一种精确检测三相不对称系统中各次谐波的新方法及其实现

提出一种精确检测不对称系统中各次谐波正、负、零序分量的新方法。该方法不直接采用对称分量法,而通过广义d_k-q_k旋转坐标变换,分别对三相电流按照相序a-b-c和a- c-b进行两次低通滤波得到三相电流的正、负序分量,同时分解零序分量并通过适当变换,之后通过低通滤波得到任意次谐波电流的零序分量,最终将对应分量求和得到检测结果。实验结果表明,无论三相电路电压是否畸变,通过该方法都能够得到精确的检测结果。对于三相不对称系统(包括缺相),仍然可以精确检测出任意次谐波电流,并可用于基波有功和无功电流的检测。利用本文提出的电流检测方法原理,研制出一台以微机为上位机的动态谐波电流检测仪,目前该装置已应用于某变电站的谐波电流检测中,运行情况良好。

A New Method of Harmonic Current Detection for Three-Phase Unbalanced System

A novel method of harmonic current detection for three-phase unbalanced system is proposed,which can detect the positive,negative and zero-sequence components of any term harmonic current precisely.While not adopting the sym- metrical components method directly,the three-phase current is transformed to generalized d_k-q_k coordinate firstly,then fil- tered by low pass filter and inverse transformation,therefore the positive sequence component is detected.Only change the phase sequence from a-b-c to a-c-h,the negative compo- nent can be detected similarly.Meanwhile,the zero-sequence component is decomposed and filtered by low pass filter to ob- tain the zero-sequence component of any term harmonic cur- rent.Finally,sum the three components correspondingly to ob- tain the detect result.The simulation result shows that this method can detect any term harmonic current effectively and precisely nevertheless the distortion and unbalance of three- phase system.It can also be used as the detection of active and reactive components of fundamental current.It can be widely applied to fault detection,protection for power system and ac- tive power filter.