Modeling and control of actuators and co-surge in turbocharged engines
The torque response of the engine is important for the driving
experience of a vehicle. In spark ignited engines, torque is
proportional to the air flow into the cylinders. Controlling torque
therefore implies controlling air flow. In modern turbocharged
engines, the driver commands are interpreted by an electronic control
unit that controls the engine through electromechanical and pneumatic
actuators. Air flow to the intake manifold is controlled by an
electronic throttle, and a wastegate controls the energy to the
turbine, affecting boost pressure and air flow. These actuators and
their dynamics affect the torque response and a lot of time is put
into calibration of controllers for these actuators. By modeling and
understanding the actuator behavior this dynamics can be compensated
for, leaving a reduced control problem, which can shorten the
calibration time.
Electronic throttle servo control is the first problem studied. By
constructing a control oriented model for the throttle servo and
inverting that model, the resulting controller becomes two static
compensators for friction and limp-home nonlinearities, together with
a PD-controller. A gain-scheduled I-part is added for robustness to
handle model errors. The sensitivity to model errors is studied and a
method for tuning the controller is presented. The performance has
been evaluated in simulation, in test vehicle, and in a throttle
control benchmark.
A model for a pneumatic wastegate actuator and solenoid control valve,
used for boost pressure control, is presented. The actuator dynamics
is shown to be important for the transient boost pressure
response. The model is incorporated in a mean value engine model and
shown to give accurate description of the transient response. A tuning
method for the feedback (PID) part of a boost controller is proposed,
based on step responses in wastegate control signal. Together with
static feedforward the controller is shown to achieve the desired
boost pressure response. Submodels for an advanced boost control
system consisting of several vacuum actuators, solenoid valves, a
vacuum tank and a vacuum pump are developed. The submodels and
integrated system are evaluated on a two stage series sequential turbo
system, and control with system voltage disturbance rejection is
demonstrated on an engine in a test cell.
Turbocharged V-type engines often have two parallel turbochargers,
each powered by one bank of cylinders. When the two air paths are
connected before the throttle an unwanted oscillation can occur. When
the compressors operate close to the surge line and a disturbance
alters the mass flow balance, the compressors can begin to alternately
go into surge, this is called co-surge. Measurements on co-surge in
parallel turbocharged engines are presented and analyzed. A mean value
engine model, augmented with a Moore-Greitzer compressor model to
handle surge, is shown to capture the co-surge behavior. A sensitivity
analysis shows which model parameters have the largest influence of
the phenomena. The compressor operation in the map during co-surge is
studied, and the alternating compressor speeds are shown to have a
major impact on the continuing oscillation. Based on the analysis,
detection methods and a controller are proposed, these detect co-surge
and control the turbo speeds to match during co-surge. The
controller is evaluated both in simulation and on a test vehicle in a
vehicle dynamometer, showing that co-surge can be detected and the
oscillations quelled.
Andreas Thomasson
2014
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Senast uppdaterad: 2021-11-10
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