Frequency domain design of fractional order PI controllers for lambda control

This paper proposes the frequency domain design of fractional order proportional-integral (FOPI) controllers for lambda control in the framework of automotive engine control systems. A simplified first order plus dead time model of the process is used in the design. The flatness of the open-loop Bode phase plot around the gain crossover frequency is imposed as a constraint in the frequency domain design that results in tuning conditions for FOPI controllers. The comparison of FOPI versus integer order PI controllers is supported by digital simulation results.