Research On Modeling For Microgrid And Its Impact On Distribution Network’s Protection

Nowadays, a large grid combined with distributed generation (DG) is introduced to reduce environmental pollution and energy consumption, and to improve the reliability and flexibility of power system. In order to maximize the advantages of distributed generation and to coordinate the contradiction between the distribution network and DG, DG and load and energy storage device and control device are composed as microgrid to connect to the distribution network. However, DG’s connection will bring great impact on protection of the distribution network. The traditional method of fault detection and protection mode cannot meet the need for safe operation of the grid. It is significant to study the microgrid and its impact on the distribution network and protection algorithm.Paper summarizes the protection methods of distribution network with DG.The characteristic of IIDG is analysed and the control theory of inverter is studied.Combined with the mathematical model in dq rotating coordinate system, PQ and VF control mode of the inverter are designed. PQ control and VF control strategy are used in microgrid.It can work in connected mode and island mode, and the microgrid operation mode can switch without changing the inverter control strategy.On this basis, PQ control and VF control DG simulation model are established by Digsilent and the models are verified correct. The microgrid model constitutes of PV (PQ control), battery (VF control), synchronous generator and load. The microgrid model is also verified correct.Then the impact of DG on current protection, distance protection and reclosing of the distribution network is studied theoretically, and the impact of IIDG and microgrid on current protection of the distribution network is also studied. Finally, the results are verified correct by simulation.For the impact of DG on current protection, the adaptive current protection is studied:In the case of synchronous generator’s access, adaptive current protection scheme with compensation coefficient is adopted; In the case of IIDG’s access, using the conventional adaptive current protection scheme without IIDG’s access still has good protection performance. The results are verified correct by simulation.