Changes

| <center>[http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220100117605%22.PGNR.&OS=DN/20100117605&RS=DN/20100117605 US20100117605A1]</center>

| <center>2010</center>

| Method of and apparatus for operating a double-fed asynchronous machine in the event of transient mains voltage changes

| The short-circuit-like currents in the case of transient mains voltage changes lead to a corresponding air gap torque which loads the drive train and transmission lines can damages or reduces the drive train and power system equipments.

| <center>[http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220090267572%22.PGNR.&OS=DN/20090267572&RS=DN/20090267572 US20090267572A1]</center>

| <center>2009</center>

| Current limitation for a double-fed asynchronous machine

| Abnormal currents can damage the widings in the doubly- fed induction gnerator. Cntrolling these currents with the subordinate current controllers cannot be an efficient way to extract the maximum amount of active power.

| <center>[http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220090008944%22.PGNR.&OS=DN/20090008944&RS=DN/20090008944 US20090008944A1]</center>

| style="background-color:#ffffff"| <center>2009</center>

| Method and system of control of the converter of an electricity generation facility connected to an electricity network in the presence of voltage sags in said network

| Double-fed asynchronous generators are very sensitive to the faults that may arise in the electricity network, such as voltage sags. During the sag conditions the current which appears in said converter may reach very high values, and may even destroy it.

| <center>[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7355295.PN.&OS=PN/7355295&RS=PN/7355295 US7355295B2]</center>

| <center>2008</center>

| Variable speed wind turbine having an exciter machine and a power converter not connected to the grid

| a) The active switching of the semiconductors of the grid side converter injects undesirable high frequency harmonics to the grid.b) The use of power electronic converters (4) connected to the grid (9) causes harmonic distortion of the network voltage.

| <center>[http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070210651%22.PGNR.&OS=DN/20070210651&RS=DN/20070210651 US20070210651A1]</center>

| <center>2007</center>

| Power converter for doubly-fed power generator system

| During the ground faults, excess currents is induced in the secondary windings and flows into power converter connected o secondar side and may danage the power converter. Conventional methos of incresing the capacity of the power cnverter increases system cost , degrade the system and takes time to activate the system to supply power again.

| <center>[http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070132248%22.PGNR.&OS=DN/20070132248&RS=DN/20070132248 US20070132248A1]</center>

| <center>2007</center>

| System and method of operating double fed induction generators

| 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 (DVR) is cost expensive.

| <center>[http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220050189896%22.PGNR.&OS=DN/20050189896&RS=DN/20050189896 US20050189896A1]</center>

| <center>2005</center>

| Method for controlling doubly-fed machine

| Controlling the double fed machines on the basis of inveter control to implement the targets set for the machine, this model is extremely complicated and includes numerous parameters that are often to be determined.