Sharif Digital Repository

In software testing, it is often desirable to find test inputs that exercise specific program features. Good testing means uncovering as many faults as possible with a potent set of tests. Thus, a test series that has the potential to uncover many faults is better than one that can only uncover a few. To find these inputs by hand is extremely time-consuming, especially when the software is complex. Therefore, many attempts have been made to automate the process. There are three major methods to generate software test data: Random test data generation, Symbolic test data generation and Dynamic test data generation. Dynamic test data generation, such as those using genetic algorithms, is... 

There are several types of uncertainty in supply chains that cause some difficulties in the planning of a supply chain. Uncertainty on the supply side can cause interruptions in the quality, quantity, or delivery time of orders. To avoid such interruptions, retailers usually contract with two different suppliers for a common good. In this setting, one of the suppliers has higher reliability and higher price, while the other supplier offers a lower price but has a lower level of reliability. In other words, to ensure a lower level of uncertainty, retailers have to pay more. This is one of the main tradeoffs in the dual sourcing strategy. In this thesis, we consider a two-echelon supply chain... 

Direct Torque Control (DTC) is one of the vector methods to control Permanent Magnet Synchronous Machines (PMSM). In order to achieve an appropriate control in vector control methods, an accurate estimation of flux is indispensable. Flux estimation should be fulfilled in a wide speed range without considerable dependence on motor parameters. Prevalent flux estimation methods are based on integration of stator voltage which is not feasible in low speed, or performed based on assumption of decoupled equations on d and q axis which is not precise for applications with fast dynamic. Different flux estimation methods are investigated in this thesis with the aim of improving the flux estimation in... 

Due to the growing oil price and environmental considerations, tendency to use local and environmentally friendly energy sources has increased.Bidirectional transmission can be one of the key features of the smart grid,so the use of car battery connected to the grid as local energy sources makes sense. This can provide network stability, especially during peak load times. Vehicles connected to grid (V2G) is an electric vehicle or a plug-in hybrid electric vehicles can delivered the electricity to the grid. These systems require either two separate power electronic converters can be used for transmission in either directions or a two-way transfer charger. The aim of this project is to design... 

In recent years, multiport bidirectional converters have been a center of attention in renewable energy systems. This research focuses on three-port bidirectional converters. First, series resonant bidirectional converter is precisely analyzed. This analysis includes sinusoidal, exact state space and small signal analysis through phasor concept. This converter can work in higher switching frequencies and higher power ratings in comparison with common DAB bidirectional converter due to its inductor impedance cancellation. To increase power rating a three-phase version is proposed which has reduced output filter capacitance. Then, three-port bidirectional resonant converter is proposed and... 

Accurate and fast position controlling is an important issue in today’s industrial needs. Drives used for position control require fast dynamics on speed control. Cascade linear controllers have sluggish response due to bandwidth limitations on speed and current loop. These structures limit the dynamics above all in high power applications where the switching frequency is low. In this thesis, deadbeat direct speed control is proposed, which overcomes limitations by cascade loops resulting in high-speed control dynamics. This approach uses a model of the plant to generate the control signals. According to measured speed and currents, the controller specifies the best voltage vector in order... 

In this project the novel zero-voltage-switching topology for power factor correction bridgeless boost rectifier is proposed. By employing an improved ZVS pulse-width-modulation (PWM) switch cell, ZVS of all the main switches is achieved without additional current or voltage stress of main switches. Also for the auxiliary switch the zero-current-switching is provided. In all modes of opretion of this converter, the power path is provided by maximum two semiconductor so the conduction loss of converter is low as in conventional converter. With this features the efficiency of proposed converter is very high  

The subject of control and stabilization of dc-dc series resonant converter (SRC) is still a challenge in power electronics. The conventional controller design and stability analysis for this converter are based on the model which is derived using the sinusoidal approximation and averaging followed by linearization about an operating point. This model is not applicable to a SRC that operates below resonance especially in discontinuous conduction mode (DCM) because the sinusoidal approximation is no longer acceptable. However, a SRC may be purposely designed to operate in DCM. Therefore, it is essential to investigate the stability analysis and controller design using a more sophisticated... 

DC-DC switching convertors are power electronic circuits that have various applications nowadays. Quasi-resonant convertors are a kind of these convertors that are of great interest due to their simple structure and soft switching. The goal of controlling these convertors is to achieve constant output voltage while varying the input voltage and the load by choosing a proper switching frequency. Classic controllers show drawbacks in the case of high input voltage and load tolerance, and this nonlinear behavior of the systems results in some practical challenges. In this thesis, nonlinear predictive controller for quasi-resonant Buck convertors is designed. Having designed the linear... 

Nowadays, power electronics converters with pulse width modulation (PWM) are widely used in different power circuits. Operation of semi-conductive switches during on and off conditions causes switching dissipation and consequently decreases the efficiency of the PWMs. Recently, by increasing the required power for power electronics applications, quasi-resonant converters attract attentions. Quasi-resonant converters, by adding resonant circuits to the PWM converters causes the soft switching operation (switching with zero current or voltage) and decreases the energy loss. In conventional control methods of these converters, the nonlinear average circuit model is linearized around the... 

Hydraulic steering technology has been used in vehicles for decades. Recently, a trend has been seen towards the use of electronic steer-by-wire systems that provide greater design flexibility by customizing the connection between the steering wheel and the steering mechanism. Steer-by-Wire systems (SbW) offer the potential to enhance steering functionality by enabling features such as automatic lane keeping, park assist, variable steer ratio, and advanced vehicle dynamics control. The lack of a steering intermediate shaft significantly enhances vehicle architectural flexibility. The task of a SbW system is two-fold: turning the steered wheels by tracking the hand wheel (HW) rotation and... 

Long lasting portable power is an ultimate desire for electronic devices. The limited capacity of the batteries in addition to the heavy weight and extra costs are the main challenges of the batteries for energy storage in large electrical devices like electric vehicles. Wireless Power Transmission (WPT) technology can address these issues by providing online electric power for these portable devices. Furthermore, this technology can supply electric devices especially portable ones by eliminating cables and connectors with more reliability.The current research is focused on optimum design of the wireless power transfer system for electric vehicle charging applications. The optimization of... 

Nowadays, non-linear loads comprise an important part of electrical grids. One of the most essential sources of nonlinear loads is switching power supplies, which mainly include power electronic rectifiers. When power outage occurs, Uninterruptible Power Supplies (UPS) must be able to supply these loads. The nonlinearity of the load has a significant effect on the Total Harmonic Distortion (THD) of the output voltage, which may not be easily reduced, especially in three-phase inverters. Furthermore, the presence of isolating transformers in these power supplies limits the control of harmonics and intensifies the nonlinear effects of the system.In this Master Thesis, a disturbance observer is... 

The electric vehicle inverter, as one of the most important components of the vehicle, needs to have a high efficiency and also be able to work at high temperatures. Due to passing a large part of the battery power through this part and being one of the components that has the biggest power in an electric vehicle , traction inverter Efficiency has a big impact on the total efficiency of the whole vehicle . By increasing the battery voltage of electric vehicles, in order to achieve a higher charging power, the electric vehicle inverter must be able to withstand a voltage of about 800 volts input .On the other hand, in electric car inverters, the goal is to reach a power density of 100kw / L.... 

In comparison to pulse width modulation (PWM) converters, the ability of soft switch-ing enables resonant converters to operate at high frequencies, as the result of which these converters enjoy high efficiency, high power density, and low electromagnetic interference (EMI). Among resonant tank topologies, the LLC resonant tank is a very desirable structure, as the LLC resonant converter can operate in boost mode and properly regulate the output voltage under light loads and despite large variations in the input voltage and/or the load. However, there are major modeling issues with resonant converters, since conventional modeling approaches cannot properly model fast dynamics of these... 

In creating a telecom battery charger there are three challenging factors which are high power density, high efficiency and modularity. A telecome battery charger consist of a rectifier with power factor correction capability and a DC-DC converter. The power stage of DC-DC converter with high output current and low output voltage has a vital role in the battery charger. The isolation transformer and magnetic component of LLC resonant tank are two huge and heavy parts of the DC-DC converter. With the emergence of GaN and SiC switches pushing frequency to to megahertz is possible which resulted in decreasing the volume of passive divices. But with increasing the frequency, designing of the... 

With the ever-increasing expansion of the fifth generation telecommunication networks, achieving high efficiency for the power sources used in these networks becomes important due to their average power and wide use. For this reason, different and strict standards have been defined for efficiency. 80 plus is a certification program that aims to promote the efficient use of energy in power supplies including computers, servers and telecommunications applications. The highest level of this standard is called 80 plus titanium. This standard defines the minimum acceptable efficiency in different loads, which for example is equal to 96% in 50% load. The power supplies consist of two layers of... 

With the rapid expansion of photovoltaic (PV) system applications and the increasing power capacity of solar inverters, the use of 1500 V DC links has become a common standard in the industry. However, employing such a high voltage level in the design of auxiliary power supplies poses challenges, including high voltage stress on switches and the need for voltage balancing across the series-connected DC link capacitors. In this thesis, an innovative auxiliary power supply topology, referred to as a centrally clamped series-input flyback converter with active clamp, is introduced. This topology provides zero-voltage switching (ZVS) by adding only one switch to the conventional series-input...