Patent Application
20130259682
The subject matter of this disclosure relates generally to wind turbines, and more particularly to a system and method that utilizes wind turbine models and estimated states to maintain continuous operation of a wind turbine without transitions to a detrimental stalled mode.
Over the last decade, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 50 or more meters in length). In addition, the wind turbines are typically mounted on towers that are at least 80 meters in height. Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.
Wind turbine blades have continually increased in size in order to increase energy capture. However, as blades have increased in size, it has become increasingly more difficult to control optimum energy capture. The blade loading is dependent on the wind speed, tip speed ratio (TSR) and/or pitch setting of the blade. TSR is the ratio of the rotational velocity of the blade tip to wind speed. It is important to optimize the operation of the wind turbine, including blade energy capture, to reduce the cost of the energy produced. Pitch setting of the blades (i.e. the angle of attack of the airfoil shaped blade), provides one of the parameters utilized in wind turbine control. Typically, controllers are configured to provide adjustment of rotor speed (i.e., the rotational speed of the hub around which the blades rotate) by adjusting the blade pitch in a manner that provides increased or decreased energy transfer from the wind, which accordingly is expected to adjust the rotor speed.
Wind turbines with sophisticated control systems maintain constant speed and power by active blade pitch control. Power production for a wind turbine is negatively impacted if the blades of the wind turbine operate in a non-optimal state. In addition, low air density or a drop in air density may also result in a loss of energy transfer from the wind to the blades.
Aerodynamic stall causes a decrease in lift and an increase in drag coefficients for a wind turbine blade. The onset of stall is signaled by a sharp change in a wind turbine's performance evident by degradation in output power versus expected power. More specifically, the rotor is said to be stalled if any increase in wind speed reduces the thrust on the rotor. In the event of aerodynamic stall, the energy transfer from the wind is reduced precipitously. Power degradation resulting from the loss of energy transfer is most significant during periods of rated winds where full power output is anticipated by the controller. That is, the control system interprets the decrease in power as a need for increased rotor torque. The control system reacts by calling for a decrease in blade pitch, which increases the angle of attack in an effort to increase the energy transfer from the wind. The increasing the angle of attack by the control system of an aerodynamically stalled blade further increases the flow separation, increasing the stall condition and further decreasing the energy transfer from the wind. As such, the current systems fail to address conditions, such as low density air operation that may cause aerodynamic stalling.
Therefore, what is needed is a method for operating a wind turbine that maintains the blade pitch angle at an angle greater than or equal to a calculated minimum pitch angle for a large variety of wind turbine and wind conditions to avoid having the wind turbine rotor enter a stall condition.
One aspect of the present disclosure includes a method for operating a wind turbine. The method includes providing a wind turbine having at least one blade having adjustable pitch angle. Wind turbine conditions are measured and wind conditions are estimated for the wind turbine. A minimum pitch angle is determined in response to the measured wind turbine conditions and the estimated wind conditions that would cause the wind turbine rotor to enter a stall condition, according to modeled aerodynamic performance of the rotor blades. A collective blade pitch is then established according to the modeled aerodynamic performance of the rotor blades to ensure a predetermined rotor stall margin is maintained.
Another aspect of the present disclosure includes a wind turbine comprising at least one blade having an adjustable pitch angle. The wind turbine further comprises sensors for measuring wind turbine conditions and wind conditions. An integrated controller is programmed to calculate a minimum pitch angle in response to the measured wind turbine conditions and the estimated wind conditions that would cause the wind turbine rotor to enter a stall condition, according to modeled aerodynamic performance of the rotor blades. The controller is further programmed to establish a collective blade pitch, according to the modeled aerodynamic performance of the rotor blades, to ensure a predetermined rotor margin is maintained.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The foregoing and other features, aspects and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
Referring to
In some configurations and referring to
The drive train of the wind turbine 100 includes a main rotor shaft 116 (also referred to as a “low speed shaft”) connected to hub 110 and supported by a main bearing 130 and, at an opposite end of shaft 116, to a gear box 118. The speed of rotation of the main rotor shaft 116 or rotor speed may be measured by suitable instrumentation or measurement devices. In some configurations, hub rotational speed is known from an encoder 117 on a high speed shaft connected to the aft end of a generator 120. In addition, the rotor speed may be determined from a proximity switch 119 on the high or low speed shaft. In addition, the rotor speed may be directly measured with sensing devices, such as optical strobing detection of a labeled high or low speed shaft. The rotor speed information may be provided to the control system along with other current turbine conditions. Gear box 118, in some configurations, utilizes a dual path geometry to drive a high speed shaft 121. The high speed shaft 121 is used to drive generator 120, which is mounted on main frame 132. In some configurations, rotor torque is transmitted via coupling 122. Generator 120 may be of any suitable type, for example, a wound rotor induction generator.
Yaw drive 124 and yaw deck 126 provide a yaw orientation system for wind turbine 100. According to one embodiment, anemometry provides information for the yaw orientation system, including measured instantaneous wind direction and wind speed at the wind turbine. Anemometry may be based on a wind vane 128. The anemometry information, including without limitation, wind force, wind speed and wind direction, may be provided to the control system to provide inputs for determination of effective wind speed, among other things. In some configurations, the yaw system is mounted on a flange provided atop tower 104.
In addition to rotor speed sensor(s) and wind speed sensors such as described herein, turbine power sensors may be employed to provide the electrical power output level, pitch angle sensors 123 may be employed to provide individual and collective blade pitch angles, and temperature sensors 125 may be employed to provide ambient temperature. The resultant generator speed, electrical power, blade pitch angle(s) and current ambient temperature information may be provided to the control system in similar fashion to the rotor speed and wind speed information described herein.
A preferred method for estimation of wind speed according to one embodiment requires measurements of electrical power, generator speed, blade pitch angles, and ambient temperature. Measurement of ambient temperature is employed according to one aspect for calculation/estimation of air density, which may alternatively be measured directly via more expensive sensors.
In some configurations and referring to
Sensor interface 314 is an interface that allows control system 300 to communicate with one or more sensors such as described herein. Sensor interface 314 can be or can comprise, for example, one or more analog-to-digital converters that convert analog signals into digital signals that can be used by processor(s) 304. In one embodiment, the sensor interface includes signals from a rotor speed determining device, anemometry from wind vane 128, electrical power sensor(s), blade pitch angle sensor(s), and ambient temperature sensor(s).
A method for operating a wind turbine 100 is illustrated according to one embodiment in the process flow diagram 400 shown in
With continued reference to
Further, current effective wind speed is estimated via the control system 300 in response to wind condition sensor readings as represented in step 405.
Using the current estimated wind speed and rotor speed based on the information provided in steps 403 and 405, the current rotor stall margin is determined via control system 300 by calculating the distance from the current collective blade pitch to the minimum collective blade pitch angle that would cause the turbine to reach the rotor stall line according to modeled aerodynamic performance of the rotor blades under the current operating conditions, as represented in step 407.
If necessary, the control system may adjust the blade pitch of one or more rotor blades 108 in response to the minimum collective blade pitch angle determined in step 407 to provide a collective blade pitch angle greater than or equal to the collective blade pitch necessary to maintain the predetermined minimum rotor stall margin according to the modeled aerodynamic performance of the rotor blades, as represented in step 409.
While the above has been described as determining the wind speed and the rotor speed directly from the corresponding systems or instruments, the wind speed and rotor speed may be provided from other locations or systems, such as weather monitoring stations, weather predicators, from a wind plant central monitoring/control, from predicted weather conditions, from externally mounted monitoring devices, from instruments mounted on other areas of the wind turbine or elsewhere in the wind turbine plant, such as directly on the blades, or by other methods or systems suitable for providing wind speed and/or rotor speed and/or other parameters suitable for calculating tip speed ratios.
Operation of the collective blade pitch angle at angles equal to or above the minimum blade pitch determined in step 409 provides operation that reduces or eliminates aerodynamic stall conditions resulting from, without limitation, low density air operation conditions susceptible to aerodynamic stalling.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
