Wastegate Actuator Modeling and Tuning of a PID Controller for Boost Pressure Control
In some turbochargers, boost pressure is reduced by opening the
wastegate valve. In a modern turbo charged car, the most common way
for opening the wastegate is with a pneumatic actuator and an air
control solenoid, controlled by the ECU. In the control systems
studied the ECU utilizes a static feedforward and a PID controller,
for the purpose of making the boost pressure follow its reference
value. With no systematic method for tuning the controller, this can
be time consuming, and a set of well defined experiments to determine
PID parameters are desired.
When test time in a real engine is limited or expensive, it is
advantageous to work in a simulation environment before doing live
tests. A model for the wastegate actuator and air control solenoid is
developed in the thesis. This is used to simulate controller
performance before any tests in a real car is performed.
In the thesis a tuning method for the PID controller based on step
responses is proposed. The tuning method evaluated is the IMC-choice
of controller for a second order system, and it has a single design
parameter not given by the experiments. The controller is shown to
give desired behavior when the static feedforward is correct or has
small error.
Andreas Thomasson
2009
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