The controlling of the DFIG based on variable speed wind turbine modeling and simulation

Grid-connected doubly-fed induction generator (DFIG) based wind energy conversion system (WECS) is widely used in harnessing wind power. The paper attempts to characterize a 15-kW grid-connected DFIG based WECS operating under variable speed and loading conditions. Back to back converter topologies are utilized consisting of rotor side converter (RSC) and grid side converter (GSC) controlled in the synchronous reference frame coordinates. The design, modeling, and control of various system components are deliberated. The interaction of the grid with the proposed DFIG-WECS is analyzed where the regulation of the machine active power is achieved through the control of RSC. The current quality, voltage regulation is achieved by the control of GSC. Case studies involving constant wind speed, variable wind speed, and variable loading are undertaken for the characterization analysis. The performance characterizations of the entire system is validated in Matlab/Simulink simulation environment where the critical performance parameters like DC link voltage, generator torque, DFIG stator current, active and reactive power delivered by the DFIG to the grid, PCC side voltage/ current profile and the PCC current Total harmonic distortion (THD) are rigorously monitored, presented and discussed for each case studies.

This proposed work presents a new control strategy for a Doubly Fed Induction Generator (DFIG) under unbalanced network voltage conditions. This proposed control strategy provides an independent operation of the Rotor Side Converter (RSC) and Grid Side Converter (GSC) for a Doubly Fed Induction Generator (DFIG) based wind energy conversion system (WECS) under unbalanced grid voltage conditions. The DFIG control targets during network unbalance, such as reducing stator current unbalance, torque, and power pulsations minimization, are identified. The RSC is controlled to achieve four different control targets, including balanced stator current, sinusoidal rotor current, smooth stator active and reactive powers, and constant DFIG electromagnetic torque. The GSC is controlled to keep the DC voltage at a constant value. The resonant feedback compensator (R) is added with proportional integral (PI) control to make PIR and this controller is used to decomposition of the positive and negative sequence component and calculations of the rotor negative current references can be avoided. Another similar compensator is used in the GSC to suppress the DC voltage fluctuates and remove the GSC reactive power oscillations without the stator or rotor power information. The proposed method can make the RSC and GSC available to an independent operation with a simple implementation for higher reliability.

This paper presents a grid-interactive doubly fed induction generator (DFIG) based wind energy conversion system (WECS) for regulated power flow through the grid. The battery energy storage (BES) is used for maintaining regulated power along the grid regardless of the wind speeds. The rotor side converter (RSC) is controlled in flux based reference frame and the grid side converter (GSC) control is based on an indirect vector control. The BES is connected at DC bus of two voltage source converters integrated back to back, which plays key role in attaining regulated grid power. This work proposes control algorithms for both RSC and GSC to achieve regulated power flow capabilities in the grid. The system is modeled and its performance is simulated under variable wind speeds, change in grid reference real and reactive powers, grid voltage dip and unbalanced nonlinear load conditions using SimPowerSystems toolbox of MATLAB. Under all such cases, the grid currents, stator currents and PCC (point of common coupling) voltages are found sinusoidal and THDs (total harmonic distortions) are under limits as per the IEEE 519 standard. Finally, a prototype is developed and experiment has been carried out to test the grid-interactive DFIG based WECS under changeover of grid power and variable wind speeds.

In this paper, a control strategy is proposed to enhance the capability in terms of active filtering, of a Wind Energy Conversion System (WECS) based on a Doubly Fed Induction Generator (DFIG). The stator of the DFIG is directly connected to the grid and the rotor is connected to the grid through a back to back AC-DC-AC PWM converter. The proposed algorithm is applied to the Rotor Side Converter (RSC) to achieve simultaneously the Maximum Power Point Tracking (MPPT) and the power quality improvement at the Point of Common Coupling (PCC). This enables the grid to supply only sinusoidal currents at Unity Power Factor (UPF). Depending on the nominal RSC power, reactive power of linear loads and harmonic currents due to the nonlinear loads can be compensated. The proposed RSC control strategy manages the WECS function's priorities between active power production, reactive power compensation and active filtering without any system over-rating. To enhance the capability of the RSC, in terms of active filtering, it is proposed to eliminate instantaneously the whole of the 5th and the 7th predominant harmonic components if possible, otherwise, the filtering operation is omitted. The Grid Side Converter (GSC) is controlled in such a way to guarantee a smooth DC voltage. The presented simulation results demonstrate the performance and the effectiveness of the proposed control strategy.

This paper presents a novel approach for reactive power compensation and active filtering capability of a variable speed wind energy conversion system (WECS) with doubly fed induction generator (DFIG), without any over‐rating. First, the WECS is capable of capturing maximum wind power under fluctuating wind speed. Second, depending on the available wind power value versus nominal WECS power, power quality can be improved by compensating the reactive power and the grid harmonic currents, without any system over‐rating. The proposed rotor side converter (RSC) control manages the WECS function's priorities, between main active power generation and power quality management. To ensure high filtering performances, we used an improved harmonic isolator in the time domain, based on a selective pass band filter (SPBF) developed in our laboratory. Moreover, we took advantage of the high amplification effect of the rotor side‐controlled DFIG to compensate harmonic currents. Consequently, no over‐rating is necessary for the proposed additional active filtering capability. Simulation results for a 2 MW WECS with DFIG confirm the effectiveness and the performances of the proposed approach. Copyright © 2009 John Wiley & Sons, Ltd.

This paper presents the study of a variable speed wind energy conversion system using a Doubly Fed Induction Generator (DFIG) based on a Fuzzy sliding mode control (FSMC) applied to achieve control of active and reactive powers exchanged between the stator of the DFIG and the grid to ensure a Maximum Power Point Tracking (MPPT) of a wind energy conversion system. However the principal drawback of the sliding mode, is the chattering effect which characterized by torque ripple, this phenomena is undesirable and harmful for the machines, it generates noises and additional forces of torsion on the machine shaft. In order to reduce the chattering effect, the Sign function of sliding mode controller’s discontinuous part is replaced by a fuzzy logic; we will have the fuzzy sliding mode controller (FSMC). The FSMC makes it possible to combine the performances of the two types of controllers (SMC and FLC) and eliminates the chattering effect. The proposed control algorithm is applied to a DFIG where the stator is directly connected to the grid and the rotor is connected to a three-level converter structure NPC to suppress low level harmonics, higher frequencies will be filtered out by the machine. Second goal of this paper is to extract a maximum of power; the rotor side converter is controlled by using a stator flux-oriented strategy. The decoupling created by the control between active and reactive stator power allows keeping the power factor close to unity. Simulation results show that the wind turbine can operate at its optimum energy for a wide range of wind speed. Both simulation and validation results show effectiveness of the proposed control strategy is in terms of power regulation. Moreover, the fuzzy sliding mode approach is arranged so as to reduce the chattering produced in the generated power that could lead to increased mechanical stress because of strong torque variations. DOI: http://dx.doi.org/10.11591/ijpeds.v3i4.4072

Due to the increasing need of electrical energy and environmental issues corresponding to fossil fuels such as global warming, renewable energy sources attracted a lot of engineers and researchers to themselves. Among renewable energy sources, wind energy as the most accessible energy source, has been among the most popular research topics in recent years. Doubly-Fed Induction Generator (DFIG) is a commonly used configuration for variable speed Wind Energy Conversion Systems (WECSs) because of its independent control of active and reactive powers and extensive range of wind speed variations. In this paper, a Pulse Width Modulation (PWM) rectifier and a Z-Source Inverter (ZSI) are used as Grid Side Converter (GSC) and Rotor Side Converter (RSC), respectively. Z-Source Inverter is a newly proposed power electronic converter which has solved the limitations and disadvantages of conventional voltage source and current source inverters. A modified Space Vector Modulation (SVM) technic based on Sliding Mode generator power control is used to control the switching pattern of the ZSI. To verify the effectiveness of the proposed control system, simulations result in MATLAB/Simulink software are presented. Different wind speeds as well as independent control of active and reactive powers are examined through these simulations.

This paper presents an optimum design procedure for the coordinated tuning of rotor side converter (RSC) and grid side converter (GSC) controllers of grid connected doubly fed induction generator (DFIG) wind turbine system. The RSC and GSC controller parameters are determined to optimize the performance indices. The performance indices considered are maximum peak overshoot (MPOSωr), settling time (Tssωr) of the generator speed and the maximum peak overshoot (MPOSVdc), maximum peak undershoot (MPUSVdc) and settling time (TssVdc) of DC link voltage. The sum squared error deviation of the dc link voltage and the generator speed is considered as the objective function. The constrained optimization problem is solved using particle swarm optimization (PSO). Simulations are performed on a sample system with DFIG based WECS. The effectiveness of the designed parameters using PSO is then compared with that obtained using simulated annealing (SA).

This paper presents an independent control of rotor side converter (RSC) and grid side converter (GSC) for a doubly fed induction generator (DFIG). A novel cascade feedback linearization (CFL) technique based on non-linear differential geometry is developed for design of RSC, which leads to decoupled currents. Here, the rotor DC link voltage can be regulated with respect to a square transform on its voltage reference and the d-axis current that satisfies conditions for zero dynamics. The controlled RSC has a capability to track DC link voltage reference faster and also attain global stability. The GSC controller has been designed by incorporating a new incremental hysteresis comparator (IHC) that utilizes the hysteresis band to produce the suitable switching signal to the GSC to get enhanced controllability during grid unbalance. The IHC produces higher duty-ratio linearity and larger fundamental GSC currents with lesser harmonics. The latter can thus achieve fast transient response for GSC. All these features are confirmed through time domain simulation on a 15 KW DFIG Wind Energy Conversion System.

In this paper we illustrate a power control approach of a doubly fed induction generator, operating in a variable speed wind energy conversion system. The aim of the control consists in maximising the electric power extracted from the wind turbine and injected to the grid, thus, by adjusting the power coefficient. The use of a variable speed wind energy conversion system permits the implementation of such a kind of strategies. The stator power and the terminal voltage are to be maintained to references that will be given while the control of the global dynamic system, this by adjusting rotor voltages

This paper deals with the analysis, design, and control of grid-interfaced doubly fed induction generator (DFIG) based variable speed wind energy conversion system (WECS) for power smoothening with maximum power point tracking (MPPT) capability. This DFIG uses rotor position computation algorithm for the sensorless control through rotor position estimation. Power fluctuations due to the unpredictable nature of the wind are eliminated by introducing battery energy storage system (BESS) in the dc link between two back-to-back connected voltage source converters. The design of BESS is presented for feeding regulated power to the grid irrespective of the wind speeds. The control algorithm of the grid-side converter is modified for feeding regulated power to the grid. Rotor-side converter is controlled for achieving MPPT and unity power factor operation at the stator terminals. A prototype of the proposed DFIG-based wind energy conversion system is developed using a digital signal processor (DSP-dSPACE DS1103). This developed DFIG is tested extensively at different wind speeds and also presented some of the steady-state test results. Dynamic performance of this DFIG is also demonstrated for the variable wind speed operation.

The main goal of this article is the control of a Wind Energy Conversion System (WECS), equipped by a Doubly Fed Induction Generator (DFIG), for maximum active power generation and power quality enhancement, in terms of reactive power compensation. The control strategy is applied to the DFIG whose rotor is connected to the grid through two converters (the RSC and the GSC). In fact, the main goal of the Rotor Side Converter (RSC) control is to accomplish simultaneously the capture of the optimum power from the wind and to ensure a unity power factor at the stator side. While, the aim of the Grid Side Converter (GSC) control is to ensure simultaneously a sleek DC bus voltage between the two converters and to compensate the reactive power of a lagging linear load coupled at the Point of Common Coupling (PCC) and achieve a unity power factor at the grid side. The presented simulation results show the Success of the different control strategies applied to the WECS.

In this paper, the authors present an efficient direct torque control (DTC) for doubly fed induction generator (DFIG) in wind energy conversation systems (WECSs). The DFIGs are most employed in the WECSs because of their advantages, such as appropriate performance in variable wind speeds, control flexibility, and low cost. Many kinds of control techniques are proposed for the DFIG. One of the most simple and efficient control strategies with the fast-dynamic response is the DTC. The proposed control strategy is developed through a proportional-integral (PI) controller. This control strategy does not require any wind speed measurement and sensors. Moreover, in this strategy, torque ripple is a small amount; and then, the DTC can be used for rotor side converter (RSC). The new control strategy was analyzed and simulated in MATLAB/SIMULINK. The test system consists of a wind turbine model that drives a DFIG connected to the power grid through DC-link. It was also applied to a 2-pole, 0.2-KW DFIG. The obtained simulation results are illustrated pleasant and attractive advantages of the proposed control strategy, including simple control system structure, fast response, and easy integration of DFIG turbines with a large-scale power grid.

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.

SUMMARY This paper analyzes two control strategies of doubly fed induction generator (DFIG)-based wind turbine under unbalanced voltage which were introduced in the previous works and then proposes a new control strategy to achieve more improved performance of DFIG. Under unbalanced conditions, the rotor side converter (RSC) and grid side converter (GSC) are controlled in two positive and negative ((dq)+ and (dq)–) reference frames. The control of these converters in the (dq)+ frame is the same as the conventional control under balanced grid conditions. In the proposed control strategy, the control of the RSC in the (dq)– frame is done to balance the stator currents, and also the total active power oscillations are removed by the control of the GSC in this frame. In this strategy, the oscillations of both the torque and stator active power are properly reduced even when the voltage unbalance is somewhat severe. Consequently, the elimination of the stator active power oscillation by the active power output from the GSC is accomplished with fewer constraints. To provide the accurate coordinated control of the RSC and GSC, this proposed control strategy is implemented in the stator-voltage oriented frame. The simulation results obtained for a 7.5-kW DFIG-based wind turbine validate the enhancement of system operation using the proposed control strategy during unbalanced voltage network. Copyright © 2012 John Wiley & Sons, Ltd.