Control method and control device for controlling soft start of induction motor

Abstract

The invention provides a control method and a control device for controlling soft start of an induction motor, which are applied to three-phase antiparallel thyristor AC (Alternating Current) voltage regulation control circuits. The control method comprises the following steps: firstly, the induction motor is started under the low frequency in a discrete frequency control manner; in the starting process, whenever a starting current of the induction motor is less than a rated current, the discrete frequency is gradually increased, wherein the relation between the discrete frequency f(HZ) and the working frequency is that f(HZ)=50HZ / K, the working frequency is 50HZ, K is a positive integer and when the K value is decreased, the discrete frequency is increased; after the discrete frequency reaches half of the working frequency, the induction motor is controlled to be switched to the working frequency to operate. According to the invention, a variable frequency speed regulation principle is utilized; the rotating speed of the induction motor is gradually increased by gradually increasing the starting frequency, so that when the induction motor is started, the air gap magnetic flux of the induction motor can be controlled to be close to the rated magnetic flux, and thus, not only is the starting current reduced, but also the starting torque is increased.

Description

technical field [0001] The invention relates to the technical field of induction motor soft start, and more specifically, relates to a control method and a control device for induction motor soft start. Background technique [0002] According to the operating characteristics of the induction motor, when the induction motor is started at the rated voltage, the starting current is large but the starting torque is not large. In order to reduce the electromagnetic and mechanical impact of the excessive current on the motor and the interference to the power grid when the induction motor starts, the starting current of the induction motor must be limited within a certain range. Generally, the method of reducing the starting voltage is used to reduce the starting current. At present, the commonly used methods include stator circuit series impedance starting, Y-△ starting, autotransformer starting, and three-phase parallel thyristor AC voltage regulation circuit starting. The piezo...

AI Technical Summary

Problems solved by technology

[0003] However, since the output frequency of the three-phase parallel thyristor AC voltage regulating circuit is still the power frequency, that is, this type of starter can only reduce the voltage but not the frequency. Therefore, when the average output voltage of the three phase-phase parallel thyristor AC voltage regulating circuit decreases, The air-gap flux of the induction motor is also reduced, and the starting torque proportional to the air-gap flux is also reduced

Therefore, this step-down starting method reduces the starting torque while reducing the starting current, which leads to a long starting time of the induction motor and cannot start with a load, which limits the application range of this type of starter

Images