130 research outputs found
EMS control system design for a Maglev vehicle - a critical system
For the effective operation of a magnetically levitated (maglev) vehicle using electro-magnetic suspension, it is necessary that the airgap between the guideway and the levitating magnets is maintained. Such systems, where the output is required to remain strictly within bounds, are known as critical systems. This paper describes the design of the suspension system for a high-speed maglev vehicle which ensures that the airgap is maintained
On the Minimization of Maximum Transient Energy Growth.
The problem of minimizing the maximum transient energy growth is considered.
This problem has importance in some fluid flow control problems and other
classes of nonlinear systems. Conditions for the existence of static controllers
that ensure strict dissipativity of the transient energy are established and an
explicit parametrization of all such controllers is provided. It also is shown
that by means of a Q-parametrization, the problem of minimizing the maximum
transient energy growth can be posed as a convex optimization problem that can
be solved by means of a Ritz approximation of the free parameter. By considering
the transient energy growth at an appropriate sequence of discrete time points,
the minimal maximum transient energy growth problem can be posed as a
semidefinite program. The theoretical developments are demonstrated on a
numerical example
Gain-scheduled H∞ control via parameter-dependent Lyapunov functions
Synthesising a gain-scheduled output feedback H∞ controller via parameter-dependent Lyapunov functions for linear parameter-varying (LPV) plant models involves solving an infinite number of linear matrix inequalities (LMIs). In practice, for affine LPV models, a finite number of LMIs can be achieved using convexifying techniques. This paper proposes an alternative approach to achieve a finite number of LMIs. By simple manipulations on the bounded real lemma inequality, a symmetric matrix polytope inequality can be formed. Hence, the LMIs need only to be evaluated at all vertices of such a symmetric matrix polytope. In addition, a construction technique of the intermediate controller variables is also proposed as an affine matrix-valued function in the polytopic coordinates of the scheduled parameters. Computational results on a numerical example using the approach were compared with those from a multi-convexity approach in order to demonstrate the impacts of the approach on parameter-dependent Lyapunov-based stability and performance analysis. Furthermore, numerical simulation results show the effectiveness of these proposed techniques
A Unifying Framework for Finite Wordlength Realizations.
A general framework for the analysis of the finite
wordlength (FWL) effects of linear time-invariant digital filter
implementations is proposed. By means of a special implicit system
description, all realization forms can be described. An algebraic
characterization of the equivalent classes is provided, which
enables a search for realizations that minimize the FWL effects
to be made. Two suitable FWL coefficient sensitivity measures
are proposed for use within the framework, these being a transfer
function sensitivity measure and a pole sensitivity measure. An
illustrative example is presented
Fault tolerant control of a quadrotor using L-1 adaptive control
Purpose – The growing use of small unmanned rotorcraft in civilian applications means that safe operation is increasingly important. The purpose of this paper is to investigate the fault tolerant properties to faults in the actuators of an L1 adaptive controller for a quadrotor vehicle.
Design/methodology/approach – L1 adaptive control provides fast adaptation along with decoupling between adaptation and robustness. This makes the approach a suitable candidate for fault tolerant control of quadrotor and other multirotor vehicles. In the paper, the design of an L1 adaptive controller is presented. The controller is compared to a fixed-gain LQR controller.
Findings – The L1 adaptive controller is shown to have improved performance when subject to actuator faults, and a higher range of actuator fault tolerance.
Research limitations/implications – The control scheme is tested in simulation of a simple model that ignores aerodynamic and gyroscopic effects. Hence for further work, testing with a more complete model is recommended followed by implementation on an actual platform and flight test. The effect of sensor noise should also be considered along with investigation into the influence of wind disturbances and tolerance to sensor failures. Furthermore, quadrotors cannot tolerate total failure of a rotor without loss of control of one of the degrees of freedom, this aspect requires further investigation.
Practical implications – Applying the L1 adaptive controller to a hexrotor or octorotor would increase the reliability of such vehicles without recourse to methods that require fault detection schemes and control reallocation as well as providing tolerance to a total loss of a rotor.
Social implications – In order for quadrotors and other similar unmanned air vehicles to undertake many proposed roles, a high level of safety is required. Hence the controllers should be fault tolerant.
Originality/value – Fault tolerance to partial actuator/effector faults is demonstrated using an L1 adaptive controller
Evaluating the Rationale for Folding Wing Tips Comparing the Exergy and Breguet Approaches
The design and development processes for future aircraft aims to address the environmental and efficiency challenges needed to facilitate the engineering of concepts that are far more integrated and require a multidisciplinary approach. This study investigates the benefit of incorporating span extension wing tips onto future aircraft configurations as a method of providing improved aerodynamic efficiency, whilst allowing the extension to fold on the ground to meet airport gate size constraints. Although the actuated wing tips are not studied in detail, the focus of this study is to compare two different methods of analysis that can be used to identify the benefit and limitations of adding such devices. The two methods considered are a quasi-steady implicit energy analysis based on the Breguet Range Equation and an explicit energy analysis based on the first and second laws of thermodynamics known as Exergy Analysis. It has been found that both methods provide agreeable results and have individual merits. The Breguet Range Equation can provide quick results in early design, whilst the Exergy Analysis has been found to be far more extensive and allows the complete dynamic behaviour of the aircraft to be assessed through a single metric. Hence, allowing comparison of losses from multiple subsystems
Decision-making for unmanned aerial vehicle operation in icing conditions
With the increased use of unmanned aerial systems
(UAS) for civil and commercial applications, there is
a strong demand for new regulations and technology that
will eventually permit for the integration of UAS in
unsegregated airspace. This requires new technology to
ensure sufficient safety and a smooth integration process.
The absence of a pilot on board a vehicle introduces new
problems that do not arise in manned flight. One challenging
and safety-critical issue is flight in known icing
conditions. Whereas in manned flight, dealing with icing is
left to the pilot and his appraisal of the situation at hand; in
unmanned flight, this is no longer an option and new
solutions are required. To address this, an icing-related
decision-making system (IRDMS) is proposed. The system
quantifies in-flight icing based on changes in aircraft performance
and measurements of environmental properties,
and evaluates what the effects on the aircraft are. Based on
this, it determines whether the aircraft can proceed, and
whether and which available icing protection systems should be activated. In this way, advice on an appropriate
response is given to the operator on the ground, to ensure
safe continuation of the flight and avoid possible accidents
Real-time obstacle collision avoidance for fixed wing aircraft using B-splines
A real-time collision avoidance algorithm is developed
based on parameterizing an optimal control problem with
B-spline curves. The optimal control problem is formulated in
output space rather than control or input space, this is feasible
because of the differential flatness of the system for a fixed wing
aircraft. The flat output trajectory is parameterized using a Bspline
curve representation. In order to reduce the computational
time of the optimal problem, the aircraft and obstacle constraints
are augmented in the cost function using a penalty function
method. The developed algorithm has been simulated and tested
in MATLAB/Simulink
Optimal realizations of floating-point implemented digital controllers with finite word length considerations.
The closed-loop stability issue of finite word length (FWL) realizations is
investigated for digital controllers implemented in floating-point arithmetic.
Unlike the existing methods which only address the effect of the mantissa bits
in floating-point implementation to the sensitivity of closed-loop stability,
the sensitivity of closed-loop stability is analysed with respect to both the
mantissa and exponent bits of floating-point implementation. A computationally
tractable FWL closed-loop stability measure is then defined, and the method of
computing the value of this measure is given. The optimal controller realization
problem is posed as searching for a floating-point realization that maximizes
the proposed FWL closed-loop stability measure, and a numerical optimization
technique is adopted to solve for the resulting optimization problem. Simulation
results show that the proposed design procedure yields computationally efficient
controller realizations with enhanced FWL closed-loop stability performance
Visual flight rules-based collision avoidance systems for UAV flying in civil aerospace
The operation of Unmanned Aerial Vehicles (UAVs) in civil airspace is restricted by the aviation authorities, which require full compliance with regulations that apply for manned aircraft. This paper proposes control algorithms for a collision avoidance system that can be used as an advisory system or a guidance system for UAVs that are flying in civil airspace under visual flight rules. A decision-making system for collision avoidance is developed based on the rules of the air. The proposed architecture of the decision-making system is engineered to be implementable in both manned aircraft and UAVs to perform different tasks ranging from collision detection to a safe avoidance manoeuvre initiation. Avoidance manoeuvres that are compliant with the rules of the air are proposed based on pilot suggestions for a subset of possible collision scenarios. The proposed avoidance manoeuvres are parameterized using a geometric approach. An optimal collision avoidance algorithm is developed for real-time local trajectory planning. Essentially, a finite-horizon optimal control problem is periodically solved in real-time hence updating the aircraft trajectory to avoid obstacles and track a predefined trajectory. The optimal control problem is formulated in output space, and parameterized by using B-splines. Then the optimal designed outputs are mapped into control inputs of the system by using the inverse dynamics of a fixed wing aircraft
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