A controller and method is disclosed for operating a variable speed turbine to better track wind speed fluctuations for greater efficiency in conversion of wind energy to electrical energy. The controller of the invention controls the rotor speed in accordance with a wind speed supplied by a wind observer in order to approximately follow the varying wind speeds. The wind observer predicts the average wind speed at a subsequent point in time over the cross-section presented to the wind by the wind turbine. The average wind speed is applied to a parameter schedule to determine desired values for rotor speed and torque which are used by arotor speed stabilizer to command a reference load torque. The load torque of the generator is controlled in accordance with the commanded load torque, and therefore the desired rotor speed is approximated. During operation, the wind speed prediction process is repeated at each subsequent time interval, and the load torque, and therefore rotor speed, is controlled accordingly. The wind observer calculates the aerodynamic torque and then calculates net torque. The wind speed is predicted as a function of the present (previously predicted) wind speed and correction terms including net torque and the difference between the predicted and actual rotor speed. The wind observer is useful whenever the wind turbine rotor is turning, whether or not it is producing power.

Speed control system for a variable speed wind turbine

The present invention provides a wind turbine with improved efficiency, reduced static as well as dynamic structural loads, reduced noise, and facilitating grid connection with improved power quality. According to the invention these and other features are fulfilled by a wind turbine comprising a wind velocity measurement system for determination of air velocities in front of the wind turbine and having an output for provision of determined air velocity values.

A wind turbine with a wind velocity measurement system

The National Renewable Energy Laboratory's (NREL's) National Wind Technology Center (NWTC), directed by the Department of Energy (DOE) is pursuing several research projects in variable speed. In the near future the laboratory will be reevaluating its ongoing experiments and plans. The starting point for this reevaluation will be a sound understanding of the current state of the art in design and application of variable-speed technology. This report, which outlines current technologies and historical applications of variable-speed, will provide a baseline in deciding the course of research in the upcoming years.

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The History and State of the Art of Variable-Speed Wind Turbine Technology

A wind turbine is provided having a lidar wind speed measurement apparatus (10, 16, 18) for achieving wind control. The lidar apparatus is arranged to scan the area (30) in front of the wind turbine so as to generate a measurement of the wind speed across the wind field. The lidar apparatus may be located in the hub (6) of the wind turbine and the look direction (32a, 32b, 32c) inclined away from the rotational axis so that rotation of the hub (6) ensures scanning. Preferably the lidar apparatus has a plurality of look directions (32a, 32b, 32c) so as to increase the scanning rate. This may be achieved by having a number of dedicated lidar systems and/or by using multiplexed lidars. Measurement of the wind field allows improved control of the wind turbine giving efficiency and reduced wear benefits.

Wind turbine control having a lidar wind speed measurement apparatus

A segmented arc generator is adapted to convert mechanical power such as wind or water power into electrical power at a wide range of wind or shaft speeds. A rotor has a plurality of salient poles disposed about a periphery of a rotor ring. A stator has a stator ring disposed radially about and in close proximity to the rotor ring. The stator ring includes a plurality of stator coils wound on a ferromagnetic structure and having permanent magnets imbedded within the structure. Relative motion between a rotor pole and a corresponding stator coil induces a coil voltage across that coil. A phase controlled converter in electrical communication with the stator coils rectifies the output voltage. A pulse width modulated inverter is in electrical communication with the phase controlled converter for converting the D.C. voltage output by the phase controlled converter to an A.C. voltage of controlled amplitude and phase relationship determined with respect to a voltage waveform present on a connected utility grid. A switching matrix selectively places the coils in series or parallel or a combination of series and parallel connections with respect to one another in response to control signals that are based on present operating conditions of the generator. A boost converter circuit provides and maintains a minimum D.C. voltage to the pulse width modulated inverter when the voltage induced in the coils falls below a threshold value.

Segmented arc generator

The wind energy conversion system includes a wind machine having a propeller connected to a generator of electric power, the propeller rotating the generator in response to force of an incident wind. The generator converts the power of the wind to electric power for use by an electric load. Circuitry for varying the duty factor of the generator output power is connected between the generator and the load to thereby alter a loading of the generator and the propeller by the electric load. Wind speed is sensed electro-optically to provide data of wind speed upwind of the propeller, to thereby permit tip speed ratio circuitry to operate the power control circuitry and thereby optimize the tip speed ratio by varying the loading of the propeller. Accordingly, the efficiency of the wind energy conversion system is maximized.

Paul Longrigg

Papers

Wind energy conversion system