Department of Electrical Engineering

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This paper presents a second order sliding mode control for a class of underactuated systems. Container motion coupled with slosh which represents a class of underactuated systems is sought. A stable sliding surface is designed to ensure asymptotic convergence of all the states. A second order twisting algorithm is used to synthesize a smooth control to ensure finite time convergence of the sliding. The proposed method is validated in simulation. © 2012 IEEE.

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Proceedings of IEEE International Workshop on Variable Structure Systems

Second order sliding mode control for a class of underactuated systems

Development of autonomous uninhibited aircraft, so called flying robots in the form of Micro Aerial Vehicles (MAVs) outfitted with autonomous autopilot controller has progressed quickly in recent years, and interest in this field continue to spread. Autopilot basically has two functionality 1) It will stabilize the plant in case it is perturbed due to some disturbances or uncertainties. 2) It will guide the MAV through a predefined path for a particular mission requirement. In this paper we propose a methodology for robust stabilization of MAVs using riccati type formulation. A nonlinear MAV model has been linearized at various operating conditions. A nominal model has been chosen among those linear models and variations from the nominal model are modeled in the from of unmatched parametric uncertainty and a robust sliding surface is designed. Design of robust sliding hyperplanes in the presence of parametric uncertainty is based on quadratic stability. The search of Lyapunov matrix along with constraints for unmatched uncertainties is formulated in terms of linear matrix inequality (LMI) which enables robust linear sliding surface design. A robust sliding controller using the linear sliding hyperplane is designed for the complete nonlinear plant model. Simulation results are done using nonlinear equations of motions to demonstrate the proposed methodology for MAVs. © 2012 IEEE.

Robust stabilization of Micro Aerial Vehicle using sliding mode control

This paper presents a technique to control the Stewart platform using Higher Order sliding Mode(HOSM). For a given position of the platform, the leg lengths are estimated using inverse kinematics and the corresponding leg velocities are estimated in finite time using a super twisting observer. The desired position of the platform has been achieved in finite time using a higher order sliding mode controller. The effectiveness of this control technique has been proved with simulation results. © 2012 IEEE.

2012 7th International Conference on Electrical and Computer Engineering, ICECE 2012

Stabilization of Stewart platform using Higher Order Sliding Mode control

The quadruple tank system is a challenging multi-variable model consisting of four interconnected tanks, two level sensors and two input pumps. This paper deals with the control and estimation of such a system. All the four levels of the system are controlled by H ∞ filter based discrete sliding mode control (SMC). A nonlinear stable sliding surface is constructed using full state information, to enhance the overall performance of the closed loop plant. In this multi-input multi-output quadruple tank system, only the first two states are available for feedback and hence it is not suitable to use any full state feedback control methods directly. To circumvent this problem, the remaining two states, which are required for the SMC design are estimated using a robust H ∞ filter. The efficacy of the proposed method is demonstrated by simulations. © 2012 IEEE.

Discrete-time sliding mode control using an H ∞ filter for a quadruple tank system

This paper investigates a problem of control of rotary slosh using integral sliding modes (ISM). Slosh coupled with vehicle dynamics represents a class of systems having coupled nonlinear and underactuated dynamics. Rotary slosh is modeled using spherical pendulum. The coordinates are chosen to avoid the singularity at equilibrium point. A stabilizing control is designed using Lyapunov approach. A stabilizing controller (SC) is made robust by adding ISM component. The integral sliding mode control (ISMC) yields robust performance over the entire state space. The effectiveness of the method is validated in simulations. © 2012 IEEE.

Robust control of rotary slosh using integral sliding modes

The present work explores the electrical transport and UV photoresponse properties of GaN nanodots (NDs) grown by molecular beam epitaxy (MBE). Single-crystalline wurtzite structure of GaN NDs is verified by X-ray diffraction and transmission electron microscopy (TEM). The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of GaN NDs were studied in a metal-semiconductor-metal configuration. Dark I-V characteristics of lateral grown GaN NDs obeyed the Frenkel-Poole emission model, and the UV response of the device was stable and reproducible with on/off. The responsivity of the detectors is found to be 330A/W with an external quantum efficiency of 1100%. © 2012 The Japan Society of Applied Physics.

Fulltext

Applied Physics Express

Structural characterization and ultraviolet photoresponse of GaN nanodots grown by molecular beam epitaxy

The growth of nonpolar a- plane (1 1 -2 0) orientation of the GaN epilayers were confirmed by high resolution x-ray diffraction studies. An in-plane orientation relationship was found to be [0 0 0 1] GaN || [-1 1 0 1] sapphire and [-1 1 0 0] GaN || [1 1 -2 0] sapphire. SEM image shows the reasonably smooth surface. The photoluminescence spectrum shows near band emission (NBE) at 3.439 eV. The room temperature I-V characteristics of Au/a-GaN schottky diode performed. The Schottky barrier height (φb) and the ideality factor (η) for the Au/a-GaN schottky diode found to be 0.50 eV and 2.01 respectively. © 2012 SPIE.

Proceedings of SPIE - The International Society for Optical Engineering

Growth and properties of nonpolar a-plane GaN grown on r-sapphire by plasma assisted molecular beam epitaxy

Nonpolar a-plane InN/GaN heterostructures were grown by plasma assisted molecular beam epitaxy. The growth of nonpolar a- plane InN / GaN heterostructures were confirmed by high resolution x-ray diffraction study. Reflection high energy electron diffraction patterns show the reasonably smooth surface of a-plane GaN and island-like growth for nonpolar a-plane InN film, which is further confirmed by scanning electron micrographs. An absorption edge in the optical spectra has the energy of 0.74 eV, showing blueshifts from the fundamental band gap of 0.7 eV. The rectifying behavior of the I-V curve indicates the existence of Schottky barrier at the InN and GaN interface. The Schottky barrier height (φ b) and the ideality factor (η) for the InN/GaN heterostructures found to be 0.58 eV and 2.05 respectively. © 2012 Materials Research Society.

Materials Research Society Symposium Proceedings

Molecular beam epitaxial growth of nonpolar a-plane InN/ GaN heterostructures

In this report, the current-voltage (I-V) characteristics of Au/GaN Schottky diodes have been carried out in the temperature range of 300-510 K. The estimated values of the Schottky-barrier height (SBH) and the ideality factor of the diodes based on the thermionic emission (TE) mechanism were found to be temperature dependent. The barrier height was found to increase and the ideality factor to decrease with increasing temperature. The conventional Richardson plot of ln(I s/T 2) versus 1/kT gives the SBH of 0.51 eV and Richardson constant value of 3.23 × 10 -5 A cm -2 K -2 which is much lower than the known value of 26.4 A cm -2 K -2 for GaN. Such discrepancies of the SBH and Richardson constant value were attributed to the existence of barrier-height inhomogeneities at the Au/GaN interface. The modified Richardson plot of ln(I s/T 2)-q 2Ï s2/2k 2T 2 versus q/kT, by assuming a Gaussian distribution of barrier heights at the Au/GaN interface, provided the SBH of 1.47 eV and Richardson constant value of 38.8 A cm -2 K -2. The temperature dependence of the barrier height is interpreted on the basis of existence of the Gaussian distribution of the barrier heights due to the barrier-height inhomogeneities at the Au/GaN interface. Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Physica Status Solidi (A) Applications and Materials Science

Analysis of the temperature-dependent current-voltage characteristics and the barrier-height inhomogeneities of Au/GaN Schottky diodes

The n-type GaN layers were grown by plasma-assisted MBE and either intentionally doped with Si or unintentionally doped. The optical characteristics of a donor level in Si-doped, GaN were studied in terms of photoluminescence (PL) spectroscopy as a function of electron concentration. Temperature dependent PL measurements allowed us to estimate the activation energy of a Si-related donor from temperature-induced decay of PL intensity. PL peak positions, full width at half maximum of PL and activation energies are found to be proportional to the cube root of carrier density. The involvement of donor levels is supported by the temperature-dependent electron concentration measurements. © 2012 Elsevier Ltd. All rights reserved.