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Critical speed

About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.


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Patent
28 Jul 1989
TL;DR: In this article, a method of computing the rotating speed of a rotating body includes the steps of setting speed computation reference time periods with respect to a pulse train signal obtained from the output of rotating speed sensor.
Abstract: A method of computing the rotating speed of a rotating body includes the steps of setting speed computation reference time periods with respect to a pulse train signal obtained from the output of a rotating speed sensor; measuring time length from the last pulse edge in the previous speed computation reference time period to the last pulse edge in the current speed computation reference time period; and computing the rotating speed of the rotating body on the basis of the result of the time length measurement. The time point when the previous procedure of speed computation terminated corresponds to the time point when the current procedure of speed computation starts, thus making it possible to achieve continuous speed computation. In this way, an enhanced accuracy can be achieved in speed measurement for low speed range, which leads to improved control performance in anti-lock control and traction control for the low speed range.

15 citations

Journal ArticleDOI
TL;DR: This paper proposes speed difference damping controller (SDDC), which is a novel and improved control technique that decouples the two above-mentioned parameters and improves the electromechanical performance significantly, reducing the torsional vibration of the driveline.
Abstract: Though power electronic interface is prone to higher failure in wind turbine system (WTS), the failure downtime due to mechanical and generator malfunctioning is highest. Unforeseen electromechanical interactions caused due to dynamic load variation and transient torsional stress is a major cause for failures in the drive-train and generator in WTS. In the literature, several techniques, such as generator speed feedback, stress damping controller, and virtual inertia damping controller, have been proposed in regards to the problem stated. Though the techniques are promising, the factor of independent control of natural frequency and damping ratio has not been considered. This paper proposes speed difference damping controller (SDDC), which is a novel and improved control technique that decouples the two above-mentioned parameters and improves the electromechanical performance significantly, reducing the torsional vibration of the driveline. The controller gains are designed based on the derived two-inertia system model that is used to represent the first natural frequency torsional vibration. In this paper, theoretical analysis and control design of SDDC are articulately addressed. A detailed comparative study of SDDC is carried out with respect to the other proposed controllers. The modeled WTS is examined for the first torsional natural frequency under two extreme wind-input conditions, i.e., sinusoidal wind condition, wind impulse, and grid dynamic, and one real-wind test case scenario. For the experimental verification, a multimass test rig operating at the critical speed and dynamic impulse load variation is analyzed in parts.

15 citations

Journal ArticleDOI
TL;DR: In this paper, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified.
Abstract: The basic operation principle of elastic support/dry friction damper in rotor system was introduced and the unbalance response of the rotor with elastic support/dry friction damper was analyzed theoretically. Based on the previous structure using an electromagnet as actuator, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified. The experimental results show that the active elastic support/dry friction damper with piezoelectric ceramic actuator can significantly reduce vibration in rotor system; the vibration amplitude of the rotor in critical speed region decreased more than 2 times, and the active damper can protect the rotor when a blade-out event happened, so the rotor can traverse the critical speed and shut down smoothly. In addition, the structure is much simpler than the previous, the weight was reduced by half and the power consumption was only 5 W.

14 citations

Journal ArticleDOI
TL;DR: In this paper, the concept of online electronic switching of windings was applied to a single-phase induction motor with two separate windings with different pole numbers p1 = 4 and p2 = 6 and an auxiliary winding required for starting.
Abstract: The concept of online electronic switching of windings will be applied to a single-phase induction motor with two separate windings with different pole numbers p1 = 4 and p2 = 6 and an auxiliary winding required for starting. During switchover from the low-speed winding to the high-speed winding, and vice versa, lasting less than a few milliseconds, small electrical torque and speed transients occur. Relying on closed-loop speed control, a smooth speed response is measured. This concept is, therefore, applicable to variable-speed drives, where a large speed range is desirable. Test data indicate that a speed-control range from 600 to 4000 r/min is obtainable with a single-phase induction motor.

14 citations

Book ChapterDOI
01 Jan 2004
TL;DR: In this paper, it was shown that the hoop stress around a mode I crack in a harmonic solid becomes bimodal at a critical speed of about 73 percent of the Rayleigh speed, in agreement with the continuum mechanics theory.
Abstract: Crack branching and instability phenomena are believed to be closely related to the circumferential or hoop stress in the vicinity of the crack tip. In this paper we show that the hoop stress around a mode I crack in a harmonic solid becomes bimodal at a critical speed of about 73 percent of the Rayleigh speed, in agreement with the continuum mechanics theory. Additionally, we compare the energy flow field predicted by continuum theory with the solution of molecular-dynamics simulations and show that the two approaches yield comparable results for the dynamic Poynting vector field. This study exemplifies joint atomistic and continuum modelling of nanoscale dynamic systems and yields insight into coupling of the atomistic scale with continuum mechanics concepts.

14 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
202343
2022120
202182
202092
2019102