Fractional order control of the injection system in a CNG engine

Common rail injection systems of compressed natural gas (CNG) engines require robust control, because of large variations in their parameters and working conditions and because of their highly nonlinear behavior. This paper shows that a noninteger (fractional) order PI (or FOPI) controller, designed by a loop-shaping approach, improves robustness to parameter variations and guarantees an optimal performance. Efficacy of the FOC is tested by simulation based on a CNG linearized model and on the approximation of the FOC by a rational transfer function.