Constant duty cycle sinusoidal output inverter with sine amplitude modulated high frequency link

Despite the increasing performance of power semi-conductors and passives components, limited timing resolution in off-the-shelf available digital control hardware often prevents the switching frequency in kW-scale dc/ac power conversion to be increased above several MHz for the sake of extreme power densities. In this paper an alternative approach to generate a sinusoidal output voltage, based on constant duty cycle frequency shift control of a high frequency resonant inverter stage and a subsequent synchronous cycloconverter, is analyzed. The design of the presented converter is facilitated by means of a derived mathematical model. A novel closed-loop control system is proposed which achieves tight regulation of the output voltage by means of controlling the switching frequencies of the involved bridge legs operated in resonant mode. Characteristic waveforms of the dc/ac converter during steady-state and load transients are presented. Two distinct implementations of the resonant inverter stage, constituting an intermediate voltage or intermediate current link, are analysed and compared.