计及分布式电源注入谐波的谐振接地系统故障选线方法

针对逆变型分布式电源接入的谐振接地系统发生单相接地故障时注入的低次谐波电流对故障特征的影响,以及在不同故障条件下暂态零序电流的主谐振频率和衰减振荡持续时间变化的特点,提出一种基于交叉小波变换的故障选线方法。该方法通过线路故障零序电流间的交叉小波变换求出高相关时频区域,并通过平稳性检验鉴别分布式电源注入谐波对交叉功率谱的影响,最终求出高相关时频窗。再对线路故障零序电流进行离散小波变换,在高相关时频窗中提取零序电流序列进行能量大小比较与相位验证,实现故障选线。该方法物理意义明确,可鉴别注入谐波电流的影响、抗干扰能力强。大量仿真结果表明,该方法选线准确可靠且适应性强。

A Fault Line Selection Method for Resonant Grounding System Considering Injected Harmonics of Distributed Generation

Aiming at the effect of injected harmonic current on resonant grounding system with distributed generation(DG) in case of single-phase-to-ground fault, and the characteristics that the main resonant frequency and duration of transient process of transient zero-sequence current will change with fault cases, a method to select fault line based on cross-wavelet transform(CWT) is proposed. In this method, the high correlation time-frequency region is obtained with CWT between zero sequence currents of lines and the influence of DG injected harmonics on cross-wavelet spectrum is eliminated with stationary test. In this way, the high relation window(HRW) is obtained. Discrete wavelet transform on zero sequence current is performed and energy comparison and phase verification under HRW is executed to achieve line selection. Physical meaning of this method is clear. The method can distinguish the influence of DG injection harmonic current from interference effectively. A large number of simulation results show that the method is accurate, reliable and adaptable.