Nonlinear control of a PEM fuel cell integrated system with water electrolyzer

In this study, a multi-input multi-output (MIMO) sliding mode control (SMC) scheme combined with a couple of low-order nonlinear observers is proposed for a proton exchange membrane fuel cell (PEMFC) integrated with water electrolyzer system. First, the PEMFC is developed coupling with a few auxiliary systems, namely air compressor, air cooler, internal humidifier, and primary, supply and return manifolds. With this, to recycle the unused hydrogen fuel and maintaining the fuel cell system temperature, the model of an ejector and cooling system, respectively, are developed. Subsequently, as a source of hydrogen fuel for the PEMFC integrated system, a proton exchange membrane (PEM) water electrolyzer is modeled. Next, a MIMO sliding mode scheme is proposed to control the fuel cell output voltage, compressor airflow and fuel cell system temperature for the PEMFC, and hydrogen production rate for the electrolyzer. To predict the unmeasured state information required for the SMC, a couple of nonlinear observers, namely adaptive state observer (ASO), sliding mode observer (SMO) and extended Kalman filter (EKF) are constructed using the low-order process model. After investigating the satisfactory state response, these three observers are coupled separately with the SMC. Finally, the comparative control performance of the hybrid SMC-ASO, SMC-SMO and SMC-EKF are evaluated against a conventional proportional integral (PI) controller.