73,711 research outputs found
Self-Commissioning Algorithm for Inverter Non-Linearity Compensation in Sensorless Induction Motor Drives
In many sensorless field-oriented control schemes for induction motor (IM) drives, flux is estimated by means of measured motor currents and control reference voltages. In most cases, flux estimation is based on the integral of back-electromotive-force (EMF) voltages. Inverter nonlinear errors (dead-time and on-state voltage drops) introduce a distortion in the estimated voltage that reduces the accuracy of the flux estimation, particularly at low speed. In the literature, most of the compensation techniques of such errors require the offline identification of the inverter model and offline postprocessing. This paper presents a simple and accurate method for the identification of inverter parameters at the drive startup. The method is integrated into the control code of the IM drive, and it is based on the information contained in the feedback signal of the flux observer. The procedure applies, more in general, to all those sensorless ac drives where the flux is estimated using the back-EMF integration, not only for IM drives but also for permanent-magnet synchronous motor drives (surface-mounted permanent magnet and interior permanent magnet). A self-commissioning algorithm is presented and tested for the sensorless control of an IM drive, implemented on a fixed-point DSP. The feasibility and effectiveness of the method are demonstrated by experimental result
Digital Current-Control Schemes
The paper is about comparing the performance of digital signal processor-based current controllers for three-phase active power filters. The wide use of nonlinear loads, such as front-end rectifiers connected to the power distribution systems for dc supply or inverter-based applications, causes significant power quality degradation in power distribution networks in terms of current/voltage harmonics, power factor, and resonance problems. Passive LC filters (together with capacitor banks for reactive power compensation) are simple, low-cost, and high-efficiency solution
A Robust Adaptive Dead-Time Compensator with Application to A Solar Collector Field
This paper describes an easy-to-use PI controller with dead-time compensation that presents robust behaviour and can be applied to plants with variable dead-time. The formulation is based on an adaptive Smith predictor structure plus the addition of a filter acting on the error between the output and its prediction in order to improve robustness. The implementation of the control law is straightforward, and the filter needs no adjustment, since it is directly related to the plant dead-time. An application to an experimentally validated nonlinear model of a solar plant shows that this controller can improve the performance of classical PID controllers without the need of complex calculations.Ministerio de Ciencia y TecnologĂa TAP95-37
G Electronics and Data Acquisition (Forward-Angle Measurements)
The G parity-violation experiment at Jefferson Lab (Newport News, VA) is
designed to determine the contribution of strange/anti-strange quark pairs to
the intrinsic properties of the proton. In the forward-angle part of the
experiment, the asymmetry in the cross section was measured for
elastic scattering by counting the recoil protons corresponding to the two
beam-helicity states. Due to the high accuracy required on the asymmetry, the
G experiment was based on a custom experimental setup with its own
associated electronics and data acquisition (DAQ) system. Highly specialized
time-encoding electronics provided time-of-flight spectra for each detector for
each helicity state. More conventional electronics was used for monitoring
(mainly FastBus). The time-encoding electronics and the DAQ system have been
designed to handle events at a mean rate of 2 MHz per detector with low
deadtime and to minimize helicity-correlated systematic errors. In this paper,
we outline the general architecture and the main features of the electronics
and the DAQ system dedicated to G forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section
A. It has been written with Latex using \documentclass{elsart}. Nuclear
Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment In Press (2007
A unified smith predictor approach for power system damping control design using remote signals
Published versio
Long-distance frequency transfer over an urban fiber link using optical phase stabilization
We transferred the frequency of an ultra-stable laser over 86 km of urban
fiber. The link is composed of two cascaded 43-km fibers connecting two
laboratories, LNE-SYRTE and LPL in Paris area. In an effort to realistically
demonstrate a link of 172 km without using spooled fiber extensions, we
implemented a recirculation loop to double the length of the urban fiber link.
The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz
linewidth. The fiber-induced phase noise is measured and cancelled with an all
fiber-based interferometer using commercial off the shelf pigtailed
telecommunication components. The compensated link shows an Allan deviation of
a few 10-16 at one second and a few 10-19 at 10,000 seconds
Suppression of line voltage related distortion in current controlled grid connected inverters
The influence of selected control strategies on the level
of low-order current harmonic distortion generated by an inverter
connected to a distorted grid is investigated through a combination
of theoretical and experimental studies. A detailed theoretical
analysis, based on the concept of harmonic impedance, establishes
the suitability of inductor current feedback versus output
current feedback with respect to inverter power quality. Experimental
results, obtained from a purpose-built 500-W, three-level,
half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an
output current total harmonic distortion (THD) some 29% lower
than that achieved using output current feedback. A feed-forward
grid voltage disturbance rejection scheme is proposed as a means to
further reduce the level of low-order current harmonic distortion.
Results obtained from an inverter with inductor current feedback
and optimized feed-forward disturbance rejection show a THD of
just 3% at full-load, representing an improvement of some 53% on
the same inverter with output current feedback and no feed-forward
compensation. Significant improvements in THD were also
achieved across the entire load range. It is concluded that the use
of inductor current feedback and feed-forward voltage disturbance
rejection represent costâeffect mechanisms for achieving improved
output current quality
Push recovery with stepping strategy based on time-projection control
In this paper, we present a simple control framework for on-line push
recovery with dynamic stepping properties. Due to relatively heavy legs in our
robot, we need to take swing dynamics into account and thus use a linear model
called 3LP which is composed of three pendulums to simulate swing and torso
dynamics. Based on 3LP equations, we formulate discrete LQR controllers and use
a particular time-projection method to adjust the next footstep location
on-line during the motion continuously. This adjustment, which is found based
on both pelvis and swing foot tracking errors, naturally takes the swing
dynamics into account. Suggested adjustments are added to the Cartesian 3LP
gaits and converted to joint-space trajectories through inverse kinematics.
Fixed and adaptive foot lift strategies also ensure enough ground clearance in
perturbed walking conditions. The proposed structure is robust, yet uses very
simple state estimation and basic position tracking. We rely on the physical
series elastic actuators to absorb impacts while introducing simple laws to
compensate their tracking bias. Extensive experiments demonstrate the
functionality of different control blocks and prove the effectiveness of
time-projection in extreme push recovery scenarios. We also show self-produced
and emergent walking gaits when the robot is subject to continuous dragging
forces. These gaits feature dynamic walking robustness due to relatively soft
springs in the ankles and avoiding any Zero Moment Point (ZMP) control in our
proposed architecture.Comment: 20 pages journal pape
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