This paper was based on the high power AC electrical locomotive,of which the highest switching fre-quency of the inverter was usually very low.The multi-mode modulation strategy based on SHEPWM was ap-plied so as to realize smooth operation of the traction motor during its whole speed course.Taking into compre-hensive consideration realization of SHEPWM,harmonic components of the output voltages and current char-acteristics,switching between different modulation methods and switching between different carrier ratios of the same modulation method were studied and the SHEPWM-based switching strategy that three-phase voltages were switched simultaneously was proposed.Thus,the algorithm for control of switching was simplified.Sim-ulation and experiment results verify the validity of the switching strategy.%以大功率电力机车牵引传动系统为背景，针对其逆变器开关频率最大值较低的特点，采用一种基于SHEPWM的多模式调制策略以实现牵引电机在速度全程范围的平滑运行。在综合考虑 SHEPWM的实现方法、分析输出电压的谐波成分及电流特性的基础上，对不同调制方式间或相同调制方式的不同载波比之间的切换策略进行深入研究，提出一种基于 SHEPWM的三相电压同时切换策略，使控制牵引电机切换的算法显著简化。最后，通过仿真和实验验证切换策略。
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