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

Power conditioner

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

[0002] Patent Document 1 discloses a grid-connected inverter, which generates an output active power command for the inverter by changing a pseudo-inertia coefficient to a predetermined value after the time when the grid frequency changes and reaches a maximum frequency fluctuation point.

[0003] Japanese Patent No. 6735039

[0004] A voltage-controlled inverter (e.g., a grid forming (GFM) inverter) can stabilize a power grid by simulating the inertial force of a generator and suppressing frequency fluctuations caused by fluctuations in power demand and output fluctuations of renewable energy sources. Consider a case where the inverter's output power changes. For example, if one of the active power and reactive power, which are the output power, changes, the inverter will change the other power during a transient state. In this case, there is a risk of an overcurrent occurring when the inverter's output power changes.

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

[0006] One aspect of the present disclosure relates to a power conditioner. The power conditioner includes an inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to a power grid, and a control device that controls the inverter. The control device coordinate-transforms a detected voltage value indicating a detected value of the inverter's output voltage into a detected d-axis voltage value and a detected q-axis voltage value. The control device then coordinate-transforms a detected current value indicating a detected value of the inverter's output current into a detected d-axis current value and a detected q-axis current value. The control device further calculates a first current command value based on a d-axis differential voltage that is the difference between the detected d-axis voltage value and a d-axis voltage command value so as to bring the detected d-axis voltage value closer to the d-axis voltage command value. The control device further calculates a second current command value based on a q-axis differential voltage that is the difference between the detected q-axis voltage value and a q-axis voltage command value so as to bring the detected q-axis voltage value closer to the q-axis voltage command value. Furthermore, the control device 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.

[0007] According to the present disclosure, a first current command value is calculated based on a d-axis differential voltage, which is the difference between a d-axis voltage detection value and a 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 a q-axis differential voltage, which is the difference between a q-axis voltage detection value and a 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 current command value and the second current command value, inverter voltage control is performed so as to bring the d-axis current detection value closer to the second current command value and bring the q-axis current detection value closer to the first current command value. This makes it possible to prevent the active power and reactive power from changing even when one of the powers changes. Therefore, it is possible to suppress overcurrent in the inverter output current.

[0008] FIG. 1 is a diagram for explaining an overview of a power conversion system. FIG. 2 is a diagram for explaining an overview of a control device. FIG. 3 is a diagram for explaining a specific example of a power calculation unit. FIG. 4 is a diagram for explaining a specific example of a rotation angle calculation unit. FIG. 5 is a diagram for explaining a specific example of a d-axis voltage command value calculation unit. FIG. 6 is a diagram for explaining an overview of a voltage control unit. FIG. 7 is a diagram for explaining an overview of a voltage control unit. FIG. 8 is a diagram for explaining an example of a voltage control unit. FIG. 9 is an explanatory diagram showing an example of a control result of a power conditioner. FIG. 10 is an explanatory diagram showing an example of a control result of a power conditioner.

[0009] A power conditioner according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Elements common to the drawings will be designated by the same reference numerals, and duplicated descriptions will be omitted.

[0010] 1. Overview of the Power Conversion System Fig. 1 is a diagram illustrating an overview of a power conversion system 1. The power conversion system 1 includes a power conditioner 10 and a transformer 20, and is provided between a DC power source 11 and a power grid 30. The power conditioner 10 includes an inverter 12 and a control device 100.

[0011] The DC power supply 11 is a power storage device (e.g., a solar cell module) that stores electricity generated by renewable energy, such as solar power, wind power, and hydropower.

[0012] The inverter 12 is a device that converts 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 control device 100 receives the output voltage Vs and output current Io output from the inverter 12. The output voltage Vs input to the control device 100 is, for example, a detected value of the output voltage Vs (referred to as a detected voltage value Vs). The output current Io input to the control device 100 is, for example, a detected value of the output current Io (also referred to as a detected current value Io). The detected voltage value Vs and the detected current value Io are detected, for example, by a detector (not shown) provided between the inverter 12 and the transformer 20. However, this is not limiting. The detected voltage value Vs and the detected current value Io may also be detected, for example, between the transformer 20 and the power grid 30.

[0014] The output voltage Vs output from the inverter 12 is made up of three-phase voltages (Vsu, Vsv, Vsw), and the output current Io output from the inverter 12 is made up of three-phase currents (Iou, Iov, Iow). That is, the above-mentioned detected voltage value Vs includes the detected Vsu value, the detected Vsv value, and the detected Vsw value, and the above-mentioned detected current value Io includes the detected Iou value, the detected Iov value, and the detected Iow value.

[0015] The control device 100 generates a voltage command Vins for voltage control of the inverter 12 based on the detected voltage value Vs and the detected current value Io. The voltage command Vins includes commands for operating in accordance with pulse width modulation signals (PWM signals) for the three-phase voltages (Vsu, Vsv, Vsw). The control device 100 then outputs the voltage command Vins to the inverter 12.

[0016] 2. Example of Control Device 2-1. Overview Fig. 2 is a diagram for explaining an overview of a control device 100 according to an 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 converter 110 converts a fixed coordinate system of the three-phase voltages (detected value Vsu, detected value Vsv, detected value Vsw) of the detected voltage value Vs into a two-phase (dq-axis) rotating coordinate system. Specifically, the coordinate converter 110 converts the detected voltage value Vs into a d-axis detected voltage value Vds (a d-axis component) and a q-axis detected voltage value Vqs (a q-axis component) based on the detected voltage value Vs and the rotation angle θinv. The coordinate converter 110 also converts a fixed coordinate system of the three-phase currents (detected value Iou, detected value Iov, detected value Iow) of the detected current value Io into a two-phase (dq-axis) rotating coordinate system. Specifically, the coordinate converter 110 converts the detected current value Io into a d-axis detected current value Ido (a d-axis component) and a q-axis detected current value Iqo (a q-axis component) based on the detected current value Io and the rotation angle θinv.

[0018] The power calculation unit 120 calculates an active power detection value Ps indicating the detected value of active power and a reactive power detection value Qs indicating the detected 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 calculation examples 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. Note that the target frequency Fref is used in the process of calculating the rotation angle θinv. A detailed example of the calculation of the rotation angle θinv will be described later.

[0020] The d-axis voltage command value calculation unit 140 calculates a d-axis voltage command value Vdref based on the reactive power detection value Qs and the reactive power command value Qref. Note that the voltage reference value Vb is used in the calculation process of the d-axis voltage command value Vdref. A detailed example of the calculation 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 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 signal (PWM signal). The control voltage Vpwm includes three-phase control voltages (Vupwm, Vvpwm, and Vwpwm).

[0023] The output control unit 170 outputs a voltage instruction Vins to the inverter 12 so that the inverter 12 operates in accordance with the control voltage Vpwm.

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

[0025] The power calculation unit 120 calculates a fourth power P4 by multiplying the detected q-axis voltage value Vqs by the detected d-axis current value Ido. The power calculation unit 120 also calculates a fifth power P5 by multiplying the detected d-axis voltage value Vds by the detected q-axis current value Iqo. The power calculation unit 120 then calculates a sixth power P6, which is obtained by subtracting the fourth power P4 from the fifth power P5, by applying the result to a low-pass filter LPF to calculate a reactive power detection value Qs.

[0026] 2-3. Example of Rotation Angle Calculation Unit FIG. 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 indicating the dynamic characteristics of a synchronous generator. The dynamic characteristics of a synchronous generator include an inertia constant H, a damping constant D, and the like. The dynamic characteristics of a synchronous generator can be obtained, for example, by VSG (Virtual Synchronous Generator) control. A VSG is a virtual synchronous generator that simulates the dynamic characteristics of a synchronous generator in the inverter 12. In other words, VSG control refers to controlling a virtual synchronous generator. For example, when 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]

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

[0029] 2-4. Example of d-Axis Voltage Command Value Calculation Unit FIG. 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 (the differential reactive power ΔQ). Examples of the second constant K include a gain that indicates the voltage droop characteristic, a P (proportional) gain, an I (integral) gain, etc. The voltage droop characteristic refers to, for example, a characteristic that adjusts the load sharing to output a stable voltage in a synchronous generator or an inverter-based power supply in accordance with 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 Voltage Control Unit FIGS. 6, 7, and 8 are diagrams illustrating an overview of the voltage control unit 150 according to the embodiment. Generally, as shown in FIG. 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 a d-axis differential voltage, which is the difference between the d-axis voltage command value Vdref and the d-axis voltage detection value Vds, thereby calculating a d-axis current command value Idref. Also, as shown in FIG. 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 a q-axis differential voltage, which is the difference between the q-axis voltage command value Vqref and the q-axis voltage detection value Vqs, thereby calculating a q-axis current command value Iqref. The compensator may be, for example, a PI controller.

[0032] Now, consider a case where the active power command value Pref is changed. For example, as shown in (A) of FIG. 7 , consider a 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) of FIG. 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 and exceeds the reference frequency (e.g., 50 Hz) according to the rotation angle calculation unit 130 (see (B) of FIG. 7 ).

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

[0034] When the q-axis voltage detection value Vqs decreases, the q-axis current command value Iqref increases due to the deviation between the q-axis voltage command value Vqref and the q-axis voltage detection value Vqs in accordance with the voltage control unit 150. In this case, the output current of the q-axis component of the output current Io of the inverter 12 also increases, and therefore the q-axis current detection value Iqo increases in accordance with the coordinate conversion unit 110 (see (A) in FIG. 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 FIG. 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 FIG. 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 of the output current Io of the inverter 12 also increases, and therefore the d-axis current detection value Ido increases according to the coordinate conversion unit 110 (see (A) in FIG. 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 FIG. 7).

[0039] As described above, 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 the active power detection value Ps but also the reactive power detection value Qs fluctuates (see (B) in FIG. 7). The flow of reactive current due to the fluctuation of the reactive power detection value Qs may cause the output current of the inverter 12 to become an overcurrent. Therefore, when the active power command value Pref is controlled, it is desirable to prevent the reactive power detection value Qs from changing.

[0040] As another example, consider a case where the reactive power command value Qref is changed. For example, as shown in (A) of FIG. 8, consider a 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) of FIG. 8, a deviation occurs between the reactive power command value Qref and the reactive power detected value Qs. When a deviation occurs between the reactive power command value Qref and the reactive power detected value Qs, the d-axis voltage command value Vdref increases according to the d-axis voltage command value calculation unit 140 (see (A) of FIG. 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 of the output current Io of the inverter 12 also increases, and therefore the d-axis current detection value Ido increases according to the coordinate conversion unit 110 (see (A) in FIG. 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 FIG. 8).

[0043] When the detected active power value Ps increases, the frequency Finv decreases according to the rotation angle calculation unit 130 and becomes smaller than the fundamental frequency (for example, 50 Hz) (see (B) in FIG. 8).

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

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

[0046] When 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 FIG. 8).

[0047] As described above, 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 the reactive power detection value Qs but also the active power detection value Ps fluctuates (see (B) in FIG. 8). If an active current flows due to the fluctuation of the active power detection value Ps, there is a risk that the output current of the inverter 12 will become an overcurrent. Therefore, when the reactive power command value Qref is controlled, it is desirable to prevent the active power detection value Ps from changing.

[0048] According to this embodiment, a voltage control unit 150 is provided for preventing the active power and the reactive power from changing when one of the active power and the reactive power is controlled. Specific examples of the voltage control unit 150 will be described in detail below.

[0049] 2-6. Example of Voltage Control Unit FIG. 9 is a diagram illustrating a specific example of the voltage control unit 150 according to the present embodiment. The voltage control unit 150 uses a compensator (e.g., PI control) to control the d-axis voltage detection value Vds to approach the d-axis voltage command value Vdref based on a d-axis differential voltage, which is the difference between the d-axis voltage detection value Vds and the d-axis voltage command value Vdref, thereby calculating a first current command value. Furthermore, 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 a q-axis differential voltage, which is the difference between the q-axis voltage detection value Vqs and the q-axis voltage command value Vqref, thereby calculating 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] In this way, 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 so that 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 prevent the active power and the reactive power from changing when one of the active power and the reactive power is controlled. Therefore, it is possible to suppress the occurrence of an overcurrent in the output power of the inverter 12.

[0051] 3. Example of Control Result Figure 10 is an explanatory diagram showing an example of the control result of the power conditioner 10 according to the embodiment. (A) in Figure 10 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 (B) in Figure 10, 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 and exceeds the reference frequency (e.g., 50 Hz) according to the rotation angle calculation unit 130 (see (B) in Figure 10).

[0052] When the frequency Finv increases, the rotation angle θinv changes according to the rotation angle calculation unit 130, causing the d- and q-axes to rotate (see (C) in FIG. 10). Specifically, the d- and q-axes rotate in the positive direction relative to the detected voltage value Vs. When the rotation angle θinv is sufficiently small, the fluctuation ΔVds in the detected d-axis voltage value Vds of the d-axis component can be approximated to zero. The detected q-axis voltage value Vqs decreases because it changes according to the magnitude of the rotation angle θinv (see (A) in FIG. 10).

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

[0055] In this way, 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 fluctuate. Since the reactive power detection value Qs does not fluctuate, no reactive current flows, and it is possible to suppress the occurrence of an overcurrent in the output current of the inverter 12.

[0056] As another example, (A) in Fig. 11 shows an example of the control result of the 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 (B) in Fig. 11, 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 Fig. 11).

[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 of the output current Io of the inverter 12 also decreases, and therefore the q-axis current detection value Iqo decreases according to the coordinate conversion unit 110 (see (A) in FIG. 11 ).

[0058] When 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 FIG. 11).

[0059] In this way, 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 fluctuate. Since the active power detection value Ps does not fluctuate, no active current flows, and it is possible to suppress the occurrence of an overcurrent in the output current of the inverter 12.

[0060] 4. Effects According to the power conditioner 10 of the embodiment, a first current command value is calculated based on a 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 as to bring the d-axis voltage detection value Vds closer to the d-axis voltage command value Vdref. A second current command value is calculated based on a 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 as to bring the q-axis voltage detection value Vqs closer to the q-axis voltage command value Vqref. After calculating the first and second current command values, voltage control of the inverter 12 is performed so as to bring the d-axis current detection value Ido closer to the second current command value and bring the q-axis current detection value Iqo closer to the first current command value. This makes it possible to prevent the active power and the reactive power from changing even when one of the two powers changes. This makes it possible to suppress overcurrent in the output current of the inverter 12.

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

Claims

1. A power conditioner comprising: an inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to a power grid; and a control device that controls the inverter, wherein the control device is configured to: coordinate-transform a detected voltage value indicating a detected value of the inverter's output voltage into a detected d-axis voltage value and a detected q-axis voltage value; coordinate-transform a detected current value indicating a detected value of the inverter's output current into a detected d-axis current value and a detected q-axis current value; calculate a first current command value based on a d-axis differential voltage that is the difference between the detected d-axis voltage value and a d-axis voltage command value so as to bring the detected d-axis voltage value closer to the d-axis voltage command value; calculate a second current command value based on a q-axis differential voltage that is the difference between the detected q-axis voltage value and a q-axis voltage command value so as to bring the detected q-axis voltage value closer to the q-axis voltage command value; and control the voltage of the inverter so as to bring the detected d-axis current value closer to the second current command value and the detected q-axis current value closer to the first current command value.

2. A power conditioner according to claim 1, wherein the control device is further configured to calculate an active power detection value indicating a detected value of active power and a reactive power detection value indicating a detected value of reactive power 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.

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

4. A power conditioner according to claim 2, wherein the coordinate transformation includes a process of 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, and wherein the rotation angle is calculated by integrating an angular frequency calculated based on a frequency obtained by adding a target frequency to a frequency change amount obtained by multiplying a differential active power, which is the difference between the active power detection value and the active power command value, by a first constant.

5. A power conditioner according to claim 4, wherein the first constant is a parameter indicating the dynamic characteristics of a synchronous generator.

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

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

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