Patent Application
20090212563
The present invention relates generally to wind power energy production, and more particularly to a method and system for improving the energy production of wind plants by increasing the nameplate rating of the installed turbines.
Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
A wind power generation system generally includes a wind plant having a plurality of wind turbine generators supplying power to a utility grid or other end user. Wind turbine power output is known to experience relatively rapid variations due to changes in wind speed, such as during gusts. Collective power output of the wind plant is greatly influenced by wind conditions on individual wind turbine generators. The inherent inertia of individual wind turbines and the varied operating conditions of wind turbines across a large wind plant may contribute, to an extent, to smoothing of some variation in power output of the wind plant. However, given the changeable nature of winds, it is possible that the collective output of a wind plant can vary from relatively low output levels to full power, and vice versa, in relatively short periods of time. Because electrical power is not stored on the power generation system in any meaningful quantities, it is essential that there always be a balance between electricity generated and electricity consumed.
It is possible to limit power output, and consequently power ramp-up rates of individual wind turbine generators at any level up to a maximum power available given the prevailing wind conditions. This is achieved by curtailing a portion of the power output, so that the power ramp rate does not exceed a maximum desired ramp rate. However this limits the capture of wind energy and increases the effective cost of energy of the wind plant. Similarly, in case of sudden fall in wind speeds, the output of the wind turbine generator may be controlled in a preemptive manner before the wind speed actually starts to fall, so that the power ramp-down rate is gradual and controlled to be within the ramp rate limits of the auxiliary power sources. Although useful as a means of controlling ramp rate, this again restricts power output of the wind turbine generator leading to a loss in wind energy capture.
Frequently a wind plant is constrained by utility regulations to an upper limit of output power that the plant must not exceed. The upper limit of the wind plant is typically the total installed capacity of the plant. A wind plant typically produces at the rated level for only a portion of time due to uncontrollable wind distribution and fluctuations, which are frequently not at the rated plant power output value. As a result, the total power produced by a typical power plant is normally less than a desired percentage of the total power capacity, and subject to significant variation in power output and ramp rates. Since the number and rating of turbine generators in the wind plant is typically equal to the upper limit of the constraint, there is no reserve power for providing ramp-down capability without sacrificing energy capture. Further, when one of the individual wind turbine generators fail, the wind plant cannot sustain the total rated capacity.
There is, hence, a need for a technique to control effective power output levels at a wind plant level to produce more energy limits and ramp rate restrictions prescribed by transmission system operators, while minimizing the loss of useful wind energy, and hence, the effective cost of energy.
The method of improving the performance of a wind turbine generating plant consists of increasing the name plate rating of the plant and limiting the output of the plant to the constrained value with an active power curtailment controller.
According to a first embodiment of the invention, there is a method for limiting an output power level in a wind turbine power generating system to a predetermined maximum power level. The method includes the steps of determining the predetermined maximum power level; providing at least one wind-driven rotor for transforming wind energy into rotational motion; connecting a plurality of turbine generators using the at least one rotor, each turbine generator of the plurality of turbine generators having a nominal maximum power output; configuring the plurality of turbine generators to provide an aggregate output power level equal to the nominal maximum power output times the number of turbine generators in the plurality of turbine generators, the aggregate power level being greater than the predetermined maximum power level when driven by the at least one rotor; and controlling the aggregate output power level at the predetermined maximum power level.
According to a second embodiment of the invention, a wind turbine power generating system includes at least one wind-driven rotor for transforming wind energy into rotational motion. A plurality of turbine generators is connected to one or more wind-driven rotors. An active power curtailment controller is also provided. The active power curtailment controller is configured to curtail an actual power output of the plurality of turbine generators at a predetermined maximum output power level, the predetermined output maximum output power level being less than an aggregate nominal power rating of the plurality of turbine generators.
One advantage is the wind turbine generating plant with capacity rating above the constrained power limit produces more energy over its lifetime by operating on average at a higher percentage of the constrained limit than a wind turbine generating plant rated the same as the constrained power limit.
Another advantage is that the power output of wind turbine generating plant with increased capacity rating is more stable than a generating plant with an aggregate power rating equal to the constrained limit, as measured by the variation in the output and the ramp rates.
A further advantage is that the impact of the unavailability of the turbines is reduced.
Yet another advantage is that reserve power can be maintained to provide down-ramp capability without large sacrifice in energy capture. These features make it easier to integrated the wind plant into the utility power system or grid.
Further aspects of the method and system are disclosed herein. The features as discussed above, as well as other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.
Referring next to
In order to meet the constrained maximum power requirements of utility transmission system 12, the wind turbine generating plant 10a is controlled by an active power curtailment controller 22, which governs the maximum output per turbine generator 18, 18a, and balances the load sharing between the turbine generators 18, 18a. Such active power curtailment controllers are well known in the art. An example of one such active power curtailment controller 22 is disclosed in U.S. Pat. No. 7,199,482, and is hereby incorporated by reference. Another active power curtailment controller is disclosed in U. S. Patent Application Publication No. 20070001461, which is also incorporated by reference. An existing active power curtailment controller 22 has the ability to constraint the plant to a given value. The controller 22 may be modified so that (1) the MW constraint becomes the upper limit; (2) algorithms that take advantage of additional turbines are implemented; and (3) algorithms that provide more intelligent control functions e.g. ramp rates both increasing and decreasing power output rates, may be implemented. These features will make the wind turbine generating plant 10a easier to integrate in a utility grid as it will have functions similar to a conventional power plant. The aforementioned active power curtailment controllers are given by way of example and not limitation, as other such power curtailment controllers are known to persons skilled in the art. The active power curtailment controller 22 is in communication with each of the turbine generators 18, 18a through a communications channel 24, used for controlling load management and other functions of the respective turbine generators 18, 18a in the generator banks 20, 20a.
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In a power simulation analysis, adding 10% power capacity of the wind turbine generating plant increased the energy capture by 5.8% while increasing the cost of energy by only 4%.
Referring now to
Similarly, if the minimum power level falls due to wind changes, to 1.3 MW, seventy generators, i.e., an additional five 1.5 MW generators, are required to reduce the variation to zero, as indicated by line 206. The greater the number of generators, the nearer to the maximum power line 202 the wind turbine generating plant will operate. For a minimum power level of 1.2 MW, as indicated by line 208, a seventy generator wind turbine generating plant will not generate the maximum power level, however, the wind turbine generating plant at the minimum power level will operate closer to the constrained limit than the standard sixty generator wind turbine generating plant.
Referring now to
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
