Power supply system and control program

Abstract

A power supply system (10) comprises: storage batteries (31, 61); and conversion circuits (40, 70) that convert power input from the storage batteries to primary-side terminal pairs (41, 42, 71, 72) by driving switching elements and output the power from secondary-side terminal pairs (47, 48, 77, 78). The positive electrode and the negative electrode of the storage battery are respectively connected to the primary-side terminal pair of the conversion circuit, and the storage battery is connected in series to the secondary-side terminal pair of the conversion circuit. The power supply system includes connection maintaining circuits (49, 79) for maintaining the secondary-side terminal pairs in a connected state.

Description

Power supply system and control program CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-108739, filed on June 30, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a power supply system.

[0003] For example, there is a storage battery management system that includes a plurality of storage batteries and a converter that controls the charge / discharge current of each storage battery (see Patent Document 1). The storage battery management system described in Patent Document 1 aims to improve the efficiency of the entire system by distributing a total current command value for the plurality of storage batteries to each converter according to the state of charge (SOC) of the storage batteries, the output voltage of the storage batteries, the total charge / discharge power amount of the storage batteries, the temperature characteristics of the storage batteries, etc.

[0004] JP 2014-207790 A

[0005] In the storage battery management system described in Patent Document 1, in order to output power from the storage batteries, the converter (conversion circuit) connected to each storage battery must be switched on and off. Therefore, even when there is no need to step up or down the voltage of the storage batteries when outputting power from the storage batteries, switching loss occurs in the converter, and there is still room for improvement in terms of improving the efficiency of the system.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its main object is to reduce losses during power supply in a power supply system including a storage battery and a conversion circuit.

[0007] A first means for solving the above problem is a power supply system comprising a storage battery and a conversion circuit that converts power input from the storage battery to a primary terminal pair by driving a switching element and outputs the converted power from a secondary terminal pair, wherein the positive and negative electrodes of the storage battery are respectively connected to the primary terminal pair of the conversion circuit, the storage battery is connected in series to the secondary terminal pair of the conversion circuit, and the system further comprises a connection maintaining circuit that maintains the secondary terminal pair in a connected state.

[0008] According to the above configuration, the power supply system includes a storage battery and a conversion circuit that converts power input from the storage battery to a pair of primary terminals by driving a switching element and outputs the converted power from a pair of secondary terminals. Therefore, the power supply system can convert the power input from the storage battery to the pair of primary terminals by driving a switching element in the conversion circuit and output the converted power from the pair of secondary terminals. When converting power using the conversion circuit, switching losses (turn-on losses and turn-off losses) occur in the switching elements. The switching losses are losses that occur due to the switching drive (turn-on drive and turn-off drive) of the switching elements.

[0009] Here, the positive and negative electrodes of the storage battery are connected to the primary terminal pair of the conversion circuit, respectively, and the storage battery is connected in series to the secondary terminal pair of the conversion circuit. With this configuration, the output voltage Vm of the storage battery module is the sum of the output voltage Vb of the storage battery and the output voltage Vo of the conversion circuit. Therefore, compared to a storage battery module in which the storage battery is connected in parallel to the secondary terminal pair of the conversion circuit, the output voltage Vo required of the conversion circuit when the output voltage Vm of the storage battery module is required can be reduced. Therefore, the rated voltage of the conversion circuit can be lowered, and therefore the rated capacity of the conversion circuit can be reduced, thereby enabling the conversion circuit to be made more compact.

[0010] Furthermore, the power supply system includes a connection maintenance circuit that maintains the secondary terminal pair in a connected state. Therefore, in situations where it is not necessary to boost the voltage higher than the battery voltage when outputting power from the storage battery, the secondary terminal pair connected in series to the storage battery can be maintained in a connected state by the connection maintenance circuit (hereinafter referred to as a "conduction mode"), allowing power to be output directly from the storage battery. Therefore, power can be output without continuous switching (turn-on and turn-off) of switching elements for power conversion, thereby reducing switching loss in the switching elements. As a result, the efficiency of the power supply system can be improved.

[0011] In a second aspect, the connection maintenance circuit is configured by a secondary circuit of the conversion circuit connected to the secondary terminal pair, and maintains the secondary terminal pair in a connected state by the secondary circuit via a secondary switching element, which is the switching element included in the secondary circuit. This configuration eliminates the need to add a new circuit to the power supply system as the connection maintenance circuit, and the secondary circuit of the conversion circuit can be used as the connection maintenance circuit. Furthermore, the main loss in the conduction mode can be limited to the conduction loss of the secondary switching element of the conversion circuit or the conduction loss of the anti-parallel diode included in the secondary switching element. Note that conduction loss is loss generated by conduction through a switching element, diode, etc.

[0012] In a third aspect, the connection maintenance circuit includes a bypass circuit that bypasses the conversion circuit and connects the secondary-side terminal pair, and a bypass switch that disconnects and connects the bypass circuit, and the bypass switch maintains the bypass circuit in a connected state, thereby maintaining the secondary-side terminal pair in a connected state. With this configuration, by maintaining the bypass circuit in a connected state with the bypass switch, power can be directly output from the storage battery. Furthermore, the main loss in the conduction mode can be reduced to the conduction loss of the bypass switch. Therefore, for example, by using a switch with a smaller conduction loss than the secondary-side switching element of the conversion circuit as the bypass switch, loss when outputting power from the storage battery can be further reduced.

[0013] In the fourth means, a storage battery module is formed by the storage battery, the conversion circuit, and the connection maintenance circuit, and the storage battery module is connected to a power supply bus. The fourth means includes a control unit that executes a conduction mode in which the connection maintenance circuit of the storage battery module maintains the secondary side terminal pair in a connected state, on the condition that the difference between a bus voltage that is the voltage of the power supply bus and the output voltage of the storage battery of the storage battery module is smaller than a voltage threshold.

[0014] According to the above configuration, the storage battery, the conversion circuit, and the connection maintenance circuit constitute a storage battery module, and the storage battery module is connected to a power supply bus. This allows power to be supplied from the storage battery module to the power supply bus. The power supply bus is a shared power path (common power path) in a power supply system that connects multiple circuits, devices, and equipment to exchange power.

[0015] The control unit executes a conduction mode in which the connection maintenance circuit of the storage battery module maintains the secondary-side terminal pair in a connected state, on the condition that the difference between the bus voltage, which is the voltage of the power supply bus, and the output voltage of the storage battery of the storage battery module is smaller than a voltage threshold. Therefore, when the difference between the bus voltage and the output voltage of the storage battery is smaller than the voltage threshold, i.e., when it is not necessary to boost the voltage higher than the storage battery voltage when outputting power from the storage battery module, the control unit executes the conduction mode, allowing power to be output directly from the storage battery. On the other hand, when the difference between the bus voltage and the output voltage of the storage battery is not smaller than the voltage threshold, i.e., when it is necessary to boost the output voltage of the storage battery module (to be boosted higher than the storage battery voltage) when outputting power from the storage battery module, the control unit can not execute the conduction mode.

[0016] When the battery module is outputting power to the power supply bus, the output voltage of the battery module is equal to the output voltage of the battery even if the converter circuit does not boost the output voltage of the battery module. Therefore, when the battery module is outputting power to the power supply bus, the bus voltage is always equal to or greater than the output voltage of the battery in the battery module.

[0017] A fifth means includes a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit selecting the storage battery module with the highest output voltage of the storage battery as the storage battery module to be placed in the conduction mode among the plurality of storage battery modules.

[0018] According to the above configuration, the power supply system includes a plurality of the storage battery modules, and the plurality of storage battery modules are connected in parallel to the power supply bus. Therefore, power can be supplied from the plurality of storage battery modules to the power supply bus. The control unit selects the storage battery module with the highest output voltage of the storage battery as the storage battery module to be placed in the conduction mode among the plurality of storage battery modules. Therefore, when the conduction mode is executed to directly output power from the storage battery, the bus voltage can be kept as high as possible.

[0019] A sixth means includes a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit selects the storage battery module to be placed in the conduction mode from among the plurality of storage battery modules, in order from the storage battery module with the highest output voltage of the storage battery.

[0020] According to the above configuration, the control unit selects the storage battery module to be placed in the conduction mode from among the plurality of storage battery modules in order, starting with the storage battery module having the highest output voltage of the storage battery. Therefore, when the conduction mode is executed to directly output power from the storage battery, a drop in bus voltage can be suppressed and power can be supplied from more storage batteries to the power supply bus.

[0021] In a seventh aspect, the control unit adjusts the output voltage of the conversion circuit in a storage battery module where the difference between the bus voltage and the output voltage of the storage battery of the storage battery module is not smaller than the voltage threshold so that the difference between the bus voltage and the output voltage of the storage battery module is smaller than the voltage threshold. With this configuration, in a storage battery module where the difference between the bus voltage and the output voltage of the storage battery of the storage battery module is not smaller than the voltage threshold, the output voltage of the storage battery module can be increased by adjusting the output voltage of the conversion circuit in the storage battery module. Therefore, power can be supplied to the power supply bus even from a storage battery module with a low output voltage of the storage battery.

[0022] The eighth means includes a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit selects the storage battery module to be placed in the conduction mode and adjusts the state of the storage battery of the selected storage battery module so that the difference between the bus voltage and the output voltage of the storage battery of the selected storage battery module is maintained smaller than the voltage threshold.

[0023] According to the above configuration, the control unit selects the storage battery module to be placed in the conduction mode. Therefore, power can be directly output from the storage battery of the selected storage battery module, provided that the difference between the bus voltage and the output voltage of the storage battery of the selected storage battery module is smaller than a voltage threshold. Furthermore, the control unit adjusts the state of the storage battery of the selected storage battery module so that the difference between the bus voltage and the output voltage of the storage battery of the selected storage battery module remains smaller than the voltage threshold. Therefore, the conduction mode can be continued while maintaining the output voltage of the storage battery of the selected storage battery module.

[0024] A ninth means includes a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and when any of the storage battery modules is in the conduction mode, the control unit places the storage battery module that is not in the conduction mode into the conduction mode, on the condition that the difference between the output voltage of the storage battery of the storage battery module that is in the conduction mode and the output voltage of the storage battery of the storage battery module that is not in the conduction mode is smaller than the voltage threshold value.

[0025] When any of the storage battery modules is in the conduction mode, the output voltage of the storage battery of the storage battery module in the conduction mode is equal to the bus voltage. According to the above configuration, when it is not necessary to boost the voltage higher than the voltage of the storage battery when outputting power from the storage battery of a storage battery module that is not in the conduction mode, the storage battery module that is not in the conduction mode can be set to the conduction mode to directly output power from the storage battery.

[0026] In a tenth aspect, when the difference between the output voltage of the storage battery of the storage battery module in the conduction mode and the output voltage of the storage battery of the storage battery module not in the conduction mode is not smaller than the voltage threshold, the control unit charges the storage battery of the storage battery module not in the conduction mode from the storage battery of the storage battery module in the conduction mode. With this configuration, the output voltage can be lowered by reducing the charge amount of the storage battery of the storage battery module in the conduction mode, and the output voltage can be raised by increasing the charge amount of the storage battery of the storage battery module not in the conduction mode. This reduces the difference between the output voltage of the storage battery of the storage battery module in the conduction mode and the output voltage of the storage battery of the storage battery module not in the conduction mode, making it easier to place the storage battery module not in the conduction mode in the conduction mode.

[0027] In the eleventh means, the control unit charges the storage battery of the storage battery module that is not in the conduction mode from the storage battery of the storage battery module that is in the conduction mode by lowering the output voltage of the conversion circuit of the storage battery module that is not in the conduction mode below the current output voltage.

[0028] According to the above configuration, by lowering the output voltage of the conversion circuit of the storage battery module not in the conduction mode below the current output voltage, the output voltage of the storage battery module not in the conduction mode can be lowered below the output voltage of the storage battery of the storage battery module in the conduction mode. Therefore, the storage battery of the storage battery module not in the conduction mode can be charged from the storage battery of the storage battery module in the conduction mode.

[0029] The twelfth means is a control program applied to a power supply system in which a storage battery module including a storage battery and a conversion circuit that converts power input from the storage battery to a primary terminal pair by driving a switching element and outputs the power from a secondary terminal pair, is connected to a power supply bus, the positive and negative electrodes of the storage battery are respectively connected to the primary terminal pair of the conversion circuit, the storage battery is connected in series to the secondary terminal pair of the conversion circuit, and the control program includes a connection maintenance circuit that maintains the secondary terminal pair in a connected state, and causes a computer to execute a conduction mode in which the connection maintenance circuit of the storage battery module maintains the secondary terminal pair in a connected state, on the condition that the difference between a bus voltage that is the voltage of the power supply bus and the output voltage of the storage battery of the storage battery module is smaller than a voltage threshold value.

[0030] According to the above configuration, by causing a computer to execute a control program applied to the power supply system, it is possible to achieve the same effects as those of the fourth means.

[0031] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a circuit diagram of a power supply system according to a first embodiment, Fig. 2 is a circuit diagram showing an example of a conversion circuit, Fig. 3 is a flowchart showing a procedure for executing the conduction mode according to the first embodiment, Fig. 4 is a circuit diagram showing a state in which the first storage battery module according to the first embodiment is in the conduction mode, Fig. 5 is a circuit diagram showing a state in which the first storage battery module and the second storage battery module according to the first embodiment are in the conduction mode, Fig. 6 is a circuit diagram showing a state in which the first storage battery module, the second storage battery module, and the third storage battery module according to the first embodiment are in the conduction mode, Fig. 7 is a diagram showing losses generated in the storage battery modules of a comparative example and the first embodiment, Fig. 8 is a circuit diagram of a power supply system according to a second embodiment, and Fig. 9 is a flowchart showing a procedure for executing the conduction mode according to the second embodiment. 10 is a circuit diagram showing a state in which the first storage battery module of the second embodiment is in a conduction mode, FIG. 11 is a circuit diagram showing a state in which the first storage battery module and the second storage battery module of the second embodiment are in a conduction mode, FIG. 12 is a circuit diagram showing a state in which the first storage battery module, the second storage battery module, and the third storage battery module of the second embodiment are in a conduction mode, FIG. 13 is a diagram showing losses generated in a comparative example and the second embodiment, FIG. 14 is a circuit diagram of another modified example of the power supply system, FIG. 15 is a circuit diagram of another modified example of the power supply system, FIG. 16 is a circuit diagram of a modified example of the conversion circuit, FIG. 17 is a circuit diagram of another modified example of the conversion circuit, FIG. 18 is a circuit diagram of a modified example of the storage battery module, and FIG. 19 is a circuit diagram of another modified example of the storage battery module.

[0032] First Embodiment Hereinafter, a first embodiment embodied in a power supply system for supplying power to a load will be described with reference to the drawings.

[0033] 1 , the power supply system 10 includes buses 11 and 12 (power supply buses), a first storage battery module 30, a second storage battery module 60, a voltage sensor 13, a current sensor 19, an ECU (Electronic Control Unit) 16, etc. The positive side of the buses is referred to as bus 11, and the negative side of the buses is referred to as bus 12. The bus 12 is grounded.

[0034] A first storage battery module 30 (storage battery module), a second storage battery module 60 (storage battery module), a load 21, and a voltage sensor 13 are connected in parallel to the buses 11 and 12. The storage battery modules 30 and 60 input and output power to and from the buses 11 and 12. The load 21 inputs power from and inputs and outputs power to and from the buses 11 and 12. The voltage sensor 13 detects a bus voltage Vbus, which is the voltage between the bus 12 and the bus 11. The current sensor 19 detects a current flowing through the bus 12 (load 21).

[0035] The load 21 is, for example, a combination of an inverter and a motor generator (MG) (inverter-equipped motor unit), an electric heater, a DC-DC converter, etc. The MG (motor generator) drives, for example, an electric vehicle using power supplied from the inverter and generates electric power regeneratively using rotational force imparted by the electric vehicle. The inverter converts electric power between the buses 11, 12 and the MG. The electric heater generates heat using high voltage supplied from the buses 11, 12, for example, to warm the interior of the vehicle and the battery. The DC-DC converter converts DC power supplied from the buses 11, 12 and supplies it, or converts DC power supplied from a solar panel or the like and supplies it to the buses 11, 12. The load 21 may be single or multiple.

[0036] The first storage battery module 30 includes a first storage battery 31, a first current sensor 33, a first drive circuit 35, a first conversion circuit 40, and relays 40a and 40b. The first storage battery 31 (storage battery) is a high-voltage secondary battery, such as a lithium-ion battery or a nickel-metal hydride battery, and may be of any type. The first current sensor 33 (current sensor) detects the current flowing through the first storage battery 31. The value detected by the first current sensor 33 is input to the ECU 16 and used, for example, to calculate the state of charge (SOC) of the first storage battery 31. The first drive circuit 35 (drive circuit) drives switching elements (described below) included in the first conversion circuit 40 to turn on and off. The first drive circuit 35 is controlled by the ECU 16. The relays 40a and 40b connect and disconnect the storage battery module 30 to and from the buses 11 and 12, respectively. The first storage battery 31 (storage battery) may be a secondary battery that is not a high voltage battery.

[0037] The first conversion circuit 40 (conversion circuit) includes a primary-side terminal pair, that is, a primary-side positive terminal 41 and a negative terminal 42, and a secondary-side terminal pair, that is, a secondary-side positive terminal 47 and a negative terminal 48. The negative terminal of the first storage battery 31 is connected to the bus 12. The primary-side positive terminal 41 is connected to the positive terminal of the first storage battery 31, and the primary-side negative terminal 42 is connected to the negative terminal of the first storage battery 31. The secondary-side negative terminal 48 is also connected to the positive terminal of the first storage battery 31. The secondary-side positive terminal 47 is connected to the bus 11. That is, the positive and negative terminals of the first storage battery 31 are connected to the primary-side terminal pair 41, 42 of the first conversion circuit 40, respectively, and the first storage battery 31 is connected in series to the secondary-side terminal pair 47, 48 of the first conversion circuit 40. The first conversion circuit 40 converts the power input from the first storage battery 31 to the pair of primary side terminals 41, 42 and outputs it from the pair of secondary side terminals 47, 48. A secondary side circuit 49 included in the first conversion circuit 40 will be described later. The first conversion circuit 40 is a bidirectional conversion circuit that can also convert the power input to the pair of secondary side terminals 47, 48 and output it from the pair of primary side terminals 41, 42.

[0038] The second storage battery module 60 has a configuration similar to that of the first storage battery module 30 and includes a second storage battery 61 (storage battery), a second current sensor 63 (current sensor), a second drive circuit 65 (drive circuit), a second conversion circuit 70, relays 70a and 70b, etc. The second conversion circuit 70 (conversion circuit) has a configuration similar to that of the first conversion circuit 40 and includes a primary-side terminal pair consisting of a primary-side positive terminal 71 and a negative terminal 72, and a secondary-side terminal pair consisting of a secondary-side positive terminal 77 and a negative terminal 78. The connection configuration of these terminals is also similar to that of the first storage battery module 30, and therefore the above description of the first storage battery module 30 is incorporated herein. The secondary-side circuit 79 included in the second conversion circuit 70 will be described later. Although the first storage battery module 30 and the second storage battery module 60 have configurations with similar functions, the ratings and withstand voltages of the respective components may differ from each other.

[0039] FIG. 2 shows an example of a first conversion circuit 40. The first conversion circuit 40 is a well-known center-tap isolated DC-DC converter. The first conversion circuit 40 includes a primary circuit and a secondary circuit 49. The first conversion circuit 40 includes switching elements 43 to 46, 54, and 55, smoothing capacitors 50 and 57, a transformer 53, a reactor 56, voltage sensors 51 and 59, and current sensors 52 and 58. The switching elements 43 to 46, 54, and 55 are, for example, FETs or IGBTs (insulated gate bipolar transistors). The switching elements 43 to 46 form a full-bridge circuit. The connection point between the switching element 43 and the switching element 44 and the connection point between the switching element 45 and the switching element 46 are connected to both ends of the primary coil of the transformer 53, respectively. The switching elements 54 and 55 are connected between both ends of the secondary coil of the transformer 53 and the reactor 56, respectively. The voltage sensor 51 detects the voltage between the negative terminal 42 and positive terminal 41 on the primary side, i.e., the output voltage Vb of the first storage battery 31 (the input voltage Vi of the first conversion circuit 40). The current sensor 52 detects the input current Ii, which is the current input to the primary circuit. The voltage sensor 59 detects the voltage between the negative terminal 48 and positive terminal 47 on the secondary side, i.e., the output voltage Vo of the first conversion circuit 40. The current sensor 58 detects the current flowing through the reactor 56, i.e., the output current Io of the first conversion circuit 40. The detected values ​​of the voltage sensors 51, 59 and the current sensors 52, 58 are input to the ECU 16. The secondary circuit 49 (connection maintenance circuit) includes the secondary coil of the transformer 53, the switching elements 54, 55, the reactor 56, and paths connecting these to the secondary terminal pair 47, 48.

[0040] The ECU 16 (control device) is configured as a microcomputer (computer) including, for example, a CPU, ROM, RAM, an input / output interface, etc. The ECU 16 controls the states of the relays 40a, 40b, 70a, and 70b and the state of the load 21. The ECU 16 executes a control program applied to the power supply system 10 to realize the functions of a bus voltage setting unit 16a, a control unit 16b, etc.

[0041] The bus voltage setting unit 16a sets a bus voltage request value Vbus*, which is a voltage that is requested to be supplied from the buses 11 and 12 to the load 21. The bus voltage setting unit 16a sets the bus voltage request value Vbus* based on the state of the load 21.

[0042] The control unit 16b controls the output voltages Vo1 and Vo2 of the conversion circuits 40 and 70 so that the output voltages Vm1 and Vm2 of the storage battery modules 30 and 60 become equal to the requested bus voltage value Vbus* (approach the requested bus voltage value Vbus*). For example, the control unit 16b controls the switching elements 43-46, 54, and 55 based on the detected values ​​of the voltage sensors 51 and 59 and the current sensors 52 and 58 to control the first output voltage Vo1 of the first conversion circuit 40 to become equal to the requested first output voltage value Vo1*. Specifically, the control unit 16b sets the requested first output voltage value Vo1* to a voltage obtained by subtracting the first output voltage Vb1 of the first storage battery 31 from the requested bus voltage value Vbus* (Vo1* = Vbus* - Vb1). Similarly, the control unit 16b controls the second output voltage Vo2 of the second conversion circuit 70 to become equal to the requested second output voltage value Vo2*. Specifically, the second output voltage request value Vo2* is set to a voltage obtained by subtracting the second output voltage Vb2 of the second storage battery 61 from the bus voltage request value Vbus* (Vo2*=Vbus*−Vb2).

[0043] When power is being output from the battery module 30 (60) to the buses 11 and 12, the output voltage Vm1 (Vm2) of the battery module 30 (60) is equal to the output voltage Vb1 (Vb2) of the battery 31 (61) even if the conversion circuit 40 (70) does not boost the output voltage Vm1 (Vm2) higher than the output voltage Vb1 (Vb2) of the battery 31 (61). Therefore, when power is being output from the battery module 30 (60) to the buses 11 and 12, the bus voltage Vbus is always equal to or higher than the output voltage Vb1 (Vb2) of the battery 31 (61) of the battery module 30 (60).

[0044] Depending on the bus voltage request value Vbus* and the charge amount of the storage batteries 31, 61, the bus voltage Vbus and the output voltages Vb1, Vb2 of the storage batteries 31, 61 may become close to each other, and a situation may arise in which it is not necessary to boost the output voltages Vm1, Vm2 of the storage battery modules 30, 60 by the conversion circuits 40, 70 when outputting power from the storage battery modules 30, 60. In this case, if the switching elements 43 to 46, 54, 55 of the conversion circuits 40, 70 are continuously switched to output power from the storage battery modules 30, 60, turn-on loss, turn-off loss (switching loss), and conduction loss of the switching elements 43 to 46, 54, 55 occur.

[0045] Therefore, in this embodiment, the control unit 16b (ECU 16) executes a conduction mode in which the secondary-side circuit 49 (79) of the storage battery module 30 (60) maintains the secondary-side terminal pair 47, 48 (77, 78) connected, provided that the difference between the bus voltage Vbus and the output voltage Vb1 (Vb2) of the storage battery 31 (61) of the storage battery module 30 (60) is smaller than the voltage threshold Vx. Specifically, the secondary-side terminal pair, i.e., the positive terminal 47 (77) and the negative terminal 48 (78) on the secondary side, are maintained connected by maintaining the switching elements 54, 55 (secondary-side switching elements) included in the secondary-side circuit 49 (79) in an on state. At this time, all of the primary-side switching elements 43 to 46 of the conversion circuit (40, 70) of the storage battery module 30 (60) in an off state.

[0046] 3 is a flowchart showing a procedure for executing the conduction mode. This series of processes is executed by the control unit 16b of the ECU 16 when the conversion circuits 40, 70 of the storage battery modules 30, 60 are driven to output power to the buses 11, 12. Note that three or more storage battery modules may be connected in parallel to the buses 11, 12.

[0047] First, among the storage battery modules that have not yet been selected in the process of S10, the storage battery module with the highest storage battery output voltage Vb is selected (S10). At the start of this series of processes, all storage battery modules have not yet been selected. If there are no storage battery modules that have not yet been selected (if all storage battery modules have already been selected), this series of processes ends (END).

[0048] Next, it is determined whether the difference (Vbus - Vb) between the bus voltage Vbus and the output voltage Vb of the storage battery of the selected storage battery module is smaller than a voltage threshold Vx (S11). The bus voltage Vbus is detected by the voltage sensor 13. The voltage threshold Vx is, for example, a value at which the bus voltage Vbus and the output voltage Vb of the storage battery can be considered equal (or approximately equal), and is a value that can suppress inrush currents and circulating currents from flowing through multiple storage battery modules. If it is determined that the difference (Vbus - Vb) between the bus voltage Vbus and the output voltage Vb of the storage battery of the selected storage battery module is smaller than the voltage threshold Vx (S11: YES), all of the secondary-side switching elements 54 and 55 of the conversion circuit of the selected storage battery module are maintained in the ON state (S12). At this time, all of the primary-side switching elements 43 to 46 of the conversion circuit of the selected storage battery module are maintained in the OFF state.

[0049] Next, it is determined whether the bus voltage Vbus is lower than the required bus voltage value Vbus* (S13). If it is determined that the bus voltage Vbus is lower than the required bus voltage value Vbus* (YES in S13), this series of processes is terminated (END). On the other hand, if it is determined that the bus voltage Vbus is not lower than the required bus voltage value Vbus* (NO in S13), the processes are executed again from S10. That is, the storage battery module to be placed in the conduction mode among the multiple storage battery modules is selected in order, starting from the storage battery module with the highest output voltage.

[0050] Furthermore, if it is determined in the process of S11 that the difference (Vbus - Vb) between the bus voltage Vbus and the output voltage Vb of the storage battery of the selected storage battery module is not smaller than the voltage threshold Vx (S11: NO), the output voltage Vo of the conversion circuit of the selected storage battery module is adjusted so that the difference (Vbus - Vm) between the bus voltage Vbus and the output voltage Vm of the selected storage battery module becomes smaller than the voltage threshold Vx (S14).Then, the process is executed again from S10.

[0051] 4 to 6 show how the conduction mode is executed when the power supply system 10 includes the first storage battery module 30, the second storage battery module 60, and the third storage battery module 90. The output voltages Vm1 (Vb1+Vo1), Vm2 (Vb2+Vo2), and Vm3 (Vb3+Vo3) of the storage battery modules 30, 60, and 90 are all equal to the bus voltage Vbus.

[0052] 4 , the difference between the bus voltage Vbus and the first output voltage Vb1 of the first storage battery 31 is smaller than the voltage threshold Vx, the difference between the bus voltage Vbus and the second output voltage Vb2 of the second storage battery 61 is equal to or greater than the voltage threshold Vx, and the difference between the bus voltage Vbus and the third output voltage Vb3 of the third storage battery 91 is equal to or greater than the voltage threshold Vx. In this case, the first storage battery module 30 is in the conduction mode, and the conversion circuits 70 and 100 of the storage battery modules 60 and 90 are performing boost operations, respectively. This reduces switching loss in the first conversion circuit 40 of the first storage battery module 30.

[0053] 5 , the difference between the bus voltage Vbus and the first output voltage Vb1 of the first storage battery 31 is smaller than the voltage threshold Vx, the difference between the bus voltage Vbus and the second output voltage Vb2 of the second storage battery 61 is smaller than the voltage threshold Vx, and the difference between the bus voltage Vbus and the third output voltage Vb3 of the third storage battery 91 is equal to or greater than the voltage threshold Vx. In this case, the storage battery modules 30 and 60 are in the conduction mode, and the third storage battery module 90 is performing a boost operation using the third conversion circuit 100. As a result, switching losses are reduced in the conversion circuits 40 and 70 of the storage battery modules 30 and 60, respectively.

[0054] 6 , the difference between the bus voltage Vbus and the first output voltage Vb1 of the first storage battery 31 is smaller than the voltage threshold Vx, the difference between the bus voltage Vbus and the second output voltage Vb2 of the second storage battery 61 is smaller than the voltage threshold Vx, and the difference between the bus voltage Vbus and the third output voltage Vb3 of the third storage battery 91 is smaller than the voltage threshold Vx. In this case, the storage battery modules 30, 60, and 90 are in the conduction mode. As a result, switching losses are reduced in the conversion circuits 40, 70, and 100 of the storage battery modules 30, 60, and 90, respectively.

[0055] FIG. 7 illustrates losses generated in the battery modules of the comparative example and the present embodiment. The comparative example illustrates losses when, for example, in the first battery module 30, the switching elements 43 to 46, 54, and 55 of the first conversion circuit 40 are turned on and off to output the first output voltage Vm1. Turn-on losses and turn-off losses occur in the switching elements 43 to 46, 54, and 55, and conduction losses occur in the switching elements 43 to 46, 54, and 55. The present embodiment illustrates losses when, for example, the first battery module 30 is in the conduction mode to output the first output voltage Vm1. In the present embodiment, the turn-on losses and turn-off losses of the switching elements 43 to 46, 54, and 55 can be reduced, and only conduction losses occur in the switching elements 54 and 55. As a result, losses in the comparative example can be reduced by three-quarters, and the resulting losses are one-quarter of the losses in the comparative example.

[0056] The present embodiment described above in detail has the following advantages.

[0057] The positive and negative electrodes of the storage batteries 31 and 61 are connected to the primary-side terminal pairs 41, 42, 71, and 72 of the conversion circuits 40 and 70, respectively, and the storage batteries 31 and 61 are connected in series to the secondary-side terminal pairs 47, 48, 77, and 78 of the conversion circuits 40 and 70, respectively. With this configuration, the output voltages Vm1 and Vm2 of the storage battery modules 30 and 60 are obtained by adding the output voltages Vb1 and Vb2 of the storage batteries 31 and 61 to the output voltages Vo1 and Vo2 of the conversion circuits 40 and 70, respectively. Therefore, compared to a storage battery module in which the storage batteries 31 and 61 are connected in parallel to the secondary-side terminal pairs 47, 48, 77, and 78 of the conversion circuits 40 and 70, respectively, the output voltages Vo1 and Vo2 required of the conversion circuits 40 and 70 can be reduced when the output voltages Vm1 and Vm2 are required of the storage battery modules 30 and 60, respectively. Therefore, the rated voltage of the conversion circuits 40, 70 can be lowered, and the rated capacity of the conversion circuits 40, 70 can be reduced, so that the conversion circuits 40, 70 can be made smaller.

[0058] The power supply system 10 includes a connection maintenance circuit (secondary-side circuits 49, 79) that maintains the secondary-side terminal pairs 47, 48, 77, 78 in a connected state. Therefore, when it is not necessary to boost the voltage of the storage batteries 31, 61 when outputting power from the storage batteries 31, 61, a conduction mode is executed in which the secondary-side terminal pairs 47, 48, 77, 78, each connected in series to the storage batteries 31, 61, are maintained in a connected state by the connection maintenance circuit, thereby enabling power to be output directly from the storage batteries 31, 61. Therefore, power can be output without continuous switching (turn-on and turn-off) of the switching elements 43-46, 54, 55 for power conversion, thereby reducing switching loss in the switching elements 43-46, 54, 55. As a result, the efficiency of the power supply system 10 can be improved.

[0059] The connection maintenance circuit is constituted by the secondary-side circuit 49 of the first conversion circuit 40 connected to the secondary-side terminal pairs 47, 48, respectively, and maintains the secondary-side terminal pairs 47, 48 in a connected state by the secondary-side circuit 49 via the secondary-side switching elements 54, 55 included in the secondary-side circuit 49. The connection maintenance circuit is also constituted by the secondary-side circuit 79 of the second conversion circuit 70 connected to the secondary-side terminal pair 77, 78, and maintains the secondary-side terminal pair 77, 78 in a connected state by maintaining the secondary-side switching elements 54, 55 included in the secondary-side circuit 79 in an on state. With this configuration, there is no need to add a new circuit as the connection maintenance circuit to the power supply system 10, and the secondary-side circuits 49, 79 of the conversion circuits 40, 70 can be used as the connection maintenance circuit. The main loss in the conduction mode can be limited to the conduction loss of the secondary-side switching elements 54, 55 of the conversion circuits 40, 70 or the conduction loss of the anti-parallel diodes included in the secondary-side switching elements 54, 55.

[0060] The control unit 16b executes a conduction mode in which the secondary-side terminal pairs 47, 48, 77, 78 are maintained connected by the secondary-side circuits 49, 79 of the storage battery modules 30, 60, 90, on the condition that the difference between the bus voltage Vbus, which is the voltage of the buses 11, 12, and the output voltages Vb1, Vb2, Vb3 of the storage batteries 31, 61, 91 of the storage battery modules 30, 60, 90 is smaller than the voltage threshold Vx. Therefore, when the difference between the bus voltage Vbus and the output voltages Vb1, Vb2, Vb3 of the storage batteries 31, 61, 91 is smaller than the voltage threshold Vx, that is, when there is no need to boost the voltage higher than the voltage of the storage batteries 31, 61, 91 when outputting power from the storage battery modules 30, 60, 90, the conduction mode is executed, allowing power to be output directly from the storage batteries 31, 61, 91. On the other hand, if the difference between the bus voltage Vbus and the output voltages Vb1, Vb2, and Vb3 of the storage batteries 31, 61, and 91 is not smaller than the voltage threshold Vx, that is, if it is necessary to boost the voltage higher than the voltage of the storage batteries 31, 61, and 91 when outputting power from the storage battery modules 30, 60, and 90, the conduction mode can be prevented from being executed.

[0061] The power supply system 10 includes multiple storage battery modules 30, 60, 90, which are connected in parallel to the buses 11, 12. This allows power to be supplied from the multiple storage battery modules 30, 60, 90 to the buses 11, 12. The control unit 16b then selects the storage battery module with the highest output voltage among the storage batteries 31, 61, 91 among the multiple storage battery modules 30, 60, 90 as the storage battery module to be placed in the conduction mode. This allows the bus voltage Vbus to be kept as high as possible when the conduction mode is executed to directly output power from the storage battery.

[0062] The control unit 16b selects the storage battery module to be placed in the conduction mode from among the multiple storage battery modules 30, 60, 90 in order from the storage battery module with the highest output voltage among the storage batteries 31, 61, 91. Therefore, when the conduction mode is executed to directly output power from the storage batteries, a drop in the bus voltage Vbus can be suppressed, and power can be supplied to the buses 11, 12 from a greater number of storage batteries.

[0063] In a storage battery module in which the difference between the bus voltage Vbus and the output voltages Vb1, Vb2, and Vb3 of the storage batteries 31, 61, and 91 of the storage battery module 30, 60, and 90 is not smaller than the voltage threshold Vx, the control unit 16b adjusts the output voltages Vo1, Vo2, and Vo3 of the conversion circuits 40, 70, and 100 so that the difference between the bus voltage Vbus and the output voltage of the storage battery module is smaller than the voltage threshold Vx. With this configuration, in a storage battery module in which the difference between the bus voltage Vbus and the output voltages Vb1, Vb2, and Vb3 of the storage batteries 31, 61, and 91 of the storage battery module 30, 60, and 90 is not smaller than the voltage threshold Vx, the output voltage of the storage battery module can be increased by adjusting the output voltage of the conversion circuit of the storage battery module. Therefore, power can be supplied to the buses 11 and 12 even from storage battery modules in which the output voltages of the storage batteries 31, 61, and 91 are low.

[0064] The above-described advantageous effects can be achieved by causing the ECU 16 (computer) to execute the conduction mode of the control program applied to the power supply system 10 .

[0065] Second Embodiment The second embodiment will be described below, focusing on the differences from the first embodiment. Note that the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0066] As shown in FIGS. 8 and 10, in this embodiment, the storage battery modules 30, 60, and 90 are provided with bypasses 36, 66, and 96 and bypass relays 37, 67, and 97, respectively, as connection maintaining circuits.

[0067] For example, the bypass 36 (detour path) bypasses the first conversion circuit 40 and connects the secondary-side positive terminal 47 and negative terminal 48, which are a secondary-side terminal pair. The bypass 36 is provided with a bypass relay 37. The bypass relay 37 (detour path switch) is a relay with lower conduction loss than the switching elements 54 and 55 of the first conversion circuit 40, and is formed, for example, by an SJ-MOSFET (Super Junction-Metal Oxide Semiconductor Field Effect Transistor). The bypass relay 37 is controlled by the control unit 16b to disconnect and connect the bypass 36. In the first storage battery module 30, the bypass relay 37 is maintained in an on state (connected state), thereby maintaining the secondary-side positive terminal 47 and negative terminal 48 connected. In other words, when the bypass 36 is connected by the bypass relay 37, the first storage battery 31 is connected to the buses 11 and 12 via the bypass 36 without via the first conversion circuit 40. It should be noted that the bypass relay 37 may be another semiconductor relay whose conduction loss is equal to or less than the conduction loss of the switching elements 54, 55. Furthermore, the bypass relay 37 is not limited to a semiconductor relay, and may also be a mechanical relay whose conduction loss is equal to or less than the conduction loss of the switching elements 54, 55. The same applies to the bypasses 66, 96 (bypass circuits) and the bypass relays 67, 97 (bypass circuit switches).

[0068] The control unit 16b (ECU 16) executes a conduction mode in which the bypass 36 (66) and bypass relay 37 (67) of the storage battery module 30 (60) maintain the secondary-side terminal pair 47, 48 (77, 78) connected, for example, on the condition that the difference between the bus voltage Vbus and the output voltage Vb1 (Vb2) of the storage battery 31 (61) of the storage battery module 30 (60) is smaller than the voltage threshold Vx. Specifically, by maintaining the bypass relay 37 (67) in an ON state, the secondary-side terminal pair, i.e., the positive terminal 47 (77) and the negative terminal 48 (78) on the secondary side, are maintained connected. At this time, all of the switching elements 43 to 46, 54, 55 of the conversion circuit 40 (70) of the storage battery module 30 (60) are maintained in an OFF state.

[0069] Figure 9 is a flowchart showing the procedure for executing the conduction mode. This series of processes is executed by the control unit 16b of the ECU 16 when the conversion circuits 40, 70, 100 of the storage battery modules 30, 60, 90 are driven to output power to the buses 11, 12. In the process of the flowchart of Figure 9, the process of S12 in the flowchart of Figure 3 is changed to the process of S22, but the rest of the process is the same as the flowchart of Figure 3. The same processes as those in the flowchart of Figure 3 are designated by the same step numbers S and the description thereof is incorporated herein.

[0070] In the process of S22, the bypass relay of the selected battery module is maintained in the ON state (S22), while all of the switching elements 43 to 46, 54, and 55 of the conversion circuit of the selected battery module are maintained in the OFF state.

[0071] 10 to 12 show how the conduction mode is executed when the power supply system 10 includes the first storage battery module 30, the second storage battery module 60, and the third storage battery module 90. The output voltages Vm1 (Vb1+Vo1), Vm2 (Vb2+Vo2), and Vm3 (Vb3+Vo3) of the storage battery modules 30, 60, and 90 are all equal to the bus voltage Vbus.

[0072] 10 , the difference between the bus voltage Vbus and the first output voltage Vb1 of the first storage battery 31 is smaller than the voltage threshold Vx, the difference between the bus voltage Vbus and the second output voltage Vb2 of the second storage battery 61 is equal to or greater than the voltage threshold Vx, and the difference between the bus voltage Vbus and the third output voltage Vb3 of the third storage battery 91 is equal to or greater than the voltage threshold Vx. In this case, the bypass relay 37 of the first storage battery module 30 is turned on, and the conversion circuits 70 and 100 of the storage battery modules 60 and 90 are performing boost operations, respectively. This reduces switching loss and conduction loss in the first conversion circuit 40 of the first storage battery module 30. Note that conduction loss occurs in the bypass relay 37.

[0073] 11 , the difference between the bus voltage Vbus and the first output voltage Vb1 of the first storage battery 31 is smaller than the voltage threshold Vx, the difference between the bus voltage Vbus and the second output voltage Vb2 of the second storage battery 61 is smaller than the voltage threshold Vx, and the difference between the bus voltage Vbus and the third output voltage Vb3 of the third storage battery 91 is equal to or greater than the voltage threshold Vx. In this case, the bypass relays 37 and 67 of the storage battery modules 30 and 60 are turned on, and the third storage battery module 90 performs a boost operation using the third conversion circuit 100. This reduces switching loss and conduction loss in the conversion circuits 40 and 70 of the storage battery modules 30 and 60, respectively. Note that conduction loss occurs in the bypass relays 37 and 67.

[0074] 12 , the difference between the bus voltage Vbus and the first output voltage Vb1 of the first storage battery 31 is smaller than the voltage threshold Vx, the difference between the bus voltage Vbus and the second output voltage Vb2 of the second storage battery 61 is smaller than the voltage threshold Vx, and the difference between the bus voltage Vbus and the third output voltage Vb3 of the third storage battery 91 is smaller than the voltage threshold Vx. In this case, the bypass relays 37, 67, and 97 of the storage battery modules 30, 60, and 90 are turned on. This reduces switching loss and conduction loss in the conversion circuits 40, 70, and 100 of the storage battery modules 30, 60, and 90, respectively. Note that conduction loss occurs in the bypass relays 37, 67, and 97.

[0075] FIG. 13 is a diagram showing losses generated in the storage battery modules of the comparative example and the present embodiment. The comparative example shows losses when, for example, in the first storage battery module 30, the switching elements 43 to 46, 54, and 55 of the first conversion circuit 40 are turned on and off to output the first output voltage Vm1. Turn-on losses and turn-off losses occur in the switching elements 43 to 46, 54, and 55, and conduction losses occur in the switching elements 43 to 46, 54, and 55. The present embodiment shows losses when, for example, the bypass relay 37 of the first storage battery module 30 is turned on to output the first output voltage Vm1. In this embodiment, the turn-on losses, turn-off losses, and conduction losses of the switching elements 43 to 46, 54, and 55 can be reduced. Furthermore, the conduction loss of the bypass relay 37 is smaller than the conduction loss of the switching elements 54 and 55. As a result, the losses of the comparative example can be reduced by four-fifths, and the resulting loss is one-fifth of the losses of the comparative example.

[0076] In addition to the same advantages as the first embodiment, this embodiment has the following advantages.

[0077] By maintaining the bypass relays 37, 67, and 97 of the bypasses 36, 66, and 96 in the on state, that is, by maintaining the bypasses 36, 66, and 96 in a connected state via the bypass relays 37, 67, and 97, it is possible to directly output power from the storage batteries 31, 61, and 91. Furthermore, the main loss in the conduction mode can be the conduction loss of the bypass relays 37, 67, and 97 alone.

[0078] The bypass relays 37, 67, 97 are relays with smaller conduction losses than the switching elements 54, 55 on the secondary side of the conversion circuits 40, 70, 100, so losses when outputting power from the storage batteries 31, 61, 91 can be further reduced.

[0079] When the control unit 16b executes the conduction mode to maintain the bypass relays 37, 67, 97 in the on state (connected state), the control unit 16b may maintain the switching elements 54, 55 on the secondary sides of the conversion circuits 40, 70, 100 in the on state (connected state). This configuration can further reduce the conduction loss of the storage battery modules 30, 60, 90.

[0080] The first and second embodiments can also be modified as follows: The same parts as those in the first and second embodiments are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0081] The control unit 16b may select a storage battery module to be placed in the conduction mode and adjust the charge amount (state) of the storage battery of the selected storage battery module so that the difference between the bus voltage Vbus and the output voltage of the storage battery of the selected storage battery module is maintained below the voltage threshold Vx. In this case, the storage battery module selected to be placed in the conduction mode is not limited to the storage battery module with the highest storage battery output voltage Vb, as long as the difference between the bus voltage Vbus and the output voltage Vb of the storage battery of the storage battery module is below the voltage threshold Vx. As a mode (configuration) for adjusting the charge amount (SOC) of the storage battery of the selected storage battery module, for example, the storage battery of the selected storage battery module may be charged from the storage battery of an unselected storage battery module.

[0082] According to the above configuration, the control unit 16b selects a storage battery module to be placed in the conduction mode. Therefore, power can be directly output from the storage battery of the selected storage battery module, provided that the difference between the bus voltage Vbus and the output voltage Vb of the storage battery of the selected storage battery module is smaller than the voltage threshold Vx. Furthermore, the control unit 16b adjusts the charge amount of the storage battery of the selected storage battery module so that the difference between the bus voltage Vbus and the output voltage Vb of the storage battery of the selected storage battery module is maintained smaller than the voltage threshold Vx. Therefore, the conduction mode can be continued while maintaining the output voltage Vb of the storage battery of the selected storage battery module.

[0083] When any storage battery module is in the conduction mode, the control unit 16b may place the storage battery module that is not in the conduction mode in the conduction mode on the condition that the difference between the output voltage Vb of the storage battery of the storage battery module in the conduction mode and the output voltage Vb of the storage battery of the storage battery module that is not in the conduction mode is smaller than the voltage threshold Vx. When the storage battery module is in the conduction mode, the output voltage Vb of the storage battery of the storage battery module in the conduction mode matches the bus voltage Vbus. Therefore, the control unit 16b may compare the output voltage Vb of the storage battery of the storage battery module in the conduction mode with the output voltage Vb of the storage battery of the storage battery module that is not in the conduction mode to determine whether to execute the conduction mode. According to the above configuration, when it is not necessary to boost the voltage of the storage battery of the storage battery module that is not in the conduction mode to output power, the storage battery module that is not in the conduction mode can be placed in the conduction mode to directly output power from the storage battery.

[0084] Furthermore, the control unit 16b may charge the storage battery of the storage battery module not in the conduction mode from the storage battery of the storage battery module in the conduction mode when the difference between the output voltage Vb of the storage battery of the storage battery module in the conduction mode and the output voltage Vb of the storage battery of the storage battery module not in the conduction mode is not smaller than the voltage threshold Vx. Specifically, the control unit 16b charges the storage battery of the storage battery module not in the conduction mode from the storage battery of the storage battery module in the conduction mode by lowering the output voltage Vo of the conversion circuit of the storage battery module not in the conduction mode below the current output voltage Vo. With the above configuration, the charge amount of the storage battery of the storage battery module in the conduction mode can be reduced to lower the output voltage Vb, and the charge amount of the storage battery of the storage battery module not in the conduction mode can be increased to raise the output voltage Vb. This reduces the difference between the output voltage Vb of the storage battery of the storage battery module in the conduction mode and the output voltage Vb of the storage battery of the storage battery module not in the conduction mode, making it easier to place the storage battery module not in the conduction mode in the conduction mode. In addition, by stopping the output of power from a storage battery module that is not in the conduction mode, the difference between the output voltage Vb of the storage battery of a storage battery module that is in the conduction mode and the output voltage Vb of the storage battery of a storage battery module that is not in the conduction mode can be reduced.

[0085] - By the bus voltage setting unit 16a lowering the bus voltage request value Vbus* below the current bus voltage request value Vbus*, the difference between the bus voltage Vbus and the output voltage Vb of the storage battery of the storage battery module can also be made smaller than the voltage threshold Vx.

[0086] As the load 21, for example, two or more combinations of an inverter and an MG (Motor Generator) (motor units with inverters) may be connected in parallel to the buses 11 and 12. In this case, the more motor units with inverters there are, the more storage battery modules may be connected to the buses 11 and 12.

[0087] As shown in FIG. 14 , the load 28 may be connected in parallel to the second storage battery 61 (storage battery) of the second storage battery module 60 (storage battery module). In this case, the charge amount of the second storage battery 61 can be reduced by supplying power from the second storage battery 61 to the load 28. This makes it easier to reduce the second output voltage Vb2 of the second storage battery 61 in the second storage battery module 60 to a value lower than the first output voltage Vb1 of the first storage battery 31 in the first storage battery module 30. This makes it easier to perform control to add the second output voltage Vo2 of the second conversion circuit 70 to the second output voltage Vb2 of the second storage battery 61 in the second storage battery module 60, thereby regulating the second output voltage Vm2 of the second storage battery module 60 to the bus voltage request value Vbus*.

[0088] As shown in FIG. 15 , the power supply system 210 may include a path 211 connecting a connection point N7 between the third conversion circuit 100 of the third storage battery module 90 and the relay 90a to a connection point N8 between the first storage battery 31 of the first storage battery module 30 and the relay 40b. Furthermore, the power supply system 210 may include a path 213 connecting a connection point N9 between the first conversion circuit 40 of the first storage battery module 30 and the relay 40a to a connection point N10 between the second storage battery 61 of the second storage battery module 60 and the relay 70b. The path 211 is provided with a relay 212 (switch) that connects and disconnects the path 211. The path 213 is provided with a relay 214 (switch) that connects and disconnects the path 213. The relays 212 and 214 are controlled by the ECU 16. The paths 211, 213, and the relays 212 and 214 form a switching circuit. That is, the power supply system 210 may include three or more storage battery modules (plurality of storage battery modules), and the switching circuit may switch the three or more storage battery modules between series connection and parallel connection with the buses 11 and 12 .

[0089] As shown in Fig. 16, in the first conversion circuit 40 (conversion circuit), the switching elements 54 and 55 in Fig. 2 may be connected between the transformer 53 and the negative terminal 48. With this configuration, it is possible to achieve the same effects as the first conversion circuit 40 in Fig. 2. The same applies to the second conversion circuit 70 and the third conversion circuit 100 (conversion circuits).

[0090] 17, the first conversion circuit 40 (conversion circuit) may be a well-known isolated DC-DC converter including a non-center-tapped transformer 153 and a secondary-side full-bridge circuit composed of switching elements 143 to 146. The switching elements 143 to 146 are, for example, FETs or IGBTs (Insulated Gate Bipolar Transistors). The switching elements 143 to 146 are controlled by the ECU 16. The same applies to the second conversion circuit 70 and the third conversion circuit 100 (conversion circuits).

[0091] A resonant DC-DC converter may be used as the first conversion circuit 40 (conversion circuit). Also, a non-isolated DC-DC converter such as a buck converter may be used as the first conversion circuit 40 (conversion circuit). The same applies to the second conversion circuit 70 and the third conversion circuit 100 (conversion circuit).

[0092] The storage battery modules 30, 60 may be configured as shown in FIG. 18 . That is, the positive electrode of the first storage battery 31 is connected to the bus 11. The positive electrode of the first storage battery 31 is connected to the primary-side positive terminal 41 of the first conversion circuit 40, and the negative electrode of the first storage battery 31 is connected to the primary-side negative terminal 42 of the first conversion circuit 40. The negative electrode of the first storage battery 31 is connected to the secondary-side positive terminal 47 of the first conversion circuit 40. The secondary-side negative terminal 48 of the first conversion circuit 40 is connected to the bus 12. In this case, too, the positive and negative electrodes of the first storage battery 31 are connected to the primary-side terminal pair 41, 42 of the first conversion circuit 40, respectively, and the first storage battery 31 is connected in series to the secondary-side terminal pair 47, 48 of the first conversion circuit 40. Even with this configuration, the same effects as those of the first embodiment can be achieved. The same applies to the second storage battery module 60, the third storage battery module 90, etc. (storage battery modules).

[0093] 19, in addition to the configuration of FIG. 18, the first storage battery module 30 may include a bypass 36 and a bypass relay 37, and the second storage battery module 60 may include a bypass 66 and a bypass relay 67. In this case, when the bypass 36 (66) is connected by the bypass relay 37 (67), the storage battery 31 (61) is connected to the buses 11 and 12 via the bypass 36 (66) without via the conversion circuit 40 (70). With this configuration, the same effects as those of the second embodiment can be achieved.

[0094] At least one of the functions of the bus voltage setting unit 16a and the control unit 16b of the ECU 16 can be realized by, for example, a power control ECU (Electronic Control Unit) that controls the power of the electric vehicle or a vehicle control ECU (host ECU) that controls the electric vehicle in an integrated manner. Furthermore, when the power supply system 10 is used as, for example, a stationary power source, the functions of the bus voltage setting unit 16a and the control unit 16b of the ECU 16 can be realized by a stationary power source control ECU (control device) that controls the stationary power source.

[0095] The ECU 16 and the methods described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to execute one or more functions (instructions) embodied in a computer program. Alternatively, the ECU 16 and the methods described herein may be implemented by a special-purpose computer configured with a processor implemented by one or more dedicated hardware logic circuits. Alternatively, the ECU 16 and the methods described herein may be implemented by one or more special-purpose computers configured with a processor and memory programmed to execute one or more functions and a processor implemented by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory storage medium.

[0096] The above-described embodiments and modifications may be combined within the scope of possible combinations.

[0097] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A power supply system (10, 210) comprising a storage battery (31, 61, 91) and a conversion circuit (40, 70, 100) that converts power input from the storage battery to a primary terminal pair (41, 42, 71, 72) by driving switching elements (43-46, 54, 55, 143-146) and outputs the power from a secondary terminal pair (47, 48, 77, 78), wherein the positive and negative electrodes of the storage battery are respectively connected to the primary terminal pair of the conversion circuit, and the storage battery is connected in series to the secondary terminal pair of the conversion circuit, and the power supply system further comprises a connection maintenance circuit (36, 37, 49, 66, 67, 79, 96, 97) that maintains the secondary terminal pair in a connected state.

2. A power supply system as described in claim 1, wherein the connection maintaining circuit is constituted by a secondary circuit (49, 79) of the conversion circuit connected to the secondary terminal pair, and maintains the secondary terminal pair in a connected state by the secondary circuit via a secondary switching element (54, 55), which is the switching element included in the secondary circuit.

3. The power supply system of claim 1, wherein the connection maintenance circuit includes a bypass circuit (36, 66, 96) that bypasses the conversion circuit and connects the secondary terminal pair, and a bypass switch (37, 67, 97) that cuts off and connects the bypass circuit, and the secondary terminal pair is maintained in a connected state by the bypass switch.

4. A power supply system as claimed in any one of claims 1 to 3, wherein a storage battery module (30, 60, 90) is constituted by the storage battery, the conversion circuit, and the connection maintenance circuit, the storage battery module is connected to a power supply bus (11, 12), and a control unit (16b) is provided which executes a conduction mode in which the connection maintenance circuit of the storage battery module maintains the secondary side terminal pair in a connected state, on condition that the difference between a bus voltage which is the voltage of the power supply bus and an output voltage of the storage battery of the storage battery module is smaller than a voltage threshold.

5. The power supply system according to claim 4, further comprising a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit selecting, among the plurality of storage battery modules, a storage battery module having the highest output voltage of the storage battery as the storage battery module to be placed into the conduction mode.

6. The power supply system according to claim 4, further comprising a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit selecting, from among the plurality of storage battery modules, the storage battery module to be placed in the conduction mode, in order from the storage battery module having the higher output voltage of the storage battery.

7. The power supply system of claim 6, wherein the control unit adjusts the output voltage of the conversion circuit so that in a storage battery module in which the difference between the bus voltage and the output voltage of the storage battery of the storage battery module is not smaller than the voltage threshold, the difference between the bus voltage and the output voltage of the storage battery module becomes smaller than the voltage threshold.

8. The power supply system of claim 4, comprising a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit selecting the storage battery module to be placed in the conduction mode and adjusting the state of the storage battery of the selected storage battery module so as to maintain a state in which the difference between the bus voltage and the output voltage of the storage battery of the selected storage battery module is smaller than the voltage threshold.

9. A power supply system as described in claim 4, comprising a plurality of the storage battery modules, the plurality of storage battery modules being connected in parallel to the power supply bus, and the control unit, when any of the storage battery modules is in the conduction mode, places the storage battery module that is not in the conduction mode in the conduction mode, on condition that the difference between the output voltage of the storage battery of the storage battery module in the conduction mode and the output voltage of the storage battery of the storage battery module that is not in the conduction mode is smaller than the voltage threshold value.

10. The power supply system of claim 9, wherein the control unit charges the storage battery of the storage battery module that is not in the conduction mode from the storage battery of the storage battery module that is in the conduction mode when a difference between an output voltage of the storage battery of the storage battery module that is in the conduction mode and an output voltage of the storage battery of the storage battery module that is not in the conduction mode is not smaller than the voltage threshold value.

11. The power supply system of claim 10, wherein the control unit charges the storage battery of the storage battery module that is not in the conduction mode from the storage battery of the storage battery module that is in the conduction mode by lowering the output voltage of the conversion circuit of the storage battery module that is not in the conduction mode below the current output voltage.

12. A control program applied to a power supply system (10, 210) including a storage battery module (30, 60, 90) including a storage battery (31, 61, 91) and a conversion circuit (40, 70, 100) that converts power input from the storage battery to a primary terminal pair (41, 42, 71, 72) by driving switching elements (43-46, 54, 55, 143-146) and outputs the power from a secondary terminal pair (47, 48, 77, 78), the storage battery module (30, 60, 90) being connected to a power supply bus (11, 12), the storage battery having a positive electrode and a negative electrode respectively connected to the primary terminal pair of the conversion circuit, the storage battery being connected in series to the secondary terminal pair of the conversion circuit, and the secondary terminal pair being connected in series, the power supply system including a connection maintaining circuit (36, 37, 49, 66, 67, 79) A control program that causes a computer (16) to execute a conduction mode in which the connection maintenance circuit of the storage battery module maintains the secondary side terminal pair in a connected state, on condition that a difference between a bus voltage, which is the voltage of the power supply bus, and an output voltage of the storage battery of the storage battery module is smaller than a voltage threshold.

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