Abstract:
The disclosure relates to a hydraulic drive train with energy dissipation for electrical generation. The disclosure is particularly adapted to wind-driven embodiments wherein the input power can fluctuate quickly. A hydraulic pump is provided in the nacelle of the windmill and powered by the wind turbine shaft. This hydraulic pump provides high pressure oil to generators, typically at ground level. The generators are protected from high pressure oil spikes by a pressure relief valve. Electric pumps on the ground level provide or supercharge the oil to the hydraulic pump in the nacelle.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application claims priority under 35 U.S.C. §119(e) of U.S. provisional application Ser. No. 61/204,288 filed Jan. 5, 2009, the disclosure of which is hereby incorporated by reference. 
       FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure pertains to a hydraulic drive train and associated components for driving a turbine driven by wind, water or similar sources. The hydraulic drive train absorbs excess energy imparted to it, and dissipates it as heat. This further allows the use of multiple, smaller generators rather than as single large generator. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    In the prior art of generating electricity from the wind or similar sources, one of the significant challenges is matching the variable and typically slow speed of the input shaft which is driven by the wind or water, to the high speed required by the electrical power generators. The typically approach in the past has been to use a gearbox to mechanically perform this function. Prior art which has used a gear box or similar mechanical devices may be found in U.S. Pat. No. 7,069,802 entitled “Distributed Power Train (DGD) with Multiple Power Paths” issued on Jul. 4, 2006 to Mikhail et al; U.S. Pat. No. 7,007,589 issued on Mar. 7, 2006 to Sanderson; U.S. Pat. No. 6,731,017 entitled “Distributed Power Train that Increases Electric Power Generator Density” issued on May 4, 2004 to Mikhail et al; U.S. Pat. No. 5,996,342 entitled “Hydrostatic Drive Train Controller” issued on Dec. 7, 1999 to Khan et al.; U.S. Pat. No. 4,585,950 entitled “Wind Turbine with Multiple Generators” issued on Apr. 29, 1986 to Lund; and U.S. Patent Application No. 2003/0138331 entitled “Metering Pump with Proportional Output” published on Jul. 24, 2003 by Fox et al. 
         [0004]    Other prior art includes commonly-invented and commonly-assigned U.S. Patent Application No. 2007/0182273 entitled “Turbine with Constant Voltage and Frequency Output”, published on Aug. 9, 2007. 
         [0005]    Additionally, the handling of excess power must be addressed, such as when the speed of the wind or other source is greater than what the electrical generators can handle. The generators may be overdriven thereby shortening the life of the generators. The power from the overdriven generators, in turn, causes spikes in output power to the grid. Additionally, the extra power can cause the gearboxes to fail early. Moreover, as the machines have increased in size, the size and weight of the gearbox and the generator has also greatly increased. 
       OBJECTS AND SUMMARY OF THE DISCLOSURE 
       [0006]    It is therefore an object of the present disclosure to provide a drive train for powering a turbine, wherein excess energy in the hydraulic system can be dissipated as heat. 
         [0007]    It is therefore a further object of the present disclosure to provide a drive train for powering a turbine wherein the back end generators are typically mechanically decoupled from each other and the input shaft. 
         [0008]    These and other objects are attained by providing an electrical generating system wherein the wind driven, or similar, components transmit energy to the turbine through a hydraulic drive train. The hydraulic fluid or oil is contained in a reservoir in sufficient quantity to provide a source for the components and to dissipate the heat generated. In an open loop arrangement, the hydraulic fluid or oil is returned to the reservoir after its completion through the circuit. 
         [0009]    The current hydraulic system configuration has the main system at the ground level and the hydraulic pump located in the wind tower directly connected to the wind turbine shaft. This means the hydraulic fluid or oil needs to be pumped from ground level up to the hydraulic pump on the tower. This practice is commonly called supercharging the pump inlet. 
         [0010]    Assuming the wind has sufficient speed and generates enough torque to turn the turbine shaft, the motor will turn and pump oil to a directional manifold block. The directional valves inside the block start and stop the fluid to the hydraulic motors which are directly coupled on a one-to-one basis with generators, providing the electric power. A proportional flow control valve is used to regulate the hydraulic motor speed and keeps the generator running at the proper revolutions per minute to generate the electrical power within the desired parameters. At this point the oil is then returned through a return filter and directed back to the reservoir. 
         [0011]    The proportional flow control valves enable both the precise control of the generator and the release of excess energy as heat. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further objects and advantages of the disclosure will become apparent from the following description and from the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a schematic of the apparatus of the present disclosure. 
           [0014]      FIG. 2  is a schematic of the control structure of the apparatus of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, one sees from  FIG. 1  that the system  10  includes a reservoir or tank  12  of oil or hydraulic fluid which includes various outlet ports  14  and inlet ports  15  throughout  FIG. 1 . The reservoir  12  is illustrated in  FIG. 1  as associated with the various ports  14 ,  15  but is not illustrated as a unitary element. The system  10  is typically configured as an open loop system. The oil is contained in the reservoir  12  in sufficient quantity to provide a source for the various components and to dissipate the heat generated. In the open loop arrangement, the oil is returned to the reservoir after completion through the circuit. The reservoir  12  is typically sized for 2.5-3.0 times the maximum gallons per minute that the system  10  requires. A typical reservoir size is 500 gallons, but those skilled in the art will recognize, after review of the present disclosure, that different embodiments may require different reservoir capacities. 
         [0016]    A wind turbine  20  and hydraulic pump  30  are located in a nacelle  22  at the top of a wind tower  24 , while most of the remaining components are placed on the ground or otherwise away from the wind tower  24 . By placing components on the ground rather than placing all components on the tower  24 , less expensive and taller towers can be built. The wind turbine  20  includes propeller  26  and turbine shaft  28 . Turbine shaft  28  drives hydraulic pump  30 . This configuration requires that the hydraulic fluid or oil be pumped from ground level up to the level of hydraulic pump  30 . This pumping of oil up to the level of the hydraulic pump  30  is typically called “supercharging”. 
         [0017]    This supercharging to hydraulic pump  30  via manifold  31  and pipe  32  is done by three independent electric motor/pump groups  34 ,  36 ,  38 , typically located at ground level or otherwise away from tower  24 . The electric motor pump groups  34 ,  36 ,  38  include motor-driven pumps  40 ,  42 ,  44 ; filters  46 ,  48 ,  50  and coolers  52 ,  54 ,  56 . The electric motor/pump groups  24 ,  26 ,  28  include inlets through outlet ports  14  of the reservoir  12  which are below the oil level height of the reservoir  12  thereby resulting in a flooded inlet configuration for motor-driven pumps  40 ,  42 ,  44 . The inlets are at the suction side of motor-driven pumps  40 ,  42 ,  44 . The filters  46 ,  48 ,  50  and coolers  52 ,  54 ,  56  clean and cool the oil prior to supercharging the oil to hydraulic pump  30  via manifold block  31  and pipe  32 . Manifold block  31  includes a low pressure, high response relief valve  58  which regulates the pressure on the low pressure side of the system and returns oil to reservoir  12  via inlet port  15  in over-pressure situations, which may occur as spikes. Concurrently, as shown in  FIG. 1 , oil from reservoir  12  is periodically being pumped from outlet port  14  by pump  45 , filtered by filter  51 , and returned to reservoir  12  via inlet port  15 . 
         [0018]    Electric motor pump groups  34 ,  36 ,  38  are typically at ground level and must be capable of supplying the required amount of oil to hydraulic pump  30  in the nacelle  22 . Some embodiments of hydraulic pump  30  may pump approximately  708  cubic inches of oil per revolution in a positive displacement configuration. Therefore, the electric motor/pump groups  24 ,  26 ,  28  include a variable frequency drive to control the speed of the motor-driven pumps  40 ,  42 ,  44 . Some embodiments of motor-driven pumps  40 ,  42 ,  44  may pump approximately 5.31 cubic inches of oil per revolution in a positive displacement configuration. Typically, a pressure of 70 pounds per square inch is sufficient to provide oil to the hydraulic pump  30  in the nacelle  22 . This configuration is particularly adaptable to cold starts of the system  10 . 
         [0019]    An encoder on the turbine shaft  28  provides the signal information to the programmable logic controller (PLC)  200  via input RPM and position block  202  and shaft coupling block (see  FIG. 2 ). PLC  200 , in turn controls the variable frequency drive of motor-driven pumps  42 ,  44 ,  46 . The positive displacement characteristics of hydraulic pump  30  and motor-driven pumps  42 ,  44 ,  46  allows for accurate control of the flow rates of the oil. 
         [0020]    The hydraulic pump  30  provides high pressure oil via return pipe  60  to high pressure directional manifold block  62  (likewise typically at ground level or otherwise away from tower  24 ) which further includes high pressure relief valve  64  to protect the system from being over-pressurized and to return excess oil to the reservoir  12  via inlet port  15  thereby dissipating the excess heat. Return pipe  60  further includes electric motors  66 ,  68  to control the flow rate of oil through return pipe  60 , thereby limiting the positive-displacement hydraulic pump  30 , and therefore wind turbine  20 , to a desired rotational speed which is determined by PLC  200  typically based on such factors as wind speed and factors relating to the various loads on system  10 . 
         [0021]    High pressure directional manifold block  62  provides oil to high pressure feeder lines  70 ,  72 ,  74 ,  76 ,  78  which further include respective proportional control flow valves  80 ,  82 ,  84 ,  86 ,  88 , responsive to PLC  200  to regulate or cut off the flow, if necessary, to some high pressure feeder lines  70 ,  72 ,  74 ,  76 ,  78 , such as at lower wind speeds. High pressure feeder lines  70 ,  72 ,  74 ,  76 ,  78  include respective proportional flow control valves  90 ,  92 ,  94 ,  96 ,  98  which, in the event of over-pressure, with a typical limit of 3000 psi, such as may occur during a gust in wind speed, relieve the over-pressure and divert oil to inlet ports  15 . Some embodiments may divert this excess pressure to the drive system for motor-driven pumps  40 ,  42 ,  44 . Similarly, an accumulator  79  (see  FIG. 2 ) may be incorporated into feeder lines  70 ,  72 ,  74 ,  76 ,  78  or otherwise proximate to or upstream from high pressure directional manifold block  62  to absorb excess energy and store if for a later time when the input power wanes. The remaining high pressure oil is used to drive respective fixed displacement motors  100 ,  102 ,  104 ,  106 ,  108  with respective output shafts connected to electrical generators  110 ,  112 ,  114 ,  116 ,  118  which provide electrical power to electrical grid  1000  (see  FIG. 2 ) via output control block  900  and transformer contractor  902 . The grid sine wave sample block  904  receives samples from grid  1000  and send control signals to output control block  900  in order to conform the output of system  10  to the electrical conditions on grid  1000 . Due to varying wind speed, the fixed displacement motors  100 ,  102 ,  104 ,  106 ,  108  need to be regulated for speed. This is done by through the proportional flow control valves  80 ,  82 ,  84 ,  86 ,  88  upstream for the inlets to fixed displacement motors  102 ,  104 ,  106 ,  108 . Encoders on pump  30  provide a signal to the PLC  200  ( FIG. 2 ) which, in turn, via auto valve control block  33 , regulates the amount of oil through proportional control flow valves  80 ,  82 ,  84 ,  86 ,  88  (or similarly, through proportional flow control valves  90 ,  92 ,  94 ,  96 ,  98 ) to the motors  100 ,  102 ,  104 ,  106 ,  108  and regulates their speed (additionally, this regulation of the flow of oil through system regulates the speed of pump  30 ). The proportional flow control valves  90 ,  92 ,  94 ,  96 ,  98  typically pass at least 95 percent of the oil to the fixed displacement motors  100 ,  102 ,  104 ,  106 ,  108  for optimum efficiency. 
         [0022]    After driving fixed displacement motors  100 ,  102 ,  104 ,  105 ,  108 , the oil is thereafter filtered by respective filters  110 ,  112 ,  114 ,  116 ,  118  and returned to reservoir  12  via inlet ports  15 . 
         [0023]    Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.