Power conversion system and power conversion device

Abstract

The present invention provides a power conversion system and power conversion device that can disconnect the power conversion unit from the power system without causing the transformer to become DC biased, even when an abnormality occurs at the connection point between the power conversion unit and the power system. [Solution] This power conversion system 100 includes a power conversion unit that converts DC power to AC power and outputs it, which includes a capacitor for smoothing the output; a control unit that controls the power conversion unit; and predetermined electrical components to which the output of the power conversion unit, which has been transformed by a transformer, is supplied. When the control unit detects an abnormality at the connection point where the power system and the power conversion unit are connected, it performs control to start a soft stop process that gradually stops the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer.

Description

Technical Field

[0001] The present invention relates to a power conversion system and a power conversion device, and particularly to a power conversion system and a power conversion device that perform intertie operation with a power system.

Background Art

[0002] Conventionally, an intertie inverter (power conversion system) that performs intertie operation with a power system has been known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an intertie inverter that converts DC power output from a solar cell into AC power and is interconnected with a commercial power system. The intertie inverter of Patent Document 1 includes a control circuit that controls an inverter unit drive circuit that drives the inverter unit. This control circuit detects the voltage of a voltage line between the inverter unit and the commercial power system via an isolation transformer connected to the voltage line between the inverter unit and the commercial power system.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, in the grid-connected inverter of Patent Document 1, the control circuit detects the voltage of the voltage line between the inverter unit and the commercial grid power supply via an isolation transformer connected to the voltage line between the inverter unit and the commercial grid power supply. Here, although not described in Patent Document 1, in such a grid-connected inverter, a capacitor for smoothing the output rectangular voltage may be provided on the output side of the inverter unit. In this case, if an abnormality occurs at the connection point between the inverter unit and the commercial grid power supply, immediately disconnecting the connection between the inverter unit (power conversion unit) and the commercial grid power supply (power system) may cause the isolation transformer to undergo DC bias due to the charge accumulated in the capacitor. This generates a large current in the isolation transformer. As a result, a large current may flow to the control circuit (electrical equipment) connected to the isolation transformer, which may cause the electrical equipment to malfunction. Therefore, there is a need for a power conversion system and power conversion device that can disconnect the connection between the power conversion unit and the power system without causing DC bias in the transformer, even when an abnormality occurs at the connection point between the power conversion unit and the power system.

[0006] This invention was made to solve the above-mentioned problems, and one objective of this invention is to provide a power conversion system and power conversion device that can disconnect the connection between the power conversion unit and the power system without causing the transformer to become DC biased, even when an abnormality occurs at the connection point between the power conversion unit and the power system. [Means for solving the problem]

[0007] To achieve the above objective, the power conversion system according to the first aspect of this invention is a power conversion system that operates in conjunction with a power grid, and comprises a power conversion unit that converts DC power to AC power and outputs it, which includes a capacitor for smoothing the output, a control unit that controls the power conversion unit, and predetermined electrical components to which the output of the power conversion unit, which has been transformed by a transformer, is supplied, wherein when the control unit detects an abnormality at the connection point where the power grid and the power conversion unit are connected, it performs control to start a soft stop process that gradually stops the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer.

[0008] In the power conversion system according to the first phase described above, the control unit, when it detects an abnormality at the connection point where the power system and the power conversion unit are connected, performs a soft stop process to gradually stop the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer. As a result, when an abnormality is detected at the connection point where the power system and the power conversion unit are connected, the output of the power conversion unit is gradually stopped, so that the charge stored in the capacitor is gradually released and the charge stored in the capacitor can be reduced to zero. Therefore, it is possible to suppress the supply of DC current caused by the charge stored in the capacitor to the transformer after the operation of the power conversion unit has stopped. As a result, even when an abnormality occurs at the connection point between the power conversion unit and the power system, the connection between the power conversion unit and the power system can be disconnected without DC biasing the transformer.

[0009] In the power conversion system according to the first phase described above, preferably, the control unit is configured to perform different controls depending on whether the abnormality at the connection point is a system open-circuit power outage condition where the connection between the power system and the power conversion unit is interrupted, or a system overvoltage condition where the power system is overvoltage, after the start of the soft stop process. With this configuration, appropriate control can be performed according to the type of abnormality at the connection point.

[0010] In this case, preferably, the control unit is configured to distinguish, after the start of the soft stop process, whether the abnormality at the connection point is a system open-circuit power outage condition or a system overvoltage condition, based on the current at the connection point. With this configuration, it is possible to easily distinguish between a system open-circuit power outage condition and a system overvoltage condition based on the current at a single location, the connection point.

[0011] In a power conversion system where the control unit performs different controls, preferably, the control unit is configured to perform control when an abnormality at the connection point is a grid open-circuit power outage based on a decrease in current at the connection point, and to perform control when an abnormality at the connection point is a grid overvoltage based on an increase in current at the connection point. With this configuration, different controls can be easily performed depending on whether it is a grid open-circuit power outage between the power system and the power conversion unit or a power system overvoltage, using the easily identifiable indicator of current increase or decrease.

[0012] In a power conversion system where the control unit performs different control functions, preferably, the control unit is configured to continue soft-stop processing until the output of the power conversion unit becomes zero if the abnormality at the connection point is a grid-opening power outage condition. With this configuration, the soft-stop processing continues until the output of the power conversion unit becomes zero, so that the charge stored in the capacitor included in the power conversion unit is gradually released from the capacitor until the charge in the capacitor becomes zero. As a result, it is possible to suppress the output of charge from the capacitor included in the power conversion unit to the transformer after the operation of the power conversion unit has stopped.

[0013] In a power conversion system where the control unit performs different control as described above, preferably, the control unit is configured to interrupt the soft stop process of the power conversion unit before the completion of the soft stop process and stop the operation of the power conversion unit if the abnormality at the connection point is a system overvoltage condition. Here, when the abnormality at the connection point is a system overvoltage condition, unlike in the case of an open-circuit power outage, the power conversion unit remains connected to the power system, and AC power is supplied to the connection point. That is, when the abnormality at the connection point is an overvoltage in the power system, an AC voltage continues to be applied to the capacitor, so DC power is not accumulated in the capacitor and supplied to the transformer. Therefore, with the above configuration, the operation of the power conversion unit can be terminated without waiting for the completion of the soft stop process. As a result, it is possible to suppress the flow of overcurrent in the power conversion unit due to connection to an overvoltage power system.

[0014] In a power conversion system in which the control unit controls the continuation of the soft stop process, or in a power conversion system in which the control unit controls the interruption of the soft stop process and stops the operation of the power conversion unit, preferably, the system further includes a circuit breaker for disconnecting the connection to the power grid, and the control unit controls the circuit breaker to disconnect the connection to the power grid after the completion of the soft stop process, or after the soft stop process is interrupted and the operation of the power conversion unit is stopped. With this configuration, the connection between the power conversion unit and the power grid can be released by the circuit breaker after the risk of DC biasing of the transformer has been eliminated, such as after the completion of the soft stop process, or after the soft stop process is interrupted and the operation of the power conversion unit is stopped.

[0015] In the power conversion system according to the first aspect described above, preferably, the electrical components include a power supply, and the control unit is configured to be powered by the power supply. With this configuration, the control unit is powered by the power supply, which is an electrical component connected to a transformer, so that the power supply can be used while suppressing failure of the power supply.

[0016] In the power conversion system according to the first aspect described above, preferably, a fuse as an electrical component is further provided between the transformer and the control unit. With this configuration, even if an abnormality is detected at the connection point, a large current will not flow to the transformer, thus preventing the fuse from blowing (melting). As a result, the number of times the fuse needs to be replaced can be reduced.

[0017] Furthermore, in order to achieve the above objective, the power conversion device according to the second aspect of this invention is a power conversion device that operates in conjunction with a power grid, and comprises a power conversion unit that includes a capacitor for smoothing the output and converts DC power to AC power for output, a control unit that controls the power conversion unit, and predetermined electrical components to which the output of the power conversion unit, which has been transformed by a transformer, is supplied, and the control unit, when it detects an abnormality at the connection point where the power grid and the power conversion unit are connected, performs control to start a soft stop process that gradually stops the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer.

[0018] In the power conversion device according to the second phase described above, the control unit, when it detects an abnormality at the connection point where the power system and the power conversion unit are connected, performs a soft-stop process to gradually stop the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer. As a result, when an abnormality is detected at the connection point where the power system and the power conversion unit are connected, the output of the power conversion unit is gradually stopped, so the charge stored in the capacitor is gradually released and reduced. Therefore, it is possible to suppress the supply of DC current caused by the charge stored in the capacitor to the transformer after the operation of the power conversion unit has stopped. As a result, it is possible to provide a power conversion device that can disconnect the connection between the power conversion unit and the power system without DC biasing the transformer, even when an abnormality occurs at the connection point between the power conversion unit and the power system. [Effects of the Invention]

[0019] According to the present invention, as described above, even when an abnormality occurs at the connection point between the power conversion unit and the power system, it is possible to provide a power conversion system and a power conversion device that can disconnect the connection between the power conversion unit and the power system without causing DC bias in the transformer.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a diagram showing the circuit configuration of a power conversion system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the voltage waveform when immediately gate-blocking the power conversion unit in the power conversion system according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram for explaining the voltage waveform when soft-stopping the power conversion unit in the power conversion system according to an embodiment of the present invention. [Figure 4] FIG. 4 is a flowchart when the power conversion unit shifts to the standby state in the power conversion system according to an embodiment. [Figure 5] FIG. 5 is a diagram for explaining the operation of the control unit when the power conversion unit shifts to the standby state in the power conversion system according to an embodiment. [Figure 6] FIG. 6 is a diagram showing the circuit configuration of a power conversion system according to a modification of an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments embodying the present invention will be described based on the drawings.

[0022] (Overall Configuration of Power Conversion System) First, referring to FIG. 1, the overall configuration of a power conversion system 100 according to an embodiment of the present invention will be described.

[0023] As shown in Figure 1, the power conversion system 100 comprises a power conversion unit 10, a control unit 20, a transformer 40, a fuse 50, a power supply 60, a converter 70, and a sensor 80. The power conversion unit 10 and the control unit 20 constitute a power conversion device 101. The power conversion system 100 is connected to an externally provided energy storage unit 30 and a power grid 200 managed by a power company, and is configured to operate in conjunction with the power of the power grid 200. The fuse 50 and the power supply 60 are examples of "electrical components" in the claims.

[0024] The power conversion unit 10 is, for example, a PCS (Power Conditioning System) and includes a power conversion circuit 10a that functions as a converter for converting AC power to DC power and an inverter for converting DC power to AC power. As a result, the power conversion unit 10 can convert AC power supplied by the power system 200 into DC power and output it to the energy storage unit 30, and can also convert DC power supplied from the energy storage unit 30 into AC power and output it to a load (not shown) and the power system 200. In other words, the power conversion circuit 10a supplies power in both directions.

[0025] Furthermore, the power conversion unit 10 includes an inductor 10b and a capacitor 10c for smoothing the AC power output by the power conversion circuit 10a to the power system 200. As a result, the rectangular pulse wave output from the power conversion circuit 10a is smoothed into a sine wave by the LC filter circuit consisting of the inductor 10b and the capacitor 10c. In other words, an AC sine wave is output from the power conversion circuit 10a to the power system 200. Note that the capacitor 10c may be connected to, for example, GND or a virtual neutral point (not shown).

[0026] The control unit 20 controls the operation of switching elements (not shown) included in the power conversion circuit 10a of the power conversion unit 10, and controls the AC power output from the power conversion circuit 10a to the power system 200. The control unit 20 includes a CPU (Central Processing Unit) as a processor and a storage unit such as a memory having ROM (Read Only Memory) and RAM (Random Access Memory). Details regarding the control of the power conversion unit 10 (power conversion circuit 10a) performed by the control unit 20 will be described later.

[0027] The transformer 40 is installed on the output line connecting the power system 200 and the power conversion circuit 10a, and steps down the voltage applied to the output line. In this embodiment, for example, the voltage supplied by the power system 200 is 6600V, and the voltage transformed by the transformer 40 is 200V. The transformer 40 is also connected to the power supply 60 via a fuse 50.

[0028] The fuse 50 is located in the wiring connecting the transformer 40 and the power supply 60. The output voltage of the power conversion unit 10, which has been transformed by the transformer 40, is applied to the fuse, causing current to flow. The fuse 50 is an electrical component that blows when the voltage or current supplied from the transformer 40 exceeds a predetermined value, electrically disconnecting the transformer 40 and the power supply 60. The fuse 50 is a replaceable consumable part.

[0029] The power supply 60 is an electrical device that supplies power to devices not shown, such as fans and dehumidifier power supplies, and to the control unit 20. The power supply 60 is supplied with the output of the power conversion unit 10, which has been transformed by the transformer 40. The power supply 60 is configured to supply power of a capacity corresponding to the power capacity required for the operation of the control unit 20.

[0030] The converter 70 includes multiple switching elements and converts the power output from the power supply 60 into power suitable for the operation of the control unit 20. In this embodiment, for example, the converter 70 converts the voltage output from the power supply 60 into 24V DC, which is suitable power for the operation of the control unit 20.

[0031] Sensor 80 is installed at the connection point P of the output line connecting the power system 200 and the power conversion circuit 10a, and has the function of detecting the voltage applied to connection point P and the function of detecting the current flowing through the output line. Sensor 80 detects the voltage and current of the output line every 0.1 ms, for example. The voltage and current values ​​detected by sensor 80 are transmitted to the control unit 20 via a signal line. The control unit 20 issues control commands to the power conversion circuit 10a based on the voltage and current detected by sensor 80.

[0032] In the power conversion system 100, a system-side circuit breaker 90a is provided on the output line connecting the power grid 200 and the power conversion circuit 10a. Furthermore, a storage unit-side circuit breaker 90b is provided on the input line connecting the energy storage unit 30 and the power conversion circuit 10a. The opening and closing operations of the system-side circuit breaker 90a and the storage unit-side circuit breaker 90b are controlled by the control unit 20.

[0033] The energy storage unit 30 connected to the power conversion system 100 is a secondary battery capable of charging and discharging DC power. For example, the energy storage unit 30 is a lithium-ion secondary battery. In grid-connected operation, where the power system 200 and the power conversion unit 10 operate in conjunction, the energy storage unit 30 charges with power supplied from the power system 200 and converted to DC by the power conversion unit 10. Furthermore, when the amount of power required by a load (not shown) increases in grid-connected operation, the energy storage unit 30 discharges power to supply DC power to the power conversion unit 10 as needed.

[0034] (Stop operation of the power conversion unit) Next, using Figures 1 to 5, we will explain the operation in which the power conversion unit 10 stops outputting when it is discharging from the power conversion unit 10 to the power system 200 in the power conversion system 100 of this embodiment.

[0035] First, we will explain the difference between the case where the power conversion unit 10 (see Figure 1) is controlled by the control unit 20 (see Figure 1) and performs gate block processing to immediately stop the output voltage, and the case where it performs soft stop processing to gradually stop the output voltage. Here, Figures 2 and 3 show the output voltage waveforms of the power conversion unit 10.

[0036] As shown in Figure 2, the power conversion unit 10 (see Figure 1) is controlled by the control unit 20 (see Figure 1) to output an AC voltage with amplitude V1 (V) until time t1. Now, suppose that at time t1, the power conversion unit 10 receives a gate block signal from the control unit 20 to stop the output. In this case, the power conversion unit 10 is controlled to immediately stop the switching operation of a switching element (not shown). That is, the output of the power conversion unit 10 immediately becomes 0V due to the gate block process and enters a standby state.

[0037] Next, as shown in Figure 3, the power conversion unit 10 (see Figure 1) is controlled by the control unit 20 (see Figure 1) to output an AC voltage with amplitude V1 (V) until time t11. Now, suppose that at time t11, the power conversion unit 10 receives a soft stop processing signal from the control unit 20 to stop the output. In this case, the power conversion unit 10 controls the switching operation of a switching element (not shown) to gradually reduce the output. For example, after the soft stop processing signal is input, at time t12, which is one cycle later of the AC waveform, the amplitude of the output voltage becomes V2 (V), which is smaller than V1 (V). As described above, the output voltage of the power conversion unit 10 gradually decreases and becomes 0V at time t13, entering a standby state. The time between time t11 and time t13 is, for example, 200ms.

[0038] (Stoppage of the power conversion unit due to a connection point abnormality) Here, we will explain the case in which the control unit 20 (see Figure 1) performs gate blocking processing as shown in Figure 2 when an abnormality is detected at connection point P. In this embodiment, for example, a state in which the connection between the power system 200 and the power conversion unit 10 (power conversion system 100) is interrupted due to a cause on the power system side (such as an accident) is defined as a system open-circuit power outage state, and we will explain the system open-circuit power outage state.

[0039] In a power outage with an open grid, the power grid 200 and the power conversion system 100 are disconnected, so there is no current path, and the current at connection point P decreases. However, as charge accumulates in capacitor 10c, the voltage at connection point P increases. At this time, the control unit 20 detects that an abnormality called instantaneous overvoltage has occurred at connection point P based on the sensor 80 indicating that the voltage at connection point P has exceeded a preset threshold.

[0040] When the control unit 20 detects an instantaneous overvoltage from the sensor 80, the control unit 20 transmits a gate block signal to the power conversion unit 10 and a trip (open) signal to the grid-side circuit breaker 90a. However, there may be a time lag between the gate block processing, which is performed instantaneously, and the trip (open) processing of the grid-side circuit breaker 90a, which physically interrupts the circuit. As a result, there may be a gap in time in which only the operation of the power conversion unit 10 is completed, and the grid-side circuit breaker 90a is not yet tripped (opened).

[0041] During this gap, the charge released from capacitor 10c causes DC bias in transformer 40, significantly reducing its excitation impedance. Consequently, a very large current flows through transformer 40. In this case, the fuse 50 located between transformer 40 and power supply 60 may blow (melt), rendering the control unit 20 inoperable. Therefore, in this embodiment, the control unit 20 performs the control shown in Figure 4 to protect the fuse 50 while stopping the operation of the power conversion system 100.

[0042] As shown in step S1 of Figure 4, first, the control unit 20 detects that the connection point P (see Figure 1) is experiencing an instantaneous overvoltage based on the voltage detected by the sensor 80. Then, the process proceeds to step S2.

[0043] Next, as shown in step S2 of Figure 4, the control unit 20 starts a soft-stop process for the output of the power conversion unit 10 so that the transformer 40 is not DC-biased by the capacitor 10c. The control unit 20 continuously detects the voltage and current at the connection point P detected by the sensor 80. After that, the process proceeds to step S3.

[0044] Then, as shown in step S3 of Figure 4, the control unit 20 checks whether the current at connection point P is decreasing. Here, in the case of a system open-out power outage state where the power system 200 (see Figure 1) is open, the current at connection point P decreases. Also, in the case of a system overvoltage state where the power conversion unit 10 and the power system 200 are not open, the current at connection point P increases because the power conversion unit 10 and the power system 200 are connected. In this way, the control unit 20 distinguishes whether the abnormality at connection point P is a system open-out power outage state or a system overvoltage state of the power system 200. If the current at connection point P is decreasing, the process proceeds to step S4, and if the current at connection point P is increasing, the process proceeds to step S5. In other words, the control unit 20 is configured to perform different control depending on whether the abnormality at connection point P is a system open-out power outage state or a system overvoltage state.

[0045] Step S4 will now be described. The control unit 20 continues the soft stop process of the power conversion unit 10 while continuously detecting the voltage and current at connection point P detected by the sensor 80. If the soft stop process is not yet complete, the control unit returns to step S3 to check if the current at connection point P has decreased. If the soft stop process is complete, the process proceeds to step S5. In this embodiment, the time required for the soft stop process to be completed is determined by the soft stop process time constant, and once that time has elapsed, the output of the power conversion unit 10 becomes zero, and the soft stop process is considered to be complete.

[0046] Step S5 will now be described. In step S5, the control unit 20 performs standby processing for the power conversion system 100. Specifically, the control unit 20 terminates the operation of the power conversion unit 10 and issues a command to turn off the system-side circuit breaker 90a, thereby disconnecting the power conversion unit 10 from the power system 200.

[0047] Here, if the current at connection point P has not decreased in step S3 and the process proceeds to step S5, the power conversion unit 10 and the power system 200 are not disconnected, so AC power is supplied to connection point P, and even if the system transitions to standby mode, DC bias will not occur in the transformer 40. For this reason, when the control unit 20 detects that the current at connection point P has not decreased, it interrupts the soft stop process, executes a gate block process that immediately reduces the output of the power conversion unit 10 to zero, and issues a command to turn off the system-side circuit breaker 90a and disconnect the connection between the power conversion unit 10 and the power system 200.

[0048] Furthermore, if the process proceeds to step S5 after the soft stop process is completed in step S4, the charge discharge in the capacitor 10c of the power conversion unit 10 is complete. Therefore, even if the system transitions to a standby state, DC bias does not occur in the transformer 40, and no large current flows. In other words, the power conversion system 100 is stopped while protecting the fuse 50.

[0049] (Control of the power conversion unit's shutdown operation by the control unit) Here, the control unit 20 includes a plurality of logic circuits as shown in Figure 5. Specifically, the control unit 20 includes a flip-flop circuit 20a, an AND circuit 20b, an AND circuit 20c, a flip-flop circuit 20d, and an OR circuit 20e.

[0050] The flip-flop circuit 20a includes a set input terminal (S), a reset input terminal (R), and an output terminal (Q). The flip-flop circuit 20a inputs and outputs a high-level signal "1" or a low-level signal "0". For example, when an input signal "1" is input to the set input terminal, the flip-flop circuit 20a outputs an output signal "1" from its output terminal. Also, when an input signal "1" is input to the reset input terminal, the flip-flop circuit 20a outputs an output signal "0" from its output terminal. Furthermore, when an input signal "1" is input to both the set input terminal and the reset input terminal, the flip-flop circuit 20a outputs an output signal "1" from its output terminal. Note that when an input signal "0" is input to both the set input terminal and the reset input terminal, the output terminal continues to output the current output signal.

[0051] For example, as in step S1 of the flowchart shown in Figure 4, if an overvoltage is detected at connection point P (see Figure 1) while the power conversion unit 10 is operating, i.e., not in a stopped state, an input signal "1" is sent to the set input terminal of the flip-flop circuit 20a in Figure 5. Consequently, an output signal "1" is output from the flip-flop circuit 20a, the soft stop process is initiated, and an input signal "1" is input to one input terminal of the AND circuit 20b. The AND circuit 20b outputs an output signal "0" until the voltage output by the power conversion unit 10 becomes zero.

[0052] Furthermore, when the soft stop process is initiated, an input signal "1" is input to one input terminal of the AND circuit 20c. At this point, as shown in step S3 of the flowchart in Figure 4, the control unit 20 detects whether the current at connection point P is increasing or not. For example, if the current at connection point P is decreasing, an input signal "0" is input to the other input terminal of the AND circuit 20c. As a result, an output signal "0" is output from the AND circuit 20c, and the flip-flop circuit 20d also outputs an output signal "0".

[0053] As described above, even when the current at connection point P decreases, the control unit 20 checks whether the soft stop process is complete or not. After a predetermined time has elapsed and the soft stop process is deemed complete, the output of the power conversion unit 10 is stopped, and an input signal "1" is input to the other input terminals of the AND circuit 20b. As a result, the AND circuit 20b outputs an output signal "1". Therefore, a signal of "1" is input to the OR circuit 20e, and a command is issued to transition to the standby state. That is, as shown in step S4 of Figure 4, the system transitions to the standby state.

[0054] Furthermore, when the current at connection point P increases, an input signal "1" is input to the other input terminal of the AND circuit 20c. As a result, the AND circuit 20c outputs an output signal "1", and the flip-flop circuit 20d also outputs an output signal "1". Consequently, a signal of "1" is input to the OR circuit 20e, and a command is issued to transition to the standby state. That is, as shown in steps S3 and S5 of Figure 4, the system transitions to the standby state.

[0055] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0056] In this embodiment, the power conversion system 100 (power converter 101) that operates in grid-connected operation with the power system 200 includes a power conversion unit 10 that converts DC power to AC power and outputs it, which includes a capacitor 10c that smooths the output, a control unit 20 that controls the power conversion unit 10, and a power supply 60 and a fuse 50 as predetermined electrical components to which the output of the power conversion unit 10 transformed by the transformer 40 is supplied. When the control unit 20 detects an abnormality at the connection point P where the power system 200 and the power conversion unit 10 are connected, it performs control to start a soft stop process that gradually stops the output of the power conversion unit 10 so that the DC power stored in the capacitor 10c is not supplied to the transformer 40. As a result, when an abnormality is detected at the connection point P where the power system 200 and the power conversion unit 10 are connected, the output of the power conversion unit 10 is gradually stopped, so that the charge stored in the capacitor 10c is gradually released and the charge stored in the capacitor 10c can be reduced to zero. Therefore, after the operation of the power conversion unit 10 stops, it is possible to suppress the supply of a DC current to the transformer 40 due to the charge accumulated in the capacitor 10c. As a result, even if an abnormality occurs at the connection point P between the power conversion unit 10 and the power system 200, the connection between the power conversion unit 10 and the power system 200 can be disconnected without causing DC bias in the transformer 40.

[0057] Furthermore, in this embodiment, as described above, the control unit 20 is configured to perform different controls depending on whether the abnormality at connection point P is a system open-circuit power outage state where the connection between the power system 200 and the power conversion unit 10 is interrupted, or a system overvoltage state where the power system 200 is overvoltage, after the start of the soft stop process. This allows for appropriate control depending on the type of abnormality at connection point P.

[0058] Furthermore, in this embodiment, as described above, the control unit 20 is configured to distinguish, based on the current at connection point P, whether the abnormality at connection point P is a system open-circuit power outage or a system overvoltage state after the start of the soft stop process. This makes it easy to distinguish between a system open-circuit power outage between the power system 200 and the power conversion unit 10 and an overvoltage in the power system 200 based on the current at a single location, connection point P.

[0059] Furthermore, in this embodiment, as described above, the control unit 20 is configured to perform control when the abnormality at connection point P is an open-circuit power outage between the power system 200 and the power conversion unit 10, based on a decrease in the current at connection point P, and to perform control when the abnormality at connection point P is a system overvoltage condition, based on an increase in the current at connection point P. This makes it easy to perform different controls depending on whether the power system 200 is open-circuit power outage or overvoltage in the power system 200, using the easily identifiable indicator of current increase or decrease.

[0060] Furthermore, in this embodiment, as described above, the control unit 20 is configured to continue the soft stop process until a sufficient amount of time has elapsed for the output of the power conversion unit 10 to become zero, in the event that the abnormality at connection point P is a grid-opening power outage state. As a result, the soft stop process continues until the output of the power conversion unit 10 becomes zero, and charge is gradually released from the capacitor 10c included in the power conversion unit 10 until the charge accumulated in the capacitor 10c is zero. Consequently, it is possible to suppress the output of charge from the capacitor 10c included in the power conversion unit 10 to the transformer 40 after the operation of the power conversion unit 10 has stopped.

[0061] Furthermore, in this embodiment, as described above, the control unit 20 is configured to interrupt the soft stop processing of the power conversion unit 10 before the completion of the soft stop processing and stop the operation of the power conversion unit 10 if the abnormality at connection point P is a system overvoltage state. Here, unlike the open-circuit blackout state, if the abnormality at connection point P is a system overvoltage state, the power conversion unit 10 remains connected to the power system 200, and AC power is supplied to connection point P. In other words, if the abnormality at connection point P is an overvoltage in the power system 200, an AC voltage continues to be applied to the capacitor 10c, so DC power is not accumulated in the capacitor 10c and supplied to the transformer 40. Therefore, with the above configuration, the operation of the power conversion unit 10 can be terminated without waiting for the completion of the soft stop processing. As a result, it is possible to suppress the flow of overcurrent to the power conversion unit 10 due to connection to the overvoltage power system 200.

[0062] Furthermore, in this embodiment, as described above, a system-side circuit breaker 90a is provided to disconnect the connection to the power system 200. The control unit 20 controls the system-side circuit breaker 90a to disconnect the connection to the power system 200 after the completion of the soft stop process, or after the soft stop process is interrupted and the operation of the power conversion unit 10 is stopped. This allows the connection between the power conversion unit 10 and the power system 200 to be released by the system-side circuit breaker 90a after there is no longer a risk of DC biasing of the transformer 40, such as after the completion of the soft stop process, or after the soft stop process is interrupted and the operation of the power conversion unit 10 is stopped.

[0063] Furthermore, in this embodiment, as described above, the electrical components include a power supply 60, and the control unit 20 is configured to be powered by the power supply 60. As a result, the control unit 20 is powered by the power supply 60, which is an electrical component connected to the transformer 40, and thus it is possible to suppress failure of the power supply 60 while utilizing the power supplied via the transformer 40.

[0064] Furthermore, in this embodiment, as described above, a fuse 50, which is an electrical component, is provided between the transformer 40 and the power conversion unit 10. Even if an abnormality is detected at the connection point P, a large current will not flow to the transformer 40, thus preventing the fuse 50 from blowing (melting). As a result, the number of times the fuse 50 needs to be replaced can be reduced.

[0065] [Differentiation] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the description of the embodiments above, and further includes all modifications (modifications) within the meaning and scope equivalent to the claims.

[0066] Furthermore, in the above embodiment, the control unit 20 is configured to distinguish, based on the current at connection point P, whether the abnormality at connection point P is an open-circuit power outage between the power system 200 and the power conversion unit 10, or an overvoltage in the power system 200, after the start of the soft stop process. However, the present invention is not limited to this. In the present invention, for example, the control unit 20 may be configured to distinguish, based on the power at connection point P, whether the abnormality at connection point P is an open-circuit power outage or a system overvoltage.

[0067] Furthermore, in the above embodiment, the control unit 20 is configured to perform control when the abnormality at connection point P is an open-circuit power outage between the power system 200 and the power conversion unit 10, based on a decrease in the current at connection point P, and to perform control when the abnormality at connection point P is an overvoltage in the power system 200, based on an increase in the current at connection point P. However, the present invention is not limited to this. In the present invention, for example, the control unit 20 may be configured to perform control when the abnormality at connection point P is an open-circuit power outage, based on a decrease in the power at connection point P, and to perform control when the abnormality at connection point P is a system overvoltage, based on an increase in the power at connection point P.

[0068] Furthermore, in the above embodiment, the control unit 20 is configured to continue the soft stop process until a time has elapsed that the output of the power conversion unit 10 becomes zero, in the event that the abnormality at connection point P is an open-circuit power outage between the power system 200 and the power conversion unit 10. However, the present invention is not limited to this. In the present invention, for example, even if the output of the power conversion unit 10 does not become zero, the soft stop process only needs to continue until the charge accumulated in the capacitor 10c becomes zero.

[0069] Furthermore, although the above embodiment shows an example in which the electrical components include a power supply 60 and the control unit 20 is configured to receive power from the power supply 60, the present invention is not limited to this. In the present invention, the power supply 60 may not be included as an electrical component, and the control unit 20 may be connected to a power supply that is not connected to the transformer 40.

[0070] Furthermore, although the above embodiment shows an example further comprising a fuse 50 as an electrical component provided between the transformer 40 and the control unit 20, the present invention is not limited thereto. In the present invention, the transformer 40 and the control unit 20 may be directly connected without a fuse 50.

[0071] Furthermore, although the above embodiment shows an example in which a power supply 60 and a fuse 50 are connected to the transformer 40 as electrical components, the present invention is not limited to this. In the present invention, any electrical component may be connected to the transformer 40. For example, a cooling fan or a power supply for a heat exchanger may be connected to the transformer 40.

[0072] Furthermore, although the above embodiment shows an example in which the control unit 20 controls the operation of one power conversion unit 10, the present invention is not limited thereto. In the present invention, for example, as shown in the modified example of Figure 6, the power conversion system 100a may be configured to include two power conversion units 10 connected in parallel, and one control unit 20 may control the operation of multiple power conversion units 10. Alternatively, the control unit 20 may be configured to control the operation of three or more power conversion units 10 connected in parallel.

[0073] Furthermore, although the above embodiment shows an example in which the power conversion system 100 is connected to the energy storage unit 30, the present invention is not limited to this. In the present invention, instead of the energy storage unit 30, another device that supplies DC power to the power conversion unit 10, such as a solar power generation system or a wind power generation system, may be connected. [Explanation of Symbols]

[0074] 10 Power conversion unit 10A power conversion circuit 10c capacitor 20 Control Unit 30 Energy storage unit 40 transformers 50 Fuses (electrical components) 60 Power supply (electrical components) 80 sensors 90a System-side circuit breaker 100V, 100A power conversion system 101 Power converter 200 Power system P connection point

Claims

1. A power conversion system that operates in conjunction with the power grid, A power conversion unit that includes a capacitor to smooth the output and converts DC power to AC power for output, A control unit that controls the power conversion unit, The system comprises a predetermined electrical component to which the output of the power conversion unit, which has been transformed by a transformer, is supplied, A power conversion system in which, when the control unit detects an abnormality at the connection point where the power system and the power conversion unit are connected, the control unit initiates a soft stop process to gradually stop the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer.

2. The power conversion system according to claim 1, wherein the control unit is configured to perform different controls after the start of the soft stop process depending on whether the abnormality at the connection point is a system open-circuit power outage state in which the connection between the power system and the power conversion unit is interrupted, or a system overvoltage state in which the power system is overvoltage.

3. The power conversion system according to claim 2, wherein the control unit is configured to distinguish, after the start of the soft stop process, whether the abnormality at the connection point is the system open power outage state or the system overvoltage state, based on the current at the connection point.

4. The control unit, Based on the decrease in current at the connection point, control is performed when the abnormality at the connection point is the same as the system open-circuit power outage condition. The power conversion system according to claim 2, configured to perform control when an abnormality at the connection point is a system overvoltage condition, based on an increase in the current at the connection point.

5. The power conversion system according to claim 2, wherein the control unit is configured to continue the soft stop process until the output of the power conversion unit becomes zero if the abnormality at the connection point is the same as the open power outage state.

6. The power conversion system according to claim 2, wherein the control unit is configured to interrupt the soft stop process of the power conversion unit before the completion of the soft stop process and stop the operation of the power conversion unit if the abnormality at the connection point is the system overvoltage condition.

7. The system further includes a circuit breaker for disconnecting the connection to the aforementioned power system. The power conversion system according to claim 5 or 6, wherein the control unit controls the circuit breaker to disconnect the connection to the power system after the completion of the soft stop process, or after the soft stop process is interrupted and the operation of the power conversion unit is stopped.

8. The aforementioned electrical component includes a power supply, The power conversion system according to claim 1, wherein the control unit is configured to be powered by the power supply.

9. The power conversion system according to claim 1, further comprising a fuse as an electrical component, provided between the transformer and the control unit.

10. A power converter that operates in conjunction with the power grid, A power conversion unit that includes a capacitor to smooth the output and converts DC power to AC power for output, A control unit that controls the power conversion unit, The control unit, when it detects an abnormality at the connection point where the power system and the power conversion unit are connected, performs control to initiate a soft stop process that gradually stops the output of the power conversion unit so that the DC power stored in the capacitor is not supplied to the transformer, in a power conversion device.

Images