Grid-connected power conversion device and method for controlling the grid-connected power conversion device

Abstract

To provide a grid-connected power conversion device that contributes to system stabilization even when an inverter is stopped to suppress inverter loss.SOLUTION: When at least one of a system frequency f and a system voltage detection value Vac deviates from a normal range, a system disturbance determination unit 8 determines that a system disturbance has occurred and outputs a system disturbance determination signal. A virtual synchronous generator model 3 outputs the phase θr based on the PLL angular frequency ΔωPLL when the DC / AC converter INV is stopped and the system disturbance determination signal is not output, and outputs the phase θr based on the VSG angular frequency Δωr when the DC / AC converter INV is operated or the system disturbance determination signal is output. A PWM control unit 6 blocks a gate signal Gate of the DC / AC converter INV when the DC / AC converter INV is not used, and start outputting the gate signal Gate to the DC / AC converter INV when the system disturbance determination signal is output.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an operating method for contributing to grid stabilization while reducing power consumption by an inverter in a grid-connected power conversion device having an inverter output characteristic with pseudo-inertia. [Background technology]

[0002] A grid-connected power conversion device having characteristics equivalent to those of a synchronous generator, as typified by Patent Document 1, acts to suppress fluctuations in grid voltage and grid frequency caused by grid accidents, supply-demand imbalances, and the like.

[0003] In general, a grid-connected power conversion device having a storage battery charges or discharges the storage battery by an operation method such as peak shift or DR (Disaster Recovery), and gates an inverter during a period when the storage battery is not in use. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6084863 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in order for a grid-connected power conversion device having pseudo-inertia to contribute to grid stabilization, it is necessary to keep the inverter running at all times. Even when the storage battery is not being used, i.e., when the inverter output power is zero, power loss occurs by driving the semiconductor switches that make up the inverter.

[0006] In view of the above, it is an object of the present invention to provide a grid-connected power conversion device that contributes to grid stabilization even when the inverter is stopped in order to suppress inverter loss. [Means for solving the problem]

[0007] The present invention has been devised in view of the above-mentioned problems in the related art, and one aspect thereof is a grid-connected power conversion device which performs virtual synchronous generator control simulating a synchronous generator, has a DC / AC converter which converts DC power of a DC power source into AC power, and an output of the DC / AC converter is connected to a power grid via an LC filter, the grid-connected power conversion device comprising: an internal induced voltage calculation unit which calculates an internal induced voltage based on an output current detection value, an effective value of a grid voltage detection value, and an AC voltage command value; a PLL which outputs a grid frequency and a PLL angular frequency based on the grid voltage detection value; a grid disturbance determination unit which determines that a grid disturbance has occurred and outputs a grid disturbance determination signal when the grid frequency is greater than an upper frequency threshold, or when the grid frequency is less than a lower frequency threshold, or when the grid voltage detection value is greater than an upper voltage threshold, or when the grid voltage detection value is less than a lower voltage threshold; a virtual synchronous generator model that calculates a VSG angular frequency simulating a synchronous generator, and outputs a phase based on the PLL angular frequency when the DC / AC converter is stopped and the grid disturbance determination signal is not output, and outputs a phase based on the VSG angular frequency when the DC / AC converter is operating or the grid disturbance determination signal is output; a virtual synchronous impedance compensation unit that simulates a voltage drop due to an internal impedance of the synchronous generator based on the internal induced voltage, the grid voltage detection value, and the output current detection value, and calculates a grid voltage command value; a PCS output voltage control unit that performs voltage control to control the grid voltage detection value to the grid voltage command value, and outputs a PWM control command value; and a PWM control unit that generates a gate signal for the DC / AC converter based on the PWM control command value and the phase, blocks the gate signal for the DC / AC converter when the DC / AC converter is not used, and starts outputting the gate signal to the DC / AC converter when the grid disturbance determination signal is output.

[0008] As one aspect of the present invention, the virtual synchronous generator model includes a mechanical input torque calculation unit that converts the mechanical input command value into a mechanical input torque, an electric output torque calculation unit that calculates an electric output torque from the internal induced voltage and the output current detection value, a first subtractor that subtracts the electric output torque from the mechanical input torque, a damping block that outputs a damping torque simulating a torque generated in a damper winding based on a previous value of an output of a switch, a second subtractor that subtracts the damping torque from an output of the first subtractor, and an inertia block that divides the output of the second subtractor by an inertia constant. a first adder that adds a previous value of the output of the switch to the output of the inertia block to output the VSG angular frequency; the switch that outputs the PLL angular frequency when the DC / AC converter is stopped and the system disturbance determination signal is not output, and outputs the VSG angular frequency when the DC / AC converter is operating or the system disturbance determination signal is output; a second adder that adds a fundamental frequency to the output of the switch and outputs the result as an angular frequency; and a first integrator that integrates the output of the second adder to output the phase.

[0009] In one aspect, the system disturbance determination unit determines that a system disturbance is occurring and outputs the system disturbance determination signal when a rate of change of the system frequency when increasing is greater than a threshold when increasing, or when a rate of change of the system frequency when decreasing is greater than a threshold when decreasing.

[0010] In one aspect, the virtual synchronous generator model varies the inertia constant in response to the output current detection value when the system frequency or the system voltage detection value fluctuates.

[0011] In one aspect, the virtual synchronous generator model is characterized by comprising: a table that outputs an inertia constant change amount based on the output current detection value; a second integrator that integrates the inertia constant change amount; a limiter that limits the output of the second integrator to a limit value and outputs the limit value as an inertia constant adjustment amount; and an adder that adds the inertia constant adjustment amount to a normal inertia constant to calculate the inertia constant. Effect of the Invention

[0012] According to the present invention, it is possible to provide a grid-connected power conversion device that contributes to grid stabilization even in a state in which the inverter is stopped in order to suppress inverter loss. [Brief description of the drawings]

[0013] [Figure 1] 1 is an overall schematic diagram of a grid-connected power conversion device according to first to third embodiments. [Diagram 2] FIG. 2 is a block diagram showing a virtual synchronous generator model according to the first embodiment. [Diagram 3] 5 is a diagram showing an example of a frequency fluctuation and an inverter output effective power when a generator goes off in the first embodiment. FIG. [Figure 4] FIG. 4 is a diagram showing an example of inverter operation when a voltage drops. [Diagram 5] 11 is a diagram showing an example of frequency fluctuation and inverter output effective power when a generator goes off in the second embodiment. FIG. [Figure 6] FIG. 11 is a block diagram showing a virtual synchronous generator model according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, first to third embodiments of the grid-connected power conversion device according to the present invention will be described in detail with reference to FIGS.

[0015] [Embodiment 1] Fig. 1 is an overall schematic diagram of a grid-connected power conversion device in the first embodiment. As shown in Fig. 1, the main circuit configuration of the grid-connected power conversion device converts DC power from a DC power source Vdc such as a storage battery into AC power using a DC / AC converter (hereinafter referred to as inverter) INV consisting of IGBTs and the like, and connects to a power system 1 via an LC filter LC and a transformer Tr. The LC filter LC includes a filter reactor Lf and a filter capacitor Cf. In addition, an output current detection value Iac and a system voltage detection value Vac between the LC filter LC and the transformer Tr are detected and output to a control unit described later.

[0016] The grid-connected power conversion device controls the grid voltage detection value Vac after the LC filter LC so that it matches the grid voltage command value Vac* obtained by subtracting the voltage drop due to the virtual synchronous impedance Zs caused by the output current Iac flowing from the internal induced voltage Ef.

[0017] As shown in FIG. 1 , the control unit of the grid-interconnected power conversion device in the present embodiment 1 includes an internal induced voltage calculation unit 2, a virtual synchronous generator model 3, a virtual synchronous impedance compensation unit 4, a PCS (Power Conversion System) output voltage control unit 5, a PWM control unit 6, a PLL (Phase Locked Loop) 7, and a grid disturbance determination unit 8.

[0018] The internal induced voltage calculation unit 2 receives the AC voltage command value Vref, the effective value |Vac| of the AC voltage detection value, and the output current detection value Iac, and calculates the internal induced voltage Ef.

[0019] The PLL 7 outputs a PLL angular frequency ΔωPLL to the virtual synchronous generator model 3 based on the grid voltage detection value Vac in order to perform synchronization control with the grid voltage when the inverter INV is stopped. The PLL 7 also outputs a grid frequency f to the grid disturbance determination unit 8 based on the grid voltage detection value Vac.

[0020] The system disturbance determination unit 8 determines whether or not a system disturbance is occurring based on the system voltage detection value Vac and the system frequency f, and outputs a system disturbance determination signal to the virtual synchronous generator model 3 if it is determined that a system disturbance is occurring.

[0021] The virtual synchronous generator model 3 calculates a VSG angular frequency Δωr simulating a synchronous generator for performing virtual synchronous generator control based on the internal induced voltage Ef, the output current detection value Iac, and the machine input command value Pm which is the output command value of the inverter INV. When the inverter INV is stopped and the system disturbance determination signal is not output, it outputs a phase θr based on the PLL angular frequency ΔωPLL, and when the inverter INV is operating or the system disturbance determination signal is output, it outputs a phase θr based on the VSG angular frequency Δωr.

[0022] A virtual synchronous impedance compensator 4 receives the system voltage detection value Vac, the output current detection value Iac, and the internal induced voltage Ef, simulates a voltage drop due to the internal impedance of the synchronous generator, and outputs a system voltage command value Vac*.

[0023] The PCS output voltage control unit 5 receives the grid voltage detection value Vac and the grid voltage command value Vac*, controls the grid voltage detection value Vac to become the grid voltage command value Vac*, and outputs a PWM control command value Vcmd.

[0024] The PWM control unit 6 receives the PWM control command value Vcmd and the phase θr to generate a gate signal Gate. When the DC power supply Vdc is not used and the system disturbance determination signal is not output, the gate signal Gate is blocked. When the system disturbance determination signal is output, the gate signal Gate is output to a switching element such as an IGBT of the inverter INV.

[0025] The internal induced voltage calculation unit 2, the virtual synchronous impedance compensation unit 4, the PCS output voltage control unit 5, and the PLL 7 are not directly related to the present invention, and therefore detailed description thereof will be omitted here.

[0026] 2 shows the virtual synchronous generator model 3 of this embodiment 1. The mechanical input torque calculation unit 9 calculates the mechanical input torque Tm by dividing the mechanical input command value Pm by the previous value of the angular frequency ωr in a divider 9a.

[0027] In the electric output torque calculation unit 10, a multiplier 10a multiplies the internal induced voltage Ef by the output current detection value Iac. A divider 10b divides the output of the multiplier 10a by the previous value of the angular frequency ωr to output an electric output torque Te.

[0028] The first subtractor 11 subtracts the electrical output torque Te from the mechanical input torque Tm. The second subtractor 12 subtracts the damping torque generated in the damper winding, which is the output of the damping block 19, from the output of the first subtractor 11.

[0029] The inertia block 13 simulates the inertia of the generator by dividing the output of the second subtractor 12 by the inertia constant M. The first adder 14 adds the previous value of the output of the switch 15 to the output of the inertia block 13, and outputs the VSG angular frequency Δωr calculated from the virtual synchronous generator model.

[0030] The switch 15 outputs a PLL angular frequency ΔωPLL when the inverter INV is stopped and the system disturbance determination signal is not output, and outputs a VSG angular frequency Δωr when the inverter INV is operating or the system disturbance determination signal is output.

[0031] The second adder 16 adds the fundamental frequency ω0 (50 Hz or 60 Hz) to the output of the switch 15 and outputs it as an angular frequency ωr. The first integrator 17 integrates the angular frequency ωr and outputs the phase θr.

[0032] Buffer 18 temporarily stores the output of switch 15 and outputs it as the previous value of the output of switch 15 to first adder 14 and damping block 19. Damping block 19 multiplies the output of buffer 18 by damping compensation term Ds / 1+TDs to simulate the damping torque generated in the damper winding and outputs it to second subtractor 12. Since damping compensation term Ds / 1+TDs is not directly related to the present invention, a detailed description thereof will be omitted here.

[0033] The buffer 20 temporarily stores the angular frequency ωr, and outputs the previous value of the angular frequency ωr to the dividers 9a and 10b.

[0034] The system disturbance determination unit 8 performs frequency determination to determine whether the system frequency f exceeds a threshold value, and voltage determination to determine whether the system voltage detection value Vac exceeds a threshold value. If either of the threshold values ​​is exceeded, the system disturbance determination unit 8 determines that "a system disturbance has occurred" and outputs a system disturbance determination signal.

[0035] Here, an upper frequency threshold and a lower frequency threshold are set for the grid frequency f, and an upper voltage threshold and a lower voltage threshold are set for the grid voltage detection value Vac. If the grid frequency f is within the normal range (below the upper frequency threshold and above the lower frequency threshold) and the grid voltage detection value Vac is within the normal range (below the upper voltage threshold and above the lower voltage threshold), it is determined that "a grid disturbance is not occurring."

[0036] When the system frequency f is greater than the upper frequency threshold, or when the system frequency f is less than the lower frequency threshold, or when the system voltage detection value Vac is greater than the upper voltage threshold, or when the system voltage detection value Vac is less than the lower voltage threshold, it is determined that "a system disturbance has occurred" and a system disturbance determination signal is output. In other words, when at least one of the system frequency f and the system voltage detection value Vac deviates from the normal range, a system disturbance determination signal is output.

[0037] During the period when the DC power supply Vdc is not used, the inverter INV is gate-blocked in the PWM control unit 6. When the inverter INV is stopped and no system disturbance is occurring, the output of the switch 15 in the virtual synchronous generator model 3 is set to the PLL angular frequency ΔωPLL, whereby synchronous control with the system voltage is performed by the PLL 7, and the angular frequency ωr is synchronized with the system frequency.

[0038] Frequency fluctuations caused by an imbalance in the power supply and demand balance and system voltage fluctuations caused by system accidents are monitored, and when such system disturbances are detected, the PWM control unit 6 immediately starts the inverter INV. In addition, the output of the switch 15 in the virtual synchronous generator model 3 is set to the VSG angular frequency Δωr, and operation is performed according to the output characteristics (pseudo inertia) of the inverter INV, thereby suppressing system frequency fluctuations.

[0039] Figure 3 shows an example of the change in system frequency and inverter output active power when a generator trips. When a generator trips, the system frequency drops. The slope of this frequency drop depends on the inertia of the system. After that, the generator output is adjusted by governor-free or LFC (load frequency control), and the system frequency returns to the rated frequency (normal frequency).

[0040] 3, the solid line indicates the case where the inverter is started, and the dotted line indicates the case where the inverter INV is not started. In the first embodiment, when the inverter INV is in a stopped state and a drop in the grid frequency is detected, the inverter INV starts outputting, so that it is possible to suppress the amount of drop in the frequency compared to when the inverter INV is not started.

[0041] Figure 4 shows an example of inverter INV operation when the system voltage drops due to a short circuit on the system side, etc. When the inverter INV is stopped and detects a system voltage drop, it starts up immediately, but because the system side is in a short circuit state, it outputs the fault current at a current value that the inverter INV can output.

[0042] That is, in the virtual synchronous impedance compensator 4, under normal circumstances, the drop voltage is calculated based on a preset virtual synchronous impedance Zs and the output current detection value Iac, and when an overcurrent occurs, the drop voltage is calculated based on a corrected virtual synchronous impedance Zs' (r' and x') required to limit the current to the current limit value Ilim that the inverter INV can output and the output current detection value Iac.

[0043] The method for calculating the corrected virtual synchronous impedance Zs' (r' and x') required to suppress overcurrent is given by the following equation (1).

[0044]

number

[0045] Here, Ed and Eq represent the d-axis component and the q-axis component of the internal induced voltage Ef, and Vd and Vq represent the d-axis component and the q-axis component of the system voltage detection value Vac.

[0046] In order to simulate the corrected virtual synchronous impedance Zs' (r' and x'), the corrected virtual synchronous impedance Zs' calculated by equation (1) must be positive. Instantaneous output current phase information is necessary to suppress overcurrent, but if the output current is disturbed due to a system accident or load fluctuation, etc., calculating the corrected virtual synchronous impedance Zs' based on the phase information extracted from the instantaneous current may result in a negative value. Therefore, the extracted output current phase θ is limited to the range of the following equation (2).

[0047]

number

[0048] In addition, by defining the internal phase based on the internal induced voltage Ef, Eq = 0, which can be simplified. In addition, the current limit value Ilim may be a fixed value, or may be a value obtained by multiplying the output current detection value Iac by a current limiter.

[0049] Returning to the explanation of Figure 4, when the fault point is removed, the system voltage recovers and the inverter output current decreases.

[0050] As distributed power sources become more widespread, the ratio of inverter power sources in the system increases, and the number of operating generators decreases, which may reduce the fault current in the event of a system fault, causing concerns that conventional protective relays may not operate normally. In the first embodiment, the inverter INV, which was stopped in this embodiment, also supplies the fault current (within the range in which semiconductor switches and the like can operate), expanding the range in which conventional protective relays can be applied.

[0051] As described above, according to the grid-connected power conversion device of the present embodiment 1, when a grid disturbance occurs, the inverter INV is quickly started from a stopped (gate blocked) state and an output according to pseudo-inertia is performed, thereby reducing the power consumption by the inverter INV and contributing to stabilization of the grid.

[0052] [Embodiment 2] In the second embodiment, a frequency change rate determination unit that determines whether or not the rate of change of the frequency exceeds a threshold value is added to the system disturbance determination unit 8 of the first embodiment.

[0053] Here, a threshold value for the frequency change rate is set for when the frequency increases and when the frequency decreases. In this specification, the frequency change rate for when the frequency decreases and the threshold value for when the frequency decreases are described as absolute values. If the system frequency f is within a normal range (below the upper frequency threshold and above the lower frequency threshold), the system voltage detection value Vac is within a normal range (below the upper voltage threshold and above the lower voltage threshold), and the frequency change rate is within a normal range (below the threshold for when the frequency increases and below the threshold for when the frequency decreases), it is determined that "system disturbance is not occurring."

[0054] When the system frequency f is greater than the upper frequency threshold, or when the system frequency f is smaller than the lower frequency threshold, or when the system voltage detection value Vac is greater than the upper voltage threshold, or when the system voltage detection value Vac is smaller than the lower voltage threshold, and in addition when the frequency change rate during increase is greater than the threshold during increase, or when the frequency change rate during decrease is greater than the threshold during decrease, it is determined that "a system disturbance is occurring" and a system disturbance determination signal is output.

[0055] Fig. 5 shows an example of the frequency fluctuation and inverter output effective power when a generator trips in embodiment 2. By adding a determination based on the frequency change rate, as shown in Fig. 5, it becomes possible to start the inverter before the system frequency f exceeds the frequency threshold when there is a frequency fluctuation due to, for example, the tripping of a large-capacity generator.

[0056] According to the second embodiment, the inverter can be started up more quickly when the frequency fluctuates, and this can contribute more to system stabilization than the first embodiment.

[0057] [Embodiment 3] In the third embodiment, a table for calculating the amount of change in the inertia constant M from the output current detection value Iac, and an integrator and limiter for the amount of change in the inertia constant M are added to the virtual synchronous generator model 3, and the inertia constant M that simulates the inertia of the generator is made variable.

[0058] By increasing the inertia constant M, frequency fluctuations become gentler, so that the effective power output by the inverter INV during frequency fluctuations increases, and frequency fluctuations in the entire system are further suppressed.

[0059] However, if the inertia constant M is made too large, the inverter INV will be overloaded and will no longer be able to produce an output commensurate with the inertia constant M.

[0060] Therefore, by changing the inertia constant M in response to the output current of the inverter INV, the inverter INV is operated with a larger inertia constant M within its operable range. habit The inertia constant M is calculated by adding the inertia constant adjustment amount Madj during grid disturbance to the normal inertia constant Mbase during normal times (when no grid disturbance occurs). The normal inertia constant Mbase is a preset value as a parameter of the PCS.

[0061] FIG. 6 shows a block diagram of the virtual synchronous generator model 3 of the third embodiment. The same reference numerals are used for the same parts as in the first embodiment, and the description thereof will be omitted. Table 21 determines the inertia constant change amount ΔM according to the magnitude of the output current detection value Iac. For example, the inertia constant change amount ΔM is determined as +ΔM when the rated current of the device is 80% or less (current at which 100% continuous operation is possible), -ΔM when the rated current of the device is 120% or more, and 0 otherwise. By determining the inertia constant change amount ΔM in this way, the inertia constant M is increased when there is a margin in the output, and is decreased when there is no margin in the output.

[0062] The second integrator 22 integrates the inertia constant change amount ΔM. The limiter 23 limits the output of the second integrator 22 to a limit value. The output of the limiter 23 becomes the inertia constant adjustment amount Madj.

[0063] The limiter 23 is provided to prevent the inertia constant M from being made too large when the fluctuations in the system frequency f and the system voltage detection value Vac are small, and to make the inertia constant M variable only when the system frequency f and the system voltage detection value Vac fluctuate.

[0064] When the fluctuations in the grid frequency f and the grid voltage detection value Vac converge (when the rate of change in the grid frequency f and the grid voltage detection value Vac becomes small), the limit value is gradually reduced to 0, and the system will operate using only the normal inertia constant Mbase.

[0065] The adder 24 adds the inertia constant adjustment amount Madj at the time of system disturbance to the normal inertia constant Mbase to obtain the inertia constant M, and outputs the inertia constant M to the inertia block 13.

[0066] As described above, according to the third embodiment, in addition to the advantageous effects of the first and second embodiments, by increasing the inertia constant M within a range in which the inverter can operate when the system frequency f and the system voltage fluctuate, the fluctuations in the system frequency f and the system voltage can be suppressed.

[0067] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0068] 1…Power system 2. Internal induced voltage calculation section 3…Virtual synchronous generator model 4. Virtual synchronous impedance compensation section 5…PCS output voltage control section 6...PWM control unit 7...PLL 8...System disturbance judgement section Vdc…DC power supply INV...DC / AC converter (inverter) LC...LC filter Tr...transformer

Claims

1. A grid-connected power conversion device that performs virtual synchronous generator control simulating a synchronous generator, has a DC / AC converter that converts DC power of a DC power supply into AC power, and an output of the DC / AC converter is connected to a power grid via an LC filter, an internal induced voltage calculation unit that calculates an internal induced voltage based on an output current detection value, an effective value of a system voltage detection value, and an AC voltage command value; a PLL that outputs a system frequency and a PLL angular frequency based on the system voltage detection value; a system disturbance determination unit that determines that a system disturbance is occurring and outputs a system disturbance determination signal when the system frequency is greater than an upper frequency threshold, or when the system frequency is less than a lower frequency threshold, or when the system voltage detection value is greater than an upper voltage threshold, or when the system voltage detection value is less than a lower voltage threshold; a virtual synchronous generator model which calculates a VSG angular frequency simulating a synchronous generator for performing the virtual synchronous generator control based on the internal induced voltage, the output current detection value, and a machine input command value which is an output command value of the DC / AC converter, and outputs a phase based on the PLL angular frequency when the DC / AC converter is stopped and the system disturbance determination signal is not output, and outputs a phase based on the VSG angular frequency when the DC / AC converter is operating or the system disturbance determination signal is output; a virtual synchronous impedance compensator that simulates a voltage drop due to an internal impedance of the synchronous generator based on the internal induced voltage, the system voltage detection value, and the output current detection value, and calculates a system voltage command value; a PCS output voltage control unit that performs voltage control to control the grid voltage detection value to the grid voltage command value and outputs a PWM control command value; a PWM control unit that generates a gate signal for the DC / AC converter based on the PWM control command value and the phase, blocks the gate signal for the DC / AC converter when the DC / AC converter is not used, and starts outputting the gate signal to the DC / AC converter when the system disturbance determination signal is output; A grid-connected power conversion device comprising:

2. The virtual synchronous generator model is a mechanical input torque calculation unit that converts the mechanical input command value into a mechanical input torque; an electric output torque calculation unit that calculates an electric output torque from the internal induced voltage and the output current detection value; a first subtractor for subtracting the electrical output torque from the mechanical input torque; a damping block that outputs a damping torque simulating a torque generated in a damper winding based on a previous value of the switch output; a second subtractor that subtracts the braking torque from the output of the first subtractor; an inertia block that divides the output of the second subtractor by an inertia constant; a first adder that adds a previous value of the output of the switch to the output of the inertia block to output the VSG angular frequency; the switch outputs the PLL angular frequency when the DC / AC converter is stopped and the system disturbance determination signal is not output, and outputs the VSG angular frequency when the DC / AC converter is operating or the system disturbance determination signal is output; a second adder that adds a fundamental frequency to the output of the switch and outputs the result as an angular frequency; a first integrator that integrates an output of the second adder and outputs the phase; 2. The grid-connected power conversion device according to claim 1, further comprising:

3. 3. The grid-interconnected power conversion device according to claim 1, wherein the grid disturbance determination unit determines that a grid disturbance is occurring and outputs the grid disturbance determination signal when a rate of change of the grid frequency when increasing is greater than a threshold when increasing, or when a rate of change of the grid frequency when decreasing is greater than a threshold when decreasing.

4. The virtual synchronous generator model is 3. The grid-interconnected power conversion device according to claim 2, wherein the inertia constant is made variable in response to the output current detection value when the grid frequency or the grid voltage detection value fluctuates.

5. The virtual synchronous generator model is a table for outputting an amount of change in inertia constant based on the detected output current value; A second integrator that integrates the inertia constant change amount; a limiter that limits an output of the second integrator by a limit value and outputs the limit value as an inertia constant adjustment amount; 5. The grid-interconnected power conversion device according to claim 4, further comprising: an adder that calculates the inertia constant by adding the inertia constant adjustment amount to a normal inertia constant.

6. A control method for a grid-connected power conversion device in which virtual synchronous generator control simulating a synchronous generator is performed, the control method includes a DC / AC converter that converts DC power of a DC power supply into AC power, and an output of the DC / AC converter is connected to a power grid via an LC filter, the control method comprising the steps of: an internal induced voltage calculation unit calculates an internal induced voltage based on an output current detection value, an effective value of a grid voltage detection value, and an AC voltage command value; The PLL outputs a system frequency and a PLL angular frequency based on the system voltage detection value, a system disturbance determination unit, when the system frequency is greater than an upper frequency threshold, or when the system frequency is less than a lower frequency threshold, or when the system voltage detection value is greater than an upper voltage threshold, or when the system voltage detection value is less than a lower voltage threshold, determines that a system disturbance is occurring and outputs a system disturbance determination signal; a virtual synchronous generator model calculates a VSG angular frequency simulating a synchronous generator for performing the virtual synchronous generator control based on the internal induced voltage, the output current detection value, and a machine input command value which is an output command value of the DC / AC converter, and outputs a phase based on the PLL angular frequency when the DC / AC converter is stopped and the system disturbance determination signal is not output, and outputs a phase based on the VSG angular frequency when the DC / AC converter is operating or the system disturbance determination signal is output; a virtual synchronous impedance compensator that simulates a voltage drop due to an internal impedance of the synchronous generator based on the internal induced voltage, the system voltage detection value, and the output current detection value, and calculates a system voltage command value; a PCS output voltage control unit that performs voltage control to control the grid voltage detection value to the grid voltage command value and outputs a PWM control command value; a PWM control unit generates a gate signal for the DC / AC converter based on the PWM control command value and the phase, blocks the gate signal for the DC / AC converter when the DC / AC converter is not used, and starts outputting the gate signal to the DC / AC converter when the system disturbance determination signal is output.

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