Unidirectional single-phase AC-DC-AC three-level and two-level three-leg converters

Four unidirectional AC-DC-AC three-level and two-level three-leg converters are proposed in this paper. This converters are composed of an unidirectional rectifier and a bidirectional inverter, using three-level and two-level legs and an unidirectional NPC leg at rectifier side. 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 systems are presented. As the converters are 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.