The Study On Harmonic Measure Algorithm In Electric Power System Based On DSC

In recent years, the problem of harmonics is growing serious in power system. Research and analysis shows that the harmonics can cause very serious harm to the devices in power system. In order to accurately monitor the harmonic content and take measures to reduce the harm caused by harmonics, this paper introduces a new harmonic measurement design which puts DSC (digital signal controller) as the core system hardware and puts FFT (fast Fourier transform) algorithm as primarily system software.The FFT algorithm which is chosen from many kinds of harmonic measurement methods is used to analyze harmonic and the algorithm is software programmed in the MAPLAB to verify whether the algorithm is correct or not.This paper takes the further study of the problems which are Spectrum aliasing which is caused when sampling frequency cannot meet sampling theorem and Spectral leakage which is caused by non- synchronous sampling. In addition, when the FFT algorithm is software programmed on MAPLAB C30, the accuracy of FFT algorithm can meet the requirements of national standard is proved.Secondly, the hardware circuit mainly includes a four-order filter circuit, the signal boost circuit, phase-locked frequency multiplier circuit.and so on. When analyzing the amplitude-frequency characteristics of filter circuit discoveres that the filter circuit can cause measurement accuracy error, and the error can be reduced by divided attenuation coefficient of each harmonic. PLL circuit can achieve synchronizing sampling to reduce the spectral leakage phenomenon. Accuracy and reliability of each circuit is verified by Proteus simulation and some experiments.In addition, this paper adopts a modular method to design software program, and FFT algorithm is programmed by the method of the combination of C language and assembly language. Based on the basic performance of the main control chip, the three-phase voltage and the three-phase current and the same-phase voltage and current can be sampled at the same time by setting AD register and PLL INT0 control program. The other electrical parameters can also be calculated on DSC chip.The FFT program based on DSC is programmed on C30, but the word length data types of C30 is limited, so the accuracy cannot meet the error requirements. The amplitude of High-order harmonic is attenuation caused by the anti-aliasing filter, and accuracy will be reduced. To solve these problems, some effective methods are used to improve the precision to meet national standards.Last but not the least, this paper also designs the keyboard module, LCD module and other Human Machine Interaction; the measure results are transmitted to a PC for real-time detection and management through RS485 serial communication unit.