Primary frequency H∞ control in stand-alone microgrids with storage units: A robustness analysis confirmed by real-time experiments

This paper proposes a robust H-infinity control design approach for primary frequency regulation in a diesel-photo-voltaic (PV)-storage hybrid power generation system operating in stand-alone mode. Based on real-time digital simulators, namely RT-LAB (R) and dSPACE (R), a rapid-prototyping test bench composed of a real supercapacitor-based energy storage system (ESS) and an emulated diesel-PV-load grid is developed in order to experimentally validate this frequency control strategy under realistic operating conditions. Starting from given desired dynamic specifications, a multi-variable H-infinity controller is designed via the linear matrix inequalities (LMI) method. In the second step, uncertainty in the steady-state value of the supercapacitor state of charge (SoC) is considered and a robustness analysis using mu-analysis is performed in order to determine its maximum variation range for which the imposed closed-loop performances are respected for the considered operating point. MATLAB (R)/Simulink (R) time-domain simulations and real-time experiments show the effectiveness of the proposed robust control approach. Then, a series of real-time experiments are performed to validate the controller's robustness and performance in the presence of various load disturbances and SoC uncertainty.