New Circuit Solutions of AC Voltage Regulators as a Soft-Start Device for Asynchronous Motors

Asynchronous motors can be started both directly and smoothly. One or another method depending on the torque is used. But the need for a soft start significantly exceeds than the direct one, since in this case the engine life increases. This problem can be solved in several ways, both by frequency start-up and voltage regulation. Several variants of AC voltage regulators are considered in this paper. We can say that all of them have become the development of a thyristor AC voltage regulator with counter-parallel connection of thyristors, further we will call this scheme classical. The main problem of such a scheme can be considered a poor form of output voltage and current curves, which are supplied to the load, namely, the motor. It can be solved by dividing the output voltage into zones. This became possible with the help of several secondary windings of the transformer or with the help of a capacitor divider. Two new circuits were proposed based on the second one with a reduced number of semiconductor switches and with the combined connection of capacitors. The paper presents the modeling results in the PSIM program, as well as an assessment of the output voltage regulation range and voltage quality with a different number of used control zones.