Multi-Agent Based Distributed Coordinated Control Of Mode Switching In Microgrid

Nowadays, our country is in the development of industrialization and urbanization process. Energy demand continues to grow and depends on external input. The environmental pressure is very big. The shortage of the energies and the environment problem make our country to use the renewable energy and the micro-grid. In different running mode, the stability of micro-grid containing some distributed energies is one of the problems to be worked out. So the control schemes in this paper are used to ensure the voltage and frequency performance when facing the outside interference and during the microgrid mode switching.Firstly, to ensure the voltage stability in the microgrid under the condition of outside interference, a mixed control method combing with the Multi-Agent technology is proposed. There are two levels in the Multi-Agent system. In the lower level, the decentralized controller is a two loop controller. One is the power controller using the droop characteristic. Another is the voltage current controllers using the fractional order PID. In the upper level, the coordinated controller uses the robust control. And build the risk indices of voltage stability to decide whether to start the upper controller. In the small disturbance, the decentralized controller can effectively compensate the voltage variation. If the large disturbance occurs, the coordinated controller starts. The two controllers restrain the interference to maintain the voltage stability.Secondly, a hierarchical control method uses to pledge the stability of the voltage and frequency in the micro-grid mode switching. In the first stage, the research focuses on constructing a hybrid control scheme, where besides that the storage 1 unit needs to implement switching control strategy by means of an upper-level switching controller, the storage 2 unit that acts as a master unit also needs to be switched between two kinds of control modes including droop control and PQ control in response to different micro-grid operating modes, and other slave DGs units operate in PQ control scheme all the time. Moreover, during the operation mode conversion, according to the assessment indexes regarding voltage and frequency, the upper-level switching controller determines to send switching commands to the storage 1 unit and storage 2 unit. In the second stage, the research focuses on designing the hierarchical control strategies in the PQ control mode and the droop control mode, as well as the upper-level switching controller to guarantee the stabilization performance of the micro-grid during operation mode conversion. In the PQ control mode, all controllers except storage 1 are designed as fractional order PID controller. In the droop control mode, the outer-loop power controllers of the master unit are designed based on droop characteristics, and the inner-loop voltage and current controllers are designed as fractional order PID controller. The upper-level switching controller is designed by means of multiple Lyapunov robust stability method.Finally, the simulations are used to show that the two control strategies are the effectiveness and rationality.