Control device, system, control method, and computer program product

Abstract

In the related art, an overvoltage can occur between a DC / DC converter and an inverter due to a problem of the system or the like. The present application provides a control device including: a first control section that controls at least one of a plurality of DC / DC converters respectively provided between a plurality of direct-current power supplies that supply direct current to a direct-current bus maintained at a reference voltage through power exchange with the inverter and the direct-current bus; and a voltage measurement section that measures a voltage of the direct-current bus, the first control section reducing output power of only a part of the plurality of DC / DC converters when the voltage of the direct-current bus exceeds a threshold voltage higher than the reference voltage.

Description

Technical Field

[0001] This invention relates to control devices, systems, control methods, and computer program products. Background Technology

[0002] In the past, various control methods have been proposed for power systems in which power is exchanged between DC / DC converters and inverters connected to DC power sources such as solar power generation devices (for example, see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2014-171359

[0004] Patent Document 2: Japanese Patent Application Publication No. 2016-158434

[0005] Patent Document 3: Japanese Patent Application Publication No. 2016-220480

[0006] The technical problem to be solved by the present invention

[0007] However, in previous technologies, overvoltage may have occurred between the DC / DC converter and the inverter due to system problems. Summary of the Invention

[0008] To address the aforementioned problems, a control device is provided in a first aspect of the present invention. The control device may include a first control unit that controls at least one of a plurality of DC / DC converters respectively disposed between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power supplies providing DC power to the DC bus. The control device may include a voltage measuring unit that measures the voltage of the DC bus. If the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage, the first control unit may reduce the output power of only a portion of the plurality of DC / DC converters.

[0009] The first control unit can control any one of the corresponding DC / DC converters among multiple DC / DC converters.

[0010] The control device may further include a change unit that causes the threshold voltage to change over time.

[0011] If the voltage on the DC bus exceeds the threshold voltage for a duration exceeding the upper limit time, the first control unit can reduce the output power of the corresponding DC / DC converter. The control device may further include a variation unit that changes the upper limit time over time.

[0012] A second aspect of the invention provides a system. The system may include an inverter that maintains the DC bus at a reference voltage through power exchange with the DC bus. The system may include multiple DC / DC converters respectively disposed between the DC bus and multiple DC power sources supplying DC power to the DC bus. The system may include multiple control devices of a first aspect for controlling any one of the corresponding DC / DC converters.

[0013] When the voltage on the DC bus exceeds the threshold voltage, multiple control devices can set a time difference between multiple DC / DC converters to reduce the output power of each DC / DC converter.

[0014] The system may further include other control devices having a second control unit for controlling the inverter. The second control unit can reduce the output power from the inverter based on receiving an output limiting command signal.

[0015] In the control device of the first method, the first control unit can control each of the multiple DC / DC converters.

[0016] If the voltage on the DC bus exceeds the threshold voltage, the first control unit can set a time difference between multiple DC / DC converters to reduce the output power of each DC / DC converter.

[0017] When the voltage on the DC bus exceeds the threshold voltage, the first control unit can increase the number of DC / DC converters with reduced output power in a stepwise manner.

[0018] If the voltage on the DC bus exceeds the threshold voltage, the first control unit can reduce the output power of each DC / DC converter in a sequence corresponding to the maximum output power of each DC power supply connected to each DC / DC converter.

[0019] The control unit may further include a storage unit that stores inherent threshold voltages associated with each of the plurality of DC / DC converters and differing from each other above a threshold voltage. If the voltage of the DC bus exceeds any of the inherent threshold voltages, the first control unit can reduce the output power of the DC / DC converter corresponding to that inherent threshold voltage.

[0020] The control unit may further include a storage unit that stores inherent upper limit times associated with and different from each of the plurality of DC / DC converters. If the voltage on the DC bus exceeds a threshold voltage for a duration exceeding any inherent upper limit time, the first control unit may reduce the output power of the DC / DC converter corresponding to that inherent upper limit time.

[0021] If the voltage on the DC bus exceeds the threshold voltage, the first control unit can reduce the output power of each DC / DC converter in a random sequence.

[0022] A third aspect of the invention provides a system. The system may include an inverter that maintains the DC bus at a reference voltage through power exchange with the DC bus. The system may include multiple DC / DC converters respectively disposed between the DC bus and multiple DC power sources supplying DC power to the DC bus. The system may include a control device of a first aspect for controlling each of the multiple DC / DC converters.

[0023] The control device may further include a second control unit for controlling the inverter. The second control unit can reduce the output power from the inverter based on receiving an output limiting command signal.

[0024] In the second or third-party system, the second control unit can determine the amount of current flowing through the inverter based on the target output power and DC bus voltage contained in the command signal.

[0025] An inverter may have multiple DC / DC converter circuits connected in parallel to a DC bus in each phase of the output. An inverter may also have multiple single-phase inverter circuits connected in series on the output side in each phase of the output and receiving power from their respective corresponding DC / DC converters.

[0026] Each of the multiple DC / DC converters can be detachably connected to at least one of a DC power supply and a DC bus.

[0027] At least a portion of the multiple DC power sources may be solar power generation devices. A first control unit that controls the DC / DC converter connected to the solar power generation device can further control the solar power generation device and can perform MPPT control in at least one of the following conditions: the voltage of the DC bus is below a threshold voltage and the output power of the DC / DC converter is not reduced, so that maximum power is provided from the solar power generation device.

[0028] When reducing the output power of a portion of the DC / DC converter, the first control unit can control the output power to a target value determined based on the voltage of the DC bus.

[0029] When the output power of a portion of the DC / DC converter is reduced, the first control unit may release the control that reduces the output power if the target value is greater than or equal to at least one of the reference output power of the DC / DC converter and the reference output power of the DC power supply connected to the DC / DC converter.

[0030] A fourth aspect of the present invention provides a control method. The control method may include a control phase in which at least one of a plurality of DC / DC converters, respectively disposed between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power sources supplying DC power to the DC bus, is controlled. The control method may include a voltage measurement phase for measuring the voltage of the DC bus. In the control phase, if the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage, the output power of only a portion of the plurality of DC / DC converters may be reduced.

[0031] A fifth aspect of the present invention provides a computer-readable medium on which a program is recorded. The program enables a computer to implement a first control unit that controls at least one of a plurality of DC / DC converters respectively disposed between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power supplies providing DC power to the DC bus. The program also enables the computer to implement a voltage measuring unit that measures the voltage of the DC bus. If the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage, the first control unit can reduce the output power of only a portion of the plurality of DC / DC converters.

[0032] Furthermore, the above description of the invention is not an enumeration of all essential features of the invention. In addition, sub-combinations of these feature groups can also constitute an invention. Attached Figure Description

[0033] Figure 1 The power system 1 involved in this embodiment is shown.

[0034] Figure 2 DC / DC converter 3 is shown.

[0035] Figure 3 Other DC / DC converters are shown 3.

[0036] Figure 4 Unit 25 is shown.

[0037] Figure 5 This shows the operation of the three-phase inverter 2.

[0038] Figure 6 The operation of control device 5 is shown.

[0039] Figure 7 The first variation illustrates the power system 1A involved.

[0040] Figure 8 The control device 7 is shown.

[0041] Figure 9 The operation of control device 7 is shown.

[0042] Figure 10 The operation of control device 5A is shown.

[0043] Figure 11 The state transition diagram of power system 1A is shown.

[0044] Figure 12 The power system 1A involved in the second variation is shown.

[0045] Figure 13 The operation of control device 5B is shown.

[0046] Figure 14 An example of a computer 2200 is shown that can be embodied in whole or in part in various ways of the present invention. Detailed Implementation

[0047] The present invention will be described below through embodiments, but these embodiments are not intended to limit the invention as defined in the claims. Furthermore, the combinations of features described in the embodiments are not all necessary technical means to solve the technical problems of the present invention.

[0048] [1. Power System 1]

[0049] Figure 1 The power system 1 according to this embodiment is shown. The power system 1 includes a three-phase inverter 2 and a plurality of DC / DC converters 3 respectively connected to a DC bus 10, a DC power supply 4 connected to the DC / DC converters 3, and a plurality of control devices 5. A load (not shown) may also be connected to the DC bus 10. A capacitor (not shown) may be provided between at least one of the DC / DC converters 3, the three-phase inverter 2A and the load and the DC bus 10.

[0050] [1.1. Three-phase inverter 2]

[0051] Three-phase inverter 2 is an example of an inverter that performs power conversion between direct current (DC) and alternating current (AC) (in this embodiment, three-phase AC). Three-phase inverter 2 maintains DC bus 10 at a reference voltage through power exchange with DC bus 10. For example, three-phase inverter 2 may be a PCS (Power Conditioning System) that can convert DC power supplied from DC bus 10 to DC / AC and output it from AC wiring 15, and convert AC power supplied from AC wiring 15 to AC / DC and supply it to DC bus 10. Three-phase inverter 2 can maintain DC bus 10 at a reference voltage by changing the control conditions for such power conversion. As an example, a 3.3kV or 6.6kV power system can be connected to AC wiring 15.

[0052] The three-phase inverter 2 may include a voltage measurement unit 20, a second control unit 21, and a single-phase inverter 22 for each of the output phases U, V, and W.

[0053] The voltage measuring unit 20 measures the voltage of the DC bus 10. The voltage measuring unit 20 can provide the measured voltage to the second control unit 21.

[0054] The second control unit 21 uses the control signal Ctrl _DC / AC Each single-phase inverter 22 is controlled. For example, the second control unit 21 can change the control conditions of each single-phase inverter 22 based on the measured voltage obtained by the voltage measuring unit 20, and maintain the voltage of the DC bus 10 at the reference voltage.

[0055] Each single-phase inverter 22 can be a so-called SST (Solid-State Transformer) inverter. For example, a single-phase inverter 22 can have three DC / DC converter circuits 23 and three single-phase inverter circuits 24. However, the number of DC / DC converter circuits 23 and the number of single-phase inverter circuits 24 can be two, four or more, the same, or different.

[0056] In this embodiment, as an example, three DC / DC converter circuits 23 are connected in parallel with the DC bus 10, respectively performing DC / DC conversion on the DC voltage from the DC bus 10 and providing it to the single-phase inverter circuit 24. The three single-phase inverter circuits 24 are configured to be connected to and receive power from the DC / DC converter 3 on their input sides, and are connected in series with each other on their output sides. Thus, the single-phase inverter 22 adds the output voltages from the three single-phase inverter circuits 24 and outputs the sum.

[0057] In this embodiment, as an example, the DC / DC converter circuit 23 and the single-phase inverter circuit 24 can be paired one-to-one, and each pair of DC / DC converter circuits 23 and single-phase inverter circuits 24 can form a unit 25. The single-phase inverters 22 of the U-phase, V-phase, and W-phase are connected to each other by a star connection (also known as a Y-connection), but they can also be connected to each other by a delta connection (also known as a Δ connection). Furthermore, the three-phase inverters 2 and the DC bus 10 can be housed in a single housing to form a PCS (Power Conditioning System) device 11. Such a PCS device 11 can be configured as a rack-mount type that can accommodate multiple DC / DC converters 3.

[0058] [1.2. DC / DC Converter 3]

[0059] Multiple DC / DC converters 3 are respectively disposed between the DC bus 10 and multiple DC power supplies 4, performing DC / DC conversion on the DC power from the DC power supplies 4 and providing it to the DC bus 10. Alternatively, in this embodiment, as an example, the power system 1 includes three DC / DC converters 3 (also referred to as DC / DC converters 3a to 3c), but the number of DC / DC converters 3 may also be two or more. Each DC / DC converter 3 can be detachably connected to at least one of the DC power supplies 4 and the DC bus 10. Each DC / DC converter 3 can be connected to the DC bus 10 by being housed in a rack-mounted PCS device 11.

[0060] [1.3. DC Power Supply 4]

[0061] Multiple DC power sources 4 supply DC power to the DC bus 10. In this embodiment, as an example, the power system 1 has three DC power sources 4 (also referred to as DC power sources 4a to 4c), the same number as the DC / DC converters 3, and each DC power source 4 supplies DC power to the DC bus 10 via a corresponding single DC / DC converter 3. Each DC power source 4 can be a distributed power source, and at least a portion of the multiple DC power sources 4 can be a residential solar power generation device outputting several kW of power or a commercial solar power generation device outputting several MW of power. In this embodiment, as an example, DC power sources 4a and 4b are solar power generation devices, and DC power source 4c is a battery.

[0062] [1.4. Control Device 5]

[0063] Multiple control devices 5 control multiple DC / DC converters 3. Each control device 5 has a voltage measuring unit 50, a first control unit 51, and a switching unit 52.

[0064] The voltage measuring unit 50 measures the voltage of the DC bus 10. The voltage measuring unit 50 can provide the measured voltage to the first control unit 51.

[0065] The first control unit 51 controls the signal Ctrl_ DC / DC The first control unit 51 controls at least one of a plurality of DC / DC converters 3. In this embodiment, as an example, it controls any one of the corresponding DC / DC converters 3. When the voltage of the DC bus 10 exceeds a threshold voltage, the first control unit 51 reduces the output power of only a portion of the plurality of DC / DC converters 3. For example, the first control unit 51 can reduce the output power of the corresponding DC / DC converter 3.

[0066] The threshold voltage can be a voltage higher than the reference voltage maintained by the three-phase inverter 2, but lower than the absolute maximum rated voltage. In cases where a problem occurs in the power system 1, or when the power supply from the DC power sources 4a and 4b (as solar power generation devices) exceeds the capacity of the load connected to the DC bus 10 or the DC power source 4c (as a battery), the voltage of the DC bus 10 can become higher than the reference voltage. The threshold voltage can vary among the multiple control devices 5.

[0067] In this situation, when the voltage of the DC bus 10 exceeds the threshold voltage of each control device 5, the multiple control devices 5 reduce the output power of each DC / DC converter 3 by setting a time difference between the multiple DC / DC converters 3. Furthermore, when the voltage of the DC bus 10 exceeds the threshold voltage of each control device 5, the multiple control devices 5 increase the number of DC / DC converters 3 with reduced output power in a stepwise manner. Additionally, if the voltage of the DC bus 10 exceeds the absolute maximum rated voltage, the first control unit 51 can stop the DC / DC converter 3.

[0068] The modification unit 52 causes the threshold voltage of the first control unit 41 to change over time. As a result, the order of the threshold voltages changes over time among the multiple control devices 5. Furthermore, even when the default threshold voltages are equal among the multiple control devices 5, the threshold voltages differ among the multiple control devices 5.

[0069] The modification unit 52 maintains the threshold voltage at a level higher than the reference voltage. The modification unit 52 can make the threshold voltage change randomly or periodically.

[0070] According to the power system 1 described above, when the voltage of the DC bus 10 exceeds the threshold voltage, the output power of a portion of the multiple DC / DC converters 3 decreases. Therefore, even if a problem occurs in the power system 1, or if the power supply from the DC power sources 4a and 4b (which are solar power generation devices) exceeds the load of the DC bus 10 or the capacity of the DC power source 4c (which is a battery), the voltage of the DC bus 10 can be suppressed below the threshold voltage to prevent overvoltage and equipment damage. Furthermore, the voltage of the DC bus 10 is maintained at a reference voltage through power exchange with the three-phase inverter 2. When the voltage exceeds the threshold voltage, the output power of a portion of the DC / DC converters 3 decreases, thereby suppressing it below the threshold voltage. Therefore, unlike the case where the voltage of the DC bus 10 is controlled below the threshold voltage solely by the control of the three-phase inverter 2, the control of the DC bus 10 voltage can be distributed among the control of the three-phase inverter 2 and the control of the DC / DC converters 3, thus simplifying control. Furthermore, since the control of the DC bus 10 voltage can be distributed among the control of the three-phase inverter 2 and the DC / DC converter 3, the degree of freedom in determining the number of DC / DC converters 3 or DC power supplies 4 in the power system 1 can be increased. The number of DC / DC converters 3 or DC power supplies 4 can be increased or decreased without changing the control structure of the three-phase inverter 2. Moreover, when the voltage of the DC bus 10 exceeds the threshold voltage, only a portion of the output power of the DC / DC converters 3 is reduced, thus allowing the power system 1 to continue operating as a whole.

[0071] Furthermore, each first control unit 51 controls any one of its corresponding DC / DC converters 3, thus enabling control of the corresponding DC / DC converter 3 regardless of the number of other DC / DC converters 3 present in the power system 1. Therefore, the number of DC / DC converters 3 can be arbitrarily increased or decreased.

[0072] Furthermore, the threshold voltage of the first control unit 51 changes over time via the change unit 52 of each control device 5. Therefore, even if the default threshold voltages of the multiple control devices 5 in the power system 1 are equal, the threshold voltage can be made different from those of the other control devices 5. Thus, since multiple DC / DC converters 3 can be controlled based on individual threshold voltages, when the voltage of the DC bus 10 rises, the output power of all DC / DC converters 3 can be prevented from decreasing, and the power system 1 as a whole can reliably continue to operate. Furthermore, the order of the threshold voltages can change over time among the multiple control devices 5. Therefore, if the voltage of the DC bus 10 repeatedly exceeds the threshold voltage, the DC / DC converters 3 that are targeted for output power reduction can be prevented from being concentrated in one group.

[0073] Furthermore, when the voltage of the DC bus 10 exceeds the threshold voltage, multiple control devices 5 reduce the output power of each DC / DC converter 3 by setting a time difference between multiple DC / DC converters 3. Thus, when the voltage of the DC bus 10 rises, the output power of all DC / DC converters 3 can be prevented from decreasing, and the power system 1 as a whole can reliably continue to operate.

[0074] Furthermore, at least a portion of the multiple DC power supplies 4 are solar power generation devices, so that the DC / DC converter 3 can be stopped when the power generation obtained from the solar power generation increases and the voltage of the DC bus 10 exceeds the threshold voltage.

[0075] Furthermore, each DC / DC converter 3 is detachably connected to at least one of the DC power supply 4 and the DC bus 10, thus the number of DC power supplies 4 connected to the DC bus 10 can be easily increased or decreased.

[0076] Furthermore, the three-phase inverter 2 includes multiple DC / DC converter circuits 23 connected in parallel with the DC bus 10 and single-phase inverter circuits 24 connected in series on the output side, thus increasing the output power compared to the case with only a single single-phase inverter circuit 24.

[0077] [2. DC / DC Converter 3]

[0078] Figure 2 A DC / DC converter 3 is shown. DC / DC converters 3a and 3b, connected to solar power generation devices, i.e., DC power supplies 4a and 4b, can be boost choppers that boost the voltage supplied from DC power supplies 4a and 4b. The DC / DC converter 3 includes a first positive terminal 31a and a first negative terminal 31b connected to the DC power supply 4, a second positive terminal 32a and a second negative terminal 32b connected to the DC bus 10, a diode 33 and a switching element 34 connected in series between the second positive terminal 32a and the second negative terminal 32b, a filter capacitor 36 disposed between the second positive terminal 32a and the second negative terminal 32b, and an inductor 37 disposed between the first positive terminal 31a and the diode 33 and the switching element 34. The first negative terminal 31b can be connected to the second negative terminal 32b.

[0079] Figure 3 Other DC / DC converters 3 are shown. The DC / DC converter 3 connected to the DC power supply 4c, which acts as a battery, can be a bidirectional DC / DC converter that boosts the voltage supplied from the DC power supply 4c and provides it to the DC bus 10, and bucks the voltage supplied from the DC bus 10 and provides it to the DC power supply 4c. The DC / DC converter 3 can be... Figure 2The structure obtained by replacing the diode 33 in the DC / DC converter 3 shown with the switching element 35.

[0080] [3. Unit 25 of single-phase inverter 22]

[0081] Figure 4 Unit 25 is shown. Unit 25 has positive terminal 251a and negative terminal 251b connected to DC bus 10, AC output terminals 252, 252 connected in series with other units 25, DC / DC converter circuit 23 and single-phase inverter circuit 24.

[0082] The DC / DC converter circuit 23 can be an isolated converter, and in this embodiment, as an example, the DC / DC converter circuit 23 is a bidirectional DC / DC converter in a full-bridge configuration. The DC / DC converter circuit 23 includes a transformer 230, a filter capacitor 231 disposed between the positive terminal 251a and the negative terminal 251b on the primary side of the transformer 230, a full-bridge circuit 232, and a full-bridge circuit 234 disposed between the positive wiring 233a and the negative wiring 233b on the secondary side of the transformer 230. The full-bridge circuit 232 may have switching elements 2321, 2322 and 2323, 2324 connected in series between the positive terminal 251a and the negative terminal 251b, and the full-bridge circuit 234 may have switching elements 2341, 2342 and 2343, 2344 connected in series between the positive wiring 233a and the negative wiring 233b. The primary coil 2301 of transformer 230 can be connected to the midpoints of switching elements 2321 and 2322, and the midpoints of switching elements 2323 and 2324, while the secondary coil 2302 can be connected to the midpoints of switching elements 2341 and 2342, and the midpoints of switching elements 2343 and 2344. Transformer 230 can operate at high frequencies of tens of kHz (e.g., 10 kHz to 90 kHz) and can be smaller than commercial power transformers operating at 50 kHz or 60 kHz.

[0083] The single-phase inverter circuit 24 has a filter capacitor 240 and a full-bridge circuit 241 connected in parallel between the positive side wiring 233a and the negative side wiring 233b. The full-bridge circuit 241 may have switching elements 2411, 2412 and switching elements 2413, 2414 connected in series between the positive side wiring 233a and the negative side wiring 233b. The midpoints of switching elements 2411, 2412 and the midpoints of switching elements 2413, 2414 may be connected to AC output terminals 252, 252.

[0084] When the AC output terminals 252, 252 of the aforementioned unit 25 are connected in series with the AC output terminals 252, 252 of other units 25, the voltage of the filter capacitor 240 needs to be kept constant between the connected units 25. In the power system 1 according to this embodiment, as described above, the voltage of the DC bus 10 is maintained at a reference voltage by the three-phase inverter 2, and when the voltage of the DC bus 10 exceeds a threshold voltage, the DC bus 10 is controlled below the threshold voltage by a portion of the DC / DC converter 3. Therefore, the voltage of the filter capacitor 240 can be reliably kept constant.

[0085] [4. Action]

[0086] [4.1. Operation of Three-Phase Inverter 2]

[0087] Figure 5 The operation of the three-phase inverter 2 is shown. The three-phase inverter 2 maintains the voltage of the DC bus 10 at the reference voltage by performing steps S11 to S15. Furthermore, at the start of this operation, the second control unit 21 of the three-phase inverter 2 can continue to control each single-phase inverter 22.

[0088] In step S11, the voltage measuring unit 20 measures the voltage of the DC bus 10. In addition to measuring the voltage of the DC bus 10, the voltage measuring unit 20 can also measure the voltage between the input terminals of the DC / DC converter circuit 23 of the single-phase inverter 22.

[0089] In step S13, the second control unit 21 determines whether the measured voltage is a reference voltage. The reference voltage may be a single voltage value or a range of voltage values ​​indicated by an upper limit and a lower limit. When it is determined that the measured voltage is a reference voltage (step S13; "Yes"), the process proceeds to step S11; when it is determined that the measured voltage is not a reference voltage (step S13; "No"), the process proceeds to step S15.

[0090] Then, in step S15, the second control unit 21 changes the control conditions of each single-phase inverter 22 to attempt to maintain the voltage of the DC bus 10 at the reference voltage. For example, the second control unit 21 may change the control conditions to increase the output of each single-phase inverter 22 when the measured voltage is higher than the reference voltage, and decrease the output of each single-phase inverter 22 when the measured voltage is lower than the reference voltage. After the processing in step S15, the three-phase inverter 2 can transfer the processing to step S11.

[0091] [4.2. Operation of control device 5]

[0092] Figure 6The operation of the control device 5 is shown. The control device 5 maintains the voltage of the DC bus 10 below the threshold voltage by performing the processes of steps S21 to S25.

[0093] Furthermore, at the start of this operation, the corresponding DC / DC converter 3 can continue to be controlled by the first control unit 51 of the control device 5. As an example, the control device 5 of the DC / DC converters 3a and 3b connected to the DC power supplies 4a and 4b, which are solar power generation devices, can perform MPPT (Maximum Power Point Tracking) control between itself and the DC power supplies 4a and 4b to provide maximum power from the DC power supplies 4a and 4b. Thus, the DC / DC converters 3a and 3b can perform DC / DC conversion on the DC power from the DC power supplies 4a and 4b and provide it to the DC bus 10. In addition, the control device 5 of the DC / DC converter 3c connected to the DC power supply 4c, which is a battery, can charge the DC power supply 4c when there is excess power from the DC power supplies 4a and 4b, which are solar power generation devices, and discharge the DC power supply 4c when there is insufficient power, based on the voltage fluctuations of the DC bus 10.

[0094] Furthermore, in this embodiment, as an example, the three-phase inverter 2 can perform the processes of steps S11 to S15 during the processing of steps S21 to S25 by the control device 5. However, the three-phase inverter 2 can also be stopped.

[0095] In step S21, the voltage measuring unit 50 measures the voltage of the DC bus 10. Since it measures the voltage of the DC bus 10, the voltage measuring unit 50 can also measure the voltage between the output terminals of the DC / DC converter 3.

[0096] In step S23, the first control unit 51 determines whether the measured voltage is below a threshold voltage. The threshold voltage may be a single voltage value. When it is determined that the measured voltage is below the threshold voltage (step S23; "Yes"), the process proceeds to step S21, and when it is determined that the measured voltage exceeds the reference voltage (step S13; "No"), the process proceeds to step S25.

[0097] In step S25, the first control unit 51 reduces the output power of the corresponding DC / DC converter 3. Reducing the output power can be done by setting the output power to zero or by setting it to a power lower than the current output power.

[0098] Here, in this embodiment, as an example, the threshold voltage differs among the multiple control devices 5. Therefore, only a portion of the multiple control devices 5 perform the processing of step S25, resulting in a reduction in output power only in a portion of the DC / DC converters 3.

[0099] Furthermore, the power system 1 includes multiple control devices 5, each independently performing steps S21 to S25. Therefore, when the threshold voltage is randomly changed by the changing unit 52, the output power of each DC / DC converter 3 can decrease in a random order as the voltage of the DC bus 10 increases.

[0100] In this embodiment, as an example, the operation of the control device 5 can be completed in step S25. Alternatively, the process can also proceed to step S21 after step S25. In this case, if it is determined in the process of step S23 that the measured voltage exceeds the threshold voltage (step S23; "No"), then in the process of step S25, the first control unit 51 can further reduce the output power of the corresponding DC / DC converter 3. As an example, for each process of step S25, the first control unit 51 can reduce the output power of the DC / DC converter 3 by a predetermined power each time. If the first control unit 51 has already set the output power of the DC / DC converter 3 to zero, in the process of step S25, the first control unit 51 can maintain the output power of the DC / DC converter 3 at zero. Furthermore, if the DC power supply 4c, which is a battery, is connected to the DC / DC converter 3, the first control unit 51 can also set the output power of the DC / DC converter 3 to a negative power (the power flow supplied from the DC bus 10 to the DC / DC converter 3) to charge the DC power supply 4c. Furthermore, if it is determined in step S23 that the measured voltage is below the threshold voltage (step S23; "Yes"), the first control unit 51 can restore the output power of the DC / DC converter 3. The threshold voltage for reducing output power and the threshold voltage for restoring output power can be the same voltage or different voltages to achieve hysteresis characteristics.

[0101] Furthermore, in the above embodiment, the control device 5 is described as a device independent of the corresponding DC / DC converter 3, but the control device 5 and the corresponding DC / DC converter 3 may also be integrated.

[0102] Furthermore, although the DC power supply 4 and DC / DC converter 3 have been described as having the same number, they may not be the same number. For example, there may be fewer DC power supplies 4 than DC / DC converter 3, with each DC power supply 4 connected to a corresponding plurality of DC / DC converters; or there may be more DC power supplies 4 than DC / DC converter 3, with each corresponding plurality of DC power supplies 4 connected to a corresponding DC / DC converter 3.

[0103] Furthermore, although it is stated that the control device 5 has a change unit 52, it may not have a change unit 52 if the threshold voltage of the fixed value is different among multiple control devices 5.

[0104] Furthermore, although it is described that when the voltage of the DC bus 10 exceeds a threshold voltage, the first control unit 51 reduces the output power of the DC / DC converter 3 corresponding to the first control unit 51, the output power of the DC / DC converter 3 corresponding to the first control unit 51 can also be reduced when the duration for which the voltage of the DC bus 10 exceeds the threshold voltage exceeds an upper limit time. In this case, the control device 5 can further include a changing unit that varies the upper limit time over time. This allows the upper limit time to be different from other control devices 5 included in the power system 1, thus enabling control of multiple DC / DC converters 3 based on individual upper limit times. Therefore, when the voltage of the DC bus 10 rises, it is possible to prevent a reduction in the output power of all DC / DC converters 3 and reliably ensure the continued operation of the power system 1 as a whole.

[0105] [5. First variation]

[0106] [5.1. Power System 1A]

[0107] Figure 7 The diagram illustrates a power system 1A as described in the first variation. Power system 1A may include a three-phase inverter 2A, a control device 5A, and a control device 7.

[0108] The three-phase inverter 2A is externally connected to the control unit 7. The three-phase inverter 2A is controlled by the control signal Ctrl provided by the control unit 7. _DC / AC control.

[0109] The control device 5A has a first control unit 51A.

[0110] The first control unit 51A controls the DC / DC converter 3a connected to the DC power supply 4a, which is a solar power generation device. The first control unit 51A can further control the DC power supply 4a. When the voltage of the DC bus 10 is below the threshold voltage, the first control unit 51A can perform MPPT control to ensure that maximum power is supplied from the DC power supply 4a.

[0111] Furthermore, if the voltage of the DC bus 10 exceeds a threshold voltage, thereby reducing the output power of a portion of the multiple DC / DC converters 3 (in this modified example, the corresponding DC / DC converter 3a), the first control unit 51A can control the output power to a target value determined based on the voltage of the DC bus 10. Details regarding the target value will be described later.

[0112] The control device 7 includes a voltage measuring unit 70 and a second control unit 71.

[0113] The voltage measuring unit 70 measures the voltage of the DC bus 10. The voltage measuring unit 70 can provide the measured voltage to the second control unit 71.

[0114] The second control unit 71 controls the signal Ctrl. _DC / AC At least one single-phase inverter 22 is controlled. In this modified example, the second control unit 71 can control each single-phase inverter 22. The second control unit 71 can change the control conditions of each single-phase inverter 22 based on the measured voltage obtained by the voltage measuring unit 70 to maintain the voltage of the DC bus 10 at the reference voltage. In addition, the second control unit 71 can reduce the output power output from the single-phase inverter 22 according to the received output limit command signal. When the output power from the three-phase inverter 2A is greater than the output limit power, the output limit command signal can be continuously provided from the operator or an external device. The output limit power can be the rated power of the three-phase inverter 2A or the upper limit of the power output from the three-phase inverter 2A to the AC wiring 15. In addition, when the power consumption generated by the load connected to the DC bus 10 increases, the output limit command signal can be provided to the second control unit 71.

[0115] According to the above power system 1A, when the voltage of DC bus 10 is below the threshold voltage, the DC power supply 4a of the solar power generation device is controlled by MPPT. Therefore, when there is no need to reduce the output power of DC / DC converter 3a, the output power of the solar power generation device can be maximized, and thus the output power of DC / DC converter 3a can be maximized.

[0116] Furthermore, when the output power of DC / DC converter 3 decreases, the output power of DC / DC converter 3 decreases based on a target value determined according to the voltage of DC bus 10, thus reliably maintaining the voltage of DC bus 10 at the reference voltage.

[0117] Furthermore, upon receiving the output limit command signal from the second control unit 71, the output power from the single-phase inverter 22 decreases. This prevents the output power from the single-phase inverter 22 from remaining constant despite the output limit command. Moreover, reducing the output power from the single-phase inverter 22 prevents the voltage of the DC bus 10 from dropping by a corresponding amount. In summary, by maintaining a higher output power of the DC / DC converter 3 through MPPT control or the like, the voltage of the DC bus 10 can be increased. Then, by reducing the output power of the DC / DC converter 3, the voltage of the DC bus 10 can be maintained. Therefore, the voltage of the DC bus 10 can be reliably maintained at the reference voltage without requiring communication between the control device 7 and the control device 5A.

[0118] [5.2. Control Device 7]

[0119] Figure 8 The control device 7 is shown. The second control unit 71 of the control device 7 includes a voltage control unit 710, an output current limiting calculation unit 711, an adjustment unit 712, and a switching unit 713.

[0120] Similar to the second control unit 21 in the above embodiment, the voltage control unit 710 controls each single-phase inverter 22. For example, the voltage control unit 710 can change the control conditions of each single-phase inverter 22 based on the measured voltage obtained by the voltage measuring unit 70, so as to maintain the voltage of the DC bus 10 at the reference voltage. The voltage control unit 710 can provide control signals Ctrl to each single-phase inverter 22 via the switching unit 713. _DC / AC .

[0121] When limiting the output power of the single-phase inverter 22, the output current limiting calculation unit 711 determines the current flowing through each single-phase inverter 22. Based on the received output limiting command signal, the output current limiting calculation unit 711 determines the command value of the current flowing through the single-phase inverter 22, using the target output power and the voltage of the DC bus 10 contained in the command signal. For example, the output current limiting calculation unit 711 can calculate the command value of the current (I) by dividing the target output power (W) by the measured voltage obtained by the voltage measuring unit 70, i.e., by the voltage (V) of the DC bus 10. The output current limiting calculation unit 711 can then provide the calculated command value of the current to the adjustment unit 712.

[0122] The regulating unit 712 corrects the command value of the current quantity provided by the output limiting current calculation unit 711 based on the insufficient amount of the voltage of the DC bus 10 (in this modified example, the measured voltage obtained by the voltage measuring unit 70) relative to the reference voltage, and controls the regulating unit 712 of each single-phase inverter 22 to generate control signal Ctrl. _DC / ACThis allows the current corresponding to the corrected command value to flow through the single-phase inverter 22, and the control signal Ctrl can be switched via the switching unit 713. _DC / AC Provided to each single-phase inverter 22.

[0123] The switching unit 713 will take the control signal Ctrl output from either the voltage control unit 710 or the adjustment unit 712. _DC / AC This is provided to each single-phase inverter 22. When an output limit command signal is received, the switching unit 713 can Ctrl the control signal from the regulating unit 712. _DC / AC The control signal is supplied to each single-phase inverter 22, and when no command signal is received, the switching unit 713 can Ctrl the control signal from the voltage control unit 710. _DC / AC Provided to each single-phase inverter 22.

[0124] According to the control device 7 described above, since the amount of current flowing through the single-phase inverter 22 is determined based on the target output power contained in the output limit command signal and the voltage of the DC bus 10, the target output power can be reliably output from the single-phase inverter 22.

[0125] [5.3. Actions]

[0126] [5.3(1). Operation of control device 7]

[0127] Figure 9 The operation of control device 7 is shown. Control device 7 controls the output voltage of the single-phase inverter 22 and the voltage of the DC bus 10 by performing steps S51 to S67. Furthermore, at the start of this operation, control device 7 can continue to control each single-phase inverter 22.

[0128] In step S51, similar to step S11 described above, the voltage measuring unit 70 measures the voltage of the DC bus 10.

[0129] In step S53, the switching unit 713 determines whether an output limiting command signal has been received. When the output power from the three-phase inverter 2A is greater than the output limiting power, the output limiting command signal can be provided to the control device 7. If it is determined in step S53 that no output limiting command signal has been received (step S53; "No"), the process proceeds to step S55. If it is determined in step S53 that an output limiting command signal has been received (step S53; "Yes"), the process proceeds to step S61.

[0130] In step S55, the switching unit 713 selects the voltage control unit 710 as the control signal Ctrl. _DC / ACThe output source. In step S55, the switching unit 713 may also enable the voltage control unit 710 and disable the regulation unit 712 as an alternative.

[0131] In step S57, similar to step S13 described above, the voltage measuring unit 710 determines whether the measured voltage is a reference voltage. If it is determined that the measured voltage is a reference voltage (step S57; "Yes"), the process proceeds to step S51; if it is determined that the measured voltage is not a reference voltage (step S13; "No"), the process proceeds to step S59.

[0132] Then, in step S59, similar to step S15 described above, the voltage control unit 710 attempts to maintain the voltage of the DC bus 10 at the reference voltage by changing the control conditions of each single-phase inverter 22. After the processing in step S59, the process can proceed to step S51.

[0133] Furthermore, in this modified example, the control is performed through steps S55 to S59 to maintain the voltage of the DC bus 10. Therefore, the state of the control device 7 during the execution of steps S55 to S59 is also referred to as the DC bus voltage maintenance state.

[0134] In step S61, the switching unit 713 selects the adjustment unit 710 as the control signal Ctrl. _DC / AC The output source. In step S61, the switching unit 713 may also enable the voltage control unit 710 and disable the regulation unit 712 as an alternative.

[0135] In step S63, the output current limiting calculation unit 711 determines the command value of the current flowing through the single-phase inverter 22 based on the target output power contained in the command signal and the measured voltage of the DC bus 10. Furthermore, the current flowing through the single-phase inverter 22 can be either the amount of DC current flowing through the single-phase inverter 22 from the DC bus 10, or the amount of AC current output from the single-phase inverter 22 (as an example, the effective value).

[0136] In step S65, the adjustment unit 712 corrects the current command value based on the deficiency of the measured voltage relative to the reference voltage. For example, the greater the deficiency voltage, the smaller the current command value can be compared to the original value by the adjustment unit 712. Therefore, compared to the case where the specified current value is not reduced, the output from the single-phase inverter 22 is smaller, which can suppress the voltage drop of the DC bus 10. The adjustment unit 712 can perform PI control on the current command value. Thus, the current command value is corrected so that the current flowing through the single-phase inverter 22 does not oscillate. In the absence of a deficiency voltage, i.e., when the measured voltage is above the reference voltage, the adjustment unit 712 does not need to correct the current command value.

[0137] In step S67, the adjustment unit 712 changes the control conditions of each single-phase inverter 22 based on the corrected command value, thereby limiting the current flowing through each single-phase inverter 22 to the corrected command value and limiting the output from each single-phase inverter 22. As a result, the power output from the single-phase inverter 22 decreases, and consequently the power output from the three-phase inverter 2A decreases, thus mitigating the voltage drop on the DC bus 10, and the voltage of the DC bus 10 increases according to the power supply from the DC / DC converter 3. The output power from the three-phase inverter 2A may be less than the output limit power. After the processing in step S67, the process can proceed to step S51.

[0138] Furthermore, in this modified example, the AC output from the three-phase inverter 2A is restricted by the processing in steps S61 to S67. Therefore, the state of the control device 7 during the processing in steps S61 to S67 is also called the AC output restriction state.

[0139] [5.3(2). Operation of control device 5A]

[0140] Figure 10 The operation of control device 5A is shown. Control device 5A controls the output power of DC / DC converter 3 and the voltage of DC bus 10 by performing steps S71 to S87. Furthermore, at the start of this operation, the corresponding DC / DC converter 3a can continue to be controlled by the first control unit 51A of control device 5A. In this modified example, control device 7 can perform steps S51 to S67 during the processing of steps S71 to S87 by control device 5A. However, control device 7 can also be stopped.

[0141] In step S71, similar to step S21 described above, the voltage measuring unit 50 measures the voltage of the DC bus 10.

[0142] In step S73, similar to step S23 described above, the first control unit 51A determines whether the measured voltage is below the reference voltage. When it is determined that the measured voltage is below the threshold voltage (step S73; "Yes"), the process proceeds to step S75, and when it is determined that the measured voltage exceeds the reference voltage (step S75; "No"), the process proceeds to step S81.

[0143] In step S75, the first control unit 51A performs MPPT control, causing the solar power generation device, i.e., the DC power supply 4a, to provide maximum power to the DC / DC converter 3a and then to the DC bus 10. As a result, the voltage of the DC bus 10 increases. After the processing in step S75, the process can proceed to step S71.

[0144] Furthermore, in this modified example, the DC power supply 4a is MPPT controlled through the processing of steps S71 to S75. Therefore, the state of the control device 5A during the processing of steps S71 to S75 is also called the MPPT state.

[0145] In step S81, the first control unit 51A controls the output power of the DC / DC converter 3a to a target value determined by the measured voltage of the DC bus 10. The target value can be determined based on the measured voltage of the DC bus 10 and the reference voltage used by the second control unit 71.

[0146] For example, when the measured voltage is greater than the reference voltage, the target value can be set to be smaller than the target value set in the previous step S81; conversely, when the measured voltage is less than the reference voltage, the target value can be set to be larger than the target value set in the previous step S81. The variation in the target value during each step S81 can be proportional to the difference between the measured voltage and the reference voltage, or it can be constant and independent of the difference.

[0147] The initial target value during step S81 can be a power lower than the output power during MPPT control. Therefore, the output power of the DC / DC converter 3a is lower than the output power obtained in step S75. Similarly, each target value during the repeated processing of step S81 can be a power lower than the output power during MPPT control.

[0148] Furthermore, when the measured voltage is equal to the reference voltage, the target value can be the same as in the previous step S81. Additionally, if the amount of solar radiation temporarily decreases, resulting in a decrease in the power output of the DC power supply 4a, i.e., the solar power generation device, the output power of the DC / DC converter 3a can also be lower than the target value.

[0149] The target value can also be calculated by the first control unit 51A. Alternatively, the target value can be provided to the first control unit 51A from outside the control device 5A. The target value may not necessarily be determined based on the reference voltage used by the second control unit 71 and the measured voltage of the DC bus 10. For example, the target value may be determined based on the threshold voltage and the measured voltage used by the first control unit 51A in the processing of step S73, or it may be determined based on other voltages and measured voltages that are different from each of the reference voltage and threshold voltage.

[0150] In step S83, similar to step S21 described above, the voltage measuring unit 50 measures the voltage of the DC bus 10.

[0151] In step S85, the first control unit 51A determines whether the target value is above the reference output power of the DC / DC converter 3a. In this modified example, the reference output power of the DC / DC converter 3a is, for instance, the rated output power at which the DC / DC converter 3a can be stably used in its design, but it could also be the maximum output power that the DC / DC converter 3a can temporarily output. If it is determined in step S85 that the target value is not above the reference output power (step S85; "No"), the process proceeds to step S87. If it is determined in step S85 that the target value is above the reference output power (step S85; "Yes"), the process proceeds to step S71. Thus, the control that caused the output power of the DC / DC converter 3a to decrease through the process in step S81 is released.

[0152] In step S87, the first control unit 51A determines whether the target value is above the reference output power of the DC power supply 4a connected to the DC / DC converter 3a. In this modified example, the reference output power of the DC power supply 4a is, as an example, the rated output power that allows the DC power supply 4a to be used stably in the design, but it may also be the maximum output power that the DC power supply 4a can temporarily output. After the processing in step S87, the processing can proceed to step S81. If it is determined in step S87 that the target value is not above the reference output power (step S87; "No"), the processing proceeds to step S87. If it is determined in step S87 that the target value is above the reference output power (step S85; "Yes"), the processing proceeds to step S71. Thus, the control that caused the output power of the DC / DC converter 3a to decrease through the processing in step S81 is released.

[0153] Alternatively, only one of steps S85 and S87 can be performed.

[0154] In this modified example, the output power from the DC / DC converter 3a is limited by the processing of steps S81 to S87. Therefore, the state of the control device 5A during the processing of steps S81 to S87 is also called the DC output limiting state.

[0155] Based on the above actions, when the output power of the DC / DC converter 3a is reduced through the processing in step S81, as a result of the second control unit 71 increasing the voltage of the DC bus 10 through the processing in steps S51 to S67, when the target value of the output power of the DC / DC converter 3a, determined by the voltage of the DC bus 10, is greater than or equal to at least one of the reference output power of the DC / DC converter 3a and the reference output power of the DC power supply 4a connected thereto, the control to reduce the output power is released. Therefore, the control can be switched appropriately when it is not necessary to reduce the output power.

[0156] Furthermore, if the measured voltage of DC bus 10 exceeds the threshold voltage, causing control device 5A to enter a DC output limiting state, control device 5A will enter an MPPT state based on the target output power value determined by the measured voltage. This allows the state transition of control device 5A to be linked to the voltage control of DC bus 10 performed by control device 7, eliminating the need for communication between control device 5A and control device 7. Moreover, since control device 5A enters the MPPT state based on the target output power value determined by the measured voltage, rather than the measured voltage itself, frequent state transitions of control device 5A can be prevented.

[0157] [5.3(3). State transition table for power system 1A]

[0158] Figure 11 The state transition diagram of power system 1A is shown.

[0159] When an output limit command signal is provided under the condition that control device 5A is in MPPT and control device 7 is in the state of DC bus voltage maintenance (S0), that is, when the AC output from three-phase inverter 2A exceeds the output limit power, power system 1A changes to the state that control device 5A is in MPPT and control device 7 is in the state of AC output limit (S1).

[0160] Furthermore, when the measured voltage of the DC bus voltage becomes greater than the threshold voltage under the state where control device 5A is in MPPT and control device 7 is in AC output limiting (S1), power system 1A changes to the state where control device 5A is in DC output limiting and control device 7 is in AC output limiting (S2).

[0161] Furthermore, when the control device 5A is in the state of DC output limiting and the control device 7 is in the state of AC output limiting (S2), and the target value of the DC output power from the DC / DC converter 3a becomes above the reference output power, the power system 1A becomes the state of control device 5A being in the state of MPPT and control device 7 being in the state of AC output limiting (S3).

[0162] Furthermore, when no output limit command signal is provided under the state of control device 5A being MPPT and control device 7 being AC output limit (S3), that is, when the AC output from the three-phase inverter 2A is below the output limit power, the power system 1A changes to the state of control device 5A being MPPT and control device 7 being DC bus voltage maintenance (S0).

[0163] Here, in the states (S0-S3) above, where control device 5A is in MPPT and control device 7 is in AC output limiting state (S1, S3), control devices 5A and 7 do not perform voltage control on the DC bus 10. Therefore, in this state, when the power supplied from DC / DC converter 3a to DC bus 10 is lower than the power supplied from DC bus 10 to three-phase inverter 2A, the voltage of DC bus 10 will decrease. In this case, control device 5A cannot increase the power supplied from DC / DC converter 3a, while control device 7 can reduce the power supplied to three-phase inverter 2a. Therefore, in this modified example, as an example, in step S63, control device 7 can reduce the command value of the current flowing through single-phase inverter 22 as the measured voltage of DC bus 10 decreases. This prevents the voltage of DC bus 10 from dropping.

[0164] In addition, in the first modified example described above, it is explained that the control device 5A performs the processing of steps S71 to 75 and the processing of steps S81 to S87 respectively, but it can also be set to perform only one of the processing.

[0165] Furthermore, it is explained that when the target value is above the reference output power of DC / DC converter 3a (step S85; "Yes"), or when the target value is above the reference output power of DC power supply 4a connected to DC / DC converter 3a (step S87; "Yes"), the first control unit 51A performs MPPT control when the measured voltage of DC bus 10 is below the threshold voltage (step S75; "Yes"). However, MPPT control can also be performed without determining whether the measured voltage is below the threshold voltage. As an example, if the determination result of step S85 or step S87 is "Yes", the first control unit 51A can proceed to the processing of step S73 after performing MPPT control.

[0166] Furthermore, the case where the control device 5A controls the DC / DC converter 3a connected to the DC power supply 4a, which is a solar power generation device, has been described. However, the control device 5A can also control the DC / DC converter 3c connected to the DC power supply 4c, which is a battery. In the process of step S81, the control device 5A connected to the DC / DC converter 3c can set the target value of the output power of the DC / DC converter 3c to positive or negative power based on the voltage fluctuation of the DC bus 10. For the positive and negative power described here, the power flow supplying power from the DC power supply 4c, which is a battery, to the DC bus 10 can be positive, while the power flow supplying power from the DC bus 10 to the DC power supply 4c, which is a battery, can be negative. Thus, the DC power supply 4c charges and discharges appropriately according to the voltage of the DC bus 10.

[0167] [6. Second variation]

[0168] [6.1. Power System 1B]

[0169] Figure 12 The diagram illustrates a power system 1B according to a second variation. The power system 1B may include a three-phase inverter 2B, and the three-phase inverter 2B may have a control device 5B. In addition to a voltage measuring unit 20 and a second control unit 21, the control device 5B may also have a storage unit 55 and a first control unit 51B.

[0170] The storage unit 55 stores inherent threshold voltages that are associated with each of the plurality of DC / DC converters 3 and are different from each other above the threshold voltage. The inherent threshold voltages can be voltages that are lower than the absolute maximum rated voltage.

[0171] The first control unit 51B controls each of the plurality of DC / DC converters 3 via the control signal Ctrl_DC / DC. When the voltage of the DC bus 10 exceeds a threshold voltage, the first control unit 51B can reduce the output power of only a portion of the plurality of DC / DC converters 3. When the voltage of the DC bus 10 exceeds the threshold voltage, the first control unit 51B can set a time difference among the plurality of DC / DC converters 3 to reduce the output power of each DC / DC converter 3. Furthermore, when the voltage of the DC bus 10 exceeds the threshold voltage, the first control unit 51B can increase the number of DC / DC converters 3 whose output power needs to be reduced in a stepwise manner. For example, when the voltage of the DC bus 10 exceeds any inherent threshold voltage, the first control unit 51B can reduce the output power of the DC / DC converter 3 corresponding to that inherent threshold voltage. When the voltage of the DC bus 10 exceeds the absolute maximum rated voltage, the first control unit 51B can stop each DC / DC converter 3.

[0172] According to the power system 1B described above, the first control unit 51B controls each of the plurality of DC / DC converters 3. Therefore, unlike the above-described embodiment where the first control unit 51 controls only a portion of the plurality of DC / DC converters 3, it is possible to control the output power while adjusting among the plurality of DC / DC converters 3.

[0173] Furthermore, when the voltage of the DC bus 10 exceeds the threshold voltage, the number of DC / DC converters 3 with reduced output power increases in a stepwise manner, thus reliably suppressing the voltage of the DC bus 10 below the threshold voltage.

[0174] Furthermore, when the voltage of the DC bus 10 exceeds the threshold voltage, a time difference is set between the multiple DC / DC converters 3 to reduce the output power of each DC / DC converter 3. Therefore, when the voltage of the DC bus 10 rises, it is possible to prevent the output power of all DC / DC converters 3 from decreasing and to reliably enable the power system 1B as a whole to continue operating.

[0175] Furthermore, when different inherent threshold voltages associated with each of the multiple DC / DC converters 3 are stored, and the voltage of the DC bus 10 exceeds any of the inherent threshold voltages, the output power of the DC / DC converter 3 corresponding to the inherent threshold voltage decreases. Therefore, when the voltage of the DC bus 10 rises, the output power of all DC / DC converters 3 can be prevented from decreasing, and the power system 1B as a whole can reliably continue to operate.

[0176] [6.2. Actions]

[0177] Figure 13 The operation of control device 5B is shown. Control device 5B maintains the voltage of DC bus 10 at a reference voltage by performing steps S31 to S41. Furthermore, at the start of this operation, the second control unit 21 can continue to control each single-phase inverter 22. Additionally, the first control unit 51B can continue to control the corresponding DC / DC converter 3. As an example, the first control unit 51B can perform MPPT (Maximum Power Point Tracking) control between DC power supplies 4a and 4b, which are solar power generation devices, to provide maximum power from DC power supplies 4a and 4b. Furthermore, the first control unit 51B can charge DC power supply 4c, which acts as a battery, when there is excess power from DC power supplies 4a and 4b, which are solar power generation devices, and discharge DC power supply 4c when there is insufficient power, based on voltage fluctuations in DC bus 10.

[0178] In step S31, the voltage measuring unit 20 measures the voltage of the DC bus 10.

[0179] In step S33, similar to step S13 described above, the second control unit 21 determines whether the measured voltage is a reference voltage. When it is determined that the measured voltage is a reference voltage (step S13; "Yes"), the process proceeds to step S31, and when it is determined that the measured voltage is not a reference voltage (step S33; "No"), the process proceeds to step S35.

[0180] Then, in step S35, similar to step S15 above, the second control unit 21 attempts to maintain the voltage of the DC bus 10 at the reference voltage by changing the control conditions of each single-phase inverter 22.

[0181] In step S37, the voltage measuring unit 20 measures the voltage of the DC bus 10.

[0182] In step S39, the first control unit 51B determines whether the measured voltage exceeds any inherent threshold voltage. When it is determined that the measured voltage exceeds any inherent threshold voltage (step S39; "Yes"), the process proceeds to step S41, and when it is determined that the measured voltage does not exceed the inherent threshold voltage (step S39; "No"), the process proceeds to step S31.

[0183] Each inherent threshold voltage can be a single voltage value. Here, in this embodiment, as an example, the inherent threshold voltage of the DC / DC converter 3 is set according to the maximum output power of the DC power supply 4 connected to the DC / DC converter 3. For example, the inherent threshold voltage of the DC / DC converter 3 is set to a larger (or smaller) value according to the descending order of the maximum output power of the connected DC power supplies 4.

[0184] In step S41, the first control unit 51B reduces the output power of the DC / DC converter 3 corresponding to an inherent threshold voltage lower than the measured voltage. For example, the first control unit 51B may set the output power to a power lower than the current time. As a result, the output power of only a portion of the multiple DC / DC converters 3 is reduced. If the processing in step S41 is completed, the process can proceed to step S31.

[0185] Here, in this embodiment, as an example, the inherent threshold voltage of the DC / DC converter 3 is set according to the order of the maximum output power of the connected DC power supplies 4. Therefore, when the process of steps S39 to S41 is repeated, the output power of each DC / DC converter is reduced in an order corresponding to the maximum output power of each DC power supply 4 connected to each DC / DC converter 3.

[0186] Based on the above operations, when the voltage of the DC bus 10 exceeds the threshold voltage, the output power of each DC / DC converter 3 decreases in order corresponding to the maximum output power of each connected DC power supply 4. Therefore, as the output power of each DC / DC converter 3 decreases in descending order of the maximum output power of the DC power supply 4, the amount of power supplied to the DC bus 10 from the multiple DC / DC converters 3 can be immediately and significantly reduced. Thus, the voltage of the DC bus can be reliably suppressed below the threshold voltage, thereby improving safety. Furthermore, as the output power of each DC / DC converter 3 decreases in ascending order of the maximum output power of the DC power supply 4, the amount of power supplied to the DC bus 10 from the multiple DC / DC converters 3 can be gradually and significantly reduced. Therefore, the overall output power of the power system 1 can be maintained at a high level.

[0187] Furthermore, in the second variation described above, the storage unit 55 stores inherent threshold voltages associated with each of the plurality of DC / DC converters 3 and different from each other. When the voltage of the DC bus 10 exceeds the inherent threshold voltage, the first control unit 51B reduces the output power of the DC / DC converter 3 corresponding to that inherent threshold voltage. Alternatively, the storage unit 55 may store inherent upper limit times associated with each of the plurality of DC / DC converters 3 and different from each other. When the duration for which the voltage of the DC bus 10 exceeds the threshold voltage exceeds any inherent upper limit time, the first control unit 51B reduces the output power of the DC / DC converter 3 corresponding to that inherent upper limit time. Thus, the upper limit times can be made different from those of the other control devices 5 included in the power system 1, and therefore, the plurality of DC / DC converters 3 can be controlled based on individual upper limit times. Therefore, when the voltage of the DC bus 10 rises, it is possible to prevent a decrease in the output power of all DC / DC converters 3 and reliably allow the power system 1 as a whole to continue operating. For example, the inherent upper limit times of each DC / DC converter 3 can be set according to the order corresponding to the maximum output power of the connected DC power supply 4.

[0188] Furthermore, although it has been stated that when the voltage of the DC bus 10 exceeds the threshold voltage, the first control unit 51B reduces the output power of each DC / DC converter 3 in an order corresponding to the maximum output power of the DC power supply 4, the output power of each DC / DC converter 3 can also be reduced in a random order. Alternatively, the history of reducing the output power of each DC / DC converter 3 can be stored, and DC / DC converters with fewer instances of output power reduction can be prioritized for reduction. Even in these cases, when the voltage of the DC bus 10 rises, it is possible to prevent the output power of all DC / DC converters 3 from decreasing, and to reliably ensure the continued operation of the power system 1 as a whole.

[0189] Furthermore, while the description describes a control device 5B having a second control unit 21 and a storage unit 55, it is also possible for the control device 5B to lack at least one of them. If the control device 5B does not have a second control unit 21, the second control unit 21 may be located externally to the control device 5B. If the control device 5B does not have a storage unit 55, the control device 5B can reduce the output power of each DC / DC converter 3 in a random order as described above, or it can reduce the output power of each DC / DC converter 3 in an order corresponding to the connection position of each DC / DC converter 3 relative to the rack-mounted PCS device 11.

[0190] Furthermore, while the case where the control device 5B has a second control unit 21 has been described, it can also be configured to have the second control unit 71 as described in the first variation. In this case, the control device 5B can perform the processing of steps S71 to S87 instead of the processing of steps S31 to S35. Furthermore, while the case where the control device 5B has a first control unit 51B has been described, it can also be configured to have the first control unit 51A as described in the first variation. In this case, when it is determined in step S39 that the measured voltage does not exceed any inherent threshold voltage (step S39; "No"), the control device 5B can perform MPPT control on the DC / DC converters 3a and 3b corresponding to inherent threshold voltages greater than the measured voltage. Furthermore, when it is determined in step S39 that the measured voltage exceeds any inherent threshold voltage (step S39; "Yes"), the control device 5B can perform the processing of steps S81 to S87 on the DC / DC converter 3 corresponding to inherent threshold voltages lower than the measured voltage.

[0191] [7. Other variations]

[0192] Furthermore, in the above embodiments and modifications, it is described that power systems 1A and 1B are equipped with three-phase inverters 2, each having a single-phase inverter 22 for each of the U, V, and W phases. However, they may also have only single-phase inverters 22, only DC / DC converter circuits 23, or only single-phase inverter circuits 24. Moreover, although it is described that the three-phase inverters 2 have a single single-phase inverter 22 for each phase, they may also have multiple single-phase inverters 22 connected in series or parallel.

[0193] Furthermore, although it is stated that the single-phase inverter 22 is a full-bridge inverter circuit with a full-bridge circuit 241, it can also be a half-bridge inverter circuit with a half-bridge circuit.

[0194] Furthermore, although it is stated that power systems 1, 1A, and 1B include DC power supply 4, power systems 1, 1A, and 1B may also be externally connected to DC power supply 4 without including DC power supply 4.

[0195] Furthermore, various embodiments of the present invention can be described with reference to flowchart and block diagrams, where a block may represent (1) a stage of the process of performing an operation or (2) a portion of a device having the function of performing an operation. Specific stages and portions may be installed using dedicated circuitry, programmable circuitry provided with computer-readable commands stored on a computer-readable medium, and / or a processor provided with computer-readable commands stored on a computer-readable medium. Dedicated circuitry may include digital and / or analog hardware circuitry, and may also include integrated circuits (ICs) and / or discrete circuitry. Programmable circuitry may include reconfigurable hardware circuitry, including logic AND, logic OR, logic XOR, logic NAND, logic NOR and other logic operations, flip-flops, registers, field-programmable gate arrays (FPGAs), programmable logic arrays (PLAs), and other memory elements.

[0196] Computer-readable media can include any tangible device capable of storing commands that can be executed by suitable devices. As a result, computer-readable media having commands stored therein include products that contain executable commands for generating units to perform operations specified by flowcharts or block diagrams. Examples of computer-readable media include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, etc. Other examples of computer-readable media may include floppy disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), electrically erasable programmable read-only memory (EEPROM), static random access memory (SRAM), optical disc read-only memory (CD-ROM), digital versatile disk (DVD), Blu-ray (RTM) optical disc, memory stick, integrated circuit cards, etc.

[0197] Computer-readable commands may include any of the following: assembly commands, instruction set architecture (ISA) commands, machine commands, machine-dependent commands, microcode, firmware commands, status setting data, or source code or object code described using any combination of one or more programming languages ​​such as Smalltalk, JAVA (registered trademark), C++, or an existing programming language such as "C" or the like.

[0198] Computer-readable commands are provided via a wide area network (WAN) such as a local area network (LAN) or the Internet to the processor or programmable circuit of a general-purpose computer, a special-purpose computer, or other programmable data processing device to execute the computer-readable commands in order to create units for performing the operations specified by the flowchart or block diagram. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, etc.

[0199] Figure 14 This is an example of a computer 2200 that can embody, in whole or in part, various aspects of the present invention. A program installed in the computer 2200 can function or execute an operation associated with a device according to an embodiment of the present invention, or one or more parts of that device, and / or execute a program according to an embodiment of the present invention or a stage of executing that program within the computer 2200. Such a program can be executed within the computer 2200 by performing specific operations corresponding to some or all of the flowcharts and block diagrams described in this specification, and by means of the CPU 2212.

[0200] The computer 2200 of this embodiment includes a CPU 2212, RAM 2214, a graphics controller 2216, and a display device 2218, which are interconnected via a main controller 2210. The computer 2200 also includes input / output units such as a communication interface 2222, a hard disk drive 2224, a DVD-ROM drive 2226, and an IC card driver, which are connected to the main controller 2210 via an input / output controller 2220. The computer also includes legacy input / output units such as a ROM 2230 and a keyboard 2242, which are connected to the output / output controller 2220 via an input / output chip 2240.

[0201] CPU 2212 operates according to the programs stored in ROM 2230 and RAM 2214, thereby controlling each unit. Graphics controller 2216 retrieves image data generated by CPU 2212 from frame buffers or other sources provided in RAM 2214 or from its own memory, and displays the image data on display device 2218.

[0202] Communication interface 2222 communicates with other electronic devices via a network. Hard disk drive 2224 stores programs and data used by CPU 2212 within computer 2200. DVD-ROM drive 2226 reads programs or data from DVD-ROM 2201 and provides programs or data to hard disk drive 2224 via RAM 2214. IC card drive reads programs and data from IC card and / or writes programs and data to IC card.

[0203] The ROM 2230 stores the boot program and / or programs that depend on the hardware of the computer 2200, which are executed by the computer 2200 upon activation. The input / output chip 2240 can also connect various input / output units to the input / output controller 2220 via parallel ports, serial ports, keyboard ports, mouse ports, etc.

[0204] The program is provided by a computer-readable medium such as a DVD-ROM 2201 or an IC card. The program is read from the computer-readable medium, which may be installed, for example, in a hard disk drive 2224, RAM 2214, or ROM 2230, and executed by the CPU 2212. The information processing described within these programs is read into the computer 2200, enabling interaction between the program and the aforementioned hardware resources. The apparatus or method may also be configured to perform information manipulation or processing according to the use of the computer 2200.

[0205] For example, when communication is performed between computer 2200 and an external device, CPU 2212 executes a communication program loaded in RAM 2214, and commands communication interface 2222 to perform communication processing based on the processing described in the communication program. Under the control of CPU 2212, communication interface 2222 reads transmission data stored in the transmission buffer processing area provided in a storage medium such as RAM 2214, hard disk drive 2224, DVD-ROM 201, or IC card, and sends the read transmission data to the network, or writes received data received by the network into the receive buffer processing area provided on the storage medium, etc.

[0206] CPU 2212 can also read all or a portion of files or databases stored in external storage media such as hard disk drive 2224, DVD-ROM drive 2226 (DVD-ROM 2201), and IC cards into RAM 2214, and perform various types of processing on the data in RAM 2214. Then, CPU 2212 writes the processed data back to the external storage media.

[0207] Various types of information, such as programs, data, tables, and databases, can be stored in storage media and processed. The CPU 2212 can perform various types of processing on data read from RAM 2214, including operations specified by a sequence of program commands, conditional checks, conditional branches, unconditional branches, information retrieval / replacement, etc., as described throughout this disclosure, and write the results back to RAM 2214. The CPU 2212 can retrieve information from files, databases, etc., within the storage medium. For example, if the storage medium stores attribute values ​​for each of a first attribute associated with a second attribute value, the CPU 2212 retrieves an entry from among these entries that matches the condition specifying the first attribute value, reads the attribute value of the second attribute stored in that entry, and thereby obtains the attribute value of the second attribute associated with the first attribute that satisfies a pre-set condition.

[0208] The programs or software modules described above may be stored on or near computer 2200 on a computer-readable medium. Furthermore, storage media such as hard disks or RAM provided in a server system connected to a dedicated communication network or the Internet may be used as computer-readable media to provide the programs to computer 2200 via the network.

[0209] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. Various changes or improvements can be made based on the above embodiments, which will be obvious to those skilled in the art. As can be seen from the claims, the various changes or improvements described above are also included within the technical scope of the present invention.

[0210] Please note that the execution order of actions, processes, steps, and stages in the apparatus, systems, programs, and methods shown in the claims, specification, and drawings can be implemented in any order, unless explicitly stated as "before" or "previously," and the output of previous processes is not used in subsequent processes. The use of terms such as "firstly" and "then" in the action flow descriptions in the claims, specification, and drawings for ease of explanation does not imply that the actions must be performed in this order.

[0211] Label Explanation

[0212] 1 Power system, 2 Three-phase inverter, 3 DC / DC converter, 4 DC power supply, 5 Control device, 10 DC bus, 11 Device, 20 Voltage measurement unit, 21 Second control unit, 22 Single-phase inverter, 23 DC / DC converter circuit, 24 Single-phase inverter circuit, 25 Unit, 31 First positive terminal, 32 Second positive terminal, 33 Diode, 34 Switching element, 35 Switching element, 36 Filter capacitor, 37 Inductor, 50 Voltage measurement unit, 51 First control unit, 52 Modulation unit, 55 Storage unit, 230 Transformer, 231 Filter capacitor, 232 Full-bridge circuit, 233 Positive wiring, 234 Full-bridge circuit, 240 Filter capacitor, 241 Full-bridge circuit, 251 Positive terminal, 252 AC output terminal, 2200 Meter Computer, 2201 DVD-ROM, 2210 Main controller, 2212 CPU, 2214 RAM, 2216 Graphics controller, 2218 Display device, 2220 Input / output controller, 2222 Communication interface, 2224 Hard disk drive, 2226 DVD-ROM drive, 2230 ROM, 2240 Input / output chip, 2242 Keyboard, 2301 Primary coil, 2302 Secondary coil, 2321 Switching element, 2322 Switching element, 2323 Switching element, 2324 Switching element, 2341 Switching element, 2342 Switching element, 2343 Switching element, 2344 Switching element, 2411 Switching element, 2412 Switching element, 2413 Switching element, 2414 Switching element.

Claims

1. A control device characterized by comprising: including: a first control section that controls a corresponding one of a plurality of DC / DC converters respectively provided between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power sources that supply DC power to the DC bus; and a voltage measurement section that measures a voltage of the DC bus, in a case where a time during which the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage exceeds an upper limit time, the first control section reduces only an output power of the corresponding DC / DC converter, the control device further includes a change section that changes the upper limit time over time.

2. The control device according to claim 1, wherein the change section changes the threshold voltage over time.

3. A system, characterized by including: an inverter that maintains a DC bus at a reference voltage through power exchange with the DC bus; a plurality of DC / DC converters respectively provided between the DC bus and a plurality of DC power sources that supply DC power to the DC bus; and a plurality of control devices according to claim 1 or 2 that respectively control a corresponding one of the plurality of DC / DC converters.

4. The system according to claim 3, wherein in a case where the voltage of the DC bus exceeds the threshold voltage, the plurality of control devices set a time difference among the plurality of DC / DC converters to reduce an output power of each DC / DC converter.

5. The system according to claim 3, further including a further control device having a second control section that controls the inverter, the second control section reduces an output power output from the inverter according to a case where an instruction signal for output limitation is received.

6. The system according to claim 5, wherein the second control section determines an amount of current flowing in the inverter based on a target output power included in the instruction signal and the voltage of the DC bus.

7. The system according to any one of claims 3 to 6, wherein at least a part of the plurality of DC power sources is a solar power generation device, the first control section that controls the DC / DC converter connected to the solar power generation device is capable of further controlling the solar power generation device, and in at least one of a case where the voltage of the DC bus is below the threshold voltage and a case where the output power of the DC / DC converter is not reduced, the first control section performs MPPT control to cause a maximum power to be supplied from the solar power generation device.

8. The system according to any one of claims 3 to 6, wherein in a case where the output power of a part of the DC / DC converters is reduced, the first control section controls the output power to a target value determined according to the voltage of the DC bus. ​ 9. The system according to claim 8, wherein the first control section cancels the control to reduce the output power of the DC / DC converter in a case where the target value is at least one of a reference output power of the DC / DC converter and a reference output power of the DC power supply connected to the DC / DC converter.

10. A control device characterized by comprising: comprises: a first control section that controls at least one of a plurality of DC / DC converters respectively provided between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power supplies that supply DC power to the DC bus; a voltage measurement section that measures a voltage of the DC bus; a storage section that stores, in association with each of the plurality of DC / DC converters, different intrinsic threshold voltages from each other that are higher than the reference voltage; and a change section that changes the intrinsic threshold voltages over time and changes the order of the intrinsic threshold voltages over time, the first control section reduces the output power of the DC / DC converter corresponding to the intrinsic threshold voltage in a case where the voltage of the DC bus exceeds any of the intrinsic threshold voltages changed over time.

11. A system, characterized by comprises: an inverter that maintains a DC bus at a reference voltage through power exchange with the DC bus; a plurality of DC / DC converters respectively provided between the DC bus and a plurality of DC power supplies that supply DC output to the DC bus; and the control device according to claim 10 controls each of the plurality of DC / DC converters.

12. The system according to claim 11, wherein the control device further has a second control section that controls the inverter, the second control section reduces the output power output from the inverter in a case where an instruction signal to limit the output is received.

13. The system according to claim 12, wherein the second control section determines an amount of current flowing in the inverter based on a target output power included in the instruction signal and the voltage of the DC bus.

14. The system according to any one of claims 11 to 13, wherein at least a part of the plurality of DC power supplies is a solar power generation device, the first control section that controls the DC / DC converter connected to the solar power generation device can further control the solar power generation device, and in at least one of a case where the voltage of the DC bus is below the threshold voltage and a case where the output power of the DC / DC converter is not reduced, the first control performs MPPT control so that maximum power is supplied from the solar power generation device.

15. The system according to any one of claims 11 to 13, wherein ​ In a case where the output power of a part of the DC / DC converters is reduced, the first control section controls the output power to a target value determined in accordance with the voltage of the direct current bus.

16. The system according to claim 15, wherein In a case where the output power of the part of the DC / DC converters is reduced, the first control section cancels the control to reduce the output power in a case where the target value is at least one of a reference output power of the DC / DC converter and a reference output power of the direct current power supply connected to the DC / DC converter.

17. A control device characterized by comprising: including: a first control section that controls at least one of a plurality of DC / DC converters respectively provided between a direct current bus maintained at a reference voltage through power exchange with an inverter and a plurality of direct current power supplies that supply direct current to the direct current bus; a voltage measurement section that measures the voltage of the direct current bus; and a storage section that stores, in association with each of the plurality of DC / DC converters, an inherent upper limit time that is different from each other, In a case where the duration in which the voltage of the direct current bus exceeds a threshold voltage higher than the reference voltage exceeds any of the inherent upper limit times, the first control section reduces the output power of the DC / DC converter corresponding to the inherent upper limit time.

18. A system, comprising: including: an inverter that maintains a direct current bus at a reference voltage through power exchange with the direct current bus; a plurality of DC / DC converters respectively provided between the direct current bus and a plurality of direct current power supplies that supply direct current output to the direct current bus; and a control device according to claim 17 that controls each of the plurality of DC / DC converters.

19. The system according to claim 18, wherein the control device further has a second control section that controls the inverter, the second control section reduces the output power output from the inverter in a case where an instruction signal to limit the output is received.

20. The system according to claim 19, wherein the second control section determines the amount of current flowing in the inverter based on a target output power included in the instruction signal and the voltage of the direct current bus.

21. The system according to any one of claims 18 to 20, wherein at least a part of the plurality of direct current power supplies is a solar power generation device, the first control section that controls the DC / DC converter connected to the solar power generation device is capable of further controlling the solar power generation device, and in at least one of a case where the voltage of the direct current bus is below the threshold voltage and a case where the output power of the DC / DC converter is not reduced, the first control performs MPPT control so that maximum power is supplied from the solar power generation device.

22. The system according to any one of claims 18 to 20, wherein ​ In a case where the output power of a part of the DC / DC converters is reduced, the first control section controls the output power to a target value determined in accordance with the voltage of the direct current bus.

23. The system of claim 22, wherein, In a case where the output power of a part of the DC / DC converters is reduced, the first control section releases the control to reduce the output power in a case where the target value is at least one of a reference output power of the DC / DC converter and a reference output power of the direct current power supply connected to the DC / DC converter.

24. A control method characterized by, Comprising: a control phase in which a corresponding one of a plurality of DC / DC converters respectively provided between a direct current bus maintained at a reference voltage through power exchange with an inverter and a plurality of direct current power supplies that supply direct current to the direct current bus is controlled; and a voltage measurement phase in which a voltage of the direct current bus is measured, in the control phase, in a case where a time during which the voltage of the direct current bus exceeds a threshold voltage higher than the reference voltage exceeds an upper limit time, only the output power of the corresponding DC / DC converter is reduced, the control method further comprising a change phase in which the upper limit time is changed over time.

25. A control method characterized by, Comprising: a control phase in which at least one of a plurality of DC / DC converters respectively provided between a direct current bus maintained at a reference voltage through power exchange with an inverter and a plurality of direct current power supplies that supply direct current to the direct current bus is controlled; a voltage measurement phase in which a voltage of the direct current bus is measured; a storage phase in which an inherent threshold voltage that is different from each other and is above the threshold voltage higher than the reference voltage is associated with each of the plurality of DC / DC converters is stored; and a change phase in which the inherent threshold voltage is changed over time, and an order of the inherent threshold voltage is changed over time, in the control phase, in a case where the voltage of the direct current bus exceeds any of the inherent threshold voltage that is changed over time, the output power of the DC / DC converter corresponding to the inherent threshold voltage is reduced.

26. A control method characterized by, Comprising: a control phase in which at least one of a plurality of DC / DC converters respectively provided between a direct current bus maintained at a reference voltage through power exchange with an inverter and a plurality of direct current power supplies that supply direct current to the direct current bus is controlled; a voltage measurement phase in which a voltage of the direct current bus is measured; and a storage phase in which an inherent upper limit time that is different from each other is associated with each of the plurality of DC / DC converters is stored, in the control phase, in a case where the voltage of the direct current bus exceeds any of the inherent threshold voltage that is changed over time, the output power of the DC / DC converter corresponding to the inherent threshold voltage is reduced. In the control phase, in a case where the duration for which the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage exceeds any of the inherent upper limit times, the output power of the DC / DC converter corresponding to the inherent upper limit time is reduced.

27. A computer program product recording a program, characterized by the program causing a computer to function as: a first control section that controls a corresponding one of a plurality of DC / DC converters respectively provided between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power sources that supply DC power to the DC bus; and a voltage measurement section that measures the voltage of the DC bus, in a case where the time for which the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage exceeds an upper limit time, the first control section reduces only the output power of the corresponding DC / DC converter, the program further causing the computer to function as a change section that changes the upper limit time over time.

28. A computer program product recording a program, characterized by the program causing a computer to function as: a first control section that controls at least one of a plurality of DC / DC converters respectively provided between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power sources that supply DC power to the DC bus; a voltage measurement section that measures the voltage of the DC bus; a storage section that stores inherent threshold voltages that are different from each other and that are above a threshold voltage higher than the reference voltage in association with each of the plurality of DC / DC converters; and a change section that changes the inherent threshold voltages over time, changes the order of the inherent threshold voltages over time, in a case where the voltage of the DC bus exceeds any of the inherent threshold voltages that change over time, the first control section reduces the output power of the DC / DC converter corresponding to the inherent threshold voltage.

29. A computer program product recording a program, characterized by the program causing a computer to function as: a first control section that controls at least one of a plurality of DC / DC converters respectively provided between a DC bus maintained at a reference voltage through power exchange with an inverter and a plurality of DC power sources that supply DC power to the DC bus; a voltage measurement section that measures the voltage of the DC bus; and a storage section that stores inherent upper limit times that are different from each other in association with each of the plurality of DC / DC converters, in a case where the duration for which the voltage of the DC bus exceeds a threshold voltage higher than the reference voltage exceeds any of the inherent upper limit times, the first control section reduces the output power of the DC / DC converter corresponding to the inherent upper limit time. ​

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