Space vector modulated and vector controlled three-level four-wire unidirectional ac-dc-ac converter

This paper presents a unidirectional neutral-point-clamped three-level four-wire AC-DC-AC converter topology and studies how space vector modulation and vector control can be applied to the converter. The modulator is based on standard complex plane space vector modulation and the zero-sequence voltage space is treated as an offset. The zero-sequence offset is realized by proper weighting of redundant vectors of the rectifier and inverter. It is shown that either the rectifier or inverter can utilize discontinuous modulation if the injected zero-sequence voltage is properly chosen and a method for balancing the partial DC link voltages is presented. The analysis and proposed modulation method are verified with 10 kVA rated system simulations.