System interconnection power conversion device and control method of system interconnection power conversion device

Abstract

To maintain synchronizing power of a virtual synchronous generator during a suppression operation of excess current and suppress step-out in a system interconnection power conversion device performing a virtual synchronous generator control of a voltage control type.SOLUTION: A DC power supply Vdc is systematically linked through an inverter INV, an LC filter LC, and a transformer Tr. An electric output calculation unit 4 calculates an electric output Pe based on an output current detection value Iac at a normal time, and calculates the electric output Pe based on an output current estimation value at a time of an output current suppression. An instantaneous voltage control unit 6 outputs instantaneous voltage command values va*, vb*, and vc* from an output phase θ calculated based on an output voltage command value Vac* and the electric output Pe. A PWM modulation unit 7 generates a gate signal Gate of the inverter INV based on the instantaneous voltage command values va*, vb*, and vc*.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control method for exerting a synchronizing force when suppressing an overcurrent caused by a system fault or the like in a grid-connected power conversion device that performs voltage-controlled virtual synchronous generator control simulating a synchronous generator. [Background technology]

[0002] Patent Document 1 discloses a current control type virtual generator control that controls the current output by the inverter based on a voltage amplitude command value, and a current command value calculated from the relationship between an instantaneous voltage command value obtained from a frequency and phase calculated based on an oscillation equation, and a virtual impedance.

[0003] Patent Document 2 discloses a technology for suppressing overcurrent in voltage-controlled virtual generator control that directly controls the voltage amplitude command value and the instantaneous voltage command value obtained from the frequency and phase calculated based on an oscillation equation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6084863 [Patent Document 2] WO2021 / 029313A1 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem with Patent Documents 1 and 2 is that when an inverter performing virtual synchronous generator control suppresses an overcurrent, a synchronizing force corresponding to the phase difference between the virtual synchronous generator and other power generating devices is not exerted, causing the virtual synchronous generator to become unstable or to lose synchronization with the grid.

[0006] In the current-controlled virtual synchronous generator control as disclosed in Patent Document 1, the inverter is controlled so that the current command value and the actual output current match, thereby simulating the driving of a virtual synchronous generator. One method for the inverter to suppress overcurrent is to limit the amplitude of the current command value, at which time the output active power and reactive power are reduced.

[0007] On the other hand, in the voltage-controlled virtual synchronous generator control as in Patent Document 2, the drive of a virtual synchronous generator is simulated by controlling the inverter so that the voltage command value and the actual output voltage match, and the output current is not directly controlled. Methods for suppressing overcurrent include a method for increasing the impedance of the virtual synchronous generator model and a method for bringing the system voltage vector and the voltage command value closer together, and the output active power and reactive power of the inverter may increase or decrease depending on external factors such as the method for suppressing overcurrent and the system impedance.

[0008] When overcurrent is not suppressed by the above-mentioned virtual synchronous generator control, the inverter performs control so as to match the current command value and voltage command value for simulating the drive of the virtual synchronous generator, and the output active power at this time is a value that reflects the result of simulating the virtual synchronous generator. The output frequency of the virtual synchronous generator is calculated from an oscillation equation that includes an element of the output active power, and the output frequency operates in a stable direction due to the action of a synchronizing force according to the phase difference between the virtual synchronous generator and other power generating devices.

[0009] On the other hand, when the overcurrent is suppressed, the inverter prioritizes the control for suppressing the overcurrent as described above, and therefore the behavior of the virtual synchronous generator is no longer simulated, and the output active power does not reflect the result of simulating the virtual synchronous generator. As a result, no synchronizing force is applied to the output frequency of the virtual synchronous generator, and the operation as a virtual synchronous generator may become unstable. Specifically, when the system is restored from a grid accident or when the output current is suppressed due to an overload, the response of the output frequency changes, causing the operation of the virtual synchronous generator to become unstable, and in some cases, causing a step-out.

[0010] As described above, in a grid-connected power conversion device that performs voltage-controlled virtual synchronous generator control, a challenge is how to maintain the synchronizing power of the virtual synchronous generator and suppress loss of synchronism during an operation to suppress an overcurrent. [Means for solving the problem]

[0011] The present invention has been devised in view of the above-mentioned problems in the conventional art, and one aspect of the present invention is a grid-connected power conversion device that connects a DC power source to a grid via an inverter, an LC filter, and a transformer, and performs voltage-controlled virtual synchronous generator control, and is characterized in that it comprises an electric output calculation unit that calculates an electric output based on an output current detection value under normal conditions, and calculates the electric output based on an output current estimation value when the output current is suppressed, an instantaneous voltage control unit that outputs an instantaneous voltage command value from an output phase calculated based on an output voltage command value and the electric output, and a PWM modulation unit that generates a gate signal for the inverter based on the instantaneous voltage command value.

[0012] In one aspect, the electrical output calculation unit normally calculates the electrical output using equation (2) or (3), and when the output current is suppressed, calculates the electrical output by adding together a value obtained by multiplying a d-axis internal induced voltage by a d-axis estimated output current and a value obtained by multiplying a q-axis internal induced voltage by a q-axis estimated output current, or by adding together a value obtained by multiplying a d-axis output voltage detection value by the d-axis estimated output current and a value obtained by multiplying a q-axis output voltage detection value by the q-axis estimated output current.

[0013]

number

[0014]

number

[0015] P e : Electric output E f_d : d-axis internal induced voltage E f_q :q-axis internal induced voltage I ac_d : d-axis output current detection value I ac_q : q-axis output current detection value V ac_d : d-axis output voltage detection value V ac_q : q-axis output voltage detection value.

[0016] In one aspect, the electric output calculation unit calculates the d-axis estimated output current and the q-axis estimated output current by using equation (4).

[0017]

number

[0018] ^I ac_d : d-axis estimated output current ^I ac_q : q-axis estimated output current r s , x s : Virtual impedance E f_d : d-axis internal induced voltage E f_q :q-axis internal induced voltage V ac_d : d-axis output voltage detection value V ac_q : q-axis output voltage detection value.

[0019] In another aspect, the electric output calculation unit calculates the d-axis estimated output current and the q-axis estimated output current by using equation (5).

[0020]

number

[0021] ^I ac_d : d-axis estimated output current ^I ac_q : q-axis estimated output current r tr , x tr : Transformer impedance Ef_d : d-axis internal induced voltage E f_q :q-axis internal induced voltage V sys_d : d-axis system voltage detection value V sys_q :q-axis system voltage detection value.

[0022] In one aspect, the inverter circuit includes a reactive power calculation unit that calculates reactive power based on an output voltage detection value and the output current detection value, a voltage amplitude command generation unit that calculates an internal induced voltage based on a reference voltage command and the reactive power, an impedance control unit that calculates a voltage drop due to a virtual impedance based on the output current detection value, a subtractor that calculates the output voltage command value by subtracting the voltage drop due to the virtual impedance from the internal induced voltage, and a voltage phase command calculation unit that calculates the output phase based on an oscillation equation from the electrical output and a mechanical input command value.

[0023] In another aspect, the inverter circuit includes a reactive power calculation unit that calculates reactive power based on an output voltage detection value and the output current detection value, a voltage amplitude command generation unit that calculates an internal induced voltage based on a reference voltage command and the reactive power and outputs it as the output voltage command value, and a voltage phase command calculation unit that calculates the output phase based on an oscillation equation from the electrical output and a machine input command value. Effect of the Invention

[0024] According to the present invention, in a grid-connected power conversion device that performs voltage-controlled virtual synchronous generator control, it is possible to maintain the synchronizing force of the virtual synchronous generator and suppress loss of synchronism during an operation to suppress an overcurrent. [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic diagram showing an overall configuration of a grid-connected power conversion device according to a first embodiment. [Diagram 2] FIG. 3 is a schematic diagram showing an electrical output calculation unit according to the first embodiment. [Diagram 3] FIG. 2 is a diagram showing a virtual synchronous generator model according to the first embodiment. [Figure 4] FIG. 13 is a diagram showing the frequency behavior when the system voltage drops (an example of a step-out) according to the conventional method. [Diagram 5] FIG. 4 is a diagram showing frequency behavior when a system voltage drops in the first embodiment. [Figure 6] FIG. 6 is a schematic diagram showing the overall configuration of a grid-connected power conversion device according to a second embodiment. [Figure 7] FIG. 11 is a schematic diagram showing an electrical output calculation unit according to a second embodiment. [Figure 8] FIG. 11 is a diagram showing a virtual synchronous generator model according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, first and second embodiments of the grid-connected power conversion device according to the present invention will be described in detail with reference to FIGS.

[0027] [Embodiment 1] FIG. 1 is an overall schematic diagram of a grid-connected power conversion device in the present embodiment 1. As shown in FIG. 1, the main circuit configuration of the grid-connected power conversion device includes a DC power source V dc This is connected to the grid via an inverter INV consisting of IGBTs, an LC filter LC, and a transformer Tr.

[0028] LC filter LC is a filter reactor L f and filter capacitor C f In addition, the output current detection value I ac and the output voltage detection value V ac is detected and output to a control block, which will be described later.

[0029] The control block of the grid-connected power conversion device in this embodiment 1 includes a reactive power calculation unit 1, a voltage amplitude command generation unit 2, an impedance control unit 3, an electrical output calculation unit 4, a voltage phase command generation unit 5, an instantaneous voltage control unit 6, a PWM modulation unit 7, and a subtractor 8.

[0030] The reactive power calculation unit 1 calculates the output voltage detection value V acand the output current detection value I ac From reactive power Q ac Calculate.

[0031] The voltage amplitude command generator 2 generates a reference voltage command value V ref and reactive power Q ac From the internal induced voltage E f The voltage amplitude command generating unit 2 includes a reactive power droop control unit 9, a subtractor 10, and a voltage amplitude control unit 11. The reactive power droop control unit 9 calculates the reactive power Q ac The subtractor 10 outputs a value that suppresses cross current between power sources based on the reference voltage command value V ref The voltage amplitude control unit 11 subtracts the output of the reactive power droop control unit 9 from the internal induced voltage E f Output.

[0032] The impedance control section 3 detects the output current I ac From the virtual impedance Z s The output characteristics are simulated by the voltage drop V z The subtractor 8 outputs the internal induced voltage E f Voltage drop V z is subtracted to obtain the output voltage command value V ac * Output.

[0033] The electrical output calculation unit 4 calculates the internal induced voltage E f Or output voltage detection value V ac and the output current detection value I ac Electric output P e The voltage phase command generating unit 5 calculates the machine input command value P m and electrical output P e The output phase θ is calculated based on the oscillation equation.

[0034] The instantaneous voltage control unit 6 controls the output voltage command value V ac * The instantaneous voltage command value v that controls the output voltage of the inverter INV from the output phase θ a * ,v b * ,v c* The PWM modulation unit 7 outputs the instantaneous voltage command value v a * ,v b * ,v c * The gate signal Gate is generated by comparing this with the carrier triangular wave.

[0035] The reactive power calculation unit 1, the voltage amplitude command generation unit 2, the impedance control unit 3, the voltage phase command generation unit 5, the instantaneous voltage control unit 6, and the PWM modulation unit 7 are not directly related to the present invention, and therefore will not be described in detail here.

[0036] 2 shows the electric output calculation unit 4 of the first embodiment. As shown in FIG. 2, the output current estimation unit 12 of the electric output calculation unit 4 calculates the internal induced voltage Ef and the output voltage detection value V ac and the virtual impedance Z s Using the estimated output current ^I ac Calculate.

[0037] In addition, the internal induced voltage E f =E f_d +jE f_q , output voltage detection value V ac =V ac_d +jV ac_q , the virtual impedance Z s =r s +jx s , estimated output current ^I ac =^I ac_d +j^I ac_q Let us assume that.

[0038] Specifically, the subtractor 13d subtracts the d-axis internal induced voltage E f_d to d-axis output voltage detection value V ac_d The subtractor 13q subtracts the q-axis internal induced voltage E f_q to q-axis output voltage detection value V ac_q Subtract.

[0039] The multiplier 14a multiplies the output of the subtractor 13d by r s / r s 2 +x s 2The multiplier 14b multiplies the output of the subtractor 13q by x s / r s 2 +x s 2 The multiplier 14c multiplies the output of the subtractor 13d by -x s / r s 2 +x s 2 The multiplier 14d multiplies the output of the subtractor 13q by r s / r s 2 +x s 2 Multiply by.

[0040] The adder 15d adds the output of the multiplier 14a and the output of the multiplier 14b to obtain the d-axis estimated output current ^I ac_d The adder 15q adds the output of the multiplier 14c and the output of the multiplier 14d to obtain the q-axis estimated output current ^I ac_q The output is as follows:

[0041] The switch SW1 normally controls the d-axis output current detection value I ac_d When the output current is suppressed, the d-axis estimated output current ^I ac_d The switch SW2 normally outputs the q-axis output current detection value I ac_q When the output current is suppressed, the q-axis estimated output current ^I ac_q Output.

[0042] Multiplier 16d is the d-axis internal induced voltage E f_d or d-axis output voltage detection value V ac_d is multiplied by the output of switch SW1. Multiplier 16q multiplies the q-axis internal induced voltage E f_q or q-axis output voltage detection value V ac_q is multiplied by the output of switch SW2. Adder 17 adds the output of multiplier 16d and the output of multiplier 16q to obtain electrical output P e The output is as follows:

[0043] The virtual synchronous generator model simulated by the first embodiment is shown in FIG. 3. The output voltage command value V ac * can be calculated using equation (1).

[0044]

number

[0045] Z s I ac is the virtual impedance Z s =r s +jx s Voltage drop due to (drop voltage V z ) and is calculated by the impedance control unit 3.

[0046] Normally, the inverter INV is at the output voltage detection value V ac is the output voltage command value V ac * The voltage is controlled so as to match the virtual synchronous generator model.

[0047] Electric output P of the electric output calculation unit 4 e can be obtained by equation (2) when considering the loss of the virtual impedance in addition to the output of the inverter INV, and by equation (3) when considering only the output of the inverter INV. Either equation can be used.

[0048]

number

[0049]

number

[0050] In addition, the output current detection value I ac =I ac_d +jI ac_q Let us assume that.

[0051] This electrical output Pe is generated by the phase difference between the virtual synchronous generator model and the grid voltage, and exerts a synchronizing force to stabilize the virtual synchronous generator.

[0052] Here, we consider the case where the output current is suppressed. As a method of suppressing the output current, a virtual impedance Z s In the first embodiment, the output current is suppressed by using the method in the patent document 2 or the like. In either case, the output current suppression is prioritized, so the inverter INV adjusts the output voltage command value V obtained from the formula (1) ac * Therefore, the virtual synchronous generator model does not hold true during output current suppression. ac Electric output P calculated from e does not act as a synchronizing force and the virtual synchronous generator may become unstable.

[0053] Therefore, the electrical output P e The output current used to derive the estimated output current ^I is calculated using equation (4). ac =^I ac_d +j^I ac_q The output current estimating unit 12 in FIG. 2 is a diagram illustrating the formula (4).

[0054]

number

[0055] Estimated output current^I ac represents the output current value that should flow when the virtual synchronous generator model is valid. This allows the output current suppression method to suppress the output current detection value I ac While suppressing the output voltage detection value V ac In this case, the same synchronizing force as that in the case where the virtual synchronous generator model holds true can be generated for the virtual synchronous generator, and the virtual synchronous generator can be operated in a stable direction.

[0056] The voltage fluctuation caused by the impedance of the upper transformer and the system and the suppressed output current is the output voltage detection value V ac Therefore, the frequency response will not be exactly the same as under normal conditions.

[0057] The effects of the first embodiment will be described by taking as an example the time when the system voltage recovers after an instantaneous voltage drop.

[0058] First, the conventional operation will be described. In the conventional operation, the switches SW1 and SW2 in FIG. ac_d , q-axis output current detection value I ac_q During an instantaneous voltage drop in the grid voltage, if the current value flowing due to the simulation of the virtual synchronous generator model exceeds the maximum output current value of the inverter INV, the inverter INV will perform output current suppression operation. The output voltage of the inverter INV will drop and the electrical output P e decreases, and the machine input command value P m If the frequency is maintained, the frequency increases.

[0059] Next, when the grid voltage is restored, the phase difference between the output phase θ of the inverter INV and the grid voltage is small, and the output current detection value I ac When the current limit of the inverter INV is reached, the output current suppression ends. e Since the virtual synchronous generator has a phase difference between the virtual synchronous generator and the grid voltage and has a synchronizing force, the phase difference between the virtual synchronous generator and the grid voltage gradually decreases and the generator operates in a stable direction.

[0060] On the other hand, when the phase difference between the output phase θ of the inverter INV and the grid voltage is large when the grid voltage is restored, and the output current suppression continues, the electrical output P e does not have a synchronizing power because it is not the power that is the phase difference between the virtual synchronous generator and the grid voltage. The power that is the phase difference between the output phase θ of the inverter INV and the grid voltage due to the output current suppression operation may increase or decrease, and the virtual synchronous generator may decelerate or accelerate.

[0061] This can cause output oscillations and step-out of the virtual synchronous generator. Figure 4 shows an example of the virtual synchronous generator accelerating and stepping out when the grid voltage is restored using the conventional method. From the relationship between the output phase θ of the inverter INV and the grid voltage phase when the grid voltage is restored, it can be seen that if the active power decreases, the frequency of the inverter INV rises, further increasing the frequency difference with the grid voltage and causing divergence.

[0062] Next, the operation of the first embodiment will be described.

[0063] If the current is suppressed during an instantaneous voltage drop in the grid voltage, the electrical output P of the virtual synchronous generator is also e decreases, and the machine input command value P m If the output current estimation flag is set, the frequency will increase. At this time, the switches SW1 and SW2 in Fig. 2 are set to the d-axis estimated output current ^I ac_d , q-axis estimated output current ^I ac_q has been switched to the other side.

[0064] Next, when the grid voltage is restored, if the phase difference between the inverter INV output phase θ and the grid voltage is large and the output current suppression operation continues, the estimated output current ^I ac Using this, we can obtain a virtual synchronous generator and its output voltage V ac The electrical output P that can be obtained from the phase relationship e At this time, the electrical output P e does not match the actual output power of the inverter INV. As a result, a synchronizing force acts even during output current suppression operation, and the virtual synchronous generator can be operated in a stable direction. FIG. 5 shows how the virtual generator operates in a stable direction when the grid voltage is restored in this embodiment 1 in the same event as in FIG. 4. From the relationship between the output phase θ of the inverter INV and the grid voltage phase when the grid voltage is restored, the active power decreases, but the electrical output Pe increases, so the frequency of the inverter INV decreases and it can be seen that it is synchronized with the grid voltage.

[0065] As described above, according to the first embodiment, in a grid-connected power conversion device that performs voltage-controlled virtual synchronous generator control, by calculating an electric output based on an estimated output current instead of a current measurement value during an output current suppression operation, it is possible to apply a synchronizing force of the virtual synchronous generator and suppress loss of synchronism.

[0066] [Embodiment 2] Fig. 6 shows an overall schematic diagram of a grid-connected power conversion device in the second embodiment, and Fig. 7 shows an electric output calculation unit 4 in the second embodiment. The second embodiment differs from the first embodiment in the following points.

[0067] As shown in FIG. 6, in the second embodiment, the impedance control unit 3 and the subtractor 8 are omitted. f is the output voltage command value V ac * to the instantaneous voltage control unit 6.

[0068] As shown in FIG. 6, the electric output calculation unit 4 calculates the internal induced voltage E f and the system voltage detection value V sys and the output current detection value I ac and the output voltage detection value V ac Input the electrical output P e Output.

[0069] The output voltage detection value V ac and the virtual impedance Z s Instead, the system voltage detection value V sys and the transformer impedance Z tr is used.

[0070] As shown in FIG. 7, in the second embodiment, the output current estimator 18 estimates the d-axis estimated output current ^I ac_d , q-axis estimated output current ^I ac_q Specifically, the subtractor 19d calculates the d-axis internal induced voltage E f_d to d-axis system voltage detection value V sys_d The subtractor 19q subtracts the q-axis internal induced voltage E f_q to q-axis system voltage detection value Vsys_q Subtract.

[0071] The multiplier 20a multiplies the output of the subtractor 19d by r tr / r tr 2 +x tr 2 The multiplier 20b multiplies the output of the subtractor 19q by x tr / r tr 2 +x tr 2 The multiplier 20c multiplies the output of the subtractor 19d by -x tr / r tr 2 +x tr 2 The multiplier 20d multiplies the output of the subtractor 19q by r tr / r tr 2 +x tr 2 Multiply by.

[0072] The adder 21d adds the output of the multiplier 20a and the output of the multiplier 20b to obtain the d-axis estimated output current ^I ac_d The adder 21q adds the output of the multiplier 20c and the output of the multiplier 20d to obtain the q-axis estimated output current ^I ac_q The subsequent steps are the same as in the first embodiment.

[0073] A virtual synchronous generator model simulated by the second embodiment is shown in FIG. 8. Since the second embodiment is a model that does not include virtual impedance, the internal induced voltage E f is the output voltage command V ac * become.

[0074] In the second embodiment, when suppressing the output current, the electric output P e The output current used to derive the estimated output current ^I ac However, the estimated output current ^I ac * is the system voltage V sys =V sys_d +jV sys_q and the transformer impedance Z on the grid sidetr ==r tr +jx tr It is calculated using formula (5).

[0075]

number

[0076] This makes it possible to maintain the synchronizing force during output current suppression even in a voltage-controlled virtual synchronous generator control that does not have a virtual impedance in the virtual synchronous generator model. tr However, the transformer is not limited to a transformer as long as it is the total value of the impedance from the inverter output to the voltage detection point on the grid side.

[0077] 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]

[0078] V dc …DC power supply INV…Inverter LC...LC filter Tr...transformer Grid…system 1...Reactive power calculation section 2...Voltage amplitude command generator 3. Impedance control section 4. Electric output calculation section 5…Voltage phase command generator 6…Instantaneous voltage control section 7…PWM modulation section 8…Subtractor

Claims

1. A grid-connected power conversion device that connects a DC power supply to a grid via an inverter, an LC filter, and a transformer and performs voltage-controlled virtual synchronous generator control, an electric output calculation unit that calculates an electric output based on an output current detection value during normal operation and calculates the electric output based on an output current estimation value during output current suppression; an instantaneous voltage control unit that outputs an instantaneous voltage command value from an output phase calculated based on an output voltage command value and the electrical output; a PWM modulation unit that generates a gate signal for the inverter based on the instantaneous voltage command value.

2. The electrical output calculation unit In normal operation, the electrical output is calculated using formula (2) or (3).

2. The grid-connected power conversion device according to claim 1, wherein, during output current suppression, the electrical output is calculated by adding together a value obtained by multiplying a d-axis internal induced voltage by a d-axis estimated output current and a value obtained by multiplying a q-axis internal induced voltage by a q-axis estimated output current, or by adding together a value obtained by multiplying a d-axis output voltage detection value by the d-axis estimated output current and a value obtained by multiplying a q-axis output voltage detection value by the q-axis estimated output current. [0025] [0030] P ｅ :Electric output E ｆ＿ｄ :d-axis internal induced voltage E ｆ＿ｑ : q-axis internal induced voltage I ａｃ＿ｄ : d-axis output current detection value I ａｃ＿ｑ : q-axis output current detection value V ａｃ＿ｄ : d-axis output voltage detection value V ａｃ＿ｑ : q-axis output voltage detection value

3. The electrical output calculation unit 3. The grid-connected power conversion device according to claim 2, wherein the d-axis estimated output current and the q-axis estimated output current are calculated by the following equation (4). [0045] ^I ａｃ＿ｄ : d-axis estimated output current ^I ａｃ＿ｑ : q-axis estimated output current r ｓ , x ｓ : Virtual impedance E ｆ＿ｄ :d-axis internal induced voltage E ｆ＿ｑ : q-axis internal induced voltage V ａｃ＿ｄ : d-axis output voltage detection value V ａｃ＿ｑ : q-axis output voltage detection value

4. The electrical output calculation unit 3. The grid-connected power conversion device according to claim 2, wherein the d-axis estimated output current and the q-axis estimated output current are calculated by the following equation (5). [0050] ^I ａｃ＿ｄ : d-axis estimated output current ^I ａｃ＿ｑ : q-axis estimated output current r ｔｒ , x ｔｒ : Transformer impedance E ｆ＿ｄ :d-axis internal induced voltage E ｆ＿ｑ : q-axis internal induced voltage V ｓｙｓ＿ｄ : d-axis system voltage detection value V ｓｙｓ＿ｑ : q-axis system voltage detection value

5. a reactive power calculation unit that calculates reactive power based on an output voltage detection value and the output current detection value; a voltage amplitude command generating unit that calculates an internal induced voltage based on a reference voltage command and the reactive power; an impedance control unit that calculates a voltage drop due to a virtual impedance based on the output current detection value; a subtractor that calculates the output voltage command value by subtracting the voltage drop due to the virtual impedance from the internal induced voltage; a voltage phase command calculation unit that calculates the output phase based on a vibration equation from the electrical output and a mechanical input command value; 4. The grid-connected power conversion device according to claim 3, further comprising:

6. a reactive power calculation unit that calculates reactive power based on an output voltage detection value and the output current detection value; a voltage amplitude command generating unit that calculates an internal induced voltage based on a reference voltage command and the reactive power and outputs the internal induced voltage as the output voltage command value; a voltage phase command calculation unit that calculates the output phase based on a vibration equation from the electrical output and a mechanical input command value; 5. The grid-connected power conversion device according to claim 4, further comprising:

7. A method for controlling a grid-connected power conversion device that connects a DC power supply to a grid via an inverter, an LC filter, and a transformer and performs voltage-controlled virtual synchronous generator control, comprising the steps of: an electric output calculation unit that calculates an electric output based on an output current detection value during normal operation, and calculates the electric output based on an output current estimation value during output current suppression; an instantaneous voltage control unit outputs an instantaneous voltage command value from an output phase calculated based on an output voltage command value and the electrical output; A method for controlling a grid-connected power conversion device, comprising the steps of: a PWM modulation unit generating a gate signal for the inverter based on the instantaneous voltage command value.

Images