Advanced sliding mode control for battery-backed hybrid power system in a fuel cell electric vehicle with a fixed-time convergence

This paper explores the behavior of a hybrid power system (HPS) in a fuel cell electric vehicle (FCEV), with a focus on its nonlinear characteristics and inherent uncertainties. The hybrid powertrain incorporates a fuel cell (FC) as the primary energy source, supported by an ultracapacitor (UC) and a battery as secondary energy sources. The system's architecture features DC/DC boost converters connecting the FC to the DC-Link, alongside separate bi-directional converters interfacing the UC and battery with the DC-Link. Dynamic models are developed to accurately capture the nonlinear dynamics of the subsystems. The primary aim is to develop a robust control mechanism that maintains a stable DC bus voltage for the motor drive, even with a wide range of energy source fluctuations. To achieve this, an integral sliding mode controller with fixed-time convergence is introduced to regulate the DC-Link voltage and ensure the current drawn from the sources aligns with the FCEV's speed demands. A suitable energy management strategy is implemented to optimize power distribution among the FC, UC, and battery during different driving conditions, including acceleration and braking. Theoretical analysis, utilizing Lyapunov stability theory, confirms fixed-time convergence of DC-Link voltage and current tracking regardless of initial conditions. Moreover, simulation and Hardware-in-the-Loop (HIL) results demonstrate the proposed control strategy's effectiveness in managing the HPS, highlighting the UC and battery's ability to meet load demands while enhancing fuel cell performance.