基于优化的VSVPWM三电平NPC逆变器控制策略

Control Strategy of Three-Level NPCs Inverter Based on Optimized VSVPWM

针对中点箝位(NPC:Neutral-Point-Clamped)型三电平逆变器直流侧上下两个电容电压不一致,以及传统的空间矢量脉宽调制(SVPWM:Spatial Vector Pulse Width Modulation)虽然可在一定的调制度范围内解决两个电容电压不一致,但在较大的调制比下中点电位无法维持平衡的问题,在传统SVPWM和虚拟空间矢量脉宽调制(VSVPWM:Virtual Space Vector Pulse Width Modulation)的基础上优化控制方法。该方法依据电流的流向对不同的正、负小矢量采用不同大小的平衡因子,同时根据中点电位差值,引入电压调差系数,并在此基础上与无差拍控制相结合。该闭环控制策略利用中点电位差值与逆变器三相电流输出值作为反馈量调整输出波形,抑制中点电位。仿真结果表明,该方法在三电平逆变器调制度较高时仍然可以维持直流侧中点电位的平衡,证明了控制策略的正确性和有效性。

Aiming at the problem of inconsistencies between the voltages of the two capacitors on the DC(Direct Current)side of the midpoint clamping(Neutral-Point-Clamped)three-level inverter and the traditional SVPWM(Space Vector Pulse Width Modulation)can solve the problem of inconsistency of the two capacitor voltages within a certain modulation system,but the midpoint potential cannot be balanced under a large modulation ratio,the control method is optimized on the basis of the traditional SVPWM and VSVPWM(Virtual Space Vector Pulse Width Modulation).The method is based on the flow direction of current,different positive and negative small vectors using different size of balance factor,is in accordance with the midpoint potential difference value,and introduces voltage adjustment coefficient.On this basis,it is combined with the beat-free control.This closed-loop control strategy adjusts the output waveform by using the midpoint potential difference and the inverter three-phase current output value as the feedback to suppress the midpoint potential.Simulation results show that the proposed method can still maintain the balance of the midpoint potential on the DC side when the three-level inverter modulation system is high,which proves the correctness and effectiveness of the control strategy.