Doubly-Fed Induction Generator Wind Power Research Articles

Distributed neural network enhanced power generation strategy of large-scale wind power plant for power expansion

Power generation is an important energy conversion process. A prominent feature of wind power plant compared with traditional power plants is that the equipment utilization has great intermittency and uncertainty. Fortunately, with the popularity of converter-based wind turbines, doubly-fed induction generator wind power plants are able to not only employ wind turbines in converting wind power to electrical power, but also use the converter capacity to produce reactive power. Traditionally, PQ curves considering current constraints are used for active and reactive power distribution, and therein the fixed maximum slip in power control is conservative for the utility of converters. To fully extract the power generation capacity, a novel power control realizing adaptive variation of maximum slip is proposed for each wind turbine to dynamically expand the reactive power capacity in the high active power region. In the meanwhile, the dispatch scheme of the wind power plant based on the conventional PQ curve has to be upgraded accordingly. Given that the unfixed maximum slip makes it impossible to obtain the PQ curve with explicit expression, an online learning method based on neural network is adopted and further developed in a distributed architecture to be consistent with natural distributed characteristics of the large-scale wind power plant. With the help of communication among agents through consensus protocol, the algorithm convergence can be guaranteed even under distinct information fragments. Case studies demonstrate that the proposed scheme is able to achieve up to 30% expansion of reactive power capacity and 16.3% voltage sag alleviation under certain conditions.

Coordinated Control of the DFIG Wind Power Generating System Based on Series Grid Side Converter and Passivity-Based Controller Under Unbalanced Grid Voltage Conditions

In order to solve the problem of excessive damage to doubly fed induction generator (DFIG) system under the condition of unbalanced voltage, this paper presents an improved coordinated control strategy based on doubly-fed induction generator (DFIG) wind power system, which can solve these problems well. The innovation of this paper is that the parallel grid-side converter (PGSC) uses a passivity-based controller (PBC) based on the Port Control Hamiltonian Dissipation (PCHD) model. Not only can four different control goals be achieved, namely, constant voltage of DC bus voltage, grid-side active power without second harmonics, grid-side reactive power without second harmonics, and grid-side current without negative sequence component, but also to ensure that the balance of stator and rotor current without distortion, the DFIG output power and electromagnetic torque without pulsation. The proposed coordinated control strategy has the characteristics of not changing the control strategy of the rotor-side converter and avoiding complex high-order matrix. The experimental results on the software platform and the hardware platform show that the proposed coordinated control strategy has the advantages of fast response, strong anti-interference ability, high stability, less control parameters.

Dynamic Control of a DFIG Wind Power Generation System to Mitigate Unbalanced Grid Voltage

This paper presents an improved control strategy for a doubly-fed induction generator (DFIG) during unbalanced grid voltage conditions. The proposed strategy was applied in both synchronization and grid-connected conditions. The synchronization process is carried by controlling the extracted positive and negative sequence components of the stator q-axis voltage to follow the grid q-axis voltage. This strategy can be accomplished by controlling the positive and negative sequence components of the rotor d-axis current. By perturbing the rotor d-axis current, the stator EMF builds up and follows the grid voltage accurately. The stator frequency and the phase difference between the stator and grid voltage are compensated by adjusting the stator d-axis positive and negative voltage components to zero. After synchronization, the proposed control strategy focuses on regulating the average stator active and reactive power control by controlling the positive components of q and d-axis currents, respectively. The second target is to minimize the generator torque ripple by controlling the rotor negative sequence components. At the same time, the grid side converter is controlled to minimize the grid power pulsations to reduce the impact of the unbalanced grid voltage. This study focuses on enhancing the dynamics of DFIG during the unbalanced grid voltage by using Multivariable State Feedback (MSF) current controllers. Experiments are carried out to validate the performance improvement by using the proposed method. The simulation and experimental results showed superior performance of the proposed control strategy.

Control of DFIG Wind Power Generators in Unbalanced Microgrids Based on Instantaneous Power Theory

This paper presents a model and a control strategy for a doubly-fed induction generator (DFIG) wind energy system in an unbalanced microgrid based on instantaneous power theory. The proposed model uses instantaneous real/reactive power components as the system state variables. In addition to the control of real/reactive powers, the controllers use the rotor-side converter for mitigating the torque and reactive power pulsations. The control scheme also uses the grid-side converter for partial compensation of unbalanced stator voltage. The main features of the proposed control method are its feedback variables are independent of reference frame transformations and it does not require sequential decomposition of current components. These features simplify the structure of required controllers under an unbalanced voltage condition and inherently improve the robustness of the controllers. A power limiting algorithm is also introduced to protect power converters against over rating and define the priority of real/reactive power references within the control scheme. The performance of the proposed strategy in reducing torque ripples and unbalanced stator voltage is investigated based on the time-domain simulation of a DFIG study system under unbalanced grid voltage.

Research on Voltage Stability Boundary under Different Reactive Power Control Mode of DFIG Wind Power Plant

A novel method is proposed to construct the voltage stability boundary of power system considering different Reactive Power Control Mode (RPCM) of Doubly-Fed Induction Generator (DFIG) Wind Power Plant (WPP). It can be used for reflecting the static stability status of grid operation with wind power penetration. The analytical derivation work of boundary search method can expound the mechanism and parameters relationship of different WPP RPCMs. In order to improve the load margin and find a practical method to assess the voltage security of power system, the approximate method of constructing voltage stability boundary and the critical points search algorithms under different RPCMs of DFIG WPP are explored, which can provide direct and effective reference data for operators.

Releasable Kinetic Energy-Based Inertial Control of a DFIG Wind Power Plant

Wind turbine generators (WTGs) in a wind power plant (WPP) contain different levels of releasable kinetic energy (KE) because of the wake effects. This paper proposes a releasable KE-based inertial control scheme for a doubly fed induction generator (DFIG) WPP that differentiates the contributions of the WTGs depending on their stored KE. The proposed KE-based gain scheme aims to make use of the releasable KE in a WPP to raise the frequency nadir. To achieve this, two additional loops for the inertial control are implemented in each DFIG controller: the rate of change of frequency and droop loops. The proposed scheme adjusts the two loop gains in a DFIG controller depending on its rotor speed so that a DFIG operating at a higher rotor speed releases more KE. The performance of the proposed scheme was investigated under various wind conditions. The results clearly indicate that the proposed scheme successfully improves the frequency nadir more than the conventional same gain scheme by releasing more KE stored in a WPP, and it helps all WTGs to ensure stable operation during inertial control by avoiding the rotor speed reaching the minimum speed limit.

Cooperated Control Strategy of DFIG Wind Power Generation System under Unbalanced Grid Condition

This paper proposes a cooperated control of the grid side converter (GSC) and rotor side converter (RSC) in doubly-fed induction generator (DFIG) wind power generation system under unbalanced grid condition. Mathematical model of doubly-fed induction generator (DFIG) and GSC under unbalanced grid voltage condition are investigated. Dual-dq current control strategies of the RSC and GSC under unbalanced grid condition are detailed studied. A cooperated control strategy of the GSC and RSC under unbalanced grid condition is proposed to provide enhance operation of DFIG system. The GSC is controlled to remove the total active power fluctuation of the system and RSC is controlled to eliminate the DFIG electromagnetic torque oscillation. Simulation based on Matlab/Simulink of a 1.5 MW DFIG prototype was carried out to validate the proposed cooperated control strategy.

Modeling and Control of a Doubly-Fed Induction Generator (DFIG) Wind Power Generation System for Real-time Simulations

This paper presents a study of a DFIG wind power generation system for real-time simulations. For real-time simulations, the Real-Time Digital Simulator (RTDS) and its user friendly interface simulation software RSCAD are used. A 2.2MW grid-connected variable speed DFIG wind power generation system is modeled and analyzed in this study. The stator-flux oriented vector control scheme is applied to the stator/rotor side converter control, and the back-to-back PWM converters are implemented for the decoupled control. The real-wind speed signal extracted by an anemometer is used for a realistic, reliable and accurate simulation analysis. Block diagrams, a mathematical presentation of the DFIG and a control scheme of the stator/rotor-side are introduced. Real-time simulation cases are carried out and analyzed for the validity of this work.