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.
软启动与传统减压启动方式的不同之处在哪里？
Where is the difference between soft start and traditional decompression mode-
笼型电机传统的减压启动方式有Y-q 启动、自耦减压启动、电抗器启动等。这些启动方式都属于有级减压启动，存在明显缺点，即启动过程中出现二次冲击电流。软启动与传统减压启动方式的不同之处是：
The traditional decompression starting modes of cage motor include Y-q start, self coupling decompression start, reactor start-up, etc.. These start-up methods belong to the stage decompression start, there are obvious shortcomings, that is, there are two shock currents in the start-up process. The difference between soft start and traditional decompression mode is that:
（1）无冲击电流。软启动器在启动电机时，通过逐渐增大晶闸管导通角，使电机启动电流从零线性上升至设定值。
(1) no impulse current. When the motor starts the motor, the starting current of the motor rises linearly from zero to the setting value by gradually increasing the turn-on angle of the thyristor.
（2）恒流启动。软启动器可以引入电流闭环控制，使电机在启动过程中保持恒流，确保电机平稳起动。
(2) constant current start up. The soft starter can introduce the current closed loop control, so that the motor keeps constant current in the starting process, and ensures the smooth starting of the motor.
（3）根据负载情况及电网继电保护特性选择，可自由地无级调整至佳的启动电流。
(3) according to the load condition and the relay protection characteristics of the power grid, the optimal starting current can be freely adjusted continuously.
