Prony Analysis for Power System Transient Harmonics
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Research Article Prony Analysis for Power System Transient Harmonics Li Qi, Lewei Qian, Stephen Woodruff, and David Cartes The Center for Advanced Power Systems, Florida State University, Tallahassee, FL 32310, USA Received 9 August 2006; Revised 15 December 2006; Accepted 18 December 2006 Recommended by Irene Y. H. Gu Proliferation of nonlinear loads in power systems has increased harmonic pollution and deteriorated power quality. Not required to have prior knowledge of existing harmonics, Prony analysis detects frequencies, magnitudes, phases, and especially damping factors of exponential decaying or growing transient harmonics. In this paper, Prony analysis is implemented to supervise power system transient harmonics, or time-varying harmonics. Further, to improve power quality when transient harmonics appear, the dominant harmonics identified from Prony analysis are used as the harmonic reference for harmonic selective active filters. Simulation results of two test systems during transformer energizing and induction motor starting confirm the effectiveness of the Prony analysis in supervising and canceling power system transient harmonics. Copyright © 2007 Li Qi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
In today’s power systems, the proliferation of nonlinear loads has increased harmonic pollution. Harmonics cause many problems in connected power systems, such as reactive power burden and low system efficiency. Harmonic supervision is highly valuable in relieving these problems in power transmission systems. Further, shunt active filters can be connected in power distribution systems to improve power quality. With the compensating currents injected by the active filters, the currents are cleaner and less harmonic pollution induced by the nonlinear load affects the operation of the connected power grid. Normally, Fourier transform-based approaches are used for supervising power system harmonics. In order to maintain the computational accuracy of Fourier transform, the stationary and periodic characteristics of signals are generally required. However, power system loads, especially industrial loads, are often dynamic in nature, and produce time varying currents. In this paper, harmonics with time varying magnitudes in power systems are called power system transient harmonics. The accuracy of Fourier transform is affected when these transient or time varying harmonics exist. To achieve controllable harmonic cancellation for power quality improvement, low filter ratings, and bandwidth requirement reductions, harmonic selective active filters are used in power distribution systems. Accurate harmonic reference generation of the harmonics is the key to these har-
monic selective active filters. Some of the harmonic reference generation methods require PLL (phase locked loops) or frequency estimators for identifying the specifi
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