Sharif Digital Repository

On account of the exhausting nature and increasing daily cost of the fossil fuels, it seems that replacing the fossil fuels by an alternative source of energy is inevitable. Moreover, in the remote areas that the electricity network is not accessible, the use of distributed sources (DSs) such as solar energy and wind energy is advantageous. Continuity of the supply and voltage control of the load in spite of the stochastic nature of the generated power of the renewable energy resources are the main concerns in the distributed generation (DG) systems. In this thesis, stand-alone operation of a DG unit comprising a solar unit and wind turbine as primary sources of energy is considered. A... 

Given the high rate of energy dissipation in electric urban rail lines, methods of saving energy in these systems have become a topic of interest. The use of energy saving equipment to save the energy wasted in braking (Because of the diode rectifier, thermal energy is usually wasted and is not reversible) can play an important role in reducing the energy loss. The role of energy storage equipment, from other aspects such as voltage regulation and increasing the system reliability is also remarkable. In this thesis, the various possible methods for saving energy in the Metro system are expressed.
The various types of storage devices with increased reuse of braking energy which is the... 

In urban rail transport systems such as subway, Trains are constantly accelerate and brake, so the braking system is of great importance in energy consumption and constitute about 30 to 40 percent of total energy consumption trains, thus retrieval braking energy will lead to significant savings in urban rail transport systems. In this paper, in the beginning, different storage equipments for storage braking energy have been studied and compared and finally Supercapacitors due to technical and economic features have been selected for the storge of equipment. These systems can be implemented in both stationary and onboard. For precise evaluation and select the appropriate storage system, by... 

In this thesis a novel T type scheme for direct ac/ac converters is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. H-bridge converters are implemented in each branches of T to make the proposed converter. Also, multilevel inverters, specially cascaded H-bridge ones can be used in branches of T. this will lead to a multilevel ac/ac converter that is suitable for high power applications such as intertie connections and high power motor drives. Using half-bridge converters as T branch converters, leads to an ac/ac converter with unity power factor by only six semiconductor... 

In this work, design and control of three-phase four-switch rectifier with input power factor correction and operation under unbalance input voltage is investigated. To control of this converter, a modified space vector modulation (SVM) method is proposed able to omit effect of capacitors voltage ripple on output voltage and input current. A small signal model and required transfer function are calculated to control converter. Then appropriate controller is designed in dq space to achieve desired condition. Another controller is added to system to compensate capacitors dc voltage difference. A useful method to decomposition of positive and negative sequence of dq component is introduced.... 

With development of power electronic science and with the existence of different power electronic converters in this field, the need for improving their operation and the fault detection methods of these converters, the need for simulation and test of them is strong felt. However, experimental constrain such as damage risks, reliability, costs, and so on obviate the need for making the converter and the need for testing it and its controller. Accordingly, we do the testing on a special platform for Real-Time simulation.Control/protection platform needs to be tested and its functionality should be verified prior to installation and commissioning.Testing in theReal-Time simulator environment... 

Real-time Simulator plays an important role in the test of power electronic converters. Using of this simulators and Hardware-in-the-loop tests, cost and time of experiments will redused, furthermore those experiments which are not operative on the real system, can be achived. However, the accuracy of the used model in simulation as well as fast and easy programming of these simulators is very important. Therefore in this thesis, design and implementation of real-time simulator for power electronic converters have been discussed that in addition to high accuracy of the simulation, implementation of the several tests will be easy. As regards the power electronic switch is the most important... 

Fault-tolerant ability is more subjected in Cascaded H-Bridge Multilevel Inverter due to its high-power medium-voltage applications and large number of semiconductors switches used in its structure. In this thesis, the goal is performance improvement of Cascaded H-bridge Multilevel Inverter under faulty conditions. Since to achieve the post-fault ability two steps; fault detection and post-fault control are required, both steps are considered in the improving process. In this dissertation, first operation of Cascaded H-Bridge Multilevel Inverter in normal and faulty condition is surveyed. Then, the conventional fault detection methods are mentioned and post-fault control methods are... 

Recently, the brushless doubly fed induction generator (BDFIG) has been proposed to be used in wind turbines due to variable speed operation with fractionally size power electronic converter and without brushes and slip rings. In this thesis, for the first time, LVRT capability of BDFIG has been assessed regarding the grid codes and several approaches have been suggested for improving it. Firstly, the steady-state performance of the BDFIG in different operating modes has been investigated and required tests have been performed. In addition, a new operating mode named as "double cascade mode" has been introduced. The fault-on performance of BDFIG has also been studied by means of torque-speed... 

AC/DC/AC converters are widely being used in a variety of power applications. Continuity of service of these systems, as well as their reliability and performance are now of the major concerns. Indeed, the failure of the converter can lead to the total or partial loss of the control of the phase currents and can cause serious system malfunction or even shutdown. Thus, uncompensated faults can quickly endanger the system. Therefore, to prevent the spread of the fault to the other system components and to ensure continuity of service, fault tolerant converter topologies associated with quick and effective fault detection and compensation methods must be implemented. In this thesis, the... 

Using superconducting synchronous machine leads to many advantages such as increasing overall efficiency, decreasing mass and valume of peropulsion system, eliminating some restrictions in hydrodynamic design , etc. The goal of this thesis is design of 200 kW, with 250 rpm superconducting synchronous motor for small ship propulsion drive application. The low speed motor can be directly coupled to the propeller whitch eliminates bulky and inefficient gearbox. After comparison of different structures of superconducting synchronous machines, finally rotating superconducting field with stationary copper armature winding is selected as the most approporiate structure for our application.
For... 

Multilevel converters are considered recently as one of the industrial solutions for high-power and power quality demanding applications. Casacade H-Bridge (CHB) converter is one of the well known topologies among multilevel converters. CHB converter is characterized by its high modularity allowing its power to be easily increased. Modularity also allows any faulty cell to be isolated, so the load can be fed by the remaining operative cells, which leads to an unbalanced output voltage of the CHB converter. To avoid the unbalanced operation, recently a solution based on modifying the phase and the magnitude of the voltage refereces has been proposed. This thesis presents a method to control... 

Five-Level Active-Neutral-Point -Clamped (5L-ANPC) converter is used for medium-voltage and high-power applications. In many of these applications, availability and robustness against fault are the most important issues. On the other hand, this converter is made of a large number of power semiconductor switches, diodes and capacitors which could increase the failure probability. Thus, fault detection of power circuit elements is necessary for fault tolerant operation of the converter. In this thesis, following an introduction to the topology and operation principles of Five-Level Active Neutral point clamped converter, a novel open-circuit fault detection and localization method is... 

In the Ion Implanter system a controled current through a tungesten filament, supplies the heat which causes the thermoionic emmition to ionize the gas molecules. Then the negativly charged electrones that are boiled off the filament, and also the ones that are removed from the outer ring of the gas molecules during the ionization process, are attracted by an adjustable voltage source. In this thesis, two resonant converter topologies are proposed to designe and to implement the adjustable current and voltage sources for ion implantation system. Unlike the PWM converters soft switching techniques, used auxiliary circuits to reduce the switching losses and EMI noises, in the proposed resonant... 

Recent developments in improving lighting efficiency and cost reduction of LED’s have caused them to be a suitable alternative for the current lighting systems. In this thesis a novel off-line structure is proposed to drive LED’s. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn’t use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) flyback converter in order to have power factor correction (PFC), a buck converter is added to the third winding of the flyback transformer in order to create two paths for the electrical power. DC... 

LED Drivers with near 1 power factor, Because of using electrolytic capacitors (to become flicker-free) have lifetime drawbacks. This research will focus on solutions to use magnetic energy storage instead of electrolytic capacitors (used for energy storage) to solve lifetime drawbacks and decrease output light flicker. Calculations show that magnetic energy density using iron powder cores are lower than electrolytic capacitors, also a little lower than ceramic capacitors, but obviously higher than film capacitors. After calculations, conventional isolated and non-isolated LED drivers will be reviewed and new non-isolated off-line 230v with 10w output power LED driver with magnetic energy... 

In this thesis, two types of smart switch & driver chips are designed in 0.18 um HV BCD technology; low side driver and high side driver. These drivers are smart, because of having various types of protection and detection circuits, which protect switch, driver and connected load, versus errors that can be occurred by the user or other environmental effects. The protection circuits are battery over & under voltage shutdown, current limit, inductive load clamper and thermal shutdown. Load status is checked by status detection circuit and reported to user by one bit flag. Battery voltage can vary from 7 V to 40 V and output current is limited to 2 A. Designed high side and low side drivers are... 

By reducing the size of the transistor, it is possible to implement systems on a chip. For this puspose, these chips require different supply voltage levels. Therefore, two types of linear and switching converters are used to convert DC voltage level. At high convertion ratios, linear regulators have lower efficiencies than switching converters. However, in switching converters, due to their nature of functionality, very high efficiencies (near 100 percent) can be achieved. The advantages of linear regulators include low output voltage ripple, no need for off-chip elements, low noise, and simplicity. For this reason, a linear regulator is usually used in the output of the switching... 

Nowadays, multilevel converters are significantly developed in industrial applications as well as energy transmission systems regarding proper quality of output waveforms and fault tolerant operation ability. Among the different topologies of multilevel converters, modular multilevel converter (MMC) due to its modularity feature it more accepted in high voltage direct current (HVDC) transmission systems. Fast fault detection in power electronics converters is necessary to bypass the defected part in order to prevent failure propagation to other Submodules and to provide continues servicing. On this basis, different researches are reported in literature for MMCs fault tolerant operation. In... 

Multilevel converters are the best solution in medium and high voltage applications because of their better output votage quality, redundant structure, less power semiconductor losses and common-mode voltages. Modular multilevel converters (MMCs) have additional advantages such as higher degree of modularity, transformerless operation capability and using a single common DC-bus. All these useful features make MMC the first alternative for HVDC systems. Fault detection, defected cells insulation and post fault operation control are necessary to ensure MMC continouse service. A simple, fast and accurate fault detection method is proposed for MMC semiconductor power switches in this thesis....