A 24-pulse rectifier cascaded multilevel inverter with minimum number of transformer windings

This paper addresses the design of a medium voltage adjustable speed drive (ASD) utilizing the benefits of cascaded inverter technology while employing a 24-pulse rectifier inspired front end. Rectifier front ends of ASDs introduce a high level of harmonics into the utility grid, creating equipment overheating problems and distorting the voltage waveform near the ASD's connection point. To greatly reduce these harmonics while limiting cost, a cascaded multilevel inverter utilizing a 24-pulse transformer with a minimum number of windings is used. This design reduces the total harmonic current to less than 5% of the full load current over the entire frequency range. Simulation and experimental results are presented to show proof of concept.