Search results for "Control theory"
showing 10 items of 1333 documents
On Large Orbits of Actions of Finite Soluble Groups: Applications
2020
The main aim of this survey paper is to present two orbit theorems and to show how to apply them to obtain a result that can be regarded as a significant step towards the solution of Gluck’s conjecture on large character degrees of finite soluble groups. We also show how to apply them to solve questions about intersections of some conjugacy families of subgroups of finite soluble groups.
Positive linear maps on normal matrices
2018
For a positive linear map [Formula: see text] and a normal matrix [Formula: see text], we show that [Formula: see text] is bounded by some simple linear combinations in the unitary orbit of [Formula: see text]. Several elegant sharp inequalities are derived, for instance for the Schur product of two normal matrices [Formula: see text], [Formula: see text] for some unitary [Formula: see text], where the constant [Formula: see text] is optimal.
Structure of the space of reducible connections for Yang-Mills theories
1990
Abstract The geometrical structure of the gauge equivalence classes of reducible connections are investigated. The general procedure to determine the set of orbit types (strata) generated by the action of the gauge group on the space of gauge potentials is given. In the so obtained classification, a stratum, containing generically certain reducible connections, corresponds to a class of isomorphic subbundles given by an orbit of the structure and gauge group. The structure of every stratum is completely clarified. A nonmain stratum can be understood in terms of the main stratum corresponding to a stratification at the level of a subbundle.
Superstable cycles for antiferromagnetic Q-state Potts and three-site interaction Ising models on recursive lattices
2013
We consider the superstable cycles of the Q-state Potts (QSP) and the three-site interaction antiferromagnetic Ising (TSAI) models on recursive lattices. The rational mappings describing the models' statistical properties are obtained via the recurrence relation technique. We provide analytical solutions for the superstable cycles of the second order for both models. A particular attention is devoted to the period three window. Here we present an exact result for the third order superstable orbit for the QSP and a numerical solution for the TSAI model. Additionally, we point out a non-trivial connection between bifurcations and superstability: in some regions of parameters a superstable cyc…
Performance Analysis of Cooperative Communication Systems with Imperfect Channel Estimation
2009
This paper investigates the effects of channel estimation errors on the symbol-error-rate (SER) performance of a cooperative communication system operating in an amplify-and- forward (AF) mode. A pilot symbol assisted modulation scheme with linear minimum mean square estimation (LMMSE) is used for the channel estimation. An accurate and easy-to-evaluate SER expression is presented for uncoded cooperative communication systems with quadrature amplitude modulation (QAM) and phase-shift keying (PSK) constellations. Numerical simulations are conducted to verify the correctness of the proposed analytical formulation. It is shown that the performance loss caused by channel estimation errors incre…
Trajectory robust control of autonomous quadcopters based on model decoupling and disturbance estimation
2021
In this article, a systematic procedure is given for determining a robust motion control law for autonomous quadcopters, starting from an input–output linearizable model. In particular, the suggested technique can be considered as a robust feedback linearization (FL), where the nonlinear state-feedback terms, which contain the aerodynamic forces and moments and other unknown disturbances, are estimated online by means of extended state observers. Therefore, the control system is made robust against unmodelled dynamics and endogenous as well as exogenous disturbances. The desired closed-loop dynamics is obtained by means of pole assignment. To have a feasible control action, that is, the fo…
Experimental validation of a quaternion-based attitude estimation with direct input to a quadcopter control system
2013
This paper presents a method to calculate the attitude quaternion of a quadcopter with few calculations. The quaternion calculation is based on accelerometers and gyroscopes from an Inertial Measurement Unit (IMU). The quaternion from the accelerometer is calculated as the shortest rotation arc from the gravity vector in the navigation frame. The quaternion from the gyroscope is calculated based on equations of the quaternion derivative. A complementary filter is combining the two quaternions with a componentwise comparison. The attitude estimation is calculated without any trigonometric functions. The quaternion is directly used as an input to the attitude controller. The attitude controll…
ROS/Gazebo-Based Simulation of Quadcopter Aircrafts
2018
The main purpose of this work is to present a tutorial description on how to design and develop an observer, which is capable of estimating the position and the orientation of a drone commanded by a controller, whose shape and structure are unknown. Starting from Newton's and Euler's laws, a mathematical model describing the dynamics of a quadcopter has first been obtained. By linearizing this model it is possible to implement a Luenberger observer and validate it with simulations in a Linux environment, thanks to the use of the Ardupilot controller and the Gazebo simulator. Finally, starting from the results obtained from the simulation, it is possible to evaluate the error made in the est…
Wind gust estimation for precise quasi-hovering control of quadrotor aircraft
2021
Abstract This paper focuses on the control of quadrotor vehicles without wind sensors that are required to accurately track low-speed trajectories in the presence of moderate yet unknown wind gusts. By modeling the wind disturbance as exogenous inputs, and assuming that compensation of its effects can be achieved through quasi-static vehicle motions, this paper proposes an innovative estimation and control scheme comprising a linear dynamic filter for the estimation of such unknown inputs and requiring only position and attitude information. The filter is built upon results from Unknown Input Observer theory and allows estimation of wind and vehicle state without measurement of the wind its…
Stochastic response of MDOF wind-excited structures by means of Volterra series approach
1998
Abstract The role played by the quadratic term of the forcing function in the response statistics of multi-degree-of-freedom (MDOF) wind-excited linear-elastic structures is investigated. This is accomplished by modeling the structural response as a Volterra series up to the second order and neglecting the wind-structure interaction. In order to reduce the computational effort due to the calculation of a large number of multiple integrals, required by the used approach, a recent model of the wind stochastic field is adopted.