Reverse Energy Transfer through an AC Line Synchronized Pulse Width Modulated Sinewave Inverter

Pulse width modulated inverters are used in battery supplied systems as AC standby power sources to supply high quality sinewaves to critical loads. In all these systems, means must be provided for battery charging. The traditional method uses a separate rectifier to charge the battery. A pulse width modulated four-quadrant inverter can be made to pass power in either direction, functioning as a synchronous rectifier to provide complete control for all battery charging requirements. In its simplest form, the charging scheme can be modelled as two synchronous AC voltage sources separated by an inductor. Power transfer is effected when one voltage source differs in amplitude and phase from the other. This report describes the basic theory of line synchronized inverter operation and the realization of this theory using a pulse width modulated inverter operating as a closed-loop switching amplifier. The piece-wise linear time domain analysis of actual inverter waveforms to battery charging conditions are presented. This analysis details the instantaneous energy flow into the battery during a full cycle of utility sinewave. System trade-offs to realize a cost-effective product are identified and discussed. Waveforms, system performance, and applications are presented.