94 research outputs found
A Human Driver Model for Autonomous Lane Changing in Highways: Predictive Fuzzy Markov Game Driving Strategy
This study presents an integrated hybrid solution to mandatory lane changing problem
to deal with accident avoidance by choosing a safe gap in highway driving. To manage
this, a comprehensive treatment to a lane change active safety design is proposed from
dynamics, control, and decision making aspects.
My effort first goes on driver behaviors and relating human reasoning of threat in
driving for modeling a decision making strategy. It consists of two main parts; threat assessment
in traffic participants, (TV s) states, and decision making. The first part utilizes
an complementary threat assessment of TV s, relative to the subject vehicle, SV , by evaluating
the traffic quantities. Then I propose a decision strategy, which is based on Markov
decision processes (MDPs) that abstract the traffic environment with a set of actions, transition
probabilities, and corresponding utility rewards. Further, the interactions of the TV s
are employed to set up a real traffic condition by using game theoretic approach. The question
to be addressed here is that how an autonomous vehicle optimally interacts with the
surrounding vehicles for a gap selection so that more effective performance of the overall
traffic flow can be captured. Finding a safe gap is performed via maximizing an objective
function among several candidates. A future prediction engine thus is embedded in the
design, which simulates and seeks for a solution such that the objective function is maximized
at each time step over a horizon. The combined system therefore forms a predictive
fuzzy Markov game (FMG) since it is to perform a predictive interactive driving strategy
to avoid accidents for a given traffic environment. I show the effect of interactions in decision
making process by proposing both cooperative and non-cooperative Markov game
strategies for enhanced traffic safety and mobility. This level is called the higher level
controller. I further focus on generating a driver controller to complement the automated
car’s safe driving. To compute this, model predictive controller (MPC) is utilized. The
success of the combined decision process and trajectory generation is evaluated with a set
of different traffic scenarios in dSPACE virtual driving environment.
Next, I consider designing an active front steering (AFS) and direct yaw moment control
(DYC) as the lower level controller that performs a lane change task with enhanced
handling performance in the presence of varying front and rear cornering stiffnesses. I propose
a new control scheme that integrates active front steering and the direct yaw moment
control to enhance the vehicle handling and stability. I obtain the nonlinear tire forces
with Pacejka model, and convert the nonlinear tire stiffnesses to parameter space to design
a linear parameter varying controller (LPV) for combined AFS and DYC to perform a
commanded lane change task. Further, the nonlinear vehicle lateral dynamics is modeled
with Takagi-Sugeno (T-S) framework. A state-feedback fuzzy H∞ controller is designed
for both stability and tracking reference. Simulation study confirms that the performance
of the proposed methods is quite satisfactory
Vehicle Stability Control Considering the Driver-in-the-Loop
A driver‐in‐the‐loop modeling framework is essential for a full analysis of vehicle stability
systems. In theory, knowing the vehicle’s desired path (driver’s intention), the problem is reduced
to a standard control system in which one can use different methods to produce a (sub) optimal
solution. In practice, however, estimation of a driver’s desired path is a challenging – if not
impossible – task. In this thesis, a new formulation of the problem that integrates the driver and
the vehicle model is proposed to improve vehicle performance without using additional
information from the future intention of the driver.
The driver’s handling technique is modeled as a general function of the road preview information
as well as the dynamic states of the vehicle. In order to cover a variety of driving styles, the time‐
varying cumulative driver's delay and model uncertainties are included in the formulation. Given
that for practical implementations, the driver’s future road preview data is not accessible, this
information is modeled as bounded uncertainties. Subsequently, a state feedback controller is
designed to counteract the negative effects of a driver’s lag while makes the system robust to
modeling and process uncertainties.
The vehicle’s performance is improved by redesigning the controller to consider a parameter
varying model of the driver‐vehicle system. An LPV controller robust to unknown time‐varying
delay is designed and the disturbance attenuation of the closed loop system is estimated. An
approach is constructed to identify the time‐varying parameters of the driver model using past
driving information. The obtained gains are clustered into several modes and the transition
probability of switching between different driving‐styles (modes) is calculated. Based on this
analysis, the driver‐vehicle system is modeled as a Markovian jump dynamical system. Moreover,
a complementary analysis is performed on the convergence properties of the mode‐dependent
controller and a tighter estimation for the maximum level of disturbance rejection of the LPV
controller is obtained. In addition, the effect of a driver’s skills in controlling the vehicle while the
tires are saturated is analyzed. A guideline for analysis of the nonlinear system performance with
consideration to the driver’s skills is suggested. Nonlinear controller design techniques are
employed to attenuate the undesirable effects of both model uncertainties and tire saturation
Robust Discrete-Time Lateral Control of Racecars by Unknown Input Observers
This brief addresses the robust lateral control problem for self-driving racecars. It proposes a discrete-time estimation and control solution consisting of a delayed unknown input-state observer (UIO) and a robust tracking controller. Based on a nominal vehicle model, describing its motion with respect to a generic desired trajectory and requiring no information about the surrounding environment, the observer reconstructs the total force disturbance signal, resulting from imperfect knowledge of the time-varying tire-road interface characteristics, presence of other vehicles nearby, wind gusts, and other model uncertainty. Then, the controller actively compensates the estimated force and asymptotically steers the tracking error to zero. The brief also presents a closed-loop stability proof of the method, ensuring perfect asymptotic estimation and tracking by the controlled vehicle. The proposed solution advantageously needs no a-priori information about the total disturbance boundedness, additional variables to model uncertainty, or observer parameters to be tuned. Its effectiveness and superiority to existing methods are studied in theory and shown in simulations where a full racecar model, based on the vehicle dynamics blockset, is required to track aggressive maneuvers. Through a faster and more accurate disturbance estimation, the solution robustly ensures better dynamic responses even with measurement noise
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