Study Of Harmonic Detection Algorithm And System On Power System

With the wide application of various electronic devices which are non-linear, the harmonics pollution in electric systems is much more serious. To prevent and manage, even charge for harmonics pollution, it is necessary to research into harmonics- monitor that is real-time, accurate and continuous-detected. The research is significant to theory and engineering.Most of present harmonics-monitors adopt the technique of Fast Fourier Transform (FFT) to detect harmonics. However, FFT needs longer time to collect and process the signal. Further more, there are grid-effect and frequency-leak in the processing, which leads to inferior real-time and precision. In addition, FFT is applicable to analyze gradually-changed signals instead of detecting harmonics when the load breaks.By analysis and comparison with present methods, this paper searches in depth into the fast fourier transform detecting principle. Therefore, a complete approach for harmonics detection is designed making use of multi-window of convolution and Interpolation algorithm and windowed apFFT algorithm theory, which the Multi-window convolution and Interpolation is has been upgraded for add windows and interpolation. A multi-window convolution and cubic spline Interpolation algorithm of more suitable for power system harmonic detection is proposed, so that the accuracy of detection of harmonic amplitude substantially improve; this algorithm solve the questions that the traditional FFT algorithm couldn't measure harmonic. It comply with National Standards of power quality and is Meaningful to measurement of harmonics. The phases measurement precision also awaits improvements from Multi-window convolution and Interpolation, then windowed apFFT algorithm is proposed. The windowed apFFT algorithm theory to achieve phase-error-free, Moreover, Amplitude and frequency detection accuracy is also a substantial increase. The detection system applies both algorithms. As a result, it could accurately complete dynamic detection for odd, even, specific, or total harmonics. As the core of harmonics detection, the approach above is realized by PC104 Embedded Motherboard. Then the embedded Motherboard receives harmonics data via communication with Data acquisition board. Deals with these data and calculates important parameter, including harmonic content, harmonic ratio, total harmonic distortion, fundamental active power, fundamental reactive power and so on. Thereby, a set of harmonics-monitor is developed. The system is integrated and intellectualized for its functions consist of harmonics detection, display, forecast and alarm.The designed harmonics-devices may be applied to single-phase circuit, balanced or unbalanced three-phase system. It provides an effective and utility method for continuous and real-time harmonics monitor.