In MATLAB, the closed-loop control of a fuel cell system with a buck converter involves designing and implementing control algorithms to regulate the output voltage of the buck converter and manage the operation of the fuel cell. The closed-loop control system typically consists of feedback mechanisms that continuously monitor the output voltage and adjust the duty cycle of the buck converter to maintain the desired voltage level. Additionally, the control system may include algorithms to manage the fuel cell's operating conditions, such as current and temperature, to ensure optimal performance and longevity. MATLAB provides tools for designing and simulating control algorithms for such systems, enabling engineers to optimize the efficiency and stability of fuel cell-based power generation systems integrated with buck converters.