JP2003284384A - Method of controlling ac motor and its apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an AC motor driven by an alternating-current which has been converted by an electric power converter to perform variable speed control stably by keeping a current control stable even if the AC motor accelerates or decelerates abruptly or a load is rapidly changed in a range where an output voltage of the electric power converter becomes saturated. <P>SOLUTION: The magnitude of a voltage which can be outputted from a DC voltage of an electric power converter is computed, a phase outputted from an output voltage computing circuit is left as it is, and inputs to an exciting current control circuit and to a torque current control circuit are compensated so as to restrict the magnitude of the output voltage by the voltage which can be outputted. In other words, in a vector diagram, at the point of the intersection of a vector of the magnitude of output a voltage signal V<SB>1</SB>* compensated with the DC voltage and an arc showing a voltage which can be outputted, an output voltage command V<SB>1</SB>*' is generated after a limit where a voltage phase θV is left as it is, and the magnitude of the output voltage is compensated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case where an AC motor driven by an AC converted by a power converter suddenly accelerates or decelerates or a load changes suddenly in a region where an output voltage of the power converter is saturated. Even if it is, it relates to a control method and a control device for an AC electric motor capable of performing stable variable speed control.

[0002]

2. Description of the Related Art Conventionally, in the control of an AC motor of this type, for example, in the invention described in Japanese Patent Laid-Open No. 10-262399, the current control operation does not become unstable in the region where the output voltage of the power converter is saturated. Adjust the current control gain to a high value within the range to keep the current control response constant, or reduce the gain to zero to prevent the current control operation from becoming unstable. I have to.

Further, for example, Japanese Patent Laid-Open No. 2001-145400.
In the invention described in the publication, the saturation amount is obtained from the ratio of the output voltage command value obtained by the output voltage command calculation circuit and the DC voltage detection value detected by the power converter, and thereby the induced voltage of the induction motor and the magnetic flux command are calculated. The gain is adjusted to reduce the magnitude, and the response of the current control is kept constant without the output voltage being saturated.

[0004]

However, even in the control of the AC motor as described above, the output voltage of the power converter gradually approaches saturation in the operation in which normal acceleration / deceleration is performed. Although the control method is sufficient, if the operation is performed with sudden acceleration / deceleration or the load changes abruptly, the control will not be in time, the current flowing to the AC motor will become unstable, and an excessive current will flow. Then, the current control becomes unstable.

The present invention is intended to solve such a conventional problem, and keeps the current control stable even when the load is suddenly accelerated or decelerated or the load is changed suddenly. It is an object of the present invention to provide an AC electric control method and a control device capable of stably accelerating and decelerating.

[0006]

In order to achieve the above object, in the invention according to claim 1 of the present application, a power converter that outputs arbitrary electric power to an AC motor and a current supplied to the AC motor are detected. A current detection circuit, a coordinate conversion circuit that converts the current supplied to the AC motor into an excitation current detection value and a torque current detection value, and outputs the same, so that the excitation current command value and the excitation current detection value match. An exciting current control circuit that controls the exciting current direction voltage, a torque current control circuit that controls the torque current direction voltage so that the torque current command value and the torque current detection value match, and the given output frequency command is integrated. The phase angle calculation circuit for calculating the phase angle obtained by performing the calculation and the magnitude and phase of the output voltage are calculated from the voltage commands output from the excitation current control circuit and the torque current control circuit. In the control method, which comprises an output voltage calculation circuit for calculating, and adds the phase angle output from the phase angle calculation circuit to the magnitude and phase of the voltage output from the output voltage calculation circuit, to determine switching of the power converter, The magnitude of the voltage that can be output is calculated from the DC voltage of the power converter, and the magnitude of the output voltage is limited by the voltage that can be output without changing the phase that is output from the output voltage arithmetic circuit. It is characterized in that inputs to the excitation current control circuit and the torque current control circuit are corrected.

Further, in the invention according to claim 2 of the present application, a power converter that outputs arbitrary power to the AC motor, a current detection circuit that detects a current supplied to the AC motor, and a power converter that is supplied to the AC motor. A coordinate conversion circuit that converts a current to an exciting current detection value and a torque current detection value and outputs the same, and an exciting current control circuit that controls the exciting current direction voltage so that the exciting current command value and the exciting current detection value match. And a torque current control circuit that controls the torque current direction voltage so that the torque current command value and the torque current detection value match.
A phase angle calculation circuit for calculating a phase angle obtained by integrating a given output frequency command, and the magnitude and phase of the output voltage from the voltage command output from the excitation current control circuit and the torque current control circuit. In a control device comprising an output voltage arithmetic circuit for arithmetic operation, adding the phase angle output from the phase angle arithmetic circuit to the magnitude and phase of the voltage output from the output voltage arithmetic circuit, and determining the switching of the power converter, The magnitude of the voltage that can be output is calculated from the DC voltage of the power converter, and the magnitude of the output voltage is limited by the voltage that can be output without changing the phase that is output from the output voltage arithmetic circuit. It is characterized in that inputs to the excitation current control circuit and the torque current control circuit are corrected.

[0008]

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

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

The control device for the electric motor in this embodiment is
Power converter 1, AC motor 2, current detector 3, current coordinate conversion circuit 4, torque current control circuit 5, excitation current control circuit 6, phase calculation circuit 7, output voltage calculation circuit 8, switching pattern generation circuit 9 and output A voltage correction circuit 10 is provided.

The power converter 1 converts a DC voltage, which has been converted into a three-phase AC by a power element, into an AC having an arbitrary frequency and voltage by a PWM control method and supplies the AC voltage to the AC motor 2.

The current detector 3 is the AC motor 2 described above.
The currents i _u and i _w supplied to the sensor are detected, and the detected current values i _u and i _w are sent to the current coordinate conversion circuit 4.

The current coordinate conversion circuit 4 includes the current detector 3
The current values i _u and i _w detected by the above are separated into a torque current detection value i _qfb and an excitation current detection value i _dfb , and both current values i _{q fb} and i _dfb are respectively controlled by the torque current control circuit 5 and the excitation current control. Send to circuit 6.

The torque current control circuit 5 receives the applied torque current command value i _qref and the detected torque current value i.
As a _qfb match, q-axis voltage command value _{V qref}
Is calculated and sent to the output voltage calculation circuit 8.

On the other hand, the exciting current control circuit 6 receives the applied exciting current command value i _dref and the exciting current detection value i.
d-axis voltage command value V _dref so that _dfb matches
Is calculated and sent to the output voltage calculation circuit 8.

The phase calculation circuit 7 calculates the phase θ by integrating the given frequency f ₁ .

The output voltage calculation circuit 8 calculates the q-axis voltage command value V _qref and the d-axis voltage command value V _dref from the q-axis voltage command value V _qref and the d-axis voltage command value V _dref .
The output voltage command value V ₁ and its voltage phase θ _V are sent to the switching pattern generation circuit 9.

The switching pattern generation circuit 9 determines the switching pattern of the power converter 1 from the output voltage command value V _{1, the} voltage phase θ _V, and the power converter output phase θ _{deg obtained} by adding the phase θ. To do.

FIG. 2 is a block diagram showing the configuration of an embodiment of the output voltage correction circuit 10 in the present invention.

The output voltage correction circuit 10 receives the DC voltage V _DC from the power converter 1, the output voltage command value V ₁ and its voltage phase θ _V from the output voltage calculation circuit 8, and outputs the output voltage command V ₁ And the DC voltage V _DC of the power converter 1
The output voltage command V ₁ ^* corrected by the DC voltage which is the ratio of
It is limited by the limit circuit of the preset level, and the output voltage command V ₁ ^* 'after the limit is output.

Output voltage command V ₁ ^* corrected by the DC voltage input to the limit circuit and output voltage command V after limit
_{1 *} ^'to calculate the correction voltage V _e, the voltage phase theta _V than the correction voltage V _e with, d-axis voltage correction value V _{e d} and the torque current control circuit to the input of the excitation current control circuit The input q-axis voltage correction value V _eq is calculated and output.

Next, the meaning of the calculation in the output voltage correction circuit 10 will be described below with reference to a vector diagram.

FIG. 3 is a vector diagram showing an embodiment of output voltage correction according to the present invention. The maximum value of the output voltage calculated from the DC voltage exists on the arc indicated by the broken line in the figure.

If the magnitude of the output voltage command V ₁ ^* corrected by the DC voltage is smaller than the maximum value of the output voltage and the voltage vector exists inside the arc, the output voltage command V corrected by the DC voltage V ₁ ^* and output voltage command V after limit
₁ ^* 'will match. However, a voltage vector exceeding this circular arc cannot be output. Therefore, in the present invention, when the voltage is saturated, the voltage phase θ _V remains unchanged with respect to the target voltage vector and only the magnitude of the voltage is limited. This is to prevent the current control from becoming unstable when the voltage phase changes, which is to be prevented. For this reason, when the magnitude V ₁ ^* of the output voltage command corrected by the DC voltage is larger than the maximum value and the voltage vector exceeds the arc, it becomes a vector of the magnitude V ₁ ^* of the output voltage command corrected by the DC voltage. An output voltage command V ₁ ^* 'after the limit in which the magnitude of the output voltage is corrected is created at the intersection of the arcs.

Output voltage magnitude V ₁ corrected by DC voltage
^{Since the} phase θ _V is the same and similar to ^* and the output voltage command V ₁ ^* 'after the limit in which the magnitude of the output voltage is corrected, the voltage vector V _e to be corrected is the output voltage command corrected with the DC voltage. which is a difference between the magnitude V ₁ ^* and the output voltage of the output voltage command of the limited corrected for size V _{1 *} ^'. Then, after the voltage vector V _e to be corrected is calculated by the difference, the d-axis component V _ed and the q-axis component V _eq can be calculated from the calculation result. The correction voltages correct the inputs to the exciting current control circuit and the torque current control circuit, respectively.

In FIG. 2, the d-axis component V_ed
To K_dAnd the above q-axis component V_eqTo K _qDivided by
But this K_dAnd K_qIs the excitation current
Proportional control of the flow control circuit 6 and the torque current control circuit 5
And for converting voltage into a dimension of current deviation
Is.

[0027]

As described above, according to the AC motor control method and apparatus of the present invention, the input to the exciting current control circuit and the torque current control circuit can be corrected so that the output voltage is not saturated, and the current is reduced. The control can be prevented from becoming unstable, and the AC motor can be stably accelerated and decelerated.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an embodiment of an output voltage correction circuit according to the present invention.

FIG. 3 is a vector diagram showing an embodiment of output voltage correction in the present invention.

[Explanation of symbols]

1 ... Power converter, 2 ... AC motor, 3 ... Current detector, 4
... current coordinate conversion circuit, 5 ... torque current control circuit, 6 ... excitation current control circuit, 7 ... phase calculation circuit, 8 ... output voltage calculation circuit, 9 ... switching pattern generation circuit, 10 ... output voltage correction circuit

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5H576 CC05 DD02 DD04 EE01 EE11                       GG04 HB01 JJ25 JJ28 LL22                       MM02

Claims (2)

[Claims] 1. A power converter that outputs arbitrary power to an AC motor, a current detection circuit that detects a current supplied to the AC motor, an exciting current detection value and a torque for the current supplied to the AC motor. A coordinate conversion circuit that converts and outputs the current detection value, an excitation current control circuit that controls the excitation current direction voltage so that the excitation current command value and the excitation current detection value match, the torque current command value and the torque A torque current control circuit that controls the torque current direction voltage so that the detected current value matches, a phase angle calculation circuit that calculates a phase angle obtained by integrating a given output frequency command, and the excitation current control Circuit and an output voltage calculation circuit that calculates the magnitude and phase of the output voltage from the voltage command output from the torque current control circuit, and outputs the output voltage from the output voltage calculation circuit. In the control method of adding the phase angle output from the phase angle calculation circuit to the magnitude and phase of the pressure and determining the switching of the power converter, the magnitude of the voltage that can be output from the DC voltage of the power converter is calculated. Correcting the inputs to the excitation current control circuit and the torque current control circuit so that the magnitude of the output voltage is limited by the outputtable voltage while leaving the phase output from the output voltage calculation circuit unchanged. Characteristic AC motor control method. 2. A power converter that outputs arbitrary power to an AC motor, a current detection circuit that detects a current supplied to the AC motor, an exciting current detection value and a torque for the current supplied to the AC motor. A coordinate conversion circuit that converts and outputs the current detection value, an excitation current control circuit that controls the excitation current direction voltage so that the excitation current command value and the excitation current detection value match, the torque current command value and the torque A torque current control circuit that controls the torque current direction voltage so that the detected current value matches, a phase angle calculation circuit that calculates a phase angle obtained by integrating a given output frequency command, and the excitation current control Circuit and an output voltage calculation circuit that calculates the magnitude and phase of the output voltage from the voltage command output from the torque current control circuit, and outputs the output voltage from the output voltage calculation circuit. In the controller that determines the switching of the power converter by adding the phase angle output from the phase angle calculation circuit to the magnitude and phase of the pressure, the magnitude of the voltage that can be output from the DC voltage of the power converter is calculated. Correcting the inputs to the excitation current control circuit and the torque current control circuit so that the magnitude of the output voltage is limited by the outputtable voltage while leaving the phase output from the output voltage calculation circuit unchanged. Characteristic AC motor control device.