中文摘要：

针对电力牵引三电平中性点钳位(NPC)逆变器系统，首先分析了因调制算法引起的中点电位振荡现象。然后分别比较两种传统空间矢量脉宽调制(SVPWM)算法对中点电位振荡及负载电流总谐波畸变率(THD)的影响；在此基础上，以中点电位平衡控制和最小负载电流THD含量为目的，提出了一种基于中点电位环宽控制的 SVPWM算法。最后，通过 MALTAB/Simulink 软件仿真和dSPACE半实物平台实验研究，对3种调制算法下中点电位及负载电流 THD值进行对比分析。计算机仿真与半实物实验结果表明，中点电位环宽控制方法不但能平衡直流侧中点电位，而且能有效地减小负载电流THD含量。

英文摘要：

The neutral-point voltage oscillation due to the modulation method is analyzed first for the three-level neutral-point-clamped (NPC) traction inverter.Then,the characteristics of the neutral-point voltage oscillation and the total harmonic distortion(THD)of load current due to two traditional space vector pulse width modulation(SVPWM)methods are compared with each other,respectively.On the basis of this,a SVPWM method with adj ustment of neutral-point hysteresis-loop width is proposed to balance the neutral-point and reduce the THD value of load current.Finally,both the amplitude of neutral-point oscillation and the THD value of load current are compared and analyzed via MATLAB/Simulink simulation and dSPACE hardware-in-the-loop experiment when the three modulation methods are adopted.Simulation and experimental results show that the adopted SVPWM method with neutral-point loop width control is efficient for balancing neutral-point voltage and reducing the THD value of load current.