• Condition parameter estimation for photovoltaic buck converters based on adaptive model observers

      Cen, Zhaohui; Stewart, Paul; Derby University (IEEE, 2016-10-31)
      DC-DC power converters such as buck converters are susceptible to degradation and failure due to operating under conditions of electrical stress and variable power sources in power conversion applications, such as electric vehicles and renewable energy. Some key components such as electrolytic capacitors degrade over time due to evaporation of the electrolyte. In this paper, a model-observer based scheme is proposed to monitor the states of Buck converters and to estimate their component parameters, such as capacitance and inductance. First, a diagnosis observer is proposed, and the generated residual vectors are applied for fault detection and isolation. Second, component condition parameters, such as capacitance and inductance are reconstructed using another novel observer with adaptive feedback law. Additionally, the observer structures and their theoretical performance are analyzed and proven. In contrast to existing reliability approaches applied in buck converters, the proposed scheme performs online-estimation for key parameters. Finally, buck converters in conventional dc–dc step-down and photovoltaic applications are investigated to test and validate the effectiveness of the proposed scheme in both simulation and laboratory experiments. Results demonstrate the feasibility, performance, and superiority of the proposed component parameter estimation scheme.
    • Integrated flight/thrust vectoring control for jet-powered unmanned aerial vehicles with ACHEON propulsion

      Cen, Zhaohui; Smith, Tim; Stewart, Paul; Stewart, Jill; University of Lincoln (2014-07-29)
      As a new alternative to tilting rotors or turbojet vector mechanical oriented nozzles, ACHEON (Aerial Coanda High Efficiency Orienting-jet Nozzle) has enormous advantages because it is free of moving elements and highly effective for Vertical/Short-Take-Off and Landing (V/STOL) aircraft. In this paper, an integrated flight/ thrust vectoring control scheme for a jet powered Unmanned Aerial Vehicle (UAV) with an ACHEON nozzle is proposed to assess its suitability in jet aircraft flight applications. Firstly, a simplified Thrust-Vectoring (TV) population model is built based on CFD simulation data and parameter identification. Secondly, this TV propulsion model is embedded as a jet actuator for a benchmark fixed-wing ‘Aerosonde’ UAV, and then a four “cascaded-loop” controller, based on nonlinear dynamic inversion (NDI), is designed to individually control the angular rates (in the body frame), attitude angles (in the wind frame), track angles (in the navigation frame), and position (in the earth-centered frame) . Unlike previous research on fixed-wing UAV flight controls or TV controls, our proposed four-cascaded NDI control law can not only coordinate surface control and TV control as well as an optimization controller, but can also implement an absolute self-position control for the autopilot flight control. Finally, flight simulations in a high-fidelity aerodynamic environment are performed to demonstrate the effectiveness and superiority of our proposed control scheme.