Modeling and Control of an Electro-Pneumatic Actuator System Using On/Off Valves
To control the exhaust gas recirculation (EGR) and the exhaust brake, the position
of a butterfly valve connected to a piston inside a pneumatic cylinder is controlled
by altering the pressure inside the cylinder. This thesis evaluates the possibility
to do this with pulse width modulation (PWM) controlled On/Off valves. The
whole electro-pneumatic actuator system is built out of two On/Off valves and a
cylinder.
A mathematical model of the system is constructed. The complete system
model on state space form consists of nine states and is nonlinear. The model
captures the dynamics of the system. The statics of the system is not captured
as accurately. The model is still good enough to be used as aid when developing
control strategies, since position feedback is available.
Automatic control strategies for the system are first developed and tested in
simulation. The first approach is PID control. Because of the nonlinear properties
of the system the results from a PID with a constant proportional part is unsat-
isfactory. To cope with the nonlinearities, a fuzzy controller is constructed; the
results prove somewhat better, but not as good as expected due to implementation
difficulties.
In a test bench the system is controlled by a P controller with feedforward from
position. The feedforward strongly reduces the nonlinear behavior of the system.
With this implementation the results that were hoped for with the fuzzy controller
are reached.
Klas Håkansson and Mikael Johansson
2007
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