Browsing by Author "Tohidi, Seyed Shahabaldin"
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Item Open Access Adaptive control allocation for constrained systems(Elsevier, 2020-06) Tohidi, Seyed Shahabaldin; Yıldız, Yıldıray; Kolmanovsky, I.This paper proposes an adaptive control allocation approach for uncertain over-actuated systems with actuator saturation. The proposed control allocation method does not require uncertainty estimation or persistency of excitation. Actuator constraints are respected by employing the projection algorithm. The stability analysis is provided for two different cases: when ideal adaptive parameters are inside and when they are outside of the projection boundary which is chosen consistently with the actuator saturation limits. Simulation results for the Aerodata Model in Research Environment (ADMIRE), which is used as an example of an over-actuated aircraft system with actuator saturation, demonstrate the effectiveness of the proposed method.Item Open Access Adaptive control allocation for over-actuated systems with actuator saturation(Elsevier B.V., 2017) Tohidi, Seyed Shahabaldin; Yıldız, Yıldıray; Kolmanovsky, IlyaThis paper proposes an adaptive control allocation approach for over-actuated systems with actuator saturation. The methodology can tolerate actuator loss of effectiveness without utilizing the control input matrix estimation, eliminating the need for persistence of excitation. Closed loop reference model adaptive controller is used for identifying adaptive parameters, which provides improved performance without introducing undesired oscillations. The modular design of the proposed control allocation method improves the flexibility to develop the outer loop controller and the control allocation strategy separately. The ADMIRE model is used as an over-actuated system, to demonstrate the effectiveness of the proposed method using simulation results.Item Open Access Adaptive control of cyberphysical human systems(Bilkent University, 2021-08) Tohidi, Seyed ShahabaldinThis dissertation focuses on the control of cyberphysical human systems in the presence of actuators’ redundancy and constraints. A novel adaptive control tech-nique is proposed to allocate control signals among redundant actuators in the presence of uncertainty and actuator saturation. The proposed method does not require any uncertainty identification or persistency of excitation assumption. The stability of the proposed method is guaranteed using Lyapunov stability analysis. In addition, a modified projection operator that can be implemented to the adaptive control allocation is proposed. This operator enables the allo-cator to handle both magnitude and rate limits of actuators. A novel sliding mode controller with time-varying sliding surface is designed to complement the adaptive allocator and guarantee stability and reference tracking in the presence of uncertainty and actuator saturation. This controller is robust to both adap-tive control allocation error and external disturbance. Furthermore, an adaptive human model is proposed to mimic the human control response in the presence of uncertainty. The proposed structure is based on the model reference adaptive control, and the adaptive laws are obtained using the Lyapunov-Krasovskii stabil-ity criteria. To validate this model, an experimental setup is employed to collect data and a statistical analysis is conducted to measure the predictive power of the pilot model. Finally, the stability limits of a human-in-the-loop closed loop control system, where the plant to be controlled has redundant actuators with uncertain dynamics, are demonstrated. Various human models with and without time delays are investigated. Simulation results are provided to demonstrate the effectiveness of the proposed methods in each chapter.Item Open Access Discrete adaptive control allocation(IEEE, 2021-07-21) Tohidi, Seyed Shahabaldin; Yıldız, YıldırayThe main purpose of a control allocator is to distribute a total control effort among redundant actuators. This paper proposes a discrete adaptive control allocator for over-actuated sampled-data systems in the presence of actuator uncertainty. The proposed method does not require uncertainty estimation or persistency of excitation. Furthermore, the presented algorithm employs a closed loop reference model, which provides fast convergence without introducing excessive oscillations. To generate the total control signal, an LQR controller with reference tracking is used to guarantee the outer loop asymptotic stability. The discretized version of the Aerodata Model in Research Environment (ADMIRE) is used as an over-actuated system, to demonstrate the efficacy of the proposed method.Item Open Access Fault tolerant control for over-actuated systems: an adaptive correction approach(IEEE, 2016) Tohidi, Seyed Shahabaldin; Yıldız, Yıldıray; Kolmanovsky, İ.This paper proposes an adaptive fault tolerant control allocation approach for over-actuated systems. The methodology does not utilize the control input matrix estimation to tolerate actuator faults and, therefore, the proposed control allocation method does not require persistence of excitation. Adaptive control approach with a closed loop reference model is used for identifying control allocation parameters, which provides improved performance without introducing undesired oscillations. Furthermore, a sliding mode controller is used to guarantee the outer loop asymptotic stability. Simulation results are provided, where the ADMIRE model is used as an over-actuated system, to demonstrate the effectiveness of the proposed method.Item Open Access A generalized human-in-the-loop stability analysis in the presence of uncertain and redundant actuator dynamics(American Automatic Control Council, 2022-06-08) Tohidi, Seyed Shahabaldin; Yildiz, YildirayThis paper demonstrates the stability limits of a human-in-the-loop closed loop control system, where the plant to be controlled has redundant actuators with uncertain dynamics. The human operator is modeled as a general transfer function, unlike earlier work where specific filters are associated with human reactions. This helps with developing a more general stability analysis, and earlier studies can be considered as special cases of the proposed framework in this paper. Adaptive control allocation is employed to distribute control signals among redundant actuators. A sliding mode controller with a time-varying sliding surface provides desired control inputs to the control allocator. A flight control task, where the pilot controls the pitch angle via a pitch rate stick input is simulated to demonstrate the accuracy of the stability analysis. The Aerodata Model in Research Environment is used as the uncertain, over-actuated aircraft model.Item Open Access Handling actuator magnitude and rate saturation in uncertain over-actuated systems: a modified projection algorithm approach(Taylor and Francis, 2020-09-24) Tohidi, Seyed Shahabaldin; Yıldız, YıldırayThis paper proposes a projection algorithm which can be employed to bound actuator signals, in terms of both magnitude and rate, for uncertain systems with redundant actuators. The investigated closed-loop control system is assumed to contain an adaptive control allocator to distribute the total control input among actuators. Although conventional control allocation methods can handle actuator rate and magnitude constraints, they cannot consider actuator uncertainty. On the other hand, adaptive allocators manage uncertainty and actuator magnitude limits. The proposed projection algorithm enables adaptive control allocators to handle both magnitude and rate saturation constraints. A mathematically rigorous analysis is provided to show that with the help of the proposed projection algorithm, the performance of the adaptive control allocator can be guaranteed, in terms of error bounds. Simulation results are presented, where the Aero-Data Model In Research Environment (ADMIRE) is used to demonstrate the effectiveness of the proposed methodItem Open Access Pilot induced oscillation mitigation for unmanned aircraft systems: an adaptive control allocation approach(Institute of Electrical and Electronics Engineers, 2018) Tohidi, Seyed Shahabaldin; Yıldız, Yıldıray; Kolmanovsky, IlyaThis paper proposes an adaptive control allocation method that can make unmanned aircraft systems recover from pilot induced oscillations. Pilot induced oscillations are undesired oscillations due to an unintentional and detrimental coupling between the aircraft and the pilot. These oscillations may be instigated due to disturbances, aggressive maneuvers and actuator saturation. Different from manned aircraft, pilot induced oscillations in unmanned aircraft systems are harder to handle due to communication time delays between the operator and the aircraft. The task of a conventional control allocator is to distribute the control effort among redundant actuators to realize a desired virtual control input. When actuators rate saturate, the difference between the desired and the achieved virtual control input introduces an effective time delay to the system dynamics which causes oscillations. In the proposed approach, instead of minimizing the error between the desired and achieved virtual control inputs, the derivative of this error is minimized which eliminates the introduced time delay effect and damps undesired oscillations. Differently from earlier works conducted by the authors, in this work, the proposed pilot induced oscillation mitigation methodology is developed for systems with parametric uncertainty. In the simulations, it is demonstrated that the proposed approach successfully damps pilot induced oscillations that are instigated by a high gain pilot command.Item Open Access Time-varying sliding mode controller for over-actuated systems with constrained and uncertain actuators in flightcontrol applications(John Wiley and Sons, Ltd, 2022-10-29) Yildiray, Yildiz; Kolmanovsky, Ilya; Tohidi, Seyed ShahabaldinOne solution to the problem of distributing the control action among redundant actuators with uncertain dynamics is employing an adaptive control allocator. This paper proposes a sliding mode controller which exploits a time-varying sliding surface to complement adaptive control allocation in the presence of actuator saturation. The proposed approach does not require error augmentation for tracking desired references, which diminishes the computational burden. Aerodata Model in Research Environment, which is an over-actuated aircraft model, is adopted to demonstrate the efficacy of the proposed controller in simulation studies.