A discrete frequency control method based on equivalent sinusoidal modulation for thyristorized soft starters

This paper proposed a DFC (discrete frequency control) method based on equivalent sinusoidal modulation for thyristorized soft starters, including the basic control method and a simplified method to search for the optimal initial phase angle combinations of three-phase DFC system. The compensation mode of freewheeling angle of a thyristor and the transition method from one discrete frequency to another are also studied. This method, based on the fixed main circuit of traditional soft starters, allows an induction motor to start with a reduced starting current and a high starting torque. Simulations based on Matlab-Simulink are carried out and a 7-stage DFC system based on DSP-TMS320F2812 is built. Experimental results confirm the proposed method has good starting torque and current performance.