Performance Of Doubly Fed Induction Generator Research Articles

Performance Evaluation of Grid-Connected Wind Turbine Generators

The risk of oscillation of grid-connected wind turbine generators (WTGs) is well known, making it all the more important to understand the characteristics of different WTGs and analyze their performance so that the problems’ causes are identified and resolved. While many studies have evaluated the performance of grid-connected WTGs, most lack clarity and precision in the modeling and simulation techniques used. Moreover, most of the literature focuses on a single mode of operation of WTGs to analyze their performances. Therefore, this paper updates the literature by considering the different operating conditions for WTGs. Using MATLAB/SIMULINK it expands the evaluation to the full range of vulnerabilities of WTGs: from the wind turbine to grid connection. A network representing grid-connected squirrel-cage induction generator (SCIG) and doubly-fed induction generator (DFIG) wind turbines are selected for simulation. The performances of SCIG and DFIG wind turbines are evaluated in terms of their energy generation capacity during constant rated wind speed, variable wind speed, and ability of fault-ride through during dynamic system transient operating conditions. The simulation results show the performance of DFIG is better than SCIG in terms of its energy generation capacity during variable wind speed conditions and active and reactive power control capability during steady-state and transient operating conditions. As a result, DFIG wind turbine is more suitable for large-scale wind power plants connected to weak utility grid applications than SCIG.

Nonlinear MPC for DFIG-based wind power generation under unbalanced grid conditions

In a modern power system with a high wind power penetrating rate, the control of the doubly-fed induction generator (DFIG) is quite important to ensure high load-following capability. It can be quite challenging when grid voltage unbalance conditions happened. Model predictive control (MPC) is an advanced control strategy that can optimize the DFIG operation, particularly under unbalanced grid voltage conditions. The detailed modeling in the positive and negative synchronous reference frames resulting from the grid unbalance is presented in nonlinear state-space form. An effective linearized technique, i.e., the input-output feedback linearization method, is adopted in the MPC design. The control law is derived by the optimization of two targets that aim to eliminate the pulsations in the active or reactive power. The simulation results prove that power pulsations are effectively suppressed under unbalanced grid voltage conditions while ensuring good track performance.

Frequency support scheme based on parametrized power curve for de-loaded wind turbine under various wind speed

With increased wind power penetration in modern power systems, wind plants are required to provide frequency support similar to conventional plants. However, for the existing frequency regulation scheme of wind turbines, the control gains in the auxiliary frequency controller are difficult to set because of the compromise of the frequency regulation performance and the stable operation of wind turbines, especially when the wind speed remains variable. This paper proposes a novel frequency regulation scheme (FRS) for de-loaded wind turbines. Instead of an auxiliary frequency controller, frequency support is provided by modifying the parametrized power versus rotor speed ( Pw-ω r) curve, including the inertia power versus rotor speed curve and the droop power versus rotor speed curve. The advantage of the proposed scheme is that it does not contain any control gains and generally adapts to different wind speeds. Further, the proposed scheme can work for the whole section of wind speed without wind speed measurement information. The compared simulation results demonstrate the scheme improves the system frequency response while ensuring the stable operation of doubly-fed induction generators (DFIGs)-based variable-speed wind turbines (VSWTs) under various wind conditions. Furthermore, the scheme prevents rotor speed overdeceleration even when the wind speed decreases during frequency regulation control.

Mitigation of subsynchronous control interaction in DFIGs using active disturbance rejection control

Recently, a new type of subsynchronous oscillation (SSO) has occurred in doubly-fed induction generator (DFIG)-based wind farms. This oscillation is also called the subsynchronous control interaction (SSCI), which is mainly caused by the interaction between the transmission series compensation and the DFIG controller. Therefore, the oscillation frequency of the SSCI is susceptibly impacted by DFIG operating conditions, which presents major challenges to conventional mitigation strategies. To solve this problem, a grid-connected series-compensated DFIG-based wind farm is established, and the formation process of the SSCI is analysed. The strategy of active disturbance rejection control (ADRC), which can automatically estimate and compensate for the total disturbance of the system in real-time, is introduced into the rotor-side converter to mitigate the SSCI in the DFIG. ADRC is designed based on dynamic parameter tuning and chaos optimization. Finally, a detailed model-based time-domain simulation is conducted to evaluate the performance of the proposed optimized ADRC (O-ADRC) compared to conventional virtual impedance and ADRC. The simulation results show that O-ADRC can effectively mitigate the SSCI under different operating conditions and provide sufficient damping for the DFIG-based wind farms.

Dynamic Performance Analysis of a Grid-Connected Doubly-Fed Induction Generator

In the field of wind energy, the doubly fed induction generator (DFIG) is commonly used in variable speed wind energy conversion systems (WECS). This paper presents a review of various topologies, configurations, power converters and control schemes used with the operation of the DFIG. The operation of DFIG based on both slip ring and brushless arrangement has been discussed. The grid integration of DFIG and its influence on system stability, system reliability, power quality and power transmission is reviewed.

A Common Capacitor Based Three Level STATCOM and Design of DFIG Converter for a Zero-Voltage Fault Ride-Through Capability

To meet the augmented load power demand, the doubly-fed induction generator (DFIG) based wind electrical power conversion system (WECS) is a better alternative. Further, to enhance the power flow capability and raise security margin in the power system, the STATCOM type FACTS devices can be adopted as an external reactive power source. In this paper, a three-level STATCOM coordinates the system with its dc terminal voltage is connected to the common back-to-back converters. Hence, a lookup table-based control scheme in the outer control loops is adopted in the Rotor Side Converter (RSC) and the grid side converter (GSC) of DFIG to improve power flow transfer and better dynamic as well as transient stability. Moreover, the DC capacitor bank of the STATCOM and DFIG converters connected to a common dc point. The main objectives of the work are to improve voltage mitigation, operation of DFIG during symmetrical and asymmetrical faults, and limit surge currents. The DFIG parameters like winding currents, torque, rotor speed are examined at 50%, 80% and 100% comparing with earlier works. Further, we studied the DFIG system performance at 30%, 60%, and 80% symmetrical voltage dip. Zero-voltage fault ride through is investigated with proposed technique under symmetrical and asymmetrical LG fault for super-synchronous (1.2 p.u.) speed and sub-synchronous (0.8 p.u.) rotor speed. Finally, the DFIG system performance is studied with different phases to ground faults with and without a three-level STATCOM.

Matlab/Simulink Based Modeling and Simulation of Decoupled Power Control for DFIG Operating in Wind Generation Systems

This paper appraises the performances of two control scenarios, for doubly fed induction generator (DFIG) operating in wind generation system (WGS), which are the direct decoupled control (DDC) and indirect decoupled control (IDC). Both control scenarios studied combines vector control and Maximum Power Point Tracking (MPPT) control theory so as to maximize the captured power through wind turbine. Modeling of DFIG based WGS and details of both control scenarios have been presented, a proportional integral controller is employed in the active and reactive power control loops for both control methods. The performance of the both control scenarios in terms of power reference tracking and robustness against machine parameters inconstancy has been shown, analyzed and compared, which can afford a reference to the operators and engineers of a wind farm. All simulations have been implemented via MATLAB/Simulink.

Multi-resistor BFCL for FRT capability improvement of DFIG-based wind farm

Grid connection of wind farms (WFs) results in increment of short circuit level and decrement of fault ride-through (FRT) capability under fault conditions. Application of bridge-type fault current limiter (BFCL) was recognised as a promising and cost effective solution to cope with these problems. However, full resistor insertion of the conventional BFCL provides high transient overvoltage at the terminal of wind generator under low voltage sag condition, which can lead to failure operation of wind generator in despite of FRT requirement. This study presents a voltage adaptive multi-resistor BFCL (MRBFCL) to solve these problems for wide voltage sag levels. According to the depth of voltage sag level at the grid coupling point voltage, the MRBFCL inserts an appropriate combinational of resistors to compensate voltage sag level at acceptable level. To verify the efficiency of the proposed MRBFCL, time domain simulations were performed in PSCAD/EMTDC software under three different voltage sag levels. Also, the MRBFCL performance is compared with the conventional single-resistor BFCL. Simulation results reveal that the MRBFCL effectively enhance the FRT performance of doubly-fed induction generator (DFIG)-based WFs under wide range of voltage sag level and alleviate over voltage for low voltage sag conditions.

Performance improvement of DPC in DFIGs during unbalanced grid voltage based on extended power theory

Doubly fed induction generator (DFIG) control process is more complex in the calculations under voltage unbalance condition because of the power oscillations, and the conventional controllers cannot maintain the system in a stable and smooth condition. In this paper, a flexible method is presented to control the DFIG based on an improved extended power theory on the direct power control platform. The proposed method can simultaneously improve electromagnetic torque oscillations, reduce total harmonic distortion (THD) of stator currents and eliminate active or reactive power oscillations by controller of rotor side converter. The main control system relations based on an analytical process are presented. The improved extended power theory method has made the proposed control independent from decomposition of the positive and negative sequence components which provides ease of the calculation and better performance accuracy. Compared to the conventional extended theory, the proposed method is capable to reduce the torque oscillations, reduction of the stator current THD, and eliminating the powers oscillations of the DFIG. Also, In order to maintain the appropriate dynamic response, a switching table is presented according to the proposed method. The simulation results are clearly confirmed that the proposed method improves the DFIG performance in view of the oscillations under the voltage unbalance conditions.

DFIG Active Damping Control Strategy Based on Remodeling of Multiple Energy Branches

Concerning subsynchronous oscillation caused by the integration of doubly-fed induction generator (DFIG) to power grid via series compensation line, an active damping control strategy based on remodeling of multiple energy branches in DFIG is proposed. First, according to the flow path of oscillation components, energy branches in DFIG are divided. Second, potential energy and dissipation energy are defined characterizing accumulation and consumption of energy during oscillation. Then, by analyzing the contribution of energy branches to potential energy and dissipation energy, key energy branches affecting the stability of system are screened. On this basis, the relations among stator voltage, potential energy, and dissipation energy are established, and frequency-dependent energy compensation functions in key branches are derived. By assessing their impact on low voltage ride through (LVRT) performance of DFIG, the compensation branch compatible with DFIG fundamental frequency characteristics are screened. Then, take sub/supersynchronous frequency stability coefficient ratio as the objective function, and the requirement on stability in sub/supersynchronous frequency band as the constraints. The compensation branch parameter optimization scheme is established. Finally, a test system is built in RT-LAB for verification. Simulation results demonstrate that, the proposed strategy can realize active damping control in multiple oscillation cases, and guarantee the stability of system in full frequency band. Besides, the strategy does not affect LVRT performance of DFIG and is well compatible with DFIG fundamental frequency characteristics.

Development and performance analysis of intelligent fault ride through control scheme in the dynamic behaviour of grid connected DFIG based wind systems

As the penetration of wind power increases, the fault ride through requirements imposed by grid code is important in grid connected wind systems. The wind systems should remain connected to the grid during grid faults satisfying the grid code which ensures grid stability during fault and post fault conditions. This paper proposes an intelligent fault ride through strategy for Doubly Fed Induction Generators (DFIG) based Wind Energy Conversion Systems (WECS) to achieve real and reactive power control during grid faults. The transient behaviour of the system is investigated under normal conditions and during grid faults. A fuzzy based wind speed estimation method in Maximum Power Point Tracking (MPPT) mode under normal conditions and coordinated Genetic Algorithm based Real-Reactive (GA-PQ) controller with DC chopper in Fault Ride Through (FRT) mode during grid faults is developed in this work. The proposed control scheme provides smooth operation of DFIG during grid faults by controlling the rotor and grid side converters, providing reactive power support to the grid and relieving stress on power converters thereby achieving system stability. The proposed strategy maintains the system parameters during the grid faults by suppressing the rotor and stator over current, dc link voltage overshoot, power oscillations and support the grid voltage under both balanced and unbalanced grid fault conditions with different voltage dips at PCC. Computer simulations in time-domain are performed by verifying the MPPT and FRT capability of the proposed strategy for 6.5MW grid connected DFIG based WECS in MATLAB/SIMULINK 2018b. The proposed coordinated intelligent PQ and DC chopper FRT strategy is compared against existing FRT schemes like crowbar, SDBR, DC Chopper, PQ controller and its hybrid combinations which yields satisfactory results. The proposed scheme is also validated in Opal-RT hardware for LLG fault at 75% dip in voltage. The simulation and real time results observed in the work station demonstrates the effectiveness of the proposed strategy in enhancing the FRT capability of the system.

Superconductor fault current limiter effect on the performance of doubly-fed induction generators

<span>Between different wind turbine-generator configurations, one of the most accepted and highly regarded structures in the industry is the wind turbine with doubly-fed induction generator. The DFIG wind turbines are very sensitive to grid disturbances especially to voltage drop during grid faults due to relatively low power of the power converters. Fault in a power system causes voltage drop, current increase in stator and rotor coils, and over voltage in the DC shin. Several control methods have been proposed so far. A model based on power electronic instruments and superconductor theory, superconductor fault current limiter (SCFCL), has been proposed in this paper to improve domain and the attenuation time of the parameters under control such as voltage, current, and speed and voltage of the DC link against various types of faults (single-phase, two-phase, and three-phase). In addition to this, in order to compare the results with convectional models (crowbar) and study the innovation of the proposed model, a simulation of the system under two-phase fault and use of crowbar method to control the fault has been conducted using MATLAB-SIMULINK and also, the performance of the proposed method has been assessed. </span>

LQG Controller for the Control of Active and Reactive Power of DFIG Operating Under Inter-turn Short Circuit Fault

Objective: This article presents a comparative study between the direct control for a Doubly- Fed Induction Generator (DFIG) in the healthy and faulty mode. Methods: First with classical IP controller then Linear Quadratic Gaussian (LQG) controller which propose an ensemble of Linear Quadratic Regulator and Kalman filter for the state estimation. The developed model of the machine allows the simulation of the inter-turn short circuit in the stator. The use of the LQG method provides very good performance for motor operation and robustness of the control law despite the external perturbation. The performance of the control is compared to a classical controller's PI. Results: The obtained results demonstrate that this type of controller allows the alleviation of the mechanical stress and it ensures good performances under fault, the continuity of this system is ensured. Conclusion: The simulation has been carried out using a MATLAB script and the results are presented.

Enhancing the performance of wind energy conversion systems using unified power flow controller

Due to the low converters rating and cost of doubly fed induction generator (DFIG) along with its ability to function under variable wind speed, DFIG has been widely employed in wind energy conversion systems (WECSs). Unfortunately, the performance of DFIG is sensitive to the variation in the operating conditions and disturbance events at the grid side. This includes wind gust, voltage fluctuation and faults at the point of common coupling of the DFIG and the grid. In this study, a model-free adaptive control (MFAC) is developed for a unified power flow controller (UPFC) in order to improve the overall dynamic performance of a DFIG-based WECS during wind gusts and enhance the fault ride through capability of the DFIG during various disturbance events. The effective performance of the proposed controller is assessed through a comparison with a conventional proportional–integral (PI) controller optimised by a modified flower pollination algorithm. Results reveal the superiority of the proposed UPFC-MFAC technique over the conventional PI controller currently used in most of the UPFC-WECS applications.

Indirect Torque Control of a Cascaded Brushless Doubly-Fed Induction Generator Operating With Unbalanced Power Grid

This article describes an indirect torque control algorithm for a cascaded brushless doubly-fed generator (CBDFIG). The control algorithm presented in the article provides a possibility for CBDFIG to work with an unbalanced power grid applying different strategies: electromagnetic torque oscillations reduction, generated active power oscillation reduction, generated phase currents balancing, sinusoidal control currents under grid imbalance . The proposed control method is based on a cascaded brushless doubly-fed induction generator equivalent model and requires fewer tuning-demanding elements in comparison to classic control methods. The control algorithm presented in the paper was implemented and tested on a CBDFIG machine model in a simulation environment PSIM and on a real physical stand with a cascaded brushless doubly-fed generator.

Improving the Performance of Doubly Fed Induction Generator Using Fault Tolerant Control—A Hierarchical Approach

The growth of using wind energy on a large scale increases the demand for wind energy conversion machines (WECMs), among these converters, the doubly-fed induction generator (DFIG) is the favorite choice. However, DFIG is very sensitive to wind speed variations and grid faults during operation. In order to overcome these undesirable characteristics, this paper proposes a hierarchical fault tolerant control (FTC) to improve the performance of DFIG. The hierarchical fault tolerant control (FTC) approach consists of pitch angle control (PAC) and maximum power point tracking (MPPT). This hierarchical approach demonstrates the robust response under various (low, rated, and high) wind speed ranges and reduces the undesirable DC voltage overshoots during short-circuit disorder. The simulation results are summarized in a logical table, which depicts the order of controlling scheme and operation for a sustainable energy generation system. The proposed control scheme achieved the healthy and the robust dynamic response without deteriorating the grid power quality or stressing the converters, and approved the effectiveness to suppress the DC voltage overshoots and tolerate the lower down short-circuit disorder to its rated range.

Improved Voltage Harmonics Compensation Strategy for a Stand-Alone DFIG Operating under Unbalanced and Nonlinear Load Conditions

The study presents an improved control and operation for a stand-alone Doubly-Fed Induction Generator (DFIG) energy system under unbalanced and nonlinear load conditions. This type of loads results in unbalance and distorted stator voltage and current at the Point of Common Coupling (PCC), with subsequent power quality degradation and electromagnetic torque pulsations of DFIG. A new and simple control strategy based Proportional-Resonant Controllers (PRCs) in the stationary reference frame is applied in the Load-Side Converter (LSC) for fully compensate the unbalance and harmonic distortion in the PCC and avoid the torque pulsations of DFIG. As a result, symmetrical and sinusoidal AC voltage is applied to the PCC, which indicates that the Rotor-Side Converter (RSC) can be still controlled with the traditional vector control strategy, to adjust the generator torque and to balance active power. This strategy is conceptually simple, it does not require for rotating coordinate transformation and the sequence decomposition process, in addition no current sensors need to be installed at load or stator side, so that the number of current sensors employed is reduced. Simulation results using MatLab/Simulink are given and show the effectiveness and validity of the proposed control scheme to eliminate the harmonics in the PCC and torque pulsations of DFIG.

A New Application of Vector Based Current Regulator for STATCOM to Improve Dynamic Performance of DFIG

Abstract. Wind turbine generator (WTG) installation has been rapidly growing globally in the last few years. In the year of 2017, the WTG installation has reached a global cumulative installation of about 539 GW. Among several types of WTG, the doubly fed induction generator (DFIG) has been taking a large portion of the overall WTG installation since 2004. This popularity is due to the DFIG several advantages that include more extracted energy when compared with the fixed speed type and low cost due to the one-third size of the used converters when compared to the full converter type. However, the DFIG is vulnerable to grid faults. In this paper, a new application of Vector Based Hysteresis Current Regulator (VBHCR) of STATCOM is introduced to enhance the dynamic performance of DFIG-based wind turbine farm. The system under study is investigated using Matlab. Robustness of the proposed VBHCR is investigated through exploring the system performance under various levels of voltage sags. Simulation results show that for certain level of voltage sags at the point of common coupling (PCC), VBHCR-STATCOM can effectively improve the performance of the DFIG. As a result, voltage profile at the PCC can comply with the fault ride through codes of Spain to avoid the disconnection of the DFIGs from the grid.

Comparative Study on Performance Improvement of SPWM/THIPWM based DCMLI Grid Connected DFIG

Multi-level voltage source converter is integrated in various fields in renewable energy power generation technologies such as wind and solar sources for applications that need higher voltage and higher power. In wind power generation market, doubly fed induction generator (DFIG) based on wind power generation is now the leading technology as they are economically feasible, they do offer a variable speed and efficient substitute to the fossil fuel. This paper proposes a DFIG based on a back to back diode clamped multilevel converter systems (DCMLI) fired comparatively by sinusoidal pulse width modulation (SPWM) and third harmonic injection pulse width modulation (THIPWM) techniques. By using these technologies, the DFIG performance is compared for different wind speeds under normal operation condition. The proposed approach shows that the DCMLI systems generate a near sinusoidal voltage with lower values in total harmonic distortion (THD) thus, upgrading the power quality that is produced by DFIG. Lastly, the variation of frequency of induced rotor voltage and the active power flow due to the wind speed changes when the rotor speed changes from super synchronous to sub synchronous speeds is investigated.

Voltage sensorless based virtual flux control of three level NPC back-to-back converter dfigunder grid fault

In this paper, a harmonic elimination of grid and stator currents of doubly fed induction generator (DFIG) in case of grid fault without line voltage sensors is proposed . This can be achieved by compensating power based on virtual flux voltage sensorless technique. Direct power control with space vector modulation (DPC-SVM) is used to control both grid-side (GSC)and rotor-side converters (RSC). To achieve the control objective, compensated active and reactive powers are calculated based on virtual flux technique with balanced and harmonic free current as a control target. A theoretical analysis of active and reactive powers under unbalanced voltage source is clearly demonstrated and the effect of grid fault on the performance of DFIG is profoundly discussed. Simulation results verified the effectiveness of the modified control strategy.