JP2000050686A - Drive control equipment of ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce torque shocks generated in an AC motor at the switching of a square wave voltage phase control mode and a PWM current control mode. SOLUTION: This drive control equipment is so constituted that a switching command can be supplied selectively to an inverter 36 from a PWM circuit 30 and a square wave generating part 32. At the switching of both control modes, a quasi-sine wave voltage which has a voltage amplitude |V| formed by a voltage amplitude controller 16 and a voltage phase ψ formed by a voltage phase controller 18 is applied to a motor 38, and control is so performed that the torque of the motor 38 remains constant.

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. Related to technology for universal use.

[0002]

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

[0003] If a PWM waveform voltage is applied to an AC motor, smooth rotation can be obtained even in a low rotation range.
However, when a PWM waveform voltage is applied to an AC motor, there is a limit in voltage utilization. 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 high rotation by passing a weak field current, but this is not appropriate because copper loss increases.

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

For this reason, it is desirable that both the PWM waveform voltage and the rectangular wave voltage are configured to be applied to the AC motor, and that they are used as needed. Japanese Patent Laying-Open No. 58-119791 discloses a technique for improving the output of a motor by applying both a PWM waveform voltage and a rectangular wave voltage to an AC motor as required.

[0006]

SUMMARY OF THE INVENTION However, PWM
Since the voltage utilization ratio differs between the waveform voltage and the rectangular wave voltage, if these waveforms are simply switched selectively, a sudden change in the voltage occurs, and as a result, a torque shock occurs in the electric motor. That is, the voltage utilization rate when using the PWM waveform voltage is √3 / 8, and when using the rectangular wave voltage, is √6 / π. Therefore, a change of about 30% occurs. Therefore, a torque shock due to a sudden change in current is likely to occur.

Therefore, even if both the PWM waveform voltage and the rectangular wave voltage can be selectively applied to the AC motor, a torque shock occurs in the motor if they are switched directly, For example, even if such a system is applied to an electric vehicle or the like, a suitable drive feeling cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention 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 an AC motor drive control device that can smoothly switch waveform voltages.

[0009]

(1) In order to solve the above problems, the present invention relates to a drive control device for an AC motor that performs switching control on an inverter that supplies power to the AC motor. First drive control means for applying pulse width modulation control to apply a pseudo sine wave voltage according to a current command value to the AC motor, and controlling the inverter to have a rectangular wave to control a phase according to a torque command value; A second drive control means for applying a rectangular wave voltage having a predetermined first amplitude to the AC motor; and the inverter being switched when control is switched from the first drive control means to the second drive control means. Is controlled by pulse width modulation so that the amplitude gradually increases from the amplitude of the pseudo sine wave voltage at the time of the switching to a predetermined second amplitude corresponding to the first amplitude, and the switching of the switching is performed. A pseudo sine wave voltage whose phase transition so that the output torque of the AC motor is continuously changed to,
And third drive control means for applying a voltage 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. Also, the second drive control means may control the phase corresponding to the torque command value to a predetermined first value.
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, during the transition period, the inverter is pulse width modulation controlled, and at that time, the amplitude of the pseudo sine wave voltage is changed. Gradually increases from the switching amplitude to the second amplitude. Further, the phase is changed in real time so that the output torque of the AC motor continuously changes. With this configuration, torque control can be suitably performed during the switching period, so that torque shock can be reduced when control using different waveforms is connected.
Further, since the voltage amplitude is gradually changed, the torque shock of the AC motor can be reduced from this point as well.

(2) Further, according to the present invention, in a drive control device for an AC motor for performing switching control on an inverter for supplying electric power to the AC motor, the inverter is controlled by pulse width modulation so as to respond to a current command value. First drive control means for applying the pseudo sine wave voltage to the AC motor, and rectangular wave control of the inverter to generate a rectangular wave voltage having a phase corresponding to a torque command value and a predetermined first amplitude,
A second drive control unit for applying the voltage to the AC motor; and when the control is switched from the second drive control unit to the first drive control unit, the inverter performs pulse width modulation control to perform the first amplitude control. The amplitude is gradually reduced from a predetermined third amplitude corresponding to the above, and a pseudo sine wave voltage whose phase changes so that the output torque of the AC motor continuously changes during the switching is applied to the AC motor. 4
And a drive control means.

According to the present invention, conversely, when the control is switched from the second drive control means to the first drive control means, during the transition period, the inverter is controlled by pulse width modulation. The amplitude gradually decreases from a predetermined third amplitude corresponding to the first amplitude. Also, during that switching 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 suitably shift from a state in which the rectangular wave voltage is applied to the AC motor to a state in which the pseudo sine wave voltage is applied without generating a torque shock.

(3) Further, in one aspect of the present invention, the fourth drive control means is provided when the current value supplied to the AC motor approaches the current command value. The control is transferred 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. For this reason, even when the AC motor is driven by the first drive control means, the control can be switched without a sudden change in the current value and without causing a torque shock.

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

According to this aspect, even when the current value supplied to the AC motor does not approach the current command value, the control is reliably performed from the fourth drive control means to the first drive control means. Can be transferred, and control failure can be prevented.

(5) In one aspect of the present invention, the third or fourth drive control means converts the pseudo sinusoidal wave voltage whose phase changes so that the output torque of the AC motor is constant, to the AC drive. It is characterized in that it is applied to a 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 is constant, so that the output torque of the AC motor at the time of switching is constant. , And the occurrence of torque shock at the time of control switching can be prevented.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of a drive control device for an AC motor according to an embodiment of the present invention. The drive control device 10 shown in FIG. 1 is mounted on an electric vehicle, and has three motor drive control modes: 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 a case where both the switches 26 and 28 are switched to the upper side in the figure. The current value is fed back so that the voltage amplitude | V | approaches the current command value. And a voltage phase ψ, and a pseudo sine wave voltage is applied to the motor 38.

Further, 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 a pseudo sine wave voltage is applied to the motor 38. At this time, the voltage amplitude | V | changes continuously with time, and the voltage phase ψ is set as needed in accordance with the change in the voltage amplitude | V | so that 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 figure to apply a rectangular wave voltage to the motor 38. The voltage amplitude | V | is determined by the DC battery voltage Vdc, and the voltage phase |
Is set according to the torque command value. At this time, the switching direction of the switch 26 may be either 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 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
2, the current command value I is 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 a proportional-integral control. Here, a voltage amplitude |
V | and the voltage phase ψ are generated. ψ is the angle of the current vector with respect to the q axis. The voltage phase ψ and the voltage amplitude | V | are supplied to the switch 26. Although not particularly shown, a 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, a voltage amplitude | V | and a voltage amplitude | V | supplied from the voltage amplitude controller 16 and the voltage phase controller 18, respectively. This is a configuration for selectively inputting a set of voltage phases に to the PWM circuit 30.

The PWM circuit 30 compares a sine wave supplied from the switch 26 with a voltage amplitude | V | and a voltage phase ψ with a previously prepared triangular wave.
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
Based on the switching command supplied from 0, a pseudo sine wave voltage is generated. 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 a power supply line from the inverter 36 to the motor 38, and the detected real-time current value is input to the adder 24 via a three-phase to 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 in real time and input to the current coincidence determination unit 22. The current coincidence 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, where a torque deviation ΔT is generated. The torque detecting means 20 can be configured using a torque sensor, but can also be configured to generate a torque by executing an operation represented by the following equation (1).

[0030]

T = Pin / ω = (iu × vu + iv × vv + iw × vw) / ω (1) Here, Pin represents electric power supplied to the motor 38.
ω represents the angular velocity of the motor 38. iu, iv, iw represent current values of each phase supplied to the motor 38, and vu, v
v and vw represent voltage values 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 to the motor 24 from the inverter 22 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]

T = Pin / ω = (IB × VB) / ω (2) Here, IB and VB represent 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 a voltage phase controller 18. Voltage phase controller 18
Generates the voltage phase ψ according to the torque deviation ΔT. The voltage phase controller 18 generates a rectangular wave voltage phase ψ in the rectangular wave voltage phase control mode. Further, in the PWM voltage phase control mode, a voltage phase 擬 似 of the pseudo sine wave voltage is generated. Specifically, the voltage phase controller 18 generates 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 parameters when generating the voltage phase ψ. Using the voltage amplitude | V | and the angular velocity ω of the motor 38, they are substituted into a predetermined arithmetic expression (or by performing equivalent processing) to generate a required voltage phase ψ. The voltage phase controller 18
May set the voltage phase ψ such that the torque is constant in the transition period between the PWM current control mode and the rectangular wave voltage phase control mode.

The voltage amplitude controller 16 is provided especially 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 generating torque shock. This 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 and sets the voltage amplitude | output by the current controller 14 at that time. V | is taken over and output, the value is gradually increased, and the voltage amplitude |
V | to the switch 26. In addition, the voltage amplitude | V |
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 is shifted from the rectangular wave voltage phase control mode to the PWM current control mode, the voltage amplitude controller 16 sets the voltage amplitude | V | The amplitude is inherited and output, and the value is gradually reduced.

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. When the switch 28 is switched to the lower side in the figure, the inverter 36 applies a rectangular wave voltage to the motor 38. I have.

FIG. 2 is a diagram showing voltage waveforms supplied to the motor 38 in each control mode. FIG. 7A is a diagram showing a voltage waveform supplied to the motor 38 in the PWM current control mode. On the upper side, a sine wave having a voltage amplitude | V | and a voltage phase ψ generated by the current controller 14 is shown. The state of 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. FIG. 3B shows a 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
And the triangular wave having | and the voltage phase ψ output from the voltage phase controller 18 are shown, and the lower side shows the waveform of the pseudo sine wave voltage as the comparison result. ing. FIG. 3C 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 configuration, and is a flow chart for particularly explaining the operation at the time of transition from the PWM current control mode to the rectangular wave voltage phase control mode. . As shown in FIG.
In, the drive control device 10 is in the PWM current control mode,
In this case, the switches 26 and 28 are both switched to the upper side in the figure. Then, the current command generation unit 1
2, current controller 14, PWM circuit 30, inverter 3
6 are functioning respectively. Next, if the shift 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 voltage initial 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, a pseudo sine wave voltage whose voltage amplitude and voltage phase are controlled is output from the inverter 36, and the motor 38 is driven by the waveform voltage. afterwards,
In S104, the voltage amplitude | V | output from voltage amplitude controller 16 is increased in a predetermined step. In S105, the voltage amplitude judging section 34 compares the voltage amplitude | V | output from the voltage amplitude controller 16 with a predetermined voltage based on the battery voltage Vdc, and outputs the voltage amplitude | V | Is smaller, S103 is performed again.
And the driving of the motor 38 in the PWM voltage phase control mode is continued.

Thereafter, if it is determined in step S105 that the voltage amplitude | V | output from the voltage amplitude controller 16 has become larger than the predetermined voltage, the switch 28 is switched to the lower side in FIG. Shifts to the rectangular wave voltage phase control mode (S106).

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

FIG. 4 shows the operation at the time of transition from the rectangular wave voltage phase control mode to the PWM current control mode. In FIG. 5, 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 figure.
The torque value is fed back to the adder 13, and the motor 38 is driven based on a torque command value output from an ECU (not shown). Then, when the shift to the PWM current control mode is instructed at a given timing, a 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 a voltage amplitude corresponding to, for example, a rectangular wave voltage is employed.

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 voltage amplitude | V | output from the voltage amplitude controller 16 and the voltage phase ψ output from the voltage phase controller 18 are supplied to the PWM circuit 30. In the PWM circuit 30, the amplitudes | V |
And a switching command is issued 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 reduced by a predetermined step. Then, in S205, the current coincidence determination unit 22 determines whether or not the current current value matches the current command value generated based on the current torque command value.

FIG. 5 is a diagram for explaining this determination processing. FIG. 4 shows a current vector on the dq plane, and a vector 50 shows a current command value generated by the current command generator 12. A vector 48 represents a current vector detected by the current sensor 40 in the case of 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 tip of the vector 50 representing the current command value. 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 figure.

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

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

It is not necessary for the current coincidence judging section 22 to exactly judge the coincidence of the two current values. If the end points of both vectors are within a certain range on the dq plane as shown in FIG. Good. In addition, it is conceivable that the vector 48 does not approach the vector 50 on the dq plane. In preparation for such a case, in the flow chart of FIG.
If the current voltage amplitude has decreased below the predetermined voltage amplitude, 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 shifting from the PWM control mode (I) to the PWM voltage phase control mode (II), the voltage amplitude 42 increases as the time elapses from the value at the switching timing. At this time, the voltage phase controller 1
Since the voltage phase ト ル ク supplied from 8 is controlled so that the torque output from the motor 38 becomes constant, the current amplitude 44 gradually decreases with time.

When the mode shifts from the PWM voltage phase control mode (II) to the rectangular wave voltage phase control mode (III), the voltage amplitude determination section 34 determines the voltage amplitude (arrow A in the figure). Then, in the rectangular wave voltage phase control mode, voltage amplitude 42 maintains a predetermined value corresponding to 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 shifting 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 matches the current command value generated by the current command generation unit 12, the PWM current phase control mode (IV) starts. The control mode shifts to the PWM current control mode (V) (arrow B in the figure).

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

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a drive control device for an AC 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 the PWM current control mode to the rectangular wave voltage phase control mode.

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

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

FIG. 6 is a diagram showing transition of a voltage amplitude and a current amplitude at the time of transition to a control mode.

[Description of Signs] 10 drive controller, 12 current command generator, 14 current controller, 16 voltage amplitude controller, 18 voltage phase controller, 20 torque detector, 22 current coincidence determiner, 2
4 adder, 26, 28 switch, 30 PWM circuit, 32 rectangular wave generator, 34 voltage amplitude determiner, 36
Inverter, 38 motor, 40 current sensor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Inakuma 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. No. 41 at Yokomichi 1 Toyota Central Research Laboratory Co., Ltd. F term (reference) 5H115 AA01 BA06 BB04 CA16 CB09 FA02 FA04 FA09 FA10 FA22 FA23 FB21 FB22 JC12 JC13 JC16 JC30 KB01 NN13 NN23 JJ24 LL01 LL22 LL24 LL29

Claims (5)

[Claims] 1. An AC motor drive control device that performs switching control on an inverter that supplies power to an AC motor, wherein the inverter performs pulse width modulation control to generate a pseudo sine wave voltage according to a current command value. First drive control means for applying to the AC motor, rectangular wave control of the inverter, and applying a rectangular wave voltage having a phase corresponding to a torque command value and a predetermined first amplitude to the AC motor. 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 is performed on the inverter to control the pseudo sine wave voltage at the time of the switching. The amplitude is gradually increased from the amplitude to a predetermined second amplitude corresponding to the first amplitude, and the phase is changed so that the output torque of the AC motor continuously changes during the switching. And a third drive control means for applying to the AC motor a pseudo sine wave voltage that changes. 2. An AC motor drive control device that performs switching control on an inverter that supplies power to an AC motor, wherein the inverter performs pulse width modulation control to generate a pseudo sine wave voltage according to a current command value. First drive control means for applying to the AC motor, rectangular wave control of the inverter, and applying a rectangular wave voltage having a phase corresponding to a torque command value and a predetermined first amplitude to the AC motor. And when the control is switched from the second drive control means to the first drive control means, the inverter performs pulse width modulation control to determine a predetermined third amplitude corresponding to the first amplitude. A pseudo sine wave voltage whose phase changes so that the output torque of the AC motor changes continuously during the switching while the amplitude gradually decreases from the switching is supplied to the AC motor. A drive control device for an AC motor, comprising: fourth drive control means for applying the voltage. 3. The drive control device for an AC motor according to claim 2, wherein the fourth drive control means is configured to output the first drive signal when the current value supplied to the AC motor approaches the current command value. A drive control device for an AC motor, wherein the control is transferred to the drive control means. 4. The drive control device for an AC motor according to claim 2, wherein the fourth drive control means reduces an amplitude of the pseudo sine wave voltage applied to the AC motor beyond a predetermined limit. If so, the control is transferred to the first drive control means. 5. The drive control device for an AC motor according to claim 1, wherein the third or fourth drive control means changes a phase so that an output torque of the AC motor becomes constant. A drive control device for an AC motor, wherein a pseudo sine wave voltage is applied to the AC motor.