A Hybrid Method of Performing Electric Power System Fault Ride-Through Evaluations on Medium Voltage Multi-Megawatt Devices

This dissertation explores the design and analysis of a Hybrid Method of performing electrical power system fault ride-through evaluations on multi-megawatt, medium voltage power conversion equipment. Fault ride-through evaluations on such equipment are needed in order to verify and validate full scale designs prior to being implemented in the field. Ultimately, these evaluations will help in reducing the deployment risks associated with bringing new technologies into the marketplace. This is especially true for renewable energy and utility scale energy storage systems, where a significant amount of attention in recent years has focused on their ever increasing role in power system security and stability. The Hybrid Method couples two existing technologies together - a reactive voltage divider network and a power electronic variable voltage source - in order to overcome the inherent limitation of both methods, namely the short circuit duty required for implementation. This work provides the background of this limitation with respect to the existing technologies and demonstrates that the Hybrid Method can minimize the fault duty required for fault evaluations. The physical system, control objectives, and operation cycle of the Hybrid Method are analyzed with respect to the overall objective of reducing the fault duty of the system. A vector controller is designed to incorporate the time variant nature of the Hybrid Method operation cycle, limit the fault current seen by the power electronic variable voltage source, and provide regulation of the voltage at the point of common coupling with the device being evaluated. In order to verify the operation of both the Hybrid Method physical system and vector controller, a controller hardware-in-the-loop experiment is created in order to simulate the physical system in real-time against the prototype implementation of the vector controller. The physical system is simulated in a Real Time Digital Simulator and is controlled with the Hybrid Method vector controller implemented on a National Instruments FPGA. In order to evaluate the complete performance of the Hybrid Method, both a synchronous generator and a doubly-fed induction generator are modeled as the device under test in the simulations of the physical system. Finally, the results of the controller hardware-in-the-loop experiments are presented which demonstrate that the Hybrid Method is a viable solution to performing fault ride-through evaluations on multi-megawatt, medium voltage power conversion equipment

The Effect of Doubly-Fed Induction Generator (DFID) Based Wind Turbine and Its Application

Renewable Energy Sources are non-pollutant of environment and environmental friendly when compared to non-renewable sources of energy. Therefore, the integration of renewable energy sources like Wind Energy Conversion System with utility grid is inevitable. Wind Energy is predominant among the non-conventional sources of energy where different conversion technology have been proposed to generate electric power .The Doubly-Fed Induction Generator (DFIG) is popular technique for variable speed wind power generation owing to its flexibility, efficiency, less mechanical stresses, extensive control ability of the generated real and reactive power and cost effective rated power electronics converter.The report x-ray a background study of DFIG in order to introduce the basic features such as variable speed and normal operation of DFIG systems for wind power applications based on three-phase wound rotor induction generator. Keywords: Word Energy, DFIG, Variable Speed, Renewable Energ

Modeling and Control of Power Converter for Doubly Fed Induction Generator Wind Turbines using Soft Computing Techniques

This paper is based on Fuzzy Logic Controller (FLC) Control of Doubly Fed Induction Generator (DFIG) wind turbine in a power system for nonlinear loads. By which the nonlinear system can be made to work as a linear system to bring out better performance. . Fuzzy logic is a logical system which provides definite solution to solve problems. It process with fuzzy variables which are defined by membership functions. The combined action of PI and FLC controls the switching actions, distortion in harmonics and provide compensation for unbalanced load if any at the point of common coupling. The proposed system consists of back to back connected converters, one is connected to the generator side and the other is connected to the grid side. The grid side connected converter is used for compensation ie, it act as an Active Power Filter (APF) and compensator hence the cost of using APF is reduced. Reduced Total Harmonic Distortion (THD) is obtained by simulating (MATLAB/SIMULINK) the performance and the result is found to be quite satisfactory. Key Words: Fuzzy Logic Controller, Harmonic Reduction, Power converter, Renewable Energy

Bank of Extended Kalman Filters for Faults Diagnosis in Wind Turbine Doubly Fed Induction Generator

In order to increase the efficiency, to ensure availability and to prevent unexpected failures of the doubly fed induction generator (DFIG), widely used in speed variable wind turbine (SVWT), a model based approach is proposed for diagnosing stator and rotor winding and current sensors faults in the generator. In this study, the Extended Kalman Filter (EKF) is used as state and parameter estimation method for this model based diagnosis approach. The generator windings faults and current instruments defects are modelled, detected and isolated with the use of the faults indicators called residuals, which are obtained based on the EKF observer. The mathematical model of DFIG for both healthy and faulty operating conditions is implemented in Matlab/Simulink software. The obtained simulation results demonstrate the effectiveness of the proposed technique for diagnosis and quantification of the faults under study

Nonlinear and sampled data control with application to power systems

Sampled data systems have come into practical importance for a variety of reasons. The earliest of these had primarily to do with economy of design. A more recent surge of interest was due to increase utilization of digital computers as controllers in feedback systems. This thesis contributes some control design for a class of nonlinear system exhibition linear output. The solution of several nonlinear control problems required the cancellation of some intrinsic dynamics (so-called zero dynamics) of the plant under feedback. It results that the so-dened control will ensure stability in closed-loop if and only if the dynamics to cancel are stable. What if those dynamics are unstable? Classical control strategies through inversion might solve the problem while making the closed loop system unstable. This thesis aims to introduce a solution for such a problem. The main idea behind our work is to stabilize the nonminimum phase system in continuous- time and undersampling using zero dynamics concept. The overall work in this thesis is divided into two parts. In Part I, we introduce a feedback control designs for the input-output stabilization and the Disturbance Decoupling problems of Single Input Single Output nonlinear systems. A case study is presented, to illustrate an engineering application of results. Part II illustrates the results obtained based on the Articial Intelligent Systems in power system machines. We note that even though the use of some of the AI techniques such as Fuzzy Logic and Neural Network does not require the computation of the model of the application, but it will still suer from some drawbacks especially regarding the implementation in practical applications. An alternative used approach is to use control techniques such as PID in the approximated linear model. This design is very well known to be used, but it does not take into account the non-linearity of the model. In fact, it seems that control design that is based on nonlinear control provide better performances

Impact assessment of large-scale penetration of permanent magnet synchronous generators on power quality

Wind power generation has gained a large share in the renewable energy market over the past few years. This study investigates the impact of large scale penetration of permanent magnet synchronous generator (PMSG) based wind turbines on power quality of the grid. PMSGs are attractive due to the absence of a gearbox in the drive-train, which results in lower maintenance costs and higher reliability. Moreover, the advancements in power electronics have facilitated PMSGs to generate optimal power at varying wind speed conditions. This is achieved through the use of maximum power point tracking algorithms. The drawbacks of PMSG-based wind energy systems are that they inject harmonics into the network and cause flicker as well as other power quality issues. Despite these disadvantages, the grid code requires that PMSGs stay connected to the grid even under grid disturbances. This is because the reactive power control capability of PMSG-based wind energy systems can actually assist with voltage support. It will be shown in this study that disconnecting large scale PMSGs based wind turbines during grid disturbances has a detrimental effect on transient stability of the grid. This study will show that PMSG-based wind energy systems improve transient stability and assist in voltage support through reactive power control. Moreover, the impacts of large scale PMSG based wind turbines on power quality of the grid can be reduced by various means, which are also addressed in the study

Design and implementation of variable speed wind energy induction generator systems for fault studies

Includes bibliographical references (leaves [136]-139).Due to the economical and environmental benefits, Wind Energy Conversion Systems (WECS) have received tremendous growth in the past decade. The increased interest in wind energy has made it necessary to model and experimentally evaluate entire WECS, so as to attain a better understanding and to assess the performance of various systems. As a direct consequence of the increase in wind generation systems, comes the need for the reduction of operational and maintenance costs of these wind generators. The most efficient way of reducing these costs is by the early detection of the degeneration of these generators health, thus facilitating a proactive response, minimizing downtime, and maximizing productivity. The more common induction machine failures are caused by the deterioration of the stator insulation and by the breaking of rotor bars. The thesis describes the design, modeling and implementation of two different variable speed induction generator systems for studying faults in wind energy applications. This project served as a platform for further research into the development and evaluation of a non-stationary fault detection technique suitable for wind energy induction generator purposes. Some common faults are implemented on the wind generators in an attempt to identify them from measurements and by using a steady state fault analysis technique (Motor Current Signature Analysis). For variable speed wind generation, there are two systems using induction generators. The first consist of a squirrel cage induction generator, which uses back-to-back converters in the stator circuit, as shown in Fig. 0.1. The second consists of a wound rotor induction generator, whereby the stator is directly connected to the grid and the rotor circuit consists of back-to-back converters, as shown in Fig. 0.2. When both the rotor and stator are capable of delivering power as with the wound rotor induction generator, they are known as doubly-fed induction generators (DFIG)