System interconnection power conversion device and method for controlling system interconnection power conversion device

Abstract

A DC power supply Vdc is system-interconnected via an inverter INV, an LC filter LC, and a transformer Tr. An electric output calculation part 4 calculates an electric output Pe on the basis of an output current detection value Iac during normal times, and calculates an electric output Pe on the basis of the output current estimation value when the output current is suppressed. An instantaneous voltage control unit 6 outputs an instantaneous voltage command value va *, vb *, vc * from an output phase θ calculated on the basis of 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 on the basis of instantaneous voltage command value va *, vb *, and vc *. In a system interconnection power conversion device for performing voltage control type virtual synchronous generator control, during an overcurrent suppression operation, the synchronization force of a virtual synchronous generator is maintained and step-out is suppressed.

Description

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

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

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

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

[0004] Patent No. 6084863 WO2021 / 029313A1

[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 lose synchronization with the grid.

[0006] In the current-controlled virtual synchronous generator control 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 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 matches the actual output voltage, and the output current is not directly controlled. Methods for suppressing overcurrent include increasing the impedance of the virtual synchronous generator model and bringing the grid voltage vector closer to the voltage command value, and the inverter's output active power and reactive power may increase or decrease depending on external factors such as the overcurrent suppression method and grid impedance.

[0008] When overcurrent is not suppressed by the virtual synchronous generator control described above, the inverter controls the current command value and voltage command value to match those used to simulate the drive of the virtual synchronous generator, and the output active power at this time reflects the results 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 output active power, and the output frequency operates in a stable direction due to the action of a synchronizing force corresponding to the phase difference between the virtual synchronous generator and other power generating devices.

[0009] On the other hand, when overcurrent is being suppressed, the inverter prioritizes the control for suppressing overcurrent as described above, and therefore no longer simulates the behavior of the virtual synchronous generator, and the output active power does not reflect the results of simulating the virtual synchronous generator. As a result, no synchronizing force is applied to the output frequency of the virtual synchronous generator, which can cause unstable operation as a virtual synchronous generator. Specifically, when the grid recovers from a fault or when the output current is suppressed due to an overload, the response of the output frequency changes, making the operation of the virtual synchronous generator unstable and, in some cases, causing loss of synchronism.

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

[0011] The present invention has been devised in view of the above-mentioned problems of the related art, and one aspect thereof is 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, and is characterized by comprising: 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]

[0014]

[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]

[0018] ^I ａｃ＿ｄ : d-axis estimated output current ^I ａｃ＿ｑ : q-axis estimated output current r ｓ , xｓ : 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]

[0021] ^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.

[0022] In one aspect, the inverter comprises 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 is characterized by comprising 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 the internal induced voltage 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 mechanical input command value.

[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 power of the virtual synchronous generator and suppress loss of synchronism during an operation to suppress an overcurrent.

[0025] 1 is a schematic diagram showing the overall configuration of a grid-connected power conversion device of embodiment 1. 2 is a schematic diagram showing an electrical output calculation unit of embodiment 1. 3 is a diagram showing a virtual synchronous generator model of embodiment 1. 4 is a diagram showing frequency behavior when the grid voltage drops in a conventional method (an example of a case where step-out occurs). 5 is a diagram showing frequency behavior when the grid voltage drops in embodiment 1. 6 is a schematic diagram showing the overall configuration of a grid-connected power conversion device of embodiment 2. 7 is a schematic diagram showing an electrical output calculation unit of embodiment 2. 8 is a diagram showing a virtual synchronous generator model of embodiment 2.

[0026] Hereinafter, first and second embodiments of the grid-connected power conversion device of 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 embodiment 1. As shown in Fig. 1, the main circuit configuration of the grid-connected power conversion device is a DC power source V ｄｃ The inverter INV is connected to the grid via an inverter INV including IGBTs, an LC filter LC, and a transformer Tr.

[0028] LC filter LC is a filter reactor L ｆ and filter capacitor C ｆ The output current detection value I between the LC filter LC and the transformer Tr is 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 ａｃ and 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 generator 2 includes a reactive power droop controller 9, a subtractor 10, and a voltage amplitude controller 11. The reactive power droop controller 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 unit 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 ＊ and 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 the voltage Vcc with the carrier triangular wave.

[0035] The reactive power calculation unit 1, voltage amplitude command generation unit 2, impedance control unit 3, voltage phase command generation unit 5, instantaneous voltage control unit 6, and PWM modulation unit 7 are not directly related to the present invention, so detailed description thereof will be omitted 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 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 , virtual impedance Z ｓ =r ｓ +jx ｓ , estimated output current ^I ａｃ =^I ａｃ＿ｄ +j^I ａｃ＿ｑ Let's say.

[0038] Specifically, the subtractor 13d subtracts the d-axis internal induced voltage E ｆ＿ｄ 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 ２ The 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 Output as

[0041] The switch SW1 is normally turned on based on the output current suppression flag to suppress 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] The multiplier 16d calculates 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 the switch SW1. The multiplier 16q multiplies the q-axis internal induced voltage E ｆ＿ｑ Or q-axis output voltage detection value V ａｃ＿ｑ The adder 17 adds the output of the multiplier 16d and the output of the multiplier 16q to obtain the electrical output P ｅ Output as

[0043] The virtual synchronous generator model simulated in the first embodiment is shown in Fig. 3. The output voltage command value V of the inverter INV when no overcurrent is suppressed (hereinafter referred to as normal time) ａｃ ＊ is calculated using equation (1).

[0044]

[0045] Z ｓ I ａｃ is the virtual impedance Z ｓ =r ｓ +jxｓ Voltage drop due to 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 to match the virtual synchronous generator model.

[0047] Electric output P of the electric output calculation unit 4 ｅ is obtained by equation (2) when the loss of the virtual impedance is taken into consideration in addition to the output of the inverter INV, and by equation (3) when only the output of the inverter INV is taken into consideration, and either may be used.

[0048]

[0049]

[0050] The output current detection value I ａｃ =I ａｃ＿ｄ +jI ａｃ＿ｑ Let's say.

[0051] This electrical output P ｅ is generated by the phase difference between the virtual synchronous generator model and the grid voltage, and exerts a synchronizing force that acts in the direction of stabilizing the virtual synchronous generator.

[0052] Here, we consider the case where output current suppression is performed. As a method for suppressing output current, a virtual impedance Z ｓ Patent Document 2 discloses a method for suppressing the output current by adjusting the output voltage command value V obtained from equation (1). In this embodiment, the output current is also suppressed using the method in Patent Document 2. In either case, priority is given to suppressing the output current, so the inverter INV is controlled by adjusting the output voltage command value V obtained from equation (1). ａｃ ＊ Therefore, the virtual synchronous generator model does not hold when the output current is suppressed. ａｃ Electrical output P obtained from ｅ does not act as a synchronizing force, and the virtual synchronous generator may become unstable.

[0053] Therefore, the flag information during the output current suppression operation is used to 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 estimation unit 12 in FIG. 2 is a diagram illustrating the formula (4).

[0054]

[0055] Estimated output current ^I ａｃ represents the output current value that should flow when the virtual synchronous generator model is valid. As a result, the output current detection value I ａｃ While suppressing the output voltage detection value V ａｃ Therefore, the same synchronizing force as when the virtual synchronous generator model is valid can be generated for the virtual synchronous generator, and the virtual synchronous generator can be operated in a stable direction.

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

[0057] The effect of the first embodiment will be described using an example in which 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. 2 are connected to the d-axis output current detection value I 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 an 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 system voltage is restored, the phase difference between the output phase θ of the inverter INV and the system voltage is small, and the output current detection value I ａｃWhen the electric output P ｅ Since the phase difference between the virtual synchronous generator and the grid voltage is a power that 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 system voltage is large when the system voltage is restored, and the output current suppression continues, the electric output P ｅ does not result in power resulting from the phase difference between the virtual synchronous generator and the grid voltage, and does not have a synchronizing power. The power resulting from the phase difference between the output phase θ of the inverter INV and the grid voltage due to output current suppression operation may increase or decrease, and the virtual synchronous generator may decelerate or accelerate.

[0061] This may cause output oscillations and step-out of the virtual synchronous generator. Figure 4 shows an example of the virtual synchronous generator accelerating and moving in the step-out direction when the grid voltage is restored using the conventional method. When the grid voltage is restored, the relationship between the output phase θ of the inverter INV and the grid voltage phase shows 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 system voltage, the electrical output P of the virtual synchronous generator is also ｅ decreases, and the machine input command value P ｍ If the d-axis estimated output current ^I is maintained, the frequency will increase. At this time, the output current estimation flag is set, so the switches SW1 and SW2 in FIG. ａｃ＿ｄ , q-axis estimated output current ^I ａｃ＿ｑ It has been switched to the other side.

[0064] Next, when the grid voltage is restored, if the phase difference between the output phase θ of the inverter INV and the grid voltage is large and the output current suppression operation continues, the estimated output current ^I ａｃ By using the virtual synchronous generator and the output voltage V ａｃ The electrical output P that can be obtained from the phase relationship ｅAt 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, allowing the virtual synchronous generator to operate in a stable direction. Figure 5 shows how the virtual generator operates in a stable direction when the grid voltage is restored in this embodiment 1, in a similar event to Figure 4. It can be seen that although the active power decreases due to the relationship between the output phase θ of the inverter INV and the grid voltage phase when the grid voltage is restored, the electrical output Pe increases, so the frequency of the inverter INV decreases and the generator 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 the electrical output based on the estimated output current rather than the measured current value during the output current suppression operation, it is possible to apply the synchronizing force of the virtual synchronous generator and suppress step-out.

[0066] [Embodiment 2] Fig. 6 shows an overall schematic diagram of a grid-connected power conversion device according to embodiment 2, and Fig. 7 shows the electric output calculation unit 4 of embodiment 2. This embodiment differs from embodiment 1 in the following respects.

[0067] As shown in FIG. 6, in the second embodiment, the impedance control unit 3 and the subtractor 8 are omitted. The internal induced voltage E calculated by the voltage amplitude command generation unit 2 is ｆ is the output voltage command value V ａｃ ＊ is output 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 electric output P ｅ Output.

[0069] The electric output calculation unit 4 calculates the estimated output current using the output voltage detection value V ａｃ and the virtual impedance Z ｓ Instead, the system voltage detection value V ｓｙｓ and 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 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 V ｓｙｓ＿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] The virtual synchronous generator model simulated in the second embodiment is shown in FIG. 8. Since the second embodiment does not include a virtual impedance, the internal induced voltage E ｆ is the output voltage command V ａｃ ＊ becomes.

[0074] In the second embodiment, when the output current is suppressed, the electric output Pｅ 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 system side transformer impedance Z ｔｒ ==r ｔｒ +jx ｔｒ It is calculated using equation (5).

[0075]

[0076] This makes it possible to maintain the synchronizing force during output current suppression even in voltage-controlled virtual synchronous generator control, which 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.

[0078] V ｄｃ ...DC power supply INV...inverter LC...LC filter Tr...transformer Grid...system 1...reactive power calculation unit 2...voltage amplitude command generation unit 3...impedance control unit 4...electrical output calculation unit 5...voltage phase command generation unit 6...instantaneous voltage control unit 7...PWM modulation unit 8...subtractor

Claims

1. 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, comprising: 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.

2. The grid-connected power conversion device according to claim 1, characterized in that the electrical output calculation unit normally calculates the electrical output using equation (2) or equation (3), and during output current suppression, 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. 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 grid-connected power conversion device according to claim 2, characterized in that the electric output calculation unit calculates the d-axis estimated output current and the q-axis estimated output current by the following equation (4). ^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 grid-connected power conversion device according to claim 2, characterized in that the electric output calculation unit calculates the d-axis estimated output current and the q-axis estimated output current by the following equation (5). ^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. The grid-interconnected power conversion device according to claim 3, further comprising: a reactive power calculation unit which calculates reactive power based on an output voltage detection value and the output current detection value; a voltage amplitude command generation unit which calculates an internal induced voltage based on a reference voltage command and the reactive power; an impedance control unit which calculates a voltage drop due to a virtual impedance based on the output current detection value; a subtractor which 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 which calculates the output phase based on an oscillation equation from the electrical output and a mechanical input command value.

6. The grid-interconnected power conversion device according to claim 4, further comprising: 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 mechanical input command value.

7. A control method for 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, characterized in that an electric output calculation unit normally calculates an electric output based on an output current detection value, and when the output current is suppressed, calculates the electric output based on an output current estimation value, 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 electric output, and a PWM modulation unit generates a gate signal for the inverter based on the instantaneous voltage command value.

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