1,721,108 research outputs found
A simplified position observer for zero-speed sensorless control of synchronous motors
No full textThis paper considers a sensorless control scheme based on pulsating high-frequency voltage injection applied to a linear permanent magnet synchronous motor (LPMSM). The injected signal is superimposed along the estimated d-axis and the mover position is obtained by minimizing the estimated q-axis current using a position observer. Three position observers, with different level of computational complexity, are considered. The first one utilizes a proportional-integral-derivative (PID) regulator, followed by the mechanical model of the LPMSM. The PID regulator output is the estimated torque and the mechanical system model is used to estimate speed and position. The second and third one employ a proportional-integral (PI) and proportional (P) regulator respectively to estimate the speed and an integrator to calculate the position. The use of the latter observer simplifies the commissioning procedure and reduces the computational burden without compromising performances. The comparison of the three schemes has been carried out with an extensive experimental study
Braking torque compensation strategy and thermal behavior of a dual three-phase winding PMSM during short-circuit fault
No full textPermanent magnet synchronous machines (PMSMs)employing the dual three-phase winding represent a suitable solution for complying with the reliability requirements typically needed in safety-critical applications. Their inherent fault-tolerant capability allows to operate the system (e.g. electro mechanical actuator or traction drive-train), even after the occurrence of a three-phase short-circuit in one winding set. Nevertheless, an appropriate post-fault control strategy is indispensable for preventing the PMSM performance derating. In this work, the design of a dual three-phase PMSM, intended for aerospace application, is presented. The PMSM performance is evaluated via finite element (FE)analysis, in both healthy and three-phase short-circuit conditions. A post-fault control strategy aimed at balancing the braking torque is then discussed. Since the implemented strategy is based on the current overload of the healthy winding, the temperature rise is experimentally investigated on the PMSM prototype. The thermal analysis verifies the compensation strategy feasibility, by proving that the thermal overload does not have a major effect on the wire insulation lifetime
On single-phase operation of three-phase synchronous generators
No full textClassical synchronous generators have been used for decades in the field of power generation. The traditional manner of operation of these systems is the balanced, three phase configuration. However, recently there has been an interest in re-configuring consolidated, commercial, three phase generators to operate in single phase operation. A main driver for this phenomenon is the aim of manufacturers to extend their range of products for minimum development cost. Such an approach however brings a number of design challenges, especially in terms of the elevated damper cage currents and the negative sequence currents, when a 3-phase machine is 'forced' to operate in 1-phase. This paper therefore investigates and analyses these challenges. Considering a commercial, 3-phase, 400 kVA alternator. Detailed models, validated against experimental validation in 3-phase operation are first obtained. The machine is then re-configured to single phase operation. This paper proposes and shows how a suitable single phase loading can be found for 3-phase generators operating in single phase
A Time-Saving Approach for the Thermal Lifetime Evaluation of Low-Voltage Electrical Machines
No full textModern electrical machines, such as those employed in transportation applications are required to provide very high performance in terms of power (and torque) density and efficiency. The reality, however, is that the more these machines are 'pushed' in relation to power density, the more is the probability of failure of their insulation systems, through enhanced electrical and thermal stresses. On the other hand, regardless the power density level, the electrical machine still needs to respect the certification processes set by the international standards and procedures. Unfortunately, today reliability and lifetime are still not considered as main design objective functions right from the start of the design process. This is a direct result of a gap in knowledge in terms of the precise understanding of failure mechanisms. If physics of failure models are available, then reliability can be included at all design stages. Therefore, this article proposes a method that shortens the time demanded for the thermal lifetime evaluation procedure or qualification of low-voltage electrical machines. The theory behind the method is presented and, then, experimentally validated on custom designed specimens
Impact of thermal overload on the insulation aging in short duty cycle motors for aerospace
No full textElectric motors for aerospace applications are often characterised by short-time duty rather than continuous-duty operations. Some of the main requirements for these machines are high torque density and reliability. Considerable torque density improvement can be achieved by supplying the windings with current greater than the rated value and thus thermally overloading the machine for short periods of time. However, if the insulation is overheated, the machine lifetime is shortened, and reliability issues can arise. This paper experimentally investigates the influence of short-time thermal overload on the insulation lifetime of low voltage, random wound electrical machines. The analysis is performed on round enamelled magnet wires coils aged by accelerated thermal cycles, and the results are statistically processed by the two-parameter Weibull distribution. The experimental data is also used for building a lifetime estimation model, which is employed for predicting the lifetime of a motor embedded into an electromechanical actuator for landing gear extension/retraction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modelling of linear motor end-effects for saliency based sensorless control
Full text linkIn linear motors, the open structure of the armature produces the so called end-effect. The end-effect introduces non-idealities in the motor magnetic model in dq-synchronous coordinates that require a specific modelling with respect to the well known models of rotating (cylindrical) machines. In particular, for saliency based sensorless control, the end-effect introduces an error in the estimated position that must be taken into account and properly compensated. This paper introduces a general mathematical modeling of the end-effect that can be applied to all linear machines. Based on such model, modified position observers are proposed for sensorless control using pulsating or rotating voltage vectors. Experimental results are presented to verify the feasibility of the proposed method, with reference to the case of a linear tubular permanent magnet motor
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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