System Stability And Power Quality Analysis Based On HHT

In order to obtain reasonable and precise results in analyzing low frequency oscillation (LFO), Ferroresonance Over Voltage(FOV) and voltage flicker signal(VFS) in power systems, a novel method based on Hilbert-Huang transform (HHT) was introduced to extract the model parameters of LFO,. FOV and VFS in this paper.It applied empirical model decomposition (EMD) to decompose the LFO signals and calculated the instantaneous parameters including magnitude, frequency and phase of every model component with Hilbert transformation, and then calculated the damping ratio of every model component based on above parameters and derived the formulas. Thus it realized effective extraction of all parameters of LFO signals and put forward a new explanation of the mechanism of very low frequency oscillation. This method can be applied to analyze strong non-linear oscillation models in power systems and design damping controllers. The simulations and example analysis indicate the feasibility and validity of the new method proposed in this paper.Ferroresonance Over Voltage(FOV) is a common fault in neutral network, due to its magnitude is times of normal voltage, strong attack and destructive accident will be caused if no anti-resonance measures are adopted. A novel method based on HHT was introduced to identify FOV fast and quantitatively. Extracted key model function using EMD and correlation coefficient method, and then calculated its corresponding instantaneous parameters including magnitude and frequency with Hilbert Transform, thus it realized quantitative analysis of the type﹑magnitude and induced time of the FOV. This paper discussed the application of HHT in identifying FOV online, and carried it out into analyzing three different types of emulated signals and a set of actual measurement signal. The results indicate that this method can reveal the primary features of FOV signals well, and be the base for online identification and corresponding anti-resonance measures adopted.Based on the characteristic that the results of VFS, which modulated by low-magnitude single frequency signal or multi-frequency complex signal distribute symmetrical to both sides of fundamental frequency signal in frequency domain, and with regard to the frequency-band of actual modulated signals. A novel method proposed to realize the purpose to modulate the voltage flicker signal in frequency domain and keep down the low-frequency parts, which named as modulated flicker signal. Then the parameters of low-magnitude modulated signal can be extracted by the formulas deduced in this paper after the parameters of modulated flicker signal extracted by the HHT. The simulation and example analyze results indicate that the method proposed in this paper can extract the parameters of low-magnitude modulated signal from voltage flicker signal easily and effectively.Above simulation and example analyze results indicate that the stability and dependence of power system can be analyzed effectively based on the precise parameters of LFO, FOV and VFS extracted by the novel method—HHT.