JPS61254098A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To suppress an unexpected noise and an iron loss increase without generating harmonic waves by reducing a torque command value in response to the excess of a terminal voltage when the terminal voltage exceeds the prescribed value. CONSTITUTION:Motor terminal voltage detecting means 6 detects the terminal voltage of an induction motor 3. Overvoltage detecting means 7 compares the detected voltage with a reference voltage such as the DC voltage of a PWM controller to detects that the terminal voltage of the motor 3 exceeds the reference voltage. Torque command reducing means 8 superposes a negative signal on the torque command signal in response to a voltage excess. Thus, when the terminal voltage becomes the prescribed value or higher, the torque command signal E decreases as compared with the normal case, the reduced torque command signal Ee is applied to a vector calculator 5, converted to a current command signal F, applied to a PWM controller 9, and the motor 3 is controlled on the basis of the command.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a control circuit for a PWM controlled induction motor. In particular, it relates to improvements to prevent noise generation at high speeds.

Among the conventional speed control methods of induction motors, the most excellent method is the variable frequency control method. One of the variable frequency control methods is a PWM control method.

As shown in the second @, the PWM control method intermittently controls each current control element constituting the multiphase bridge circuit 2 that is supplied with current from the DC power source 1 with a desired variable duty ratio, and adjusts both the frequency and the current. This is a control method for controlling to a desired value, and is a control method for controlling the frequency and torque of the induction electric motor Ja3 whose speed is controlled thereby.

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Therefore, the winding actance increases in proportion to the frequency ′
As the frequency increases and the rotational speed increases, the terminal voltage of the induction motor increases. If this terminal voltage exceeds a certain range, the magnetic flux of the induction motor will become saturated, and elements such as the amplifier that make up the control circuit will become saturated, generating harmonics, and noise at twice the frequency of these harmonics will be generated. increase,
Since this frequency band happens to be within the range of human hearing sensitivity, actual harm will occur. Furthermore, this harmonic causes disadvantages such as increased iron loss.

The purpose of the present invention is to eliminate this drawback, and to
In a control circuit for an induction motor that is controlled by M, when the frequency increases and the rotational speed increases by E, the terminal voltage of the induction motor is reduced to the extent that there is no actual damage, thereby preventing the generation of harmful noise. Another object of the present invention is to provide an improvement that prevents an unexpected increase in iron loss, etc.

Means for Solving the Problems The present invention provides a control circuit for a PWM-controlled induction motor.
A means 6 for detecting the terminal voltage of the induction motor is provided, and when the terminal voltage exceeds a certain value, a means 8 is added for reducing the torque command value in response to the excess, so that the terminal voltage of the induction motor is kept at a constant value. This is to prevent harmonics from being generated due to the saturation of each element constituting the control circuit due to the increase in the power consumption.

The PWM control circuit of an induction motor is generally configured with three loops: a position control loop, a speed control loop, and a current control loop, so the terminal voltage of the induction motor may rise beyond a certain value. In this case, if a negative signal is superimposed on the torque command signal in response, the torque command value decreases, and accordingly, the current command value also decreases and the terminal voltage of the induction motor decreases.

Embodiment Hereinafter, with reference to the drawings, a portion of a control circuit for an induction motor according to an embodiment of the present invention, which is related to the gist of the present invention, will be further described.

In the diagram shown in Fig. 1, A is a position command signal, which is compared with a position error signal B detected by a resol, a hull coder, etc., and this deviation is amplified by an amplifier 4 to become a speed command signal C. The speed command signal C is compared with a speed signal detected by a tachometer generator or the like, and this deviation is amplified by an amplifier 10 to provide a torque command signal E.

Here, 6 is an electric current aI that detects the terminal voltage of the induction motor 3.
& terminal voltage detection means, 7 compares this voltage with a reference voltage, for example, the DC voltage of the PWM control circuit, and detects the induction motor 3.
Excess voltage detection means detects that the terminal voltage of the terminal exceeds the reference voltage. 8 is a device (torque command reduction means) that superimposes a negative signal on the torque command signal in response to excess voltage;
It is.

Therefore, when the terminal voltage of the induction motor 3 exceeds a certain value, the torque command signal E is decreased compared to the normal case, and this decreased torque command signal Ee is transmitted to the vector calculation unit 5, for example.
is converted into a current command signal F and given to the PWM control circuit 9, and based on this command, the induction motor Ia
3 is controlled.

Therefore, the terminal voltage of the induction motor controlled by the induction motor control circuit according to this embodiment will not rise beyond a certain value, for example, the DC voltage of the PWM control circuit, and will not generate harmonics. Therefore, it does not cause unexpected noise generation or increase in iron loss.

As described in detail, in the present invention, a control circuit for an induction motor controlled by 2 wM is provided with means for detecting the terminal voltage of the induction motor, and when the terminal voltage exceeds a certain value, the control circuit detects the terminal voltage of the induction motor. Since a means for responsively reducing the torque command value is added, the terminal voltage of the induction motor controlled by the induction motor control circuit according to the present invention increases beyond a constant value, for example, the DC voltage of the PWM control circuit. Therefore, harmonics are not generated, and unexpected noise generation and iron loss increase are not caused.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a control circuit for an induction motor according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a PWM control circuit according to the prior art. 1Φ・Contact DC current, 2@・Φ Multiphase AC current. 3.--training motor, 4-φ amplifier, 5. vector calculation section, 6.--motor terminal voltage detection means, 7.--excess voltage detection means, 8.-torque command reduction means. , 9--- PWM
Control circuit, A...Position command signal, B8...Position signal, (: aa a speed command signal, D...Speed signal, E...Torque command signal, Eeeφ number decreased torque command signal, F-・Φ current command signal.

Claims (1)

[Claims] A control circuit for a PWM-controlled induction motor, comprising: means 6 for detecting a terminal voltage of the induction motor; and means 7 for detecting that the terminal voltage exceeds a certain value.
A control circuit for an induction motor, comprising: and means 8 for reducing a torque command value in response to the excess.