Micro-grid Frequency Control Based On H_∞ Mixed Sensitivity

Renewable energy is always rich in remote areas, highlands, islands, constructing long-distance transmission lines and building substations were too expensive, maintaining fees were high, losses of transmission process were huge. Micro-grid has become an important research subject. Output power fluctuation of wind power system, photovoltaic power system, and user loads’ fluctuation lead to micro-grid power unbalance, micro-grid frequency fluctuated. Stable frequency is an important performance index of power micro-grid, this paper did research in micro-grid frequency control based on mixed sensitivity of H∞ robust control.Robust control method was discussed in this paper, as well as H∞ robust control theory which based on mixed sensitivity; The parameterization method of building weighting functions was proposed based on the current ways of building weighting function were too difficult in the process of design robust H∞ controller with mixed sensitivity theory, the proposed method overcome shortcoming that it’s need too much experience in the process of building weighting function; Then, the way of optimizing the weighting function parameters with particle swarm optimization and genetic algorithm was proposed, and the optimization process was separated with several steps, made the built weighting functions more reasonable; The interactive GUI interface was designed based on the proposed method of building weighting functions, it can completely optimize the parameter of weighting functions by inputting controller objects and constrains, and the optimized results, time and performances were showed on the GUI interface, so that weighting functions’ building and parameters’ optimization were more intuitive and convenient; The model of micro-grid frequency control was set up, the strategy of micro-grid frequency control was proposed after analyzing the controllability of each distributed generator; The micro-grid frequency H∞ controller was designed based on robust control theory, particle swarm optimization and the proposed method of building weighting functions for the proposed control strategy,.To analyze effectiveness of the proposed method and to analyses control performances of the H∞ controller, the analysis was made from time domain and frequency domain based on micro-grid with H∞ control. The simulation was simultaneously did on the Simulink, simulation results show that the micro-grid frequency fluctuation was controlled under standard limits with H∞ controller, and the proposed method of designing H∞ controller was effective. Furthermore, the analysis compare with PI control was made, the results show that the H∞ control performance was more superior when plus the load or minus the load by suddenly, and the robustness was more good too.