不对称三相四线制系统有害电流的检测方法

A Detecting Method of Harmful Currents in Three-Phase Four-Wire Asymmetrical System

ip-iq 法能准确、实时地检测不对称三相系统中的有害电流 ,被广泛应用于三相电力有源滤波器。目前 ,在检测不对称三相四线系统的有害电流时 ,均事先剔除零序电流 ,然后再采用ip-iq 法。通过理论分析证明 ,ip-iq 法经过 3 2变换后iα、iβ 中都不含零序电流分量 ,并且基波正序分量不会受到影响 ,因此含有 3 2变换的p -q法、d -q法、ip-iq 法都不会受到零序电流的影响 ,所以这些检测方法都不用先剔除零序电流而直接用于不对称三相四线系统有害电流检测。理论和仿真结果表明这种方法能正确检测出基波零序、负序及谐波分量 ,从而改变了长期以来认为ip-iq 不能直接用于三相四线系统的观点。

Because i p-i q detecting method can detect harmful currents accurately and real-timely under three phase four wire unsymmetrical system, it is widely used in active power filters. At present, detecting harmful currents under three phase four wire unsymmetrical system we should subtract zero sequence current before adopt i p-i q detecting method. It is proved that for the i p-i q detecting method, there is no zero sequence current in i α and i β and the positive sequence current doesn't be affected after 3/2 transformation, so p-q?d-q and i p-i q detecting methods that include 3/2 transformation can be directly used to the three phase four wire unsymmetrical system for the harmful currents detecting and need not subtract zero sequence current in advance. The results of theoretical analysis and simulation verify that this method can correctly detect fundamental zero, negative sequence and harmonic currents, which changes former viewpoint that i p-i q detecting method can not directly be used to three phase four wire unsymmetrical system.