Doubly fed induction generator

This paper describes the dynamic behaviour of a doubly-fed induction machine, operating with wind turbine. The rotor circuit of the machine consists only of a generator-side converter working under abnormal condition at stator side (fault condition and voltage drop take place in transmission lines of the grid system). The induction machine model is based on the stationary reference frame and the control-unit model is based on the line-voltage oriented reference frame. The generator-side controller provides good decoupling between active and reactive power. A powerful MATLAB/SIMULINK was used for the simulation of the wind energy conversion system of a 4 kW wind generator. The simulation results of the generator side converter show that the speed, torque and the ϕ sin (power factor) can be regulated independently to match the reference signals. The effects of assumed abnormal condition in the grid system are discussed with regard to stator current and rotor current of the induction m...

This paper presents the mathematical modelling of DFIG based on load convention and explains the reduction of fault current in the rotor windings. The reduction of fault current is done by using virtual resistance control in which enhanced approach towards Fault Ride Through (FRT) controller is made. The enhanced FRT approach overcomes the usage of the conventional crowbar technique and uses a virtual resistance, where it meets the new grid code requirements during grid faults. Hence the whole system is always connected to the grid during abnormal conditions. The simulations are carried out in MATLAB /SIMULINK and the results are compared with those of the conventional crowbar method.

The performance of doubly fed induction generator (DFIG) variable speed wind turbine under network fault is studied using simulator developed in MATLAB/SIMULINK. Simulation results show the transient behavior of the doubly fed induction generator when a sudden short circuit at the generator bus is introduced. After the clearance of the short-circuit fault the control schemes manage to restore the wind

The increasing size of wind farms requires power system stability analysis including dynamic models of the wind power generation. Doubly-fed induction machines allow active and reactive power control through a rotor-side converter, while the stator is directly connected to the grid. In this paper, a new control of doubly-fed induction machines of field oriented for multilevel inverter is advanced and based on imaginary coordinate. The additional control could be implemented easily with this method, so that the inverter performance could be improved.

Abstract:- The aim of this work is to analyze a typical configuration of a Wind Turbine Generator System (WTGS) equipped with a Variable Speed Generator. Nowadays, doubly-fed induction generators are being widely used on WTGS, although synchronous generators are being ...

This paper deals with a protection and control strategy to enhance the low voltage ride through capability of a wind turbine driven doubly fed induction generator (DFIG). As the wind power penetration continues to increase, wind turbines are required to provide Low Voltage Ride-Through (LVRT) capability. Crowbars are commonly used to protect the power converters during voltage dips and their main drawback is that the DFIG absorbs reactive power from the grid during grid faults. According to emergency grid code requirements, wind farms should have the ability to stay connected and continue generation under external voltage failure conditions, that is, wind turbines have to keep in connection with grid and own continue reactive power supply. This paper proposes a hysteresis current control strategy for the crowbar protection and a reactive power control to satisfy the grid code requirements. Consequently, the dynamic model of double fed wind turbines is established to study the transient behavior of DFIG. Simulation results are presented to show the effectiveness of the proposed control scheme. Nomenclature f Grid frequency (Hz) n s Synchronous speed (rpm) ρ Air density (around 1.23 kg/m 3 at sea level) V Wind velocity (m/s) A Swept area (m 2) n g Generator speed (rpm) Z p Number of pole pairs V ds , V qs Stator voltage in the dq frame (V) i ds , i qs Stator current in the dq frame (A) i dr , i qr Rotor current in the dq frame (A) φ ds , φ qs Stator flux in the dq frame (Vs) L s Stator inductance (H), L m Magnetising inductance (H) R s Stator resistance () R r Rotor resistance () J Inertia of the rotor and turbine (kg.m 2) F Coefficient of friction m i Modulation index of each converter phase λ Tip speed ratio R Radius of the blade (m)

Brushless Doubly Fed Induction Generator (BDFIG) has been recently proposed to be used in variable speed wind turbines. This paper intends to investigate the influence of certain model simplifications to obtain a reduced-order model of a wind turbine with BDFIG suitable for transient studies. To achieve this goal, small signal analysis is performed for a recently manufactured 250 kVA BDFIG to obtain system modes and their participation factors. Identifying highly damped modes, influences of neglecting dynamics of their participated states are studied through time-domain simulation in MATLAB/Simulink.

Doubly Fed Induction Generator (DFIG) is the most popular variable speed generator for wind energy application due to its superior performance, lower cost and control flexibility. The DFIG has been widely used and researched in wind generator application. Instead of back-to-back converters, matrix converter (MC) can be a good alternative for connecting the DFIG rotor to the grid. This paper presents a matrix converter based control for a variable speed constant frequency (VSCF) DFIG. Design of DFIG based wind power generation system with the help of matrix converter is analyzed by means of MATLAB/SIMULINK block set.

The purpose of this work is to design and to discuss various strategies to optimize the production of a wind energy conversion chain based on the doubly fed induction generator (DFIG), by capturing the maximum power at the wind turbine, using maximum power point tracking (MPPT) and pitch control. The proposed controls allow the generator to monitor the optimal operating points of the turbines regardless of wind speed variations, system parameters disturbance, and parameters variation. Simulation of WECS based on a 1.5 MW wound rotor induction generator under MATLAB/SIMULINK is carried out using the PI controller (PIC), RST controller and fuzzy logic controller (FLC). Analysis and comparisons are made for different operating scenarios: Reference tracking, robustness under variable wind speed conditions and parameters variation. The application of FLC provides a very interesting outcome for the robustness and the dynamic challenges.

With the increasing penetration of wind power into electric power grids, energy storage devices will be required to dynamically match the intermittency of wind energy. This paper proposes a novel two-layer constant power control scheme for a wind farm equipped with doubly fed induction generator (DFIG) wind turbines. Each DFIG wind turbine is equipped with a supercapacitor energy storage system (ESS) and is controlled by the low-layer wind turbine generator (WTG) controllers and coordinated by a high-layer wind farm supervisory controller (WFSC). The WFSC generates the active power references for the low-layer WTG controllers according to the active power demand from or generation commitment to the grid operator; the low-layer WTG controllers then regulate each DFIG wind turbine to generate the desired amount of active power, where the deviations between the available wind energy input and desired active power output are compensated by the ESS. Simulation studies are carried out in PSCAD/EMTDC on a wind farm equipped with 15 DFIG wind turbines to verify the effectiveness of the proposed control scheme.

Abstract- This work presents a control strategy of a dynamic voltage restorer (DVR) to improve the doubly fed induction generator (DFIG) based wind turbine in case of fault. The application of a dynamic voltage restorer (DVR) connected to a doubly fed induction generator (DFIG) based wind-turbine-driven is investigated.Voltage in faulty line can be compensated using DVR, while nominal operation of DFIG wind turbine is continued as demanded in actual grid codes.

Due to increasing wind power generation in the electric power system, the reactive power generation by the wind farms is a major concern during both steady state and faulty conditions. This work, first, presents the reactive power capability (RPC) curve of doubly-fed induction generator (DFIG) considering three limitations (rotor voltage, rotor current and stator current) for reactive power production/consumption, for the complete operating range which is obtained by optimal rotor speed employing maximum power point tracking (MPPT) algorithm. It is established that the total reactive power generation is limited by rotor voltage at low speeds and by rotor current at higher speed. However, the total reactive power consumption is limited by stator current, for entire operating region. Selection of partial rated converter rating is crucial in terms of cost, efficiency, operating speed range and reactive power capability. The effect of converters rating on the enhancement of RPC of doubly fed induction generation is analyzed. Complete capability curves of DFIG for different stator voltages are developed considering grid-side converter (GSC) contribution towards reactive power capability.

Wind Energy Conversion Systems (WECS) have become a focal point in the research of renewable energy sources. This paper provides then a comparative study of past and present generator technologies used in WECS. This study is based on an exhaustive review of the state of the art and on an effective comparison of the performances of the four main topologies that are permanent magnet generators, synchronous generators, induction generators and doubly-fed induction generators. The different generator-WECS schemes are compared on the basis of topology, cost, efficiency, power consumption and control complexity. Moreover, attempts are made to highlight future issues so as to index some emerging solutions.

This paper develops a framework of maximum power point tracking (MPPT) of doubly-fed induction generator (DFIG) based and permanent magnet synchronous generator (PMSG) based wind energy systems. The principles of MPPT in various wind generators are firstly investigated and feedback control schemes to realize MPPT with/without wind speed measurements are presented. Stability analysis of the wind energy conversion system with sensorless MPPT is investigated. Case studies of various wind energy system configurations are given to demonstrate the MPPT control schemes.

This paper presents a new sensorless method for the vector control of doubly-fed induction machines (DFIMs) without using speed sensors or rotor position measurements. The proposed sensorless method is based on the model reference adaptive system (MRAS) estimating the rotor position and speed from the machine rotor currents. The method is appropriate for both stand-alone and grid-connected operation of variable

This paper treats the modeling, and the control of a wind power system based on a doubly fed induction generator DFIG, the stator is directly connected to the grid, while the rotor is powered by multilevel inverters. In order to get a decoupled system of controlfor an independently transits of active and reactive power, a vector control method based on stator flux orientation SFOC is considered: Direct vector control based on PI controllers. Cascaded H-bridge CHBI multilevel inverters are used in the rotor circuit to study its effect on supply power quality. All simulation models are built in MATLAB/Simulink software. Results and waveforms clearly show the effectiveness of vector control strategy. Finally, performances of the system will tested and compared for each levels of inverter.