JP7802137B2 - Power Conversion Device - Google Patents

Description

This disclosure relates to a power conversion device.

JP 7-28534 A (Patent Document 1) discloses a control device for a power conversion device connected to a power grid or load via a transformer. The power conversion device is composed of self-extinguishing elements. If the power grid voltage or the output voltage of the power conversion device contains a DC component, an excitation current containing a DC component flows through the transformer, and the DC component of this excitation current causes the transformer to become biased. In Patent Document 1, the control device is configured to detect the DC component contained in the difference between the transformer's primary winding current and secondary winding current, and correct the output voltage command value of the power conversion device based on the DC component.

Japanese Patent Application Publication No. 7-28534

In the control device described above, the output voltage command value for 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, current feedback control is performed to cause the d-axis current and q-axis current, which are obtained by dq-transforming the primary winding current, to follow the d-axis current command value and 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 q-axis current are derived as DC amounts. These DC amounts are feedback signals for feedback control, and command values for them are given to form the current control system.

However, when a three-phase imbalance occurs due to voltage fluctuations in the power system or biased magnetism in a transformer, a zero-phase current flows in phase with each phase. Because the current control system described above does not control the zero-phase current, it is unable to suppress disturbances to the output current of the power converter, and there is a risk of an overcurrent flowing through the power converter.

In Patent Document 1, a filter is used to detect the DC component contained in the difference between the primary winding current and secondary winding current of a transformer. This filter uses a slow-response filter, 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 fast-response filter, the harmonic components that pass 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 slow-response filter is used, bias magnetization cannot be suppressed quickly, which could result in an overcurrent flowing through the power converter.

The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a power conversion device that can quickly control the three-phase AC current output from a power converter.

A power conversion device according to one aspect of the present disclosure includes a power converter that converts DC voltage into three-phase AC voltage and outputs it to AC terminals, a first current detector that detects the output current of the power converter, and a control device that controls the power converter. The AC terminals of the power converter are connected to the 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 through feedback control to compensate for the deviation of the detection value of the first current detector from the AC current command value. The PWM circuit PWM controls 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 performs at least proportional control calculations using as input the deviation between a current value with three degrees of freedom based on the detection value of the first current detector and a current command value with three degrees of freedom based on the AC current command value.

This disclosure provides a power conversion device that can quickly control the three-phase AC current output from a power converter.

1 is a circuit block diagram showing a configuration of a power conversion device according to a first embodiment; FIG. 2 is a circuit diagram showing a configuration example of the power converter shown in FIG. 1 . FIG. 2 is a block diagram showing an example configuration of a first compensator and a second compensator. FIG. 10 is a circuit block diagram showing a configuration of a power conversion device according to a second embodiment. FIG. 10 is a circuit block diagram showing a configuration of a power conversion device according to a third embodiment. FIG. 10 is a circuit block diagram showing the configuration of a power conversion device according to a fourth embodiment. FIG. 10 is a circuit block diagram showing the configuration of a power conversion device according to a fifth embodiment. FIG. 13 is a circuit block diagram showing the configuration of a power conversion device according to a sixth embodiment. FIG. 13 is a circuit block diagram showing the configuration of a power conversion device according to a seventh embodiment. FIG. 13 is a circuit block diagram showing the configuration of a power conversion device according to an eighth embodiment. FIG. 13 is a circuit block diagram showing the configuration of a power conversion device according to a ninth embodiment. FIG. 22 is a circuit block diagram showing the configuration of a power conversion device according to a tenth embodiment. FIG. 1 is a circuit block diagram showing a configuration of a power conversion device according to a reference example.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that, below, identical or equivalent parts in the drawings will be designated by the same reference numerals, and their descriptions will generally not be repeated.

[First Embodiment]
1 is a circuit block diagram showing the 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).

As shown in FIG. 1, the power conversion device according to embodiment 1 includes a power converter 3, a voltage detector 4, a current detector 5, and a control device 7. The 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 U, V, and W phases.

The DC terminals of the power converter 3 are connected to a power storage device that stores DC power, such as a battery or capacitor, or to a DC power source that generates DC power. Figure 2 is a circuit diagram showing an example configuration of the power converter 3 shown in Figure 1.

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

The IGBT elements Q1 to Q6 are controlled to be turned on and off by control signals (gate pulses) provided by the control device 7. In this embodiment, PWM (Pulse Width Modulation) control can be applied as the control method for the IGBT elements Q1 to Q6.

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

Returning to Figure 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.

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.

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

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 DFT (Discrete Fourier Transform) circuit. The reference phase θ is the positive-sequence voltage phase of the system voltage of the three-phase AC power system 1.

The current control unit 8 calculates a feedback control amount through control calculations to compensate 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 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 a constant value. The AC current command value is generally generated by a host controller. When voltage control of the three-phase AC power system 1 is performed by a power conversion device, the system control system is the host controller. In the example of Figure 1, the AC current command value includes a d-axis current command value id* and a q-axis current command value iq*.

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

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 a fixed coordinate conversion (two-phase to three-phase conversion) using the 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*.

Subtractor 11 calculates the 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). Subtractor 12 calculates the 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). Subtractor 13 calculates the 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).

The first compensators CP11 to CP13 are compensators with frequency characteristics that result in a finite DC gain. In other words, 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 using proportional control calculations to reduce the deviations Δiu, Δiv, and Δiw of the three-phase AC current from the three-phase AC current command value. Note that the first compensators CP11 to CP13 can also be given phase lead/lag characteristics and notch filter characteristics for components other than DC. The first compensators CP11 to CP13 correspond to one example of a "first compensator."

The dq converter 14 converts the deviations Δiu, Δiv, and Δiw from the subtractors 11-13 into a d-axis deviation Δid and a q-axis deviation Δiq by performing a dq transformation (three-phase to two-phase transformation) using the reference phase θ. Three-phase to two-phase transformation 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).

The second compensators CP21 and CP22 are compensators that have at least an integral element. The second compensators CP21 and CP22 calculate integral control amounts through integral control calculations to reduce the d-axis deviation Δid and the q-axis deviation Δiq. The second compensators CP21 and CP22 can further include a filter and/or a proportional element to remove components other than DC. The second compensators CP21 and CP22 correspond to one example of a "second compensator."

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

Figure 3 is a block diagram showing an example configuration of the first compensators CP11 to CP13 and the second compensators CP21 and CP22.

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 the 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 the 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 the deviation Δiw of the W-phase current iw from the W-phase current command value iw*.

If the DC gain of the first compensators CP11 to CP13 is finite, they may have frequency characteristics 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 magnetization occurs in the three-phase transformer 2. Alternatively, the filter 82 is a filter for removing specific harmonic components from the proportional control amount, or a filter with phase lead/lag characteristics for improving control stability.

Note that the DC components contained in the deviations Δiu, Δiv, and Δiw are not removed by filter 82, and therefore do not change even when passing through filter 82. Therefore, current control using first compensators CP11 to CP13 is suitable for suppressing bias magnetization in three-phase transformer 2.

Furthermore, a filter with a faster response than the filters (typically LPFs) used to detect DC bias magnetic fields in conventional power conversion devices can be used for filter 82. Because the first compensators CP11 to CP13 are compensators for current control, their fast response does not disturb the current control.

Each of the second compensators CP21 and CP22 has a multiplier 83 and an integrator 84. Ki is the integral control gain. 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. Note that the second compensators CP21 and CP22 may further include a filter (e.g., a moving average filter) and/or a proportional element to remove components other than DC.

Returning to Figure 1, adder 16 adds the proportional control variables for three phases, which are values calculated by first compensators CP11 to CP13, to the integral control variables for three phases, which are calculated by inverse dq converter 15, to generate the three-phase AC voltage command values Vu*, Vv*, and Vw* required for feedback control to reduce the deviations Δiu, Δiv, and Δiw.

Multipliers 18-20 and inverse dq converter 21 generate correction amounts corresponding to the d-axis current command value id* and the q-axis current command value iq*. Specifically, 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. ωL is the reactance between the power converter 3 and the three-phase AC power system 1, and includes the leakage reactance component of the three-phase transformer 2. Multiplier 20 multiplies the value calculated by multiplier 19 by -1. Inverse dq converter 21 converts the d-axis and q-axis correction amounts into correction amounts for three phases by performing an inverse dq transformation (two-phase to three-phase transformation) using equation (1). In this way, the output voltage of the power converter 3 can be controlled by correcting for voltage drops that occur in the wiring from the power converter 3 to the three-phase AC power system 1. However, multipliers 18-20 and inverse dq transformer 21 can be added or omitted as needed.

Adder 17 generates a three-phase AC voltage command value by adding the correction amount from inverse dq converter 21 and the three-phase AC voltages Vu, Vv, and Vw detected by voltage detector 4 to the three-phase AC voltage command value from 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 PWM circuit 22.

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 generating gate pulses using a carrier wave, the PWM circuit 22 can also generate gate pulses according to the three-phase AC voltage command values Vu*, Vv*, and Vw* by referencing a predetermined table, or by performing 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.

The following describes the effects of the power conversion device according to embodiment 1, comparing it with a power conversion device serving as a reference example (see Figure 13).

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

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.

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.

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 through dq transformation using the reference phase θ.

The current control unit 8A calculates a feedback control amount through control calculations to reduce 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*.

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.

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 a dq conversion (three-phase to two-phase conversion) using equation (2).

Subtractor 201 calculates the deviation (d-axis deviation) Δid of the d-axis current id from the d-axis current command value id*. Subtractor 202 calculates the deviation (q-axis deviation) Δiq of the q-axis current iq from the q-axis current command value iq*.

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

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

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

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 that correspond to the d-axis current command value id* and the q-axis current command value iq*.

Subtractor 209 subtracts the correction amount from multiplier 19 from the d-axis voltage command value Vd* from adder 207. Adder 210 adds the correction amount from multiplier 18 to the q-axis voltage command value Vq* from adder 208.

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

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

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.

In the reference example shown in Figure 13, the primary winding current (three-phase AC current) of the three-phase transformer 2 detected by the current detector 6 is subjected to dq conversion (three-phase to two-phase conversion) to generate a d-axis current id and a q-axis current iq. Then, proportional-integral control calculations are 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*.

The dq transformation used in the reference example assumes that the three-phase AC current is 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), so the zero-phase current is zero.

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

However, if a transient voltage fluctuation occurs in the three-phase AC power system 1 or if biased magnetization 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 enters a three-phase unbalanced state and a zero-phase current flows. However, with the current feedback control of the reference example, the zero-phase current is not controlled, making it difficult to suppress the above-mentioned disturbances.

In contrast, in the power conversion device according to embodiment 1, 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 performed to reduce the deviation of the three-phase AC current from these 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, resulting in two degrees of freedom for control, whereas in embodiment 1, a control system is configured for each phase current of the three-phase AC current, resulting in three degrees of freedom for current feedback control. Therefore, the degrees of freedom for current feedback control are the same as the number of AC terminals of the power converter 3, making it possible to suppress disturbances occurring at each of the AC terminals Tu, Tv, and Tw of the power converter 3 through current feedback control.

Furthermore, in the power conversion device according to embodiment 1, 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-described current feedback control of each phase is performed using this detected value. When feedback controlling the output current of the power converter 3, the excitation circuit of the three-phase transformer 2 is included in the controlled object, but handling the excitation circuit is difficult because its impedance changes when magnetic bias occurs. Furthermore, because the feedback current includes the magnetic bias current, the waveform of the generated voltage command value is distorted, which may result in the generation of harmonics. In embodiment 1, a control system is configured for each phase current of the three-phase AC current output from the power converter 3, so that each phase can respond individually even when magnetic bias occurs. As a result, the output current of the power converter 3 is controlled to eliminate magnetic bias in the three-phase transformer 2, thereby preventing overcurrent from flowing through the power converter 3 due to magnetic bias.

Here, a conventional method for suppressing bias currents is described in Patent Document 1, which corrects the output voltage command value of a power converter based on the DC component contained in the difference between the primary winding current and secondary winding current of a three-phase transformer 2. However, this method uses a slow-response filter such as an LPF to detect the DC component, and there is a concern that the response of the bias current suppression control will be slowed due to the delay of the filter. On the other hand, with the power conversion device of embodiment 1, each of the first compensators CP11 to CP13, which are responsible for proportional control, performs control calculations to reduce the DC component contained in each phase current, enabling bias currents to be suppressed more quickly.

Note that the current feedback control in embodiment 1 is configured to calculate a proportional control variable based on the deviations Δiu, Δiv, and Δiw of the three-phase AC current from the three-phase AC current command value, while calculating an integral control variable based on the deviations Δid and Δiq of the d-axis and q-axis current from the d-axis and q-axis current command values. This is because the three-phase AC current is an AC quantity that oscillates at the frequency of the three-phase AC power system 1, and therefore integral control that integrates the change in the deviation of the three-phase AC current over time cannot eliminate steady-state deviation. On the other hand, the d-axis and q-axis currents are DC quantities, and therefore the control variable continues to increase due to the time integration of the deviations of the d-axis and q-axis currents, thereby eliminating steady-state deviation.

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

As shown in Figure 4, the power conversion device of embodiment 2 basically has the same configuration as the power conversion device of embodiment 1 shown in Figure 1, but differs from the power conversion device of 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.

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

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.

The magnetization bias detector 24 determines whether or not magnetization bias has occurred in the three-phase transformer 2 based on the difference (excitation current) calculated by the subtractor 23. Specifically, when magnetization bias occurs in the three-phase transformer 2, the iron core that makes up the transformer saturates, reducing the excitation inductance and increasing the excitation current. If the excitation current exceeds a predetermined threshold, the magnetization bias detector 24 determines that magnetization bias has occurred in the three-phase transformer 2.

If the magnetic bias detector 24 determines that magnetic bias has occurred in the three-phase transformer 2, it reduces the proportional gain Kp in the first compensators CP11 to CP13 and reduces the integral gain Ki in the second compensators CP21 and CP22.

This occurs 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 current feedback control is kept constant, the loop gain increases as the output impedance decreases, which increases the output current of the power converter 3 and may cause the current feedback control to become unstable. Therefore, when biased magnetization occurs in the three-phase transformer 2, the stability of the current feedback control can be ensured by reducing the proportional gain Kp of the first compensator and the integral gain Ki of the second compensator.

In the second embodiment, an example configuration was described in which the proportional gain Kp and integral gain Ki are reduced when magnetic bias occurs in the three-phase transformer 2, but it is also possible to configure it so that at least the proportional gain Kp is reduced.

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

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

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

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 a dq conversion (three-phase to two-phase conversion) using equation (2).

Subtractor 41 calculates the deviation of the d-axis current id from the d-axis current command value id* (d-axis deviation) Δid. Subtractor 42 calculates the deviation of the q-axis current iq from the q-axis current command value iq* (q-axis deviation) Δiq.

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

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

Multipliers 18-20 and inverse dq converter 21 generate correction amounts corresponding to the d-axis current command value id* and the q-axis current command value iq*.

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

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.

As described above, the power conversion device according to embodiment 3 has 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 power converter 3 (i.e., the secondary winding current of three-phase transformer 2) and the three-phase current command value, thereby enabling rapid suppression of bias magnetization in three-phase transformer 2.

Furthermore, the power conversion device according to 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.

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

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

The multiplexing transformer 2 has two secondary windings 2a and 2b connected to the AC terminals of the two power converters 3a and 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 and 3b for each phase is output to the three-phase AC power system 1. Note that while the example in Figure 6 shows a two-stage series multiplexing configuration in which the two power converters 3a and 3b are serially multiplexed by the multiplexing transformer 2, the number of series multiplexing is not limited to two.

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 Figure 2. The series circuit (capacitor C1 in the example of Figure 2) is common to the power converters 3a and 3b.

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

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 includes a U-phase current i1u, a V-phase current i1v, and a W-phase current i1w.

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

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 includes a U-phase current iu, a V-phase current iv, and a W-phase current iw.

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. Control device 7 basically has the same configuration as control device 7 shown in FIG. 1, but differs from control device 7 in embodiment 1 in that current control unit 8 includes a dq converter 40, subtractors 41, 42, 51-53, and first compensators CP14-CP16, and an adder 57.

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*, and iw* using an inverse dq transformation (two-phase to three-phase transformation) using equation (1).

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). 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). 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).

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. Note that Kp is the proportional gain.

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

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. Note that Kp is the proportional gain. The proportional gains of the first compensators CP14 to CP16 may be the same as or different from the proportional gains of the first compensators CP11 to CP13.

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 through dq conversion (three-phase to two-phase conversion) using equation (2).

Subtractor 41 calculates the deviation of the d-axis current id from the d-axis current command value id* (d-axis deviation) Δid. Subtractor 42 calculates the deviation of the q-axis current iq from the q-axis current command value iq* (q-axis deviation) Δiq.

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

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

Adder 17 generates three-phase AC voltage command values V1u*, V1v*, and V1w* 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 adder 16. The three-phase AC voltage command values are provided to the PWM circuit 22.

The adder 56 adds the proportional control variables for three phases, which are the values calculated by the first compensators CP14 to CP16, and the integral control variables for three phases, which are the values calculated 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.

Adder 57 generates three-phase AC voltage command values V2u*, V2v*, and V2w* 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 adder 56. The three-phase AC voltage command values are provided to the PWM circuit 22.

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.

As described above, with the power conversion device according to embodiment 4, even in a configuration in which multiple power converters 3a, 3b are serially multiplexed using a multiplex transformer 2, proportional control with the same number of degrees of freedom as the number of AC terminals is performed for each power converter, making it possible to suppress disturbances occurring at the AC terminals of each power converter. This makes it possible to deal with differences in the susceptibility to bias magnetization between multiple power converters 3a, 3b due to transformer characteristics or carrier wave phase differences.

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

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

As shown in Figure 7, the power conversion device of embodiment 5 basically has the same configuration as the power conversion device of embodiment 4 shown in Figure 6, but the configuration of the control device 7 differs from that of the power conversion device of embodiment 4.

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. Control device 7 has a configuration similar to that of the control device 7 shown in FIG. 4, but differs from control device 7 in embodiment 4 in that current control unit 8 includes a mean/deviation calculator 60, subtractors 61-66, first compensators CP17-CP19, and adders 67-69.

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.

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).

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

Similarly, the average/deviation calculator 60 calculates the deviations di2u, di2v, and di2w of the three-phase AC currents i2u, i2v, and i2w relative 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).

Subtractor 11 calculates the deviation Δiau between the U-phase current command value iu* and the U-phase average current iau (Δiau = iu* - iau). Subtractor 12 calculates the deviation Δiav between the V-phase current command value iv* and the V-phase average current iav (Δiav = iv* - iav). Subtractor 13 calculates the deviation Δiaw between the W-phase current command value iw* and the W-phase average current iaw (Δiaw = iw* - iaw).

The first compensators CP11 to CP13 calculate the proportional control amounts Kp·Δiau, Kp·Δiav, and Kp·Δiaw, respectively, by proportional control calculations for the deviations Δiau, Δiav, and Δiaw. Note that Kp is the proportional gain.

Subtractor 61 calculates the deviation Δdi1u between the U-phase deviation command value di1u* and the U-phase deviation di1u (Δdi1u = di1u* - di1u). Subtractor 62 calculates the deviation Δdi1v between the V-phase deviation command value di1v* and the V-phase deviation di1v (Δdi1v = di1v* - di1v). Subtractor 63 calculates the deviation Δdi1w between the W-phase deviation command value di1w* and the W-phase deviation di1w (Δdi1w = di1w* - di1w). The three-phase deviation command values di1u*, di1v*, and di1w* can be generated by a higher-level controller, just like the three-phase current command values iu*, iv*, and iw*.

The first compensators CP14 to CP16 calculate the proportional control amounts Kp·Δdi1u, Kp·Δdi1v, and Kp·Δdi1w, respectively, by proportional control calculations for the deviations Δdi1u, Δdi1v, and Δdi1w. Note that Kp is the proportional gain.

Subtractor 64 calculates the deviation Δdi2u between the U-phase deviation command value di2u* and the U-phase deviation di2u (Δdi2u = di2u* - di2u). Subtractor 65 calculates the deviation Δdi2v between the V-phase deviation command value di2v* and the V-phase deviation di2v (Δdi2v = di2v* - di2v). Subtractor 66 calculates the 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*, and di2w* can be generated by a higher-level controller, just like the three-phase current command values iu*, iv*, and iw*.

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

Adder 67 adds the three-phase proportional control variables calculated by first compensators CP11 to CP13 to the three-phase proportional control variables calculated by first compensators CP14 to CP16. Adder 16 adds the calculation result of adder 67 to the three-phase integral control variables calculated by 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*.

Adder 17 generates a three-phase AC voltage command value by adding the correction amount from inverse dq converter 21 and the three-phase AC voltages Vu, Vv, and Vw detected by voltage detector 4 to the three-phase AC voltage command value from 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 PWM circuit 22.

Adder 68 adds the three-phase proportional control variables calculated by first compensators CP11 to CP13 to the three-phase proportional control variables calculated by first compensators CP17 to CP19. Adder 69 adds the calculation result of adder 68 to the three-phase integral control variables calculated by 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*.

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 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.

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.

As explained above, with the power conversion device according to embodiment 5, even in a configuration in which multiple power converters 3a, 3b are connected in series with the multiplex transformer 2, proportional control with the same number of degrees of freedom as the number of AC terminals is performed for each power converter, and the primary winding current of the multiplex transformer 2 is converted into a d-axis current and a q-axis current for integral control, thereby achieving the same effects as the power conversion device according to embodiment 4 described above.

Furthermore, in the power conversion device according to embodiment 5, the output currents of the multiple power converters 3a, 3b are decomposed into three-phase average currents iau, iav, and iaw; deviations di1u, di1v, and di1w of the output current of power converter 3a relative to the three-phase average current; and deviations di2u, di2v, and di2w of the output current of power converter 3b relative to the three-phase average current. Then, proportional control is executed to match the three-phase average currents to three-phase current command values; proportional control to match the deviations di1u, di1v, and di1w to deviation command values di1u*, di1v*, and di1w*; and proportional control to match the deviations di2u, di2v, and di2w to deviation command values di2u*, di2v*, and di2w*. This allows the proportional gains Kp in these proportional controls to be set independently of each other, enabling more precise control.

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

As shown in Figure 8, the power conversion device of embodiment 6 basically has the same configuration as the power conversion device of embodiment 5 shown in Figure 7, but the configuration of the control device 7 differs from that of the power conversion device of embodiment 5.

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. Control device 7 basically has the same configuration as control device 7 shown in FIG. 5, but differs from control device 7 in embodiment 5 in that current control unit 8 does not have subtractors 61-66, first compensators CP14-CP19, or adders 67-69.

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.

The average/deviation calculator 60 calculates the average value of each phase current using the detection values of the current detectors 5a and 5b. 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).

Subtractor 11 calculates the deviation Δiau between the U-phase current command value iu* and the U-phase average current iau. Subtractor 12 calculates the deviation Δiav between the V-phase current command value iv* and the V-phase average current iav. Subtractor 13 calculates the deviation Δiaw between the W-phase current command value iw* and the W-phase average current iaw.

The first compensators CP11 to CP13 calculate the proportional control amounts Kp·Δiau, Kp·Δiav, and Kp·Δiaw, respectively, by proportional control calculations for the deviations Δiau, Δiav, and Δiaw. Note that Kp is the proportional gain.

The adder 16 adds the proportional control variables for three phases, which are calculated values by the first compensators CP11 to CP13, and the integral control variables for three phases by the inverse dq converter 15, to generate the three-phase AC voltage command values 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*.

Adder 17 generates a three-phase AC voltage command value by adding the feedforward control amount from inverse dq converter 21 and the three-phase AC voltage detected by voltage detector 4 to the three-phase AC voltage command value from 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 PWM circuit 22.

The adder 56 adds the three-phase proportional control variables calculated by the first compensators CP11 to CP13 to the three-phase integral control variables calculated by the inverse dq converter 15 to generate the three-phase AC voltage command values 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*.

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 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.

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.

As described above, in the power conversion device of embodiment 6, in a configuration in which multiple power converters 3a, 3b are serially multiplexed by a multiplex transformer 2, proportional control is performed to match the three-phase average currents iau, iav, and iaw of the output currents of the multiple power converters 3a, 3b with the three-phase current command values. This does not perform the proportional control for each power converter as shown in embodiments 4 and 5, but it is possible to reduce the amount of calculations required by the current control unit 8. Therefore, when there is little variation in the transformer characteristics between the multiple power converters 3a, 3b and there is not much difference in the susceptibility to bias magnetization, current control can be simplified by adopting the control system shown in embodiment 6.

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

As shown in Figure 9, the power conversion device of embodiment 7 basically has the same configuration as the power conversion device of embodiment 4 shown in Figure 6, but the configuration of the control device 7 differs from that of the power conversion device of embodiment 4.

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. Control device 7 basically has the same configuration as control device 7 shown in FIG. 4, but differs from control device 7 in embodiment 4 in that current control unit 8 includes an average calculator 100 and a dq converter 101.

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

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 through a dq conversion (three-phase to two-phase conversion) using equation (2).

Subtractor 102 calculates the deviation Δiad of the d-axis average current iad from the d-axis current command value id*. Subtractor 103 calculates the deviation Δiaq of the q-axis average current iaq from the q-axis current command value iq*.

The second compensators CP21 and CP22 calculate integral control variables by performing integral control calculations on the deviations Δiad and Δiaq. The inverse dq converter 104 converts the integral control variables calculated by the second compensators CP21 and CP22 into integral control variables for three phases by inverse dq transformation (two-phase to three-phase transformation) using equation (1).

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

Multipliers 18-20 and inverse dq converter 21 generate correction amounts corresponding to the d-axis current command value id* and the q-axis current command value iq*.

Adder 17 generates three-phase AC voltage command values V1u*, V1v*, and V1w* 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 adder 16. The three-phase AC voltage command values are provided to the PWM circuit 22.

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

Adder 57 generates three-phase AC voltage command values V2u*, V2v*, and V2w* 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 adder 56. The three-phase AC voltage command values are provided to the PWM circuit 22.

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.

As explained above, with the power conversion device according to embodiment 7, even in a configuration in which multiple power converters 3a, 3b are serially multiplexed using a multiplex transformer 2, proportional control with the same number of degrees of freedom as the number of AC terminals is performed for each power converter, making it possible to suppress disturbances occurring at the AC terminals of each power converter.

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

If there is an impedance difference between the excitation circuit between the primary winding 2c and secondary winding 2a and the excitation circuit between the primary winding 2c and secondary winding 2b in the multiplex transformer 2, or if there is a detection error between the current detector 5a and the current detector 5b, providing separate second compensators CP21 and CP22 for the output current of power converter 3a and the output current of power converter 3b may result in a large voltage difference between the output voltages of power converters 3a and 3b, making it difficult for the power conversion device to operate normally. This is because, when there is no bias in the multiplex transformer 2, the impedance of the excitation circuit is sufficiently greater than the leakage impedance of the primary winding and secondary winding. Therefore, if integral control is performed on the deviation in the output current of each power converter, the output voltage of each power converter may increase separately. In embodiment 7, as described above, integral control is performed using the three-phase average current of the output currents of multiple power converters 3a and 3b, thereby avoiding such concerns.

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

As shown in Figure 10, the power conversion device of embodiment 8 basically has the same configuration as the power conversion device of embodiment 4 shown in Figure 6, but the configuration of the control device 7 differs from that of the power conversion device of embodiment 4.

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. Control device 7 basically has the same configuration as control device 7 shown in FIG. 4, but differs from control device 7 in embodiment 4 in that current control unit 8 includes a dq converter 105.

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 through dq conversion (three-phase to two-phase conversion) using equation (2).

Subtractor 41 calculates the deviation Δi1d of the d-axis current i1d from the d-axis current command value id* (Δi1d = id* - i1d). Subtractor 42 calculates the deviation Δi1q of the q-axis current i1q from the q-axis current command value iq* (Δi1q = iq* - i1q).

The second compensators CP21 and CP22 calculate integral control variables by performing integral control calculations on the deviations Δi1d and Δi1q. The inverse dq converter 15 converts the integral control variables calculated by the second compensators CP21 and CP22 into integral control variables for three phases by inverse dq transformation (two-phase to three-phase transformation) using equation (1).

Adder 16 adds the proportional control variables for three phases, which are calculated values by first compensators CP11 to CP13, and the integral control variables for three phases by inverse dq converter 15, to generate the three-phase AC voltage command values required for feedback control to reduce the current deviations Δi1u, Δi1v, and Δi1w.

Multipliers 18-20 and inverse dq converter 21 generate correction amounts corresponding to the d-axis current command value id* and the q-axis current command value iq*.

Adder 17 generates three-phase AC voltage command values V1u*, V1v*, and V1w* 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 adder 16. The three-phase AC voltage command values are provided to the PWM circuit 22.

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

Adder 57 generates three-phase AC voltage command values V2u*, V2v*, and V2w* 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 adder 56. The three-phase AC voltage command values are provided to the PWM circuit 22.

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.

In the example of Figure 10, a configuration was described in which the integral control amount for three phases is calculated using the output current of power converter 3a, but a configuration in which the integral control amount for three phases is calculated using the output current of power converter 3b may also be used. In other words, the integral control amount for three phases can be calculated using the output current of one of the multiple power converters 3a, 3b as a representative value.

As described above, with the power conversion device according to embodiment 8, even in a configuration in which multiple power converters 3a, 3b are serially multiplexed using a multiplex transformer 2, proportional control with the same number of degrees of freedom as the AC terminals is executed for each power converter. This makes it possible to suppress disturbances occurring at the AC terminals of each power converter, even if there are differences in the susceptibility to bias magnetization between the multiple power converters 3a, 3b due to transformer characteristics or carrier wave phase differences.

Furthermore, the output current of one of the multiple power converters 3a, 3b is used as a representative value, and this 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 embodiment 7, if second compensators CP21, CP22 were provided separately for the output current of power converter 3a and the output current of power converter 3b, a large voltage difference could occur in the output voltages of power converters 3a, 3b, making it difficult for the power conversion device to operate normally. In embodiment 8, integral control is performed using the output current of one of the multiple power converters 3a, 3b, thereby avoiding such concerns.

Ninth Embodiment
In the above-described first to eighth embodiments, the 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, but the control configuration can also be applied to the control of the output current of a power converter connected to a single-phase AC power system via a single-phase transformer.

FIG. 11 is a circuit block diagram showing the configuration of a power conversion device according to the ninth embodiment.
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. The AC terminals of the power converter 3 are connected to a single-phase transmission line of a single-phase AC power system 1A via a single-phase transformer 2A.

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

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

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

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

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

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

The current control unit 8 calculates a feedback control amount through control calculations to reduce 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*.

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.

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).

The subtractor 11 calculates the 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).

The first compensator CP11 has a proportional element and calculates the proportional control amount through proportional control calculations to reduce the deviation Δi of the single-phase AC current from the single-phase AC current command value.

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 a coordinate transformation using the reference phase θ. The coordinate transformation is expressed by the following equation (13):

Subtractor 41 calculates the deviation of the d-axis current id from the d-axis current command value id* (d-axis deviation) Δid. Subtractor 42 calculates the deviation of the q-axis current iq from the q-axis current command value iq* (q-axis deviation) Δiq.

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).

Adder 16 adds the single-phase proportional control variable calculated by first compensator CP11 to the single-phase integral control variable from inverse dq converter 15 to generate the single-phase AC voltage command value required for feedback control to reduce deviation Δi.

Multipliers 18-20 and inverse dq converter 21 generate correction amounts corresponding to the d-axis current command value id* and the q-axis current command value iq*.

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 adder 16. The single-phase AC voltage command value V* is provided to the PWM circuit 22.

The PWM circuit 22 generates gate pulses 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 pulses.

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 rapid suppression of bias magnetization of single-phase transformer 2A.

Furthermore, the power conversion device according to 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 single-phase transformer 2A into d-axis current and q-axis current, and performs integral control to reduce the deviation of the d-axis current and q-axis current from the d-axis current command value and q-axis current command value, thereby eliminating the steady-state deviation contained in the primary winding current.

[Embodiment 10]
In the above-described first to eighth embodiments, 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," which is the same number as the number of AC terminals of the power converter 3.

In embodiment 10, as another configuration for achieving three degrees of freedom in 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.

FIG. 12 is a circuit block diagram showing the configuration of a power conversion device according to the tenth embodiment.
As shown in Figure 12, the power conversion device of embodiment 10 basically has the same configuration as the power conversion device of embodiment 1 shown in Figure 1, but the configuration of the control device 7 is different from that of the power conversion device of embodiment 1.

The control device 7 includes a phase detector 9, a current control unit 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.

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

The current control unit 8 calculates a feedback control amount through control calculations to reduce the deviation of the detection value of the current detector 5 from the AC current command value. In embodiment 10, 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*.

The zero-phase current command value iz* does not flow to the three-phase AC power system 1, so it is generated based on circumstances within the power conversion device. For example, 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 desired to flow through the delta winding.

The current control unit 8 includes subtractors 25, 26, and 36, first compensators CP11 to CP13, second compensators CP21 and CP22, a dq converter 34, and a zero-phase sequence calculator 35.

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 the reference phase θ.

The zero-phase current calculator 35 calculates the zero-phase current iz from the three-phase AC current detected by the current detector 5. Specifically, the zero-phase current calculator 35 calculates the zero-phase current iz by dividing the sum of the U-phase current iu, V-phase current iv, and W-phase current iw by 3.

Subtractor 25 calculates the 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. Subtractor 26 calculates the 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. Subtractor 36 calculates the 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 the zero-phase deviation).

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

The second compensators CP21 and CP22 calculate integral control amounts through 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. Note that Ki is the integral control gain.

Adder 27 generates the d-axis voltage command value Vd* by adding the proportional control variable Kp·Δid from the first compensator CP11 and the integral control variable Σ(Ki·Δid) from the second compensator CP21. Adder 28 generates the q-axis voltage command value Vq* by adding the proportional control variable Kp·Δiq from the first compensator CP12 and the integral control variable Σ(Ki·Δiq) from the second compensator CP22.

Multiplier 18 multiplies the d-axis current command value id* by gain ωL. Multiplier 19 multiplies the q-axis current command value iq* by 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.

Adder 31 adds the d-axis voltage Vd from the dq converter 23 to the d-axis voltage command value Vd* from the subtractor 29. Adder 32 adds the q-axis voltage Vq from the dq converter 23 to the q-axis voltage command value Vq* from the adder 30.

The inverse dq converter 33 performs an inverse dq transformation (two-phase to three-phase transformation) 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 to generate three-phase voltage command values Vu*, Vv*, and Vw*. The three-phase AC voltage command values are provided to the PWM circuit 22.

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.

As described above, according to the power conversion device of embodiment 10, 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 performed 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*. In other words, in embodiment 10, a control system is configured for each of the d-axis current, the q-axis current, and the zero-phase current, so the degrees of freedom of the current feedback control are three. Therefore, because the degrees of freedom of the current feedback control are the same as the number of AC terminals of the power converter 3, it is possible to suppress disturbances occurring at each AC terminal of the power converter 3 by current feedback control.

In addition, the current feedback control in embodiment 10, like the current feedback control in embodiment 1, performs integral control on the deviations Δid and Δiq of the d-axis and q-axis currents from the d-axis and q-axis current command values, thereby eliminating steady-state deviations.

It is intended from the outset that the configurations described in the above-mentioned embodiments and modified examples may be combined as appropriate, including combinations not mentioned in the specification, to the extent that no inconvenience or contradiction arises.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

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 integrator, CP11 to CP19 first compensator, CP21, CP22 second compensator.

Claims (7)

a plurality of power converters that convert DC voltages into three-phase AC voltages and output the voltages to AC terminals;
a plurality of first current detectors that detect output currents of the plurality of power converters, respectively;
a control device for controlling the plurality of power converters,
the AC terminals of the plurality of power converters are respectively connected to a plurality of secondary windings of a multi-transformer, and the plurality of primary windings of the multi-transformer are connected in series to each other and connected to a three-phase AC power system or a three-phase AC load;
The control device
a current control unit that generates a plurality of three-phase AC voltage command values by feedback control for compensating for deviations of detection values of the plurality of first current detectors from an AC current command value;
a PWM circuit that generates control signals for the plurality of power converters based on the plurality of three-phase AC voltage command values, thereby PWM-controlling the plurality of power converters;
the AC current command value includes a d-axis current command value and a q-axis current command value,
The current control unit
a first coordinate converter that converts the d-axis current command value and the q-axis current command value into three-phase AC current command values;
a first compensator that receives as input a deviation of the output current detected by each of the plurality of first current detectors from the three-phase AC current command value and performs at least a proportional control calculation;
a second current detector for detecting a primary winding current of the multiple transformer;
The current control unit
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 operation;
a third coordinate converter for converting a calculated value by the second compensator from two phases to three phases;
an adder that generates the plurality of three-phase AC voltage command values by adding together a calculated value by the first compensator for each of the detection values of the plurality of first current detectors and a calculated value by the third coordinate converter. a plurality of power converters that convert DC voltages into three-phase AC voltages and output the voltages to AC terminals;
a plurality of first current detectors that detect output currents of the plurality of power converters, respectively;
a control device for controlling the plurality of power converters,
the AC terminals of the plurality of power converters are respectively connected to a plurality of secondary windings of a multi-transformer, and the plurality of primary windings of the multi-transformer are connected in series to each other and connected to a three-phase AC power system or a three-phase AC load;
The control device
a current control unit that generates a plurality of three-phase AC voltage command values by feedback control for compensating for deviations of detection values of the plurality of first current detectors from an AC current command value;
a PWM circuit that generates control signals for the plurality of power converters based on the plurality of three-phase AC voltage command values, thereby PWM-controlling the plurality of power converters;
the AC current command value includes a d-axis current command value and a q-axis current command value,
The current control unit
a first coordinate converter that converts the d-axis current command value and the q-axis current command value into three-phase AC current command values;
a first compensator that receives as input a deviation of the output current detected by each of the plurality of first current detectors from the three-phase AC current command value and performs at least a proportional control calculation;
The current control unit
a calculator that calculates an average current of the output currents of the plurality of power converters detected by the plurality of first current detectors;
a second coordinate converter that converts the average current 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 operation;
a third coordinate converter for converting a calculated value by the second compensator from two phases to three phases;
an adder that generates the plurality of three-phase AC voltage command values by adding together a calculated value by the first compensator for each first current detection value and a calculated value by the third coordinate converter. a plurality of power converters that convert DC voltages into three-phase AC voltages and output the voltages to AC terminals;
a plurality of first current detectors that detect output currents of the plurality of power converters, respectively;
a control device for controlling the plurality of power converters,
the AC terminals of the plurality of power converters are respectively connected to a plurality of secondary windings of a multi-transformer, and the plurality of primary windings of the multi-transformer are connected in series to each other and connected to a three-phase AC power system or a three-phase AC load;
The control device
a current control unit that generates a plurality of three-phase AC voltage command values by feedback control for compensating for deviations of detection values of the plurality of first current detectors from an AC current command value;
a PWM circuit that generates control signals for the plurality of power converters based on the plurality of three-phase AC voltage command values, thereby PWM-controlling the plurality of power converters;
the AC current command value includes a d-axis current command value and a q-axis current command value,
The current control unit
a first coordinate converter that converts the d-axis current command value and the q-axis current command value into three-phase AC current command values;
a first compensator that receives as input a deviation of the output current detected by each of the plurality of first current detectors from the three-phase AC current command value and performs at least a proportional control calculation;
The current control unit
a second coordinate converter that converts a detection value of any one of the plurality of first current detectors 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 operation;
a third coordinate converter for converting a calculated value by the second compensator from two phases to three phases;
an adder that generates the plurality of three-phase AC voltage command values by adding together a value calculated by the first compensator for each first current detection value and a value calculated by the third coordinate converter. a plurality of power converters that convert DC voltages into three-phase AC voltages and output the voltages to AC terminals;
a plurality of first current detectors that detect output currents of the plurality of power converters, respectively;
a control device for controlling the plurality of power converters,
the AC terminals of the plurality of power converters are respectively connected to a plurality of secondary windings of a multi-transformer, and the plurality of primary windings of the multi-transformer are connected in series to each other and connected to a three-phase AC power system or a three-phase AC load;
a second current detector for detecting a primary winding current of the multiple transformer;
The control device
a current control unit that generates a plurality of three-phase AC voltage command values by feedback control for compensating for deviations of detection values of the plurality of first current detectors from an AC current command value;
a PWM circuit that generates control signals for the plurality of power converters based on the plurality of three-phase AC voltage command values, thereby PWM-controlling the plurality of power converters;
the AC current command value includes a d-axis current command value and a q-axis current command value,
The current control unit
a first coordinate converter that converts the d-axis current command value and the q-axis current command value into three-phase AC current command values;
a calculator that calculates an average current of the output currents of the plurality of power converters detected by the plurality of first current detectors;
a first compensator that receives the deviation of the average current from the three-phase AC current command value as an input and performs at least a proportional control calculation;
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 operation;
a third coordinate converter for converting a calculated value by the second compensator from two phases to three phases;
an adder that generates the plurality of three-phase AC voltage command values by adding together a value calculated by the first compensator and a value calculated by the third coordinate converter. the calculator further calculates a deviation of the output current of each of the plurality of power converters from the average current;
the first compensator further performs a proportional control operation to reduce a deviation of an output current of each of the plurality of power converters;
5. The power conversion device according to claim 4, wherein the adder generates the plurality of three-phase AC voltage command values by adding together a value calculated by the first compensator for the deviation of the average current, a value calculated by the first compensator for the deviation of the output current of each of the plurality of power converters, and a value calculated by the third coordinate converter. the first compensator includes at least a proportional element;
6. The power conversion device according to claim 1, wherein the first compensator further includes 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. 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.