Research On Microgrid Protection And Inverter Control Theory

Microgrid composed of a variety of distributed generation(DG) and local load are not only connected with power system,but also supply off the grid for the local load.Microgrid improves reliability of grid and becomes useful complement to power system. Inverter control, islanding detection and protection are important issues of microgrid research.Inverter control is the key issue of microgrid control. Photovoltaic power generation model and microturbine model are made.The PQ control and v/f control based on LCL filter are proposed in this paper.The control parameters are calculated by forward combined method of zero-pole offset and Routh-Hurwitz criterion. The simulation results verify that control system is stable.To solve critical problems of the non-detection zone and devastating,three methods are proposed.According to the IEEE Std.1547,theoretical analysis and simulation tests are conducted. The results indicate that the proposed methods are able to detect the islanding rapidly in the worst case. Also, these methods are effective when single-phase and two-phase of breaker are disconnected. Furthermore, trip on false islanding can be avoided. The methods achieve the goals of islanding detection without devastation and without non-detection zone.A new adaptive protection approach suitable for distribution network connected with distributed generations (DG) is proposed. Based on operational modes and topological structure of the distribution network the equivalent transform of the network back against the protection is performed and according to the contribution factor matrix of branches the influences of DG on branch currents are eliminated. On this basis, the criteria of main protection and backup protection are constructed. Comparing with traditional current protection, the proposed method expands the protection zones of protection and backup protection, and the calculation of the criteria is simple and easy to set. Simulation results show that the proposed method is not impacted by network-connected DGs, and its adaptive functions of main protection and backup protection can be implemented under symmetrical and unsymmetrical faults.