Sharif Digital Repository

Brushless doubly fed machine (BDFM) shows promising results for wind power and adjustable-speed drive applications. Due to poor rotor magnetic coupling and relatively high value of slip, core loss is more emphasized in this machine than the conventional machines. By now, there are few comprehensive researches on core loss effect on performance characteristics of BDFM in the literature. In this paper, based on the derived relations and by applying suitable rules for transformation of parameters from one winding to another one, the steady state equivalent circuit model of BDFM referred to power winding stator side is obtained. Comparison between simulation and experimental results verifies the... 

Partial Discharge (PD) measurements in Ultra High Frequency (UHF) band requires modern techniques for monitoring of power transformer. This is a topic of interest investigated in this field, especially in recent years. Different experimental models, such as: defect models, and winding models are used in PD studies of power transformer. The purpose in application of these models is to represent and simulate the real transformer performance using a simple model. The proposed model needs to be a simplified one which can be implemented of them. However, the applied simplifications may result in some changes (inaccuracy) into the recorded PD current signals captured by UHF sensors. These changes... 

Accurate Partial Discharge (PD) measurement requires the expansion of the measurement frequency range to Ultra High Frequency (UHF) band. For this it is needed to implement modern techniques when monitoring an important element of power system, such as power transformer. Different kind of experimental models, such as insulation defect models, and the complete transformer windings models are used to simulate the partial insulation failure situations which occur in a real transformer. However, since in these models, some kind of simplifications are employed which may result in an electromagnetic waves (EM) propagation pattern different from what exists in a real transformer and encounter... 

Propagation of Hypergeometric-Gaussian laser beam in a nonlinear plasma medium is investigated by considering the Source Dependent Expansion method. A subfamily of Hypergeometric-Gaussian beams with a non-negative, even and integer radial index, can be expressed as the linear superposition of finite number of Laguerre-Gaussian functions. Propagation of Hypergeometric-Gaussian beams in a nonlinear plasma medium depends on the value of radial index. The bright rings' number of these beams is changed during the propagation in plasma medium. The effect of beam vortex charge number l and initial (input) beam intensity on the self-focusing of Hypergeometric-Gaussian beams is explored. Also, by... 

Linear position sensors are widely used in linear motion-control systems. In this paper, the design, optimization, performance analysis, and prototyping of a linear resolver (LR) are discussed. Mathematical model of the proposed structure is presented based on a simple design-oriented method. Then, a comprehensive iterative design algorithm considering design constraints of linear electromagnetic sensors is proposed. All resistances and inductances of the designed LR are calculated based on the design parameters. Then, a 3-D time-stepping finite-element method is used to validate the design, optimization, and analytical model. Finally, a prototype of the sensor is built and tested.... 

High pole number permanent magnet (PM) motors, due to their high torque density, have been receiving considerable attentions in recent years. To achieve an accurate position control in PM machines, resolvers are suggested for industrial applications. Mechanical and electromagnetic considerations in the case of high pole number resolvers lead the machine designers to choose small cores with low slot numbers. This paper proposes two different on-tooth winding configurations to achieve high pole number without increasing the slot numbers, while the accuracy of the detected position is intended to be the maximum value. Variable turn on tooth winding (VTTW) is compared with fractional slot... 

Stray capacitance of transformer winding is an important parasitic element influencing the behavior of the switching power converters, especially for high-voltage transformers. There are various methods for calculating the stray capacitance in transformers and inductors with ordered windings. However, an ordered winding is less likely with an increased number of turns and layers. In this paper, it is shown that a slight disorderliness in winding leads to a considerable difference between the value of winding stray capacitance of the former ordered winding and its slightly disordered scheme. Therefore, regular methods for calculating the stray capacitance have significant errors in a... 

Installation of a significant number of distributed generators (DGs), besides the application of non-sinusoidal loads such as; Plug-in Hybrid Electric Vehicles (PHEVs), in the emerging smart distribution networks and the industrial plants have posed a major challenge to the existing methods of optimal transformer sizing (OTS). The harmonic currents generated in these new environments not only substantially increase the transformer load losses, but also cause abnormal winding temperature rise and hence transformer excessive loss of life. Therefore, the harmonic contents of the loads currents should be accounted in choosing the appropriate size of distribution transformers. To address this... 

Resolvers are widely used in the control of industrial inverter driven motors. Among different types of resolvers, disk-type wound-rotor resolvers have superior performance under mechanical faults. However, the rotary transformer's (RT's) presence in the inner side of the resolver's core leads to additional radial length. To overcome this problem, disk-type wound-rotor resolver without RT's core has been proposed. However, the optimization using time stepping finite-element method (TSFEM) is time consuming due to 3-D structure of this resolver. Accordingly, in this paper, an analytical model based on the magnetic equivalent circuit is proposed for the design and optimization process. The... 

Linear variable reluctance (LVR) resolvers have substantial benefits that make them suitable for linear motion control drives. The optimal design of LVR resolvers needs an accurate modeling that is usually achieved by a three-dimensional (3-D) time-stepping finite element method (TSFEM). However, the 3-D TSFEM is a very time-consuming method and is unsuitable for cousage with optimization algorithms. So, in this paper an accurate analytical model based on an improved winding function method is proposed. The proposed model is used to calculate the inductances, air-gap flux density, induced voltages, and linear position error. The distinguished feature of the proposed model is the direct usage... 

Road speed cameras are usually used in photovoltaic power plants, especially in the areas with limited or no access to grid power. However, there are many areas in Iran where wind power is more accessible than solar energy. So, in this study, a small permanent magnet vernier generator is designed to meet power concussion requirements of traffic enforcement camera. The designed generator is optimized to achieve lower harmonic content of no-load induced voltage and lower cogging torque. In this regard, the effect of geometrical dimensions and the configuration of permanent magnets are investigated using three-dimensional time stepping finite element method. Both no-load and full-load... 

Axial flux variable reluctance (AFVR) resolvers have substantial benefits that make them suitable for motion control drives. However, they suffer from insufficient accuracy, especially in high-accuracy applications. Hence, optimizing the AFVR resolver structure is necessary for improving its commercial usage. However, its accurate modelling needs three-dimensional (3-D) time stepping finite element analysis (TSFEA) that is computationally expensive and unsuitable for co-usage with optimization algorithms. The aim of this paper is to establish an accurate, yet computationally fast, model suitable for optimal design of AFVR resolvers. The working of the proposed model is based on magnetic... 

Nowadays position sensors are increasingly used in many applications. One of the most commonly used sensors are resolvers. There are different types of resolvers including Wound Rotor (WR) resolvers, Variable Air-gap Length Variable Reluctance (VAGL-VR) resolvers, and Sinusoidal Rotor Variable Reluctance (SR-VR) resolvers. Regardless of the resolvers’ configurations, including linear, cylindrical and disk type, finite element analysis (FEA) is inseparable part of design and performance evaluation of these magnetic sensors. The scope of this study is to discuss challenges in the FEA of resolvers. The influence of mesh quality, time steps, stop time, excitation methods including volt-age... 

In this paper, a single-inductor dual-output (SIDO) DC/DC converter is proposed. The significant feature of the proposed converter is feeding a constant power load in low voltage side (LVS) port, where even feeding a variable load at LVS doesn't have any cross regulation to high voltage side port with the desired approximation. Magnificently, both merits are obtained in open-loop manner which is an outstanding characteristic in comparison with existed converters. In this paper, soft commutation and soft switching of switches and diodes are investigated along with the aforementioned main novelty. Moreover, detailed theoretical analyses of the proposed SIDO DC/DC converter in continuous... 

Rubber modification of hoop filament wound epoxy composites was investigated using amine-terminated butadiene acrylonitrile (ATBN) and carboxyl-terminated butadiene acrylonitrile (CTBN) oligomers. Both mechanical and physical properties of modified composites were investigated and the morphology of the samples was studied via scanning electron microscopy. Results indicated that, when added to the epoxy matrix, ATBN effected a superior increase in toughness, yet a more severe decline in compressive and flexural strength, compared to CTBN. In contrast, in the case of composite samples, incorporation of ATBN led to more favorable mechanical properties, from the viewpoint of both toughness and... 

Nowadays, position sensors are increasingly used in many applications. One of the most commonly used sensors are resolvers. There are different types of resolvers including wound rotor resolvers, variable air-gap length variable reluctance resolvers, and sinusoidal rotor variable reluctance resolvers. Regardless of the resolvers' configurations, including linear, cylindrical and disk type, finite element analysis (FEA) is inseparable part of design and the performance evaluation of these magnetic sensors. The scope of this study is to discuss challenges in the FEA of resolvers. The influence of mesh quality, time steps, stop time, excitation methods including voltage source and current... 

Accurate position estimation is an integral part of any motion control system. Besides, instantaneous position of poles plays an important role in electronic drive system of modern PM machines. Resolvers, due to their structure, are the most reliable position sensors in harsh environments. However, resolvers are not as accurate as optical encoders in normal conditions. To increase the accuracy of these sensors, various solutions are used, such as optimization in winding arrangement, rotor and stator contour, slot-pole combinations, and improvements in resolver-to-digital converter. In this paper, fractional slot concentrated winding is used in an axial flux resolver. By the aid of winding... 

Cost, durability and reliability are three critical issues in electrical/hybrid electrical vehicles (EV/HEV). In this regard, resolvers are often used as position and speed sensors in such applications. In this paper design and analysis of a novel multi-turn resolver is discussed to address all the mentioned issues. The proposed resolver has got one stator core and one rotor core. Double sets of signal windings on the stator and a special excitation winding on the rotor are designed to achieve both absolute and multi-speed operations. Mathematical model of the proposed resolver is verified using time stepping finite element analysis and experimental measurements. © 1967-2012 IEEE  

In this paper, advantages of energy-efficient motors over standard-motors in terms of electrical energy saving and demand reduction in a tire-rubber factory are thoroughly evaluated. Energy-efficient motors reduce losses because of their better design, materials, and manufacturing. These motors are 2 to 8% more efficient than standard ones. Lengthening the core and using lower-electrical-loss steel, thinner stator laminations, and more copper in the windings reduce electrical losses. Because a motor consumes energy worth 4 to 10 times its own cost each year, energy-efficient motors often make economic sense in a wide variety of applications. At the end of this study, the amount of energy... 

Partial discharges are well known as a source for insulation degradation in power transformers. A hybrid transformer model is introduced to simulate the transformer winding transient response. Transformer structural data is used to determine the hybrid model parameters. Calculations of the hybrid transient model parameters are based on the parameters of the lumped parameter equivalent transformer model and electromagnetic rules. Modern computation techniques and optimizations are employed beside this model for PD location using the multi conductor transmission line model and also to analyze its propagation aimed at achieving (i) more reliable simulation results (ii) less computational time...