JPH04289798A - Driving method and device for ac motor at the time of failure of converter - Google Patents

Abstract

PURPOSE:To suppress fluctuation of speed by switching to driving through other sound phase, upon failure of one phase converter driving an AC motor, thereby quickly generating same torque as that prevailing before failure. CONSTITUTION:When a faulty phase converter 1U is stopped, neutral points of a motor 2 and a converter 1 are connected each other, current phases of other sound phase converters 1V, 1W are modified in predetermined relation and then the firing angle is controlled according to thus modified AC current command and AC voltage command to sustain operation of the motor 2, a command for compensating the zero-phase current component flowing through the motor 2 during faulty operation is added to the AC voltage command (23) in order to compensate for the influence onto the vector control. Furthermore, terminal voltage of the motor 2 is detected until the firing angle control resumes and thus detected terminal voltage is employed, as the AC voltage command, in the control of firing angle(21, 22) thus matching the voltage phases of the converter 1 and the motor 2 and suppressing the surge current. At the same time, a predetermined current is fed quickly to the motor thus suppressing fluctuation of speed.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method and device for driving a polyphase AC motor driven by a cycloconverter or an inverter frequency converter, and particularly relates to a method and apparatus for driving a multiphase AC motor driven by a cycloconverter or an inverter frequency converter. The present invention relates to a driving method and apparatus for continuing operation using the remaining healthy phase converter.

0002

[Prior Art] A variable speed drive device for a polyphase AC motor (hereinafter simply referred to as an electric motor) uses a frequency converter (hereinafter simply referred to as a converter) such as a cycloconverter or an inverter, and uses large-capacity and important equipment. It is being applied to In addition, in order to improve the reliability of the equipment, even if some converters fail, the remaining converters can be used to continue operation or to maintain speed consistency with other normal AC variable speed drives. There are needs such as wanting to stop. As a method to meet these needs, there is a conventional method as described in Japanese Patent Publication No. 10679/1983.

[0003] The method described in the publication disconnects the converter of the faulty phase, connects the neutral point of the motor to the neutral point of the converter, and then connects the current phase of the converter of the other healthy phase to the motor. The current phase is changed to a predetermined relationship that generates a circular magnetic field, and the firing angle control of the converter in the healthy phase is restarted using the voltage command based on this changed current phase to continue the operation of the AC motor. be.

0004

However, according to the above-mentioned conventional technology, a zero-sequence current flows in the neutral point circuit when the converter is in the failure operation mode, but when the motor is an induction motor, When vector controlling the induction motor, that is, when separating the motor current command into torque current and excitation current and controlling the motor current according to each command signal, the zero-sequence current affects these current controls. No consideration was given to this issue.

[0005] Also, regardless of whether vector control is used or not,
When a failure occurs in one of the converters, the firing phase of all phases is changed to the maximum firing angle αmax in order to reduce the current that has been flowing until now to zero, so the magnetic flux of the motor decreases. and the phase will shift with respect to the control signal. Moreover, until the neutral point connection switch is closed and the supply of drive current to the motor is restarted, the back electromotive force of the motor is
It decreases according to the following time constant. For this reason, when it is time to restart drive by the converter in a healthy phase, at least the phase of the terminal voltage of the motor and the output voltage phase of the converter do not match, and an inrush current flows, or conversely, a current flows for a while. The problem is that sometimes there isn't.

[0006] Such a problem results in the problem that it takes time to output the same torque as before the occurrence of the failure, and speed fluctuations become large. In the worst case, a large inrush current flows, causing the overcurrent protection circuit to operate and failure to continue operation.

[0007] The object of the present invention is to solve the problem when a certain converter malfunctions.
It is an object of the present invention to provide a method and device for driving an AC motor when a converter fails, which can quickly generate the same torque as before the failure after switching to drive by another healthy phase, and can reduce speed fluctuations.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the method and device for driving an AC motor when a converter fails according to the present invention provides a method and an apparatus for driving an AC motor when a converter fails. In the event of a failure, the converter of the faulty phase is disconnected, the neutral point of the motor is connected to the neutral point of the converter, and then the current phase of the converter of the other healthy phase is applied to the motor by applying a circular magnetic field. converter failure, in which the firing angle of the converter of the healthy phase is controlled based on the alternating current command and the alternating voltage command of the changed current phase to continue operation of the motor; In the method for driving an AC motor, adding a command to compensate for the zero-sequence current flowing through the motor during failure operation to the AC voltage command of the healthy phase, or until the firing angle control is restarted. The present invention is characterized in that the magnitude and phase of the terminal voltage of the electric motor are detected, and the detected value is used as the voltage command to control the firing angle of the converter of the healthy phase, or a combination thereof is used.

[0009]

[Operations] With the above structure, according to the present invention, the above object is achieved by the following operations.

First, when driving by the healthy phase converter is resumed, a current flows through the neutral point circuit and a zero-sequence current flows into the healthy phase. By adding the voltage command to the AC voltage command, when performing vector control of the motor, it is possible to eliminate the influence on control based on the respective command values of torque current and excitation current, and quickly generate the specified torque. be able to.

[0011] Furthermore, until a failure occurs in a converter and the drive is switched to the remaining healthy phase converter, the magnitude and phase of the terminal voltage of the motor are detected, and the detected value is used as a voltage command to convert the healthy phase. By controlling the firing angle of the converter, the phases of the converter output voltage and the motor terminal voltage match. As a result, no inrush current will flow when driving is restarted in a healthy phase, and a predetermined current can be quickly passed through the motor.

0012

[Examples] The details of the present invention will be explained below with reference to Examples. FIGS. 1 to 4 show configuration diagrams of an embodiment of the present invention. This embodiment is an example in which a three-phase induction motor is driven by a drive device using a cycloconverter, as shown in the overall configuration diagram shown in FIG. As shown in the figure, a cycloconverter 1 is connected to each phase winding of a three-phase induction motor 2 as a polyphase AC motor.
A sine wave current is supplied from U, 1V, 1W. The speed of the three-phase induction motor 2 is detected by a speed detector 3, and the deviation of the detected speed from the speed command output from the speed command circuit 4 is determined by an adder and inputted to a speed deviation amplifier 5. Further, the detected speed is also input to the frequency command calculator 7. The speed deviation amplifier 5 generates and outputs a torque current command signal It* according to the input speed deviation. The frequency command calculation circuit 7 calculates the torque current command It.
The detected speed is added to the slip frequency command signal ωs* determined from *, and this is output as the primary frequency command signal ω1*. The output ω1* of the frequency command calculation circuit 7 is input to the two-phase sine wave generation circuit 8, from which the two-phase sine wave signal cosθ
, sin θ are output. The AC current command calculation circuit 9 is
The excitation current command Im*, which is the output of the excitation current command circuit 6, the torque current command It*, and the two-phase sinusoidal signal cos θ, si
Using nθ as input, the induction motor generates and outputs alternating current commands iu*, iv*, iw* for each phase necessary for outputting torque corresponding to torque current command It*. The alternating current commands iu*, iv*, iw* of each phase are input to current deviation amplifiers 11U, 11V, 11W as current control means, where the currents provided at the outputs of each phase of the cycloconverters 1U, 1V, 1W are The deviation from the detected current input from the detectors 10U, 10V, and 10W is taken, and the AC voltage command necessary to make this current deviation zero is sent to the automatic pulse phase shifter 12.
Output to U, 12V, 12W. With this automatic pulse phase shifter 12U, 12V, 12W, the cycloconverter 1
The ignition phase of each phase is controlled, and the induction motor 2 is driven at a speed according to the speed command.

FIG. 2 shows a detailed configuration of the alternating current command calculation circuit 9. In the figure, an AC current command calculation circuit 13 inputs current commands It*, Im* and two-phase sine wave signals (cos θ, sin θ), and receives three-phase AC current commands iu**, iv**, iw*. Output *. During normal operation, this AC current command passes through the current command switching circuit 14 and is output as iu*, iv*, and iw* signals. When one phase of the cycloconverter 1 fails, the current command switching circuit 14 is switched, and the current command of the failed phase is added to the current command of the healthy phase with opposite polarity. For example, as shown in the illustrated example, when a U-phase failure occurs, the switch 15 is turned on by a command from a failure control means (not shown), and the U-phase current command iu** in the normal state changes from the V-phase and W-phase current command iv. **,i
It is added to w** with the opposite polarity, and new V-phase and W-phase current commands (failure current commands) iv* and iw* are output. As a result, currents according to the changed current commands iv*, iw* flow in the V-phase and W-phase of the induction motor 2, and the composite magnetomotive force created by the V-phase and W-phase currents is generated when the U-phase is normal. The magnetomotive force is the same as that of the failed phase, and operation continues using the remaining healthy phases other than the failed phase. Note that the AC current command switching circuit 14 in FIG. 2 shows a state diagram in the case of a U-phase failure, and in the case of other V-phase and W-phase failures, circuits with the same concept are used, but are not shown here.

The above configuration is the same as the conventional one, and the features of the present invention will be explained below. Voltage detectors 20U, 20V, and 20W are provided to detect the terminal voltages of the induction motor 2, and the motor terminal voltages vu, vv, and vw of each phase detected by these voltage detectors are detected by the voltage vector detector 2.
1 is entered. This voltage vector detector 21 is
Two-phase sine wave signal c output from two-phase sine wave generation circuit 8
Input osθ, sinθ, and calculate the terminal voltages vu, vv,
vw is converted to d and q axis component voltage VdFB using a well-known processing method.
, VqFB and detected. The vector component voltage command circuit 22 outputs the torque current command Im* and the excitation current command I.
t*, primary frequency command signal ω1*, and voltage vector detection signals VdFB, VqFB are input, and d and q axis component voltage commands Vd* and Vq* are generated and output. The AC voltage command calculation circuit 23 calculates the d and q axis component voltage commands Vd*, V
q* and two-phase sine wave signals cos θ, sin θ are input, and AC voltage commands vu*, vv*, vw* of each phase are generated and output. These AC voltage commands vu*, vv*, vw*
is the current deviation amplifier 11U, 11 by the adder 24.
It is added to the output signal of V, 11W.

FIG. 3 shows details of the vector component voltage command circuit 22. As shown in the figure, it is composed of a motor voltage calculation circuit 25 and a vector voltage command switching circuit 26. The motor voltage calculation circuit 25 generates voltage commands Vd** and Vq** for the d and q axes in a state where the induction motor 2 is vector-controlled and outputs them using Equation 1, which will be described later. During normal operation, these Vd** and Vq** pass through the vector voltage command switching circuit 26 and are output as voltage commands Vd* and Vq*. The switch 27 of the vector voltage command switching circuit 26 controls the voltage vector detection signal VdFB by a failure control means (not shown) after one phase of the cycloconverter 1 fails until the remaining healthy phase of the cycloconverter resumes operation. Switched to VqFB side.

FIG. 4 shows details of the AC voltage command calculation circuit 23. As shown in the figure, it is composed of a three-phase voltage command calculation circuit 28, an AC voltage command switching circuit 29, and a zero-phase voltage calculation circuit 30. The AC voltage command switching circuit 29 and the zero-phase voltage calculation circuit 30 constitute a zero-phase voltage compensating means. As is well known, the three-phase voltage command calculation 28 calculates voltage commands Vd*, Vq* output from the vector component voltage command circuit 22.
is converted into three-phase AC voltage commands vu**, vv**, vw** using two-phase sine wave signals cos θ and sin θ. During normal operation, this signal passes through the AC voltage command switching circuit 29 and is outputted, and is passed through the adder 24 to the current deviation amplifier 1.
It is combined with the outputs of 1U, 11V, and 11W, and the firing angle of each phase of the cycloconverter 2 is controlled via automatic pulse phasers 12U, 12V, and 12W. The zero-sequence voltage calculation circuit 30 estimates the zero-sequence voltage from the three-phase current command iu** output from the AC current command calculation circuit 13 in FIG. do. The AC voltage command switching circuit 29 converts the zero-phase voltage command v0* into the AC voltage commands vu**, vv* via the switch 15.
*, vw**, AC voltage commands vu*, vv*
, vw* are output. The switch 15 is turned on by a failure control means (not shown) when the cycloconverter in the healthy phase resumes driving.

The operation of the embodiment thus constructed will now be described. First, the principle of operation of this embodiment will be explained. During normal operation, three-phase sinusoidal AC current commands iu*, iv*, iw* are output from the AC current command calculation circuit 9, and three-phase current is supplied to the induction motor 2 by the action of the current deviation amplifiers 11U, 11V, and 11W. flows, a torque is generated according to the torque current command It*, and speed control is performed according to the speed command. Here, when vector control is performed by flowing torque current It and excitation current Im through the induction motor, if the terminal voltage V1 of the motor is expressed by voltages Vd and Vq in the d and q axis coordinate system, Equations 1 to 3 are obtained. Become.

[0018]

[Math 1]

[0019]

[Math 2]

[0020]

[Math 3]

[0021] Here, r1; Motor primary resistance L1, L2; Motor primary and secondary leakage inductance L
m; Motor excitation inductance ω1; Primary angular frequency φ; Motor magnetic flux T2; When motor secondary time constant vector control is performed, Im, It and Vd
, Vq is shown in the vector diagram of FIG. Therefore, the magnitude and phase of the voltage can be detected by separating and detecting the terminal voltage V1 into It and the in-phase component Vq, and Im and the in-phase component Vd.

Now, let us consider a case where a failure occurs in the cycloconverter 1 and the output current is reduced to zero. In formula 1, if Im=0, It=0, Vd=0, Vq=ω
1×φ, and the term ω1×φ remains in the terminal voltage. If this term is considered as an induced electromotive force (EMF), the EMF will be expressed as Equation 4.

[0023]

[Math 4]

Therefore, after the failure occurs, the motor terminal voltage changes according to Equation 4 until the two-phase drive is restarted using the remaining healthy phases. In other words, since Im=0, the magnetic flux φ decreases with the time constant of T2, and the speed decreases due to this, that is, ω1
The EMF changes due to a decrease in the amount of energy. Therefore, while switching to two-phase drive, Vd and Vq shown in Formula 1 are detected,
When this is given as a voltage command to the cycloconverter 1, it is possible to make the firing angle control signal match the phase of the actual motor terminal voltage and wait.

On the other hand, under normal conditions, when vector control is performed by flowing currents Im and It, each phase motor current iu
, iv, iw and the zero-sequence current i0 have the relationships shown in Equations 5 to 7.

[0026]

[Math 5]

[0027]

[Math 6]

[0028]

[Math 7]

[0029] Equation 6 is transformed into Equation 8.

[0030]

[Math. 8]

At this time, motor phase voltages vu, vv, vw
Similarly, the zero-phase voltage v0 is expressed by Equations 9 to 11.

[0032]

[Math. 9]

[0033]

[Math. 10]

[0034]

[Math. 11]

[0035] Equation 10 is transformed into Equation 12.

[0036]

[Math. 12]

Next, for example, when the U-phase cycloconverter 1U fails, currents ivf and iwf are determined so that the same electromotive force as in normal times is generated in the V-phase and W-phase. Formula 7
, 8, iu=0 and ivf, iwf, and i0 are obtained as Equations 13 and 14.

[0038]

[Math. 13]

[0039]

[Formula 14] i0=-iα Here, the first term in Equation 13 is the V-phase and W-phase currents when healthy, and the second term corresponds to the current when the faulty phase is healthy. Furthermore, it can be seen that the zero-sequence current i0 is a reverse polarity current when the faulty phase is healthy. When the zero-sequence current i0 flows, a zero-sequence voltage v0 is generated, and its value is expressed by Equation 15.

[0040]

[Formula 15]v0=(r1+L1S)×i0Similarly, when the motor terminal voltage when the above currents ivf and iwf are flowing at the time of a U-phase failure is calculated from Equations 11 and 12, Equation 16
becomes.

[0041]

[Math. 16]

The first term in Equation 16 is the voltage of each phase during normal operation, and the second term is the zero-phase voltage.

As mentioned above, the current and voltage of each phase of the motor are controlled to be proportional to each current command signal and voltage command signal, so each command signal can be expressed by equations 13 and 16.
The above-mentioned control becomes possible by adding the signals according to the relationship and controlling the obtained signals as the current command and voltage command signals at the time of failure. In other words, the current command at the time of failure can be obtained by adding the current command at the normal state of the failed phase to the current command at the normal state with opposite polarity. Further, the voltage command at the time of failure may be the voltage command at the time of normal operation plus the zero-phase voltage command v0*.

Therefore, in the embodiment shown in FIG. 1, if any of the thyristor converters 1U to 1W constituting the cycloconverter 1 should fail, the main circuit connects the failed converter and the induction motor 2 electrically. The fault control means (not shown) operates, and the other remaining healthy phase converters connect their neutral points to the neutral point N of the induction motor 2 through the switch 16.
Switch to two-phase circuit configuration. Then, the control circuit changes the phase of the current command of the healthy phases other than the faulty phase, generates a circular magnetic field equal to the magnetomotive force generated under normal conditions, and continues operation with the remaining healthy phases.

[0045] Here, taking as an example a case where the U-phase cycloconverter 1U fails, the operation will be explained with reference to the time chart shown in FIG. The horizontal axis of FIG. 6 indicates time, the time t1 is the failure occurrence point, the t2 point is the point at which the neutral point circuit connection switch 16 closes, as shown in FIG. 6(b),
Point t3 indicates the point in time when the induction motor 2 outputs the same torque as before the failure occurred, as shown in FIG. 2(d). Furthermore, in the figure, the solid line represents the operation of the present invention, and the dotted line represents the conventional operation.

Now, at time t1, cycloconverter 1
When a failure occurs in U, the firing phases of all phases are changed to the position αmax in terms of firing angle in order to reduce the current that has been flowing to zero (FIG. 4(c)). For this reason, the magnitude and phase of the magnetic flux of the induction motor 2 are shifted from the control signal. On the other hand, until the neutral point connection switch 16 is closed and the two-phase drive is restarted (between times t1 and t2), as the speed decreases, the back electromotive force of the induction motor 2 increases due to the motor secondary time constant. It starts to decline. Therefore, when two-phase control is resumed at time t2, the motor voltage phase and the control output voltage phase do not match, and an inrush current may flow, or conversely, no current may flow for a while. In this regard, according to this embodiment, the switch 2 of the vector voltage command switching circuit 26 in FIG.
7 is turned on only until the start of two-phase drive, and voltage vector detection signals VdFB and VdFB representing detected values of the induced electromotive force of the induction motor 2 are output as d and q axis voltage commands Vd* and Vq*. As a result, automatic pulse phasers 12U, 12
AC voltage command signals vu*, vv*, vw* having the same phase as the changing motor terminal voltage are input to V and 12W, and the output voltage phase of the cycloconverter 1 is determined by the induced voltage of the induction motor 2. It is expected to wait at a position that matches the electromotive force. Therefore, it is possible to eliminate the inconvenience that an inrush current flows at the start of two-phase drive, or conversely, that no current flows. As a result, it is possible to quickly output the torque before the occurrence of a failure, and it is also possible to avoid operation of the protection circuit due to rush current.

Thereafter, at time t2, the switch 16 is actually closed, and two-phase drive by the remaining healthy cycloconverters 1V and 1W is started. in this case,
Similar to the conventional method, the switch 15 of the AC current command calculation circuit 9 shown in FIG. 2 is turned on, and the AC current commands iv*, i
iu* of opposite polarity is added to w*. When two-phase drive starts, current flows through the neutral point circuit, and this zero-phase current affects vector control of the motor, resulting in a delay in outputting the same torque as before the failure, and speed fluctuations. becomes larger. Therefore, in this embodiment, when two-phase drive is started, the switch 27 is turned off and the d and q axis voltage commands V
d* and Vq* are switched to voltage commands Vd** and Vq** when performing vector control. At the same time,
The switch 15 in the AC voltage command calculation circuit 23 is turned on, and the zero-phase voltage calculation circuit 30 generates a zero-phase voltage command as shown in Equation 15 based on the current command iu** when the U phase is healthy, which is the failed phase. v0* is calculated, and v is the voltage command during normal operation.
The zero-phase voltage command v0* is added to the u**, vv**, and vw** signals, and this is used as the AC voltage command vu*,
Output as vv*, vw*. As a result, when switching to two-phase drive, the current and voltage commands shown in Equations 13 and 16 above can be given, and a predetermined torque can be immediately output by vector control. In other words, it is possible to operate as if the U phase were healthy. As a result, it is possible to quickly output the torque before the occurrence of the failure, and it is possible to reduce speed fluctuations.

In the embodiment described above, after the occurrence of a failure, until the two-phase drive control is restarted, the voltage detection values VdFB, VdFB are used as the voltage commands Vd*, Vq*.
In this method, the induced electromotive force EMF is calculated from the excitation current command Im* and the primary frequency command ω1* as shown in Equation 4 above, and this EMF is given as the voltage command Vq*, and the voltage command Vd* is The same result can be obtained even if it is set to "0".

Furthermore, the present invention is applicable not only to induction motors but also to synchronous motors, and is not limited to cycloconverters but can also be applied to other converters such as inverters.

[0050]

[Effects of the Invention] As explained above, according to the present invention,
When a phase of a converter such as a cycloconverter fails and the AC motor continues to operate on another healthy phase, the zero-sequence voltage corresponding to the zero-sequence current flowing through the converter and the neutral point circuit of the AC motor is Since it is added to the voltage command related to vector control, vector control by the remaining healthy phase converters can be performed without any problems, and the torque before the failure can be output immediately. can be made smaller.

[0051] Furthermore, until the drive control is resumed due to the healthy phase,
Since the output voltage of the converter is controlled according to the magnitude and phase of the induced voltage of the AC motor, it is possible to eliminate the inconvenience of inrush current flowing when the drive is resumed, or conversely, that current does not flow, thereby quickly preventing failure. It is possible to output the torque before generation, and to avoid operation of the protection circuit due to rush current.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an AC motor drive device using a cycloconverter according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an embodiment of an alternating current command calculation circuit according to the present invention.

FIG. 3 is a configuration diagram of an embodiment of a vector component voltage command circuit according to the present invention.

FIG. 4 is a configuration diagram of an embodiment of an alternating current command calculation circuit according to the present invention.

FIG. 5 is a time chart explaining the operation of the present invention.

FIG. 6 is a diagram illustrating the phase relationship between current and voltage.

[Explanation of symbols]

1U~W Cyclo converter 2 Induction motor 4 Speed command circuit 7 Frequency command calculation circuit 8 Two-phase sine wave generation circuit 9 AC current command calculation circuit 11U~W Current deviation amplifier 12U~W Automatic pulse phase shifter 15, 27 Switch 21 Voltage vector detector 22 Vector component voltage command circuit 23 AC voltage command calculation circuit 30 Zero-phase voltage calculation circuit

Claims (9)

[Claims] Claim 1: When a converter of a certain phase of a converter that drives a multi-phase AC motor fails, the converter of the failed phase is stopped and the neutral point of the motor is connected to the neutral point of the converter. After connecting, the current phase of the converter of the other healthy phase is changed to a predetermined relationship that generates a circular magnetic field in the motor, and the healthy phase is changed based on the AC current command and AC voltage command of the changed current phase. In a method for driving an AC motor when a converter fails, the firing angle of a phase converter is controlled to continue operation of the motor, in which a command to compensate for a zero-sequence current flowing through the motor during failure operation is set to A method for driving an AC motor when a converter fails, the method comprising adding the voltage command to a phase AC voltage command. 2. When a converter of a certain phase of a converter that drives a multiphase AC motor fails, the converter of the failed phase is disconnected, and the neutral point of the motor and the neutral point of the converter are separated. After the connection, the current phase of the converter of the other healthy phase is changed to a predetermined relationship that generates a circular magnetic field in the motor, and the point of the converter of the healthy phase is changed based on the alternating current command of the changed current phase. In a method of driving an AC motor when a converter fails, the motor continues to operate by controlling the firing angle, and the magnitude and phase of the terminal voltage of the motor are detected until the firing angle control is restarted. A method for driving an AC motor when a converter fails, characterized in that the detected value is used as a voltage command to control the firing angle of the converter in the healthy phase. 3. When a converter of a certain phase of a converter that drives a multiphase AC motor fails, the converter of the failed phase is disconnected, and the neutral point of the motor and the neutral point of the converter are separated. After the connection, the current phase of the converter of the other healthy phase is changed to a predetermined relationship that generates a circular magnetic field in the motor, and the current phase of the converter of the healthy phase is changed based on the AC current command and AC voltage command of the changed current phase. In the method of driving an AC motor when a converter fails, the firing angle of the converter is controlled to continue operation of the motor, the magnitude of the terminal voltage of the motor and the The phase is detected, the detected value is used as a voltage command to control the firing angle of the converter of the healthy phase, and after the firing angle control is restarted, the zero-sequence current flowing through the motor at the time of failure operation is A method for driving an AC motor when a converter fails, the method comprising: adding a command to compensate for the AC voltage command of the healthy phase to the AC voltage command of the healthy phase. 4. When a converter of a certain phase of a converter that drives a multiphase AC motor fails, the converter of the failed phase is disconnected, and the neutral point of the motor and the neutral point of the converter are separated. After the connection, the current phase of the converter of the other healthy phase is changed to a predetermined relationship that generates a circular magnetic field in the motor, and the current phase of the converter of the healthy phase is changed based on the AC current command and AC voltage command of the changed current phase. In the AC motor drive device, the AC motor is configured to continue operating the motor by controlling the firing angle of the converter of the certain phase, in which a zero-sequence current flows through the motor during failure operation due to a converter failure of the certain phase. A driving device for an AC motor, comprising: zero-phase voltage compensating means for adding a command to compensate for the normal phase AC voltage command to the AC voltage command of the healthy phase. 5. A converter provided for each phase of a polyphase AC motor and supplying current to each phase, and generating and outputting a current command signal for each phase of the motor according to an output torque command. current command calculation means; current control means for generating and outputting a voltage command signal that causes a current corresponding to the current command signal to flow through each phase of the motor; and an output of the converter based on the voltage command signal. firing angle control means for controlling the firing angle of the converter in order to control voltage; and neutral point switching means inserted into a connection line between the neutral point of the motor and the neutral point of the converter. , a failure current command signal in which the current phase of the current command signal to be supplied to a healthy phase is changed to a predetermined relationship in order to generate a circular magnetic field in the motor when a converter of a certain phase among the converters fails; In the drive device for an AC motor, the AC motor has a fault control means for switching the neutral point switching means to the neutral point switching means and closing the neutral point switching means. An alternating current motor drive device, comprising means for adding the zero-phase voltage command to the healthy phase voltage command signal. 6. According to claim 5, the failure control means detects the magnitude and phase of the terminal voltage of the motor until the firing angle control based on the failure current command is restarted; A driving device for an AC motor, comprising means for controlling the firing angle of the healthy phase converter using the detected value as a voltage command. 7. A converter provided for each phase of a polyphase AC motor to supply current to each phase, and a current that generates and outputs a current command for each phase of the motor according to an output torque command. a command calculation means, a voltage command calculation means for generating and outputting a voltage command for each phase of the motor according to the output torque command, and control for causing a current corresponding to the current command to flow through each phase of the motor. Current control means for generating and outputting a command, and firing angle control means for controlling a firing angle of the converter to control the output voltage of the converter based on a composite command of the control command and the voltage command. and a neutral point switching means inserted in a connection line between the neutral point of the motor and the neutral point of the converter, and a neutral point switching means inserted in a connection line between the neutral point of the electric motor and the neutral point of the converter, and a neutral point switching means inserted in a connecting line between the neutral point of the motor and the neutral point of the converter, and a failure control means for switching the signal to a failure current command signal in which the phase of the current supplied to the healthy phase is changed to a predetermined relationship in order to generate a circular magnetic field in the electric motor, and for closing the neutral point switching means. In the drive device for an AC motor, the failure control means obtains a zero-sequence voltage command corresponding to the zero-sequence voltage generated in the motor, and adds the zero-sequence voltage command to the voltage command signal of the healthy phase for zero-sequence voltage compensation. 1. A drive device for an AC motor, comprising: means. 8. The AC motor drive device according to claim 7, wherein the zero-sequence voltage compensating means determines the zero-sequence voltage based on the current command of the failed phase output from the current command calculating means. . 9. According to claim 7, the failure control means detects the magnitude and phase of the terminal voltage of the motor until the firing angle control based on the failure current command is restarted; A driving device for an AC motor, comprising means for controlling the firing angle of the healthy phase converter using the detected value as a voltage command.