Sharif Digital Repository

Doubly fed induction generators (DFIGs) are widely used in wind power systems; hence their reliability model is an important consideration for production assessment and economic analysis of wind energy conversion systems. However, to date mutual influences of reliability analysis, production estimations and economic assessments of wind farms have not been fully investigated. This study proposes a reliability model for DFIG wind turbines considering their subcomponent failure rates and downtimes. The proposed production estimation algorithm leads to an economic assessment for wind farms. A comprehensive spare parts management procedure is then presented in the study. As a case study,... 

Wind speed is the most important parameter in the design and study of wind energy conversion systems. The weibull distribution is commonly used for wind energy analysis as it can represent the wind variations with an acceptable level of accuracy. In this study, the wind data for 11 cities in Iran have been analysed over a period of one year. The Goodness of fit test is used for testing data fit to weibull distribution. The results show that this data fit to weibull function very well. The scale and shape factors are two parameters of the weibull distribution that depend on the area under study. The kinds of numerical methods commonly used for estimating weibull parameters are reviewed. Their... 

Continuity of service of wind energy conversion systems as well as their reliability and performances are some of the major concerns in this power generation area. Six-legs AC/DC/AC converters are normally used in modern wind energy systems like as in the system with a doubly-fed induction generator (DFIG). A sudden 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 shutdown. Therefore, to prevent the spread of the fault to the other system components and to ensure continuity of service, fault tolerant converter topologies associated to quick and effective fault detection and compensation methods... 

In this paper, application of a five-leg converter in Doubly Fed Induction Generator (DFIG) for Wind Energy Conversion Systems (WECS) is investigated. The five-leg structure and its PWM control are studied and performances are compared with the classical six-leg topology. The main drawback of five-leg converter with respect to the six-leg back-to-back converter is the need to increase the dc-link voltage for the same operation point, i.e. the same powers in case of WECS. So, different methods for the reduction of the required dc-link voltage in the five-leg case are studied. The five-leg converter is used to replace the conventional six-leg one, with the same ability. For the performance... 

Fast fault detection and converter reconfiguration is necessary for fault tolerant doubly fed induction generator (DFIG) in wind energy conversion systems (WECS) to prevent further damage and to make possible the continuity of service. Extra sensors are needed in order to detect the faults rapidly. In this paper, a very fast FPGA-based fault detection scheme is presented that minimizes the number of additional voltage sensors. A fault tolerant converter topology for this application is studied. Control and fault detection system are implemented on a single FPGA and Hardware in the Loop experiments are performed to evaluate the proposed detection scheme, the digital controller and the fault... 

In this paper, an FPGA-controlled fault tolerant back-to-back converter for DFIG-based wind energy conversion application is studied. Before an open-circuit failure in one of the semiconductors, the fault tolerant converter operates as a conventional back-to-back six-leg one. After the fault occurrence in one of the switches, the converter will continue its operation with the remaining five healthy legs. Design, implementation, simulation and experimental verification of a reconfigurable control strategy for the fault tolerant six/five leg converter used in wind energy conversion are discussed. The proposed reconfigurable control strategy allows the uninterrupted operation of the converter...