A multikilowatt polyphase ac/dc converter with reversible power flow and without passive low frequency filters

An efficient ac to dc converter with reversible power flow, which embodies an active, low frequency filter, is presented. A non-dissipatively controlled, nonlinear resonant oscillator is used to extract electric energy directly from the phase pairs of the polyphase supply line and to generate a mixed amplitude and frequency modulated carrier. The demodulated carrier and the therefrom resulting 20 kHz pulse train produces, after being processed by a high frequency filter, an active, low frequency filtering effect for attenuation of the 360 Hz ripple of the apparently 'rectified' three phase supply line. The system is governed by means of a pulse area control mechanism with a verified response time of one 10 kHz cycle, or 100 microseconds. The customary dc link between the three phase line and the converter's 20 kHz pulse processing mechanism in the form of a common rectifier-filter is completely eliminated. Data obtained from the test of a 3 kW feasibility model are analyzed in support of presentation of the significant aspects of design and technology.