Voltage-Current Control in Fully Active Hybrid Energy Storage Systems

The paper presents control design and analysis of the fully active hybrid energy storage systems (HESS) based on batteries and supercapacitors (SC). Using standard averaged model of the bidirectional DC-DC buck-boost power converters, an improved partially feedback linearizing cascaded voltage-current controller has been designed. For stability analysis and controller tuning, the linearized system dynamics is studied. The proposed nonlinear transformations and feedback linearizing controllers allow, for the first time, to justify the tuning of the DC-link voltage and current controllers parameters for the original nonlinear non-minimum phase system using its linear approximation around the trajectories, corresponding to power balance equation. It is shown that a time-scale separation between voltage and current dynamics is required in order to ensure asymptotic stability and desired transient performances. For HESS, a modified frequency decoupling filter is derived with added SC charge current component. A novel SC average voltage controller and its tuning technique guarantee relatively slow dynamics of SC voltage regulation with limited effect on DC-link voltage regulation and currents distribution. The results of simulation study confirm the effectiveness of the proposed control system.