U.S. patent application number 12/821814 was filed with the patent office on 2011-06-16 for overspeed protection system and method.
Invention is credited to Friedrich LOH, Detlef MENKE.
Application Number | 20110142634 12/821814 |
Document ID | / |
Family ID | 44143124 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110142634 |
Kind Code |
A1 |
MENKE; Detlef ; et
al. |
June 16, 2011 |
OVERSPEED PROTECTION SYSTEM AND METHOD
Abstract
An overspeed protection system for a wind turbine having a hub
and at least one rotor blade mounted to the hub includes a rotation
sensor adapted for measuring a rotor speed of said wind turbine; a
comparator connected to the rotation sensor and adapted for
comparing the measured rotor speed with a predetermined threshold
value of the rotor speed wherein the comparator outputs a signal
indicative of the comparison; and an auxiliary pitch drive
controller connected to the comparator and adapted to receive the
signal indicative of the comparison, the auxiliary pitch drive
controller being further adapted for controlling a pitch drive unit
of the wind turbine independently of a main turbine controller and,
if the threshold value is exceeded, to adjust a pitch angle of the
rotor blade of the wind turbine so that aerodynamic braking of the
wind turbine is effected.
Inventors: |
MENKE; Detlef; (Lotte,
DE) ; LOH; Friedrich; (Schuettorf, DE) |
Family ID: |
44143124 |
Appl. No.: |
12/821814 |
Filed: |
June 23, 2010 |
Current U.S.
Class: |
416/46 ;
416/1 |
Current CPC
Class: |
F05B 2270/327 20130101;
Y02E 10/72 20130101; F03D 7/0252 20130101; F03D 7/0224 20130101;
Y02E 10/723 20130101; F05B 2270/1011 20130101; F03D 7/0268
20130101; F03D 7/047 20130101 |
Class at
Publication: |
416/46 ;
416/1 |
International
Class: |
F04D 29/18 20060101
F04D029/18; F04D 27/00 20060101 F04D027/00 |
Claims
1. An overspeed protection system for a wind turbine having a hub
and at least one rotor blade mounted to said hub, comprising: a
rotation sensor adapted for measuring a rotor speed of said wind
turbine; a comparator connected to said rotation sensor and adapted
for comparing the measured rotor speed with a predetermined
threshold value of said rotor speed wherein the comparator outputs
a signal indicative of said comparison; and, an auxiliary pitch
drive controller connected to said comparator and adapted to
receive said signal indicative of the comparison, the auxiliary
pitch drive controller being further adapted for controlling a
pitch drive unit of the wind turbine independently of a main
turbine controller and, if said threshold value is exceeded, to
adjust a pitch angle of the rotor blade of the wind turbine so that
aerodynamic braking of the wind turbine is effected.
2. The overspeed protection system according to claim 1, wherein
the system is adapted to be installed in the hub of said wind
turbine and to operate self-sustained therein.
3. The overspeed protection system according to claim 1, wherein
the rotation sensor is selected from the group consisting of a
pendulum device, a gravitational force detection element, an
acceleration sensor, a dynamo-electric generator, an optical
detector, and any combination thereof.
4. The overspeed protection system according to claim 3, wherein
the rotation sensor is a pendulum device adapted to oscillate in
accordance with the rotor speed.
5. The overspeed protection system according to claim 4, wherein
the pendulum device comprises a pendulum coupled to an electric
switch such that the switch is operated in accordance with the
rotor speed.
6. The overspeed protection system according to claim 5, further
comprising a low-pass filter adapted for low-pass filtering an
output signal of the electric switch.
7. The overspeed protection system according to claim 6, further
wherein the low-pass filter has a cut-off frequency which is in the
range from about 50% to about 150% of the rotor speed threshold
value.
8. The overspeed protection system according to claim 1, wherein
the system is connectable to an auxiliary power supply located at
the hub.
9. The overspeed protection system according to claim 8, wherein
the auxiliary power supply is selected from the group consisting of
a battery, a capacitor, an electric generator, a solar panel, and
any combination thereof.
10. The overspeed protection system according to claim 1, further
comprising a switching device adapted to connect the pitch drive
unit of the wind turbine to the auxiliary pitch drive controller,
the switching device being activated if said rotor speed threshold
value is exceeded.
11. The overspeed protection system according to claim 1, wherein
the pitch drive unit comprises at least one electric pitch motor
and said auxiliary pitch drive controller is adapted to control
said electric pitch motor.
12. A wind turbine, comprising: a rotatable hub and at least one
rotor blade mounted to said hub, wherein a pitch angle of said
rotor blade can be adjusted by a pitch drive system; a speed sensor
adapted for measuring a rotational speed of said wind turbine; a
detection unit connected to said speed sensor and adapted for
detecting if the measured rotational speed exceeds a predetermined
threshold value; and, an auxiliary pitch drive controller adapted
to adjust a pitch angle of said rotor blade to effect aerodynamic
braking of the wind turbine if said threshold value is exceeded,
the auxiliary pitch drive controller being located within said hub
and operable independent of wind turbine components not located in
or at the hub.
13. The wind turbine according to claim 12, wherein the rotation
sensor is a pendulum device adapted to oscillate in accordance with
the rotor speed, the pendulum being coupled to an electric switch
such that the switch is operated in accordance with the rotor
speed.
14. The wind turbine according to claim 13, further comprising a
low-pass filter adapted for low-pass filtering an output signal of
the electric switch, the low-pass filter having a cut-off frequency
which is in the range from about 50% to about 150% of the
rotational speed threshold value.
15. The wind turbine according to claim 12, wherein the auxiliary
pitch drive controller is connected to an auxiliary power supply
located at the hub via a switching device, the switching device
being operated upon exceeding of the rotational speed threshold
value.
16. The wind turbine according to claim 12, wherein the wind
turbine comprises a plurality of rotor blades and the auxiliary
pitch drive controller is adapted to adjust the pitch angle of each
rotor blade.
17. The wind turbine according to claim 12, wherein the wind
turbine comprises a plurality of rotor blades and a plurality of
auxiliary pitch drive controllers, each rotor blade being connected
to an auxiliary pitch drive controller, each auxiliary pitch drive
controller being adapted to adjust the pitch angle of the rotor
blade to which it is connected.
18. A method for preventing an overspeed condition of a wind
turbine, the method comprising: measuring a rotational speed of a
hub of said wind turbine; comparing the measured rotational speed
with a predetermined threshold value; if the measured rotational
speed exceeds the threshold value, operating an auxiliary pitch
drive controller independent of a main turbine controller so that a
pitch angle of at least one rotor blade of the wind turbine is
adjusted to effect aerodynamic braking of the wind turbine.
19. The method according to claim 18, wherein the gradient of an
acceleration signal is evaluated for determining the rotational
speed.
20. The method according to claim 18, wherein an overspeed relais
is operated on the basis of the measured rotational speed, the
overspeed relais connecting the auxiliary pitch drive controller to
a pitch drive unit of said rotor blade.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter described herein relates generally to
methods and systems for controlling the operation of a wind
turbine, and more particularly, to methods and systems for
preventing an overspeed condition of a wind turbine.
[0002] Generally, a wind turbine includes a turbine that has a
rotor that includes a rotatable hub assembly having multiple
blades. The blades transform wind energy into a mechanical
rotational torque that drives one or more generators via the rotor.
The generators are sometimes, but not always, rotationally coupled
to the rotor through a gearbox. The gearbox steps up the inherently
low rotational speed of the rotor for the generator to efficiently
convert the rotational mechanical energy to electrical energy,
which is fed into a utility grid via at least one electrical
connection. Gearless direct drive wind turbines also exist. The
rotor, generator, gearbox and other components are typically
mounted within a housing, or nacelle, that is positioned on top of
a base that may be a truss or tubular tower.
[0003] Some wind turbine configurations include double-fed
induction generators (DFIGs). Such configurations may also include
power converters that are used to convert a frequency of generated
electric power to a frequency substantially similar to a utility
grid frequency. Moreover, such converters, in conjunction with the
DFIG, also transmit electric power between the utility grid and the
generator as well as transmit generator excitation power to a wound
generator rotor from one of the connections to the electric utility
grid connection. Alternatively, some wind turbine configurations
include, but are not limited to, alternative types of induction
generators, permanent magnet (PM) synchronous generators and
electrically-excited synchronous generators and switched reluctance
generators. These alternative configurations may also include power
converters that are used to convert the frequencies as described
above and transmit electrical power between the utility grid and
the generator.
[0004] Known wind turbines have a plurality of mechanical and
electrical components. Each electrical and/or mechanical component
may have independent or different operating limitations, such as
current, voltage, power, and/or temperature limits, than other
components. Moreover, known wind turbines typically are designed
and/or assembled with predefined rated power limits. To operate
within such rated power limits, the electrical and/or mechanical
components may be operated with large margins for the operating
limitations. Such operation may result in inefficient wind turbine
operation, and a power generation capability of the wind turbine
may be underutilized.
[0005] A particular operating limitation of a wind turbine is a
maximum rotational speed of the wind rotor. This threshold value of
the rotor speed typically depends on the layout of the entire wind
turbine. In order to maintain safe operating conditions, the
maximum rotor speed should not be exceeded. Therefore, braking of
the wind rotor is usually initiated if an overspeed condition is
detected, i.e. if the rotor speed exceeds a threshold value.
Typically, this threshold value is lower or equal to the maximum
allowable rotor speed.
[0006] For larger wind turbine, the rotor may not be stopped by
mechanical rotor brakes alone since the torque generated from the
wind is too high. Therefore, aerodynamic braking of the wind
turbine is used in these cases to reduce the rotor speed.
Aerodynamic braking involves adjustment of the pitch angles of the
rotor blades. For example, the pitch angles may be adjusted so that
only a smaller fraction of power is captured from the incoming
wind. Thus, the internal friction and the electrical load from the
generator will slow down the rotor speed of the wind turbine.
Typically, the aerodynamic braking is controlled by the wind
turbine controller which is an electronic control device adapted to
control the various processes of a wind turbine.
[0007] In view of the above, it would be desirable to provide a
system capable of preventing a turbine from entering an overspeed
condition even in cases where the internal communication system of
the wind turbine is corrupted and the electric or electronic system
of the wind turbine is damaged.
BRIEF DESCRIPTION OF THE INVENTION
[0008] In view of the above, an overspeed protection system for a
wind turbine having a hub and at least one rotor blade mounted to
said hub includes a rotation sensor adapted for measuring a rotor
speed of the wind turbine; a comparator connected to the rotation
sensor and adapted for comparing the measured rotor speed with a
predetermined threshold value of the rotor speed wherein the
comparator outputs a signal indicative of the comparison; and, an
auxiliary pitch drive controller connected to the comparator and
adapted to receive the signal indicative of the comparison, the
auxiliary pitch drive controller being further adapted for
controlling a pitch drive unit of the wind turbine independently of
a main turbine controller and, if the threshold value is exceeded,
to adjust a pitch angle of the rotor blade of the wind turbine so
that aerodynamic braking of the wind turbine is effected.
[0009] According to a further embodiment, a wind turbine includes a
rotatable hub and at least one rotor blade mounted to the hub,
wherein a pitch angle of the rotor blade can be adjusted by a pitch
drive system; a speed sensor adapted for measuring a rotational
speed of the wind turbine; a detection unit connected to the speed
sensor and adapted for detecting if the measured rotational speed
exceeds a predetermined threshold value; and, an auxiliary pitch
drive controller adapted to adjust a pitch angle of the rotor blade
to effect aerodynamic braking of the wind turbine if the threshold
value is exceeded, the auxiliary pitch drive controller being
located within the hub and operable independent of wind turbine
components not located in or at the hub.
[0010] According to another embodiment, a method for preventing an
overspeed condition of a wind turbine includes measuring a
rotational speed of a hub of the wind turbine; comparing the
measured rotational speed with a predetermined threshold value; if
the measured rotational speed exceeds the threshold value,
operating an auxiliary pitch drive controller independent of a main
turbine controller so that a pitch angle of at least one rotor
blade of the wind turbine is adjusted to effect aerodynamic braking
of the wind turbine.
[0011] Further aspects, advantages and features of the present
invention are apparent from the dependent claims, the description
and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A full and enabling disclosure including the best mode
thereof, to one of ordinary skill in the art, is set forth more
particularly in the remainder of the specification, including
reference to the accompanying figures wherein:
[0013] FIG. 1 is a perspective view of a portion of an exemplary
wind turbine.
[0014] FIG. 2 is a schematic view of an exemplary electrical and
control system suitable for use with the wind turbine shown in FIG.
1.
[0015] FIG. 3 is a block diagram showing a detection of a sensor
signal from a rotation sensor and an adjustment of a pitch angle by
means of a pitch drive unit, according to a typical embodiment;
[0016] FIG. 4 is another block diagram illustrating an overspeed
protection system into acting with a main turbine controller, the
wind turbine, according to another typical embodiment;
[0017] FIG. 5 is a block diagram illustrating a main turbine
controller of the wind turbine interacting with an overspeed
protection system, according to a typical embodiment;
[0018] FIG. 6 is a circuit diagram of a rotation sensor connected
to a filter unit for providing a control signal for the overspeed
protection system;
[0019] FIG. 7 is a front view of a rotor of a wind turbine for
illustrating the action of the gravitational force on a rotation
sensor provided as a pendulum, according to another typical
embodiment; and
DETAILED DESCRIPTION OF THE INVENTION
[0020] Reference will now be made in detail to the various
embodiments, one or more examples of which are illustrated in each
figure. Each example is provided by way of explanation and is not
meant as a limitation. For example, features illustrated or
described as part of one embodiment can be used on or in
conjunction with other embodiments to yield yet further
embodiments. It is intended that the present disclosure includes
such modifications and variations.
[0021] As used herein, the term "blade" is intended to be
representative of any device that provides a reactive force when in
motion relative to a surrounding fluid. As used herein, the term
"wind turbine" is intended to be representative of any device that
generates rotational energy from wind energy, and more
specifically, converts kinetic energy of wind into mechanical
energy. As used herein, the term "wind generator" is intended to be
representative of any wind turbine that generates electrical power
from rotational energy generated from wind energy, and more
specifically, converts mechanical energy converted from kinetic
energy of wind to electrical power.
[0022] FIG. 1 is a perspective view of a portion of an exemplary
wind turbine 100. Wind turbine 100 includes a nacelle 102 housing a
generator (not shown in FIG. 1). Nacelle 102 is mounted on a tower
104 (a portion of tower 104 being shown in FIG. 1). Tower 104 may
have any suitable height that facilitates operation of wind turbine
100 as described herein. Wind turbine 100 also includes a rotor 106
that includes three blades 108 attached to a rotating hub 110.
Alternatively, wind turbine 100 includes any number of blades 108
that facilitates operation of wind turbine 100 as described herein.
In the exemplary embodiment, wind turbine 100 includes a gearbox
(not shown in FIG. 1) operatively coupled to rotor 106 and a
generator (not shown in FIG. 1).
[0023] FIG. 2 is a schematic view of an exemplary electrical and
control system 200 that may be used with wind turbine 100. Rotor
106 includes blades 108 coupled to hub 110. Rotor 106 also includes
a low-speed shaft 112 rotatably coupled to hub 110. Low-speed shaft
112 is coupled to a step-up gearbox 114 that is configured to step
up the rotational speed of low-speed shaft 112 and transfer that
speed to a high-speed shaft 116. In the exemplary embodiment,
gearbox 114 has a step-up ratio of approximately 70:1. For example,
low-speed shaft 112 rotating at approximately 20 revolutions per
minute (rpm) coupled to gearbox 114 with an approximately 70:1
step-up ratio generates a speed for high-speed shaft 116 of
approximately 1400 rpm. Alternatively, gearbox 114 has any suitable
step-up ratio that facilitates operation of wind turbine 100 as
described herein. As a further alternative, wind turbine 100
includes a direct-drive generator that is rotatably coupled to
rotor 106 without any intervening gearbox.
[0024] High-speed shaft 116 is rotatably coupled to generator 118.
In the exemplary embodiment, generator 118 is a wound rotor,
three-phase, double-fed induction (asynchronous) generator (DFIG)
that includes a generator stator 120 magnetically coupled to a
generator rotor 122. In an alternative embodiment, generator rotor
122 includes a plurality of permanent magnets in place of rotor
windings.
[0025] Electrical and control system 200 includes a turbine
controller 202. Turbine controller 202 includes at least one
processor and a memory, at least one processor input channel, at
least one processor output channel, and may include at least one
computer (none shown in FIG. 2). As used herein, the term computer
is not limited to integrated circuits referred to in the art as a
computer, but broadly refers to a processor, a microcontroller, a
microcomputer, a programmable logic controller (PLC), an
application specific integrated circuit, and other programmable
circuits (none shown in FIG. 2), and these terms are used
interchangeably herein. In the exemplary embodiment, memory may
include, but is not limited to, a computer-readable medium, such as
a random access memory (RAM) (none shown in FIG. 2). Alternatively,
one or more storage devices, such as a floppy disk, a compact disc
read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a
digital versatile disc (DVD) (none shown in FIG. 2) may also be
used. Also, in the exemplary embodiment, additional input channels
(not shown in FIG. 2) may be, but are not limited to, computer
peripherals associated with an operator interface such as a mouse
and a keyboard (neither shown in FIG. 2). Further, in the exemplary
embodiment, additional output channels may include, but are not
limited to, an operator interface monitor (not shown in FIG.
2).
[0026] Processors for turbine controller 202 process information
transmitted from a plurality of electrical and electronic devices
that may include, but are not limited to, voltage and current
transducers. RAM and/or storage devices store and transfer
information and instructions to be executed by the processor. RAM
and/or storage devices can also be used to store and provide
temporary variables, static (i.e., non-changing) information and
instructions, or other intermediate information to the processors
during execution of instructions by the processors. Instructions
that are executed include, but are not limited to, resident
conversion and/or comparator algorithms. The execution of sequences
of instructions is not limited to any specific combination of
hardware circuitry and software instructions.
[0027] Generator stator 120 is electrically coupled to a stator
synchronizing switch 206 via a stator bus 208. In an exemplary
embodiment, to facilitate the DFIG configuration, generator rotor
122 is electrically coupled to a bi-directional power conversion
assembly 210 via a rotor bus 212. Alternatively, generator rotor
122 is electrically coupled to rotor bus 212 via any other device
that facilitates operation of electrical and control system 200 as
described herein. As a further alternative, electrical and control
system 200 is configured as a full power conversion system (not
shown) that includes a full power conversion assembly (not shown in
FIG. 2) similar in design and operation to power conversion
assembly 210 and electrically coupled to generator stator 120. The
full power conversion assembly facilitates channeling electric
power between generator stator 120 and an electric power
transmission and distribution grid (not shown). In the exemplary
embodiment, stator bus 208 transmits three-phase power from
generator stator 120 to stator synchronizing switch 206. Rotor bus
212 transmits three-phase power from generator rotor 122 to power
conversion assembly 210. In the exemplary embodiment, stator
synchronizing switch 206 is electrically coupled to a main
transformer circuit breaker 214 via a system bus 216. In an
alternative embodiment, one or more fuses (not shown) are used
instead of main transformer circuit breaker 214. In another
embodiment, neither fuses nor main transformer circuit breaker 214
is used.
[0028] Power conversion assembly 210 includes a rotor filter 218
that is electrically coupled to generator rotor 122 via rotor bus
212. A rotor filter bus 219 electrically couples rotor filter 218
to a rotor-side power converter 220, and rotor-side power converter
220 is electrically coupled to a line-side power converter 222.
Rotor-side power converter 220 and line-side power converter 222
are power converter bridges including power semiconductors (not
shown). In the exemplary embodiment, rotor-side power converter 220
and line-side power converter 222 are configured in a three-phase,
pulse width modulation (PWM) configuration including insulated gate
bipolar transistor (IGBT) switching devices (not shown in FIG. 2)
that operate as known in the art. Alternatively, rotor-side power
converter 220 and line-side power converter 222 have any
configuration using any switching devices that facilitate operation
of electrical and control system 200 as described herein. Power
conversion assembly 210 is coupled in electronic data communication
with turbine controller 202 to control the operation of rotor-side
power converter 220 and line-side power converter 222.
[0029] In the exemplary embodiment, a line-side power converter bus
223 electrically couples line-side power converter 222 to a line
filter 224. Also, a line bus 225 electrically couples line filter
224 to a line contactor 226. Moreover, line contactor 226 is
electrically coupled to a conversion circuit breaker 228 via a
conversion circuit breaker bus 230. In addition, conversion circuit
breaker 228 is electrically coupled to main transformer circuit
breaker 214 via system bus 216 and a connection bus 232.
Alternatively, line filter 224 is electrically coupled to system
bus 216 directly via connection bus 232 and includes any suitable
protection scheme (not shown) configured to account for removal of
line contactor 226 and conversion circuit breaker 228 from
electrical and control system 200. Main transformer circuit breaker
214 is electrically coupled to an electric power main transformer
234 via a generator-side bus 236. Main transformer 234 is
electrically coupled to a grid circuit breaker 238 via a
breaker-side bus 240. Grid circuit breaker 238 is connected to the
electric power transmission and distribution grid via a grid bus
242. In an alternative embodiment, main transformer 234 is
electrically coupled to one or more fuses (not shown), rather than
to grid circuit breaker 238, via breaker-side bus 240. In another
embodiment, neither fuses nor grid circuit breaker 238 is used, but
rather main transformer 234 is coupled to the electric power
transmission and distribution grid via breaker-side bus 240 and
grid bus 242.
[0030] In the exemplary embodiment, rotor-side power converter 220
is coupled in electrical communication with line-side power
converter 222 via a single direct current (DC) link 244.
Alternatively, rotor-side power converter 220 and line-side power
converter 222 are electrically coupled via individual and separate
DC links (not shown in FIG. 2). DC link 244 includes a positive
rail 246, a negative rail 248, and at least one capacitor 250
coupled between positive rail 246 and negative rail 248.
Alternatively, capacitor 250 includes one or more capacitors
configured in series and/or in parallel between positive rail 246
and negative rail 248.
[0031] Turbine controller 202 is configured to receive a plurality
of voltage and electric current measurement signals from a first
set of voltage and electric current sensors 252. Moreover, turbine
controller 202 is configured to monitor and control at least some
of the operational variables associated with wind turbine 100. In
the exemplary embodiment, each of three voltage and electric
current sensors 252 are electrically coupled to each one of the
three phases of grid bus 242. Alternatively, voltage and electric
current sensors 252 are electrically coupled to system bus 216. As
a further alternative, voltage and electric current sensors 252 are
electrically coupled to any portion of electrical and control
system 200 that facilitates operation of electrical and control
system 200 as described herein. As a still further alternative,
turbine controller 202 is configured to receive any number of
voltage and electric current measurement signals from any number of
voltage and electric current sensors 252 including, but not limited
to, one voltage and electric current measurement signal from one
transducer.
[0032] As shown in FIG. 2, electrical and control system 200 also
includes a converter controller 262 that is configured to receive a
plurality of voltage and electric current measurement signals. For
example, in one embodiment, converter controller 262 receives
voltage and electric current measurement signals from a second set
of voltage and electric current sensors 254 coupled in electronic
data communication with stator bus 208. Converter controller 262
receives a third set of voltage and electric current measurement
signals from a third set of voltage and electric current sensors
256 coupled in electronic data communication with rotor bus 212.
Converter controller 262 also receives a fourth set of voltage and
electric current measurement signals from a fourth set of voltage
and electric current sensors 264 coupled in electronic data
communication with conversion circuit breaker bus 230. Second set
of voltage and electric current sensors 254 is substantially
similar to first set of voltage and electric current sensors 252,
and fourth set of voltage and electric current sensors 264 is
substantially similar to third set of voltage and electric current
sensors 256. Converter controller 262 is substantially similar to
turbine controller 202 and is coupled in electronic data
communication with turbine controller 202. Moreover, in the
exemplary embodiment, converter controller 262 is physically
integrated within power conversion assembly 210. Alternatively,
converter controller 262 has any configuration that facilitates
operation of electrical and control system 200 as described
herein.
[0033] During operation, wind impacts blades 108 and blades 108
transform wind energy into a mechanical rotational torque that
rotatably drives low-speed shaft 112 via hub 110. Low-speed shaft
112 drives gearbox 114 that subsequently steps up the low
rotational speed of low-speed shaft 112 to drive high-speed shaft
116 at an increased rotational speed. High speed shaft 116
rotatably drives generator rotor 122. A rotating magnetic field is
induced by generator rotor 122 and a voltage is induced within
generator stator 120 that is magnetically coupled to generator
rotor 122. Generator 118 converts the rotational mechanical energy
to a sinusoidal, three-phase alternating current (AC) electrical
energy signal in generator stator 120. The associated electrical
power is transmitted to main transformer 234 via stator bus 208,
stator synchronizing switch 206, system bus 216, main transformer
circuit breaker 214 and generator-side bus 236. Main transformer
234 steps up the voltage amplitude of the electrical power and the
transformed electrical power is further transmitted to a grid via
breaker-side bus 240, grid circuit breaker 238 and grid bus
242.
[0034] In the exemplary embodiment, a second electrical power
transmission path is provided. Electrical, three-phase, sinusoidal,
AC power is generated within generator rotor 122 and is transmitted
to power conversion assembly 210 via rotor bus 212. Within power
conversion assembly 210, the electrical power is transmitted to
rotor filter 218 and the electrical power is modified for the rate
of change of the PWM signals associated with rotor-side power
converter 220. Rotor-side power converter 220 acts as a rectifier
and rectifies the sinusoidal, three-phase AC power to DC power. The
DC power is transmitted into DC link 244. Capacitor 250 facilitates
mitigating DC link 244 voltage amplitude variations by facilitating
mitigation of a DC ripple associated with AC rectification.
[0035] The DC power is subsequently transmitted from DC link 244 to
line-side power converter 222 and line-side power converter 222
acts as an inverter configured to convert the DC electrical power
from DC link 244 to three-phase, sinusoidal AC electrical power
with pre-determined voltages, currents, and frequencies. This
conversion is monitored and controlled via converter controller
262. The converted AC power is transmitted from line-side power
converter 222 to system bus 216 via line-side power converter bus
223 and line bus 225, line contactor 226, conversion circuit
breaker bus 230, conversion circuit breaker 228, and connection bus
232. Line filter 224 compensates or adjusts for harmonic currents
in the electric power transmitted from line-side power converter
222. Stator synchronizing switch 206 is configured to close to
facilitate connecting the three-phase power from generator stator
120 with the three-phase power from power conversion assembly
210.
[0036] Conversion circuit breaker 228, main transformer circuit
breaker 214, and grid circuit breaker 238 are configured to
disconnect corresponding buses, for example, when excessive current
flow may damage the components of electrical and control system
200. Additional protection components are also provided including
line contactor 226, which may be controlled to form a disconnect by
opening a switch (not shown in FIG. 2) corresponding to each line
of line bus 225.
[0037] Power conversion assembly 210 compensates or adjusts the
frequency of the three-phase power from generator rotor 122 for
changes, for example, in the wind speed at hub 110 and blades 108.
Therefore, in this manner, mechanical and electrical rotor
frequencies are decoupled from stator frequency.
[0038] Under some conditions, the bi-directional characteristics of
power conversion assembly 210, and specifically, the bi-directional
characteristics of rotor-side power converter 220 and line-side
power converter 222, facilitate feeding back at least some of the
generated electrical power into generator rotor 122. More
specifically, electrical power is transmitted from system bus 216
to connection bus 232 and subsequently through conversion circuit
breaker 228 and conversion circuit breaker bus 230 into power
conversion assembly 210. Within power conversion assembly 210, the
electrical power is transmitted through line contactor 226, line
bus 225, and line-side power converter bus 223 into line-side power
converter 222. Line-side power converter 222 acts as a rectifier
and rectifies the sinusoidal, three-phase AC power to DC power. The
DC power is transmitted into DC link 244. Capacitor 250 facilitates
mitigating DC link 244 voltage amplitude variations by facilitating
mitigation of a DC ripple sometimes associated with three-phase AC
rectification.
[0039] The DC power is subsequently transmitted from DC link 244 to
rotor-side power converter 220 and rotor-side power converter 220
acts as an inverter configured to convert the DC electrical power
transmitted from DC link 244 to a three-phase, sinusoidal AC
electrical power with pre-determined voltages, currents, and
frequencies. This conversion is monitored and controlled via
converter controller 262. The converted AC power is transmitted
from rotor-side power converter 220 to rotor filter 218 via rotor
filter bus 219 and is subsequently transmitted to generator rotor
122 via rotor bus 212, thereby facilitating sub-synchronous
operation.
[0040] Power conversion assembly 210 is configured to receive
control signals from turbine controller 202. The control signals
are based on sensed conditions or operating characteristics of wind
turbine 100 and electrical and control system 200. The control
signals are received by turbine controller 202 and used to control
operation of power conversion assembly 210. Feedback from one or
more sensors may be used by electrical and control system 200 to
control power conversion assembly 210 via converter controller 262
including, for example, conversion circuit breaker bus 230, stator
bus and rotor bus voltages or current feedbacks via second set of
voltage and electric current sensors 254, third set of voltage and
electric current sensors 256, and fourth set of voltage and
electric current sensors 264. Using this feedback information, and
for example, switching control signals, stator synchronizing switch
control signals and system circuit breaker control (trip) signals
may be generated in any known manner. For example, for a grid
voltage transient with predetermined characteristics, converter
controller 262 will at least temporarily substantially suspend the
IGBTs from conducting within line-side power converter 222. Such
suspension of operation of line-side power converter 222 will
substantially mitigate electric power being channeled through power
conversion assembly 210 to approximately zero.
[0041] A number of embodiments will be explained below. In this
case, identical structural features are identified by identical
reference symbols in the drawings. The structures shown in the
drawings are not depicted true to scale but rather serve only for
the better understanding of the embodiments.
[0042] FIG. 3 is a schematic block diagram of an overspeed
protection system 300 according to a typical embodiment. FIG. 3
depicts components of the rotor of the wind turbine such as the hub
110 having attached at least one rotor blade 108. The hub is
connected to the main shaft 112 which in turn is connected to a
rotation sensor 301.
[0043] According to a typical embodiment the overspeed protection
system 300 may be arranged within the hub 110 of the wind turbine
100. This means that an auxiliary pitch drive controller 303 may be
provided which is adapted for controlling the pitch drive unit 304.
According to a typical embodiment of the present invention, the
auxiliary pitch drive controller 303 is adapted to operate
independently of the main turbine controller 110 in a
self-sustained manner. In case of a failure occurring during the
operation of the wind turbine 100, e.g. if the main controller 202
is not capable of appropriately controlling the rotor speed, the
auxiliary pitch drive controller 303 provides such control.
[0044] The main turbine controller 202 is typically located within
the machine nacelle 102 of the wind turbine 100 and, thus, outside
hub 110. Accordingly, main controller 202 is not rotating together
with the rotor. In case of a failure of the main controller 202,
the auxiliary pitch drive controller 303 installed within hub 110
may take over control functions of the main controller 202 such as,
but not limited to, overspeed protection such that the rotor speed
of the wind turbine 100 is controlled to remain within operational
limits. For such adjustment, the actual rotational speed of the
rotor may be measured independently of rotation detection means
provided for the main wind turbine controller 202. Such independent
rotation measurement may be provided within the hub 110 by means of
a rotation sensor 301 adapted for detecting a gravitational force
direction such as a pendulum unit 514 described herein below with
respect to FIG. 5.
[0045] Thus, according to one embodiment which may be combined with
other embodiments described herein, the overspeed protection system
300 including the rotation sensor 301, the auxiliary pitch drive
controller 303 and an auxiliary power supply 307 for providing the
rotation sensor 301, the auxiliary pitch drive controller 303 and
the pitch drive unit 304 with electrical energy, is completely
installed within the hub 110 of wind turbine 100 and adapted to
function on a self-sustained basis.
[0046] The main shaft 112 is connected to the input of the gear box
114. An output signal of the rotation sensor 301, i.e. a sensor
signal 309 is fed to the auxiliary pitch drive controller 303 which
is used for a pitch control in case of an emergency operation. Such
kind of emergency operation may occur if the main turbine
controller (not shown in FIG. 3) fails or if an energy supply
system for the main turbine controller 202 and/or other components
break down. The auxiliary pitch drive controller 303 is provided
with electrical energy by means of the auxiliary power supply 307,
for example a battery or a capacitor. Typically, wind turbines are
equipped with such auxiliary power supplies to enable operation of
the pitch drive during power outage od in emergency situations.
[0047] As indicated in FIG. 3, an overspeed protection system 300
according to a typical embodiment, includes the auxiliary pitch
drive controller 303, the auxiliary power supply 307 and the pitch
drive unit 304 adapted for adjusting the pitch angle of at least
one rotor blade 108. The rotation sensor 301 which is connected to
the main shaft 112 for detecting a rotational frequency of the
rotor shaft 112, i.e. a signal indicating how many rotations per
minute are presently carried out by the rotor of the wind turbine,
may include, but is not restricted to, a pendulum unit, a
gravitational force detection element, an acceleration sensor, a
dynamo-electric generator, an optical detector, and any combination
thereof.
[0048] The overspeed protection system 300 is configured to provide
a battery-driven shut-down which is independent of a communication
established between a turbine controller, e.g. the main turbine
controller 202 (see FIG. 4) and the pitch drive unit 304. The
auxiliary power supply 307 may be selected from the group
consisting of a battery, a capacitor, in particular an ultracap, an
electrical generator, e.g. driven by the rotor, a solar panel, and
any combination of the foregoing. According to one embodiment, the
auxiliary power supply may be charged or recharged during normal
operation of the wind turbine.
[0049] It is noted here that the entire overspeed protection system
300 may be housed within the hub 110 of the rotor 106 of wind
turbine 100. Furthermore, the rotational frequency of the rotor,
i.e. the actual rotor speed, may be measured by detecting an
acceleration signal provided by an acceleration sensor installed
within the hub 110.
[0050] According to one embodiment, the output signal of the
acceleration sensor may be used for evaluating the rotational
frequency of the rotor. Furthermore, a gradient of the acceleration
signal provided by the acceleration sensor may be evaluated
additionally or alternatively for determining the rotational
frequency. For example, the gradient of the acceleration sensor may
be the first derivative in time of the acceleration signal.
[0051] In order to avoid excess rotor speed, i.e. in order to avoid
that the measured rotational frequency exceeds the permissible
rotational frequency, the auxiliary pitch drive controller 303 is
operated such that the pitch angle of one or more rotor blades 108
is adjusted such that the measured rotational frequency of the
rotor 106 drops below the permissible rotational frequency.
Furthermore, it is possible to adjust the pitch angle of an
individual rotor blade 108 such that the rotor blade 108 assumes a
feathered position. If all rotor blades 108 of the rotor 106 are in
the feathered position, the rotor 106 stops rotating even if
incoming wind impinges onto the blades.
[0052] FIG. 4 is a signal flow diagram illustrating an overspeed
protection system according to a typical embodiment. Reference
numeral 202 indicates the main turbine controller of the wind
turbine 100 which is, inter alia, responsible for adjusting the
individual rotor blades 108 of the rotor by means of respective
pitch drive units 304. Thus, the main turbine controller 202 is
connected to the pitch drive unit 304 of an individual rotor
blade.
[0053] According to a typical embodiment, the pitch angle of an
individual rotor blade 108 may also be adjusted by auxiliary pitch
drive controller 303 which sends a signal representing a rotor
speed threshold value from a memory unit 310 to a comparator 308.
At a second input terminal, the comparator 308 receives the sensor
signal 309 provided by the rotation sensor 301 which is connected
to the main shaft 112. The comparator 308 is adapted for comparing
the measured rotational frequency of the rotor with the
predetermined (e.g. stored in the memory unit 310) threshold value
of the rotational frequency of the rotor and for outputting a
signal 319 indicative of the result of the comparison. The
comparison signal 319 is fed to a switching unit 306 which is
adapted for switching its output between the main turbine
controller 202 and the pitch drive unit 304.
[0054] It is noted here that, in order to ease the explanation of
the drawings, only a schematic block diagram of the overspeed
protection system 300 is shown. The switching unit 306 is provided
for switching between normal operation and "emergency operation".
During normal operation, the main turbine controller 202 is active
and receives a normal operation signal 311. In an emergency case,
e.g. if a rotational frequency of the rotor exceeds the permissible
rotational frequency of the rotor, an overspeed detection signal
312 is sent to the pitch drive unit 304. The pitch drive unit 304
then controls the pitch angle of an individual rotor blade 108 in
accordance with the comparison signal 319 provided by the
comparator 308.
[0055] As both the pitch drive unit 304 and the auxiliary pitch
drive controller 303 together with the comparator 308 are provided
with electrical energy from the auxiliary power supply 307, the
overspeed protection system 300 operates even in case the main
turbine controller 202 or a power supply for the entire wind
turbine control system fails or is switched off.
[0056] Thus it is possible to prevent an overspeed rotation of the
rotor and to provide a safe operation for the wind turbine. In
addition to that, albeit not shown in the drawings, instead of
operating the pitch drive unit 304 such that an excessive rotation
speed of the rotor is prevented, rotor brakes may be operated by
the overspeed protection system 300. Rotor brakes may be provided
such that, in case an overspeed rotation of the rotor is detected,
the main shaft 112 of the rotor is stopped. Thus even in heavy wind
situations, damage to the wind turbine may be avoided.
[0057] The overspeed protection system 300 according to at least
one of the embodiments described herein above, may thus operate as
an emergency system which is an independent back-up system for
providing a safe operation of the wind turbine, i.e. for ensuring
that the actual rotational frequency of the rotor does not exceed
the permissible rotational frequency of the rotor. The pitch drive
unit 304 of the wind turbine 100 may thus be adjusted on the basis
of the detected overspeed.
[0058] FIG. 5 is a schematic block diagram of an overspeed
protection system 300 according to a typical embodiment. As shown
in FIG. 5, a main turbine controller 202 is connected to a pitch
drive switch 313. The pitch drive switch 313 is adapted for
connecting the auxiliary power supply 307 directly to the pitch
drive unit 304. A direct connection of the pitch drive switch 313,
which is controlled by the main turbine controller 202, to the
auxiliary power supply 307 occurs in cases where the main turbine
controller 202 exhibits a failure.
[0059] It is noted here that the connection of the pitch drive unit
304 with the auxiliary power supply 307 is only schematic, i.e. the
connection results in an operation state in which the pitch drive
unit 304 drives the rotor blades 202 in such a position that the
rotor of the wind turbine stops rotating.
[0060] The overspeed detection system 300 in accordance with the
typical embodiment includes the rotation sensor 301, which is based
on the detection of a gravitational force and is detailed in FIG. 6
described below. The rotation sensor 301 and the comparator 308
output a comparison signal 319 which drives the switching unit 306.
The switching unit 306 acts in a similar way as the pitch drive
switch 313 described herein above.
[0061] If an emergency situation occurs, e.g. if the actual
rotational frequency of the rotor exceeds the permissible
rotational frequency of the rotor, the switching unit 306 is
actuated on the basis of the comparison signal 319 such that the
switching unit 306 connects the pitch drive unit 304 to the
auxiliary power supply. Again, this connection results in an
operation state in which the rotor blades are adjusted to assume a
feathered position, i.e. in a position which causes the rotor 106
to stop rotating.
[0062] Thus, a shut-down or at least a speed reduction of the wind
turbine is performed. The switching unit 306 may be provided as an
overspeed relais, which is operated on the basis of the measured
rotational frequency. The overspeed relay connects the pitch drive
unit 304 to the auxiliary pitch drive controller (not shown).
[0063] FIG. 6 is a schematic circuit diagram of an arrangement
adapted for providing a signal which controls the switching unit
306. The system shown in FIG. 6 includes a rotation sensor 301
provided as a pendulum unit 514, and a filter unit 505 including
two resistors 515 and a capacitor 516. The pendulum 514 includes
two switches 520, 521 driven by the gravitational force acting on
the pendulum unit 514.
[0064] The pendulum unit 514 acts as a gravitational force
detection element adapted for detecting a change rate in a
gravitational force direction. The pendulum unit 514 therefore
includes a weight held by a bar such that the axis of the bar
approximately corresponds to the direction of the gravitational
force. Another end of the bar may be mounted at a shaft rotatably
arranged within the hub of the wind turbine. The shaft, which is
rotating as the rotor of the wind turbine rotates, may drive at
least one switching unit. The at least one switching unit may
output a sensor signal 509 which is related to the rotation of the
shaft, and thus is related to the rotation of the rotor of the wind
turbine. The switching unit, for example, may be designed such that
it outputs a single pulse for each full rotation of the rotor. The
rotational frequency of the rotor of the wind turbine is then
evaluated from the detected change rate in the gravitational force
direction. The rotational frequency may be detected by determining
the gravitation sensor output signal 509, as indicated in FIG. 6.
From the measured rotational frequency a possible overspeed
condition may be detected.
[0065] A voltage source 518 is connected via the switches 520, 521
to the filter unit 505, i.e. a first (+) terminal of the voltage
supply source 518 is connected to a first pendulum switch 520,
wherein a (-) terminal of the voltage supply source 518 is
connected to a second pendulum switch 521.
[0066] As shown in FIG. 6, the sensor signal 509 is provided as a
polarity reversal voltage corresponding to the change rate of the
detected gravitational force direction measured by the
gravitational sensor operated as the pendulum unit 514. Thus the
rotation sensor 301 indicated in FIG. 6 provides one voltage
reversal per one full rotation of the rotor, i.e. during one full
rotation of the rotor the sensor signal successively assumes the
voltage of the voltage supply source 518, the reversed voltage of
the voltage supply source 518, and the voltage of the voltage
supply source 518, in this order. In accordance with the rotational
frequency of the rotor 106, a frequency f.sub.out of the sensor
signal 509 is applied at the filter unit 505. The filter unit has a
cut-off frequency which is given by the following equation:
f.sub.filter,cut-off=1/(2.pi.RC)=f.sub.limit
[0067] The relation of the actual rotational frequency of the rotor
f.sub.out with respect to the cut-off frequency of the filter
f.sub.limit determines the filter unit output signal 517, if the
following relation holds:
f.sub.out<f.sub.limit
[0068] This means that the filter unit output signal 517
corresponds approximately to the amplitude of the voltage provided
by the voltage supply source 518. If, however, the frequency
f.sub.out of the sensor signal 509 is equal to or exceeds the
filter cut-off frequency f.sub.limit, the amplitude of the filter
unit output signal 517 drops to a lower value than the amplitude of
the voltage supply source. Typically, the filter unit output signal
517 amounts to about 70% of the sensor signal 509 in amplitude
units, if the relation holds:
f.sub.out=f.sub.limit
[0069] The filter unit is adapted for filtering the sensor signal
509 output by the rotation sensor 301, wherein the filter unit has
a cut-off frequency which is in a range from 0.5 times the
permissible rotational frequency to 1.5 times the permissible
rotational frequency, and approximately corresponds to the
permissible rotational frequency of the rotor.
[0070] The filter unit output signal 517 then is used as a control
signal for the switching unit 306 (not shown in FIG. 6). Thus, if
the filter unit output signal 517 drops below a predetermined
level, the switching unit 306 is switched such that the overspeed
protection system 300 in accordance with one of the embodiments
described above is active.
[0071] FIG. 7 is a front view of the rotor of a wind turbine
including the hub 110 and three rotor blades 108. The gravitational
force 701 acts downwards and also acts on a rotation sensor 301
provided as the pendulum unit 514 in accordance with the schematic
set-up shown in FIG. 6. If the rotor of the wind turbine is
rotating in a rotational direction indicated by an arrow 702, a
switching of the polarity of the voltage supply source 518 occurs,
as described above. The pendulum unit 514 illustrated in FIG. 6
acts as a toggling mass and provides the sensor output signal 509
without the use of electronic components such as transistors,
integrated circuits etc.
[0072] Exemplary embodiments of systems and methods for preventing
an overspeed condition of a wind turbine are described above in
detail. The systems and methods are not limited to the specific
embodiments described herein, but rather, components of the systems
and/or steps of the methods may be utilized independently and
separately from other components and/or steps described herein. For
example, the embodiments described herein can also be applied in a
wind turbine without a gearbox, and are not limited to practice
with only the wind turbine systems as described herein. Rather, the
exemplary embodiment can be implemented and utilized in connection
with many other rotor blade applications.
[0073] Although specific features of various embodiments of the
invention may be shown in some drawings and not in others, this is
for convenience only. In accordance with the principles of the
invention, any feature of a drawing may be referenced and/or
claimed in combination with any feature of any other drawing.
[0074] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. While various specific embodiments have been disclosed in
the foregoing, those skilled in the art will recognize that the
spirit and scope of the claims allows for equally effective
modifications. Especially, mutually non-exclusive features of the
embodiments described above may be combined with each other. The
patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such
other examples are intended to be within the scope of the claims if
they have structural elements that do not differ from the literal
language of the claims, or if they include equivalent structural
elements with insubstantial differences from the literal language
of the claims.
* * * * *