Title of Invention	"METHOD FOR CONTROLLING A POWER-GRID CONNNECTED WIND TURBINE GENERATOR DURING GRID FAULTS AND A POWER GRID CONNECTED WITH TURBINE GENERATOR"
Abstract	The present invention relates to a method and an controlling a power grid connected wind terbine generator during grid faults,the staker windings of the wind turbine generator are disconnected from the wind turbine during grid fault condition are connected to the swtalor windings.In this way a certain megnetisation of the generator can be maintained and after removal of the grid fault condition the generator is synchronished to the power grid and the impedence are disconnected and the stator windings are reconnected to the power grid, In thisw way it is possible to keep the wind turbine generotor at least party magnitished during grid faults and thus ready for delivering power to the power grid,as soon as the grid voltage is re-established after the fault. (It is suggested that Figure 1 be published with the Abstract)

Title of Invention

"METHOD FOR CONTROLLING A POWER-GRID CONNNECTED WIND TURBINE GENERATOR DURING GRID FAULTS AND A POWER GRID CONNECTED WITH TURBINE GENERATOR"

Abstract

The present invention relates to a method and an controlling a power grid connected wind terbine generator during grid faults,the staker windings of the wind turbine generator are disconnected from the wind turbine during grid fault condition are connected to the swtalor windings.In this way a certain megnetisation of the generator can be maintained and after removal of the grid fault condition the generator is synchronished to the power grid and the impedence are disconnected and the stator windings are reconnected to the power grid, In thisw way it is possible to keep the wind turbine generotor at least party magnitished during grid faults and thus ready for delivering power to the power grid,as soon as the grid voltage is re-established after the fault. (It is suggested that Figure 1 be published with the Abstract)

Full Text	TURBINE GENERATOR DURING GRID FAULTS AND A POWER GRID CONNECTED WIND TURBINE GENERATOR TECHNICAL FIELD The present invention relates to a method for controlling a power-grid connected wind turbine generator during grid faults and a power grid connected wind turbine generator. BACKGROUND ART In wind turbine systems it is known to provide some kind of control of the wind turbine during grid faults. However, the general concept of such control apparatus aims at stopping the wind turbine by pitching the blades of the wind turbine out of the wind and disconnecting the generator from the grid. After a certain time, when the grid voltage has been re-established, the wind turbine is started up in the normal fashion in order to deliver power to the grid, and the time from disconnection to restart of the wind turbine has traditionally been in the order of 1-10 minutes. The short circuit current contribution from the wind turbine generator has generally been limited to last approximately 40-50 ms, after which the current from the wind turbine generator has been zero. Thus, the wind turbine generator does not contribute to the re-establishment of the grid voltage and does not contribute to the short circuit current in the grid over a longer period of time, which may be necessary in order to activate the grid protection means for disconnecting the faulty parts of the power grid. 2 From EP-0 984 552 it is known to disconnect the stator windings of a generator from the power grid when a fault is detected and to connect impedances to the stator windings for dissipating the power generated during such grid fault conditions, and to maintain a certain magnetization of the generator. After clearance of the fault the generator is resynchronized to the power grid and the stator windings are reconnected to the power grid. DISCLOSURE OF THE INVENTION It is the object of the present invention to provide a method for controlling a power grid connected wind turbine generator during grid faults of the kind referred to above, with which it is possible to keep the wind turbine generator magnetized and ready for delivering power to the power grid, as soon as the grid voltage is re-established after the fault, and this object is achieved with a method for controlling a power-grid connected wind turbine generator during grid faults of said kind. Accordingly, the present invention provides a method for controlling a power-grid connected wind turbine generator during grid faults, said generator comprising a wind turbine driven rotor and a normally grid-connected stator, and during normal operation being connected to deliver power to the power grid, and the generator is a double-fed asynchronous generator, the rotor windings being normally connected to the grid through a back-to-back converter for transferring energy between the rotor windings and the grid in a controlled manner, said method comprising the steps of: 2A a) disconnecting the stator windings from the power grid when a fault is detected, b) connecting the stator windings to impedances for dissipating between 0 and 100% of the power generated by the wind turbine during grid fault condition, c) maintaining a certain magnetization of the generator during grid fault conditions, and d) after removal of the grid fault condition, synchronizing the generator to the power grid and disconnecting the impedances and reconnecting the stator windings to the power grid, characterized by comprising the step of keeping the back-to-back converter connected to the grid during fault condition and controlling the back-to- back converter to deliver a controlled short-circuit contribution to the grid during fault condition. With this method, it is possible to dissipate the generated power in the impedances, whenever the generated power cannot be delivered to the power grid, due to fault conditions, such as low voltages or zero voltages on the power grid, and as soon as the power grid is re-established, the wind turbine generator can be re-connected to deliver the power to the power grid almost instantaneously. The invention also provides a power-grid connected wind turbine generator comprising a wind turbine-driven rotor, a stator, said stator during normal operation being connected to deliver power to the power grid, means for 2B disconnecting the stator windings from the power grid when a fault is detected and means for connecting impedances to the stator windings, said impedances being dimensioned to dissipate between 0 and 100% of the power generated by the wind turbine during grid fault conditions and comprising means for maintaining a certain magnetization of the generator during disconnection and means for synchronizing the generator to the grid before reconnection to grid after fault clearance, characterized by the generator being a double fed asynchronous generator comprising a back-to-back converter connected between the rotor and the grid, and that the means for disconnecting the stator windings from the power grid do not disconnect the connection between the back-to-back converter and the power grid. Furthermore, the maintained connection between the back-to-back converter and the grid provides the possibility of delivering a certain power to the grid, thus contributing to the short circuit current in the grid necessary to activate the grid protection means for disconnecting the faulty parts of the power grid. Preferred embodiments of the method according to the invention and their advantages will be evident from the following detailed description. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS In the following detailed part of the present description, the invention will be explained in more detail with reference to the exemplary embodiments of different apparatus for implementing the method for controlling a power-grid connected wind turbine generator during grid faults according to the invention shown in the drawings, in which - 8 WE CLAIM : 1. Method for controlling a power-grid connected wind turbine generator (G) during grid faults, said generator (0) comprising a wind turbine driven rotor and a normally grid-connected stator, and during normal operation being connected to deliver power to the power grid, and the generator (G) is a double-fed asynchronous generator (G), the rotor windings being normally connected to the grid through a back-to-back converter for transferring energy between the rotor windings and the grid in a controlled manner, said method comprising the steps of: a) disconnecting the stator windings from the power grid when a fault is detected, b) connecting the stator windings to impedances for dissipating between 0 and 100% of the power generated by the wind turbine during grid fault condition, c) maintaining a certain magnetization of the generator during grid fault conditions, and d) after removal of the grid fault condition, synchronizing the generator to the power grid and disconnecting the impedances and reconnecting the stator windings to the power grid, characterized by comprising the step of keeping the back-to-back converter connected to the grid during fault condition and controlling the back-to- back converter to deliver a controlled short-circuit contribution to the grid during fault condition. 9 2. Method as claimed in claim 1, comprising the step of connecting the impedances in star or delta configuration and connecting the stator windings in star or delta configuration, all dependent on measured parameters for the wind turbine. 3. Method as claimed in any one of claims 1 to 2, wherein the generator is a double fed asynchronous generator comprising electronically controlled impedances connected to the rotor windings, said method comprising the step of controlling the electronically controlled impedances connected to the rotor windings during fault conditions in such a way that a certain magnetization of the generator is maintained during fault conditions. 4. A power-grid connected wind turbine generator (G) comprising a wind turbine-driven rotor, a stator, said stator during normal operation being connected to deliver power to the power grid, means (S1) for disconnecting the stator windings from the power grid when a fault is detected and means (S5, S6) for connecting impedances to the stator windings, said impedances being dimensioned to dissipate between 0 and 100% of the power generated by the wind turbine during grid fault conditions and comprising means for maintaining a certain magnetization of the generator during disconnection and means for synchronizing the generator to the grid before reconnection to grid after fault clearance, characterized by the generator (G) being a double fed asynchronous generator comprising a back-to-back converter connected between the rotor and 10 the grid, and that the means (S1) for disconnecting the stator windings from the power grid do not disconnect the connection between the back-to-back converter and the power grid. 5. The generator as claimed in claim 4, wherein the means (S1) for disconnecting the stator windings from the power grid and the means (S5, S6) for connecting the stator windings to the impedances comprise contactors. 6. The generator as claimed in claim 4, wherein the means for disconnecting the stator windings from the power grid and the means for connecting the stator windings to the impedances comprise power electronic switches. 7. The generator as claimed in any one of claims 4 to 6, comprising contactors (S2, S3, S4) and/or power electronic switches for connecting the impedances and/or the stator windings in star and/or delta configuration. 8. The generator as claimed in claim 7, comprising electronically controlled impedances connected to the rotor windings. The present invention relates to a method and an controlling a power grid connected wind terbine generator during grid faults,the staker windings of the wind turbine generator are disconnected from the wind turbine during grid fault condition are connected to the swtalor windings.In this way a certain megnetisation of the generator can be maintained and after removal of the grid fault condition the generator is synchronished to the power grid and the impedence are disconnected and the stator windings are reconnected to the power grid, In thisw way it is possible to keep the wind turbine generotor at least party magnitished during grid faults and thus ready for delivering power to the power grid,as soon as the grid voltage is re-established after the fault. (It is suggested that Figure 1 be published with the Abstract)

Full Text

TURBINE GENERATOR DURING GRID FAULTS AND A POWER GRID
CONNECTED WIND TURBINE GENERATOR
TECHNICAL FIELD
The present invention relates to a method for controlling a power-grid
connected wind turbine generator during grid faults and a power grid connected
wind turbine generator.
BACKGROUND ART
In wind turbine systems it is known to provide some kind of control of the
wind turbine during grid faults. However, the general concept of such control
apparatus aims at stopping the wind turbine by pitching the blades of the wind
turbine out of the wind and disconnecting the generator from the grid. After a
certain time, when the grid voltage has been re-established, the wind turbine is
started up in the normal fashion in order to deliver power to the grid, and the time
from disconnection to restart of the wind turbine has traditionally been in the
order of 1-10 minutes. The short circuit current contribution from the wind turbine
generator has generally been limited to last approximately 40-50 ms, after which
the current from the wind turbine generator has been zero. Thus, the wind
turbine generator does not contribute to the re-establishment of the grid voltage
and does not contribute to the short circuit current in the grid over a longer period
of time, which may be necessary in order to activate the grid protection means
for disconnecting the faulty parts of the power grid.

2
From EP-0 984 552 it is known to disconnect the stator windings of a
generator from the power grid when a fault is detected and to connect
impedances to the stator windings for dissipating the power generated during
such grid fault conditions, and to maintain a certain magnetization of the
generator. After clearance of the fault the generator is resynchronized to the
power grid and the stator windings are reconnected to the power grid.
DISCLOSURE OF THE INVENTION
It is the object of the present invention to provide a method for controlling
a power grid connected wind turbine generator during grid faults of the kind
referred to above, with which it is possible to keep the wind turbine generator
magnetized and ready for delivering power to the power grid, as soon as the grid
voltage is re-established after the fault, and this object is achieved with a method
for controlling a power-grid connected wind turbine generator during grid faults of
said kind.
Accordingly, the present invention provides a method for controlling a
power-grid connected wind turbine generator during grid faults, said generator
comprising a wind turbine driven rotor and a normally grid-connected stator, and
during normal operation being connected to deliver power to the power grid, and
the generator is a double-fed asynchronous generator, the rotor windings being
normally connected to the grid through a back-to-back converter for transferring
energy between the rotor windings and the grid in a controlled manner, said
method comprising the steps of:

2A
a) disconnecting the stator windings from the power grid when a fault is
detected,
b) connecting the stator windings to impedances for dissipating between
0 and 100% of the power generated by the wind turbine during grid fault
condition,
c) maintaining a certain magnetization of the generator during grid fault
conditions, and
d) after removal of the grid fault condition, synchronizing the generator to the
power grid and disconnecting the impedances and reconnecting the stator
windings to the power grid,
characterized by comprising the step of keeping the back-to-back
converter connected to the grid during fault condition and controlling the back-to-
back converter to deliver a controlled short-circuit contribution to the grid during
fault condition.
With this method, it is possible to dissipate the generated power in the
impedances, whenever the generated power cannot be delivered to the power
grid, due to fault conditions, such as low voltages or zero voltages on the power
grid, and as soon as the power grid is re-established, the wind turbine generator
can be re-connected to deliver the power to the power grid almost
instantaneously.
The invention also provides a power-grid connected wind turbine
generator comprising a wind turbine-driven rotor, a stator, said stator during
normal operation being connected to deliver power to the power grid, means for

2B
disconnecting the stator windings from the power grid when a fault is detected
and means for connecting impedances to the stator windings, said impedances
being dimensioned to dissipate between 0 and 100% of the power generated by
the wind turbine during grid fault conditions and comprising means for
maintaining a certain magnetization of the generator during disconnection and
means for synchronizing the generator to the grid before reconnection to grid
after fault clearance, characterized by the generator being a double fed
asynchronous generator comprising a back-to-back converter connected
between the rotor and the grid, and that the means for disconnecting the stator
windings from the power grid do not disconnect the connection between the
back-to-back converter and the power grid.
Furthermore, the maintained connection between the back-to-back
converter and the grid provides the possibility of delivering a certain power to the
grid, thus contributing to the short circuit current in the grid necessary to activate
the grid protection means for disconnecting the faulty parts of the power grid.
Preferred embodiments of the method according to the invention and their
advantages will be evident from the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the following detailed part of the present description, the invention will
be explained in more detail with reference to the exemplary embodiments of
different apparatus for implementing the method for controlling a power-grid
connected wind turbine generator during grid faults according to the invention
shown in the drawings, in which -

8
WE CLAIM :
1. Method for controlling a power-grid connected wind turbine generator (G)
during grid faults, said generator (0) comprising a wind turbine driven rotor and a
normally grid-connected stator, and during normal operation being connected to
deliver power to the power grid, and the generator (G) is a double-fed
asynchronous generator (G), the rotor windings being normally connected to the
grid through a back-to-back converter for transferring energy between the rotor
windings and the grid in a controlled manner, said method comprising the steps
of:
a) disconnecting the stator windings from the power grid when a fault is
detected,
b) connecting the stator windings to impedances for dissipating between 0
and 100% of the power generated by the wind turbine during grid fault
condition,
c) maintaining a certain magnetization of the generator during grid fault
conditions, and
d) after removal of the grid fault condition, synchronizing the generator to the
power grid and disconnecting the impedances and reconnecting the stator
windings to the power grid,
characterized by comprising the step of keeping the back-to-back
converter connected to the grid during fault condition and controlling the back-to-
back converter to deliver a controlled short-circuit contribution to the grid during
fault condition.

9
2. Method as claimed in claim 1, comprising the step of connecting the
impedances in star or delta configuration and connecting the stator windings in
star or delta configuration, all dependent on measured parameters for the wind
turbine.
3. Method as claimed in any one of claims 1 to 2, wherein the generator is a
double fed asynchronous generator comprising electronically controlled
impedances connected to the rotor windings, said method comprising the step of
controlling the electronically controlled impedances connected to the rotor
windings during fault conditions in such a way that a certain magnetization of the
generator is maintained during fault conditions.
4. A power-grid connected wind turbine generator (G) comprising a wind
turbine-driven rotor, a stator, said stator during normal operation being
connected to deliver power to the power grid, means (S1) for disconnecting the
stator windings from the power grid when a fault is detected and means (S5, S6)
for connecting impedances to the stator windings, said impedances being
dimensioned to dissipate between 0 and 100% of the power generated by the
wind turbine during grid fault conditions and comprising means for maintaining a
certain magnetization of the generator during disconnection and means for
synchronizing the generator to the grid before reconnection to grid after fault
clearance, characterized by the generator (G) being a double fed asynchronous
generator comprising a back-to-back converter connected between the rotor and

10
the grid, and that the means (S1) for disconnecting the stator windings from the
power grid do not disconnect the connection between the back-to-back converter
and the power grid.
5. The generator as claimed in claim 4, wherein the means (S1) for
disconnecting the stator windings from the power grid and the means (S5, S6)
for connecting the stator windings to the impedances comprise contactors.
6. The generator as claimed in claim 4, wherein the means for disconnecting
the stator windings from the power grid and the means for connecting the stator
windings to the impedances comprise power electronic switches.
7. The generator as claimed in any one of claims 4 to 6, comprising
contactors (S2, S3, S4) and/or power electronic switches for connecting the
impedances and/or the stator windings in star and/or delta configuration.
8. The generator as claimed in claim 7, comprising electronically controlled
impedances connected to the rotor windings.

The present invention relates to a method and an controlling a power grid connected wind terbine generator during grid faults,the staker windings of the wind turbine generator are disconnected from the wind turbine during grid fault condition are connected to the swtalor windings.In this way a certain megnetisation of the generator can be maintained and after removal of the grid fault condition the generator is synchronished to the power grid and the impedence are disconnected and the stator windings are reconnected to the power grid, In thisw way it is possible to keep the wind turbine generotor at least party magnitished during grid faults and thus ready for delivering power to the power grid,as soon as the grid voltage is re-established after the fault.
(It is suggested that Figure 1 be published with the Abstract)

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Patent Number

219328

Indian Patent Application Number

01547/KOLNP/2005

PG Journal Number

18/2008

Publication Date

02-May-2008

Grant Date

30-Apr-2008

Date of Filing

04-Aug-2005

Name of Patentee

VESTAS WIND SYSTEMS A/S

Applicant Address

SEMED SORENSENS VEJ 5, DK-6950, RINGKOBOING, DENMARK

Inventors:

#	Inventor's Name	Inventor's Address
1	NIELSEN JHON GODSK	GAMMEL OUSTRUPVEJ 25, DK-8544, MORKE, DENMARK

PCT International Classification Number

H02P 9/10.

PCT International Application Number

PCT/DK2003/000078

PCT International Filing date

2003-02-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	PCT/DK2003/000078	2003-02-07	IB