Sharif Digital Repository

The interinjection locking of microwave oscillators is investigated using differential equations governing the locking behaviour of two mutually coupled oscillators. The behaviour of the oscillators before and after locking is described, and the common oscillation frequencies, locking range and transient time constant are calculated. The spectra of the oscillators in the unlocked condition are also investigated, with particular attention to the spacing and amplitude variation of the spectral lines. Experimental results in connection with the theoretical investigations are also presented  

The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux oriented reference frame. The rotor flux oriented reference frame is well known in the standard AC machines analysis and control. Similar benefits can be sought by employing this method for the BDFM The vector model is implemented in MATLAB/SIVIULINK to simulate the BDFM dynamic performance under different operating conditions. The predictions from the vector model are compared to those from the coupled circuit model in simulation. The results are shown for the cascade mode of operation. © 2008 IEEE  

The Brushless Doubly-fed Induction Generator (BDFIG) has high potential for wind energy systems, especially for offshore applications where minimum maintenance is vital. The machine low voltage ride through (LVRT) capability in the light of current grid code requirements was investigated using a precise dynamic model. This is particularly important for future multi- MW BDFIGs. This paper shows the necessity for improvements of the BDFIG LVRT capability with presenting a comprehensive analytical study during asymmetrical voltage dips. Analytical studies are conducted to extract a more precise equivalent circuit model of the BDFIG used for analyzing machine dynamic behavior under various fault... 

A comparator comprises a cross coupled circuit which produces a positive feedback. In conventional comparators, the mismatch between the cross coupled circuits determines the trade-off between the speed, offset and the power consumption of the comparator. A new low-offset low-power dynamic comparator for analog-to-digital converters is introduced. The comparator benefits from two stages and two operational phases to reduce the offset voltage caused by the mismatch effect inside the positive feedback circuit. Rigorous statistical analysis yields the input referred offset voltage and the delay of the comparator based on the circuit random parameters. The derivations are verified with... 

This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nested-loop rotor. The vector model is presented for a generic p1/p2 pole-pair BDFM which may have any number of loops per nest. The vector transformations utilized in the derivation of the vector model are provided in general form such that the model can be represented in any appropriate reference frames according to the specific application of the model, such as BDFM analysis, simulations, or control system synthesis. The derived vector model benefits from the feature of reduced order in comparison with the coupled-circuit model, which is the most detailed model for the BDFM, while maintaining the... 

The cause of about 10% of faults in induction machines is related to the rotor part. In this paper, an analytical method for general modeling of brushless doubly-fed machines (BDFMs) with broken rotor loops and end ring is presented. The approach is based on calculation of resistance and inductance matrices through the winding function of the machine, so the assumption of sinusoidal MMF is not needed. It is also shown that a fault in a loop can lead to faults in other parts of the rotor. To validate the method a simulation in MATLAB/Simulink is performed based on the D180-frame prototype BDFM  

In this paper an array of N weakly coupled oscillators Is considered. The stability of the main mode (In phase mode) In linear arrangement of oscillators has been proven and the Instability of other modes In this configuration Is demonstrated. For circular arrangement It Is shown that other stable modes may exist If N Is greater than 5  

This paper proposes effective approach for determining appropriate crowbar resistance value to be able to improve the brushless doubly fed induction generator ride through capability during any asymmetrical voltage dip scenarios. The brushless DFIG has great potential for wind power plants particularly in offshore applications where maintenance is a major concern. Dynamic behavior of the machine is studied using two axis model and a more precise equivalent circuit model is extracted for analyzing machine behavior under fault conditions. Important limits and constraints in the use of crowbar are identified and discussed in detail. It is shown that large crowbar values can lead to considerable... 

Crosstalk due to the capacitive and inductive coupling has adverse effect on the circuit performance. In this paper crosstalk voltage and its induced power are studied for a stochastic environment bus with specific physical structure. Input switching pattern, driver, and load are swept in wide range for VLSI application to study crosstalk variation. Crosstalk and power is extracted to drive mean and standard deviation for implemented structures. The crosstalk mean and its induced power get lower with increasing of the load and driver resistance. This phenomenon is proportional to shrinking the technology  

In this paper, a detailed analytical model for dynamic analysis of the Brushless Doubly-Fed Machine is presented. The model is capable to predict the machine behavior under different modes of operation including: simple induction mode, cascade mode and synchronous mode, both with and without winding faults and unbalanced excitations. The proposed approach employs the basic principles of the generalized harmonic theory for calculating self inductances and mutual inductances of circuits with any distribution of conductors. Dynamic equations of modified coupled-circuit method are then solved to compute the currents flowing in the stator windings and rotor loops  

We have investigated the rf SQUID (radio-frequency superconducting quantum interference device) and its coupling to tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation of the YBCO rf SQUID coupling to the conventional LC tank circuits revealed that coupling from the back of the SQUID substrate enhances the SQUID signal while facilitating the front-end assembly configuration. The optimal thickness of the substrate material between the SQUID and the tank circuit is 0.4 mm for LaAlO3 resulting in an increase of the SQUID flux-voltage transfer function signal, Vspp, of 1.5 times, and 0.5 mm for... 

This paper discusses the dynamic behavior of the brushless doubly fed induction generator during the grid faults which lead to a decrease in the generator's terminal voltage. The variation of the fluxes, back EMFs, and currents are analyzed during and after the voltage dip. Furthermore, two alternative approaches are proposed to improve the generator ride-through capability using crowbar and series dynamic resistor circuits. Appropriate values for their resistances are calculated analytically. Finally, the coupled circuit model and the generator's speed and reactive power controllers are simulated to validate the theoretical results and the effectiveness of the proposed solutions. Moreover,... 

Thermal behavior and require power in hot continuous strip rolling are predicted by means of a coupled finite element-upper bound approach. A thermal-finite element analysis is utilized to simultaneously determine temperature distributions within the work-piece and the work-rolls while an upper bound solution is employed at the same time to estimate the rate of heat of deformation and the required power in each rolling stand. The proposed model can be applied for determining thermal behaviors of the strip and the work-rolls in single and multi- pass rolling schedules while the effects of different parameters including initial temperature and rolling speed can be considered in the analysis.... 

This paper is aimed at proposing a current based vector control model of the brushless doubly fed induction generator, modelling the presented control method, as well as implementing the proposed algorithm by DSP. In order to achieve the purpose, by presenting a detailed coupled circuit model of BDFIG, the vector model and then the current based vector control algorithm of the mentioned machine are acquired. The way of independent control of torque and power, and also the structure of speed controller amongst the proposed control model are discussed. Additionally, the concepts behind the proposed structure of the speed control system and the way of determining the model parameters are... 

Harmonic producing loads, which are increasingly used in industries, cause power quality problems as well as increase in system losses. To deal with the problems associated with harmonics and to reduce their effects on power networks, study of the effects of non-linear loads on distribution networks is essential. In this paper, the non-linear loads of residential consumers are modeled and simulated. A typical residential consumer and a simplified short feeder are simulated in order to make an estimation of the power and energy losses and their corresponding costs. The simulations are verified using practical measurements from real customers. ©2013 IEEE  

A coupled cellular automata and finite element model has been proposed to evaluate static recrystallization kinetics during non-isothermal annealing of cold deformed low carbon steels. The effects of various factors including heating rate, annealing temperature, and initial microstructures have been considered in the model to accurately predict the static recrystallization kinetics and the final microstructures. In order to examine the employed algorithm, the predicted results have been compared with the experimental observations and a good agreement was found between the two sets of results  

This paper presents different applications of a vector model developed by the authors in Brushless Doubly-Fed Machine (BDFM) studies including analysis, control and simulations. The BDFM considered consists of a nested-loop type rotor. The vector model, which considers all the loops in each rotor nest, is derived using BDFM coupled-circuit model equations and by applying appropriate vector transformations. Three vector transformations are employed for the derivation of vector model corresponding to two three-phase windings in the stator and the rotor circuit. Each transformation consists of an angle which is, in general, unspecified and must be assigned appropriately depending on the... 

Application of piezoelectric materials in vibration energy harvesters is expanding rapidly, especially in MEMS-based devices, due to their uncomplicated fabrication processes and reasonable power generation potential. In addition to standard power extraction methods, nonlinear switched techniques with capability of generated power enhancement, are previously developed and extensively applied in energy harvesting using piezoelectric materials. In this article, vibratory behavior of bimorph resonant harvesters coupled to nonlinear circuits of energy harvesting including standard and switched techniques is investigated. An analytical approach employing some perturbation technique, is utilized... 

Application of piezoelectric materials in vibration energy harvesters is expanding rapidly, especially in MEMS-based devices, due to their uncomplicated fabrication processes and reasonable power generation potential. In addition to standard power extraction methods, nonlinear switched techniques with capability of generated power enhancement, are previously developed and extensively applied in energy harvesting using piezoelectric materials. In this article, vibratory behavior of bimorph resonant harvesters coupled to nonlinear circuits of energy harvesting including standard and switched techniques is investigated. An analytical approach employing some perturbation technique, is utilized... 

A complete nonlinear finite element model for coupled-domain microelectromechanical system devices with electrostatic actuation and squeeze film effect was developed. for this purpose, a corotational finite element formulation for the dynamic analysis of planer Euler-Bernoulli microbeams considering geometrical nonlinearities due to both large structural deformation and electrostatic actuation is developed. In this method, the internal forces due to deformation and residual stresses, the elemental inertias, and the damping effect of the squeeze-film are systematically derived by consistent linearization of the fully geometrically nonlinear beam theory using d'Alembert and the virtual work...