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This report presents a brief summary about introduction to wind energy and present day technologies available for horizontal wind turbines. A detailed taxonomy for horizontal axis wind turbines is presented covering parts of the turbine, control systems, applications among others. A detailed landscape analysis of patent and non-patent literature is done with a focus on '''Doubly-fed Induction Generator Generators (DFIG)''' used in the horizontal axis wind turbines for efficient power generation. Existing The product's information of major players in the market is also compiled captured for doublyDoubly-fed induction generatorsInduction Generators. Existing market The final section of the report covers the existing and future market prediction predictions for wind energy -based power generation is presented.

* Humans We have been using wind power for at least since 5000 BC to propel sailboats and sailing ships, and architects have used wind-driven natural ventilation in buildings since similarly ancient times. The use of wind to provide mechanical power came later.

For variable-speed systems with limited variable-speed range, e.g. ±30% of synchronous speed, the doubly-fed induction generator(DFIG) can be an interesting solution.This is mainly due to the fact that the power electronic converter only has to handle a fraction (20-30%) of the total power as the converters are connected to the rotor and not to the stator. Therefore, the losses in the power electronic converter can be reduced, compared to a system where the converter has to handle the total power.The overall structure of wind power generation through DFIG as shown in the figure below.

|<font color="#0000FF"><u>[http://v3.espacenet.com/eclasrch?classification=ecla&locale=en_EP&ECLA=f03d9/00c F03D9/00C ]</u></font>

'''Patent coverage:''' US Grant, GB AppG, US AppA, FR AppEP G, EP A, WO App, DE UtilGB A, EP GrantFR A, DE GrantG, EP AppDE A, DE AppUtil, JP UtilG, JP GrantA, JP AppUtil, CN Util, CN AppA, KR Util , KR GrantG, KR AppA, Other, DWPI<br>

|bgcolor = "#DCE6F1"|The method presents that the stator connecting with the network and the rotor with a converter. The converter is formed to set a reference value of an electrical amplitude in the rotor, by which a reference value of the electrical amplitude is set in the rotor after attaining a transient mains voltage change, such that the rotor flux approaches the stator flux.

|A compensation block is arranged, which feeds a compensation control output to the rotor of the generator. The computation unit computes the control output during operation of the turbine to compensate partly for dependencies on a rotor angular speed of locations of poles of a generator transfer function, so that the transfer function is made independent of variations in the speed during operation of the turbine which eliminates the osicllations oscillations and increases the efficinecy efficiency of the wind turbine.

|bgcolor = "#DCE6F1"|Abnormal currents can damage the widings windings in the doubly- fed induction gneratorgenerator. Cntrolling Controlling these currents with the subordinate current controllers cannot be an efficient way to extract the maximum amount of active power.

|During the event of a voltage sag occurring, the converter imposes a new setpoint set point current which is the result of adding to the previous setpoint set point current a new term, called demagnetizing current, It is is proportional to a value of free flow of a generator stator. A difference between a value of a magnetic flow in the stator of the generator and a value of a stator flow associated to a direct component of a stator voltage is estimated. A value of a preset calculated difference is multiplied by a factor for producing the demagnetizing current.

|Optislip circuit with a resistor is used when speed is above synchronous speed, results in heating the resistor and thus the generator leads to limitation of operation in supersynchronous super synchronous range which results in tower fluctionsfluctuations.|Providing a back-to-back converter whic which contains the inverter circuit has direct current (DC) inputs , DC outputs, and a rotor-rectifier connected to a rotor of a dual feed asynchronous generator. A mains inverter is connected to a power grid, and an intermediate circuit connects one of the DC inputs with the DC outputs. The intermediate circuit has a semiconductor switch between the DC outputs, an intermediate circuit condenser between the DC inputs, and a diode provided between the semiconductor switch and the condenser. Thus the sysem system is allowed for any speed of wind and reduces the tower fluctuations.

|bgcolor = "#DCE6F1"|During the ground faults, excess currents is induced in the secondary windings and flows into power converter connected o secondar to secondary side and may danage damage the power converter. Conventional methos methods of incresing increasing the capacity of the power cnverter converter increases system cost , degrade the system and takes time to activate the system to supply power again.|bgcolor = "#DCE6F1"|The generator provided with a excitation power converter connected to secondary windings of a doubly-fed generator via impedance e.g. reactor, and a diode rectifier connected in parallel to the second windings of the doubly-fed generator via another impedance. A direct current link of the rectifier is connected in parallel to a DC link of the converter. A controller outputs an on-command to a power semiconductor switching element of the converter if a value of current flowing in the power semiconductor switching element is a predetermined value or larger.

|Wind turbines with double fed induction generators are sensitive to grid faults.Conventional methods are not effective to reduce the shaft stress during grid faults and slow response and using dynamic vltage restoreer voltage restorer (DVR) is cost expensive.|The protection system has a controlled impedance devicesdevice.Impedance device has bidirectional semiconductors such triac, assembly of thyristors or anti-parallel thyristors. Each of the controlled impedance devices is coupled between a respective phase of a stator winding of a double fed induction generator and a respective phase of a grid side converter. The protection system also includes a controller configured for coupling and decoupling impedance in one or more of the controlled impedance devices in response to changes in utility grid voltage and a utility grid current. High impedance is offered to the grid during network faults to isolate the dual fed wind turbine generator.

|bgcolor = "#DCE6F1"|A AA short-circuit in the grid causes the generator to feed high stator-currents into the short-circuit and the rotor-currents increase very rapidly which cause damage to the power-electronic components of the converter connecting the rotor windings with the rotor-inverter.|bgcolor = "#DCE6F1"|The converter is provided with a clamping unit which is triggered from a non-operation state to an operation state, during detection of over-current in the rotor windings. The clamping unit comprises passive voltage-dependent resistor element for providing a clamping voltage over the rotor windings when the clamping unit is triggered.

|Controlling the double fed machines on the basis of inveter inverter control to implement the targets set for the machine, this model is extremely complicated and includes numerous parameters that are often to be determined.|A method is provided to use a standard scalar-controlled frequency converter for machine control. A frequency reference for the inverter with a control circuit, and reactive power reference are set for the machine. An A rotor current compensation reference is set based on reactive power reference and reactive power. A scalar-controlled inverter is controlled for producing voltage for the rotor of the machine, based on the set frequency reference and rotor current compensation reference.

|bgcolor = "#DCE6F1"|<font color="#0000FF"><u>[http://ieeexplore.ieee.org/search/freesrchabstract.jsp?tp=&arnumber=1709031&queryText=Study+on+the+Control+of+DFIG+and+Its+Responses+to+Grid+Disturbances&openedRefinements=*&searchField=Search+All Study on the Control of DFIG and it's its Responses to Grid Disturbances ]</u></font>

|bgcolor = "#DCE6F1"|Presented dynamic model of the DFIG, including mechanical model, generator model, and PWM voltage source converters. Vector control strategies adapted for both the RSC and GSC to control speed and reactive power independently. controlling Control designing methods, such as pole-placement method and the internal model control are used. MatlabMATLAB/Simulink is used for simulation.

|bgcolor = "#DCE6F1"|Proposed a new optimal control strategy of maximum wind power extraction strategies and testified by simulation. The control algorithm also used to minimize the losses in the generator. The dual passage excitation control strategy is applied to decouple the active and reactive powers. With this control system, the simulation results shows show the good robustness and high generator efficiency is achieved.

|bgcolor = "#DCE6F1"|'''Rated Power:''' 3.0 MW, '''Frequency:''' 50 Hz/60 Hz, '''Number of Poles :''' 4-pole, '''Operating Temperature: '''-30°C to 40°

|bgcolor = "#DCE6F1"|1.5MW DFIG