Power conversion device and power conversion system

Abstract

To provide a power conversion device capable of downsizing by suppressing enlargement of a transformer of an initial charging part even when the transformer is provided on the initial charging part.SOLUTION: A power conversion device 4 for a storage battery 3 comprises: a plurality of power conversion parts 41-44 for charging / discharging the storage battery 3; an AC side switch 45 for connecting the plurality of power conversion parts 41-44 to an AC power source side; an initial charging part 47 including a transformer 47c connecting the plurality of power conversion parts 41-44 to the AC power source side by bypassing the AC side switch 45, and charging the plurality of power conversion parts 41-44; and a control part 48 performing control to generate starting AC voltage corresponding to AC voltage supplied from the AC power source side by operating a part of the power conversion parts among the plurality of power conversion parts 41-44 when the AC side switch 45 is turned on in a state where the plurality of power conversion parts 41-44 are charged by the initial charging part 47 at the time of starting.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a power conversion device and a power conversion system, and more particularly to a power conversion device and a power conversion system for a storage battery. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a power conversion device for a storage battery is known (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a voltage sag countermeasure device (power conversion device) for compensating for a power supply voltage to be supplied to a load facility when a voltage sag occurs. This voltage sag countermeasure device includes a power converter for charging and discharging a storage battery, a DC circuit breaker for connecting the power converter to the storage battery, and an AC circuit breaker for connecting the power converter to an AC power source. This power converter also includes a plurality (six) of power conversion units each having a transistor. This voltage sag countermeasure device also includes an auxiliary transformer and an initial charging circuit for initially charging the power converter when the voltage sag countermeasure device is started. In this voltage sag countermeasure device, the auxiliary transformer and the initial charging circuit charge the power converter, and after the operation of the plurality of power conversion units of the power converter is started, the AC circuit breaker is turned on and the power converter is connected to the AC power source. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-139553 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, although it is not specified in the above Patent Document 1, in the conventional voltage drop countermeasure device as described in the above Patent Document 1, when the AC circuit breaker is turned on to connect the AC power supply side and the power converter, in order not to affect the AC power supply side, a startup AC voltage (counter voltage) corresponding to the AC voltage supplied from the AC power supply side may be generated by all of the multiple power conversion units of the power converter. However, when the startup AC voltage is generated by all of the multiple power conversion units of the power converter, there is a disadvantage that the capacity of the initial charging transformer becomes large because the capacity corresponds to the number of power conversion units operated to generate the startup AC voltage and the device specifications. In this case, the initial charging transformer becomes large, so it is desired to reduce the size of the initial charging transformer.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a power conversion device and a power conversion system that can prevent the transformer of the initial charging section from becoming large and can be made smaller, even when a transformer is provided in the initial charging section. [Means for solving the problem]

[0007] In order to achieve the above object, a power conversion device according to a first aspect of the present invention is a power conversion device for a storage battery, and includes a plurality of power conversion units for charging and discharging the storage battery, an AC-side switch for connecting the plurality of power conversion units to an AC power supply side, and a transformer for connecting the plurality of power conversion units to the AC power supply side, bypassing the AC-side switch, and includes an initial charging unit for charging the plurality of power conversion units, and a control unit that, at startup, when the AC-side switch is turned on in a state in which the plurality of power conversion units are charged by the initial charging unit, operates some of the plurality of power conversion units to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side.

[0008] In the power conversion device according to the first aspect of the present invention, as described above, a control unit is provided that performs control to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side by operating some of the power conversion units when the AC side switch is turned on in a state in which the multiple power conversion units are charged by the initial charging unit. As a result, the startup AC voltage (counter voltage) is generated by some, not all, of the multiple power conversion units, so that the capacity of the transformer of the initial charging unit required to operate the power conversion units when the startup AC voltage is generated can be made smaller than when the startup AC voltage is generated by all of the multiple power conversion units. As a result, even when a transformer is provided in the initial charging unit, the transformer of the initial charging unit can be prevented from becoming large and can be made smaller.

[0009] In the power conversion device according to the first aspect, the control unit is preferably configured to perform control to start up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage after turning on the AC side switch. As a result of such a configuration, it is possible to start up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage in a state in which the AC side switch is turned on to avoid affecting the AC power supply side. As a result, it is possible to suppress the influence of the start-up of the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage on the AC power supply side.

[0010] In this case, preferably, the initial charging unit includes an initial charging unit switch for connecting the multiple power conversion units to the AC power supply side by bypassing the AC side switch, and the control unit is configured to perform control to start up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage after turning off the initial charging unit switch after the initial charging is completed. As a result of this configuration, it is possible to start up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage when the initial charging is completed. As a result, it is possible to easily start up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage.

[0011] In the above-mentioned configuration for starting up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage, preferably, a DC side switch for connecting the multiple power conversion units to the storage battery is further provided, and the control unit is configured to perform control for starting up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage before turning on the DC side switch. As a result of this configuration, in a state in which all of the multiple power conversion units are started, the DC side switch can be turned on to connect the multiple power conversion units to the storage battery. As a result, after connecting the multiple power conversion units to the storage battery, the storage battery can be charged and discharged without capacity limitations.

[0012] In this case, the control unit is preferably configured to control activation of the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage, based on the fact that the power conversion unit among the multiple power conversion units that generated the startup AC voltage has boosted the DC voltage applied to the storage battery to be equal to or higher than the DC voltage of the storage battery before turning on the DC side switch. As a result of this configuration, the operation of boosting the DC voltage applied to the storage battery to be equal to or higher than the DC voltage of the storage battery can be performed only by the power conversion unit among the multiple power conversion units that generated the startup AC voltage, in order to suppress inrush current from the storage battery to the multiple power conversion units.

[0013] In the configuration for starting up the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage based on the DC voltage applied to the storage battery being boosted to be equal to or higher than the DC voltage of the storage battery, the control unit is preferably configured to control the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage to be started by a soft start that gradually boosts the output voltage based on the DC voltage applied to the storage battery being boosted to be equal to or higher than the DC voltage of the storage battery by the power conversion unit among the multiple power conversion units that generated the startup AC voltage. As a result of this configuration, it is possible to suppress the output voltage of the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage from affecting the DC voltage applied to the storage battery.

[0014] In the power conversion device according to the first aspect, the control unit is preferably configured to perform control to select a power conversion unit that generates a startup AC voltage from among the multiple power conversion units based on the state of the multiple power conversion units. As a result of this configuration, unlike a case in which a power conversion unit that generates the startup AC voltage from among the multiple power conversion units is fixed, it is possible to select a power conversion unit that is suitable for generating the startup AC voltage from among the multiple power conversion units. As a result, the startup AC voltage can be appropriately generated by the selected power conversion unit.

[0015] In the power conversion device according to the first aspect, the control unit is preferably configured to control the generation of a startup AC voltage by operating one of the plurality of power conversion units when the AC side switch is turned on. As a result of such a configuration, the startup AC voltage (counter voltage) can be generated by one of the plurality of power conversion units, not by all of them, so that the capacity of the transformer of the initial charging unit required to operate the power conversion units when the startup AC voltage is generated can be made smaller than when the startup AC voltage is generated by two or more of the plurality of power conversion units. As a result, even when a transformer is provided in the initial charging unit, the transformer of the initial charging unit can be prevented from becoming large and can be made smaller.

[0016] A power conversion system according to a second aspect of the present invention includes a storage battery and a power conversion device connected to the storage battery. The power conversion device includes a plurality of power conversion units for charging and discharging the storage battery, an AC-side switch for connecting the plurality of power conversion units to an AC power supply side, and a transformer for connecting the plurality of power conversion units to the AC power supply side, bypassing the AC-side switch, and includes an initial charging unit for charging the plurality of power conversion units, and a control unit that performs control at startup to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side by operating some of the plurality of power conversion units when the AC-side switch is turned on with the plurality of power conversion units charged by the initial charging unit.

[0017] In the power conversion system according to the second aspect of the present invention, as described above, when the AC side switch is turned on in a state where the multiple power conversion units are charged by the initial charging unit at the time of startup, a control unit is provided that performs control to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side by operating some of the multiple power conversion units. This allows the startup AC voltage (counter voltage) to be generated by some, not all, of the multiple power conversion units, so that the capacity of the transformer of the initial charging unit required to operate the power conversion units when the startup AC voltage is generated can be made smaller than when the startup AC voltage is generated by all of the multiple power conversion units. As a result, even when a transformer is provided in the initial charging unit, it is possible to provide a power conversion system that can suppress an increase in the size of the transformer of the initial charging unit and can be made smaller. Effect of the Invention

[0018] According to the present invention, even when a transformer is provided in the initial charging section as described above, the transformer of the initial charging section can be prevented from increasing in size and can be made smaller. [Brief description of the drawings]

[0019] [Figure 1]FIG. 1 is a diagram for explaining a configuration of a power conversion system according to an embodiment. [Diagram 2] 1 is a diagram for explaining a configuration of a power conversion device according to an embodiment; [Diagram 3] 10 is a flowchart illustrating a startup process according to an embodiment. [Figure 4] FIG. 4 is a diagram for explaining the operations in steps S1 and S2 in FIG. [Diagram 5] FIG. 4 is a diagram for explaining the operations in steps S3 and S4 in FIG. [Figure 6] FIG. 4 is a diagram for explaining the operation of step S5 in FIG. [Figure 7] FIG. 4 is a diagram for explaining the operations in steps S6 and S7 in FIG. [Figure 8] FIG. 4 is a diagram for explaining the operations in steps S8 and S9 in FIG. [Figure 9] 4 is a diagram for explaining the operations in steps S10 and S11 in FIG. 3. [Figure 10] FIG. 4 is a diagram for explaining the operation of step S12 in FIG. [Figure 11] FIG. 4 is a diagram for explaining the operation of step S13 in FIG. [Figure 12] FIG. 11 is a diagram for explaining a state in which a startup process according to an embodiment is completed; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0021] The configuration of a power conversion system 100 according to this embodiment will be described with reference to FIG.

[0022] (Power Conversion System Configuration) 1, a power conversion system 100 according to the present embodiment is a system that generates power and supplies the generated power. Specifically, the power conversion system 100 includes a power generation device 1, a power conversion device 2 for the power generation device 1, a storage battery 3, and a power conversion device 4 for the storage battery 3.

[0023] The power generation device 1 is a solar cell and is configured to be capable of generating DC power. The power conversion device 2 is provided as a power conditioner for the power generation device 1. The power conversion device 2 is configured to convert DC power from the power generation device 1 into AC power and link it to a system power source 5 connected to a load 6. The storage battery 3 is a chargeable and dischargeable battery and is configured to be charged with surplus power generated by the power generation device 1 and to discharge a shortage of power generated by the power generation device 1 using the charged power. The power conversion device 4 is provided as a power conditioner for the storage battery 3. When the storage battery 3 is charged, the power conversion device 4 is configured to convert AC power from the power conversion device 2 into DC power and supply the charging power to the storage battery 3. When the storage battery 3 is discharged, the power conversion device 4 is configured to convert DC power from the storage battery 3 into AC power and link it to the system power source 5. The storage battery 3 and the power conversion device 4 function to suppress output fluctuations in the power generated by the power generation device 1.

[0024] (Configuration of power conversion device) Next, the configuration of the power conversion device 4 according to this embodiment will be described with reference to FIG.

[0025] As shown in FIG. 2, the power conversion device 4 includes a plurality of (four) power conversion units 41 to , an AC side switch 45, a DC side switch , an initial charging unit 47, and a control unit .

[0026] The power conversion units 41-44 are provided to charge and discharge the storage battery 3. The power conversion units 41-44 are configured to be capable of performing an inverter operation for converting DC power to AC power and a converter operation for converting AC power to DC power under the control of a control unit 48. Each of the power conversion units 41-44 has a semiconductor switching element such as an IGBT (Insulated Gate Bipolar Transistor). In addition, an AC reactor 41a (42a-44a) and a filter capacitor 41b (42b-44b) are connected to the AC side of the power conversion unit 41 (42-44).

[0027] The AC-side switch 45 is provided between the multiple power conversion units 41-44 and the AC power supply side (the system power supply 5 side). The AC-side switch 45 is provided to connect the multiple power conversion units 41-44 to the AC power supply side. The AC-side switch 45 connects the AC sides of the multiple power conversion units 41-44 to the AC power supply side by being turned on under the control of the control unit 48. Also, the AC-side switch 45 disconnects the connection between the AC sides of the multiple power conversion units 41-44 and the AC power supply side by being turned off under the control of the control unit 48. When the power conversion device 4 is started up, the AC-side switch 45 is controlled to be changed from off to on.

[0028] The DC side switch 46 is provided between the multiple power conversion units 41-44 and the storage battery 3. The DC side switch 46 is provided to connect the multiple power conversion units 41-44 to the storage battery 3. The DC side switch 46 connects the DC sides of the multiple power conversion units 41-44 to the storage battery 3 by being turned on under the control of the control unit 48. Also, the DC side switch 46 disconnects the DC sides of the multiple power conversion units 41-44 from the storage battery 3 by being turned off under the control of the control unit 48. When the power conversion device 4 is started up, the DC side switch 46 is controlled to be changed from off to on.

[0029] The initial charging unit 47 is provided to connect the multiple power conversion units 41-44 to the AC power supply side (system power supply 5 side) by bypassing the AC side switch 45. The initial charging unit 47 is a circuit that charges the DC side voltage of the multiple power conversion units 41-44 when the power conversion device 4 is started up. The initial charging unit 47 includes a fuse 47a, a first initial charging unit switch 47b, a transformer 47c, a resistor 47d, a second initial charging unit switch 47e, and a rectifier circuit 47f. Both the first initial charging unit switch 47b and the second initial charging unit switch 47e are examples of the "initial charging unit switch" in the claims.

[0030] The fuse 47a is provided between the AC power supply side (system power supply 5 side) of the AC-side switch 45 and the first initial charging unit switch 47b in order to protect the initial charging unit 47.

[0031] The first initial charging unit switch 47b is provided between the fuse 47a and the transformer 47c. The first initial charging unit switch 47b is provided to connect the multiple power conversion units 41-44 to the AC power supply side (the system power supply 5 side) by bypassing the AC side switch 45. The first initial charging unit switch 47b connects the DC sides of the multiple power conversion units 41-44 to the AC power supply side by being turned on under the control of the control unit 48. Also, the first initial charging unit switch 47b disconnects the DC sides of the multiple power conversion units 41-44 from the AC power supply side by being turned off under the control of the control unit 48. When the power conversion device 4 is started up, the first initial charging unit switch 47b is controlled to be changed from off to on.

[0032] The transformer 47c is provided between the first initial charging unit switch 47b and the resistor 47d and the second initial charging unit switch 47e. The transformer 47c bypasses the AC side switch 45 and connects the power conversion units 41 to 44 to the AC power supply side (the system power supply 5 side). The transformer 47c transforms AC power from the AC power supply side and outputs it to the rectifier circuit 47f. Note that the transformer 47c needs to have a capacity corresponding to the number of power conversion units that operate when a startup AC voltage is generated and the device specifications in order to operate the power conversion units when a startup AC voltage is generated, which will be described later. Although it varies depending on the capacity of the power conversion device 4, for example, when the capacity of the power conversion device 4 is 2600 kVA and all four power conversion units 41 to 44 are operated to generate a startup AC voltage, the capacity required for the transformer 47c is about 26 kVA (about 1% of the device capacity). Furthermore, when the capacity of the power conversion device 4 is 2600 kVA and one power conversion unit 41 is operated to generate a startup AC voltage, the capacity required for the transformer 47c is about 6.5 kVA (about 0.25% of the device capacity). In this embodiment, the transformer 47c has a capacity (for example, 6.5 kVA) required to operate one power conversion unit when a startup AC voltage is generated.

[0033] The resistor 47d and the second initial charging section switch 47e are provided between the transformer 47c and the rectifier circuit 47f. The resistor 47d is provided to suppress an inrush current to the power conversion units 41 to 44 during initial charging. The second initial charging section switch 47e is provided to connect the power conversion units 41 to 44 to the AC power supply side, bypassing the resistor 47d. The second initial charging section switch 47e is connected in parallel to the resistor 47d. The second initial charging section switch 47e is turned on under the control of the control unit 48 to connect the DC sides of the power conversion units 41 to 44 to the AC power supply side, bypassing the resistor 47d. The second initial charging section switch 47e is turned off under the control of the control unit 48 to release the connection between the DC sides of the power conversion units 41 to 44 and the AC power supply side, bypassing the resistor 47d. When the power conversion device 4 is started up, the second initial charging unit switch 47e is controlled to be changed from OFF to ON after the first initial charging unit switch 47b is turned ON and a predetermined voltage condition is satisfied.

[0034] The rectifier circuit 47f is provided between the resistor 47d and the second initial charging unit switch 47e and the DC sides of the power conversion units 41 to 44. The rectifier circuit 47f converts the AC power from the transformer 47c into DC power and outputs it to the DC sides of the power conversion units 41 to 44. This charges the DC sides of the power conversion units 41 to 44 (initial charging). Details of the startup process including the initial charging will be described later.

[0035] The control unit 48 controls the operation of each unit of the power conversion device 4. The control unit 48 is a control circuit including a processor such as a CPU (Central Processing Unit) and a memory such as a flash memory. The control unit 48 is configured, for example, by a PLC (Programmable Logic Controller). The control unit 48 controls the operation of the multiple power conversion units 41 to 44, the AC side switch 45, the DC side switch 46, and the initial charging unit 47 by outputting various control signals.

[0036] (Startup control process) The control unit 48 is configured to perform control to charge the DC sides of the plurality of power conversion units 41-44 by turning on the first initial charging unit switch 47b and the second initial charging unit switch 47e at the time of starting up the power conversion device 4, by connecting the AC power supply side (the system power supply 5 side) and the DC sides of the plurality of power conversion units 41-44 by the initial charging unit 47. The control unit 48 is configured to perform control to generate a startup AC voltage (counter voltage) corresponding to the AC voltage supplied from the AC power supply side in a state in which the startup AC voltage is generated by the initial charging unit 47. The control unit 48 is configured to perform control to connect the AC sides of the plurality of power conversion units 41-44 and the AC power supply side by turning on the AC side switch 45 in a state in which the AC side switch 45 is turned on. The control unit 48 is configured to perform control to connect the DC sides of the plurality of power conversion units 41-44 and the storage battery 3 by turning on the DC side switch 46 in a state in which the AC side switch 45 is turned on. This completes the start-up of the power conversion device 4.

[0037] In this embodiment, when turning on the AC-side switch 45 in a state in which the multiple power conversion units 41-44 are charged by the initial charging unit 47 at the time of starting up the power conversion device 4, the control unit 48 is configured to perform control to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power source side (the system power source 5 side) by operating some of the multiple power conversion units 41-44. Specifically, when turning on the AC-side switch 45, the control unit 48 is configured to perform control to generate a startup AC voltage by operating one of the multiple power conversion units 41-44.

[0038] In the present embodiment, the control unit 48 is configured to perform control to select a power conversion unit that generates a startup AC voltage from among the multiple power conversion units 41 to 44 based on the state of the multiple power conversion units 41 to 44. Specifically, the control unit 48 is configured to perform control to select a power conversion unit that generates a startup AC voltage from among the multiple power conversion units 41 to 44 based on the failure state of the multiple power conversion units 41 to 44. The control unit 48 is configured to perform control to select a power conversion unit that generates a startup AC voltage from among the power conversion units 41 to 44 that are not faulty, according to priority. Note that the failure does not mean a failure that is inoperable, but a failure that is operable.

[0039] For example, the power conversion units 44, 43, 42, and 41 are set to have higher priorities in this order. In this case, for example, when none of the multiple power conversion units 41 to 44 is broken, the control unit 48 selects the power conversion unit 41 with the highest priority as the power conversion unit that generates the start-up AC voltage. Also, for example, when the power conversion unit 41 with the highest priority is broken and the power conversion units 42 to 44 are not broken, the control unit 48 selects the power conversion unit 42 with the highest priority among the non-failed power conversion units 42 to 44 as the power conversion unit that generates the start-up AC voltage. That is, when any of the multiple power conversion units 41 to 44 is broken, the control unit 48 selects the power conversion unit with the highest priority among the non-failed power conversion units as the power conversion unit that generates the start-up AC voltage. Note that, for convenience, the following description will be given assuming that the power conversion unit 41 is the power conversion unit that generates the start-up AC voltage.

[0040] Furthermore, in this embodiment, the control unit 48 is configured to perform control to start up the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 after turning on the AC side switch 45. That is, the control unit 48 is configured to perform control to start up the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 after turning on the AC side switch 45 to connect the AC sides of the multiple power conversion units 41-44 to the AC power supply side (the system power supply 5 side).

[0041] In the present embodiment, the control unit 48 is configured to perform control to start up the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44, after turning off the first initial charging unit switch 47b and the second initial charging unit switch 47e after completing the initial charging. That is, the control unit 48 is configured to perform control to start up the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44, after turning off the first initial charging unit switch 47b and the second initial charging unit switch 47e to release the connection between the multiple power conversion units 41-44 and the AC power supply side (the system power supply 5 side) via the initial charging unit 47.

[0042] Furthermore, in this embodiment, the control unit 48 is configured to perform control to start up the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 before turning on the DC side switch 46. That is, the control unit 48 is configured to perform control to start up the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 before turning on the DC side switch 46 to connect the DC sides of the multiple power conversion units 41-44 to the storage battery 3.

[0043] In the present embodiment, the control unit 48 is configured to perform control to start the power conversion units 42 to 44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 based on the fact that the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 has boosted the DC voltage applied to the storage battery 3 to be equal to or higher than the DC voltage of the storage battery 3 before turning on the DC side switch 46. At this time, the control unit 48 is configured to perform control to start the power conversion units 42 to 44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 by a soft start that gradually boosts the output voltage based on the fact that the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 has boosted the DC voltage applied to the storage battery 3 to be equal to or higher than the DC voltage of the storage battery 3.

[0044] Next, the start-up process by the power conversion device 4 of this embodiment will be described based on a flowchart with reference to Fig. 3 to Fig. 12. The start-up process is performed at the time of initial start-up and at the time of recovery from maintenance. Each process in the flowchart is performed by the control unit 48. Figs. 4 to 12 also show the voltage on the AC power supply side, the voltage on the AC side of the multiple power conversion units 41 to 44, the voltage on the DC side of the multiple power conversion units 41 to 44, and the voltage of the storage battery 3.

[0045] As shown in FIG. 3 and FIG. 4, in step S1, a start command based on a user's operation to start driving is received.

[0046] Then, in step S2, it is determined whether or not the start-up conditions are met. The start-up conditions include, for example, that the power conversion units 41-44 have no malfunctions that would disable operation, and that the voltage of the storage battery 3 is sufficient for operation. If it is determined that the start-up conditions are met, the process proceeds to step S3. If it is determined that the start-up conditions are not met, the process of step S2 is repeated. At this time, an error may be output.

[0047] 3 and 5, in step S3, the first initial charging unit switch 47b is turned on. This connects the AC power supply side (the system power supply 5 side) and the DC sides of the multiple power conversion units 41-44 via the resistor 47d of the initial charging unit 47. Then, while the resistor 47d of the initial charging unit 47 suppresses inrush current, the DC sides of the multiple power conversion units 41-44 are charged (boosted).

[0048] Then, in step S4, it is determined whether the DC voltage of the power conversion units 41-44 has reached or exceeded the voltage that turns on the second initial charging unit switch 47e. If it is determined that the DC voltage of the power conversion units 41-44 has reached or exceeded the voltage that turns on the second initial charging unit switch 47e, the process proceeds to step S5. If it is determined that the DC voltage of the power conversion units 41-44 has not reached or exceeded the voltage that turns on the second initial charging unit switch 47e, the process of step S4 is repeated.

[0049] 3 and 6, in step S5, the second initial charging unit switch 47e is turned on. This connects the AC power supply side (the system power supply 5 side) and the DC sides of the power conversion units 41-44, bypassing the resistor 47d of the initial charging unit 47. The DC sides of the power conversion units 41-44 are further charged (boosted) by the voltage division of the resistor 47d of the initial charging unit 47. Since the resistor 47d is short-circuited in step S5, it is possible to suppress the resistor 47d from affecting the generation of the start-up AC voltage in step S7, which will be described later.

[0050] Then, as shown in FIG. 3 and FIG. 7, in step S6, one power conversion unit 41 of the plurality of power conversion units 41 to 44 is started up.

[0051] Then, in step S7, one power conversion unit 41 among the multiple power conversion units 41 to 44 is operated to generate a startup AC voltage (counter voltage) corresponding to the AC voltage supplied from the AC power supply side (system power supply 5 side). That is, a startup AC voltage synchronized with the AC voltage supplied from the AC power supply side is generated as an output voltage on the AC side of the power conversion unit 41.

[0052] 3 and 8, in step S8, the AC-side switch 45 is turned on. This connects the AC power supply side (the system power supply 5 side) and the AC sides of the multiple power conversion units 41 to 44. At this time, since the power conversion unit 41 generates a startup AC voltage, the connection between the AC sides of the multiple power conversion units 41 to 44 and the AC power supply side does not affect the AC power supply side.

[0053] Then, in step S9, the first initial charging unit switch 47b and the second initial charging unit switch 47e are turned off, thereby disconnecting the AC power supply side (the system power supply 5 side) and the DC sides of the multiple power conversion units 41-44 via the initial charging unit 47.

[0054] Then, as shown in Figs. 3 and 9, in step S10, the power conversion unit 41 among the plurality of power conversion units 41 to 44 is operated, thereby boosting the DC side of the power conversion unit 41.

[0055] Then, in step S11, it is determined whether or not the DC side voltages of the multiple power conversion units 41-44 have reached or exceeded the voltage at which the DC side switch 46 is turned on. That is, it is determined whether or not the DC voltage applied to the storage battery 3 has been boosted by the power conversion unit 41 to or exceeded the DC voltage (storage voltage) of the storage battery 3. If it is determined that the DC side voltages of the multiple power conversion units 41-44 have reached or exceeded the voltage at which the DC side switch 46 is turned on, the process proceeds to step S12. If it is determined that the DC side voltages of the multiple power conversion units 41-44 have not reached or exceeded the voltage at which the DC side switch 46 is turned on, the process of step S11 is repeated.

[0056] 3 and 10, in step S12, the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 are started up. At this time, the power conversion units 42-44 are operated by a soft start in which the voltage rise is more gradual than in normal operation. As a result, the DC sides of the power conversion units 42-44 are gradually boosted so as not to affect the DC voltage generated by the power conversion unit 41.

[0057] 3 and 11, in step S13, the DC side switch 46 is turned on. This connects the storage battery 3 to the DC sides of the multiple power conversion units 41-44. At this time, a DC voltage equal to or higher than the DC voltage of the storage battery 3 is generated in the storage battery 3, so that inrush current from the storage battery 3 to the multiple power conversion units 41-44 is suppressed.

[0058] Then, the startup process is completed as shown in Fig. 3 and Fig. 12. When the startup process is completed, the storage battery 3, the power conversion device 4, and the AC power supply side (the system power supply 5 side) are connected. Therefore, after the startup process is completed, it is possible to perform an operation of charging the storage battery 3 via the power conversion device 4 with power from the AC power supply side, and an operation of discharging power from the storage battery 3 to the AC power supply side via the power conversion device 4.

[0059] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0060] In this embodiment, as described above, when the AC side switch 45 is turned on in a state where the multiple power conversion units 41 to 44 are charged by the initial charging unit 47, a control unit 48 is provided that performs control to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side by operating some of the multiple power conversion units 41 to 44. As a result, since the startup AC voltage (counter voltage) can be generated by some, not all, of the multiple power conversion units 41 to 44, the capacity of the transformer 47c of the initial charging unit 47 required to operate the power conversion unit 41 when the startup AC voltage is generated can be made smaller than when the startup AC voltage is generated by all of the multiple power conversion units 41 to 44. As a result, even when the transformer 47c is provided in the initial charging unit 47, the transformer 47c of the initial charging unit 47 can be prevented from becoming large and can be made smaller.

[0061] In addition, in this embodiment, as described above, the control unit 48 is configured to perform control to start the power conversion units 42 to 44 other than the power conversion unit 41 that generates the startup AC voltage among the multiple power conversion units 41 to 44 after turning on the AC side switch 45. This makes it possible to start the power conversion units 42 to 44 other than the power conversion unit 41 that generates the startup AC voltage among the multiple power conversion units 41 to 44 in a state in which the AC side switch 45 is turned on to prevent any influence on the AC power supply side. As a result, it is possible to suppress the influence on the AC power supply side of the activation of the power conversion units 42 to 44 other than the power conversion unit 41 that generates the startup AC voltage among the multiple power conversion units 41 to 44.

[0062] In addition, in this embodiment, as described above, the initial charging unit 47 includes a first initial charging unit switch 47b and a second initial charging unit switch 47e for connecting the multiple power conversion units 41 to 44 to the AC power supply side by bypassing the AC side switch 45. The control unit 48 is configured to perform control to start the power conversion units 42 to 44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 after turning off the first initial charging unit switch 47b and the second initial charging unit switch 47e after the initial charging is completed. This makes it possible to start the power conversion units 42 to 44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 in a state where the initial charging is completed. As a result, it is possible to easily start the power conversion units 42 to 44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44.

[0063] In the present embodiment, as described above, the power conversion device 4 includes the DC side switch 46 for connecting the multiple power conversion units 41 to 44 to the storage battery 3. The control unit 48 is configured to perform control for starting the power conversion units 42 to 44 other than the power conversion unit 41 that generates the startup AC voltage among the multiple power conversion units 41 to 44 before turning on the DC side switch 46. This makes it possible to connect the multiple power conversion units 41 to 44 to the storage battery 3 by turning on the DC side switch 46 in a state in which all of the multiple power conversion units 41 to 44 are started. As a result, after the multiple power conversion units 41 to 44 are connected to the storage battery 3, the charging and discharging operation of the storage battery 3 can be performed without any capacity restrictions.

[0064] In the present embodiment, as described above, the control unit 48 is configured to perform control to start the power conversion units 42 to 44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44, based on the fact that the DC voltage applied to the storage battery 3 is boosted to the DC voltage of the storage battery 3 or higher by the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44 before turning on the DC side switch 46. As a result, in order to suppress an inrush current from the storage battery 3 to the multiple power conversion units 41 to 44, the operation of boosting the DC voltage applied to the storage battery 3 to the DC voltage of the storage battery 3 or higher can be performed only by the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41 to 44.

[0065] In addition, in this embodiment, as described above, the control unit 48 is configured to perform control to start the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 by a soft start that gradually boosts the output voltage, based on the fact that the DC voltage applied to the storage battery 3 has been boosted to equal to or higher than the DC voltage of the storage battery 3 by the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44. This makes it possible to suppress the output voltages of the power conversion units 42-44 other than the power conversion unit 41 that generated the startup AC voltage among the multiple power conversion units 41-44 from affecting the DC voltage applied to the storage battery 3.

[0066] In the present embodiment, as described above, the control unit 48 is configured to perform control to select a power conversion unit that generates a startup AC voltage from among the multiple power conversion units 41 to 44 based on the state of the multiple power conversion units 41 to 44. This makes it possible to select a power conversion unit that is suitable for generating the startup AC voltage from among the multiple power conversion units 41 to 44, unlike a case in which a power conversion unit that generates the startup AC voltage from among the multiple power conversion units 41 to 44 is fixed. As a result, the startup AC voltage can be appropriately generated by the selected power conversion unit.

[0067] In the present embodiment, as described above, the control unit 48 is configured to perform control to generate a startup AC voltage by operating one of the power conversion units 41 to 44 when turning on the AC side switch 45. This allows the startup AC voltage (counter voltage) to be generated by one of the power conversion units 41 to 44, not by all of them. Therefore, the capacity of the transformer 47c of the initial charging unit 47 required to operate the power conversion units when the startup AC voltage is generated can be made smaller than when the startup AC voltage is generated by two or more of the power conversion units 41 to 44. As a result, even when the transformer 47c is provided in the initial charging unit 47, the transformer 47c of the initial charging unit 47 can be prevented from becoming large and can be made smaller.

[0068] (Modification) The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments above, and further includes all modifications (variations) within the meaning and scope of the claims.

[0069] For example, in the above embodiment, the power generation device is a solar cell, but the present invention is not limited to this. For example, the power generation device may be a power generation device other than a solar cell, such as a wind power generation device or a gas turbine power generation device.

[0070] In the above embodiment, the power conversion device includes four power conversion units, but the present invention is not limited to this. For example, the power conversion device may include two, three, five or more power conversion units.

[0071] In the above embodiment, an example is shown in which a startup AC voltage is generated by operating one of the multiple power conversion units, but the present invention is not limited to this. In the present invention, the startup AC voltage may be generated by operating two or more of the multiple power conversion units, if not all of the multiple power conversion units.

[0072] In the above embodiment, the power conversion units other than the power conversion unit that generates the startup AC voltage among the multiple power conversion units are started after the initial charging unit switch is turned off, but the present invention is not limited to this. For example, the power conversion units other than the power conversion unit that generates the startup AC voltage among the multiple power conversion units may be started before the initial charging unit switch is turned off.

[0073] In the above embodiment, the power conversion units other than the power conversion unit that generates the startup AC voltage among the multiple power conversion units are started before the DC side switch is turned on, but the present invention is not limited to this. For example, the power conversion units other than the power conversion unit that generates the startup AC voltage among the multiple power conversion units may be started after the DC side switch is turned on.

[0074] In the above embodiment, an example is shown in which, based on the fact that the power conversion unit among the multiple power conversion units that generated the startup AC voltage has boosted the DC voltage applied to the storage battery to equal to or higher than the DC voltage of the storage battery by the power conversion unit among the multiple power conversion units that generated the startup AC voltage before the DC side switch is turned on, the present invention is not limited to this. For example, before the DC side switch is turned on, the power conversion units among the multiple power conversion units other than the power conversion unit that generated the startup AC voltage may be started, and the DC voltage applied to the storage battery may be boosted to equal to or higher than the DC voltage of the storage battery by all of the multiple power conversion units.

[0075] In the above embodiment, an example is shown in which a power conversion unit that generates a startup AC voltage is selected from among the multiple power conversion units based on the state of the multiple power conversion units, but the present invention is not limited to this. For example, the power conversion unit that generates the startup AC voltage from among the multiple power conversion units may be fixed. [Explanation of symbols]

[0076] 3. Storage battery 4. Power conversion device 41~44 Power conversion section 45 AC side switch 46 DC side switch 47 Initial charging part 47b First initial charging switch (initial charging switch) 47c Trans 47e Second initial charging section switch (initial charging section switch) 48 Control Unit 100 Power Conversion System

Claims

1. A power conversion device for a storage battery, comprising: A plurality of power conversion units for charging and discharging the storage battery; an AC side switch for connecting the plurality of power conversion units to an AC power supply side; an initial charging unit including a transformer that connects the plurality of power conversion units to the AC power supply side by bypassing the AC side switch, and that charges the plurality of power conversion units; and a control unit that performs control to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side by operating some of the power conversion units when the AC-side switch is turned on at startup with the multiple power conversion units charged by the initial charging unit.

2. 2. The power conversion device according to claim 1, wherein the control unit is configured to perform control to start up a power conversion unit among the plurality of power conversion units other than a power conversion unit that generates the startup AC voltage after turning on the AC side switch.

3. the initial charging unit includes an initial charging unit switch for bypassing the AC side switch and connecting the plurality of power conversion units to the AC power supply side, 3. The power conversion device according to claim 2, wherein the control unit is configured to perform control to start up a power conversion unit among the plurality of power conversion units other than the power conversion unit that generated the startup AC voltage, after turning off the initial charging unit switch after initial charging is completed.

4. a DC side switch for connecting the plurality of power conversion units to the storage battery, 4. The power conversion device according to claim 2, wherein the control unit is configured to perform control to start up a power conversion unit among the plurality of power conversion units other than a power conversion unit that generates the startup AC voltage before turning on the DC side switch.

5. 5. The power conversion device according to claim 4, wherein the control unit is configured to perform control to start up a power conversion unit among the plurality of power conversion units other than the power conversion unit that generated the startup AC voltage, based on a fact that a DC voltage to be applied to the storage battery has been boosted to or higher than a DC voltage of the storage battery by a power conversion unit among the plurality of power conversion units that generated the startup AC voltage before turning on the DC side switch.

6. 6. The power conversion device according to claim 5, wherein the control unit is configured to control the power conversion units among the plurality of power conversion units other than the power conversion unit that generated the startup AC voltage to start up an output voltage by a soft start that gradually boosts an output voltage, based on the DC voltage applied to the storage battery being boosted to or higher than the DC voltage of the storage battery by a power conversion unit among the plurality of power conversion units that generated the startup AC voltage.

7. The control unit is configured to perform control to select a power conversion unit that generates the startup AC voltage from among the plurality of power conversion units based on a state of the plurality of power conversion units. The power conversion device according to any one of claims 1 to 6.

8. The control unit is configured to perform control to generate the startup AC voltage by operating one of the plurality of power conversion units when the AC side switch is turned on. The power conversion device according to any one of claims 1 to 7.

9. A storage battery, a power conversion device connected to the storage battery, The power conversion device is A plurality of power conversion units for charging and discharging the storage battery; an AC side switch for connecting the plurality of power conversion units to an AC power supply side; an initial charging unit including a transformer that connects the plurality of power conversion units to the AC power supply side by bypassing the AC side switch, and that charges the plurality of power conversion units; a control unit that performs control to generate a startup AC voltage corresponding to the AC voltage supplied from the AC power supply side by operating some of the power conversion units when the AC-side switch is turned on at startup with the multiple power conversion units charged by the initial charging unit.

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