Mitigation of voltage sags/swells using PWM switched autotransformer

Dynamic voltage restorer and STATCOM are normally employed as a solution for mitigation of voltage sag and swell. This paper presents modelling and analysis of PWM switched autotransformer as a mitigating device for voltage sag and swell disturbances. The proposed system has less number of switching devices and has good compensating capability in comparison to commonly used compensators. Simulation analysis of three-phase compensator is performed in PSCAD/EMTDC and performance analysis of the system is presented for various levels of sag and swell. The THD of the load voltage when the compensator is functioning during disturbance condition are within the limits. Also the compensator can maintain the load real and reactive powers constant. Simulation results are presented for various conditions of sag and swell disturbances in the supply voltage to show the compensation effectiveness.