中文摘要：

三相电压型PWM整流器（voltage source PWM rectifier,VSR）是分布式电源接入小电流接地系统的关键设备。通过分析三相VSR开关函数sj的频率扰动，以及直流侧正极和负极对地绝缘状态的改变，得出了中性点电压偏移是影响系统绝缘监测装置（insulation monitoring device，IMD）响应的重要因素。据此，提出基于直流信号注入和Duffing混沌振子分析的三相VSR中性点电压偏移检测方法，该方法以中性点电压的时域平均值及频域分布状态为特征量，通过直流信号注入监测中性点电压的时域平均值，并通过Duffing混沌振子分析判别中性点电压的频域分布状态，由中性点电压偏移引起的特征量变化得出检测结果。实验分析结果表明：由三相VSR直流侧对地绝缘不平衡引起的中性点电压偏移是影响绝缘电阻检测的主要原因，当未发生中性点电压偏移时，IMD的绝缘电阻检测值最大相对误差为4％，而当发生中性点电压偏移时，IMD的绝缘电阻检测值最小相对误差为41％；采用本文提出的方法可有效检测出中性点电压偏移，为提高IMD响应精度提供依据。

英文摘要：

The three-phase voltage source PWM rectifier （VSR） is key equipment in connecting the distributed generators to the small-current neutral grounding system. So, we have analyzed the frequency disturbance of the switching function as well as the change of positive-pole/negative-pole insulation for the DC side of VSR. The results demonstrate that the neutral-point voltage deviation （NPVD） of the three-phase VSR is a crucial factor which affects the response of insulation monitoring device （IMD）. Thus, a pair of methods that take the mean and spectra of the neutral-point voltage as the char- acteristics, are proposed to detect the NPVD, one is adopted to detect the mean value of the neutral-point voltage based on DC signal injection, and the other one is adopted to determine the frequency disturbance of the neutral-point voltage based on Duffing oscillator. So, the detection result for NPVD is obtained by the variety of the characteristics mentioned above, which is induced by the deviation of the neutral-point voltage. The test results demonstrate that the neutral point deviation caused by the change of DC-side insulation balancing is the primary factor which distorts the detection of insu- lation resistance; the relative error of detection results obtained by IMD is less than 4% under normal condition, and the relative error is no less than 41% while the neutral point deviation occurs. Further, the test results certify the feasibility of the proposed method, which can be used for improving the response precision of IMD.