Doubly Fed Induction Generator Wind Turbine Research Articles

Improvement of power system stability in wind connected generator by using PSAT

Voltage stability in power systems is a major problem that receives international attention. An open and free source piece of software, Power System Analysis Toolbox (PSAT) is used in this study to create a model of modified IEEE 14 bus system. Models of two recently created wind turbines—the Squirrel Cage Induction Generator (SCIG) and Doubly Fed Induction Generator (DFIG)—are connected to a modified IEEE 14 bus system. The stability of the power system is examined in this work in relation to the effects of Squirrel Cage Induction Generator (SCIG) and Doubly Fed Induction Generators (DFIG). Here, both DFIG and SCIG, which have variable speeds, are regarded as wind generators. In this work, a small signal stability investigation using SCIG and DFIG wind turbine systems was carried out on a modified IEEE 14 bus system. The results of their simulation were analysed.

Stability Analysis of Microgrid with Load Shedding Scheme using RTDS

A microgrid system was simulated using the powerful RTDS simulator, the modelling was done on the RSCAD software, and the microgrid comprised of a diesel generator, a photovoltaic (PV) system and a Doubly-Fed Induction Generator (DFIG) wind turbine system as DERs. The paper comprises the study on stability analysis of the microgrid in grid-connected and islanded modes of operation, along with a successful load shedding scheme which was implemented based on the loads distinguished as low priority and high priority loads in order to keep the system balanced during faults.

Damping of Frequency and Power System Oscillations with DFIG Wind Turbine and DE Optimization

Wind power is one of the most promising renewable energy resources and could become a solution to contribute to the present energy and global warming crisis of the world. The commonly used doubly fed induction generator (DFIG) wind turbines have a general trend of increasing oscillation damping. Unless properly controlled, the high penetration of wind energy will increase the oscillation and affect the control and dynamic interaction of the interconnected generators. This paper discusses power oscillation damping control in the automatic generation control (AGC) of two-area power systems with DFIG wind turbines and Matlab code/Simulink interfacing optimization methods. The differential evolution (DE) optimization technique is used to obtain the controller gain parameters. In the optimization process, a step load perturbation (SLP) of 1% has been considered in Area 1 only, and the integral of time weighted absolute error (ITAE) cost function is used. Three different test studies have been examined on the same power system model with non-reheat turbine thermal power plants. In the first case, the power system model is simulated without a controller. In Case Study 2, the system is simulated with the presence of DFIG and without a controller. In Case Study 3, the system is simulated with a PID controller and DFIG. Most of the studies available in the literature do not optimize the appropriate wind penetrating speed gain parameters for the system and do not consider the ITAE as an objective function to reduce area control error. In this regard, the main contribution and result of this paper is—with the proposed PID+DFIG optimized DE—the ITAE objective function error value in the case study without a controller being 6.7865, which is reduced to 1.6008 in the case study with PID+DFIG-optimized DE. In addition, with the proposed controller methods, the dynamic system time responses such as rise time, settling time, overshoot, and undershoot are improved for system tie-line power, change in frequency, and system area controller error. Similarly, with the proposed controller, fast system convergence and fast system oscillation damping are achieved. Generally, it is inferred that the incorporation of DFIG wind turbines in both areas has appreciably improved the dynamic performance and system stability under consideration.

Effectiveness analysis of twelve sectors of DTC based on a newly modified switching table implemented on a wind turbine DFIG system under variable wind velocity

This paper aims to present a novel Direct Torque Control (DTC) strategy based on twelve sectors and a new Modified Switching Table (12-MST-DTC) used to control the Doubly Fed Induction Generator (DFIG) powered by Wind Turbine (WT) and operating under random wind speed. Robustness and fast dynamic performances have made Conventional DTC (C-DTC) popular and widely used, but presents major drawbacks which are high torque and flux ripples. Therefore, the 12-DTC has been proposed in the literature as an improvement but suffers from significant oscillations during super-synchronous operation mode as well as the case of overspeed. The proposed control strategy maintains the performances that offer (C-DTC and 12-DTC) and furthermore minimizes those drawbacks. The newly modified switching table is designed with additional input to cover all WT-DFIG system operation modes (sub-, super- and synchronous modes in addition to the case of over-speed) in order to diminish the flux, torque ripples and THD of the AC-grid injected currents. For optimal operating of variable-speed WT, MPPT algorithm and blade pitch control are invested. Simulation results of the 12-MST-DTC are compared with those of C-DTC and 12-DTC using MATLAB/Simulink environment treating all operation modes of WT-DFIG system and even in case of wind over speeds. The comparison results demonstrate the efficiency of the proposed control strategy in terms of flux/torque ripples and THD reduction, therefore fewer DFIG mechanical vibration and acoustic noise.

Comparative Performance of DFIG and PMSG Wind Turbines during Transient State in Weak and Strong Grid Conditions Considering Series Dynamic Braking Resistor

The recently stipulated grid codes require wind generators to re-initiate normal power production after grid voltage sag. This paper presents a comparative performance of two commonly employed variable speed wind turbines in today’s electricity market, the doubly fed induction generator (DFIG) and the permanent magnet synchronous generator (PMSG) wind turbines. The evaluation of both wind turbines was performed for weak, normal and strong grids, considering the same machine ratings of the wind turbines. Because of the critical situations of the wind turbines during faulty conditions in the weak grids, an analysis was done considering the use of effective series dynamic braking resistor (SDBR) for both wind turbines. The grid voltage variable was employed as the signal for switching the SDBR in both wind turbines during transient state. Additionally, an overvoltage protection system was considered for both wind turbines using the DC chopper in the DC-link excitation circuitry of both wind turbines. Furthermore, a combination of the SDBR over-voltage protection scheme (OVPS) was employed in both wind turbines at weak grid condition in order to improve the performance of the variable speed wind turbines and keep the operation of the power converters within their permissible limits. Furthermore, the performance of the DFIG and PMSG wind turbines in weak grids were further investigated, considering the combination of 75% and 50% effectively sized SDBR and OVPS. It was observed that, even with a 50% reduction in SDBR or OVPS, the performance of both wind turbines is still satisfactory with faulty conditions. Therefore, it is recommended to use a combination of the SDBR and OVPS with DFIG- or PMSG-based variable speed wind turbines to achieve a superior fault ride through performance, especially in weak grids. The system performance was evaluated using the power system computer design and electromagnetic transient including DC (PSCAD/EMTDC) platform.

Evaluating a Hybrid Circuit Topology for Fault-Ride through in DFIG-Based Wind Turbines

Large-scale wind power integration has raised concerns about the reliability and stability of power systems. The rotor circuit of a doubly fed induction generator (DFIG) is highly vulnerable to unexpected voltage dips, which can cause considerable electromotive force in the circuit. Consequently, the DFIG must fulfil the fault-ride through (FRT) criteria to ensure the system's performance and contribute to voltage regulation during severe grid outages. This paper provides a hybrid solution for DFIG wind turbines with FRT capabilities, using both a modified switch-type fault current limiter (MSFTCL) and a direct current (DC) chopper. The proposed system has the merit of keeping the rotor current and the DC-link voltage within the permissible limits, enhancing the FRT capability of generators. Moreover, the boundness of supply voltage into its reference value ensures dynamic stability during symmetric and asymmetric grid failures. Further, electromagnetic torque variations are significantly reduced during fault events. Finally, the performance validation of the proposed scheme is performed in a simulation setup, and the results are compared with the existing sliding mode control (SMC) and proportional-integral (PI) controller-based approaches. The comparison results show that a hybrid strategy with advanced controllers provides superior performance for all critical parameters.

High-Gain Observer-Based Advanced Nonlinear Control of a Grid-Connected Wind Energy Conversion System with Sensorless Maximum Power Point Tracking

This paper deals with the control development of a wind energy conversion system (WECS) interfaced to a utility grid by using a doubly fed induction generator (DFIG), a back-to-back (B2B) converter and an RL filter for optimal power extraction. The aim was to design a sensorless controller to improve the system reliability and to simultaneously achieve the regulation of the generator speed, reactive power and DC-link voltage. The proposed global control scheme combines: (i) a high-gain observer employed to estimate the generator speed and the mechanical torque, usually regarded as accessible, (ii) a sensorless MPPT block developed to provide optimal generator speed reference, which is designed on the basis of the mechanical observer and a polynomial wind-speed estimator and (iii) a finite-time controller (FTC) applied to the B2B converter to meet the output reference’s tracking objectives in a short predefined finite time by using the backstepping and Lyapunov approaches. The proposed controller performance is formally analysed, and its capabilities are verified by numerical simulations using a 2 MW DFIG wind turbine (WT) under different operating conditions.

Supervisory Control Scheme of a Wind Farm Connected to a Hybrid Microgrid

Nowadays, the generation of wind power combined with a battery energy storage system offers a viable solution for electricity supply to isolated areas with no access to the grid. However, the speed of the wind is unpredictable and the inherent nonlinearities of the wind turbine and generator system cause fluctuations in the voltage, power, and frequency. This paper proposes a new three-layered control technique applied to a wind farm that uses doubly-fed induction generators (DFIGs) connected to a remote hybrid microgrid. The first layer provides local control to each DFIG wind turbine based on a nonlinear and robust control strategy. The second layer coordinates and controls the flow of power between the turbine and the storage system to make sure that load demand is being satisfied and the desired limits of the state of charge are respected. Finally, and in the third layer, we implement a supervisory controller that will be responsible for the generation of the references for the active power as per the load demand. The proposed off-grid wind power system and battery storage and its three-layer hierarchical control scheme are simulated under MATLAB/Simulink environment and tested under various load and speed profiles. Through the numerous test data obtained, it has been shown that the control strategy under study is robust and effective.

Wind turbine doubly-fed induction generator defects diagnosis under voltage dips

Voltage dips are brief but frequent disturbances that can be defined as the most important problem affecting all electrical grids, it cannot be completely avoided and represent the main priority for the industry. This study remains part of monitoring the quality of electrical energy’s field. Its aim is to apply two approaches signals for improving the failure recognition in wind turbine conversion chain. One is based on the combination of spectral analysis of stator current by fast Fourier transform and Lissajous curves technique of grid currents. The second approach is based on the stator current analysis by discrete wavelet transform which is considered an ideal tool for this purpose due to its time-frequency localization. These defects diagnosis methods have shown their efficiency in detection, visualization and analysis of voltage dips in order to develop a control strategy for a wind turbine requiring continuity of its service despite the presence of voltage dips.

Improved nonlinear generalized model predictive control for robustness and power enhancement of a DFIG-based wind energy converter

Many studies have been made on the double-fed induction generator wind turbine system (DFIG-WTS) in recent decades due to its power management capability, speed control operation, low converter cost, and minimized energy losses. In contrast, induction machine control is a more complex task because of its multivariable and nonlinear nature. In this work, a new robust nonlinear generalized predictive control (RNGPC) is developed to maximize the extracted energy from the wind without the use of aerodynamic torque measurements or an observer. The aim of the predictive control is to produce an anticipated impact by employing explicit knowledge of the present condition. By revisiting the cost function of the conventional nonlinear generalized predictive control (NGPC), which is based on Taylor series expansion, in that way, the resilience of the system is improved. An integral action is included in the nonlinear predictive controller. As a result, if the closed loop system is stable, the suggested controller totally eliminates the steady state error, even if unknown perturbations and mismatched parameters are present. The output locating error’s convergence to the source is utilized to show the locked system’s stability. Simulation results demonstrate and verify the efficiency, the good performance, and robustness of this proposed control technique.

Nonlinear Control Strategies for Enhancing the Performance of DFIG-Based WECS under a Real Wind Profile

Wind speed variations affect the performance of the wind energy conversion systems (WECSs) negatively. This paper addressed an advanced law of the backstepping controller (ABC) for enhancing the integration of doubly fed induction generator (DFIG)-based grid-connected WECS under wind range of wind speed. This enhancement was achieved through three control schemes, which were blade pitch control, rotor-side control, and grid-side control. The blade pitch control was presented to adjust the wind turbine speed when the wind speed exceeds its rated value. In addition, the rotor and grid-side converter controllers were presented for improving the direct current link voltage profile and achieving maximum power point tracking (MPPT) under speed variations, respectively. To evaluate the effectiveness of the proposed ABC control, a comparison between PI and sliding-mode control (SMC) was presented, considering the parameters of a 1.5 MW DFIG wind turbine in the Assilah zone in Morocco. Moreover, some changes in the DFIG parameters were introduced to investigate the robustness of the proposed controller under parameter uncertainties. Simulation results showed the capability of the proposed ABC controller to enhance the performance of the DFIG-WECS based on variable speed and variable pitch turbine, at both below and above-rated speed, leading to an error around 10−3 (p.u), with an ATE = 0.4194 in the partial load region; in terms of blade pitch control, an error of 2.10−4 (p.u) was obtained, and the DC-link voltage profile showed a measured performance of 5 V and remarkable THD value reduction compared to other techniques, with a measured THD value of 2.03%, 1.67%, and 1.46% respectively, in hyposynchronous, hypersynchronous, and pitch activation modes of operation. All simulations were performed using MATLAB/SIMULINK based on real wind profiles in order to make an exhaustive analysis with realistic operating conditions and parameters.

Sub-synchronous resonance in wind energy integrated grid – problem and mitigation techniques – a review

<p>When wind energy conversion systems (WECS) are integrated with the Grid system then there are power quality issues arises. The fluctuation in the wind power delivery to the grid demands robust control for a better power quality. Therefore, voltage and frequency stability due to integration of wind to the grid is the primary concern to improve the overall grid integration capability for WECS. This paper reviews the power quality issues in the power grid due to introduction of WECS. The WECS integration with the grid introduces dynamic issues that include sub-synchronous resonance (SSR), low voltage ride through (LVRT), frequency support from wind generation, synchronization, and transients. Also, it focusses on the sub synchronous resonance introduced due to introduction of doubly-fed induction generator (DFIG) wind turbines to the transmission lines with capacitive seriescompensation. The review of various power quality issues and methods used by the researcher’s mitigations are discussed and detailed further research perspective.</p>

Performance analysis of reactive power control management for doubly fed induction generator wind turbines

The efficient operation of the Doubly Fed Induction Generator (DFIG) in wind power systems is significantly affected by reactive power flow. Depending on its excitation, the DFIG’s reactive power drawn either from the grid or fed into the grid, affects the voltage quality and stability of the wind turbine systems. In addition, an increase in DFIG excitation through the Machine Site Converter (MSC) above or below the rated excitation results in over-excited or under-excited operations of the generator respectively. Therefore, reactive power control management for DFIG wind turbines is crucial to overcoming these problems, thus, enhancing the performance of the DFIG wind turbine systems. The performance analysis of reactive power control management for DFIG wind turbines using the Lucas Nulle Wind Power Plant (LNWPP) WindSim software is presented.

Detailed Transients Simulation of a Doubly Fed Induction Generator Wind Turbine System with the EMTP-Type OVNI Simulator

Doubly fed induction generator wind turbines are increasingly used in new wind turbine installations all over the world. Growing concerns about the impact of a large number of these generators on transient and voltage stability of power system networks has led engineers to revisit modelling and simulation practices used for system stability analyses. In this paper, the latest advancements in design of the general purpose power system simulator OVNI developed at the University of British Columbia are presented, and its application to the simulation of a doubly fed induction generator (DFIG) wind turbine system is shown. Because OVNI is based on the EMTP methodology for accurate detailed modelling, and the Multilevel MATE (Multi-Area Thévenin Equivalent) concept, which, combined with hardware solutions, allows for fast simulation of large power system networks, it represents an ideal tool for testing and developing benchmark models of different wind turbine installations. Using the EMTP approach for modelling of a DFIG wind turbine system and its feeding power network we were able to study the responses of the wind turbine generator to different network events. The ultimate goal of our investigations is the development of a benchmarking process for testing different models of wind turbine generators and determining the range of validity of various degrees of approximations normally used for stability simulation purposes. Due to the rapid development of wind generation technology, it is essential to determine the minimum requirements for dynamic modeling of wind turbine generators for assessing impacts of their installations on the dynamic security and stability of power systems.

Improved Performance of Doubly-Fed Induction Generator Wind Turbine During Transient State Considering Supercapacitor Control Strategy

Improved Performance of Doubly-Fed Induction Generator Wind Turbine During Transient State Considering Supercapacitor Control Strategy

Influences on the LVRT behavior of DFIG wind turbine systems

Grid faults introduce highly dynamic electrical and mechanical loads to a wind turbine (WT). Especially WTs with a direct grid connection like the doubly-fed induction generator (DFIG) are strongly affected. The behavior of a WT during grid faults can be tested in low voltage ride through tests (LVRT). But there are numerous influencing factors on the behavior of the DFIG during a LVRT which have not yet been fully investigated. The pre-fault operating point of the DFIG, the grid inductance, the pre-fault phase angle of the grid voltage, the fall time of the voltage as well as the start and end values of the voltage drop affect the electromagnetic torque and the short circuit current of the generator. Therefore, many LVRT test results for DFIGs are neither comparable nor representative. In this paper it is shown that the peaks of electromagnetic torque and currents during LVRTs can be reduced. A low pre-fault torque and rotational speed, a high grid inductance and a slow voltage drop can minimize the impact of a grid fault. The rotational speed is especially critical because it influences the slip of the DFIG and, thus, has an influence on the dynamics of the fault.

Reduction of gearbox loads of a DFIG wind turbine during grid faults with optimized converter configurations

Grid faults in wind turbines (WT) with doubly fed induction generator (DFIG) result in dynamic generator torque excitations, which can lead to dynamic load changes within the gearbox. Dynamic load changes in combination with changing rotational speeds can increase the risk of damage in the gearbox. WT gearbox damage occurs mainly on the high speed shaft (HSS) components. The torque excitations have the highest influence on the HSS since it is coupled to the generator. Therefore, an investigation of the correlation between grid faults and gearbox damage is necessary. The torque excitation in DFIG WTs due to grid faults is dependent on the converter and its fault ride through capabilities. The load analysis in this paper is done for a state of the art converter configuration and for one that is optimized in order to stabilize the performance during grid faults. It is shown via simulation with a WT drivetrain model that dynamic load changes of the HSS gear wheel are prevented for symmetrical grid faults with the optimized configuration. The analysis of a HSS bearing shows that the smearing damage risk can be significantly reduced (minus up to 56 percent) by using the optimized configuration. Therefore, the possibility to decrease the gearbox damage risk during grid faults via an optimization of the converter configuration is shown in this paper.

Online Estimation of the Mechanical Parameters of a Wind Turbine with Doubly Fed Induction Generator by Utilizing Turbulence Excitations

In this paper, a new method using wind turbulence excitation is proposed to estimate the parameters of the mechanical system (drivetrain and pitch angle controller) in a Doubly Fed Induction Generator (DFIG) Wind Turbine (WT). Firstly, simulations were carried out for a DFIG WT under turbulence excitations. The spectral contents of the responses imply that the transients of the electrical system (generator and converter), which are much faster than those of the mechanical system, can be neglected when estimating the mechanical parameters. Based on this, a simplified model related to the mechanical system of the DFIG WT was derived by applying the model reduction technique. Secondly, the parameter sensitivity of Power Spectral Density (PSD) was used to quantify the impacts of individual parameters on the dynamics of the mechanical system, and the influential parameters were selected on the basis of the sensitivity results. Finally, a weighted least-squares optimization problem, which is suitable for a system with close oscillation modes, was formulated for parameter estimation. The estimation results based on two different types of optimization methods were compared, and their estimation accuracies validate the effectiveness of the proposed method.

Diagnosing multiple short circuit switches faults in wind turbine doubly-fed induction generator

In the current paper, the inverter feeding doubly fed induction generator (DFIG) in the case of short circuit switches fault is presented. Defects diagnosis is based on the so-called the Lissajous curves of DFIG rotor currents. For this purpose, the modeling of the variable speed wind energy conversion chain based on the DFIG, is firstly introduced, after that a description of the voltage source inverter operating mode is presented. Finally, rotor currents Lissajous curves are analyzed in case of a non-defective and defective inverter. Simulation results were achieved using MATLAB^®- SIMULINK^® package, thus confirming the efficiency of the proposed method.

Impedance Modeling and Stability Analysis of DFIG Wind Farm With LCC-HVDC Transmission

In China, the high-penetrated doubly-fed induction generators (DFIG) wind turbine (WT) is undergoing the centralized collection and long-distance line-commutated converter (LCC) high voltage DC (HVDC) transmission. In such high-penetrated renewable generation and transmission system, the dynamics of power electronics become dominant over the conventional synchronous generator so that its modeling and stability analysis needs re-examining. However, the interaction among interconnected wind farm, and LCC-HVDC, and weak grid remains unclear but may easily incur the stability issue. This paper firstly builds the wind farm model by aggregating each WT and collection transmission with the consideration about the frequency coupling. The double Fourier transform is further used to derive the mapping function in frequency-domain relates the current and voltage harmonics between DC and AC sides of the 6-pulse LCC converter, based on which the analytical 6-pulse LCC-HVDC impedance from AC side can be theoretically developed. The developed analytical impedance of DFIG wind farm with LCC-HVDC transmission system is verified by the comparison with the frequency sweeping simulation results and the oscillation reproduction in MATLAB/Simulink. The major parameter influence on system impedance characteristics is finally analyzed and compared in detail.