Analysis of Symmetrical and Asymmetrical PWM Based Three Phase Ac to Ac Converter for Power Quality Improvement

Abstract

A Three phase bidirectional AC to AC buck converter circuit using power MOSFET operating in high frequency chopping mode is simulated and analyzed for electrical parameters such as output phase voltage, input line current, input power factor, harmonic profile and efficiency using MATLAB/simulink software package. The various PWM techniques such as symmetrical ramp-DC PWM (SRDPWM), asymmetrical ramp-triangular PWM (ARTPWM), asymmetrical sinusoidal PWM type-1 [ASPWM1] and asymmetrical sinusoidal PWM type-2 [ASPWM2] techniques are adopted to analyze the harmonic profile, input power factor and efficiency of the converter. The rms value of the output phase voltage, output line current and source current can be significantly increased by varying the duty ratio K in case of symmetrical PWM control strategy and modulation index MI in case of asymmetrical PWM control strategies independent of variation in switching frequency. It is observed from the simulation results that the ASPWM1 switching strategy gives more output phase voltage, input power factor, efficiency by increasing modulation index MI and reduced low order harmonics of output voltage and source current by increasing the number of pulses per half cycle P compared to other PWM techniques rendering easy and economical filteration.