软启动器是一种集电机软启动、软停车、轻载节能和多种保护功能于一体的新颖电机控制装置，国外称为Soft Starter。它的主要构成是串接于电源与被控电机之间的三相反并联晶闸管及其电子控制电路。
Soft starter is a new motor control device, which integrates soft start of motor, soft stop, light load, energy saving and various protection functions. It is called Soft Starter abroad. Its main structure is a three-phase anti parallel thyristor connected to the power supply and the controlled motor and its electronic control circuit.
运用不同的方法，控制三相反并联晶闸管的导通角，使被控电机的输入电压按不同的要求而变化，就可实现不同的功能。
Different methods are adopted to control the conduction angle of the three-phase anti parallel thyristor, so that the input voltage of the controlled motor varies according to different requirements, and different functions can be realized.
运用串接于电源与被控电机之间的软启动器，控制其内部晶闸管的导通角，使电机输入电压从零以预设函数关系逐渐上升，直至启动结束，赋予电机全电压，即为软起动，在软起动过程中，电机启动转矩逐渐增加，转速也逐渐增加。
Based on the soft starter is connected between the power supply and controlled motor, control the turn-on angle of thyristor, the motor input voltage from zero to a preset function increased gradually, until the start end, with full voltage motor, namely soft starter, soft starter in the process, the motor starting torque increases gradually, speed increased gradually.