JP3533091B2 - AC motor drive controller - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for an AC motor, and more particularly to a drive control device for an AC motor capable of applying both a pseudo sine wave voltage and a rectangular wave voltage to the AC motor. Technology for intelligent use.

[0002]

2. Description of the Related Art An inverter is used when driving an AC motor using a DC power supply. Such an inverter is switching-controlled by an inverter drive circuit,
Generally, a pulse width modulation (PWM) waveform voltage is applied to the AC motor.

If a PWM waveform voltage is applied to the AC motor, smooth rotation drive can be obtained even in a low rotation range.
However, when the PWM waveform voltage is applied to the AC motor, the voltage utilization rate is limited. Therefore, this control method has a problem that a sufficient output of the AC motor cannot be obtained. On the other hand, there is a method of obtaining a high rotation by passing a field weakening current, but it is not appropriate because copper loss increases.

On the other hand, for driving control of an AC motor, there is also a method of applying a rectangular wave voltage to the AC motor. According to this method, the voltage utilization rate can be improved, and as a result,
It is possible to improve the output in the high rotation range. Further, since the field weakening current can be reduced, it is possible to suppress the occurrence of copper loss and improve energy efficiency.
Furthermore, since the number of switching times in the inverter can be reduced, switching loss can be suppressed.

Therefore, it is desirable that both the PWM waveform voltage and the rectangular wave voltage can be applied to the AC motor, and they can be selectively used as needed. Japanese Patent Laid-Open No. 58-119791 discloses a technique of applying both a PWM waveform voltage and a rectangular wave voltage to an AC electric motor as needed to improve the output of the electric motor.

[0006]

However, the PWM
Since the voltage utilization factor is different between the waveform voltage and the rectangular wave voltage, a simple change of these waveforms causes a sudden change in voltage, resulting in a torque shock in the motor. That is, the voltage utilization factor when the PWM waveform voltage is used is √3 / 8, and when the rectangular wave voltage is used, it is √6 / π. Therefore, a change of about 30% will occur. Therefore, torque shock is likely to occur due to a sudden change in current.

Therefore, even if both the PWM waveform voltage and the rectangular wave voltage can be selectively applied to the AC electric motor, if they are directly switched, a torque shock occurs in the electric motor. For example, even if such a system is applied to an electric vehicle, it is impossible to obtain a suitable drive feeling.

The present invention has been made in view of the above problems, and an object thereof is to provide a drive control device capable of selectively applying both a PWM waveform voltage and a rectangular wave voltage to an AC motor. An object of the present invention is to provide a drive control device for an AC electric motor that can smoothly switch waveform voltages.

[0009]

(1) In order to solve the above problems, the present invention provides a drive control device for an AC electric motor, which performs switching control on an inverter that supplies electric power to the AC electric motor. A pulse width modulation control is performed to apply a pseudo sine wave voltage corresponding to a current command value to the AC motor, and the inverter is subjected to rectangular wave control so that a phase corresponding to a torque command value is obtained. The second drive control means for applying a rectangular wave voltage having a predetermined first amplitude to the AC motor and the inverter when the control is switched from the first drive control means to the second drive control means. Pulse width modulation control is performed to gradually increase the amplitude from the amplitude of the pseudo sine wave voltage at the time of switching to a predetermined second amplitude corresponding to the first amplitude, and A pseudo sine wave voltage whose phase transition so that the output torque of the AC motor is continuously changed to,
Third drive control means for applying to the AC motor.

According to the present invention, a pseudo sine wave voltage (PWM waveform voltage) corresponding to the current command value is applied to the AC motor by the first drive control means. Further, the second drive control means sets a phase corresponding to the torque command value and a predetermined first phase.
A rectangular wave voltage having an amplitude is applied to the AC motor.

When the control method is switched from the first drive control means to the second drive control means, the inverter is subjected to pulse width modulation control during the transition period, and at this time, the amplitude of the pseudo sine wave voltage is controlled. Gradually increases from the switching amplitude to the second amplitude. The phase is changed in real time so that the output torque of the AC motor changes continuously. This makes it possible to suitably perform the torque control during the switching period, so that it is possible to reduce the torque shock when connecting the control using different waveforms.
Further, since the voltage amplitude is gradually changed, the torque shock of the AC motor can be reduced also from this point.

(2) Further, according to the present invention, in an AC electric motor drive control device for performing switching control on an inverter for supplying electric power to an AC electric motor, the inverter is subjected to pulse width modulation control, and according to a current command value. A rectangular wave voltage having a phase corresponding to a torque command value and a predetermined first amplitude by rectangular wave controlling the first drive control means for applying the pseudo sine wave voltage to the AC motor and the inverter.
When the control is switched from the second drive control means to be applied to the AC motor to the first drive control means from the second drive control means, the inverter is subjected to pulse width modulation control to control the first amplitude. A pseudo sine wave voltage whose amplitude gradually decreases from a predetermined third amplitude corresponding to the above, and whose phase shifts so that the output torque of the AC motor continuously changes during the switching, is applied to the AC motor. Four
And a drive control means of.

According to the present invention, contrary to the above, when the control is switched from the second drive control means to the first drive control means, the inverter is subjected to pulse width modulation control during the transition period, The amplitude gradually decreases from the predetermined third amplitude corresponding to the first amplitude. Also, during that transition period,
The phase is changed in real time so that the output torque of the AC motor changes continuously. With this configuration, it is possible to preferably shift from the state in which the rectangular wave voltage is applied to the AC motor to the state in which the pseudo sine wave voltage is applied without generating torque shock.

(3) Further, in one aspect of the present invention, the fourth drive control means is configured such that, when a current value supplied to the AC motor approaches the current command value, the first drive control means. It is characterized by transferring control to.

According to this aspect, when the current value supplied to the AC motor by the fourth drive control means approaches the current command value at that time, the control is transferred to the first drive control means. Therefore, even when the AC motor is driven by the first drive control means, the current value does not change suddenly, and the control can be switched without causing torque shock.

(4) Further, in one aspect of the present invention, the fourth drive control means is configured to: when the amplitude of the pseudo sine wave voltage applied to the AC electric motor decreases beyond a predetermined limit, The control is transferred to the first drive control means.

According to this aspect, even if the current value supplied to the AC motor does not approach the current command value, the fourth drive control means can surely control the first drive control means. Therefore, the control failure can be prevented.

(5) In one aspect of the present invention, the third or fourth drive control means applies the pseudo sine wave voltage whose phase changes so that the output torque of the AC motor becomes constant. It is characterized by being applied to an electric motor.

According to this aspect, the third or fourth drive control means changes the phase in real time so that the output torque of the AC motor becomes constant, so that the output torque of the AC motor at the time of switching is constant. Therefore, it is possible to prevent the occurrence of torque shock when switching the control.

[0020]

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

FIG. 1 is a diagram showing an overall configuration of a drive control device for an AC electric motor according to an embodiment of the present invention. The drive control device 10 shown in the figure is installed in an electric vehicle, and has three motor drive control modes of a PWM current control mode, a PWM voltage phase control mode, and a rectangular wave voltage phase control mode. .

Here, the PWM current control mode is a control mode in which both the switches 26 and 28 are switched to the upper side in the figure, and the current value is fed back so that the voltage amplitude | V | And the voltage phase ψ are set, and the pseudo sine wave voltage is applied to the motor 38.

In the PWM voltage phase control mode, the switch 26 is switched to the lower side in the figure and the switch 28 is switched to the upper side in the figure, and the pseudo sine wave voltage is applied to the motor 38. At that time, the voltage amplitude | V | continuously changes with time, and the voltage phase ψ is set at any time according to the change of the voltage amplitude | V | so that the torque shock of the motor 38 does not occur.

Further, in the rectangular wave voltage phase control mode,
The switch 28 is switched to the lower side in the drawing to apply a rectangular wave voltage to the motor 38, and its voltage amplitude | V | is determined by the DC battery voltage Vdc, and the voltage phase ψ
Is set according to the torque command value. At this time, the switch 26 may be switched up or down.

In the drive control device 10 shown in FIG.
An electronic control unit (ECU) (not shown) generates a torque command value according to the accelerator opening degree and the brake depression angle, and the torque command value is input to the current command generation unit 12 and the addition unit 13 in parallel. Has become. Current command generator 1
In 2, the current command value I based on the input torque command value
Generate q and Id. Then, the current command value is input to the current controller 14. The current controller 14 performs proportional-plus-integral control, and the voltage amplitude |
V | and the voltage phase ψ are generated. ψ is the angle of the current vector with reference to the q-axis. The voltage phase ψ and the voltage amplitude | V | are supplied to the switch 26. Although not shown, the current value is fed back from the current sensor 40 to the current controller 14.

The switch 26 includes a set of a voltage amplitude | V | and a voltage phase ψ supplied from the current controller 14, and a voltage amplitude | V | and a voltage amplitude | V | supplied from the voltage amplitude controller 16 and the voltage phase controller 18, respectively. And a set of voltage phases ψ are selectively input to the PWM circuit 30.

In the PWM circuit 30, by comparing the sine wave having the voltage amplitude | V | and the voltage phase ψ supplied from the switch 26 with the triangular wave prepared in advance,
Generate a switching command. This switching command is supplied to the inverter 36 via the switch 28. The inverter 36 is a voltage type inverter, and the PWM circuit 3
A pseudo sine wave voltage is generated based on the switching command supplied from 0. The pseudo sine wave voltage is supplied to the motor 38.

The motor 38 is a permanent magnet synchronous (PM) motor. A current sensor 40 is provided on the power supply line from the inverter 36 to the motor 38, and the real-time current value detected there is input to the adder 24 via a three-phase / two-phase converter (not shown). . On the other hand, the current command value generated by the current command generator 12 is also input to the adder 24. Then, the current deviation ΔI is generated here in real time and is input to the current coincidence determination unit 22. The current matching determination unit 22 switches the switch 26 when the current value detected by the current sensor 40 and the current command value generated by the current command generation unit 12 match.

The torque command value generated by the ECU (not shown) is also supplied to the adder 13 as described above.
The real-time torque value detected by the torque detecting means 20 is also input to the adder 13, and the torque deviation ΔT is generated there. The torque detection means 20 can be configured using a torque sensor, but can also be configured to execute the calculation shown in the following equation (1) to generate torque.

[0030]

## EQU1 ## T = Pin / ω = (iu × vu + iv × vv + iw × vw) / ω (1) where Pin represents the electric power supplied to the motor 38.
ω represents the angular velocity of the motor 38. iu, iv, iw represent the current value of each phase supplied to the motor 38, and vu, v
v and vw represent the voltage value of each phase supplied to the motor 38. As vu, vv, and vw, a voltage command value set in the inverter 22 may be used, or an actual value supplied from the inverter 22 to the motor 24 may be detected by a voltage sensor and used.

Alternatively, as shown in the following equation (2), the input power of the inverter may be calculated from the DC current and the DC voltage to calculate and generate the torque.

[0032]

## EQU00002 ## T = Pin / .omega. = (IB.times.VB) /. Omega. (2) where IB and VB represent the DC current and DC voltage of a battery (not shown) connected to the inverter 22.

The torque deviation ΔT generated by the adder 13 is supplied to the voltage phase controller 18. Voltage phase controller 18
Then, the voltage phase ψ is generated according to the torque deviation ΔT. This voltage phase controller 18 generates a voltage phase ψ of a rectangular wave in the rectangular wave voltage phase control mode. In the PWM voltage phase control mode, the voltage phase ψ of the pseudo sine wave voltage is generated. Specifically, the voltage phase controller 18 is generated by the voltage Vdc of the battery (not shown) connected to the inverter 36 and the voltage amplitude controller 16 together with the torque deviation ΔT as a parameter for generating the voltage phase ψ. Using the voltage amplitude | V | and the angular velocity ω of the motor 38, these are substituted into a predetermined arithmetic expression (or equivalent processing is performed) to generate the necessary voltage phase ψ. The voltage phase controller 18
In the transition period between the PWM current control mode and the rectangular wave voltage phase control mode, the voltage phase ψ may be set so that the torque becomes constant.

The voltage amplitude controller 16 is specially provided for the PWM voltage phase control mode, and is for connecting the PWM current control mode and the rectangular wave voltage phase control mode without causing torque shock. It is one of the configurations. That is, when the control shifts from the PWM current control mode to the rectangular wave voltage phase control mode, the voltage amplitude controller 16 starts the operation of the voltage amplitude controller 16 and outputs the voltage amplitude | V | is taken over and output, and the value is gradually increased, and the voltage amplitude |
V | is supplied to the switch 26. Further, the voltage amplitude | V | output from the voltage amplitude controller 16 is the voltage amplitude determination unit 34.
The voltage amplitude | V | generated by the voltage amplitude controller 16 is compared with the voltage amplitude corresponding to the rectangular wave voltage, and the switch 28 is switched based on the comparison result. ing.

On the other hand, when the control shifts from the rectangular wave voltage phase control mode to the PWM current control mode, the voltage amplitude controller 16 sets the basic amplitude of the rectangular wave voltage as voltage amplitude | V | at the start of its operation. The amplitude is taken over and output, and the value is gradually decreased.

In the rectangular wave generator 32, the voltage phase controller 18
A switching command is issued so as to generate a rectangular wave voltage based on the voltage phase ψ output from. This switching command is supplied to the inverter 36 via the switch 28, and when the switch 28 is switched to the lower side in the drawing, a rectangular wave voltage is applied from the inverter 36 to the motor 38. There is.

FIG. 2 is a diagram showing voltage waveforms supplied to the motor 38 in each control mode. FIG. 11A is a diagram showing a voltage waveform supplied to the motor 38 in the PWM current control mode, and a sine wave having a voltage amplitude | V | and a voltage phase ψ generated by the current controller 14 is shown on the upper side. The comparison with the triangular wave is shown, and the waveform of the pseudo sine wave voltage actually output from the inverter 36 is shown on the lower side. Further, FIG. 7B shows the voltage waveform supplied to the motor 38 in the PWM voltage phase control mode. On the upper side, the voltage amplitude | V output from the voltage amplitude controller 16
It is shown that the sine wave having the | and the voltage phase ψ output from the voltage phase controller 18 is compared with the triangular wave, and the waveform of the pseudo sine wave voltage which is the comparison result is shown on the lower side. ing. Further, FIG. 7C shows a voltage waveform in the rectangular wave voltage phase control mode.

FIG. 3 is a diagram for explaining the operation of the drive control device 10 having the above-mentioned configuration, and is a flow chart for explaining the operation particularly when shifting from the PWM current control mode to the rectangular wave voltage phase control mode. . As shown in FIG.
Then, the drive control device 10 is in the PWM current control mode,
In this case, both the switch 26 and the switch 28 are switched to the upper side in the figure. Then, the current command generator 1
2, current controller 14, PWM circuit 30, inverter 3
6 are functioning respectively. Next, if the transition to the rectangular wave voltage phase control mode is instructed at a given timing,
An initial voltage value is set in the voltage amplitude controller 16 (S10
2). This initial voltage value is the voltage amplitude | V | output from the current controller 14 at that time. Thereafter, the switch 26 is switched to the lower side in the figure, and the voltage amplitude | V | output from the voltage amplitude controller 16 and the voltage phase ψ output from the voltage phase controller 18 are input to the PWM circuit 30. (S103).

In this case, the inverter 36 outputs a pseudo sine wave voltage whose voltage amplitude and voltage phase are controlled, and the waveform voltage drives the motor 38. afterwards,
In S104, the voltage amplitude | V | output from the voltage amplitude controller 16 is increased in a predetermined step. In S105, the voltage amplitude determination unit 34 compares the voltage amplitude | V | output from the voltage amplitude controller 16 with a predetermined voltage based on the battery voltage Vdc, and the voltage amplitude | V | output from the voltage amplitude controller 16 is compared. If is smaller, S103 is again set.
Then, the drive of the motor 38 in the PWM voltage phase control mode is continued.

After that, if it is determined in S105 that the voltage amplitude | V | output from the voltage amplitude controller 16 becomes larger than the above-mentioned predetermined voltage, the switch 28 is switched to the lower side in the figure, and the drive control unit 10 is operated. Shifts to the rectangular wave voltage phase control mode (S106).

According to the above, when the PWM current control mode is changed to the rectangular wave voltage phase control mode, the voltage amplitude | V | and the voltage phase ψ can be smoothly connected, and the torque in the motor 38 can be changed. Shock can be reduced.

Next, FIG. 4 is a diagram for explaining the operation at the time of shifting from the rectangular wave voltage phase control mode to the PWM current control mode. In the figure, in S201, the drive control device 10 is in the rectangular wave voltage phase control mode. That is, here, the switch 28 is switched to the lower side in the drawing.
The torque value is fed back to the adder 13, and the motor 38 is driven based on the torque command value output from the ECU (not shown). Then, when the shift to the PWM current control mode is instructed at the given timing, the voltage initial value is set in the voltage amplitude controller 16 (S202). This voltage initial value is a voltage set based on a battery voltage (not shown) connected to the inverter 36, and for example, a voltage amplitude corresponding to a rectangular wave voltage is adopted.

Next, in S203, the switch 26 is switched to the lower side in the figure and the switch 28 is switched to the upper side in the figure. The PWM circuit 30 is supplied with the voltage amplitude | V | output from the voltage amplitude controller 16 and the voltage phase ψ output from the voltage phase controller 18. In the PWM circuit 30, those amplitudes | V |
And a switching command to the inverter 36 to generate a pseudo sine wave voltage having the voltage phase ψ.

In S204, the value of the voltage amplitude output from the voltage amplitude controller 16 is decreased by a predetermined step. Then, in S205, the current matching determination unit 22 determines whether the current value and the current command value generated based on the current torque command value match.

FIG. 5 is a diagram for explaining this determination processing. In the figure, the current vector is represented on the dq plane, and the vector 50 represents the current command value generated by the current command generation unit 12. The vector 48 represents the current vector detected by the current sensor 40 in the rectangular wave voltage phase control mode. The end point of the vector 48 changes as shown by the locus 46 in the transition period of the control mode, and approaches the leading end of the vector 50 representing the current command value. Then, when the end point of the current vector 48 moves within a circle having a predetermined radius centered on the end point of the vector 50, the current coincidence determination unit 22 sends a switching signal to switch the switch 26 to the upper side in the drawing.

As a result of the above determination process, if it is determined that the two currents match each other, then the current control initial value is set to the current controller 14 (S206). That is, the current controller 14 is configured using the proportional-plus-integral controller as described above. Therefore, in the control, the voltage amplitude | V output from the voltage amplitude controller 16 is added to the integral term.
By setting a value according to |, it is possible to shift the voltage amplitude to the PWM current control mode while continuously connecting the voltage amplitude. After that, the switch 26 switches
Based on the switching signal output from the switch, the switch is switched to the upper side in the figure, and the PWM current control mode is entered (S207).

With the above arrangement, when the rectangular wave voltage phase control mode is changed to the PWM current control mode, the voltage amplitude values can be continuously connected and the current values can also be continuously connected. can do. As a result,
The motor 38 can reduce the torque shock.

In the current coincidence determination section 22, it is not necessary to strictly determine the coincidence of both current values, and if the end points of both vectors are within a certain range on the dq plane as shown in FIG. Good. Further, it is possible that the vector 48 does not approach the vector 50 on the dq plane, but in preparation for such a case, even if it is determined that the currents do not match in the determination of S205 in the flowchart of FIG. 4,
If the current voltage amplitude has decreased to the predetermined voltage amplitude or less, the process may proceed to S206.

FIG. 6 is a diagram showing changes in the amplitude of the voltage and the amplitude of the current supplied to the motor 38 when the control mode is switched. As shown in the figure, when the PWM control mode (I) is shifted to the PWM voltage phase control mode (II), the voltage amplitude 42 increases from the value at the switching timing with time. At this time, the voltage phase controller 1
Since the voltage phase ψ supplied from 8 is controlled so that the torque output from the motor 38 is constant, the current amplitude 44 gradually decreases with time.

When the PWM voltage phase control mode (II) shifts to the rectangular wave voltage phase control mode (III), the voltage amplitude determination unit 34 determines the voltage amplitude (arrow A in the figure). Then, in the rectangular wave voltage phase control mode, the voltage amplitude 42 maintains a predetermined value corresponding to the battery voltage Vdc. The current amplitude 44 also takes a value according to the torque command value.

Further, the rectangular wave voltage phase control mode (II
When transitioning from I) to the PWM voltage phase control mode (IV), the voltage amplitude 42 gradually decreases from the voltage amplitude in the rectangular wave voltage phase control mode. On the other hand, the current amplitude 44 gradually increases from the current in the rectangular wave voltage phase control mode. When the current match determination unit 22 detects that the current value detected by the current sensor 40 and the current command value generated by the current command generation unit 12 match, the PWM current phase control mode (IV) The control mode shifts to the PWM current control mode (V) (arrow B in the figure).

According to the drive controller 10 described above,
PWM for controlling both the voltage amplitude | V | and the voltage phase ψ between the PWM current control mode and the rectangular wave voltage phase mode
Since the voltage phase control mode is interposed, the switching between the control modes can be performed without causing a large torque shock.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a drive control device for an AC electric motor according to an embodiment of the present invention.

FIG. 2 is a diagram showing voltage waveforms in each control mode.

FIG. 3 is a flowchart illustrating an operation when shifting from a PWM current control mode to a rectangular wave voltage phase control mode.

FIG. 4 is a flowchart illustrating an operation at the time of transition from the rectangular wave voltage phase control mode to the PWM current control mode.

FIG. 5 is a diagram illustrating current coincidence determination processing.

FIG. 6 is a diagram showing changes in voltage amplitude and current amplitude when shifting to a control mode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 drive control device, 12 current command generation part, 14 current controller, 16 voltage amplitude controller, 18 voltage phase controller, 20 torque detection means, 22 current coincidence determination part, 2
4 adder, 26, 28 switch, 30 PWM circuit, 32 rectangular wave generating section, 34 voltage amplitude determining section, 36
Inverter, 38 motor, 40 current sensor.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Otani No. 41 Yokomichi, Nagakute-cho, Aichi-gun, Aichi-gun 1-chome, Toyota Central Research Institute Co., Ltd. (56) Reference JP-A-10-146090 (JP, A) JP 2000-50689 (JP, A) JP 58-119791 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02P 5 / 00,6 / 00,7 / 00 B60L 15/08

Claims (5)

(57) [Claims] 1. A drive control device for an AC electric motor that performs switching control on an inverter that supplies electric power to the AC electric motor, wherein pulse width modulation control is performed on the inverter to generate a pseudo sine wave voltage according to a current command value. A first drive control means for applying to the alternating-current motor; and a rectangular-wave voltage for controlling the inverter to apply a rectangular-wave voltage having a phase corresponding to a torque command value and a predetermined first amplitude to the alternating-current motor. 2 drive control means, and when the control is switched from the first drive control means to the second drive control means, pulse width modulation control of the inverter is performed, and the pseudo sine wave voltage at the time of switching is controlled. The amplitude gradually increases from the amplitude to a predetermined second amplitude corresponding to the first amplitude, and the phase is such that the output torque of the AC motor continuously changes during the switching. A drive control device for an AC electric motor, comprising: a third drive control unit that applies a pseudo sine wave voltage that changes to the AC electric motor to the AC electric motor. 2. A drive control device for an AC electric motor that performs switching control on an inverter that supplies electric power to the AC electric motor, wherein pulse width modulation control is performed on the inverter to generate a pseudo sine wave voltage according to a current command value. A first drive control means for applying to the alternating-current motor; and a rectangular-wave voltage for controlling the inverter to apply a rectangular-wave voltage having a phase corresponding to a torque command value and a predetermined first amplitude to the alternating-current motor. 2 drive control means, and when the control is switched from the second drive control means to the first drive control means, pulse width modulation control is performed on the inverter to control a predetermined third amplitude corresponding to the first amplitude. To the AC motor, the amplitude gradually decreases and the phase shifts so that the output torque of the AC motor continuously changes during the switching. A fourth drive control means for applying the voltage, and a drive control device for an AC electric motor. 3. The drive control device for an AC electric motor according to claim 2, wherein the fourth drive control means controls the first drive control means when the current value supplied to the AC electric motor approaches the current command value. The drive control device for an AC motor, wherein control is transferred to the drive control means of the above. 4. The drive control device for an AC electric motor according to claim 2, wherein the fourth drive control means reduces the amplitude of the pseudo sine wave voltage applied to the AC electric motor beyond a predetermined limit. In this case, the control is transferred to the first drive control means, and the drive control device for the AC electric motor. 5. The drive control device for an AC electric motor according to claim 1, wherein the third or fourth drive control means changes a phase so that an output torque of the AC electric motor becomes constant. A drive control device for an AC electric motor, characterized in that a pseudo sine wave voltage is applied to the AC electric motor.