Power conversion device and power system

Abstract

To provide a power conversion device capable of parallel independent operation even if no voltage sensor is provided between an inverter circuit and an opening / closing unit, and a power system.SOLUTION: A power conversion device A1 includes: an inverter circuit 11 for converting DC power to AC power; a control circuit 14 for controlling the inverter circuit 11; an opening / closing unit 12 connected in series to an AC-side output terminal of the inverter circuit 11 and capable of switching between an open state and a closed state; and a voltage sensor 13 that is arranged on an opposite side of the inverter circuit 11 with respect to the opening / closing unit 12 and detects an output voltage of the inverter circuit 11. The control circuit 14 controls the inverter circuit 11 based on a differential voltage ΔV between a target voltage Vref and a feedback voltage Vfb detected by the voltage sensor 13 during a self-sustaining operation. When the self-sustaining operation is started, the control circuit sets a fixed value Vx in place of the differential voltage ΔV in a state where the opening / closing unit 12 is opened, and closes the opening / closing unit 12 when a predetermined time Tx elapses.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device and a power system. [Background technology]

[0002] Patent Document 1 discloses a grid-connected inverter system. The grid-connected inverter system includes an inverter circuit that converts a DC voltage input from a DC power source into an AC voltage and outputs the converted voltage, a switch for connecting and disconnecting the system from the power system, and a system voltage sensor that is disposed between the switch and the power system and detects the system voltage. When the grid-connected inverter system is connected to the power system, the system-connected inverter system brings its own output voltage closer to the system voltage and closes the switch when the voltages match. This makes it possible to suppress the inrush current at the moment of connection. Since no current flows when the switch is open, the output voltage of the inverter circuit can be controlled by open-loop control. Therefore, there is no need to provide a voltage sensor between the inverter circuit and the switch.

[0003] Some grid-connected inverter systems are also equipped with an independent operation function that starts up as an independent voltage source when disconnected from the power grid. The grid-connected inverter system disclosed in Patent Document 1 can also be equipped with an independent operation function if the switch is closed first and the output voltage of the inverter circuit is detected by a grid voltage sensor. That is, the target voltage of the output voltage of the inverter circuit may be gradually increased to the rated voltage while performing voltage feedback control. Note that, since a load is connected to the inverter circuit and a current flows according to the voltage, the output voltage cannot be controlled by open loop control and voltage feedback control is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-188665 A Summary of the Invention [Problem to be solved by the invention]

[0005] Problems arise when multiple grid-connected inverter systems that do not have a voltage sensor between the inverter circuit and the switch are connected in parallel to perform parallel isolated operation. That is, when connecting a second grid-connected inverter system in parallel, if the switch is closed before increasing the output voltage of the grid-connected inverter system, current may flow from the first grid-connected inverter system to the second grid-connected inverter system, causing an overcurrent to be detected. However, since there is no voltage sensor between the inverter circuit and the switch, the voltage of the inverter circuit cannot be detected before closing the switch.

[0006] The present invention has been devised in light of the above-mentioned circumstances, and aims to provide a power conversion device and a power system that enable parallel independent operation even without a voltage sensor between the inverter circuit and the switching unit. [Means for solving the problem]

[0007] A power conversion device provided by a first aspect of the present invention comprises an inverter circuit that converts DC power into AC power, a control circuit that controls the inverter circuit, an opening / closing unit connected in series to the AC side output terminal of the inverter circuit and switched between an open state and a closed state, and a voltage sensor arranged on the opposite side of the inverter circuit from the opening / closing unit and detecting the output voltage of the inverter circuit, wherein during autonomous operation, the control circuit controls the inverter circuit based on the differential voltage between a target voltage and a feedback voltage detected by the voltage sensor, and at the start of autonomous operation, with the opening / closing unit open, a fixed value is set in place of the differential voltage, and the opening / closing unit is closed when a predetermined time has elapsed.

[0008] In a preferred embodiment of the present invention, at the start of the independent operation, the control circuit changes the fixed value to "0" when the predetermined time has elapsed, and then closes the opening / closing unit.

[0009] In a preferred embodiment of the present invention, the control circuit includes a subtractor that calculates the difference between a first input and a second input, and a switching unit that switches between a first state in which the first input is the fixed value and the second input is "0" and a second state in which the first input is the target voltage and the second input is the feedback voltage, and the switching unit is in the first state at the start of autonomous operation and switches to the second state after closing the opening / closing unit.

[0010] A power conversion device provided by a second aspect of the present invention comprises an inverter circuit that converts DC power into AC power, a control circuit that controls the inverter circuit, an opening / closing unit connected in series to the AC output terminal of the inverter circuit and switched between an open state and a closed state, a voltage sensor arranged on the opposite side of the inverter circuit with respect to the opening / closing unit and detecting the output voltage of the inverter circuit, and a second opening / closing unit connected on the opposite side of the inverter circuit with respect to the voltage sensor and switched between an open state and a closed state, wherein the control circuit controls the inverter circuit based on a differential voltage between a target voltage and a feedback voltage detected by the voltage sensor during autonomous operation, and at the start of autonomous operation, closes the second opening / closing unit while keeping the second opening / closing unit open, and closes the second opening / closing unit when the feedback voltage matches the target voltage.

[0011] A power system provided by a third aspect of the present invention includes a plurality of power conversion devices provided by the first and second aspects of the present invention, and AC side output terminals of the plurality of power conversion devices are connected in parallel with each other. Effect of the Invention

[0012] According to the present invention, at the start of independent operation, the control circuit sets a fixed value instead of the differential voltage with the switching unit open and controls the inverter circuit. As a result, the output voltage of the inverter circuit increases according to the fixed value. The time (predetermined time) required for the output voltage to increase to the rated voltage can be obtained in advance. The control circuit closes the switching unit when the predetermined time has elapsed, thereby enabling parallel connection when the output voltage reaches the rated voltage. In this way, the power conversion device according to the present invention enables parallel independent operation even without a voltage sensor between the inverter circuit and the switching unit. [Brief description of the drawings]

[0013] [Figure 1] 1A and 1B are diagrams for explaining a power conversion device according to a first embodiment, in which (a) is a block diagram showing the overall configuration of a power system equipped with the power conversion device, and (b) is a block diagram showing the internal configuration of a control circuit. [Diagram 2] 5 is an example of a flowchart showing an independent operation startup process according to the first embodiment. [Diagram 3] 4 is a timing chart for explaining the independent operation startup process according to the first embodiment. [Figure 4] FIG. 13 is a block diagram showing an internal configuration of a control circuit according to a modified example. [Diagram 5] 10A and 10B are diagrams for explaining a power conversion device according to a second embodiment, where FIG. 10A is a block diagram showing the internal configuration of the power conversion device, and FIG. 10B is a block diagram showing the internal configuration of a control circuit. [Figure 6] 13 is an example of a flowchart showing an independent operation startup process according to a second embodiment. [Figure 7] 10 is a timing chart for explaining the independent operation startup process according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0015] Fig. 1 is a diagram for explaining a power conversion device A1 according to a first embodiment. Fig. 1(a) is a block diagram showing an overall configuration of a power system B including the power conversion device A1. Fig. 1(b) is a block diagram showing an internal configuration of a control circuit 14 of the power conversion device A1.

[0016] The power system B includes a storage battery, and charges the storage battery with power supplied from the power system, and in a predetermined case, discharges the storage battery to output power. The power system B is usually connected to the power system and operates in an interconnected manner, and operates autonomously during a power outage. As shown in FIG. 1(a), the power system B includes a plurality of power conversion devices A1, each of which is connected to a storage battery 2, and switching units 3 and 4. In this embodiment, a case will be described in which the power system B includes three power conversion devices A1. The number of the power conversion devices A1 is not limited, and the power system B may include two or four or more power conversion devices A1. The AC side output terminals of the plurality of power conversion devices A1 are connected in parallel to each other at a connection point 5. The connection point 5 is connected to the power system via the switching unit 3 on the connection point 5 side and the switching unit 4 on the power system side. A load L is connected to a connection line connecting the switching unit 3 and the switching unit 4. The switching units 3 and 4 are, for example, circuit breakers. During grid-connected operation, both switches 3 and 4 are closed, and power system B is connected to the power grid and can transmit and receive power to and from the power grid. Load L is supplied with power from a plurality of power conversion devices A1 (storage batteries 2) or the power grid.

[0017] In the event of an accident in the power system, the switch units 3 and 4 are opened by a protection device provided on the power system side, and the power system B and the load L are separated from the power system (power failure state). In this case, the power system B is switched to independent operation, and the switch unit 4 is kept open and the switch unit 3 is closed to supply power to the load L. If the output voltages of each power conversion device A1 do not match when connected to the connection point 5, a current may flow between the power conversion device A1 and the other power conversion devices A1, causing the power conversion device A1 to stop due to an overcurrent. Each power conversion device A1 is connected to the connection point 5 when the output voltage reaches the rated voltage by the independent operation start-up process. The independent operation start-up process is a process for starting the power conversion device A1 to start the independent operation, and will be described in detail later.

[0018] In this embodiment, the storage battery 2 is a secondary battery that can be repeatedly charged and discharged, for example, a lithium ion battery. The storage battery 2 may be another secondary battery such as a nickel-metal hydride battery, a nickel-cadmium battery, or a lead-acid battery. The storage battery 2 may be a capacitor such as an electric double layer capacitor instead of a secondary battery.

[0019] The power conversion device A1 is a so-called power conditioner, and charges and discharges the storage battery 2. The DC output terminal of each power conversion device A1 is connected to the storage battery 2, and the AC output terminals are connected in parallel to each other at a connection point 5. The power conversion device A1 includes an inverter circuit 11, a switching unit 12, a voltage sensor 13, and a control circuit 14. Note that the power conversion device A1 actually includes other components, but descriptions and explanations thereof will be omitted.

[0020] The inverter circuit 11 has a DC output terminal connected to the storage battery 2, and charges and discharges the storage battery 2. The inverter circuit 11 charges the storage battery 2 by converting AC power input from the AC side into DC power and supplying it to the storage battery 2. The inverter circuit 11 also converts DC power stored in the storage battery 2 into AC power and outputs it to the AC side, thereby discharging the storage battery 2. The charging and discharging performed by the inverter circuit 11 is controlled by a control circuit 14. The inverter circuit 11 converts DC power and AC power by switching a switching element (not shown) on and off based on a drive signal input from the control circuit 14.

[0021] The switching unit 12 is connected in series to the AC side output terminal of the inverter circuit 11, and is switched between an open state and a closed state. The switching unit 12 is, for example, but not limited to, an electromagnetic contactor, and switches between an open state and a closed state in response to a command from the control circuit 14. When the switching unit 12 is in the closed state, the power conversion device A1 (inverter circuit 11) is connected to the connection point 5. On the other hand, when the switching unit 12 is in the open state, the power conversion device A1 (inverter circuit 11) is disconnected from the connection point 5.

[0022] The voltage sensor 13 is disposed on the downstream side of the switching unit 12 (the opposite side of the switching unit 12 from the inverter circuit 11) in the connection line connecting the switching unit 12 and the connection point 5. When the switching unit 12 is in the closed state, the voltage sensor 13 detects the output voltage of the inverter circuit 11 and outputs the detected voltage detection signal to the control circuit 14.

[0023] The control circuit 14 is realized by, for example, a microcomputer, and controls the power conversion device A1. The control circuit 14 controls the opening and closing of the switching unit 12 by inputting a command to the switching unit 12. When the switching unit 12 is closed, the voltage sensor 13 can detect the output voltage of the inverter circuit 11. The control circuit 14 calculates a feedback voltage Vfb based on a voltage detection signal input from the voltage sensor 13. The feedback voltage Vfb is an effective value of the output voltage of the inverter circuit 11. The control circuit 14 also generates a drive signal and inputs it to the inverter circuit 11 to control the power conversion by the inverter circuit 11.

[0024] During grid-connected operation and stand-alone operation, the control circuit 14 closes the switch 12, so that the output voltage of the inverter circuit 11 can be detected by the voltage sensor 13. The control circuit 14 feedback-controls the output voltage of the inverter circuit 11 by outputting to the inverter circuit 11 a drive signal generated based on a differential voltage ΔV (=Vref−Vfb) between the feedback voltage Vfb and the target voltage Vref.

[0025] On the other hand, when the grid-connected operation is stopped and the independent operation is started, the control circuit 14 opens the switching unit 12, so that the output voltage of the inverter circuit 11 cannot be acquired. However, if the switching unit 12 is closed and the power conversion device A1 is connected to the connection point 5 when the output voltage of the inverter circuit 11 is low, a current may flow from the other power conversion device A1 and an overcurrent may be detected. When the control circuit 14 detects an overcurrent, it opens the switching unit 12 and stops the inverter circuit 11, so that the power conversion device A1 cannot participate in the parallel independent operation. In this embodiment, when the independent operation is started, the control circuit 14 performs an independent operation start process in which, with the switching unit 12 open, a fixed value Vx is set instead of the differential voltage ΔV, and the switching unit 12 is closed when a predetermined time Tx has elapsed. The predetermined time Tx is the time required for the output voltage of the inverter circuit 11 to increase to the rated voltage when the fixed value Vx is set instead of the differential voltage ΔV, and is acquired in advance by an experiment or a simulation. The larger the fixed value Vx, the larger the increase rate of the output voltage of the inverter circuit 11, so that the predetermined time Tx becomes smaller. Therefore, if it is desired to shorten the time required for startup, a large value should be set as the fixed value Vx. Also, by setting a small value as the fixed value Vx, the output voltage of the inverter circuit 11 increases slowly, so that the control circuit 14 can more reliably close the switch 12 at the timing when the output voltage becomes the rated voltage. When connecting each power conversion device A1 in parallel, the phases of the output voltages of the inverter circuits 11 of each power conversion device A1 must be sufficiently synchronized. The method of synchronizing the phases is not limited, and any well-known method may be used.

[0026] As shown in Fig. 1(b), the control circuit 14 includes, as functional components, a timer 141, a switching unit 142, a subtractor 143, a control unit 144, and a drive signal generating unit 145. Each unit may be configured with a digital circuit or an analog circuit. The control circuit 14 includes other functional components, but descriptions of functional components unrelated to the independent operation startup process are omitted.

[0027] The timer 141 is a functional component for measuring the time from the start of the independent operation startup process. The timer 141 outputs the measured time to the switching unit 142.

[0028] The switching unit 142 is a functional configuration for switching a value to be input to the subtractor 143. From the start of the independent operation startup process, the switching unit 142 inputs a fixed value Vx (>0) to the first input of the subtractor 143 and inputs "0" to the second input (hereinafter, this state is referred to as "first state"). Then, when the time input from the timer 141 reaches a predetermined time Tx, the switching unit 142 inputs "0" to the first input of the subtractor 143 and commands the opening / closing unit 12 to close. Thereafter, the switching unit 142 inputs a target voltage Vref to the first input of the subtractor 143 and inputs a feedback voltage Vfb based on the detection of the voltage sensor 13 to the second input (hereinafter, this state is referred to as "second state").

[0029] The subtractor 143 is a functional component for performing subtraction processing, and outputs a value obtained by subtracting the second input from the first input to the control unit 144. Therefore, when the switching unit 142 is in the first state, the subtractor 143 outputs a fixed value Vx. On the other hand, when the switching unit 142 is in the second state, the subtractor 143 outputs a differential voltage ΔV between the target voltage Vref and the feedback voltage Vfb.

[0030] The control unit 144 calculates a compensation value by PI control (proportional-integral control) based on the input from the subtractor 143, and outputs it as a compensation value signal to the drive signal generating unit 145. Note that the control unit 144 may perform control other than PI control.

[0031] The drive signal generating unit 145 generates a drive signal based on the compensation value signal input from the control unit 144. Incidentally, a compensation value signal other than the compensation value signal input from the control unit 144 may also be input to the drive signal generating unit 145. The drive signal generating unit 145 generates a command value signal based on these compensation value signals, and generates a drive signal by comparing the command value signal with a carrier signal such as a triangular wave. Incidentally, the method in which the drive signal generating unit 145 generates a drive signal is not limited. When the switching unit 142 is in the second state, the differential voltage ΔV is input to the control unit 144, so that the drive signal generating unit 145 generates a drive signal that sets the feedback voltage Vfb to the target voltage Vref (sets the differential voltage ΔV to "0"). On the other hand, when the switching unit 142 is in the first state, a fixed value Vx (>0) is input to the control unit 144, so that the drive signal generating unit 145 generates a drive signal that increases the output voltage of the inverter circuit 11. The drive signal generated by the drive signal generating unit 145 is output to the inverter circuit 11.

[0032] 2 is an example of a flowchart showing the independent operation startup process performed by the control circuit 14. The independent operation startup process is executed when the independent operation is started.

[0033] First, a fixed value Vx is set instead of the differential voltage ΔV (S1). Specifically, the switching unit 142 is in the first state, and the fixed value Vx is input to the first input of the subtractor 143, and "0" is input to the second input. Next, time measurement is started (S2). Specifically, the timer 141 starts time measurement. Next, it is determined whether the measured time has reached a predetermined time Tx (S3). If the measured time has not reached the predetermined time Tx (S3: NO), the process returns to step S3, and the determination of step S3 is repeated. If the measured time has reached the predetermined time Tx (S3: YES), the process proceeds to step S4. That is, the control circuit 14 waits until the measured time reaches the predetermined time Tx. During this time, the control circuit 14 generates a drive signal using the fixed value Vx instead of the differential voltage ΔV and outputs the drive signal to the inverter circuit 11. As a result, the output voltage of the inverter circuit 11 increases from "0" to the rated voltage.

[0034] Next, the fixed value Vx is changed to "0" (S4). Specifically, the switching unit 142 changes the input to the first input of the subtractor 143 from the fixed value Vx to "0". The control circuit 14 generates a drive signal using "0" instead of the differential voltage ΔV and outputs it to the inverter circuit 11. As a result, the output voltage of the inverter circuit 11 is fixed at the rated voltage. Next, the switching unit 12 is closed (S5). Specifically, the control circuit 14 outputs a closing command to the switching unit 12. Next, the voltage is changed from "0" to the differential voltage ΔV (S6), and the independent operation start-up process ends. Specifically, the switching unit 142 goes into the second state, and the target voltage Vref is input to the first input of the subtractor 143, and the feedback voltage Vfb is input to the second input. Since the switching unit 12 is closed, the voltage sensor 13 can detect the output voltage of the inverter circuit 11. When the independent operation start-up process is completed, the control circuit 14 performs feedback control of the output voltage of the inverter circuit 11 based on the differential voltage ΔV. Note that the process shown in the flowchart of Fig. 2 is an example, and the independent operation start-up process performed by the control circuit 14 is not limited to the above.

[0035] 3 is a timing chart for explaining the independent operation start-up process performed by the control circuit 14. (a) in the figure shows the time change in the output of the subtractor 143. (b) in the figure shows the time change in the output of the timer 141. (c) in the figure shows the time change in the output voltage of the inverter circuit 11. (d) in the figure shows the time change in the state of the opening / closing unit 12.

[0036] At time t0, the independent operation start-up process is started, the output of the subtractor 143 becomes a fixed value Vx, and the timer 141 starts timing. Since the output of the subtractor 143 is a fixed value Vx, the output voltage of the inverter circuit 11 increases over time. Then, at time t1, when a predetermined time Tx has elapsed from time t0, the time counted by the timer 141 becomes the predetermined time Tx, and the output voltage of the inverter circuit 11 becomes the rated voltage. At this time, the output of the subtractor 143 is switched to "0", and the opening / closing unit 12 is switched from the open state to the closed state. Thereafter, the output voltage of the inverter circuit 11 is controlled to become the rated voltage (the output of the subtractor 143 becomes "0").

[0037] Next, the operation and effects of the power conversion device and the power system according to the present embodiment will be described.

[0038] According to this embodiment, at the start of the independent operation, the control circuit 14 sets a fixed value Vx instead of the difference voltage ΔV and controls the inverter circuit 11 with the switching unit 12 open. As a result, the output voltage of the inverter circuit 11 increases according to the fixed value Vx. Then, the control circuit 14 closes the switching unit 12 when a predetermined time Tx has elapsed. Since the predetermined time Tx is a time for the output voltage of the inverter circuit 11 to increase to the rated voltage when the fixed value Vx is set, the control circuit 14 can close the switching unit 12 when the output voltage becomes the rated voltage. In this way, the power conversion device A1 enables parallel independent operation even if a voltage sensor is not provided between the inverter circuit 11 and the switching unit 12. In addition, the power conversion device A1 only changes the control method of the control circuit 14, and the conventional hardware configuration can be used as it is, so there is no need to add any further hardware configuration. Therefore, the power conversion device A1 can reduce costs and can be made smaller and lighter than when a hardware configuration is added.

[0039] According to the present embodiment, the control circuit 14 includes a subtractor 143 that calculates the difference between the first input and the second input, and a switching unit 142 that switches between a first state in which the first input is a fixed value Vx and the second input is "0" and a second state in which the first input is a target voltage and the second input is a feedback voltage Vfb. The switching unit 142 is in the first state at the start of the independent operation, and switches to the second state after closing the opening / closing unit 12. This allows the control circuit 14 to switch between control at the start of the independent operation and control during the independent operation.

[0040] Furthermore, according to this embodiment, at the start of independent operation, the control circuit 14 changes the fixed value Vx to "0" when the predetermined time Tx has elapsed, and then closes the switching unit 12. This allows the control circuit 14 to close the switching unit 12 with the output voltage of the inverter circuit 11 fixed to the rated voltage.

[0041] In the present embodiment, the storage battery 2 is connected to each power conversion device A1, but the present invention is not limited to this. The power conversion device A1 may be connected to a DC power source that generates DC power, such as a solar cell or a fuel cell. The power conversion device A1 may also be connected to a power source that converts AC power generated by a diesel engine generator or a wind turbine generator into DC power and outputs the DC power.

[0042] 4 is a diagram for explaining a modified example of the control circuit 14 of the power conversion device A1 according to the first embodiment, and is a block diagram showing the internal configuration of the control circuit 14. Note that in this modified example, the configuration other than the control circuit 14 is common to the first embodiment, and therefore illustration and description are omitted.

[0043] 4, in the control circuit 14 according to the modification, the subtractor 143 outputs a difference voltage ΔV between the target voltage Vref and the feedback voltage Vfb. Then, the switching unit 142 outputs a fixed value Vx in the first state, and outputs an input from the subtractor 143 in the second state. In this modification as well, the control circuit 14 sets a fixed value Vx instead of the difference voltage ΔV in a state in which the switching unit 12 is open at the start of independent operation, and controls the inverter circuit 11 to close the switching unit 12 when a predetermined time Tx has elapsed.

[0044] FIG. 5 is a diagram for explaining a power conversion device A2 according to a second embodiment. FIG. 5(a) is a block diagram showing an internal configuration of the power conversion device A2. FIG. 5(b) is a block diagram showing an internal configuration of a control circuit 16 of the power conversion device A2. In FIG. 5, elements that are the same as or similar to those of the power conversion device A1 according to the first embodiment are given the same reference numerals, and duplicated explanations are omitted. The power conversion device A2 according to this embodiment differs from the power conversion device A1 according to the first embodiment in that it further includes a switching unit 15 and the contents of the independent operation start-up process are different.

[0045] The power conversion device A2 according to the second embodiment further includes a switching unit 15. The switching unit 15 is connected to the downstream side of the voltage sensor 13 (the opposite side of the inverter circuit 11 with respect to the voltage sensor 13) and is switched between an open state and a closed state. The switching unit 15 is, for example, a circuit breaker, but is not limited thereto, and switches between an open state and a closed state in response to a command from the control circuit 16.

[0046] The power conversion device A2 according to the second embodiment includes a control circuit 16 instead of the control circuit 14. The control circuit 16 is similar to the control circuit 14, except that the control circuit 16 controls the content of the independent operation startup process when independent operation is started, and further controls the opening and closing of the switching unit 15. In this embodiment, when independent operation is started, the control circuit 16 closes the switching unit 12 while keeping the switching unit 15 open, and closes the switching unit 15 when the feedback voltage Vfb matches the target voltage Vref (rated voltage).

[0047] 5(b), the control circuit 16 includes, as its functional components, a subtractor 143, a control unit 144, a drive signal generating unit 145, and a determination unit 146. The subtractor 143, the control unit 144, and the drive signal generating unit 145 are common to the control circuit 14. In the control circuit 16, the subtractor 143 outputs a differential voltage ΔV between the target voltage Vref and the feedback voltage Vfb.

[0048] The determination unit 146 is a functional configuration for instructing the opening and closing of the switching unit 15 based on the feedback voltage Vfb. The determination unit 146 receives the feedback voltage Vfb, instructs the switching unit 15 to open while the feedback voltage Vfb is less than the target voltage Vref, and instructs the switching unit 15 to close when the feedback voltage Vfb becomes the target voltage Vref. In this embodiment, a rated voltage is set as the target voltage Vref during the independent operation startup process.

[0049] 6 is an example of a flowchart showing the independent operation startup process performed by the control circuit 16 according to the second embodiment. The independent operation startup process is executed when the independent operation is started.

[0050] First, the switching unit 12 is closed (S11). Specifically, the control circuit 16 outputs a closing command to the switching unit 12. This enables the voltage sensor 13 to detect the output voltage of the inverter circuit 11, and the control circuit 16 to obtain the feedback voltage Vfb. Next, the rated voltage is set to the target voltage Vref (S12). Next, it is determined whether the feedback voltage Vfb has reached the target voltage Vref (S13). If the feedback voltage Vfb has not reached the target voltage Vref (S13: NO), the process returns to step S13, and the determination in step S13 is repeated. If the feedback voltage Vfb has reached the target voltage Vref (S13: YES), the switching unit 15 is closed (S14), and the independent operation start-up process is terminated. Specifically, the control circuit 16 outputs a closing command to the switching unit 15. Note that the process shown in the flowchart of FIG. 6 is an example, and the independent operation start-up process performed by the control circuit 16 is not limited to the one described above.

[0051] 7 is a timing chart for explaining the independent operation start-up process performed by the control circuit 16. (a) in the figure shows the change over time of the state of the switching unit 12. (b) in the figure shows the change over time of the output voltage of the inverter circuit 11 detected by the voltage sensor 13. (c) in the figure shows the change over time of the state of the switching unit 15.

[0052] At time t2, the independent operation start-up process is started, and the switching unit 12 is switched from the open state to the closed state. This enables the voltage sensor 13 to detect the output voltage of the inverter circuit 11. Also, the rated voltage is set to the target voltage Vref. This causes the feedback voltage Vfb to increase over time from "0". Then, at time t3, the feedback voltage Vfb becomes the target voltage Vref (rated voltage), and the switching unit 15 is switched from the open state to the closed state. Thereafter, the feedback voltage Vfb is controlled to become the target voltage Vref (rated voltage) (the output of the subtractor 143 becomes "0").

[0053] According to this embodiment, at the start of the independent operation, the control circuit 16 closes the switching unit 12 while keeping the switching unit 15 open. This allows the control circuit 16 to acquire the feedback voltage Vfb. The feedback voltage Vfb increases to reach the target voltage Vref (rated voltage). Then, the control circuit 16 closes the switching unit 15 when the feedback voltage Vfb matches the target voltage Vref (rated voltage). In this way, the power conversion device A2 enables parallel independent operation even without a voltage sensor between the inverter circuit 11 and the switching unit 12. In addition, the power conversion device A2 has a configuration in common with the power conversion device A1, and thus achieves the same effects as the power conversion device A1.

[0054] The power conversion device and the power system according to the present invention are not limited to the above-described embodiment. The specific configurations of the components of the power conversion device and the power system according to the present invention can be freely designed in various ways. [Explanation of symbols]

[0055] A1, A2: power conversion device, 11: inverter circuit, 12, 15: opening / closing unit, 13: voltage sensor, 14: control circuit, 142: switching unit, 143: subtractor, B: power system

Claims

1. An inverter circuit that converts DC power into AC power; A control circuit for controlling the inverter circuit; an opening / closing unit connected in series to an output terminal on the AC side of the inverter circuit and switched between an open state and a closed state; a voltage sensor disposed on an opposite side of the opening / closing unit from the inverter circuit, the voltage sensor detecting an output voltage of the inverter circuit; Equipped with The control circuit includes: During the independent operation, the inverter circuit is controlled based on a difference voltage between a target voltage and a feedback voltage detected by the voltage sensor. At the start of the independent operation, a fixed value is set instead of the differential voltage with the switching unit open, and the switching unit is closed when a predetermined time has elapsed. Power conversion equipment.

2. The control circuit changes the fixed value to "0" when the predetermined time has elapsed at the start of the independent operation, and then closes the opening / closing unit. The power conversion device according to claim 1 .

3. The control circuit includes: a subtractor for calculating a difference between the first input and the second input; a switching unit that switches between a first state in which the first input is the fixed value and the second input is “0” and a second state in which the first input is the target voltage and the second input is the feedback voltage; Equipped with The switching unit is in the first state at the start of independent operation, and switches to the second state after closing the opening / closing unit. The power conversion device according to claim 1 .

4. An inverter circuit that converts DC power into AC power; A control circuit for controlling the inverter circuit; an opening / closing unit connected in series to an output terminal on the AC side of the inverter circuit and switched between an open state and a closed state; a voltage sensor disposed on an opposite side of the opening / closing unit from the inverter circuit, the voltage sensor detecting an output voltage of the inverter circuit; a second opening / closing unit that is connected to the voltage sensor on an opposite side to the inverter circuit and that is switched between an open state and a closed state; Equipped with The control circuit includes: During the independent operation, the inverter circuit is controlled based on a difference voltage between a target voltage and a feedback voltage detected by the voltage sensor. At the start of an independent operation, the switching unit is closed while the second switching unit is open, and when the feedback voltage coincides with the target voltage, the second switching unit is closed. Power conversion equipment.

5. A power conversion device according to any one of claims 1 to 4, The AC output terminals of the plurality of power conversion devices are connected in parallel with each other. Power system.

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