Grid Signal Prediction Model And Analysis

With the improvement of both industrial technology and living condition, many nonlinear power electronic equipments with a variety of capacities are connected to the power system, which causes the distortion of the signals in the power system and presents to be nonlinear. To describe and analyze the signals in the power net, the interharmonics and subharmonics are introduced on the basis of the original fundamental and harmonics. Such problems as the attenuation of DC elements and Sine waveform, voltage sag and frequency deviation should be taken into account in order to analyze the transient process in the power system.Based on the analysis of stable and transient waveforms in the power system, the paper use the exponent-typed signal to describe the signals in the power system including the DC element, fundamental, harmonics, interharmonics, subharmonics and the attenuation of the DC element and the sine waveform. On the basis of this, a set of equations are derived to calculate the signal parameters (frequency, amplitude, phase and the rate of attenuation). The set of equations can lead to FT, CZT,STFT and PRONY methods.The method has perfect effect on calculating the voltage swell and sag, voltage notch and frequency deviation. Numerous simulations also prove the effectiveness of the method. As for the frequency deviation, the method in the paper is a simplified method in calculating frequency deviation. Simulation results show the result obtained by this method is very approaching to the value in theory. What is more, the method can be used not only to detect the time of the occurrence of abnormal signals in the power system and but in real time monitoring and analysis.Sometimes polynomial is adopted to describe signals in order to simplify the analysis. Therefore the paper merges the polynomial-typed signals into the formula obtained using exponent-typed signals.In addition, the paper makes a research into FFT in asynchronous sampling from the angle of iteration, and obtains a iterative formula. Some information such as amplitude and phase can be obtained from this formula very fast.