Sharif Digital Repository

Nowadays high efficiency and power density are desired for designing a power electronic converter. Technology advances in power semiconductor devices, makes it possible to design converters for operation in higher frequencies to reduce size of the converters. As the frequency is increased, switching losses and temperature is also increased, so designing a converter for high frequency operation needs some tradeoffs. LLC resonant converter as a promising solution for battery chargers has ability to adjust its output voltage during Constant Current and Constant Voltage modes. However, its operation mode would change based on switching frequency change. Therefore, for efficiency-oriented... 

Resolvers, due to their robust structure, are widely used in automation systems. Among the types of resolvers, the accuracy of the Wound Rotor (WR) resolver in the occurrence of common mechanical errors is higher than other types of resolvers. therefore, in this thesis, an AFWRR is studied to improve the performance. Increasing the number of poles in WR resolvers is a good solution for increasing the accuracy of these electromagnetic position sensors. However, high-speed WR resolvers due to employing fractional slot windings suffer from rich sub-harmonics in the induced voltages. A common solution for suppressing the undesirable sub-harmonics is using multi-layer winding with appropriate... 

Linear position sensors are widely used in linear motion-control systems. In this thesis, the design, optimization, performance analysis, and prototyping of a linear variable reluctance, variable air-gap length resolver are discussed. The accurate modelling of the studied sensor needs three-dimensional (3-D) time stepping finite element analysis (TSFEA) that is computationally expensive and unsuitable for co-usage with optimization algorithms. Therefore, the aim of this thesis is to establish an accurate, yet computationally fast, model suitable for optimal design of linear variable reluctance resolvers. The proposed mathematical model is presented based on modified winding function method. ... 

Position sensors are inseparable parts of motion control systems. The variable reluctance resolvers, as position sensors, are widely used in the drive of permanent magnet motors due to their simple and reliable strucutre. One of the most possible installation faults in these sensors is rotor and stator eccentricities that deteriorate the accuracy of the resolver. Therefore, axial flux variable reluctance (AFVR) resolvers have been proposed to decrease the influence of eccentricities on the output accuracy. 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... 

Linear position sensors are widely used in linear motion-control drives. In this thesis, the design, optimization, performance analysis, and prototyping of a linear variable reluctance, variable area resolver is discussed. To test the new design approach of the studied sensor, three-dimensional time-stepping finite element analysis (3-D TSFEA) is crucial. However, the 3D TSFEA is a very time-consuming method which leads to an inappropriate choice for co-using with optimization algorithms. Hence, an accurate analytical model based on a winding function (WF) method presented in favor of calculating the inductances, air-gap flux density, induced voltages precisely and yet is a very fast method,... 

A resolver is a position sensor that converts the angular position information of a mechanical shaft to electrical signals. Due to their machine-like structure, resolvers have been preferred to other position sensors like optical encoders for working in harsh environments with wide temperature variations, high vibrations, moisture, and dust. Besides, the resolution of a resolver is infinite, and it can provide absolute position information. A multi-turn resolver is a type of resolver that has been developed to provide absolute position information with very high precision. Conventional multi-turn resolver consists of two individual resolvers in a common frame. One of them determines... 

Position sensors are an integral part of electric machine control systems. There are different ways to determine the position. The most common methods are using resolvers or optical encoders. Resolver is the recommended in harsh environments where there is wide temperature variation, vibration, and dust. Despite their good features, resolvers face challenges such as eccentricity, short circuit fault, single-phase disconnection, and non-ideal signal voltage. The Resolver chosen in this research is the variable reluctance resolver with variable air gap length. Although this type of resolvers is cheaper than wound rotor resolvers, but its position error is high under electrical and mechanical... 

Measuring the speed and position of the rotating part and using the speed and position information in the closed loop control of electric machines is very important. Various sensors are available for this purpose, including resistive sensors, capacitive sensors, encoders, synchros, resolvers, Halleffect sensors, and etc. Common encoders include optical and magnetic types. There are two main problems in using an encoder as a sensor: determining/maintaining accuracy during change of rotational direction and determining the absolute position. Both of the mentioned challenges have been investigated in the case of optical encoders and some solutions have been provided to overcome them. Although... 

Position sensors are an inevitable part of motion control mechanisms with inverter-driven electric machines. Encoders and resolvers are two common types of position sensors. Resolvers are preferred over encoders due to their superior performance in polluted and noisy environments with wide temperature variation or high vibration. Conventional resolvers are synchronous generators whose excitation winding is fed by an AC instead of a DC voltage. There are different types of resolvers for determining position in linear or rotational motions. However, increasing usage of two-degree of freedom (2-DOF) motors for simultaneous rotational and linear motion leads to request for helical motion... 

With the recent developments in power electronics and electrical drives, there is a need for precise position sensors today more than ever. Having high precision and high reliability in harsh environments, resolvers are the most preferred position sensors among other types of prevalent position detectors. In order to control linear machines, which are widely used in different industries, linear resolvers are employed. This project aims to propose a structure for tubular variable reluctance resolvers, formulate an analytical model for and optimize the proposed structure. In addition to having an acceptable precision, the proposed model should be less time-consuming compared with finite... 

Linear motors are mostly used in industrial applications and linear position sensors are one of the main components of their motion-control systems. The most common position sensors are optical encoders and resolvers. The optical encoders are not suitable for use in high temperature and high-vibration environments. In addition, their mechanical installation is difficult. In contrast, the resolvers are capable of generating absolute position signals with high precision, and low cost. Resolvers can be used in the polluted environments with the wide range of frequency, temperature and vibration. Among different linear sensors, linear resolvers are appropriate choice for harsh environments.... 

One of the main challenges of resolver as a position sensor is using at high speeds. Because in a situation where the speed of moving part is close to the frequency of the resolver excitation voltage, the speed-dependent part in the resolver output signals will be significant and cannot be ignored. In this project, the aim is to provide a method to solve the problem of using a variable reluctance linear resolver with a sinusoidal cross section in a wide speed range. This method is based on the hybrid use of AC and DC excitation in such a way that AC excitation is used at low speeds and DC excitation at high speeds. Considering that determining the threshold speed requires a large number of... 

Today, position sensors are inseparable parts of engineering systems. Encoders and resolvers are the most common types of position sensors that are widely used in industries. Due to low price and high accuracy, encoders are the first choice of engineers. Yet, their performance deteriorates under harsh conditions, namely wide temperature range operation, intense vibration and polluted environments. On the contrary, resolvers are rigid and robust which make them resistant to polluted environments.According to principle of operation, resolvers are divided to two main types: variable reluctance (VR) and wound-rotor (WR). Researches has shown that wound rotor resolvers have better performance... 

Nowadays, with the increasing need of various industries and applications to directly create linear motion, linear resolvers are attracting more attention than ever. Achieving high accuracy as well as measuring absolute position leads to the introduction of a new generation of resolvers, called multi-turn resolvers. Usually, a multi-turn resolver consisted of two individual resolvers in one frame, while using a common core for both resolvers can help to make the multi-turn sensor smaller, cheaper, and lighter. Nevertheless, the studies conducted on linear and multi-turn resolvers are very limited. Therefore, this research proposes an integrated core linear variable reluctance multi-turn... 

Once damaged, articular cartilage has very little capacity for spontaneous healing because of the avascular nature of the tissue. Although many repair techniques have been proposed over the past decades, none has successfully regenerated long-lasting tissue to replace damaged cartilage. Tissue engineering have recently demonstrated tremendous approaches for regeneration of cartilage tissue lesions. Tissue engineering is based on three principles: cells, scaffolds for cell adhesion and growth factors. Three-dimensional biodegradable scaffolds play an important role in tissue engineering. In this study, novel cross-linked hybrid chitosan/ECM scaffolds were prepared for articular cartilage... 

Power system operators are facing with imperative challenges to integrate high penetration of renewable power plants. The main challenge is required investment cost for accommodating the grid with uncertainties of renewable resources. In addition, intermittency and fluctuations of renewable resources are another challenges of system operators. Therefore, choosing a proper control procedure to respond the grid disturbances is a crucial task. However, the strategic behaviours of generation companies lead to a competition between them which affects the control performance. In this thesis, an integrated mechanism is proposed that consider both dynamic and strategic behaviours of generation... 

In this thesis, no-load and full-load performance of Permanent Magnet Vernier Generators (PMVGs) is investigated in fully-aligned condition and under different types of mechanical faults. The studied mechanical faults are Static Eccentricity (SE), Dynamic Eccentricity (DE), Inclined Rotor (IR), and Run-out (RO). Furthermore, an analytical model is also developed to calculate the permeance of the air-gap and the induced voltages in the health machine and under studied mechanical faults. Then, 2-D and 3-D non-linear, time stepping finite element method is utilized for performance evaluation of the generator in no-load and full-load (with resistive, inductive and capacitive loads). In continue,... 

Nowadays, due to gearbox drawbacks, the direct-drive wind turbines have received much more attention. Permanent magnet synchronous machines are commonly used for this purpose. The flux reversal machine with a magnetic gearbox and high power density could be an appropriate alternative. Due to placement of permanent magnets on the stator, the machine has a simple and robust structure and provides more reliability. There is limited study on optimization of the flux reversal machine and the existing papers are not complete and many parameters like PM dimension, working temperature, and winding reactance are not considered in the optimization process.Considering the flux reversal machine... 

Resolver is the recommended position sensor in harsh environments where there is wide temperature variation, vibration, and dust. Resolvers are divided into two groups: Wound-Rotor (WR) resolvers and Variable Reluctance (VR) ones. The most commercial resolvers are WR resolvers that they have 2-phase, orthogonal, signal windings on their stator and a single-phase excitation winding on their rotor. Due to the electromechanical structure of the resolver, the mechanical and electrical faults of electrical machines are expected in resolvers. Therefore, in this dissertation, the effect of mentioned faults in WR resolvers was investigated.In this dissertation, a non-invasive method with the help of... 

Resolver is a position sensor that is suited to be used in polluted environments with wide temperature variation, and high vibration. An important factor to determine the accuracy of resolver is its number of windings’ pole pairs that so-called “Speed” of resolver. Higher speed resolvers have higher accuracy in the price of losing absolute position information. Therefore, multi-turn resolvers are employed to have the high accuracy and high reliability along with absolute position information simultaneously. Multi-turn resolvers are consisted of two individual resolvers with different speeds in a common frame. In this thesis design considerations of multi-turn resolvers include proper...