Research On Active-passive Combination Islanding Detection Method Based On Non-Detection Zone

Under the background of energy exhaustion,photovoltaic grid-connected power generation technology has been widely used,and its proportion in the power grid has gradually increased.However,a large number of grid-connected photovoltaic systems will increase the possibility of islanding,which will reduce the stability of the grid system.Therefore,the facing main problem of the grid-connected photovoltaic technology development is the island effect.Island effect not only poses a threat to the human body,but also causes damage to power system equipment,involving property and security issues,affecting the development of photovoltaic technology.Therefore,the photovoltaic grid-connected power generation system must have the ability of islanding detection.Aiming at the slow detection speed of traditional active frequency drift(AFD)method and the high total harmonic distortion rate of the distorted current,a new abrupt current disturbance signal is proposed,which can make the fundamental component produce the necessary phase angle drift instead of the traditional gentle current disturbance signal.On this basis,the current phase is changed to further accelerate the low distortion of the current phase angle drift speed.The non-detection zone of traditional AFD method,new frequency drift active method and low distortion active method are plotted by constructing the coordinate system of non-detection zone.The model control group is built by using MATLAB software.The conclusion that low distortion active method has faster detection speed and smaller harmonic distortion is obtained.To overcome the shortcomings of passive detection and active detection,an islanding detection method based on non-detection zone discrimination is proposed,which combines passive over/under voltage,over/under frequency detection and active detection.When the operation state of grid-connected system is in the non-detection zone of passive detection method,the system will choose active detection method to detect islanding effect,and vice versa.Therefore,the active islanding detection method will be selectively introduced into the active-passive combination islanding detection method,which further reduces the problem of harmonic distortion in the non-islanding state of the active islanding detection method.Finally,a model is built by using MATLAB to verify that the active detection method is chosen when the system is in the non-detection zone of passive detection method.The control group is set up to verify the advantages of the combination of passive over/under voltage,over/under frequency detection method and low distortion active method,which has the fastest detection speed and the lowest harmonic distortion.