The Research Of Parallel Inverters Control System Based On Microgrid

Inverters, working as the key equipments in the new energy distributed generation systems, are important for guaranteeing the efficiency and the reliability of energy conversation, the control strategies of inverters are increasingly receiving attentions of scholars all over the world. In this article, emphasis is put on the analysis of the utility of parallel inverters with the function of grid-tie mode and islanding mode. Characteristics and control strategies of the double-mode inverters have been researched in this thesis, including the injection current control and mode transfer control.Firstly, the current loop control strategy for grid-tie mode and voltage dual-loop control strategy for islanding mode is mainly studied after some common control strategies being introduced. Combining control objective and system parameters, we analyze the controller under two kinds of modes mentioned above. Here, a PR controller is introduced in order to ensure good dynamic performance and reduce the steady-error.Secondly, in order to keep a smooth voltage profile across the critical load for the transition between grid-tie mode and islanding mode, a control strategy comprising the islanding detection algorithm and the seamless transition algorithm is proposed. In this thesis, combination of active current disturbance and passive voltage phase mutations is studied, and simulation results show that this method could effectively abate non-detection zone (NDZ).Thirdly, Master-slave control is adopted through a controller area network (CAN) bus among parallel inverters, this optimization substantially make the system communicate conveniently, controlled simplly, at the same time, it decreases the cost of the system, and increases the service efficiency of the information. Based on analysing the transient voltages and currents in the mode switching, this thesis brings forward a new kind of seamless switch control strategy, which can effectively restrain the transient in the switch, realize the current distribution, using the inverter switch control algorithm in two working mode.Finally, considering the importance of the filter in the inverter units, LCL filter is discussed and the design guide line is proposed based on the design method of the dc filter capacitance in order to restrain the high order harmonics. The simulation results show that the reasonable design of LCL filter can inhibit the high-frequency harmonic.