Svpwm Algorithm Of Single-phase Three-level Multi-cell Cascaded H-bridge Converter

Generally,the AC-DC rectifier in the front stage of the Power Electronic Traction Transformer(PETT),adapts the structure of H-bridge cascade,which improved the capacity and voltage greatly.The stable operation of the converter is on the condition of the DC-link voltage balancing of the H-bridge cascaded converter.Therefore,the DC voltages unbalance is one of the critical problem in the cascaded converter.Aiming at this problem,this paper adopts a single-phase space vector pulse width modulation(SVPWM)method with voltage balancing capability.In one-dimension space,the vector distribution of two-cell cascaded converter is analyzed and proposed a one-dimension space vector pulse width modulation(1D-SVPWM)algorithm.This algorithm gets the real-time redundant vector with voltage balancing capability by calculating the levels of port voltage.Meanwhile,it designs a smooth vector conversion method on the basis of the vector conversion,and make sure that the terminal voltage will not lever-cross jump through adjacent-level selection.What's more,all the redundant vector was reserved,and then the vector with the strongest capability of voltage balance was output,making the algorithm has a better voltage balance capability.Thus the algorithm realizes voltage balancing of inner-cell and mutual-cells of the cascaded converter.Based on 1D-SVPWM algorithm of two-cell cascaded converter,the 1D-SVPWM algorithm of the three-cell cascaded converter is studied.The principle of equalization,equalization priority and adjacent vector selection rule are derived in this paper.Finally,according to these rules,the algorithm is extended to the multi-cell cascade converter.In order to verify the correctness and feasibility of the algorithm,the SVPWM algorithm of two-cell,three-cell and six-cell cascaded converter are simulated by Matlab/Similink in the third and fourth chapters respectively.The simulation results are basically consistent with the theory analysis.Furthermore,in order to verify the algorithm,the software program of the algorithm is designed in this paper,and two modules and three modules cascaded converter experimental platforms are set up in the fifth chapter.The software program of the algorithm is applied to the two platforms,and a good dynamic,steady-state and unbalanced experimental results are obtained.