Input Power Factor of AC to AC Power Converters

AC to ac power converters are static systems using solid-state switching devices that directly convert ac power of a given frequency to ac power of some desired frequency. They are used to link ac power systems of different frequencies, to provide variable power frequency supplies for ac motor drives, and to generate constant frequency power from the output of variable-speed ac generators. The power conversion process requires the construction of output voltage waveforms, with the required frequency and amplitude, from the ac supply voltages given. The method of output waveform construction determines the input power factor of the ac to ac converter. The practical methods of output waveform construction are summarized and their effects on the input power factor are examined. The relationships between the output and input phase angles for differently controlled ac to ac converters are presented in graphical forms. It is shown that the input power factor of an ac to ac converter can be varied or kept at unity, without the use of passive reactive components, and independently of the output load.