Modeling Of Micro Grid And Simulation Analysis Of Short Faults Characteristic

In the world, traditional power system is confronted with the depletion of fossil energy, the low efficiency of energy conversion and the problems of pollution to the ecological environment. Micro grid is an active power distribution network which combines distributed generation, energy storage device and load. The operation of the micro grid contains the islanded and grid-connected modes. The most of distributed generations are consisted of renewable energies which include natural gas, biogas, wind power, solar photovoltaic battery, fuel cell and so on. The analysis of the characteristics of the distributed generation is the premise of micro grid operation and controlling.The characteristics of PV power and battery energy storage were analyzed by the paper. It is established that the mathematical model for inverter based on dq synchronous rotating coordinate system. Some research is made on the PQ, V/F control principle in this paper. Based on microgrid operation control of the influence of electromagnetic transient process, the paper analyzes the different control modes on micro power supply electromagnetic transient impact characteristics.Firstly, this paper focuses on the photovoltaic micro source model, model of inverter and energy storage mathematical model.Then the model of the micro grid is established.Voltage and current is calculated by the use of positive sequence network diagrams based on the three-phase short circuit fault theory when three-phase short circuit fault of the system occurs. With the use of simulation software for three-phase short circuit fault research of photovoltaic micro power supply, simulation results show that, after fault removal, photovoltaic micro power of constant voltage and frequency runs into the island. In that condition, the voltage leap is distinct and harmonic is more. The use of V/f strategy cannot suppress voltage mutations effectively. A small voltage mutation occurs and fewer harmonics are there.It is acknowledged that the energy storage device to a certain extent improves the conditions of the voltage leap and the ability of harmonic suppression.Finally, based on asymmetric short-circuit fault theory, composite sequence network diagrams of the asymmetric short circuit can be obtained in the boundary conditions of asymmetric short-circuit fault. Asymmetric short-circuit voltage and current under fault can be calculated and analyzed with the use of composite sequence network diagrams. It is inferred that short circuit current of short circuit of inter phase fault is the biggest threat when phase to phase short circuit occurred. The research on Asymmetric short-circuit has a support for theoretical study of micro-grid power quality and provides a theoretical basis for protection.