Improved PWM method of forced commutated cycloconvertors

An unrestricted frequency changer (UFC), a well known forced commutated cycloconverter (FCC), is known to be suitable for variable speed AC drives, because it operates in all four quadrants and generates no subharmonic components. However, lower order undesired components in the output voltage and in the input current are still large and cause problems in practical applications. In the paper, an improved PWM method is proposed to reduce lower order harmonic components. The new method can completely eliminate two undesired harmonic components in the low output voltage ranges with a relatively low switching frequency. This harmonic elimination occurs both on the output voltage and on the input current simultaneously. The harmonic characteristics of the proposed FCC are shown by computer simulations and verified by experiments.<>