Frequency Estimation And Tracking For Harmonics Analysis Of Power Systems

With more and more non-linear loads such as power electronic semi-conductor devices used in power systems , a large quantity of high orders harmonics are putted into power systems .The wave-form of voltage or current is aberrant,which makes it very difficult to meaure frequency and analyse harmonics accurately .In this paper, the concepts,standards and analysis method of power quality are proposed.The product and endangerment of harmonics are pointed out. Some hot-point on harmonics analysis are discussed,for example, spectrum leak, barrier effect, Synchronous sampling etc.The control methods of harmonics are expatiated.Many scholars have maken scientific researches on frequency estimation in recent years. There are many kinds of methods to estimate frequency.In this paper, the disadvantage of methods which is pracitsed usually in engineering are analysed. That is cycle-counting method and phase difference method.The former is easily affected by aberrances near zero point of signal;The latter is only adapt to sine signal with single frequency abstractly.Based on the latter, a new kind of method of frequency measurement is brought forward which is adapt to sine signal with multi-frequency.In this paper, a set of formulas for frequency estimation ofmultiple frequency signal is deduced and a method of frequency estimation and tracking for harmonics analysis of power systems is developed. The set of formulas consists of DFT of sampled data, phase difference calculation and frequency calculation. Frequency tracking means that sampling intervals of following sampling is updated according to new frequency estimation, so synchronous sampling error will be reduce step by step. The method can provide very high accuracy for real time harmonics analysis of power signal and it's computation is very simply . Matlab simulations show efficiency of the method .Finally, a high performance electric harmonic monitoring device is introduced which is based on TMS320VC5470 processor, the design of hardware frame,function module,the development flow of DSP signal sampling program and signal processing program and ARM control program are discussed in this paper.