JP2001258259A - Ac/ac direct power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC/AC power converter that can be normally operated for continuing the driving of a motor or the like even if the voltage of a three- phase AC power supply becomes unbalanced. SOLUTION: The three linear voltage of the three-phase AC power supply are detected by a voltage detection circuit 100, the maximum linear voltage is generated by a rectifying circuit 101 and is multiplied using a multiplier 102 a specific number for outputting a voltage of VMAX/√2. The voltage VMAX/√2 is compared with the command of voltage command equipment 110 for outputting the smaller one as a voltage V1. PWM control where the effective value of three-phase output is set to the voltage V1 by a PWM control circuit 111 controls bidirectional switches SUR, SUS, SUT, SVR, SVS, SVT, SWR, SWS, and SWT via a gate drive circuit 60 for obtaining the three-phase output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / AC power converter for converting an AC voltage into an AC voltage having an arbitrary frequency, and more particularly, to an AC / AC power converter using a PWM (pulse amplitude modulation) control method. About.

[0002]

2. Description of the Related Art As a conventionally used method for driving a frequency control motor or the like, there is a method using an AC / AC power converter using a PWM inverter. Conventional PW
Since the M inverter is connected to the AC power supply via the rectifier circuit, the maximum voltage of the AC power supply is secured as the input DC voltage value. Therefore, even if the voltage of the AC power supply is in an unbalanced state, the input DC voltage to the PWM inverter is maintained at a certain value or more, so that the motor or the like can be driven.

In some cases, a method using a PWM cycloconverter, which is an AC / AC direct power converter, is suitable for driving a frequency control motor or the like. The PWM cycloconverter is also called a matrix converter.

[0004]

However, since the three-phase AC power supply is directly connected to a load such as a motor via a bidirectional switch, the matrix converter normally operates when the voltage of the three-phase AC power supply becomes unbalanced. Can not work.

[0005] It is an object of the present invention to provide an AC / AC power converter that can operate normally and continue driving a motor or the like even when an unbalanced state occurs in the voltage of a three-phase AC power supply. It is.

[0006]

In order to achieve the above object, an AC / AC direct power converter of the present invention comprises an input filter for shaping a three-phase output waveform of a three-phase AC power supply, and an input filter. A plurality of bidirectional switches connected to a waveform-shaped three-phase signal for power conversion by on / off, and controlling on / off of the bidirectional switch based on a commanded voltage and a commanded frequency. A PWM control circuit, a commutation control circuit for controlling commutation of the bidirectional switch,
A voltage detection circuit that detects and outputs three line voltages of a three-phase AC power supply, a maximum voltage generation circuit that generates a maximum line voltage from the line voltage, and a three-phase output that is always equal to or less than the maximum line voltage As described above, a control circuit for instructing a voltage to the PWM control circuit is provided.

[0007] When the three-phase AC power source becomes unbalanced and cannot operate normally at a desired output voltage, PWM control is performed to the maximum voltage possible as a three-phase output in that state, so that AC / AC direct power conversion is performed. The device can continue to operate.

According to an embodiment of the present invention, the maximum voltage generating circuit includes a rectifying circuit for rectifying a line voltage and a multiplier for multiplying the output of the rectifying circuit by a predetermined number. And a comparator for comparing the output of the multiplier with the command of the voltage commander and outputting the smaller one.

Another AC / AC direct power converter of the present invention is connected to an input filter for shaping a three-phase output waveform of a three-phase AC power supply, and a three-phase signal whose waveform is shaped by the input filter. Plural bidirectional switches for power conversion by ON / OFF, and P for controlling ON / OFF of the bidirectional switch based on a commanded voltage and a commanded frequency
A WM control circuit, a commutation control circuit for controlling commutation of the bidirectional switch, a voltage detection circuit for detecting three line voltages of the three-phase AC power supply, and a maximum for generating a maximum line voltage from the line voltage It has a voltage generation circuit and a control circuit for instructing the PWM control circuit on the voltage and frequency so that the output is always less than or equal to the maximum line voltage.

When the output of the three-phase AC power supply becomes unbalanced and cannot operate normally at a desired frequency, PWM control is performed to the maximum frequency possible as a three-phase output in that state, so that the AC / AC direct type The power converter can continue to operate.

According to an embodiment of the present invention, the maximum voltage generating circuit includes a rectifying circuit for rectifying a line voltage and a multiplier for multiplying an output of the rectifying circuit by a predetermined number. A voltage commander, a first comparator that compares the output voltage of the multiplier and the command of the voltage commander and outputs the smaller one, a frequency commander that commands a desired frequency, and an output of the multiplier. It comprises a function generator that calculates the maximum frequency that can be obtained as a three-phase output, and a second comparator that compares the frequency calculated by the function generator with a command from the frequency commander and outputs the smaller one.

Another AC / AC direct power converter according to the present invention is an input filter for shaping a three-phase output waveform of a three-phase AC power supply, and is connected to a three-phase signal shaped by the input filter. A plurality of bidirectional switches for power conversion by on / off; a PWM control circuit for controlling on / off of the bidirectional switches based on a commanded voltage and a commanded frequency; A commutation control circuit for controlling commutation, a voltage detection circuit for detecting three line voltages of the three-phase AC power supply, a maximum voltage generation circuit for generating a maximum line voltage from the line voltage, and an output. PW so that the terminal voltage of the motor
It has a control circuit for instructing the speed and magnetic flux to the M control circuit.

When the three-phase AC power source becomes unbalanced and cannot operate normally at a desired speed, PWM control is performed to the maximum speed that the three-phase output can provide to the motor in that state, thereby making the AC / AC direct type The power converter can continue to operate.

Further, when a torque due to a desired magnetic flux cannot be applied to the motor, the three-phase output is changed to a maximum magnetic flux corresponding to the maximum torque that can be applied to the motor in this state.
By performing the control, the AC / AC direct power converter can continue to operate.

According to an embodiment of the present invention, the maximum voltage generating circuit comprises a rectifying circuit for rectifying the line voltage and a multiplier for multiplying the output of the rectifying circuit by a predetermined number, and the control circuit instructs a desired speed. A speed commander, a first function generator that calculates the maximum speed obtainable as a three-phase output from the output of the multiplier, and a second function that compares the maximum speed with the command of the speed commander and outputs the smaller one. 1, a magnetic flux commander that commands a desired magnetic flux, a second function generator that calculates a maximum magnetic flux that a three-phase output can give to the motor from an output of the multiplier, and a maximum magnetic flux. A second comparator for comparing the command of the magnetic flux commander and outputting the smaller one.

Further, according to an embodiment of the present invention, the first
The function generator instructs a speed of a predetermined lower limit when the maximum line voltage falls below a predetermined value, and sets the second function generator when the maximum line voltage falls below a predetermined value. Command a magnetic flux of a predetermined lower limit.

When the three-phase AC power supply is momentarily interrupted and falls below a predetermined value, PWM control is performed so that the three-phase AC power supply rotates at a predetermined lower limit value of speed and magnetic flux, so that the motor is not stopped by PWM control. In addition, rotation by inertia can be continued until the three-phase AC power supply recovers.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Referring to FIG. 1, the matrix converter of an embodiment of the present invention includes a three-phase AC power source 1, an input filter 2, the bidirectional switch _{S UR, S US, S UT} , S VR, S
_{VS, S VT, S WR,} S WS, and S _WT, load R _1, R _2, R
₃ , current detectors CT ₁ , CT ₂ , CT ₃ , voltage detection circuit 100, rectifier circuit 101, multiplier 102, comparator 103, voltage commander 110, PWM control circuit 111
And a commutation control circuit 50 and a gate drive circuit 60.

The three-phase AC power supply 1 outputs R-phase, S-phase, and T-phase AC power supplies.

The input filter 2 includes reactors L ₁ , L ₂ , and L ₃ connected in series to the respective phases R, S, and T of the three-phase AC power supply 1, and one end of each of the reactors R, S, and T. Capacitors C ₁ , C ₂ , C
A _three, and outputs a signal of the three-phase shapes the waveform of the output of the three-phase AC power source 1.

Bidirectional switch S_UR, S_US, S_UT, S_VR,
S_VS, S_VT, S_WR, S_WS, S_WTAre two IGs
BT (insulated gate bipolar transistor)
On / off bidirectional signal by commutation control
Can be controlled. Bidirectional switch S_UR, S_VR, S
_WRThe input of the R-phase output of the input filter 2 is input to one end of
ing. Bidirectional switch S_US, S_VS, S_WSAt one end,
The S-phase output of the input filter 2 is input. Bidirectional
Switch S_UT, S_VT, S_WTInput filter 2
Is output. And a two-way switch
Chi S_UR, S_US, S_UTAre connected in common as U-phase output.
And the load R₁Is connected to one end. Bidirectional switch
S_VR, S_VS, S_VTAre connected in common as V-phase output.
And the load R _TwoIs connected to one end. Bidirectional switch
S_WR, S_WS, S_WTAre connected in common as W-phase output.
And the load R_ThreeIs connected to one end.

The other ends of the loads R ₁ , R ₂ and R ₃ are commonly connected.

The current detectors CT ₁ , CT ₂ , and CT ₃ detect U-phase, V-phase, and W-phase currents, respectively, and detect commutation control circuits 50.
Notify.

The voltage detection circuit 100 operates between the R phase and the S phase,
The line voltages between the S and T phases and between the T and R phases are detected and output.

The rectifier circuit 101 rectifies the three line voltage of the voltage detection circuit 100 outputs, outputs the maximum value thereof as between lines maximum voltage V _MAX.

The multiplier 102 calculates the maximum voltage V _MAX between lines.

[0028]

[Outside 1] Multiply.

Voltage commander 110 has a voltage V which is a desired effective value of the three-phase output, regardless of the output of three-phase AC power supply 1.
Command _REF .

The comparator 103 has a voltage

[0031]

[Outside 2] And the voltage V _REF , and outputs the smaller voltage as the voltage V ₁ .

The PWM control circuit 111 outputs a U-phase, a V-phase, and a W-phase of the commanded frequency f _{R EF with} the three-phase output being the voltage V _1.
Bidirectional switches S _UR , S _US ,
_{S UT, S VR, S VS} , S VT, S WR, S WS, and outputs a PWM signal for turning on / off control of the S _WT. In the example, PW
The M signal is output to a bus composed of a plurality of signal lines.

The commutation control circuit 50 converts the PWM signal into a signal corresponding to the bidirectional switch, and outputs the signals from the current detectors CT ₁ , CT ₁ ,
CT _2, CT ₃ obtained in bidirectional switch S _UR based on the polarity of the _{current, S US, S UT, S} VR, S VS, S VT, S WR,
S _WS, giving commutation control in each direction IGBT of S _WT to that signal, and outputs a signal for performing ON / OFF control of each IGBT.

The gate driver circuit 60 controls the bidirectional switches S _UR , S _US ,
_{S UT, S VR, S VS} , S VT, S WR, S WS, to turn on / off 18 of the IGBT that make up the S _WT.

As the operation of the matrix converter of the present embodiment, first, the output of the three-phase AC power supply 1 is shaped by the filter 2. The voltage which is the effective value of the maximum three-phase output obtained from the three-phase AC power supply 1 by the voltage detection circuit 100, the rectification circuit 101, and the multiplier 102 based on the waveform-shaped signal.

[0036]

[Outside 3] Is generated. In the comparator 110, the voltage

[0037]

[Outside 4] Is compared with the voltage _VREF commanded by the voltage commander 110,
The smaller voltage is set as the voltage V ₁ and the PWM control circuit 111
Is input to When the three-phase AC power supply 1 normally outputs the three-phase power supply,

[0038]

[Outside 5] _Does not fall below the command V _REF of the voltage command unit 110,

[0039]

[Outside 6]

When the voltage drops

[0041]

[Outside 7] _May be lower than the command _VREF of the voltage commander 110.

The PWM control circuit 111 controls the bi-directional switches S _UR , S _US , based on the commanded frequency f _REF and the voltage V ₁ .
_{S UT, S VR, S VS} , S VT, S WR, S WS, and outputs a PWM signal indicating a timing of turning on / off the S _WT. Further, in the commutation control circuit 50, the current detectors CT ₁ , CT ₂ , C
T ₃ is a signal timing of the commutation is given based on the polarity of the current detected, via the gate drive circuit 60, bidirectional switch _{S UR, S US, S UT} , S VR, S VS, S
Turn on / off the IGBTs constituting _VT , _SWR , _SWS , _SWT . The signals obtained as three-phase outputs are the loads R ₁ , R ₂ ,
It is given to R _3.

The output of the three-phase AC power supply 1 becomes unbalanced,

[0044]

[Outside 8] _Falls below the voltage V _REF commanded by the voltage commander 110,
The matrix converter cannot operate normally with the voltage _VREF commanded by the voltage commander 110. Maximum voltage that can be output normally at that time

[0045]

[Outside 9] , The matrix converter can continue the operation.

The rectifier circuit 101 for outputting the maximum line voltage V _MAX can be constituted by an absolute value circuit and a maximum value priority circuit.

Referring to FIG. 2, a matrix converter according to another embodiment of the present invention is configured by adding a function generator 120, a frequency commander 121, and a comparator 104 to the matrix converter of FIG. I have.

The function generator 120 calculates the output voltage of the multiplier 102

[0049]

[Outside 10] _Is calculated, and the maximum frequency f _MAX obtained in the state of the three-phase AC power supply 1 output at that time is calculated and output. As an example of the maximum frequency f _MAX , when the output of the three-phase AC power supply 1 is normal, the maximum frequency f _MAX becomes maximum,

[0050]

[Outside 11] May decrease linearly in proportion to the decrease.

The frequency commander 121 receives the frequency f, which is the desired value of the three-phase output, regardless of the output of the three-phase AC power supply 1.
Command _REF .

[0052] The comparator 104 compares the command frequency f _{R EF} of the maximum frequency f _MAX and the frequency command unit 121, the frequency of the smaller and outputs the frequency f _1. Frequency f ₁ is PW
It is input to the M control circuit 111. The three-phase AC power supply 1
Is normally outputting the three-phase power supply, the maximum frequency f _MAX does not fall below the command f _REF of the frequency command device 121, but when the maximum frequency F _MAX decreases due to an unbalanced state or the like, the frequency command device 121 It may fall below the command f _REF .

When the output of the three-phase AC power supply 1 becomes unbalanced and the maximum frequency f _MAX falls below the frequency f _REF commanded by the frequency commander 121, the matrix converter _operates at the frequency f _REF commanded by the frequency commander 121. It cannot operate normally. By performing the PWM control based on the maximum frequency f _MAX of the three-phase output that can be normally output at that time, the matrix converter can continue to operate.

Referring to FIG. 3, a matrix converter according to still another embodiment of the present invention includes a three-phase AC power supply 1,
The input filter 2 and the bidirectional switches S _UR , S _US , S _UT ,
S _VR , S _VS , S _VT , S _WR , _SW S, _SW T and current detector C
T ₁ , CT ₂ , CT ₃ , voltage detection circuit 100, rectifier circuit 101, multiplier 102, commutation control circuit 50, gate drive circuit 60, speed detector 161, function generator 130, 140, speed commander 131, comparator 105, speed controller 132, magnetic flux commander 141
, The comparator 106, the frequency commander 121, the voltage commander 110, and the PWM control circuit 111, and drives the motor 160.

Three-phase AC power supply 1, input filter 2, bidirectional switches S _UR , S _US , S _UT , S _VR , S _VS , S _VT , S _WR ,
And S _WS, S _WT, the current detector CT _1, CT _2, CT _3, the voltage detection circuit 100, the rectifier circuit 101, multiplier 102, commutation control circuit 50, the gate drive circuit 60, the matrix converter of FIG. 1 Same as the ones.

The motor 160 is an AC motor driven by U-phase, V-phase, and W-phase voltages.

The speed detector 161 detects the speed at which the motor 160 rotates.

The function generator 130 outputs the voltage

[0059]

[Outside 12] As input, and outputs the maximum speed N _MAX of the motor 160 which is obtained in the form of three-phase AC power supply 1 output at that time. In addition, the function indicating the relationship between the input and output it is possible to set the lower limit of the maximum speed N _{M AX,} voltage

[0060]

[Outside 13] Is smaller than a predetermined value, the maximum speed N _MAX becomes a preset lower limit value. FIG. 4 shows an example of this function.

The speed commander 131 outputs the speed N _{REF at} which the motor 160 should be driven regardless of the output of the three-phase AC power supply 1.
Command.

The comparator 105 compares the maximum speed N _MAX with the output N _REF of the speed command unit 131, and outputs the smaller speed as the speed N ₁ . Note that when the three-phase AC power supply 1 normally outputs the three-phase power supply, the maximum speed N _MAX does not fall below the command N _REF of the speed command device 131, but the maximum speed N _MAX due to an unbalanced state or the like. When the speed decreases, the speed may fall below the command N _REF of the speed command device 131.

The speed controller 132 inputs the speed N ₁ and the rotation speed of the motor 160 detected by the speed detector 161.
Rotational speed of the motor 160 is controlled to be N _1.

The function generator 140 generates a voltage

[0065]

[Outside 14] And outputs the maximum magnetic flux Φ _MAX of the motor 160 obtained from the state of the three-phase AC power supply 1 output at that time. The lower limit value of the maximum magnetic flux Φ _MAX can be set for the function indicating the input / output relationship.

[0066]

[Outside 15] Is smaller than a predetermined value, the maximum magnetic flux Φ _MAX becomes a preset lower limit value. FIG. 5 shows an example of this function.

Flux commander 141 commands a magnetic flux corresponding to the torque to be applied to motor 160 irrespective of the output of three-phase AC power supply 1.

The comparator 106 compares the maximum magnetic flux Φ _MAX with the output of the magnetic flux commander 141 and determines the smaller magnetic flux as the magnetic flux Φ ₁
Output as Incidentally, when the three-phase AC power supply 1 is outputting three-phase power normally, the maximum magnetic flux [Phi _MAX is never below the command [Phi _REF flux command unit 141, the maximum magnetic flux [Phi _MAX due unbalanced state Magnetic flux commander 1 when lowered
41 command Φ _REF below.

The vector control circuit 142 receives the speed N ₁ and the magnetic flux Φ ₁ as inputs, and calculates and instructs a current flowing through the motor 160 to rotate with a torque based on the speed N ₁ and the magnetic flux Φ ₁ . Since the sum of the balanced three-phase currents becomes zero, the current command indicates two of the three phases U, V, and W.

The current control circuit 143 receives the current command output from the vector control circuit 142 and the current detectors CT ₁ and C ₁ .
A voltage command V _REF and a frequency command f _REF to be given to the PWM control circuit 111 are output from the deviation from the current value detected at T ₂ and CT ₃ .

When the output of the three-phase AC power supply 1 becomes unbalanced and the matrix converter cannot operate normally according to the command of the speed commander 131, the maximum speed that the three-phase output can give to the motor 160 in that state. By performing the PWM control based on N _MAX , the matrix converter can continue the operation. In addition, the voltage

[0072]

[Outside 16] Is smaller than a predetermined value, PWM control is performed so that the motor 160 rotates at a speed of a predetermined lower limit value. Accordingly, the rotation by inertia can be continued until the three-phase AC power supply 1 recovers without stopping the motor 160 by the PWM control when the three-phase AC power supply 1 is momentarily interrupted.

The magnetic flux Φ commanded by the magnetic flux commander 141
_{When the} torque due to _REF cannot be given to the motor 160, the matrix converter performs PWM control based on the maximum magnetic flux Φ _MAX corresponding to the maximum torque that the three-phase output can give to the motor 160 in that state. The operation can be continued. In addition, the voltage

[0074]

[Outside 17] Is smaller than a predetermined value, PWM control is performed so that the motor rotates with a magnetic flux having a predetermined lower limit value. Accordingly, the rotation by inertia can be continued until the three-phase AC power supply 1 recovers without stopping the motor 160 by the PWM control when the three-phase AC power supply 1 is momentarily interrupted.

[0075]

As described above, according to the present invention, when the three-phase AC power source becomes unbalanced or loses phase,
The AC direct power converter can continue to operate and drive a motor or the like. In addition, when the three-phase AC power supply is momentarily interrupted, the rotation due to the inertia of the motor can be continued.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a matrix converter according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a matrix converter according to another embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a matrix converter according to still another embodiment of the present invention.

FIG. 4 is a graph showing an example of a function of a function generator 130.

FIG. 5 is a graph showing an example of a function of a function generator 140.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Three-phase AC power supply 2 Input filter 50 Commutation control circuit 60 Gate drive circuit 100 Voltage detection circuit 101 Rectifier circuit 102 Magnifier 103, 104, 105, 106 Comparator 110 Voltage commander 111 PWM control circuit 120, 130, 140 Function generator 121 frequency command unit 131 speed command 132 speed controller 141 flux indicator 142 vector control circuit 143 a current control circuit 160 motor 161 speed detector CT _1, CT _2, CT ₃ current detector E _U, E _V, E _W current detector _{S UR, S US, S UT} , S VR, S VS, S VT, S WR, S WS, S
_WT bidirectional switch C _1, C _2, C ₃ capacitors L _1, L _2, L ₃ reactor R _1, R _2, R ₃ load

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hidenori Hara 2-1 Kurosaki Castle Stone, Yawata Nishi-ku, Kitakyushu City, Fukuoka Prefecture Inside Yaskawa Electric Co., Ltd. (72) Eiji Yamamoto 2-1 Kurosaki Castle Stone, Yawata Nishi-ku, Kitakyushu City, Fukuoka Prefecture Yasukawa Electric Co., Ltd. F-term (reference) 5H576 BB06 CC05 DD02 EE01 EE11 GG02 GG04 GG05 HA04 HB04 LL01 LL22 LL24 LL32 MM13 MM14 5H750 AA10 BA01 BA06 CC06 DD01 DD25 FF02 FF05

Claims (7)

[Claims] 1. An input filter for shaping a three-phase output waveform of a three-phase AC power supply, and a plurality of input filters connected to a three-phase signal whose waveform is shaped by the input filter and for power conversion by on / off. A direction control switch; a PWM control circuit that controls on / off of the bidirectional switch based on a commanded voltage and a commanded frequency; a commutation control circuit that controls commutation of the bidirectional switch; A voltage detection circuit that detects and outputs three line voltages of the phase AC power supply, a maximum voltage generation circuit that generates a line maximum voltage from the line voltage, and a three-phase output that is always equal to or less than the line maximum voltage. An AC / AC direct power converter having a control circuit for instructing a voltage to the PWM control circuit. 2. The maximum voltage generation circuit includes a rectifier circuit for rectifying the line voltage, and a multiplier for multiplying an output of the rectifier circuit by a predetermined number. The control circuit includes a voltage command for commanding a desired voltage. Vessels,
2. The AC / AC direct power converter according to claim 1, further comprising a comparator that compares the output of the multiplier with the command of the voltage commander and outputs the smaller one. 3. An input filter for shaping a three-phase output waveform of a three-phase AC power supply, and a plurality of input filters connected to the three-phase signal whose waveform has been shaped by the input filter, for power conversion by ON / OFF. A direction control switch; a PWM control circuit that controls on / off of the bidirectional switch based on a commanded voltage and a commanded frequency; a commutation control circuit that controls commutation of the bidirectional switch; A voltage detection circuit for detecting three line voltages of the phase AC power supply; a maximum voltage generation circuit for generating a line maximum voltage from the line voltage; and a PW so that an output is always equal to or less than the line maximum voltage.
An AC / AC direct power converter having a control circuit for commanding voltage and frequency to an M control circuit. 4. The maximum voltage generation circuit includes a rectifier circuit for rectifying the line voltage, and a multiplier for multiplying an output of the rectifier circuit by a predetermined number. The control circuit includes a voltage command for commanding a desired voltage. Vessels,
A first comparator for comparing the output voltage of the multiplier with the command of the voltage commander and outputting a smaller one; a frequency commander for commanding a desired frequency; and a three-phase output from the output of the multiplier. 4. The function generator according to claim 3, comprising: a function generator that calculates a maximum frequency that can be obtained as a function; and a second comparator that compares a frequency calculated by the function generator with a command from a frequency commander and outputs a smaller one. AC / AC direct power converter. 5. An input filter for shaping a three-phase output waveform of a three-phase AC power supply, and a plurality of input filters connected to the three-phase signal whose waveform has been shaped by the input filter for power conversion by ON / OFF. Three-phase switch; a PWM control circuit that controls on / off of the bidirectional switch based on a commanded voltage and a commanded frequency; a commutation control circuit that controls commutation of the bidirectional switch; A voltage detection circuit for detecting three line voltages of an AC power supply, a maximum voltage generation circuit for generating a line maximum voltage from the line voltage, and a terminal voltage of a motor connected to an output being always the line maximum voltage An AC / AC direct power converter having a control circuit for commanding a speed and a magnetic flux to the PWM control circuit as follows. 6. The maximum voltage generation circuit includes a rectifier circuit for rectifying the line voltage, and a multiplier for multiplying an output of the rectifier circuit by a predetermined number. The control circuit includes a speed command for commanding a desired speed. Vessels,
A first function generator for calculating a maximum speed obtainable as a three-phase output from an output of the multiplier, and a first comparison for comparing the maximum speed with a command from the speed commander and outputting a smaller one. A magnetic flux commander that commands a desired magnetic flux; a second function generator that calculates a maximum magnetic flux that a three-phase output can give to the motor from an output of the multiplier; 6. The AC / AC direct power converter according to claim 5, further comprising a second comparator for comparing commands from the magnetic flux commander and outputting a smaller one. 7. The first function generator, when the line-to-line maximum voltage falls below a predetermined value, instructs a speed of a predetermined lower limit, and the second function generator outputs the line speed. 7. The AC / AC direct power converter according to claim 6, wherein when the maximum voltage falls below a predetermined value, a magnetic flux having a predetermined lower limit is commanded.