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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


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