721 research outputs found
A two stage hybrid maximum power point tracking technique for photovoltaic applications
No full textPhotovoltaic (PV) systems are widely used now a days for coping the growing energy demands all across the globe. The non-linear behavior of the characteristic curve of solar module requires special arrangement to harvest maximum amount of power. To track the Maximum Power Point (MPP) across the non linear IV curve of PV module, techniques are used in addition to the power electronic circuit and are called Maximum Power Point Tacking (MPPT). Various methods of MPPT exists in literature, each bearing its own pros and cons. In this paper we presents a novel technique to improve the performance of conventional Perturb and Observe (P&O) algorithm of MPPT. Our technique removes the drawbacks of P&O under rapidly changing environmental conditions. It also executes less power oscillations under steady state conditions. The algorithm is a hybrid of Fractional Short Circuit current (FSCC) and P&O algorithms. The system takes the advantage of rapid tracking near to MPP using the FSCC and then carry on to track the exact MPP using the traditional P&O technique. The technique is verified through simulation using Matlab/SIMULIN
Microprocessor Based Power Factor Improvement of Induction Motor
No full textThis paper describes the design of a microprocessor controller for a fixed-capacitor, thyristor controller reactor (FC-TCR) compensator to achieve on line and fast power factor improvement of a dynamic load. The microprocessor system monitors the power factor of the load and uses a look-up table to adjust the FC-TCR compensator to give a unity supply power factor. The results show that under all loading conditions, the power factor of almost unity is achieved automatically. The response time of the system is very fast
K.E. Løgstrups tanker tangeret
No full textIn his philosophical dissertation that can be translated as K.E. Løgstrup. A Modern Prophet (1992), Hans Hauge proposed the thesis that the philosophy of Løgstrup, from first to last, tales leave of any epistemological foundation. In this critical evaluation, the author supports the interpretation by Hauge that Løgstrup's appeal to ontology in fact refers to ever changing life situations with each of their own characteristics. However, one has to distinguish between epistemologies. Already in 1933, Løgstrup opposed Husserl's epistemology of the transcendental ego. But only much later, Løgstrup criticized Heidegger for his universalization of the regional ontology of historicity. This metaphysical "Kehre" can be dated between January and September 1969. Furthermore, in his late philosophy, Løgstrup not simply abandoned epistemology. Rather, he developed a non-foundational epistemology on the basis of an interplay between historical understanding, rooted in the need for self-preservation, and the "useless", albeit penetrating sense qualities of the world.</jats:p
Microprocessor based power factor improvement of induction motor
No full textThis paper describes the design of a microprocessor controller for a fixed-capacitor, thyristor controller reactor (FC- TCR) compensator to achieve on line and fast power factor improvement of a dynamic load. The microprocessor system monitors the power factor of the load and uses a look-up table to adjust the FC- TCR compensator to give a unity supply power factor. The results show that under all loading conditions, the power factor of almost unity is achieved automatically. The response time of the system is very fast
A New Sensorless Hybrid MPPT Algorithm Based on Fractional Short-Circuit Current Measurement and P&O MPPT
No full textThis paper presents a new maximum power point tracking (MPPT) method for photovoltaic (PV) systems. The proposed method improves the working of the conventional perturb and observe (P&O) method in changing environmental conditions by using the fractional short-circuit current (FSCC) method. It takes the initial operating point of a PV system by using the short-circuit current method and later shifts to the conventional P&O technique. The advantage of having this two-stage algorithm is rapid tracking under changing environmental conditions. In addition, this scheme offers low-power oscillations around MPP and, therefore, more power harvesting compared with the common P&O method. The proposed MPPT decides intelligently about the moment of measuring short-circuit current and is, therefore, an irradiance sensorless scheme. The proposed method is validated with computer software simulation followed by a dSPACE DS1104-based experimental setup. A buck-boost dc-dc converter is used for simulation and experimental confirmation. Furthermore, the reliability of the proposed method is also calculated. The results show that the proposed MPPT technique works satisfactorily under given environmental scenario
A new irradiance sensorless hybrid MPPT technique for photovoltaic power plants
No full textA hybrid Maximum Power Point Tracking (MPPT) method without using an irradiance sensor is proposed in this paper. The hybrid MPPT method is a combination of conventional Perturb and Observe (P&O) and Fractional Short Circuit Current (FSCC) MPPT technique. The proposed hybrid MPPT decides intelligently about the initial operating point of P&O by using the FSCC MPPT method. This method requires no sensor for irradiation measurement because it detects intelligently about the change in irradiance. Therefore, under dynamic weather conditions the decision about measuring the initial operating point of P&O is intelligent. After finding the initial operating point the system shifts to the conventional P&O method and starts to perturb with a small perturbation size. The use of small perturbation steps enables the system to work with less power oscillations around the Maximum Power Point (MPP), while the use of FSCC helps in rapid tracking of MPP especially under the varying environmental conditions. Thus, the proposed method is fast in tracking the MPP with less power oscillations and hence better performance in terms of energy harvesting when compared with the conventional P&O technique. Impedance matching between solar panel and load is achieved using a DC-DC boost converter and the proposed method is simulated in MATLAB/SIMULINK environment. The system is simulated against the steady and dynamic weather conditions. The results shows that under steady weather condition the proposed method harvests 5% extra energy as compared with the conventional P&O. For dynamic weather conditions the proposed method harness an additional 3.5% energy when compared with the P&O method, which makes it very promisin
Author index
No full textThe index have been scanned in colour with a HP Scanjet 5590; 300dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.Since. the issue of the "Author and Subject Index to the Government Veterinary Reports of
the Transvaal and Union of South Africa 1903-1932" which appeared in June 1937, thirty five
volumes consisting of one hundred and twenty-six numbers of the "Onderstepoort Journal of
Veterinary Research" and two supplements have been puJlished. These represent a written record
of research work done in veterinary science and allied disciplines in the Republic of South Africa
during the past thirty-six years. Many subjects have been covered by many authors and the task of
fmding a particular reference in these volumes is no easy one. As a result an author and subject
index has been compiled to cover volumes 1 to 35 and it is hoped that this will be of material
benefit to research workers all over the world
Harmonic minimization in a Chopper-type AC voltage controller
No full textElectrical Engineering Department, College of Engineering, King Saud University, P.O. Box-800 Riyadh 11421, Saudi Arabia
email: [email protected] AC voltage regulator of the chopper-type presents an attractive alternative for AC voltage control. This is attributed to its extended range of control coupled with independence of the switching angles with respect to load phase angle. Moreover. using microprocessors to determine firing instances makes it possible to change regulator's ON and OFF periods at will with appreciable ease. This adds a new merit for this type of controllers since it would be possible to alter the magnitudes of harmonics present in load voltage or even eliminating selected orders. In this paper the values of switching angles yielding minimum harmonic content in load current are determined. Profiles of these angles at different values of load phase angle are presented for cases of out-put load voltage with three, five and seven pulses per haf cycle. Optimal values of switching angles are evaluated using an algorithm based on optimization technique of the direct search method. Validity of the results obtained is confirmed by comparing it with relevant values obtained by direct manipulation for the possible combinations of switching angles. Experimental results obtained from a microprocessor-control-led AC chopper confirming the theoretical analysis are presented. The approach presented is general and can be well extended for harmonic minimization with any number of pulses per half cycle and specific values of load phase angle
I paradigmi traduttivi di Simeon Polockij
No full textThe article focuses on translation in the Russian area. The author argues that translation was pivotal in the westernisation of Moscovia during the baroque era through the investigation and categorisation of translation procedures in Simeon Polockij's work
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