Reference In Presence Research Articles

EFFICACY OF NAVIGATOR-TRIGGERED PACE TECHNIQUE MRCP IN CHOLEDOCHOLITHIASIS

Aim: The navigator-triggered Prospective Acquisition Correction Enhancement technique is a method used to eliminate respiratory motion artifacts caused in magnetic resonance cholangiopancreatography examinations. The purpose of this study was to compare the diagnostic accuracy of navigator-triggered Prospective Acquisition Correction Enhancement tecnique magnetic resonance cholangiopancreatography examination with endoscopic retrograde cholangiopancreatography as a gold standard reference in presence of choledocholithiasis. 
 Materıal and Method: The diagnostic rates of magnetic resonance cholangiopancreatography examination performed with Prospective Acquisition Correction Enhancement technique in the diagnosis of choledocholithiasis were compared according to the results of the endoscopic retrograde cholangiopancreatography examination, which was accepted as a gold standard reference. 
 Results: Among 107 patients included in the study, 40 patients with magnetic resonance cholangiopancreatography and 36 patients with endoscopic retrograde cholangiopancreatography were diagnosed with choledocholithiasis. endoscopic retrograde cholangiopancreatography showed the presence of choledocholithiasis in 36 patients among 40 patients diagnosed as choledocholithiasis with magnetic resonance cholangiopancreatography. The positive predictivity value of the magnetic resonance cholangiopancreatography examination performed with the Prospective Acquisition Correction Enhancement technique was 90%, the negative predictivity value was 98.5%, the sensitivity was 97.3%, the specificity was 94.3%, and the diagnostic accuracy was 95.3%. 
 Conclusıon: We think that navigator-triggered magnetic resonance cholangiopancreatography examination obtained with Prospective Acquisition Correction Enhancement technique is a reliable method with high accuracy in the diagnosis of choledocholithiasis.

High-performance MPPT control of DFIG with optimized flux reference in presence of nonlinear magnetic characteristic

In recent years, an expansive research exertion has been devoted to the control for aeorogenerators conforming of a Doubly Fed Induction Generator (DFIG) coupled to a wind turbine. Most preceding controllers based on standard models (whose magnetic induction characteristic is considered linear and iron losses have not been taken into account). Since such a magnetic characteristic is nonlinear in practice, this work develops a variable speed control strategy on the basis of a DFIG model in presence of nonlinear magnetic characteristic and iron losses. The main contribution of this paper is to present a high-performance maximum power point (MPPT) control of DFIG based on rotor flux optimization, designed to reach an optimal operational conditions. Of the foregoing, the control goal is twofold: i) minimization of the stator and rotor currents circulating by controlling the rotor flux for a maximum electromagnetic torque; ii) captured the maximum wind power to insure the attainment of MPPT. The performances of the proposed command has been studied theoretically and validated by simulation studies with Matlab/Simulink.

Proposal of Sliding Mode Controller based on Backstepping Technique for Control of Magnetic Levitation System

Magnetic Levitation System (MLS) is a nonlinear system and it is used extensively in many areas. The system's goal is to use the non-contact principle to magnetize the coil and cause the objects to float to a specific height. The magnetic force and the current flowing through the coil have a nonlinear relationship. In this paper first design of the backstepping controller is done to attain the wanted floating in presence of system related uncertainties and system behavior is witnessed. Then a Sliding Mode Controller (SMC) based on backstepping procedure is formulated. The control gains in this controller are designed in such a way that the characteristics polynomial whose coefficients are control gains is strictly Hurwitz and the closed loop system's asymptotic stability is assured. Simulations are performed and the magnetic ball tracking is observed considering step signal as reference in presence of disturbances. More accuracy is observed in terms of following the reference by the magnetic ball when it is used Sliding Mode Controller based on Backstepping technique instead of backstepping controller by considering pulse type disturbance. By simulation and analyzing results it is confirmed that the proposed control strategy is more effective.

Homogeneous integral controllers for a magnetic suspension system

In this work a discontinuous integral controller is applied to a magnetic suspension system to robustly track a time-varying reference, while rejecting non-vanishing time-varying perturbations or uncertainties. Moreover, a family of continuous integral controllers, including a linear one, are derived and its performance is compared with the discontinuous algorithm using both, theoretical arguments, simulations and experiments, performed at a laboratory scale suspension system. The theoretical results are established for the family of controllers using smooth Lyapunov functions. It is shown experimentally that the discontinuous integral controller outperforms the continuous controllers, including the linear one, because it can achieve a high tracking precision for constant and time-varying references in presence of time-varying perturbations and despite of the sensor noise. Moreover, it avoids the limit cycle oscillation caused by the dry friction on the system controlled by the linear algorithm.

Terminal synergetic design of a nonlinear robot manipulator in the presence of disturbances

PurposeThe purpose of this paper is to design a synergetic controller to precisely and quickly track reference signals in robot manipulators. Having smooth control signal this controller enables the nonlinear robot system to track desired references in presence of disturbances in a finite time.Design/methodology/approachA new synergetic manifold is introduced here, followed by adding a nonlinear exponential term to it have a precise tracking within a finite time of the desired references with disturbances. Previously the nonlinear term was inserted in the main synergetic equation which makes it complicated due to its hard mathematical approach. Using Lyapunov function, the stability of the system in the presence of disturbances is proved. The validity of the resulted system is confirmed by simulating it in Simulink.FindingsUsing a terminal synergetic controller with new manifold proposed in this work enables system’s state variables to track desired reference signal in the presence of disturbances from any initial condition with proper precision and rate. Simulation results show that compared to similar methods it provides a more proper speed and a finite time convergence with high precision and speed.Originality/valueProviding fast and precise convergence, the proposed controller can be used in robot manipulator systems which need fast response and also have a precise performance such as in printing 3D objects and any industrial process.

Robust nonlinear predictive control of permanent magnet synchronous generator turbine using Dspace hardware

In this paper, a robust nonlinear predictive control (NLPC) is applied to a wind energy conversion system, using a variable speed turbine coupled directly to permanent magnet synchronous generator (PMSG) with PWM rectifier and a load. The principle of this control consists in elaborating a control law such that the predicted output can optimally track a desired predicted reference in presence of the disturbance. The predictive control will be optimal if the finite horizon cost function is minimized. The purpose of control in our case is to adjust the rectifier voltage amplitude and the stator current of the PMSG even with the change in wind speed. This control has-been Implemented using Dspace DS1104 card, the latter allowed us to control the system in real time. Finally, the practical results and those obtained by simulation using MATLAB/Simulink are compared to illustrate the performances of the proposed control regarding tracking of the reference and the disturbance rejection.

Current sensorless position–flux tracking controller for induction motor drives

An innovative indirect field-oriented output feedback controller for induction motor drives is presented. This solution is based on output feedback since only speed and position of the motor shaft are measured, while current sensors are avoided. This approach is suitable for low cost applications, where the position sensor cannot be removed to guarantee accurate position tracking. The proposed method provides global asymptotic tracking of smooth position and flux references in presence of unknown constant load torque. It is based on the natural passivity of the electromagnetic part of the machine and it guarantees asymptotic decoupling of the induction motor mechanical and electrical subsystems achieving at the same time asymptotic field orientation. Lyapunov analysis and nonlinear control design have been adopted to obtain good position tracking performances and effective torque–flux decoupling. The cascaded structure of the controller allows performing a constructive tuning procedure for speed and position control loops. Results of experimental tests are presented to demonstrate the tracking and robustness features of the proposed solution.