Fault ride-through improvement of DFIG-WT by integrating a two-degrees-of-freedom internal model control

A novel two-degree-of-freedom internal model control (IMC) controller that improves the fault ride-through (FRT) capabilities and crowbar dynamics of doubly fed induction generator (DFIG) wind turbines is presented. As opposed to other control strategies available in the open literature, the proposed IMC controller takes into account the power limit characteristic of the DFIG back-to-back converters and their dc-link voltage response in the event of a fault and consequent crowbar operation. Results from a digital model implemented in Matlab/Simulink and verified by a laboratory scale-down prototype demonstrate the improved DFIG FRT performance with the proposed controller

Symmetrical Short-Circuit Parameters Comparison of DFIG–WT

Renewable energy with new resources is depleting the fossil fuel-based energy resources. Renewable energy sources (such as wind energy) based power generators are important energy conversion machines and have widely industrial and commercial applications due to their superior performance, and the fact that they endure faults well and are environmentally friendly. The study of the transient behavior of such generators under fault condition has drawn much attention. This study presents Doubly-Fed Induction Generator (DFIG) perturbation during a symmetrical (three-phase) short circuit (SSC) at different points. Simulation results reveal that after a fault occurs, there is decay of SC parameters (transient time, maximum current, steady-state and voltage dip) at the point of common coupling (PCC) and the grid-side converter (GSC) of DFIG. Simulation results depict a more sensitive and robust point during a SSC of DFIG. Current findings present the main difference between the PCC and the GSC during SSC faults. These comparisons provide a more precise understanding of fault diagnosis reliability with reduced complexity, stability, and optimization of the system. This study verified by the simulation results helps us understand and improve the performance of sensor sensibility (measurements), develop control schemes, protection strategy and select a more accurate and proficient system among other wind energy conversion systems (WECS)

Power Quality Issue of Grid Connected DFIG Wind Farm System

Quality of power is known as any power problem manifested as a non-standard frequency, current and voltage which cause failure of end customer apparatus. The wind utilization, generation and its penetration in utility grid are increasing worldwide. One of the master issues in wind generation is the insertion to the network. When the wind energy is injected to the grid generally controls the voltage disturbances on the system power quality, variation of voltage is the almost prevalent kind of disturbance which affects stability and the quality of power for grid-inserted wind system. This study investigates the two widespread kinds of voltage variations such as voltage dip and swell, which can happen if large amount of wind system is connected to an electrical grid. This research also studies the response and performance under faults of a wind farm inserted to distribution systems. In this paper, a wind turbine with induction machine (DFIG) is simulated by using MATLAB/Simulink program. The simulated model is subjected to disturbances which known as; voltages (dip and rise). The results of simulation presents that, how both variations; voltage dip & voltage rise lead to mal-operation as well as shut-down of entire system, therefore deteriorating the improvement of power quality for the grid

Large Grid-Connected Wind Turbines

This book covers the technological progress and developments of a large-scale wind energy conversion system along with its future trends, with each chapter constituting a contribution by a different leader in the wind energy arena. Recent developments in wind energy conversion systems, system optimization, stability augmentation, power smoothing, and many other fascinating topics are included in this book. Chapters are supported through modeling, control, and simulation analysis. This book contains both technical and review articles

Doubly-Fed Induction Machines: Model, Control and Applications

Renewable energy resources far outweigh fossil fuels in several terms of benefits, i.e. environmentally friendly, and economically. Wind Energy Conversion Systems are the fastest grown units among renewables within recent years. Due to large penetration of wind units in nowadays power systems, some specific regulations have been issued through modern national grid codes to manage their technical commitments. Low Voltage Ride Through (LVRT), as one of the most important requirements, asks wind units to ride through some predefined grid low voltage conditions in terms of amplitude reduction and time duration, mainly caused by different types of balanced and/or unbalanced power network faults. Doubly-Fed Induction Generators (DFIGs) as the most popular machines among the current driven wind turbines, are electrically connected to the grid through a three-phase winding placed at stator, while rotor is electromagnetically connected to stator. Hence, a sudden reduction of voltage profile, will trigger large current/flux oscillations in the machine, may hit the physical limits and consequently, violate grid codes. The main topic of this thesis is modeling and control of DFIG-based wind turbine systems to substantiate LVRT requirements without imposing any additional hardware to installed components. To achieve this objective, system/control theory tools are applied to investigate the effects of grid faults on DFIG dynamics, and design proper control-based countermeasures. More specifically, taking advantage from analyzing the internal dynamics of DFIG, various feedforward-feedback controllers have been designed to deal with line faults having increasing complexity. A crucial role in such approach is played by a suitable state reference trajectory design, based on the feature of the DFIG internal dynamics. Such kind of method has been applied to deal with the mechanical dynamics, as well. Numerical realistic simulations validate the benefits of the proposed controller, in crucially improving the machine response under severe grid faults

Impact analysis and optimized control in renewable energy Integrated power network

This thesis quantifies the power quality impacts in hybrid renewable energy integrated power network and explores the voltage regulation method under various network conditions. This thesis also provides an optimized controller for DFIG to significantly ride through the symmetric and asymmetric faults meeting Australian grid code requirements. Thesis has extensive implications in terms of voltage improvement and LVRT enhancement in a grid tied renewable energy integrated power network

Studies in Electrical Machines & Wind Turbines associated with developing Reliable Power Generation

The publications listed in date order in this document are offered for the Degree of Doctor of Science in Durham University and have been selected from the author’s full publication list. The papers in this thesis constitute a continuum of original work in fundamental and applied electrical science, spanning 30 years, deployed on real industrial problems, making a significant contribution to conventional and renewable energy power generation. This is the basis of a claim of high distinction, constituting an original and substantial contribution to engineering science

Advanced control of doubly-fed induction generator based variable speed wind turbine

This thesis deals with the modeling, control and analysis of doubly fed induction generators (DFIG) based wind turbines (DFIG-WT). The DFIG-WT is one of the mostly employed wind power generation systems (WPGS), due to its merits including variable speed operation for achieving the maximum power conversion, smaller capacity requirement for power electronic devices, and full controllability of active and reactive powers of the DFIG. The dynamic modeling of DFIG-WT has been carried out at first in Chapter 2, with the conventional vector control (VC) strategies for both rotor-side and grid-side converters. The vector control strategy works in a synchronous reference frame, aligned with the stator-flux vector, became very popular for control of the DFIG. Although the conventional VC strategy is simple and reliable, it is not capable of providing a satisfactory transient response for DFIG-WT under grid faults. As the VC is usually designed and optimized based on one operation point, thus the overall energy conversion efficiency cannot be maintained at the optimal point when the WPGS operation point moves away from that designed point due to the time-varying wind power inputs. Compared with VC methods which are designed based on linear model obtained from one operation point, nonlinear control methods can provide consistent optimal performance across the operation envelope rather than at one operation point. To improve the asymptotical regulation provided by the VC, which can't provide satisfactory performance under voltage sags caused by grid faults or load disturbance of the grid, input-output feedback linearization control (IOFLC) has been applied to develop a fully decoupled controller of the active $\&$ reactive powers of the DFIG in Chapter 3. Furthermore, a cascade control strategy is proposed for power regulation of DFIG-WT, which can provide better performance against the varying operation points and grid disturbance. Moreover, to improve the overall energy conversion efficiency of the DFIG-WT, FLC-based maximum power point tracking (MPPT) has been investigated. The main objective of the FLC-based MPPT in Chapter 4 is to design a global optimal controller to deal with the time-varying operation points and nonlinear characteristic of the DFIG-WT. Modal analysis and simulation studies have been used to verify the effectiveness of the FLC-based MPPT, compared with the VC. The system mode trajectory, including the internal zero-dynamic of the FLC-MPPT are carefully examined in the face of varied operation ranges and parameter uncertainties. In a realistic DFIG-WT, the parameter variability, the uncertain and time-varying wind power inputs are existed. To enhance the robustness of the controller, a nonlinear adaptive controller (NAC) via state and perturbation observer for feedback linearizable nonlinear systems is applied for MPPT control of DFIG-WT in Chapter 5. In the design of the controller, a perturbation term is defined to describe the combined effect of the system nonlinearities and uncertainties, and represented by introducing a fictitious state in the state equations. As follows, a state and perturbation observer is designed to estimate the system states and perturbation, leading to an adaptive output-feedback linearizing controller which uses the estimated perturbation to cancel system perturbations and the estimated states to implement a linear output feedback control law for the equivalent linear system. Case studies including with and without wind speed measurement are carried out and proved that the proposed NAC for MPPT of DFIG-WT can provide better robustness performance against the parameter uncertainties. Simulation studies for demonstrating the performance of the proposed control methods in each chapter, are carried out based on MATLAB/SIMULINK