This paper presents a sensorless motor drive scheme by a fusion of the electrical model-based estimation and the mechanical model-based observer with respect to the position servo with a heavy load. ...The signal injection is applied to extract the position information from the magnetic saliency. However, in the low-speed and heavy-load scenarios, the position observability degenerates in the electrical model due to the core saturation. Nevertheless, the mechanical motion states, including the rotor position, can always be adequately extracted from the mechanical motion model. The extended Kalman filter (EKF) is adopted to fuse the information from the mechanical motion perception and the signal injection-based estimation so that the speed estimate quality gets significant improvement especially when the core saturation occurs. A disturbance-rejection mechanism is introduced to resist the parameter inaccuracy and inconstancy of the EKF model. The fused estimates are applied with a model predictive control in the speed loop to realize the servo control. The sensorless scheme is validated in a heavy-load pendulum servo bench, 200% of the machine rating torque, driven by a surface-mounted permanent magnet synchronous machine.
Review of propulsion systems on LNG carriers Fernández, Ignacio Arias; Gómez, Manuel Romero; Gómez, Javier Romero ...
Renewable & sustainable energy reviews,
January 2017, 2017-01-00, Volume:
67
Journal Article
Peer reviewed
Vessel ozone depleting emission regulations are regulated in Annex VI of the MARPOL Convention, wherein the maximum levels of NOx, SOx and suspended particles are established. These increasingly ...strict regulations, together with the increase in natural gas consumption and its price, have conditioned propulsion systems implemented on board vessels.
This article reviews the different propulsion systems used on board vessels for the transport of Liquefied Natural Gas (LNG). The study describes the main characteristics of the propulsion systems, and the advantages and drawbacks that come along with these, from its very beginnings up to the systems installed to date. The described propulsion systems include both gas and steam turbines, combined cycles, 2 and 4 stroke internal combustion engines, as well as reliquefaction plants, while encompassing mechanical, electric and Dual Fuel (DF) technology systems.
The propulsion systems implemented have undergone continual alteration in order to adjust to market needs, which were always governed by both efficiency and the possibility of consuming boil-off gas (BOG), always in compliance with the strict antipollution regulations in force.
The current direction of LNG vessel propulsion systems is the installation of 2-stroke DF low pressure engines due to their high efficiency and their possibility of installing a BOG reliquefaction plant. Another great advantage of this propulsion system is its compliance with the IMO TIER III emission regulations, without the need to install any supplementary gas treatment system.
This paper presents an empirical study of feature extraction methods for the application of low-speed slew bearing condition monitoring. The aim of the study is to find the proper features that ...represent the degradation condition of slew bearing rotating at very low speed (≈ 1 r/min) with naturally defect. The literature study of existing research, related to feature extraction methods or algorithms in a wide range of applications such as vibration analysis, time series analysis and bio-medical signal processing, is discussed. Some features are applied in vibration slew bearing data acquired from laboratory tests. The selected features such as impulse factor, margin factor, approximate entropy and largest Lyapunov exponent (LLE) show obvious changes in bearing condition from normal condition to final failure.
This paper presents an acoustic emission-based method for the condition monitoring of low speed reversible slew bearings. Several acoustic emission (AE) hit parameters as the monitoring parameters ...for the detection of impending failure of slew bearings are reviewed first. The review focuses on: (1) the application of AE in typical rolling element bearings running at different speed classifications, i.e. high speed (>600rpm), low speed (10–600rpm) and very low speed (<10rpm); (2) the commonly used AE hit parameters in rolling element bearings and (3) AE signal processing, feature extraction and pattern recognition methods. In the experiment, impending failure of the slew bearing was detected by the AE hit parameters after the new bearing had run continuously for approximately 15 months. The slew bearing was then dismantled and the evidence of the early defect was analysed. Based on the result, we propose a feature extraction method of the AE waveform signal using the largest Lyapunov exponent (LLE) algorithm and demonstrate that the LLE feature can detect the sign of failure earlier than the AE hit parameters with improved prediction of the progressive trend of the defect.
•This paper presents an AE-based method for the condition monitoring of low speed slew bearing.•The use of AE as the condition monitoring method of rolling element bearings is reviewed.•A feature extraction method of the AE waveform signal using the largest Lyapunov exponent (LLE) algorithm is proposed.
This paper presents a speed estimation scheme by combining a second-order sliding-mode observer (SMO) with the model reference adaptive system (MRAS) in the sensorless-vector-controlled linear ...induction motor (LIM) drives for medium-low speed maglev applications. A state space-vector model of the LIM considering the dynamic end effects is rearranged in order to be represented by the form of the super-twisting algorithm (STA). Then, an STA-SMO-based stator current observer of the LIM with Popov's hyperstability theory is designed, which is used to replace the reference model of the MRAS-based scheme. Correspondingly, the actual stator current model is regarded as the adaptive model of the MRAS for speed estimation. Meanwhile, because the variation of stator resistance associated with stator temperature may lead to a large estimated error and even system instability, a parallel stator resistance on-line identification scheme is adopted in the proposed speed estimation scheme to reduce the speed error and improve the stability of the sensorless control system. Compared to the speed estimation schemes based on the Luerberger observer with MRAS and the single-manifold SMO, the proposed speed estimation scheme exhibits better estimated performance. The effectiveness and feasibility of the proposed speed estimation scheme have been verified by simulation and hardware-in-the-loop tests.
ZusammenfassungMittlerweile ist die Verwendung von autologen Blutkonzentratsystemen wie dem plättchenreichen Fibrin („platelet-rich fibrin“, PRF) in vielen Praxen und Kliniken angekommen. Auch ist es ...Gegenstand umfassender Forschung zur klinischen Effizienz in verschiedenen Anwendungen. Dennoch mangelt es immer noch an ausreichend systematischen Untersuchungen zum Einfluss von PRF auf die Regeneration des Kieferkamms nach Zahnextraktion in Vorbereitung auf eine Implantation. Die Einführung und Anwendung des Low-Speed Centrifugation Concept (LSCC) ermöglicht reproduzierbare, systematische Untersuchungen in diesem Bereich. Neueste klinische Studienerkenntnisse deuten darauf hin, dass PRF als Promotor der Wundheilungskaskade fungiert. Dabei sorgt scheinbar seine Eigenschaft als Leitstruktur und natürliches Drug-Delivery-System endogener Wachstumsfaktoren für eine Beschleunigung der Geweberegeneration des Kieferkamms. Dies resultiert in suffizientem und narbenarmem Weichgewebe, welches insbesondere für eine nachfolgende Implantation im ehemaligen Extraktionsgebiet eine weichgewebige funktionell-ästhetische Schutzfunktion bieten kann.
Abstract This paper introduces a direct torque control technology based on NPC three-level SVPWM. It uses the Matlab platform to build a simulation model. It verifies the ideal waveform of the ...torque, magnetic chain, and current of the NPC-SVPWM direct torque control system under high speed and low speed with no load and load. This technique improves the waveform of the stator current and stator magnetic chain and solves the problem of the switching frequency not being fixed. Through this technique, it not only retains the robustness of the direct torque technique to the parameter change, but also effectively reduces the torque pulsation.
More than thirty years ago, it was theoretically predicted that friction for incommensurate contacts between atomically smooth, infinite, crystalline materials (e.g., graphite, MoS2) is vanishing in ...the low speed limit, and this corresponding state was called structural superlubricity (SSL). However, experimental validation of this prediction has met challenges, since real contacts always have a finite size, and the overall friction arises not only from the atoms located within the contact area, but also from those at the contact edges which can contribute a finite amount of friction even when the incommensurate area does not. Here, we report, using a novel method, the decoupling of these contributions for the first time. The results obtained from nanoscale to microscale incommensurate contacts of graphite under ambient conditions verify that the average frictional contribution of an inner atom is no more than 10−4 that of an atom at the edge. Correspondingly, the total friction force is dominated by friction between the contact edges for contacts up to 10 μ m in lateral size. We discuss the physical mechanisms of friction observed in SSL contacts, and provide guidelines for the rational design of large-scale SSL contacts.
To evaluate the dynamics of the coupled medium-low-speed maglev train-turnout system, a rigid-flexible dynamics model of the coupled system was developed based on multi-body dynamics theory and ...finite element method. The modal and dynamic responses results obtained from the model calculations were compared with the field test results, and the dynamic interaction characteristics of the coupled system under different operating conditions were investigated using the validated simulation model. Research results show that both the increase in the support stiffness of the turnout and the rational choice of some key parameters of the coupled system will ensure the levitation stability of the train. Increasing the support stiffness of the turnout by means of adding a trolley to support in the middle of the long-span girder (LSG) facilitates the stable levitation of the train when standing still above the turnout and improves the dynamic performance of the coupled system. By optimising some key parameters, including limiting the flatness of the magnetic pole surface of the turnout track within 1.5 mm, and taking the vertical damping of the air springs for overloaded train within 9000∼11,000 N·s/m, significant improvements in the dynamic performance of the train and the turnout can also be achieved.
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