中文摘要：

在电磁轴承用功率放大器中,目前普遍采用三电平调制技术来改善开关功率放大器的电流纹波问题,从而提高电磁轴承系统的性能。在研究中发现,一种应用较多的改进型三电平脉宽调制（pulse width modulation,PWM）技术应用于电磁轴承用功率放大器时输出的电流波形有时会与理论上的三电平波形不一致,在相同的开关频率下,其电流纹波比理论值大很多,出现了波形失真的情况。首先介绍这种失真现象,然后在分析改进型三电平PWM调制技术的基础上,结合不同的三角波载波方式,具体分析失真现象背后改进型三电平PWM开关功率放大器调制失效的机制。结果发现调制失效的主要原因是改进型三电平PWM调制电路中的电压偏置设置存在偏差,并发现不同的载波形式产生的失效机制大不相同。仿真和实验结果验证了理论分析的正确性。最后提出一些避免改进型三电平PWM开关功率放大器失效的措施。

英文摘要：

In power amplifiers for active magnetic bearings,three-level modulation technique is commonly used to reduce the current ripple of the switching mode power amplifiers,so as to improve the performance of active magnetic bearing system.In our research,it is found that when a modified three-level pulse width modulation（PWM） modulation technique is used in power amplifiers for active magnetic bearings,the output current waveform of the power amplifier is inconsistent with the theoretical three-level waveform sometimes,and at the same switching frequency,the current ripple of the modified three-level PWM power amplifier is much bigger than the theoretical value.The failure phenomenon was introduced and the failure mechanism of the modified three-level PWM power amplifier was theoretically analyzed for different carrier waves based on the analysis of the modified three-level PWM modulation technology in this paper.It is found that the deviation of bias voltage setting in the modified three-level PWM generation circuit results in its failure,and the failure mechanism is different for different carrier waves.Simulation and experimental results are in agreement with the theoretical analyses.Finally,some suggestions about avoiding the failure of the modified three-level PWM power amplifier are presented.