The role of wind power yaw system
The yaw system is a servo system unique to wind turbines. It mainly has two functions: one is to enable the wind turbine to track stable changes in wind direction; The second is that when the wind turbine generator system is affected by yaw and the cables leading out of the cabin become tangled, the cables will be automatically untied.
Yaw control system
The yaw system is a servo system. The wind direction indicator transmits the collected signal to the I/O board of the PLC in the engine room cabinet, calculates the 10 minute average wind direction, compares it with the absolute value encoder of the yaw angle, outputs commands to drive four yaw motors (with power loss braking), adjusts the head in the direction opposite to the wind, records the current adjusted angle, stops the motor after adjustment and starts the yaw braking. The block diagram of the yaw control system is shown in the following figure:
The following text will analyze the various mechanisms of the yaw control system:
- Anemometer
The wind turbine should have two heatable anemometers. During normal operation or when the wind speed exceeds the minimum limit wind speed, the anemometer program continuously checks and monitors the synchronized operation of all anemometers. The computer collects wind speed data from the anemometer once per second; Calculate the average value every 10 minutes to determine the starting wind speed and stopping wind speed. The difference in measurement data should be within the difference limit of 1.5m/s. If all anemometers send reasonable signals, the control system will take an average value. - Wind vane
The wind vane is installed on both sides of the top of the engine room, mainly measuring the deviation angle between the wind direction and the centerline of the engine room. Generally, two wind indicators are used to verify each other and eliminate possible false signals. The controller starts the yaw system based on the wind direction signal. When two wind indicators are inconsistent, the yaw will be automatically interrupted. When the wind speed is below 3m/s, the yaw system will not start. - Twist switch
The twisted cable switch works by transmitting signals to the PLC for processing and issuing instructions through a gear meshing mechanical device. In addition to programming the direction counting program in the control software, a travel switch is generally installed at the cable location. When its contact is connected to the cable bundle, the switch is activated when the cable bundle rotates to a certain degree with the engine room. Taking the 1.5MW wind turbine produced by a well-known domestic company as an example, when the body has rotated 2 revolutions (720 degrees) in the same direction and the wind turbine is not in the working area (i.e. 10 minutes)
The system enters the cable removal procedure when the average wind speed is lower than the cutting in wind speed. During the cable removal process, when the wind turbine returns to the working area (i.e. the average wind speed for 10 minutes is higher than the cutting in wind speed), the system stops the cable removal program and enters the power generation program. However, when the body has rotated 2.5 revolutions (900 degrees) in the same direction and the yaw limit action is twisted for cable protection, the system forcibly enters the cable removal program. At this time, the system stops all work until the cable removal is completed. When the wind speed exceeds 25 m/s, the automatic cable release stops. The automatic release of cable winding can be checked for normality through manual alignment. When the directional stop contact changes from normally closed to normally open, the wind turbine automatically releases the cable winding. At this time, the wind turbine should not be in maintenance mode, so the automatic directional function cannot be used during maintenance. - Yaw encoder
Yaw encoder is an absolute value encoder that can accurately record the yaw position. Because the accuracy of each position determined by the mechanical position of the encoder, it does not require memory, reference points, or continuous counting. It reads its position whenever it needs to be known. In this way, the anti-interference characteristics of the encoder and the reliability of the data are greatly improved. - Soft starter
The soft starter uses three-phase anti parallel thyristors as voltage regulators, which are connected between the power supply and the motor stator. This type of circuit, such as a three-phase fully controlled bridge rectifier circuit, uses a soft starter to start the motor. The output voltage of the thyristor gradually increases, and the motor gradually accelerates until the thyristor is fully conductive. The motor operates on the mechanical characteristics of the rated voltage, achieving smooth starting, reducing starting current, and avoiding starting overcurrent tripping. When the motor reaches the rated speed, the starting process ends, and the soft starter automatically replaces the completed thyristor with a bypass contactor to provide the rated voltage for the normal operation of the motor, reducing the heat loss of the thyristor, extending the service life of the soft starter, improving its working efficiency, and avoiding harmonic pollution in the power grid. The soft starter also provides a soft stop function, which is the opposite of the soft start process. The voltage gradually decreases and the speed gradually drops to zero, avoiding torque shock caused by free parking. - Yaw mechanism
The yaw system is composed of a slewing support bearing, a spring damping device, and a gear transmission mechanism driven by four motors. The yaw bearing with internal teeth is bolted to the top of the tower, the outer ring is connected to the engine compartment seat, and the inner ring is connected to the tower flange. In a yaw system, the driving mechanism is generally composed of a motor and a reducer. The motor is the power source for yaw, and the reducer is the mechanism that converts the high-speed output of the motor into low-speed output. Therefore, in a typical yaw system, the yaw brake part is generally composed of two parts: one is the motor electromagnetic brake installed at the rear end of the driving motor, and the other is the hydraulic yaw installed near the yaw bearing. During yaw, 10 brake discs are in a semi released state, and the yaw system pressure is about 45 bar;