There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this ...paper, a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, is proposed. The topology is simulated and experimentally validated, and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current are demonstrated.
Investigations were carried out on a novel direct torque control system, which not only reduces the undesirable torque ripple by up to 98% by means of introducing a modulation between the selected ...active state and a zero state, but also maintains constant switching frequency. Additionally, this two-state modulator is fuzzy adaptive and may be applied to any induction motor. Simulation and the results of experiment illustrate the operation and performance of the proposed fuzzy-logic-based controller.
Investigations were carried out on a novel sensorless drive for induction motors, based on the combination of an open-loop (OL) estimator and a steady-state (SS) estimator. The novelty of this new ...sensorless structure is obtained by an intelligent mixing of the OL estimator response with the SS one. A fuzzy system weights the two estimated speed values according to the motor operating point. Then, the final speed value is obtained averaging the previously weighted speed values. Moreover, the OL estimator response is improved by means of using a fuzzy-controlled adaptive filter that selects the optimum cutoff frequency. The aim of this paper is to obtain a moderate performance sensorless drive for induction motors that could be easily implemented for industrial applications without a high computational effort. Simulation and experimental results illustrate the operation and performance of the proposed fuzzy-logic-based sensorless drive
Direct Torque Control (DTC) has, over the years, become one of the most popular methods of control for induction motors (IM) drive systems.
There still remain, however, many disadvantages with this ...method of control, which have to be overcome. In the present paper we, therefore, consider a method of improving conventional DTC by reducing the undesirable torque ripple that can occur in the output torque. This new method, which is fully described in the paper, also has the additional advantage of maintaining the switching frequency of the power switching devices constant.
The average torque ripple reduction achieved by this new method of control can be greater than 50%. This significant reduction in torque ripple is realised by the introduction of a two state modulation process between the active selected state from conventional DTC and an additional null state. The control of the two state modulation process is achieved by the application of an adaptive Fuzzy Logic controller (FLC).
Additionally, a novel flux optimiser strategy is also introduced into the new DTC system, which together with the two state modulation process further reduces the torque ripple.
Simulation and experimental results for the drive system presented are included in the paper and it is shown that not only good agreement exists between both sets of results but they also support the claims made in the paper.
This paper investigates the use of short voltage vectors of matrix converters to reduce the electromagnetic torque ripple which appears when direct torque control technique is used in induction ...motors. Direct torque control for induction motors using matrix converters is reviewed and it is pointed out the problem of the electromagnetic torque ripple which is one of the most important drawbacks of the direct torque control. The standard look up table for direct torque control, when using matrix converters, is improved in order to include the uncommonly used short voltage vectors. This novel direct torque control approach can differentiate between small and large torque errors and consequently the electromagnetic torque ripple is reduced. Finally, some results, which prove the improvement of the novel direct torque control when using small matrix converter voltage vectors, are shown.
This paper presents a new software-implemented current regulator for three phase loads based on orthogonal two-phase /spl alpha/-/spl beta/ system. The controller uses the module of the error for ...defining two control situations, called of steady state and transitory, which depend on the position of the current error inside or outside of the hysteresis margin. In the steady state, a new active vector voltage application strategy is used for assuring the nearest trajectory to the diameter of the current error within the circular boundary hysteresis when a null vector is applied. Moreover, this null vector is chosen between V(0) and V(7) for reducing the number of inverter's switches commutations. On the other hand, in the transitory zone the control applies only active vectors, for reducing quickly the error inside the hysteresis margins. Computer simulations were carried out in order to investigate the performance of the regulator, and results show the effectiveness of the proposed control scheme.
In this paper an approach to the use of audiovisual material (AM) is presented as an important resource for university education. Some AM has been created, which not only has been used in laboratory ...and master lecturing but also it has helped us in the task of increasing the efficiency of teaching. This work intends to show some examples of production and use of AM for university education.
Assessment of students and the evaluation of their satisfaction has been an important element in the improvement of teaching quality in all the Higher Education areas. Specifically the student ...participation in Computer Science (CS) and Information System (IS) has been highlight valued. Thus a large number of methodologies and standard tools regarding student evaluation has been developed. Specifically, the Students' Evaluation of Education Quality (SEEQ) is a tool that is validated for international use. But its use leads to several problems, such as the low voluntary participation of students. To solve these problems, a short version of this questionnaire developed using statistic tools is proposed. After using the proposed new version, the voluntary participation of students increased. The reduction of the number of questions facilitates the analysis of data, improving the flow of information and feedback between professors and students.
Industrijske primjene sve više trebaju električne pogone s dobrim svojstvima pozicioniranja i regulacije tereta. To se može postići jedino adaptivnim načinom upravljanja, jer se uvjeti terećenja, ...momenti inercije kao i ostali parametri sustava mijenjaju tijekom gibanja. U članku je razvijen adaptivni regulator brzine vrtnje za izmjenični pogon s asinkronim motorom koji koristi jednostavan računski algoritam. Autori predlažu samopodešavajuće upravljanje zasnovano na neizrazitoj adaptaciji s nadzornog nivoa. Nadzorni algoritam neprestano prati stanje sustava i mijenja parametar Ki standardnog PDF regulatora da bi ga adaptirao na promjene stanja u postrojenju. Neizrazita adaptivna strategija realizirana je bez poteškoća, sa svojstvom vrlo brzog učenja te vrlo dobrim svojstvima pozicioniranja i regulacije tereta. Analiza stabilnosti razvijenog regulatora također je napravljena, a eksperimentalni rezultati pokazuju robustnost predloženog algoritma pri uvjetima djelovanja poremećaja u obliku promjenljivog momenta tereta.
Moving towards a more electric aircraft Rosero, J.A.; Ortega, J.A.; Aldabas, E. ...
IEEE aerospace and electronic systems magazine,
03/2007, Letnik:
22, Številka:
3
Magazine Article, Publication
Odprti dostop
The latest advances in electric and electronic aircraft technologies from the point of view of an "all-electric" aircraft are presented herein. Specifically, we describe the concept of a "more ...electric aircraft" (MEA), which involves removing the need for on-engine hydraulic power generation and bleed air off-takes, and the increasing use of power electronics in the starter/generation system of the main engine. Removal of the engine hydraulic pumps requires fully-operative electrical power actuators and mastery of the flight control architecture. The paper presents a general overview of the electrical power generation system and electric drives for the MEA, with special regard to the flight controls. Some discussion regarding the interconnection of nodes and safety of buses and protocols in distributed systems is also presented
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