AC-choppers using instantaneous voltage control technique to solve voltage sag problems

AC-Choppers using instantaneous voltage control technique to solve voltage sag problems are proposed in this paper. The developed AC-chopper for series voltage sag compensation is applied for three phase four wire system; therefore, three single phase ac chopper circuits and three series transformers are utilized. By using AC-chopper, there are no required for a dc bus; thereupon, the size of proposed voltage sag compensator is smaller. Each AC-chopper cell is independently controlled by using instantaneous voltage control method. With this proposed technique, the AC-chopper can rapidly compensate the related voltage sag and provide constant output voltages. Positive sequence PLL is applied to generate angle velocity (ω) thus the proposed AC-chopper can perform both balance and unbalance voltage sag. MATLAB/Simulink is used to simulate the proposed control algorithm and circuit operation. The 2-kW prototype is also developed for experimental validation. The results illustrate that the developed voltage sag compensator can perform within 3 ms responding time and the total harmonic voltage distortion is less than 2 % with overall system efficiency about 90%.