Power Conversion Device

Abstract

A power conversion device that can appropriately perform back excitation of an interconnection transformer with a simpler configuration is provided. [Solution] A power conversion device is provided which comprises a main circuit section having a converter connected to a power grid via an interconnection transformer and a charge storage element provided on the DC side of the converter, an initial charging circuit which performs initial charging of the charge storage element when operation of the main circuit section begins, and a control device which controls the operation of the main circuit section and the initial charging circuit, wherein the initial charging circuit has a resistor provided between the auxiliary power supply and the charge storage element and a switch provided in parallel with the resistor, and the control device starts initial charging of the charge storage element with the switch in an open state, switches the switch to an on state when the voltage of the charge storage element exceeds a threshold, and then controls the operation of the converter so that a voltage whose phase and amplitude match the AC voltage of the power grid is generated on the AC side of the converter.

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] There is a power conversion device that includes an interconnection transformer for interconnecting with an AC power system, a circuit breaker provided between the power system and the interconnection transformer, a converter that is connected to the power system via the circuit breaker and the interconnection transformer and converts DC power to AC power, and a charge storage element provided on the DC side of the converter.

[0003] In such a power conversion device, when starting operation, the charge storage element is charged to a predetermined voltage by a pre-charging circuit with the circuit breaker open. Furthermore, in the power conversion device, before closing the circuit breaker, power corresponding to the phase and amplitude of the AC voltage of the power grid is supplied from the converter to the interconnection transformer. This prevents the magnetizing inrush current of the interconnection transformer from flowing into the power grid when the circuit breaker is closed. For example, it prevents the magnetizing inrush current from fluctuating the voltage of the power grid or causing malfunctions in other devices connected to the power grid. Such excitation of the interconnection transformer from the converter side is called, for example, back-excitation.

[0004] However, when reverse excitation is implemented, it is necessary to supply energy equivalent to the losses (e.g., iron loss) of the interconnection transformer from the DC side of the converter. This requires a sufficient capacity for the charge storage element, which may lead to factors such as an increase in the size of the device and manufacturing costs. It is also possible to supply energy equivalent to the losses of the interconnection transformer from an initial charging circuit, but in this case, there is a concern that the resistor used to limit the magnitude of the current flowing during initial charging of the charge storage element may overheat.

[0005] For this reason, it is desirable for the power conversion device to be able to appropriately perform back excitation of the interconnection transformer with a simpler configuration. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-195348 Summary of the Invention [Problem to be solved by the invention]

[0007] An embodiment of the present invention provides a power conversion device that can appropriately perform back excitation of an interconnection transformer with a simpler configuration. [Means for solving the problem]

[0008] According to an embodiment of the present invention, a power generating device includes: a main circuit unit having an interconnection transformer for interconnecting with an AC power system; a converter connected to the power system via the interconnection transformer and connected to a DC circuit for converting DC power to AC power; and a charge storage element provided on the DC side of the converter; an initial charging circuit connected to the charge storage element and connected to an auxiliary power supply for initially charging the charge storage element by supplying DC power to the charge storage element based on power supplied from the auxiliary power supply when operation of the main circuit unit starts; and a control device for controlling operation of the main circuit unit and the initial charging circuit, wherein the initial charging circuit is provided between the auxiliary power supply and the charge storage element. and a switch disposed in parallel with the resistor and having an on state in which both ends of the resistor are conductive and an open state in which both ends of the resistor are not conductive, wherein when operation of the main circuit section starts, the control device sets the switch to the open state to start initial charging of the charge storage element, and when the magnitude of the voltage of the charge storage element becomes equal to or greater than a threshold, switches the switch from the open state to the on state, and after switching the switch to the on state, controls the operation of the converter so that a voltage whose phase and amplitude match those of the AC voltage of the power system is generated on the AC side of the converter, thereby performing back excitation of the interconnection transformer. [Effects of the Invention]

[0009] A power conversion device is provided that can appropriately perform back excitation of an interconnection transformer with a simpler configuration. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram schematically illustrating a power conversion device according to an embodiment. [Figure 2] 2(a) to 2(d) are graphs that schematically show an example of the operation of the power conversion device according to the embodiment. [Figure 3] FIG. 10 is a block diagram schematically illustrating a modified example of the power conversion device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Each embodiment will be described below with reference to the drawings. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0012] FIG. 1 is a block diagram schematically illustrating a power conversion device according to an embodiment. As shown in FIG. 1, the power conversion device 10 includes a main circuit unit 12, an initial charging circuit 14, and a control device 16.

[0013] The main circuit section 12 includes an interconnection transformer 20, a circuit breaker 22, a converter 24, a charge storage element 26, and a voltage detector 28.

[0014] The interconnection transformer 20 is a transformer for interconnecting with the AC power system 2. The interconnection transformer 20, for example, steps down the AC voltage of the power system 2 and supplies the stepped-down AC power to the converter 24, and also steps up the AC voltage of the converter 24 and supplies the stepped-up AC power to the power system 2. The AC power of the power system 2 is, for example, three-phase AC power. The interconnection transformer 20 converts the magnitude of the three-phase AC voltage between the power system 2 and the converter 24, for example.

[0015] Circuit breaker 22 is provided between power system 2 and interconnection transformer 20. Circuit breaker 22 switches between a state in which interconnection transformer 20 is connected to power system 2 and a state in which interconnection transformer 20 is disconnected from power system 2 (a state in which the connection between interconnection transformer 20 and power system 2 is released).

[0016] The converter 24 is connected to the power system 2 via the circuit breaker 22 and the interconnection transformer 20. The converter 24 converts AC power to DC power and DC power to AC power.

[0017] The main circuit unit 12 has a pair of DC terminals d1 and d2. The main circuit unit 12 is connected to an AC power system 2 and is also connected to a DC circuit (not shown) via the pair of DC terminals d1 and d2. The converter 24 is connected to the power system 2 via a circuit breaker 22 and an interconnection transformer 20, and is also connected to the DC circuit via the pair of DC terminals d1 and d2. The DC circuit may be a DC load that requires a supply of DC power, or a DC power source that supplies DC power. The DC circuit may be, for example, another converter that converts the DC power supplied from the converter 24 into another power and / or converts the other power into DC power according to the converter 24.

[0018] Converter 24, for example, converts AC power supplied from power system 2 into DC power according to the DC circuit and supplies the converted DC power to the DC circuit, and also converts DC power supplied from the DC circuit into AC power according to power system 2 and supplies the converted AC power to power system 2.

[0019] The converter 24 has, for example, a plurality of switching elements, and converts AC power to DC power and DC power to AC power by switching the plurality of switching elements.

[0020] The multiple switching elements have a pair of main terminals and a control terminal. The multiple switching elements have an on state and an off state. The on state is a state in which current flows between the pair of main terminals. The off state is a state in which current flow between the pair of main terminals is blocked. Each of the multiple switching elements switches between the on state and the off state depending on the voltage between the pair of main terminals and the voltage of the control terminal. Note that the off state is not limited to a state in which no current flows between the pair of main terminals, but may also be a state in which a weak current flows between the pair of main terminals within a range that does not affect the operation of the converter 24.

[0021] The multiple switching elements are, for example, self-excited semiconductor switching elements such as IGBTs and MOSFETs. The converter 24 is, for example, a self-excited converter. However, the multiple switching elements are not limited to this and may be any elements that can be arbitrarily switched between an on state and an off state.

[0022] The converter 24 is, for example, a three-phase full-bridge circuit having six switching elements connected in a three-phase full-bridge configuration. However, the configuration of the converter 24 is not limited to this. The converter 24 does not necessarily have the function of converting AC power to DC power. The converter 24 may have any configuration that is at least capable of converting DC power to AC power.

[0023] The charge storage element 26 is provided on the DC side of the converter 24. In other words, the charge storage element 26 is provided between a pair of DC terminals d1 and d2. The charge storage element 26 suppresses fluctuations in the voltage on the DC side of the converter 24. For example, a capacitor or a storage battery is used as the charge storage element 26. However, the charge storage element 26 is not limited to these, and may be any element that can store DC power and suppress fluctuations in the voltage on the DC side of the converter 24.

[0024] The voltage detector 28 detects the magnitude (instantaneous value) of the AC voltage of the power system 2 and inputs the detection result to the control device 16. The voltage detector 28 detects, for example, the magnitude of the voltage of each phase of the three-phase AC voltage of the power system 2 and inputs the detection result to the control device 16.

[0025] The main circuit unit 12 does not necessarily have to include the circuit breaker 22 and the voltage detector 28. The circuit breaker 22 and the voltage detector 28 may be, for example, devices on the facility side where the power conversion device 10 is installed. The configuration of the main circuit unit 12 is not limited to the above, and may be any configuration that includes at least the interconnection transformer 20, the converter 24, and the charge storage element 26.

[0026] When the main circuit unit 12 starts operating, the initial charging circuit 14 supplies DC power to the charge storage element 26 to initially charge the charge storage element 26. The initial charging circuit 14 is connected to the charge storage element 26 and also to the auxiliary power supply 4, and initially charges the charge storage element 26 based on the power supplied from the auxiliary power supply 4.

[0027] The auxiliary power supply 4 is, for example, a transformer that steps down the AC voltage of the power grid 2 to a voltage level appropriate for the initial charging circuit 14. The power supplied from the auxiliary power supply 4 to the initial charging circuit 14 is, for example, AC power.

[0028] When AC power is supplied from the auxiliary power supply 4 in this way, the initial charging circuit 14 includes, for example, a circuit breaker 30, a transformer 32, and a conversion unit 34. The circuit breaker 30 switches between a state in which the transformer 32 (initial charging circuit 14) is connected to the auxiliary power supply 4 and a state in which the transformer 32 is disconnected from the auxiliary power supply 4.

[0029] The transformer 32 is provided between the auxiliary power supply 4 and the conversion unit 34. The transformer 32, for example, boosts the AC voltage of the auxiliary power supply 4 and supplies the boosted AC power to the conversion unit 34. The conversion unit 34 converts the AC power supplied from the transformer 32 (auxiliary power supply 4) into DC power according to the charge storage element 26. The conversion unit 34 is, for example, a rectifier that rectifies the AC power supplied from the transformer 32 to convert it into DC power (rectified power).

[0030] The power supplied from the auxiliary power supply 4 to the initial charging circuit 14 may be DC power. In this case, the transformer 32 and the conversion unit 34 are omitted. As described above, the transformer 32 and the conversion unit 34 are provided in the initial charging circuit 14 as needed and can be omitted. In the initial charging circuit 14, the configuration for initially charging the charge storage element 26 based on the power supplied from the auxiliary power supply 4 (the configuration for supplying DC power to the charge storage element 26) is not limited to the configuration described above and may be any configuration that can appropriately initially charge the charge storage element 26. For example, depending on the voltage of the auxiliary power supply 4, only the transformer 32 may be omitted. The configuration of the conversion unit 34 is not limited to a rectifier and may be any configuration that can convert the AC power supplied from the auxiliary power supply 4 into DC power appropriate for the charge storage element 26. The configuration of the initial charging circuit 14 may be appropriately set depending on the configuration of the auxiliary power supply 4, etc.

[0031] The initial charging circuit 14 further includes a resistor 36 and a switch 38. The resistor 36 is provided between the auxiliary power supply 4 and the charge storage element 26, and prevents a current greater than a predetermined value from flowing through the initial charging circuit 14 and the charge storage element 26 when DC power is supplied to the charge storage element 26 based on the power supplied from the auxiliary power supply 4. In other words, the resistor 36 is a current limiting resistor that limits the amount of current flowing through the initial charging circuit 14 and the charge storage element 26 when the charge storage element 26 is initially charged.

[0032] The resistor 36 is provided, for example, between the conversion unit 34 and the charge storage element 26. The initial charging circuit 14 has two resistors 36: one resistor 36 provided between the high-potential terminal of the conversion unit 34 (auxiliary power supply 4) and the high-potential terminal of the charge storage element 26, and the other resistor 36 provided between the low-potential terminal of the conversion unit 34 (auxiliary power supply 4) and the low-potential terminal of the charge storage element 26. This more appropriately prevents a current greater than a predetermined value from flowing through the initial charging circuit 14 and the charge storage element 26 during initial charging of the charge storage element 26. However, the initial charging circuit 14 may be configured to have a single resistor 36 provided between only one of the high-potential terminal and the low-potential terminal of the charge storage element 26.

[0033] The switch 38 is provided in parallel with the resistor 36. The initial charging circuit 14 has, for example, two switches 38 corresponding to the two resistors 36, respectively. The switch 38 has, for example, a closed state in which both ends of the resistor 36 are conductive, and an open state in which the conductivity between both ends of the resistor 36 is released. In other words, the closed state is a state in which the resistor 36 is bypassed. In other words, the open state is a state in which the bypass of the resistor 36 is released. In other words, the switch 38 is a bypass switch for bypassing the resistor 36.

[0034] As a result, in the initial charging circuit 14, by opening the switch 38, current is supplied to the charge storage element 26 via the resistor 36, and when the charge storage element 26 is initially charged, a current greater than a predetermined value can be prevented from flowing through the initial charging circuit 14 and the charge storage element 26.

[0035] In the initial charging circuit 14, by closing the switch 38, a current is supplied to the charge storage element 26 via the switch 38, and the current can be supplied to the charge storage element 26 in a state of lower resistance during the initial charging of the charge storage element 26. For example, by closing the switch 38, a larger current can be supplied to the charge storage element 26 than when the switch 38 is open.

[0036] The control device 16 controls the operation of the main circuit unit 12 and the operation of the initial charging circuit 14. The control device 16 controls the power conversion operation by the converter 24. For example, the control device 16 generates a control signal for controlling the switching of a plurality of switching elements provided in the converter 24, and controls the power conversion operation by the converter 24 by inputting the generated control signal to the converter 24. The control device 16 also controls, for example, the switching between the open state and the closed state of the circuit breaker 22 of the main circuit unit 12.

[0037] The control device 16 controls the switching between the open state and the closed state of the switch 38 of the initial charging circuit 14. The control device 16 also controls the switching between the open state and the closed state of the circuit breaker 30 of the initial charging circuit 14, for example. In this way, the control device 16 controls the initial charging operation of the charge storage element 26 by the initial charging circuit 14.

[0038] The control device 16 may be configured as a single device, or may be configured as two devices: a device that controls the operation of the main circuit unit 12 and a device that controls the operation of the initial charging circuit 14. In other words, the control device 16 may have a control unit that controls the operation of the main circuit unit 12 and a control unit that controls the operation of the initial charging circuit 14.

[0039] 2(a) to 2(d) are graphs that schematically show an example of the operation of the power conversion device according to the embodiment. FIG. 2(a) shows a schematic example of the change over time in the AC voltage on the primary side of the transformer 32 of the initial charging circuit 14. FIG. 2(b) shows a schematic example of the change over time of the AC current on the primary side of the transformer 32 of the initial charging circuit 14. FIG. 2(c) shows a schematic example of the change over time in the output current of the conversion unit 34 of the initial charging circuit 14. FIG. 2(d) shows a schematic example of the change in the voltage of the charge storage element 26 over time. 2(a) to 2(d) schematically show an example of the operation of initial charging of the charge storage element 26 by the initial charging circuit 14. Note that, due to the scale of the drawings, in Fig. 2(a) and Fig. 2(b), the lines representing the amplitude of the AC waveform are shown as being substantially joined together in the time axis direction and observed as a band.

[0040] When the operation of the main circuit unit 12 is stopped, the control device 16 stops the operation of the converter 24 and opens the circuit breaker 22 to separate the main circuit unit 12 from the power grid 2. When the operation of the main circuit unit 12 is stopped, the control device 16 also opens the circuit breaker 30 to separate the initial charging circuit 14 from the auxiliary power supply 4 and opens the switch 38.

[0041] When the main circuit unit 12 starts operating, the control device 16 first switches the circuit breaker 30 from the above state to the closed state (time t0 in FIG. 2).

[0042] When the circuit breaker 30 is switched from an open state to a closed state, power is supplied from the auxiliary power supply 4 to the initial charging circuit 14. The initial charging circuit 14 starts initial charging of the charge storage element 26 in response to the supply of power from the auxiliary power supply 4. At this time, by opening the switch 38, a current is supplied to the charge storage element 26 via the resistor 36, and the charge storage element 26 is gradually charged based on the current via the resistor 36 (times t0 to t1 in FIG. 2 ).

[0043] As the charge storage element 26 is gradually charged, the magnitude of the voltage across the charge storage element 26 gradually increases, and the magnitude of the AC current on the primary side of the transformer 32 and the magnitude of the output current of the conversion unit 34 gradually decrease.

[0044] When the magnitude of the voltage of the charge storage element 26 becomes equal to or greater than the threshold value, the control device 16 switches the switch 38 from the open state to the closed state (time t1 in FIG. 2). The control device 16, for example, acquires the magnitude of the voltage of the charge storage element 26 from a voltage detector (not shown). The control device 16 may also acquire the magnitude of the voltage of the charge storage element 26 from an external device such as a higher-level controller via communication. The method by which the control device 16 acquires the magnitude of the voltage of the charge storage element 26 is not limited to the above, and any method that can appropriately acquire the magnitude of the voltage of the charge storage element 26 may be used.

[0045] 2, when the switch 38 is switched from the open state to the closed state and a current is supplied to the charge storage element 26 through the switch 38 in a state of lower resistance, the magnitude of the current supplied to the charge storage element 26 (the magnitude of the AC current on the primary side of the transformer 32 and the magnitude of the output current of the conversion unit 34) temporarily rises. In addition, the slope of the rise in the magnitude of the voltage of the charge storage element 26 also temporarily increases.

[0046] For example, the control device 16 adjusts the timing of switching the switch 38 (the voltage threshold of the charge storage element 26) so that the magnitude of the current flowing through the initial charging circuit 14 and the charge storage element 26 remains within an allowable range even when the switch 38 is switched from an open state to a closed state. For example, the characteristics of other elements of the initial charging circuit 14, such as the resistance value and leakage inductance of the transformer 32, may be adjusted so that the magnitude of the current flowing through the initial charging circuit 14 and the charge storage element 26 remains within an allowable range even when the switch 38 is switched from an open state to a closed state.

[0047] After switching the switch 38 from an open state to a closed state, the control device 16 controls the operation of the converter 24 based on the detection result of the voltage detector 28 so as to generate a voltage on the AC side of the converter 24 that matches the phase and amplitude of the AC voltage of the power grid 2. In other words, the control device 16 controls the operation of the converter 24 so as to convert DC power to AC power based on the DC power stored in the charge storage element 26, and to generate a voltage on the AC side of the converter 24 that matches the phase and amplitude of the AC voltage of the power grid 2. The control device 16 controls the operation of the converter 24 as described above, thereby performing back excitation of the interconnection transformer 20.

[0048] The information on the phase and amplitude of the AC voltage of the power system 2 is not limited to the detection result of the voltage detector 28, but may be acquired via communication from an external device such as a higher-level controller. The method for acquiring the information on the phase and amplitude of the AC voltage of the power system 2 is not limited to the above, and any method that can appropriately acquire the information on the phase and amplitude of the AC voltage of the power system 2 may be used.

[0049] After performing back excitation of interconnection transformer 20, control device 16 switches circuit breaker 22 from an open state to a closed state. For example, control device 16 performs back excitation of interconnection transformer 20 for a predetermined time, and then switches circuit breaker 22 from an open state to a closed state. This makes it possible to prevent an excitation inrush current of interconnection transformer 20 from flowing into power grid 2 when circuit breaker 22 is closed.

[0050] For example, a voltage detector may be further provided that detects the magnitude of the AC voltage on the secondary side of the circuit breaker 22 (the AC voltage between the circuit breaker 22 and the interconnection transformer 20). For example, after performing back excitation of the interconnection transformer 20, the control device 16 may switch the circuit breaker 22 from the open state to the closed state after confirming that the phase and amplitude of the AC voltage on the secondary side of the circuit breaker 22 match the phase and amplitude of the AC voltage of the power grid 2 (the deviations of the phase and amplitude are equal to or less than predetermined values). This makes it possible to more appropriately prevent the magnetizing inrush current of the interconnection transformer 20 from flowing into the power grid 2 when the circuit breaker 22 is closed.

[0051] The control device 16 switches the circuit breaker 22 from an open state to a closed state, connects the main circuit unit 12 to the power grid 2, and then starts operation of the main circuit unit 12. In other words, after switching the circuit breaker 22 from an open state to a closed state, the control device 16 switches the operating state of the main circuit unit 12 from a state in which the interconnection transformer 20 is reversely excited to a state in which normal operation is performed.

[0052] As described above, in the power conversion device 10 according to this embodiment, the initial charging circuit 14 has the switch 38 connected in parallel with the resistor 36. In the power conversion device 10, when the main circuit unit 12 starts operating, the control device 16 opens the switch 38 to start initial charging of the charge storage element 26, and when the magnitude of the voltage of the charge storage element 26 becomes equal to or greater than a threshold, switches the switch 38 from the open state to the closed state. After switching the switch 38 to the closed state, the control device 16 controls the operation of the converter 24 so that a voltage whose phase and amplitude match those of the AC voltage of the power grid 2 is generated on the AC side of the converter 24, thereby performing back excitation of the interconnection transformer 20.

[0053] As a result, in the power conversion device 10 according to this embodiment, when the interconnection transformer 20 is reversely excited, the energy equivalent to the loss (for example, iron loss) of the interconnection transformer 20 can be supplied from the initial charging circuit 14.

[0054] For example, if the energy loss of the interconnection transformer 20 is to be supplied from the charge storage element 26, the charge storage element 26 will need to have sufficient capacity, which may result in an increase in the size of the device and manufacturing costs.

[0055] Furthermore, for example, if energy equivalent to the loss of the interconnection transformer 20 is supplied from an initial charging circuit that does not have a switch 38, there is a concern that the resistor 36 may overheat. The resistor 36 is designed to be large enough to perform initial charging of the charge storage element 26. Therefore, if the energy equivalent to the loss of the interconnection transformer 20 is supplied from the initial charging circuit and a current greater than the current required for initial charging of the charge storage element 26 flows through the resistor 36, the resistor 36 may overheat. For example, there is a concern that the resistor 36 may fail due to overheating. Furthermore, if the resistor 36 is designed to be able to supply energy equivalent to the loss of the interconnection transformer 20, it would be necessary to increase the capacity of the resistor 36 and the cooling mechanism for the resistor 36. This would complicate the configuration of the resistor 36 and the initial charging circuit, which could lead to an increase in the size of the device and an increase in manufacturing costs.

[0056] In the power conversion device 10 according to this embodiment, the energy loss of the interconnection transformer 20 can be supplied from the initial charging circuit 14 with a relatively simple configuration in which a switch 38 is provided in parallel with the resistor 36. Therefore, in the power conversion device 10 according to this embodiment, the back-excitation of the interconnection transformer 20 can be appropriately performed with a simpler configuration than when the energy loss of the interconnection transformer 20 is supplied from the charge storage element 26 or when the resistor 36 is designed to be able to supply the energy loss of the interconnection transformer 20. In the power conversion device 10 according to this embodiment, even when the energy loss of the interconnection transformer 20 is supplied from the initial charging circuit 14, an increase in the size of the device and an increase in manufacturing costs can be suppressed. Furthermore, by bypassing the resistor 36 during initial charging and increasing the current charging the charge storage element 26, the time required for initial charging can be shortened.

[0057] FIG. 3 is a block diagram schematically illustrating a modified example of the power conversion device according to the embodiment. 3, in the initial charging circuit 14a of the power conversion device 10a, the resistor 36 is replaced with a resistor 40, and the switch 38 is replaced with a switch 42. Note that parts that are substantially the same in function and configuration as those in the above embodiment are given the same reference numerals, and detailed description thereof will be omitted.

[0058] The resistor 40 is provided between the auxiliary power supply 4 and the conversion unit 34. The resistor 40 is provided, for example, between the transformer 32 and the conversion unit 34. The initial charging circuit 14a has, for example, three resistors 40 corresponding to the respective phases of the three-phase AC power supplied from the auxiliary power supply 4 to the conversion unit 34. This makes it possible to more appropriately prevent a current greater than or equal to a predetermined value from flowing through the initial charging circuit 14a and the charge storage element 26 during initial charging of the charge storage element 26.

[0059] The switch 42 is provided in parallel with the resistor 40. The switch 42 is provided in parallel with, for example, each of the three resistors 40. The switch 42 has, for example, three paths corresponding to each of the three resistors 40. When a plurality of resistors 40 (resistors 36) is provided, the switch 42 (switch 38) may have any configuration that can appropriately switch between a closed state in which both ends of each resistor 40 (resistors 36) are conductive and an open state in which both ends of each resistor 40 (resistors 36) are not conductive.

[0060] In this way, when the power supplied from the auxiliary power supply 4 is AC power, the current limiting resistor may be provided on the DC path between the conversion unit 34 and the charge storage element 26, as shown in Fig. 1, or on the AC path between the auxiliary power supply 4 and the conversion unit 34, as shown in Fig. 3. The resistor 40 may be provided, for example, between the circuit breaker 30 and the transformer 32. When the resistor 40 is provided on the AC path, the position at which the resistor 40 is provided is not limited to the above, and the resistor 40 may be provided at any position between the auxiliary power supply 4 and the conversion unit 34.

[0061] Furthermore, when the power supplied from the auxiliary power supply 4 is DC power, the resistor may be provided at any position between the auxiliary power supply 4 and the charge storage element 26 .

[0062] The present embodiment includes the following aspects. (Appendix 1) an interconnection transformer for interconnecting with an AC power system; a converter connected to the power grid via the interconnection transformer and to a DC circuit for converting DC power into AC power; a charge storage element provided on the DC side of the converter; a main circuit section having an initial charging circuit connected to the charge storage element and also connected to an auxiliary power supply, which supplies DC power to the charge storage element based on power supplied from the auxiliary power supply when the main circuit unit starts operating, thereby initially charging the charge storage element; a control device that controls the operation of the main circuit unit and the operation of the initial charging circuit; Equipped with The initial charging circuit a resistor provided between the auxiliary power supply and the charge storage element; a switch provided in parallel with the resistor, the switch having a closed state in which both ends of the resistor are electrically connected and an open state in which both ends of the resistor are not electrically connected; and When the main circuit unit starts operating, the control device sets the switch to the open state to start initial charging of the charge storage element, and when the voltage of the charge storage element becomes equal to or greater than a threshold value, switches the switch from the open state to the closed state, and after switching the switch to the closed state, controls the operation of the converter so that a voltage whose phase and amplitude match those of the AC voltage of the power grid is generated on the AC side of the converter, thereby performing back excitation of the interconnection transformer.

[0063] (Appendix 2) the power supplied from the auxiliary power supply to the initial charging circuit is AC power, the initial charging circuit has a conversion unit that converts AC power supplied from the auxiliary power supply into DC power corresponding to the charge storage element, 2. The power conversion device according to claim 1, wherein the resistor is provided between the conversion unit and the charge storage element.

[0064] (Appendix 3) The power conversion device according to Appendix 2, wherein the initial charging circuit has two resistors: the resistor provided between a high-potential terminal of the conversion unit and a high-potential terminal of the charge storage element; and the resistor provided between a low-potential terminal of the conversion unit and a low-potential terminal of the charge storage element.

[0065] (Appendix 4) the power supplied from the auxiliary power supply to the initial charging circuit is AC power, the initial charging circuit has a conversion unit that converts AC power supplied from the auxiliary power supply into DC power corresponding to the charge storage element, 2. The power conversion device according to claim 1, wherein the resistor is provided between the auxiliary power supply and the conversion unit.

[0066] (Appendix 5) the initial charging circuit has a transformer provided between the auxiliary power supply and the conversion unit, 5. The power conversion device according to claim 4, wherein the resistor is provided between the transformer and the conversion unit.

[0067] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0068] 2...power system, 4...auxiliary power supply, 10, 10a...power conversion device, 12...main circuit section, 14, 14a...initial charging circuit, 16...control device, 20...interconnection transformer, 22...circuit breaker, 24...converter, 26...charge storage element, 28...voltage detector, 30...circuit breaker, 32...transformer, 34...conversion section, 36...resistor, 38...switch, 40...resistor, 42...switch

Claims

1. an interconnection transformer for interconnecting with an AC power system; a converter connected to the power grid via the interconnection transformer and to a DC circuit for converting DC power into AC power; a charge storage element provided on the DC side of the converter; a main circuit section having an initial charging circuit connected to the charge storage element and also connected to an auxiliary power supply, which supplies DC power to the charge storage element based on power supplied from the auxiliary power supply when the main circuit unit starts operating, thereby initially charging the charge storage element; a control device that controls the operation of the main circuit unit and the operation of the initial charging circuit; Equipped with The initial charging circuit a resistor provided between the auxiliary power supply and the charge storage element; a switch provided in parallel with the resistor, the switch having a closed state in which both ends of the resistor are electrically connected and an open state in which both ends of the resistor are not electrically connected; and When the main circuit unit starts operating, the control device sets the switch to the open state to start initial charging of the charge storage element, and when the voltage of the charge storage element becomes equal to or greater than a threshold value, switches the switch from the open state to the closed state, and after switching the switch to the closed state, controls the operation of the converter so that a voltage whose phase and amplitude match those of the AC voltage of the power grid is generated on the AC side of the converter, thereby performing back excitation of the interconnection transformer.

2. the power supplied from the auxiliary power supply to the initial charging circuit is AC power, the initial charging circuit has a conversion unit that converts AC power supplied from the auxiliary power supply into DC power corresponding to the charge storage element, The power conversion device according to claim 1 , wherein the resistor is provided between the conversion section and the charge storage element.

3. 3. The power conversion device according to claim 2, wherein the initial charging circuit has two resistors: the resistor provided between the high-potential terminal of the conversion unit and the high-potential terminal of the charge storage element, and the resistor provided between the low-potential terminal of the conversion unit and the low-potential terminal of the charge storage element.

4. the power supplied from the auxiliary power supply to the initial charging circuit is AC power, the initial charging circuit has a conversion unit that converts AC power supplied from the auxiliary power supply into DC power corresponding to the charge storage element, The power conversion device according to claim 1 , wherein the resistor is provided between the auxiliary power supply and the conversion unit.

5. the initial charging circuit has a transformer provided between the auxiliary power supply and the conversion unit, The power conversion device according to claim 4 , wherein the resistor is provided between the transformer and the conversion unit.

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