Non-linear Compensator for handling non-linear Effects in EGR VGT Diesel Engines
A non-linear compensator is investigated for handling of non-linear
effects in diesel engines. This non-linear compensator is a non-linear
state dependent input transformation that is developed by inverting
the models for EGR-flow and turbine flow having actuator position as
input and flow as output. The non-linear compensator is used in an
inner loop in a control structure for coordinated control of
EGR-fraction and oxygen/fuel ratio. A stability analysis of the
open-loop system with a non-linear compensator shows that it is
unstable in a large operating region. This system is stabilized by a
control structure that consists of PID controllers and
min/max-selectors. The EGR flow and the exhaust manifold pressure are
chosen as feedback variables in this structure. Further, the
set-points for EGR-fraction and oxygen/fuel ratio are transformed to
set-points for the feedback variables. In order to handle model errors
in this set-point transformation, an integral action on oxygen/fuel
ratio is used in an outer loop. Experimental validations of the
proposed control structure show that it handles nonlinear effects, and
that it reduces EGR-errors but increases the pumping losses compared
to a control structure without non-linear compensator.
Johan Wahlström and Lars Eriksson
2009
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