Research On Relay Protection And Cooperative Control Of Micro - Grid

Micro-grid has been developed rapidly so as to solve a range of problems as environmental degradation, fossil fuels depletion, and made full use of clean energy and for a range of issues. It will become an important way to provide energy for power grid in the future. The protection for Micro-grid is always the research emphasis in the development process of micro-grid. At this stage, the research in micro-grid protection is still in developing stage. The protection strategy which is suitable for both operations of grid connected and in island is still not perfect. At present, The double-loop PI control is the most used method in micro sources such as photovoltaic system and wind power system. But this method can’t meet dynamic property of the system gradually. Therefore it has very important meaning to design perfect relay protection system for micro-grid and research new controlling method for micro-grid.Relay protection of micro-grid has been researched and protection strategy for micro-grid has been designed at first. The relay protection of micro-grid is consisted of main protection and backup protection. Arc protection for buses and distance protection with power directional elements make up the main protection. Distance protection acts as starting element which adopts the full impedance relay and set in the third phase of distance protection. Power directional elements are used to judge the fault section. The centralized backup protection is used as the backup protection for the whole micro-grid. All the protectors of branches and buses transmit the information of bus voltage, branch currents and arc signals to the host of centralized backup protection. The host will judge the faults with the information, and then take time-delay operation.Test relay protection equipment has been designed with the core of DSP F28335. It can realize main functions of hardware and software. Simulink model of Micro-grid in RT-LAB equipment has been built which can be used to execute the real-time simulation with the hardware in the loop in real-time simulator RT-LAB. Then to connect the test equipment with RT-LAB equipment. The real-time semi-physical simulation tested and verified the performance of the test equipment and the protection of micro-grid can operate correctly. To cut the fault in the power grid rapidly, reliably and selectively.Cooperative control has been used to micro-grid. Differential-algebraic equation of two-stage photovoltaic system has been deduced firstly. Two different control strategies were used in normal operation and in low voltage ride-through period of grid-connected photovoltaic system. Cooperative control algorithms of the two control strategies have been deduced. This thesis has add cooperative control module to grid-connected photovoltaic system simulink model. Then to execute the simulations of normal operation and low voltage ride-through. Then to simulate and analysis the cooperative control in a grid-connected photovoltaic-storage micro-grid which is consisted of photovoltaic system and energy storage system.The micro-grid protection designed in this thesis has relatively comprehensive function. It has reference function for the development of micro-grid protection equipment. The research in micro-grid cooperative control has explored a new method for micro-grid control. It made micro-grid has good performance in both normal operation and in low voltage ride-through period.