A Multikilowatt Polyphase AC/DC Converter with Reversible Power Flow and without Passive Low-Frequency Filters

Abstract
An efficient ac-to-dc converter with reversible power flow, which embodies an active, low-frequency filter, is presented. A nondissipatively 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 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 µs. 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 the presentation of the significant aspects of design and technology.

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