Seminar on Industrial Problems

Robust Nonlinear Controller Design: Application to Diesel Engines

May 25, 1998

Presented by: Mrdjan Jankovic, Ford Research Laboratories

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A method of designing robust controllers for nonlinear systems is applied to a turbocharged diesel engine equipped with a variable geometry turbocharger (VGT) and an exhaust gas recirculation (EGR) valve. VGT varies the turbine flow area as a function of the engine operating condition thus providing faster torque response. EGR valve allows controlled recirculation of the exhaust gas into the intake manifold to reduce NOx emissions. However, simultaneous operation of the two actuators results in significant interactions between them. The control design problem is additionally complicated by inherently nonlinear nature of the diesel engine.

For this design problem we propose a recently developed robust control design method which applies to multi-input nonlinear systems with a known control Lyapunov function (CLF). The robustness achieved by the design is the nonlinear equivalent of that guaranteed by the theory for linear optimal regulators: infinite gain margin and 60 degrees phase margin. A CLF is constructed by employing the tools of geometric control theory. Simplicity of the resulting controller is achieved by judiciously choosing the control oriented model and the CLF. Performance will be illustrated by simulations on a detailed model of a diesel engine and by experimental data.

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