Modeling and stability analysis of hybrid energy storage system under hierarchical control

Energy storages (ESs) are widely used in DC distribution system to compensate power imbalance. Hybrid energy storage system (HESS), which combines various ESs, can optimize energy density, power density and dynamic response. Hierarchical control of HESS is shown able to achieve dynamic power sharing among ESs with improved system reliability. However, system stability of HESS under hierarchical control, which is essential for parameter design and system operation, has not been investigated. In addition, with high penetration of constant power loads (CPLs) in DC distribution system, impact of CPL on system stability should be studied. This paper investigates stability problem in HESS with CPL under hierarchical control. A detailed small signal model for stability analysis is developed. Impacts of CPL and system parameters are analyzed. Effectiveness of the control strategy and analytical results are validated by time domain simulations.