Study Of Composite Islanding Detection Method Based On Digital Phase-Locked Loop

With the aggravation of the energy problem, more and more distributed generation composed of new energy was put into use. Islanding effect is a kind of special status in grid connected distributed generation system, which is harmful to the safe operation of power equipment and power grid. To oriented the fundamental component of power grid voltage with phase-locked loop and anti-islanding are two key technical problems in the distributed power generation grid connected process with inverter.In this paper,based on the theoretical analysis of basic problems of islanding effect and a kind of three-phase digital phase-locked loop,firstly,made improvement to the PI control secton and then put forward a composite islanding detection method based on the three-phase digital phase-locked loop.Including a new type of active phase shift protection method, a new type of over/under voltage protection based on the principle of Park transform theory,phase jump protection and over/under frequency protection.This composite islanding detection mothod which based on digital phase-locked loop improves the detection speed and system integration,on the other hand,it can eliminates the non-detection zone at the same time.In order to achieve the composite islanding detection method in application of distributed generation in the single phase grid connected system, this paper puts forward a new single phase grid-connected digital phase-locked loop based on perturbed frequency divider. The single phase digital phase-locked loop generates two orthogonal vectors with a second-order generalized integrator and the adaptive design of center frequency can lower harmonic interference and improve the phase locked accuracy. The design of perturbed frequency divider can improve the accuracy and frequency range which can be phase locked.At last, the feasibility and correctness of designs in this paper are verified by modeling and simulation in Simulink environment.