Sliding Mode Integral Separation PID Control for Hydrogen Fuel Cell Systems

Abstract

The stability of hydrogen fuel cell system power generation is affected by key variables such as oxygen excess ratio (OER), electric stack temperature, and cathode–anode differential pressure. To increase the fuel cell’s stability, a sliding mode integral separation proportional–integral–derivative (SMC−IS−PID) control strategy was proposed by combining the four−segment integral separation PID (IS−PID) control with the switching control in the sliding mode control (SMC). The control mode is selected through the system variable error and the current variable value; if there are significant systematic variable errors, the switching control in the SMC adopts the four−segment integral separation PID control, which determines the values of the segmentation thresholds and controls the integral weights to reduce the amount of overshoot. When the error of the system variables is small, the switching control in the SMC adopts the improved convergence law control, which introduces the hyperbolic tangent exponential power term, the nonlinear function term, and the saturation function term to improve the convergence law and decrease the control’s convergence time. Experimentally verifying the effectiveness of the control strategy above, the results show that for the OER, the SMC−IS−PID overshoots 0 and realizes no overshooting with a regulation time of 5.019 s. For the temperature of the stack, the SMC−IS−PID overshoots only 0.134% with a regulation time of 40.521 s. For the pressure of the stack, the SMC−IS−PID realizes the system is basically free of oscillation.