开关点预置的四桥臂三相逆变器

提出以四桥臂三相逆变器作为变速恒频电源变换器的主电路拓扑，省去了三相三桥臂逆变器中所需的中点形成变压器，减小了变换器的体积和重量。在三相三桥臂采用的开关点预置最优正弦脉宽调制(sine pulse width modulation，SPWM)控制方案的基础上，提出了适用于四桥臂三相逆变的开关点预置最优SPWM控制方案：ABC三桥臂的开关角预置仅消除不含零序谐波的低次奇次谐波，通过对N桥臂的预置来抵消前三桥臂所含的低次零序谐波。并在主电路中引入中线电感，减小了第四桥臂的开关电流。仿真和实验结果表明：该变换器不仅具有开关频率低，输出总谐波含量小以及直流电压利用率高的优点，且在不平衡负载时有较好的输出电压对称性。

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.