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Frequency stability of microgrids based on H∞ methods

The widespread use of renewable energy in microgrid power systems would cause frequency fluctuation. Discussed in this work, is the frequency stability of the microgrid consisting of wind power systems, photovoltaic systems, micro-turbines, electrolyzers and fuel cells with the variation of load power. A novel robust controller is designed for the microgrid to suppress frequency fluctuation by tuning the output of the micro-turbine, electrolyzer and fuel cell. The generation-rate constraint of the micro-turbine is investigated. By integrating the switching states of the fuel cell and electrolyzer with the micro-turbine power output in order to prevent too large changing rate of the micro-turbine power and improve the utilization of renewable energy. It is well known that the key point of design a H∞ mixed sensitivity controller is how to select appropriate weighting functions. However, there are no effective rules to do it. For this reason, the Particle Swarm Optimization (PSO) algorithm is used to optimize the weighting functions to enable the system to achieve optimal performance. Simulation results show that the mentioned frequency control strategy can effectively stabilize the frequency fluctuation and improve the utilization of renewable energy, and is still effective for the case of large-scale renewable energy penetration.