JP6796809B2 - Power converter, power conversion system - Google Patents

Description

The present invention relates to a power conversion device and a power conversion system that are connected in parallel to supply AC power to a load.

As a method of supplying AC power to a load from a plurality of power converters connected in parallel, droop control that controls the output voltage and frequency according to preset drooping characteristics may be used (see, for example, Patent Document 1). ). In parallel operation using conventional droop control, phase control is performed based on the power output of the own unit. Therefore, if the start timing of each power converter is different, a phase difference will occur between the output voltages of multiple power converters. Was there.

For example, if a commercial power system (hereinafter, simply referred to as a system) loses power during grid interconnection operation, the plurality of power conversion devices temporarily stop operating. After that, when the predetermined period elapses or the user performs an operation to start the independent operation, the plurality of power conversion devices restart the power supply. At that time, the start timing of the independent operation of each power conversion device differs due to the difference in the timing at which each power conversion device detects a power failure or the difference in the operation timing of the user with respect to the plurality of power conversion devices.

Japanese Unexamined Patent Publication No. 2006-271024

If the phase difference between the output voltages of a plurality of power converters becomes large, an overcurrent may flow at the start of parallel operation, resulting in an error stop. For example, when the phase difference between the output voltages of the two power converters is close to 180 °, an overcurrent flows through the two power converters.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a power conversion device and a power conversion system capable of suppressing an overcurrent from flowing at the start of parallel operation.

In order to solve the above problems, the power conversion device of a certain aspect of the present invention is a power conversion device that supplies AC power to a common load together with other power conversion devices connected in parallel, and is supplied from a DC power supply. An AC voltage command that generates an AC voltage command value based on the power converter that converts the DC power to be converted to AC power, the output power of this power converter, the reference voltage for droop control, and the reference frequency for droop control. A control unit that controls the power conversion unit so that the output voltage of the power conversion unit matches the value generation unit and the AC voltage command value generated by the AC voltage command value generation unit, and the other power conversion unit. The frequency / phase detection unit that detects the frequency and phase of the detection voltage of the output terminal of the power conversion device connected to the output terminal of the device, and the AC voltage command value generation unit are from the power conversion unit to the load. Before starting the power supply, the phase of the AC voltage command value is determined based on the frequency and phase detected by the frequency / phase detection unit.

According to the present invention, it is possible to suppress the flow of an overcurrent at the start of parallel operation of a plurality of power conversion devices.

It is a figure which shows the structure of the power conversion system which concerns on embodiment of this invention. It is a figure which shows the configuration example of a control device. 3 (a) and 3 (b) are diagrams showing the drooping characteristics used in the droop control. It is a figure which shows the voltage waveform at the time of starting the self-sustaining operation mode of two power conversion devices.

FIG. 1 is a diagram showing a configuration of a power conversion system 2s according to an embodiment of the present invention. The power conversion system 2s includes a plurality of power conversion devices 2 connected in parallel. The output paths of the plurality of power conversion devices 2 are combined into one and connected to a commercial power system (hereinafter, simply referred to as system 4) via a distribution line. A load 3 is connected to the distribution line. FIG. 1 shows an example in which two of the first power conversion device 2a and the second power conversion device 2b are connected in parallel. Generally, the distribution line is composed of a single-phase two-wire system, a single-phase three-wire system, or a three-phase three-wire system. Therefore, originally, the wiring between the first power conversion device 2a, the second power conversion device 2b, and the system 4 in FIG. 1 should be drawn with two or three lines, respectively, but one line is used to simplify the drawing. It is drawn with.

The first power conversion device 2a converts the DC power supplied from the first DC power supply 1a into AC power and outputs it. Similarly, the second power conversion device 2b converts the DC power supplied from the second DC power supply 1b into AC power and outputs it. The first DC power supply 1a and the second DC power supply 1b include storage batteries (for example, lithium ion storage batteries, nickel hydrogen storage batteries, lead storage batteries), capacitors (for example, electric double layer capacitors, lithium ion capacitors), solar cells, fuel cells and the like. Can be used. The same type of DC power supply may be used for the first DC power supply 1a and the second DC power supply 1b, or different types of DC power supplies may be used.

The first power conversion device 2a includes a first inverter device 21a, a first control device 22a, a first inductor La, a first filter current sensor CT1a, a first capacitor Ca, a first relay RYa, a first output current sensor CT2a, and A first output voltage sensor VTa is provided. The first inductor La and the first capacitor Ca form an output filter.

The first inverter device 21a converts the DC power supplied from the first DC power supply 1a into AC power and outputs it to the output filter. When the first DC power supply 1a is a storage battery, a bidirectional inverter device is used for the first inverter device 21a. When charging the storage battery, the first inverter device 21a converts the AC power supplied from the system 4 into DC power to charge the storage battery.

A DC-DC converter may be provided between the first DC power supply 1a and the first inverter device 21a. For example, when the first DC power supply 1a is a solar cell, the DC-DC converter executes MPPT (Maximum Power Point Tracking) control. When the first DC power supply 1a is a storage battery, a bidirectional DC-DC converter may be provided between the first DC power supply 1a and the first inverter device 21a. The bidirectional DC-DC converter performs constant current (CC) charging / discharging or constant voltage (CV) charging / discharging of the storage battery.

The first inverter device 21a and the DC-DC converter each include, for example, a bridge circuit in which four or six switching elements are bridge-connected. By controlling the duty ratio of the switching element, the input / output of each of the first inverter device 21a and the DC-DC converter can be adjusted. For example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used as the switching element.

The output filter attenuates the harmonic component of the AC power output from the first inverter device 21a, and brings the output voltage and output current of the first inverter device 21a closer to a sine wave. The first filter current sensor CT1a detects the current IL flowing through the output filter and outputs the current IL to the first control device 22a.

The first relay RYa is inserted between the output filter and the output terminal Ta of the first power conversion device 2a. The first output current sensor CT2a detects the output current Io of the first power conversion device 2a and outputs it to the first control device 22a. The first output voltage sensor VTa detects the output voltage Vo of the first power conversion device 2a and outputs it to the first control device 22a.

The first control device 22a controls the first inverter device 21a, the first relay RYa, and the like. The configuration of the first control device 22a can be realized by the cooperation of the hardware resource and the software resource, or only by the hardware resource. Analog devices, microcomputers, DSPs, ROMs, RAMs, FPGAs, and other LSIs can be used as hardware resources. Programs such as firmware can be used as software resources.

The second power conversion device 2b includes a second inverter device 21b, a second control device 22b, a second inductor Lb, a second filter current sensor CT1b, a second capacitor Cb, a second relay RYb, a second output current sensor CT2b, and A second output voltage sensor VTb is provided. The second inductor Lb and the second capacitor Cb form an output filter. Since the configuration of the second power conversion device 2b is the same as the configuration of the first power conversion device 2a, the description thereof will be omitted.

FIG. 2 is a diagram showing a configuration example of the control device 22. The control device 22 includes a droop control unit 221, a drive control unit 222, a PWM signal generation unit 223, a drive circuit 224, and an operation mode management unit 225. The droop control unit 221 includes an effective / reactive power calculation unit 221a, a first multiplication unit 221b, a first subtraction unit 221c, a second multiplication unit 221d, a first addition unit 221e, a frequency / phase detection unit 221f, and a phase determination unit 221g. And the AC voltage command value generation unit 221h is included.

The operation mode management unit 225 manages the operation mode of the power conversion device 2 and notifies the drive control unit 222 and the phase determination unit 221g of the current operation mode. The operation mode management unit 225 selects the grid interconnection mode when the grid 4 is normal. In the grid interconnection mode, the operation mode management unit 225 controls the relay RY to a closed state (on state). The operation mode management unit 225 selects the independent operation mode when the system 4 has a power failure. The operation mode management unit 225 determines that the system 4 has a power failure when the voltage Vo detected by the output voltage sensor VT becomes less than the predetermined voltage value for a predetermined time. When the operation mode management unit 225 detects a power failure in the system 4, the operation mode management unit 225 controls the relay RY from the closed state (on state) to the open state (off state). This state is the standby mode.

Switching from the standby mode to the independent operation mode has a setting to start automatically and a setting to start manually. In the case of the setting to start automatically, the operation mode management unit 225 detects the power failure of the system 4 and controls the relay RY to the open state (off state), and then closes the relay RY when the set time elapses. Control to state (on state). In the case of the setting to start manually, the operation mode management unit 225 controls the relay RY to the closed state (on state) when it receives the operation signal based on the start operation of the independent operation mode performed by the user.

The drive control unit 222 generates a current command value based on the input voltage Vdc of the inverter device 21 in the grid interconnection mode. When a DC-DC converter is provided between the DC power supply 1 and the inverter device 21, a current command value is generated based on the DC bus voltage Vdc between the DC-DC converter and the inverter device 21.

More specifically, the drive control unit 222 generates an output current command value of the inverter device 21 so that the output power of the DC power supply 1 or the DC-DC converter and the input power of the inverter device 21 are balanced. The input voltage Vdc increases when the output power of the DC power supply 1 or the DC-DC converter is higher than the input power of the inverter device 21, and decreases when the output power is lower. The drive control unit 222 generates a current command value for increasing the output power of the inverter device 21 when the detected input voltage Vdc is higher than the set voltage, and when the detected input voltage Vdc is lower than the set voltage, the drive control unit 222 generates a current command value. A current command value for reducing the output power of the inverter device 21 is generated. The drive control unit 222 has a current command value I ^* defined by the duty ratio of the switching element in the inverter device 21 based on the deviation between the generated current command value and the current IL detected by the filter current sensor CT1 ^. To generate. The drive control unit 222 outputs the generated current command value I ^* to the PWM signal generation unit 223.

The PWM signal generation unit 223 includes a comparator. The comparator compares the current command value I ^* with the carrier wave (triangle wave), and generates a PWM signal according to the comparison result. The comparator outputs the generated PWM signal to the drive circuit 224. The drive circuit 224 supplies a drive signal based on the PWM signal input from the PWM signal generation unit 223 to the gate terminal of the switching element in the inverter device 21.

When the drive control unit 222 is in the self-sustaining operation mode, the switching in the inverter device 21 is performed based on the deviation between the AC voltage command value Esin θ supplied from the droop control unit 221 and the voltage Vo detected by the output voltage sensor VT. Generates the voltage command value V ^* specified by the duty ratio of the element. The drive control unit 222 outputs the generated voltage command value V ^* to the PWM signal generation unit 223. The comparator of the PWM signal generation unit 223 compares the voltage command value V ^* with the carrier wave, and generates a PWM signal according to the comparison result. The comparator outputs the generated PWM signal to the drive circuit 224. The drive circuit 224 supplies a drive signal based on the PWM signal input from the PWM signal generation unit 223 to the gate terminal of the switching element in the inverter device 21. In the self-sustaining operation mode, the voltage is not defined by the system 4, so it is necessary to define the voltage by the power converter 2.

The active / reactive power calculation unit 221a of the droop control unit 221 is based on the current Io detected by the output current sensor CT2 and the voltage Vo detected by the output voltage sensor VT, and the output active power of its own power conversion device 2. P, output reactive power Q is calculated. The output active power P and the output reactive power Q can be calculated by the following (Equation 1) and (Equation 2).

P = Vo × Io × cos θ ・ ・ ・ (Equation 1)
Q = Vo × Io × sinθ ・ ・ ・ (Equation 2)

The AC voltage command value generation unit 221h generates an AC voltage command value Esin θ based on the active power P, the reactive power Q, the reference voltage E ^* for droop control, and the reference angular frequency ω ^* for droop control. E is the voltage and θ (= ωt) is the phase.

3 (a) and 3 (b) are diagrams showing the drooping characteristics used in the droop control. FIG. 3A shows the drooping characteristic of the frequency droop, and FIG. 3B shows the drooping characteristic of the voltage droop. In the droop control, the output voltage E of the power conversion device 2 is calculated by the following (Equation 3), and the angular frequency ω of the output voltage E of the power conversion device 2 is calculated by the following (Equation 4).

E = E ^* -nP ... (Equation 3)
ω = ω ^* + mQ ・ ・ ・ (Equation 4)

The reference voltage E ^* is the output voltage when there is no load, and the reference angular frequency ω ^* is the nominal frequency when there is no load. For example, the reference voltage E ^* is set to 200 V, and the reference angular frequency ω ^* is set to 314 rad / s (≈ frequency 50 Hz). The coefficient n is a voltage droop coefficient, and the coefficient m is a frequency droop coefficient. The coefficient n and the coefficient m are determined by the output impedance of the power conversion device 2 or the rated output.

Return to FIG. The first multiplication unit 221b multiplies the active power P calculated by the active / reactive power calculation unit 221a by the voltage droop coefficient n, and outputs the obtained voltage value to the first subtraction unit 221c. The first subtraction unit 221c subtracts the voltage value calculated by the first multiplication unit 221b from the value of the reference voltage E ^* , and outputs the obtained voltage value E to the AC voltage command value generation unit 221h.

The second multiplication unit 221d multiplies the reactive power Q calculated by the active / reactive power calculation unit 221a by the frequency droop coefficient m, and outputs the obtained angular frequency to the first addition unit 221e. The first addition unit 221e adds the angular frequency calculated by the second multiplication unit 221d to the reference angular frequency ω ^* , and outputs the obtained angular frequency ω to the phase determination unit 221g.

The frequency / phase detection unit 221f detects the frequency Fp and the phase θd of the voltage Vo detected by the output voltage sensor VT, and outputs the detected frequency Fp and the phase θp to the phase determination unit 221g. The frequency / phase detection unit 221f can detect the frequency and the phase by detecting, for example, the position of the zero crossing point of the detected voltage Vo.

In principle, the phase determining unit 221g outputs the phase θ (= ωt) based on the angular frequency ω input from the second multiplication unit 221d to the AC voltage command value generating unit 221h. Exceptionally, the frequency Fp input from the frequency / phase detection unit 221f and the phase θ based on the phase θp are output to the AC voltage command value generation unit 221h.

As shown in FIG. 1, in a configuration in which two power conversion devices 2 are connected in parallel to the system 4, when the system 4 fails, the two power conversion devices 2 independently detect the power failure. Therefore, the power failure detection timing may shift. In the case of the setting that the self-sustaining operation mode is automatically started from the standby mode, if the power failure detection timing is deviated, the start timing of the self-sustained operation mode is also deviated. Further, in the case of the setting in which the independent operation mode is manually activated from the standby mode, if the timing at which the user presses the operation buttons of the two power conversion devices 2 is deviated, the activation timing of the independent operation mode is also deviated.

Droop control adjusts the voltage and angular frequency of the reference AC voltage waveform based on the reference voltage E ^* and the reference angle frequency ω ^* based on the output active power P and output reactive power Q of the own power converter 2. Is. In the state where the relay RY is controlled to the open state after the power failure of the system 4, the output power of the own power conversion device 2 is not detected, so basically the reference AC voltage waveform is used as it is as the voltage command value.

However, when the start timings of the independent operation modes of the two power conversion devices 2 are different, a phase difference occurs between the output voltages of the two power conversion devices 2. If this phase difference is large, an overcurrent will occur, resulting in an error stop. In addition, stress due to overcurrent may cause problems in electronic components.

Therefore, in the state where the relay RY is controlled to be open after the power failure of the system 4 (that is, the power conversion device 2 and the load 3 are non-conducting), the frequency of the voltage Vo of the output terminal T of the own power conversion device 2 The phase θ of the AC voltage waveform is determined based on Fp and the phase θp. When the voltage Vo of the output terminal T of the own power conversion device 2 is substantially zero, it means that the own power conversion device 2 is the power conversion device 2 that first starts the self-sustaining operation mode. , The reference AC voltage waveform based on the reference voltage E ^* and the reference angle frequency ω ^* is used as the voltage command value.

When the voltage Vo of the output terminal T of the own power conversion device 2 is substantially other than zero, it means that the own power conversion device 2 is the power conversion device 2 that starts the self-sustaining operation mode from the second time onward. Therefore, the phase θ of the AC voltage waveform is determined based on the frequency Fp and the phase θp of the voltage Vo of the output terminal T of the own power conversion device 2. That is, the AC voltage waveform synchronized with the phase θp of the detected voltage Vo is used as the voltage command value.

In FIG. 3, when the standby mode is instructed by the operation mode management unit 225, the phase determination unit 221g generates an AC voltage command value for the phase θ based on the frequency Fp and the phase θp input from the frequency / phase detection unit 221f. Output to unit 221h. When the independent operation mode is instructed by the operation mode management unit 225, the phase determination unit 221g outputs the phase θ based on the angular frequency ω input from the second multiplication unit 221d to the AC voltage command value generation unit 221h.

At the timing when the self-sustaining operation mode is activated, the phase determining unit 221g sets the phase θ based on the output voltage Vo of the other power conversion device 2 to the phase θ based on the frequency droop control based on the output power of the own power conversion device 2. Take over as an offset value. In frequency droop control, the phase θ is calculated by the following (Equation 5). The conversion coefficient k (= 360 ° / sampling frequency) is a coefficient for converting the frequency into an angle. The initial value of θ (previous value) is set to the phase θ based on the output voltage Vo of the other power conversion device 2 immediately before switching.

θ (current value) = θ (previous value) + ω × k ・ ・ ・ (Equation 5)

FIG. 4 is a diagram showing voltage waveforms of the two power conversion devices 2 at the time of starting the independent operation mode. The first power conversion device 2 generates an AC voltage by droop control from the beginning without synchronizing with the output voltage Vo of the other power conversion device 2. In the comparative example, the second power conversion device 2 also generates an AC voltage by droop control from the beginning, like the first power conversion device 2. In the comparative example, since it is not synchronized with the output voltage Vo of the first power conversion device 2, an overcurrent occurs due to the voltage phase difference when the independent operation mode is started (when the parallel operation is started).

In the embodiment, the second power conversion device 2 generates an AC voltage whose phase is synchronized with the output voltage Vo of the first power conversion device 2 before the start of the self-sustaining operation mode, and starts the self-sustaining operation mode. After that, AC voltage is generated by droop control. In the embodiment, since the phase at the start of the parallel operation matches the phase of the output voltage Vo of the first power conversion device 2, no overcurrent occurs at the start of the parallel operation.

As described above, according to the present embodiment, before the start of parallel operation in the self-sustaining operation mode, the phase of the output voltage of the own power conversion device 2 is synchronized with the phase of the output voltage of the other power conversion device 2. As a result, the droop control can be started in a state where the voltage phase is synchronized with the other power conversion device 2. As a result, an overcurrent due to the voltage phase difference is not generated at the start of parallel operation, and stable parallel operation can be performed.

Further, even if the first power conversion device 2a and the second power conversion device 2b are connected by a communication line and the synchronization signal is not exchanged, the phase at the start of parallel operation in the independent operation mode can be synchronized. Therefore, the wiring can be simplified.

Even if the first power conversion device 2a and the second power conversion device 2b are connected by a communication line, if the distance between the first power conversion device 2a and the second power conversion device 2b is large, the communication delay occurs. Out of sync can occur. In this respect, according to the present embodiment, it is not necessary to consider the error due to the communication delay.

The present invention has been described above based on the embodiments. Embodiments are examples, and it is understood by those skilled in the art that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present invention. ..

In the above-described embodiment, the case where two power conversion devices 2 are operated in parallel has been described as an example, but even when three or more power conversion devices 2 are operated in parallel, the second and subsequent power conversion devices The above phase switching control can be applied to 2.

Further, the power conversion system 2s may be a distributed power supply system having a DC power source (solar cell or the like) that does not have a grid interconnection mode and generates power based on renewable energy. In this case, the above phase switching control is activated whenever the distributed power supply system is started.

In addition, the embodiment may be specified by the following items.

[Item 1]
A power conversion device (2b) that supplies AC power to a common load (3) together with other power conversion devices (2a) connected in parallel.
A power conversion unit (21b) that converts DC power supplied from a DC power supply (1b) into AC power, and
An AC voltage command value generator (221h) that generates an AC voltage command value based on the output power of the power converter (2b), a reference voltage for droop control, and a reference frequency for droop control.
A control unit (222) that controls the power conversion unit (21b) so that the output voltage of the power conversion unit (21b) matches the AC voltage command value generated by the AC voltage command value generation unit (221h). When,
Frequency / phase detection unit (221f) that detects the frequency and phase of the detection voltage of the output terminal (Tb) of this power conversion device (2b) connected to the output terminal (Ta) of the other power conversion device (2a). When,
The AC voltage command value generation unit (221h) has a frequency and a phase detected by the frequency / phase detection unit (221h) before starting power supply from the power conversion unit (21b) to the load (3). The power conversion device (2b), characterized in that the phase of the AC voltage command value is determined based on the above.
According to this, it is possible to suppress the flow of overcurrent at the start of parallel operation.
[Item 2]
The AC voltage command value generation unit (221h) starts supplying power from the power conversion unit (21b) to the load (3), and then outputs power from the power conversion unit (21b) and controls the droop. Determine the phase of the AC voltage command value based on the reference frequency of
The AC voltage command value generation unit (221h) takes over the phase detected by the frequency / phase detection unit (211f) when starting power supply from the power conversion unit (21b) to the load (3). The power conversion device (2b) according to item 1, wherein the power conversion device (2b) is characterized in that.
According to this, at the start of parallel operation, it is possible to output an AC voltage whose phase is synchronized with that of the other power converter (2a).
[Item 3]
The power conversion device (2b) is also connected to the power system (4) together with the other power conversion device (2a) and the load (3).
This power converter (2b)
A switch (RYb) inserted between the power conversion unit (21b) and the detection point of the detection voltage, and
When the power failure of the power system (4) is detected, the switch (RYb) is turned off, and when the user activates the independent operation mode, or when a predetermined time elapses after the power failure is detected, the switch (RYb) ) Is further provided with a mode management unit (225) to turn on.
The AC voltage command value generation unit (221h) synchronizes with the timing at which the switch (RYb) turns on, and the AC voltage command is based on the frequency and phase detected by the frequency / phase detection unit (221f). The process of determining the phase of the value is switched to the process of determining the phase of the AC voltage command value based on the output power from the power conversion unit (21b) and the reference frequency for the droop control. The power converter (2b) according to item 1 or 2.
According to this, it is possible to suppress the flow of overcurrent at the start of parallel operation in the self-sustaining operation mode.
[Item 4]
A power conversion system (2s), wherein a plurality of power conversion devices (2) according to any one of items 1 to 3 are connected in parallel.
According to this, it is possible to construct a system in which an overcurrent is suppressed from flowing at the start of parallel operation.

1a 1st DC power supply, La 1st inverter, Ca 1st capacitor, CT1a 1st filter current sensor, RYa 1st relay, VTa 1st output voltage sensor, 1b 2nd DC power supply, CT1b 2nd filter current sensor, 2s power Conversion system, 2a 1st power converter, CT2a 1st output current sensor, 2b 2nd power converter, Lb 2nd inverter, Cb 2nd capacitor, CT2b 2nd output current sensor, RYb 2nd relay, VTb 2nd output Voltage sensor, 3 loads, 4 systems, 21a 1st inverter device, 21b 2nd inverter device, 22a 1st control device, 22b 2nd control device, 221 droop control unit, 221a effective / invalid power calculation unit, 221b 1st multiplication Unit, 221c 1st subtraction unit, 221d 2nd multiplication unit, 221e 1st addition unit, 221f frequency / phase detection unit, 221g phase determination unit, 221h AC voltage command value generation unit, 222 drive control unit, 223 PWM signal generation unit , 224 drive circuit, 225 operation mode management unit.

The present invention can be used in a power conversion system in which a plurality of power conversion devices are connected in parallel.

Claims (4)

A power converter that supplies AC power to a common load along with other power converters connected in parallel.
A power converter that converts DC power supplied from a DC power supply into AC power,
An AC voltage command value generator that generates an AC voltage command value based on the output power of this power converter, a reference voltage for droop control, and a reference frequency for droop control.
A control unit that controls the power conversion unit so that the output voltage of the power conversion unit matches the AC voltage command value generated by the AC voltage command value generation unit.
It is provided with a frequency / phase detection unit for detecting the frequency and phase of the detection voltage of the output terminal of this power conversion device connected to the output terminal of the other power conversion device .
The AC voltage command value generation unit determines the phase of the AC voltage command value based on the frequency and phase detected by the frequency / phase detection unit before starting power supply from the power conversion unit to the load. Decide and
The AC voltage command value generation unit is a power conversion device that takes over the phase detected by the frequency / phase detection unit when starting power supply from the power conversion unit to the load . After starting the power supply from the power conversion unit to the load, the AC voltage command value generation unit starts the AC voltage command value based on the output power from the power conversion unit and the reference frequency for droop control. power converter according to claim 1, wherein the determining child phase of. A power converter that supplies AC power to a common load along with other power converters connected in parallel.
A power converter that converts DC power supplied from a DC power supply into AC power,
An AC voltage command value generator that generates an AC voltage command value based on the output power of this power converter, a reference voltage for droop control, and a reference frequency for droop control.
A control unit that controls the power conversion unit so that the output voltage of the power conversion unit matches the AC voltage command value generated by the AC voltage command value generation unit.
It is provided with a frequency / phase detection unit for detecting the frequency and phase of the detection voltage of the output terminal of this power conversion device connected to the output terminal of the other power conversion device.
The AC voltage command value generation unit determines the phase of the AC voltage command value based on the frequency and phase detected by the frequency / phase detection unit before starting power supply from the power conversion unit to the load. Decide and
This power conversion device is connected to the power system together with the other power conversion device and the load.
This power converter is
A relay inserted between the power conversion unit and the detection point of the detection voltage,
Said turning off the relay and detects the power failure of the power system, the start operation of the isolated operation mode by the user is made, or the power outage from detecting that the predetermined time has elapsed to turn on the relay mode management unit, With more
The AC voltage command value generation unit determines the phase of the AC voltage command value based on the frequency and phase detected by the frequency / phase detection unit in synchronization with the timing at which the relay turns on. The power conversion device according to claim 1 or 2, wherein the process is switched to a process of determining the phase of the AC voltage command value based on the output power from the power conversion unit and the reference frequency for droop control. A power conversion system according to any one of claims 1 to 3, wherein a plurality of power conversion devices are connected in parallel.

Images