Single-phase three-wire AC power converter

Abstract

To improve an effect by reducing power loss generated in a conventional circuit which creates a single-phase three-wire AC power source from a DC power source.SOLUTION: An inverter circuit is formed of first to fourth switch elements, a first reactor, and a second reactor. In the inverter circuit, a bidirectional switch circuit is connected between a connection point between the first and second switch elements and a connection point between the third and fourth switch elements, a drive signal of a prescribed cycle, a prescribed phase, and a prescribed pulse width is applied to the first to fourth switch elements and a control terminal of the bidirectional switch circuit, and excitation energy in the first reactor and the second reactor is discharged via the bidirectional switch circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power supply device capable of converting between a DC power supply and an AC power supply. [Background Art]

[0002] Devices that generate AC power from the battery of an electric vehicle (EV) are increasingly used during power outages. Further, in order to supply AC power to the entire building to be evacuated in the event of a disaster, AC generated from an EV is connected to the switchboard of the building. When connecting AC to a switchboard, it is necessary to temporarily disconnect the connection from the grid and supply single-phase three-wire AC. A single-phase three-wire AC inverter has three output terminals. If the output terminals are named L1, N, and L2, 100V is generated between L1-N and between N-L2, and 200V is generated between L1-L2. Also, N is protectively grounded. A single-phase three-wire AC inverter employs a different circuit and a different control method from a single-phase two-wire AC inverter that generates one AC voltage.

[0003] Patent Document 1 discloses an inverter circuit that generates single-phase three-wire AC. According to the disclosed circuit, a DC voltage is divided by two capacitors connected in series, and single-phase three-wire AC is generated from each of the voltages via an inverter circuit. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Laid-Open No. 2014-79133 [Disclosure of the Invention] [Problem to be Solved by the Invention]

[0005] Figure 2 of Patent Document 1 shows the current path for discharge operation 1. In the figure, when Q1 and Q4 are turned on, the charge of capacitor C1 flows to one load via Q1 and L1, and the charge of capacitor C2 flows to the other load via Q4 and L2.

[0006] Next, when Q1 and Q4 are turned off and Q2 and Q3 are turned on, the excitation energy of L1 is recovered to capacitor C2 through one load, and the excitation energy of L2 is recovered to capacitor C1 through the other load.

[0007] In other words, the charge energy discharged from capacitors C1 and C2 is supplied to the load and simultaneously stored as excitation energy in L1 and L2. However, some of this stored energy returns to capacitors C1 and C2, resulting in an energy exchange between the capacitors (C1 and C2) and the reactors (L1 and L2), causing power loss.

[0008] Therefore, the present invention aims to provide a highly efficient inverter that does not experience the energy exchange seen in conventional single-phase three-wire AC inverters.

[0009] Conventional single-phase three-wire AC inverters experience a voltage increase and a waveform deviating from a sine wave when the output is no load or light load.

[0010] Therefore, another objective of the present invention is to provide a single-phase three-wire AC inverter in which there is no voltage increase even when the load is no load or light load, and the AC voltage waveform does not deviate from a sine wave. [Means for solving the problem]

[0011] To achieve the above objective, the present invention provides a first DC power supply, a series circuit consisting of a first capacitor and a second capacitor connected in parallel to the first DC power supply, a series circuit consisting of a first switch element and a second switch element connected in parallel to the first DC power supply, a series circuit consisting of a third switch element and a fourth switch element connected in parallel to the first DC power supply, a bidirectional switch circuit connected between the connection point of the first switch element and the second switch element and the connection point of the third switch element and the fourth switch element, a third capacitor connected between one terminal of the bidirectional switch circuit and the connection point of the first capacitor and the second capacitor, and the other terminal of the bidirectional switch circuit and the connection between the first capacitor and the second capacitor. The device comprises a fourth capacitor connected between the terminals, a first reactor inserted in series with the terminal on the bidirectional switch circuit side of the third capacitor, a second reactor inserted in series with the terminal on the bidirectional switch circuit side of the fourth capacitor, a first load connected in parallel with the third capacitor, a second load connected in parallel with the fourth capacitor, and a third load connected between the terminal on the first reactor side of the third capacitor and the terminal on the second reactor side of the fourth capacitor. The device is characterized by applying a drive signal having a predetermined period, phase, and pulse width to the control electrodes of the first to fourth switch elements and the bidirectional switch circuit, thereby converting the power of the first DC power supply into AC power and supplying it to the first to third loads. [Effects of the Invention]

[0012] According to the present invention, a single-phase three-wire AC inverter can be made more efficient than conventional inverters. [Brief explanation of the drawing]

[0013] [Figure 1] This is a circuit diagram showing an embodiment of the present invention. [Figure 2] This is a circuit diagram showing another embodiment of the present invention. [Figure 3] This is a waveform diagram illustrating the operation of the circuit of the present invention. [Figure 4] This is a waveform diagram illustrating the operation of the circuit of the present invention. [Figure 5] It is a circuit diagram showing the discharge current of the present invention. [Figure 6] It is a circuit diagram showing a conventional discharge current.

Best Mode for Carrying Out the Invention

[0014] FIG. 1 is a circuit diagram of a power conversion device showing an embodiment of the present invention. The voltage of a DC power supply 1 is divided by capacitors 2 and 3. An AND signal (hereinafter referred to as "&") of a pulse that goes high only during a period corresponding to a positive half-wave of an AC voltage serving as a first signal (hereinafter referred to as "AC positive") and a pulse having a duty ratio proportional to the amplitude of an AC voltage serving as a third signal (hereinafter referred to as "DT") is applied to MOSFETs 4 and 7. An AND of DT and a pulse that goes high only during a period corresponding to a negative half-wave of an AC voltage serving as a second signal (hereinafter referred to as "AC negative") is applied to switching elements 5 and 6. A complementary signal of DT serving as a fourth signal is provided to the gates of MOSFETs 8 and 9 TIFF0007927245000001.tif10170, so that MOSFETs 4 to 7 and MOSFETs 8 and 9 will not be in an on state at the same time.

[0015] the relationship between an AC waveform and AC positive and AC negative signals is Figure 3 shown in.

[0016] TIFF0007927245000002.tif10108

[0017] When AC positive & DT goes high and is applied to the gates of MOSFETs 4 and 7, the charge of capacitor 2 flows through MOSFET 4, reactor 12 and capacitor 10, and the charge of capacitor 3 flows through MOSFET 7, reactor 13 and capacitor 11.

[0018] Even if the AC positive pulse is high, when DT goes low, MOSFETs 4 and 7 are turned off. On TIFF0007927245000003.tif11170T charges capacitors 10 and 11 through 8 and 9.

[0019] The current for exciting reactors 12 and 13 in FIG. 1 and the current path when the excitation energy is released are Figure 5 shown in.

[0020] Figure 6 is an equivalent circuit corresponding to FIG. 2 of Patent Document 1, which is one conventional circuit configuration. TIFF0007927245000004.tif91691 and the current for exciting L2 is Figure 5 the same as that in the circuit of , but when Q1 and Q4 are turned off and Q2 and Q3 are turned on, part of the excitation energy of reactors L1 and L2 returns to input capacitors C1 and C2; however, Figure 5 in the circuit of , the excitation energy of reactors (12 and 13) only charges output capacitors (10 and 11). That is, Figure 5 and Figure 6 have different current paths for the release of excitation energy.

[0021] Figure 6 In the conventional method shown in , part of the excitation energy returns to C1 and C2, which degrades conversion efficiency. Additionally, if there is a difference in the AC power extracted from C3 and C4, a difference occurs in the voltages of C1 and C2, so a voltage balance circuit composed of Q5, Q6, and L3 is required as shown in FIG. 1 of Patent Document 1, and this balance circuit also causes power loss.

[0022] TIFF0007927245000005.tif9170 is a duty ratio proportional to the amplitude of , but in the conventional method, the value of DT is simply proportional to the AC voltage TIFF0007927245000006.tif9119

[0023] FIG. 2 shows a power converter according to another embodiment of the present invention. The difference from FIG. 1 is that the gates of MOSFETs 8 and 9 constituting the bidirectional switch circuit are separate, and positive AC and negative AC signals are applied to the gates respectively.

[0024] In Figure 2, positive AC current (&DT) is applied to MOSFETs 4 and 7, and positive AC current is applied to the gate of MOSFET 9 in the bidirectional switch circuit formed by MOSFETs 8 and 9. While the positive AC pulse is high, the bidirectional switch circuit conducts only in the direction from bottom to top in the diagram.

[0025] When the AC positive pulse is high and DT is also high, switch elements 4 and 7 turn on, and current flows through reactors 12 and 13, exciting both reactors and charging capacitors 10 and 11. When DT goes low, even while the AC positive pulse is high, MOSFETs 4 and 7 turn off, and the excitation energy of reactors 12 and 13 is released by flowing through the body diodes of MOSFETs 9 and MOSFET 8, which are conductive in the direction of excitation energy release.

[0026] When the AC negative pulse is high and DT is also high, MOSFETs 6 and 5 turn on, and the current flows through reactors 13 and 12, exciting both reactors and charging capacitors 11 and 10. When DT goes low, even while the AC negative pulse is high, MOSFETs 6 and 5 turn off, and the excitation energy of reactors 13 and 12 is released by flowing through the body diodes of MOSFETs 8 and MOSFET 9, which are conductive in the direction of excitation energy release.

[0027] The key point of TIFF0007927245000007.tif10170 is whether it switches on and off, or on and off in cycles of positive and negative AC.

[0028] TIFF0007927245000008.tif10168 introduces a dead time where the other side is in a low state, but this is one of the reasons for reduced efficiency.

[0029] In Figure 2, current flows through the body diode of either MOSFET 8 or 9, resulting in losses due to the diode's forward voltage drop (VF), which is one of the causes of reduced efficiency.

[0030] Figure 1 to Figure 2In this configuration, all or some of the MOSFETs may be replaced with IGBTs connected in antiparallel to diodes.

[0031] In the single-phase three-wire AC inverter of the present invention, the fact that DT only needs to be made proportional to the amplitude of the AC voltage is the same as in the conventional single-phase two-wire AC inverter. Therefore, the AC voltage supplied to the three loads is stable, and the AC waveform remains a sine wave regardless of the load. [Explanation of Symbols]

[0032] 1 DC power supply 2, 3, 10, 11 Capacitors 4-9 MOSFETs 12, 13 Reactors 14, 15, 16 Load 17 Signal source

Claims

1. A series circuit comprising a first DC power supply, a first capacitor and a second capacitor connected in parallel to the first DC power supply, a series circuit comprising a first switch element and a second switch element connected in parallel to the first DC power supply, a series circuit comprising a third switch element and a fourth switch element connected in parallel to the first DC power supply, a bidirectional switch circuit connected between the connection point of the first switch element and the second switch element and the connection point of the third switch element and the fourth switch element, a third capacitor connected between one terminal of the bidirectional switch circuit and the connection point of the first capacitor and the second capacitor, a fourth capacitor connected between the other terminal of the bidirectional switch circuit and the connection point of the first capacitor and the second capacitor, and the A single-phase three-wire AC power converter comprising: a first reactor inserted in series with the terminal of the third capacitor on the bidirectional switch circuit side; a second reactor inserted in series with the terminal of the fourth capacitor on the bidirectional switch circuit side; a first load connected in parallel with the third capacitor; a second load connected in parallel with the fourth capacitor; a third load connected between the terminal of the third capacitor on the first reactor side and the terminal of the fourth capacitor on the second reactor side; and a signal source that applies a drive signal having a predetermined period, phase, and pulse width to the control electrodes of the first to fourth switch elements and the bidirectional switch circuit, thereby converting the power of the first DC power supply into AC power and supplying it to the first to third loads.

2. The single-phase three-wire AC power converter according to claim 1, wherein the bidirectional switch circuit comprises a first control electrode that controls conduction in one direction and a second control electrode that controls conduction in another direction, the signal source comprises a first signal that outputs a pulse for a period corresponding to the positive half-wave of the AC voltage, a second signal that outputs a pulse for a period corresponding to the negative half-wave of the AC voltage, a third signal that outputs a pulse with a duty cycle proportional to the amplitude of the sinusoidal wave of the AC voltage, and a fourth signal that outputs a complementary signal to the third signal, the AND signal of the first signal and the third signal is applied to the control electrodes of the first switch element and the fourth switch element, the AND signal of the second signal and the third signal is applied to the control electrodes of the second switch element and the third switch element, and the fourth signal is applied to the first and second control electrodes of the bidirectional switch circuit.

3. The single-phase three-wire AC power converter according to claim 2, wherein the first signal is applied to the first control electrode of the bidirectional switch circuit in place of the fourth signal, and the second signal is applied to the second control electrode of the bidirectional switch circuit in place of the fourth signal.

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