| Extra-high voltage, long-distance and centralized power system leads to several problems in following respects, such as power quality, safety, reliability, economy, flexibility and so on. Therefore, the distributed generation technology is developing rapidly, which is mainly based on renewable energy. With the popularization of this power generation technology, different requirements from power grid companies, power plants, and customers can not be met by the existing distributed generation operating mode. Although there are many advantages from single distributed generation source, there are also many problems, especially the impact on the power grid when a fault occurs. In order to coordinate contradictions between power grid and distributed generation and promote the compositive application of distributed generation, the concept of microgrid is proposed. Microgrid 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 islanding mode. It represents the new developing trend and becomes a research focus of power system.Most micro sources are connected to microgrid through power electronic inverters. Therefor, the control of micro sources is realized through the control of power electronic inverters. Whether the mircrogrid operates in grid-connected mode or islanding mode, the effective control of power electronic inverters in microgrid is need to keep the volatge and frequency within acceptable limits from a standard and consequently guarantee the power quality. So the study on the control technology and the problem of paralleled inverters forming grid is one of key technologies for development of microgrid. Based on the mathematical model of two phase synchronous rotating reference frame for three-phase inverters, the V/f and PQ control methods of micro sources are analyzed particularly. The corresponding controllers are also designed according to the engineering design method. In addition, regarding to voltage-current double loop control system of V/f control, the mathematical formula of inverter output impedance is deduced. Moreover, the controller parameters of voltage-loop and current-loop are optimized on the basis of the principle that is X>>R in the output impedance of inverters.The models of microgrid and inverter control system are established with Matlab/Simulink. According to the simulation in different operating modes, the dynamic characteristics of system are analyzed and the validity of control strategy for inverters is verified. The simulation results show that, using reasonable control strategy can guarantee the frequency and voltage of loads within acceptable limits from a standard.A new scheme of using inductive FCLs to suppress the transient process is presented in this thesis. With the microgrid model installed with FCLs which are connected with the micro sources, different fault types and fault locations in different operating modes are analyzed by simulation. The results show that the fault transient process of voltage, current, frequency and power can be effectively suppressed by FCL whether the fault occurs in grid-connected mode or islanding mode. Besides, the simulation results also show that the oscillation phenomenon of voltage and current in PQ control mode can be significantly reduced by FCL. Consequently, the system stability is ensured.In addition, the simplified DC voltage source model of micro sources in the former simulation can be replaced by the concrete mathematical models of micro sources, such as wind generator, diesel generator system, storage battery and so on. In view of the conversion between grid-connected mode and islanding mode, the variation of load in islanding mode and the power change of a certain micro source in microgrid, the operating characteristics of micro sources are simulated. And for the wind and diesel generator system, the impact of prime mover on microgrid is also analyzed.
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