Optimal discrete pulse modulation waveforms for resonant link inverters

Abstract

The advent of zero-voltage-switching resonant link inverters has raised the question of modulation strategies that satisfy the regular sampling constraints of such systems. An easy and elegant approach to the synthesis of optimal discrete pulse modulation waveforms is presented. Utilizing the finiteness of the set of possible waveforms, an exhaustive search algorithm is deployed to derive a set of optimum waveforms simultaneously satisfying specified fundamental voltage constraints and cost functions. For frequency ratios of up to around 80, the technique is tractable and gives excellent results. For aerospace applications with 400 Hz outputs, which result in frequency ratios of 50 for 20 kHz link frequency, the strategy results in substantially higher levels of performance. For larger frequency ratios of 100-2000, typical of industrial resonant link inverter drive systems, this technique requires unworkably high computation times. A suboptimal limited search technique is proposed with reasonable performance characteristics is proposed for this case.<>