Fault Characteristics Of Photovoltaic Microgrid And Its Protection

Micro-grid with its protection is an important research direction of the smart grid, but also an important part of the power system in the future. With the gradual intension of the world’s energy crisis, photovoltaic power generation catches more and more people’s attention because of its rich resources, no geographical restrictions, safety and environment friendliness. It will reduce a lot of impact and influence to the grid and improve efficiency of using energy in the form of micro-grid photovoltaic system.This paper sets PV generation, micro-grid,BIPV as the research background, studies on the internal and external fault characteristics, there are two main aspects below:First, when the external fault occurs, because of the power characteristics of micro-grid, it changes the public grid’s character of being single-supplied, type of radiation, one-way flow, which has a impact on the original relay protection and the backflow power produced by micro-grid will cause a lot of damage to the machines and equipmentsso severely that may even endanger the safety of maintenance person; Second, when the internal fault occurs, different operation mode of PV micro-grid and the PV inverter has different fault characteristics,so the widely used over current protection is not able to work in micro-grids.Considering the external fault, this paper proposes a control method for PV micro-grid backflow protection. By collecting solar power and comparing with the power load,battery power and micro-grid mode,using the dual-threshold determination method and logical energy management to achieve the target of controlling the backflow. And on thisbasis, this paper proposed a corresponding improved power strategy for the national policy of sending rest electricity recently to the outergrid to avoid having impact on the outer public grid with taking fulladvantage of renewable energy to generate. This article used Simulinkto simulate the controlling logic of the backflow prevention device and designed a testing platform of backflow prevention, which proved the strategy of backflow prevention.Considering the internal fault,this paper impoved the distance protect algorithm.By setting the impedance value changes in time so that it can work in both micro-grid operationmodes.Simulink simulation results show that although the measured impedance value becomes larger after the micro-grid accessd, but the d istance protection setting values can be updated in time, to avoid misoperation, which can properly protect the alectric circuit in the PV micro-grid...