Research On Decentralized Robust Control Strategy Of DC-MG Based On Convex Polyhedron Method

DC microgrid is easy to integrate with distributed generation,and has the characteristics of high efficiency and good economy,so it is widely used.When operating a DC microgrid,the switching of distributed generation units,sudden load changes and topology changes will cause bus voltage to fluctuate and reduce the stability of the system.Therefore,it is of great significance to research on the stability control methods of DC microgrid bus voltage.The problem of bus voltage fluctuations caused by uncertain changes in DC microgrids is researched and analysed in depth from three aspects in the thesis.(1)A convex polyhedron method is introduced to improve the robustness of the designed controller under different operating conditions.Firstly,the state space model of the interconnection of two distributed generation units is established,and the deterministic model of the parameters of the DC microgrid with a general topology structure is developed.Then,the convex polyhedron model of the DC microgrid is established to describe the uncertainties of plug-and-play,load mutation and topology changes of distributed generation units in the DC microgrid by convex polyhedron method.(2)A decentralized robust H_∞control strategy for DC microgrid based on convex polyhedron method is studied for system stability problem caused by uncertainty changes in DC microgrid.The asymptotic stability conditions of the distributed generation unit subsystem and the DC microgrid system are obtained by using the extended linear matrix inequality,and the dynamic performance of the distributed generation unit is improved by closed-loop pole position constraints.Then,a decentralized robust controller for DC microgrid based on convex polyhedron method is obtained by solving the convex optimization problem of distributed generation unit subsystem.To observe the dynamic performance of the system,the plug and play,sudden load changes and topology change of distributed generation units in DC microgrid are simulated in MATLAB/Simulink.The results show that the decentralized robust H_∞control based on the convex polyhedron method can effectively maintain the voltage stability and this method can better restrain the bus voltage fluctuation caused by the sudden load changes compared to the robust H_∞control of the parameter deterministic model.(3)A decentralized Tube robust model predictive control strategy based on convex polyhedron method for DC microgrid is studied to reduce the influence of uncertainty changes on the bus voltage of DC microgrid.First,the convex polyhedron model of the DC microgrid is discretization,and the interconnection coupling term is regarded as a disturbance.The convex polyhedron discretization model of the DC microgrid is established.Then,the convex polyhedron discretization model of the DC microgrid is decomposed into the nominal system and the error system.The optimal state trajectory of the distributed generation unit is obtained by solving the model predictive controller.An auxiliary feedback controller is designed for the error system to ensure the asymptotic stability of the error system.To observe the fluctuation of system output voltage,the plug and play,sudden load changes and topology change of distributed generation units in DC microgrid are simulated in MATLAB/Simulink.The results show that the decentralized Tube robust model control based on the convex polyhedron method can effectively suppress the bus voltage fluctuation of the system and this method is more robust to sudden load changes in the DC microgrid compared to the decentralized robust H_∞control method.