基于中性点对地电压高频开关振荡的变频电机绕组内部绝缘在线监测

Online Condition Monitoring of Winding Internal Insulation for Inverter-fed Machine Using Neutral-to-ground High-frequency Switching Oscillation Voltage

绝缘状态在线监测是提高变频电机可靠性的有效手段。在高速PWM开关暂态激励下,电机绕组漏感与内部分布电容发生谐振会产生几十至几百k Hz的电压振荡,威胁绕组内部绝缘安全可靠运行。该文利用逆变器自激高频开关振荡在线监测绕组内部绝缘状态。为避免开关振荡多模态混叠并提高状态监测灵敏度,提出一种基于中性点对地电压高频开关振荡的绝缘在线监测方法。首先,分析变频电机共模电压激励特性;然后,研究中性点对地电压高频开关振荡的形成机理与特性,从理论上推导出振荡频率与绕组内部绝缘电容状态之间的关系。设计绕组内部绝缘在线监测方案,包括开关振荡频率提取以及内部绝缘状态评估等。最后,通过热疲劳与老化模拟等实验对该方法的可行性与有效性进行验证。结果表明,该方法能有效监测变频电机内部绕组绝缘状态的微弱变化,具有信噪比高、工况鲁棒等优点。

Online insulation monitoring is an effective means to improve the reliability of inverter-fed machines.Under the excitation of fast PWM switching,the machine winding leakage inductance will resonate with the internal distributed capacitance producing a voltage oscillation of tens to hundreds of kHz,which will threaten the safe and reliable operation of the winding internal insulation.In this paper,the self-excited high-frequency(HF)switching oscillations are utilized for winding internal insulation online condition monitoring.To avoid the multi-mode aliasing of switching oscillations and improve the monitoring sensitivity,a neutral-to-ground voltage HF switching oscillation-based monitoring method is proposed.First,the characteristics of the common mode voltage excitation of an inverter-fed machine are analyzed.Then,the mechanism and characteristics of the HF switching oscillation are studied.The relationship between the oscillation frequency and the winding internal insulation capacitance is deduced theoretically.Next,the online monitoring scheme is devised,including the switching oscillation frequency extraction,and the internal insulation state evaluation.Finally,the feasibility and effectiveness of the method are verified by the accelerated thermal aging and the aging emulation tests,respectively.The results show that the method can effectively monitor the weak change in the internal insulation condition with the advantages of a high signal-to-noise ratio and robustness to working conditions.