Four-leg Three-phase Inverter Based on Switching-node Preset

A novel four-leg voltage source inverter(VSI)is proposed to be the main topology of variable speed constant frequency(VSCF)power system,which eliminates the neutral form transformer existed in the conventional three-leg VSI,and greatly reduces the overall weight and size.Based on the research about strategy of Switching-Node Preset Optimal SPWM(SNPOS)for three-leg VSI,the influence of different search parameters is analyzed and then control strategy of SNPOS for four-leg VSI is proposed.The three-leg of A.B.C swithing-node preset eliminates the low odd harmonics,and switch-node preset N leg eliminates the zero-sequence harmonic preduced by the three-leg.Also,a neutral inductor is introduced in the main circuit,which reduces the current stress of the power switch of the fouth leg.The simulation and experimental results verify the advantages of the four-leg VSI based on the control strategy of SNPOS which includes low switching frequency,low total harmonic distortion,high utilization of DC bus and good unbalanced loading ability.