Inverter-based Microgrid Islanding Detection

Great changes were brought out as the appearing of the distributed generation technology:on one kind, the generators increased in the distribution network, the reliability of electrical system improved, on the other hand, some problems brought in to the power system and users as the application of the distributed generation such as the impact when they connected to the grid. And when fail or repair occurred in the power system, the distributed generation and the load may separate from the grid and change into island.The concept of island and island running were quoted in this paper, the cause of the island was analyzed, the effect of the island to the grid was resumed which contains the running of the planed island can improve the reliability of the power supply network, while the running of the unscheduled island pose a threat to the stability of the power system and the safety of the maintenance staff. The policy of the island was analyzed which is either the distributed generators stop running when the island appears or the distributed generators keep running. The means of island separation was detailed which laid the foundation for the deeper study of the island separation.The research meaning and status of the island detection were analyzed. The standard and basic principle of the island detection was resumed. Long distance communications island detection way, local initiative island detection way and local passive island detection way were detailed in this paper. The initiative island detection way includes impedance measurement detection way, the reactive power measurement detection way, the slip-mode frequency shift detection way, the active frequency drift detection way, the sandia voltage shift detection way, the sandia frequency shift detection way, the frequency jump detection way, the active power or reactive power disturbance detection way and the positive feedback detection way. The passive island detection way includes the frequency detection way, the voltage detection way, the frequency gradient detection way, the voltage phase shift detection way, the voltage harmonic detection way and the electrical parameters gradient detection way.The theory of the positive feedback island detection way was detailed in the paper, according to the theory, this paper designed line-connected inverter, the current arguments needed, the feedback enhancement, the proportional integrated controller PI, the phase locked loop PLL for improving the stability of the power system, the PWM control unit for regulating the feedback current phase, the grid current phase and the island current phase which are needed by the positive feedback island detection way simulation model. In the end of the paper, the validity of the positive island detection way was confirmed according to the simulation results of the simulation calculation.