Power supply system, control device, and control method

Abstract

Provided is a technology for a power supply system in which multiple power conversion devices are connected in parallel, each of which outputs power via a transformer, that enables power output to continue using the remaining normal power conversion units even if some of the multiple power conversion units included in the power conversion devices stop. [Solution] A power supply system SYS according to one embodiment of the present disclosure comprises a plurality of power conversion devices 10 connected in parallel on the output side, and a transformer 12 electrically connected to the output side of each of the plurality of power conversion devices 10, and the plurality of power conversion devices 10 each include a plurality of power conversion modules 9 connected in parallel, and when some of the plurality of power conversion modules 9 stop, the output current balance control according to the capacity of the plurality of power conversion devices 10 is continued so that the phases of the AC output from the transformer 12 on the output side of the target power conversion device 10 and the transformers 12 on the output sides of the other power conversion devices 10 are synchronized and the voltage levels are the same.

Description

[Technical field]

[0001] The present disclosure relates to a power supply system and the like. [Background technology]

[0002] For example, a power supply system is known in which a plurality of power conversion devices are connected in parallel, each of which outputs power via a transformer (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7523193 [Patent Document 2] Patent No. 7408820 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, there are cases where a power conversion device is configured by connecting a plurality of power conversion units in parallel (for example, Patent Document 2). In this case, even if some of the power conversion units of the power conversion device stop due to an abnormality or the like, it is desirable that the remaining power conversion units that are functioning normally can continue to output power from the power conversion device.

[0005] In view of the above problems, an object of the present invention is to provide a technology for a power supply system in which multiple power conversion devices are connected in parallel and each outputs power via a transformer, which enables the output of power to be continued by the remaining normal power conversion units even if some of the multiple power conversion units included in the power conversion device stop. [Means for solving the problem]

[0006] In order to achieve the above object, in one embodiment of the present disclosure, A plurality of power conversion devices each outputting AC power using power supplied from a power source and connected in parallel on the output side; a transformer provided for each of the plurality of power conversion devices and electrically connected to an output side of a target power conversion device; Each of the plurality of power conversion devices includes a plurality of power conversion units that are connected in parallel to an input unit and an output unit of a target power conversion device and output AC using power input to the target power conversion device, Each of the multiple power conversion devices performs balance control of output currents according to the capacities of the multiple power conversion units, and performs balance control of output currents according to the capacities of the multiple power conversion devices by droop control, and when some of the multiple power conversion units stop, continues balance control of output currents according to the capacities of the multiple power conversion devices so that the phases of the AC output from the transformer on the output side of the target power conversion device and the AC output from the transformer on the output side of the other power conversion devices are synchronized and the voltage levels are the same. A power system is provided.

[0007] In another embodiment of the present disclosure, A control device for a power supply system including a plurality of power conversion devices each outputting AC using power supplied from a power source and connected in parallel on an output side, and a transformer provided for each of the plurality of power conversion devices and electrically connected to an output side of a target power conversion device, the plurality of power conversion devices each including a plurality of power conversion units each connected in parallel to an input unit and an output unit of the target power conversion device and outputting AC using power input to the target power conversion device, the control device controlling one of the power conversion devices, performing balance control of output currents according to the capacities of the plurality of power conversion units, and performing balance control of output currents according to the capacities of the plurality of power conversion devices by droop control, and when a portion of the plurality of power conversion units stops, continuing balance control of output currents according to the capacities of the plurality of power conversion devices so that the phases of AC output from the transformer on the output side of the target power conversion device and AC output from the transformer on the output side of another power conversion device are synchronized and the voltage levels are the same; A controller is provided.

[0008] In still another embodiment of the present disclosure, A control method for controlling one of the power conversion devices in a power supply system, the power conversion devices including a plurality of power conversion units each of which outputs AC using power supplied from a power source and is connected in parallel on an output side, and a transformer provided for each of the plurality of power conversion devices and electrically connected to an output side of a target power conversion device, the plurality of power conversion devices each including a plurality of power conversion units each of which is connected in parallel to an input unit and an output unit of the target power conversion device and outputs AC using power input to the target power conversion device, performing balance control of output currents according to the capacities of the plurality of power conversion units, and performing balance control of output currents according to the capacities of the plurality of power conversion devices by droop control, and when a portion of the plurality of power conversion units stops, continuing balance control of output currents according to the capacities of the plurality of power conversion devices so that the phases of AC output from the transformer on the output side of the target power conversion device and AC output from the transformer on the output side of another power conversion device are synchronized and the voltage levels are the same; A control method is provided. Effect of the Invention

[0009] According to the above-described embodiment, in a power supply system in which a plurality of power conversion devices are connected in parallel and each outputs power via a transformer, even if some of the plurality of power conversion units included in the power conversion devices stop, the output of power can be continued by the remaining power conversion units that are functioning normally. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a first example of a power supply system. [Diagram 2] FIG. 13 is a diagram illustrating a configuration of a second example of a power supply system. [Diagram 3] FIG. 1 is a diagram illustrating an example of a configuration of a power conversion device. [Figure 4] FIG. 4 is a control block diagram showing an example of a control process of a control unit. [Diagram 5]FIG. 11 is a diagram showing an example of the relationship between the total number of modules and the number of power-supplying modules, and the module gain and transformer gain. [Figure 6] FIG. 4 is a control block diagram showing an example of a control process of a module control unit. [Figure 7] FIG. 2 is a diagram illustrating an example of a normal operating state of the power supply system. [Figure 8] FIG. 1 is a diagram illustrating an example of an operating state when an abnormality occurs in a power supply system. [Figure 9] FIG. 13 is a diagram illustrating an example of a characteristic of a transformer. [Figure 10] FIG. 11 is a diagram illustrating an example of a method for correcting voltage characteristics of a transformer. [Figure 11] FIG. 2 is a diagram illustrating an example of phase synchronization control of an AC current output from a transformer. [Figure 12] FIG. 1 is a diagram illustrating an example of an operation of a power supply system according to a comparative example. [Figure 13] FIG. 2 is a diagram illustrating an example of an operation of the power supply system according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment will be described with reference to the drawings.

[0012] [Power supply system configuration] The configuration of a power supply system SYS according to this embodiment will be described with reference to FIGS.

[0013] Fig. 1 is a diagram showing a configuration of a first example of the power supply system SYS, and Fig. 2 is a diagram showing a configuration of a second example of the power supply system SYS.

[0014] Note that the power source 1 is omitted in Fig. 2. Also, since the configuration of the power conversion module 9 in Fig. 2 is the same as that of the power conversion module 9 in Fig. 1, detailed components of the power conversion module 9 are omitted in Fig. 2.

[0015] As shown in FIGS. 1 and 2, the power supply system SYS includes a power supply 1, a transformer 2, a plurality of power conversion devices 10, a transformer 12, a power feeder breaker 13, and a load 14.

[0016] The power supply 1 supplies power to the power conversion device 10. For example, the power supply 1 is an AC power supply such as a commercial power supply.

[0017] The transformer 2 is an insulating transformer electrically connected to the input side (i.e., the power source 1 side) of each of the multiple power conversion devices 10 connected in parallel. The primary side of the transformer 2 is electrically connected to the power source 1 and is also electrically connected to the primary side of another transformer 2 provided on the input side of the other power conversion device 10, and the secondary side of the transformer 2 is electrically connected to the power conversion device 10, and power from the power source 1 is supplied to the power conversion device 10 through the transformer 2.

[0018] The multiple power conversion devices 10 are connected in parallel to the power source 1 and the load 14, respectively.

[0019] The number of power conversion devices 10 connected in parallel to the power source 1 and the load 14 is arbitrary. For example, as shown in FIG. 1, two power conversion devices 10 are connected in parallel to each of the power source 1 and the load 14. Also, for example, as shown in FIG. 2, eight power conversion devices 10 are connected in parallel to each of the power source 1 and the load 14. The power supply system SYS in FIG. 2 is a shore power supply (shore power) system provided at a pier 20 where a ship SP is docked. Also, three to seven power conversion devices 10 may be connected in parallel to each of the power source 1 and the load 14, or nine or more power conversion devices 10 may be connected in parallel to each of the power source and the load 14. The following description will be focused on the case where two power conversion devices 10 are connected in parallel.

[0020] For example, all of the power conversion devices 10 have the same output capacity. In addition, some or all of the power conversion devices 10 may have different output capacities. The following description will be centered on the case where all of the power conversion devices 10 have the same output capacity.

[0021] Note that one power conversion device 10 and another power conversion device 10 may receive power from different power sources. For example, a plurality of power conversion devices 10 may receive power from different power sources.

[0022] The power conversion devices 10 may be installed at different locations. For example, as shown in FIG. 2, the power conversion devices 10 are installed inside different buildings 17 (or containers) on a wharf 20. Therefore, it may be difficult for the power conversion device 10 to perform current balance control for balancing the output currents between the power conversion devices 10 while acquiring information on the states of the other power conversion devices 10 (for example, detected values ​​of output currents). In particular, in the case of the wharf 20 of FIG. 2, the distance between the buildings 17 (or containers) in which the power conversion devices 10 are installed is several hundred meters, so that it is practically impossible for the power conversion device 10 to perform output current balance control between the power conversion devices 10 and the other power conversion devices 10 while acquiring information on the states of the other power conversion devices 10. Therefore, in this embodiment, as described later, each power conversion device 10 autonomously performs output current balance control for the multiple power conversion devices 10 by droop control.

[0023] Since the multiple power conversion devices 10 have the same configuration, the configuration of one power conversion device 10 will be representatively described below.

[0024] The power conversion device 10 includes a plurality of power conversion modules 9 .

[0025] The multiple power conversion modules 9 are connected in parallel to each of the input and output parts of the power conversion device 10.

[0026] The number of power conversion modules 9 connected in parallel to the input section and the output section of the power conversion device 10 is arbitrary. For example, as shown in Fig. 1 and Fig. 2, two power conversion modules 9 are connected in parallel to the input section and the output section of the power conversion device 10. Also, three or more power conversion modules 9 may be connected in parallel to the input section and the output section of the power conversion device 10. The following description will be centered on the case where the number of power conversion modules 9 connected in parallel to the input section and the output section of the power conversion device 10 is two.

[0027] 1 and 2, for example, the number of power conversion modules 9 for each power conversion device 10 is the same in all of the multiple power conversion devices 10. The number of power conversion modules 9 for each power conversion device 10 may be different from each other in some or all of the multiple power conversion devices 10. The following description will be centered on the case where the number of power conversion modules 9 for each power conversion device 10 is the same in all of the multiple power conversion devices 10.

[0028] For example, all of the power conversion modules 9 have the same output capacity. In addition, some or all of the power conversion modules 9 may have different output capacities. In the following, the description will be given on the assumption that all of the power conversion modules 9 have the same output capacity.

[0029] Since the multiple power conversion modules 9 have the same configuration, the configuration of one power conversion module 9 will be representatively described below.

[0030] The power conversion module 9 includes an input circuit breaker 3, an input filter 4, an AC / DC (Alternating Current to Direct Current) converter 5, a DC / AC (Direct Current to Alternating Current) converter 6, an output filter 7, and an output circuit breaker 8.

[0031] The input circuit breaker 3 opens and closes the power path at the input of the power conversion module 9 , and can interrupt the current from the transformer 2 .

[0032] The input filter 4 is an LC filter including an inductor and a capacitor, and suppresses undesirable components in the AC input from the transformer 2. For example, the input filter 4 suppresses high-frequency components higher than the frequency of the fundamental wave in the AC input from the transformer 2.

[0033] The AC / DC converter 5 converts the AC input through the input filter 4 into a DC. The AC / DC converter 5 is configured, for example, by a diode bridge circuit. Alternatively, it may be configured by a bridge circuit using semiconductor switches (also referred to as "switching elements").

[0034] The DC / AC converter 6 converts the direct current output from the AC / DC converter 5 into an alternating current of a desired voltage and frequency. The DC / AC converter 6 is formed of, for example, a bridge circuit using semiconductor switches.

[0035] The output filter 7 is an LC filter including an inductor and a capacitor 72, and suppresses undesirable components in the AC output from the DC / AC converter 6. For example, the output filter 7 suppresses high-frequency components higher than the frequency of the fundamental wave in the AC output from the DC / AC converter 6.

[0036] The output breaker 8 opens and closes the power path of the output section of the power conversion module 9 , and cuts off the current to the outside of the power conversion module 9 .

[0037] The AC that has passed through the output filter 7 is output from the power conversion module 9 and merged with the AC output from the other power conversion modules 9, and the merged AC is output from the power conversion device 10.

[0038] The current detection device 11 detects a current output from the power conversion device 10. The current detection device 11 is a current transformer (CT).

[0039] The transformer 12 is an insulating transformer electrically connected to the output side of each of the multiple power conversion devices 10 connected in parallel. The primary side of the transformer 12 is electrically connected to the power conversion device 10, and the secondary side of the transformer 12 is electrically connected to the load 14 and is also electrically connected to the secondary side of another transformer 12 provided on the output side of the other power conversion device 10.

[0040] The power feed circuit breaker 13 is provided in the power path on the output side of each of the transformers 12. The power feed circuit breaker 13 opens and closes the power path on the output side of each of the transformers 12, and can interrupt the current (i.e., power supply) from the power conversion device 10 to the load 14 through the transformer 12.

[0041] The load 14 is an AC load that operates with AC supplied from the multiple power conversion devices 10 via the transformer 12. The load 14 is, for example, an AC motor such as an induction motor or a synchronous motor.

[0042] For example, as shown in Fig. 1, there is one load 14. Also, as shown in Fig. 2, there may be multiple loads 14. In the example of Fig. 2, the ship SP is electrically connected to multiple power conversion devices 10 through an output connection board 18 or an output connection board 19, and the loads 14 in the ship SP are operated by power supplied from the multiple power conversion devices 10.

[0043] 2, it is not necessary for all the power conversion devices 10 to be operated. This is because, depending on the number of ships SP docked at the wharf 20 and the amount of power supply required by the ships SP, it is not necessary to operate all the power conversion devices 10.

[0044] [Configuration for controlling power conversion equipment] A configuration relating to control of the power conversion device 10 will be described with reference to FIG.

[0045] FIG. 3 is a diagram showing an example of the configuration of the power conversion device 10. As shown in FIG.

[0046] As shown in FIG. 3, the power conversion device 10 includes a control unit 33 and a module control unit 25.

[0047] The control unit 33 performs balance control of the output currents according to the output capacities of the multiple power conversion modules 9. The control unit 33 also performs balance control of the output currents according to the output capacities of the multiple power conversion devices 10 by droop control.

[0048] The functions of the control unit 33 are realized by any hardware or any combination of hardware and software. The control unit 33 is realized, for example, mainly by a computer including a processor, a memory device, an auxiliary storage device, and an interface device for input / output. The control unit 33 may also be realized only by hardware such as a logic circuit.

[0049] The control unit 33 receives the output current detection value 29, the output voltage detection value 30, the total number of modules 31, and a module power supply in progress signal .

[0050] The output current detection value 29 is a detection value of the output current of the power conversion device 10. The output current detection value 29 is output from the current detector .

[0051] The current detector 28 receives the output current of the current detection device 11 (current transformer) and outputs a detection value of the output current of the power conversion device 10.

[0052] The output voltage detection value 30 is a detection value of the output voltage of the power conversion device 10.

[0053] The total number of modules 31 is the total number of power conversion modules 9 included in the power conversion device 10. In this example, the total number of modules 31 is "2." For example, the total number of modules 31 is input to the control unit 33 by being read from a memory or the like external to the control unit 33, or by input from a user. The total number of modules 31 may also be read from a memory or the like internal to the control unit 33.

[0054] The module power supplying signal 70 is input from the module control unit 25 for each of the multiple power conversion modules 9. The module power supplying signal 70 is a signal indicating that the power conversion module 9 to be controlled by the module control unit 25 is supplying power to the output side of the power conversion device 10. When the module power supplying signal is not input from the module control unit 25, the control unit 33 can determine that the power conversion module 9 corresponding to the target module control unit 25 is stopped.

[0055] Based on the various inputs described above, the control unit 33 outputs a voltage command 34, a transformer phase 35, and a frequency command 36. The voltage command 34, the transformer phase 35, and the frequency command 36 are input to the module control units 25 of the multiple power conversion modules 9.

[0056] The voltage command 34 is a command value for the output voltage of the power conversion module 9 .

[0057] The transformer phase 35 is the phase of the transformer 12 provided on the output side of the power conversion device 10 (specifically, a lag phase or a lead phase).

[0058] In addition, since the transformer phase 35 is information required when some of the multiple power conversion modules 9 stop, as described below, it does not need to be output when the module power supply in progress signal 70 is input from all module control units 25.

[0059] The frequency command 36 is a command value for the frequency of the output current of the power conversion module 9 .

[0060] The module control unit 25 drives and controls the main circuit of the power conversion module 9 under the control of the control unit 33. The main circuit of the power conversion module 9 means a circuit section in which the input circuit breaker 3, the input filter 4, the AC / DC converter 5, the DC / AC converter 6, the output filter 7, and the output circuit breaker 8 are arranged.

[0061] The module control unit 25 receives an output current detection value 22, an output voltage detection value 23, and a shared current command 26.

[0062] The output current detection value 22 is a detection value of the output current of the power conversion module 9. The output current detection value 22 is input from a current detection device 15 (for example, a current transformer) provided at the output section of the power conversion module 9.

[0063] The output voltage detection value 23 is the detection value of the output voltage of the power conversion module 9.

[0064] The shared current command 26 is a command value for the output current (shared current) that should be shared by each power conversion module 9 out of the output current of the power conversion device 10. In this example, since the multiple power conversion modules 9 all have the same output capacity, the shared current commands 26 input to the module control unit 25 are all the same. The shared current command 26 is input from the shared current detector 21.

[0065] A shared current detector 21 is provided for each of the multiple power conversion modules 9. The current output from the current detection device 11 and passing through the current detector 28 is divided approximately equally and input to each shared current detector 21. As a result, the shared current detector 21 can output a shared current command 26 by detecting the divided current.

[0066] As described above, the module control unit 25 receives the voltage command 34, the transformer phase 35, and the frequency command 36 from the control unit 33.

[0067] The module control unit 25 generates a PWM (Pulse Width Modulation) signal 24 based on the various inputs described above, and outputs it to the DC / AC converter 6, thereby controlling the current, voltage, frequency, phase, etc. of the AC (specifically, a sine wave) output from the DC / AC converter 6.

[0068] The module control unit 25 also includes a determination unit 68. The determination unit 68 may be realized, for example, by hardware alone or by a combination of hardware and software.

[0069] The determination unit 68 determines whether or not there is a failure in the power conversion module 9. A failure in the power conversion module 9 means an abnormality that requires the power conversion module 9 to be stopped. A failure in the power conversion module 9 may include not only a failure in the main circuit, but also a failure other than the main circuit, such as a failure in the module control unit 25, and a failure in a component involved in the control of the power conversion module 9. For example, the determination unit 68 determines whether or not there is a failure in the power conversion module 9 based on a deviation state between a command from the control unit 33 and the actual state of the power conversion module 9. The determination unit 68 may also determine whether or not there is a failure in the power conversion module 9 by using a different method by arbitrarily applying a known method.

[0070] When the determination unit 68 determines that the power conversion module 9 is not faulty, it outputs a module power supplying signal 70 to the control unit 33. On the other hand, when the determination unit 68 determines that the power conversion module 9 is faulty, it outputs a command to switch from on to off the switch 27 provided on the signal line on the primary side of the shared current detector 21 that inputs the shared current command 26 to the module control unit 25. This prevents current from being input to the primary side of the shared current detector 21, and as a result, the shared current command 26 input from the shared current detector 21 to the module control unit 25 can be set to zero (0). Therefore, the module control unit 25 can stop the power conversion module 9 in response to the shared current command 26 of zero, which is triggered by the failure of the power conversion module 9.

[0071] [Specific examples of control processing in the control unit] A specific example of the control process of the control unit 33 will be described with reference to FIGS.

[0072] Fig. 4 is a control block diagram showing an example of the control process of the control unit 33. Fig. 5 is a diagram showing an example of the relationship between the total number of modules 31 and the number of power-supplying modules 32, and the module gain 39 and transformer gain 42.

[0073] As shown in FIG. 4, the control unit 33 performs an addition process 71 on the module power supplying signals 70 from the multiple module control units 25 to obtain the number of power supplying modules 32.

[0074] The control unit 33 performs division processing 38 to divide (i.e., divide) the total number of modules 31 by the number of power-supplying modules 32, and obtains a module gain 39 (see FIG. 5).

[0075] However, if no module power supply signals 70 are input, the number of power supply modules 32 will be zero (0), but to avoid execution of division process 38 by zero (0), the lower limiter 37 is set to "1" for the number of power supply modules 32. As a result, even if the result of addition process 71 is zero (0), the number of power supply modules 32 is corrected to "1" (see FIG. 5).

[0076] The control unit 33 performs an active power calculation process 48 based on the result of multiplication process 40 a of the output current detection value 29 and the module gain 39 and the output voltage detection value 30 , and obtains an active power calculation value 54 .

[0077] The control unit 33 acquires a frequency correction amount 57 of the output current of the power conversion module 9 based on the active power calculation value 54 and the frequency droop characteristic 47. The frequency droop characteristic 47 is configured by, for example, the frequency droop characteristic of the output current of the power conversion module 9 of the target power conversion device 10 and the power conversion module 9 of the other power conversion device 10.

[0078] The control unit 33 performs a subtraction process 41 b to subtract the frequency correction amount 57 from the output frequency setting value 53 , obtains a frequency command 36 , and outputs it to the module control unit 25 .

[0079] Furthermore, the control unit 33 performs reactive power calculation processing 49 based on the result of multiplication processing 40 c of the output current detection value 29 and the module gain 39 and the output voltage detection value 30 , to obtain a reactive power calculation value 50 .

[0080] The control unit 33 acquires a voltage correction amount 51 based on the reactive power calculation value 50 and the voltage droop characteristics 46 (i.e., the output voltage droop characteristics of the power conversion module 9). The frequency droop characteristics 47 are configured by, for example, the frequency droop characteristics of the output current of the power conversion module 9 of the target power conversion device 10 and the power conversion modules 9 of the other power conversion devices 10.

[0081] Furthermore, the control unit 33 performs a subtraction process 41 a to subtract “1” from the module gain 39 to obtain a transformer gain 42 .

[0082] 5, the transformer gain 42 is "0" when all the power conversion modules 9 included in the power conversion device 10 are in operation (i.e., the total number of modules 31 is the same as the number of power-supplied modules 32). On the other hand, the transformer gain 42 takes a positive value when some of the power conversion modules 9 included in the power conversion device 10 are stopped (i.e., the number of power-supplied modules 32 is less than the total number of modules 31).

[0083] Returning to FIG. 4, the control unit 33 performs a multiplication process 40 b to multiply the output current detection value 29 by a transformer gain 42 , and obtains a transformer load factor 43 .

[0084] The control unit 33 acquires a voltage correction amount 56 based on the transformer load rate 43 and the transformer voltage characteristics 45. The transformer voltage characteristics 45 represent the relationship between the output voltage (i.e., the secondary voltage) of the transformer 12 arranged on the output side of the target power conversion device 10 and the transformer load rate 43 (see Figs. 9 and 10 described later). The transformer voltage characteristics 45 can be calculated from information such as the rated current, phase voltage, load loss, and short circuit % impedance in the performance report of the transformer 12. The transformer voltage characteristics 45 are given as, for example, a data table. The transformer voltage characteristics 45 may also be given as an arithmetic expression with the transformer load rate as a variable.

[0085] The control unit 33 performs subtraction processing 55 to subtract the voltage correction amount 51 and the voltage correction amount 56 from the output voltage set value 52 , obtains the voltage command 34 , and outputs it to the module control unit 25 .

[0086] Furthermore, the control unit 33 acquires a transformer phase 35 based on a transformer load rate 43 and a transformer phase characteristic 44, and outputs the transformer phase 35 to the module control unit 25. The transformer phase characteristic 44 represents the relationship between the frequency of the output current of the transformer 12 arranged on the output side of the target power conversion device 10 and the transformer load rate 43 (see FIG. 9 described later).

[0087] [Specific example of control processing in the module control section] A specific example of the control process of the module control unit 25 will be described with reference to FIG.

[0088] FIG. 6 is a control block diagram showing an example of the control process of the module control unit 25. As shown in FIG.

[0089] 6, the module control unit 25 performs an addition process 71 of the shared current command 26 and a capacitor current command 73, and then performs a subtraction process 41d of subtracting the output current detection value 22 from the result to obtain a cross current 58. The capacitor current command 73 is a command value for a current flowing through a capacitor 72 of the output filter 7. The capacitor current command 73 is, for example, specified in advance as a current value to be flowed through the capacitor 72.

[0090] The module control unit 25 performs a cross current calculation process 60 based on the cross current 58 and a sine waveform 65 described below, and obtains the correction amounts (voltage correction amount 61 and phase correction amount 62) of the output voltage and output frequency to bring the cross current 58 closer to zero.

[0091] Furthermore, the module control unit 25 performs a sine wave generation process 64 based on the transformer phase 35 (θ), the frequency command 36 (ωt), and the phase correction amount 62 (Δθs) to obtain a sine wave 65. The sine wave 65 is expressed as sin(ωt+Δθs-θ).

[0092] Furthermore, the module control unit 25 performs a subtraction process 41c to subtract the output voltage detection value 23 from the voltage command 34, and also performs a subtraction process 41e to subtract the voltage correction amount 61 from the deviation obtained by the subtraction process 41c.

[0093] Based on the deviation obtained by the subtraction process 41e, the module control unit 25 acquires a voltage amplitude command value 63 using a voltage regulator 59. The voltage regulator 59 is, for example, a proportional integral (PI) compensator.

[0094] The module control unit 25 performs a multiplication process 40 d to multiply the sine waveform 65 by a voltage amplitude command value 63 , and obtains an output control waveform 66 .

[0095] The module control unit 25 performs PWM control processing 67 based on the output control waveform 66 , generates the PWM signal 24 , and outputs it to the DC / AC converter 6 .

[0096] [Normal operating state of the power system] A normal operating state of the power supply system SYS will be described with reference to Fig. 7. Specifically, the operating state of the power supply system SYS will be described when all of the multiple power conversion modules 9 included in each of the multiple power conversion devices 10 are operating normally.

[0097] Fig. 7 is a diagram showing an example of a normal operating state of the power supply system SYS. Fig. 7 includes Figs. 7A and 7B.

[0098] In addition, in FIG. 7B, with respect to the two power conversion devices 10, the upper power conversion device 10 in FIG. 7A is referred to as "power conversion device (1)" and the lower power conversion device 10 in FIG. 7A is referred to as "power conversion device (2)."

[0099] In the following, in this example, a description will be given using a load factor based on the rated output of the power conversion module 9.

[0100] As shown in Fig. 7A, the two power conversion modules 9 included in each of the two power conversion devices 10 are operating normally, and therefore the module gains of the two power conversion devices 10 are both "1". Therefore, as shown in Fig. 7B, the frequency droop characteristics 47 and the voltage droop characteristics 46 of the two power conversion devices 10 are the same. As a result, all (four) power conversion modules 9 operate at the same load factor, and the two power conversion devices 10 output AC with the same output voltage and output frequency.

[0101] Furthermore, as shown in FIG. 7A, the two power conversion devices 10 output alternating currents of the same phase.

[0102] In this example, the power conversion modules 9 included in the multiple (two) power conversion devices 10 are operated at the same load factor (60%).

[0103] Since the load 14 is supplied with power equivalent to that of four power conversion modules 9, the power supply system SYS is operated at a load factor of 240 (= 60 x 4)% compared to a maximum load factor of 400 (= 100 x 4)%.

[0104] Furthermore, because the power conversion modules 9 included in each of the two power conversion devices 10 are operating normally, the load factors of the transformers 12 arranged on the output side of each are also the same, 60%. Therefore, the delay phase and voltage fluctuation (voltage drop) in the two transformers 12 are the same, and as a result, the AC output from the two transformers 12 are synchronized so that the output voltages and phases match. Therefore, the power supply system SYS can realize stable parallel operation of the two power conversion devices 10.

[0105] [Operating state when power system is abnormal] An operating state of the power supply system SYS during an abnormality will be described with reference to Fig. 8 to Fig. 13. Specifically, an operating state of the power supply system will be described when some of the multiple power conversion modules 9 included in each of the multiple power conversion devices 10 have failed and stopped.

[0106] FIG. 8 is a diagram showing an operating state of the power supply system SYS when an abnormality occurs. FIG. 8 includes FIGS. 8A and 8B. FIG. 9 is a diagram showing an example of the characteristics of the transformer 12. FIG. 9 includes FIG. 9A showing the phase characteristics of the transformer 12 and FIG. 9B showing the voltage characteristics of the transformer 12. FIG. 10 is a diagram showing an example of a method for correcting the voltage characteristics of the transformer 12. FIG. 11 is a diagram explaining an example of phase synchronization control of the AC output from the transformer 12. FIG. 12 is a diagram showing an example of the operation of the power supply system according to the comparative example. FIG. 13 is a diagram showing an example of the operation of the power supply system SYS according to the embodiment.

[0107] In Fig. 8B, with regard to the two power conversion devices 10, the upper power conversion device 10 in Fig. 8A is referred to as "power conversion device (1)," and the lower power conversion device 10 in Fig. 8A is referred to as "power conversion device (2)." In the following description, the upper power conversion device 10 and the lower power conversion device 10 in Fig. 8A may be simply referred to as the "upper power conversion device 10" and the "lower power conversion device 10," respectively.

[0108] In the following, in this example, a description will be given using a load factor based on the rated output of the power conversion module 9.

[0109] As shown in FIG. 8A, in this example, the upper power conversion device 10 has two power conversion modules 9 operating normally, while the lower power conversion device 10 has two power conversion modules 9, of which only one is operating and the other is stopped due to a failure. Therefore, the module gain 39 in the upper power conversion device 10 is "1", while the module gain 39 in the lower power conversion device 10 is "2". Therefore, as shown in FIG. 8B, the frequency droop characteristic 47 and the voltage droop characteristic 46 of the upper power conversion device 10 are the same as those in FIG. 7B, while the frequency droop characteristic 47 and the voltage droop characteristic 46 of the lower power conversion device 10 are changed from the state in FIG. 7B to a direction in which the degree of droop of the frequency or the output voltage relative to an increase in the output power (active power or reactive power) increases. As a result, an operating point (frequency or voltage) is determined such that the load factor of the upper power conversion device 10 increases, while the load factor of the lower power conversion device 10 decreases.

[0110] As shown in Fig. 8A, in this example, the two power conversion modules 9 of the upper power conversion device 10 and the one operating power conversion module 9 of the lower power conversion device 10 are both operating at the same 80%. However, when comparing the two power conversion devices 10, the load factor of the upper power conversion device 10 is 160 (= 80 × 2)%, which is 40% higher than in Fig. 7, while the load factor of the lower power conversion device 10 is 80%, which is 40% lower than in Fig. 7. As a result, AC corresponding to a load factor of 240% similar to that in Fig. 7 is supplied to the load 14.

[0111] As shown in FIG. 8A, the load factors of the two power conversion devices 10 are different, and therefore the load factors of the transformers 12 disposed on the output side of each of the two power conversion devices 10 are also different. In this example, the load factor of the transformer 12 corresponding to the upper power conversion device 10 is 80%, while the load factor of the transformer 12 corresponding to the lower power conversion device 10 is 40%. Therefore, a difference occurs in the delay phase and voltage drop in the two transformers 12. Therefore, if the output voltage and phase of the AC voltage output from the two power conversion devices 10 are the same, the voltage and phase of the AC voltage output from the two transformers 12 will not match, and there is a possibility that the lower power conversion device 10 will be overloaded during the transient response until settling to a stable point.

[0112] In contrast to this, in this example, the AC output from the lower power conversion device 10 in Fig. 8A is compensated in advance for the delay phase (θ) corresponding to the transformer phase 35 and the voltage correction amount 56 (Vt) as described above (see Figs. 5 and 6). This can provide the same effect as when the AC output from the lower power conversion device 10 is further passed through a virtual transformer (hereinafter, "virtual transformer") 12v having the same characteristics as the transformer 12, as shown in Fig. 8A. This can reduce the difference in voltage and phase of the AC output from the two transformers 12, and suppress overload of the lower power conversion device 10.

[0113] For example, as shown in Figures 9A and 9B, when the four power conversion modules 9 are operating normally (see Figure 7), the two transformers 12 have the same load factor (60% in this example), and also have the same delay phase and output voltage (see operating points 901, 911).

[0114] On the other hand, when one power conversion module 9 of the lower power conversion device 10 in Fig. 8A stops, the load factor of the transformer 12 corresponding to the lower power conversion device 10 drops to 40%, while the load factor of the transformer 12 corresponding to the upper power conversion device 10 in Fig. 8A increases to 80%. Therefore, as shown in Fig. 9A, the delay phase of the transformer 12 corresponding to the lower power conversion device 10 is reduced (see operating point 902), while the delay phase of the transformer 12 corresponding to the upper power conversion device 10 increases (see operating point 903). Similarly, as shown in Fig. 9B, the voltage drop of the transformer 12 corresponding to the lower power conversion device 10 decreases (see operating point 912), while the voltage drop of the transformer 12 corresponding to the upper power conversion device 10 increases (see operating point 913).

[0115] In this case, the control unit 33 can obtain the transformer phase 35 (1.28 in this example) corresponding to the operating point 902 using the transformer phase characteristic 44 in Fig. 9A. Similarly, the control unit 33 can obtain the voltage correction amount 56 corresponding to the operating point 912 using the transformer voltage characteristic 45 in Fig. 9B. Therefore, the control unit 33 can compensate for the delay phase and voltage drop corresponding to the virtual transformer 12v having characteristics similar to those of the transformer 12 for the AC output from the lower power conversion device 10.

[0116] In this example, a delay phase (1.28 degrees) corresponding to the virtual transformer 12v is added to the AC output from the transformer 12 corresponding to the lower power conversion device 10 in addition to the delay phase (1.28 degrees) at the transformer 12. Therefore, the delay phase (1.28 degrees + 1.28 degrees = 2.56 degrees) of the AC output from the transformer 12 corresponding to the lower power conversion device 10 is approximately the same as the delay phase (2.55 degrees) of the AC output from the transformer 12 corresponding to the upper power conversion device 10.

[0117] Furthermore, the AC output from the transformer 12 corresponding to the lower power conversion device 10 is added with a voltage drop (0.26%) corresponding to the virtual transformer 12v in addition to the voltage drop (0.26%) in the transformer 12. Therefore, the difference between the substantial voltage drop amount (0.26%+0.26%=0.52%) of the AC output from the transformer 12 corresponding to the lower power conversion device 10 and the voltage drop amount (0.58%) of the AC output from the transformer 12 corresponding to the upper power conversion device 10 is reduced to some extent.

[0118] 9B, the voltage characteristic of the actual transformer 12 is not linear but is an upwardly convex curve. Therefore, a difference (0.06%) remains between the substantial voltage drop (0.52%) of the AC output from the transformer 12 corresponding to the lower power conversion device 10 and the voltage drop (0.58%) of the AC output from the transformer 12 corresponding to the upper power conversion device 10.

[0119] 10, the transformer voltage characteristic 45 used to obtain the voltage correction amount 56 may be obtained by linearly approximating the voltage characteristic of the actual transformer 12 (see the dashed line in the figure). This allows the voltage correction amount 56 to be increased (see the operating point 1001) compared to the case where the voltage characteristic of the actual transformer 12 is used. In this example, the voltage drop in the virtual transformer 12v is increased from 0.26% to 0.30%, and as a result, the substantial voltage drop amount of the AC output from the transformer 12 corresponding to the lower power conversion device 10 can be increased from 0.52% to 0.56%. Therefore, the overload of the lower power conversion device 10 can be further suppressed.

[0120] FIG. 11 shows phase characteristics 1101 of the transformer 12 corresponding to the upper power conversion device 10, phase characteristics 1102 of the transformer 12 corresponding to the lower power conversion device 10, and phase characteristics 1103 of the virtual transformer 12v.

[0121] As shown in FIG. 11, there is a large discrepancy between phase characteristics 1101 of the transformer 12 corresponding to the upper power conversion device 10 and phase characteristics 1102 of the transformer 12 corresponding to the lower power conversion device 10.

[0122] In contrast to this, by combining the phase characteristic 1103 of the virtual transformer 12v with the phase characteristic 1102 of the transformer 12 corresponding to the lower power conversion device 10, it is possible to establish a phase characteristic equivalent to the phase characteristic 1101 of the transformer 12 corresponding to the upper power conversion device 10.

[0123] For example, as shown in FIG. 12, in a comparative example in which the lag phase and voltage drop corresponding to the virtual transformer 12v are not compensated for, when one of the power conversion modules 9 of the lower power conversion device 10 transitions from an operating state to a fault shutdown, a transient response occurs, and as a result, the operating power conversion module 9 of the lower power conversion device 10 becomes overloaded.

[0124] 13, by compensating for the delay phase and voltage drop corresponding to the virtual transformer 12v, it is possible to suppress the transient response when one power conversion module 9 of the lower power conversion device 10 transitions from an operating state to a fault stop state. As a result, it is possible to suppress the overload of the operating power conversion module 9 of the lower power conversion device 10.

[0125] [Effect] The operation of the power supply system, the control device, and the control method according to the present embodiment will be described.

[0126] In a first aspect of the present embodiment, a power supply system is provided that includes a plurality of power conversion devices and a transformer, and each of the plurality of power conversion devices includes a plurality of power conversion units. The plurality of power conversion devices are, for example, the plurality of power conversion devices 10 described above. The transformer is, for example, the transformer 12 described above. The plurality of power conversion units are, for example, the plurality of power conversion modules 9 described above. Specifically, each of the plurality of power conversion devices outputs an AC current using power supplied from a power source, and is connected in parallel on the output side. The power source is, for example, the power source 1 described above. In addition, the transformer is provided for each of the plurality of power conversion devices, and is electrically connected to the output side of the target power conversion device. In addition, the plurality of power conversion units are connected in parallel to the input unit and the output unit of the target power conversion device, and output an AC current using the power input to the target power conversion device. The multiple power conversion devices each perform balance control of the output current according to the capacity of the multiple power conversion units, and also perform balance control of the output current according to the capacity of the multiple power conversion devices by droop control.When some of the multiple power conversion units stop, the output current balance control is continued according to the capacity of the multiple power conversion devices so that the phases of the AC output from the transformer on the output side of the target power conversion device and the AC output from the transformer on the output side of the other power conversion devices are synchronized and the voltage levels are the same.

[0127] As a result, even if some of the multiple power conversion units included in the power conversion device stop, the power supply system can continue to output power using the remaining power conversion units that are normal. Specifically, the power supply system can synchronize the AC output from the transformer corresponding to the power conversion device in which some of the power conversion units have stopped with the AC output from the transformer corresponding to the other power conversion devices, thereby suppressing a transient response. Therefore, the power supply system can suppress a situation in which the power conversion device in which some of the power conversion units have stopped becomes overloaded due to a transient response, and can continue stable parallel operation even when some of the power conversion units have stopped.

[0128] In addition, in a second aspect of this embodiment, assuming the above-mentioned first aspect, each of the multiple power conversion devices may, when a portion of the multiple power conversion units stops, adjust the output voltage and phase of an operating power conversion unit among the multiple power conversion units so that the phase of the AC output from the transformer on the output side of the target power conversion device and the phase of the AC output from the transformer on the output side of the other power conversion devices are synchronized and have the same voltage level, and continue to control the balance of output currents according to the capacity of the multiple power conversion devices.

[0129] This enables the power supply system to synchronize the AC output from the transformer corresponding to the power conversion device in which some of the power conversion units have stopped with the AC output from the transformer corresponding to the other power conversion devices, thereby suppressing transient responses.

[0130] In addition, in a third aspect of the present embodiment, based on the second aspect described above, each of the multiple power conversion devices performs balance control of the output currents of the multiple power conversion units, and performs balance control of the output currents in accordance with the capacities of the multiple power conversion devices by the droop control based on the frequency drooping characteristics and voltage drooping characteristics of the multiple power conversion units. When some of the multiple power conversion units stop, the phase and voltage fluctuation of the transformer on the output side of the target power conversion device is obtained based on the total number of the multiple power conversion units and the number of the operating power conversion units, and the detection value of the output current of the target power conversion device. Based on the obtained phase and voltage fluctuation of the transformer, the output voltage and phase of the operating power conversion unit are changed, and the frequency drooping characteristics and the voltage drooping characteristics of the operating power conversion unit are changed, and the droop control is used to perform balance control of the output current in accordance with the capacities of the multiple power conversion devices.

[0131] This allows the power supply system to continue balancing control of the output currents of multiple power conversion devices while synchronizing the AC output from the transformer corresponding to a power conversion device where some of the power conversion units have stopped with the AC output from the transformer corresponding to the other power conversion devices.

[0132] In addition, in a fourth aspect of the present embodiment, based on the above-mentioned third aspect, when some of the power conversion units are stopped, each of the multiple power conversion devices may acquire the phase and voltage fluctuation of the transformer on the output side of the target power conversion device based on the total number of the multiple power conversion units and the number of the operating power conversion units and the detection value of the output current of the target power conversion device, and may change the output voltage and phase of the operating power conversion unit using the phase characteristic and voltage characteristic of the transformer based on the acquired phase and voltage fluctuation of the transformer. The voltage characteristic of the transformer may be obtained by linearly approximating the actual voltage characteristic of the transformer.

[0133] This enables the power supply system to more appropriately synchronize the AC output from the transformer corresponding to the power conversion device in which some of the power conversion units have stopped with the AC output from the transformer corresponding to the other power conversion devices, thereby more appropriately suppressing transient responses.

[0134] In addition, in a fifth aspect of the present embodiment, a control device is provided for a power supply system including a plurality of power conversion devices that output AC using power supplied from a power source and are connected in parallel on the output side, and a transformer provided for each of the plurality of power conversion devices and electrically connected to the output side of a target power conversion device, the plurality of power conversion devices each being connected in parallel to an input section and an output section of the target power conversion device, and outputting AC using power input to the target power conversion device. The control device is, for example, the above-mentioned control unit 33. Specifically, the control device performs balance control of output currents according to the capacities of the plurality of power conversion devices, and performs balance control of output currents according to the capacities of the plurality of power conversion devices by droop control, and when a part of the plurality of power conversion devices stops, the control device continues to perform balance control of output currents according to the capacities of the plurality of power conversion devices so that the phases of the AC output from the transformer on the output side of the target power conversion device and the AC output from the transformer on the output side of the other power conversion device are synchronized and the voltage levels are the same.

[0135] As a result, even if some of the multiple power conversion units included in the power conversion device stop, the control device can continue to output power using the remaining power conversion units that are normal. Specifically, the control device can synchronize the AC output from the transformer corresponding to the power conversion device in which some of the power conversion units have stopped with the AC output from the transformer corresponding to the other power conversion devices, thereby suppressing the transient response. Therefore, the control device can suppress a situation in which the power conversion device in which some of the power conversion units have stopped becomes overloaded due to the transient response, and can continue stable parallel operation even when some of the power conversion units have stopped.

[0136] Also, with respect to the control device, on the premise of the above-mentioned fifth aspect, aspects similar to the second to fourth aspects of the power supply system can be realized.

[0137] This provides the same effects as the second to fourth aspects described above.

[0138] In addition, in a sixth aspect of the present embodiment, a control method is provided for a power supply system including a plurality of power conversion devices, each of which outputs AC using power supplied from a power source and is connected in parallel on the output side, and a transformer provided for each of the plurality of power conversion devices and electrically connected to the output side of a target power conversion device, the plurality of power conversion devices each including a plurality of power conversion units connected in parallel to the input unit and the output unit of the target power conversion device and outputting AC using power input to the target power conversion device. Specifically, the control method performs balance control of output currents according to the capacities of the plurality of power conversion units, and performs balance control of output currents according to the capacities of the plurality of power conversion devices by droop control, and when a part of the plurality of power conversion units stops, continues to perform balance control of output currents according to the capacities of the plurality of power conversion devices so that the phases of the AC output from the transformer on the output side of the target power conversion device and the AC output from the transformer on the output side of the other power conversion device are synchronized and the voltage levels are the same.

[0139] As a result, even if some of the multiple power conversion units included in the power conversion device stop, the control method allows the remaining power conversion units that are normal to continue outputting power. Specifically, the control method can synchronize the AC output from the transformer corresponding to the power conversion device in which some of the power conversion units have stopped with the AC output from the transformer corresponding to the other power conversion devices, thereby suppressing a transient response. Therefore, the control method can suppress a situation in which the power conversion device in which some of the power conversion units have stopped becomes overloaded due to a transient response, and can continue stable parallel operation even when some of the power conversion units have stopped.

[0140] Furthermore, with respect to the control method as well, on the premise of the above-mentioned sixth aspect, aspects similar to the second to fourth aspects of the power supply system can be realized.

[0141] This provides the same effects as the second to fourth aspects described above.

[0142] Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist described in the claims. [Explanation of symbols]

[0143] 1 power supply 2. Transformer 3 Input circuit breaker 4 Input Filter 5 AC / DC Converter 6 DC / AC Converter 7 Output Filters 8 Output circuit breaker 9 Power Conversion Module 10 Power conversion device 11 Current detection device 12. Transformer 12v Virtual Transformer 13 Power supply circuit breaker 14 Load 15 Current detection device 21 Shared current detector 22 Output current detection value 23 Output voltage detection value 24 PWM signals 25 Module control section 26 Shared current command 27 Switch 28 Current detector 29 Output current detection value 30 Output voltage detection value 31 total modules 32 Module power supply units 33 Control Unit 34 Voltage Command 35 Transformer Phase 36 Frequency Command 37 Lower Limiter 38 Division 39 Module Gain 40a Multiplication 40b Multiplication 40c Multiplication 40d Multiplication 41a Subtraction 41b Subtraction process 41c Subtraction 41d Subtraction 41e Subtraction 42 Trans Gain 43 Transformer load factor 44 Transformer Phase Characteristics 45 Transformer voltage characteristics 46 Voltage droop characteristics 47 Frequency droop characteristics 48 Active power calculation processing 49 Reactive power calculation processing 50 Reactive power calculation value 51 Voltage correction amount 52 Output voltage setting value 53 Output frequency setting value 54 Calculated active power value 55 Subtraction 56 Voltage correction amount 57 Frequency correction amount 58 Cross current 59 Voltage Regulator 60 Cross-current processing 61 Voltage correction amount 62 Phase correction amount 63 Voltage amplitude command value 64 Sine wave generation processing 65 Sine waveform 66 Output control waveform 67 PWM control processing 68 Judgment section 70 Module power supply signal 71 Addition Processing 72 Capacitor 73 Capacitor current command SYS Power System

Claims

1. A plurality of power conversion devices each outputting AC power using power supplied from a power source and connected in parallel on the output side; a transformer provided for each of the plurality of power conversion devices and electrically connected to an output side of a target power conversion device; Each of the plurality of power conversion devices includes a plurality of power conversion units that are connected in parallel to an input unit and an output unit of a target power conversion device and output AC using power input to the target power conversion device, Each of the multiple power conversion devices performs balance control of output currents according to the capacities of the multiple power conversion units, and performs balance control of output currents according to the capacities of the multiple power conversion devices by droop control, and when some of the multiple power conversion units stop, continues balance control of output currents according to the capacities of the multiple power conversion devices so that the phases of the AC output from the transformer on the output side of the target power conversion device and the AC output from the transformer on the output side of the other power conversion devices are synchronized and the voltage levels are the same. Power supply system.

2. When a part of the power conversion units stops, each of the multiple power conversion devices adjusts the output voltage and phase of an operating power conversion unit among the multiple power conversion units so that the phase of the AC output from the transformer on the output side of the target power conversion device and the phase of the AC output from the transformer on the output side of the other power conversion devices are synchronized and have the same voltage level, and continues to control the balance of output currents according to the capacities of the multiple power conversion devices. The power supply system of claim 1 .

3. Each of the multiple power conversion devices performs balance control of output currents of the multiple power conversion units, and performs balance control of output currents according to the capacities of the multiple power conversion devices by the droop control based on the frequency drooping characteristics and voltage drooping characteristics of the multiple power conversion units. When a part of the multiple power conversion units stops, the phase and voltage fluctuation of the transformer on the output side of the target power conversion device is acquired based on the total number of the multiple power conversion units and the number of the operating power conversion units, and the detection value of the output current of the target power conversion device, and changes the output voltage and phase of the operating power conversion units based on the acquired phase and voltage fluctuation of the transformer, and changes the frequency drooping characteristics and voltage drooping characteristics of the operating power conversion units, and performs balance control of output currents according to the capacities of the multiple power conversion devices by the droop control. The power supply system of claim 2 .

4. When a part of the plurality of power conversion units stops, each of the plurality of power conversion devices acquires a phase and voltage fluctuation of the transformer on the output side of the target power conversion device based on the total number of the plurality of power conversion units and the number of the operating power conversion units, and a detection value of an output current of the target power conversion device, and changes an output voltage and phase of the operating power conversion unit using a phase characteristic and a voltage characteristic of the transformer based on the acquired phase and voltage fluctuation of the transformer; The voltage characteristic of the transformer is obtained by linearly approximating an actual voltage characteristic of the transformer. The power supply system of claim 3.

5. A control device for a power supply system including a plurality of power conversion devices each outputting AC using power supplied from a power source and connected in parallel on an output side, and a transformer provided for each of the plurality of power conversion devices and electrically connected to an output side of a target power conversion device, the plurality of power conversion devices each including a plurality of power conversion units each connected in parallel to an input unit and an output unit of the target power conversion device and outputting AC using power input to the target power conversion device, the control device controlling one of the power conversion devices, performing balance control of output currents according to the capacities of the plurality of power conversion units, and performing balance control of output currents according to the capacities of the plurality of power conversion devices by droop control, and when a portion of the plurality of power conversion units stops, continuing balance control of output currents according to the capacities of the plurality of power conversion devices so that the phases of AC output from the transformer on the output side of the target power conversion device and AC output from the transformer on the output side of another power conversion device are synchronized and the voltage levels are the same; Control device.

6. A control method for controlling one of the power conversion devices in a power supply system, the power conversion devices including a plurality of power conversion units each of which outputs AC using power supplied from a power source and is connected in parallel on an output side, and a transformer provided for each of the plurality of power conversion devices and electrically connected to an output side of a target power conversion device, the plurality of power conversion devices each including a plurality of power conversion units each of which is connected in parallel to an input unit and an output unit of the target power conversion device and outputs AC using power input to the target power conversion device, performing balance control of output currents according to the capacities of the plurality of power conversion units, and performing balance control of output currents according to the capacities of the plurality of power conversion devices by droop control, and when a portion of the plurality of power conversion units stops, continuing balance control of output currents according to the capacities of the plurality of power conversion devices so that the phases of AC output from the transformer on the output side of the target power conversion device and AC output from the transformer on the output side of another power conversion device are synchronized and the voltage levels are the same; Control methods.

Images