Digital control strategies for sinewave-output cycloconverters

Digital control strategies for obtaining sinewave output for a current-source cycloconverter with fast dynamic response are presented. The proposed dual-multiprocessor control system ensures high-quality output. By means of a parameter estimator, it is possible to deduce the instantaneous voltage reference for the cycloconverter without resorting to a high-gain loop. With an appropriate forgetting factor chosen, the estimator is capable of fast tracking, and a reliable, stable voltage reference is thereby produced. Improvement using digital feedback control is achieved by adjusting the loop gain according to the instantaneous input reference level. The resulting current source shows excellent steady-state and transient performance in response to system disturbances, and it generally achieves good waveforms. It also works for induction motor loads under normal running conditions and should find wide application as an adjustable-frequency high-performance power convertor