Harmonic Reduction in Single Phase AC-AC Converter

Objective: To design the trapezoidal pulse width modulation (TPWM) technique in order to reduce the total harmonic distortions at the output of the converter particularly the AC-AC frequency converter. Methods/Analysis: The proposed scheme of modulation technique is used as a modification as compared to that of an unmodulated converter. Two different parameters, namely frequency of the output from the converter and the frequency of the carrier wave, were varied to obtain the harmonic profile of the output voltage of the converter. Results were verified using MATLAB/SIMULINK software environment. Findings: The generalized 1 ϕ AC-AC frequency converter discussed, can be operated both as cyclo-converter (step down) and cyclo-inverter (step up). The output from these converters contain high THD values at the output. The techniques of filtering cannot be used due to numerous reasons. So the TPWM technique is implemented on the frequency converters. The least THD obtain was 0.983 % at 250 Hz for a step up configuration and THD was about 0.8019 % at 25 Hz in case of a step down converter. In addition to varying the output frequency, carrier frequency, fc, of the carrier wave was also varied to check the THD response of the converter and it was least at 1 kHz of about 0.9316 %. In all case, magnitude of output voltage was on higher side of fundamental frequency component. Novelty/Improvement: Simulation results shows that the THD values have been reduced with the application of modulation techniques as compared to that of the output from an unmodulated converter which can help in various application requiring AC-AC converters.