Impact of Different Control Strategies on Cycloconverter Harmonic Behavior

A cycloconverter is a power electronic converter which produces adjustable voltage adjustable frequency AC voltage from a constant voltage constant frequency AC source without any DC link. Cycloconverters produce significant harmonics and inter-harmonics in their output voltages. However harmonic behavior of cycloconverters widely depends on their pulse number, structure and switching strategy. Cycloconverter output voltage sub-harmonics, i.e. interharmonics with frequencies lower than fundamental frequency, greatly influence its performance and limit its maximum achievable output frequency. Several control strategies have been developed in years for reducing subharmonics and increasing cycloconverter performance quality. In this paper, two main control systems, i.e. cosine wave modulation and cosine wave modulation with voltage integral feedback are compared. Simulation results using MATLAB software are used to evaluate the analysis and signal THDs and harmonic components are calculated for further comparison. Experimental results obtained from a 6-pulse cycloconverter which was built in laboratory are used to evaluate the analysis.

Keywords:

cycloconverter , harmonics , sub-harmonics , power quality , Cosinewave modulation , Integral voltage feedback