An unidirectional single-phase AC-DC-AC three-level three-leg converter

An unidirectional AC-DC-AC three-level three-leg converter is proposed in this paper. This converter is composed of an unidirectional rectifier and a bidirectional inverter, using two bidirectional NPC legs and an unidirectional NPC leg. A bidirectional NPC leg is shared between rectifier and inverter. When compared with the two-level leg, the three-level leg presents voltage stress reduction on switches for the same DC-link voltage level and also allows a reduction in harmonic distortion for the same switching frequency. Suitable modeling, PWM and control strategies of the system are presented. As the converter is unidirectional, the grid current and the generated voltage at load side must be synchronized with generated voltage at grid side. That eliminates the zero-crossover distortion in the grid current caused by the use of diodes without the hysteresis control. Simulation and experimental results are also presented.