Power Conversion Equipment

Abstract

To provide a power converting apparatus capable of controlling a three-phase AC current output from a power converter at a high speed.SOLUTION: A power converter 3 converts a DC voltage into a three-phase AC voltage and outputs to an AC terminal. A first current detector 5 detects an output current of the power converter 3. The AC terminal of the power converter 3 is connected with a secondary winding of a transformer. A primary winding of the transformer is connected with a three-phase AC power system 1. In a controller 7, a current control section 7 includes a first current compensator which takes, as an input, a deviation between a current value with three degrees-of-freedom based on a detection value of the first current detector 5 and a current command value with three degrees-of-freedom based on the AC current command value and executes at least proportional control arithmetic, and generates a three-phase AC voltage command value by feedback control for compensating for the deviation. A PWM circuit 22 generates a control signal of the power converter 3 based on the three-phase AC voltage command value, thereby PWM controlling the power converter 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 7-28534 (Patent Document 1) discloses a control device for a power conversion device connected to a power system or a load via a transformer. The power conversion device is composed of a self-extinguishing element. When the voltage of the power system or the output voltage of the power conversion device contains a DC component, an excitation current containing a DC component flows in the transformer, and the DC component of this excitation current biases the transformer. In Patent Document 1, the control device is configured to detect the DC component contained in the difference between the primary winding current and the secondary winding current of the transformer, and correct the output voltage command value of the power conversion device based on the DC component. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-28534 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned control device, the output voltage command value of the power conversion device is generated using the system voltage detected by the voltage detector and the primary winding current of the transformer detected by the current detector. Specifically, a current feedback control is executed to make the d-axis current and q-axis current obtained by dq conversion of the primary winding current follow the d-axis current command value and the q-axis current command value, respectively, to generate the output voltage command value. When the primary winding current is in a three-phase balanced state, the d-axis current and the q-axis current are derived as DC amounts. These DC amounts are feedback signals for the feedback control, and command values ​​for these are given to configure the current control system.

[0005] However, when a three-phase unbalanced state occurs due to voltage fluctuations in the power system or bias magnetism in a transformer, a zero-sequence current flows in each phase in the same phase. Since the current control system described above does not control the zero-sequence current, it is not possible to suppress disturbances to the output current of the power converter, and there is a risk that an overcurrent will flow in the power converter.

[0006] In the above-mentioned Patent Document 1, a filter is used to detect the DC component contained in the difference between the primary winding current and the secondary winding current of the transformer. This filter uses a filter with slow response such as a low pass filter (LPF) to attenuate the fundamental wave component and higher frequency components of the input. This is because with a filter with fast response, the harmonic components passing through the filter become disturbances in the current feedback control, making the output current of the power converter more likely to be distorted. On the other hand, if a filter with slow response is used, bias magnetization cannot be suppressed quickly, and as a result, there is a risk of an overcurrent flowing through the power converter.

[0007] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a power conversion device capable of quickly controlling a three-phase AC current output from a power converter. [Means for solving the problem]

[0008] A power conversion device according to an embodiment of the present disclosure includes a power converter that converts a DC voltage into a three-phase AC voltage and outputs the voltage to an AC terminal, a first current detector that detects an output current of the power converter, and a control device that controls the power converter. The AC terminal of the power converter is connected to a secondary winding of a transformer. The primary winding of the transformer is connected to a three-phase AC power system or a three-phase AC load. The control device includes a current control unit and a PWM circuit. The current control unit generates a three-phase AC voltage command value by feedback control for compensating for a deviation of a detection value of the first current detector from an AC current command value. The PWM circuit performs PWM control of the power converter by generating a control signal for the power converter based on the three-phase AC voltage command value. The current control unit includes a first compensator that receives as input a deviation between a current value having three degrees of freedom based on the detection value of the first current detector and a current command value having three degrees of freedom based on the AC current command value, and performs at least a proportional control calculation. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a power conversion device capable of quickly controlling a three-phase AC current output from a power converter. [Brief description of the drawings]

[0010] [Figure 1] 1 is a circuit block diagram showing a configuration of a power conversion device according to a first embodiment. [Diagram 2] 2 is a circuit diagram showing a configuration example of the power converter shown in FIG. 1. [Diagram 3] 3 is a block diagram showing an example configuration of a first compensator and a second compensator. FIG. [Figure 4] FIG. 11 is a circuit block diagram showing a configuration of a power conversion device according to a second embodiment. [Diagram 5] FIG. 11 is a circuit block diagram showing a configuration of a power conversion device according to a third embodiment. [Figure 6] FIG. 11 is a circuit block diagram showing a configuration of a power conversion device according to a fourth embodiment. [Figure 7] FIG. 11 is a circuit block diagram showing a configuration of a power conversion device according to a fifth embodiment. [Figure 8] FIG. 13 is a circuit block diagram showing a configuration of a power conversion device according to a sixth embodiment. [Figure 9] FIG. 13 is a circuit block diagram showing a configuration of a power conversion device according to a seventh embodiment. [Figure 10] FIG. 13 is a circuit block diagram showing a configuration of a power conversion device according to an eighth embodiment. [Figure 11] FIG. 13 is a circuit block diagram showing a configuration of a power conversion device according to a ninth embodiment. [Figure 12] FIG. 23 is a circuit block diagram showing a configuration of a power conversion device according to a tenth embodiment. [Figure 13] 1 is a circuit block diagram showing a configuration of a power conversion device according to a reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference characters, and their description will not be repeated in principle.

[0012] [Embodiment 1] 1 is a circuit block diagram showing a configuration of a power conversion device according to embodiment 1. The power conversion device according to embodiment 1 is used, for example, as a reactive power compensator that compensates for reactive power in a three-phase AC power system 1. Alternatively, the power conversion device according to embodiment 1 is used as a power supply device that supplies power to a three-phase AC load (not shown).

[0013] 1, the power conversion device according to the first embodiment includes a power converter 3, a voltage detector 4, a current detector 5, and a control device 7. Three AC terminals of the power converter 3 are connected via a three-phase transformer 2 to a three-phase transmission line of a three-phase AC power system 1 having a U phase, a V phase, and a W phase.

[0014] A DC terminal of the power converter 3 is connected to a power storage device such as a battery or a capacitor that stores DC power, or a DC power source that generates DC power. Fig. 2 is a circuit diagram showing an example of the configuration of the power converter 3 shown in Fig. 1.

[0015] As shown in FIG. 2, the power converter 3 has a self-extinguishing switching element. In the example of FIG. 2, an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element. The power converter 3 has IGBT elements Q1-Q6 and diodes D1-D6. The collectors of the IGBT elements Q1, Q3, and Q5 are all connected to the DC positive bus PL, and their emitters are connected to the AC terminals Tu, Tv, and Tw, respectively. The collectors of the IGBT elements Q2, Q4, and Q6 are connected to the AC terminals Tu, Tv, and Tw, respectively, and their emitters are connected to the DC negative bus NL. The diodes D1-D6 are connected in anti-parallel to the IGBT elements Q1-Q6, respectively.

[0016] IGBT elements Q1-Q6 are on / off controlled by a control signal (gate pulse) provided from control device 7. In this embodiment, PWM (Pulse Width Modulation) control can be applied as a control method for IGBT elements Q1-Q6.

[0017] The power converter 3 converts DC power from a power storage device (for example, a capacitor C1) into three-phase AC power in accordance with a gate pulse provided by the control device 7. The three-phase AC power generated by the power converter 3 is supplied to the three-phase AC power system 1 via the three-phase transformer 2. The three-phase AC power system 1 side of the three-phase transformer 2 is the primary side, and the power converter 3 side of the three-phase transformer 2 is the secondary side.

[0018] Returning to Fig. 1, the voltage detector 4 detects the three-phase AC voltage of the three-phase AC power system 1, and provides a signal indicating the detected value to the control device 7. The three-phase AC voltage has a U-phase voltage Vu, a V-phase voltage Vv, and a W-phase voltage Vw.

[0019] The current detector 5 detects the output current (three-phase AC current) of the power converter 3, and provides a signal indicating the detected value to the control device 7. The output current of the power converter 3 corresponds to the current flowing through the secondary winding of the three-phase transformer 2 (hereinafter also referred to as the secondary winding current), and has a U-phase current iu, a V-phase current iv, and a W-phase current iw.

[0020] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18 to 20, an inverse dq converter 21, an adder 17, and a PWM circuit 22.

[0021] The phase detector 9 generates a reference phase θ based on the output signal of the voltage detector 4, using a well-known PLL (Phase Locked Loop) circuit or a DFT (Discrete Fourier Transform) circuit. The reference phase θ is a positive-sequence voltage phase of the system voltage of the three-phase AC power system 1.

[0022] The current control unit 8 calculates a feedback control amount by a control calculation for compensating for the deviation of the detection value of the current detector 5 from the AC current command value. The AC current command value is generated in order to maintain the system voltage of the three-phase AC power system 1 constant or to control the DC voltage input to the power converter 3 to be constant. The AC current command value is generally generated by a higher-level controller. When the voltage of the three-phase AC power system 1 is controlled by a power conversion device, the system control system is the higher-level controller. In the example of FIG. 1, the AC current command value includes a d-axis current command value id* and a q-axis current command value iq*.

[0023] The current control unit 8 includes a fixed coordinate converter 10, subtractors 11 to 13, a dq converter 14, an inverse dq converter 15, an adder 16, first compensators CP11 to CP13, and second compensators CP21 and CP22.

[0024] The fixed coordinate converter 10 converts the d-axis current command value id* and the q-axis current command value iq* into three-phase AC current command values ​​by performing fixed coordinate conversion (two-phase to three-phase conversion) using a reference phase θ. The two-phase to three-phase conversion is expressed by the following equation (1). The three-phase AC current command values ​​are output current command values ​​of the power converter 3, and have a U-phase current command value iu*, a V-phase current command value iv*, and a W-phase current command value iw*.

[0025]

number

[0026] A subtractor 11 calculates a deviation Δiu between the U-phase current command value iu* and the U-phase current iu detected by the current detector 5 (Δiu=iu*-iu). A subtractor 12 calculates a deviation Δiv between the V-phase current command value iv* and the V-phase current iv detected by the current detector 5 (Δiv=iv*-iv). A subtractor 13 calculates a deviation Δiw between the W-phase current command value iw* and the W-phase current iw detected by the current detector 5 (Δiw=iw*-iw).

[0027] The first compensators CP11 to CP13 are compensators having frequency characteristics that make the DC gain finite. That is, the first compensators CP11 to CP13 do not have an integral element. The first compensators CP11 to CP13 have at least a proportional element, and calculate a proportional control amount by a proportional control calculation for reducing the deviations Δiu, Δiv, and Δiw of the three-phase AC current from the three-phase AC current command value. The first compensators CP11 to CP13 can further have phase lead / lag characteristics and notch filter characteristics for components other than DC. The first compensators CP11 to CP13 correspond to one embodiment of the "first compensator".

[0028] The dq converter 14 converts the deviations Δiu, Δiv, Δiw from the subtractors 11 to 13 into a d-axis deviation Δid and a q-axis deviation Δiq by performing dq conversion (three-phase to two-phase conversion) using a reference phase θ. The three-phase to two-phase conversion is expressed by the following equation (2). The d-axis deviation Δid corresponds to the deviation of the d-axis current id from the d-axis current command value id* (Δid=id*-id). The q-axis deviation Δiq corresponds to the deviation of the q-axis current iq from the q-axis current command value iq* (Δiq=iq*-iq).

[0029]

number

[0030] The second compensators CP21 and CP22 are compensators having at least an integral element. The second compensators CP21 and CP22 calculate integral control amounts by integral control calculations for reducing the d-axis deviation Δid and the q-axis deviation Δiq. The second compensators CP21 and CP22 may further include a filter and / or a proportional element for removing components other than DC. The second compensators CP21 and CP22 correspond to one embodiment of the "second compensator."

[0031] The inverse dq converter 15 converts the integral control amounts calculated by the second compensators CP21 and CP22 into integral control amounts for three phases by performing an inverse dq conversion (two-phase to three-phase conversion) using equation (1).

[0032] FIG. 3 is a block diagram showing a configuration example of the first compensators CP11 to CP13 and the second compensators CP21 and CP22.

[0033] As shown in Fig. 3, each of the first compensators CP11 to CP13 has a multiplier 81. Kp is a proportional gain. The first compensator CP11 calculates a proportional control amount Kp·Δiu based on a deviation Δiu of the U-phase current iu from the U-phase current command value iu*. The first compensator CP12 calculates a proportional control amount Kp·Δiv based on a deviation Δiv of the V-phase current iv from the V-phase current command value iv*. The first compensator CP13 calculates a proportional control amount Kp·Δiw based on a deviation Δiw of the W-phase current iw from the W-phase current command value iw*.

[0034] As long as the DC gain is finite, the first compensators CP11 to CP13 may have a frequency characteristic and may further include a filter 82. This filter 82 is, for example, a filter for reducing distortion of the three-phase AC voltage command value when bias magnetism occurs in the three-phase transformer 2. Alternatively, the filter 82 is a filter for removing a specific harmonic component from the proportional control amount, or a filter having a phase lead / lag characteristic for improving control stability.

[0035] It should be noted that the DC components included in the deviations Δiu, Δiv, and Δiw are not removed by the filter 82, and therefore do not change even when passing through the filter 82. For this reason, the current control using the first compensators CP11 to CP13 is suitable for suppressing bias magnetism in the three-phase transformer 2.

[0036] Moreover, a filter with a faster response than a filter (typically an LPF) used to detect the amount of DC bias magnetism in a conventional power conversion device can be applied to the filter 82. Since the first compensators CP11 to CP13 are compensators for current control, a fast response does not cause a disturbance to the current control.

[0037] Each of the second compensators CP21 and CP22 has a multiplier 83 and an integrator 84. Ki is an integral control gain. The second compensator CP21 calculates an integral control amount Σ(Ki·Δid) based on the d-axis deviation Δid. The second compensator CP22 calculates an integral control amount Σ(Ki·Δiq) based on the q-axis deviation Δiq. Note that the second compensators CP21 and CP22 may further have a filter (e.g., a moving average filter) for removing components other than DC and / or a proportional element.

[0038] Returning to FIG. 1, the adder 16 generates the three-phase AC voltage command values ​​Vu*, Vv*, Vw* required for feedback control to reduce the deviations Δiu, Δiv, Δiw by adding the proportional control amounts for the three phases, which are the calculated values ​​by the first compensators CP11 to CP13, and the integral control amounts for the three phases by the inverse dq converter 15.

[0039] The multipliers 18-20 and the inverse dq converter 21 generate correction amounts whose values ​​correspond to the d-axis current command value id* and the q-axis current command value iq*. Specifically, the multiplier 18 multiplies the d-axis current command value id* by a gain ωL. The multiplier 19 multiplies the q-axis current command value iq* by a gain ωL. Here, ωL is a reactance present between the power converter 3 and the three-phase AC power system 1, and includes a leakage reactance component of the three-phase transformer 2. The multiplier 20 multiplies the value calculated by the multiplier 19 by "-1". The inverse dq converter 21 converts the correction amounts of the d-axis and q-axis into correction amounts for three phases by performing an inverse dq conversion (two-phase to three-phase conversion) using the formula (1). In this way, the output voltage of the power converter 3 can be controlled in a manner that corrects the voltage drop that occurs in the wiring from the power converter 3 to the three-phase AC power system 1. However, the multipliers 18 to 20 and the inverse dq transformer 21 can be added or omitted as necessary.

[0040] The adder 17 generates a three-phase AC voltage command value by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, and Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command value has a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw*. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0041] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​Vu*, Vv*, and Vw*. For example, the PWM circuit 22 generates gate pulses based on a comparison between the three-phase AC voltage command values ​​Vu*, Vv*, and Vw* and a carrier wave (e.g., a triangular wave). In addition to a method of generating gate pulses using a carrier wave, the PWM circuit 22 can use a method of generating gate pulses according to the three-phase AC voltage command values ​​Vu*, Vv*, and Vw* by referring to a predetermined table, or a method of generating gate pulses by arithmetic processing using the amplitude and phase of the three-phase AC voltage command values ​​Vu*, Vv*, and Vw*. The power converter 3 supplies three-phase AC power to the three-phase AC power system 1 via the three-phase transformer 2 in accordance with the gate pulses.

[0042] The effects of the power conversion device according to the first embodiment will be described below in comparison with a power conversion device (see FIG. 13) serving as a reference example.

[0043] FIG. 13 is a circuit block diagram showing a configuration of a power conversion device according to a reference example.

[0044] As shown in Fig. 13, the power conversion device according to the reference example includes a power converter 3, a voltage detector 4, a current detector 6, and a control device 7A. The power conversion device according to the reference example basically has the same configuration as the power conversion device according to the first embodiment shown in Fig. 1, but differs from the power conversion device according to the first embodiment in that it includes a current detector 6 and a control device 7A instead of the current detector 5 and the control device 7.

[0045] The current detector 6 detects the current flowing through the primary winding of the three-phase transformer 2 (hereinafter also referred to as the primary winding current), and provides a signal indicating the detected value to the control device 7A.

[0046] The control device 7A includes a phase detector 9, a dq converter 200, a current control unit 8A, multipliers 18 and 19, a subtractor 209, adders 210 to 212, an inverse dq converter 213, and a PWM circuit 22.

[0047] The phase detector 9 generates a reference phase θ based on the output signal of the voltage detector 4. The dq converter 200 converts the three-phase AC voltages Vu, Vv, and Vw detected by the voltage detector 4 into a d-axis voltage Vd and a q-axis voltage Vq by dq conversion using the reference phase θ.

[0048] The current control unit 8A calculates a feedback control amount by a control calculation for reducing the deviation of the detection value of the current detector 6 from the AC current command value. The AC current command value includes a d-axis current command value id* and a q-axis current command value iq*.

[0049] Specifically, the current control unit 8A includes a dq converter 214, subtractors 201 and 202, proportional converters 203 and 204, integrators 205 and 206, and adders 207 and 208.

[0050] The dq converter 214 converts the primary winding current (three-phase AC current) detected by the current detector 6 into a d-axis current id and a q-axis current iq by performing dq conversion (three-phase to two-phase conversion) using equation (2).

[0051] A subtractor 201 calculates a deviation (d-axis deviation) Δid of the d-axis current id from a d-axis current command value id*. A subtractor 202 calculates a deviation (q-axis deviation) Δiq of the q-axis current iq from a q-axis current command value iq*.

[0052] The proportional controller 203 calculates a proportional control amount Kp·Δid based on the d-axis deviation Δid. The proportional controller 204 calculates a proportional control amount Kp·Δiq based on the q-axis deviation Δiq. Kp is a proportional gain.

[0053] The integrator 205 calculates an integral control amount Σ(Ki·Δid) based on the d-axis deviation Δid. The integrator 206 calculates an integral control amount Σ(Ki·Δiq) based on the q-axis deviation Δiq. Ki is an integral gain.

[0054] The adder 207 adds the proportional control amount Kp·Δid from the proportional unit 203 and the integral control amount Σ(Ki·Δid) from the integrator 205 to generate a d-axis voltage command value Vd* required for feedback control to reduce the d-axis deviation Δid. The adder 208 adds the proportional control amount Kp·Δiq from the proportional unit 204 to the integral control amount Σ(Ki·Δiq) from the integrator 206 to generate a q-axis voltage command value Vq* required for feedback control to reduce the q-axis deviation Δiq.

[0055] Multiplier 18 multiplies the d-axis current command value id* by a gain ωL. Multiplier 19 multiplies the q-axis current command value iq* by a gain ωL. Multipliers 18 and 19 generate correction amounts whose values ​​correspond to the d-axis current command value id* and the q-axis current command value iq*.

[0056] The subtractor 209 subtracts the correction amount from the multiplier 19 from the d-axis voltage command value Vd* from the adder 207. The adder 210 adds the correction amount from the multiplier 18 to the q-axis voltage command value Vq* from the adder 208.

[0057] The adder 211 adds the d-axis voltage Vd from the dq converter 200 to the d-axis voltage command value Vd* from the adder 209. The adder 212 adds the q-axis voltage Vq from the dq converter 200 to the q-axis voltage command value Vq* from the adder 210.

[0058] The inverse dq converter 213 generates three-phase voltage command values ​​Vu*, Vv*, and Vw* by performing inverse dq conversion (two-phase to three-phase conversion) using the d-axis voltage command value Vd* from the adder 211 and the q-axis voltage command value Vq* from the adder 212 using equation (1). The three-phase AC voltage command values ​​are provided to the PWM circuit 22.

[0059] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command value. The power converter 3 supplies three-phase AC power to the three-phase AC power system 1 via the three-phase transformer 2 in accordance with the gate pulses.

[0060] 13, the primary winding current (three-phase AC current) of the three-phase transformer 2 detected by the current detector 6 is dq converted (three-phase to two-phase conversion) to a d-axis current id and a q-axis current iq. Then, a proportional-integral control calculation is performed on the deviation Δid of the d-axis current id from the d-axis current command value id* and the deviation Δiq of the q-axis current iq from the q-axis current command value iq* to generate a d-axis voltage command value Vd* and a q-axis voltage command value Vq*.

[0061] Here, the dq transformation used in the reference example is premised on the three-phase AC current being in a three-phase balanced state. A three-phase balanced state is a state in which the amplitudes of the phase currents are equal and the phases are shifted by 120°. In a three-phase balanced state, the sum of the phase currents is zero (i.e., iu+iv+iw=0), and therefore the zero-sequence current is zero.

[0062] According to the dq transformation, the state quantities on each axis in a two-axis orthogonal coordinate system (dq coordinate system) rotating at the power supply angular velocity can be treated as DC quantities, making it possible to suppress interference in the control between each phase of the three-phase AC current.

[0063] However, when a transient voltage fluctuation occurs in the three-phase AC power system 1 or when bias magnetism occurs in the three-phase transformer 2, disturbances such as distortion of the sinusoidal waveform of the three-phase AC current or superposition of a DC component on the three-phase AC current may occur. In such cases, the three-phase AC current becomes unbalanced and a zero-phase current flows. However, in the current feedback control according to the reference example, since the zero-phase current is not controlled, it is difficult to suppress the above-mentioned disturbances.

[0064] In contrast, in the power conversion device according to the first embodiment, the d-axis current command value id* and the q-axis current command value iq* are converted into three-phase AC current command values ​​iu*, iv*, and iw*, and current feedback control is executed to reduce the deviation of the three-phase AC current from the three-phase AC current command values. That is, in the reference example, the current feedback control is composed of a d-axis current control system and a q-axis current control system, and the degree of freedom of the control is two, whereas in the first embodiment, a control system is composed for each phase current of the three-phase AC current, and the degree of freedom of the current feedback control is three. Therefore, the degree of freedom of the current feedback control is the same as the number of AC terminals of the power converter 3, and therefore it is possible to suppress disturbances occurring at each of the AC terminals Tu, Tv, and Tw of the power converter 3 by the current feedback control.

[0065] Furthermore, in the power conversion device according to the first embodiment, the output current of the power converter 3 (i.e., the secondary winding current of the three-phase transformer 2) is detected, and the above-mentioned feedback control of the current of each phase is executed using the detected value. When feedback control of the output current of the power converter 3 is performed, the excitation circuit of the three-phase transformer 2 is included in the controlled object, but the impedance of the excitation circuit is difficult to handle because it changes when the bias magnetization occurs. In addition, since the feedback current includes the bias magnetization current, the waveform of the generated voltage command value is distorted, and there is a possibility that harmonics are generated. In the first embodiment, a control system is configured for each phase current of the three-phase AC current output from the power converter 3, so that even when the bias magnetization occurs, it is possible to respond to each phase individually. As a result, the output current of the power converter 3 is controlled so as to eliminate the bias magnetization of the three-phase transformer 2, so that it is possible to suppress an overcurrent from flowing through the power converter 3 due to the occurrence of the bias magnetization.

[0066] Here, as a conventional method for suppressing the bias current, as described in Patent Document 1, there is a method of correcting the output voltage command value of the power converter based on the DC component contained in the difference between the primary winding current and the secondary winding current of the three-phase transformer 2. However, in this method, a filter with a slow response such as an LPF is used to detect the DC component, and there is a concern that the response of the bias current suppression control will be slowed down due to the influence of the delay of the filter. On the other hand, according to the power conversion device of the first embodiment, each of the first compensators CP11 to CP13 responsible for proportional control executes a control calculation to reduce the DC component contained in each phase current, so that the bias current can be suppressed more quickly.

[0067] The current feedback control in the first embodiment is configured to calculate a proportional control amount based on the deviations Δiu, Δiv, Δiw of the three-phase AC current from the three-phase AC current command value, while calculating an integral control amount based on the deviations Δid, Δiq of the d-axis current and the q-axis current from the d-axis current command value and the q-axis current command value. This is because the three-phase AC current is an AC amount that oscillates at the frequency of the three-phase AC power system 1, and therefore the steady-state deviation cannot be eliminated by integral control that time-integrates the change in the deviation of the three-phase AC current. On the other hand, the d-axis current and the q-axis current are DC amounts, and therefore the control amount continues to increase by the time integration of the deviation of the d-axis current and the q-axis current, and therefore the steady-state deviation can be eliminated.

[0068] [Embodiment 2] FIG. 4 is a circuit block diagram showing a configuration of a power conversion device according to the second embodiment.

[0069] As shown in FIG. 4, the power conversion device according to embodiment 2 basically has the same configuration as the power conversion device according to embodiment 1 shown in FIG. 1, but differs from the power conversion device according to embodiment 1 in that it includes a current detector 6 and that the control device 7 has a subtractor 23 and a magnetic bias detector 24.

[0070] The current detector 6 detects the current (primary winding current) flowing through the primary winding of the three-phase transformer 2, and provides the control device 7 with a signal indicating the detected value.

[0071] Subtractor 23 calculates the difference between the primary winding current detected by current detector 6 and the output current (secondary winding current) of power converter 3 detected by current detector 5. The difference calculated by subtractor 23 corresponds to the excitation current flowing through the excitation circuit of three-phase transformer 2.

[0072] The magnetism bias detector 24 determines whether magnetism bias has occurred in the three-phase transformer 2 based on the difference (excitation current) calculated by the subtractor 23. Specifically, when magnetism bias occurs in the three-phase transformer 2, the iron core constituting the transformer becomes saturated, decreasing the excitation inductance, and the excitation current increases. When the excitation current exceeds a predetermined threshold, the magnetism bias detector 24 determines that magnetism bias has occurred in the three-phase transformer 2.

[0073] When it is determined that magnetism bias occurs in the three-phase transformer 2, the magnetism bias detector 24 reduces the proportional gains Kp in the first compensators CP11 to CP13 and reduces the integral gains Ki in the second compensators CP21 and CP22.

[0074] This is because when magnetic saturation occurs in the three-phase transformer 2, the excitation inductance decreases, causing a decrease in the impedance on the output side of the power converter 3. If the control gain in the current feedback control is constant, the loop gain increases as the impedance on the output side decreases, which may increase the output current of the power converter 3 and cause the current feedback control to become unstable. Therefore, when biased magnetism occurs in the three-phase transformer 2, the proportional gain Kp of the first compensator and the integral gain Ki of the second compensator can be reduced to ensure the stability of the current feedback control.

[0075] In the second embodiment, the configuration example in which the proportional gain Kp and the integral gain Ki are reduced when magnetic bias occurs in the three-phase transformer 2 has been described, but a configuration in which at least the proportional gain Kp is reduced may also be used.

[0076] [Embodiment 3] FIG. 5 is a circuit block diagram showing a configuration of a power conversion device according to the third embodiment.

[0077] As shown in FIG. 5, the power conversion device of embodiment 3 basically has the same configuration as the power conversion device of embodiment 1 shown in FIG. 1, but differs from the power conversion device of embodiment 1 in that it is equipped with a current detector 6 and that the current control unit 8 in the control device 7 has a dq converter 40 and subtractors 41, 42.

[0078] The current detector 6 detects the current (primary winding current) flowing through the primary winding of the three-phase transformer 2, and provides the control device 7 with a signal indicating the detected value.

[0079] In the current control unit 8, the dq converter 40 converts the primary winding current (three-phase AC current) detected by the current detector 6 into a d-axis current id and a q-axis current iq by performing dq conversion (three-phase to two-phase conversion) using equation (2).

[0080] A subtractor 41 calculates a deviation (d-axis deviation) Δid of the d-axis current id from the d-axis current command value id*. A subtractor 42 calculates a deviation (q-axis deviation) Δiq of the q-axis current iq from the q-axis current command value iq*.

[0081] The second compensators CP21 and CP22 calculate integral control amounts by integral control calculations for the d-axis deviation Δid and the q-axis deviation Δiq. The inverse dq converter 15 converts the integral control amounts calculated by the second compensators CP21 and CP22 into integral control amounts for three phases by inverse dq conversion (two-phase to three-phase conversion) using equation (1).

[0082] The adder 16 adds the proportional control amounts for the three phases, which are the calculated values ​​by the first compensators CP11 to CP13, and the integral control amounts for the three phases from the inverse dq converter 15, to generate the three-phase AC voltage command values ​​Vu*, Vv*, Vw* required for feedback control to reduce the deviations Δiu, Δiv, Δiw.

[0083] Multipliers 18 to 20 and an inverse dq converter 21 generate correction amounts whose values ​​correspond to the d-axis current command value id* and the q-axis current command value iq*.

[0084] The adder 17 generates three-phase AC voltage command values ​​Vu*, Vv*, Vw* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0085] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command value. The power converter 3 supplies three-phase AC power to the three-phase AC power system 1 via the three-phase transformer 2 in accordance with the gate pulses.

[0086] As described above, the power conversion device of embodiment 3 can quickly suppress bias magnetism in the three-phase transformer 2 by having a control system (fixed coordinate converter 10, subtractors 11-13, and first compensators CP11-CP13) that performs proportional control to reduce the deviation between the output current of the power converter 3 (i.e., the secondary winding current of the three-phase transformer 2) and the three-phase current command value.

[0087] Furthermore, the power conversion device of embodiment 3 has a control system (dq converter 40, subtractors 41, 42, second compensators CP21, CP22, and inverse dq converter 15) that converts the primary winding current of the three-phase transformer 2 into a d-axis current and a q-axis current, and performs integral control to reduce the deviation of the d-axis current and the q-axis current from the d-axis current command value and the q-axis current command value, thereby eliminating the steady-state deviation contained in the primary winding current.

[0088] [Embodiment 4] FIG. 6 is a circuit block diagram showing a configuration of a power conversion device according to the fourth embodiment.

[0089] As shown in FIG. 6, the power conversion device of embodiment 4 basically has the same configuration as the power conversion device of embodiment 1 shown in FIG. 1, but differs from the power conversion device of embodiment 1 in that the three-phase transformer 2 is a multiple transformer and that it is equipped with current detectors 5a, 5b, a current detector 6, and power converters 3a, 3b.

[0090] The multiple transformer 2 has two secondary windings 2a, 2b connected to the AC terminals of the two power converters 3a, 3b, respectively, and two primary windings 2c connected in series to each other and connected to the three-phase AC power system 1. As a result, a voltage obtained by serially combining the AC output voltages of the power converters 3a, 3b for each phase is output to the three-phase AC power system 1. Note that, although the example of Fig. 6 shows a two-stage series multiplexing configuration in which the two power converters 3a, 3b are series multiplexed by the multiple transformer 2, the number of series multiplexing is not limited to two.

[0091] Each of the power converters 3a and 3b has a self-extinguishing switching element and has a configuration similar to that of the power converter 3 shown in Fig. 2. The series circuit (capacitor C1 in the example of Fig. 2) of the power converters 3a and 3b is common.

[0092] Each of the power converters 3a and 3b converts DC power into three-phase AC power in accordance with a gate pulse provided by the control device 7. The three-phase AC power generated by the power converters 3a and 3b is serially combined by the three-phase transformer 2 and supplied to the three-phase AC power system 1.

[0093] The current detector 5a detects the output current (three-phase AC current) of the power converter 3a, and provides a signal indicating the detected value to the control device 7. The output current of the power converter 3a corresponds to the current (secondary winding current) flowing through the secondary winding 2a of the three-phase transformer 2, and has a U-phase current i1u, a V-phase current i1v, and a W-phase current i1w.

[0094] The current detector 5b detects the output current (three-phase AC current) of the power converter 3b, and provides a signal indicating the detected value to the control device 7. The output current of the power converter 3b corresponds to the current (secondary winding current) flowing through the secondary winding 2b of the three-phase transformer 2, and has a U-phase current i2u, a V-phase current i2v, and a W-phase current i2w.

[0095] The current detector 6 detects the current (primary winding current) flowing through the primary winding 2c of the three-phase transformer 2, and provides a signal indicating the detected value to the control device 7. The primary winding current has a U-phase current iu, a V-phase current iv, and a W-phase current iw.

[0096] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18-20, an inverse dq converter 21, adders 17 and 57, and a PWM circuit 22. The control device 7 basically has the same configuration as the control device 7 shown in Fig. 1, but differs from the control device 7 in the first embodiment in that the current control unit 8 has a dq converter 40, subtractors 41, 42, 51-53, and first compensators CP14-CP16, and has an adder 57.

[0097] The fixed coordinate converter 10 converts the d-axis current command value id* and the q-axis current command value iq* into three-phase AC current command values ​​iu*, iv*, iw* by inverse dq transformation (two-phase to three-phase transformation) using equation (1).

[0098] The subtractor 11 calculates the deviation Δi1u between the U-phase current command value iu* and the U-phase current i1u detected by the current detector 5a (Δi1u=iu*-i1u). The subtractor 12 calculates the deviation Δi1v between the V-phase current command value iv* and the V-phase current i1v detected by the current detector 5a (Δi1v=iv*-i1v). The subtractor 13 calculates the deviation Δi1w between the W-phase current command value iw* and the W-phase current i1w detected by the current detector 5a (Δi1w=iw*-i1w).

[0099] The first compensators CP11 to CP13 calculate proportional control amounts by proportional control calculations for the deviations Δi1u, Δi1v, and Δi1w. The first compensator CP11 calculates the proportional control amount Kp·Δi1u based on the deviation Δi1u. The first compensator CP12 calculates the proportional control amount Kp·Δi1v based on the deviation Δi1v. The first compensator CP13 calculates the proportional control amount Kp·Δi1w based on the deviation Δi1w. Here, Kp is the proportional gain.

[0100] The subtractor 51 calculates the deviation Δi2u between the U-phase current command value iu* and the U-phase current i2u detected by the current detector 5b (Δi2u=iu*-i2u). The subtractor 52 calculates the deviation Δi2v between the V-phase current command value iv* and the V-phase current i2v detected by the current detector 5b (Δi2v=iv*-i2v). The subtractor 53 calculates the deviation Δi2w between the W-phase current command value iw* and the W-phase current i2w detected by the current detector 5b (Δi2w=iw*-i2w).

[0101] The first compensators CP14 to CP16 calculate proportional control amounts by proportional control calculations for the deviations Δi2u, Δi2v, and Δi2w. The first compensator CP14 calculates the proportional control amount Kp·Δi2u based on the deviation Δi2u. The first compensator CP15 calculates the proportional control amount Kp·Δi2v based on the deviation Δi2v. The first compensator CP16 calculates the proportional control amount Kp·Δi2w based on the deviation Δi2w. Kp is a proportional gain. The proportional gains of the first compensators CP14 to CP16 may be the same value as or different from the proportional gains of the first compensators CP11 to CP13.

[0102] The dq converter 40 converts the primary winding current (three-phase AC current) detected by the current detector 6 into a d-axis current id and a q-axis current iq by dq conversion (three-phase to two-phase conversion) using equation (2).

[0103] A subtractor 41 calculates a deviation (d-axis deviation) Δid of the d-axis current id from the d-axis current command value id*. A subtractor 42 calculates a deviation (q-axis deviation) Δiq of the q-axis current iq from the q-axis current command value iq*.

[0104] The second compensators CP21 and CP22 calculate integral control amounts by integral control calculations for the d-axis deviation Δid and the q-axis deviation Δiq. The inverse dq converter 15 converts the integral control amounts calculated by the second compensators CP21 and CP22 into integral control amounts for three phases by inverse dq conversion (two-phase to three-phase conversion) using equation (1).

[0105] The adder 16 adds the proportional control amounts for the three phases, which are the calculated values ​​by the first compensators CP11 to CP13, and the integral control amounts for the three phases by the inverse dq converter 15, to generate the three-phase AC voltage command values ​​V1u*, V1v*, V1w* required for feedback control to reduce the deviations Δi1u, Δi1v, Δi1w.

[0106] The adder 17 generates three-phase AC voltage command values ​​V1u*, V1v*, V1w* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command values ​​are provided to the PWM circuit 22.

[0107] The adder 56 adds the proportional control amount for three phases, which is the calculated value by the first compensators CP14 to CP16, and the integral control amount for three phases by the inverse dq converter 15, to generate the three-phase AC voltage command values ​​V2u*, V2v*, and V2w* required for feedback control to reduce the deviations Δi2u, Δi2v, and Δi2w.

[0108] The adder 57 generates three-phase AC voltage command values ​​V2u*, V2v*, V2w* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 56. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0109] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V1u*, V1v*, and V1w*. The power converter 3a generates three-phase AC power in accordance with the gate pulses.

[0110] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V2u*, V2v*, and V2w*. The power converter 3b generates three-phase AC power in accordance with the gate pulses.

[0111] As described above, according to the power conversion device of the fourth embodiment, even in a configuration in which a plurality of power converters 3a, 3b are serially multiplexed by the multiple transformer 2, a proportional control having the same number of degrees of freedom as the AC terminals is executed for each power converter, so that disturbances occurring at the AC terminals of each power converter can be suppressed. This makes it possible to deal with cases in which there is a difference in the susceptibility to bias magnetization between the plurality of power converters 3a, 3b due to the characteristics of the transformers or the phase difference of the carrier wave.

[0112] In addition, the primary winding current of the multiple transformer 2 is converted into a d-axis current and a q-axis current, and integral control is performed to reduce the d-axis deviation and the q-axis deviation, thereby eliminating the steady-state deviation contained in the primary winding current.

[0113] [Embodiment 5] FIG. 7 is a circuit block diagram showing a configuration of a power conversion device according to the fifth embodiment.

[0114] As shown in FIG. 7, the power conversion device of embodiment 5 basically has the same configuration as the power conversion device of embodiment 4 shown in FIG. 6, but the configuration of the control device 7 is different from that of the power conversion device of embodiment 4.

[0115] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18-20, an inverse dq converter 21, adders 17 and 57, and a PWM circuit 22. The control device 7 basically has the same configuration as the control device 7 shown in Fig. 4, but differs from the control device 7 in the fourth embodiment in that the current control unit 8 has a mean / deviation calculator 60, subtractors 61-66, first compensators CP17-CP19, and adders 67-69.

[0116] The average / deviation calculator 60 receives the output current (three-phase AC currents i1u, i1v, i1w) of the power converter 3a detected by the current detector 5a and the output current (three-phase AC currents i2u, i2v, i2w) of the power converter 3b detected by the current detector 5b.

[0117] The average / deviation calculator 60 calculates the average value ia of each phase current using the detection values ​​of the current detectors 5a and 5b. If the average value of the U-phase current (hereinafter also referred to as the U-phase average current) is iau, the average value of the V-phase current (hereinafter also referred to as the V-phase average current) is iav, and the average value of the W-phase current (hereinafter also referred to as the W-phase average current) is iaw, the three-phase average currents iau, iav, and iaw are given by the following equations (3) to (5).

[0118]

number

[0119] The mean / deviation calculator 60 calculates the deviation of the output current (three-phase AC current) of each power converter with respect to the three-phase average current. Specifically, the mean / deviation calculator 60 calculates the deviations di1u, di1v, and di1w of the three-phase AC currents i1u, i1v, and i1w with respect to the three-phase average currents iau, iav, and iaw. The deviations di1u, di1v, and di1w are given by the following equations (6) to (8).

[0120]

number

[0121] Similarly, the average / deviation calculator 60 calculates deviations di2u, di2v, and di2w of the three-phase AC currents i2u, i2v, and i2w with respect to the three-phase average currents iau, iav, and iaw. The deviations di2u, di2v, and di2w are given by the following equations (9) to (11).

[0122]

number

[0123] A subtractor 11 calculates a deviation Δiau between a U-phase current command value iu* and a U-phase average current iau (Δiau=iu*-iau). A subtractor 12 calculates a deviation Δiav between a V-phase current command value iv* and a V-phase average current iav (Δiav=iv*-iav). A subtractor 13 calculates a deviation Δiaw between a W-phase current command value iw* and a W-phase average current iaw (Δiaw=iw*-iaw).

[0124] The first compensators CP11 to CP13 calculate proportional control amounts Kp·Δiau, Kp·Δiav, and Kp·Δiaw, respectively, by proportional control calculations for the deviations Δiau, Δiav, and Δiaw, where Kp is a proportional gain.

[0125] A subtractor 61 calculates a deviation Δdi1u between a U-phase deviation command value di1u* and a U-phase deviation di1u (Δdi1u=di1u*-di1u). A subtractor 62 calculates a deviation Δdi1v between a V-phase deviation command value di1v* and a V-phase deviation di1v (Δdi1v=di1v*-di1v). A subtractor 63 calculates a deviation Δdi1w between a W-phase deviation command value di1w* and a W-phase deviation di1w (Δdi1w=di1w*-di1w). The three-phase deviation command values ​​di1u*, di1v*, di1w* can be generated by a higher-level controller, similar to the three-phase current command values ​​iu*, iv*, iw*.

[0126] The first compensators CP14 to CP16 calculate proportional control amounts Kp·Δdi1u, Kp·Δdi1v, and Kp·Δdi1w by proportional control calculations for the deviations Δdi1u, Δdi1v, and Δdi1w, respectively, where Kp is a proportional gain.

[0127] A subtractor 64 calculates a deviation Δdi2u between the U-phase deviation command value di2u* and the U-phase deviation di2u (Δdi2u=di2u*-di2u). A subtractor 65 calculates a deviation Δdi2v between the V-phase deviation command value di2v* and the V-phase deviation di2v (Δdi2v=di2v*-di2v). A subtractor 66 calculates a deviation Δdi2w between the W-phase deviation command value di2w* and the W-phase deviation di2w (Δdi2w=di2w*-di2w). The three-phase deviation command values ​​di2u*, di2v*, di2w* can be generated by a higher-level controller, similar to the three-phase current command values ​​iu*, iv*, iw*.

[0128] The first compensators CP17 to CP19 calculate proportional control amounts Kp·Δdi2u, Kp·Δdi2v, and Kp·Δdi2w by proportional control calculations for the deviations Δdi2u, Δdi2v, and Δdi2w, respectively.

[0129] The adder 67 adds the proportional control amount for three phases, which is the value calculated by the first compensators CP11 to CP13, and the proportional control amount for three phases, which is the value calculated by the first compensators CP14 to CP16. The adder 16 adds the calculation result by the adder 67 and the integral control amount for three phases by the inverse dq converter 15, thereby generating a three-phase AC voltage command value required for feedback control to reduce deviations Δi1u, Δi1v, Δi1w of the three-phase AC currents i1u, i1v, i1w from the three-phase AC current command values ​​iu*, iv*, iw*.

[0130] The adder 17 generates a three-phase AC voltage command value by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, and Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command value has a U-phase voltage command value V1u*, a V-phase voltage command value V1v*, and a W-phase voltage command value V1w*. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0131] The adder 68 adds the proportional control amount for three phases, which is the value calculated by the first compensators CP11 to CP13, and the proportional control amount for three phases, which is the value calculated by the first compensators CP17 to CP19. The adder 69 adds the calculation result by the adder 68 and the integral control amount for three phases by the inverse dq converter 15, thereby generating a three-phase AC voltage command value required for feedback control to reduce deviations Δi2u, Δi2v, Δi2w of the three-phase AC currents i2u, i2v, i2w from the three-phase AC current command values ​​iu*, iv*, iw*.

[0132] The adder 57 generates a three-phase AC voltage command value by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, and Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 69. The three-phase AC voltage command value has a U-phase voltage command value V2u*, a V-phase voltage command value V2v*, and a W-phase voltage command value V2w*. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0133] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V1u*, V1v*, and V1w*. The power converter 3a generates three-phase AC power in accordance with the gate pulses. The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V2u*, V2v*, and V2w*. The power converter 3b generates three-phase AC power in accordance with the gate pulses.

[0134] As described above, according to the power conversion device of embodiment 5, even in a configuration in which a plurality of power converters 3a, 3b are serially multiplexed by the multiple transformer 2, proportional control having the same number of degrees of freedom as the AC terminals is executed for each power converter, and the primary winding current of the multiple transformer 2 is converted into a d-axis current and a q-axis current for integral control, so that it is possible to obtain the same effects as the power conversion device of embodiment 4 described above.

[0135] Furthermore, in the power conversion device according to the fifth embodiment, the output currents of the multiple power converters 3a and 3b are decomposed into three-phase average currents iau, iav, and iaw, deviations di1u, di1v, and di1w of the output currents of the power converter 3a relative to the three-phase average currents, and deviations di2u, di2v, and di2w of the output currents of the power converter 3b relative to the three-phase average currents. Then, proportional control is performed to make the three-phase average currents coincide with the three-phase current command values, proportional control to make the deviations di1u, di1v, and di1w coincide with the deviation command values ​​di1u*, di1v*, and di1w*, and proportional control to make the deviations di2u, di2v, and di2w coincide with the deviation command values ​​di2u*, di2v*, and di2w*. This allows the proportional gains Kp in these proportional controls to be set independently of each other, thereby enabling more precise control to be realized.

[0136] [Embodiment 6] FIG. 8 is a circuit block diagram showing a configuration of a power conversion device according to the sixth embodiment.

[0137] As shown in FIG. 8, the power conversion device of embodiment 6 basically has the same configuration as the power conversion device of embodiment 5 shown in FIG. 7, but the configuration of the control device 7 is different from that of the power conversion device of embodiment 5.

[0138] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18-20, an inverse dq converter 21, adders 17 and 57, and a PWM circuit 22. The control device 7 basically has the same configuration as the control device 7 shown in Fig. 5, but differs from the control device 7 in the fifth embodiment in that the current control unit 8 does not have the subtractors 61-66, the first compensators CP14-CP19, and the adders 67-69.

[0139] The average / deviation calculator 60 receives the output current (three-phase AC currents i1u, i1v, i1w) of the power converter 3a detected by the current detector 5a and the output current (three-phase AC currents i2u, i2v, i2w) of the power converter 3b detected by the current detector 5b.

[0140] The average / deviation calculator 60 calculates the average value of each phase current using the detection values ​​of the current detectors 5 a and 5 b. The average / deviation calculator 60 calculates the U-phase average current iau, the V-phase average current iav, and the W-phase average current iaw using the above equations (3) to (5).

[0141] A subtractor 11 calculates a deviation Δiau between a U-phase current command value iu* and a U-phase average current iau. A subtractor 12 calculates a deviation Δiav between a V-phase current command value iv* and a V-phase average current iav. A subtractor 13 calculates a deviation Δiaw between a W-phase current command value iw* and a W-phase average current iaw.

[0142] The first compensators CP11 to CP13 calculate proportional control amounts Kp·Δiau, Kp·Δiav, and Kp·Δiaw, respectively, by proportional control calculations for the deviations Δiau, Δiav, and Δiaw, where Kp is a proportional gain.

[0143] The adder 16 adds the proportional control amounts for the three phases, which are values ​​calculated by the first compensators CP11 to CP13, and the integral control amounts for the three phases by the inverse dq converter 15, to generate a three-phase AC voltage command value required for feedback control to reduce the deviations Δi1u, Δi1v, Δi1w of the three-phase AC currents i1u, i1v, i1w from the three-phase AC current command values ​​iu*, iv*, iw*.

[0144] The adder 17 generates a three-phase AC voltage command value by adding the feedforward control amount from the inverse dq converter 21 and the three-phase AC voltage detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command value has a U-phase voltage command value V1u*, a V-phase voltage command value V1v*, and a W-phase voltage command value V1w*. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0145] The adder 56 adds the proportional control amounts for the three phases, which are values ​​calculated by the first compensators CP11 to CP13, and the integral control amounts for the three phases by the inverse dq converter 15, to generate a three-phase AC voltage command value required for feedback control to reduce the deviations Δi2u, Δi2v, Δi2w of the three-phase AC currents i2u, i2v, i2w from the three-phase AC current command values ​​iu*, iv*, iw*.

[0146] The adder 57 generates a three-phase AC voltage command value by adding the feedforward control amount from the inverse dq converter 21 and the three-phase AC voltage detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 56. The three-phase AC voltage command value has a U-phase voltage command value V2u*, a V-phase voltage command value V2v*, and a W-phase voltage command value V2w*. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0147] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V1u*, V1v*, and V1w*. The power converter 3a generates three-phase AC power in accordance with the gate pulses. The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V2u*, V2v*, and V2w*. The power converter 3b generates three-phase AC power in accordance with the gate pulses.

[0148] As described above, in the power conversion device according to the sixth embodiment, in a configuration in which a plurality of power converters 3a, 3b are serially multiplexed by the multiplex transformer 2, proportional control is performed to make the three-phase average currents iau, iav, and iaw of the output currents of the plurality of power converters 3a, 3b coincide with the three-phase current command value. This does not perform the proportional control for each power converter shown in the fourth and fifth embodiments, but it is possible to reduce the amount of calculation in the current control unit 8. Therefore, when there is little variation in the characteristics of the transformers between the plurality of power converters 3a, 3b and there is no significant difference in the susceptibility to bias magnetization, it is possible to simplify the current control by employing the control system shown in the sixth embodiment.

[0149] [Embodiment 7] FIG. 9 is a circuit block diagram showing a configuration of a power conversion device according to the seventh embodiment.

[0150] As shown in FIG. 9, the power conversion device of embodiment 7 basically has the same configuration as the power conversion device of embodiment 4 shown in FIG. 6, but the configuration of the control device 7 is different from that of the power conversion device of embodiment 4.

[0151] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18 to 20, an inverse dq converter 21, adders 17 and 57, and a PWM circuit 22. The control device 7 basically has the same configuration as the control device 7 shown in Fig. 4, but differs from the control device 7 in the fourth embodiment in that the current control unit 8 has an average calculator 100 and a dq converter 101.

[0152] The average calculator 100 receives the output current (three-phase AC currents i1u, i1v, i1w) of the power converter 3a detected by the current detector 5a and the output current (three-phase AC currents i2u, i2v, i2w) of the power converter 3b detected by the current detector 5b. The average calculator 100 calculates the average values ​​of the phase currents (U-phase average current iau, V-phase average current iav, W-phase average current iaw) using the detection values ​​of the current detectors 5a and 5b.

[0153] The dq converter 101 converts the three-phase average currents iau, iav, and iaw into a d-axis average current iad and a q-axis average current iaq by dq conversion (three-phase to two-phase conversion) using equation (2).

[0154] A subtractor 102 calculates a deviation Δiad of the d-axis average current iad from the d-axis current command value id*. A subtractor 103 calculates a deviation Δiaq of the q-axis average current iaq from the q-axis current command value iq*.

[0155] The second compensators CP21 and CP22 calculate integral control amounts by integral control calculation for the deviations Δiad and Δiaq. The inverse dq converter 104 converts the integral control amounts calculated by the second compensators CP21 and CP22 into integral control amounts for three phases by inverse dq conversion (two-phase to three-phase conversion) using equation (1).

[0156] The adder 16 adds the proportional control amount for three phases, which is the calculated value by the first compensators CP11 to CP13, and the integral control amount for three phases by the inverse dq converter 104, to generate a three-phase AC voltage command value required for feedback control to reduce the current deviations Δi1u, Δi1v, and Δi1w.

[0157] Multipliers 18 to 20 and an inverse dq converter 21 generate correction amounts whose values ​​correspond to the d-axis current command value id* and the q-axis current command value iq*.

[0158] The adder 17 generates three-phase AC voltage command values ​​V1u*, V1v*, V1w* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command values ​​are provided to the PWM circuit 22.

[0159] The adder 56 adds the proportional control amount for three phases, which is the calculated value by the first compensators CP14 to CP16, and the integral control amount for three phases by the inverse dq converter 104, to generate a three-phase AC voltage command value required for feedback control to reduce the current deviations Δi2u, Δi2v, and Δi2w.

[0160] The adder 57 generates three-phase AC voltage command values ​​V2u*, V2v*, V2w* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 56. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0161] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V1u*, V1v*, and V1w*. The power converter 3a generates three-phase AC power in accordance with the gate pulses. The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V2u*, V2v*, and V2w*. The power converter 3b generates three-phase AC power in accordance with the gate pulses.

[0162] As described above, according to the power conversion device of embodiment 7, even in a configuration in which a plurality of power converters 3a, 3b are serially multiplexed by the multiple transformer 2, proportional control having the same number of degrees of freedom as the AC terminals is executed for each power converter, so that disturbances occurring at the AC terminals of each power converter can be suppressed.

[0163] Moreover, in the power conversion device of embodiment 7, the three-phase average currents of the output currents of the multiple power converters 3a, 3b are converted into d-axis currents and q-axis currents, and integral control is performed to reduce the d-axis deviation and the q-axis deviation, thereby eliminating the steady-state deviation contained in the output current of each power converter.

[0164] In addition, when there is a difference in impedance between the excitation circuit between the primary winding 2c and the secondary winding 2a in the multiple transformer 2 and the excitation circuit between the primary winding 2c and the secondary winding 2b, or when there is a detection error between the current detector 5a and the current detector 5b, if the second compensators CP21 and CP22 are provided separately for the output current of the power converter 3a and the output current of the power converter 3b, a large voltage difference may occur in the output voltage of the power converters 3a and 3b, making it difficult for the power converter to operate normally. This is because, when there is no bias in the multiple transformer 2, the impedance of the excitation circuit is sufficiently larger than the leakage impedance of the primary winding and the secondary winding, so that when integral control is performed on the deviation contained in the output current of each power converter, the output voltage of each power converter may increase separately. In the seventh embodiment, as described above, integral control is performed using the three-phase average current of the output currents of the multiple power converters 3a and 3b, so that such a concern can be avoided.

[0165] [Embodiment 8] FIG. 10 is a circuit block diagram showing a configuration of a power conversion device according to the eighth embodiment.

[0166] As shown in FIG. 10, the power conversion device of embodiment 8 basically has the same configuration as the power conversion device of embodiment 4 shown in FIG. 6, but the configuration of the control device 7 is different from that of the power conversion device of embodiment 4.

[0167] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18 to 20, an inverse dq converter 21, adders 17 and 57, and a PWM circuit 22. The control device 7 basically has the same configuration as the control device 7 shown in Fig. 4, but differs from the control device 7 in the fourth embodiment in that the current control unit 8 has a dq converter 105.

[0168] The dq converter 105 converts the output current (three-phase AC currents i1u, i1v, i1w) of the power converter 3a detected by the current detector 5a into a d-axis current i1d and a q-axis current i1q by dq conversion (three-phase to two-phase conversion) using equation (2).

[0169] A subtractor 41 calculates a deviation Δi1d of the d-axis current i1d from the d-axis current command value id* (Δi1d=id*-i1d).A subtractor 42 calculates a deviation Δi1q of the q-axis current i1q from the q-axis current command value iq* (Δi1q=iq*-i1q).

[0170] The second compensators CP21 and CP22 calculate integral control amounts by integral control calculations for the deviations Δi1d and Δi1q. The inverse dq converter 15 converts the integral control amounts calculated by the second compensators CP21 and CP22 into integral control amounts for three phases by inverse dq conversion (two-phase to three-phase conversion) using equation (1).

[0171] The adder 16 adds the proportional control amount for three phases, which is the calculated value by the first compensators CP11 to CP13, and the integral control amount for three phases by the inverse dq converter 15, to generate a three-phase AC voltage command value required for feedback control to reduce the current deviations Δi1u, Δi1v, and Δi1w.

[0172] Multipliers 18 to 20 and an inverse dq converter 21 generate correction amounts whose values ​​correspond to the d-axis current command value id* and the q-axis current command value iq*.

[0173] The adder 17 generates three-phase AC voltage command values ​​V1u*, V1v*, V1w* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 16. The three-phase AC voltage command values ​​are provided to the PWM circuit 22.

[0174] The adder 56 adds the proportional control amount for three phases, which is the calculated value by the first compensators CP14 to CP16, and the integral control amount for three phases by the inverse dq converter 15, to generate a three-phase AC voltage command value required for feedback control to reduce the current deviations Δi2u, Δi2v, and Δi2w.

[0175] The adder 57 generates three-phase AC voltage command values ​​V2u*, V2v*, V2w* by adding the correction amount from the inverse dq converter 21 and the three-phase AC voltages Vu, Vv, Vw detected by the voltage detector 4 to the three-phase AC voltage command value from the adder 56. The three-phase AC voltage command value is provided to the PWM circuit 22.

[0176] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V1u*, V1v*, and V1w*. The power converter 3a generates three-phase AC power in accordance with the gate pulses. The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command values ​​V2u*, V2v*, and V2w*. The power converter 3b generates three-phase AC power in accordance with the gate pulses.

[0177] 10, the integral control amount for three phases is calculated using the output current of the power converter 3a, but the integral control amount for three phases may be calculated using the output current of the power converter 3b. That is, the integral control amount for three phases can be calculated using the output current of any one of the multiple power converters 3a and 3b as a representative value.

[0178] As described above, according to the power conversion device of the eighth embodiment, proportional control having the same number of degrees of freedom as the AC terminals is executed for each power converter, even in a configuration in which a plurality of power converters 3a, 3b are serially multiplexed by the multiple transformer 2. As a result, even if there is a difference in susceptibility to biased magnetism between the plurality of power converters 3a, 3b due to the characteristics of the transformers or the phase difference of the carrier wave, disturbances occurring at the AC terminals of each power converter can be suppressed.

[0179] Moreover, the output current of any one of the multiple power converters 3a, 3b is used as a representative value, and the output current is converted into a d-axis current and a q-axis current, and integral control is performed to reduce the d-axis deviation and the q-axis deviation. As described in the seventh embodiment, if the second compensators CP21, CP22 are provided separately for the output current of the power converter 3a and the output current of the power converter 3b, a large voltage difference may occur in the output voltages of the power converters 3a, 3b, making it difficult for the power converter to operate normally. In the eighth embodiment, the integral control is performed using the output current of any one of the multiple power converters 3a, 3b, so that such a concern can be avoided.

[0180] [Embodiment 9] In the above-mentioned first to eighth embodiments, a control configuration for controlling the output current of the power converter 3 connected to the three-phase AC power system 1 via the three-phase transformer 2 has been described. However, the control configuration can also be applied to control the output current of a power converter connected to a single-phase AC power system via a single-phase transformer.

[0181] FIG. 11 is a circuit block diagram showing a configuration of a power conversion device according to the ninth embodiment.

[0182] 11, the power conversion device according to the ninth embodiment includes a power converter 3, a voltage detector 4, current detectors 5 and 6, and a control device 7. An AC terminal of the power converter 3 is connected to a single-phase transmission line of a single-phase AC power system 1A via a single-phase transformer 2A.

[0183] The DC terminal of the power converter 3 is connected to a power storage device such as a battery or a capacitor that stores DC power, or a DC power source that generates DC power. The power converter 3 has a self-extinguishing switching element. The power converter 3 converts DC power into single-phase AC power in accordance with a gate pulse provided by a control device 7. The single-phase AC power generated by the power converter 3 is supplied to a single-phase AC power system 1A via a single-phase transformer 2A. The single-phase AC power system 1A side of the single-phase transformer 2A is the primary side, and the power converter 3 side of the single-phase transformer 2A is the secondary side.

[0184] The voltage detector 4 detects the single-phase AC voltage V of the single-phase AC power system 1A, and provides the control device 7 with a signal indicating the detected value.

[0185] The current detector 5 detects the output current (single-phase AC current) of the power converter 3, and provides the control device 7 with a signal indicating the detected value.

[0186] The current detector 6 detects the current (primary winding current) flowing through the primary winding of the single-phase transformer 2A, and provides the control device 7 with a signal indicating the detected value.

[0187] The control device 7 includes a phase detector 9, a current control unit 8, multipliers 18 to 20, an inverse dq converter 21, an adder 17, and a PWM circuit 22.

[0188] The phase detector 9 generates a reference phase θ based on the output signal of the voltage detector 4. The reference phase θ is a single-phase voltage phase of the system voltage of the single-phase AC power system 1A.

[0189] The current control unit 8 calculates a feedback control amount by a control calculation for reducing the deviation of the detection value of the current detector 5 from the AC current command value. The AC current command value includes a d-axis current command value id* and a q-axis current command value iq*.

[0190] The current control unit 8 includes a fixed coordinate converter 10, a subtractor 11, a first compensator CP11, an adder 16, a dq converter 40, subtractors 41 and 42, second compensators CP21 and CP22, and an inverse dq converter 15.

[0191] The fixed coordinate converter 10 converts the d-axis current command value id* and the q-axis current command value iq* into a single-phase AC current command value i* by performing coordinate conversion using the reference phase θ. The coordinate conversion is expressed by the following equation (12).

[0192]

number

[0193] The subtractor 11 calculates a deviation Δi between the single-phase AC current command value i* and the single-phase AC current i detected by the current detector 5 (Δi=i*−i).

[0194] The first compensator CP11 has a proportional element, and calculates a proportional control amount by proportional control calculation for reducing the deviation Δi of the single-phase AC current from the single-phase AC current command value.

[0195] The dq converter 40 converts the primary winding current detected by the current detector 6 into a d-axis current id and a q-axis current iq by performing coordinate conversion using the reference phase θ. The coordinate conversion is expressed by the following equation (13).

[0196]

number

[0197] A subtractor 41 calculates a deviation (d-axis deviation) Δid of the d-axis current id from the d-axis current command value id*. A subtractor 42 calculates a deviation (q-axis deviation) Δiq of the q-axis current iq from the q-axis current command value iq*.

[0198] The second compensators CP21 and CP22 calculate integral control amounts by integral control calculations for the d-axis deviation Δid and the q-axis deviation Δiq. The inverse dq converter 15 converts the integral control amounts calculated by the second compensators CP21 and CP22 into integral control amounts for a single phase by coordinate transformation using equation (12).

[0199] The adder 16 adds the single-phase proportional control amount, which is the calculated value by the first compensator CP11, and the single-phase integral control amount from the inverse dq converter 15, to generate a single-phase AC voltage command value required for feedback control to reduce the deviation Δi.

[0200] Multipliers 18 to 20 and an inverse dq converter 21 generate correction amounts whose values ​​correspond to the d-axis current command value id* and the q-axis current command value iq*.

[0201] The adder 17 generates a single-phase AC voltage command value V* by adding the correction amount from the inverse dq converter 21 and the single-phase AC voltage V detected by the voltage detector 4 to the single-phase AC voltage command value from the adder 16. The single-phase AC voltage command value V* is provided to the PWM circuit 22.

[0202] The PWM circuit 22 generates a gate pulse based on the single-phase AC voltage command value V*. The power converter 3 supplies single-phase AC power to the single-phase AC power system 1A via the single-phase transformer 2A in accordance with the gate pulse.

[0203] As described above, the power conversion device of embodiment 9 has a control system (fixed coordinate converter 10, subtractor 11 and first compensator CP11) that performs proportional control to reduce the deviation between the output current of power converter 3 (i.e., the secondary winding current of single-phase transformer 2A) and the single-phase current command value, thereby enabling bias magnetization of single-phase transformer 2A to be quickly suppressed.

[0204] Furthermore, the power conversion device of embodiment 9 has a control system (dq converter 40, subtractors 41, 42, second compensators CP21, CP22, and inverse dq converter 15) that converts the primary winding current of the single-phase transformer 2A into a d-axis current and a q-axis current, and performs integral control to reduce the deviation of the d-axis current and the q-axis current from the d-axis current command value and the q-axis current command value, thereby eliminating the steady-state deviation contained in the primary winding current.

[0205] [Embodiment 10] In the above-mentioned embodiments 1 to 8, a configuration has been described in which the d-axis current command value id* and the q-axis current command value iq* are converted into three-phase current command values ​​iu*, iv*, iw*, and a control system is provided that performs proportional control on each of the U-phase current, V-phase current, and W-phase current, in order to set the degree of freedom in proportional control in the feedback control of the output current of the power converter 3 to "3", the same number as the number of AC terminals of the power converter 3.

[0206] In embodiment 10, as another configuration for achieving "3" degrees of freedom for proportional control, a configuration is described in which a control system is provided that performs proportional control for each of the d-axis current id, the q-axis current iq, and the zero-phase current iz.

[0207] FIG. 12 is a circuit block diagram showing a configuration of a power conversion device according to the tenth embodiment.

[0208] As shown in FIG. 12, the power conversion device of embodiment 10 basically has the same configuration as the power conversion device of embodiment 1 shown in FIG. 1, but the configuration of the control device 7 is different from that of the power conversion device of embodiment 1.

[0209] The control device 7 includes a phase detector 9, a current control section 8, a dq converter 23, multipliers 18 and 19, a subtractor 29, adders 30, 31 and 32, an inverse dq converter 33, and a PWM circuit 22.

[0210] The phase detector 9 generates a reference phase θ based on the output signal of the voltage detector 4 .

[0211] The dq converter 23 converts the three-phase AC voltage detected by the voltage detector 4 into a d-axis voltage Vd and a q-axis voltage Vq based on the reference phase θ.

[0212] The current control unit 8 calculates a feedback control amount by a control calculation for reducing the deviation of the detection value of the current detector 5 from the AC current command value. In the tenth embodiment, the AC current command value includes a d-axis current command value id*, a q-axis current command value iq*, and a zero-phase current command value iz*.

[0213] The zero-phase current command value iz* is generated due to circumstances inside the power conversion device, since it does not flow to the three-phase AC power system 1. For example, in order to suppress the peak value of the output current of the power converter 3, iz* can be set to 0. Alternatively, if the secondary winding of the three-phase transformer 2 is open delta connected, the zero-phase current command value iz* can be set based on the value of the circulating current to be flowed through the delta winding.

[0214] The current control unit 8 includes subtractors 25, 26, and , first compensators CP11 to CP13, second compensators CP21 and CP22, a dq converter and a zero-phase sequence calculator .

[0215] The dq converter 34 converts the three-phase AC current detected by the current detector 5 into a d-axis current id and a q-axis current iq using a reference phase θ.

[0216] The zero-phase calculator 35 calculates the zero-phase current iz from the three-phase AC current detected by the current detector 5. Specifically, the zero-phase calculator 35 obtains the zero-phase current iz by dividing the sum of the U-phase current iu, the V-phase current iv, and the W-phase current iw by three.

[0217] The subtractor 25 calculates a deviation (d-axis deviation) Δid between the d-axis current command value id* and the d-axis current id calculated by the dq converter 34. The subtractor 26 calculates a deviation (q-axis deviation) Δiq between the q-axis current command value iq* and the q-axis current iq calculated by the dq converter 34. The subtractor 36 calculates a deviation (q-axis deviation) Δiz between the zero-phase current command value iz* and the zero-phase current iz calculated by the zero-phase calculator 35 (hereinafter also referred to as zero-phase deviation).

[0218] The first compensators CP11 to CP13 calculate proportional control amounts by proportional control calculations to reduce the deviations of the d-axis current id, the q-axis current iq, and the zero-phase current iz from the d-axis current command value id*, the q-axis current command value iq*, and the zero-phase current command value iz*. Specifically, the first compensator CP11 calculates the proportional control amount Kp·Δid based on the d-axis deviation Δid. The first compensator CP12 calculates the proportional control amount Kp·Δiq based on the q-axis deviation Δiq. The first compensator CP13 calculates the proportional control amount Kp·Δiz based on the zero-phase deviation Δiz. Kp is the proportional gain.

[0219] The second compensators CP21 and CP22 calculate integral control amounts by integral control calculations to reduce the d-axis deviation Δid and the q-axis deviation Δiq. Specifically, the second compensator CP21 calculates the integral control amount Σ(Ki·Δid) based on the d-axis deviation Δid. The second compensator CP22 calculates the integral control amount Σ(Ki·Δiq) based on the q-axis deviation Δiq. Here, Ki is the integral control gain.

[0220] The adder 27 generates a d-axis voltage command value Vd* by adding together the proportional control amount Kp·Δid from the first compensator CP11 and the integral control amount Σ(Ki·Δid) from the second compensator CP21. The adder 28 generates a q-axis voltage command value Vq* by adding together the proportional control amount Kp·Δiq from the first compensator CP12 and the integral control amount Σ(Ki·Δiq) from the second compensator CP22.

[0221] Multiplier 18 multiplies the d-axis current command value id* by a gain ωL. Multiplier 19 multiplies the q-axis current command value iq* by a gain ωL. Subtractor 29 subtracts the correction amount from multiplier 19 from the d-axis voltage command value Vd* from adder 27. Adder 30 adds the correction amount from multiplier 18 to the q-axis voltage command value Vq* from adder 28.

[0222] The adder 31 adds the d-axis voltage Vd from the dq converter to the d-axis voltage command value Vd* from the subtractor 29. The adder 32 adds the q-axis voltage Vq from the dq converter to the q-axis voltage command value Vq* from the adder 30.

[0223] The inverse dq converter 33 performs inverse dq conversion (two-phase to three-phase conversion) using equation (1) on the d-axis voltage command value Vd* from the adder 31 and the q-axis voltage command value Vq* from the adder 32, thereby generating three-phase voltage command values ​​Vu*, Vv*, and Vw*. The three-phase AC voltage command values ​​are provided to the PWM circuit 22.

[0224] The PWM circuit 22 generates gate pulses based on the three-phase AC voltage command value. The power converter 3 supplies three-phase AC power to the three-phase AC power system 1 via the three-phase transformer 2 in accordance with the gate pulses.

[0225] As described above, according to the power conversion device of the tenth embodiment, the output current (three-phase AC current) of the power converter 3 is converted into a d-axis current id, a q-axis current iq, and a zero-phase current iz, and current feedback control is executed to reduce deviations from the d-axis current command value id*, the q-axis current command value iq*, and the zero-phase current command value iz*. That is, in the tenth embodiment, a control system is configured for each of the d-axis current, the q-axis current, and the zero-phase current, so that the degree of freedom of the current feedback control is three. Therefore, since the degree of freedom of the current feedback control is the same as the number of AC terminals of the power converter 3, it becomes possible to suppress disturbances occurring at each AC terminal of the power converter 3 by the current feedback control.

[0226] In addition, as with the current feedback control in embodiment 1, the current feedback control in embodiment 10 performs integral control on the deviations Δid, Δiq of the d-axis current and the q-axis current from the d-axis current command value and the q-axis current command value, and therefore can eliminate steady-state deviation.

[0227] With regard to the above-mentioned embodiments and modified examples, it has been intended from the outset of the application that the configurations described in the embodiments may be appropriately combined, including combinations not mentioned in the specification, to the extent that no inconvenience or contradiction arises.

[0228] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0229] 1 Three-phase AC power system, 1A Single-phase AC power system, 2 Three-phase transformer (multiple transformer), 2A Single-phase transformer, 2a, 2b Secondary winding, 2c Primary winding, 3, 3a, 3b Power converter, 4 Voltage detector, 5, 6 Current detector, 7, 7A Control device, 8, 8A Current control section, 9 Phase detector, 10 Fixed coordinate converter, 11-13, 23, 25, 26, 29, 36, 41, 42, 51-53, 61-66, 201, 202, 209 Subtractor, 14, 40 dq converter, 15, 21 Inverse dq converter, 16, 17, 27-32, 56, 57, 67-69, 207-212 Adder, 18-20, 81, 83 Multiplier, 22 PWM circuit, 24 Magnetic bias detector, 35 zero-phase calculator, 60 average / deviation calculator, 82 filter, 100 average calculator, 203, 204 proportional calculator, 84, 205, 206 integrators, CP11 to CP19 first compensators, CP21, CP22 second compensators.

Claims

1. a power converter that converts a DC voltage into a three-phase AC voltage and outputs the voltage to an AC terminal; a first current detector that detects an output current of the power converter; A control device for controlling the power converter, The AC terminal of the power converter is connected to a secondary winding of a transformer, and the primary winding of the transformer is connected to a three-phase AC power system or a three-phase AC load; The control device includes: a current control unit that generates a three-phase AC voltage command value by feedback control for compensating for a deviation of a detection value of the first current detector from an AC current command value; a PWM circuit that generates a control signal for the power converter based on the three-phase AC voltage command value, thereby PWM-controlling the power converter, the current control unit includes a first compensator that receives as input a deviation between a current value having three degrees of freedom based on a detection value of the first current detector and a current command value having three degrees of freedom based on the AC current command value, and performs at least a proportional control calculation; the AC current command value includes a d-axis current command value and a q-axis current command value, the current control unit further includes a first coordinate converter that converts the d-axis current command value and the q-axis current command value into a three-phase AC current command value; the first compensator receives a deviation between the three-phase AC current command value and the three-phase AC current detected by the first current detector as an input; a second coordinate converter that converts a deviation of the three-phase AC current from the three-phase AC current command value into a deviation of a d-axis current from the d-axis current command value and a deviation of a q-axis current from the q-axis current command value; a second compensator that receives the deviation of the d-axis current and the deviation of the q-axis current and performs at least an integral control operation; a third coordinate converter for converting a calculated value by the second compensator from two-phase to three-phase; an adder that generates the three-phase AC voltage command value by adding a value calculated by the first compensator and a value calculated by the third coordinate converter.

2. a second current detector for detecting a primary winding current of the transformer; 2. The power conversion device according to claim 1, further comprising a magnetic bias detector that detects a magnetic bias of the transformer based on a difference between a detection value of the first current detector and a detection value of the second current detector.

3. A power converter that converts a DC voltage into a three-phase AC voltage and outputs the voltage to an AC terminal; a first current detector that detects an output current of the power converter; A control device for controlling the power converter, The AC terminal of the power converter is connected to a secondary winding of a transformer, and the primary winding of the transformer is connected to a three-phase AC power system or a three-phase AC load; The control device includes: a current control unit that generates a three-phase AC voltage command value by feedback control for compensating for a deviation of a detection value of the first current detector from an AC current command value; a PWM circuit that generates a control signal for the power converter based on the three-phase AC voltage command value, thereby PWM-controlling the power converter, the current control unit includes a first compensator that receives as input a deviation between a current value having three degrees of freedom based on a detection value of the first current detector and a current command value having three degrees of freedom based on the AC current command value, and performs at least a proportional control calculation; the AC current command value includes a d-axis current command value and a q-axis current command value, the current control unit further includes a first coordinate converter that converts the d-axis current command value and the q-axis current command value into a three-phase AC current command value; the first compensator receives a deviation between the three-phase AC current command value and the three-phase AC current detected by the first current detector as an input; a second current detector for detecting a primary winding current of the transformer; The current control unit is a second coordinate converter that converts the primary winding current detected by the second current detector into a d-axis current value and a q-axis current value; a second compensator that receives as input a deviation of the d-axis current value from the d-axis current command value and a deviation of the q-axis current value from the q-axis current command value and performs at least an integral control calculation; a third coordinate converter for converting a calculated value by the second compensator from two-phase to three-phase; an adder that generates the three-phase AC voltage command value by adding a value calculated by the first compensator and a value calculated by the third coordinate converter.

4. A power converter that converts a DC voltage into a three-phase AC voltage and outputs the voltage to an AC terminal; a first current detector that detects an output current of the power converter; A control device for controlling the power converter, The AC terminal of the power converter is connected to a secondary winding of a transformer, and the primary winding of the transformer is connected to a three-phase AC power system or a three-phase AC load; The control device includes: a current control unit that generates a three-phase AC voltage command value by feedback control for compensating for a deviation of a detection value of the first current detector from an AC current command value; a PWM circuit that generates a control signal for the power converter based on the three-phase AC voltage command value, thereby PWM-controlling the power converter, the current control unit includes a first compensator that receives as input a deviation between a current value having three degrees of freedom based on a detection value of the first current detector and a current command value having three degrees of freedom based on the AC current command value, and performs at least a proportional control calculation; the AC current command value includes a d-axis current command value, a q-axis current command value, and a zero-phase current command value, The current control unit is a first coordinate converter that converts a detection value of the first current detector into a d-axis current value and a q-axis current value; a calculator that calculates a zero-phase current value based on a detection value of the first current detector, the first compensator receives as input a deviation of the d-axis current value from the d-axis current command value, a deviation of the q-axis current value from the q-axis current command value, and a deviation of the zero-phase current value from the zero-phase current command value; a second compensator that receives the deviation of the d-axis current value and the deviation of the q-axis current value and performs at least an integral control operation; a second coordinate converter that performs a two-phase to three-phase conversion on the sum of a calculated value by the first compensator and a calculated value by the second compensator for the deviation of the d-axis current value and the deviation of the q-axis current value; an adder that generates the three-phase AC voltage command value by adding a value calculated by the first compensator with respect to the deviation of the zero-phase current value and a value calculated by the second coordinate converter.

5. the first compensator includes at least a proportional element; 5. The power conversion device according to claim 1, wherein the first compensator further includes any one of a filter that passes a DC component of the input signal and attenuates a specific frequency component, a filter having a phase lead / lag characteristic, and a notch filter.

6. the second compensator includes at least an integral element; The power conversion device according to claim 1 , wherein the second compensator further includes at least one of a filter and a proportional element that passes a DC component of the input signal and attenuates a specific frequency component.

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