JP2012222854A - Power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion system in which an inverter is connected to a commercial power supply system, for initial charging of a smoothing capacitor with an AC power.SOLUTION: The power conversion system includes smoothing capacitors 21-23 for smoothing output voltages of single-phase inverters 17-20 which are subjected to gradation control, first switches 31-33 connected between the single-phase inverters 17-20 and an AC power source 30, and serial connection bodies 40-42 which comprise current limiting resistors 34-36 and second switches 37-39 both connected in parallel to the switches 31-33 respectively. The initial charging is performed from the AC power source 30 to the smoothing capacitors 21-23 by way of the serial connection bodies 40-42.

Description

  The present invention relates to a power conversion device used for a power conditioner or the like that links a distributed power supply to a commercial power supply system, and more particularly to a power conversion device that obtains a desired output waveform by gradation control by combining a plurality of inverters. is there.

In a conventional power conditioner, for example, as shown in a solar power conditioner, a DC voltage from a distributed power source that is a solar cell is boosted by a chopper circuit, and a PWM control inverter is inserted in the subsequent stage to output an AC voltage. Is occurring. A circuit configuration of a conventional power conditioner composed of the gradation control inverter will be described with reference to FIG.
In FIG. 6, the power conditioner 100 is provided with a chopper circuit 14 as a booster circuit including a switching element 11 such as an IGBT, a reactor 12, and a diode 13 at a subsequent stage of the DC power supply 10 that is a solar battery. The chopper circuit 14 boosts the DC voltage obtained by the DC power supply 10 and charges the smoothing capacitors 15 and 16. The charging voltage of the smoothing capacitors 15 and 16 serves as a DC power source for the first inverter 17.

  The first inverter 17 and the second inverter 18, the first inverter 17 and the third inverter 19, and the first inverter 17 and the fourth inverter 20 are connected in series, respectively. The second inverter 18, the third inverter 19, and the fourth inverter 20 are provided with smoothing capacitors 21, 22, and 23, respectively. In addition, filter reactors 24, 25, and 26 and filter capacitors 27, 28, and 29 that form sine waves from the output voltages of the second inverter 18, the third inverter 19, and the fourth inverter 20 are provided. 6 is connected to an AC power supply 30 which is a commercial power supply system as shown in FIG.

  As shown in FIG. 6, the first inverter 17 includes switching elements T1P to T3P, T1N to T3N and flywheel diodes connected in antiparallel to the respective switching elements, and the second inverter 18 , Switching elements T11P, T12P, T13N, T14N and flywheel diodes connected in antiparallel to the respective switching elements. The third inverter 19 includes switching elements T21P, T22P, T23N, T24N and the respective switching elements. The fourth inverter 20 includes a switching element T31P, T32P, T33N, T34N and a flywheel diode connected in antiparallel to each switching element. It is constituted by de.

Next, a charging method at the time of starting the smoothing capacitors 21, 22, 23 connected to the second inverter 18, the third inverter 19, and the fourth inverter 20 will be described with reference to FIGS.
The smoothing capacitors 21, 22, and 23 are charged by switching the switching elements T1P to T3P and T1N to T3N of the first inverter 17. As an operation, the states of FIGS. 7 and 8 are alternately repeated.

  First, when charging the smoothing capacitor 21, as shown in FIG. 7, the switching elements T1P to T3P are turned on and the switching elements T11P and T14N are turned on. As shown in FIG. 8, the switching element T1N is turned on. -T3N is turned on, and the switching elements T13N and T12P are turned on to charge the smoothing capacitor 21. 7 and 8 indicate the charging path to the smoothing capacitor 21. In addition, since it is the same as that of the above also when charging the smoothing capacitors 22 and 23, description is abbreviate | omitted about the charging operation of these smoothing capacitors 22 and 23. FIG.

  Note that a power conversion device having a gradation control inverter configuration used in the above conventional power conditioner or the like is disclosed in, for example, Patent Document 1, and the operation of the gradation control inverter will be described in detail with reference to these. Omitted.

  In addition, in a power storage device linked to a commercial power supply system, an initial charging circuit for initially charging a smoothing main capacitor is connected to the DC side of the sine wave converter for the purpose of simplifying the initial charging circuit and Patent Document 2 proposes a technique for sharing a plurality of phases or a plurality of line voltages of a power supply system.

JP 2010-94024 A JP 2002-320390 A

  In the conventional power conditioner constituted by the gradation control inverter, as described above, the filter capacitors 27, 28, and 29 are required as current paths when the smoothing capacitor 21 is charged. , 28 and 29, a path connecting to the midpoint of the smoothing capacitor 15 and the smoothing capacitor 16 is necessary.

  In addition, since power is supplied from the DC power supply 10 that is a solar cell, it takes time to start the power conditioner when the output of the DC power supply 10 is small.

  The present invention has been made in view of the above-described problems, and provides a power converter that connects an inverter to a commercial power supply system and performs initial charging of a smoothing capacitor with AC power.

  A power converter according to the present invention includes a plurality of single-phase inverters that are connected in series to convert DC power of a DC power source into AC power, and a sum of each generated voltage by a predetermined combination selected from the plurality of single-phase inverters. In the power converter connected to the AC power supply, the output voltage is gradation controlled by the smoothing capacitor for smoothing the output voltage of the plurality of single-phase inverters connected in series, and between the single-phase inverter and the AC power supply. A first connection means connected to the first opening and closing means, and a series connection body of a current limiting resistor and a second opening and closing means connected in parallel to the first opening and closing means, and the series connection body from the AC power supply In this way, the smoothing capacitor is initially charged.

  According to the power conversion device of the present invention, an inverter is connected to the commercial power supply system, and the smoothing capacitor is initially charged with AC power, thereby omitting the filter capacitor that is necessary when charging with DC power. be able to.

It is a circuit block diagram explaining the power conditioner using the power converter device which concerns on Embodiment 1 of this invention. It is operation | movement explanatory drawing at the time of the initial stage charge of the smoothing capacitor of the power converter device which concerns on Embodiment 1 of this invention. It is operation | movement explanatory drawing at the time of the initial stage charge of the smoothing capacitor of the power converter device which concerns on Embodiment 1 of this invention. It is a figure explaining the power converter device which concerns on Embodiment 2 of this invention. FIG. 5 is a diagram for explaining an equivalent circuit of the circuit shown in FIG. 4. It is a circuit block diagram explaining the power conditioner using the conventional power converter device. It is operation | movement explanatory drawing at the time of the initial stage charge of the smoothing capacitor of the conventional power converter device. It is operation | movement explanatory drawing at the time of the initial stage charge of the smoothing capacitor of the conventional power converter device.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a power conversion device according to the invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment, and includes various design changes.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram illustrating a power conditioner using the power conversion device according to Embodiment 1 of the present invention. In FIG. 1, the code | symbol 200 has shown the power conditioner using the power converter device which concerns on Embodiment 1. FIG. The power conversion device used in the power conditioner 200 includes filter reactors 24, 25, and 26 that form sine waves from the output voltages of the second inverter 18, the third inverter 19, and the fourth inverter 20, and commercial power supplies. Switches 31 to 33 serving as first opening / closing means are connected between the AC power supply 30 serving as the power supply system, and the current limiting resistors 34 to 36 and the second opening / closing are connected in parallel with the switches 31 to 33, respectively. Charging circuits 40 to 42 constituted by series connected bodies of switches 37 to 39 as means are connected. Other configurations are the same as those of the conventional apparatus of FIG. 1, and the description thereof is omitted by giving the same reference numerals.

The power conversion device according to Embodiment 1 is configured as described above, and the operation thereof will be described next.
During initial charging of the smoothing capacitors 21, 22, and 23 of the second inverter 18, the third inverter 19, and the fourth inverter 20, the switches 31 to 33 are turned off, and the switches on the side of the current limiting resistors 34 to 36 are turned on. Turn on 37-39. As a result, the smoothing capacitors 21 to 23 are charged while the current is limited by the current limiting resistors 34 to 36.

  In the conventional device, the switching capacitors T1P to T3P and T1N to T3N are switched to charge the smoothing capacitors 21 to 23. However, according to the first embodiment, the switching elements T1P to T3P and T1N to T3N need not be controlled. In addition, since all the elements remain in the off state, complicated control becomes unnecessary.

  The charging current path at that time flows from the AC power supply 30 which is a commercial power supply system through the flywheel diode of each switching element as shown by the thick arrows in FIGS. Charge 23 sequentially. Then, when the voltages of the smoothing capacitors 21 to 23 of the second to fourth inverters 18 to 20 are charged to a desired voltage, the switches 37 to 39 are turned off and the switches 31 to 33 are turned on, so that the current limiting resistor is turned on. The power conditioner 200 shifts to a normal operation so that no current flows through the 34-36 side. 2 and 3 illustrate the charging operation of the smoothing capacitor 21 of the second inverter 18.

  As mentioned above, according to the power converter device which concerns on Embodiment 1, it is a solar cell by obtaining the electric power for charge of the smoothing capacitors 21-23 of the inverters 18-20 from the alternating current power supply 30 which is a commercial power supply system. Charging is possible when power is not supplied from the DC power supply 10. Therefore, in the conventional apparatus, the smoothing capacitors 21 to 23 are charged only after power is supplied from the DC power supply 10 that is a solar cell, and then the power conditioner starts the power conversion operation. Then, it becomes possible to stand by in the state where charging of the smoothing capacitors 21 to 23 is completed, and when sufficient power is supplied from the DC power supply 10 that is a solar battery, it is possible to immediately start the power conversion operation.

Embodiment 2. FIG.
Next, a power converter according to Embodiment 2 will be described. FIG. 4 is a diagram illustrating a power conditioner using the power conversion device according to the second embodiment. In the power conditioner 300 according to the second embodiment, the switches 31 to 33 and the charging circuits 40 to 42 of the first embodiment are replaced with bidirectional switch elements M1 and M2 configured by silicon carbide MOSFETs. FIG. 4 illustrates a charging circuit for the smoothing capacitor 21 of the second inverter 18. Other configurations are the same as those of the first embodiment, and the illustration and description thereof are omitted.

  In the power conversion device according to the second embodiment, the switches 31 to 33 and the charging circuits 40 to 42 are the bidirectional switch elements M1 and M2 formed of silicon carbide MOSFETs. The resistors 34 to 36 can be omitted. Specifically, the equivalent resistance value is adjusted by the gate-source voltage of the switch elements M1 and M2. When the drain-source voltage is constant, the MOSFET can change the drain current according to the gate-source voltage. In a general enhancement type MOSFET, the drain current decreases as the gate-source voltage decreases, and the drain current increases as the gate-source voltage increases. Since the drain-source voltage is constant, the equivalent resistance increases as the gate-source voltage decreases, and the equivalent resistance decreases as the gate-source voltage increases.

  FIG. 5 shows an explanatory diagram when the silicon carbide MOSFET is operated as an equivalent resistance. During the initial charging of the smoothing capacitors 21 to 23 of the gradation control inverter, the equivalent resistance is increased by lowering the gate-source voltage of the MOSFET to limit the charging current. After the charging of the smoothing capacitors 21 to 23 is completed, the gate-source voltage is increased to reduce the equivalent resistance and transmit power.

  As described above, according to the power conversion device according to the second embodiment, by using silicon carbide MOSFETs as the switch elements M1 and M2, the current limiting resistors 34 to 36 and the switches 37 to 39, and the switch 31 used during normal operation. .About.33 are not required, and an equivalent function can be realized simply by changing the gate-source voltage, and the device can be greatly reduced in size.

  In addition, this circuit is made possible by the characteristic that the equivalent resistance of the silicon carbide MOSFET is as small as 1/10 or less than that of the conventional MOSFET. This is because a large current flows when power is transmitted, so that the element loss is very large in the conventional MOSFET, and the efficiency of the power conditioner is greatly reduced.

  In addition, since the thermal duty of the switch element becomes very strict, a cooling mechanism for the element is also required, which is difficult to realize with a conventional MOSFET. A general silicon MOSFET can cope with a channel temperature of up to about 150 ° C. However, since a silicon carbide MOSFET allows a higher channel temperature, there is a great advantage in the use of the power conversion device according to the second embodiment. In other words, since the cooling system can be simplified if the allowable channel temperature becomes high, the cooling fins can be downsized and the fan can be omitted, so that the conversion efficiency of the power conditioner is expected to be improved. Use as a switch element is very effective.

DESCRIPTION OF SYMBOLS 10 DC power supply 11 Switching element 12 Reactor 13 Diode 14 Chopper circuit 15, 16 Smoothing capacitor 17, 18, 19, 20 Inverter 21, 22, 23 Smoothing capacitor 24, 25, 26 Filter reactor 27, 28, 29 Filter capacitor 30 AC power supply 31, 32, 33, 37, 38, 39 Switch 34, 35, 36 Current limiting resistor 40, 41, 42 Charging circuit 100, 200, 300 Power conditioner M1, M2 Bidirectional switch element

Claims (2)

A plurality of single-phase inverters that convert DC power of a DC power source into AC power are connected in series, and the output voltage is gradation controlled by the sum of each generated voltage by a predetermined combination selected from the plurality of single-phase inverters, In the power converter connected to the AC power supply,
A smoothing capacitor for smoothing the output voltage of the plurality of single-phase inverters connected in series;
A first switching means connected between the single-phase inverter and the AC power source;
A series connection body of a current limiting resistor and a second switching means connected in parallel to the first switching means;
With
A power conversion device, wherein the smoothing capacitor is initially charged from the AC power source through the series connection body.   2. The power conversion device according to claim 1, wherein a parallel circuit of the first opening / closing means and the series connection body is constituted by a bidirectional switch using a silicon carbide MOSFET.

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