Fed Induction Generator-based Wind Turbine Research Articles

Dynamic behavior analysis under a grid fault scenario of a 2 MW double fed induction generator-based wind turbine: comparative study of the reference frame orientation approach

This paper investigates a comprehensive analysis of the dynamic behavior of a typical 2 mw grid-connected double fed induction generator-based wind turbine during a symmetrical grid voltage dip scenario. The stator flux dynamics and the induced rotor electromotive force have been investigated aiming to undertake an accurate assessment of the DFIG behavior. Furthermore, without any complication of the DFIG vector control scheme, the paper offers a comparative study between the use of the stator flux reference frame orientation approach and the grid voltage reference frame orientation approach, this, in order to accurately assess the appropriate choice regarding the stability of the vector control scheme and hence, to have a good background about the LVRT capability of the DFIG during the studied grid fault. The simulation results have been performed through Matlab/Simulink environment.

Highly Reliable Back-to-Back Power Converter Without Redundant Bridge Arm for Doubly Fed Induction Generator-Based Wind Turbine

In this paper, a highly reliable back-to-back (BTB) power converter is proposed for doubly fed induction generator-based wind turbines (DFIG-WTs). When a power switch open-circuit fault is encountered in either the grid-side converter (GSC) or the rotor-side converter (RSC), a four-switch three-phase (FSTP) topology is formed to avoid using redundant bridge arms, which reduces the power circuit complexity and minimizes the conduction and switching losses. A simplified space vector pulsewidth modulation technique is used to eliminate sector identification and complex trigonometric calculations. In addition, the influence of dc-bus capacitor voltage unbalance on the electromagnetic torque is analyzed in detail. The offset current components are calculated, and they are deducted from the reference values in the modified control strategies to suppress the dc-bus voltage deviation. Moreover, the power loss model of a BTB converter is analyzed in detail, and the efficiency study is performed in various post-fault situations. Simulations in MATLAB/Simulink are carried out to verify the performance of a DFIG-WT based on a FSTP BTB converter. Furthermore, the control hardware-in-the-loop setup with RSC and GSC separately simulated in a digital real-time simulator is applied for experimental verification of the proposed control strategy.

Dynamic Modeling and Robust Controllers Design for Doubly Fed Induction Generator-Based Wind Turbines under Unbalanced Grid Fault Conditions

High penetration of large capacity wind turbines into power grid has led to serious concern about its influence on the dynamic behaviors of the power system. Unbalanced grid voltage causing DC-voltage fluctuations and DC-link capacitor large harmonic current which results in degrading reliability and lifespan of capacitor used in voltage source converter. Furthermore, due to magnetic saturation in the generator and non-linear loads distorted active and reactive power delivered to the grid, violating grid code. This paper provides a detailed investigation of dynamic behavior and transient characteristics of Doubly Fed Induction Generator (DFIG) during grid faults and voltage sags. It also presents novel grid side controllers, Adaptive Proportional Integral Controller (API) and Proportional Resonant with Resonant Harmonic Compensator (PR+RHC) which eliminate the negative impact of unbalanced grid voltage on the DC-capacitor as well as achieving harmonic filtering by compensating harmonics which improve power quality. Proposed algorithm focuses on mitigation of harmonic currents and voltage fluctuation in DC-capacitor making capacitor more reliable under transient grid conditions as well as distorted active and reactive power delivered to the electric grid. MATLAB/Simulink simulation of 2 MW DFIG model with 1150 V DC-linked voltage has been considered for validating the effectiveness of proposed control algorithms. The proposed controllers performance authenticates robust, ripples free, and fault-tolerant capability. In addition, performance indices and Total Harmonic Distortions (THD) are also calculated to verify the robustness of the designed controller.

Reliability assessment and performance analysis of DFIG-based WT for wind energy conversion system

This paper presents the reliability assessment and performance analysis of Doubly Fed Induction Generator-based Wind Turbine (WT) for accurate DFIG-based WT modelling. This model calculates and describes the reliability of each unit and component of the WECs by using Markov process. To analyse the DFIG-based WT during transient and steady-state operations, both the control and modelling of the system have been illustrated in detail. The main contributions of this paper are the reliability assessment of the DFIG based WT units in terms of failures as well as repair rate and performance analysis in normal as well as faulted conditions. For fault analysis of the WECs, DFIG-based WT has been simulated in MATLAB Simulink for line to line, line to ground and double line to ground fault studies.

Fault-Tolerant Operation of DFIG-WT With Four-Switch Three-Phase Grid-Side Converter by Using Simplified SVPWM Technique and Compensation Schemes

In this paper, in response to the open-circuit fault scenario in the grid-side converter (GSC) of doubly fed induction generator-based wind turbines (DFIG-WTs), a fault-tolerant four-switch three-phase (FSTP) topology-based GSC is studied. Compared with other switch-level fault-tolerant converter topologies, fewer switches, less switching and conduction losses, and simpler converter structure are derived. A simplified space vector pulse width modulation (SVPWM) technique is proposed to improve the output current quality and reduce the computational complexity in the control process. Unified expressions of duty ratios for the two remaining healthy bridge arms are obtained. In addition, the three-phase unbalance phenomenon caused by the capacitive impedance in the faulty phase is analyzed from the ac point of view, and a current distortion compensation scheme is illustrated. Furthermore, a dc-bus voltage deviation suppression strategy is proposed to maximize the dc-bus voltage utilization rate and mitigate the damage to the dc-link capacitors. Simulations are carried out in MATLAB/Simulink2017a to demonstrate the validity of the proposed SVPWM technique and compensation schemes in FSTP GSC for a 1.5-MW grid-connected DFIG-WT when different working conditions are considered.

Reliability assessment and performance analysis of DFIG-based WT for wind energy conversion system

This paper presents the reliability assessment and performance analysis of Doubly Fed Induction Generator-based Wind Turbine (WT) for accurate DFIG-based WT modelling. This model calculates and describes the reliability of each unit and component of the WECs by using Markov process. To analyse the DFIG-based WT during transient and steady-state operations, both the control and modelling of the system have been illustrated in detail. The main contributions of this paper are the reliability assessment of the DFIG based WT units in terms of failures as well as repair rate and performance analysis in normal as well as faulted conditions. For fault analysis of the WECs, DFIG-based WT has been simulated in MATLAB Simulink for line to line, line to ground and double line to ground fault studies.

Multi-Physics Graphical Model-Based Fault Detection and Isolation in Wind Turbines

Early detection and isolation of faults in wind power generators increases the availability of wind turbines and reduces their down times and maintenance costs. Wind turbines constitute a complex system that includes sub-systems from different physical domains such as electrical, mechanical, and hydraulic systems. They constitute hybrid dynamical systems comprising discrete parts due to presence of power electronic switches and continuous parts such as induction machines, pitch actuator and mechanical drive-train. In this paper, a multi-physics graphical model-based fault detection and isolation (FDI) method is developed for doubly fed induction generator-based wind turbines. The model of the wind turbine is developed using hybrid bond-graph theory that captures causal, temporal, and structural properties of the system. Causality inversion method is then employed to derive analytical redundancy relations (ARRs) based on the developed model. The FDI is performed based on the changes in the values of ARRs. A systematic approach based on Chi-square criterion is developed to determine the values of thresholds, based on which the change in ARRs due to occurrence of faults are detected. The capability of the proposed method in accurate and fast detection and identification of mechanical, electrical, and hydraulic faults is demonstrated by the simulation results.

PSO–GSA based fuzzy sliding mode controller for DFIG-based wind turbine

In this paper an optimal fuzzy sliding mode control (FSMC) strategy is introduced for doubly fed induction generator-based wind turbine (DFIG-based WT). The control objective is to ensure power extraction maximization and null stator reactive power regulation according to the grid requirements. To this end, the sliding mode control (SMC) technique is combined with a simple fuzzy inference system to avoid the undesirable chattering phenomenon inherent to the conventional SMC. The proposed FSMC strategy is derived using the Lyapunov approach to guarantee the closed loop system’s stability. To obtain optimal control performances, the membership function parameters of the incorporated fuzzy system are tuned using an improved population-based optimization algorithm, which consists on the combination of particle swarm optimization (PSO) and gravitational search algorithm (GSA). Finally, the performances of the proposed control scheme, called PSO–GSA based FSMC are evaluated in comparison with PSO based FSMC and GSA based FSMC systems.

Design and Hardware-in-the-Loop Experiment of Multiloop Adaptive Control for DFIG-WT

An improved perturbation observer-based mu-ltiloop adaptive control (POMAC) method is proposed for the integrated control of a doubly fed induction generator-based wind turbine (DFIG-WT). In the proposed method, the DFIG-WT is first broken down into four independent subsystems in accordance with four outputs. Meanwhile, the compensation terms used in the vector control (VC) are adopted in order to achieve the complete decoupling among the subsystems. Then, in each subsystem, a perturbation term is introduced to describe the nonlinear dynamics and uncertainties of the subsystem. Estimates of the system's states and perturbation term are obtained by a high-gain state and perturbation observer (HGSPO). Finally, the optimal output feedback control of DFIG-WT is achieved using these estimations instead of the actual values. Simulation studies are carried out using MATLAB/Simulink. Meanwhile, a hardware-in-the-loop test platform is set up using the combination of digital signal processing and control engineering and real-time digital simulator, on which the experiment is carried out to test the validity of the proposed method. Results of the simulation and experiment reveal that POMAC performs better than VC in various cases, including variable wind speed conditions, slight grid voltage dip, and severe three-phase bolted fault. Moreover, its hardware implementation illustrates that POMAC can be used in real time in practice.

Sensor Fault Tolerance Enhancement of DFIG-WTs via Perturbation Observer-Based DPC and Two-Stage Kalman Filters

This paper presents a sensor fault-tolerant control (SFTC) strategy, combining perturbation observer-based direct power control (PODPC) and two-stage Kalman filter (TSKF) to enhance the fault tolerance of a doubly fed induction generator-based wind turbine (DFIG-WT) subject to rotor and stator current sensor faults. In the PODPC scheme, the interactions between active and reactive power control loops are represented by newly introduced perturbation states, and the feedback linearization control is realized with the state estimations derived from perturbation observers to achieve the decoupled power control. No rotor current sensors nor parameters of DFIG-WT are required in the implementation of PODPC. Stator current TSKFs are designed to generate residuals for fault detection and isolation, and provide current estimations to replace the faulty current measurements for system reconfiguration under stator current sensor faults. Simulation studies undertaken on a grid-connected DFIG-WT system reveal that the proposed SFTC strategy is immune to rotor current sensor faults, and it provides strong fault tolerance to stator current sensor faults.

Phase Current Reconstruction for the Grid-Side Converter With Four-Switch Three-Phase Topology in a DFIG-WT

To increase the reliability of a doubly fed induction generator-based wind turbine (DFIG-WT), this paper proposes a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) with a phase current reconstruction strategy. The proposed strategy is effective when the semiconductor open-circuit fault and phase current sensor failure occur simultaneously, which is a kind of hybrid fault. Only one current sensor is applied for measuring the currents flowing between the ac and dc sides of the GSC, and the phase current information can be derived by combining this information with the switching states of FSTP GSC. In the proposed current reconstruction strategy, only two scenarios of duty ratio allocation are needed to be considered. In addition, the space vector pulsewidth modulation (SVPWM) technique is simplified by obtaining the unified expressions for the duty ratios for the remaining four switches in GSC, and the sector identification is removed. Besides, the voltage balancing on the dc bus is achieved. Furthermore, the limitation of the proposed current reconstruction strategy is presented, and the dead zones for SVPWM techniques in both six-switch three-phase and FSTP converters are analyzed. Simulations are carried out in MATLAB/Simulink to verify the proposed hybrid fault-tolerant strategy for the GSC in a 1.5-MW DFIG-WT.

Optimal power tracking of doubly fed induction generator-based wind turbine using swarm moth–flame optimizer

This paper proposes a novel swarm moth–flame optimizer (SMFO) to obtain the optimal parameters of four interacting proportional–integral (PI) loops of a doubly fed induction generator (DFIG)-based wind turbine, so that maximum power point tracking (MPPT) may be achieved together with an improved fault ride-through (FRT) capability. The SMFO is inspired by a moth swarm encircling a flame at night, in which each flame is simultaneously encircled by multiple moths for a greater exploitation, whereas the flame with a higher brightness (i.e. a smaller fitness function) will attract more moths than those of its adjacent flames. In order to achieve a wider exploration, a ring network is then constructed among the flames such that the moths may be guided to search for a brighter flame more effectively. Three case studies are undertaken, which verify that an improved global convergence, more optimal power tracking and enhanced FRT capability may be achieved by SMFO compared with those of existing meta-heuristic techniques.

Replacing the Grid Interface Transformer in Wind Energy Conversion System With Solid-State Transformer

In wind energy conversion systems, the fundamental frequency step-up transformer acts as a key interface between the wind turbine and the grid. Recently, there have been efforts to replace this transformer by an advanced power-electronics-based solid-state transformer (SST). This paper proposes a configuration that combines the doubly fed induction generator-based wind turbine and SST operation. The main objective of the proposed configuration is to interface the turbine with the grid while providing enhanced operation and performance. In this paper, SST controls the active power to/from the rotor side converter, thus, eliminating the grid side converter. The proposed system meets the recent grid code requirements of wind turbine operation under fault conditions. Additionally, it has the ability to supply reactive power to the grid when the wind generation is not up to its rated value. A detailed simulation study is conducted to validate the performance of the proposed configuration.

Effective protection for doubly fed induction generator-based wind turbines under three-phase fault conditions

This paper proposes an effective protection strategy which combines three-crowbar circuit configuration (TCCC), a small bypass resistor (SBR) for wind turbines (WTs) based on the doubly fed induction generators (DFIGs). The TCCC includes (i) resistive crowbar, (ii) inductive crowbar, and (iii) capacitive crowbar. Conventionally, applying only resistive-crowbar circuit as the only means of protection on the DFIG WT, the rotor-side power converter (RSPC) and dc-link capacitor are protected against the effects of a severe voltage dip. However, tripping the RSPC leads to loss of excitation control, and the DFIG behaves like the squirrel-cage induction generator which obtains its magnetization current from the grid which further deepen the terminal voltage. Moreover, integrating the resistive crowbar with series R–L branch keeps the RSPC connection active, but the generator excitation control is partially retained and the oscillations of the rotor currents and dc-link voltage can heavily deteriorate the performance of the generator. Thus, the TCCC-SBR circuit is proposed to compensate for the deficiency when the two conventional circuits are applied. Its performance validation is performed via extensive simulation studies using MATLAB/Simulink software. From the comparative simulation results, more improved fault ride-through capability of the DFIG is achieved with the proposed protection circuit than the conventional protection circuits.

ACMC‐based hybrid AC/LVDC micro‐grid

This study proposes the detailed modelling of a novel automatic centralised micro-grid controller (ACMC)-based hybrid AC/low-voltage DC (LVDC) micro-grid network, capable of off-grid and on-grid operation of the system with a coordinated control. The micro-grid is designed to work majorly with renewable power sources. This hybrid micro-grid is capable of interconnecting very large AC and LVDC networks, using a bi-directional AC/DC/AC converter. The AC and the LVDC networks consist of different feeders with loads connected at various voltages. The ACMC design proposed is responsible for controlling the real(P) and reactive(Q) power from the sources based on load requirement and voltage control of the LVDC network. It enables the system to have a plug and play feature. The proposed ACMC has been implemented on a test system consisting of AC and LVDC radial distribution networks designed, with a bi-directional converter. A doubly fed induction generator-based wind turbine and solar photovoltaic array with maximum power point tracking have been used as the sources. The system has been simulated in Simulink. The results show the ACMC successfully performs the four quadrant operation of P,Q in the system for various system conditions.

Grid voltage local regulation by a doubly fed induction generator–based wind turbine

Voltage regulation at point of common coupling using a doubly fed induction generator–based wind energy conversion system is achieved through reactive power control. Wind energy conversion system produces reactive power when the voltage is less than grid nominal voltage and it consumes it in the opposite case. In this article, a method to achieve this goal is proposed. It consists of controlling the reference value of the vector control system in order to affect the wind energy conversion system reactive power output. Two situations have been simulated. Sudden voltage increase and decrease were applied to the control system. Satisfying results have been obtained since the voltage at point of common coupling has been restored back to its initial value.

Subsynchronous Control Interaction Analysis and Trigger-based Damping Control for Doubly Fed Induction Generator-based Wind Turbines

Doubly fed induction generator-based wind turbines are vulnerable to subsynchronous oscillations. Subsynchronous control interaction is a recently emerging subsynchronous oscillation phenomenon, which means the interaction between the rotor-side converter of a doubly fed induction generator-based wind turbine and a fixed series-compensated transmission line. In this article, subsynchronous control interaction is quantitatively analyzed, and an subsynchronous control interaction-triggered condition is created to detect the existence of subsynchronous control interaction. The subsynchronous control interaction-triggered condition is then combined with impedance scanning to effectively identify the induction generator effect and subsynchronous control interaction. Further, a subsynchronous control interaction-triggered damping control strategy is developed to effectively alleviate subsynchronous control interaction. The mitigation ability and the robustness of the presented control strategy are, respectively, verified by time-domain simulation.

The fault ride through technologies for doubly fed induction generator wind turbines

The penetration of large-scale wind power generators to the grid has resulted in an increasing focus on the study on their fault ride through issue that is becoming imminent. The doubly fed induction generator-based wind turbine is still one of the most frequently adopted wind generation units in the market of the installed wind power worldwide due to its good behavior during normal grid conditions. However, due to the sensitivity of doubly fed induction generator to power disturbances, especially to voltage sags, the transient characteristic improvement of doubly fed induction generator during fault, thus meeting the fault ride through requirements, has become a problem of particular interest to wind turbine manufacturers. So, in this article, a comprehensive comparative study on the fault ride through techniques for doubly fed induction generator wind turbine is provided based to three broad subcategories: control algorithms, additional hardware circuit, and combined approaches. Furthermore, a discussion on the different characteristics of the fault ride through capability of these methods has been made, and a case study has been carried out to show the performance of different schemes. Finally, the article suggests a likely future outlook for the fault ride through technique for doubly fed induction generator wind turbines.

A Maximum Power Tracking Technique for Grid-Connected DFIG-Based Wind Turbines

In this paper, a maximum power tracking technique is presented for doubly fed induction generator-based wind turbines. The presented technique is a novel version of the conventional method, i.e., the electrical torque is proportional to the square of the rotor speed, in which the proportional coefficient is adaptively adjusted in real-time through three control laws. The first control law calculates the desired electrical torque using feedback linearization, assuming that the power capture coefficient and the desired rotor speed are instantaneously identified. The second control law estimates the real-time values of the power capture coefficient from a Lyapunov-based analysis, and the third control law provides the desired rotor speed. These control laws cause the turbine to adaptively adjust the rotor speed toward a desired speed in which the operating point moves in the direction of increasing the power capture coefficient. The proposed maximum power tracking method differs distinctly from the perturb-and-observe scheme by eliminating a need for adding a dither or perturbation signal, and robustly tracks the trajectory of maximum power points even in the event of a sudden wind speed change that can cause the perturb-and-observe technique to fail. In this paper, the National Renewal Energy Laboratory 5-MW reference wind turbine model is used to demonstrate the validity and robustness of the proposed method.

Fault Current Contribution Analysis of Doubly Fed Induction Generator-Based Wind Turbines

The fault current contribution of the doubly fed induction generator-based wind turbines (DFIG-WTs) is dictated by a combination of factors, including the electrical parameters of the machine and the controller configuration of the converters. This paper presents an analytical derivation of short-circuit current quantities considering the controller influences. Mathematical models of the short-circuit current were first developed based on the closed-loop transfer functions, and approximate expressions for time constants and frequencies were derived. The mathematical models and the expressions for time constants and frequencies were later validated using a manufacturer-based simulation model and a nonlinear optimization for parameter extraction.