Multi-Objective Optimal Control Strategy Of Converter In A Microgrid System

With developing of distributed generation(DG), the usage of DG has been one of the developments of power systems in the future, especially with the help of microgrid technology, which solves the problems of high access costs and single DG control. In the sight of the system, microgrid makes the generators, load, energy storage devices and control devices, etc. to form a single control unit. And the generators in the microgrid, including fuel cells, micro gas turbines, photovoltaic cells, batteries and super capacitors, are all small units with electronic interface. Microgrid not only solves the large-scale access of DGs, take full advantages of them, but also give users a variety of other benefits. This article focuses on the inverter control strategies in the microgrid and optimal scheduling for DGs through multi-objective niche evolutionary immune algorithm, and a solution for microgrid coordination control a well as energy management has been proposed.Inverter is a distributed generation interface for energy exchange, after detailed analyzing of the components' characteristics in the microgrid, a layered microgrid control system based on multi-agent technology has been proposed in this paper. This system is divided into upper and lower layers, and the communication between the two layers and the agents in the lower layer is realized by Internet via Ethernet. The upper layer is energy management system, which is mainly responsible for monitoring the various components and optimizing the algorithm to determine the output of DGs, and distributes the results to the lower agent by Internet. The lower layer is coordinated control system, which on the one hand is controlled by the upper agents, on the other hand has the ability to operate independently, mainly takes charge of the coordinated control of DGs in the microgrid.Each controller in the Coordination control layer has two control strategies: PQ control and V/f control. The former is mainly used in the DGs without the ability of power regulation, while the latter is mainly used in the DGs with the ability of power regulation and distributed storage. When the microgrid operates in the grid-connecting mode, all the DGs can be scheduled to PQ control, according to the management of stable output power settings. When microgrid is islanding, the DGs with power adjustment ability and distributed storage immediately switch to the V/f control mode to maintain the microgrid voltage and frequency stable, and other DGs are still running on PQ control to export stable electric power.Space vector pulse width modulation is introduced to control the three-level inverter, which not only quickly and accurately control the output, but also to expand capacity to meet future demands. A simple microgrid has been simulated and analyzed by PSCAD/EMTDC simulation software, and the results showed that the control strategy both considered the coordination and energy management with good feasibility and practicability.