Power conditioner

Abstract

This power conditioner performs coordinate conversion of a voltage detection value indicating the detection value of the output voltage of an inverter into a d-axis voltage detection value and a q-axis voltage detection value. The power conditioner performs coordinate conversion of a current detection value indicating the detection value of the output current of the inverter into a d-axis current detection value and a q-axis current detection value. Furthermore, the power conditioner calculates, on the basis of a d-axis difference voltage that is the difference between the d-axis voltage detection value and a d-axis voltage command value, a first current command value so that the d-axis voltage detection value approaches the d-axis voltage command value. Furthermore, the power conditioner calculates, on the basis of a q-axis difference voltage that is the difference between the q-axis voltage detection value and a q-axis voltage command value, a second current command value so that the q-axis voltage detection value approaches the q-axis voltage command value. Furthermore, the power conditioner controls the voltage of the inverter so that the d-axis current detection value approaches the second current command value and the q-axis current detection value approaches the first current command value.

Description

Technical Field

[0001] This disclosure relates to a technique for controlling a power conditioner.

Background Art

[0002] Patent Document 1 discloses a grid-connected inverter. Specifically, when the grid frequency changes and reaches the time point of the maximum frequency fluctuation amount, the grid-connected inverter changes the virtual inertia coefficient after that time point to a predetermined value to generate an inverter output active power command.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A voltage-controlled inverter (e.g., a GFM (Grid Forming) inverter) can simulate the inertia force of a generator to suppress frequency fluctuations caused by fluctuations in power demand, output fluctuations of renewable energy, etc., and stabilize the power grid. Consider the case where the output power of the inverter changes. For example, when one of the active power and reactive power, which is the output power, changes, the inverter changes the other power during the transient period. In this case, there is a risk of overcurrent generation when the output power of the inverter changes.

[0005] One object of this disclosure is to provide a technique capable of suppressing the generation of overcurrent when the output power of an inverter changes.

Means for Solving the Problems

[0006] One aspect of this disclosure relates to a power conditioner. The power conditioner comprises an inverter that converts DC power supplied from a DC power source into AC power and supplies AC power to a power grid, and a control device that controls the inverter. The control device transforms the voltage detection value, which indicates the detected output voltage of the inverter, into a d-axis voltage detection value and a q-axis voltage detection value. The control device then transforms the current detection value, which indicates the detected output current of the inverter, into a d-axis current detection value and a q-axis current detection value. Furthermore, the control device calculates a first current command value based on the d-axis differential voltage, which is the difference between the d-axis voltage detection value and the d-axis voltage command value, so that the d-axis voltage detection value approaches the d-axis voltage command value. Furthermore, the control device calculates a second current command value based on the q-axis differential voltage, which is the difference between the q-axis voltage detection value and the q-axis voltage command value, so that the q-axis voltage detection value approaches the q-axis voltage command value. Furthermore, the control device controls the inverter voltage so that the d-axis current detection value approaches the second current command value and the q-axis current detection value approaches the first current command value. [Effects of the Invention]

[0007] According to this disclosure, a first current command value is calculated based on the d-axis differential voltage, which is the difference between the d-axis voltage detection value and the d-axis voltage command value, so as to bring the d-axis voltage detection value closer to the d-axis voltage command value. A second current command value is calculated based on the q-axis differential voltage, which is the difference between the q-axis voltage detection value and the q-axis voltage command value, so as to bring the q-axis voltage detection value closer to the q-axis voltage command value. After calculating the first and second current command values, the inverter's voltage control is performed so as to bring the d-axis current detection value closer to the second current command value and the q-axis current detection value closer to the first current command value. This makes it possible to prevent a change in the power of either active power or reactive power even if one of the powers changes. Therefore, it is possible to suppress the occurrence of overcurrent in the inverter's output current. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the overview of a power conversion system. [Figure 2]This is a diagram illustrating the general structure of the control device. [Figure 3] This is a diagram illustrating a specific example of the power calculation unit. [Figure 4] This is a diagram illustrating a specific example of the rotation angle calculation unit. [Figure 5] This is a diagram illustrating a specific example of the d-axis voltage command value calculation unit. [Figure 6] This is a diagram illustrating the overview of the voltage control unit. [Figure 7] This is a diagram illustrating the overview of the voltage control unit. [Figure 8] This is a diagram illustrating the overview of the voltage control unit. [Figure 9] This is a diagram illustrating a specific example of a voltage control unit. [Figure 10] This is an explanatory diagram showing an example of the control results of a power conditioner. [Figure 11] This is an explanatory diagram showing an example of the control results of a power conditioner. [Modes for carrying out the invention]

[0009] A power conditioner according to an embodiment of the present disclosure will be described with reference to the attached drawings. In addition, elements common to each figure are denoted by the same reference numerals, and redundant explanations are omitted.

[0010] 1. Overview of the power conversion system Figure 1 is a diagram illustrating the overview of power conversion system 1. Power conversion system 1 includes a power conditioner 10 and a transformer 20, and is installed between a DC power supply 11 and a power grid 30. Power conditioner 10 is composed of an inverter 12 and a control device 100.

[0011] The DC power supply 11 is an energy storage device (e.g., a solar cell module) that stores electricity generated from renewable energy sources. Examples of renewable energy sources include solar power, wind power, hydropower, etc.

[0012] The inverter 12 is a device that converts the DC power output from the DC power supply 11 into AC power and supplies the AC power to the power grid 30 via the transformer 20. The inverter 12 is a voltage-controlled GFM inverter.

[0013] The control device 100 is connected to the inverter 12 and controls the inverter 12. The output voltage Vs and the output current Io output from the inverter 12 are input to the control device 100. Note that the output voltage Vs input to the control device 100 is, for example, a detected value of the output voltage Vs (referred to as the voltage detection value Vs). Also, the output current Io input to the control device 100 is a detected value of the output current Io (also referred to as the current detection value Io). The voltage detection value Vs and the current detection value Io are detected by, for example, a detector (not shown) provided between the inverter 12 and the transformer 20. However, it may not be limited to this. The voltage detection value Vs and the current detection value Io may be detected, for example, between the transformer 20 and the power grid 30.

[0014] The output voltage Vs output from the inverter 12 is composed of three-phase voltages (Vsu, Vsv, Vsw), and the output current Io output from the inverter 12 is composed of three-phase currents (Iou, Iov, Iow). That is, the above-described voltage detection value Vs includes a Vsu detection value, a Vsv detection value, and a Vsw detection value, and the above-described current detection value Io includes an Iou detection value, an Iov detection value, and an Iow detection value.

[0015] Based on the voltage detection value Vs and the current detection value Io, the control device 100 generates a voltage instruction Vins for performing voltage control on the inverter 12. The voltage instruction Vins includes an instruction for operating according to the pulse width modulation signal (PWM signal) of each of the three-phase voltages (Vsu, Vsv, Vsw). Then, the control device 100 issues the voltage instruction Vins to the inverter 12.

[0016] 2. Example of the control device 2-1. Overview FIG. 2 is a diagram for explaining the outline of the control device 100 according to the embodiment. The control device 100 performs various processes. Specifically, the control device 100 includes a coordinate conversion unit 110, a power calculation unit 120, a rotation angle calculation unit 130, a d-axis voltage command value calculation unit 140, a voltage control unit 150, a current control unit 160, and an output control unit 170.

[0017] The coordinate conversion unit 110 converts the fixed coordinate system of the three-phase voltages (Vsu detection value, Vsv detection value, Vsw detection value) of the voltage detection value Vs into a two-phase (dq-axis) rotating coordinate system. Specifically, the coordinate conversion unit 110 performs coordinate conversion of the voltage detection value Vs into a d-axis voltage detection value Vds of the d-axis component and a q-axis voltage detection value Vqs of the q-axis component based on the voltage detection value Vs and the rotation angle θinv. Further, the coordinate conversion unit 110 converts the fixed coordinate system of the three-phase currents (Iou detection value, Iov detection value, Iow detection value) of the current detection value Io into a two-phase (dq-axis) rotating coordinate system. Specifically, the coordinate conversion unit 110 performs coordinate conversion of the current detection value Io into a d-axis current detection value Ido of the d-axis component and a q-axis current detection value Iqo of the q-axis component based on the current detection value Io and the rotation angle θinv.

[0018] The power calculation unit 120 calculates an active power detection value Ps indicating the detection value of active power and a reactive power detection value Qs indicating the detection value of reactive power based on the d-axis voltage detection value Vds, the q-axis voltage detection value Vqs, the d-axis current detection value Ido, and the q-axis current detection value Iqo. Details of the calculation example of the active power detection value Ps and the reactive power detection value Qs will be described later.

[0019] The rotation angle calculation unit 130 calculates the rotation angle θinv based on the active power detection value Ps and the active power command value Pref. In the process of calculating the rotation angle θinv, the target frequency Fref is used. Details of the calculation example of the rotation angle θinv will be described later.

[0020] The d-axis voltage command value calculation unit 140 calculates the d-axis voltage command value Vdref based on the reactive power detection value Qs and the reactive power command value Qref. The voltage reference value Vb is used in the calculation process of the d-axis voltage command value Vdref. Details of the calculation example of the d-axis voltage command value Vdref will be described later.

[0021] The voltage control unit 150 calculates the d-axis current command value Idref and the q-axis current command value Iqref based on the d-axis voltage detection value Vds, the q-axis voltage detection value Vqs, the d-axis voltage command value Vdref, and the q-axis voltage command value Vqref. Details of the calculation examples of the d-axis current command value Idref and the q-axis current command value Iqref will be described later.

[0022] The current control unit 160 generates a control voltage Vpwm for voltage control of the inverter 12 based on the d-axis current detection value Ido, the q-axis current detection value Iqo, the d-axis current command value Idref, and the q-axis current command value Iqref. The control voltage Vpwm is a pulse width modulation (PWM) signal. The control voltage Vpwm includes three phase control voltages (Vupwm, Vvpwm, Vwpwm).

[0023] The output control unit 170 issues a voltage instruction Vins to the inverter 12 so that it operates according to the control voltage Vpwm.

[0024] 2-2. Example of a power calculation unit Figure 3 is a diagram illustrating a specific example of the power calculation unit 120 according to the embodiment. The power calculation unit 120 calculates the first power P1 by multiplying the d-axis voltage detection value Vds and the d-axis current detection value Ido. The power calculation unit 120 also calculates the second power P2 by multiplying the q-axis voltage detection value Vqs and the q-axis current detection value Iqo. Then, the power calculation unit 120 calculates the active power detection value Ps by applying a low-pass filter LPF to the third power P3 obtained by adding the first power P1 and the second power P2.

[0025] The power calculation unit 120 calculates the fourth power P4 by multiplying the q-axis voltage detection value Vqs and the d-axis current detection value Ido. The power calculation unit 120 also calculates the fifth power P5 by multiplying the d-axis voltage detection value Vds and the q-axis current detection value Iqo. Then, the power calculation unit 120 calculates the reactive power detection value Qs by applying a low-pass filter (LPF) to the sixth power P6, which is obtained by taking the difference between the fourth power P4 and the fifth power P5.

[0026] 2-3. Example of a rotation angle calculation unit Figure 4 is a diagram illustrating a specific example of the rotation angle calculation unit 130 according to the embodiment. The rotation angle calculation unit 130 calculates the frequency change amount ΔF by multiplying the differential active power ΔP, which is the difference between the active power detection value Ps and the active power command value Pref, by a first constant. The first constant is a parameter that indicates the dynamic characteristics of the synchronous generator. The dynamic characteristics of the synchronous generator include the inertia constant H, the damping constant D, etc. The dynamic characteristics of the synchronous generator can be obtained, for example, by VSG (Virtual Synchronous Generator) control. VSG is a virtual synchronous generator that simulates the dynamic characteristics of a synchronous generator in the inverter 12. In other words, VSG control means controlling a virtual synchronous generator. For example, if the various parameters of the first constant are the inertia constant H, the damping constant D, and the unit time s, the frequency change amount ΔF is expressed by the following equation (1).

[0027]

number

[0028] The rotation angle calculation unit 130 then calculates the rotation angle θinv by integrating the angular frequency ω, which is calculated based on the frequency Finv obtained by adding the frequency change amount ΔF and the target frequency Fref.

[0029] 2-4. Example of a d-axis voltage command value calculation unit Figure 5 is a diagram illustrating a specific example of the d-axis voltage command value calculation unit 140 according to the embodiment. The d-axis voltage command value calculation unit 140 calculates the voltage V1 by multiplying the differential reactive power ΔQ, which is the difference between the reactive power detection value Qs and the reactive power command value Qref, by a second constant K. The second constant K is a gain that changes the sensitivity of the controlled object (differential reactive power ΔQ). Examples of the second constant K include a gain that shows voltage droop characteristics, a P (proportional) gain, an I (integral) gain, etc. Voltage droop characteristics refer to, for example, the characteristic in a synchronous generator or inverter-based power supply that adjusts the load distribution in order to output a stable voltage according to the deviation between the power command value and the power detection value. The second constant K may include not only one gain but also multiple gains.

[0030] Then, the d-axis voltage command value calculation unit 140 calculates the d-axis voltage command value Vdref by adding the voltage V1 and the voltage reference value Vb.

[0031] 2-5. Overview of the Voltage Control Unit Figures 6, 7, and 8 are diagrams illustrating the overview of the voltage control unit 150 according to the embodiment. Generally, as shown in Figure 6, the voltage control unit 150 uses a compensator to control the d-axis voltage detection value Vds to approach the d-axis voltage command value Vdref based on the d-axis differential voltage, which is the difference between the d-axis voltage command value Vdref and the d-axis voltage detection value Vds, and calculates the d-axis current command value Idref. Also, as shown in Figure 6, the voltage control unit 150 uses a compensator to control the q-axis voltage detection value Vqs to approach the q-axis voltage command value Vqref based on the q-axis differential voltage, which is the difference between the q-axis voltage command value Vqref and the q-axis voltage detection value Vqs, and calculates the q-axis current command value Iqref. The compensator is, for example, PI control. vessel That is the case.

[0032] Now, let's consider the case where the active power command value Pref is changed. For example, as shown in (A) in Figure 7, let's consider the case where the active power command value Pref is changed from 0 [pu (Per Unit)] to 1 [pu] and the reactive power command value Qref is fixed at 0 [pu]. In this case, as shown in (B) in Figure 7, a deviation occurs between the active power command value Pref and the active power detection value Ps. When a deviation occurs between the active power command value Pref and the active power detection value Ps, the frequency Finv increases according to the rotation angle calculation unit 130 and exceeds the reference frequency (e.g., 50 Hz) (see (B) in Figure 7).

[0033] When the frequency Finv increases, the rotation angle θinv changes according to the rotation angle calculation unit 130, causing the dq axis to rotate (see (C) in Figure 7). Specifically, the dq axis rotates in the positive direction with respect to the voltage detection value Vs. When the rotation angle θinv is sufficiently small, the fluctuation ΔVds of the d-axis voltage detection value Vds of the d-axis component can be approximated as zero. The q-axis voltage detection value Vqs decreases as it changes according to the magnitude of the rotation angle θinv (see (A) in Figure 7).

[0034] When the q-axis voltage detection value Vqs decreases, the q-axis current command value Iqref increases according to the voltage control unit 150, based on the difference between the q-axis voltage command value Vqref and the q-axis voltage detection value Vqs. In this case, the output current of the q-axis component in the output current Io of the inverter 12 also increases, and therefore, according to the coordinate transformation unit 110, the q-axis current detection value Iqo increases (see (A) in Figure 7).

[0035] When the q-axis current detection value Iqo increases, the reactive power detection value Qs decreases according to the power calculation unit 120 (see (A) in Figure 7).

[0036] When the reactive power detection value Qs decreases, the d-axis voltage command value Vdref increases according to the d-axis voltage command value calculation unit 140 (see (A) in Figure 7).

[0037] When the d-axis voltage command value Vdref increases, the d-axis current command value Idref increases according to the voltage control unit 150. In this case, the output current of the d-axis component in the output current Io of the inverter 12 also increases, and therefore, the d-axis current detection value Ido increases according to the coordinate transformation unit 110 (see (A) in Figure 7).

[0038] When the d-axis current detection value Ido increases, the active power detection value Ps increases according to the power calculation unit 120 (see (A) in Figure 7).

[0039] Thus, when the active power command value Pref is changed, a deviation occurs between the active power command value Pref and the active power detection value Ps. In this case, not only does the active power detection value Ps fluctuate, but the reactive power detection value Qs also fluctuates (see (B) in Figure 7). The fluctuation in the reactive power detection value Qs causes a reactive current to flow, which may lead to an overcurrent in the output current of the inverter 12. Therefore, when controlling the active power command value Pref, it is desirable to avoid changing the reactive power detection value Qs.

[0040] As another example, consider the case where the reactive power command value Qref is changed. For example, as shown in (A) in Figure 8, consider the case where the active power command value Pref is fixed at 0 [pu] and the reactive power command value Qref is changed to a value greater than 0 [pu] and less than 1 [pu]. In this case, as shown in (B) in Figure 8, a deviation occurs between the reactive power command value Qref and the reactive power detection value Qs. When a deviation occurs between the reactive power command value Qref and the reactive power detection value Qs, the d-axis voltage command value Vdref increases according to the d-axis voltage command value calculation unit 140 (see (A) in Figure 8).

[0041] When the d-axis voltage command value Vdref increases, the d-axis current command value Idref increases according to the voltage control unit 150. In this case, the output current of the d-axis component in the output current Io of the inverter 12 also increases, so the d-axis current detection value Ido increases according to the coordinate transformation unit 110 (see (A) in Figure 8).

[0042] When the d-axis current detection value Ido increases, the active power detection value Ps increases according to the power calculation unit 120 (see (A) in Figure 8).

[0043] If the detected active power value Ps increases, the frequency Finv decreases according to the rotation angle calculation unit 130. standard The frequency becomes smaller than (e.g., 50Hz) (see (B) in Figure 8).

[0044] When the frequency Finv decreases, the rotation angle θinv changes according to the rotation angle calculation unit 130, causing the dq axis to rotate (see (C) in Figure 8). Specifically, the dq axis rotates in a negative direction with respect to the voltage detection value Vs. When the rotation angle θinv is sufficiently small, the fluctuation ΔVds of the d-axis voltage detection value Vds of the d-axis component can be approximated as zero. The q-axis voltage detection value Vqs increases because it changes according to the magnitude of the rotation angle θinv (see (A) in Figure 8).

[0045] When the detected q-axis voltage Vqs increases, the voltage control unit 150 determines that the q-axis current command value Iqref decreases due to the difference between the q-axis voltage command value Vqref and the detected q-axis voltage Vqs. In this case, the output current of the q-axis component in the output current Io of the inverter 12 also decreases, and therefore, the coordinate transformation unit 110 determines that the detected q-axis current value Iqo decreases (see (A) in Figure 8).

[0046] If the q-axis current detection value Iqo decreases, the reactive power detection value Qs increases according to the power calculation unit 120 (see (A) in Figure 8).

[0047] Thus, when the reactive power command value Qref is changed, a deviation occurs between the reactive power command value Qref and the reactive power detection value Qs. In this case, not only does the reactive power detection value Qs fluctuate, but the active power detection value Ps also fluctuates (see (B) in Figure 8). As the active current flows due to the fluctuation in the active power detection value Ps, there is a risk that the output current of the inverter 12 will become overcurrent. Therefore, when controlling the reactive power command value Qref, it is desirable to avoid changing the active power detection value Ps.

[0048] According to this embodiment, a voltage control unit 150 is provided to prevent the power of the other power from changing when one of the powers, active power or reactive power, is controlled. A specific example of the voltage control unit 150 will be described in detail below.

[0049] 2-6. Example of a voltage control unit Figure 9 is a diagram illustrating a specific example of the voltage control unit 150 according to this embodiment. The voltage control unit 150 is a compensator (e.g., PI control). vessel The voltage control unit 150 uses a compensator to control the q-axis voltage detection value Vds to approach the q-axis voltage command value Vdref based on the d-axis differential voltage, which is the difference between the d-axis voltage detection value Vds and the d-axis voltage command value Vdref, and calculates a first current command value. The voltage control unit 150 also uses a compensator to control the q-axis voltage detection value Vqs to approach the q-axis voltage command value Vqref based on the q-axis differential voltage, which is the difference between the q-axis voltage detection value Vqs and the q-axis voltage command value Vqref, and calculates a second current command value. The first current command value is used as the q-axis current command value Iqref, and the second current command value is used as the d-axis current command value Idref.

[0050] Thus, the power conditioner 10 controls the voltage of the inverter 12 so that the d-axis current detection value Ido approaches the second current command value calculated by the voltage control unit 150, and the q-axis current detection value Iqo approaches the first current command value calculated by the voltage control unit 150. This makes it possible to control one of the power components, active power or reactive power, without changing the other. Therefore, the inverter 12 Output current This can suppress the generation of overcurrents.

[0051] 3. Example of control results Figure 10 is an explanatory diagram showing an example of the control result of the power conditioner 10 according to the embodiment. Figure 10(A) shows an example of the control result of the power conditioner when the active power command value Pref is changed from 0[pu] to 1[pu] and the reactive power command value Qref is fixed at 0[pu]. In this case, as shown in Figure 10(B), a deviation occurs between the active power command value Pref and the active power detection value Ps. When a deviation occurs between the active power command value Pref and the active power detection value Ps, the frequency Finv increases according to the rotation angle calculation unit 130 and exceeds the reference frequency (e.g., 50Hz) (see Figure 10(B)).

[0052] When the frequency Finv increases, the rotation angle θinv changes according to the rotation angle calculation unit 130, causing the dq axis to rotate (see (C) in Figure 10). Specifically, the dq axis rotates in the positive direction with respect to the voltage detection value Vs. When the rotation angle θinv is sufficiently small, the fluctuation ΔVds of the d-axis voltage detection value Vds for the d-axis component can be approximated as zero. The q-axis voltage detection value Vqs decreases as it changes according to the magnitude of the rotation angle θinv (see (A) in Figure 10).

[0053] When the q-axis voltage detection value Vqs decreases, the d-axis current command value Idref increases according to the voltage control unit 150, based on the deviation between the q-axis voltage command value Vqref and the q-axis voltage detection value Vqs. In this case, the output current of the d-axis component in the output current Io of the inverter 12 also increases, and therefore, according to the coordinate transformation unit 110, the d-axis current detection value Ido increases (see (A) in Figure 10).

[0054] When the d-axis current detection value Ido increases, the active power detection value Ps increases according to the power calculation unit 120 (see (A) in Figure 10).

[0055] Thus, when the active power command value Pref is changed, a deviation occurs between the active power command value Pref and the active power detection value Ps. In this case, the active power detection value Ps fluctuates, but the reactive power detection value Qs does not. Since the reactive power detection value Qs does not fluctuate, no reactive current flows, and therefore the occurrence of overcurrent in the output current of the inverter 12 can be suppressed.

[0056] As another example, Figure 11(A) shows an example of the control result of a power conditioner when the active power command value Pref is fixed at 0[pu] and the reactive power command value Qref is changed to a value greater than 0[pu] and less than 1[pu]. In this case, as shown in Figure 11(B), a deviation occurs between the reactive power command value Qref and the reactive power detection value Qs. When a deviation occurs between the reactive power command value Qref and the reactive power detection value Qs, the d-axis voltage command value Vdref increases according to the d-axis voltage command value calculation unit 140 (see Figure 11(A)).

[0057] When the d-axis voltage command value Vdref increases, the q-axis current command value Iqref decreases according to the voltage control unit 150. In this case, the output current of the q-axis component in the output current Io of the inverter 12 also decreases, so the q-axis current detection value Iqo decreases according to the coordinate transformation unit 110 (see (A) in Figure 11).

[0058] If the q-axis current detection value Iqo decreases, the reactive power detection value Qs increases according to the power calculation unit 120 (see (A) in Figure 11).

[0059] Thus, when the reactive power command value Qref is changed, a deviation occurs between the reactive power command value Qref and the reactive power detection value Qs. In this case, the reactive power detection value Qs fluctuates, but the active power detection value Ps does not. Since the active power detection value Ps does not fluctuate, no active current flows, and therefore the occurrence of overcurrent in the output current of the inverter 12 can be suppressed.

[0060] 4. Effects According to the power conditioner 10 of this embodiment, a first current command value is calculated based on the d-axis differential voltage, which is the difference between the d-axis voltage detection value Vds and the d-axis voltage command value Vdref, so that the d-axis voltage detection value Vds approaches the d-axis voltage command value Vdref. A second current command value is calculated based on the q-axis differential voltage, which is the difference between the q-axis voltage detection value Vqs and the q-axis voltage command value Vqref, so that the q-axis voltage detection value Vqs approaches the q-axis voltage command value Vqref. After calculating the first and second current command values, the voltage of the inverter 12 is controlled so that the d-axis current detection value Ido approaches the second current command value and the q-axis current detection value Iqo approaches the first current command value. As a result, even if one of the powers, active power or reactive power, changes, the other power does not change. Therefore, it is possible to suppress the occurrence of overcurrent in the output current of the inverter 12. [Explanation of symbols]

[0061] 1...Power conversion system, 10...Power conditioner, 11...DC power supply, 12...Inverter, 20...Transformer, 30...Power system, 100...Control device

Claims

1. An inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to the power grid, The system comprises a control device for controlling the inverter, The control device is The voltage detection value indicating the detected output voltage of the inverter is transformed into a d-axis voltage detection value and a q-axis voltage detection value. The current detection value indicating the detected output current of the inverter is transformed into a d-axis current detection value and a q-axis current detection value. Based on the d-axis differential voltage, which is the difference between the d-axis voltage detection value and the d-axis voltage command value, a first current command value is calculated so that the d-axis voltage detection value approaches the d-axis voltage command value. Based on the q-axis differential voltage, which is the difference between the q-axis voltage detection value and the q-axis voltage command value, a second current command value is calculated to bring the q-axis voltage detection value closer to the q-axis voltage command value. The inverter is configured to control its voltage so that the d-axis current detection value approaches the second current command value and the q-axis current detection value approaches the first current command value. A power conditioner characterized by the following.

2. A power conditioner according to claim 1, The control device further, Based on the d-axis voltage detection value, the d-axis current detection value, the q-axis voltage detection value, and the q-axis current detection value, the system is configured to calculate an active power detection value indicating the detected value of active power and a reactive power detection value indicating the detected value of reactive power. A power conditioner characterized by the following.

3. A power conditioner according to claim 2, The active power detection value is calculated by applying a low-pass filter to the third power obtained by adding the first power obtained by multiplying the d-axis voltage detection value and the d-axis current detection value, and the second power obtained by multiplying the q-axis voltage detection value and the q-axis current detection value. The reactive power detection value is calculated by applying a low-pass filter to the sixth power obtained by subtracting the fourth power, which is obtained by multiplying the q-axis voltage detection value and the d-axis current detection value, from the fifth power, which is obtained by multiplying the d-axis voltage detection value and the q-axis current detection value. A power conditioner characterized by the following.

4. A power conditioner according to claim 2, The coordinate transformation includes a process for calculating the d-axis voltage detection value and the d-axis current detection value of the d-axis component, and the q-axis voltage detection value and the q-axis current detection value of the q-axis component, based on the voltage detection value, the current detection value and the rotation angle. The rotation angle is calculated by integrating the angular frequency, which is calculated based on the frequency obtained by adding the frequency change amount (obtained by multiplying the difference between the detected active power value and the commanded active power value by a first constant) and the target frequency. A power conditioner characterized by the following.

5. A power conditioner according to claim 4, The first constant is a parameter that indicates the dynamic characteristics of the synchronous generator. A power conditioner characterized by the following.

6. A power conditioner according to claim 2, The d-axis voltage command value is calculated by adding the voltage obtained by multiplying the differential reactive power, which is the difference between the reactive power detection value and the reactive power command value, by a second constant, and the voltage reference value. A power conditioner characterized by the following.

7. A power conditioner according to claim 6, The second constant is a gain that changes the sensitivity of the differential reactive power. A power conditioner characterized by the following.