DC-AC Series-Resonant Converter System with High Internal Frequency Generating Multiphase AC Waveforms for Multikilowatt Power Levels

Abstract

A new method of power pulse modulation with internal frequencies of tens of kHz which is also suitable for multikilowatt power levels is applied to a series-resonant converter system for generating synthesized multiphase bipolar waveforms with reversible power flow. The power circuitry of the converter is provided with one single high-frequency resonant link in the direct energy path. Natural current commutation of the thyristors is obtained by the use of a series-resonant circuit for power transfer and control. Consequently, switching losses can be reduced to a minimum without compromising the reliability of the solid-state components. The high pulse frequency allows the principle of modulation and demodulation for fast system response and output waveforms with reversible power flow with low distortion. Test results of a converter system generating three phases-sinusoidal waveforms independent of the load characteristics-demonstrate the significant aspects of this class of power conversion. The material presented indicates the possibilities for fast-acting polyphase dc-ac and ac-ac converter systems.