Research On Control And Energy Management Strategies In A Microgrid

As the problems of energy shortage, environmental pollution and power demand growing become increasingly serious, microgrid is the effective means to use renewable energy and solve potential problems of centralized power supply. It has important role and significance to apply clean and safe PV power generation units in the microgrid. Consequently, this paper has researched on microgrid combined with PV power generation units and battery energy storage unit, for the purpose of using clean energy, relieving pressure of power supply and improving power supply reliability.According to the microgrid structure and integrated control target, control strategies of PV power generation units during grid-connected mode were designed. By adding shadow judgement algorithm into perturbation and observation method, the maximum power point tracking for PV array under normal sunlight and partially shaded condition has been achieved. Since conventional control technology for PV array and charging or discharging methods for storage battery fail to meet stable operation requirements during island mode, suitable control strategies for PV array and battery have been designed. Moreover, overall control strategies with a center controller, combined with master-slave control and peer control were adopted to achieve parallel operation for interface inverters in the microgrid.Based on steady-state operation, novel energy management strategies were put forward, according to several energy supply and demand situations between PV power generation units and loads. Battery charging or discharging current was adjusted. Meanwhile, the cycling times of battery charging and discharging were limited properly and battery state was monitored. In addition, dc bus voltage of PV power generation unit was fine-tuned. As a result, energy balance with sunlight or loads changing during island mode was maintained. Since control strategies of interface inverters changed between grid-connected mode and island mode, the judgement conditions and control strategies for mode changing were researched in details to realize smooth transition between two modes.In MATLAB/Simulink environment, the simulation model of microgrid was established, and simulation analysises were accomplished on the maximum power point tracking for PV array, battery charging and discharging, Droop control of interface inverters, energy management of grid-connected mode, island mode and transition between two modes. The simulation results verified that the control and energy management strategies were correct and effective. Then the experimental platform has been built, and experiments of PV power generation units during grid-connected mode and island mode have been completed.