4,037 research outputs found
Wind turbines controllers design based on the super-twisting algorithm
The continuous increase in the size of wind turbines (WTs) has led to new challenges in the design of novel torque and pitch controllers. Today’s WT control design must fulfill numerous specifications to assure effective electrical energy production and to hold the tower vibrations inside acceptable levels of operation. Hence, this paper presents modern torque and pitch control developments based on the super-twisting algorithm (STA) by using feedback of the fore- aft and side-to-side acceleration signals of the WT tower. According to numerical experiments realized using FAST, these controllers mitigate vibrations in the tower without affecting the quality of electrical power production. Moreover, the proposed controllers’ performance is better than the baseline controllers used for comparison.Postprint (author's final draft
Second Order Sliding Mode Control of a STATCOM with Saturated Inputs
This paper presents a robust controller for a STATCOM device with saturated inputs. As the primary assumption, the proposed design considers the presence of unknown but bounded external perturbations and parametric variations. This proposal has a cascade structure, where a saturated super twisting control algorithm closes the currents control loop, and a high-gain proportional-integral (PI) algorithm ensures the voltage regulation. Thus, the exposed scheme provides an adequate performance of the STATCOM, considering the saturation of the inputs with the anti-windup feature. Posteriorly, a proper stability analysis presents the conditions for the appropriate operation of the closed-loop system in saturation and non-saturation regimes. Numerical simulations are also included to show the performance of the proposed controller
Autonomous space processor for orbital debris
The development of an Autonomous Space Processor for Orbital Debris (ASPOD) was the goal. The nature of this craft, which will process, in situ, orbital debris using resources available in low Earth orbit (LEO) is explained. The serious problem of orbital debris is briefly described and the nature of the large debris population is outlined. The focus was on the development of a versatile robotic manipulator to augment an existing robotic arm, the incorporation of remote operation of the robotic arms, and the formulation of optimal (time and energy) trajectory planning algorithms for coordinated robotic arms. The mechanical design of the new arm is described in detail. The work envelope is explained showing the flexibility of the new design. Several telemetry communication systems are described which will enable the remote operation of the robotic arms. The trajectory planning algorithms are fully developed for both the time optimal and energy optimal problems. The time optimal problem is solved using phase plane techniques while the energy optimal problem is solved using dynamic programming
Performance of first and second-order sliding mode observers for nonlinear systems
This paper presents a brief study on the design and performance comparison of conventional first-order and super-twisting second-order sliding mode observers for some nonlinear control systems. Estimation accuracy, fast response, chattering effect, peaking phenomenon and robustness are considered for nonlinear ystems under observer-based output feedback control and state feedback control
Acceleration-based fault-tolerant control design of offshore fixed wind turbines
Wind turbines (WTs) are basically controlled by varying the generator load torque (with the so-called torque control) and the blade pitch angles (with the so-called pitch control) based on measurement of the generator shaft speed. These two controllers unitedly work to satisfy the control objectives, and it is crucial that they are tolerant to possible faults in the WT system. Passive fault-tolerant control comprises the design of robust controllers against disturbances and uncertainties. This enables the controller to counteract the effect of a fault without requiring reconfiguration or fault detection. In this regard, the main contribution of this paper is to propose new control techniques that not only provide fault tolerance capabilities to the WT system but also improve the overall performance of the system in both fault-free and faulty conditions. Coupling nonlinear aero-hydro-servo-elastic simulations of an offshore WT with jacket platform is carried out for several pitch actuator faults. The jacket platform motions and structural loads caused by fault events with the proposed controllers are compared with loads encountered during normal operation and with respect to a well-known baseline controller in the literature. The proposed controllers are based in the super-twisting algorithm by using feedback of the generator shaft speed as well as the fore-aft and side-to-side acceleration signals of the WT tower.Preprin
Lagrangian coherent structures in nonlinear dynamos
Turbulence and chaos play a fundamental role in stellar convective zones
through the transportof particles, energy and momentum, and in fast dynamos,
through the stretching, twisting and folding of magnetic flux tubes. A
particularly revealing way to describe turbulent motions is through the
analysis of Lagrangian coherent structures (LCS), which are material lines or
surfaces that act as transport barriers in the fluid. We report the detection
of Lagrangian coherent structures in helical MHD dynamo simulations with scale
separation. In an ABC--flow, two dynamo regimes, a propagating coherent
mean--field regime and an intermittent regime, are identified as the magnetic
diffusivity is varied. The sharp contrast between the chaotic tangle of
attracting and repelling LCS in both regimes permits a unique analysis of the
impact of the magnetic field on the velocity field. In a second example, LCS
reveal the link between the level of chaotic mixing of the velocity field and
the saturation of a large--scale dynamo when the magnetic field exceeds the
equipartition value
Sliding Mode Control with Chattering Attenuation and Hardware Constraints in Spacecraft Applications
Slope filtrations for relative Frobenius
The slope filtration theorem gives a partial analogue of the eigenspace
decomposition of a linear transformation, for a Frobenius-semilinear
endomorphism of a finite free module over the Robba ring (the ring of germs of
rigid analytic functions on an unspecified open annulus of outer radius 1) over
a discretely valued field. In this paper, we give a third-generation proof of
this theorem, which both introduces some new simplifications (particularly the
use of faithfully flat descent, to recover the theorem from a classification
theorem of Dieudonne-Manin type) and extends the result to allow an arbitrary
action on coefficients (previously the action on coefficients had to itself be
a lift of an absolute Frobenius). This extension is relevant to a study of
(phi, Gamma)-modules associated to families of p-adic Galois representations,
presently being initiated by Berger and Colmez.Comment: 40 pages; v2: refereed version, minor change
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