Design and Simulation of Fractional-Order Controllers of Injection in CNG Engines

Injection systems of compressed natural gas engines exhibit large variations in their parameters and working conditions and are characterized by a highly nonlinear behavior. Therefore, to address the issue of robustness and take into account the different equilibrium points, this paper proposes fractional-order controllers combined with a gain scheduling technique. In particular, a fractional-order PI (or FOPI) controller is designed by loop-shaping, approximated by a rational transfer function, and compared by simulation with an integer order gain-scheduled PI controller. The FOPI controller reduces oscillations in the rail pressure. The scheduling of the FOPI gains improves the robustness to changing work conditions.