JPS58224587A - Control system for induction motor - Google Patents

Abstract

PURPOSE:To enable to start an induction motor even when a speed command voltage is low by providing a starting time frequency setter which adds the prescribed voltage to the output of a speed command amplifier when the motor is started. CONSTITUTION:Set voltages by a power drive side slip clamp setting variable resistor 7 and a recovery side slip clamp setting variable resistor 8 are applied to the output of a slip amplifier 3 which detects the slip of an induction motor, the output is applied to a speed command amplifier 4 together with a feedback amount via an inverting amplifier 9, an inverter is controlled by the frequency command voltage value fed from the amplifier 4, and the motor is controlled. The voltage set by the inverter output frequency setting variable resistor 10b at the starting time is applied to the output of the amplifier 4 via a diode by closing the switch 10a which is interlocked to the start switch at the starting time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for an induction motor, and particularly to an improvement in a frequency setting circuit that provides a frequency command value to an inverter that controls the speed of an induction motor.

1 - Conventionally, there was a method shown in FIG. 1 to explain this type of control method. In the figure, (1) is a speed setting device that sets the rotational speed of an induction motor (not shown), and (2) is a generated voltage of a finger speed generator (not shown) that detects the rotational speed of the induction motor. (8) is an amplifier that detects and amplifies the amount of power of the induction motor, and (4) is an inverter (not shown) that arbitrarily controls the frequency and voltage of AC power applied to the induction motor to control its speed. The voltage set by the speed setting device (1) is applied to the cushion circuit (6) by turning on the start switch (5), and The voltage generated by the speed generator is rectified by the PG speed dock circuit (2),
The output of the cushion circuit jf5 (6) and the output of the PG speed dock circuit (2) are added to the illustrated polarity and applied to the bass amplifier (8). The output of this basic amplifier (8) is the error between the fast reaction setting voltage V8 and the PG feedback voltage ■Pg, that is, it corresponds to the total FJf of the motor, and then the output Vpg of the PG feedback circuit (2) and the above The output of the Naveshi amplifier (3) is added to the speed command amplifier (4), and the output of the amplifier (4) becomes the output frequency command voltage of the inverter and the speed command voltage of the induction motor. There is.

Therefore, in the configuration shown in FIG. 1, the output voltage is generally clamped so that the output voltage is not corrected beyond the maximum permissible base determined by the rating of the induction motor, and the inverter speed The control range is 1:10 or 1:20, and it is common practice to apply a base cutoff to the switching elements inside the inverter so that the induction motor does not rotate at a rotation speed below that.

However, if we now give a speed command while the induction motor is stopped, the output of the Navesi amplifier (3) becomes the clamp value, which becomes the speed command voltage.ゎ, 2゜□□,!
,EkaE(7/<L(D) If the voltage is lower than the voltage at which the base of the hooking element is cut off, no output will be sent from the inverter and the induction motor will not accelerate forever.

Therefore, the present invention has been made to solve the problems of the conventional ones as described above, and includes providing a starting frequency setting circuit that adds a predetermined voltage to the output of the speed command amplifier when starting the induction motor. The object of the present invention is to provide a control method for an induction motor that can start the induction motor.

(8) is the volume for setting the side slip clamp, (9) is the inverting amplifier with a gain of 1, and (0) is the volume for setting the output frequency of the inverter when starting the induction motor. In the frequency setting circuit, a switch (10a) linked to the start switch (5) in Fig.
), the setting signal voltage value determined by the setting volume (10b) is added to the frequency command voltage value output from the speed command amplifier (4). is about to start.

That is, in the configuration shown in Fig. 2, the output of the subvesiamp (8) that detects the fullness of the induction motor is set by the vesi clamp setting volume (γ) on the negative side and the set voltage by the vesi clamp setting volume (8) on the regeneration side. are applied through diodes, and the output is applied to the speed command amplifier (4) along with the feedback amount V via the inverting amplifier (9) with a gain of 1 to the speed command amplifier (4), and the frequency command voltage value sent out from this amplifier (4) The configuration is such that the inverter is controlled by the inverter to control the induction motor.

Therefore, at the time of starting, by turning on the switch (10a) linked to the starting switch shown in Fig. 1), the voltage set by the inverter output frequency setting volume (10b) at the time of starting is changed to the speed command amplifier ( The induction motor can be started even if the frequency command voltage value of the speed command amplifier (4) is lower than the voltage at which the base of the switching element of the inverter is cut off. become.

As described above, according to the present invention, since the starting frequency setting circuit is provided, the speed command voltage sent from the speed i-h command amplifier is lower than the voltage at which the base of the switching elements constituting the inverter is cut off. .

This has the effect that the induction motor can be started even when the

[Brief explanation of drawings]

FIG. 1 is a circuit book diagram for explaining a conventional induction motor control system, and FIG. 2 is a circuit block diagram showing an embodiment of the present invention. (1)...Speed setter (2)...PG feedback circuit (3)@Svesiamp (4)...Speed command amplifier α frequency setting circuit for starting or a corresponding portion. Agent Shin Kuzuno − 6 −

Claims (1)

[Claims] A voltage corresponding to the desired amount of power is added to the voltage generated by the finger speed generator that detects the rotational speed of the induction motor, and the frequency and voltage of the AC power applied to the induction motor are arbitrarily controlled to control the speed of the induction motor. In a control method for an induction motor in which the frequency command voltage value of the inverter to be controlled is set as the frequency command voltage value, a starting frequency setting circuit is provided to set the output frequency of the inverter at the time of starting the induction motor, and the setting signal voltage value of this setting circuit is set as above. A control method for an induction motor, characterized in that the induction motor is started by adding a frequency to a command voltage value.