Study On Distributed Optimization Control Approach For Microgrid Based On Multi-agent Theory

As an effective manager for distributed generation, microgrid plays an importantrole in clean energy development, stability and reliability of future distribution network,and can also improve the penetration of renewable energy. However, DGs in microgridare characterized by fluctuation and intermittent and microgrids are distributedembedded into distribution network, which lead to the microgrid and microgrids indistribution network is difficult to control. The research of optimization control methodfor microgrid and coordination control strategy between microgrids could providevaluable references for reliable and economic operation of microgrid and developmentof smart distribution network.Generally, different controllable level of microgrid has different operation mode,where the local constraints for optimization control are varied and sometime the globalinformation is not available. For these complex distribution networks withmulti-microgrid, the centralized optimization control method is not suitable for dealingwith the control problem because of model building and computing cost, but it issuggested that multi-agent based distributed control method should be good at solvingsuch problems. Therefore, a hybrid microgrid optimization control framework is buildin this thesis based on multi-agent control theory, and the corresponding optimizationcontrol algorithms and strategies from top to bottom structure are designed for differentoperating environment. First, a distributed constrained optimization algorithm which isused to distributed optimization control for microgrid is proposed on the top controllevel of multi-microgrid; Second, in order to maintain a rapid control advantage ofcentralized method for small system, a centralized optimization algorithm is presentedin the middle control level for single microgrid; Finally, different execution controlapproaches for different DG at the bottom control level in microgrid are build. The mainresearch contents of this thesis are shown as follows:(1) Based on multi-agent theory, the optimization control system of microgrid isestablished first in this thesis, where the distributed control problem is regarded as adistributed constraint optimization problem (DCOP). To meet the requirement ofpotential game theory, the distributed optimization control algorithm WRM-DSAN isproposed. In this algorithm, global optimization that is based on local searching can beexecuted due to the communication between Agents and optimization control rules. Test results show that the proposed distributed optimization algorithm can satisfy therequirement of distributed design structure and the algorithm can converge to globaloptimal Nash equilibrium almost everywhere. It is proved that distributed optimizationalgorithm is more suitable for solving complex system problems in contrast withcentralized algorithms.(2) Distribution network with microgrids is build based on the IEEE39system.According to DCOP theory, the optimization control model of microgrid is consideredas an distributed constraint optimization problem. Utility function for each Agent inmicrogrid are formulated with the local optimization constraints. And potential gamedistributed optimization algorithm, WRM-DSAN, is applied to solve this distributedconstraint optimization problems. Under the ring and mesh control structure, theoptimal control results are analyzed, and it is indicated that distributed optimizationcontrol method is viable for multi-microgrid. After optimization, it is easy to find thatthe mesh control structure has better fault tolerance ability.(3) Firstly, a centralized optimization control algorithm IEPSO is designed fordynamic centralized control of small microgrid system. Then a dynamic centralizedoptimization control model of microgrid is established, including DG placement model,wind power and load fluctuation model and centralized optimization controlmathematical model. Considering the change of load and DG, energy storage controlstrategy of microgrid is formulated, and the effects of different DG contribution rate onthe optimal operation are analyzed. Results indicate that the dynamic DG contributionrate can provided more effective coordination control.(4) Microgrid simulation platform is built under the standard of CERTS with windpower, small hydro and energy storage model. Control performance of microgrid issimulated under island operation mode. Finally, the digital simulation platform ofmicrogrid is built in Matlab/simulink for future research of microgrid control.