Browsing by Author "Chen, Lejun"

Now showing 1 - 9 of 9
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    Active stall flutter suppression for a revised Leishman/Beddoes model
    (American Society of Civil Engineers, 2023-12-25) Zheng, Junruoyu; Pontillo, Alessandro; Chen, Lejun; Whidborne, James F.
    This paper proposes a nonlinear disturbance observer (NDO) based sliding mode control (SMC) method to the problem of stall flutter suppression for a revised Leishman/Beddoes (L/B) model. To capture accurate aerodynamic characteristics whilst reducing the plant model mismatch, the dynamics of the separation point and the shift of the aerodynamic centre are analysed to improve the structure of the L/B model. Based on this revised L/B model, an active flutter suppression problem which includes aerodynamic disturbances and actuator dynamics is addressed. The inclusion of the actuator dynamics means that the aerodynamic disturbance from the flow separation, induced by the revised L/B model, is considered as an ‘unmatched’ disturbance. To counteract the effect of unmatched disturbances, an NDO-based sliding mode control scheme is applied to suppress stall flutter and to ensure rapid reference tracking performance in both steady and unsteady flow conditions. Simulation results show the improvements of the proposed revised L/B model via a comparative analysis. In addition, the efficacy of the proposed stall flutter suppression scheme is demonstrated
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    Experimental verification of an LiDAR based gust rejection system for a quadrotor UAV
    (IEEE, 2022-07-26) Mendez, Arthur P.; Whidborne, James F.; Chen, Lejun
    This paper assesses the use of a ground-based wind measuring LiDAR (Light Detection and Ranging) for remote sensing of incoming wind gusts at the landing site of an autonomous quadrotor. The experimental verification results show that the scalar measurements from the LiDAR were able to recreate the horizontal wind vector even with wind direction variation. Comparisons were conducted against conventional cup anemometers with wind vanes, and these show a good correlation. Upwind LiDAR measurements were used to predict the downstream wind using a transport model. This prediction compared with the downwind measurement shows a good correlation. This wind preview information from the LiDAR is then incorporated into a disturbance feedforward control scheme to increase the gust resilience of the vehicle. Simulation and experimental results demonstrate the system's efficacy.
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    Flight data validation of an icing accretion estimation scheme using super-twisting observers
    (Elsevier, 2023-06-15) Chen, Lejun; Whidborne, James F.
    This paper develops a generalised multivariable super-twisting observer for a class of nonlinear systems in which the unmeasured variables linked to the known state dependent matrix function appear multiplicatively. A sufficient condition is given to guarantee that the reconstruction errors associated with the unmeasurable variables converge to zero in finite time. This approach is then used to address the aircraft icing accretion estimation problem despite unreliable sensor measurement. The efficacy of the approach has been evaluated via real flight data recorded under natural icing conditions. Results show that the observer has the capability to estimate the change of the drag coefficient induced by icing accretion and to reconstruct the unreliable pitch rate sensor measurement simultaneously.
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    Flight evaluation of a sliding mode online control allocation scheme for fault tolerant control
    (Elsevier, 2020-01-21) Chen, Lejun; Edwards, Christopher; Alwi, Halim; Sato, Masayuki
    This paper develops a sliding mode fault tolerant control scheme based on a Linear Parameter Varying (LPV) system representation of the plant. The scheme includes a control allocation component, which is capable of utilizing the available healthy actuators in the face of actuator faults/failures, in an effort to retain close to nominal fault free performance. The proposed scheme is validated using the Japan Aerospace Exploration Agency’s Multi-Purpose Aviation Laboratory (MuPAL-α" role="presentation">) research aircraft. The flight test results demonstrate good lateral-directional state tracking performance with no visible performance degradation in the presence of rudder and aileron faults.
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    Flight evaluation of an LPV sliding mode observer for sensor FTC
    (IEEE, 2021-07-29) Chen, Lejun; Alwi, H.; Edwards, C.; Sato, M.
    This brief develops a sliding mode sensor fault-tolerant control scheme for a class of linear parameter varying (LPV) systems. It incorporates a sliding mode observer that reconstructs the unknown sensor faults based on only the system inputs and outputs. The reconstructed sensor faults are used to compensate for the corrupted sensor measurements before they are used in the feedback controller. Provided accurate fault estimates can be computed; near nominal control performance can be retained without any controller reconfiguration. Furthermore, the closed-loop stability of the fault-tolerant control (FTC) scheme, involving both a sliding mode controller and a sliding mode observer, is rigorously analyzed. The proposed scheme is validated using the Japan Aerospace Exploration Agency's Multipurpose Aviation Laboratory (MuPAL-α) research aircraft. These flight tests represent the first validation tests of a sliding mode sensor FTC scheme on a full-scale aircraft.
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    Simultaneous fault and input time delay estimation for an actuator system: theory and flight data validation
    (IEEE, 2021-06-18) Chen, Lejun; Edwards, Christopher; Alwi, Halim; Sato, Masayuki
    This paper proposes a first order sliding mode observer for the purpose of simultaneously estimating the unknown input time delay and reconstructing the loss of effectiveness in a model of an actuator. The adaptive algorithm is driven by the ‘equivalent output error injection’ signal associated with the sliding motion. Sufficient conditions are given to ensure finite time convergence of the state estimation error system, ensuring both the time delay estimation error and the estimation error associated with the actuator fault converge to a small region around zero. The efficacy of the approach has been evaluated via both a numerical simulation and flight data validation.
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    Sliding mode control of a class of underactuated system with non-integrable momentum
    (Elsevier, 2020-07-20) Chen, Lejun; Van, Mien
    In this paper, a sliding mode control scheme is developed to stabilise a class of nonlinear perturbed underactuated system with a non-integral momentum. In this scheme, by initially maintaining a subset of actuated variables on sliding manifolds, the underactuated system with the non-integrable momentum can be approximated by one with the integrable momentum in finite time. During sliding, a subset of the actuated variables converge to zero and a physically meaningful diffeomorphism is systematically calculated to transform the reduced order sliding motion into one in a strict feedback normal form in which the control signals are decoupled from the underactuated subsystem. Furthermore, based on the perturbed strict feedback form, it is possible to find a sliding mode control law to ensure the asymptotic stability of the remaining actuated and unactuated variables. The design efficacy is verified via a multi-link planar robot case study.
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    Sliding mode observers for a class of LPV systems
    (Wiley, 2020-03-04) Chen, Lejun; Edwards, C.; Alwi, H.
    In this paper, a new framework for the synthesis of a class of sliding mode observers for affine linear parameter varying (LPV) systems is proposed. The sliding mode observer is synthesized by selecting the design freedom via LMIs. Posing the problem from a small gain perspective allows existing numerical techniques from the literature to be used for the purpose of synthesizing the observer gains. In particular, the framework allows affine parameterdependent Lyapunov functions to be considered for analyzing the stability of the state estimation error dynamics, to help reduce design conservatism. Initially a variable structure observer formulation is proposed, but by imposing further constraints on the LMIs, a stable sliding mode is introduced, which can force and maintain the output estimation error to be zero in finite time. The efficacy of the scheme is demonstrated using an LPV model of the short period dynamics of an aircraft and demonstrates simultaneous asymptotic estimation of the states and disturbances.
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    Wind preview-based model predictive control of multi-rotor UAVs using LiDAR
    (MDPI, 2023-04-03) Mendez, Arthur P.; Whidborne, James F.; Chen, Lejun
    Autonomous outdoor operations of Unmanned Aerial Vehicles (UAVs), such as quadrotors, expose the aircraft to wind gusts causing a significant reduction in their position-holding performance. This vulnerability becomes more critical during the automated docking of these vehicles to outdoor charging stations. Utilising real-time wind preview information for the gust rejection control of UAVs has become more feasible due to the advancement of remote wind sensing technology such as LiDAR. This work proposes the use of a wind-preview-based Model Predictive Controller (MPC) to utilise remote wind measurements from a LiDAR for disturbance rejection. Here a ground-based LiDAR unit is used to predict the incoming wind disturbance at the takeoff and landing site of an autonomous quadrotor UAV. This preview information is then utilised by an MPC to provide the optimal compensation over the defined horizon. Simulations were conducted with LiDAR data gathered from field tests to verify the efficacy of the proposed system and to test the robustness of the wind-preview-based control. The results show a favourable improvement in the aircraft response to wind gusts with the addition of wind preview to the MPC; An 80% improvement in its position-holding performance combined with reduced rotational rates and peak rotational angles signifying a less aggressive approach to increased performance when compared with only feedback based MPC disturbance rejection. System robustness tests demonstrated a 1.75 s or 120% margin in the gust preview’s timing or strength respectively before adverse performance impact. The addition of wind-preview to an MPC has been shown to increase the gust rejection of UAVs over standard feedback-based MPC thus enabling their precision landing onto docking stations in the presence of wind gusts.