Sharif Digital Repository

Elastic joints in 2-mass drive systems, because of their limited stiffness, can decrease the performance of the control system and lead to motor and load speed oscillation. Shaft torque ignoring can also stress both mechanical and electrical drive components. Because of low degree of freedom, conventional controllers, such as the PI controllers, cannot improve the performance of the system and keep the system stable at the same time. In this thesis, the dynamic response and stability of the 2-mass systems is improved using state controller. State estimation of 2-mass system is required for state space controller . In the thesis, different state observer is analyzed and compared with each... 

The global wind energy capacity has been increased rapidly in the past few years and became the fastest developing renewable energy technology. Small Permanent Magnet Synchronous Generators (PMSG’s) are widely used in low power wind turbines because they don’t need a gearbox and complicated control systems. In order to inject the electrical power generated by PMSG to the grid, an AC-DC-AC power electronic converter is required. A novel low cost efficient AC-DC converter is proposed to obtain the maximum power per ampere of PMSG. The new structure for the rectifier stage of the AC/AC converter is based on a DCM operated SEPIC converter and can convert the variable voltage and frequency of... 

Nowadays, despite the special position of power electronic converters in the world, and the fact that they become an integral part of human life, still in the wake of a serious necessity the development process has not stopped and the increasingly fast pace, it opens up new horizons. This important necessity emerges from the environmental concerns regarding consumption of fossil fuels and their limited and imbalanced distribution which can be effectively addressed with the use renewable energy systems. By improving the quality of the semiconductor switches and offering new topologies in different functions as well as using new control methods, scholars try to develop enhanced converters in... 

Integral abutment bridges (IABs) are bridges in which the deck is cast monolithically with abutment backwalls. These bridges are also jointless through deck length, due to which they act as a frame in their longitudinal direction. These differences with common seat-type bridge construction, have made IABs more economical to build and maintain and superior in seismic performance. As such, in various countries, this method of construction have been prescribed whenever possible. As an instance, integral construction is mandatory for bridges up to 60 meters in total length in England. IABs have become more of a geotechnical problem rather than simple structural problem of conventional bridges in... 

Wireless power transfer has been found to be a practical replacement for cable power transfer in a wide range of applications. For instance, this technology offers significant solutions for medical and industrial applications as well as electrical home appliances and electric vehicle chargers. All over the world, researchers are investigating and implementing experimental prototypes to simplify power transfer in applications in which the use of cables is impossible, troublesome, or hazardous. There are different issues in each of the mentioned applications which should be solved in order to use wireless power transfer systems more beneficially. These issues include power transfer efficiency,... 

Nowadays, due to environmental problems, electric cars are becoming more and more popular. The main drawback of these cars is due to the large volume, weight, and price of the battery and its long charging time. Charging the battery at short intervals or even in moving, can help to use a smaller battery and reduce battery problems. Therefore, the dynamic wireless power transmission technology that provides power without having to stop the car to recharge its batteries can revolutionize the electric car industry. The ever-expanding advance of power electronics and wireless power transmission technologies has made it possible to transfer power to moving electric cars. Barriers to this industry... 

Electrical machines represent an important research area in electrical engineering with numerous industrial applications. Multiphase induction machines are considered as the new generation of electrical machines in industrial applications because of their structure, robustness, simplicity, reasonable cost, long lifetime, and high reliability. A solution in the way of improving induction machine performances is using concentrated windings because they have many advantages such as short non-overlapping end turns, high fault-tolerant capabilities, and easy manufacturing. The main drawback of concentrated windings is its low-quality air gap flux density which significantly deteriorates induction... 

converters in electric vehicles, it is necessary to reduce their dimensions and increase their efficiency. It is expected that in the near future wide band gap semiconductors will be used to achieve these goals. On the other hand, usage of planar transformers is necessary to achieve slim and compact converter designs in electric vehicles. Clearly, planar transformers offer a significant advantage in replacing bulky wired transformers in high frequency LLC resonant converters with WBG transistors. planar transformers also have several other advantages, including low flux leakage, modular structure, and low thermal resistance.However, in planar transformers, due to the proximity and large area... 

Ealstic joints in 2-mass drive systems, because of their limited stiffness, can decrease the performance of the control system and lead to motor and load speed oscillation. Shaft torque ignoring can also stress both mechanical and electrical dirve components.
Because of low degree of freedom, conventional controllers, such as the PI controllers, cannot improve the performance of the system and keep the system stable at the same time.
In this thesis, the dynamic response and stability of the 2-mass systems is improved using fractional order controller. By fixing cut-off frequency and increasing phase margin of the system, damping oscilation and fast response have been realized.
In... 

The Brushless Doubly Fed Machine (BDFM) has the capability to be employed as a motor in drive applications and as a generator in variable speed wind power applications. The Doubly Fed Induction Generator (DFIG) is currently the main candidate for use in wind power applications while it suffers from the existence of slip-rings and brushes. The BDFM can potentially achieve comparable characteristics to those of DFIG while having brushless operation. This dissertation aims at modeling the BDFM in its steady and dynamic states taking core loss into account. After a short review on structures, advantages and disadvantages of different wind energy conversion systems, the BDFM is introduced as a... 

Three-phase inverters as a UPS are very common in industry and non-linear loads such as rectifiers are growing in industry. Three phase inverter with non-linear load can lead to highly distorted output voltage which can make problem for sensitive loads such as servers etc. Parallel configuration of three-phase inverters, also have the same problem with non-linear loads. Droop control and Master/slave control methods are two major methods which investigated in this thesis. This paper proposes a method for reducing voltage THD in three phase inverters with non-linear load. The proposed method considers the load current as a disturbance and provide a control strategy to reject it using the... 

Poly (Lacticacid) belongs to the family of aliphatic polyesters. PLA can be made from annually renewable resources to yield articles for use in either the industrial packaging field or the biocompatible /bioabsorbable medical device market. Production of PLA through polycondensation in an industrial way was the aim of this project. In order to have the appropriate reaction conditions a steel reactor was designed and constructed. Feasibilty of PLA production in the constructed reactor was investigated and the product was analyzed, using H-NMR and FT-IR spectrum analysis. The average molecular weight was measured by GPC and ubbelohde viscometery method. Studies have shown that oligomerization... 

In this thesis one of the sensorless methods which exploits the existing anisotropies of the rotor is utilized to estimate rotor position. In order to implement this method, first a high frequency voltage is injected in a specific, time-varying direction and then the corresponding current response would be observed in order to estimate the rotor saliency position. The estimation of rotor position would be more precise as the magnetic anisotropy due to rotor saliency increases and as a result the effect of noise and different disturbances in estimation of rotor position would be decresed. The effect of stator resistence is one of these disturbances which is usually neglected as a result of... 

Aerosols are significant two-phase systems that have an important effect on environmental, biological, health, industrial and other scientific and engineering fields. According to chief aerosol effects, various instruments namely “Aerosol Spectrometer” have been developed to measure aerosols. Optical Particle Counters (OPCs) are one of this instruments that can count and measure the particles size distribution in the aerosols.
In the current project, an optical particle counter has been designed. For validating the correct operation of the designed plan, it is needed to simulate the instrument optically and mechanically, so the Mie theory was used to simulate the intensity of the... 

In this study melting and casting process of Ag-6.3%wt Cu-1.2%wt Ge alloy with NaBH4 additive for grain refining was investigated. ICP and XRF chemical analysis was used for calculating of Boron and Germanium lost in the processing section then an appropriate route for manufacturing of this alloy was suggested. With SEM and EDS chemical analysis which was installed on SEM sample’s microstructures after cold work and heat treatment was investigated. Solidification’s phases were identified with using DTA, XRD and EDS. To introduce a mechanism for increasing of tarnishing resistance in Argentium alloy, XPS analysis were employed. Optical microscope images reveals that casting samples with grain... 

A DC-DC quasi-resonant converter has the advantage of reducing switching losses and electromagnetic interference which are the main limitations of high frequency power converters. The conventional model of the quasi-resonant converter is derived using state space averaging followed by linearization about an operating point. Nevertheless, the state variables have large variations and the validity of the linearized averaged model is violated. Therefore it is essential to investigate the stability of quasi-resonant converter using a more precise model. Quasi-resonant converters are intrinsically hybrid systems consisting of discrete input and continuous states. In this paper the discrete... 

According to epidemiological studies conducted in Iran, nowadays, about 200 to 300 people in Iran suffer from stroke. The hands, including fingers, are the most injured and cause one’s disability and creates many direct and indirect costs for the person and the government. In addition to stroke, injuries caused by the use of various apparatus are responsible for hands disruption. It is usually referred to a physiotherapist for the physical disabilities treatment, the treatment process is quite long and time-consuming (usually a one-year physiotherapy). After this treatment, the physiotherapist will prescribe exercise and radiation therapies for the patient. Therefore, in recent years the... 

In this work, multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were synthesized in an aqueous solution of iron chloride and solfate via arc discharge. Thermogravimetric (TG) analysis showed that the multi layer structures including carbon nanotubes (CNTs) and multi-shell graphite particles were formed when DI-water was used. SWCNTs were synthezied in the presence of the iron ions. The effect of [Fe3+]/[Fe2+] ratio on the CNTs yield were investigated. Raman spectroscopy investigations showed that the highest yield was obtained when the ferric to ferro ratio was one. When the concentration of Fe3+ ion was higher than that of Fe2+, many short tubes were...