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Harmonic source identification and current separation in distribution systems Yong Zhao a , b , Jianhua Li a , Daozhi Xia a ,* a
Department of Electrical Engineering Xi’an Jiaotong University, 28 West Xianning Road, Xi’an, Shaanxi 710049, China
b Fujian Electric Power Dispatch and Telecommunication Center, 264 Wusi Road, Fuzhou, Fujian, 350003, China Abstract To effectively diminish harmonic distortions, the locations of harmonic sources have to be identified and their currents have to be separated from that absorbed by conventional linear loads connected to the same CCP. In this paper, based on the intrinsic difference between linear and nonlinear loads in their V – I characteristics and by utilizing a new simplified harmonic source model, a new principle for harmonic source identification and harmonic current separation is proposed. By using this method, not only the existence of harmonic source can be determined, but also the contributions of the harmonic source and the linear loads to harmonic voltage distortion can be distinguished. The detailed procedure based on least squares approximation is given. The effectiveness of the approach is illustrated by test results on a composite load. 2004 Elsevier Ltd. All rights reserved.
Keywords: Distribution system; Harmonic source identification; Harmonic current separation; Least squares approximation 1. Introduction Harmonic distortion has experienced a continuous increase in distribution systems owing to the growing use of nonlinear loads. Many studies have shown that harmonics may cause serious effects on power systems, communication systems, and various apparatus [1 – 3] . Harmonic voltages at each point on a distribution network are not only determined by the harmonic currents produced by harmonic sources (nonlinear loads), but also related to all linear loads (harmonic current sinks) as well as the structure and parameters of the network. To effectively evaluate and diminish the harmonic distortion in power systems, the locations of harmonic sources have to be identified and the responsibility of the distortion caused by related individual customers has to be separated.
As to harmonic source identification, most commonly the negative harmonic power is considered as an essential evidence of existing harmonic source [4 – 7] . Several approaches aiming at evaluating the contribution of an individual customer can also be found in the literatures. Schemes based on power factor measurement to penalize the customer’s harmonic currents are discussed in Ref. [8] . However, it would be unfair to use economical penalization if we could not distinguish whether the measured harmonic current is from nonlinear load or from linear load. In fact, the intrinsic difference between linear and nonlinear loads lies in their V – I characteristics. Harmonic currents of a linear load are i n linear proportion to its supply |
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