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energy storages can be characterized based on energy and power densities, ramp rate, etc. Hybridization takes advantages of all energy storages to enhance system performance. Hierarchical control which is comprised of both centralized and distributed control is proposed for HESS operation in this paper. In normal state, system operates with energy management system. The central controller is used to coordinate the power sharing among various energy storages based on their characteristics and operating statuses. In case of communication failure, distributed control which operates with local information is to be activated. The bus voltage is used as indicator for system power balance to realize distributed control of system units. MATLAB/Simulink is used for the verification of the proposed methods.

Power sharing performance is a critical issue of hybrid energy storage system (HESS) in autonomous DC microgrid (MG). In this paper, a novel integral droop (ID) is proposed to mimic dynamic characteristics of the capacitor by using energy storages (ESs) with quick response. The main advantage of the proposed controller is that dynamic power sharing among ESs is automatically realized in the decentralized level. For a given HESS, ESs with the proposed ID enables to compensate fast power change while ESs with conventional voltage-power (V-P) droop provide low frequency components of power demand. With coordinated control between ID and V-P droop, high/low pass filters (LPF/HPF) are intrinsically formulated in HESS in order to obtain reasonable dynamic power allocations among ESs. Matlab/Simulink model of HESS is established for the verification of ID controller, in which the impacts of different ID coefficients on transient performances of the system are analyzed in detail. Finally, the effectiveness of proposed ID is experimentally validated on a HIL (hardware in loop) HESS platform.

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