High-Frequency Link Power Conversion

A class of electrical power conditioners incorporating an intermediate variable high-frequency link concept is introduced by considering a converter with dc source and variable voltage and frequency polyphase output, then extending the concept to polyphase ac source voltage. The ac60 Hz-achigh-freq-acoutput-freq system is essentially comprised of two cascade 12-thyristor cycloconverters separated by a parallel resonant tank circuit. The tank circuit provides commutation means for both cycloconverters. Normally, the input cycloconverter operates in the inverting mode and the output cycloconverter in the rectifying mode, although during regeneration their roles are reversed. For static var control applications, the output cycloconverter is not required. The input cycloconverter separating the 60-Hz supply from the resonant tank circuit can be envisioned as a ``solid-state synchronous machine´´ capable of controlling real and reactive power independently. Various control strategies for doing this is discussed. The design and potential performance characteristics for a 50-kVA system suitable for motor drives is illustrated with regard to power capability and tank frequency versus tank-to-supply voltage radio, input power factor setting, load voltage, and power factor.