Study On Grid-tied Inverter Of Microgrid And Control Of DC Microgrid

With the rapid development of the world industry and economy, the energy crisis is showing before the humans. Meanwhile, the malpractice of super large-scale power system appears increasingly, and the vulnerability of the grid has been fully exposed. Based on this, the distributed generation technology with renewable energy as the main energy has got the fast development. The key problem in using of renewable energy is how to convert it to electrical energy and connect to the utility. Micro-grid is a small-sized grid that integrates a number of micro-sources and loads, which is controllable, and can either be connected to distribution grid as a special load, or disconnected from the utility to operate in island model. As a good supplementation to the traditional high voltage and long distance bulk power supply model, the development of microgrid has changed the single power supply pattern and has greatly improved power supply reliability and efficiency.As the interface between grid and distributed generators, the grid-connected converter has very important influence to the interconnection performance of the distributed generators. Microgrid can operate when connecting to the large grid and also can run in island mode when separated with the large grid. Whether the microgrid operates in grid-connected mode or islanding mode, it needs to keep the voltage and frequency within acceptable limits from a standard and consequently guarantee the power quality. So the study on the grid-connected converter of the microgrid is one of key technologies for development of microgrid.Several conventional control methods of micro sources are analyzed in this paper. Combined with the characteristics of different micro sources, two typical control strategies are researched and simulated. Based on the mathematical model of two phase synchronous rotating reference frame for three-phase inverters, the principle of V/f and PQ control methods of micro sources inverters are analyzed particularly. And the models of microgrid and inverter control system are established with Matlab. According to the simulation in many different operating modes, the dynamic characteristics of system are analyzed and the validity of control strategy for inverters of the micro sources is verified.In addition, the basic structure of DC microgrid is analyzed in this paper. And the paper also sets up the model of micro sources, such as photovoltaic generation, wind power generation, fuel cells generation and so on. The control method and operating characteristic of the energy storage element (battery and super-capacitor) are analyzed both in grid-connected mode and islanding mode respectively. The power management methods and control block diagram of each component in DC microgrid are elaborated. A new control method of the DC microgrid based on multi-agent is researched, the simulation results show that in terms of grid-connected mode or islanding mode, the system can guarantee energy balance in DC microgrid, so the validity of the method is verified.