JP7807950B2 - Power Conversion Device - Google Patents

Description

The present invention relates to a power conversion device.

A power conversion device is known that is a non-isolated uninterruptible power supply and performs PWM control by switching between two-phase modulation and three-phase modulation.

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 the inverter circuit, and then performs PWM control using a three-phase modulation method while the two-phase modulation phases are being switched. This reduces distortion in the output AC waveform when the two-phase modulation phases are being switched.

Japanese Patent Application Publication No. 09-149660

However, in Patent Document 1, the time width for PWM control in three-phase modulation is determined based on the angle of the sine wave. Therefore, if the frequency of the input AC fluctuates, the time width for three-phase modulation also fluctuates, which could reduce the efficiency of two-phase modulation.

The present invention therefore provides a power conversion device that can perform efficient two-phase modulation.

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 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 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.

According to the present invention, the time width for three-phase modulation is constant, enabling efficient two-phase modulation.

1 is a circuit diagram showing a circuit configuration of a power conversion device according to an embodiment of the present invention. FIG. 1 is a block diagram showing a circuit configuration of a conventional converter control unit. FIG. 1 is a block diagram showing a circuit configuration of a conventional inverter control unit. FIG. 2 is a block diagram showing a circuit configuration of a converter control unit according to the present embodiment. FIG. 2 is a block diagram showing a circuit configuration of an inverter control unit according to the present embodiment. 5A and 5B are diagrams illustrating internal signal waveforms of an inverter control unit according to the present embodiment.

This embodiment will now be described with reference to the drawings. For the sake of simplicity, descriptions of components with the same reference numbers as components already described in the embodiment will be omitted.

Figure 1 is a diagram showing the circuit configuration of a power conversion device 1 according to this embodiment. As shown in Figure 1, a three-phase AC power supply 91 is connected to device input terminals 31a-31c of the power conversion device 1, and an AC load 92, to which three-phase AC output from an inverter circuit I is supplied, is connected to device output terminals 71a-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, an 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.

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

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

Converter circuit C has six semiconductor switching elements 4a-4f connected in a three-phase bridge. The semiconductor switching elements 4a-4f are composed of, for example, IGBTs (insulated gate bipolar transistors) and anti-parallel freewheeling diodes. Converter circuit C is composed of a three-phase (r-phase, s-phase, t-phase) full-bridge circuit. Converter circuit C converts the three-phase AC input from a three-phase AC power source 91 into DC.

The smoothing circuit S includes 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.

Inverter circuit I has six semiconductor switching elements 6a-6f connected in a three-phase bridge. Semiconductor switching elements 6a-6f are composed, for example, of IGBTs and anti-parallel freewheeling diodes. Inverter circuit I is composed of a three-phase (u-phase, v-phase, w-phase) full-bridge circuit. DC input terminals 61a and 61b of inverter circuit I are connected to both pole terminals of smoothing capacitor 5 and one terminal of each DC filter reactor 9a and 9b, respectively. Through the switching operation of semiconductor switching elements 6a-6f, inverter circuit I converts DC from smoothing circuit S (DC output by converter circuit C) to AC, or converts DC from DC circuit D to AC.

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 the 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 the device output terminals 71a-71c of the power conversion device 1, respectively.

One terminal 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 output filter capacitors 8a to 8c is connected to neutral conductor n1, respectively. Output filter F2 passes the AC output from inverter circuit I to AC load 92, while preventing carrier frequency signals generated by inverter circuit I from flowing into AC load 92.

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, respectively. The other terminals of the DC filter reactors 9a and 9b are connected to the DC filter capacitors 10a and 10b and the DC power supply 11, respectively.

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

The converter control unit 12 generates PWM drive signals Vgr, Vgs, and Vgt (see Figure 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 the desired state.

Similarly, the inverter control unit 13 generates PWM drive signals Vgu, Vgv, and Vgw (see Figure 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 the desired state.

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.

The first phase-synchronized circuit 120 is a circuit for outputting a waveform synchronized in phase with the three-phase AC of the three-phase AC power supply 91, 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 the 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 AC of frequency f based on the input voltage V, outputs it to the converter modulation command generation unit 121 and the first two-phase modulation signal generation unit 124, and feeds it back to the phase comparison circuit 126.

The converter modulation command generation 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 generation 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 generation unit 121, and receives the converter two-phase modulation signals AC1 to AC6 from the first two-phase modulation signal generation 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 generation unit 123.

2, the frequency f of the AC generated by the voltage-controlled oscillator 128 is calculated using the voltage V and the frequency conversion coefficient K of the voltage-controlled oscillator 128, as f = V·K. 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 preset in the first two-phase modulation signal generation unit 124, fluctuations in the AC frequency f will also cause fluctuations in the three-phase modulation control times Tα and Tβ, potentially reducing the efficiency of two-phase modulation. Therefore, it is necessary to input the three-phase modulation control angles α and β that keep the three-phase modulation control times Tα and Tβ constant to the first two-phase modulation signal generation unit 124.

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

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.

The second phase-locked loop 130 shown in Figure 3 has a phase comparison circuit 136, a low-pass filter (LPF) 137, a voltage-controlled oscillator (VCO) 138, and a switching circuit SW. During normal operation, the switching circuit SW connects the low-pass filter 137 and the voltage-controlled oscillator 138, 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. Additionally, the configurations of the 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 are similar to the configurations of the 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. 2, respectively, and therefore will not be described here.

Figure 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 Figure 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 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.

The converter modulation command generation 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 generation 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 generation unit 121 and the converter two-phase modulation signals AC1 to AC6 from the first two-phase modulation signal generation 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 generation unit 123.

In Figure 4, the V/θ conversion unit 129 generates three-phase modulation control angles α and β, calculated as α = Tα x 2πVK and β = Tα x 2πVK, based on the input voltage V and preset values Tα and Tβ. Here, the frequency f of the AC generated by the voltage-controlled oscillator 128 has the relationship f = V·K, where f is the voltage V and the frequency conversion coefficient K of the voltage-controlled oscillator 128. Therefore, the α and β generated by the V/θ conversion unit 129 are α = Tα x 2πf and β = Tα x 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.

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, so the time width over which three-phase modulation is performed can be kept constant. This allows for efficient two-phase modulation.

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 will not be described again.

Figure 6 shows internal signal waveforms of the inverter control unit 13 according to this embodiment. In Figure 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'.

The inverter modulation command signals Vu, Vv, and Vw are three-phase modulated signals generated by the inverter modulation command generator 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 generated by partially two-phase modulating the inverter modulation command signals Vu, Vv, and Vw based on the inverter two-phase modulation signals AI1 to AI6.

Specifically, for the 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 the inverter two-phase modulation signal AI1 is High, the 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 the inverter two-phase modulation signal AI2 is High, the 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 the inverter two-phase modulation signal AI3 is High, the inverter modulation command signal Vw is fixed to High and Vu' and Vv' are two-phase modulated. At a two-phase modulation control angle θ4 (4π/3+α≦θ4≦5π/3−β) where the inverter two-phase modulation signal AI4 is High, the inverter modulation command signal Vu′ is fixed to Low, and Vv′ and Vw′ are two-phase modulated.
At a two-phase modulation control angle θ5 (α≦θ5≦π/3−β) where the inverter two-phase modulation signal AI5 is High, the inverter modulation command signal Vv' is fixed Low and Vu' and Vw' are two-phase modulated. At a two-phase modulation control angle θ6 (2π/3+α≦θ6≦π−β) where the inverter two-phase modulation signal AI6 is High, the inverter modulation command signal Vw' is fixed Low and Vu' and Vv' are two-phase modulated.

As shown in FIG. 6 , the inverter two-phase modulation command signals Vu', Vv', and Vw' are signals in which one of the three phases is fixed to high or low at two-phase modulation control angles θ1, θ2, θ3, θ4, θ5, and θ6, and the remaining two phases are two-phase modulated. The inverter two-phase modulation command signals Vu', Vv', and Vw' are signals in which all three phases are three-phase modulated 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 begins, 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.

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 the two-phase modulation control angles θ1, θ2, θ3, θ4, θ5, and θ6, and performs PWM control using the three-phase modulation method at the 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 that the time width for performing three-phase modulation can be kept constant regardless of the frequency, thereby enabling efficient two-phase modulation.

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 using Figure 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.

The present embodiment has been described above, but it goes without saying that the technical scope of this embodiment should not be interpreted as being limited by the description of this embodiment. This 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 this embodiment should be determined based on the scope of the invention described in the claims and its equivalents.

1: Power conversion devices 2a to 2c: Input filter capacitors 3a to 3c: Input filter reactors 4a to 4f: Semiconductor switching elements 5: Smoothing capacitors 6a to 6f: Semiconductor switching elements 7a to 7c: Output filter reactors 8a to 8c: Output filter capacitors 9a, 9b: DC filter reactors 10a, 10b: DC filter capacitor 11: DC power supply (storage battery)
12: Converter control unit 13: Inverter control unit 121: Converter modulation command generation unit 131: Inverter modulation command generation unit 122: First two-phase modulation control unit 132: Second two-phase modulation control unit 123: First PWM signal generation unit 133: Second PWM signal generation unit 123a, 133a: Comparators 123b, 133b: Carrier signal generation units 124, 134: Two-phase modulation signal generation unit 120: First phase locked loop (PLL circuit)
130: Second phase locked circuit (PLL circuit)
126, 136: Phase comparison circuits 127, 137: Low-pass filters (LPF)
128, 138: Voltage controlled oscillator (VCO)
129, 139: V/θ conversion units 31a to 31c: device input terminals 41a to 41c: AC input terminals 42a to 42b: DC output terminals 61a to 61b: DC input terminals 62a to 62c: AC output terminals 71a to 71c: device output terminal 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 wire S: smoothing circuit

Claims (2)

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. 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.