Example of pitch control system:
Z-type hydraulic pitch control mechanism of Zond Company of the United States
The hydraulic pitch control mechanism belongs to an electro-hydraulic servo system, and the principle of a typical pitch hydraulic actuator is as shown in the above figure. The blade is connected to the hydraulic cylinder through a mechanical linkage mechanism, and the change in the pitch angle is substantially proportional to the displacement of the hydraulic cylinder. When the hydraulic cylinder piston rod is moved to the left to the maximum position, the pitch angle is 88°, and when the piston moves to the right to the maximum position, the pitch angle is -5°. When the system is working normally, the two-way three-way electromagnetic reversing valves a, b, c are energized, the hydraulic control check valve is opened, and the displacement of the hydraulic cylinder is precisely controlled by the electro-hydraulic proportional valve reversing valve. When the wind speed is lower than the rated wind speed, the electro-hydraulic proportional directional control valve maintains the blade pitch angle of 3° regardless of the wind speed change. The electro-hydraulic proportional directional control valve is finely adjusted to maintain the pitch angle in consideration of the cylinder leakage. When the wind speed is higher than the rated wind speed, according to the output power, the electro-hydraulic proportional directional control valve is used to precisely change the output flow rate, thereby controlling the pitch angle of the blade, so that the output power is constant.
3. Hydraulic brake system
The high-speed shaft slewing system of the engine room and the main shaft uses a hydraulic disc brake. The high-speed shaft slewing system is used for braking the blades with a diameter of 60 to 100 m. Rapid braking can cause strong vibrations in the blades and the slewing system and create a large load. For this reason, it is necessary to feedback the rotation speed of the shaft, and the method of adjusting the brake pressure by changing the amplitude (soft brake) can reduce the load several times.
Parker, Eaton and Rexroth also manufacture disc-blade brake systems that can withstand harsh conditions and are safe. Less leakage, small size, space saving, hydraulic source is supplied by separate hydraulic station
Hydraulic brake system example Danish BONUS-150KW fan brake hydraulic system
1) Start the machine: When the control system issues a start command (can be automatic or manual), the motor starts immediately, the pressure enters the valve block from the “P” port, the left half of the valve block is the pressure part for the tip; the right half is The disc brakes provide pressure. At the same time of starting the motor, the solenoid valves 10# and 11# are energized from on to off, and the pressure oil can only enter the right half along the check valve 6#-2. When the pressure reaches the pressure switch 7# At 10.3MPa, the valve 10# opens, the pressure begins to enter the tip portion, and the blade damping plate is retracted. At the same time, the solenoid valve 12# is opened, the solenoid valve 13# is closed, the pressure of the circular disc is relieved, and the starting is completed. ready. When the tip of the blade is closed, the disc is also released at the same time. When the pressure of the pressure switch 15# reaches 7 MPa, the motor stops rotating. 17#, 18# are accumulators, which use compressed gas to store the energy in the pressure oil to supplement the leakage of the tip resistance plate and the circular disc during operation, reducing the frequent starting of the motor.
2) Brake stop: When the stop command of the wind control system is issued, the solenoid valve 10# is immediately charged, 11# is de-energized, the 10# solenoid valve is closed, the 11# solenoid valve is opened, and the 12#, 13# solenoid valve is lost. Electric, that is, open 13#, close 12#, and after the tip damper plate is ejected, the disk brake also acts to brake the wind turbine to stop smoothly.
3), performance characteristics
From the design point of view, the braking torque of this wind turbine comes from two aspects, one is the tip damper brake, the other is the disc brake brake, the braking torque is on the low speed shaft, so in the braking process The impact on the gearbox is small. In addition to this, there are the following characteristics:
a) The braking process is stable and the vibration is small. Since the braking process is firstly operated by the tip damper of the three blades evenly distributed, the speed is reduced, and then the disc brake is applied, which makes the braking process smoother. ;
b) The brake mechanism is independent of each other: the two brake mechanisms of the brake system are independent of each other, that is, the other brake set will not be able to work due to the failure of one brake system. For example, when the hydraulic system fails, the pressure cannot be established. When the disc brake is not able to brake normally, the tip damper plate is ejected just because of the pressure loss, which acts as a damping brake, thus enhancing the reliability of the brake system.
c), with a stall protection mechanism: the brake system is equipped with a centrifugal pressure cylinder at the root of the blade. When the wind turbine loses control and will fly, under the action of centrifugal force, the pressure rises to the setting of the pressure switch 14#. The value, 14# action is opened, the fly safety valve 16# is turned on, the pressure in the tip damper plate is released, and the damper plate is ejected, which serves as a protection.
