Research On Frequency/Voltage Control And Optimal Energy Storage Configuration In Microgrids

As the power industry facing problems like energy shortages and environmental pollution,the microgrid becomes the trend of the future power system.However,there are some problems in the operation and control of the microgrid: 1)When a microgrid is in an island state,due to the loss of support from the external grid and its low inertia,the power disturbance will make the voltage and frequency of the microgrid difficult to stabilize.2)The random power fluctuation of the renewable energy sources and load in microgrid brings hidden dangers to the economic,reliable and safe operation of the microgrid.If a certain amount of energy storage can be properly allocated in the microgrid,it will bring huge benefits to the operation of the microgrid.Therefore,it is of great theoretical significance and engineering application value to study the frequency/voltage control and the optimal energy storage configuration of microgrid.For the frequency and voltage control of islanded microgrid.First,take the recovery of the frequency/voltage and the economic operation of the microgrid into account,set the frequency /voltage recovery index as an objective and the microgrid operating cost as the other,a multiobjective unified optimization model for economic operation and secondary frequency voltage control of island microgrid is established.By using the normalized normal constraint method(NNC)to obtain Pareto solution set,the Pareto frontier point with uniform distribution is obtained,which can fully depict the Pareto frontier and facilitate the selection of the compromise solution in decision-making.We take an actual microgrid as an example to verify the effectiveness of proposed model,and the NNC method is compared with the weight method so as to show the benefits of the NNC method.Then,a microgrid electromagnetic transient simulation model containing wind turbine,photovoltaic,energy storage device and micro gas turbine was established on Simulink platform.Based on the simulation model,the electromagnetic transient simulation of the primary and secondary control of the islanded microgrid is completed.The primary control is completed by building control models,the secondary control signal is obtained by the proposed method in this paper and sent to the local controller.Finally,the simulation curves verified the correctness of the proposed secondary control model.For configuring energy storage capacity to optimize the operation of the grid-connected microgrid.The scenario method and Monte Carlo sampling method are used to deal with the random fluctuation of photovoltaic and load in the microgrid.Based on the economic dispatch of grid-connected microgrid,an energy storage configuration optimization model including photovoltaic and biogas power generation for grid-connected microgrid is established.Configuring energy storage capacity with the goal of reducing the operating costs of the microgrid per day,the investment cost of energy storage,and the power fluctuations of the microgrid tie line,considering the power balance constraint,the limits of the output of all power sources,the energy storage device constraints,unit climbing constraints,the tie line power limits in each scenario,and transfer constraints between scenes.The model is then equivalently simplified to solve more effectively.Finally,the model is verified by an actual microgrid,and the results before and after the simplification is compared.