초록

A variable speed wind turbine utilizes a hydraulic transmission including a hydraulic pump coupled to a rotor and a hydraulic motor coupled to an induction generator to produce variable frequency power that is converted to grid frequency power by electronic controls.

대표청구항 ▼

What is claimed is: 1. A variable speed wind turbine transmission system comprising: a turbine rotor driven by wind; a fixed displacement hydraulic pump coupled to the rotor; a fixed displacement hydraulic motor coupled to a generator; a hydraulic circuit to transfer fluid from the pump to the moto

What is claimed is: 1. A variable speed wind turbine transmission system comprising: a turbine rotor driven by wind; a fixed displacement hydraulic pump coupled to the rotor; a fixed displacement hydraulic motor coupled to a generator; a hydraulic circuit to transfer fluid from the pump to the motor; wherein the generator rotates at a variable speed directly related to rotation of the turbine rotor and produces an electrical output at a variable frequency; and a power converter to convert the variable frequency electrical output of the generator into grid frequency power. 2. The system of claim 1, wherein the power converter comprises: an inverter which converts AC power to DC power, an active front end which converts the DC power into grid frequency AC power; and an L-C-L filter which reduces power line harmonics. 3. The system of claim 2, wherein the active front end synthesizes a sinusoidal input voltage from the inverter by Pulse-Width-Modulation (PWM). 4. The system of claim 3, wherein the power converter is capable of controlling a load on the generator based on the speed of rotation of the rotor. 5. The system of claim 3, wherein the power converter controls the inverter by a generator rotor speed feedback device to regulate the amount of negative slip of the induction generator. 6. The system of claim 3, wherein the power converter controls the inverter using a sensorless vector control. 7. The system of claim 3, wherein the power converter is capable of controlling both speed and torque of the generator shaft. 8. The system of claim 3 which utilizes the energy from the spinning rotor to maintain control during a failure of the power grid. 9. The system of claim 1, wherein the system does not utilize a gearbox. 10. A variable speed wind turbine system comprising: a turbine rotor driven by the wind; a fixed displacement hydraulic pump directly driven by the rotor; a fixed displacement hydraulic motor; a closed loop hydraulic fluid circuit for carrying pressurized oil to the hydraulic motor from the hydraulic pump and to return hydraulic fluid to the hydraulic pump from the hydraulic motor; an induction generator directly driven by the fixed displacement hydraulic motor, the induction generator producing AC power at variable frequency; a power converter including an inverter which converts the AC power to DC power, an active front end which converts the DC power into grid frequency AC power, and an L-C-L filter which reduces power line harmonics. 11. The system of claim 10, wherein the active front end synthesizes a sinusoidal input voltage from the inverter by Pulse-Width-Modulation (PWM). 12. The system of claim 11, wherein the power converter is capable of controlling a load on the generator based on the speed of rotation of the rotor. 13. The system of claim 11, wherein the power converter controls the inverter by a generator rotor speed feedback device to regulate the amount of negative slip of the induction generator. 14. The system of claim 11, wherein the power converter controls the inverter using a sensorless vector control. 15. The system of claim 11, wherein the power converter is capable of controlling both speed and torque of the generator shaft. 16. A method for producing a grid frequency power with a variable speed wind turbine, the method comprising the steps of: providing a variable speed wind turbine comprising a turbine rotor driven by wind, a fixed displacement hydraulic pump coupled to the rotor, a fixed displacement hydraulic motor coupled to a generator, and a hydraulic circuit to transfer fluid from the pump to the motor; subjecting the rotor of the variable speed wind turbine to a source of wind such that the generator produces an electrical output at a variable frequency related to a speed of rotation of the rotor; and converting the variable frequency electrical output of the generator into grid frequency power. 17. The method of claim 16, wherein the step of converting the variable frequency electrical output of the generator into a fixed grid frequency power comprises the steps of: inverting the variable frequency electrical output to direct current power; converting the direct current power into a fixed grid frequency AC power output. 18. The method of claim 17, wherein the step of converting the variable frequency electrical output of the generator into a fixed grid frequency power further comprises the step of: filtering the fixed frequency grid power using an L-C-L filter.