Dynamic power sharing strategy for hybrid energy storage system based on sliding mode control

This paper presents a strategy to control the dynamic power sharing in a hybrid energy-storage system (HESS). The HESS is composed of a battery array of 24 V, a supercapacitor module of 16 V and 2 DC-DC converters allowing the connection of the system to an extra low voltage DC (ELVDC) bus of 48 V within a hybrid microgrid. The proposed strategy consists in a nested loop controller per converter enforcing charge and discharge regimes of the energy storage devices (ESD). The charging modes of the ESD are independent, whereas the discharging modes are coupled. Namely, the supercapacitor module injects power and regulates the ELVDC bus voltage, while the battery array injects the energy into the bus to maintain the levels imposed by the supercapacitor module until its contribution is cancelled. Furthermore, the battery array slowly injects the additional energy needed to restore the optimal supercapacitor voltage. Operation modes and transitions of the HESS control strategy are synthesized in a secondary control level. The entire proposal is validated through simulation results with scenario-based tests, where the modes of operations and the transient response to different loads and boundary conditions are verified.