The problem of microcomputer-based digital control of a naturally commutated cycloconverter (NCC) operating with variable frequency input voltage waveform is discussed. A method based on cosine wave crossing pulse timing control is proposed. The proposed algorithm provides a very simple and yet quite accurate method for operation of a circulating-current NCC with variable frequency input voltage. The output voltage will stabilize in less than two-thirds of the input voltage period even for abrupt changes in the input frequency. The variation of the magnitude of the input voltage can be easily corrected by simple voltage feedback. A computer simulation was performed for preliminary testing of the proposed algorithm.
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