Innovative power management of hybrid energy storage systems coupled to RES plants: The Simultaneous Perturbation Stochastic Approximation approach

To account for renewable energy sources stochastic nature, storage devices are often coupled in integrated systems. This paper addresses a power management strategy for a Li-ion battery / flywheel hybrid energy storage system coupled to a PV array for an interconnected microgrid application. The power sharing among the storage devices and the power grid is based on the Simultaneous Perturbation Stochastic Approximation (SPSA) algorithm, aiming two objectives: a smoother battery profile (emphasizing flywheel peak shaving capability) and lower energy exchanges with the mains. PV generation profile, load profile and torque-speed saturation curve of the electrical machine driving the flywheel are considered, based on real records and measurements. Microgrid model is implemented in Matlab/Simulink environment. The outcomes of this study prove that a power management strategy based on SPSA reduces significantly the sudden variations of the power imposed to the battery in terms of the current's slope. Furthermore, the stochastic approach allows an enhanced robustness, results being consistent regardless the initial state of charge of the battery and the meteorological conditions (i.e. PV production).