JP2012147528A - Ac power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a conventional AC power source in which when an IGBT is turned on while a current of a reactor is being refluxing through a serially connected IGBT, the IGBT used in the reflux is reversely recovered by a voltage of the AC power source, a large surge voltage is generated in blocking the reverse recovery, and hence, noise is generated in a larger quantity and a reverse recovery loss is large.SOLUTION: A capacitor series circuit and a bidirectional switch series circuit are connected in parallel to an AC power source, and another bidirectional switch is connected between a series connection point inside the capacitor series circuit and a series connection point inside the bidirectional switch series circuit. A voltage at which an IGBT performing a diode operation is reversely recovered because an IGBT is turned on and a voltage at which the IGBT is turned on/off are set to a voltage approximately a half of a voltage of the AC power source as a first step, and are set to the voltage of the AC power source itself as a second step.

Description

The present invention relates to an AC power supply apparatus that supplies AC voltage or AC power to a load by controlling voltage or power of an AC input voltage.

FIG. 8 shows a conventional AC power supply circuit disclosed in Patent Document 1. FIG. 8A is a step-down AC chopper circuit diagram that outputs an AC voltage lower than the AC power source Vs, and FIG. 8B is a step-up AC chopper circuit diagram that outputs an AC voltage higher than the AC power source Vs.
First, FIG. 8A will be described. A bidirectional switch series circuit in which a first bidirectional switch in which reverse blocking IGBTs 1a and S1b are connected in reverse parallel and a second bidirectional switch in which reverse blocking IGBTs 2a and S2b are connected in reverse parallel are connected in series; and an AC power supply This is a so-called step-down AC chopper circuit in which Vs and a capacitor Ci are connected in parallel and a load LD is connected in parallel with the second bidirectional switch.

  In such a configuration, when the polarity of the AC power source Vs is positive, when the IGBT TS 1a is turned on, the same voltage as that of the AC power source is applied to the load, and when the IGBT TS 1a is turned off and the IGBT TS 2b is turned on, the load voltage becomes zero. When the polarity of the voltage of the AC power supply Vs is negative, when the IGBT TS1b is turned on, the same voltage as that of the AC power supply is applied to the load LD, and when the IGBTTS1b is turned off and the IGBTTS2a is turned on, the load voltage becomes zero. In these switching operations, the voltage applied to the IGBT when the IGBT is turned off is the same as the power supply voltage. By performing such a switching operation at a high frequency and adjusting the ON / OFF ratio, a desired AC voltage having the same frequency as the AC power source Vs and a low voltage is applied to the load LD.

  Next, FIG. 8B will be described. A bidirectional switch series circuit in which a fourth bidirectional switch in which reverse blocking IGBTs 4a and S4b are connected in reverse parallel and a fifth bidirectional switch in which reverse blocking IGBTs 5a and S5b are connected in reverse parallel are connected in series, and a capacitor Co And a load LD, and a so-called step-up AC chopper circuit in which a series circuit of an AC power supply Vs and a reactor L is connected in parallel with the fifth bidirectional switch. In such a configuration, when the polarity of the AC power supply Vs is positive, when the IGBT TS 5a is turned on, energy is accumulated in the reactor L, and when the IGBT TS 5a is turned off and the IGBT TS 4b is turned on, the energy of the reactor L is forward to the capacitor Co via the IGBT TS 4b. To be higher than the voltage of the AC power source Vi. At this time, the voltage of the IGBTTS 5a is the same voltage as the capacitor Co.

  Further, when the polarity of the voltage of the AC power supply Vs is negative, when the IGBT TS 5b is turned on, energy is accumulated in the reactor L. When the IGBT TS 5b is turned off and the IGBT TS 4a is turned on, the energy of the reactor L is charged in the negative direction to the capacitor Co via the IGBT TS 4a. Is done. At this time, the voltage of the IGBTTS 5b is the same voltage as the capacitor Co. By performing such a switching operation at a high frequency and adjusting the ON / OFF ratio, a desired voltage having the same frequency and high voltage as the AC power supply Vs is applied to the load LD.

  In these switching operations, the voltage applied to the IGBT and the voltage waveform applied to the load are as follows. In the case of a step-down AC chopper circuit, the voltage changes between the AC power supply voltage and zero, and in the case of a step-up AC chopper circuit, the voltage changes between the boosted load voltage and zero. A high-speed switching waveform with a large rate (dv / dt) is obtained.

Japanese Patent No. 3216759

As described above, in any circuit configuration, when the IGBT connected in series is turned on when the current of the reactor is refluxing or charging the output capacitor via the IGBT, the IGBT being refluxed is the voltage of the AC power supply Vs. Alternatively, the reverse recovery operation similar to the diode is performed by the voltage of the AC output capacitor Co. If the AC power supply voltage or AC output voltage is as high as several hundred volts or more, the IGBT will reversely recover at high speed, and a large surge voltage will be generated when the IGBT reverse recovery is cut off, increasing the amount of noise generated and reverse recovery. Loss increases. Further, the amount of voltage change at the time of switching of the switching element is a voltage obtained by adding a surge voltage to the AC power supply voltage or the AC output voltage. As a result, the withstand voltage of the IGBT requires a high withstand voltage product that can withstand this voltage, and the cooling device becomes large.
Accordingly, an object of the present invention is to moderate reverse recovery and reduce the amount of noise generated, to reduce loss at the time of reverse recovery, and to reduce noise generation amount and switching loss at the time of switching.

  In order to solve the above-described problem, in the first invention, a capacitor series circuit in which two capacitors are connected in series and a first bidirectional switch series in which two first and second bidirectional switches are connected in series. A third bidirectional switch between the series connection point inside the capacitor series circuit and the series connection point inside the first bidirectional switch series circuit, A load is connected in parallel with one bidirectional switch or the second bidirectional switch, and an AC voltage having a fundamental frequency equal to that of the AC power source and a low voltage is supplied to the load.

  In the second invention, the capacitor series circuit in the first invention and the transformer winding with the intermediate tap are connected in parallel, and the intermediate tap and the connection point inside the capacitor series circuit are connected.

  In the third invention, when the first to third bidirectional switches in the first or second invention are controlled to be turned on / off, and each half cycle period of the AC power source is converted into a pulse train by high frequency PWM control, each pulse is Control means for outputting a composite waveform of a first step waveform for outputting one capacitor voltage of the capacitor series circuit and a second step waveform for outputting the voltage of the entire capacitor series circuit is provided.

  In a fourth aspect of the invention, a capacitor series circuit in which two capacitors are connected in series and a bidirectional switch series circuit in which two first and second bidirectional switches are connected in series are connected in parallel with a load, and the capacitor A third bidirectional switch is connected between a connection point inside the series circuit and a connection point inside the bidirectional switch series circuit, and an AC power supply is connected in parallel with the first bidirectional switch or the second bidirectional switch. A series circuit with a reactor is connected to each other, and an AC voltage having the same fundamental frequency as that of the AC power source and a high voltage is supplied to the load.

  In the fifth invention, the capacitor series circuit and the transformer winding with an intermediate tap in the fourth invention are connected in parallel, and the intermediate tap and a connection point inside the capacitor series circuit are connected.

  In a sixth aspect of the invention, the first to third bidirectional switches in the fourth or fifth aspect of the invention are turned on and off, the reactor current is controlled by high-frequency PWM control during each half cycle period of the AC power supply, When the capacitor series circuit is charged with a current pulse and a voltage higher than the voltage of the AC power supply is obtained, each current pulse charges a first period during which one capacitor of the capacitor series circuit is charged and a first period during which the entire capacitor series circuit is charged. 2 periods.

  In the seventh invention, a first capacitor series circuit in which two capacitors are connected in series, a first bidirectional switch series circuit in which two first and second bidirectional switches are connected in series, an AC power source, Are connected in parallel, and a step-down AC chopper circuit in which a third bidirectional switch is connected between a connection point inside the first capacitor series circuit and a series connection point inside the first bidirectional switch series circuit And a second capacitor series circuit in which two capacitors are connected in series and a second bidirectional switch series circuit in which two fourth and fifth bidirectional switches are connected in series are connected in parallel with the load, A step-up AC chopper circuit in which a sixth bidirectional switch is connected between a connection point inside the second capacitor series circuit and a series connection point inside the second bidirectional switch series circuit, 1 bidirectional switch A reactor is connected between the series connection point inside the series circuit and the series connection point inside the second bidirectional switch series circuit, and one end of the first bidirectional switch series circuit and the second bidirectional switch series circuit One end is connected to each other, and by the operation of the step-down AC chopper circuit, an AC voltage having the same fundamental frequency as that of the AC power source and a voltage lower than that of the AC power source is supplied to the load. Thus, an AC voltage having the same fundamental frequency as that of the AC power supply and a voltage higher than that of the AC power supply is supplied to the load.

  In an eighth invention, the first capacitor series circuit and the first intermediate tap transformer in the seventh invention, the second capacitor series circuit and the second intermediate tap transformer, The intermediate taps of the first intermediate tap transformer winding and the series connection point inside the first capacitor series circuit are respectively connected in parallel, and the intermediate tap of the second intermediate tap transformer winding is The second connection point in the second capacitor series circuit is connected to each other.

  In the ninth invention, when the first to third bidirectional switches in the seventh or eighth invention are turned on / off, and each half cycle period of the AC power supply is converted into a pulse train by high-frequency PWM control, each pulse is First control means is provided for outputting as a combined waveform of a first step waveform for outputting one capacitor voltage of the first capacitor series circuit and a second step waveform for outputting the voltage of the entire first capacitor series circuit. .

  In a tenth invention, the fourth to sixth bidirectional switches in the seventh to ninth inventions are controlled to be turned on / off, the reactor current is controlled by high-frequency PWM control during each half cycle period of the AC power supply, When the second capacitor series circuit is charged with a current pulse and a voltage higher than the voltage of the AC power supply is obtained, each current pulse is charged with a first period for charging one capacitor of the second capacitor series circuit and the capacitor series. A second control unit having a second period for charging the entire circuit.

In the present invention, the voltage when the IGBT is turned on and reversely recovering the diode-operated IGBT and the voltage when the IGBT (switching element) is turned on and off are set to about half of the AC power supply voltage or the AC output voltage as the first step. In the second step, the AC power supply voltage or the AC output voltage itself is used. For this reason, the voltage applied to the switching element at the time of reverse recovery of the diode-operated IGBT or when the IGBT (switching element) is turned off can be reduced.
As a result, the voltage at the time of reverse recovery of the diode-operated IGBT becomes a low voltage, the surge voltage at the time of reverse recovery is suppressed low, and the reverse recovery loss is reduced. Furthermore, the amount of voltage change at the time of switching of the IGBT (switching element) is about half, and the amount of noise generation is reduced.

1 is a circuit diagram showing a first embodiment of the present invention. It is the operation | movement waveform example 1 of FIG. It is the operation | movement waveform example 2 of FIG. It is a circuit diagram which shows the 2nd Example of this invention. It is a circuit diagram which shows the 3rd Example of this invention. 6 is an operation waveform example of FIG. 5. It is a circuit diagram which shows the 4th Example of this invention. It is a circuit diagram which shows a prior art example.

  The gist of the present invention is that a bidirectional switch series circuit in which bidirectional switches are connected in series and a capacitor series circuit in which capacitors are connected in series are connected in parallel with an AC power source, and the series connection point and the capacitor series circuit inside the bidirectional switch series circuit. In a step-down AC chopper circuit configuration in which a bidirectional switch is further connected between the internal series connection point, half of the AC power supply is applied in the first step as the voltage applied to the switching element during switching, and in the second step. The control is such that the AC power supply voltage itself is applied.

  In addition, a bidirectional switch series circuit in which bidirectional switches are connected in series and a capacitor series circuit in which capacitors are connected in series are connected in parallel with the load, and the AC power supply and the reactor are connected in parallel with one of the bidirectional switches in the bidirectional switch series circuit. In a boost AC chopper circuit configuration with a series circuit connected, half of the load voltage is applied in the first step as the voltage applied to the switching element during switching, and the load voltage itself is controlled in the second step. It is a point.

  FIG. 1 shows a first embodiment of the present invention. A bidirectional switch series circuit in which a first bidirectional switch in which reverse blocking IGBTs 1a and S1b are connected in anti-parallel and a second bidirectional switch in which reverse blocking IGBTs 2a and S2b are connected in anti-parallel are connected in series, and capacitor C1 A capacitor series circuit in which C2 and C2 are connected in series and an AC power supply Vs are connected in parallel, and reverse blocking IGBTs 3a and S3b are connected between the series connection point inside the bidirectional switch series circuit and the series connection point inside the capacitor series circuit. This is a step-down AC chopper circuit in which a third bidirectional switch connected in reverse parallel is connected to a load LD in parallel with the second bidirectional switch. The voltages of the capacitors C1 and C2 are connected to the control circuit CNT via the voltage detector VD1.

  Operation diagrams in such a configuration are shown in FIGS. FIG. 2 shows an operation example when the polarity of the AC power supply Vs is positive, and FIG. 3 shows an operation example when the polarity of the AC power supply Vs is negative. In any case, the fundamental frequency of the AC voltage supplied to the load LD is the same as the frequency of the AC power supply. As can be seen from FIG. 2, when the IGBT TS3a is turned on in a mode in which the current of the load LD is circulating through the IGBTTS2b, the IGBTTS2b is reversely recovered by the voltage of the capacitor C2 and turned off, and the voltage of the capacitor C2 is applied to the load LD. Applied. Next, when the IGBTTS1a is turned on, the IGBTTS3a is reversely recovered by the voltage of the capacitor C1 and turned off, and the sum of the voltage of the capacitor C1 and the voltage of C2 (AC power supply voltage) is applied to the load LD.

When the IGBTTS1a is turned off from this state, the voltage of the capacitor C2 is supplied to the load LD via the IGBTTS3a. Next, when the IGBT TS 3a is turned off and the IGBT TS 2b is turned on, the load current is circulated in the IGBT TS 2b, and the voltage of the load LD becomes zero. As a result of these operations, the voltage waveform applied to the load LD becomes a power supply voltage or zero voltage once via the voltage of the capacitor C2 in the switching process as shown in the figure. Here, the time difference from turning on the IGBT TS 3a to turning on the IGBT TS 1a and the time difference from turning off the IGBT TS 1a to turning off the IGBT TS 3a may be a little longer than the switching time of the IGBT. good. Capacitors C1 and C2 have substantially the same capacitance in order to have a role of dividing the AC power supply voltage into two. Therefore, when the AC power supply voltage is Vi as shown in FIG. 2, the voltages of the capacitors C1 and C2 are Vi / 2.

The voltage detector VD1 detects the voltage difference between the capacitors C1 and C2 and sends it to the control circuit CNT1. When the difference becomes large, the control circuit CNT1 stops and protects the device.
When the polarity of the AC power supply Vs is positive, when the IGBT TS2b is reversely recovered, the discharge amount of the capacitor C2 is large, so the voltage of the capacitor C2 is low. However, when the IGBTTS3a is reversely recovered, the discharge amount of the capacitor C1 is large. The voltage of C1 becomes low. Therefore, the charges for reverse recovery are almost the same. If the time from turning on the IGBT TS 3a to turning on the IGBT TS 1a and the time from turning off the IGBT TS 1a to turning off the IGBT TS 3a are increased, the voltage of the capacitor C2 is lowered from the voltage of the C1.

  FIG. 3 shows an operation example when the polarity of the AC power supply Vs is negative. As can be seen from FIG. 3, when the IGBT TS 3b is turned on in a mode in which the current of the load LD is circulating through the IGBT 2a, the IGBT TS 2a is reversely recovered by the voltage of the capacitor C2 and turned off, and the voltage of the capacitor C2 is applied to the load LD. Applied. Next, when the IGBTTS1b is turned on, the IGBTTS3b is reversely recovered by the voltage of the capacitor C1 and turned off, and the sum of the voltage of the capacitor C1 and the voltage of C2 (AC power supply voltage) is applied to the load LD. When the IGBTTS1b is turned off from this state, the voltage of the capacitor C2 is supplied to the load LD via the IGBTTS3b. Next, when the IGBT TS 3b is turned off and the IGBT TS 2a is turned on, the load current circulates in the IGBT TS 2a, and the voltage of the load LD becomes zero.

As a result of these operations, the voltage applied to the load LD becomes a power supply voltage or zero voltage once via the voltage of the capacitor C2 in the switching process as shown in the figure. If the time from turning off the IGBT TS 3b to turning on the IGBT TS 1b and the time from turning off the IGBT TS 1b to turning off the IGBT TS 3b are increased, the voltage of the C2 is lowered as compared with the voltage of the capacitor C1. The load voltage can be adjusted by changing the on / off ratio of the bidirectional switches 1 and 2 as in the conventional case.

FIG. 4 shows a second embodiment of the present invention. The difference from the first embodiment is that the winding of the intermediate tap transformer BAL is connected in parallel with the capacitors C1 and C2.
As described in the first embodiment, when the polarity of the AC power supply Vs is positive, the time from turning on the IGBT TS 3a to turning on the IGBT TS 1a, and the time from turning off the IGBT TS 1a to turning off the IGBT TS 3a. If it is increased, the voltage of the capacitor C2 will be lower than the voltage of C1. Further, when the polarity of the AC power source Vs is negative, if the time from turning off the IGBT TS 3b to turning on the IGBT TS 1b and the time from turning off the IGBT TS 1b to turning off the IGBT TS 3b are increased, the voltage is compared with the voltage of the capacitor C1. As a result, the voltage of C2 decreases.

If the voltage difference between the voltage of the capacitor C1 and the voltage of C2 is too large, the effects of reducing loss and noise during reverse recovery, which are the objects of the present invention, are reduced. The present embodiment is an embodiment for solving this problem. By connecting the transformer BAL with an intermediate tap in parallel with the series circuit of the capacitors C1 and C2, and connecting the intermediate tap and the series connection point inside the capacitor series circuit, the control state of the bidirectional switch is not affected. Each capacitor voltage can be equalized. Here, by adjusting the tap position, it is possible to adjust the voltage applied to each bidirectional switch and the generated loss.

  FIG. 5 shows a third embodiment of the present invention. This circuit boosts the voltage Vi of the AC power supply Vs and supplies a voltage higher than the AC power supply voltage to the load LD. A second bidirectional switch in which a fourth bidirectional switch configured by connecting the reverse blocking IGBTs 4a and S4b in reverse parallel and a fifth bidirectional switch configured by connecting the reverse blocking IGBTs 5a and S5b in reverse parallel are both connected in series. A direction switch series circuit, a second capacitor series circuit in which capacitors C3 and C4 are connected in series, and a load LD are connected in parallel. In addition, a sixth bidirectional configuration in which reverse blocking IGBTs 6a and S6b are connected in reverse parallel between a series connection point inside the second bidirectional switch series circuit and a series connection point inside the second capacitor series circuit. The switch is connected to the AC power source Vs and the reactor L1 in parallel with the fifth bidirectional switch. The voltages of the capacitors C3 and C4 are input to the control circuit CNT2 via the voltage detector VD2.

The operation in such a configuration is shown in FIG. It is an operation | movement figure in case the polarity of alternating current power supply Vs is positive. When the IGBTTS 5a is turned on, a current flows through the path of the AC power supply Vs → the reactor L1 → the IGBTTS 5a, and energy is accumulated in the reactor L1. Next, when the IGBTTS 5a is turned off and the IGBTTS 6a is turned on, the current of the reactor L1 is charged in the capacitor C4. Next, when the IGBT 6a is turned off and the IGBT TS 4b is turned on, the current of the reactor L1 charges the capacitors C3 and C4 through a path of IGBTTS4b → capacitor C3 → capacitor C4 → AC power supply Vs → reactor L1. Next, when the IGBT TS4b is turned off and the IGBTTS 6a is turned on, the capacitor C4 is charged.
As a result of these operations, the voltage waveform at the series connection point U in the second bidirectional switch series circuit becomes a waveform having a step at half the load voltage.

  The operation when the polarity of the AC power supply Vs is negative is the same. When the IGBTTS 5b is turned on, a current flows through the path of the AC power source Vs → IGBTS5b → reactor L1, and energy is accumulated in the reactor L1. Next, when IGBTTS5b is turned off and IGBTTS6b is turned on, the current of reactor L1 is charged in capacitor C4. Next, when the IGBT 6b is turned off and the IGBT TS 4a is turned on, the current of the reactor L1 charges the capacitors C4 and C3 through the path of the AC power source Vs → capacitor C4 → capacitor C3 → IGBTTS 4a → reactor L1. Next, when the IGBTTS 4a is turned off and the IGBTTS 6b is turned on, the capacitor C4 is charged. As a result of these operations, the voltage waveform at the series connection point U inside the second bidirectional switch series circuit becomes a waveform having a step with a half voltage of the load voltage obtained by inverting the waveform of FIG. 6 to the negative side.

  Also in this configuration, a transformer with an intermediate tap is connected in parallel with the second capacitor series circuit, and the voltage of the capacitors C3 and C4 is balanced by connecting the series connection point inside the capacitor series circuit and the intermediate tap. be able to. The voltage detector VD2 detects the voltage balance between the capacitors C3 and C4 and is input to the control circuit CNT2 to protect the device. Other operations are the same as those in the first and second embodiments. The load voltage can be adjusted by changing the on / off ratio of the bidirectional switches 4 and 5 as in the conventional case.

FIG. 7 shows a fourth embodiment of the present invention. The step-down AC chopper circuit of FIG. 1 and the step-up AC chopper circuit of FIG. 5 are combined to supply a wide range of AC voltages from a voltage lower than the AC power supply voltage to a higher voltage.
The step-down AC chopper circuit unit includes a first bidirectional switch in which reverse blocking IGBTs 1a and S1b are connected in reverse parallel and a second bidirectional switch in which reverse blocking IGBTs 2a and S2b are connected in reverse parallel. A bidirectional switch series circuit, a first capacitor series circuit in which capacitors C1 and C2 are connected in series, and an AC power supply Vs are connected in parallel, and a series connection point in the bidirectional switch series circuit and a capacitor series circuit A third bidirectional switch in which reverse blocking IGBTs 3a and S3b are connected in reverse parallel to each other is connected to the series connection point, and the series connection point in the first bidirectional switch series circuit is connected to one terminal of the reactor L1. Connected.

  The step-up AC chopper circuit unit includes a fourth bidirectional switch configured by connecting reverse blocking IGBTs 4a and S4b in reverse parallel, and a fifth bidirectional switch configured by connecting reverse blocking IGBTs 5a and S5b in reverse parallel. Are connected in series, a second capacitor series circuit in which capacitors C3 and C4 are connected in series, and a load LD are connected in parallel. A sixth bidirectional switch configured by connecting anti-blocking IGBTs 6a and S6b in reverse parallel connection between the point and the series connection point in the second capacitor series circuit, and connecting the second bidirectional switch series circuit An internal series connection point is connected to the other end of the reactor L1. The configuration in which the first intermediate tap transformer is connected in parallel with the first capacitor series circuit, and the second intermediate tap transformer is connected in parallel with the second capacitor series circuit is the first to third embodiments. Can be applied as well.

In such a configuration, the step-down operation is performed by turning on and off the bidirectional switches 1 to 3 in the same manner as in the first or second embodiment with the fourth bidirectional switch turned on. An AC voltage lower than the voltage is supplied. In the step-up operation, with the first bidirectional switch turned on, the bidirectional switches 4 to 6 are controlled to be turned on / off in the same manner as in the third embodiment, so that an AC voltage higher than the AC power supply voltage is supplied to the load LD. Is done.
In the above embodiment, an example is shown in which reverse blocking IGBTs are connected in reverse parallel as bidirectional switches. However, the present invention can also be realized by combining a diode and a switch element having no reverse breakdown voltage.
Further, although the output voltage control has been described as a base, the same can be realized by power control.

  The present invention relates to a power supply circuit that steps down or boosts an AC power supply voltage and supplies it to a load, and can be applied to an AC voltage regulator (AVR), an AC power regulator (APR), and the like.

Vs: AC power supply LD: Load Ci, Co, C1 to C4: Capacitor L1: Reactor S1a, S1b, S2a, S2b, S3a, S3b ... Reverse blocking IGBT
S4a, S4b, S5a, S5b, S6a, S6b ... Reverse blocking IGBT
VD1, VD2 ... Voltage detector CNT1, CNT2 ... Control circuit BAL ... Transformer with intermediate tap

Claims (10)

  A capacitor series circuit in which two capacitors are connected in series and a first bidirectional switch series circuit in which two first and second bidirectional switches are connected in series are connected in parallel with an AC power source, and the capacitor series circuit A third bidirectional switch is connected in parallel with the first bidirectional switch or the second bidirectional switch between an internal series connection point and a series connection point inside the first bidirectional switch series circuit. An AC power supply apparatus, wherein loads are connected to each other, and an AC voltage having a fundamental frequency equal to that of the AC power supply and a low voltage is supplied to the load.   2. The AC power supply device according to claim 1, wherein the capacitor series circuit and the transformer winding with an intermediate tap are connected in parallel, and the intermediate tap and a series connection point inside the capacitor series circuit are connected.   A first step waveform for outputting one capacitor voltage of the capacitor series circuit when each of the first to third bidirectional switches is turned on and off and each half cycle period of the AC power source is converted to a pulse train by high frequency PWM control. 3. The AC power supply apparatus according to claim 1, further comprising a control unit that outputs a combined waveform of the second step waveform that outputs the voltage of the entire capacitor series circuit and the second step waveform. 4.   A capacitor series circuit in which two capacitors are connected in series and a first bidirectional switch series circuit in which two first and second bidirectional switches are connected in series are connected in parallel with a load, An AC power supply is connected in parallel with the first bidirectional switch or the second bidirectional switch between the series connection point and the series connection point in the first bidirectional switch series circuit. And an AC power supply apparatus, characterized in that an AC voltage having a fundamental frequency equal to and higher than that of the AC power supply is supplied to the load.   5. The AC power supply device according to claim 4, wherein the capacitor series circuit and a transformer winding with an intermediate tap are connected in parallel, and the intermediate tap and a series connection point inside the capacitor series circuit are connected.   The on-off control of the first to third bidirectional switches, the reactor current is controlled by high frequency PWM control during each half cycle period of the AC power supply, the capacitor series circuit is charged with current pulses, and the voltage of the AC power supply is controlled. When obtaining a higher voltage, each current pulse is a control means comprising a first period for charging one capacitor of a capacitor series circuit and a second period for charging the entire capacitor series circuit. Item 6. The AC power supply device according to Item 4 or 5.   A first capacitor series circuit in which two capacitors are connected in series; a first bidirectional switch series circuit in which two first and second bidirectional switches are connected in series; and an AC power supply connected in parallel; A step-down AC chopper circuit in which a third bidirectional switch is connected between a series connection point in the first capacitor series circuit and a series connection point in the first bidirectional switch series circuit, and two capacitors A second capacitor series circuit connected in series and a second bidirectional switch series circuit in which two fourth and fifth bidirectional switches are connected in series are connected in parallel with a load, and the second capacitor series circuit A step-up AC chopper circuit in which a sixth bidirectional switch is connected between an internal series connection point and a series connection point inside the second bidirectional switch series circuit, and the first bidirectional switch In series circuit A reactor between a series connection point of the first bidirectional switch series circuit and a series connection point in the second bidirectional switch series circuit, and one end of the first bidirectional switch series circuit and one end of the second bidirectional switch series circuit, The AC power supply is connected to the load by the operation of the step-down AC chopper circuit and the fundamental frequency is equal to that of the AC power supply and the voltage is lower than that of the AC power supply, and the AC power supply is operated by the operation of the boost AC chopper circuit. And an AC power supply device that supplies an AC voltage having a fundamental frequency equal to that of the AC power supply to the load.   The first capacitor series circuit and the first intermediate tapped transformer winding are connected in parallel with the second capacitor series circuit and the second middle tapped transformer winding, respectively. The intermediate tap of the transformer winding with the intermediate tap and the series connection point inside the first capacitor series circuit are connected to the intermediate tap of the transformer winding with the second intermediate tap and the inside of the second capacitor series circuit. The AC power supply device according to claim 7, wherein the series connection points are connected to each other.   When the first to third bidirectional switches are turned on / off and each half cycle period of the AC power supply is converted into a pulse train by high-frequency PWM control, each pulse outputs one capacitor voltage of the first capacitor series circuit. 9. The AC power supply according to claim 7, further comprising: a first control unit that outputs a combined waveform of a one-step waveform and a second step waveform that outputs a voltage of the entire first capacitor series circuit. apparatus.   The on-off control of the fourth to sixth bidirectional switches is performed, the reactor current is controlled by high-frequency PWM control during each half cycle period of the AC power supply, the second capacitor series circuit is charged with current pulses, and the AC In obtaining a voltage higher than the voltage of the power supply, each current pulse has a second control period having a first period for charging one capacitor of the second capacitor series circuit and a second period for charging the entire capacitor series circuit. The AC power supply device according to any one of claims 7 to 9, further comprising means.