The Power Flow Algorithm For Islanded Microgrid

Fossil energy crisis and environmental pollution problems reverses renewable, clean energy development rapidity. In recent years renewable energy sources such as wind power, photovoltaic power generation technology get rapid development, however, because of the wind, photovoltaic, and other distributed generations are greatly influenced by environmental factors, such as weather, its power output has stronger intermittent, so in order to reduce the impact of the distributed generations to power grid.Many kinds of distributed generations and energy storage device with which different characteristics and complement each other can be connected to a power systems called microgrid of protection, control, management functions. Microgrid can operate both in mode connected-to-distribute grid and mode disconnected-to-distribute grid. Its economic environmental benefits are considerable.The faults in distribution sometimes will lead to islanded microgrids operating using distribution generator(DG) droop control method, to sharing real and reactive power and so as to improve power supply reliability. As we all know, power flow algorithm is fundament to analysis of different kinds of power system stabilization?reliability and security,while conventional power flow depends on the availability of slack buses which has load balance, so it is urgently need to a novel power flow algorithm considering real characteristics of islanded microgrids.This paper deeply considered control methods of different distributed generations,including the droop control, PQ control and PV control, and then proposes a novel power flow calculation algorithm of modified initial value selection method based on Newton-Raphson. Besides, it also considers problems of type switching between various kinds of nodes. Under different DG control methods and cutting DG scenarios, the proposed method was performed on 6-bus and 33-bus islanded microgrid in Matlab environment, and results testify the correctness and validity. The results of simulations demonstrate that although modified Newton-Raphson power flow calculation algorithms can be influenced by droop control parameters of distributed generations, this algorithm can still be convergence under circumstance of cutting one distributed generation, and turn out to be a faster convergence comparing to send-order power flow calculation algorithm.To validate the proposed novel power flow calculation algorithm, structure and principle of droop control inverter modules are analysised in detail, and then electromagnetic transient simulation software PSCAD/EMTDC which recognized highly in global academics is employed to model accurately. The results of simulations demonstrate that the difference between those two way is very small, turn out to be 0.5% in maximum deviation of voltage phase and 0.03% in maximum deviation of voltage amplitude that both are in allowable error range, verifying the correctness and effectiveness of the method once again.