Research Of Harmonic Analysis And Design Of The Controller In Electric Power Quality Monitoring Instrument

In recent years, with the development of economic and technology, non-linear loads and power electronic converters are widely used, resulted in the deteriorating power quality. Therefore, the power quality has become a hot research point of scientists. While monitoring the power quality accurately and timely is a prerequisite of the research.This thesis, according to national standards, designs a dual-CPU power quality monitoring instrument, and focuses on an algorithm of harmonic analysis– windowed interpolation Fast Fourier Transform (FFT). The hardware and software of its host controller are also designed.It is effective to decrease the grid effect and energy leakage of FFT by using windowed interpolation algorithm. Some classic cosine windows and convolution windows are researched in this thesis, and the theory of windowed double-spectrum-line interpolation is analyzed, obtaining the computational formulas of frequency, amplitude, especially an improved formula of phase. A theory of polynomials fitting is used to simplifying the inverting formula of interpolation coefficient. And some parameters of interpolation polynomials are computed in MATLAB. Meanwhile, the self-convolution-windows are analyzed. On this basis, the author gives a new convolution window– mixed-convolution-window, which is actually the convolution of two cosine windows. By researching the characteristics of centrallobe and sidelobe, it is obvious that the Hanning-Blackman mixed-convolution-windows can be used for windowed interpolation algorithm. The inverting formula of interpolation coefficient and some parameters of interpolation polynomials are given along with the formulas of harmonics parameters.In this thesis, an optimized method based on Shannon's sampling theorem is given. In addition, a program flow chart is provided for scanning the spectrum line. A complex signal with 21 order harmonics is constructed for the simulation of Cosine-windowed and Convolution-windowed interpolation algorithm. The result shows that: Rife-Vincent(III) window interpolation algorithm is the most precise, the precision is steady under fundamental frequency variation.According to demand, the S3c2410 processor is designed as the core, with RAM and Flash memory. Some modules such as the power, reset, LEDs, buttons, serial port, even LCD and touch screen are designed on base board. Simultaneously, the thesis discusses the transportation of Embedded Linux System, QT/E GUI and some driver programs. The host controller is tested completely, it can work independently.