Critical Impedance Method—A New Detecting Harmonic Sources Method in Distribution Systems

In this paper, a new method for detecting harmonic sources in distribution systems, which is so called "critical impedance method" (CIM), is proposed. The principle of CIM is to compare two magnitudes of harmonic voltage sources in the Thevenin equivalent circuit and choose the larger one as the main harmonic source. A critical impedance is introduced to "measure" the equivalent harmonic voltage source through the measurements of voltage and current at the point of common coupling (PCC). The accomplishment of CIM in different situations is discussed in detail. Several simulation case studies and a series of real system switching tests are performed. The testing results show that the CIM is correct in detecting harmonic sources, simple and realizable in practical applications.