Variable Structure Systems

A simple procedure for tuning the parameters of the Super-Twisting (STW) second-order sliding mode control (2-SMC) algorithm, used for the feedback control of uncertain linear plants, is presented. When the plant relative degree is higher than one, it is known [10] that a self-sustained periodic oscillation takes place in the feedback system. The purpose of the present work is that of illustrating a systematic procedure for control tuning based on Describing Function (DF) approach guaranteeing pre-specified frequency and magnitude of the
resulting oscillation. The knowledge of the plant’s Harmonic Response (magnitude and phase) at the desired chattering frequency is the only required prior information. By means of a simulation example, we show the effectiveness of the proposed procedure.

This paper deals with an approach to estimate the road profile, by use of second order sliding mode observer. The method is based on a robust observer designed with a nominal dynamic model of vehicle. The estimation accuracy of observer has been validated experimentally using a trailer equiped with position sensors and accelerometers

This paper uses second-order sliding mode observers to build up an estimation scheme allowing to identify the tire longitudinal equivalent stiffness and the effective wheel radius using the existing ABS angular sensors. This estimation strategy, based on use of the proposed observer could be used with data acquired experimentally to identify the longitudinal stiffness and effective radius of vehicle tires. The actual results show effectiveness and robustness of the proposed method

Most physical systems inherently contain nonlinearities which are commonly unknown to the system designer. Therefore, in modeling and analysis of such dynamic systems, one needs to handle unknown nonlinearities and/or uncertain parameters. This paper proposes a new adaptive tracking fuzzy sliding mode controller for a class of nonlinear systems in the presence of uncertainties and external disturbances. The main contribution of the proposed method is that the structure of the controlled system is partially unknown and does not require the bounds of uncertainty and disturbance of the system to be known; meanwhile, the chattering phenomenon that frequently appears in the conventional variable structure systems is also eliminated without deteriorating the system robustness. The performance of the proposed approach is evaluated for two well-known benchmark problems. The simulation results illustrate the effectiveness of our proposed controller.

A simple adaptive control scheme for position control of an inverter-fed permanent magnet synchronous motor drive is presented. In the proposed control strategy, model reference and variable structure algorithms are combined to provide fast response and robustness. The adaptive control strategy is analyzed. The performance was studied by computer simulation using actual parameters of a 1 kW drive system. Simulation results are given and discussed

We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with HST, and compare them with X-ray data obtained with the Chandra X-ray Observatory. We have studied the bright region southwest of the pulsar where a bright "blob" is seen in 1999. We show that it may be a result of local energy deposition around 1999, and that the emission from this then faded away. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-"blob" orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the "blob" position, faster orthogonal to the pulsar-"blob" direction than along this axis of orientation. This could indicate that the pulsar-"blob" orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that the high [S II]/[O III] ratio is not due to time-dependent photoionization caused by possible rapid Xray emission variations in the "blob" region. We have also created a multiwavelength energy spectrum for the "blob" position showing that one can, to within 2sigma, connect the optical and X-ray emission by a single power law. We obtain best power-law fits for the X-ray spectrum if we include "extra" oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.

The 5' leader is documented to be an important regulatory element in many (+) ssRNAvirus genome. To understand the significance of the 5' leader RNA of PRRSV, we determined the complete leader sequences of fifteen different North American strains of PRRSV and predicted their secondary structures. Viruses analysed included three reference strains and nine field strains originating from different geographic locations. To further examine the leader region, one of the field strains was adapted to grow in tissue culture, and three clones were isolated. We also predicted the secondary structures of two European strains based on their published sequences. The predicted RNA secondary structures of the leader sequences suggested the existence of three conserved domains formed by the 5' region of the leader among the North American strains, two of which were conserved in the European strains. A variable structural domain was predicted from the 3' region of the leader sequences...

Message Passing Interface (MPI) Collective Communication Functions (MCCF) are usually implemented in programming libraries utilizing invariable algorithms. Not always do such algorithms yield the best performance with all kinds of applications and over all execution environments. In this paper, we present, simulate, analytically model, verify and analyze reconfigurable MCCF that present variable structures and behaviors, in order to provide optimized configurations, flexibility and performance. In this paper we propose and present a set of optimized reconfigurable MCCF, which add flexibility and high performance to collective communications. We simulate, analytically model, verify and analyze the proposed functions, and compare them with invariable implementations. Our results show that reconfiguration at the algorithm level really yields flexibility and performance gains in MCCF.

In the case of linear and nonlinear dynamical systems, the full state vector is generally unknown on account of the nature of the system and the difficulty of measuring some components of the state vector. The objective of the paper is an experimental comparison between two different sliding surface algorithms applied to the two real one link manipulators. The first algorithm is a variable structure adaptive control with reference model using only the measurements of input and output; the other algorithm is a variable structure adaptive control with reference model using the full state vector. To increase the switching frequency and reduce the amplitude of switching oscillations a variable related to the acceleration of the manipulator shaft is introduced in the switching surface