Equalization strategy for fast energy regulation of supercapacitor in hybrid energy storage system

In hybrid energy storage system (HESS) composed of the battery pack and supercapacitor (SC), power allocation technology can improve the service life of the system. However, the serious imbalance charging and discharging of HESS may degrade the performance of power allocation, especially when the energy of SC is saturated or exhausted due to non-alternating load changes. This paper presents a power allocation method with energy bus based equalization technology for HESS. An equalization algorithm based on model predictive control (MPC) is used to not only balance the state of charge (SOC) of cells in the battery pack, but also regulate the SOC of SC stably at a reference point. It can prevent SC from energy saturation and exhaustion due to non-alternating load changes effectively, which allows smaller capacitance of SC to reduce the size and cost significantly. Furthermore, a high-pass filter (HPF) and low-pass filter (LPF) based droop controller for power allocation of the HESS is designed to separate high-frequency component of power to the SC and low-frequency component of that to the battery pack, and improve dynamic response of the bus voltage of power allocation. Simulation and experimental results verify the performance of the presented method.