Power conditioner

Abstract

A power conditioner according to the present invention generates a d-axis second voltage and a q-axis second voltage, which are obtained by removing a specific frequency from a d-axis first voltage and a q-axis first voltage that are generated on the basis of a d-axis system voltage and a q-axis system voltage. The power conditioner then generates a d-axis third voltage and a q-axis third voltage by removing harmonic components from the d-axis system voltage and the q-axis system voltage, and generates a d-axis compensation voltage and a q-axis compensation voltage for compensating for the d-axis third voltage and the q-axis third voltage that attenuate when the impedance of the three-phase lines of the electric power system is imbalanced. Furthermore, the power conditioner generates a first three-phase voltage command by performing current control on a three-phase current command that is generated on the basis of a d-axis current command and a q-axis current command. Furthermore, the power conditioner controls a power converter on the basis of a second three-phase voltage command, which is obtained by adding a three-phase voltage generated on the basis of the d-axis third voltage and the q-axis third voltage, a three-phase compensation voltage generated on the basis of the d-axis compensation voltage and the q-axis compensation voltage, and the first three-phase voltage command.

Description

Power conditioner

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

[0002] Patent Document 1 discloses a power converter control device that suppresses oscillations in the output voltage of a power converter during an overvoltage. Specifically, when an overvoltage is detected on the output side of the power converter, the power converter control device temporarily increases the cutoff frequency of a low-pass filter of a DC voltage detector provided between a photovoltaic power generation facility and the power converter, after reducing a current command value for the output current of the power converter and before performing gate blocking.

[0003] Japanese Patent No. 7156555

[0004] When the impedance of a three-phase line in a power system becomes unbalanced, the loads on each phase become uneven. In this case, the system voltage may be attenuated due to the influence of a low-pass filter installed for noise suppression, etc. This causes a voltage difference between the system voltage and the voltage command for the power converter, causing the output current of the power converter to oscillate at a frequency different from the rated frequency. This can cause unstable operation of the power conditioner.

[0005] One object of the present disclosure is to provide a technique that can improve the stability of the operation of a power conditioner when the power grid is unbalanced.

[0006] One aspect of the present disclosure relates to a power conditioner. The power conditioner includes a power converter that converts DC power supplied from a DC power source into AC power and supplies the AC power to a power grid, and a controller that controls the power converter. The controller generates a d-axis first voltage by removing harmonic components from a d-axis grid voltage obtained by converting a grid voltage of the power grid onto a d-axis. The controller also generates a q-axis first voltage by removing harmonic components from a q-axis grid voltage obtained by converting the grid voltage onto a q-axis. The controller also generates a d-axis second voltage by removing a specific frequency from the d-axis first voltage. The controller also generates a q-axis second voltage by removing a specific frequency from the q-axis first voltage. The controller also calculates a phase difference with the grid voltage based on the d-axis second voltage and the q-axis second voltage. The controller also generates a d-axis third voltage by removing harmonic components from the d-axis grid voltage. The controller also generates a q-axis third voltage by removing harmonic components from the q-axis grid voltage. The controller generates, based on the d-axis system voltage, a d-axis compensating voltage for compensating for a d-axis third voltage that attenuates when an impedance imbalance occurs in a three-phase line of the power system. The controller generates, based on the q-axis system voltage, a q-axis compensating voltage for compensating for a q-axis third voltage that attenuates when an impedance imbalance occurs. The controller generates a three-phase sum voltage by adding together a three-phase voltage generated based on the d-axis third voltage, the q-axis third voltage, and a reference phase synchronized with the system voltage calculated based on a phase difference between the d-axis third voltage and the q-axis third voltage, and a three-phase compensating voltage generated based on the d-axis compensating voltage, the q-axis compensating voltage, and the reference phase. The controller generates a first three-phase voltage command by current-controlling a three-phase current command generated based on the d-axis current command, the q-axis current command, and the reference phase. The controller generates a second three-phase voltage command by adding together the three-phase sum voltage and the first three-phase voltage command. The controller controls the power converter based on the second three-phase voltage command.

[0007] According to the present disclosure, even if the power grid is unbalanced, it is possible to reduce the voltage difference between the grid voltage and the voltage command for the power converter, and to prevent the output current of the power converter from oscillating at a frequency different from the rated frequency, thereby improving the operational stability of the power conditioner.

[0008] It is a diagram for explaining an overview of a power conversion system according to an embodiment. It is a schematic diagram showing characteristics of a grid voltage during unbalance. It is a block diagram showing an example of functions of a controller according to an embodiment. It is a block diagram showing a specific example of a compensation term generation unit according to an embodiment.

[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 for explaining an overview of a power conversion system 1. The power conversion system 1 includes a DC power supply 11, a power conditioner 10, a transformer 20, a power system 30, and a diode 50.

[0011] The DC power supply 11 is connected to the DC end (input end) of the power conditioner 10 via a diode 50. In the present embodiment, the DC power supply 11 is described as a solar panel (e.g., a solar cell panel, a PV panel), but may also be, for example, a power storage device that stores generated electricity. The DC power supply 11 supplies DC power generated by, for example, a solar panel to the power conditioner 10.

[0012] The power conditioner 10 includes a DC switch 21, a power converter 12, a DC side circuit unit 13, an AC side circuit unit 14, an AC switch 22, and a controller 100. The power converter 12 converts DC power output from a DC power source 11 into AC power and supplies the AC power to a power grid 30 via a transformer 20. The power converter 12 is configured with switching elements such as IGBTs. The power converter 12 is controlled by, for example, a pulse width modulation (PWM) signal, which is a gate drive signal (gate signal) for the switching elements, generated by the controller 100. In other words, the power converter 12 is controlled by the gate signal for operating the power converter 12.

[0013] The DC switch (DC circuit breaker) 21 is provided in series between the DC power supply 11 and the DC side circuit unit 13. The DC switch 21 makes (connects) or opens (disconnects) the connection between the DC power supply 11 and the DC side circuit unit 13 in response to an on or off instruction from, for example, the controller 100, a higher-level device (not shown), or an operator. The DC switch 21 is, for example, an electrical contactor that can be opened or closed in response to an instruction from the controller 100. Note that the DC switch 21 may also be, for example, a DC circuit breaker that is normally manually opened or closed and automatically shuts off when an overcurrent such as a short-circuit current is detected. When the DC switch 21 is opened, it is possible to prevent DC power supplied from the DC power supply 11 from flowing into the DC side circuit unit 13.

[0014] The DC side circuit unit 13 is provided on the DC side of the power converter 12. The DC side circuit unit 13 includes a capacitor C1. The capacitor C1 smoothes the DC voltage supplied from the DC power supply 11, for example. The capacitor C1 is also referred to as a smoothing capacitor C1.

[0015] The AC side circuit unit 14 is provided on the AC side of the power converter 12. The AC side circuit unit 14 includes, for example, an LC filter (inductance L, capacitor C2) for removing noise from the current output from the power converter 12. The capacitor C2 is also referred to as an AC capacitor C2.

[0016] The AC switch (AC circuit breaker) 22 is provided in series between the AC side circuit unit 14 and the transformer 20. The AC switch 22 makes (connects) or opens (disconnects) the connection between the AC side circuit unit 14 and the power grid 30 in response to, for example, an AC switch operation signal from the controller 100 or an on / off instruction from a higher-level device (not shown) or an operator. When the AC switch 22 is opened, it is possible to prevent AC power supplied from the power converter 12 from flowing into the power grid 30.

[0017] The controller 100 is connected to the power converter 12 and controls the power converter 12. The controller 100 receives as input the output voltage Vs and output current Is output from the power converter 12. The output voltage Vs is also referred to as the system voltage Vs. The controller 100 also receives as input the DC voltage Vdc between the DC power supply 11 and the power converter 12, the DC current Idc between the DC power supply 11 and the power converter 12, and the AC current Iac between the power converter 12 and the LC filter. The system voltage Vs on the AC side of the power converter 12 is composed of three-phase voltage components (Vsu, Vsv, Vsw). The output current Is on the AC side of the power converter 12 is composed of three-phase current components (Isu, Isv, Isw), and the AC current Iac on the AC side of the power converter 12 is composed of three-phase current components (Iacu, Iacv, Iacw).

[0018] The controller 100 generates a pulse width modulation signal (PWM signal) for controlling the system voltage Vs based on the system voltage Vs, the output current Is, the DC voltage Vdc, the DC current Idc, and the AC current Iac. The controller 100 then outputs the PWM signal to the power converter 12 so that the power converter 12 operates in accordance with the PWM signal. An example of the functional configuration of the controller 100 will be described in detail later.

[0019] 2. System Voltage in an Unbalanced State Figure 2 is a schematic diagram showing the characteristics of the system voltage Vs in an unbalanced state. When the impedance of a three-phase line in the power system 30 becomes unbalanced, the three-phase line becomes completely unbalanced, and the loads on each phase become uneven. In this case, as shown in Figure 2, the d-axis system voltage Vds and the q-axis system voltage Vqs obtained by converting the three-phase components of the system voltage Vs into d-axis and q-axis components have a period twice the rated frequency. The rated frequency is 50 Hz or 60 Hz. In the example shown in Figure 2, the rated frequency is 50 Hz, and the frequencies of the d-axis system voltage Vds and the q-axis system voltage Vqs are 100 Hz, twice the rated frequency, with a period of 0.01 seconds.

[0020] Consider the phase difference Δθ between the voltages of the d-axis and q-axis components (the d-axis system voltage Vds and the q-axis system voltage Vqs) and the system voltage Vs. The phase difference Δθ is typically calculated by a phase detector (e.g., PLL) provided inside the controller 100. As an example, the phase difference Δθ is expressed by the following equation (1).

[0021]

[0022] As shown in FIG. 2, the phase difference Δθ oscillates at a period twice the rated frequency, similar to the d-axis system voltage Vds and the q-axis system voltage Vqs.

[0023] Thus, when an unbalance occurs in the power grid 30, the grid voltage Vs oscillates at a period twice the rated frequency. In this case, if the output current Is also oscillates at a period twice the rated frequency, the charging voltage of the capacitor C1 provided in the DC side circuit unit 13 of the power converter 12 may be overcharged, causing the operation of the power conditioner 10 to become unstable. As shown in FIG. 1 , when a diode 50 is provided to protect the DC power source 11, the overcharging of the charging voltage of the capacitor C1 becomes more pronounced. This may cause the operation of the power conditioner 10 to become unstable. Therefore, when an unbalance occurs in the power grid 30, it is desirable to prevent the output current Is from oscillating at a period different from the rated frequency (twice the rated frequency).

[0024] 3. Controller 3-1. Configuration Example The controller 100 has hardware that realizes various functions. The hardware includes a processing circuit capable of high-speed calculations. Examples of the processing circuit include an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). In addition to the processing circuit, the hardware may also include a storage device and a computing unit (e.g., a CPU) that executes programs stored in the storage device.

[0025] 3 is a block diagram showing an example of functions of the controller 100 according to the embodiment. The controller 100 includes an abc / dq axis converter 110, a first harmonic elimination unit 111, a double frequency elimination unit 112, a phase difference calculator 113, a second harmonic elimination unit 114, a dq / abc axis converter 115, a compensation term generator 116, an abc / dq axis converter 120, a phase detector 121, an abc / dq axis converter 122, a power controller 123, an MPPT unit 124, a voltage controller 125, a dq / abc axis converter 126, a current controller 127, and a PWM controller 128.

[0026] The abc / dq axis converter 110 converts the system voltage Vs from the abc axis to the dq axis. The system voltage Vs converted to the dq axis is referred to as a d-axis system voltage Vds and a q-axis system voltage Vqs.

[0027] The first harmonic elimination unit 111 removes high-frequency components from the d-axis system voltage Vds. The d-axis system voltage Vds after the high-frequency components have been removed is referred to as the d-axis first voltage Vd1. The first harmonic elimination unit 111 also removes high-frequency components from the q-axis system voltage Vqs. The q-axis system voltage Vqs after the high-frequency components have been removed is referred to as the q-axis first voltage Vq1. An example of the first harmonic elimination unit 111 is a low-pass filter (LPF). A time constant is set in the low-pass filter. The time constant can be set arbitrarily. This makes it possible to remove noise components from measuring instruments, harmonic components superimposed on the system voltage Vs, and the like.

[0028] The double frequency removal unit 112 removes a specific frequency from the d-axis first voltage Vd1. The d-axis first voltage Vd1 after the removal of the specific frequency is referred to as the d-axis second voltage Vd2. The double frequency removal unit 112 also removes a specific frequency from the q-axis first voltage Vq1. The q-axis first voltage Vq1 after the removal of the specific frequency is referred to as the q-axis second voltage Vq2. An example of the double frequency removal unit 112 is a band-stop filter (BSP). The specific frequency is a frequency that is twice the rated frequency. For example, the band-stop filter removes a frequency that is twice the rated frequency superimposed on the system voltage Vs.

[0029] The phase difference calculation unit 113 calculates a phase difference Δθ between the voltages of the d-axis and q-axis components (the d-axis second voltage Vd2 and the q-axis second voltage Vq2) and the system voltage Vs based on the d-axis second voltage Vd2 and the q-axis second voltage Vq2. The phase difference Δθ is calculated using, for example, the above-mentioned equation (1). In this case, "Vds" in equation (1) is replaced with "Vd2," and "Vqs" in equation (1) is replaced with "Vq2."

[0030] The second harmonic elimination unit 114 removes high-frequency components from the d-axis system voltage Vds. The d-axis system voltage Vds after the high-frequency components have been removed is referred to as the d-axis third voltage Vd3. The second harmonic elimination unit 114 also removes high-frequency components from the q-axis system voltage Vqs. The q-axis system voltage Vqs after the high-frequency components have been removed is referred to as the q-axis third voltage Vq3. An example of the second harmonic elimination unit 114 is a low-pass filter (LPF). A time constant is set in the low-pass filter. The time constant set in the low-pass filter of the second harmonic elimination unit 114 may be the same as or different from the time constant set in the low-pass filter of the first harmonic elimination unit 111 described above.

[0031] The dq / abc-axis converter 115 generates a three-phase voltage Vtp based on the d-axis third voltage Vd3, the q-axis third voltage Vq3, and a reference phase θ synchronized with the system voltage Vs. Specifically, the dq / abc-axis converter 115 converts the d-axis third voltage Vd3 and the q-axis third voltage Vq3 into abc-axis three-phase components. The reference phase θ is calculated based on the phase difference Δθ. A detailed example of calculating the reference phase θ will be described later.

[0032] When an unbalance occurs in the power grid 30, components with a period twice the rated frequency included in the d-axis third voltage Vd3 and the q-axis third voltage Vq3 generated by the second harmonic elimination unit 114 are attenuated due to the influence of the time constant of the second harmonic elimination unit 114 (low-pass filter). Therefore, the compensation term generation unit 116 generates compensation terms to compensate for the d-axis third voltage Vd3 and the q-axis third voltage Vq3 that attenuate during the unbalance. Specifically, the compensation term generation unit 116 generates three-phase compensation voltages Vc based on the d-axis system voltage Vds, the q-axis system voltage Vqs, and the reference phase θ. Details of the compensation term generation unit 116 (generation of the three-phase compensation voltages Vc) will be described later.

[0033] The abc / dq axis converter 120 converts the output current Is from the abc axis to the dq axis. The output current Is after conversion to the dq axis is called a d-axis output current Ids and a q-axis output current Iqs.

[0034] The phase detector 121 calculates information about a reference phase θ synchronized with the grid voltage Vs. An example of the phase detector 121 is a phase locked loop (PLL). For example, the phase detector 121 calculates information about the reference phase θ synchronized with the grid voltage Vs by performing phase control so as to set the q-axis second voltage Vq2 having the phase difference Δθ calculated by the phase difference calculator 113 to zero.

[0035] The abc / dq axis converter 122 converts the AC current Iac from the abc axis to the dq axis. The AC current Iac converted to the dq axis is called a d-axis AC current Idac and a q-axis AC current Iqac.

[0036] The power control unit 123 controls the power output to the power grid 30 in accordance with operation commands from a higher-level device (not shown) or an operator, and performs power compensation for the AC capacitor C2. Specifically, when the power grid 30 is normal, i.e., when no imbalance occurs in the power grid 30, the controller 100 generates a d-axis current command Id_ins and a q-axis current command Iq_ins as power control for performing power compensation for the AC capacitor C2. In this case, the d-axis current command Id_ins is, for example, the d-axis output current Ids, and the q-axis current command Iq_ins is, for example, the q-axis output current Iqs. The d-axis output current Ids (d-axis current command Id_ins) and the q-axis output current Iqs (q-axis current command Iq_ins) are added to d-axis current command values ​​and q-axis current command values ​​calculated to control the power output to the power grid 30 in accordance with operation commands from a higher-level device (not shown) or an operator, and are expressed by the following equation (2), for example: That is, the d-axis current command Id_ins and the q-axis current command Iq_ins include not only the power compensation amount of the AC capacitor C2 when the power system 30 is in equilibrium, but also current command values ​​(d-axis current command value and q-axis current command value) calculated based on operation commands from a higher-level device, etc. c is the capacitance of the AC capacitor C2. C ｕｖｗｄｑ０ is a transformation matrix that transforms dq0 into uvw. C ｄｑ０ｕｖｗ is a transformation matrix that transforms uvw into dq0, where dq0 means the d-axis component, q-axis component, and zero-phase component.

[0037]

[0038] Further expanding equation (2) gives the following equation (3): ω is the angular frequency [rad / s].

[0039]

[0040] Consider a case where an unbalance occurs in the power grid 30. In this case, a voltage difference occurs between the grid voltage Vs and a voltage command generated in a subsequent stage based on the current command expressed by equation (3). This causes the grid voltage Vs and the output current Is to oscillate at a period twice the rated frequency. Therefore, the power control unit 123 takes into account the occurrence of an unbalance in the power grid 30 and performs additional power compensation for the AC capacitor C2.

[0041] Specifically, the power control unit 123 generates a d-axis current compensation command Idm_ins and a q-axis current compensation command Iqm_ins for compensating for the current command expressed by equation (3). The d-axis current compensation command Idm_ins and the q-axis current compensation command Iqm_ins are expressed, for example, by the following equation (4). Vdsn is a d-axis negative-phase-sequence voltage of the system voltage Vs, Vqsn is a q-axis negative-phase-sequence voltage of the system voltage Vs, and I ０ is the zero-sequence current.

[0042]

[0043] The MPPT (Maximum Power Point Tracking) unit 124 performs MPPT based on, for example, the well-known Hill Climbing (HC) method, based on the acquired information on the DC voltage Vdc and information on the DC current Idc, and calculates a DC voltage command value Vdca. The range of the limiter for MPPT by the MPPT unit 124 may be determined for each device, for example.

[0044] The voltage control unit 125 generates a DC current command value Idc_ins based on a DC differential voltage Vdcs obtained by calculating the difference between the DC voltage command value Vdca and the DC voltage Vdc.

[0045] The dq / abc-axis converter 126 generates a three-phase current command Itp_ins based on a d-axis additional current command Ida_ins obtained by adding the d-axis current command Id_ins and the d-axis current compensation command Idm_ins, a q-axis additional current command Iqa_ins obtained by adding the q-axis current command Iq_ins and the q-axis current compensation command Iqm_ins, and the reference phase θ. Specifically, the dq / abc-axis converter 126 converts the d-axis additional current command Ida_ins and the q-axis additional current command Iqa_ins into the abc-axes of the three-phase components.

[0046] The d-axis added current command Ida_ins and the q-axis added current command Iqa_ins are expressed, for example, by the following equation (5). Also, V'ds and V'qs shown in equation (5) are expressed, for example, by the following equation (6). Vdsp is a d-axis positive-sequence voltage calculated based on the d-axis system voltage Vds. Vqsp is a q-axis positive-sequence voltage calculated based on the q-axis system voltage Vqs. V ０ is the zero-phase voltage. The second term in equation (5) corresponds to equation (4).

[0047]

[0048]

[0049] The d-axis additional current command Ida_ins may include the DC current command value Idc_ins. In this case, the dq / abc-axis converter 126 generates the three-phase current command Itp_ins based on the d-axis additional current command Ida_ins obtained by adding the d-axis current command Id_ins, the d-axis current compensation command Idm_ins, and the DC current command value Idc_ins, the q-axis additional current command Iqa_ins obtained by adding the q-axis current command Iq_ins and the q-axis current compensation command Iqm_ins, and the reference phase θ.

[0050] The current control unit 127 performs current control based on the three-phase current command Itp_ins to generate a three-phase voltage command Vtp1_ins. The three-phase voltage command Vtp1_ins is also referred to as a first three-phase voltage command Vtp1_ins.

[0051] The PWM control unit 128 generates a PWM signal for controlling the power converter 12 based on a three-phase sum voltage Vtpa obtained by adding the three-phase compensation voltage Vc and the three-phase voltage Vtp, and a second three-phase voltage command Vtp2_ins obtained by adding the first three-phase voltage command Vtp1_ins.

[0052] 4 is a block diagram showing a specific example of the compensation term generation unit 116 according to the embodiment. The compensation term generation unit 116 includes a double frequency elimination unit 112A, a double frequency elimination unit 112B, a second harmonic elimination unit 114A, a second harmonic elimination unit 114B, a d-axis reverse phase conversion unit 131, a q-axis reverse phase conversion unit 132, a double frequency elimination unit 112C, a double frequency elimination unit 112D, a second harmonic elimination unit 114C, a second harmonic elimination unit 114D, and a dq / abc-axis conversion unit 133.

[0053] The double frequency removal unit 112A removes a specific frequency from the d-axis system voltage Vds. The d-axis system voltage Vds after the removal of the specific frequency is referred to as a d-axis fourth voltage Vd4. The double frequency removal unit 112A has the same function as the double frequency removal unit 112 described above.

[0054] The double frequency removal unit 112B removes a specific frequency from the q-axis system voltage Vqs. The q-axis system voltage Vqs after the removal of the specific frequency is referred to as a fourth q-axis voltage Vq4. The double frequency removal unit 112B has the same function as the double frequency removal unit 112 described above.

[0055] The second harmonic elimination unit 114A eliminates high-frequency components from the d-axis first differential voltage Vd_s1, which is the difference between the d-axis system voltage Vds and the d-axis fourth voltage Vd4, based on the d-axis first differential voltage Vd_s1. The d-axis first differential voltage Vd_s1 after the high-frequency components have been eliminated is referred to as the d-axis fifth voltage Vd5. The second harmonic elimination unit 114A has the same function as the second harmonic elimination unit 114 described above.

[0056] The second harmonic elimination unit 114B eliminates high-frequency components from the q-axis first differential voltage Vq_s1 based on the q-axis first differential voltage Vq_s1, which is the difference between the q-axis system voltage Vqs and the q-axis fourth voltage Vq4. The q-axis first differential voltage Vq_s1 after the high-frequency components have been eliminated is referred to as the q-axis fifth voltage Vq5. The second harmonic elimination unit 114B has the same function as the second harmonic elimination unit 114 described above.

[0057] The d-axis negative-phase-sequence converter 131 generates the d-axis negative-phase-sequence voltage Vdn based on the d-axis second differential voltage Vd_s2 obtained by subtracting the d-axis first differential voltage Vd_s1 from the d-axis fifth voltage Vd5. Specifically, the d-axis negative-phase-sequence converter 131 converts the d-axis positive-phase-sequence voltage Vdp, which is generated based on the d-axis second differential voltage Vd_s2, into a negative-phase-sequence component. This allows the d-axis negative-phase-sequence voltage Vdn to be generated.

[0058] The q-axis negative-phase-sequence converter 132 generates the q-axis negative-phase-sequence voltage Vqn based on the q-axis second differential voltage Vq_s2, which is the difference between the q-axis first differential voltage Vq_s1 and the q-axis fifth voltage Vq5. Specifically, the q-axis negative-phase-sequence converter 132 converts the q-axis positive-phase-sequence voltage Vqp, which is generated based on the q-axis second differential voltage Vq_s2, into a negative-phase-sequence component. This allows the q-axis negative-phase-sequence voltage Vqn to be generated.

[0059] The double frequency removal unit 112C removes a specific frequency from the d-axis negative-phase-sequence voltage Vdn. The d-axis negative-phase-sequence voltage Vdn after the specific frequency removal is referred to as a d-axis sixth voltage Vd6. The double frequency removal unit 112C has the same function as the double frequency removal unit 112 described above.

[0060] The double frequency removal unit 112D removes a specific frequency from the q-axis negative-phase-sequence voltage Vqn. The q-axis negative-phase-sequence voltage Vqn after the specific frequency removal is referred to as a sixth q-axis voltage Vq6. The double frequency removal unit 112D has the same function as the double frequency removal unit 112 described above.

[0061] The second harmonic elimination unit 114C removes high-frequency components from the d-axis sixth voltage Vd6. The d-axis sixth voltage Vd6 after the high-frequency components are removed is referred to as the d-axis seventh voltage Vd7. The d-axis seventh voltage Vd7 is also referred to as the d-axis compensation voltage. The second harmonic elimination unit 114C has the same function as the second harmonic elimination unit 114 described above.

[0062] The second harmonic elimination unit 114D removes high-frequency components from the q-axis sixth voltage Vq6. The q-axis sixth voltage Vq6 after the high-frequency components are removed is referred to as the q-axis seventh voltage Vq7. The q-axis seventh voltage Vq7 is also referred to as the q-axis compensation voltage. The second harmonic elimination unit 114D has the same function as the second harmonic elimination unit 114 described above.

[0063] The dq / abc-axis converter 133 generates a three-phase compensation voltage Vc based on the d-axis seventh voltage Vd7, the q-axis seventh voltage Vq7, and the reference phase θ. Specifically, the dq / abc-axis converter 133 converts the d-axis seventh voltage Vd7 and the q-axis seventh voltage Vq7 into abc-axis three-phase components.

[0064] 4. Effects The power conditioner 10 (controller 100) generates a d-axis first voltage Vd1 by removing harmonic components from a d-axis system voltage Vds obtained by converting the system voltage Vs of the power system 30 to a d-axis, and generates a q-axis first voltage Vq1 by removing harmonic components from a q-axis system voltage Vqs obtained by converting the system voltage Vs to a q-axis. Furthermore, the power conditioner 10 generates a d-axis second voltage Vd2 by removing specific frequencies from the d-axis first voltage Vd1, and generates a q-axis second voltage Vq2 by removing specific frequencies from the q-axis first voltage Vq1. Furthermore, when the impedance of the three-phase line of the power system 30 is unbalanced, the power conditioner 10 stably calculates the phase difference Δθ with respect to the system voltage Vs based on the d-axis second voltage Vd2 and the q-axis second voltage Vq2 because the specific frequencies have been removed from the d-axis second voltage Vd2 and the q-axis second voltage Vq2. Furthermore, the power conditioner 10 generates a d-axis third voltage Vd3 by removing harmonic components from the d-axis system voltage Vds, and generates a q-axis third voltage Vq3 by removing harmonic components from the q-axis system voltage Vqs. Furthermore, the power conditioner 10 generates a d-axis compensating voltage based on the d-axis system voltage Vds to compensate for the d-axis third voltage Vd3 that attenuates when the impedance of the three-phase lines of the power system 30 is unbalanced, and generates a q-axis compensating voltage based on the q-axis system voltage Vqs to compensate for the q-axis third voltage Vq3 that attenuates when the impedance is unbalanced. Furthermore, the power conditioner 10 generates a three-phase sum voltage Vtpa by adding together a three-phase voltage Vtp that is generated based on the d-axis third voltage Vd3, the q-axis third voltage Vq3, and a reference phase θ synchronized with the system voltage Vs calculated based on the phase difference Δθ, and a three-phase compensating voltage Vc that is generated based on the d-axis compensating voltage, the q-axis compensating voltage, and the reference phase θ. Furthermore, according to the power conditioner 10, a first three-phase voltage command Vtp1_ins is generated by current-controlling a three-phase current command Itp_ins, which is generated based on the d-axis current command Id_ins, the q-axis current command Iq_ins, and the reference phase θ. Furthermore, according to the power conditioner 10, a second three-phase voltage command Vtp2_ins is generated by adding the three-phase sum voltage Vtpa and the first three-phase voltage command Vtp1_ins, and the power converter 12 is controlled based on the second three-phase voltage command Vtp2_ins.As a result, even if the power grid 30 is unbalanced, the voltage difference between the grid voltage Vs and the voltage command for the power converter 12 can be reduced, and the output current Is of the power converter 12 can be prevented from oscillating at a frequency different from the rated frequency (twice the rated frequency), thereby improving the operational stability of the power conditioner 10.

[0065] REFERENCE SIGNS LIST 1... power conversion system, 10... power conditioner, 11... DC power source, 12... power converter, 13... DC side circuit section, 14... AC side circuit section, 20... transformer, 21... DC switch, 22... AC switch, 30... power system, 50... diode, 100... controller

Claims

1. A power converter that converts DC power supplied from a DC power source into AC power and supplies the AC power to the power grid, The system includes a controller for controlling the power converter, The aforementioned controller, A first d-axis voltage is generated by converting the system voltage of the power system to the d-axis and removing the harmonic components of the d-axis system voltage. A first q-axis voltage is generated by converting the aforementioned system voltage to the q-axis and removing the harmonic components of the q-axis system voltage. A second d-axis voltage is generated by removing a specific frequency from the first d-axis voltage. A second q-axis voltage is generated by removing the specific frequency from the first q-axis voltage. Based on the d-axis second voltage and the q-axis second voltage, the phase difference with the system voltage is calculated. A third d-axis voltage is generated by removing the harmonic components of the aforementioned d-axis system voltage. A third q-axis voltage is generated by removing the harmonic components of the aforementioned q-axis system voltage. Based on the d-axis system voltage, a d-axis compensation voltage is generated to compensate for the d-axis third voltage that is attenuated when there is an impedance imbalance in the three-phase transmission lines of the power system. Based on the q-axis system voltage, a q-axis compensation voltage is generated to compensate for the third q-axis voltage that is attenuated when the impedance is unbalanced. A three-phase summation voltage is generated by adding a three-phase voltage generated based on the d-axis third voltage, the q-axis third voltage, and a reference phase synchronized with the system voltage calculated based on the phase difference, and a three-phase compensation voltage generated based on the d-axis compensation voltage, the q-axis compensation voltage, and the reference phase. A first three-phase voltage command is generated by current control of the three-phase current command, which is generated based on the d-axis current command, the q-axis current command, and the reference phase. A second three-phase voltage command is generated by adding the three-phase summation voltage and the first three-phase voltage command. The power converter is configured to be controlled based on the second three-phase voltage command. A power conditioner characterized by the following.

2. A power conditioner according to claim 1, The controller, in generating the d-axis compensation voltage, A fourth d-axis voltage is generated by removing the specific frequency from the d-axis system voltage. Based on the first d-axis differential voltage obtained by differentiating the d-axis system voltage and the fourth d-axis voltage, a fifth d-axis voltage is generated by removing the harmonic components of the first d-axis differential voltage. Based on the second d-axis differential voltage obtained by differentiating the first d-axis differential voltage and the fifth d-axis voltage, a d-axis inverse phase voltage is generated. A sixth d-axis voltage is generated by removing the specific frequency from the aforementioned d-axis inverse phase voltage. The system is configured to generate a d-axis compensation voltage, which is a d-axis seventh voltage obtained by removing the harmonic components of the d-axis sixth voltage. A power conditioner characterized by the following.

3. A power conditioner according to claim 1, In generating the q-axis compensation voltage, the controller A fourth q-axis voltage is generated by removing the specific frequency from the aforementioned q-axis system voltage. Based on the first q-axis differential voltage obtained by subtracting the q-axis system voltage and the fourth q-axis voltage, a fifth q-axis voltage is generated by removing the harmonic components of the first q-axis differential voltage. A q-axis inverse phase voltage is generated based on the q-axis second differential voltage, which is the difference between the q-axis first differential voltage and the q-axis fifth voltage. A sixth q-axis voltage is generated by removing the specific frequency from the aforementioned q-axis inverse phase voltage. The system is configured to generate a q-axis compensation voltage, which is a q-axis 7th voltage obtained by removing the harmonic components of the q-axis 6th voltage. A power conditioner characterized by the following.

4. A power conditioner according to claim 1, In generating the three-phase current command, the controller When the impedance is unbalanced, a d-axis current compensation command and a q-axis current compensation command are generated to perform power compensation on the AC capacitor provided on the AC side of the power converter. At least the d-axis current command and the d-axis current compensation command are added together to generate a d-axis added current command, A q-axis sum current command is generated by adding the q-axis current command and the q-axis current compensation command. The system is configured to generate a current command as the three-phase current command, based on the d-axis summing current command, the q-axis summing current command, and the reference phase. A power conditioner characterized by the following.

5. A power conditioner according to claim 4, The d-axis current compensation command is calculated based on the angular frequency, the capacitance of the AC capacitor, and the d-axis reverse-phase voltage calculated based on the d-axis system voltage. The q-axis current compensation command is calculated based on the angular frequency, the capacitance of the AC capacitor, and the q-axis reverse-phase voltage calculated based on the q-axis system voltage. A power conditioner characterized by the following.

6. A power conditioner according to any one of claims 1 to 5, The aforementioned specific frequency is twice the rated frequency. A power conditioner characterized by the following.