The Study On Microgrid Experiment Systems

A microgrid is a cluster of interconnected distributed generators, loads and intermediate storage units that cooperate with each other to be collectively treated by the grid as a controllable load or generator. A microgrid system can operate interconnected to the main distribution grid, or in an islanded mode. Now the interest on microgrid has increased significantly triggered by the increasing demand of reliable, secure and sustainable electricity. This thesis summarizes the ongoing microgrid research, development and demonstration efforts currently in progress around the world. According to their structural characteristics and control approaches, the microgrid demonstration projects and related experiment test systems are classified and analyzed intensively. This thesis concentrates on a control strategy and field testbed of an inverter-interfaced MicroGrid. The main jobs of the thesis are as the following.Firstly, a comprehensive summary and compare on current control technology is given. Microgrids are dominated by inverter interfaced distributed sources; the inverter model is derived according to the following control strategies, PQ inverter control, V/f inverter control and droop control. And the characteristic, applicability, implementation of the three control strategies discussed above are particularly analyzed. Based on the power and energy management, three control modes may be used in the microgrid, peer-to-peer control, master slave control and hierarchical control. Furthermore, the implementation methods of these three modes and which control modes within a microgrid were selected based on the required functions and possible operational scenarios were given.Secondly,to provide a test platform for possible demonstrations of advanced distributed generation system integration strategies, a single-phase laboratory-scale Microgrid system was set up. Two microsources are included in this Microgrid, a photovoltaic simulator and a wind turbine simulator. Both of them are connected to the AC grid via flexible power electronic interface respectively. For stable collaborative operation, a battery energy storage interfaced with a bi-directional inverter is necessary in this Microgrid. In the grid-connected mode, both the microsources inverters and the bi-directional inverter are the P controlled inverter. While switching from grid-connected mode to islanded mode, the bi-directional inverter is setting the voltage and frequency of the Microgrid through absorbing or releasing energy. The operation experimental results show that the laboratory-scale Microgrid system can operate in grid-connected or islanded mode, with a seamless transfer from one mode to another, and hence increase the reliability of energy supplies.Thirdly, a design and realization of a practical small-scale photovoltaic microgrid system was proposed according to the characteristics of competition building. The PV installed capacity and the microgrid schematic diagram were first given based on the space and the load consumption of the building, then the energy balance was simulated and the operation modes were analyzed. The operation experimental results show that the real energy balance was consistent with the simulation of energy balance, and the photovoltaic microgrid system can operate in grid-connected or islanded mode, with a seamless transfer from one mode to another, and hence increase the reliability of energy supplies.Finally, from overseas successful field tests experience for microgrids, a microgrid pilot scheme in which controllable generation along with controllable loads needs to be gathered in order to operate them in a microgrid environment was given. Within the proposed microgrid systems, several alternative microgird configurations would be developed and different control modes would be used.