arXiv subjects

Jahanzeb Rajput

Publications and source records attributed to Jahanzeb Rajput.

3 recordsLinked to original sources

arXiv2024

Nonlinear Control Allocation: A Learning Based Approach

Modern aircraft are designed with redundant control effectors to cater for fault tolerance and maneuverability requirements. This leads to aircraft being over-actuated and requires control allocation schemes to distribute the control commands among control effectors. Traditionally, optimization-based control allocation schemes are used; however, for nonlinear allocation problems, these methods require large computational resources. In this work, an artificial neural network (ANN) based nonlinear control allocation scheme is proposed. The proposed scheme is composed of learning the inverse of the control effectiveness map through ANN, and then implementing it as an allocator instead of solving an online optimization problem. Stability conditions are presented for closed-loop systems incorporating the allocator, and computational challenges are explored with piece-wise linear effectiveness functions and ANN-based allocators. To demonstrate the efficacy of the proposed scheme, it is compared with a standard quadratic programming-based method for control allocation.

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arXiv2022

Nonlinear Control Allocation Using A Piecewise Multi-Linear Representation

Nonlinear control allocation is an important part of modern nonlinear dynamic inversion based flight control systems which require highly accurate model of aircraft aerodynamics. Generally, an accurately implemented onboard model determines how well the system nonlinearities can be canceled. Thus, more accurate model results in better cancellation, leading to the higher performance of the controller. In this paper, a new control system is presented that combines nonlinear dynamic inversion with a piecewise multi-linear representation based control allocation. The piecewise multi-linear representation is developed through a new generalization of Kronecker product for block matrices, combined with the canonical piecewise linear representation of nonlinear functions. Analytical expressions for the Jacobian of the piecewise multi-linear model are also presented. Proposed formulation gives an exact representation of piecewise multi-linear aerodynamic data and thus is capable of accurately modeling nonlinear aerodynamics over the entire flight envelope of an aircraft. Resulting nonlinear controller is applied to control of a tailless flying wing aircraft with ten independently operating control surfaces. The simulation results for two innovative control surface configurations indicate that perfect control allocation performance can be achieved, leading to better tracking performance compared with ordinary polynomial-based control allocation.

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arXiv2022

Reconfigurable Control of a Class of Multicopters

In this paper, a reconfigurable control scheme for a generalized class of multicopters is presented to overcome single or multiple rotor failures. In a multicopter, the rotor failure heavily affects its dynamics and thus its controllability. Limited controllability leads to limited or no reconfigurability. \emph{Available Control Authority Index} has been recently developed \cite{Du2015} as a measure of controllability of multicopters. In this work, the notion of \emph{Available Reduced-Control Authority Index} (ArCAI) is introduced, which shows that in some uncontrollable failures it is still possible to control reduced set of states. Based on this notion, a reconfigurable control scheme is presented, which comprises a \emph{Nonlinear Dynamic Inversion} based baseline control law, a constrained control allocation scheme along with some modifications to incorporate reconfiguration, and a simplified fault detection and isolation technique. Simulation results for a commonly used configuration of Hexacopter are presented in the presence of single and multiple rotor failures.

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