Elastic image registration versus speckle tracking for 2-D myocardial motion estimation: a direct comparison in vivo

Despite the availability of multiple solutions for assessing myocardial strain by ultrasound, little is currently known about the relative performance of the different methods. In this study, we sought to contrast two strain estimation techniques directly (speckle tracking and elastic registration) in an in vivo setting by comparing both to a gold standard reference measurement. In five open-chest sheep instrumented with ultrasonic microcrystals, 2-D images were acquired with a GE Vivid7 ultrasound system. Radial (epsilon(RR)) , longitudinal (epsilon(LL)) , and circumferential strain (epsilon(CC)) were estimated during four inotropic stages: at rest, during esmolol and dobutamine infusion, and during acute ischemia. The correlation of the end-systolic strain values of a well-validated speckle tracking approach and an elastic registration method against sonomicrometry were comparable for epsilon(LL) (r = 0.70 versus r = 0.61, respectively; p = 0.32) and epsilon(CC) (r = 0.73 versus r = 0.80 respectively; p = 0.31). However, the elastic registration method performed considerably better for epsilon(RR) (r = 0.64 versus r = 0.85 respectively; p = 0.09). Moreover, the bias and limits of agreement with respect to the reference strain estimates were statistically significantly smaller in this direction (p < 0.001). This could be related to regularization which is imposed during the motion estimation process as opposed to an a posteriori regularization step in the speckle tracking method. Whether one method outperforms the other in detecting dysfunctional regions remains the topic of future research

Universal Digital Controller for Boost CCM Power Factor Correction Stages Based on Current Rebuilding Concept

Continuous conduction mode power factor correction (PFC) without input current measurement is a step forward with respect to previously proposed PFC digital controllers. Inductor volt-second (vsL) measurement in each switching period enables digital estimation of the input current; however, an accurate compensation of the small errors in the measured vsL is required for the estimation to match the actual current. Otherwise, they are accumulated every switching period over the half-line cycle, leading to an appreciable current distortion. A vsL estimation method is proposed, measuring the input (vg) and output voltage (vo). Discontinuous conduction mode (DCM) occurs near input line zero crossings and is detected by measuring the drain-to-source MOSFET voltage vds. Parasitic elements cause a small difference between the estimated voltage across the inductor based on input and output voltage measurements and the actual one, which must be taken into account to estimate the input current in the proposed sensorless PFC digital controller. This paper analyzes the current estimation error caused by errors in the ON-time estimation, voltage measurements, and the parasitic elements. A new digital feedback control with high resolution is also proposed. It cancels the difference between DCM operation time of the real input current, (TDCMg) and the estimated DCM time (TDCMreb). Therefore, the current estimation is calibrated using digital signals during operation in DCM. A fast feedforward coarse time error compensation is carried out with the measured delay of the drive signal, and a fine compensation is achieved with a feedback loop that matches the estimated and real DCM time. The digital controller can be used in universal applications due to the ability of the DCM time feedback loop to autotune based on the operation conditions (power level, input voltage, output v- ltage...), which improves the operation range in comparison with previous solutions. Experimental results are shown for a 1-kW boost PFC converter over a wide power and voltage range

Current error compensation for current-sensorless power factor corrector stage in continuous conduction mode

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. V. M. Lopez-Martin, F. J. Azcondo, and A. de Castro, "Current error compensation for current-sensorless power factor corrector stage in continuous conduction mode", 2012 IEEE 13th Workshop on Control and Modeling for Power Electronics (COMPEL), Kyoto (Japan), 2012, pp. 1-8A universal digital PFC current-sensorless controller based on control of estimated current is presented. Parasitic elements cause a small difference between the measured input voltage and the voltage across the inductance in a boost converter, which must be taken into account to estimate the input current in a sensorless PFC digital controller. To compensate for the deviation caused by the parasitic elements, and so minimize the current estimation error, the article proposes a digital feedback control technique that cancels the time difference between DCM operation time of the real input current (TinDCM) and the estimated current (TrebDCM). Experimental results, obtained using a boost PFC converter under different conditions, are shown for verification purposes.This work was supported by the Spanish Ministry of Science TEC FEDER 2011-2361

Auto-tuning of Digitally Controlled Single-Phase Low Harmonic Rectifiers and Inverters

Effective power transfer has been one of the main issues in power electronics. In particular, low-harmonic alternating current (AC) shaping is required by various regulations at the interface between AC power grid and direct current (DC) loads or sources,. In order to meet rapidly evolving efficiency standards and environmental concerns, intelligent AC current shaping strategies are required. In the power converter stage, however, inherent uncertainties caused by passive component tolerances and changes in operating conditions may impair the control loop stability, while mis-detection of operating modes over wide load range aggravates the situation further. This thesis introduces an auto-tuning technique in digitally controlled single-phase AC-DC rectifiers and DC-AC inverters. The approach is capable of precise on-line estimation of the power stage passive component values. The control loop compensator parameters are modified adaptively to maintain the nominal stability margins and control loop bandwidth based on the estimated component values. Furthermore, accurate continuous conduction mode (CCM) and discontinuous conduction mode (DCM) boundary detection is achieved as a result of the tuning process, without the need for additional circuitry. Implementation of the tuning approach is relatively simple. The proposed tuning approach is verified on experimental AC-DC and DC-AC prototypes

High-resolution error compensation in continuous conduction mode power factor correction stage without current sensor

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. V. M. López-Martín, F. J. Azcondo, and Á. de Castro, "High-resolution error compensation in continuous conduction mode power factor correction stage without current sensor", in 2012 15th International Power Electronics and Motion Control Conference (EPE/PEMC), Novi Sad (Serbia), 2012.Continuous conduction mode power factor correction (PFC) without input current measurement is a step forward with respect to previously proposed PFC digital controllers. Inductance volt-second (vsL) measurement in each switching period enables the estimation of input current, but an accurate compensation of the small errors in the measured vsL is required. Otherwise, they are accumulated over a half-cycle line, leading to an appreciable current distortion. A vsL estimation is proposed, measuring the input (vin) and the the output voltage (vo). Discontinuous conduction mode (DCM) occurs near input line zero crossings, and is also detected by measuring MOSFET vds. This article analyzes the current estimation error caused by errors in the on-time estimation and voltage measurements, and proposes the minimization of vsL errors by cancelling the difference between estimated DCM (TDCMinereb) and real DCM (TDCMin) times with a signal (vdig), generated in the digital device. Therefore, the current estimation is calibrated using digital signals during the operation in DCM. Feedfoward coarse time error compensation is carried out with the measured delay of the drive signal, and then a fine compensation is achieved with a feedback loop that adjusts vdig. Experimental results are shown for a 1 kW boost PFC converter.This work was supported in part by the Spanish Ministry of Science TEC - FEDER 2011-2361