The Coordinated Control Of Multi-Inverters In Microgrid

More and more attention have been paid to microgrid due to its huge environmental benefits, social benefits and economic benefits. As the interface device between distributed generation and microgrid, inverter plays a crucial role in microgrid. Solving the problem of multi-inverters parallel connection and making inverters can operate in both grid-connection mode and islanding mode are the difficulties and the hot of inverter control technology and the key technology for microgrid’s reliable operation. The main object of this paper is parallel inverters of microgrid,The main contents of this paper are as follows:Firstly, in this paper, a three-phase four-leg inver tertopology is proposed to solve the problem of unbalanced output voltage in the condition of unbalanced load in microgrid. According to the requirements of stable operation of microgrid, some Scholars pointing out that traditional control strategy of distributed generation does not apply to the islanding mode of microgrid. And then analyzing the advantages and disadvantages of several current control strategies of inverter in microgrid. A hierarchical control strategy is proposed based on traditional droop control. In the first place, hierarchical control method can realize V/f control in islanding mode, which can provide voltage and frequency reference and have a good power sharing. Hierarchical control method also can realize PQ control in grid-connection mode, which can allocate Active and reactive power according to the power dispatch commands. At the same time, hierarchical control method make the output of voltage of inverter controllable either in islanding mode or grid-connection mode, which can achieving a smooth transition between two modes.Secondly, analyzes the decoupling control strategy of three-phase four-leg inver. After setting up the simulition model of the decoupling control strategy of three-phase four-leg inver, the hardware platform and software framework of three-phase four-leg inver system are setted up. The experimental results shows that output voltage of three-phase four-leg inver are symmetrical under erther the conditions of balanced load or the conditions of unbalanced load, which verifies the decoupling control strategy of three-phase inverter are correct and possible.Finally, 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. Simulation model are built in Matlab/Simulink to analyze and verify the performance of controllers designed above The transition process between islanding mode to grid-connection mode are analyt according to the simulation model designed above. The simulation results demonstrate the the proposed hierarchical control strategy and the switching control strategy are effective.