Power regeneration converter

Abstract

The invention provides a power supply regenerative converter which is arranged between an inverter for outputting three-phase alternating current to a motor and a three-phase alternating current power supply as an input system and regenerates induced electromotive force generated by the motor to the three-phase alternating current power supply. The control unit calculates a three-phase AC voltage target value for PWM modulation on the basis of a three-phase AC voltage of the input system detected by the AC voltage detection unit, a three-phase AC current detected by the AC current detection unit, and a DC voltage between the power regenerative converter and the inverter detected by the DC voltage detection unit. The DC voltage between the power regenerative converter and the inverter is controlled on the basis of the calculated three-phase AC voltage target value. Thus, in the power conversion device, the output DC voltage can be kept at an appropriate value, and overmodulation, an increase in noise, an increase in switching loss, heat generation of a filter including a reactor, and an increase in insulation deterioration of a device as a load can be reduced.

Description

Technical Field

[0001] The present invention relates to a power regeneration converter, and more particularly to a power regeneration converter suitable for maintaining an output DC voltage at an appropriate value, suppressing heat generation, and preventing deterioration of a motor or the like as a load system. Background Art

[0002] In a power supply system that uses three-phase AC as the input system power supply and supplies power to the motor of the load system via a power conversion device composed of a converter and an inverter, when the frequency setting drops sharply or the actual speed of the motor is greater than the output frequency of the inverter during deceleration, electric energy may return from the motor to the inverter. This is generally called "regeneration" or "power regeneration".

[0003] Generally, regenerative energy is converted into heat and consumed by a regenerative discharge resistor connected to a DC section of an inverter, but a power regenerative converter is a device that can reuse energy that was previously wasted by returning the regenerative energy to the power supply side.

[0004] In such a power regeneration converter, control is generally performed using a DC voltage converted from AC to DC as a control command. The control command value of the DC voltage is preferably set so that the PWM modulation performed on the system side by the inverter connected to the power regeneration converter or the power regeneration converter itself does not become overmodulation, and the lower limit value of the setting is determined according to the AC voltage that the power conversion device as a whole should output to the load side or the input system side.

[0005] In this regard, Patent Document 1 describes a technology that can improve operating efficiency by changing a DC voltage command according to the rotation speed of a motor as a load in a power conversion device used in a drive system.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-3746 Summary of the invention

[0009] Technical problem to be solved by the invention

[0010] Conventional power conversion devices having converter and inverter functions assume various operating conditions and determine the setting value of the DC voltage based on the output AC voltage during regeneration being the maximum value. When setting the DC voltage in this way, a high voltage is always applied to the lower limit value that changes according to the operating state, which causes an increase in switching losses of both main elements of the converter and inverter, an increase in heat generation of filters including reactors, and insulation degradation of devices as loads.

[0011] Therefore, in order to suppress the DC voltage outputted by the converter, it is conceivable to apply the technology described in Patent Document 1 for reducing the load applied to each part by making the DC voltage variable to the power regeneration converter.

[0012] However, since a filter or the like is usually provided between the power regeneration converter and the system power supply, a difference occurs between the voltage outputted by the power regeneration converter to the load system side and the input system voltage. Therefore, due to the voltage fluctuation, the DC voltage outputted by the power regeneration converter to the inverter side becomes a voltage different from the expected voltage, resulting in technical problems such as overmodulation, increased switching loss, and increased noise.

[0013] The object of the present invention is to provide a power regeneration converter capable of maintaining an output DC voltage at an appropriate value, reducing overmodulation, increase in noise, increase in switching loss, heating of filters including inductors, and increase in insulation degradation of a device serving as a load.

[0014] Technical solutions for solving technical problems

[0015] The structure of the power regeneration converter of the present invention is preferably configured between an inverter that outputs three-phase AC to the motor and a three-phase AC power supply as an input system, and a conversion unit performs bidirectional conversion between DC and AC to regenerate the induced electromotive force generated in the motor to the three-phase AC power supply. The power regeneration converter includes: a filter unit configured between the conversion unit and the three-phase AC power supply; an AC voltage detection unit connected to the three-phase AC power supply as the input system and detecting the three-phase AC voltage supplied from the three-phase AC power supply; an AC current detection unit that detects the three-phase AC current flowing in the power regeneration converter; a DC voltage detection unit that detects the DC voltage between the power regeneration converter and the inverter; and a control unit, which calculates a three-phase AC voltage target value for PWM modulation based on the three-phase AC voltage detected by the AC voltage detection unit, the three-phase AC current detected by the AC current detection unit, and the DC voltage between the power regeneration converter and the inverter detected by the DC voltage detection unit, and the control unit controls the DC voltage between the power regeneration converter and the inverter based on the calculated three-phase AC voltage target value.

[0016] Effects of the Invention

[0017] According to the present invention, it is possible to provide a power regeneration converter that can maintain the output DC voltage at an appropriate value, reduce overmodulation, increase in noise, increase in switching loss, heating of filters including reactors, and increase in insulation degradation of a device serving as a load. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a circuit configuration diagram of the power conversion device according to the first embodiment.

[0019] Figure 2 It is a block diagram showing the detailed functions of the control unit.

[0020] Figure 3A This is a diagram (part 1) showing the vector relationship among the power supply voltage, the filter step-down voltage, and the input and output AC voltages of the conversion section using the dq axis of the AC current.

[0021] Figure 3B This is a diagram (part 2) showing the vector relationship between the power supply voltage, the filter drop voltage, and the input and output AC voltages of the conversion section using the dq axis of the AC current.

[0022] Figure 3C This is a diagram (part 3) showing the vector relationship between the power supply voltage, the filter drop voltage, and the input and output AC voltages of the conversion section using the dq axis of the AC current.

[0023] Figure 3D This is a diagram (part 4) showing the vector relationship between the power supply voltage, the filter drop voltage, and the input and output AC voltages of the conversion unit using the dq axis of the AC current.

[0024] Figure 3E This is a diagram (part 5) showing the vector relationship between the power supply voltage, the filter drop voltage, and the input and output AC voltages of the conversion section using the dq axis of the AC current.

[0025] Figure 3F This is a diagram (part 6) showing the vector relationship between the power supply voltage, the filter drop voltage, and the input and output AC voltages of the conversion section using the dq axis of the AC current.

[0026] Figure 4 This is a circuit configuration diagram of a power conversion device according to the second embodiment.

[0027] Figure 5 This is a circuit configuration diagram of a power conversion device according to a third embodiment. DETAILED DESCRIPTION

[0028] Below, use Figure 1 to Figure 5 Each embodiment of the present invention will be described.

[0029] [Implementation method 1]

[0030] Below, use Figure 1 to Figure 3F Embodiment 1 of the present invention will be described.

[0031] First, use Figure 1 The circuit configuration of the power conversion device according to the first embodiment will be described.

[0032] The power conversion device 100 of the first embodiment is as follows: Figure 1As shown, a three-phase AC main power source 1 is input, a motor 7 operating with a three-phase AC is connected as a load system, and a power regeneration converter 20 and an inverter 6 are provided.

[0033] exist Figure 1 In a circuit, the ( / n) on a line indicates that it is composed of n physical lines, where n is an integer greater than 1.

[0034] During power operation (the state of supplying power to the motor 7), the power regeneration converter 20 converts the three-phase AC input power from the main power supply 1 into DC. During regeneration (the state of the motor 7 generating induced electromotive force), it converts DC into three-phase AC and releases power to the main power supply 1.

[0035] The power regeneration converter 20 includes a filter unit 2 , a control unit 3 , a conversion unit 4 , a smoothing capacitor 5 , a power phase detection transformer 8 , a current detector 9 , and a DC voltage detector 10 .

[0036] The filter unit 2 is connected to the main power supply 1 to reduce noise. The conversion unit 4 is a circuit that performs bidirectional conversion by converting AC to DC during power operation or converting DC to AC during regeneration. The power supply phase detection transformer 8 is a transformer for detecting the amplitude and phase of the power supply voltage.

[0037] During power operation, the conversion unit 4 converts the three-phase AC power supplied from the main power supply 1 into a variable voltage DC power (voltage Vdc) and supplies power to the inverter 6. In addition, during regeneration, the return energy from the inverter 6 as a load is regenerated to the main power supply 1 side through PWM modulation (Pulse Width Modulation).

[0038] The smoothing capacitor 5 is a capacitor element for storing electrostatic capacitance for converting AC into DC. The current detector 9 is a circuit for detecting the filter unit converter AC current Iac between the filter unit 2 and the converter 4. The DC voltage detector 10 is a circuit for detecting the DC voltage Vdc as the voltage across the smoothing capacitor 5.

[0039] The conversion unit 4 is composed of, for example, six sets of main switch elements, each of which is an IGBT (Insulated Gate Bipolar Transistor) element and a freewheeling diode connected in parallel. IGBT is a type of power transistor, which is characterized by having both a low saturation voltage and a relatively fast switching characteristic. In addition, the freewheeling diode is a diode for releasing a flyback voltage.

[0040] The control unit 3 is a circuit that issues a voltage conversion instruction to the conversion unit. The power supply voltage Vgrid is input to the control unit 3 via the power supply phase detection transformer 8, and the detected AC current Iac between the filter unit and the conversion unit is input to the control unit 3 from the current detector 9, and the detected DC voltage Vdc is input to the control unit 3 from the DC voltage detector 10. For example, the 6 groups of main switch elements of the conversion unit 4, which are connected in parallel with the IGBT elements and the freewheeling diodes, are controlled by PWM control.

[0041] The inverter 6 converts the direct current output from the power regeneration converter 20 into a three-phase alternating current supplied to the load system during power operation, and allows the regenerative energy from the motor 7 to flow into the power regeneration converter 20 during regeneration.

[0042] In the above configuration, when the converter 4 starts operating and the DC voltage Vdc is output from both ends of the smoothing capacitor 5, the lower limit value of the output DC voltage changes depending on the operating conditions of the inverter 6 and the motor 7. The reason is described below.

[0043] In a conversion circuit of any type ("unlimited type" means that it includes converters and inverters), when an AC voltage waveform is generated from a DC voltage through PWM modulation, the output AC voltage is regulated by adjusting the width of the pulse. In order to obtain the required AC voltage, the pulse width is reduced as the DC voltage is higher, and the pulse width is increased as the DC voltage is lower, even when the output is the same, and the regulation is performed in this way. At this time, if the pulse interval cannot be maintained above a certain value, overmodulation occurs and accurate output cannot be performed. Therefore, the lower limit value of the DC voltage depends on the required AC output voltage. Figure 1 In the case of the converter 4 shown in FIG. 1 , specifically, the lower limit value of the DC voltage Vdc to be output depends on the converter input / output AC voltage Vac output by the converter 4 to the main power supply 1 side.

[0044] However, in Figure 1 In the power conversion device 100 shown, the conversion unit input-output AC voltage Vac that the conversion unit 4 should output requires a higher AC voltage than when the motor 7 is regenerating, for example. This is also the case when the load applied to the motor 7 changes, the required torque changes, etc. In the case of high load, a higher AC voltage is required than in the case of low load. In this way, the required AC voltage changes according to the operating conditions such as power operation / regeneration, the load condition, etc. Therefore, the lower limit value of the DC voltage also changes according to the operating conditions.

[0045] For the above-mentioned reasons, it is difficult to set a constant lower limit value for the DC voltage Vdc for each operating condition, and therefore the maximum DC voltage value under the assumed operating condition is often set constant.

[0046] However, when the DC voltage Vdc is set constant, even when a high voltage is not required depending on the operating conditions, the maximum value is always output.

[0047] In the case of driving using such a conversion circuit, when the DC voltage becomes high, there are disadvantages and problems such as increase in main element switching loss, increase in heat generation of filters including reactors, deterioration of motor insulation, increase in noise, etc. From these viewpoints, it is preferable that the DC voltage Vdc is a variable appropriate value together with the input and output AC voltage Vac of the conversion unit that changes according to the operating conditions, so as to keep the output low.

[0048] As an example of a control method for making the DC voltage Vdc variable, there can be cited a method of monitoring the voltage of the power supply as the AC voltage that the converter should output, and making the DC voltage variable according to the three-phase AC value of the power supply. Figure 1 In the example of the power conversion device 100 in FIG. 1 , as the input quantity used by the control unit 3, the conversion unit input-output AC voltage Vac output by the conversion unit 4 to the main power supply 1 side is not used, but the power supply voltage Vgrid is used to calculate the output DC voltage Vdc. However, in the case of using Figure 1 In the case of the power conversion device 100 shown, for example, since a portion such as the filter unit 2 located between the main power supply 1 and the conversion unit 4 is required, a difference of the filter drop voltage VL consumed by the filter unit 2 occurs between the power supply voltage Vgrid and the conversion unit input / output AC voltage Vac originally required for calculation. In the control unit 3 of the present embodiment, this difference is eliminated and the conversion unit input / output AC voltage Vac actually required is calculated.

[0049] Below, use Figure 2 to Figure 3F The operation of the control unit will be described.

[0050] The control unit 3 includes a PI control unit 11 , an AC voltage control value calculation unit 12 , and a PWM modulation unit 13 .

[0051] The PI control unit 11 calculates the difference between the DC voltage control command value Vdc_ref and the DC voltage Vdc actually detected by the DC voltage detector 10 using a subtractor, and calculates the target value Iq_ref of the q-axis current based on the difference.

[0052] The AC voltage control value calculation unit 12 calculates the AC voltage control value Vacr in the dq axis coordinate system based on the q axis current target value Iq_ref, the separately given d axis current target value Id_ref, and the filter unit converter AC current Iac detected by the current detector 9. Here, the d axis current target value Id_ref is set to 0.

[0053] The d-axis and the q-axis are coordinate axes of a dq rotating coordinate system which is a unique coordinate system used in the field of motors and generators, and are coordinate axes that rotate while being synchronized with a rotating magnetic field or a rotor generated by a three-phase alternating current.

[0054] The control unit 3 calculates the command value Vac_ref of the AC voltage output from the conversion unit 4 using the AC voltage control value Vacr and the power supply voltage Vgrid detected by the power supply phase detection transformer 8. The PWM modulation unit 13 performs PWM control based on the command value Vac_ref to bring the AC voltage output Vac close to the command value Vac_ref.

[0055] The power supply voltage Vgrid is detected by the power supply phase detection transformer 8 and holds the instantaneous value of the voltage of each of the three phases of the power supply voltage, and is input to the control unit 3. The power supply voltage Vgrid is expressed as values ​​Vd and Vq of the dq coordinate system by dq conversion.

[0056] In addition, the filter unit conversion unit AC current Iac detected by the current detector 9 is a value that maintains the instantaneous value of the current of each of the three phases between the filter unit 2 and the conversion unit 4, and is expressed as a reactive current Id and an effective current Iq on the DC coordinate system by performing dq conversion using the voltage phase θ. These reactive current Id, effective current Iq, q-axis current target value Iq_ref, and d-axis current target value Id_ref are input to the AC voltage control value calculation unit 12.

[0057] The AC voltage control value calculation unit 12 adds the filter drop voltage VL of the filter unit 2 as a filter compensation term, and on this basis compares the command value and the detection value for the dq axis respectively, and calculates the difference between the two through proportional integral (PI), thereby obtaining the voltage command vd of the d axis and the voltage command vq of the q axis.

[0058] The control unit 3 adds the d-axis value Vd and the q-axis value Vq of the power supply voltage Vgrid to the d-axis voltage command vd and the q-axis voltage command vq calculated by the AC voltage control value calculation unit 12, thereby obtaining the d-axis output voltage command value Vd_ref and the q-axis output voltage command value Vq_ref. By performing an inverse dq transformation on this, the three-phase instantaneous AC voltage command value Vac_ref is obtained. The instantaneous AC voltage command value Vac_ref is input to the PWM modulation unit 13, and six PWM switching signals are obtained by comparing it with the carrier.

[0059] The instantaneous AC voltage command value Vac_ref is a calculated value of the AC voltage output by the converter to the main power supply 1. Since the instantaneous AC voltage command value Vac_ref is a control command value of the converter input / output AC voltage Vac, the converter input / output AC voltage Vac gradually approaches the instantaneous AC voltage command value Vac_ref.

[0060] The relationship between the converter input / output AC voltage Vac, the power supply voltage Vgrid, and the filter step-down voltage VL of the filter unit 2 is expressed by the following (Equation 1).

[0061] Vgrid=Vac+VL…(Formula 1)

[0062] The relationship expressed by (Equation 1) can be obtained by Figure 3A to Figure 3F The graph shown in the figure shows the positive and negative of the effective current Id and the ineffective current Iq. In the figure, it is represented as a vector, and I = (Id, Iq). Assuming that the power supply voltage Vgrid is constant, the vector of the input and output AC voltage Vac of the converter and the filter drop voltage VL represented on the dq axis changes according to the relationship between the effective current Id and the ineffective current Iq.

[0063] For example, in Figure 3A to Figure 3F When such a relationship is established, the AC voltage Vac to be output is variable, and the lower limit value of the DC voltage Vdc to be output is also variable.

[0064] In the conventional method, for example, when obtaining the value of the DC voltage control command value Vdc_ref, the constant k is used to perform calculation using the following (Formula 2).

[0065] Vdc_ref = Vgrid × k (Formula 2)

[0066] by Figure 3A and Figure 3C Taking (Equation 2) as an example, because the output Vac value is different, the Vdc_ref actually required is different, but because Vgrid is constant, the value of Vdc_ref is Figure 3A and Figure 3C Therefore, in the conventional method of calculating the DC voltage control command value Vdc_ref using (Formula 2), it is not possible to follow the change of Vac, and an error occurs in the DC voltage command value Vdc_ref.

[0067] Therefore, in order to calculate the DC voltage command value Vdc_ref as in the present embodiment, the control unit 3 uses the instantaneous AC voltage command value Vac_ref input to the PWM modulation unit 13 instead of Vgrid for calculation. When the constant k is used, the DC voltage command value Vdc_ref can be expressed by the following (Formula 3).

[0068] Vdc_ref=Vac_ref×k…(Formula 3)

[0069] The instantaneous AC voltage command value Vac_ref in (Equation 3) is the calculated value of the input / output AC voltage Vac of the conversion unit, and thus becomes the reference value of the input / output AC voltage Vac of the conversion unit. Therefore, it is possible to follow the same as when Vac is measured and calculated using a measuring instrument. Figure 3A to Figure 3F The changes in the values ​​of the effective current Iq and the reactive current Id shown above can input a command value of the amount required for the converter to output the alternating current to the DC voltage command value Vdc_ref.

[0070] As described above, this embodiment provides a regenerative converter, which is connected to an AC power supply and can convert AC power into DC power and convert DC power into AC power. The regenerative converter controls the output AC voltage based on the difference between the detected value of the system power supply voltage, the detected value of the DC voltage unit, and the detected value of the AC current and the command voltage, and during the control process, a DC voltage command proportional to the calculated AC voltage value is performed.

[0071] Thus, the value of the DC voltage used to output the AC voltage can be maintained at a value suitable for changes in operating conditions, thereby reducing overmodulation, increase in noise, increase in switching losses, heating of filters including reactors, and increase in insulation degradation of the device serving as a load.

[0072] Furthermore, in the case of a power conversion device constructed using the power conversion device of this embodiment, there is no need to add a new signal.

[0073] [Implementation method 2]

[0074] Below, use Figure 4 Embodiment 2 of the present invention will be described.

[0075] Figure 4 This is a circuit configuration diagram of a power conversion device according to the second embodiment.

[0076] The structure and function of the power conversion device of this embodiment are similar to Figure 1 The power conversion device 100 of the first embodiment shown in FIG. 1 is substantially the same, but as shown in FIG. Figure 4 As shown, a conversion unit input / output AC voltage detector 30 is added between the filter unit 2 and the conversion unit 4, and the conversion unit input / output AC voltage Vac detected by the conversion unit input / output AC voltage detector 30 is input.

[0077] In the internal calculation, in order to calculate the DC voltage command value Vdc_ref, the conversion unit input and output AC voltage Vac is used, and the following (Formula 4) is used for calculation using a constant k.

[0078] Vdc_ref=Vac×k…(Equation 4)

[0079] The relationship between the DC voltage Vdc and the command value Vdc_ref and the subsequent control are the same as those in the first embodiment.

[0080] [Implementation method 3]

[0081] Below, use Figure 5 Embodiment 3 of the present invention will be described.

[0082] Figure 5 This is a circuit configuration diagram of a power conversion device according to a third embodiment.

[0083] The structure and function of the power conversion device of this embodiment are similar to Figure 1 The power conversion device 100 of the first embodiment shown in FIG. 1 is substantially the same, but as shown in FIG. Figure 5 As shown, a filter drop voltage detection circuit 40 is mounted on the filter unit 2, and a filter drop voltage VL is input.

[0084] The AC voltage value Vac output by the converter is calculated by using the filter drop voltage VL, the power supply voltage Vgrid, and the AC current value Iac, and the DC voltage Vdc_ref to be output is calculated based on this value.

[0085] The subsequent processing of the command value Vdc_ref is the same as that of the first embodiment.

[0086] Description of Reference Numerals

[0087] 1…Main power supply, 2…Filter unit, 3…Control unit, 4…Conversion unit, 5…Smoothing capacitor, 6…Inverter, 7…Motor, 8…Power supply phase detection transformer, 9…Current detector, 10…DC voltage detector, 11…PI control unit, 12…AC voltage control value calculation unit, 13…PWM modulation unit,

[0088] 20…Power regeneration converter,

[0089] 30…Conversion unit input and output AC voltage detector

[0090] 40…Filter drop voltage detection circuit

[0091] 100…Power conversion device.

Claims

1. A power regeneration converter, arranged between an inverter that outputs three-phase AC to a motor and a three-phase AC power supply as an input system, performs bidirectional conversion between DC and AC using a conversion unit, and regenerates the induced electromotive force generated in the motor to the three-phase AC power supply, the power regeneration converter being characterized in that it comprises: A filter unit disposed between the conversion unit and the three-phase AC power supply; an AC voltage detection unit connected to the three-phase AC power supply as an input system and detecting three-phase AC voltages supplied from the three-phase AC power supply; an AC current detection unit that detects three-phase AC current flowing between the filter and the conversion unit; a DC voltage detection unit that detects a DC voltage between the power regeneration converter and the inverter; and a control unit that calculates a target value of the three-phase AC voltage for performing the PWM modulation based on the three-phase AC voltage detected by the AC voltage detection unit, the three-phase AC current detected by the AC current detection unit, and the DC voltage between the power regeneration converter and the inverter detected by the DC voltage detection unit, The control unit controls a DC voltage between the power regeneration converter and the inverter based on the calculated three-phase AC voltage target value.

2. The power regeneration converter according to claim 1, wherein: A target value of a DC voltage between the power regeneration converter and the inverter is a constant multiple of a target value of an AC voltage of the three phases.

3. A power regeneration converter, arranged between an inverter that outputs three-phase AC to a motor and a three-phase AC power supply as an input system, performs bidirectional conversion between DC and AC using a conversion unit, and regenerates the induced electromotive force generated in the motor to the three-phase AC power supply, the power regeneration converter being characterized in that it includes: A filter unit disposed between the conversion unit and the three-phase AC power supply; an AC voltage detection unit for detecting a three-phase AC voltage outputted by the power regeneration converter; an AC current detection unit for detecting a three-phase AC current flowing between the conversion units; a DC voltage detection unit that detects a DC voltage between the power regeneration converter and the inverter; and a control unit that calculates a target value of the three-phase AC voltage for performing the PWM modulation based on the three-phase AC voltage detected by the AC voltage detection unit, the three-phase AC current detected by the AC current detection unit, and the DC voltage between the power regeneration converter and the inverter detected by the DC voltage detection unit, A DC voltage target value between the power regeneration converter and the inverter is calculated based on the AC voltage value detected by the AC voltage detection unit and is input as the DC voltage target value to the control unit.

4. A power regeneration converter, arranged between an inverter that outputs three-phase AC to a motor and a three-phase AC power supply as an input system, performs bidirectional conversion between DC and AC using a conversion unit, and regenerates the induced electromotive force generated in the motor to the three-phase AC power supply, the power regeneration converter being characterized in that it includes: A filter unit disposed between the conversion unit and the three-phase AC power supply; a filter drop voltage detection circuit for detecting a voltage drop amount of the filter section; an AC voltage detection unit connected to the three-phase AC power supply as the input system and detecting three-phase AC voltages supplied from the three-phase AC power supply; an AC current detection unit that detects three-phase AC current flowing between the filter and the conversion unit; a DC voltage detection unit that detects a DC voltage between the power regeneration converter and the inverter; and a control unit that calculates a target value of the three-phase AC voltage for performing the PWM modulation based on the three-phase AC voltage detected by the AC voltage detection unit, the three-phase AC current detected by the AC current detection unit, and the DC voltage between the power regeneration converter and the inverter detected by the DC voltage detection unit, Based on the voltage drop detected by the filter drop voltage detection circuit, the power supply voltage detected by the AC voltage detection unit and the AC current detected by the AC current detection unit, the DC voltage between the power regeneration converter and the inverter is calculated as a DC voltage target value input to the control unit.

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