The many different approaches to soft starting

摘要

Solid-state soft starters are reduced-voltage starters that control the voltage applied to a motor by the use of a solid-state AC switch in series with the power supply. They comprise a contactor, motor overload protection, and three solid-state AC switches. The AC switch can take the form of a bidirectional thyristor (triac), or two thyristors in reverse parallel connection, or a thyristor reverse-parallel connected with a diode. Both the triac and the thyristor-thyristor controllers control both halves of the waveform symmetrically. This is commonly termed full-wave control, whereas the thyristor- diode approach is an asymmetric or half-wave control system. All three methods of control are used in commercially available equipment.