Sharif Digital Repository

Interleaved DC-DC boost converters are interesting choices in applications like fuel cells and photovoltaic systems. Although this converter offers low current ripple, but an open-circuit switch fault can lead to unacceptable current ripples. In this paper, a very fast and simple method is proposed to detect an open-circuit switch fault and its location. This method doesn't need any additional sensors, is efficient in CCM and DCM modes of operation, and can detect the fault in less than one switching period. Moreover, this method is suitable for implementation on an FPGA, due to the use of simple math and state machine blocks. Simulations are carried out to validate the effectiveness of this... 

In this paper, a new post-fault vector control of an induction motor, fed by a faulty Cascaded H-Bridge (CHB) inverter, is presented. Among fault tolerant control methods, waveform based methods are suitable for closed-loop control and provide higher output voltage. In order to control the speed of the motor, a rotor field oriented control (RFOC) is used. During the fault, the FOC is modified to decrease the fault impact on the motor as low as possible. The proposed method is validated by means of simulation results for different loads and faults. The results show an improvement in both the final operating point and the transient response of the motor  

Cascaded H-bridge converter has been utilized recently in different high-power applications due to its modular and simple structure. In order to have a balanced operation after a fault occurrence in this converter, it is necessary to detect the switch fault and its location. In this paper, a fast power-switch fault detection method is presented to identify a fault and its location. Only one voltage measurement per phase is required by this method, and the fault detection is faster compared to the existing methods. Moreover, it is suitable for implementation on an FPGA device due to the use of simple math, relational, and state machine blocks. The proposed method is verified by computer... 

In a transformerless grid-connected photovoltaic system, many issues arise from the leakage current flow into the ground, as EMI problems. The leakage current is originated from the common-mode voltage fluctuations. In this paper, the common-mode voltage harmonics in a three-phase quasi-Z-source inverter are analyzed using Fourier transform and a closed-loop formulation is presented for the harmonics value. The shoot-through mode in a quasi-Z-source inverter causes extra fluctuations in the common-mode voltage comparing to a classic inverter. The proposed harmonic analysis method provides a systematic way to figure out how shoot-through mode and also other parameters affect the common-mode... 

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... 

In this paper, a small signal model is proposed for four-switch rectifier with input power factor correction. The required transfer functions are determined and calculated for a typical rectifier. This model is used to design an appropriate controller with defined characteristic to improve the rectifier performance. Another controller is used to compensate capacitors dc voltage difference. The system is simulated in Simulink and the results are provided. These results confirm the accuracy of the developed model, and also the effectiveness of the proposed controllers  

This study presents an analytical approach for proper selection of output functions to be regulated for the Vienna rectifier such that the resultant closed-loop systems are minimum phase. Specifically, two different adaptive control methodologies based on the input-output linearisation are developed and categorised. In the first category, three output functions are introduced and imposed to be zero by using three dynamic feedback laws. On the basis of states to be regulated, four different cases are studied and it is shown that only one of these cases results in a one-dimensional zero dynamics with an asymptotically stable equilibrium point. In the second category, two output functions are... 

The objective of this work is to study the effects of harmonics on energy meters. This study is canied out based on IEEE 1459 standard through extensive tests on some energy meters installed at Gil an utility consumers. First, a review on IEEE 1459 standard on power definitions will be given. The definitions are then ervaluated for a compact Fluorescent Lamp (CFL) as a harmonic generating load. Then, the results of the performance e-alnation of two energy meters are presented for different linear and nonlinear loads based on IEEE1459 standard power definitions. Two different test procedures are performed for this putpose. In the first series of tests, a harmonic polluted voltage is applied... 

Nowadays, reduced switch rectifiers are more interested because of less expense. Control of these rectifiers is an important part of their designing process. In this paper, a method is proposed for four-switch rectifier to continue working under unbalanced input voltage. To achieve this goal, first a method is introduced to separate positive and negative sequences of dq components. Also, the necessary condition is determined. Considering this condition, the control method is modified and new reference value for the control signals is calculated. Finally, the system is simulated in Simulink and the results are provided. These results confirm the accuracy of the developed model, and also the... 

Conventional back-to-back converters with input power factor correction are still the best solution for motor drive applications which are usually subjected to considerable load changes during their operation. Since converter components, especially input-side inductances are designed for nominal power rating, the rated input power factor and input current distortion aren't achievable in light loads. In this paper a control method is proposed to improve the input current distortion and input power factor in light loads. This is achieved by increasing the switching frequency according to the reduction in load. Since conduction and switching losses decrease in light loads, the overall losses by... 

Multilevel converters are mainly used in high power applications (usually more than a few hundred kW). It is therefore important that they can continue working under faulty condition. In this paper, a new method is proposed to improve performance of CHB inverter under faulty condition. The proposed method will be compared with existing methods in term of voltage availability. The converter is simulated in Simulink and the results are provided. These results confirm the effectiveness of the proposed scheme, and are in accordance with the theoretical results  

In this paper, a novel reduced switch cascaded transformer multilevel inverter is proposed. In this structure, a new structure is replaced with conventional H-bridge inverter. It consists of four high frequency switches, two line frequency switches, and two transformers which can be assembled in one core with a specific winding connection. This topology can produce 5 or 7 voltage levels depending on transformers turns ratio. The simplicity and modularity are its advantages compared to the existing structures. Beside these advantages, due to its similarity with H-Bridge converter, it is possible to use a modified technique based on conventional phase shift pulse width modulation to generate... 

Fast and accurate fault detection is the primary step and one of the most important tasks in fault tolerant converters. In this paper, a fast and simple method is proposed to detect and diagnosis the faulty cell in a cascaded H-bridge multilevel inverter under a short circuit fault. In this method, the reference voltage is calculated using switching control pulses and DC-Link voltages. The comparison result of the output voltage and the reference voltage is used in conjunction with active cell pulses to detect the faulty cell. To achieve this goal, the cell which is active when the Fault signal turns to “0” is detected as the faulty cell. Furthermore, consideration of generating the active... 

Fault detection is one of the most important tasks in fault tolerant converters. In this paper, a new method is proposed to detect the faulty cell in a cascaded H-bridge multilevel inverter. The detection technique is based on comparison of the output voltage with reference voltage made by using switching control pulses and DC-Link voltage. Because of the simplicity of this method, it is possible to use a single field-programmable gate array (FPGA) to implement this method and inverter control. The simulation and experimental results confirm the effectiveness of the proposed fault detection technique  

Fault tolerant ability is one of the most important tasks in high power converters. In this paper, a comparison between conventional fault tolerant methods is done for four applicable methods. For this purpose, their performance is investigated in specific case study and simulation results are used to illustrate their advantages and disadvantages. The most important features taken into account are maximum available voltage, harmonic distortion of output voltage and input current, and magnitude of common mode voltage. Finally, a decision algorithm based on the results is suggested to select suitable method to control inverter under specific faulty condition  

This paper is focused on improving the post-fault performance of cascaded H-bridge multilevel inverters by decreasing the common-mode voltage. First, an algorithm is proposed to determine the optimal post-fault state among all possible states, which have the same maximum available voltage. Furthermore, a modified technique is proposed to calculate the references of inverter phase voltages under faulty conditions. This technique leads to a decrease in the common-mode voltage when the required output voltage is less than its maximum value. These solutions are mutually employed in the post-fault control system. Simulation and experimental results confirm the effectiveness of the proposed... 

Learning a foreign language encompasses a process of trial and error that can lead to the progression of the learner's interlanguage, meaning that the learners make use of their language knowledge that receives feedback and brings about progress through diagnosis of the problems and being corrected by the teacher. Therefore, there exists a need to analyze the underlying reasons causing the students to remain taciturn with a low willingness to communicate (WTC) during a language class. There has been much work done investigating the role of the learner's stable personal characteristics (traits) along with their situational changes at a specific time (states) that influence the student's... 

Accurate system identification (SI) is essential for flight controller design of unmanned aerial vehicles and microaerial vehicles (MAVs). SI can be performed either in frequency or time domain using flight test data. As flight testing is often costly and may even lead to catastrophic events before some flight stability analysis is at hand, a low-cost 5 degree-of-freedom free motion platform (FMP) is designed and used for initial identification of MAVs via wind tunnel testing. A typical MAV is constructed as a test case and equipped with inertial sensors for testing and validation purposes. The proposed FMP allows for both rotational as well as translational motions that in turn provide for... 

Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's characteristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using city-block distance function and watershed segmentation algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images...