Doubly Fed Induction Generator Wind Generation System Research Articles

Performance analysis and enhancement of direct power control of DFIG based wind system

<span lang="EN-US">The paper proposes a complete modeling and control technique of variable speed wind turbine system (WTS) based on the doubly fed induction generator (DFIG). Two levels back-to-back converter is used to ensure the energy transfer between the DFIG rotor and the grid. The wind turbine to operate efficiently, a maximum power point tracking (MPPT) algorithm is implemented. Then, direct power control (DPC) strategy has been combined with the MPPT technique in order to guarantee the selection of the appropriate rotor voltage vectors and to minimize the active and reactive power errors. Finally, the simulation is performed by using MATLAB/simulink platform basing on 7.5KW DFIG wind generation system, and the results prove the effectiveness of our proposed control technique.</span>

Modeling of Nine-Switch-Converter Based on Virtual Leg and Its Application in DFIG Wind Generation System

This article proposes a doubly fed induction generator (DFIG) wind energy conversion system (WECS) based on nine-switch converter. In this article, a new concept of virtual-leg is proposed, and the equivalent mechanism between the nine-switch converter and the dual six-switch converter is first proposed. Furthermore, a mathematical model of the nine-switch converter based on the unipolar binary logic switching function is established. In order to simplify the mathematical model of the nine-switch-converter-based DFIG-WECS, the parameter mapping relationship between the nine-switch converter with loads and the nine-switch-converter-based DFIG-WECS under dq coordinate system is given. Meanwhile, the adaptive resonant proportional integral (PI) (AR-PI) current controller based on the resonant controller, the PI controller, and the adaptive genetic algorithm is applied for the DFIG wind generation system. As a result, harmonic current content, overshoot, and dynamic response speed of the nine-switch-converter-based DFIG-WECS have been significantly improved. Finally, the simulations and experimental results verify the validity and reliability of the proposed mathematical model and control algorithm.

Compensation of Magnetizing Current for Enhanced Operation of DFIG Under Grid Unbalance

In the context of a doubly fed induction generator (DFIG) connected to the utility grid under unbalanced voltage conditions, the controller design needs to ensure additional challenges such as restricting the total harmonic distortion (THD) in grid current, minimizing the pulsations in generated power, torque, dc-link voltage, etc., apart from facilitating the generator power control. In this study, a negative-sequence compensation scheme for the magnetizing current in a DFIG is investigated. The reference currents are modified to include the negative-sequence compensating component for the magnetizing current. A rotor-side converter is employed to compensate the pulsations in magnetizing current thereby minimizing the ripple in power and torque. A grid-side converter is used to maintain unity power factor and a constant dc-link voltage. It is revealed that controlling the magnetizing current as a single control target enables simultaneous reduction of pulsations in torque, power, and dc-link voltage and also minimizes unbalance in currents. The effectiveness of the scheme is validated through detailed analysis and numerical simulations in PSCAD/EMTDC for a practical 250 kW DFIG wind generation system and further, through experimental results for a 2.3 kW DFIG test setup. Typical experimental results for the laboratory test setup show an improved performance.

Intelligent Backstepping Control of Variable Speed DFIG-Wind Turbine Under Unbalanced Grid Voltage Conditions Using Genetic Algorithm Optimization

This paper deals with the problem of controlling a Doubly Fed Induction Generator (DFIG) coupled to a wind turbine to enhance the wind integration under unbalanced grid operations. Previous works generally designed the control for DFIG based on standard models assuming that the iron losses are neglected. Also, the main negative aspect of the use of DFIGs is their large sensitivity to grid disturbances, principally to asymmetrical voltage dips. Moreover, in most controllers it is required that wind speed distribution along the turbine blades is known. The contribution of this paper is to present a novel nonlinear control scheme using an intelligent Backstepping approach implemented in both the dq+ and dq- reference frames rotating to achieve an optimal varying speed control under unbalanced grid operations involving online wind speed estimation and the iron losses. The control objective is threefold: (i) tracking the maximum available wind power to ensure the achievement of maximum power point (MPPT) based on the wind speed estimate; (ii) keeping a safe operation of the DFIG and wind speed estimator during unbalanced grid voltage conditions; (iii) efficient tuning based on Genetic Algorithm to determine the optimal parameters of the Backstepping controller. The performances of the control laws are validated by simulation studies on a 4 kW DFIG wind generation system during steady-state and transient grid unbalance using Matlab/Simulink® environment.

Adaptive Fuzzy Gain Scheduling of PI Controller for Control of the Wind Energy Conversion Systems

In this work, the Wind Energy Conversion Systems (WECS) based on doubly fed induction generator (DFIG) model is built. First, we consider the vector control strategy of the active and reactive powers in order to ensure an optimum operation. The whole system is presented in d-q-synchronous reference frame. After, the design of Adaptive Fuzzy Gain Scheduling of Proportional Integral Controller (AFGPI) for WECS is described, where the optimization by Fuzzy rules is utilized online to adjust the parameters of PI controller based on the error and its first derivative. Finally, the control of the active and reactive power using fuzzy-PI controller is simulated using software Matlab/Simulink, studies on a 1.5 MW DFIG wind generation system compared with conventional proportional integral controller. Performance and robustness results obtained are presented and analyzed.

Modeling and improvement of direct power control of DFIG under unbalanced grid voltage condition

This paper presents analysis and control of a doubly-fed induction generator (DFIG)-based wind generation system operating under unbalanced grid voltage condition. The DFIG system is modeled in synchronous positive reference frame. System behavior and operation of both the generator and the grid side converter (GSC) under unbalanced condition is illustrated by definition of oscillating power terms in the synchronous reference frame. This analysis makes it possible to control both the active and reactive power generation by means of direct power control (DPC) technique. It is shown that considering the DFIG model in synchronous reference frame simplifies the power terms extraction. Moreover, alternative DFIG control targets such as reducing unbalanced stator current, torque and power pulsations minimization, are considered. In addition, by the proposed method, the oscillation of the stator output power is compensated by the GSC, to ensure constant power output from the overall DFIG generation system. The validation of results has been performed through simulation results on a 2MW DFIG wind generation system.

Enhanced Control and Operation of DFIG-Based Wind Farms During Network Unbalance

This paper investigates the control and operation of doubly fed induction generator (DFIG)-based wind generation systems under unbalanced voltage conditions. DFIG system behaviors under unbalanced voltage are analyzed and different control targets are discussed. A new rotor current control strategy containing a main controller and an auxiliary controller is proposed. The main controller is implemented in the positive (dq)+ frame without involving positive/negative sequence decomposition, whereas the auxiliary controller is implemented in the negative (dq)- frame with negative sequence current extracted. The impact of providing unbalanced control on converter voltage rating is investigated. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system to validate the proposed control scheme and to demonstrate the enhanced system operation during ldquosmallrdquo steady state and ldquolargerdquo transient unbalances.

Coordinated Control of DFIG's Rotor and Grid Side Converters During Network Unbalance

This paper proposes a coordinated control of the rotor side converters (RSCs) and grid side converters (GSCs) of doubly-fed induction generator (DFIG) based wind generation systems under unbalanced voltage conditions. System behaviors and operations of the RSC and GSC under unbalanced voltage are illustrated. To provide enhanced operation, the RSC is controlled to eliminate the torque oscillations at double supply frequency under unbalanced stator supply. The oscillation of the stator output active power is then cancelled by the active power output from the GSC, to ensure constant active power output from the overall DFIG generation system. To provide the required positive and negative sequence currents control for the RSC and GSC, a current control strategy containing a main controller and an auxiliary controller is analyzed. The main controller is implemented in the positive (dq)+ frame without involving positive/negative sequence decomposition whereas the auxiliary controller is implemented in the negative sequence (dq)- frame with negative sequence current extracted. Simulation results using EMTDC/PSCAD are presented for a 2 MW DFIG wind generation system to validate the proposed control scheme and to show the enhanced system operation during unbalanced voltage supply.

Dynamic Modeling and Control of DFIG-Based Wind Turbines Under Unbalanced Network Conditions

This paper presents an analysis and control design of a doubly-fed induction generator (DFIG)-based wind generation system operating under unbalanced network conditions. A DFIG system model in the positive and negative synchronous reference frames is presented. Variations of stator active and reactive powers and generator torque are fully defined in the presence of negative sequence voltage and current. Alternative DFIG control targets during network unbalance, such as reducing stator current unbalance, torque, and power pulsations minimization, are identified. A rotor current control strategy based on positive and negative (dq) reference frames is used to provide precise control of the rotor positive and negative sequence currents. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system. It shows that conventional vector control of DFIG without considering network unbalance results in excessive oscillations on the stator active/reactive power, electromagnetic torque, and stator/rotor currents even with a small stator voltage unbalance. In contrast, with the proposed control strategy, enhanced system control and operation such as minimizing oscillations in either active power, or electromagnetic torque, or stator or rotor currents can be achieved