Power Conversion Equipment

Abstract

To provide a power converter that can reduce fluctuation of the potential to the ground of each DC part without using an insulation transformer, and can suppress occurrence of leakage current due to a stray capacitance of each DC part.SOLUTION: A power converter comprises: a boosting chopper circuit 2 for boosting a voltage supplied by a DC power supply 7; voltage dividing capacitors C3 and C4; an inverter circuit 4 having two sets of half-bridge circuits 41 and 42 for converting a DC voltage supplied from the boosting chopper circuit 2 to an AC voltage; a commercial power supply 8 of a three-phase system to which an AC voltage outputted from the inverter circuit 4 is supplied; and a boosting chopper control unit 10 for controlling the boosting chopper circuit 2. The boosting chopper circuit 2 has serially connected switching elements Q1-Q3, reactors L1 and L2, and smoothing capacitors C1 and C2. The chopper control unit 10 controls the switching element Q2 at a constant duty ratio, and also controls each of the switching elements Q1 and Q3 at a periodically fluctuated duty ratio.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, there has been known a power conversion device that converts DC power generated by a solar cell into AC power of a commercial frequency, connects to a commercial grid, and sends the AC power to the grid. For example, Patent Document 1 discloses a solar power conversion device that converts DC power from a solar cell into AC power with a three-phase output, connects to a three-phase grid with one phase grounded, and sends the AC power to the grid.

[0003] The solar power converter of Patent Document 1 includes an inverter circuit having two sets of two switching elements connected in series, two capacitors for dividing a DC voltage are connected in series between the DC inputs of the inverter circuit, an output line is drawn from the connection of the capacitor as one of the three-phase outputs, and output lines are drawn from the midpoints of the two sets of switching elements as the other two three-phase outputs to configure a half-bridge inverter circuit, and the output line drawn from the connection of the capacitor is connected to one phase that is grounded. In addition, the solar power converter of Patent Document 1 uses a DC / DC converter of a boost chopper type to convert a DC power source such as sunlight, which has a low voltage, into a DC voltage for the inverter. By configuring the solar power converter in this way, the fluctuation of the potential to ground in the DC part of the inverter is suppressed without using an insulating transformer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-103768 A Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, Patent Document 1 describes a power conversion device configured to be connected to a three-phase system with one phase grounded (for example, a configuration to be connected to a three-phase, three-wire, V-phase grounded system that is widely used in Japan). However, it does not describe a power conversion device configured to be connected to a system with other grounding systems, such as a system in which one of the windings of a V-connected or delta-connected transformer is grounded at the midpoint of the winding, or a system in which the neutral point of a Y-connected transformer is grounded. Therefore, there is room for further improvement in terms of suppressing fluctuations in the potential to ground of the DC section in a transformerless power conversion device using a boost chopper DC / DC converter.

[0006] The present invention provides a power conversion device that can reduce fluctuations in the potential to ground of each DC part without using an insulating transformer and suppress the occurrence of leakage current due to stray capacitance of each DC part. [Means for solving the problem]

[0007] A power conversion device according to one aspect of the present invention comprises: a boost chopper circuit that boosts a first DC voltage input from a DC power supply and outputs a second DC voltage; a plurality of voltage dividing capacitors connected in series between the positive output terminal and the negative output terminal of the boost chopper circuit; an inverter circuit that converts the second DC voltage into an AC voltage and outputs the AC voltage; a three-phase commercial power source to which the AC voltage output from the inverter circuit is supplied; A boost chopper control unit that controls the boost chopper circuit; Equipped with The boost chopper circuit includes: a first switching element, a second switching element, and a third switching element connected in series between the positive output terminal and the negative output terminal; a first reactor connected between a first connection point between the first switching element and the second switching element and a positive terminal of the DC power supply; a second reactor connected between a second connection point between the second switching element and the third switching element and a negative terminal of the DC power supply; a first smoothing capacitor connected between the positive terminal and the positive output terminal; a second smoothing capacitor connected between the negative terminal and the negative output terminal; having The inverter circuit includes: A first half-bridge circuit and a second half-bridge circuit are configured by connecting two switching elements in series between the positive output terminal and the negative output terminal, one phase of the three-phase system of the commercial power supply is connected to a midpoint of the plurality of voltage dividing capacitors, and the other two phases are connected to a midpoint between a fourth switching element and a fifth switching element in the first half-bridge circuit and a midpoint between a sixth switching element and a seventh switching element in the second half-bridge circuit, the boost chopper control unit on-off controls the first switching element at a first duty ratio, on-off controls the second switching element at a second duty ratio, and on-off controls the third switching element at a third duty ratio; The second duty ratio is constant, and the boost chopper control section periodically varies each of the first duty ratio and the third duty ratio.

[0008] Moreover, a power conversion device according to one aspect of the present invention includes: a boost chopper circuit that boosts a first DC voltage input from a DC power supply and outputs a second DC voltage; a plurality of voltage dividing capacitors connected in series between the positive output terminal and the negative output terminal of the boost chopper circuit; an inverter circuit that converts the second DC voltage into an AC voltage and outputs the AC voltage; a three-phase commercial power source to which the AC voltage output from the inverter circuit is supplied; A boost chopper control unit that controls the boost chopper circuit; Equipped with The boost chopper circuit includes: a first switching element, a second switching element, and a third switching element connected in series between the positive output terminal and the negative output terminal; a first reactor connected between a first connection point between the first switching element and the second switching element and a positive terminal of the DC power supply; a second reactor connected between a second connection point between the second switching element and the third switching element and a negative terminal of the DC power supply; a first smoothing capacitor and a second smoothing capacitor connected in series between the positive electrode terminal and the negative electrode terminal, a midpoint between the first smoothing capacitor and the second smoothing capacitor is connected to a midpoint between the plurality of voltage dividing capacitors; The inverter circuit includes: A first half-bridge circuit and a second half-bridge circuit are configured by connecting two switching elements in series between the positive output terminal and the negative output terminal, one phase of the three-phase system of the commercial power supply is connected to a midpoint of the plurality of voltage dividing capacitors, and the other two phases are connected to a midpoint between a fourth switching element and a fifth switching element in the first half-bridge circuit and a midpoint between a sixth switching element and a seventh switching element in the second half-bridge circuit, the boost chopper control unit on-off controls the first switching element at a first duty ratio, on-off controls the second switching element at a second duty ratio, and on-off controls the third switching element at a third duty ratio; The second duty ratio is constant, and the boost chopper control section periodically varies each of the first duty ratio and the third duty ratio. Effect of the Invention

[0009] According to the present invention, it is possible to provide a power conversion device capable of reducing fluctuations in the potential to ground of each DC part without using an insulating transformer and suppressing the occurrence of leakage current due to stray capacitance of each DC part. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing a circuit configuration of a power conversion device according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a block diagram of a boost chopper control unit that controls the on / off of a switching element at a constant duty ratio. [Diagram 3] 3 is a diagram showing a switching pattern generated by the boost chopper control unit of FIG. 2; FIG. [Figure 4] 4 is a diagram showing a busP-P voltage and a busN-N voltage when switching elements are controlled in accordance with the switching pattern shown in FIG. 3. FIG. [Diagram 5] 4 is a diagram showing voltage waveforms at various points viewed from the midpoint of a transformer winding when switching elements are controlled according to the switching pattern shown in FIG. [Figure 6] This is a configuration diagram of a boost chopper control unit that controls the on / off of a switching element by periodically varying a duty ratio. [Figure 7] 7 is a diagram showing a switching pattern generated by the boost chopper control unit of FIG. 6. FIG. [Figure 8] 7 is a diagram showing a busP-P voltage and a busN-N voltage when switching elements are controlled in accordance with the switching pattern shown in FIG. 6. FIG. [Figure 9] 7 is a diagram showing voltage waveforms at various points as viewed from the midpoint of a transformer winding when switching elements are controlled according to the switching pattern shown in FIG. 6. [Figure 10] 1A shows a system in which the neutral point of a Y-connected transformer is grounded, and FIG. 1B shows a system in which the S phase of a delta-connected transformer is grounded. [Figure 11]10(a) shows voltage waveforms at various points when switching elements are on-off controlled at a constant duty ratio in the system shown in FIG. [Figure 12] 10(a) shows voltage waveforms at various points when switching elements are on / off controlled with a duty ratio that periodically varies the switching elements in the system shown in FIG. [Figure 13] 10(b) shows voltage waveforms at various points when switching elements are on-off controlled at a constant duty ratio in the system shown in FIG. [Figure 14] FIG. 13 is a diagram showing a circuit configuration of a power conversion device according to a modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For the sake of convenience, the description of the components having the same reference numbers as those already described in the description of the embodiment will be omitted. Also, for the sake of convenience, the dimensions of each component shown in the drawings may differ from the actual dimensions of each component.

[0012] Fig. 1 is a diagram showing a circuit configuration of a power conversion device according to an embodiment of the present invention. The power conversion device converts DC power into three-phase AC power and transmits the AC power to an interconnected three-phase system. As shown in Fig. 1, the power conversion device 1 includes a boost chopper circuit 2, a voltage dividing capacitor 3, an inverter circuit 4, a filter circuit 5, and a control circuit 6. A DC power source 7 is connected to the input side of the boost chopper circuit 2. A three-phase commercial power source 8 is connected to the output side of the filter circuit 5. The control circuit 6 includes a boost chopper control unit 10 that controls the boost chopper circuit 2, and an inverter control unit 20 that controls the inverter circuit 4.

[0013] The boost chopper circuit 2 boosts a first DC voltage input from a DC power source 7 to a second DC voltage, and outputs the boosted second DC voltage to the inverter circuit 4. The boost chopper circuit 2 has a first switching element Q1, a second switching element Q2, a third switching element Q3, a first reactor L1, a second reactor L2, a first smoothing capacitor C1, and a second smoothing capacitor C2.

[0014] The first switching element Q1, the second switching element Q2, and the third switching element Q3 are connected in series between the positive output terminal 21a and the negative output terminal 21b of the boost chopper circuit 2. These switching elements Q1 to Q3 are each composed of, for example, an IGBT (insulated gate bipolar transistor) and a free wheel diode connected in anti-parallel.

[0015] The first reactor L1 is connected between a first connection point 22a between the first switching element Q1 and the second switching element Q2 and the positive terminal P of the DC power supply 7. The second reactor L2 is connected between a second connection point 22b between the second switching element Q2 and the third switching element Q3 and the negative terminal N of the DC power supply 7.

[0016] The first smoothing capacitor C1 is connected between the positive terminal P of the DC power supply 7 and the positive output terminal 21a of the boost chopper circuit 2. The second smoothing capacitor C2 is connected between the negative terminal N of the DC power supply 7 and the negative output terminal 21b of the boost chopper circuit 2.

[0017] The voltage dividing capacitor 3 is connected between the positive output terminal 21a and the negative output terminal 21b of the boost chopper circuit 2. The voltage dividing capacitor 3 is connected in parallel with the first switching element Q1, the second switching element Q2, and the third switching element Q3, which are connected in series in the boost chopper circuit 2. In the example shown in the figure, the voltage dividing capacitor 3 is composed of a first voltage dividing capacitor C3 and a second voltage dividing capacitor C4. The first voltage dividing capacitor C3 and the second voltage dividing capacitor C4 are connected in series. The number of capacitors is not limited to two.

[0018] An intermediate point 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4 is connected to the S-phase of the three-phase commercial power source 8. A terminal 31a of the first voltage dividing capacitor C3 opposite to the intermediate point 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4 is connected to the positive output terminal 21a of the boost chopper circuit 2. A terminal 31b of the second voltage dividing capacitor C4 opposite to the intermediate point 31c between the first voltage dividing capacitor C3 and the negative output terminal 21b of the boost chopper circuit 2. It is preferable that the capacitance of the first voltage dividing capacitor C3 and the capacitance of the second voltage dividing capacitor C4 are as close as possible.

[0019] The inverter circuit 4 converts the second DC voltage, which is the output voltage of the boost chopper circuit 2, into an AC voltage and outputs it. The inverter circuit 4 has a first half-bridge circuit 41 and a second half-bridge circuit 42. The first half-bridge circuit 41 is composed of a fourth switching element Q11 and a fifth switching element Q12. The second half-bridge circuit 42 is composed of a sixth switching element Q13 and a seventh switching element Q14.

[0020] The fourth switching element Q11 and the fifth switching element Q12 are connected in series. The sixth switching element Q13 and the seventh switching element Q14 are connected in series. The fourth switching element Q11 and the fifth switching element Q12, and the sixth switching element Q13 and the seventh switching element Q14 are connected between the positive output terminal 21a and the negative output terminal 21b of the boost chopper circuit 2, similar to the voltage dividing capacitor 3 (the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4).

[0021] The filter circuit 5 includes a first filter reactor L3, a second filter reactor L4, a first filter capacitor C5, and a second filter capacitor C6. One terminal of the first filter reactor L3 is connected to an intermediate point 43 between the fourth switching element Q11 and the fifth switching element Q12 in the first half-bridge circuit 41 of the inverter circuit 4. The other terminal of the first filter reactor L3 is connected to the R phase of the three-phase commercial power supply 8. One terminal of the second filter reactor L4 is connected to an intermediate point 44 between the sixth switching element Q13 and the seventh switching element Q14 in the second half-bridge circuit 42 of the inverter circuit 4. The other terminal of the second filter reactor L4 is connected to the T phase of the three-phase commercial power supply 8.

[0022] One terminal of the first filter capacitor C5 is connected to a terminal of the first filter reactor L3 on the commercial power supply 8 side. The other terminal of the first filter capacitor C5 is connected to an intermediate point 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4. One terminal of the second filter capacitor C6 is connected to a terminal of the second filter reactor L4 on the commercial power supply 8 side. The other terminal of the second filter capacitor C6 is connected to the intermediate point 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4.

[0023] The first half-bridge circuit 41 generates an AC voltage between an intermediate point 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4, and an intermediate point 43 between the fourth switching element Q11 and the fifth switching element Q12. The first filter reactor L3 and the first filter capacitor C5 of the filter circuit 5 allow the AC voltage output from the first half-bridge circuit 41 to pass to the commercial power supply 8, and prevent a carrier frequency signal generated by the switching of the first half-bridge circuit 41 from passing to the commercial power supply 8.

[0024] The second half-bridge circuit 42 generates an AC voltage between an intermediate point 31c between the first voltage-dividing capacitor C3 and the second voltage-dividing capacitor C4 and an intermediate point 44 between the sixth switching element Q13 and the seventh switching element Q14. The second filter reactor L4 and the second filter capacitor C6 of the filter circuit 5 allow the AC voltage output from the second half-bridge circuit 42 to pass to the commercial power supply 8, and prevent a carrier frequency signal generated by the switching of the second half-bridge circuit 42 from passing to the commercial power supply 8.

[0025] The DC power supply 7 has a positive terminal P connected to a connection point between the first reactor L1 and the first smoothing capacitor C1, and a negative terminal N connected to a connection point between the second reactor L2 and the second smoothing capacitor C2. An example of the DC voltage of the DC power supply 7 is a DC voltage generated by a solar cell. Reference characters CE1 and CE2 connected to the positive terminal P and the negative terminal N of the DC power supply 7 represent floating capacitance of the DC power supply 7 to ground.

[0026] The commercial power supply 8 is supplied with the AC voltage output from the inverter circuit 4. The commercial power supply 8 is, for example, a three-phase, three-wire system. For example, the commercial power supply 8 has one of the V-connected transformer windings grounded at midpoint M. The commercial power supply 8 shown in the figure is grounded at midpoint M between the R and S wires of the V-connected transformer winding. The S-phase voltage with respect to midpoint M is half the line-to-line voltage between RS. Therefore, the voltage at midpoint 31c of the voltage-dividing capacitor 3 connected to the S-phase is half the voltage between RS.

[0027] The boost chopper control unit 10 controls the on / off of the switching elements Q1 to Q3 of the boost chopper circuit 2 with a predetermined duty ratio. For example, the boost chopper control unit 10 controls the on / off of the second switching element Q2 with a constant duty ratio, and controls the on / off of the first switching element Q1 and the third switching element Q3 with a duty ratio that varies periodically. Specifically, the boost chopper control unit 10 controls the on / off of the first switching element Q1 and the third switching element Q3 by varying the duty ratio periodically based on the voltage applied between the grounded midpoint M of the commercial power source 8 and the S phase to which the midpoint 31c of the voltage dividing capacitor 3 is connected.

[0028] The inverter control unit 20 controls the switching of the switching elements Q11 to Q14 of the inverter circuit 4 to a desired state. The inverter control unit 20 controls the inverter circuit 4 so that R-phase AC power is output from a midpoint 43 between the fourth switching element Q11 and the fifth switching element Q12 of the first half-bridge circuit 41, and T-phase AC power is output from a midpoint 44 between the sixth switching element Q13 and the seventh switching element Q14 of the second half-bridge circuit 42. Specifically, the inverter control unit 20 compares the control waveform with a carrier triangular wave, and generates a drive waveform in which the upper switching elements Q11 and Q13 are turned on and the lower switching elements Q12 and Q14 are turned off when the control waveform is smaller. In addition, the inverter control unit 20 generates a drive waveform in which the lower switching elements Q12 and Q14 are turned on and the upper switching elements Q11 and Q13 are turned off when the control waveform is smaller.

[0029] Next, the switching control of the boost chopper circuit 2 (switching elements Q1 to Q3) by the boost chopper control unit 10 will be described below.

[0030] As described above, the boost chopper control unit 10 in the power conversion device 1 of the present invention controls the on-off of the second switching element Q2 of the boost chopper circuit 2 at a constant duty ratio, and controls the on-off of the first switching element Q1 and the third switching element Q3 at duty ratios that vary periodically. First, as a comparative example, a case in which the boost chopper control unit 10 controls the first switching element Q1 to the third switching element Q3 of the boost chopper circuit 2 to turn on and off with a constant duty ratio will be described with reference to FIGS. 2 to 5.

[0031] Fig. 2 is a configuration diagram of the boost chopper control unit 10 when controlling the on / off of the first switching element Q1 to the third switching element Q3 at a constant duty ratio. As shown in Fig. 2, the boost chopper control unit 10 compares a constant voltage chopper control signal 11 with a carrier triangular wave 12 by a comparator 13 to generate a second gate signal that controls the second switching element Q2. Then, the boost chopper control unit 10 inverts the generated second gate signal by an inverter 14 to generate a first gate signal and a third gate signal that control the first switching element Q1 and the third switching element Q3.

[0032] Fig. 3 is a diagram showing switching patterns of the first gate signal to the third gate signal generated by the boost chopper control unit 10. As shown in Fig. 3, the switching patterns of the first gate signal to the third gate signal which control the on / off of the first switching element Q1 to the third switching element Q3 all have a constant duty ratio. The switching patterns of the first gate signal which controls the first switching element Q1 and the third gate signal which controls the third switching element Q3 are switching patterns in which the on / off is inverted with respect to the switching pattern of the second gate signal which controls the second switching element Q2.

[0033] FIG. 4 is a diagram showing the voltage of the positive output terminal 21a of the boost chopper circuit 2 with respect to the voltage of the positive terminal P of the DC power supply 7, and the voltage of the negative output terminal 21b of the boost chopper circuit 2 with respect to the voltage of the negative terminal N of the DC power supply 7, when the first switching element Q1 to the third switching element Q3 are on-off controlled by the switching pattern of the first gate signal to the third gate signal shown in FIG.

[0034] As shown in FIG. 4, the voltage of the positive output terminal 21a of the boost chopper circuit 2 with respect to the voltage of the positive terminal P of the DC power supply 7 at this time is a constant voltage of "busP-P voltage" = "bus voltage / 2" - "DC input voltage / 2" = 150V. Also, the voltage of the negative output terminal 21b of the boost chopper circuit 2 with respect to the voltage of the negative terminal N of the DC power supply 7 is a constant voltage of "busN-N voltage" = "DC input voltage / 2" - "bus voltage / 2" = -150V. Note that the boost chopper circuit 2 of this embodiment is a circuit that boosts DC 300V (first DC voltage) between the positive terminal P and the negative terminal N input from the DC power supply 7 to DC 600V (second DC voltage) and outputs it between the positive output terminal 21a and the negative output terminal 21b.

[0035] Fig. 5 is a diagram showing voltage waveforms of each part as viewed from midpoint M of commercial power supply 8 when the first switching element Q1 to the third switching element Q3 are on / off controlled by the switching pattern of the first gate signal to the third gate signal shown in Fig. 3. As described above, midpoint M is a grounded point (E).

[0036] As shown in Figure 5, the voltage at midpoint 31c of voltage-dividing capacitor 3 as viewed from midpoint M of commercial power supply 8 at this time ("voltage between bus0 and E") is the S-phase voltage as viewed from midpoint M (ground E) (the voltage between SE of the three-phase system), and has a voltage waveform centered on DC 0V with an AC component of AC 100V superimposed.

[0037] Furthermore, the voltage at the positive terminal P of the DC power supply 7 as viewed from the midpoint M of the commercial power supply 8 ("voltage between PE") has a voltage waveform centered at DC 150 V with an AC component of AC 100 V superimposed thereon. The voltage at the negative terminal N of the DC power supply 7 as viewed from the midpoint M of the commercial power supply 8 ("voltage between NE") has a voltage waveform centered at DC -150 V with an AC component of AC 100 V superimposed thereon.

[0038] Also, the voltage at the positive output terminal 21a of the boost chopper circuit 2 as viewed from the midpoint M of the commercial power supply 8 ("bus P-E voltage") has a voltage waveform with an AC component of AC 100V superimposed around DC 300V. The voltage at the negative output terminal 21b of the boost chopper circuit 2 as viewed from the midpoint M of the commercial power supply 8 ("bus N-E voltage") has a voltage waveform with an AC component of AC 100V superimposed around DC -300V.

[0039] 3, the potential to ground of the positive electrode terminal P and the negative electrode terminal N of the DC power supply 7 and the voltage to ground of the positive electrode output terminal 21a and the negative electrode output terminal 21b of the boost chopper circuit 2 fluctuate with the frequency (50 / 60 Hz) and voltage (AC component AC100V) of the commercial power supply 8. For this reason, for example, a leakage current flows between the positive electrode terminal P and the negative electrode terminal N and the ground via the stray capacitances to ground CE1 and CE2.

[0040] Next, a case where the boost chopper control unit 10 controls the second switching element Q2 of the boost chopper circuit 2 to be on / off controlled at a constant duty ratio, and controls the first switching element Q1 and the third switching element Q3 to be on / off controlled at duty ratios that vary periodically will be described with reference to Figs. 6 to 9.

[0041] 6 is a configuration diagram of the boost chopper control unit 10 when controlling the on / off of the second switching element Q2 with a constant duty ratio, and the first switching element Q1 and the third switching element Q3 with duty ratios that vary periodically. As shown in Fig. 6, the boost chopper control unit 10 compares a chopper control signal 11 with a carrier triangular wave 12 by a comparator 13 to generate a second gate signal that controls the second switching element Q2. This control is the same as that described in Fig. 2.

[0042] The boost chopper control unit 10 inputs the duty modulation signal 15 for varying the duty ratio for controlling the on / off of the first switching element Q1 and the third switching element Q3, and the chopper control signal 11, to a subtractor 16 to calculate the difference. The boost chopper control unit 10 inputs the output of the subtractor 16 to a comparator 17, which compares it with the carrier triangular wave 12 to generate a first gate signal for controlling the first switching element Q1. The duty modulation signal 15 is a signal that matches the voltage between the midpoints M and S of the power supply system, or a half voltage of the line voltage between RS of the power supply system, to a voltage level controlled in the boost chopper control unit 10. The voltage between the midpoints M and S, and the half voltage of the line voltage between RS, are voltages with AC 100V of AC component superimposed around DC 0V as described in FIG. 2.

[0043] The boost chopper control unit 10 also inputs a duty modulation signal 15 for varying the duty ratio for controlling the on / off of the first switching element Q1 and the third switching element Q3, and the chopper control signal 11 to an adder 18 for addition. The boost chopper control unit 10 inputs the output of the adder 18 to a comparator 19, which compares the output with the carrier triangular wave 12 to generate a third gate signal for controlling the third switching element Q3.

[0044] Furthermore, the boost chopper control unit 10 differentiates the polarity of the input terminals of the comparators 17 and 19 to which the carrier triangular wave 12 is input from the polarity of the input terminal of the comparator 13 to which the carrier triangular wave 12 is input, so that the first gate signal output from the comparator 17 and the third gate signal output from the comparator 19 have polarity that is inverted with respect to the second gate signal output from the comparator 13. In the illustrated example, the carrier triangular wave 12 is input to the inverting input terminal of the comparator 13, and the carrier triangular wave 12 is input to the non-inverting input terminal of the comparators 17 and 19.

[0045] FIG. 7 is a diagram showing switching patterns of the first gate signal to the third gate signal generated by the boost chopper control unit 10 shown in FIG. 6. As shown in FIG. 7, the switching pattern of the second gate signal for controlling the on / off of the second switching element Q2 has a constant duty ratio as shown by the dashed line 51. The switching patterns of the first gate signal for controlling the on / off of the first switching element Q1 and the third gate signal for controlling the on / off of the third switching element Q3 are modulated by the duty modulation signal 15, and the duty ratios are periodically changed based on a switching pattern in which the on / off is inverted with respect to the switching pattern of the second gate signal as shown by the dashed lines 52 and 53. Furthermore, the switching patterns of the first gate signal and the third gate signal have a duty ratio that is periodically changed in magnitude inverse to that of the switching pattern of the first gate signal.

[0046] FIG. 8 is a diagram showing the voltage of the positive output terminal 21a of the boost chopper circuit 2 relative to the voltage of the positive terminal P of the DC power supply 7 (busP voltage) and the voltage of the negative output terminal 21b of the boost chopper circuit 2 relative to the voltage of the negative terminal N of the DC power supply 7 (busN voltage) when the first switching element Q1 to the third switching element Q3 are on / off controlled by the switching pattern of the first gate signal to the third gate signal shown in FIG.

[0047] 8, the voltage of the positive output terminal 21a of the boost chopper circuit 2 relative to the voltage of the positive terminal P of the DC power supply 7 at this time is "busP-P voltage" = "bus voltage / 2" - "DC input voltage / 2" + "SE voltage of the three-phase system" = "voltage with AC component of AC100V superimposed around DC150V." Also, the voltage of the negative output terminal 21b of the boost chopper circuit 2 relative to the voltage of the negative terminal N of the DC power supply 7 is "busN-N voltage" = "DC input voltage / 2" - "bus voltage / 2" + "SE voltage of the three-phase system" = "voltage with AC component of AC100V superimposed around DC-150V."

[0048] FIG. 9 is a diagram showing voltage waveforms at various parts viewed from midpoint M of commercial power supply 8 when the first switching element Q1 to the third switching element Q3 are on / off controlled by the switching pattern of the first gate signal to the third gate signal shown in FIG.

[0049] As shown in Figure 9, the voltage at midpoint 31c of voltage-dividing capacitor 3 as viewed from midpoint M of commercial power supply 8 at this time ("voltage between bus0 and E") is the S-phase voltage as viewed from midpoint M (ground E) (the voltage between SE of the three-phase system), and has a voltage waveform centered on DC 0V with an AC component of AC 100V superimposed.

[0050] Also, the voltage at the positive terminal P of the DC power supply 7 as viewed from the midpoint M of the commercial power supply 8 ("PE voltage") becomes a constant DC voltage of DC 150V as the superimposed S-E voltage of the three-phase system (AC 100V with AC component centered around DC 150V) as shown in Fig. 5 is cancelled out. Similarly, the voltage at the negative terminal N of the DC power supply 7 ("NE voltage") as viewed from the midpoint M of the commercial power supply 8 becomes a constant DC voltage of DC 150V as the superimposed N-E voltage of the three-phase system is cancelled out.

[0051] Also, the voltage at the positive output terminal 21a of the boost chopper circuit 2 as viewed from the midpoint M of the commercial power supply 8 ("bus P-E voltage") has a voltage waveform with an AC component of AC 100V superimposed around DC 300V. The voltage at the negative output terminal 21b of the boost chopper circuit 2 as viewed from the midpoint M of the commercial power supply 8 ("bus N-E voltage") has a voltage waveform with an AC component of AC 100V superimposed around DC -300V.

[0052] In this way, when the switching elements Q1 to Q3 are on / off controlled in the switching pattern shown in Fig. 7, the SE voltage of the three-phase system is added to the busP-P and busN-N voltages, so that the "PE voltage" and "NE voltage", i.e., the ground potentials of the positive terminal P and negative terminal N of the DC power supply 7, become DC voltages that do not fluctuate. Therefore, for example, leakage currents flowing to the ground stray capacitances CE1 and CE2 between the positive terminal P and negative terminal N and ground are suppressed. Note that, in the example shown in the figure, the case where the midpoint M of the R line and S line of the transformer winding is grounded has been described, but even when the midpoint of the S line and T line is grounded, the ground potentials of the positive terminal P and negative terminal N of the DC power supply 7 become DC voltages that do not fluctuate.

[0053] In the above embodiment, the commercial power source 8 is a three-phase system in which the midpoint of one of the V-connected transformer windings is grounded, but the present invention is not limited to this. For example, the commercial power source 8 may be of a system in which the neutral point of a Y-connected transformer is grounded, as shown in Fig. 10(a). Moreover, the commercial power source 8 may be of a system in which, for example, the S phase of a delta connection is grounded, as shown in Fig. 10(b).

[0054] FIG. 11 is a diagram showing voltage waveforms of various parts viewed from the neutral point of commercial power supply 8 when the first switching element Q1 to the third switching element Q3 are on / off controlled by the switching patterns of the first gate signal to the third gate signal shown in FIG. 3 in commercial power supply 8 with a Y connection and neutral point grounded as shown in FIG. 10(a), i.e., when the switching patterns of the first gate signal to the third gate signal all have a constant duty ratio.

[0055] As shown in Figure 11, when the switching patterns of the first gate signal to the third gate signal all have a constant duty ratio, the ground potentials of the positive terminal P and negative terminal N of the DC power supply 7 ("PE voltage" and "NE voltage") and the ground voltages of the positive output terminal 21a and negative output terminal 21b of the boost chopper circuit 2 ("busP-E voltage" and "busN-E voltage") fluctuate with the frequency (50 / 60Hz) and voltage (AC component AC115V in this system) of the commercial power supply 8, similar to the voltage waveforms (see Figure 5) when the midpoint M of the R line and S line of the V connection is grounded.

[0056] Fig. 12 is a diagram showing voltage waveforms of each part seen from the neutral point of the commercial power supply 8 when the duty modulation signal 15 shown in Fig. 6 is replaced with a signal that matches the voltage level between the neutral point of the Y connection and S in the boost chopper control unit 10, and the first switching element Q1 to the third switching element Q3 are on / off controlled with the switching patterns of the first gate signal to the third gate signal shown in Fig. 7 in the commercial power supply 8 with the neutral point of the Y connection grounded shown in Fig. 10(a), that is, when the switching pattern of the second gate signal has a constant duty ratio and the switching patterns of the first gate signal and the third gate signal each have a duty ratio that varies periodically. Here, the neutral point voltage of the Y connection may be a voltage obtained by resistor division from R, S, and T or by capacitor division. It may also be a voltage obtained by (RS voltage + TS voltage) / 3.

[0057] As shown in Figure 12, when the switching pattern of the second gate signal has a constant duty ratio and the switching patterns of the first gate signal and the third gate signal each have a duty ratio that varies periodically, the SE voltage of the three-phase system is added to the busP-P and busN-N voltages, similar to the voltage waveform (see Figure 9) when the midpoint M of the R and S lines of the V connection is grounded, so that the "PE voltage" and "NE voltage", i.e., the ground potentials of the positive terminal P and negative terminal N of the DC power supply 7, become DC voltages that do not fluctuate.

[0058] FIG. 13 is a diagram showing voltage waveforms of each part as viewed from the S phase of commercial power supply 8 when the first switching element Q1 to the third switching element Q3 are on / off controlled by the switching patterns of the first to third gate signals shown in FIG. 3 in the delta-connected S-phase-grounded commercial power supply 8 shown in FIG. 10(b), i.e., when the switching patterns of the first to third gate signals all have a constant duty ratio.

[0059] 13, in the case of delta connection with S-phase ground, even if the switching patterns of the first gate signal to the third gate signal all have a constant duty ratio, the potentials to ground of the positive terminal P and negative terminal N of the DC power supply 7 ("PE voltage" and "NE voltage") and the voltages to ground of the positive output terminal 21a and negative output terminal 21b of the boost chopper circuit 2 ("busP-E voltage" and "busN-E voltage") become DC voltages that do not fluctuate. Therefore, in the case of delta connection with S-phase ground, there is no need to perform control that periodically varies the duty ratio in the switching patterns of the gate signals when the commercial power supply 8 is delta connection with S-phase ground.

[0060] As described above, the power conversion device 1 according to this embodiment includes the boost chopper circuit 2 that boosts a first DC voltage input from a DC power source 7 and outputs a second DC voltage, a voltage dividing capacitor 3 that is composed of a first voltage dividing capacitor C3 and a second voltage dividing capacitor C4 connected in series between the positive output terminal 21a and the negative output terminal 21b of the boost chopper circuit 2, an inverter circuit 4 that converts the second DC voltage into an AC voltage and outputs it, a three-phase commercial power source 8 to which the AC voltage output from the inverter circuit 4 is supplied, and a boost chopper control unit 10 that controls the boost chopper circuit 2. The boost chopper circuit 2 includes a first switching element Q1, a second switching element Q2, and a third switching element Q3 connected in series between the positive output terminal 21a and the negative output terminal 21b, a first reactor L1 connected between a first connection point 22a between the first switching element Q1 and the second switching element Q2 and the positive terminal P of the DC power source 7, a second reactor L2 connected between a second connection point 22b between the second switching element Q2 and the third switching element Q3 and the negative terminal N of the DC power source 7, a first smoothing capacitor C1 connected between the positive terminal P of the DC power source 7 and the positive output terminal 21a, and a second smoothing capacitor C2 connected between the negative terminal N of the DC power source 7 and the negative output terminal 21b. The inverter circuit 4 includes a first half-bridge circuit including switching elements Q11 and Q12 connected in series between the positive output terminal 21a and the negative output terminal 21b, and a second half-bridge circuit 42 including switching elements Q13 and Q14 connected in series. One phase of the three-phase system of the commercial power source 8 is connected to an intermediate point 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4, and the other two phases are connected to an intermediate point 43 between the fourth switching element Q11 and the fifth switching element Q12 in the first half-bridge circuit 41 and an intermediate point 44 between the sixth switching element Q13 and the seventh switching element Q14 in the second half-bridge circuit 42, respectively.The chopper control unit 10 controls the first switching element Q1 to be turned on and off at a first duty ratio, controls the second switching element Q2 to be turned on and off at a second duty ratio, controls the third switching element Q3 to be turned on and off at a third duty ratio, controls the second duty ratio to be constant, and periodically varies the first duty ratio and the third duty ratio. According to this configuration, by periodically varying the on and off duty ratios of the first switching element Q1 and the third switching element Q3 constituting the boost chopper circuit 2, it is possible to suppress the fluctuation of the potential to ground at the positive terminal P and the negative terminal N of the DC power supply 7. This makes it possible to suppress the occurrence of leakage current due to the stray capacitance of the DC power supply 7 without using an insulating transformer.

[0061] Furthermore, the power conversion device 1 can suppress fluctuations in the ground potential of the DC voltage for a commercial power supply 8 in which one of the V-connected or delta-connected transformer windings is grounded at the midpoint of the transformer winding, or for a commercial power supply 8 in which the neutral point of a Y-connected transformer is grounded.

[0062] Moreover, according to the power conversion device 1, the boost chopper control unit 10 periodically varies the first duty ratio and the third duty ratio, based on the voltage applied between the grounded midpoint M or the grounded neutral point and one phase to which the midpoint 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4 is connected. In this way, by varying the duty ratios of the switching elements Q1 and Q3 using the voltage applied between the grounded midpoint M or the neutral point and one phase to which the midpoint 31c of the voltage dividing capacitors is connected, it is possible to appropriately suppress the variation in the potential to ground at the positive terminal P and the negative terminal N of the DC power source 7.

[0063] (Modification) Next, a modification of the power conversion device will be described. Fig. 14 is a diagram showing a circuit configuration of a power conversion device 100 according to a modified example. As shown in Fig. 14, the power conversion device 100 has a boost chopper circuit 120 having a different configuration from the boost chopper circuit 2 of the power conversion device 1 shown in Fig. 1.

[0064] In the boost chopper circuit 120 of the power conversion device 100, a first smoothing capacitor C1 and a second smoothing capacitor C2 are connected in series between the positive terminal P and the negative terminal N of the DC power supply 7. That is, the first smoothing capacitor C1 and the second smoothing capacitor C2 are connected in series between a connection point 23a between the first reactor L1 and the positive terminal P and a connection point 23b between the second reactor L2 and the negative terminal N. Then, a midpoint 23c between the first smoothing capacitor C1 and the second smoothing capacitor C2 is connected to a midpoint 31c between the first voltage dividing capacitor C3 and the second voltage dividing capacitor C4.

[0065] The configurations of the voltage dividing capacitor 3, inverter circuit 4, filter circuit 5, and control circuit 6 (boost chopper control unit 10, inverter control unit 20) in the power conversion device 100 are similar to those in the power conversion device 1. In addition, the DC power supply 7 connected to the input side of the boost chopper circuit 2 and the commercial power supply 8 connected to the output side of the filter circuit 5 are also similar to those in the power conversion device 1.

[0066] 6 and 7 in the power conversion device 1, the boost chopper control unit 10 controls the second switching element Q2 to be on / off at a constant duty ratio, and controls the first switching element Q1 and the third switching element Q3 to be on / off at duty ratios that vary periodically. The boost chopper control unit 10 controls the first switching element Q1 and the third switching element Q3 to be on / off by periodically varying the duty ratios, based on the voltage applied between the grounded midpoint M of the commercial power source 8 and the S phase to which the midpoint 31c of the voltage dividing capacitor 3 is connected.

[0067] Similarly to the power conversion device 1 of the embodiment, the configuration of the power conversion device 100 according to the above modification also makes it possible to suppress fluctuations in the ground potential at the positive terminal P and the negative terminal N of the DC power supply 7 by periodically varying the on-off duty ratio of the first switching element Q1 and the third switching element Q3 that constitute the boost chopper circuit 120. This makes it possible to suppress the occurrence of leakage current due to the stray capacitance of the DC power supply 7 without using an insulating transformer.

[0068] Although the embodiment of the present invention has been described above, it goes without saying that the technical scope of the present invention should not be interpreted as being limited by the description of the embodiment. The embodiment is merely an example, and it is 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 invention should be determined based on the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0069] 1 Power conversion device 2. Boost chopper circuit 3. Voltage divider capacitor 4. Inverter Circuit 5. Filter Circuit 6 Control Circuit 7 DC power supply 8 Commercial power supply 10 Boost chopper control section 13,17,19 Comparator 14 Inverter 15 Duty Modulation Signal 16 Subtractor 18 Adder 20 Inverter control unit 21a Positive output terminal 21b Negative output terminal 22a First connection point 22b Second connection point 31a Terminal 31b terminal 31c midpoint 41 First half-bridge circuit 42 Second half-bridge circuit 43,44 Midpoint C1 First smoothing capacitor C2 Second smoothing capacitor C3 First voltage divider capacitor C4 Second voltage divider capacitor C5 First filter capacitor C6 Second filter capacitor L1 First reactor L2 Second reactor L3 First filter reactor L4 Second filter reactor N negative terminal P positive terminal Q1 First switching element Q2 Second switching element Q3 Third switching element Q11 Fourth switching element Q12 Fifth switching element Q13 Sixth switching element Q14 Seventh switching element

Claims

1. a boost chopper circuit that boosts a first DC voltage input from a DC power supply and outputs a second DC voltage; a plurality of voltage dividing capacitors connected in series between the positive output terminal and the negative output terminal of the boost chopper circuit; an inverter circuit that converts the second DC voltage into an AC voltage and outputs the AC voltage; a three-phase commercial power source to which the AC voltage output from the inverter circuit is supplied; A boost chopper control unit that controls the boost chopper circuit; Equipped with The boost chopper circuit includes: a first switching element, a second switching element, and a third switching element connected in series between the positive output terminal and the negative output terminal; a first reactor connected between a first connection point between the first switching element and the second switching element and a positive terminal of the DC power supply; a second reactor connected between a second connection point between the second switching element and the third switching element and a negative terminal of the DC power supply; a first smoothing capacitor connected between the positive terminal and the positive output terminal; a second smoothing capacitor connected between the negative terminal and the negative output terminal; having The inverter circuit includes: A first half-bridge circuit and a second half-bridge circuit are configured by connecting two switching elements in series between the positive output terminal and the negative output terminal, one phase of the three-phase system of the commercial power supply is connected to a midpoint of the plurality of voltage dividing capacitors, and the other two phases are connected to a midpoint between a fourth switching element and a fifth switching element in the first half-bridge circuit and a midpoint between a sixth switching element and a seventh switching element in the second half-bridge circuit, the boost chopper control unit controls the first switching element to be turned on and off at a first duty ratio, controls the second switching element to be turned on and off at a second duty ratio, and controls the third switching element to be turned on and off at a third duty ratio; the second duty ratio is constant, and the boost chopper control unit periodically varies each of the first duty ratio and the third duty ratio. Power conversion equipment.

2. a boost chopper circuit that boosts a first DC voltage input from a DC power supply and outputs a second DC voltage; a plurality of voltage dividing capacitors connected in series between the positive output terminal and the negative output terminal of the boost chopper circuit; an inverter circuit that converts the second DC voltage into an AC voltage and outputs the AC voltage; a three-phase commercial power source to which the AC voltage output from the inverter circuit is supplied; A boost chopper control unit that controls the boost chopper circuit; Equipped with The boost chopper circuit includes: a first switching element, a second switching element, and a third switching element connected in series between the positive output terminal and the negative output terminal; a first reactor connected between a first connection point between the first switching element and the second switching element and a positive terminal of the DC power supply; a second reactor connected between a second connection point between the second switching element and the third switching element and a negative terminal of the DC power supply; a first smoothing capacitor and a second smoothing capacitor connected in series between the positive electrode terminal and the negative electrode terminal, a midpoint between the first smoothing capacitor and the second smoothing capacitor is connected to a midpoint between the plurality of voltage dividing capacitors; The inverter circuit includes: A first half-bridge circuit and a second half-bridge circuit are configured by connecting two switching elements in series between the positive output terminal and the negative output terminal, one phase of the three-phase system of the commercial power supply is connected to a midpoint of the plurality of voltage dividing capacitors, and the other two phases are connected to a midpoint between a fourth switching element and a fifth switching element in the first half-bridge circuit and a midpoint between a sixth switching element and a seventh switching element in the second half-bridge circuit, the boost chopper control unit controls the first switching element to be turned on and off at a first duty ratio, controls the second switching element to be turned on and off at a second duty ratio, and controls the third switching element to be turned on and off at a third duty ratio; the second duty ratio is constant, and the boost chopper control unit periodically varies each of the first duty ratio and the third duty ratio. Power conversion equipment.

3. In the commercial power supply, one of the V-connected or delta-connected transformer windings is grounded at the midpoint of the transformer winding, or the neutral point of the Y-connected transformer is grounded. The power conversion device according to claim 1 or 2.

4. the boost chopper control unit periodically varies the first duty ratio and the third duty ratio based on a voltage applied between the grounded midpoint or the grounded neutral point and the one phase to which a midpoint of the plurality of voltage dividing capacitors is connected; The power conversion device according to claim 3 .

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