The influences of different switching mode of PWM are discussed. Then a practical method, "three-state algorithm of invariable duty cycle under forced output mode" is brought out to eliminate the commutation dead band generated by switching among the output interfaces of PWM waveform. 详细分析了PWM脉冲的不同切换方式对电机换相控制的影响,提出消除换相死区的具体算法&强迫输出方式下的2001年上海大学博士学位论文三状态恒定占空比算法。