Control device, program, and control method

Abstract

A control device (40) is applied to a system (10) comprising: a first power storage unit (11A) and a second power storage unit (11B) connected in series to each other; and a first power converter (21A) and a second power converter (21B) respectively connected to both ends of the respective power storage units. The control device controls the first power converter and the second power converter so as to generate an output difference between the first power converter and the second power converter. Each power converter has a characteristic such that, in the relationship between operating point and power conversion efficiency, the power conversion efficiency decreases on the lower output side and the higher output side with respect to a predetermined operating point. The control device comprises: a command setting unit (41) that sets an output command value for each power converter so as to operate each power converter within a predetermined high-efficiency operation region including the predetermined operation point when generating an output difference between the power conversions; and control units (42A, 42B) that control the power converters on the basis of the output command value set by the command setting unit.

Description

Control Device, Program, and Control Method ,

[0008] Cross - Reference to Related Applications

[0001] This application is based on Japanese Application No. 2025 - 006976 filed on January 17, 2025, the contents of which are incorporated herein by reference.

[0002] This disclosure relates to a control device, a program, and a control method.

[0003] Conventionally, a system is known that includes a power converter connected to both ends of each of a plurality of power storage units connected in series with each other, and a control device. The control device controls each power converter. As an example of such a technology, the technology disclosed in Patent Document 1 can be cited.

[0004] Japanese Patent Application Laid - Open No. 2020 - 124060

[0005] The control device may control each power converter so as to cause an output difference between the power converters. In this case, due to at least one of the power converters having a low power conversion efficiency, there is a concern that the operating efficiency of the system is low.

[0006] An object of the present disclosure is to provide a control device, a program, and a control method that can improve the operating efficiency of a system.

[0007] This disclosure is applied to a system including a first power storage unit and a second power storage unit connected in series with each other, and a first power converter and a second power converter respectively connected to both ends of each of the power storage units. In a control device that controls the first power converter and the second power converter so as to cause an output difference between the first power converter and the second power converter, each of the power converters has a characteristic in which the power conversion efficiency decreases on the lower - output side and the higher - output side than a predetermined operating point in the relationship between the operating point and the power conversion efficiency. When causing the output difference, a command setting unit that sets an output command value of each of the power converters so as to operate each of the power converters within a predetermined high - efficiency operating region including the predetermined operating point, and a control unit that controls each of the power converters based on the output command value set by the command setting unit are provided.

[0008] In this disclosure, when an output difference is generated between the power converters, the output command value of each power converter is set so that each power converter operates within a high-efficiency operating region. By controlling each power converter based on the set output command value, each power converter can be operated at an operating point with higher power conversion efficiency compared to a comparative example where the operating point of each power converter is not restricted and an output difference is generated. As a result, the operating efficiency of the system can be improved.

[0009] The above-mentioned objectives and other objectives, features and advantages of this disclosure will become clearer from the following detailed description with reference to the attached drawings. The drawings are as follows: Figure 1 is an overall configuration diagram of the power supply system according to the first embodiment; Figure 2 is a diagram showing the relationship between the operating point of the power converter and the power conversion efficiency; Figure 3 is a flowchart showing the control processing procedure executed by the control device; Figure 4 is a time chart showing an example of the operation of the power supply system; Figure 5 is a diagram showing an example of the case where the operating point of each power converter is shifted; Figure 6 is a diagram showing an example of the operating point of each power converter according to a modification of the first embodiment; Figure 7 is a diagram for explaining the method of setting the current lower limit; Figure 8 is a diagram for explaining the method of setting the current lower limit; Figure 9 is a flowchart showing the control processing procedure executed by the control device according to the second embodiment; Figure 10 is a diagram showing an example of the operating point of each power converter; Figure 11 is a flowchart showing the control processing procedure executed by the control device according to the third embodiment; and Figure 12 is a diagram for explaining the method of determining whether or not to limit the operating point of the power converter to within the high-efficiency operating region.

[0010] Multiple embodiments will be described with reference to the drawings. In multiple embodiments, functionally and / or structurally corresponding and / or related parts may be given the same reference numeral, or reference numerals that differ by hundreds or more digits. For corresponding and / or related parts, refer to the descriptions of other embodiments.

[0011] <First Embodiment> Hereinafter, a first embodiment of the control device according to the present disclosure will be described with reference to the drawings. In this embodiment, the control device is applied to an on-board power supply system. The power supply system is mounted on an electric vehicle that uses a motor as a driving power source.

[0012] As shown in Figure 1, the power supply system 10 includes a high-voltage storage battery 11, a high-voltage load 12, and high-voltage side switches 15 and 16. The high-voltage storage battery 11 is a battery pack comprising a series connection of multiple unit batteries. A unit battery is a single battery cell or a series connection of multiple battery cells. The battery cells are, for example, secondary batteries such as lithium-ion batteries. The rated voltage of the high-voltage storage battery 11 is, for example, several hundred volts. Both ends of the high-voltage storage battery 11 are connected to the high-voltage load 12.

[0013] In this embodiment, the high-voltage load 12 consists of a three-phase inverter 13 and a rotating electric machine 14. The rotating electric machine 14 has armature windings electrically connected to the inverter 13 for each phase. The inverter 13 controls the current flowing through each phase winding. The rotating electric machine 14 is a vehicle-mounted main machine, and the rotor of the rotating electric machine 14 is capable of transmitting power to the vehicle's drive wheels. The rotating electric machine 14 is, for example, a permanent magnet synchronous machine.

[0014] The inverter 13 converts the DC power supplied from the high-voltage battery 11 into AC power and supplies power to each phase winding of the rotating electric machine 14. In this case, the rotating electric machine 14 becomes the power source for the vehicle's movement. The rotating electric machine 14 also performs regenerative power generation using the rotational force applied to the rotor. The inverter 13 converts the generated AC power back into DC power and outputs power to the high-voltage battery 11.

[0015] The high-voltage switches 15 and 16 are located in the path connecting the high-voltage load 12 and the high-voltage battery 11. Specifically, the high-voltage switches are a first high-voltage switch 15 and a second high-voltage switch 16. The first high-voltage switch 15 is located in the path connecting the positive terminal of the inverter 13 and the positive terminal of the high-voltage battery 11. The second high-voltage switch 16 is located in the path connecting the negative terminal of the inverter 13 and the negative terminal of the high-voltage battery 11. Each of the switches 15 and 16 is controlled by a control device 40 provided in the power supply system 10.

[0016] The power supply system 10 includes a low-voltage load 20 and a power converter 21. The low-voltage load 20 is connected to a high-voltage battery 11 via the power converter 21. The power converter 21 is a DC-DC converter, which steps down the voltage of the high-voltage battery 11 and supplies the stepped-down voltage to the low-voltage load 20. For example, an isolated DC-DC converter can be used as the power converter 21.

[0017] The power supply system 10 is capable of redundantly supplying power from the high-voltage battery 11 to the low-voltage load 20.

[0018] More specifically, of the unit batteries constituting the high-voltage storage battery 11, some unit batteries constitute the first storage battery 11A (corresponding to the "first energy storage section"), and the remaining unit batteries constitute the second storage battery 11B (corresponding to the "second energy storage section"). In other words, the high-voltage storage battery 11 is divided into two blocks. In the series connection of the first storage battery 11A and the second storage battery 11B, the first storage battery 11A is on the high-potential side, and the second storage battery 11B is on the low-potential side. In this embodiment, the number of unit batteries constituting the first storage battery 11A is the same as the number of unit batteries constituting the second storage battery 11B. Therefore, the voltage of the first storage battery 11A (e.g., rated voltage) and the voltage of the second storage battery 11B (e.g., rated voltage) are the same.

[0019] The power supply system 10 is equipped with two power converters 21, which are connected to both ends of each battery 11A and 11B, respectively. Hereinafter, the power converter 21A connected to both ends of the first battery 11A will be referred to as the "first power converter 21A," and the power converter 21B connected to both ends of the second battery 11B will be referred to as the "second power converter 21B."

[0020] The positive terminal of the first battery 11A is connected to the first power converter 21A. The negative terminal of the first battery 11A and the positive terminal of the second battery 11B are connected to the respective power converters 21A and 21B. The negative terminal of the second battery 11B is connected to the second power converter 21B.

[0021] The low-voltage load 20 includes a low-voltage battery 22, a normal auxiliary device 23, and a protective auxiliary device 24. The rated voltage of the low-voltage battery 22 is lower than that of the high-voltage battery 11, for example, 12V. The low-voltage battery 22 is a rechargeable battery, for example, a lead-acid battery or a lithium-ion battery.

[0022] The normal auxiliary equipment 23 and protective auxiliary equipment 24 are electrical loads that operate by being supplied with power from the low-voltage battery 22 and the respective power converters 21A and 21B. For example, the normal auxiliary equipment 23 is a general electrical load, specifically including an air conditioner, audio system, power windows, electric fan for the radiator that cools the engine coolant, stop lamps, interior lights, USB power sockets, and motors that drive mirrors located outside the passenger compartment. For example, the protective auxiliary equipment 24 is an electrical load used for vehicle driver assistance control, specifically including an electric power steering system that generates assist torque to assist the driver's steering, an electric brake system that applies braking force to the wheels, cameras for monitoring the situation around the vehicle, laser radar such as LIDAR (Laser Imaging Detection and Ranging), millimeter-wave radar, and drive-by-wire systems.

[0023] The power supply system 10 includes first to fifth electrical paths 31 to 35 and a low-voltage side switch 36 for electrically connecting each power converter 21A, 21B and the low-voltage load 20.

[0024] The first power converter 21A is connected to the positive side of the normal auxiliary equipment 23 via the first electrical path 31. The positive side of the protective auxiliary equipment 24 is connected to the first electrical path 31 via the second electrical path 32. The positive side of the low-voltage battery 22 is connected to the first electrical path 31 via the third electrical path 33. The negative side of the low-voltage battery 22, the negative side of the normal auxiliary equipment 23, and the negative side of the protective auxiliary equipment 24 are connected to the ground. This allows power to be supplied from the first power converter 21A to the low-voltage battery 22, the normal auxiliary equipment 23, and the protective auxiliary equipment 24.

[0025] The second power converter 21B is connected to the first electrical path 31 via the fourth electrical path 34. When the second power converter 21B is connected to the first electrical path 31 via the fourth electrical path 34, power is supplied to the low-voltage load 20 in parallel from both power converters 21A and 21B.

[0026] The positive terminal side of the protective accessory 24 is connected to the fourth electrical path 34 via a fifth electrical path 35, which is a separate path from the second electrical path 32. A low-voltage side switch 36 is provided between the connection point of the fourth electrical path 34 with the first electrical path 31 and the connection point with the fifth electrical path 35. The low-voltage side switch 36 is a relay or a semiconductor switching element. The low-voltage side switch 36 is controlled by the control device 40. In this case, even if power supply to the protective accessory 24 becomes impossible from either of the power converters 21A or 21B, power supply to the protective accessory 24 can be continued from the other.

[0027] The power supply system 10 includes a voltage sensor 50, a battery current sensor 51, and a converter current sensor 52. The voltage sensor 50 detects the voltage of each unit battery that makes up the high-voltage storage battery 11. The battery current sensor 51 detects the current flowing through the high-voltage storage battery 11. The converter current sensor 52 detects the output currents IA and IB of each power converter 21A and 21B. The detected values ​​of each sensor 50 to 52 are input to the control device 40.

[0028] The control device 40 is an electronic control unit (ECU) that performs various controls on the power supply system 10, and includes a processor and a memory unit as hardware. In the power supply system 10, each device can be controlled by an ECU corresponding to the inverter 13, each power converter 21A, 21B, and protective auxiliary equipment 24. However, for convenience, Figure 1 shows multiple ECUs as a single control device 40.

[0029] The storage unit of the control device 40 includes memory and storage as hardware. The memory is a storage device for storing data used in the processing of the control device 40. The memory provides the processor with a workspace for temporary use when the processor is performing processing. The memory includes, for example, ROM or RAM. The storage is a storage device that stores various programs and data for the processor to read and execute, and is a non-transitory tangible storage medium. The storage includes, for example, an HDD or flash memory. The storage stores program information for processing, such as those shown in Figures 3, 9, and 11 described later.

[0030] For example, program information stored on a non-transitional physical recording medium is installed in the storage unit of the control device 40. The recording medium is, for example, a USB memory stick, CD-ROM, or DVD. In addition, program information transmitted via a communication network, such as OTA (Over The Air), is also installed in the storage unit.

[0031] The control device 40 includes a command setting unit 41, a first control unit 42A, and a second control unit 42B, as configured for controlling the output power of each power converter 21A, 21B.

[0032] The command setting unit 41 sets command voltages VAc and VBc (corresponding to "output command values") that command the output voltages VA and VB of each power converter 21A and 21B. For example, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to a value higher than the lower limit value VL of the drive voltage of the low voltage load 20.

[0033] The first control unit 42A receives the command voltage VAc set by the command setting unit 41. The first control unit 42A controls the switching of the first power converter 21A so that the output voltage VA of the first power converter 21A becomes the command voltage VAc. The second control unit 42B receives the command voltage VBc set by the command setting unit 41. The second control unit 42B controls the switching of the second power converter 21B so that the output voltage VB of the second power converter 21B becomes the command voltage VBc.

[0034] The control device 40 controls the output power of each power converter 21A, 21B so as to create an output difference between them. For example, when power is redundantly supplied to the low-voltage load 20 from each battery 11A, 11B, a difference in SOC (corresponding to "storage amount") may occur in each battery 11A, 11B. In this case, the control device 40 creates a difference in the output power of each power converter 21A, 21B in order to reduce the SOC difference between each battery 11A, 11B. The control for creating an output difference between each power converter 21A, 21B will be described below.

[0035] The control device 40 comprises an acquisition unit 43 and a processing unit 44. The acquisition unit 43 acquires the amount of charge stored in each of the batteries 11A and 11B. In this embodiment, the acquisition unit 43 receives the detected value from the voltage sensor 50 and the detected value from the battery current sensor 51 as input. Based on the detected values ​​from the input sensors 50 and 51, the acquisition unit 43 calculates the SOC calculation value of the first battery 11A (hereinafter referred to as "first calculated value SOCA") and the SOC calculation value of the second battery 11B (hereinafter referred to as "second calculated value SOCB"). The acquisition unit 43 acquires the first and second calculated values ​​SOCA and SOCB as the amount of charge stored in the first and second batteries 11A and 11B.

[0036] The processing unit 44 receives the calculated values ​​SOCA and SOCB obtained by the acquisition unit 43. The processing unit 44 determines whether the difference in energy storage amount ΔSOC, which is the difference between the calculated values ​​SOCA and SOCB, is greater than the determination value TH.

[0037] The command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to create an output difference between them, provided that the processing unit 44 determines that the difference in stored energy ΔSOC is greater than the determination value TH. For example, if the SOC of the first battery 11A is higher than the SOC of the second battery 11B, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to be higher than the output voltage VB of the second power converter 21B. This makes the power output from the first battery 11A higher than that from the second battery 11B, and reduces the SOC difference between the batteries 11A and 11B.

[0038] Incidentally, when generating an output difference between the power converters 21A and 21B, the power converters 21A and 21B are operated at different operating points. In this case, the power conversion efficiency η of at least one of the power converters 21A and 21B may decrease.

[0039] The power conversion efficiency η of each power converter 21A and 21B varies depending on the operating point of each power converter 21A and 21B. The operating points of each power converter 21A and 21B are determined by the output voltages VA and VB and the output currents IA and IB. When the output voltages VA and VB of each power converter 21A and 21B are constant and the output currents IA and IB change, the power conversion efficiency η of each power converter 21A and 21B follows the trend shown in Figure 2. In more detail, the power conversion efficiency η of each power converter 21A and 21B decreases at both the lower and higher output sides of a predetermined efficiency peak current Ip. At the lower output side of the efficiency peak current Ip, the decrease in power conversion efficiency η with respect to output current is more pronounced compared to the higher output side of the efficiency peak current Ip. In this case, the decrease in power conversion efficiency η may be more pronounced in the power converter 21A or 21B that is operated at a lower output.

[0040] The reason why the degree of decrease in power conversion efficiency η differs between the lower and higher output power levels below the efficiency peak current Ip is that the main causes of power loss differ between the region below the efficiency peak current Ip and the region above the efficiency peak current Ip. In the region below the efficiency peak current Ip, the ratio of the switching loss of each power converter 21A, 21B to the input power of each power converter 21A, 21B increases, and the power conversion efficiency η decreases. In the region above the efficiency peak current Ip, the conduction loss increases with the increase in the output currents IA, IB of each power converter 21A, 21B, and the power conversion efficiency η decreases.

[0041] There are concerns that the operating efficiency of the power supply system 10 is low due to the low power conversion efficiency η of at least one of the power converters 21A and 21B.

[0042] In detail, the overall efficiency ηt of each power converter 21A and 21B is expressed as shown in equation (1) below, where PA is the output power of the first power converter 21A and PB is the output power of the second power converter 21B.

[0043] ηt = (PA + PB) / (PA / ηA + PB / ηB) (1) In equation (1) above, ηA is the power conversion efficiency of the first power converter 21A, and ηB is the power conversion efficiency of the second power converter 21B. The lower at least one of the power conversion efficiencies ηA and ηB becomes, the lower the overall efficiency ηt becomes. Therefore, there is concern that the operating efficiency of the power supply system 10 is low due to at least one of the power conversion efficiencies ηA and ηB being low.

[0044] Therefore, the command setting unit 41 sets the command voltages Vac and Vbc of the power converters 21A and 21B so as to operate the power converters 21A and 21B within the high-efficiency operation region Ra. As shown in FIG. 2, the high-efficiency operation region Ra is a region on the high-output side with respect to the efficiency peak current Ip. In other words, the lower current limit IL (corresponding to the "output lower limit value") of the current when operating the power converters 21A and 21B within the high-efficiency operation region Ra is defined as the efficiency peak current Ip. On the high-output side with respect to the efficiency peak current Ip, since the decrease in the power conversion efficiency η is gentler than on the low-output side with respect to the efficiency peak current Ip, the upper current limit of the output currents IA and IB of the power converters 21A and 21B may not be defined in the high-efficiency operation region Ra.

[0045] Specifically, when the SOC of the first storage battery 11A is higher than the SOC of the second storage battery 11B, the command setting unit 41 sets the command voltages Vac and Vbc of the power converters 21A and 21B so as to satisfy the following first condition and second condition. The first condition is the condition that the output current IA of the first power converter 21A is larger than the output current IB of the second power converter 21B. The second condition is the condition that the output currents IA and IB of the power converters 21A and 21B are larger than the lower current limit IL.

[0046] When the SOC of the second storage battery 11B is higher than the SOC of the first storage battery 11A, the command setting unit 41 sets the command voltages Vac and Vbc of the power converters 21A and 21B so as to satisfy the second condition and the following third condition. The third condition is the condition that the output current IB of the second power converter 21B is larger than the output current IA of the first power converter 21A.

[0047] Due to the small load current Io flowing through the low-voltage load 20, it may be impossible to make the output currents IA and IB of the power converters 21A and 21B larger than the lower current limit IL. In this case, it is conceivable to supply the load current Io to the low-voltage load 20 from only one of the power converters 21A and 21B to avoid the power converter operating at a low-efficiency operating point.

[0048] The control device 40 includes a power determination unit 45. The power determination unit 45 determines whether the power condition is met, which is that the required drive power required for the low-voltage load 20 is lower than the total power that can be output when each power converter 21A and 21B is operated at the lower current limit IL. In this embodiment, the power determination unit 45 determines that the power condition is met when it determines that the load current Io flowing through the low-voltage load 20 is smaller than the total current "2 × IL" (i.e., "2 × Ip") that can be output when each power converter 21A and 21B is operated at the lower current limit IL.

[0049] If the power determination unit 45 determines that the power conditions are met, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B so that load current Io is supplied to the low voltage load 20 from only one of the power converters 21A and 21B. If the power determination unit 45 determines that the power conditions are not met, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B so that each power converter 21A and 21B is operated in the high-efficiency operating region Ra.

[0050] Figure 3 shows the control process performed by the control device 40. This control is executed repeatedly at predetermined intervals.

[0051] In step S10, the acquisition unit 43 acquires the first calculated value SOCA and the second calculated value SOCB. In step S11, the processing unit 44 determines whether the energy storage difference ΔSOC is greater than the determination value TH. If a negative determination is made in step S11, the process proceeds to step S12. In this embodiment, the processing in step S11 performed by the processing unit 44 corresponds to the "energy storage amount determination unit".

[0052] In step S12, the command setting unit 41 sets the command voltages VAc and VBc for each power converter 21A and 21B. Here, the command voltages VAc and VBc for each power converter 21A and 21B are set without restricting the operating point of each power converter 21A and 21B according to the first to third conditions described above. For example, the command voltages VAc and VBc for each power converter 21A and 21B are set so that the power output from each battery 11A and 11B is the same. In step S13, the first control unit 42A and the second control unit 42B perform switching control of each power converter 21A and 21B so that the output voltages VA and VB of each power converter 21A and 21B become the set command voltages VAc and VBc.

[0053] If a positive determination is made in step S11, the process proceeds to step S14. In step S14, the processing unit 44 determines whether the first calculated value SOCA is higher than the second calculated value SOCB. If a positive determination is made in step S13, the process proceeds to step S15.

[0054] In step S15, the power determination unit 45 acquires the load current Io flowing through the low-voltage load 20. For example, the sum of the rated currents of the operating normal auxiliary equipment 23 and protective auxiliary equipment 24, and the rated current of the low-voltage storage battery 22 can be acquired as the load current Io. Alternatively, for example, the detected value of the current flowing through the low-voltage load 20 can be acquired as the load current Io. In this case, the power supply system 10 may be provided with a load current sensor that detects the current flowing through the low-voltage load 20. In step S16, the power determination unit 45 determines whether the power conditions are met based on the acquired load current Io.

[0055] If a negative determination is made in step S16, the process proceeds to step S17. In step S17, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to satisfy the first and second conditions. On the other hand, if an affirmative determination is made in step S16, the process proceeds to step S18. In step S18, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to output current from the first power converter 21A and to stop the current output of the second power converter 21B.

[0056] If a negative result is obtained in step S14, proceed to step S19. The processing in step S19 is the same as in step S15. The processing in step S20 is the same as in step S16.

[0057] If a negative result is obtained in step S20, the process proceeds to step S21. In step S21, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to satisfy the second and third conditions. On the other hand, if an affirmative result is obtained in step S20, the process proceeds to step S22. In step S22, the command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A and 21B to stop the current output of the first power converter 21A and to output current from the second power converter 21B. After processing in steps S17, S18, S21, and S22, the process proceeds to step S13.

[0058] Figure 4 shows an example of the control operation performed by the control device 40. In Figure 4, (a) shows the transition of the voltage VbatA of the first battery 11A and the transition of the voltage VbatB of the second battery 11B, (b) shows the transition of the command voltage VAc of the first power converter 21A, (c) shows the transition of the command voltage VBc of the second power converter 21B, (d) shows the transition of the output current IA of the first power converter 21A, (e) shows the transition of the output current IB of the second power converter 21B, and (f) shows the transition of the load current Io flowing to the low-voltage load 20. Here, we will explain the operation when the output difference between the power converters 21A and 21B is generated in order to reduce the SOC difference between the batteries 11A and 11B when the SOC of the first battery 11A is higher than the SOC of the second battery 11B.

[0059] At time t1, the power supply system 10 is started up. Consequently, power can be supplied from each power converter 21A, 21B to the low-voltage load 20. During the period from time t1 to time t2, the power determination unit 45 determines that the power conditions are met. The command setting unit 41 sets the command voltages VAc and VBc of each power converter 21A, 21B to a value higher than the lower limit value VL of the drive voltage of the low-voltage load 20. The command setting unit 41 sets the command voltage VBc of the second power converter 21B to a value lower than the command voltage VAc of the first power converter 21A, and to a value such that the output current of the second power converter 21B is 0 [A].

[0060] Specifically, the command setting unit 41 sets the command voltage VBc of the second power converter 21B as a value obtained by subtracting the voltage drop caused by the wiring resistance between each power converter 21A and 21B in the first and fourth electrical paths 31 and 34 from the command voltage VAc of the first power converter 21A. This makes it possible to stop the current output from the second power converter 21B. The voltage drop that occurs between each power converter 21A and 21B can be a value that has been calculated in advance during the design phase. For example, the lower limit VL of the drive voltage of the low voltage load 20 is 10.0 [V]. For example, if the voltage drop that occurs between each power converter 21A and 21B is 2.0 [V], the command voltage VAc of the first power converter 21A is 14.5 [V], and the command voltage VBc of the second power converter 21B is 12.5 [V]. The command voltage VBc of the second power converter 21B may be a value obtained by subtracting a value greater than the voltage drop across the wiring resistance from the command voltage VAc of the first power converter 21A, for example, 10.0 [V] < VBc < 12.5 [V].

[0061] During the period from time t1 to time t2, power is supplied to the low-voltage load 20 only from the first power converter 21A among the power converters 21A and 21B. In this case, as the output current IA of the first power converter 21A increases, the load current Io increases.

[0062] At time t2, the load current Io exceeds twice the current lower limit IL. In this case, the power determination unit 45 determines that the power condition is not met. The command setting unit 41 sets the command voltage VBc of the second power converter 21B to a value higher than the value set during the period from time t1 to time t2. In this embodiment, the command setting unit 41 increases the command voltage VBc of the second power converter 21B within the range VBc < VAc until the output current IB of the second power converter 21B reaches the current lower limit IL.

[0063] The command setting unit 41 may also set the command voltage VBc as a calculated value obtained by determining that the output current IB of the second power converter 21B becomes the lower current limit IL. In this case, the command setting unit 41 may calculate the command voltage VBc that causes the output current IB of the second power converter 21B to become the lower current limit IL based on the circuit constants of the power supply system 10.

[0064] At time t3, current output from the second power converter 21B begins. After time t3, if the output current IB of the second power converter 21B reaches the current lower limit IL, the output current IA of the first power converter 21A is reduced by the amount of the current lower limit IL compared to time t3. Note that the command voltage VBc of the second power converter 21B is set to a lower value than the command voltage VAc of the first power converter 21A, so the output current IB of the second power converter 21B is smaller than the output current IA of the first power converter 21A.

[0065] Figure 5 shows an example of the case where the operating points of each power converter 21A and 21B are shifted. The operating point before the shift is after time t3 in Figure 4, and represents the timing before the output current IB of the second power converter 21B reaches the current lower limit IL. The operating point after the shift is after time t3 in Figure 4, and represents the timing when the output currents IA and IB of each power converter 21A and 21B become constant.

[0066] At the operating point before the shift, the power conversion efficiency ηB of the second power converter 21B is significantly reduced because the output current IB of the second power converter 21B is smaller than the efficiency peak current Ip. From this state, the output current IB of the second power converter 21B is set to the current lower limit IL. In this embodiment, the current lower limit IL is set to the efficiency peak current Ip. Therefore, when operating each power converter 21A and 21B within the high-efficiency operating region Ra, the power conversion efficiency ηB of the second power converter 21B can be accurately improved. Furthermore, when the output current IB of the second power converter 21B is set to the efficiency peak current Ip, the power conversion efficiency ηB of the second power converter 21B can be increased compared to a configuration in which the output current IB of the second power converter 21B is controlled to a value larger than the efficiency peak current Ip. As a result, the operating efficiency of the power supply system 10 can be accurately improved.

[0067] According to the embodiment described in detail above, the following effects can be obtained.

[0068] When an output difference is generated between the power converters 21A and 21B, the command voltages VAc and VBc of each power converter 21A and 21B are set so that each power converter 21A and 21B operates within the high-efficiency operating region Ra. By controlling each power converter 21A and 21B based on the set command voltages VAc and VBc, each power converter 21A and 21B can be operated at an operating point with higher power conversion efficiencies ηA and ηB compared to a comparative example where the operating point of each power converter 21A and 21B is not restricted and an output difference is generated. As a result, the operating efficiency of the power supply system 10 can be improved.

[0069] When operating the power converters 21A and 21B within the high-efficiency operating region Ra, while creating an output difference by reducing the output current IB of the second power converter 21B relative to the output current IA of the first power converter 21A, the command voltage VAc of the first power converter 21A is set to VL ≤ VAc. This ensures that the voltage necessary to drive the low-voltage load 20 is secured. The command voltage VBc of the second power converter 21B is set to a value within the range VL ≤ VBc < VAc. This makes it possible to adjust the ratio of the output currents IA and IB of the power converters 21A and 21B while maintaining the voltage necessary to drive the low-voltage load 20. Therefore, suitable control can be achieved to adjust the output currents IA and IB of the power converters 21A and 21B while supplying power to drive the low-voltage load 20.

[0070] If it is determined that the power conditions are not met, the command voltages VAc and VBc are set so that each power converter 21A and 21B operates within the high-efficiency operating region Ra. On the other hand, if it is determined that the power conditions are met, power output to the low-voltage load 20 from either one of the power converters 21A or 21B is stopped. In this case, the number of power converters that output power when the required drive power of the low-voltage load 20 is low is reduced. This prevents a situation in which the power conversion efficiencies ηA and ηB of each power converter 21A and 21B decrease due to each power converter 21A and 21B operating at an operating point lower than the current lower limit IL when under low load. As a result, the operating efficiency of the power supply system 10 at low load can be improved.

[0071] When it is determined that the power conditions are met, the command voltage is set in the power converter 21A, 21B that is to be shut down, such that the output voltage becomes higher than the lower limit VL of the drive voltage of the low-voltage load 20 and the output current becomes 0 [A]. This allows power supply from the shut-down power converter to be quickly started when the load current Io of the low-voltage load 20 increases. Therefore, the operating efficiency of the power supply system 10 at low loads is improved, and load fluctuations of the low-voltage load 20 can be responded to quickly.

[0072] The command voltages VAc and VBc are set so that each power converter 21A and 21B operates within the high-efficiency operating region Ra, provided that the difference in stored energy ΔSOC is determined to be greater than the determination value TH. This prevents the unnecessary execution of control that limits the operating point of each power converter 21A and 21B.

[0073] <Modification of the First Embodiment> The command setting unit 41 may set the command voltage such that, when operating each power converter 21A and 21B within the high-efficiency operating region Ra, the output current of the low-output operating converter is greater than the current lower limit value IL. The low-output operating converter is the power converter among the power converters 21A and 21B that is operated at a lower output. In Figure 6, the low-output operating converter is the second power converter 21B. Even in this case, it is possible to suppress a decrease in the power conversion efficiency of the second power converter 21B compared to the comparative example in which the operating point of the second power converter 21B is not limited to within the high-efficiency operating region Ra.

[0074] For example, when setting the command voltage of a low-power converter so that the output current of the low-power converter is greater than the current lower limit IL, the command setting unit 41 may set the command voltage of the low-power converter higher the larger the load current Io is. This ensures that the power supplied to the low-voltage load 20 is adequately secured. Alternatively, for example, the command setting unit 41 may set the command voltage of the low-power converter higher the larger the output current of the high-power converter among the power converters 21A and 21B. This increases the output current of the low-power converter above the current lower limit IL while bringing the output current of the high-power converter as close as possible to the efficiency peak current Ip. As a result, the power conversion efficiencies ηA and ηB of each power converter 21A and 21B can be adequately improved.

[0075] The lower limit of the current IL in the high-efficiency operating region Ra is not limited to the efficiency peak current Ip; it may also be set to a lower output level than the efficiency peak current Ip.

[0076] For example, it is possible to determine the current lower limit IL by considering the rate of change of power conversion efficiencies ηA and ηB with respect to the output currents IA and IB of each power converter 21A and 21B. Figure 7 shows the characteristics of the relationship between the output currents IA and IB of each power converter 21A and 21B and the power conversion efficiencies ηA and ηB, and the rate of change of power conversion efficiencies ηA and ηB with respect to each output current IA and IB. The rate of change of power conversion efficiencies ηA and ηB with respect to each output current IA and IB is shown with a positive slope indicating a decrease in power conversion efficiencies ηA and ηB. The slope of efficiency decrease of power conversion efficiencies ηA and ηB is 0 at the efficiency peak current Ip, and increases on the high output side and low output side relative to the efficiency peak current Ip. However, on the low output side relative to the efficiency peak current Ip, the slope of efficiency decrease of power conversion efficiencies ηA and ηB is higher than the predetermined rate of change αk at the upper limit Ik of the output currents IA and IB of each power converter 21A and 21B. For example, the upper limit Ik is determined based on the performance of each power converter 21A, 21B.

[0077] The current lower limit IL may be a value on the lower output side of the efficiency peak current Ip, and may be set to a value such that the slope of the efficiency decrease of power conversion efficiencies ηA and ηB is less than or equal to a predetermined rate of change αk. In this case, the current lower limit IL can be set within a range where the degree of decrease in power conversion efficiencies ηA and ηB from the efficiency peak current Ip is not as large as when the current lower limit IL is set such that the slope of the efficiency decrease of power conversion efficiencies ηA and ηB is greater than the predetermined rate of change αk. For example, the current lower limit IL may be a value within the setting region Rb shown in Figure 7, and may be set to a value on the lower output side of the efficiency peak current Ip. In this case, the current lower limit IL can be set within a range where the decrease in power conversion efficiencies ηA and ηB is not as large when the predetermined current is reduced from the efficiency peak current Ip as it is when the predetermined current is increased from the efficiency peak current Ip. Therefore, even if the command voltage of each power converter 21A, 21B is set so that the output current of either one of the power converters 21A, 21B becomes the current lower limit value IL, it is possible to suppress a significant decrease in the power conversion efficiencies ηA, ηB.

[0078] The lower limit current value IL in the high-efficiency operating region Ra may be set to a higher output value than the efficiency peak current Ip. For example, it may be a value within the setting region Rb shown in Figure 7, and set to a value on the higher output side than the efficiency peak current Ip.

[0079] The high-efficiency operating region Ra may be defined as the region in which the power conversion efficiencies ηA and ηB are equal to or greater than a predetermined efficiency ηa, as shown in Figure 8. For example, the predetermined efficiency ηa is a value of 90% or higher. In this case, the high-efficiency operating region Ra is defined by the current lower limit IL and the current upper limit IH, which is higher than the efficiency peak current Ip.

[0080] <Second Embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings. In this embodiment, the processing performed by the processing unit 44 has been changed.

[0081] Figure 9 shows the control processing procedure performed by the control device 40.

[0082] After processing in step S15, the process proceeds to step S30. In step S30, the processing unit 44 sets the current lower limit IL of the high-efficiency operating region Ra to a variable value. In this embodiment, when the energy storage difference ΔSOC is less than or equal to a predetermined difference value, the current lower limit IL is set to the efficiency peak current Ip. When the energy storage difference ΔSOC is greater than the predetermined difference value, the current lower limit IL is set to a value smaller than the efficiency peak current Ip. In this case, as shown in Figure 10, when the energy storage difference ΔSOC is large, it is possible to increase the output difference between each power converter 21A, 21B compared to when the current lower limit IL is set to the efficiency peak current Ip. This makes it possible to quickly reduce the energy storage difference ΔSOC while limiting the operating point of each power converter 21A, 21B to within the high-efficiency operating region Ra. Also, when the energy storage difference ΔSOC is less than or equal to a predetermined difference value, the current lower limit IL is set to the efficiency peak current Ip. Therefore, control can be suitably implemented to operate each power converter 21A and 21B with high efficiency.

[0083] For example, the current lower limit IL can be set to be variable by changing it in steps with respect to the energy storage difference ΔSOC, or by changing it continuously with respect to the energy storage difference ΔSOC. When setting the current lower limit IL by changing it continuously, the current lower limit IL may be set to decrease from the efficiency peak current Ip as the energy storage difference ΔSOC becomes larger. After processing in step S30, the process proceeds to step S16.

[0084] After processing in step S19, the process proceeds to step S31. In step S31, the same processing as in step S30 is performed. After processing in step S31, the process proceeds to step S20. In this embodiment, the processing in steps S30 and S31 performed by the processing unit 44 corresponds to the "region setting unit".

[0085] <Third Embodiment> The third embodiment will now be described, focusing on the differences from the first embodiment, with reference to the drawings. In this embodiment, the processing performed by the command setting unit 41 and the processing unit 44 has been modified.

[0086] Figure 11 shows the control processing procedure performed by the control device 40.

[0087] If step S16 is determined to be negative, the process proceeds to step S40. In step S40, the processing unit 44 acquires load information indicating the driving status of the high-voltage load 12. In this embodiment, the load information indicates whether or not the rotating electric machine 14 is being driven by power supplied from the high-voltage battery 11.

[0088] In step S41, the processing unit 44 determines whether to restrict the operating points of each power converter 21A and 21B to within the high-efficiency operating region Ra, based on the load information and the calculated values ​​SOCA and SOCB. In this embodiment, if the load information indicates that the rotating electric machine 14 is not being driven, it is determined to restrict the operating points of each power converter 21A and 21B to within the high-efficiency operating region Ra. In this case, the process proceeds to step S17.

[0089] On the other hand, if the load information indicates that the rotating electric machine 14 is being driven, and it is determined that there is no margin of charge in either of the batteries 11A or 11B relative to the discharge limit, it is determined that the operating point of each power converter 21A or 21B is not restricted to the high-efficiency operating region Ra. For example, if either of the calculated values ​​SOCA or SOCB is lower than the predetermined discharge value SOCd shown in Figure 12, it is possible to determine that there is no margin of charge in either of the batteries 11A or 11B relative to the discharge limit. The predetermined discharge value SOCd is a value higher than the discharge limit value SOCL of each battery 11A or 11B. If a negative determination is made in step S41, the process proceeds to step S42. In step S42, the command voltages VAc and VBc of each power converter 21A or 21B are set so that only the first condition of the two conditions is satisfied. After processing in step S42, the process proceeds to step S13.

[0090] If step S20 is determined to be negative, proceed to step S43. In step S43, the same process as in step S40 is performed. In step S44, the same process as in step S41 is performed. If the result in step S44 is positive, proceed to step S21. If the result in step S44 is negative, proceed to step S45. In step S45, set the command voltages VAc and VBc of each power converter 21A and 21B so that only the third condition of the second and third conditions is satisfied. After the processing in step S45, proceed to step S13.

[0091] According to this embodiment, when the rotating electric machine 14 is being driven and the State of Charge (SOC) of each battery 11A and 11B is low, the operating point of each power converter 21A and 21B is not limited to the high-efficiency operating region Ra. As a result, in situations where each battery 11A and 11B may be discharged to its lower discharge limit, the equalization of the SOC of each battery 11A and 11B is performed without being limited by the high-efficiency operating region Ra. Therefore, proper use of each battery 11A and 11B can be ensured.

[0092] Load information is used to determine whether or not to limit the operating point of each power converter 21A, 21B to within the high-efficiency operating region Ra. This makes it possible to accurately determine whether or not each battery 11A, 11B is being discharged to its lower discharge limit.

[0093] <Modification of the third embodiment> The high-voltage load 12 may be an external charger instead of the inverter 13 and the rotating electric machine 14. The external charger is, for example, a stationary charger installed outside the vehicle, which charges the high-voltage storage battery 11.

[0094] In steps S40 and S43 of Figure 11, information indicating that there is a charge request for the high-voltage battery 11 by an external charger may be acquired as load information. In steps S41 and S44, if the load information indicates that the high-voltage battery 11 is not being charged by the external charger, it may be determined to restrict the operating points of each power converter 21A and 21B to within the high-efficiency operating region Ra. On the other hand, if the load information indicates that the high-voltage battery 11 is being charged by the external charger, and it is determined that there is no margin for the amount of stored energy relative to the charge limit in either of the batteries 11A and 11B, it may be determined not to restrict the operating points of each power converter 21A and 21B to within the high-efficiency operating region Ra. For example, if either of the calculated values ​​SOCA and SOCB is higher than the predetermined charge value SOCc shown in Figure 12, it is possible to determine that there is no margin for the amount of stored energy relative to the charge limit in either of the batteries 11A and 11B. The predetermined charge value SOCc is a value lower than the charge limit value SOCH of each battery 11A and 11B.

[0095] According to this embodiment, when the high-voltage battery 11 is being charged and each battery 11A and 11B is likely to be charged to its maximum charge limit, the equalization of the State of Charge (SOC) of each battery 11A and 11B can be performed without being limited by the high-efficiency operating region Ra.

[0096] - In steps S40 and S43 of Figure 11, it is not necessary to acquire load information. In steps S41 and S44, if each calculated value SOCA and SOCB is greater than or equal to the predetermined discharge value SOCd and less than or equal to the predetermined charge value SOCc, it may be determined that there is a margin of stored energy relative to the lower discharge limit and upper charge limit in each battery 11A and 11B. In this case, steps S41 and S44 may be determined affirmatively. If either each calculated value SOCA or SOCB is lower than the predetermined discharge value SOCd, or if either each calculated value SOCA or SOCB is higher than the predetermined charge value SOCc, it may be determined that there is no margin of stored energy relative to the lower discharge limit or upper charge limit in either battery 11A or 11B. In this case, steps S41 and S44 may be determined negatively.

[0097] <Other Embodiments> The above embodiments may be modified and implemented as follows.

[0098] The command setting unit 41 may set a command current (corresponding to the "output command value") that commands the output currents IA and IB of each power converter 21A and 21B. In this case as well, the command setting unit 41 can set the command current of each power converter 21A and 21B so that each power converter 21A and 21B operates within the high-efficiency operating region Ra.

[0099] - The command setting unit 41 may set the command voltages VAc and VBc of each power converter 21A and 21B to create an output difference between each power converter 21A and 21B in order to increase the SOC difference between each battery 11A and 11B, rather than reducing the SOC difference between each battery 11A and 11B. In this case, in step S11 of Figure 3, the processing unit 44 may determine whether or not there is a request to increase the SOC difference between each battery 11A and 11B. For example, if one of the batteries 11A and 11B is degraded and it is necessary to replace the degraded battery in a factory or the like, it is conceivable that there is a situation where it is desirable to use up the SOC of the degraded battery preferentially over that of a normal battery. In this case, a request to increase the SOC difference between each battery 11A and 11B may arise.

[0100] The power determination unit 45 is not limited to determining that the power condition is met when it determines that Io < 2 × IL. For example, the power determination unit 45 may determine that the power condition is met when it determines that the sum of the rated power of the operating normal auxiliary equipment 23 and protective auxiliary equipment 24, and the rated power of the low-voltage storage battery 22 is lower than the sum of the power that can be output when operating each power converter 21A, 21B at the lower limit current value IL.

[0101] In the second embodiment, in steps S30 and S31 of Figure 9, if the difference in stored energy ΔSOC is less than or equal to a predetermined difference value, the current lower limit IL may be set to the value described in Figures 7 and 8 instead of the efficiency peak current Ip. In this case, the current lower limit IL set when the difference in stored energy ΔSOC is greater than the predetermined difference value may be set to a smaller value than the current lower limit IL set when the difference in stored energy ΔSOC is less than or equal to the predetermined difference value.

[0102] The acquisition unit 43 may acquire not only the State of Charge (SOC) of each battery 11A and 11B, but also energy storage parameters indicating the amount of stored energy, such as energy and open-circuit voltage (OCV). In this case as well, the processing unit 44 can perform the various processes described in Figures 3, 9, and 11 above.

[0103] The high-voltage storage battery 11 is not limited to having two storage batteries, but may also have three or more storage batteries. In this case, a power converter corresponding to each storage battery may be connected to both ends of each of the three or more storage batteries.

[0104] - When the power supply system is equipped with N (N ≥ 3) power converters, in steps S16 and S20 of Figure 3 above, it may be determined whether the load current Io of the low-voltage load 20 is smaller than the total output current "N × IL" that can be produced when the N power converters are operated at the current lower limit value IL.

[0105] The first and second energy storage units are not limited to batteries, but may include, for example, a large-capacity electric double-layer capacitor, or both a battery and an electric double-layer capacitor. Furthermore, the first and second energy storage units may be fuel cells.

[0106] The power supply system may not be mounted on a vehicle; for example, it may be on a mobile body such as an aircraft or a ship. If the mobile body is an aircraft, the rotating electric machine will be the power source for the aircraft's flight; if the mobile body is a ship, the rotating electric machine will be the power source for the ship's navigation. Furthermore, the power supply system is not limited to being mounted on a mobile body; it can also be used as a stationary power source.

[0107] In this disclosure or claims, the term "processor" means one or more hardware processors configured to execute processing defined by computer program code (i.e., one or more instructions of a computer program) contained in a computer program by reading the computer program code each time. In other words, a "processor" is a hardware device that executes one or more programmed processes. Therefore, computer program code can also be said to be software that can define the processing of the processor according to its content. A "processor" can be a general-purpose or specific-purpose processor, and may be, but is not limited to, a CPU, microprocessor, GPU, and DFP (Data Flow Processor).

[0108] In this disclosure or claims, the term “memory” means one or more hardware memories that are non-transitional tangible recording media configured to record computer program code and / or data in a manner accessible from a processor. “Memory” can be implemented by memory technologies such as SRAM, SDRAM, non-volatile / flash memory, or other types of memory. The computer program code that constitutes the program is recorded in memory and executed by a processor, thereby enabling the processor to perform the various functions described above.

[0109] In this disclosure or claims, the term “circuit” refers to one or more logic circuits as hardware, configured to perform specific operations defined by a pre-designed circuit configuration. In other words (and, in contrast to “processor”), “circuit” in this disclosure or claims refers to a hardware device that performs specific operations based on a circuit configuration, rather than having operations defined by software such as the computer program code described above. For example, “circuit” may include custom ICs such as ASICs (Application Specific Integrated Circuits) and FPGAs (Field Programmable Gate Arrays) designed with a Hardware Description Language (HDL). That is, “circuit” in this disclosure or claims includes all hardware circuits except for the processor described above, which performs operations by reading computer program code.

[0110] In this disclosure or claims, the expression "at least one of the circuit and processor" should be interpreted as disjunctive (logical OR) and not as "at least one circuit and at least one processor." Therefore, in this disclosure or claims, "at least one of the circuit and processor causes the control device to perform functions" includes cases where the circuit alone causes the control device to perform all functions. Furthermore, "at least one of the circuit and processor causes the control device to perform functions" includes cases where the processor alone causes the control device to perform all functions. In addition, "at least one of the circuit and processor causes the control device to perform functions" includes cases where the circuit causes the control device to perform some functions and the processor causes the control device to perform the remaining functions. In the last example, for example, if the control device performs functions A to C, functions A and B may be implemented by the circuit, and the remaining C may be implemented by the processor.

[0111] The technical concept extracted from the above-described embodiment is described below. [Configuration 1] A control device (40) applied to a system (10) comprising: a first energy storage unit (11A) and a second energy storage unit (11B) connected in series with each other; a first power converter (21A) and a second power converter (21B) connected to both ends of each energy storage unit, wherein the control device (40) controls the first power converter and the second power converter to create an output difference between the first power converter and the second power converter, wherein each power converter has the characteristic that the power conversion efficiency decreases on the lower output side and the higher output side than a predetermined operating point in relation to the operating point and power conversion efficiency; a command setting unit (41) that sets an output command value for each power converter so that when the output difference is created, each power converter is operated within a predetermined high-efficiency operating region including the predetermined operating point; and a control unit (42A, 42B) that controls each power converter based on the output command value set by the command setting unit. [Configuration 2] The control device according to Configuration 1, wherein each power converter is connected to an electrical load (20), and the command setting unit generates a difference in the output current of each power converter as the output difference, and when each power converter is operated within the high-efficiency operating region, it sets the output command value to command the output voltage of the power converter with the larger output current among the power converters so that the voltage applied to the electrical load is equal to or greater than the lower limit of the drive voltage, and sets the output command value to command the output voltage of the power converter with the smaller output current among the power converters so that the output voltage of the power converter with the smaller output current is equal to or greater than the lower limit and less than the output voltage of the power converter with the larger output current.[Configuration 3] The control device according to Configuration 2, wherein the command setting unit sets the output command value of each power converter so that when the amount of charge stored in the first power storage unit is higher than the amount of charge stored in the second power storage unit, the output difference is such that the output current of the first power converter is greater than the output current of the second power converter, and each power converter is operated within the high-efficiency operating region, and when the amount of charge stored in the second power storage unit is higher than the amount of charge stored in the first power storage unit, the output command value of each power converter is set so that when the amount of charge stored in the second power storage unit is higher than the amount of charge stored in the first power storage unit, the output difference is such that the output current of the second power converter is greater than the output current of the first power converter, and each power converter is operated within the high-efficiency operating region. [Configuration 4] The control device according to any one of Configurations 1 to 3, further comprising a region setting unit (44) that sets the lower limit of the output of the high-efficiency operating region to a smaller value when the difference in the amount of charge stored between the amount of charge stored in the first power storage unit and the amount of charge stored in the second power storage unit is greater than a predetermined difference value, compared to when the difference in the amount of charge stored is less than or equal to the predetermined difference value. [Configuration 5] The control device according to Configuration 4, wherein the region setting unit sets the output corresponding to the predetermined operating point as the lower output limit when the difference in stored energy is less than or equal to the predetermined difference value. [Configuration 6] The control device according to Configuration 4, wherein the region setting unit sets the output lower limit when the difference in stored energy is less than or equal to the predetermined difference value, such that the slope of efficiency decrease on the lower output side below the predetermined operating point in the characteristics is less than or equal to a predetermined value. [Configuration 7] The control device according to Configuration 4, wherein the region setting unit sets the output lower limit when the difference in stored energy is less than or equal to the predetermined difference value, such that the slope of efficiency decrease on the lower output side below the predetermined operating point in the characteristics is smaller than the slope of output decrease on the higher output side above the predetermined operating point.[Configuration 8] The control device according to any one of Configurations 1 to 7, wherein each power converter is connected to an electrical load (20), and includes a power determination unit (45) that determines whether or not a power condition is met such that the required drive power required by the electrical load is lower than the total power that can be output when each power converter is operated at the lower limit of the output of the high-efficiency operating region, and the command setting unit sets the output command value so that each power converter is operated within the high-efficiency operating region when the power determination unit determines that the power condition is not met, and sets the output command value so that the power output from one of the power converters is stopped when the power determination unit determines that the power condition is met. [Configuration 9] The control device according to Configuration 8, wherein the command setting unit sets the output command value so that, when the power determination unit determines that the power condition is met, the output voltage of the power converter whose power output is stopped is higher than the lower limit of the drive voltage of the electrical load and the output current is 0. [Configuration 10] A control device according to any one of Configurations 1 to 9, comprising a power storage amount determination unit (44) that determines whether or not to generate the output difference based on the difference in power storage amounts between the power storage amount of the first power storage unit and the power storage amount of the second power storage unit, wherein the command setting unit sets the output command value so as to operate each power converter within the high-efficiency operating range, on the condition that the power storage amount determination unit has determined that to generate the output difference.[Configuration 11] The system enables power supply to low-voltage loads (20) connected to each power converter and power supply to high-voltage loads (12) to which a higher voltage than that applied to the low-voltage loads is performed, wherein power is supplied from each energy storage unit to the low-voltage loads via the power converters, while power is supplied from the series connection of each energy storage unit to the high-voltage loads, wherein the energy storage amount determination unit determines whether there is a margin of energy storage amount relative to the discharge lower limit or charge upper limit when it determines that the output difference will occur, the command setting unit sets the output command value of each power converter so as to operate each power converter within the high-efficiency operating region when the energy storage amount determination unit determines that there is a margin, and sets the output command value of each power converter without restricting the operating point of each power converter to within the high-efficiency operating region when the energy storage amount determination unit determines that there is no margin, the control device according to Configuration 10.

[0112] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure.

Claims

1. A control device (40) applied to a system (10) comprising: a first energy storage unit (11A) and a second energy storage unit (11B) connected in series with respect to each other; and a first power converter (21A) and a second power converter (21B) connected to both ends of each energy storage unit, wherein the control device (40) controls the first power converter and the second power converter to create an output difference between the first power converter and the second power converter, wherein each power converter has the characteristic that, in relation to the operating point and power conversion efficiency, the power conversion efficiency decreases on the lower output side and the higher output side than a predetermined operating point; a command setting unit (41) that sets an output command value for each power converter so that when the output difference is created, each power converter operates within a predetermined high-efficiency operating region including the predetermined operating point; and a control unit (42A, 42B) that controls each power converter based on the output command value set by the command setting unit.

2. The control device according to claim 1, wherein each power converter is connected to an electrical load (20), and the command setting unit generates a difference in the output current of each power converter as the output difference, and when each power converter is operated within the high-efficiency operating region, it sets the output command value to command the output voltage of the power converter with the larger output current among the power converters so that the voltage applied to the electrical load is equal to or greater than the lower limit of the drive voltage, and sets the output command value to command the output voltage of the power converter with the smaller output current among the power converters so that the output voltage of the power converter with the smaller output current is equal to or greater than the lower limit and less than the output voltage of the power converter with the larger output current.

3. The control device according to claim 2, wherein the command setting unit sets the output command value of each power converter so that, when the amount of energy stored in the first energy storage unit is higher than the amount of energy stored in the second energy storage unit, the output difference is such that the output current of the first power converter is greater than the output current of the second power converter, and each power converter is operated within the high-efficiency operating region, and the command setting unit sets the output command value of each power converter so that, when the amount of energy stored in the second energy storage unit is higher than the amount of energy stored in the first energy storage unit, the output difference is such that the output current of the second power converter is greater than the output current of the first power converter, and each power converter is operated within the high-efficiency operating region.

4. The control device according to any one of claims 1 to 3, further comprising a region setting unit (44) that sets a smaller output lower limit value for the high-efficiency operating region when the difference in the amount of stored energy between the amount of stored energy in the first energy storage unit and the amount of stored energy in the second energy storage unit is greater than a predetermined difference value, compared to when the difference in the amount of stored energy is less than or equal to the predetermined difference value.

5. The control device according to claim 4, wherein the region setting unit sets the output corresponding to the predetermined operating point as the lower limit of the output when the difference in stored energy is less than or equal to the predetermined difference value.

6. The control device according to claim 4, wherein the region setting unit sets a value as the lower output value such that, when the difference in stored energy is less than or equal to the predetermined difference value, the slope of the efficiency decrease on the lower output side below the predetermined operating point in the characteristics is less than or equal to a predetermined value.

7. The control device according to claim 4, wherein, when the difference in stored energy is less than or equal to the predetermined difference value, the region setting unit sets the lower output value to a value in the characteristics where the slope of efficiency reduction on the lower output side below the predetermined operating point is smaller than the slope of output reduction on the higher output side above the predetermined operating point.

8. The control device according to any one of claims 1 to 3, wherein each power converter is connected to an electrical load (20), and includes a power determination unit (45) that determines whether or not a power condition is met such that the required drive power required by the electrical load is lower than the total power that can be output when each power converter is operated at the lower limit of the output of the high-efficiency operating region, and the command setting unit sets the output command value so as to operate each power converter within the high-efficiency operating region when the power determination unit determines that the power condition is met, and sets the output command value so as to stop the power output from one of the power converters when the power determination unit determines that the power condition is met.

9. The control device according to claim 8, wherein the command setting unit, when the power determination unit determines that the power condition is met, sets the output command value for the power converter that stops the power output, such that the output voltage is higher than the lower limit of the drive voltage of the electrical load and the output current is zero.

10. The control device according to any one of claims 1 to 3, further comprising: an energy storage amount determination unit (44) that determines whether or not to generate the output difference based on the difference in energy storage amount between the energy storage amount of the first energy storage unit and the energy storage amount of the second energy storage unit, wherein the command setting unit sets the output command value so as to operate each power converter within the high-efficiency operating region, on the condition that the energy storage amount determination unit has determined that to generate the output difference.

11. The control device according to claim 10, wherein the system enables power supply to low-voltage loads (20) connected to each power converter and power supply to high-voltage loads (12) to which a higher voltage than that applied to the low-voltage loads is performed, power is supplied from each energy storage unit to the low-voltage loads via the power converters, while power is supplied from the series connection of each energy storage unit to the high-voltage loads, the energy storage amount determination unit determines whether there is a margin of energy storage amount relative to the discharge lower limit or charge upper limit when it determines that the output difference will occur, the command setting unit sets the output command value of each power converter so as to operate each power converter within the high-efficiency operating region when the energy storage amount determination unit determines that there is a margin, and sets the output command value of each power converter without restricting the operating point of each power converter to within the high-efficiency operating region when the energy storage amount determination unit determines that there is no margin.

12. A program applied to a system (10) comprising: a first energy storage unit (11A) and a second energy storage unit (11B) connected in series with respect to each other; and a first power converter (21A) and a second power converter (21B) connected to both ends of each energy storage unit, wherein the program causes at least one of the circuit and the processor (40) to execute a process to control the first power converter and the second power converter so as to create an output difference between the first power converter and the second power converter, wherein each power converter has the characteristic that, in relation to the operating point and power conversion efficiency, the power conversion efficiency decreases on the lower output side and the higher output side of a predetermined operating point; and the program causes at least one of the circuit and the processor to execute a command setting process to set an output command value for each power converter so as to operate each power converter within a predetermined high-efficiency operating region including the predetermined operating point when the output difference is created; and a control process to control each power converter based on the output command value set by the command setting process.

13. A control method applied to a system (10) comprising: a first energy storage unit (11A) and a second energy storage unit (11B) connected in series with respect to each other; and a first power converter (21A) and a second power converter (21B) connected to both ends of each energy storage unit, wherein the control method controls the first power converter and the second power converter to create an output difference between the first power converter and the second power converter, wherein each power converter has the characteristic that, in relation to the operating point and power conversion efficiency, the power conversion efficiency decreases on the lower output side and the higher output side of a predetermined operating point; and a control method causing at least one of the circuit and processor (40) to execute: a command setting step of setting an output command value for each power converter so that when the output difference is created, each power converter is operated within a predetermined high-efficiency operating region including the predetermined operating point; and a control step of controlling each power converter based on the output command value set in the command setting step.

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