Research On Control Strategy Of Distributed Generation And Decentrialized Microgrid

This paper focuses on control and technology of the decentralized microgrid. The microgrid is composed of many distributed generations. Cooperating with energy storage systems, many distributed energy resources supply power for the loads in the microgrid. Microgrid is the reliable power supply for the consumers in the future. Compared with conventional power supply, distributed generations are close to the loads, which reduced the loss caused by the power transmission. It also can improve the penetration of the renewable energy resources. In order to keep the reliable power supply, distributed generations should supply power for the load even if the grid is disconnected. Moreover, the power quality of the power supply should meet the requirement. The amplitude and frequency of the voltage should be stable.Firstly, this paper is based on parallel-connected inverters. According to the modeling of the parallel-connected inverters, an improved droop control is proposed to achieve accurate active and reactive power sharing. The stability and control design is analyzed. The simulation and experimental results verify the effectiveness of the control strategy.Secondly, the modeling of the distributed generation is built. Accoding to the modeling, a small signal analysis is made to analyse the steady state and dynamic response. In terms of the analyses, an optimized controller design is proposed. The simulation and experimental results verify the analyses.According to the dynamic response of the distributed generation, a seamless transfer between the grid-tied mode and islanded mode for distributed generation is investigated. When the grid is normal, the distributed generation works in grid-tied mode. As the grid is abnormal, the distributed generation should be switched to islanded mode. According to the proposed anti-islanded and synchronization strategies, the distributed generation can switch between the grid-tied mode and islanded mode without current rush and voltage sag.Furthermore, the control strategy of the distributed generation under nonlinear load is porposed. Acctually, droop control is a power control loop. When calculating the output power, a low pass filter is used to filter out the harmonic power. Facing nonlinear loads, the output current of the distributed generation in grid-tied mode will be distorted. In order to improve the power quality, a control strategy of droop control integrated with active power filter is porposed. Moreover, the control strategy can achive reactive power compensation. Finally, the simulation and experimental results verify the control strategy.Energy storagy system is the important backup in the microgrid. Therefore, a unified control strategy of the distributed storage is proposed. In this case, the distributed storage can work as a distributed generation. It not only can supply power for the loads, but also can balance the power mismatch among the distributed generations and load demands. The simulation and experimental results verify the control strategy.Furthermore, a decntrilized nonlinear control decentralized energy management using point of common coupling(PCC) frequency as a communication agent is proposed. By using proposed control strategy, the powe balance among the power supply and load demands can be achieve without any communicationsIn the end, the chargers for energy storage devices are investigated. Two types of battery chargers used in high input voltage are proposed. The input series output parallel phase shift full bridge DC-DC converter and three-level DC-DC converter are employed in this application. In this case, the voltage stress of the switch is reduced to half of the input voltage. Therefore, these two chargers can be effectively used in high input voltage applications..