This paper proposes a motion-sensorless control system using direct torque control with space vector modulation for interior permanent magnet synchronous motor (IPMSM) drives, for wide speed range ...operation, including standstill. A novel stator flux observer with variable structure uses a combined voltage-current model with PI compensator for low-speed operations. As speed increases, the observer switches gradually to a PI compensated closed-loop voltage model, which is solely used at high speeds. High-frequency rotating-voltage injection with a single D-module bandpass vector filter and a phase-locked loop state observer with a new synchronization procedure are used to estimate the rotor position, which is needed only by the current model in stator flux observer at low speeds. A new rotor speed estimator for the whole speed-loop range, based on the stator flux speed estimation with a new dynamic correction depending on estimated torque, is proposed and tested. Extensive simulation results and significant experimental results provided good performance for the proposed IPMSM sensorless system in more than 1:1000 speed range, under full-load operation, from very low speeds (1 r/min experimental) up to rated speed.
This study introduces a novel fast dynamic sensorless control for high-speed surface permanent magnet synchronous motor (SPMSM) drives based on a V/f control, with two stabilising loops to correct ...the stator voltage amplitude and phase by a closed loop for zero interior reactive power. This solution avoids Park transformations, speed and current closed-loop control. Comprehensive experimental test results are given with a 50 Vdc MOSFET inverter and a SPMSM with very low electrical time constant of 0.5 ms and low inertia. Fast speed reversal of ±10,000 rpm within 160 ms with good load rejection, starting from any initial rotor position and running to 20,000 rpm constitute the paper core. The speed (torque) dynamics are similar to those of vector control method with encoder, but online computation effort is notably lower, with superior control robustness. This solution should be particularly suitable for very high-speed drives with rated frequency of 0.5 KHz-10 kHz, where online computation time cycle is inherently small.
Two flux observers for wide speed range direct torque control (DTC) of sensorless induction-motor drives are presented and compared. The first one is a full-order sliding-mode observer with ...proportional plus integral (PI) compensation, without rotor speed adaptation. The second one is based on a zero phase-delay-improved integrator of the voltage model, which uses only a PI flux amplitude control with stator-flux reference magnitude in the correction loop. In both cases, an estimated dc offset is built up and memorized by the PI integral component and this totally compensates for all dc offsets and drifts originated in the acquisition channels. Two feasible solutions for on-line stator-resistance identification are proposed. Simulation and experimental results prove the accuracy, robustness, and high-dynamic performance of both observers when employed in sensorless DTC drives. The effectiveness of state estimation is confirmed by a steady state and transient sensorless operation at very low speed with rated load torque and step-speed reversal.
We present the largest, most homogeneous catalogue of merging galaxies in the nearby Universe obtained through the Galaxy Zoo project – an interface on the World Wide Web enabling large-scale ...morphological classification of galaxies through visual inspection of images from the Sloan Digital Sky Survey (SDSS). The method converts a set of visually inspected classifications for each galaxy into a single parameter (the ‘weighted-merger-vote fraction,’fm) which describes our confidence that the system is part of an ongoing merger. We describe how fm is used to create a catalogue of 3003 visually selected pairs of merging galaxies from the SDSS in the redshift range 0.005 < z < 0.1. We use our merger sample and values of fm applied to the SDSS Main Galaxy Spectral sample to estimate that the fraction of volume-limited (Mr < −20.55) major mergers (1/3 < M*1/M*2 < 3) in the nearby Universe is 1–3 ×C per cent, where C∼ 1.5 is a correction factor for spectroscopic incompleteness. Having visually classified the morphologies of the constituent galaxies in our mergers, we find that the spiral-to-elliptical ratio of galaxies in mergers is higher by a factor of ∼2 relative to the global population. In a companion paper, we examine the internal properties of these merging galaxies and conclude that this high spiral-to-elliptical ratio in mergers is due to a longer time-scale over which mergers with spirals are detectable compared to mergers with ellipticals.
This study is focused on very low speed performance comparison between two sensorless control systems based on the novel 'active flux' concept, that is, the current/voltage vector control versus ...direct torque and flux control for interior permanent magnet synchronous motor (IPMSM) drives with space vector modulation, without signal injection. The active flux, defined as the flux that multiplies i^sub q^ current in the dq-model torque expression of all ac machines, is easily obtained from the stator-flux vector and has the rotor position orientation. Therefore, notable simplification in the rotor position and speed estimation is obtained. For IPMSM, a stator-flux observer is employed based on combined current and voltage models, with speed-dependent smooth transition between them using a PI compensator of flux error. The comparative experimental results using both sensorless control systems are presented to verify the principles and to demonstrate the effectiveness of the active flux observer at very low speeds from 20 rpm to 2 rpm.
Following the study of Darg et al., we explore the environments, optical colours, stellar masses, star formation and active galactic nucleus activity in a sample of 3003 pairs of merging galaxies ...drawn from the Sloan Digital Sky Survey using visual classifications from the Galaxy Zoo project. While Darg et al. found that the spiral-to-elliptical ratio in (major) mergers appeared higher than that of the global galaxy population, no significant differences are found between the environmental distributions of mergers and a randomly selected control sample. This makes the high occurrence of spirals in mergers unlikely to be an environmental effect and must therefore arise from differing time-scales of detectability for spirals and ellipticals. We find that merging galaxies have a wider spread in colour than the global galaxy population, with a significant blue tail resulting from intense star formation in spiral mergers. Galaxies classed as star-forming using their emission-line properties have average star formation rates approximately doubled by the merger process though star formation is negligibly enhanced in merging elliptical galaxies. We conclude that the internal properties of galaxies significantly affect the time-scales over which merging systems can be detected (as suggested by recent theoretical studies) which leads to spirals being ‘over-observed’ in mergers. We also suggest that the transition mass 3 × 1010 M⊙, noted by Kauffmann et al., below which ellipticals are rare could be linked to disc survival/destruction in mergers.
Rotor and stator flux orientations are now standard concepts in vector and direct torque control of ac drives. The salient-pole rotor machines, where magnetic saturation plays a key role, still pose ...notable problems in flux, rotor position and speed estimations for motion-sensorless control, especially in the low-speed range (below 30 rpm in general), leading to numerous dedicated state observers. This letter introduces a rather novel (or generalization) concept- active flux or torque-producing flux -and its utilization in all ac drives by employing a unified state observer for motion-sensorless control in a wide speed range. The active-flux concept turns all salient-pole traveling field machines into nonsalient-pole ones. The active-flux vector is aligned to the rotor d axis for all synchronous machines and to the rotor-flux vector axis for induction machines. This way, the rotor position and speed observer seems more amenable to a wide speed range, with smaller dynamic errors. This observer, based on the active-flux concept, is pretty much the same for all ac drives. An example of implementation for an interior permanent-magnet synchronous motor with weak permanent magnets and large magnetic saliency that compares very favorably with respect to most signal injection methods, down to 1 rpm and up to 4000 rpm, is provided through digital simulations. Experiments are under way.
We present a study of local post-starburst galaxies (PSGs) using the photometric and spectroscopic observations from the Sloan Digital Sky Survey and the results from the Galaxy Zoo project. We find ...that the majority of our local PSG population have neither early- nor late-type morphologies but occupy a well-defined space within the colour-stellar mass diagram, most notably, the low-mass end of the 'green valley' below the transition mass thought to be the mass division between low-mass star-forming galaxies and high-mass passively evolving bulge-dominated galaxies. Our analysis suggests that it is likely that local PSGs will quickly transform into 'red', low-mass early-type galaxies as the stellar morphologies of the 'green' PSGs largely resemble that of the early-type galaxies within the same mass range. We propose that the current population of PSGs represents a population of galaxies which is rapidly transitioning between the star-forming and the passively evolving phases. Subsequently, these PSGs will contribute towards the build-up of the low-mass end of the 'red sequence' once the current population of young stars fade and stars are no longer being formed. These results are consistent with the idea of 'downsizing' where the build-up of smaller galaxies occurs at later epochs.
Permanent magnet-assisted reluctance synchronous machine (PM-RSM) starter alternator systems are credited with good performance for wide speed range in hybrid electric vehicles. This paper proposes a ...motion-sensorless motor/generator control of PM-RSM from zero speed up to maximum speed, using direct torque and flux control with space vector modulation. A quasioptimal stator flux reference with a flux versus torque functional is proposed. A stator flux observer in wide speed range uses combined voltage-current models for low speeds, and only the voltage model for medium to high speeds, both in proportional-integral closed loop. A novel rotor speed and position observer with a fusion strategy employs signal injection and only one D-module vector filter in stator reference for low speed, combined with a speed observer from the stator flux vector estimation-for medium-high speed. The proposed system is introduced piece by piece and then implemented on a dSpace 1103 control board with a 350-A metal-oxide-semiconductor field-effect transistor-pulse-width modulation converter connected to a 42-Vdc, 55-Ah battery, and a 140-Nm peak torque PM-RSM. Extensive experimental results from very low speed to high speed, regarding observers and drive responses, including artificial loading (motoring and generating), seem very encouraging for future starter-alternator systems
This paper proposes an implementation of a motion-sensorless control system in wide speed range based on "active flux" observer, and direct torque and flux control with space vector modulation ...(DTFC-SVM) for the interior permanent magnet synchronous motor (IPMSM), without signal injection. The concept of "active flux" (or "torque producing flux") turns all the rotor salient-pole ac machines into fully nonsalient-pole ones. A new function for L q inductance depending on torque is introduced to model the magnetic saturation. Notable simplification in the rotor position and speed estimation is obtained, because the active flux position is identical with the rotor position. Extensive experimental results are presented to verify the principles and to demonstrate the effectiveness of the proposed sensorless control system. With the active flux observer, the IPMSM drive system operates from very low speed of 2 r/min at half full-load up to 1400 r/min. Higher speed is possible, in principle, with flux weakening.
PDF
