Power Conversion Device

Abstract

To provide a power conversion device in which a time width for three-phase modulation during switching of phases of two-phase modulation is optimized.SOLUTION: A power conversion device 1 is connected to a three-phase AC power supply 91 and an AC load 92, and comprises: a converter circuit C; a smoothing circuit S; a DC circuit D; an inverter circuit I; a converter control unit 12; and an inverter control unit 13. A 60° cycle of a control period of the inverter circuit I and the converter circuit C includes a two-phase modulation control period for executing PWM control by a two-phase modulation method and a three-phase modulation control period for executing PWM control by a thee-phase modulation method. The inverter control unit and the converter control unit control a three-phase modulation control angle on the basis of the frequency of AC from the three-phase AC power supply or AC of the inverter circuit so that the time width of the three-phase modulation control period can be constant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] BACKGROUND ART A power conversion device is known that is a non-insulated uninterruptible power supply and performs PWM control by switching between two-phase modulation and three-phase modulation.

[0003] For example, Patent Document 1 discloses a power conversion device that performs PWM control using a two-phase modulation method that turns off the switching elements of an inverter circuit, and performs PWM control using a three-phase modulation method while switching the phases of the two-phase modulation, thereby reducing distortion of the output AC waveform when switching the phases of the two-phase modulation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 09-149660 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, the time width for PWM control in the three-phase modulation method is determined based on the angle of a sine wave. Therefore, if the frequency of the input AC varies, the time width for three-phase modulation also varies, which may reduce the efficiency of two-phase modulation.

[0006] Therefore, the present invention provides a power conversion device capable of performing efficient two-phase modulation. [Means for solving the problem]

[0007] A power conversion device according to one aspect of this embodiment includes: a converter circuit connected to a three-phase AC power source and converting AC from the three-phase AC power source into DC; a smoothing circuit connected to a DC output terminal of the converter circuit and including a capacitor; a DC circuit connected to the DC output terminal of the converter circuit and connected in parallel with the smoothing circuit, the DC circuit comprising a DC power supply; an inverter circuit connected to a DC output terminal of the smoothing circuit and a DC output terminal of the DC circuit, for converting the DC from the smoothing circuit or the DC from the DC circuit into AC and outputting the AC to an AC load; a converter control unit that controls the converter circuit by PWM using a two-phase modulation method or a three-phase modulation method; an inverter control unit that controls the inverter circuit by PWM using a two-phase modulation method or a three-phase modulation method; Equipped with the converter circuit and the inverter circuit are configured as three-phase full-bridge circuits made up of switching elements, a 60° cycle of a control period of the converter circuit and the inverter circuit includes a two-phase modulation control period in which PWM control is performed by a two-phase modulation method and a three-phase modulation control period in which PWM control is performed by a three-phase modulation method; The converter control unit and the inverter control unit control the three-phase modulation control angle based on the frequency of the AC from the three-phase AC power supply and the frequency of the output AC from the inverter circuit so that the time width of the three-phase modulation control period is constant. [Effects of the Invention]

[0008] According to the present invention, the time width for performing three-phase modulation becomes constant, and efficient two-phase modulation can be performed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit diagram showing a circuit configuration of a power conversion device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a block diagram showing a circuit configuration of a conventional converter control unit. [Figure 3] FIG. 1 is a block diagram showing a circuit configuration of a conventional inverter control unit. [Figure 4] FIG. 2 is a block diagram showing a circuit configuration of a converter control unit according to the present embodiment. [Figure 5] FIG. 2 is a block diagram showing a circuit configuration of an inverter control unit according to the present embodiment. [Figure 6] 5A and 5B are diagrams illustrating internal signal waveforms of an inverter control unit according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the present embodiment will be described with reference to the drawings. For the sake of convenience, the description of the components having the same reference numerals as those already described in the description of the embodiment will be omitted.

[0011] Fig. 1 is a diagram showing a circuit configuration of a power conversion device 1 according to this embodiment. As shown in Fig. 1, a three-phase AC power supply 91 is connected to device input terminals 31a to 31c of the power conversion device 1, and an AC load 92 to which a three-phase AC output from an inverter circuit I is supplied is connected to device output terminals 71a to 71c of the power conversion device 1. The power conversion device 1 includes an input filter F1, a converter circuit C, a smoothing circuit S, the inverter circuit I, an output filter F2, a DC filter F3, a DC circuit D, a converter control unit 12, and an inverter control unit 13.

[0012] The input filter F1 has input filter capacitors 2a to 2c and input filter reactors 3a to 3c. One terminal of each of the input filter reactors 3a to 3c is connected to device input terminals 31a to 31c, respectively, of the power conversion device 1. The other terminal of each of the input filter reactors 3a to 3c is connected to three-phase (r-phase, s-phase, t-phase) AC input terminals 41a to 41c, respectively, of the converter circuit C.

[0013] One terminal of each of the input filter capacitors 2a to 2c is connected to the corresponding terminal of the input filter reactors 3a to 3c on the device input terminals 31a to 31c side. The other terminal of each of the input filter capacitors 2a to 2c is connected to the neutral conductor n1. The input filter F1 passes three-phase AC from the three-phase AC power supply 91 to the converter circuit C, while preventing a signal of the carrier frequency (a frequency that determines the pulse width modulation period in the PWM control system) generated by the converter circuit C from flowing into the three-phase AC power supply 91.

[0014] The converter circuit C has six semiconductor switching elements 4a to 4f connected in a three-phase bridge. The semiconductor switching elements 4a to 4f are configured, for example, with IGBTs (insulated gate bipolar transistors) and anti-parallel freewheeling diodes. The converter circuit C is configured as a three-phase (r-phase, s-phase, t-phase) full bridge circuit. The converter circuit C converts three-phase AC input from a three-phase AC power supply 91 into DC.

[0015] The smoothing circuit S has a smoothing capacitor 5 of the converter circuit C. The smoothing capacitor 5 is, for example, an electrolytic capacitor, and is connected to the DC output terminals 42a and 42b of the converter circuit C. The smoothing capacitor 5 smoothes the output of the converter circuit C.

[0016] The inverter circuit I has six semiconductor switching elements 6a to 6f connected in a three-phase bridge. The semiconductor switching elements 6a to 6f are configured, for example, with IGBTs and anti-parallel connected freewheeling diodes. The inverter circuit I is configured as a three-phase (u-phase, v-phase, w-phase) full-bridge circuit. The inverter circuit I has DC input terminals 61a and 61b connected to both polarity terminals of a smoothing capacitor 5 and one terminal of each of DC filter reactors 9a and 9b, respectively. The inverter circuit I converts the DC from the smoothing circuit S (the DC output from the converter circuit C) into AC, or converts the DC from the DC circuit D into AC, through the switching operation of the semiconductor switching elements 6a to 6f.

[0017] The output filter F2 has output filter reactors 7a-7c and output filter capacitors 8a-8c. One terminal of each of the output filter reactors 7a-7c is connected to AC output terminals 62a-62c of the three-phase (u-phase, v-phase, w-phase) inverter circuit I. The other terminal of each of the output filter reactors 7a-7c is connected to device output terminals 71a-71c of the power conversion device 1.

[0018] One terminal of each of output filter capacitors 8a to 8c is connected to the terminal of output filter reactors 7a to 7c on the device output terminals 71a to 71c side, respectively. The other terminal of each of output filter capacitors 8a to 8c is connected to neutral conductor n1. Output filter F2 passes AC output from inverter circuit I to AC load 92 and prevents a carrier frequency signal generated by inverter circuit I from flowing into AC load 92.

[0019] The DC filter F3 has DC filter reactors 9a and 9b and DC filter capacitors 10a and 10b. The DC circuit D has a DC power supply (storage battery) 11. One terminal of each of the DC filter reactors 9a and 9b is connected to the DC input terminals 61a and 61b of the inverter circuit I. The other terminal of each of the DC filter reactors 9a and 9b is connected to the DC filter capacitors 10a and 10b and the DC power supply 11, respectively.

[0020] The DC circuit D is connected in parallel with the smoothing circuit S, and is configured to continue supplying power to the AC load 92 when a power outage or momentary interruption occurs. Specifically, during normal operation of the power conversion device 1, the DC output from the converter circuit C is input to the inverter circuit I. During battery operation of the power conversion device 1, the DC from the DC circuit D is input to the inverter circuit I.

[0021] The converter control unit 12 generates PWM drive signals Vgr, Vgs, and Vgt (see FIG. 4) from the three-phase AC input from the three-phase AC power supply 91, and controls the switching of the semiconductor switching elements 4a to 4f of the converter circuit C to a desired state.

[0022] Similarly, the inverter control unit 13 generates PWM drive signals Vgu, Vgv, and Vgw (see FIG. 5) from the three-phase AC input from the three-phase AC power supply 91 or from a preset three-phase AC signal, and controls the switching of the semiconductor switching elements 6a to 6f of the inverter circuit I to a desired state.

[0023] In order to explain the circuit configuration of the converter control unit 12 according to this embodiment, the circuit configuration of a conventional converter control unit 12 is shown in FIG. 2 for comparison. As shown in FIG. 2, the conventional converter control unit 12 includes a phase-locked loop (PLL circuit) 120, a converter modulation command generation unit 121, a first two-phase modulation control unit 122, a first PWM signal generation unit 123, and a first two-phase modulation signal generation unit 124.

[0024] The first phase-synchronized loop 120 is a circuit for outputting a waveform in which the phases of the three-phase AC from the three-phase AC power supply 91 are synchronized, and includes a phase comparison circuit 126, a low-pass filter (LPF) 127, and a voltage-controlled oscillator (VCO) 128. The phase comparison circuit 126 receives the three-phase AC from the three-phase AC power supply 91 and the AC fed back from the voltage-controlled oscillator 128, compares them to detect a phase difference, converts the phase difference into a voltage, and outputs it to the low-pass filter 127. The low-pass filter 127 suppresses sudden changes in the voltage output from the phase comparison circuit 126. The voltage-controlled oscillator 128 receives the voltage V from the low-pass filter 127, generates an AC with a frequency f based on the input voltage V, outputs it to the converter modulation command generator 121 and the first two-phase modulation signal generator 124, and feeds it back to the phase comparison circuit 126.

[0025] The converter modulation command generating unit 121 receives three-phase AC from the voltage controlled oscillator 128, generates converter modulation command signals Vr, Vs, and Vt consisting of three-phase AC sine waves, and outputs them to the first two-phase modulation control unit 122. The first two-phase modulation signal generating unit 124 receives three-phase AC from the voltage controlled oscillator 128, generates converter two-phase modulation signals AC1 to AC6, and outputs them to the first two-phase modulation control unit 122. The first two-phase modulation control unit 122 receives the converter modulation command signals Vr, Vs, and Vt from the converter modulation command generating unit 121, and receives the converter two-phase modulation signals AC1 to AC6 from the first two-phase modulation signal generating unit 124. The first two-phase modulation control unit 122 further generates converter two-phase modulation command signals Vr', Vs', and Vt' and outputs them to the first PWM signal generating unit 123.

[0026] In FIG. 2, the frequency f of the AC generated by the voltage-controlled oscillator 128 is calculated as f = V·K using the voltage V and the frequency conversion coefficient K of the voltage-controlled oscillator 128. Here, the rotation angles of the three-phase modulation control period are defined as three-phase modulation control angles α and β (see FIG. 6), and the duration of the three-phase modulation control period is defined as three-phase modulation control times Tα and Tβ. The relationship between the three-phase modulation control angle α and the three-phase modulation control time Tα is Tα = α / 2πf, and the relationship between the three-phase modulation control angle β and the three-phase modulation control time Tβ is Tβ = β / 2πf. Because the three-phase modulation control angles α and β are values ​​preset in the first two-phase modulation signal generator 124, fluctuations in the AC frequency f also cause fluctuations in the three-phase modulation control times Tα and Tβ, which may reduce the efficiency of two-phase modulation. Therefore, it is necessary to input to the first two-phase modulation signal generator 124 the three-phase modulation control angles α and β that keep the three-phase modulation control times Tα and Tβ constant.

[0027] The first PWM signal generator 123 includes a comparator 123a and a carrier signal generator 123b. The comparator 123a receives converter two-phase modulation command signals Vr', Vs', and Vt' and a carrier signal Vc, such as a triangular wave, generated by the carrier signal generator 123b. The comparator 123a compares the two signals and outputs PWM drive signals Vgr, Vgs, and Vgt. The PWM drive signals Vgr and their inverted signals / Vgr, the PWM drive signals Vgs and their inverted signals / Vgs, and the PWM drive signals Vgt and their inverted signals / Vgt are input to the gates of the semiconductor switching elements 4a to 4f of the converter circuit C, respectively. In other words, the PWM drive signals Vgr, Vgs, and Vgt have waveforms that turn on the upper semiconductor switching elements 4a, 4c, and 4e in FIG. 1 and turn off the lower semiconductor switching elements 4b, 4d, and 4f in FIG. 1 when the converter two-phase modulation command signals Vr', Vs', and Vt' are greater than the carrier signal Vc. In addition, when the converter two-phase modulation command signals Vr', Vs', Vt' are smaller than the carrier signal Vc, the waveforms turn on the lower semiconductor switching elements 4b, 4d, and 4f in Figure 1 and turn off the upper semiconductor switching elements 4a, 4c, and 4e in Figure 1.

[0028] In order to explain the circuit configuration of the inverter control unit 13 according to this embodiment, the circuit configuration of a conventional inverter control unit 13 is shown in FIG. 3 for comparison. As shown in FIG. 3, the conventional inverter control unit 13 includes a second phase locked loop 130, an inverter modulation command generating unit 131, a second two-phase modulation control unit 132, a second PWM signal generating unit 133, and a second two-phase modulation signal generating unit 134.

[0029] 3 includes a phase comparison circuit 136, a low-pass filter (LPF) 137, a voltage-controlled oscillator (VCO) 138, and a switching circuit SW, and during normal operation, the low-pass filter 137 and the voltage-controlled oscillator 138 are connected by the switching circuit SW, and a three-phase AC waveform that is in phase with the three-phase AC is output from the second phase locked loop 130. During battery operation, a reference voltage that serves as a reference for the frequency output by the inverter circuit I is input to the voltage-controlled oscillator 138, and the reference three-phase AC waveform is output from the phase locked loop 130. Furthermore, the configurations of the inverter modulation command generating unit 131, the second two-phase modulation control unit 132, the second PWM signal generating unit 133, and the second two-phase modulation signal generating unit 134 are similar to the configurations of the converter modulation command generating unit 121, the first two-phase modulation control unit 122, the first PWM signal generating unit 123, and the first two-phase modulation signal generating unit 124 of the converter control unit 12 shown in FIG. 2, respectively, and therefore will not be described.

[0030] 4 is a diagram showing the circuit configuration of the converter control unit 12 according to this embodiment. The circuit configuration of the converter control unit 12 according to this embodiment differs from the circuit configuration of the conventional converter control unit 12 shown in FIG. 2 in that a V / θ conversion unit 129 is added to the first phase locked loop 120. The V / θ conversion unit 129 receives the voltage V from the low-pass filter 127, converts the input voltage V into three-phase modulation control angles α and β, which are rotation angles for three-phase modulation control, and outputs the converted voltage V to the first two-phase modulation signal generation unit 124. The first two-phase modulation signal generation unit 124 receives the three-phase AC from the three-phase AC power supply 91 and the three-phase modulation control angles α and β from the V / θ conversion unit 129, generates converter two-phase modulation signals AC1 to AC6, and outputs the converted voltage V to the first two-phase modulation control unit 122.

[0031] The converter modulation command generating unit 121 receives three-phase AC from the three-phase AC power supply 91, generates converter modulation command signals Vr, Vs, and Vt consisting of three-phase AC sine waves, and outputs them to the first two-phase modulation control unit 122. The first two-phase modulation signal generating unit 124 receives three-phase AC from the three-phase AC power supply 91, generates converter two-phase modulation signals AC1 to AC6, and outputs them to the first two-phase modulation control unit 122. The first two-phase modulation control unit 122 receives the converter modulation command signals Vr, Vs, and Vt from the converter modulation command generating unit 121, and receives the converter two-phase modulation signals AC1 to AC6 from the first two-phase modulation signal generating unit 124. The first two-phase modulation control unit 122 further generates converter two-phase modulation command signals Vr', Vs', and Vt' and outputs them to the first PWM signal generating unit 123.

[0032] 4, V / θ conversion unit 129 generates three-phase modulation control angles α and β, which are calculated as α = Tα × 2πVK and β = Tα × 2πVK, based on the input voltage V and preset values ​​Tα and Tβ. Here, the frequency f of the AC generated by voltage-controlled oscillator 128 has the relationship f = V·K, using the voltage V and the frequency conversion coefficient K of voltage-controlled oscillator 128. Therefore, α and β generated by V / θ conversion unit 129 are α = Tα × 2πf and β = Tα × 2πf, and change depending on the frequency f. In this way, by varying the three-phase modulation control angles α and β depending on the AC frequency f, the three-phase modulation control times Tα and Tβ can be kept constant.

[0033] In the converter control unit 12 according to this embodiment, the first two-phase modulation signal generation unit 124 generates the converter two-phase modulation signals AC1 to AC6 from the three-phase modulation control angles α and β, which are values ​​that are not affected by the AC frequency f, and therefore the time width for performing the three-phase modulation can be made constant, thereby enabling efficient two-phase modulation.

[0034] 5 is a diagram showing the circuit configuration of the inverter control unit 13 according to this embodiment. The circuit configuration of the converter control unit 13 according to this embodiment differs from the circuit configuration of the conventional inverter control unit 13 shown in FIG. 4 in that a V / θ conversion unit 139 is added to the second phase locked loop 130. The V / θ conversion unit 139 receives the voltage V from the switching circuit SW, converts the input voltage V into three-phase modulation control angles α and β, which are rotation angles for three-phase modulation control, and outputs the converted voltage V to the first two-phase modulation signal generation unit 124. The configurations of the phase comparison circuit 136, low-pass filter (LPF) 137, voltage-controlled oscillator (VCO) 138, inverter modulation command generation unit 131, second two-phase modulation control unit 132, second PWM signal generation unit 133, and second two-phase modulation signal generation unit 134 shown in FIG. 5 are similar to the configurations of the phase comparison circuit 126, low-pass filter (LPF) 127, voltage-controlled oscillator (VCO) 128, converter modulation command generation unit 121, first two-phase modulation control unit 122, first PWM signal generation unit 123, and first two-phase modulation signal generation unit 124 of the converter control unit 12 shown in FIG. 4, respectively, and therefore description thereof will be omitted.

[0035] Fig. 6 is a diagram showing internal signal waveforms of the inverter control unit 13 according to this embodiment. In Fig. 4, the upper row shows inverter modulation command signals Vu, Vv, and Vw, the middle row shows inverter two-phase modulation signals AI1 to AI6, and the lower row shows inverter two-phase modulation command signals Vu', Vv', and Vw'.

[0036] The inverter modulation command signals Vu, Vv, and Vw are signals that are three-phase modulated by the inverter modulation command generation unit 131 based on three-phase AC sine waves that are 120° out of phase with each other. The inverter two-phase modulation signals AI1 to AI6 are signals for two-phase modulating the inverter modulation command signals Vu, Vv, and Vw. The inverter two-phase modulation command signals Vu', Vv', and Vw' are signals that are partially two-phase modulated from the inverter modulation command signals Vu, Vv, and Vw based on the inverter two-phase modulation signals AI1 to AI6.

[0037] Specifically, for inverter two-phase modulation command signals Vu', Vv', and Vw', at a two-phase modulation control angle θ1 (π / 3 + α≦θ1≦2π / 3-β) where inverter two-phase modulation signal AI1 is high, inverter modulation command signal Vu' is fixed to high and Vv' and Vw' are two-phase modulated. At a two-phase modulation control angle θ2 (π + α≦θ2≦4π / 3-β) where inverter two-phase modulation signal AI2 is high, inverter modulation command signal Vv is fixed to high and Vu' and Vw' are two-phase modulated. At a two-phase modulation control angle θ3 (5π / 3 + α≦θ3≦2π-β) where inverter two-phase modulation signal AI3 is high, inverter modulation command signal Vw is fixed to high and Vu' and Vv' are two-phase modulated. At the two-phase modulation control angle θ4 (4π / 3+α≦θ4≦5π / 3-β) when the inverter two-phase modulation signal AI4 is high, the inverter modulation command signal Vu' is fixed low and Vv' and Vw' are two-phase modulated. At a two-phase modulation control angle θ5 (α≦θ5≦π / 3-β) where inverter two-phase modulation signal AI5 is High, inverter modulation command signal Vv' is fixed to Low and Vu' and Vw' are two-phase modulated. At a two-phase modulation control angle θ6 (2π / 3+α≦θ6≦π-β) where inverter two-phase modulation signal AI6 is High, inverter modulation command signal Vw' is fixed to Low and Vu' and Vv' are two-phase modulated.

[0038] As shown in Figure 6, the inverter two-phase modulation command signals Vu', Vv', and Vw' are signals that fix one of the three phases to high or low at two-phase modulation control angles θ1, θ2, θ3, θ4, θ5, and θ6, and two-phase modulate the remaining two phases. The inverter two-phase modulation command signals Vu', Vv', and Vw' are signals that modulate all three phases at three-phase modulation control angles α and β, i.e., Vu' = Vu, Vv' = Vv, and Vw' = Vw. The three-phase modulation control angle α is the period from when the phase θ reaches nπ / 3 (n is an integer) until the next two-phase modulation control starts, and the three-phase modulation control angle β is the period from when the two-phase modulation control ends until the phase θ reaches nπ / 3.

[0039] Therefore, during the control period with a phase cycle of 60°, the inverter control unit 13 performs PWM control using the two-phase modulation method at two-phase modulation control angles θ1, θ2, θ3, θ4, θ5, and θ6, and PWM control using the three-phase modulation method at three-phase modulation control angles α and β. Here, the three-phase modulation control angles α and β are varied depending on the AC frequency f so that Tα and Tβ are constant, so the time width for three-phase modulation can be kept constant regardless of the frequency, thereby enabling efficient two-phase modulation.

[0040] The configuration in which the inverter control unit 13 according to this embodiment PWM controls the inverter circuit I using two-phase modulation or three-phase modulation has been described with reference to Fig. 6. The converter control unit 12 according to this embodiment may also be configured to similarly PWM control the converter circuit C using two-phase modulation or three-phase modulation.

[0041] Although the present embodiment has been described above, it goes without saying that the technical scope of the present embodiment should not be construed as being limited by the description of the present embodiment. The present embodiment is merely an example, and it will be understood by those skilled in the art that various modifications of the embodiment are possible within the scope of the invention described in the claims. The technical scope of the present embodiment should be determined based on the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0042] 1: Power conversion device 2a to 2c: Input filter capacitors 3a to 3c: Input filter reactor 4a to 4f: semiconductor switching elements 5: Smoothing capacitor 6a to 6f: semiconductor switching elements 7a to 7c: Output filter reactor 8a to 8c: Output filter capacitors 9a, 9b: DC filter reactor 10a, 10b: DC filter capacitors 11: DC power supply (storage battery) 12: Converter control section 13: Inverter control unit 121: Converter modulation command generation unit 131: Inverter modulation command generation unit 122: First two-phase modulation control section 132: Second two-phase modulation control section 123: 1st PWM signal generation section 133: 2nd PWM signal generation section 123a, 133a: Comparator 123b, 133b: Carrier signal generation unit 124, 134: Two-phase modulation signal generator 120: 1st phase locked circuit (PLL circuit) 130:Second phase synchronization circuit (PLL circuit) 126,136: Phase comparison circuit 127,137: Low-pass filter (LPF) 128,138: Voltage controlled oscillator (VCO) 129,139:V / θ conversion section 31a to 31c: Device input terminals 41a to 41c: AC input terminals 42a~42b: DC output terminal 61a to 61b: DC input terminals 62a~62c: AC output terminals 71a to 71c: Device output terminals 91: Three-phase AC power supply 92: AC load C: Converter circuit I: Inverter circuit D: DC circuit F1: Input filter F2: Output filter F3: DC filter n1:neutral line S: Smoothing circuit

Claims

1. a converter circuit connected to a three-phase AC power source and converting AC from the three-phase AC power source into DC; a smoothing circuit connected to a DC output terminal of the converter circuit and including a capacitor; a DC circuit connected to the DC output terminal of the converter circuit and connected in parallel with the smoothing circuit, the DC circuit comprising a DC power supply; an inverter circuit connected to a DC output terminal of the smoothing circuit and a DC output terminal of the DC circuit, for converting the DC from the smoothing circuit or the DC from the DC circuit into AC and outputting the AC to an AC load; a converter control unit that PWM controls the converter circuit using a two-phase modulation method or a three-phase modulation method; an inverter control unit that PWM controls the inverter circuit using a two-phase modulation method or a three-phase modulation method; Equipped with the converter circuit and the inverter circuit are configured as three-phase full-bridge circuits made up of switching elements, a 60° cycle of a control period of the converter circuit and the inverter circuit includes a two-phase modulation control period in which PWM control is performed by a two-phase modulation method and a three-phase modulation control period in which PWM control is performed by a three-phase modulation method; the converter control unit and the inverter control unit control an angle of the three-phase modulation control period based on the frequency of the AC from the three-phase AC power supply and the frequency of the output AC from the inverter circuit so that the time width of the three-phase modulation control period is constant. Power conversion device.

2. the converter control unit and the inverter control unit each have a phase locked loop circuit to which AC is input from the three-phase AC power supply, The power conversion device according to claim 1 , wherein the angle of the three-phase modulation control period is set based on an input value of a voltage-controlled oscillator of the phase-locked loop.

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