| With the wide application of power electronic equipments and impact nonlinear devices, harmonic polluting problem resulted has become increasingly serious in the power system. The influx of massive harmonics caused voltage waveform distortion, deteriorated power quality, and brought serious damage to power generation equipment and electrical equipment. Harmonic detection and suppressing is the prerequisite of the security and economic operation of power system, accurate measurement is the basis to guarantee the reasonable charge of power sector.The basic concepts of harmonic and its main source are outlined at the beginning of this thesis. In addition, the harm generated by harmonics to power system and users, and the influence of the electric energy metering to power sector are introduced. Then the relative merits of current harmonic analysis and power measurement methods are analyzed.Aiming at the problems of asynchronous sampling resulted in frequency fluctuations, spectral leakage caused by signal truncation and complex parameters calculation, an improved algorithm of triple-spectrum-line interpolation based on 4-term Rife-Vincent(Ⅰ) window is established. After analyzed the indicators of windows, a 4-term RV(Ⅰ) window which has good sidelobe is selected to tuncate signal for reducing spectral leakage errors; the triple-spectrum-line interpolation algorithm which modified the results is used to reduce the error of fence effect; besides, the phase characteristic of adjacent spectrum lines in mainlobe of cosine window can be used to reduce computing capacity. The simulation results show that the method can effectively overcome the influence of frequency fluctuations and white noise, also obtain a high metering accuracy when measureing harmonic parameters and harmonic active power. To solve the problem of low precision when measuring reactive power, a method based on Hilbert transform is studied in the thesis. A type of FIR Hilbert digital filter which has a linear-phase property is designed to shift 90 degrees of harmonic waves, then calculate the reactive power with the method of calculating active power. The simulation results show that the filter can keep the amplitude of harmonics unchanged when shift phase 90 degrees, so as to achieve the accurate calculation of reactive power.On the basis of above algorithm studied in the thesis, a harmonic metering device based on the structure of ADC+DSP is designed. According to the modular design process, the hardware and software of system are designed, the signal conditioning circuit, the data acquisition module with the core of ADS8556 and the data processing module with the core of TMS320C6745 are introduced in detail, then the system main program module and initialization module are introduced briefly. Finallly, the error sources of system are analyzed from two aspect of hardware circuit and software algorithm, and the specific solutions and the calibration scheme of electric power parameters are given. |
