Improving Lifetime of Fuel Cell in Hybrid Energy Management System by Lure-Lyapunov-Based Control Formulation

Fuel cell (FC) is emerging as a clean and non-pollutant energy source and is being used widely in most of the transport and microgrid applications. However, certain applications demanding fast dynamic response are restricting usage of FC on account of its lifetime issues. Slow dynamic response of FC is not suitable to provide transient load demands, typically arising in electrical vehicles during acceleration and in braking. This paper presents a novel control strategy and associated power electronics for such applications. We propose a Lure-Lyapunov-based controller executed in cascade mode for the control of hybrid energy management system of FC and ultracapacitor (UC). In the proposed scheme, UC responds to transients in load demand whereas FC takes care of the nominal load bus requirements. This combination helps in improving lifetime of FC as auxiliary storage device such as UC provides a cushion for sudden transients. The proposed control strategy also helps in maintaining state of charge of UC for better performance. The inherent nonlinearities in DC-DC converter are efficiently handled by the outer-loop Lure-Lyapunov framework. Mathematical modeling and a proof for absolute stability of the system is presented. The proposed controller strategy is robust by virtue of being passivity based control methodology. The paper also presents analysis of the required power electronics involving DC-DC converters and inner-loop current control action. The synthesized controller is experimentally validated and the results are presented with their analysis.