter referred to as a “first condition”) and a condition that the load3has a lower minimum guaranteed operating voltage than the second load32(hereinafter referred to as a “second condition”). As used herein, the “operating current” refers to an electric current to be supplied to allow the load3to operate. Also, the “minimum guaranteed operating voltage” as used herein refers to a minimum required voltage to be applied for the load3to operate. That is to say, the first load31is a load which requires a larger operating current, but of which the operating voltage may decrease to a certain degree (i.e., which allows its operating voltage to decrease to a certain degree). Specifically, examples of the first load31include a braking device31A that produces braking force (as labeled “brake” inFIG.1) and an electronic power steering system (EPS)31B for electronically assisting the driver in steering.

The second load32is a control system load for controlling the actuator. The second load32is a plurality of loads3that satisfy a condition that the loads3have smaller power consumption (i.e., requires a smaller operating current) than the first load31and a condition that the loads3have a higher minimum guaranteed operating voltage than the first load31. That is to say, the second load32is a load which requires a smaller operating current, but which requires a relatively high operating voltage (i.e., which does not allow the operating voltage to decrease). Specifically, examples of the second load32include an electronic control unit (ECU)32A for braking (i.e., for controlling the braking device31A), an ECU32B for controlling the electronic power steering system31B, and an ECU32C for controlling an advanced driver assistance system (ADAS). Note that these are only examples of the first load31and the second load32and should not be construed as limiting.

(1.1) Detailed Description of Backup Power Supply System

As described above, the backup power supply system1includes the plurality of power storage devices C1and the switching unit12. Also, as shown inFIG.1, the backup power supply system1supplies the output power of the power supply2to the plurality of loads3while the power supply2is causing no failure and supplies the output power of the plurality of power storage devices C1to the plurality of loads3, instead of the output power of the power supply2, if the power supply2has caused a failure. That is to say, the backup power supply system1has a power supply path5, through which the output power of the power supply2is supplied to the plurality of loads3while the power supply2is causing no failure, and through which the output power of the plurality of power storage devices C1is supplied to the plurality of loads3if the power supply2has caused a failure. The backup power supply system1further includes a main switch10, a voltage detector circuit11, dropper power supply circuits13for charging, a voltage transformer circuit14, a switch15, a control circuit16, and a controller17.

Next, these constituent elements of the backup power supply system1will be described in detail one by one.

(1.1.1) Power Supply Path

The power supply path5is an electrical path through which the output power of the power supply2is supplied to the plurality of loads3and the plurality of power storage devices C1and through which the output power of the plurality of power storage devices C1is supplied to the plurality of loads3. The power supply path5includes a first power supply path51, a second power supply path52, a third power supply path53, and a fourth power supply path54.

The first power supply path51is a power supply path through which the output power of the power supply2is supplied to the plurality of loads3(as indicated by the arrow F1inFIG.1). That is to say, the backup power supply system1includes a power supply path5(first power supply path51) for supplying power from the power supply2to the one or more loads3(e.g., a plurality of loads3in this embodiment). The first power supply path51includes a main electrical path51aand a plurality of branch paths51bbranched from the main electrical path51a. The main electrical path51ais connected to an output unit of the power supply2. The plurality of branch paths51bare associated one to one with the plurality of loads3. The plurality of branch paths51bare branched from the main electrical path51aat multiple different points and connected to their associated loads3.

The second power supply path52(as indicated by the arrow F2inFIG.1) and the third power supply path53(as indicated by the arrow F3inFIG.1) are backup power supply paths, through which the output power of the plurality of power storage devices C1is supplied to the plurality of loads3. In this case, the plurality of (e.g., two in this embodiment) power storage devices C1includes a first power storage device C11to have the lower potential in the second state (where the two power storage devices C1are connected to each other in series) and a second power storage device C12to have the higher potential in the second state. The second power supply path52is a main power supply path for supplying power from both of the two power storage devices C1, which are connected to each other in series, to the loads3in a situation where the power supply2has caused a failure. The second power supply path52is an electrical path through which the output voltage of the two power storage devices C1is supplied to the loads3via the voltage transformer circuit14. The third power supply path53is a bypass path, through which power is supplied from the second power storage device C12having the lower potential to the one or more loads3. The third power supply path53(bypass path) is an electrical path for supplying the output voltage of the second power storage device C12to the loads3not via the voltage transformer circuit14.

The fourth power supply path54is an electrical path through which the output power of the power supply2is supplied to the power storage devices C1. The fourth power supply path54includes a first charge path541(as indicated by the arrow F41inFIG.1) for supplying the output power of the power supply2to the first power storage device C11and a second charge path542(as indicated by the arrow F42inFIG.1) for supplying the output power of the power supply2to the second power storage device C12. The dropper power supply circuits13are inserted into the fourth power supply path54. That is to say, the backup power supply system1further includes the dropper power supply circuits13for charging the plurality of power storage devices C1with the power supplied from the power supply2. The dropper power supply circuits13include a first dropper power supply circuit131inserted into the first charge path541and a second dropper power supply circuit132inserted into the second charge path542.

(1.1.2) Main Switch

The main switch10is inserted into the main electrical path51aof the first power supply path51. The main switch10is connected between the power supply2and a branch node between the first power supply path51and the fourth power supply path54. Also, the main switch10is connected between the power supply2and a node where the second power supply path52and the third power supply path53are confluent with the first power supply path51.

The main switch10includes, for example, two switching elements Q1, Q2which are inserted into the main electrical path51ain series. The switching elements Q1, Q2may be semiconductor switches (such as p-channel metal-oxide semiconductor field effect transistors (MOSFETs)), for example. These switching elements Q1, Q2have their drains electrically connected to each other and have their gates also electrically connected to each other and are switchable from a state where a current flows bidirectionally to a state where the current is cut off, or vice versa.

These switching elements Q1, Q2are turned ON and OFF in response to a power failure signal supplied from the voltage detector circuit11. Turning the switching elements Q1, Q2ON allows power to be supplied from the power supply2to the loads3through the first power supply path51and also allows power to be supplied from the power supply2to the power storage devices C1through the fourth power supply path54. Turning the switching elements Q1, Q2OFF causes the first power supply path51and the fourth power supply path54to be cut off.

(1.1.3) Voltage Detector Circuit

The voltage detector circuit11monitors the output voltage (e.g., 12.5 V in a normal state) of the power supply2. When finding the output voltage of the power supply2equal to or greater than a predetermined threshold value (of 9 V, for example), the voltage detector circuit11decides that the power supply2be causing no failure. On the other hand, when finding the output voltage of the power supply2less than the threshold value, the voltage detector circuit11decides that the power supply2have caused a failure and outputs the power failure signal indicating that a failure of the power supply2has been detected.

Note that the threshold value described above is only an example and may be changed as appropriate according to the output voltage of the power supply2or the minimum guaranteed operating voltage of the loads3, for example.

(1.1.4) Power Storage Devices

The power storage devices C1(namely, the first power storage device C11and the second power storage device C12) are provided as backup power supplies (i.e., either auxiliary or reserve power supplies) for the power supply2. In other words, the power storage devices C1are power supplies that may supply power to the plurality of loads3in a situation where the power supply2has caused a failure. The power storage devices C1may be, for example, electrical double layer capacitors (EDLCs) which may be charged and discharged rapidly. Each power storage device C1may be made up of two or more power storage devices (such as EDLCs) which are electrically connected to each other in parallel, in series, or in parallel and series. That is to say, each power storage device C1may be implemented as a parallel or series circuit of two or more power storage devices or a combination thereof.

(1.1.5) Dropper Power Supply Circuit

The dropper power supply circuits13include the first dropper power supply circuit131and the second dropper power supply circuit132. The first power storage device C11is connected between the output terminal of the first dropper power supply circuit131and a reference potential for the backup power supply system1. The second power storage device C12and a switching element Q4of the switching unit12are connected to each other in series between the output terminal of the second dropper power supply circuit132and the reference potential. The first dropper power supply circuit131is provided for the first charge path541. The second dropper power supply circuit132is provided for the second charge path542. The first dropper power supply circuit131and the second dropper power supply circuit132have the same circuit configuration. Thus, the following description will be focused on the first dropper power supply circuit131with description of the second dropper power supply circuit132omitted.

The first dropper power supply circuit131is a constant-voltage circuit for charging the first power storage device C11by lowering the output voltage (which is a first voltage of 12.5 V, for example) of the power supply2to a constant voltage (which is a second voltage of 12 V, for example), maintaining the constant voltage, and outputting the constant voltage to the first power storage device C11. The first dropper power supply circuit131may be, for example, a regulator circuit including a series circuit of a switching element Q7and a resistor R2, which are inserted into the first charge path541, an amplifier A2, and a switching element Q8. The switching elements Q7, Q8may be semiconductor switches, for example. In this embodiment, the switching element Q7may be a p-channel MOSFET, for example. The switching element Q8may be an NPN transistor, for example, and connected between the control terminal of the switching element Q7and the reference potential. The resistor R2is a resistor for detecting the charge current flowing through the first power storage device C11. The voltage across the resistor R2is supplied to the amplifier A2. The output terminal of the amplifier A2is connected to the control terminal of the switching element Q8. The first dropper power supply circuit131is configured to regulate the current for charging the first power storage device C11as the voltage across the resistor R2increases. This makes the voltage when the first power storage device C11is fully charged lower than the output voltage of the power supply2. Note that the circuit configuration of the first dropper power supply circuit131shown inFIG.1is only an example and may be modified as appropriate.

(1.1.6) Switching Unit

The switching unit12switches the electrical connection between the first power storage device C11and the second power storage device C12to either the first state where the first power storage device C11and the second power storage device C12are connected to the power supply2in parallel or the second state where the first power storage device C11and the second power storage device C12are connected to each other in series.

The switching unit12includes switching elements Q3, Q4and an inverter121.

The switching element Q3may be a semiconductor switching element (such as a MOSFET), for example. The switching element Q3is connected between the high-potential terminal of the first power storage device C11and the low-potential terminal of the second power storage device C12. An output signal of the inverter121, i.e., an inverted one of the output signal of the voltage detector circuit11, is supplied to the control terminal of the switching element Q3.

The switching element Q4may be a semiconductor switching element (such as a MOSFET), for example. The switching element Q4is connected between the low-potential terminal of the second power storage device C12and the reference potential. The output signal of the voltage detector circuit11is supplied to the control terminal of the switching element Q3.

Thus, while the voltage detector circuit11is not outputting the power failure signal, the switching element Q3turns OFF and the switching element Q4turns ON, thus switching the electrical connection between the first power storage device C11and the second power storage device C12to the first state where the first power storage device C11and the second power storage device C12are connected to the power supply2in parallel. In the first state, the first power storage device C11and the second power storage device C12that are electrically connected to the power supply2in parallel are charged with the power supplied from the power supply2. The first power storage device C11and the second power storage device C12are electrically connected to the power supply2in parallel, and therefore, are both charged to approximately 12 V.

On the other hand, while the voltage detector circuit11is outputting the power failure signal, the switching element Q3turns ON and the switching element Q4turns OFF, thus switching the electrical connection between the first power storage device C11and the second power storage device C12to the second state where the first power storage device C11and the second power storage device C12are connected to each other in series. In the second state, a sum of the respective voltages of the first power storage device C11and the second power storage device C12(i.e., a voltage of approximately 24 V) is output from the first power storage device C11and the second power storage device C12which are connected to each other in series.

Note that this circuit configuration of the switching unit12is only an example and should not be construed as limiting. Rather, the circuit configuration of the switching unit12may be modified as appropriate as long as the electrical connection between the first power storage device C11and the second power storage device C12may be switched to either the first state or the second state.

(1.1.7) Voltage Transformer Circuit

The voltage transformer circuit14is a constant-voltage circuit for transforming the output voltage of the first power storage device C11and the second power storage device C12that are connected to each other in series into a constant voltage, maintaining the constant voltage, and outputting the constant voltage thus maintained. The voltage transformer circuit14is provided for the second power supply path52. That is to say, the voltage transformer circuit14transforms the output voltage of the plurality of power storage devices C1that are connected to each other in series into an output voltage adapted to the one or more loads3in a situation where the power supply2has caused a failure (i.e., at the time of discharging).

The voltage transformer circuit14may be, for example, a step-up DC/DC converter. The voltage transformer circuit14includes switching elements Q9, Q10, a Zener diode ZD1, an inductor L1, a diode D3, a capacitor C2, and a control unit141. The switching elements Q9, Q10may be semiconductor switching elements (such as MOSFETs), for example. The switching element Q9and the Zener diode ZD1are connected to each other in series between the high-potential terminal of the second power storage device C12and the reference potential. The inductor L1and the switching element Q10are connected to each other in series between the two terminals of the Zener diode ZD1. The diode D3and the capacitor C2are connected to each other in series between the two terminals of the switching element Q10.

The control unit141controls the ON/OFF states of the switching elements Q9, Q10.

While receiving no output instruction from the control circuit16, the control unit141controls the switching element Q9to OFF state to make the switching element Q10stop performing the switching operation. In this manner, the control unit141stops the supply of power from the voltage transformer circuit14to the loads3.

On the other hand, while receiving an output instruction from the control circuit16, the control unit141controls the switching element Q9to ON state and performs a PWM control on the switching element Q10. When the switching element Q9turns ON, a voltage is applied from the first power storage device C11and the second power storage device C12which are connected to each other in series to the Zener diode ZD1via the switching element Q9. Then, the control unit141performs a PWM control on the switching element Q10, thereby transforming the voltage across the Zener diode ZD1into a predetermined voltage value and outputting the voltage value. The voltage transformer circuit14keeps the voltage slightly higher than the minimum guaranteed operating voltage (of 11.5 V, for example) of the loads3and outputs the voltage. This allows, even if the output voltage of the first power storage device C11and the second power storage device C12that are connected to each other in series decreases, the voltage output from the first power storage device C11and the second power storage device C12to the loads3to be maintained at a voltage higher than the minimum guaranteed operating voltage.

The switch15is inserted into the third power supply path53(bypass path).

The switch15may include, for example, two switching elements Q11, Q12, which are inserted in series into the third power supply path53. The switching elements Q11, Q12may be semiconductor switches (such as p-channel MOSFETs), for example. These switching elements Q11, Q12have their drains electrically connected to each other and have their gates also electrically connected to each other and are switchable from a state where a current flows bidirectionally to a state where the current is cut off, or vice versa.

These switching elements Q11, Q12are turned ON and OFF in response to a control signal supplied from the control circuit16. Turning the switching elements Q1, Q2ON allows power to be supplied from the first power storage device C11to the loads3through the third power supply path53. Turning the switching elements Q11, Q12OFF causes the third power supply path53to be cut off. If the power supply2has caused a failure, the switch15will remain ON until the voltage transformer circuit14is activated and will turn OFF when the voltage transformer circuit14is fully activated.

(1.1.9) Control Circuit

The control circuit16is implemented as, for example, a microcomputer including a processor and a memory. That is to say, the control circuit16is implemented as a computer system including a processor and a memory. The computer system performs the function of the control circuit16by making the processor execute an appropriate program. The program may be stored in advance in the memory. Alternatively, the program may also be downloaded via a telecommunications line such as the Internet or distributed after having been stored in a non-transitory storage medium such as a memory card.

In response to the power failure signal supplied from the voltage detector circuit11, control circuit16controls not only the operation of the voltage transformer circuit14but also the ON/OFF states of the switch15. In this embodiment, when the power supply2has caused a failure, the control circuit16starts to activate the voltage transformer circuit14and controls the switch15to keep the switch15ON until the voltage transformer circuit14is activated and to turn the switch15OFF when the voltage transformer circuit14is fully activated.

While the voltage detector circuit11is outputting no power failure signal, the control circuit16controls the switch15to OFF state to make the voltage transformer circuit14stop performing the voltage transformation operation. Thus, while the voltage detector circuit11is outputting no power failure signal, the second power supply path52and the third power supply path53are cut off.

When the voltage detector circuit11outputs the power failure signal, the control circuit16gives an output instruction to the voltage transformer circuit14, thereby activating the voltage transformer circuit14. On receiving the output instruction, the control unit141of the voltage transformer circuit14turns the switching element Q9ON and starts performing a PWM control on the switching element Q10.

In addition, until a predetermined time (of 100 milliseconds (ms), for example) passes since the timing when the control circuit16received the power failure signal from the voltage detector circuit11, the control circuit16keeps the switch15ON to allow power to be supplied from the first power storage device C11having the lower potential to the loads3through the third power supply path53. In this case, the predetermined time is set to be slightly longer than the time it takes for the voltage transformer circuit14to be ready to output a voltage equal to or higher than the minimum guaranteed operating voltage (i.e., for the voltage transformer circuit14to be fully activated) since the voltage transformer circuit14started to be activated. This allows, when the output voltage of the voltage transformer circuit14is lower than the minimum guaranteed operating voltage, the power to be supplied from the first power storage device C11having the lower potential to the loads3through the third power supply path53. Thereafter, when the predetermined time passes since the timing when the control circuit16received the power failure signal from the voltage detector circuit11, the control circuit16turns the switch15OFF, cuts off the third power supply path53, and has the power supplied from the voltage transformer circuit14to the loads3.

The controller17is implemented as, for example, a microcomputer including a processor and a memory. That is to say, the controller17is implemented as a computer system including a processor and a memory. The computer system performs the function of the controller17by making the processor execute an appropriate program. The program may be stored in advance in the memory. Alternatively, the program may also be downloaded via a telecommunications line such as the Internet or distributed after having been stored in a non-transitory storage medium such as a memory card.

The controller17performs the function of a selection unit171that selects, according to the status of use of a target device (e.g., a vehicle9in this embodiment) provided with the plurality of loads3, any one of the plurality of loads3as a target load to which power is to be supplied (hereinafter simply referred to as a “target load3”). The controller17receives, from an ECU4of the vehicle9, notification information indicating the status of use of the vehicle9. The selection unit171selects, in accordance with the notification information provided by the ECU4, the target load3. The backup power supply system1according to this embodiment further includes a plurality of switches Q20-Q24for selectively supplying power to the plurality of loads3. These switches Q20-Q24are respectively inserted into a branch path51bleading to the braking device31A, a branch path51bleading to the electronic power steering system31B, a branch path51bleading to the ECU32A for braking, a branch path51bleading to the ECU32B for EPS, and a branch path51bleading to the ECU32C for ADAS. Each of these switches Q20-Q24may be a semiconductor switch (such as a p-channel MOSFET), for example. Turning these switches Q20-Q24ON or OFF under the control of the controller17makes the branch paths51bprovided with the switch Q20-Q24electrically conductive or non-conductive. This allows the supply of the power from the power storage devices C1to the loads3connected to the branch paths51bto be selectively provided or cut off.

While the power supply2is causing no failure, the controller17turns these switches Q20-Q24ON to allow power to be supplied from the power supply2to all the loads3.

In a situation where the power supply2has caused a failure, the selection unit171selects, in accordance with the notification information provided by the ECU4, the target load3. Then, the controller17turns ON only a switch associated with the target load3out of the switches Q20-Q24to allow power to be supplied from the power storage devices C1to only the target load3.

In this embodiment, the selection unit171may select, for example, the target load3in the following manner according to the status of use of the vehicle9. If the vehicle9is being driven autonomously when the power supply2has caused a failure, then the selection unit171selects all the loads3as target loads and the controller17controls all the switches Q20-Q24to ON state. This allows power to be supplied from the power storage devices C1to all the loads3. As a result, if the vehicle9is being driven autonomously when the power supply2has caused a failure, then power is supplied from the power storage devices C1to all the loads3participating in autonomous driving.

On the other hand, unless the vehicle9is being driven autonomously when the power supply2has caused a failure, the controller17controls the switch Q20to ON state and controls the switches Q21-Q24to OFF state. This allows cutting off the supply of power from the power storage devices C1to the loads3connected to the switches Q21-Q24. As a result, power is supplied from the power storage devices C1to the load (such as the braking device31A) engaged in braking the vehicle9and requiring the driver's participation. On the other hand, no power is supplied from the power storage devices C1to the other loads (such as the electronic power steering system and its ECU and the ECU of the braking device) not engaged in braking the vehicle9and not requiring the driver's participation.

(1.2) Description of Operation

Next, it will be described with reference toFIGS.1-7mainly how the backup power supply system1operates.

(1.2.1) When Power Supply is Operating Properly

While the power supply2is causing no failure, the voltage detector circuit11does not output the power failure signal. Thus, the main switch10turns ON and the control circuit16controls the switch15to OFF state to deactivate the voltage transformer circuit14. Thus, the output power of the power supply2is suppled through the first power supply path51(specifically, the main electrical path51aand the plurality of branch paths51b) to the plurality of loads3(namely, the first load31and the second load32).

Also, while the power supply2is causing no failure, the switching element Q3of the switching unit12turns OFF and the switching element Q4thereof turns ON, thus making the first power storage device C11and the second power storage device C12electrically connected to the power supply2in parallel. As a result, the first dropper power supply circuit131and the second dropper power supply circuit132charge the first power storage device C11and the second power storage device C12while lowering the output voltage of the power supply2. InFIG.3, the arrows F21and F22indicate the current paths in such a situation. As can be seen, at the time of charging, the plurality of power storage devices C1are connected to the power supply2in parallel and are charged by the dropper power supply circuits13. Thus, the voltage of the plurality of power storage devices C1that have been fully charged becomes equal to or lower than the output voltage of the power supply2. At this time, the first dropper power supply circuit131and the second dropper power supply circuit132that charge the first power storage device C11and the second power storage device C12, respectively, do not perform any switching operation, thus reducing the heat and noise involved with the switching operation.

(1.2.2) When Power Supply has Caused Failure

When the power supply2has caused a failure and the voltage detector circuit11outputs the power failure signal, the main switch10turns OFF and the first power supply path51and the fourth power supply path54are cut off. In addition, when the voltage detector circuit11outputs the power failure signal, the switching element Q3of the switching unit12turns ON and the switching element Q4thereof turns OFF, thus making the first power storage device C11and the second power storage device C12connected to each other in series. Meanwhile, upon receiving the power failure signal from the voltage detector circuit11, the control circuit16outputs an activate instruction to the control unit141of the voltage transformer circuit14to activate the voltage transformer circuit14. In this case, it takes some time for the voltage transformer circuit14to output a voltage equal to or higher than the minimum guaranteed operating voltage since the voltage transformer circuit14has started its transformation operation (i.e., it takes some time to fully activate the voltage transformer circuit14). Therefore, the control circuit16controls the switch15to keep the switch15ON until a predetermined time passes since the timing when the power failure signal was received. If the switch15turns ON, the third power supply path53becomes electrically conductive. This allows power to be supplied from the first power storage device C11having the lower potential to the loads3through the third power supply path53. At this time, a current flows from the first power storage device C11to the plurality of loads3along the path indicated by the arrow F23inFIG.4. The first power storage device C11has been charged to a voltage equal to or higher than the minimum guaranteed operating voltage. This allows the loads3to be operated with power supplied from the first power storage device C11to the loads3until the voltage transformer circuit14is fully activated, thus reducing the chances of the supply of the output voltage to the loads3being cut off.

Thereafter, when a predetermined time passes since the timing when the power supply2caused the failure, the control circuit16turns the switch15OFF and the voltage transformer circuit14lowers the output voltages of the first power storage device C11and the second power storage device C12and supplies the output voltage thus generated to the loads3. At this time, a current flows from the voltage transformer circuit14to the loads3along the path indicated by the arrow F24inFIG.4. In this case, if the power supply2has caused a failure, the first power storage device C11and the second power storage device C12are connected to each other in series, thus making the output voltages of the first power storage device C11and the second power storage device C12higher than the minimum guaranteed operating voltage of the loads3. This allows the voltage transformer circuit14to supply an output voltage, generated by lowering the output voltages of the first power storage device C11and the second power storage device C12, to the loads3. This enables reducing the amount of current flowing through the primary circuit section of the voltage transformer circuit14, thus reducing the heat and noise to be generated by the switching element Q10when the voltage transformer circuit14performs the switching operation.

In this case, a diode, which causes a current to flow in the direction in which power is supplied to the one or more loads3, is inserted into the third power supply path53(bypass path). In this embodiment, a parasitic diode of a MOSFET serving as the switching element Q12functions as the diode causing a current to flow in the direction in which power is supplied to the loads3. The parasitic diode of the MOSFET serving as the switching element Q12substantially prevents a current from flowing in the opposite direction from the direction in which power is supplied from the first power storage device C11to the loads3. This may reduce the chances of the power that should be supplied to the loads3flowing through the first power storage device C11to cause shortage of the power to be supplied to the loads3. Optionally, in this embodiment, another diode which causes a current to flow in the direction in which power is supplied to the loads3may be connected to the third power supply path53separately from the parasitic diode of the MOSFET serving as the switching element Q12. This may substantially prevent a current from flowing in the opposite direction.

Note that on the first power supply path51, a diode D4is connected between the branch path51bto which the first load31is connected and the branch path51bto which the second load32is connected. Thus, the diode D4may prevent, in a situation where power is supplied from the power storage devices C1to the second load32through either the second power supply path52or the third power supply path53, the power supplied to the second load32from flowing backward through the first power supply path51into the first load31.

(1.2.3) Operation of Selecting Target Load

As described above, in the backup power supply system1according to this embodiment, the selection unit171of the controller17selects the target load3in accordance with the notification information provided by the ECU4of the vehicle9.

For example, if the power supply2has caused a failure in a vehicle9traveling at a predetermined speed (e.g., 60 km/h), then the selection unit171turns the switch Q20ON and turns the switches Q21-Q24OFF to supply power from the power storage device C1to only the braking device31A (refer toFIG.6). Even so, until the voltage transformer circuit14is fully activated since the timing when the power supply2caused the failure, power is also supplied from the first power storage device C11to the braking device31A through the third power supply path53(bypass path) (i.e., along the path indicated by the arrow F25inFIG.6). Then, when the voltage transformer circuit14is fully activated, power is supplied from the voltage transformer circuit14to the braking device31A through the second power supply path52(i.e., along the path indicated by the arrow F26inFIG.6).

In this embodiment, a constant voltage equal to or higher than the minimum guaranteed operating voltage is supplied continuously to the loads3for a certain time (of 6 seconds, for example) since the power supply2caused the failure. The certain time may be, for example, longer than the time it takes for the vehicle9traveling at the predetermined speed (of 60 km/h, for example) to stop safely on the same lane. This allows, even if the power supply2has caused a failure while the vehicle9is traveling at the predetermined speed, the driver to stop the vehicle9safely.

In addition, the backup power supply system1also allows, when parking the vehicle9by remote control (i.e., when making so-called “remote parking”) while the power supply2of the vehicle9is operating properly, for example, power to be supplied from the voltage transformer circuit14to the braking device31A through the second power supply path52. Stated otherwise, only when the power supply2is operating properly and power may be supplied from the backup power supply system1to the braking device31A, the vehicle9may make remote parking. That is to say, the vehicle9may make remote parking only when a path for supplying power from the power supply2to the braking device31A (i.e., the path indicated by the arrow F27) and the path for supplying power from the voltage transformer circuit14to the braking device31A (i.e., the path indicated by the arrow F28) are both secured as shown inFIG.7. In that case, the selection unit171of the controller17allows, in accordance with the notification information provided by the ECU4that remote parking is going to be made, the power to be supplied from the power storage device C1to only the braking device31A by turning the switch Q20ON and turning the switches Q21-Q24OFF. Then, the controller17controls the switching unit12to switch the electrical connection to the second state where the first power storage device C11and the second power storage device C12are connected to each other in series, outputs a control signal to the control circuit16to control the switch15to OFF state, and activates the voltage transformer circuit14. This makes power suppliable from the voltage transformer circuit14to the braking device31A, thus allowing the vehicle9to make remote parking.

If the power supply2causes a failure while the vehicle9is making remote parking, then power starts to be supplied from the voltage transformer circuit14to the braking device31A (along the path indicated by the arrow F28inFIG.7), thus allowing the driver to stop the vehicle9safely.

Note that if the voltage transformer circuit14does not start to be activated until the power supply2has caused a failure while the vehicle9is making remote parking, then the controller17may control the switch15to ON state to supply power from the first power storage device C11to the braking device31A until the voltage transformer circuit14is fully activated. In that case, when the voltage transformer circuit14is fully activated, the controller17may control the switch15to OFF state to supply power from the voltage transformer circuit14to the braking device31A.

Note that the backup power supply system1still allows the vehicle9to make remote parking even if the vehicle9has not been used for a predetermined period (of 75 days, for example). The power storage devices C1discharge when left unused for a long time. However, the charging and discharging performance thereof is set to make the braking device31A operable even after the predetermined period has passed.

Next, variations of the exemplary embodiment will be enumerated one after another. Note that the variations to be described below may be adopted in combination as appropriate. The following description of variations will be focused on differences from the exemplary embodiment described above. Any constituent element of the variations, having the same function as a counterpart of the exemplary embodiment described above, will be designated by the same reference numeral as that counterpart's, and description thereof will be omitted herein.

In the exemplary embodiment described above, the power storage devices C1may each be a secondary battery such as a lithium-ion capacitor (LIC) or a lithium-ion battery (LIB). In the lithium-ion capacitor, the cathode thereof may be made of the same material (such as activated carbon) as an EDLC and the anode thereof may be made of the same material (e.g., a carbon material such as graphite) as an LIB.

Also, the power storage device C1does not have to be an EDLC but may also be an electrochemical device having a configuration to be described below. As used herein, the “electrochemical device” includes a cathode member, an anode member, and a nonaqueous electrolyte solution. The cathode member includes a cathode current collector and a cathode material layer supported by the cathode current collector and containing a cathode active material. The cathode material layer contains a conductive polymer serving as a cathode active material for doping and de-doping an anion (dopant). The anode member includes an anode material layer containing an anode active material. The anode active material may be, for example, a material that advances an oxidation-reduction reaction involving occlusion and release of a lithium ion. Specifically, examples of the anode active material include carbon materials, metal compounds, alloys, and ceramics. The nonaqueous electrolyte solution may have, for example, lithium-ion conductivity. A nonaqueous electrolyte solution of this type includes a lithium salt and a nonaqueous solution that dissolves the lithium salt. An electrochemical device having such a configuration has a higher energy density than an electrical double layer capacitor, for example.

Furthermore, in the embodiment described above, the voltage transformer circuit14includes a step-up DC/DC converter. However, the circuit configuration of the voltage transformer circuit14may be modified as appropriate as long as the voltage transformer circuit14may transform the input voltage into a voltage value adapted to the loads3. For example, the voltage transformer circuit14may include a step-up/step-down DC/DC converter.

Furthermore, in the exemplary embodiment described above, the power storage devices C1are charged with the output of the dropper power supply circuits13. However, the circuit for supplying a charge current to the power storage devices C1does not have to be the dropper power supply circuits13. The circuit for supplying the charge current to the power storage devices C1is preferably a circuit other than a switching power supply circuit and may be a series regulator circuit or a circuit including a current limiting resistor connected between the power supply2and the power storage devices C1.

Furthermore, in the exemplary embodiment described above, each of the first load31and the second load32is a group of loads (i.e., includes a plurality of loads). However, this is only an example and should not be construed as limiting. Alternatively, each of the first load31and the second load32may be a single load. Still alternatively, at least one of the first load31or the second load32may be a group of loads.

Furthermore, in the exemplary embodiment described above, the first load31satisfies both the first condition and the second condition in contrast to the second load32. However, this is only an example and should not be construed as limiting. Alternatively, the first load31may satisfy at least one of the first condition or the second condition. Note that the first condition is that the load have a relatively large power consumption (i.e., require a relatively large operating current). The second condition is that the load require a relatively low minimum guaranteed operating voltage.

Furthermore, in the exemplary embodiment described above, the target device including the plurality of loads3is a vehicle9(moving vehicle). However, the target device does not have to be a vehicle9(moving vehicle) but may also be a piece of electrical equipment for use in a facility, for example.

As can be seen from the foregoing description, a backup power supply system (1) according to a first aspect supplies power to one or more loads (3) in a situation where a power supply (2) has caused a failure. The backup power supply system (1) includes a plurality of power storage devices (C1) and a switching unit (12). The plurality of power storage devices (C1) are charged by the power supply (2). The switching unit (12) switches electrical connection between the plurality of power storage devices (C1) to either a first state where the plurality of power storage devices (C1) are connected to the power supply (2) in parallel or a second state where the plurality of power storage devices (C1) are connected to each other in series. The switching unit (12) switches the electrical connection to the first state while the plurality of power storage devices (C1) are being charged and switches the electrical connection to the second state when the power supply (2) has caused the failure.

According to this aspect, when charged, the plurality of power storage devices (C1) are connected to the power supply (2) in parallel. This allows the plurality of power storage devices (C1) to be charged with a lower voltage than in a situation where the plurality of power storage devices (C1) are connected to each other in series. Thus, there is no need for a charger circuit for charging the plurality of power storage devices (C1) to boost the voltage of the power supply (2) to a higher voltage, thus reducing the chances of the switching operation by the charger circuit generating noise and/or heat. In addition, when the power supply (2) has caused a failure, the plurality of power storage devices (C1) are connected to each other in series. This allows the plurality of power storage devices (C1) to output a higher voltage than in a situation where the plurality of power storage devices (C1) are connected to each other in parallel. Thus, there is no need for a voltage transformer circuit for transforming the output voltage of the plurality of power storage devices (C1) into a voltage required for the loads (3) to boost the output voltage of the plurality of power storage devices (C1) to a higher voltage, thus reducing the chances of the switching operation by the voltage transformer circuit generating noise and/or heat. Consequently, the present disclosure enables providing a backup power supply system (1) with ability to reduce the noise to be generated and providing a backup power supply system (1) with ability to reduce the heat to be generated.

In a backup power supply system (1) according to a second aspect, which may be implemented in conjunction with the first aspect, the plurality of power storage devices (C1) includes: a first power storage device (C11) to have a lower potential in the second state; and a second power storage device (C12) to have a higher potential in the second state. The backup power supply system (1) further includes a bypass path (53), through which power is supplied from the first power storage device (C11) to the one or more loads (3) in a situation where the power supply (2) has caused the failure.

This aspect enables supplying power from the first power storage device (C11) to the one or more loads (3) through the bypass path (53).

In a backup power supply system (1) according to a third aspect, which may be implemented in conjunction with the second aspect, a diode is inserted into the bypass path (53). The diode allows a current to flow in a direction in which power is supplied to the one or more loads (3).

This aspect enables reducing the chances of a current flowing through the bypass path (53) in an opposite direction from the direction in which the power is supplied.

A backup power supply system (1) according to a fourth aspect, which may be implemented in conjunction with the second or third aspect, further includes a voltage transformer circuit (14) and a switch (15). The voltage transformer circuit (14) transforms, in a situation where the power supply (2) has caused the failure, an output voltage of the plurality of power storage devices (C1) that are connected to each other in series into an output voltage adapted to the one or more loads (3). The switch (15) is inserted into the bypass path (53). In a situation where the power supply (2) has caused the failure, the switch (15) remains ON until the voltage transformer circuit (14) is activated and turns OFF when the voltage transformer circuit (14) is fully activated.

According to this aspect, power is supplied continuously through the bypass path (53) to the one or more loads (3) until the voltage transformer circuit (14) is activated. This may reduce the chances of the supply of power to the one or more loads (3) being cut off.

A backup power supply system (1) according to a fifth aspect, which may be implemented in conjunction with the fourth aspect, further includes a control circuit (16). The control circuit (16) starts activating the voltage transformer circuit (14) when the power supply (2) has caused the failure and controls the switch (15) to keep the switch (15) ON until the voltage transformer circuit (14) is activated and to turn the switch (15) OFF when the voltage transformer circuit (14) is fully activated.

According to this aspect, power is supplied continuously through the bypass path (53) to the one or more loads (3) until the voltage transformer circuit (14) is activated. This may reduce the chances of the supply of power to the one or more loads (3) being cut off.

A backup power supply system (1) according to a sixth aspect, which may be implemented in conjunction with any one of the first to fifth aspects, further includes dropper power supply circuits (13). The dropper power supply circuits (13) charge the plurality of power storage devices (C1) with the power supplied from the power supply (2).

According to this aspect, the dropper power supply circuits (13) charge the plurality of power storage devices (C1). This may reduce, compared to a situation where the plurality of power storage devices (C1) are charged with a voltage boosted by a switching power supply, the chances of the switching power supply generating noise and/or heat.

In a backup power supply system (1) according to a seventh aspect, which may be implemented in conjunction with any one of the first to sixth aspects, the one or more loads (3) include a plurality of loads (3). The backup power supply system (1) further includes a selection unit (171). The selection unit (171) selects, according to a status of use of a target device (9) provided with the plurality of loads (3), any one of the plurality of loads (3) as a target load to which power is to be supplied.

According to this aspect, power is supplied to only the load (3) selected according to the status of use of the target device (9). This enables supplying power for a longer time than in a situation where power is supplied to all of the plurality of loads (3).

In a backup power supply system (1) according to an eighth aspect, which may be implemented in conjunction with the seventh aspect, the plurality of loads (3) includes: a first load (31) including an actuator; and a second load (32) serving as a control system to control the actuator.

This aspect enables selecting, according to the status of use of the target device (9), the target load (3) from the first load (31) and the second load (32).

A backup power supply system (1) according to a ninth aspect, which may be implemented in conjunction with any one of the first to eighth aspects, further includes a power supply path (51) through which power is supplied from the power supply (2) to the one or more loads (3).

This aspect enables supplying power from the power supply (2) to the one or more loads (3) through the power supply path (51).

A moving vehicle (9) according to a tenth aspect includes the backup power supply system (1) according to any one of the first to ninth aspects and a moving vehicle body (91). The moving vehicle body (91) is equipped with the backup power supply system (1) and the one or more loads (3).

This aspect enables providing a moving vehicle (9) with the ability to reduce the noise to be generated.

Note that these are not the only aspects of the present disclosure but various configurations (including variations) of the backup power supply system (1) according to the exemplary embodiment described above may also be implemented as a method for controlling the backup power supply system (1), a (computer) program, or a non-transitory storage medium that stores the program thereon.

Note that the constituent elements according to the second to eighth aspects are not essential constituent elements for the backup power supply system (1) but may be omitted as appropriate.

REFERENCE SIGNS LIST