AC power source based on series-connection between cascaded PWM multilevel inverter and linear power amplifier

This paper proposes a hybrid ac power source by associating a symmetrical cascaded PWM multilevel inverter (main amplifier) with a low-voltage and low-power linear power amplifier (correction amplifier) with the aim of synthesizing high-fidelity voltage waveforms without penalizing the system efficiency. The main amplifier operates with phase-shift pulse-width modulation, enabling to reduce the output low-pass filter requirements. An accurate analysis of the main amplifier parameters, such as the number of cells and the output filter devices, which have impact on the current and voltage ripples, phase displacement and under/overshoots caused by load variation, is carried out through the paper, since the correction amplifier must be designed to compensate for any distortion on main amplifier voltage waveform. As a result, the compensation capability of the correction amplifier is defined. Thereafter, a design methodology for both main and correction amplifiers is introduced as well as a control circuit is proposed. Experimental results are presented to validate the proposed approach.