JPH07337036A - Ac power converter - Google Patents

Abstract

PURPOSE:To lower the cost of the circuit elements in a half bridge AC/DC/AC conversion circuit by lowering the voltage across the capacitor serving as a DC power supply. CONSTITUTION:First and second transistors 3, 4 and first and second diodes 5, 6 constitute a half bridge type AC/DC conversion circuit. First and second capacitors 7, 8 at the output stage of the AC/DC conversion circuit serve as the DC power supply for a half bridge DC/AC inverter. A load 14 is connected between the output terminal B of the DC/AC inverter and the terminal A of an AC power supply 1. The voltage of the DC/AC inverter is superposed on the power supply voltage and fed to the load 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power converter capable of converting an AC voltage into an AC voltage having a different amplitude without using a transformer.

[0002]

2. Description of the Related Art A method of using a transformer and an AC method for converting an AC voltage into AC voltages of different levels.
There is a method of combining a -DC converter and a DC-AC converter.

FIG. 1 shows an example of the latter method, in which an AC power supply 1, a boosting reactor 2, first and second transistors 3 and 4, and first and second diodes 5 are provided. , 6, first and second capacitors 7 and 8, third and fourth transistors 9 and 10, third and fourth diodes 11 and 12, a smoothing reactor 13, and a load 1.
It consists of 4 and. The first capacitor 7 is charged through the first diode 5, the second capacitor 8 is charged through the second diode 6, and the first and second transistors 3 and 4 are connected to the reactor 2 with respect to the reactor 2. Energy storage is controlled, and the capacitors 7 and 8 are charged with a voltage obtained by adding the voltage of the power supply 1 and the voltage of the reactor 2. The capacitors 7 and 8 function as a DC power source for the half bridge type inverter, and this DC voltage is applied to the third and fourth DC power sources.
Alternating ON / OFF of the transistors 9 and 10 is converted into an AC voltage and supplied to the load 14.

[0004]

By the way, an AC converter including a transformer is inevitably large in size and high in cost. Further, the method shown in FIG. 1 has a problem that when obtaining an output voltage higher than the input voltage, it is necessary to increase the voltage of the capacitors 7 and 8 functioning as a DC power supply.
For example, using a 100 V AC power source 1 to load 14
When supplying AC voltage of 00V, capacitors 7, 8
It becomes necessary to charge each to 282V or more,
The voltage V _PN between the P point and the N point becomes 564V or more. That is, when the effective value of 200 V is obtained for the load 14, the capacitors 7 and 8 are required to have a withstand voltage of 282 V or higher corresponding to the peak value or higher. Further, even when the AC power supply 1 has a voltage of 200V and the load 14 obtains a voltage of 200V or less, the capacitors 7 and 8 are charged with 282V corresponding to the peak value of the input voltage at least. Therefore, the capacitor 7,
8, transistors 3, 4, 9, 10, diode 5,
It became necessary to use high withstand voltage components as 6, 11, and 12, and the cost of the AC power converter was inevitably high.

Therefore, an object of the present invention is AC-DC-A.
An AC power conversion device capable of reducing a DC voltage in C conversion.

[0006]

According to the present invention for achieving the above object, a series circuit of first and second switches and a series circuit of the first and second switches are connected in parallel. A series circuit of first and second capacitors, a series circuit of third and fourth switches connected in parallel to the series circuit of the first and second capacitors, and the first and second AC power supply connected between the interconnection middle point of the switch and the interconnection middle point of the first and second capacitors, and is connected to the interconnection middle point of the first and second switches. The load connected between the terminal of the AC power supply on the side and the interconnection middle point of the third and fourth switches and the first and second switches to perform AC-DC conversion, Synchronize the third and fourth switches to the input AC power phase DC - those related to AC power converter and a control circuit for controlling to AC conversion. As described in claim 2, an AC power source is connected between the interconnection middle point of the first and second switches and the interconnection middle point of the third and fourth switches, and the third and fourth A load may be connected between the interconnection midpoints of the switches and the interconnection midpoints of the first and second capacitors. Also,
As described in claim 3, each of the first and second switches can be an anti-parallel circuit including a control switch element and a diode. Further, as described in claim 4, the first and second switches can be diodes.

[0007]

According to the first aspect of the present invention, the AC power supply voltage is applied between the midpoint of interconnection of the first and second capacitors and the midpoint of interconnection of the third and fourth switches. It becomes possible to supply a voltage having a value obtained by adding the voltages to the load. Therefore, the voltage of the first and second capacitors is
It is possible to obtain the same load voltage as the conventional method even if the load voltage is lower than the conventional method. Therefore, it is possible to reduce the withstand voltage of the first and second capacitors and the first to fourth switches to achieve cost reduction. According to the invention of claim 2, the voltage (load voltage) between the midpoint of interconnection of the first and second capacitors and the midpoint of interconnection of the third and fourth switches is subtracted from the AC power supply voltage. Voltage of different values is applied between the middle point of interconnection of the first and second switches and the interconnection point of the first and second capacitors, and the voltage of the first and second capacitors is lowered. You can This allows
It is possible to reduce the breakdown voltage and cost of the first and second capacitors and the first to fourth switches. According to the third aspect, the DC voltage boosting control can be performed by the functions of the control switch element and the reactor. According to claim 4, A
The C-DC conversion circuit becomes simple.

[0008]

[First Embodiment] Next, an AC power converter according to a first embodiment of the present invention will be described with reference to FIGS. The AC power converter shown in FIG. 2 is an embodiment in the case of outputting a high load voltage with a low capacitor voltage, and an effective value of 10
One terminal A of the 0 V sine wave AC power supply 1 is connected via a boosting reactor 2 to an interconnection midpoint of a series circuit of the first and second transistors 3 and 4. First and second
The first and second diodes 5 and 6 are connected in anti-parallel to the transistors 3 and 4, and the parallel circuit of these is a half-bridge type AC-DC converter (AC-DC converter).
Functioning as the first and second switches of the. The series circuit of the first and second capacitors 7 and 8 is connected in parallel to the series circuit of the first and second transistors 3 and 4. The middle point of interconnection between the first and second capacitors 7 and 8 is connected to the terminal C. AC power supply 1 is terminal A
Connected between C and C.

The series circuit of the third and fourth transistors 9 and 10 as the third and fourth switches is composed of the first and second switches.
Are connected in parallel to the series circuit of the capacitors 7 and 8. Diodes 11 and 12 are connected in antiparallel to the third and fourth transistors 9 and 10. Third
The fourth transistors 9, 10 and the third and fourth diodes 11, 12 constitute a half-bridge type DC-AC converter (DC-AC converter).
The interconnection middle point of the third and fourth transistors 9 and 10 is connected to the terminal B via the smoothing reactor 13. The load 14 is connected between the terminals B and A.

The AC-DC control circuit 15 alternately turns on / off the first and second transistors 3 and 4 at a frequency sufficiently higher than the frequency of the voltage of the AC power supply 1, and also controls the first and second transistors. The voltage V _PN across the series circuit of the capacitors 7 and 8 is controlled to be constant. Therefore, AC-D
The C control circuit 15 includes lines 16 and 17 connected to the bases of the first and second transistors 3 and 4, a line 18 connected to the terminal A, and a current detector 19 for detecting a current from the AC power supply 1. It has a line 20 connected to, and lines 21 and 22 for detecting the voltage between the points P and N. Details of the AC-DC control circuit 15 will be described later.

The DC-AC control circuit 23 includes third and fourth DC-AC control circuits 23.
The transistors 9 and 10 are alternately turned on and off so that a sinusoidal AC voltage can be obtained. Therefore, this D
The C-AC control circuit 23 includes lines 24 and 25 connected to the bases of the third and fourth transistors 9 and 10, a line 26 connected to the terminal A, and a line 27 connected to the terminal B. Have. Details of the DC-AC control circuit 23 will be described later.

FIG. 3 shows the AC-DC control circuit 15 of FIG. 2 in detail. This control circuit 15 includes a voltage detection circuit 3 connected to the lines 21 and 22 for detecting the output voltage V _PN.
0, a reference voltage source 31, an error amplifier 32 connected to the voltage detection circuit 30 and the reference voltage source 31, a multiplier 33 connected to the power supply voltage detection line 18 and an output line of the error amplifier 32, and a current detection An error amplifier 34 connected to the line 20 and the multiplier 33, a triangular wave generation circuit 35 that generates a triangular wave at a frequency sufficiently higher than the voltage of the AC power supply 1,
It comprises a voltage comparator (comparator) 36 connected to the error amplifier 34 and the triangular wave generating circuit 35, and a transistor control signal forming circuit 37 connected to the comparator 36.
The control signal forming circuit 37 forms the control signals of the first and second transistors 3 and 4 based on the output of the comparator 36,
Send to lines 16 and 17.

The DC-AC control circuit 23 of FIG. 2 is formed as shown in FIG. That is, the DC-AC control circuit 23 includes a phase inversion circuit 40 connected to the line 26 that detects the voltage between the terminals A and C, and the phase inversion circuit 40.
An error amplifier 41 for forming an operation signal based on an error between the output signal of B and the voltage V _BC between terminals B and C obtained from the line 27, and a triangular wave at a frequency sufficiently higher than the frequency of the AC power supply 1. And a voltage comparator 4 connected to the error amplifier 41 and the triangular wave generating circuit 42.
3 and a transistor control signal forming circuit 44 connected to the comparator 43. The control signal forming circuit 44 forms the control signals of the third and fourth transistors 9 and 10 based on the output of the comparator 43 and sends them to the lines 24 and 25.

Next, the operation of the AC power converter of FIG. 2 will be described. When the first transistor 3 is off-controlled and the second transistor 4 is on-controlled during the forward voltage period of the AC power supply 1, the second capacitor 8 and the power supply 1 are
And a reactor 2 and a second transistor 4
The closed circuit is formed, the sum of the voltage of the second capacitor 8 and the voltage of the power source 1 is added to the reactor 2, and energy is accumulated in the reactor 2. Next, when the first transistor 3 is on-controlled and the second transistor 4 is off-controlled, a second closed circuit including the power supply 1, the reactor 2, the first diode 5 and the first capacitor 7 is formed. And first
Capacitor 7 is charged to a value higher than the power supply voltage.

Next, in the negative voltage period of the power source 1,
When the first transistor 3 is on-controlled and the second transistor 4 is off-controlled, a third closed circuit including the power source 1, the first capacitor 7, the first transistor 3 and the reactor 2 is formed. , The voltage of the sum of the voltage of the power source 1 and the voltage of the capacitor 7 is applied to the reactor 2, and energy is accumulated in the reactor 2. Next, when the second transistor 4 is on-controlled and the first transistor 3 is off-controlled, a fourth closed circuit including the power source 1, the second capacitor 8, the second diode 6 and the reactor 2 is formed. The second capacitor 8 is formed and is charged by the stored energy of the reactor 2 and the power supply 1 to a value higher than the power supply voltage.

In order to facilitate understanding of the AC-DC conversion operation, it is assumed that the voltage V _PN between _PN is controlled to 282 V, which is twice the 141 V corresponding to the peak value of the voltage (100 V) of the power supply 1.

Next, constant voltage control and current waveform control in the AC-DC conversion circuit will be described. The output voltage detection circuit 30 in FIG. 3 detects the voltage V _PN across _PN . Reference voltage source 3
1 outputs the reference voltage Vr corresponding to the desired voltage value of V _PN . The error amplifier 32 outputs an operation signal based on the error between the reference voltage Vr and the V _PN detection voltage, and the multiplier 33 outputs a waveform (sine wave) obtained by multiplying the input AC voltage waveform of the line 18 by the output of the error amplifier 32. . Error amplifier 34 is line 20
The operation signal is output based on the error between the input current waveform obtained from the above and the reference waveform of the multiplier output. The voltage comparator 36 compares the triangular wave of the triangular wave generating circuit 35 with the output of the error amplifier 34 and outputs a PWM wave. The control signal forming circuit 37 outputs a control signal corresponding to the PWM wave of the comparator 36 to the line 16, and outputs a signal having an opposite phase to the control signal to the line 17.
As a result, the voltage of the capacitors 7 and 8 can be controlled to be constant, and the input current waveform from the AC power source 1 can be approximated to a sine wave.

In order to perform DC-AC conversion using the first and second capacitors 7 and 8 as a DC power source, the third and fourth transistors 9 and 10 are alternately turned on and off. During the ON period of the third transistor 9, a closed circuit of the first capacitor 7, the third transistor 9 (or the diode 11), the smoothing reactor 13, the load 14 and the power supply 1 is formed, and During the ON period of the transistor 10, the second capacitor 8, the power source 1, the load 14, the smoothing reactor 13
And a second transistor 10 (or diode 12) form a closed circuit. Following equation between the loads 14 to which is connected between the terminals B and A, and the supply voltage V _AC, the load voltage i.e. AB voltage V _AB voltage V _BC between the terminals B and C The relationship is established. V _AB = V _AC -V _BC Thus, by forming the power supply voltage voltage V _AC and opposite phase as the BC voltage V _BC, the power supply voltage V higher load voltage V than _AC
You can get _AB . V _BC has a phase opposite to the power supply voltage V _AB ,
When controlled with the same amplitude, V _AB is given by the following equation. _{V AB = V AC - (-} V AC) = 2V AC

Now, a DC having the same phase as the power supply voltage V _AC but an opposite phase
Control circuit to make -AC conversion output voltage V _BC is in FIG.
Phase inverting circuit 40 in FIG. 4 AC voltage i.e. the supply voltage V _AC
Form the phase inversion signal of The error amplifier 41 forms an operation signal V ₄₁ from the error between the inverted signal of V _AC and the voltage V _BC between BC on the line 27 and sends it to the comparator 43. The comparator 43 compares the triangular wave V ₄₂ with that shown in FIG.
The PWM wave shown in (B) is formed. Control signal forming circuit 4
4 sends a signal for turning on the third transistor 9 to the line 24 in the high level period of FIG. 5B, and FIG.
The signal for turning on the fourth transistor 10 is sent to the line 25 during the low level period of.

FIG. 6 shows that the output voltage of the DC-AC converter composed of the third and fourth transistors 9 and 10 of FIG. 2, that is, the voltage V _BC between _{BC and the} AC power supply voltage, that is, the voltage V _AC between _AC , has the opposite phase and amplitude. V _AC when controlled to be
The relationship between V _BC and V _AB is shown. When the power supply voltage V _AC as shown in FIG. 6 (A) is a sine wave of a predetermined amplitude Vm, the BC voltage V _BC against V _AC shown in FIG. 6 (A) as shown in FIG. 6 (B) If the opposite phase and the same amplitude Vm are used, the load voltage V _AB is as shown in FIG.
As shown in (C), the value is twice the power supply voltage V _AC . 1
A load voltage V _{AB of} 200V with a power supply voltage V _{AC of} 00V
The voltage V _BC between BC required to obtain
The voltage of the capacitors 7 and 8 required to obtain the 100V BC effective voltage (effective value) may be 141V corresponding to the peak value of the effective value 100V. Therefore, the capacitors 7, 8,
Transistors 3, 4, 9, 10, diodes 5, 6, 1
It is possible to reduce the breakdown voltage of 1 and 12 and reduce the cost.

[0021]

[Second Embodiment] Next, an AC power converter of a second embodiment will be described with reference to FIG. However, in FIG. 7 and FIGS. 8 and 10 to be described later, substantially the same parts as those in FIG. The circuit of FIG. 7 corresponds to the circuit of FIG. 2 from which the first and second transistors 3 and 4, the boosting reactor 2 and the AC-DC control circuit 15 are omitted, and other configurations are the same as those of FIG. Has been done.
Therefore, the circuit of FIG. 7 has the same action and effect as those of FIG. 2 except that it does not have the boosting action by the reactor. In addition,
When the voltage of the power source 1 is 100V, the capacitors 7 and 8
Are each charged to about 141V. This gives about 2
It is possible to obtain a load voltage V _{AB of} 00V.

[0022]

[Third Embodiment] The AC power converter according to the third embodiment of FIG. 8 is an embodiment in which a high power supply voltage is input to a low capacitor voltage, and the AC power supply 1 and the load 14 in the circuit of FIG. Equivalent to the connection position of was changed. That is, in the circuit of FIG. 8, the AC power supply 1 is connected between the terminals A and B, the load 14 is connected between the terminals B and C, and the others are configured substantially the same as in FIG. It was done.

In FIG. 8, the power supply 1, the reactor 2, the first diode 5,
The first capacitor 7 is charged in a closed circuit composed of the first capacitor 7 and the load 14. Since a load is interposed in this closed circuit, the voltage V _{AB of the} power supply 1 and the voltage V _AB of the load 14
_The voltage to which _BC is added becomes the charging voltage for the first capacitor 7. Here, the charging voltage of the first capacitor 7 can be lowered by controlling V _BC in the opposite phase to V _AC .
Further, during the negative voltage period of the power supply 1, the second capacitor 8 is charged by the closed circuit of the power supply 1, the load 14, the second capacitor 8, the second diode 6 and the reactor 2.
In this case also, since the load 14 is included in the closed circuit, the voltage of the second capacitor 8 can be lowered by controlling V _BC in the same manner.

The operation of converting the DC voltage of the first and second capacitors 7 and 8 into the AC voltage V _BC by the third and fourth transistors 9 and 10 is performed by the half bridge type DC-AC shown in FIGS. It is the same as the converter.

The voltage between _{AB and the} power supply voltage V _AB of the circuit of FIG.
And the voltage between _BC, that is, the load voltage V _BC and the voltage between _AC V _AC , the following relationship is established. V _AC = V _AB + V _BC Here, V _BC has a phase opposite to the power supply voltage V _AB and the amplitude is 1 of V _AB .
When controlled to / 2, V _AC becomes the following equation. _VAC = _VAB + ( _-VAB / 2) = _VAB / 2 FIG. 9 (A) (B) (C) shows these relationships. Figure 1
In the conventional circuit of, for example, when the power supply 1 is set to 200 V (effective value), the capacitor voltage is a peak value of the power supply 1 of 282 V.
Although it is charged as described above, according to the circuit of FIG. 8, by controlling the load voltage in a phase opposite to that of the power source 1 and controlling the amplitude to 1/2 of that of the power source 1, the voltage V _AC between _AC is 100 V (effective). It can be reduced to a value), whereby the Condesa voltage, V _AC of peak - will be live in charge of click value 141V. Thus, at low capacitor voltage, higher peak
It is possible to control the AC voltage having a negative value.

[0026]

[Fourth Embodiment] The AC power converter according to the fourth embodiment shown in FIG. 10 is similar to that shown in FIG.
And the second transistors 3 and 4, the AC-DC control circuit 1
5, which corresponds to the current detector 19 removed. That is,
In FIG. 8, the AC-DC converter is composed of only two diodes 5 and 6. The other circuit configuration of FIG. 10 is shown in FIG.
Since it is the same as that of FIG.

[0027]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) In FIGS. 2 and 7, as shown in FIG.
The amplitude adjusting circuit 52 adjusts the amplitude of the detection line 26 of the _AC-to- AC voltage V _{AC according} to the amplitude command given from the line 53 to form a reference waveform (desired voltage waveform) with respect to V _BC , and the error amplifier 41 performs the reference. It is also possible to form an operation signal from the error between the waveform and the BC voltage V _BC of the line 27, and thereby form the PWM pulse. Note that FIG.
The circuit subsequent to the error amplifier 41 of No. 1 has the same circuit configuration as that of FIG. According to the method of FIG. 11, the amplitude command is changed from 1 to -1.
By doubling, the load voltage V _AB can be varied from zero to twice the power supply voltage V _AC . In particular, in FIG. 2, since the electric power is bidirectional and the input current from the AC power source 1 can be made into a sine wave, it can be used as an AC voltage variable device for experiments without pollution of the input power source. (2) In FIGS. 2 and 7, as shown in FIG.
The detection line 26 of the _AC-to- AC voltage V _AC is arbitrarily adjusted by the phase command given from the line 51 in the phase adjustment circuit 50 to create a reference waveform (desired voltage waveform) with respect to V _BC, and the reference is provided in the error amplifier 41. It is also possible to form an operation signal from the error between the waveform and the BC voltage V _BC of the line 27, and thereby form the PWM pulse. Note that FIG.
The circuit subsequent to the second error amplifier 41 has the same circuit configuration as that of FIG. According to the method of FIG. 12, the phase command is changed from 0 degree to 18 degrees.
By changing to 0 degree, the load voltage V _AB can be varied from zero to twice the power supply voltage V _AC . (3) In FIGS. 2 and 7, as shown in FIG.
The phase synchronization circuit 54 and the reference waveform generation circuit 55 are provided, and the AC
Between voltage V _AC detection line 26 as a reference phase, and controls the output waveform of the reference waveform generating circuit 55 (amplitude constant sinusoidal waveform) in V _AC and the same phase by the phase synchronization circuit 54, which V
_{This is} the reference waveform for _AB . In the error amplifier 41, an operation signal may be generated from the error between the reference waveform and the AB voltage V _AB on the line 56, and the PWM pulse may be formed by this. The circuit subsequent to the error amplifier 41 of FIG. 13 has the same circuit configuration as that of FIG. According to the method of FIG. 13, the load voltage V _AB can be made a sine waveform with a constant amplitude regardless of the fluctuation of the power supply voltage V _AC . (4) In FIGS. 8 and 10, the same control as in FIGS. 11, 12, and 13 can be performed. In Examples 3 and 4, the phase or amplitude of the output voltage of the DC-AC converter is
It is possible to adjust the voltage applied between the midpoint of the first and second switch interconnections and the first and the second contentor interconnection points by changing the phase opposite to that of the power supply 1 and ½ the amplitude. is there. (5) Instead of the anti-parallel circuit of the transistors 3, 4, 9, 10 and the diodes 5, 6, 11, 12, the reverse of the IGBT (insulated gate bipolar transistor) and the diode D shown in FIG. A parallel circuit, or an insulated gate field effect transistor FET having a diode D therein as shown in FIG.
Or it could be another semiconductor controlled switch.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a conventional AC power converter.

FIG. 2 is a circuit diagram showing an AC power converter according to a first embodiment of the present invention.

FIG. 3 is a block diagram showing in detail the AC-DC control circuit of FIG.

FIG. 4 is a block diagram showing the DC-AC control circuit of FIG. 2 in detail.

5 is a waveform diagram showing a state of each part of FIG.

FIG. 6 is a waveform diagram of each part of FIG.

FIG. 7 is a circuit diagram showing an AC power converter of a second embodiment.

FIG. 8 is a circuit diagram showing an AC power converter according to a third embodiment.

9 is a waveform diagram of each part of FIG.

FIG. 10 is a circuit diagram showing an AC power converter of a fourth embodiment.

FIG. 11 is a block diagram showing a modification of the DC-AC control circuit.

FIG. 12 is a block diagram showing a DC-AC control circuit of another modification.

FIG. 13 is a block diagram showing a DC-AC control circuit according to still another modification.

FIG. 14 is a diagram showing a modification of the switch.

FIG. 15 is a diagram showing another modification of the switch.

[Explanation of symbols]

 1 AC power supply 7, 8 Capacitor 14 Load

Claims (4)

[Claims] 1. A series circuit of first and second switches; a series circuit of first and second capacitors connected in parallel to the series circuit of the first and second switches; A series circuit of third and fourth switches connected in parallel to a series circuit of first and second capacitors, a middle point of mutual connection of the first and second switches, and the first circuit
And an AC power supply connected to a middle point of mutual connection of the second capacitor, a terminal of the AC power supply on a side connected to a middle point of mutual connection of the first and second switches, and the third And a load connected between a middle point of interconnection of the fourth switch and the first and second switches so as to perform AC-DC conversion, and the third and fourth switches are input AC input. An AC power converter comprising: a control circuit that controls to perform DC-AC conversion in synchronization with a power supply phase. 2. A series circuit of first and second switches; a series circuit of first and second capacitors connected in parallel to the series circuit of the first and second switches; A series circuit of third and fourth switches connected in parallel to a series circuit of first and second capacitors, a middle point of mutual connection of the first and second switches, and the third circuit
And an AC power source connected between the interconnection switch midpoint of the fourth switch and the interconnection midpoint of the third and fourth switches, and the first switch.
And a load connected between the middle point of interconnection of the second capacitor and the first and second switches so as to perform AC-DC conversion, and the third and fourth switches as input AC. An AC power converter comprising: a control circuit that controls to perform DC-AC conversion in synchronization with a power supply phase. 3. The first and second switches are anti-parallel circuits of a control switch element and a diode, and a reactor is provided between the AC power supply and a middle point of mutual connection of the first and second switches. The AC power converter according to claim 1 or 2, characterized in that the AC power converter is connected. 4. The AC power converter according to claim 1, wherein the first and second switches are diodes, and the control circuit converts the third and fourth switches from DC to AC. .