CN1035547A - Wind Turbine Pitch Control Hub - Google Patents

Abstract

In a variable pitch wind turbine system, the pitch angle is determined by a pneumatic-hydraulic actuator connected between cranks on the pitch shafts of the blades. The hydraulic circuit runs concentrically through the rotor drive shaft and, via the rotary union, reaches the gas-filled accumulator on the deflection carrier. The pitch axis is positively connected by a gear train for 1: 1 counter rotation, preferably on one side of the rotor axis, opposite the hydraulic actuator.

Description

The invention is patented by Hong Kong Delta Energy Ltd. (Hong Kong). The invention relates generally to a control system for the rotor of a wind turbine, and in particular to an automatic control system for the pitch of the blades of a wind turbine for a generator connected to a power supply network. The angle of the blades, that is, the pitch, can be controlled to adjust the output torque and achieve the highest output power within a design range of wind speed. This is an all-mechanical passive system, which is particularly desirable for reliability because it is relatively immune to environmental factors and failures in the sensing or control systems.

Most existing pitch controllable rotors use positive pitch control. The sensor senses the need, so that the electric system or the hydraulic system will change the pitch. An inherent potential weakness of such systems is the inability to adjust to high pitch angles to slow down or stop the turbine when the sensing system, or the microprocessor system, or the actuation system or mechanism fails.

On the contrary, even if the control system fails, the negative automatic recovery system can automatically return to the safe pitch, that is, the high-angle pitch.

A general object of the present invention is to control the output torque of a variable pitch wind turbine by utilizing a reliable power mechanical system which automatically controls the pitch of the blades as the blade torque changes due to wind load and centrifugal input.

In the passive pitch control system of a double-bladed rotor of the present invention, the two blades are parallel to the pitch-adjusting shaft, and are directly connected by a gear transmission system. The pitch angle is determined by a gas-hydraulic linear actuator connected between the cranks on the shafts of the two blades. The hydraulic line runs concentrically through the rotor drive shaft and connects to a gas-charged accumulator through a rotary union.

In the ideal configuration of an upwind stable deflection wind turbine with an oscillating hub, the parallel blade pitch axes form a rotor plane, transverse to the rotor drive axis, and the rotor drive axis intersects the rotor plane at the midpoint between the two pitch axes. The propeller shafts coaxial with the propeller axis respectively are supported on the hub shell. The shaft ends of the blades overlap each other by a considerable length. In an ideal embodiment, a gear train connects the two shafts on one side of the rotor axis. On the other side there is a linear actuator connected between the crank on the shaft. The actuator preferably works in parallel with the gear train. A retractable hydraulic linkage and "gas spring" between the blade pitch shafts provides direct override capability for manual and automatic shutdown through blade feathering.

Fig. 1 is a side view of a tower-type double-bladed upwind turbine of the present invention, and its pitch-controlled rotor hub is in working condition.

Fig. 2 is a top view of the wind turbine along the line 2-2 in Fig. 1 .

Fig. 3 is a bottom view of the rotor hub along the line 3-3 in Fig. 1 .

Fig. 4 is a sectional view of the shaft end of the hub in Fig. 1 along line 4-4.

Figure 5 is a schematic diagram of the hydraulic system.

Figure 6 is a graph of predicted power versus wind speed for a wind turbine provided with a pitch control hub of the present invention.

Figure 1 shows the installation of a stably deflected upwind two-blade wind turbine used by a generator synchronously connected to the electricity network. A tower 10 supports a horizontal turntable assembly 12 approximately 70 feet above the ground. A carrier 14 is mounted on the turntable assembly 12 for rotation in a yaw direction around the vertical axis of the turntable assembly 12 . The transmission shaft shell 16 is installed on the carrier 14, and the high-torque hollow transmission shaft 17 inside is supported by the shell 16.

The double-blade rotor 18 is connected to the front end of the transmission shaft, and the rear end of the transmission shaft is connected to a pair of induction generators 22 and 24 through the gearbox 20. The generators can operate optimally under high and low wind speed conditions respectively, so that the rotor can According to two corresponding design requirements, rotate at the optimum operating speed. An overturning sprag clutch (not shown) mounted on the gearbox output shaft reduces the number of powertrain control loops and relay boxes, thereby increasing overall equipment life and reducing maintenance. A one-way sprag clutch improves alternator/grid connection and disconnection.

The rotor 18 generally has a rectangular hub 28, as shown in FIG. 4, which rotates on a drive axis a. Mounted on the hub 28 are two identical wind turbine blades 30 and 32 . In a design rated at 100 kilowatts, the diameter of the rotor blades is approximately 58 feet. The ideal blade has a zero degree taper, with an elastomeric wobble hub. The rotor is designed to run in two speeds (48/72 RPM) and should start automatically at about 7 mph. The designed tip speed ratio is 7-9.

Details of the hub 28 are shown in FIGS. 2-4. The hub 28 has a pair of cylindrical bearings 34 and 36, and the blade shafts 38 and 40 are respectively supported for rotation inside. The cylindrical bearings 34 and 36 determine the positions of the blade pitching axes b and c respectively. Circular eccentric mounting lugs 42 and 44 are respectively connected to opposite ends of blade pitch shafts 38 and 40 . Blades 30 and 32 (FIG. 1) have mating flanges 46 and 48 which are bolted to flanges 42 and 44, respectively.

The bearing cylinders 34 and 36 form a solid rigid frame with box-shaped tubular cross braces 50 and 52 welded thereto. The rotor shaft 17 is connected to the hub as shown in FIGS. 3 and 4 . Mounting bracket 54 rigidly connects swing hub assembly 55 , to box tubes 50 and 52 . A gearbox 60 straddles bearing cylinders 34 and 36 at about respective ends. A set of four spur gears 60' are mounted to rotate in the gearbox, as shown in FIGS. 1 and 4 . The pitch diameter of the prototype gear is 9 inches. Two driving gears 62 and 64 are installed coaxially on the pitch adjustment shafts 38 and 40 . Eccentric mounting lug 42 is connected to spur gear 62 . The two shaft gears 62 and 64 are connected for transmission by a pair of transmission gears 66 and 68, which are supported in the gearbox 60 and offset from the plane formed by the axes b and c, as shown in FIG. 4 .

On the other end of the bearing cylinders 34 and 36, the axes are connected by a rotational bias assembly, in which a pair of crank throws 70 and 72 placed in the same direction are rigidly connected with the pitch shafts 38 and 40 respectively. The bellcrank 72 and the eccentric mounting flange 44 can be integrally cast when needed. The outer ends of the bellcranks 70 and 72 are pivotally connected with the hydraulic linear actuator 74. The actuator 74 has a cylinder body 76, which is pivotally connected with the bellcrank 70. The piston rod 78 slides in the cylinder and is connected with the bellcrank 72. Make a pivot connection. Ideally, to keep the design as compact as possible, the bellcrank extends towards the circular mounting flange in the same direction as the raised center portion of the gearbox 60, as shown in FIG. The linear actuator 74 may be assisted by a spring bias if desired.

The hydraulic system is shown in Figure 5. The hydraulic pipeline passes through the rotor drive shaft concentrically towards the gearbox 20 and is connected to the air pressure accumulator through a rotary joint pipe fitting. Other components are installed in the deflection carrier 14, as shown in FIG. 5 . Turning the valve to the closed position frees hydraulic fluid to the sump, allowing centrifugal force to fully feather the blades.

The hydraulic system in FIG. 5 is used to control the pitch actuator 74, so that the pitch of the two blades is adjusted by about 70° between the feathered state and the working state. In operation, the pitching moment caused by centrifugal force and aerodynamic loading on the blades tends to draw the piston rod out of the reciprocating cylinder. This moment increases with wind speed and is in the same direction as the wind direction. There is a bladder-type air-filled accumulator 80, which absorbs the propeller torque caused by the elongation of the piston rod 78 and squeezes out the liquid of the reciprocating cylinder. The air bladder acts as a spring, absorbing the force of the aerodynamic moment, thereby providing an increased restoring moment to return the blade to the operational position.

Some components of the hydraulic system are placed in a NEMA 4 box as shown in Figure 5 (NEMA is the National Electrical Manufacturers Association of the United States)

This system has four working conditions:

A. Pressurization to start the process;

B. Feathering pitch under load;

C. The pitch of the propeller to the working state when unloading;

D. Quickly feather (command to stop).

When the power is turned on, the stop valve 82 is closed, and the motor pump 84 is started to increase the system pressure to the operating pressure. The gas spring pressure and liquid stock in the accumulator 80 are balanced, and the reciprocating cylinder 76 is fully retracted to the starting position (opposite the working position in FIG. 5 ). When the operating pressure is reached, the pump 84 is stopped by a pressure switch 86 . The pump starts as needed to maintain the system pressure required by the pressure switch range. But when the pump stopped working, the check valve 88 was isolated from the hydraulic system.

In operating condition B (pitch turned to feathering under load), centrifugal force in turbine operation and aerodynamic increased pitching torque at increased wind speed tend to draw piston rod 78 out of reciprocating cylinder 76 . The liquid discharged from the reciprocating cylinder will be sucked into the accumulator 80 through the hydraulic circuit. In the circuit, there is an air release valve 90, a quick breaker 92, a hydraulic circuit passing through the turbine shaft 17 and the rotary joint 94, a quick breaker 96, and a backstop Valve 98, quick disconnect 100 and pressure reducer 102. An increase in liquid inventory will increase the gas spring pressure in accumulator 80 and the system pressure. Accumulators shall be sized to absorb the storage at the highest system pressure. Fluid flowing from the reciprocating cylinder into the accumulator tends to feather the rotor blades.

In working condition C (pitch transition to running state when the blade is unloaded), the hydraulic fluid flows in reverse. When the pitching moment on the blades decreases due to the decrease of wind speed, the gas elastic force in the accumulator 80 provides the control force to return the reciprocating cylinder 74 to the working position. This control force is stored in case B due to spring compression. As the spring returns to equilibrium, fluid is expelled from the accumulator, out of the same hydraulic circuit with valve 104 but without check valve 98, into the actuator.

Conditions B and C often occur when the turbine is running. Due to the loss of stored energy due to flow friction and actuator friction, the paddle pump must be activated to maintain pressure in the system.

Working condition D (quick feathering for shutdown) is obtained by de-energizing the solenoid valve 82 to discharge the pressure fluid to the liquid storage tank 106. The liquid discharged from the reciprocating cylinder 76 is discharged into the liquid storage tank through the check valve 98 and the solenoid valve 82 by centrifugal force or aerodynamic feathering torque. The fluid flow from the accumulator is also directed into the reservoir. After shutdown, the pump 84 must be restarted to restore system pressure.

Increasing wind loads on the blades cause the blade moment to rise, which twists the pitch shaft. This increased torque will encounter increasing resistance from the linear actuator 74 . The greater the wind load, the greater the control torque of the blade, and the more the blade tends to feather.

As shown in the curves for this scenario in Figure 6, the power curves were made to cover the range of wind speeds from 7 to 30 mph. Adding a spring to the linear actuator 74 widens the envelope of the curve of operation. The shape of the curve, the maximum power output straight section curve, and the power curve of the shutdown inclined section, are all determined by the pitch change program with the wind speed. The double descending curve represents the design criteria for negative control, which may be hydraulic or, in the load control region, a combination of increased spring bias. The approximate value of the blade pitch angle for negative control is represented by the curve.

The blade pitch controller is a passive mechanical device that allows the blade to find its own equilibrium position in the degree of freedom of pitch adjustment when conditions change. The synthesis of several pitching moments determines the pitch balance procedure of the rotor. The blade shape, blade thrust offset and blade centrifugal force offset generate the pitching torque, the vector sum of which determines the pitch balance procedure, and the pitch balance procedure determines the characteristics of the power curve. The magnitude and change of each moment can be changed by carefully placing the axis of the center of gravity of the blade, the offset of the control axis and the aerodynamic axis, etc. The Euler angles of the blade sweep and the cone axis are as important in the analysis as the swing dynamic feedback angles △1 and △3.

This fully passive rotor control system uses wind force, and the inherent inertia of the blades, to automatically change the pitch of the rotor, protecting the turbine in gusts, strong winds and no load. By selecting the appropriate gas spring, the rotor pitch can be adjusted at a given position to obtain the maximum power curve. The level of reliability and safety provided by the automatic rotor hub allows the brakes to be eliminated, making feathering a manual operation.

The 100 kW wind turbine system disclosed in this application is designed to utilize the pitch control hub, and also has the following mechanical technical requirements:

Gearbox 20:

The speed ratio of the two outputs is 25:1 and 37.5:1,

Full load efficiency 95%

low starting torque

1st stage planetary gear

Second stage helical gear with dual output

output sprag clutch

Double seal structure

Continuous Oil Lubricated Bearings

dynamo:

Power 100 kW 20 kW

Speed 1800 rpm 1800 rpm

Type Inductive Inductive

480 AC voltage 480 AC voltage

Power factor 0.95 0.85

Efficiency 94% 91%

Base frame 405 turbine transmission 284 turbine transmission

Drip-proof Drip-proof

Structure Class H Class H

yaw drive:

Drive deflection rate 4°/second

Overspeed idle design

Gear ratio 800:1

1/2 hp reversible induction motor

Gears 62 and 64 on the pitch shaft are preferably heat-hardened gears, AGMA (American Gear Manufacturers Association) tolerance class 11. It is better to install these gears on the mixing shaft. The mounting flange of the rotor blades uses a conical clamp (not shown) to make adjustable installation on the gears and the shaft. The clamps can be adjusted loosely so that the blades can be very One degree of "timing", then tighten. The idle gear is pushed and pulled and rotated to engage the new tooth. Since the idler gear is replaceable, it can be made of a softer metal than the end gear to accommodate wear. For the convenience of adjustment, it is better to install the idler gear on the eccentric.

This hub is designed to handle the extreme alternating loads of mid-size range two-blade wind turbines, ranging in size from 50 to 80 feet. Blade weight grows as the third power of radius. The gravitational load on the hub and blades varies with the orientation of the blades as they rotate about the rotor axis. Furthermore, since the center of gravity of the blade is aft of the pitch axis, the gravity term has a secondary angle-dependent alternating effect on the pitch angle. This alternating loading and unloading is accommodated by the rigid frame hub design.

The centrifugal force term, which is proportional to the square of the angular velocity, is more important than the aerodynamic term in the design, so that the rotational speed can be reflected in the blade pitching torque.

If desired, several accumulators of different pressures can be used, and one or more actuators can be used to handle different load ranges. However, a single actuator/single accumulator can represent an elegant all-encompassing pitch control design.

In addition to normal operation as shown in Figure 6, the pitch control hub also compensates for gusts and loss of electrical load. Wind gusts are reflected on the blades as an increase in pitch down moment due to control axis offset. This results in a corresponding immediate change in pitch angle, corrected by the inertia of the blade, relieving the bending moment of the blade. The negative spring arrangement of the pitch control hub, instead of generating high torque peaks and momentary bending moments of the blades, reduces them by a corresponding negative release of the gust load.

As the load decreases, a corresponding overspeed of the rotor occurs. The negative rotor design also keeps load drops due to overspeed within safe limits. Finally, the use of passive pitch control hubs also eliminates the need for complex electronic control logic, interactive sensors and feedback loops that are difficult to check and complex to operate. A telescopic hydraulic link system is used between the blade pitch load and the air spring to form a direct and effective override capability, further improving the reliability of the system. Automatic and manual shutdown is provided through feathering of the blades, eliminating the need for additional brake or control components.

The above-described embodiments are intended to be illustrative only and not limiting. Many changes, additions and subtractions can be made to the disclosed system without departing from the principles and spirit of the invention. For example, the drive train of the spur gears 62, 64, 66 and 68 can be modified as desired to produce counter-rotation directly connected to the blades. Also, the position of the gear train and the linear actuator along the pitch axes b and c can be changed. If there is enough space, the drive train can also be placed in other locations, such as in the center of the hub, with one (as shown) or more linear actuators and cambers on the shaft ends of the blades protruding from the bearing cylinder. turn connection. Other modifications to the hydraulic system can also be made. For example, a double-acting cylinder can be used to actively push the blades to full feathering when required. In any event, the scope of the invention is to be determined by the appended claims, and the equivalents thereof.

Claims (22)

1. The pitch control wind turbine hub has the following items: a housing constrains the pitch axes of a pair of spaced parallel blades in a plane that intersects the rotor axis near the midpoint between the two pitch axes, a pair of blade shafts supported on the shell for at least partial rotation about respective pitch axes, A gear train (device) is connected transversely between the two pitching axes (on one side of the rotor axis), and the blade shafts are directly connected for counter-rotation to withstand the alternating load of the blades and make the paddles of the two blades The distance angles are related to each other, A mechanical control device separate from the gear train and not acting directly on the gear train biases the blade axially at a calibrated starting pitch angle to withstand the total blade load and actively determines the pitch angle during operation. 2. A hub as claimed in claim 1, characterized in that the gear train has quadruple co-planar spur gears. 3. The hub as claimed in claim 2, characterized in that the four spur gears have two driving gears, each of which is coaxially installed on the corresponding propeller shaft, and at least two transmission gears are connected to the driving gear. 4. The hub of claim 1, wherein said control means includes the following: Each blade shaft has a radially extending crank, A device connected between the cranks controls the relative displacement of the cranks as the blade load changes. 5. The hub of claim 4, wherein said mechanical control means connected between said cranks has a linear actuator, the cylinder of which is pivotally connected to a crank and a piston rod to the other crank. Pivot connection. 6. The hub of claim 5, wherein the linear actuator is a hydraulic cylinder. 7. A hub as claimed in claim 5, further comprising a hydraulic system including pressurization means and a hydraulic circuit coaxial with the rotor axis, the pressurization means being connected to the hydraulic cylinder. 8. A hub as claimed in claim 7, characterized in that said pressurizing means and said rotor axis are fixed relative to each other. 9. A hub as claimed in claim 8, characterized in that the hydraulic system further comprises on-off valve means in the hydraulic circuit means for manual feathering. 10. The hub of claim 6 wherein the linear actuator is spring loaded. 11. The hub as claimed in claim 5, and there are another pair of circular blade mounting flanges, each of which determines a blade mounting flange plane, and a device is provided to eccentrically connect each mounting flange with the corresponding blade shaft, and the flange planes are horizontally adjusted axis, while the center of the blade flange is offset. 12. A hub as claimed in claim 11, characterized in that the blade mounting flanges are offset in the same direction, the crank extending generally towards the axis of the respective blade flange. 13. There are the following items in the pitch control wind turbine system: a deflection carrier, A rotor having a hub with at least two variable pitch blades mounted on the hub on an offset pitch shaft, a transmission shaft device rotatably connects the rotor to the carrier, A hydraulic actuator (device) is directly pivoted between the two pitch shafts so that the corresponding blade pitch loads act directly on each other through the actuator, The air-filled hydraulic accumulator on the carrier pressurizes the pressure oil inside, The hydraulic linkage guides the hydraulic fluid to connect the actuator device and the accumulator device. 14. The system of claim 13, further having means for counter-rotating the pitch shaft 1:1. 15. A system as claimed in claim 13 and further valve means for relieving pressure in said hydraulic linkage means in response to a shutdown command. 16. A system as claimed in claim 15, further having motor pump means for injecting hydraulic fluid into said accumulator means through said hydraulic linkage to raise to a predetermined operating pressure. 17. The system as claimed in claim 16, and another pressure switch device is connected with the hydraulic rod system to energize or de-energize the motor pump device to maintain the rated working pressure. 18. The system of claim 15 wherein said valve means is a solenoid valve. 19. The system of claim 13 wherein said linkage means passes substantially concentrically within said drive shaft means. 20. The pitch control wind turbine hub has the following items: a housing constrains the pitch axes of a pair of spaced parallel blades in a plane that intersects the rotor axis near the midpoint between the two pitch axes, A pair of turbine blades are shaft supported on the shell for at least partial rotation about respective pitch axes, A coplanar gear train transversely connected between the pitching axes, directly connected to the blade shaft for counter-rotation, bears the alternating load of the blades, and makes the pitch angles of the blades interrelated, a pair of corresponding cranks mounted on the pair of blade shafts spaced from the gear train, A remotely controllable gas-hydraulic linear actuator is directly connected between the cranks. 21. The hub of claim 20 wherein said gear train is coupled to said shaft on one side of said rotor axis and said linear actuator is coupled between said shafts on the other side of said rotor axis. 22. The hub of claim 1 wherein said housing includes an elastomeric wobble hub.

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