Research On Hybrid Isolated Island Detection Method

With the depletion of non-renewable energy such as coal,oil and natural gas,the deteriorating ecological environment and the rapid growth of power load,distributed power generation system has been developed rapidly in all countries.Therefore,the stability of distributed power generation system research is necessary.Unprotected island production will cause great harm to the power system,so accurate and rapid detection of unplanned island has important theoretical significance.In this paper,the principle of detecting the island of the distributed power generation system and are explained by analyzing the influence of the power shortage on the frequency and voltage.And summarize the relevant standards of island detection methods,and analyzes several coordinate system methods for judging the non-detection zones of islanding.Mainly studied Over/under Voltage,Over/under Frequency methods and Frequency Change Rate method these two passive detection methods,and Active Frequency Drift(AFD),Active Frequency Drift with Positive Feedback(AFDPF)and Slide-Mode Frequency Shift(SFS)these three active detection methods,and use the coordinate system to describe their non-detection zones.The influence of the parameters of the active detection method on the detection performance is studied,and the optimal disturbance parameters are determined.Aiming at the shortcomings of passive and active detection methods,a hybrid island detection method combining Over/under Voltage,Over/under Frequency methods and Active Frequency Drift with Positive Feedback(AFDPF)is studied.It determines the operating state of the system through the blind disc discriminant analysis to determine whether to introduce the disturbance current using the Active Frequency Drift with Positive Feedback(AFDPF)for island detection.In this paper,a new type of current perturbation active method and passive method are selected by contrast analysis.In this method,the positive half-cycle amplitude of the voltage at the common node of the grid is reduced and the negative half-cycle amplitude increases when the negative step disturbance is added to the positive and negative half cycle of the reference current waveform.When the absolute value of the negative half-cycle voltage amplitude is greater than the positive half-cycle voltage amplitude,and this number of cycles of continuously reaches the threshold,it is judged as the islanding state,and the grid-connected inverter is disconnected.The validity and feasibility of this method are verified by MATLAB.And the comparison shows that this method has better power quality and smaller detection dead zone than the previous hybrid detection method.