JP3446793B2 - Power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device used as a single-phase AC power supply of a commercial frequency or the like, and more particularly to a cycloconverter whose input side is a generator with a relatively small output power. In this case, the present invention relates to a measure against withstand voltage of the converter due to an increase in no-load voltage due to load characteristics.

[0002]

2. Description of the Related Art Conventionally, what is called a cycloconverter is known as a device for directly converting AC power of a constant frequency into AC power of another different frequency.

Such a conventional cycloconverter is usually used as an input for the output of a commercial frequency power supply line or a high-power generator (for example, Japanese Patent Publication No. 60).
No. 9429), generally used for driving an AC motor.

The operating principle of the cycloconverter will be described below with reference to FIGS.

FIG. 6 is an electric circuit diagram showing an example of the configuration of a conventional cycloconverter.

As shown in the figure, the cycloconverter CC includes 12 thyristors SCRs.
A positive current is output from a bridge circuit (hereinafter, referred to as a “positive converter”) BC1 that is configured by k ± (k = 1, ..., 6) and that includes six thyristors SCRk +. Bridge circuit composed of a thyristor SCRk- (hereinafter referred to as "negative converter") B
A negative current is output from C2.

For example, 27 poles driven by an internal combustion engine (3 poles of which are used to generate a synchronization signal for controlling each gate of the thyristor SCRk ±)
The three-phase AC output of the three-phase generator is a cycloconverter CC
If the input is to, the alternating current of 9 cycles can be obtained per one rotation of the crankshaft. Then, when the engine speed range is set to, for example, 1200 rpm to 4500 rpm (that is, 20 Hz to 75 Hz), the above 3
The frequency of the phase AC output is 180, which is nine times the engine speed.
Hz to 675 Hz.

The three-pole coil (hereinafter, this coil is referred to as a "sub coil", and the other coils are referred to as "main coils").
7), three-phase currents (U-phase, V-phase, and W-phase currents) are obtained from the primary sides of the six photocouplers PCk (k = 1, ..., 6) as shown in FIG. Light emitting diode (LED) and 6 diodes Dk (k = 1, ..., 6)
Bridge type three-phase full-wave rectifier circuit FR
Is supplied to. The three-phase current that is full-wave rectified by the three-phase full-wave rectifier circuit FR is converted into light by the primary side LED, and this light output is a current by each secondary side photosensor (not shown) of the photocoupler PCk. Is converted to. That is,
A current corresponding to the three-phase current that is full-wave rectified by the three-phase full-wave rectifier circuit FR is taken out by the secondary side photosensor. Then, the extracted current is used to generate a synchronization signal (for example, a sawtooth wave) that controls the conduction angle of each gate of the thyristor SCRk ±, as described later.

FIG. 8 shows the transition of the voltage applied between the U-phase, V-phase and W-phase of FIG. 6 or 7, and the photocoupler P.
It is a figure which shows the timing which Ck turns on.

Each line voltage (U-V, U-W, V-W, V
-U, W-U, W-V) changes as shown in FIG. 8, the output waveform that is full-wave rectified by the three-phase full-wave rectifying circuit FR is the waveform of each line voltage obtained from the main coil. It becomes 1/6 of the cycle. For example, the phase angle is 60 ° to 120 °
When the voltage between U and V is the highest as compared with the other line voltage, the photocouplers PC1 and PC5 are turned on in pairs (the other photocouplers are turned off).
From the phase full-wave rectifier circuit FR, a voltage corresponding to the voltage between U and V is output. That is, since the voltage corresponding to the maximum value of each line voltage is output from the three-phase full-wave rectification circuit FR, the cycle of this voltage is 60 °, which is 1 with respect to the main coil voltage cycle of 360 °. It becomes / 6.

FIG. 8 also shows the timing at which each gate of the thyristor SCRk ± is turned on. In FIG. 8, the conduction angle of each gate is set within the range of 120 ° to 0 °. The timing when making it is shown.

According to this timing, when the current is output from the cycloconverter CC, the positive converter B
While igniting each gate of C1, cycloconverter C
When absorbing (supplying) the current to C, the negative converter B
Ignite each gate of C2.

It is not necessary to carry out the ignition continuously over the range shown in the figure, and the same operation can be obtained by applying the pulse shown by the hatched line in the figure to the gate.

FIG. 9 shows the thyristors SC of the positive or negative converters BC1 and BC2 with the conduction angles α = 120 ° and 60 °.
It is a figure which shows the waveform output from the cycloconverter CC when Rk ± is ignited.

In the figure, (a) shows the conduction angle α = 12.
The waveform output from the cycloconverter CC when each thyristor SCRk + of the positive converter BC1 is ignited at 0 ° is shown in (b), and each thyristor SCRk− of the negative converter BC2 is ignited at the conduction angle α = 120 °. Shows the waveform output from the cycloconverter CC when
(C) shows a waveform output from the cycloconverter CC when each thyristor SCRk + of the positive converter BC1 is fired at a conduction angle α = 60 °, and (d) shows a negative converter at a conduction angle α = 60 °. Each thyristor SCR of BC2
The waveform output from the cycloconverter CC when k-is fired is shown.

For example, when each thyristor SCRk + of the positive converter BC1 is ignited at the conduction angle α = 120 °, the waveform output from the cycloconverter CC is a full-wave rectified waveform as shown in FIG. 9 (a). Becomes Further, each thyristor S of the positive converter BC1 has a conduction angle α = 60 °.
When CRk + is ignited, the waveform output from the cycloconverter CC is a waveform including a large amount of harmonic components as shown in FIG. 9C, but the cycloconverter C
When a high cut filter is connected to the output side of C, this harmonic component is removed and the average voltage is output. As described above, assuming that the input generator is a 27-pole three-phase generator and the engine speed is 3600 rpm, the frequency of the harmonic fundamental wave is as follows.

60 Hz (= 3600 rpm) × 9th harmonic ×
3 phases × 2 (full wave) = 3.24 kHz, and the conduction angle α of the positive converter BC1 is 0 ° to 120.
By changing in the range of °, the cycloconverter CC can output any positive voltage whose average voltage is in the range of 0V to the full-wave rectified voltage. Further, by changing the conduction angle α of the negative converter BC2 in the same manner, the cycloconverter CC can output an arbitrary negative voltage whose average voltage is in the range of 0 V to −full-wave rectified voltage.

Next, a method of changing the conduction angle α in the range of 0 ° to 120 ° will be described.

FIG. 10 is a diagram showing a reference sawtooth wave generated for controlling the conduction angle α. The reference sawtooth wave in FIG. 10 is detected by the secondary side photosensor of the photocoupler PCk in FIG. It is generated based on the applied current.

Thyristor SCR1 of the positive converter BC1
The reference sawtooth wave corresponding to + has a conduction angle α of 120 ° ~
In the range of 0 °, the sawtooth wave that becomes 0 V when α = 0 ° corresponds. Then, sawtooth waves having a phase difference of 60 ° are generated in the thyristors SCR1 +, 6+, 2+,
It corresponds to each thyristor SCRk + in the order of 4+, 3+, 5+.

On the other hand, the thyristor S of the negative converter BC2
For CR1-, a sawtooth wave that is vertically symmetrical with the thyristor SCR1 + and has a phase shift of 180 ° is generated. Then, similarly to the positive converter BC1, sawtooth waves having a phase difference of 60 ° are generated in the thyristor SCR1.
It corresponds to each thyristor SCRk- in the order of-, 6-, 2-, 4-, 3-, 5-.

As described above, the reference waveform is composed of twelve sawtooth waves corresponding to the thyristors SCRk ± of the positive and negative converters BC1 and BC2. These sawtooth waves are compared with the target waveform r by a 12-system comparator (not shown), and the intersection (for example, the point TO in the thyristor SCR1 +) is the thyristor SCR.
The conduction angle is k ±.

By taking a sine wave as the target wave and changing the conduction angle α into a sine wave, a sine wave output can be obtained from the cycloconverter CC as shown in FIG. The frequency of the input waveform is, for example, 540
Hz, and when a 50 Hz sine wave output is obtained from this input waveform, a waveform is formed by connecting about 65 parts of the input sine wave.

[0024]

By the way, when the output of the cycloconverter is used as a sinusoidal single-phase alternating current, the cycloconverter does not have a portion for accumulating energy. The input energy of will also change in a sinusoidal manner.

Therefore, when a small output, for example, a generator of several hundred to several kW is connected to the input side of the cycloconverter to output a single-phase sine wave, the input energy can be used except for the peak portion of the sine wave. Since it is not available, the utilization efficiency is very poor, and the output that can be taken out as a single-phase AC becomes very small.

In particular, when a magnet generator is used as the above-mentioned small-output generator, its energy is limited. Therefore, for example, when a motor load is connected, even a temporary large current at the time of starting is overloaded. There was a problem such as being in a state of being unable to operate.

The present invention has been made in view of the above problems, and when a generator with a small output capacity is connected to the input side of a cycloconverter, even if a temporary overload condition occurs,
It is an object of the present invention to provide a power supply device that can be operated smoothly.

[0028]

In order to achieve the above-mentioned object, a power supply device according to claim 1 is connected to a three-phase generator and a three-phase winding output of the generator, and is connected in antiparallel with each other. And a pair of variable control bridge circuits forming a cycloconverter that outputs a single-phase current, and the variable control bridge circuits connected in anti-parallel to each other are alternately arranged every half cycle of the current supplied to the load. In a power supply device that outputs a single-phase alternating current by switching operation, the three-phase generator is composed of a magnet generator having a permanent magnet rotor, and maintains a single-phase output voltage waveform of the variable bridge circuit in a sine wave shape. In addition, as the load increases, the sine wave is changed to a rectangular wave whose maximum amplitude is limited by the set output voltage so as to cope with an overload state.

Further, in order to achieve the above-mentioned object, claim 2
The power supply device described in 1. is a three-phase generator and a set of variable control bridges that are connected to the three-phase winding outputs of the generator and are connected in anti-parallel to each other to form a cycloconverter that outputs a single-phase current. and a circuit, the variable control bridge circuits connected in antiparallel to each other, in the electric power supply apparatus is operated alternately switched to output an alternating current having a single phase in each half cycle of the current supplied to the load, the 3-phase Generator is a permanent magnet
The variable bridge circuit is composed of a magnet generator with a trochanter.
While maintaining the single-phase output voltage waveform of the path as a sine wave,
By changing the target waveform of the drive signal for operating the variable bridge circuit to output AC power from a sine wave to a rectangular wave as the load increases , the single-phase output wave
The shape is changed from a sine wave to a square wave to handle overload conditions.
It is characterized by doing so.

[0030]

[0031] it is et al., Preferably, together with changing the amplitude of the target wave based on a result of comparison between the output voltage and the set voltage of the cycloconverter, by limiting the upper or lower limit of the amplitude, the target It is characterized in that the shape of the wave is changed from a sine wave to a rectangular wave.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic structure of a power supply device according to an embodiment of the present invention. In the figure, constituent elements corresponding to those described in FIG. , The description is omitted.

In FIG. 1, 1 and 2 are output windings independently wound around the stator of the AC generator,
Reference numeral 1 is a 3-phase main output winding (main coil), and 2 is a 3-phase auxiliary output winding (sub coil).

FIG. 2 is a sectional view of the above AC generator,
In the figure, the three-phase main coil 1 has two
The three-phase sub-coil 2 is composed of a one-pole coil
It is composed of 3 pole coils in 2. Then, the rotor R is formed with eight pairs of magnetic poles of permanent magnets, and is configured to be rotationally driven by an internal combustion engine (not shown).

Returning to FIG. 1, the three output terminals U, V, W of the three-phase main coil 1 are connected to the positive and negative converters B, respectively.
It is connected to the input terminals U, V, W of C1, BC2, the output side of the cycloconverter CC is connected to the LC filter 3 for removing the harmonic components of its output current, and the output side of the LC filter 3 is This output is connected to an output voltage detection circuit 5 for detecting a voltage corresponding to the current from which the harmonic component has been removed. The negative input terminal of the output voltage detection circuit 5 is connected to the ground GND of the control system,
The output voltage detection circuit 5 is configured to obtain a single-phase output from both positive and negative input terminals.

The output side of the output voltage detection circuit 5 is connected to an approximate effective value calculation circuit 8 which calculates and outputs the approximate effective value of the output voltage. The output side of the approximate effective value calculation circuit 8 is a comparator 9 It is connected to the negative input terminal of. A reference voltage output circuit 10 that outputs the reference voltage value of the power supply device is connected to the positive input terminal of the comparator 9, and the output side of the comparator 9 is
Control function according to the result of this comparison (eg proportional function)
A control function calculation circuit 11 for calculating and outputting is connected.

The output side of the control function operation circuit 11 is connected to an amplitude control circuit 12 for controlling the amplitude of a sine wave having a commercial frequency of 50 Hz or 60 Hz output from the sine wave oscillator 13, and the amplitude control circuit 12 is connected. The output side of the sine wave oscillator 13 is also connected to. The amplitude control circuit 12 outputs an amplitude control signal for controlling the amplitude of the sine wave output from the sine wave oscillator 13 according to the control function output from the control function calculation circuit 11.

The output side of the amplitude control circuit 12 is connected to a target wave output circuit 14 which outputs a target wave according to this output signal (amplitude control signal), and the output side of the target wave output circuit 14 is a cycloconverter CC. Each thyristor S that composes
Conduction angle control unit 15 for controlling the conduction angle of the gates of CRk ±
And the positive side input terminal of the comparator 16.

The conduction angle control unit 15 includes a positive converter BC1.
Positive gate control unit 15a for controlling the conduction angle of the gate of each thyristor SCRk + (hereinafter, referred to as "positive gate")
And a negative gate control unit 15b that controls the conduction angle of the gate of each thyristor SCRk− of the negative converter BC2 (hereinafter referred to as “negative gate”).

Each of the gate control units 15a and 15b has six comparators (not shown), and each comparator has the target wave and the sync signal (to be described later) as described with reference to FIG. The standard sawtooth wave) is compared, and the gate is ignited when the two coincide.

The output side of the output voltage detecting circuit 5 is connected to the negative side input terminal of the comparator 16, and the output side of the comparator 16 has a positive gate control section 15a and a negative gate control section 15.
connected to b. The comparator 16 compares the voltage output from the output voltage detection circuit 5 with the target wave, and outputs a high (H) level signal or a low (L) level signal according to the comparison result.

When the H level signal is output from the comparator 16, the positive gate control section 15a operates, while the negative gate control section 15b stops, and when the L level signal is output, conversely, The positive gate controller 15a is stopped while the negative gate controller 15b is activated.

The output side of the three-phase sub-coil 2 is connected to the synchronizing signal forming circuit 18 having the three-phase full-wave rectifying circuit FR of FIG. 7, for example. Sync signal forming circuit 18
Generates and outputs the sawtooth wave shown in FIG. 3 according to the three-phase output from the three-phase subcoil 2.

FIG. 3 is a diagram showing an example of a sawtooth wave capable of controlling the conduction angle within this range when the control range of the conduction angle of each thyristor SCRk ± is set to 120 ° to −60 °. The sawtooth wave shown in FIG. 10 differs from the sawtooth wave shown in FIG. 10 in that the width of the sawtooth wave is enlarged. The reason for expanding the control range of the conduction angle of each thyristor SCRk ± to the negative side with respect to the conventional cycloconverter CC is as follows.

In the conventional cycloconverter CC,
When a capacitive load is connected to the output terminal and the output voltage is controlled to decrease when there is a positive potential on the load side, the discontinuity point in the relationship between the conduction angle of each thyristor SCRk ± and the output voltage. Occurred, and the output voltage could not be maintained stably. That is, in order to reduce the output voltage when there is a positive potential on the load side, it is necessary to absorb the positive charge of the load. At this time, the conventional cycloconverter CC described above is used.
Since the conduction angle α is limited to the range of 120 ° to 0 °, the positive converter BC1 cannot absorb the positive charge of the load, and therefore the negative converter BC2 must absorb it. When the negative converter BC2 absorbs this positive charge, the output current from the negative converter BC2 is −full-wave rectified voltage to 0V as described above, so the positive potential of the load sharply drops to 0V. As a result, a discontinuity occurs in the output voltage. At this time, if the conduction angle is expanded to 120 ° to −60 °, the negative converter BC
Since the charge of the load can be absorbed up to a positive voltage by 2, the discontinuity does not occur in the output voltage and the control stability can be maintained.

However, when the conduction angle is expanded to the negative side in this way, as shown in FIG.
Since the output ranges of 1 and BC2 overlap, the intersection of the target wave r and the sawtooth wave becomes two points, TO1 and TO2, and either the positive or negative converter BC1 or BC2 is selected, and the corresponding thyristor SCRk is selected. I couldn't decide whether to fire the ± gate. Therefore, in the present embodiment, as described above, one of the positive or negative converters BC1 and BC2 is selected according to the comparison result of the comparator 16.

The output side of the synchronization signal forming circuit 18 is connected to the positive gate controller 15a and the negative gate controller 15b. Here, each connection line connecting the synchronization signal forming circuit 18 and each of the gate control units 15a and 15b is composed of six signal lines, and each signal line of each of the gate control units 15a and 15b. It is connected to each comparator, and each comparator is supplied with the sawtooth wave at the timing described in FIG.

The outputs of the six comparators of the positive gate controller 15a are respectively connected to the thyristors S of the positive converter BC1.
The output side of the six comparators of the negative gate controller 15b, which are connected to the gate of CRk +, are respectively connected to the negative converter BC2.
Is connected to the gate of each thyristor SCRk-.

In the present embodiment, the synchronizing signal forming circuit 18 is configured to form the synchronizing signal in accordance with the three-phase output from the three-phase sub-coil 2, but the present invention is not limited to this.
Instead of the phase sub-coil 2, a single-phase sub-coil may be used and a synchronization signal (reference sawtooth wave) may be formed according to the single-phase output.

The operation of the power supply device configured as described above will be described below.

When the rotor R is rotationally driven by the engine, a voltage is applied between the respective phases of the three-phase main coil 1 as described above. When each gate of the thyristor SCRk ± is fired by the conduction angle control unit 15, a current is output from the cycloconverter CC in response to this, the harmonic component of this current is removed by the filter 3, and the output voltage is increased. The voltage is detected by the detection circuit 5. Each voltage thus detected is calculated by the approximate effective value calculation circuit 8 and output.

This approximate RMS voltage is
It is compared with the reference voltage value output from the reference voltage output circuit 10, and a control function (proportional function) is calculated by the control function calculation circuit 11 according to the comparison result and output. Specifically, the control function calculation circuit 11 increases the output value from the comparator 9, that is, the reference voltage output circuit 10
The proportional function is calculated and output such that the proportional coefficient increases as the difference between the reference voltage output from the device and the approximate effective value from the approximate effective value calculation circuit 8 increases.

In accordance with the calculated and output control function, the amplitude control circuit 12 generates a control signal for controlling the amplitude of the sine wave of 50 Hz or 60 Hz output from the sine wave oscillator 13, and outputs the control signal. The wave output circuit 14 outputs a target wave according to this control signal. Here, upper and lower limit values are provided for the output value from the target wave output circuit 14, so that the target wave output circuit 14 cannot output a value larger than the predetermined upper limit value or smaller than the predetermined lower limit value. It is configured. That is, as the output value from the comparator 9 increases and the proportional coefficient of the proportional function output from the control function arithmetic circuit 11 increases, the shape of the target wave output from the target wave output circuit 14 changes from a sine wave. It is transformed into a rectangular wave.

The target wave output from the target wave output circuit 14 is compared with the detection voltage output from the output voltage detection circuit 5 by the comparator 16, and if the voltage of the target wave is higher than the detection voltage, the comparison is performed. The H-level signal is output from the comparator 16, and the positive gate controller 15a is selected to operate. On the other hand, when the voltage of the target wave is lower than the detection voltage, the L-level signal is output from the comparator 16. , The negative gate controller 15b is selected to operate.

In each comparator of the gate control units selected from the positive gate control unit 15a and the negative gate control unit 15b, the target wave from the target wave output circuit 14 and the sawtooth wave from the synchronization signal forming circuit 18 are detected. When they are compared with each other and the two coincide with each other, a one-shot pulse having a predetermined width is output to the gate of the thyristor SCRk ± to control the conduction angle.

FIG. 5 is a diagram showing an example of an output waveform of 50 Hz generated by the power supply device of this embodiment,
(A) shows an output waveform at no load, (b) shows an output waveform at a rated load, and (c) shows an output waveform at an overload.

As shown in the figure, when, for example, a temporary overload occurs, the reference voltage output from the reference voltage output circuit 10 and the approximate effective value calculation circuit 8 will depend on the state of the overload. The output waveform is transformed from a sine wave to a rectangular wave according to the difference from the approximate effective value.

In the present embodiment, the shape of the target wave is changed from the sine wave to the rectangular wave according to the load condition, but the present invention is not limited to this, and the output voltage is limited to the maximum amplitude. When the power supply device is configured as described above, the amplitude of the target wave may be increased according to the state of the load.

As described above, in the present embodiment, when the load becomes temporarily large, the output is increased to near the upper limit of the total input energy from the generator, so that the output is increased. Even when a temporary overload condition occurs, it is possible to continue operation without difficulty.

[0061]

As described above, according to the present invention,
Since the single-phase output waveform of the variable bridge circuit changes from a sine wave to a rectangular wave whose maximum amplitude is limited by the set output voltage as the load increases, a generator with a small output capacity is installed on the input side of the cycloconverter. Even if a temporary overload state occurs when the connection is made, it is possible to continue the operation without difficulty.

Further, the target wave of the drive signal for operating the variable bridge circuit to output AC power changes from a sine wave to a rectangular wave as the load increases, and in response to this, a single phase output from the power supply device. Since the output waveform is also transformed from the sine wave to the rectangular wave, the same effect as the above effect can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a power supply device according to an embodiment of the present invention.

2 is a cross-sectional view of the AC generator of FIG.

FIG. 3 shows a control range of the conduction angle of each thyristor in FIG.
It is a figure which shows an example of the sawtooth wave which can perform conduction angle control within this range, when it is set to 0 ° to −60 °.

FIG. 4 is a diagram for explaining a problem that occurs when the conduction angle is 120 ° to −60 °.

5 is a diagram showing an example of an output waveform of 50 Hz generated by the power supply device of FIG.

FIG. 6 is an electric circuit diagram showing an example of a configuration of a conventional cycloconverter.

FIG. 7 is an electric circuit diagram showing a configuration of a bridge type three-phase full-wave rectifier circuit.

FIG. 8 is a diagram showing a transition of a voltage applied between the U-phase, V-phase and W-phase of FIG. 6 or 7, timing of turning on the photocoupler, and timing of firing each gate of the thyristor.

FIG. 9 is a diagram showing a waveform output from the cycloconverter when each thyristor of the positive or negative converter is fired at the conduction angles α = 120 ° and 60 °.

FIG. 10 shows a reference sawtooth wave generated to control the conduction angle.

11 is a diagram showing a 50 Hz sine wave generated by the cycloconverter of FIG. 6;

[Explanation of symbols]

1 3-phase main coil (3-phase output winding) 5 Output voltage detection circuit 14 Target wave output circuit 15 Conduction angle control unit 16 Comparator BC1 Positive converter (variable control bridge) BC2 Negative converter (variable control bridge) CC cyclo converter

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Claims (3)

(57) [Claims] 1. A three-phase generator and a set of variable control bridge circuits connected to the three-phase winding outputs of the generator and connected in anti-parallel with each other to form a cycloconverter that outputs a single-phase current. A variable control bridge circuit connected in antiparallel to each other and alternately switching operation for every half cycle of a current supplied to a load to output a single-phase alternating current. limited by the output voltage maximum amplitude is set from the sine wave in accordance constituted by magneto generator, while maintaining a single-phase output voltage waveform of the variable bridge circuit sinusoidally, the load increases with the permanent magnet rotor The power supply device is characterized in that it is adapted to cope with an overload state by changing to a rectangular wave. 2. A three-phase generator and a set of variable control bridge circuits connected to the three-phase winding outputs of the generator and connected in anti-parallel with each other to form a cycloconverter that outputs a single-phase current. A variable control bridge circuit connected in antiparallel to each other and alternately switching operation for every half cycle of a current supplied to a load to output a single-phase alternating current. Is a magnet generator having a permanent magnet rotor, maintains a single-phase output voltage waveform of the variable bridge circuit in a sine wave shape, and operates the variable bridge circuit to output an AC power target waveform of a drive signal. By changing the sine wave from a sine wave to a rectangular wave as the load increases, thereby changing the single-phase output waveform from a sine wave to a rectangular wave to cope with an overload condition. Power supply that. 3. The shape of the target wave is sinusoidal by changing the amplitude of the target wave based on the result of comparison between the output voltage of the cycloconverter and the set voltage and limiting the upper limit or the lower limit of this amplitude. The power supply device according to claim 2, wherein the wave is changed to a rectangular wave.