Research on the Topology and Control Policy of Composite Energy Feedback Cascaded Multi-Level Inverter

Abstract

Traditional uncontrolled or phase controlled cascade multilevel inverter only can realize one-direction transmission of energy. This paper presents a complex energy feedback cascade inverter topology with full-controlled, phase controlled Power units and its control strategy. For the full-controlled units, use PWM converter to replace the traditional rectifier bridge, and then combine with H-bridge inverter, the two-direction inverter is realized. The others remain phase controlled structure. According to the pump-up voltage in the energy feedback process ,a new method using the output side DC voltage closed loop control is proposed to prevent DC voltage shock and make all energy feedback to grid .Then it was verified in a cascade inverter with five units in which only three units are full-controlled. This inverter has the merits that it can automatic realize two-way flow of energy, the input currents approximate sine, the DC voltages control stability, the output voltage waveform is good and the phase shifting transformer structure is also simplified, etc. Simulation showed its feasibility and effectiveness.