A brief description of a wind power control system
The wind power control system includes on-site wind turbine generator control units, a high-speed ring-redundant fiber optic Ethernet network, and a remote host computer operator station. The on-site wind turbine generator control unit is the core of each wind turbine's control, enabling functions such as parameter monitoring, automatic power generation control, and equipment protection. Each wind turbine generator is equipped with a local HMI (Human-Machine Interface) for local operation, commissioning, and maintenance. The high-speed ring-redundant fiber optic Ethernet network serves as the system's data highway, transmitting real-time data from the generator to the host computer interface. The host computer operator station is the core of the wind farm's operation monitoring, possessing comprehensive functions such as generator status monitoring, parameter alarms, and real-time/historical data recording and display. Operators can monitor and operate the generators at the wind farm from the control room.
The wind turbine control unit (WPCU) is the core of each wind turbine's control system, distributed throughout the tower and nacelle. Due to the harsh operating environment of wind turbines, the reliability requirements for the control system are extremely high. Wind power control systems are specifically designed for the operational needs of large-scale wind farms and must possess extremely high environmental adaptability and resistance to electromagnetic interference. Its system structure is as follows:
The field control station of a wind power control system includes: tower main controller cabinet, nacelle control station cabinet, pitch control system, converter system, field touch screen station, Ethernet switch, fieldbus communication network, UPS power supply, emergency shutdown backup system, etc. The network structure of the wind power control system is shown in Figure 1.
1. Tower base control station
The tower control station, also known as the main controller cabinet, is the core of wind turbine equipment control, mainly including controllers and I/O modules. The controller hardware uses a 32-bit processor, and the system software uses a highly real-time operating system. Various complex main control logics of the turbine are communicated in real time with the nacelle controller cabinet, pitch system, and converter system via fieldbus to ensure that the turbine operates in the optimal state.
The controller is configured using feature-rich and user-friendly configuration software, and adopts configuration methods that comply with the IEC61131-3 standard, including: Function Diagram (FBD), Instruction List (LD), Sequential Function Block (SFC), Ladder Diagram, Structured Text and other configuration methods.
2. Cabin control station
The nacelle control station collects signals such as temperature, pressure, speed and environmental parameters measured by the unit's sensors, and communicates with the unit's main control station via fieldbus. The main controller uses the nacelle control frame to realize functions such as yaw and unmooring of the unit. In addition, it controls various auxiliary motors, oil pumps and fans in the nacelle to ensure that the unit operates in the best condition.
3. Variable pitch system
Large-scale wind turbines with a capacity of MW or higher typically employ hydraulic or electric pitch control systems. The pitch control system, controlled by a front-end controller, manages the pitch drive mechanism for the three turbine blades. This front-end controller is the execution unit of the main controller and communicates with it via CANOPEN to adjust the pitch of the three blades to operate at their optimal state. The pitch control system includes a backup power system and safety chain protection to ensure emergency shutdown in critical operating conditions.
4. Converter System
Large wind turbine generator sets generally use high-power converters to convert generated energy. The converter system communicates with the main controller through a fieldbus to regulate the unit's speed, active power, and reactive power.
5. On-site touch screen station
The on-site touch screen station is a local operating station for unit monitoring, enabling local parameter setting, equipment debugging, maintenance, and other functions for wind turbine units. It serves as the on-site supervisory and controller operator station for the unit's control system.
6. Ethernet switch (HUB)
The system uses industrial-grade Ethernet switches to connect the controller of a single unit, the field touchscreen, and the remote control center network. Standard twisted-pair cables are used for connections within the field cabinets, while fiber optic cables connect to the host computer in the remote control room.
7. On-site communication network
The main controller has multiple fieldbus interfaces such as CANOPEN, PROFIBUS, MODBUS, and Ethernet, which can be configured according to the actual needs of the project.
8. UPS power supply
UPS power supplies are used to ensure the power supply to the unit's control system, emergency protection system, and related execution units in the event of an external power outage.
9. Backup emergency safety chain system
The backup emergency safety chain system is independent of the computer system's hardware protection measures. Even if the control system malfunctions, it will not affect the normal operation of the safety chain. The safety chain connects extraordinary faults that could cause fatal damage to the wind turbine into a loop. When the safety chain is activated, it will cause an emergency shutdown and disconnect the unit from the grid, thereby maximizing the safety of the unit.
All wind turbines are connected to the host computer operator station in the main control room via fiber optic Ethernet, enabling remote monitoring of the entire wind farm. The host computer monitoring software should have the following functions:
① The system has a user-friendly control interface. When developing the monitoring software, the requirements for wind farm operation and management were fully considered. A Chinese menu was used to simplify operation and facilitate wind farm management as much as possible.
② The system displays the operating data of each unit, such as the instantaneous power generation, cumulative power generation, power generation hours, wind turbine and motor speed, wind speed, wind direction, etc. The data from the lower-level machine is loaded into the upper-level machine and displayed on the monitor. If necessary, it can also be displayed intuitively in the form of curves or charts.
③ The system displays the operating status of each wind turbine, such as start-up, shutdown, direction adjustment, manual/automatic control, and the operation of large/small generators. By observing the status of each wind turbine, one can understand the overall operation of the wind farm.
④ The system can promptly display faults occurring during the operation of each unit. When displaying a fault, it can show the type of fault and the time of occurrence, so that operators can handle and eliminate the fault in a timely manner, ensuring the safe and continuous operation of the wind turbine units.
⑤ The system enables centralized control of wind turbine units. From the central control room, operators can change settings and control lower-level units simply by pressing the corresponding keys labeled with specific functions. This includes actions such as starting, stopping, and adjusting the direction of the turbine. However, these operations have certain access restrictions to ensure the safe operation of the entire wind farm.
⑥ System Management. The monitoring software has the functions of timed printing of operating data, manual real-time printing, and automatic recording of faults, so as to view the historical records of the wind farm's operating status at any time.
II. Basic Functions of Wind Power Control System
(1) Data Acquisition (DAS) function: including the acquisition of power grid, meteorological and unit parameters, and to realize control, alarm, recording and curve functions, etc.;
(2) Unit control functions: including automatic start-up of the unit, grid connection control, speed control, power control, reactive power compensation control, automatic wind control, cable unwinding control, automatic grid disconnection, and safe shutdown control, etc.
(3) Remote monitoring system functions: including monitoring of unit parameters and related equipment status, historical and real-time curve functions, and cumulative monitoring of unit operation status.
1. Data Acquisition (DAS) Function
The relevant parameters monitored during unit operation include:
(1) Power grid parameters, including three-phase voltage, three-phase current, power grid frequency, power factor, etc. Voltage fault detection: power grid voltage flicker, overvoltage, undervoltage, voltage drop, phase sequence fault, three-phase asymmetry, etc.
(2) Meteorological parameters, including wind speed, wind direction, ambient temperature, etc.
(3) Detection of unit status parameters, including: wind turbine speed, generator speed, generator coil temperature, generator front and rear bearing temperature, gearbox oil temperature, gearbox front and rear bearing temperature, hydraulic system oil temperature, oil pressure, oil level, nacelle vibration, cable twisting, nacelle temperature, etc.
Both the host computer and the touch screen station at the wind farm remote monitoring center can monitor the status of the units and display, record, generate curves, and issue alarms for relevant parameters.
2. Unit start-up and shutdown, power generation control
(1) The main control system detects the grid parameters, meteorological parameters and unit operating parameters. When the conditions are met, the yaw system is started to perform automatic cable release and wind control, release the unit's brake disc, adjust the pitch angle, and the wind turbine begins to rotate freely and enters standby mode.
(2) When the wind speed monitored by the external meteorological system is greater than a certain value, the main control system starts the converter system to start rotor excitation. When the generator stator output power is in the same frequency, phase and amplitude as the power grid, the output circuit breaker is closed to realize grid-connected power generation.
(3) Wind turbine power and speed regulation
Based on the characteristics of wind turbines, the turbine will capture the maximum energy when operating at the optimal tip speed ratio λ. Although theoretically the turbine can operate at any speed, due to actual turbine speed limitations and system power limitations, this stage must be divided into the following operating regions: variable speed operation region, constant speed operation region, and constant power operation region. The operating states within the rated power range include: the variable speed operation region (optimal λ) and the constant speed operation region.
When the wind turbine is connected to the grid, if the speed is lower than the limit speed and the power is lower than the rated power, the speed of the wind turbine is adjusted according to the current actual wind speed so that the unit operates in the state of capturing maximum wind energy.
Because there is a certain error between the wind speed measured at the anemometer's measuring point and the wind speed acting on the blades, a torque observer is used to predict the mechanical transmission torque of the wind turbine unit. The generator speed is then derived from the relationship between the generator speed and the torque. ω is the expected generator speed. Tm is the observed torque. Kopt is the proportionality constant at the optimal speed.
When the wind speed increases and the generator speed reaches its upper limit, the main controller needs to maintain a constant speed. The power output of the wind turbine increases with the increase of wind speed. At this time, the unit deviates from the optimal λ curve of the wind turbine.
As the wind speed continues to increase, the speed and power reach their upper limits, and the unit enters the constant power operation zone. In this state, the main controller maintains the unit's power constant through the converter. On the one hand, the main controller reduces the wind angle of attack by adjusting the pitch system, thereby reducing the wind energy captured by the blades; on the other hand, it reduces the generator speed by adjusting the converter, causing the wind turbine to deviate from the optimal λ curve and maintain the generator's output power stable.
3. Logic of auxiliary equipment in wind power control system
(1) Generator system
The generator's operating parameters are monitored, and the generator coil temperature, bearing temperature, and slip ring chamber temperature are controlled within appropriate ranges through three cooling fans and four electric heaters. The relevant logic is as follows:
When the generator temperature rises to a certain set value, the cooling fan starts; when the temperature drops to a certain set value, the fan stops running. When the generator temperature is too high or too low and exceeds the limit, an alarm signal is issued and a safety shutdown procedure is executed.
When the temperature drops to a certain set value, the electric heater is started; when the temperature rises to a certain set value, the heater stops operating. At the same time, the electric heater is also used to control the temperature difference of the generator within a reasonable range.
(2) Hydraulic system
The unit's hydraulic system is used for yaw system braking and mechanical brake disc drive. Under normal conditions, the unit must maintain operation within the rated pressure range.
The hydraulic pump controls the pressure of the hydraulic system. When the pressure drops to a set value, the oil pump starts running. When the pressure rises to a certain set value, the pump stops. (3) Meteorological system
The meteorological system is an intelligent meteorological measuring instrument that communicates with the controller via an RS485 port to collect meteorological parameters from outside the cabin and transmit them to the control system. The system's heaters are controlled based on the ambient temperature to prevent icing.
Flashing obstruction light control: A flashing obstruction light is installed at the end of each blade to illuminate at night.
The cabin fan controls the ambient temperature inside the cabin.
(4) Electric pitch control system
The variable pitch system includes a motor, driver, and main control PLC on each blade. This PLC communicates with the turbine's main control system via a CAN bus and is the pitch adjustment control unit in the wind power control system. The variable pitch system has a backup DO feathering control interface. The main functions of the pitch system are as follows: emergency braking feathering system control, enabling feathering control of the wind turbine in emergency situations; and communication with the main controller via the CAN communication interface, receiving main control commands and adjusting the blade pitch to a predetermined position. The communication content between the pitch system and the main controller includes:
Blade A position feedback
Blade B position feedback
Blade C position feedback
Blade pitch given command
Comprehensive fault status of pitch system
The blades are in a feathering position
feathering command
(5) Speed-increasing gearbox system
The gearbox system is used to increase the wind turbine speed to the normal operating speed range of the doubly-fed generator. It is necessary to monitor and control the gear oil pump, gear oil cooler, heater, lubricating oil pump, etc.
When the gear oil pressure is lower than the set value, the gear oil pump starts; when the pressure is higher than the set value, the gear oil pump stops. When the pressure exceeds the limit, an alarm is issued and the shutdown procedure is executed.
Gear oil cooler/heater controls gear oil temperature: when the temperature is lower than the set value, the heater starts; when the temperature is higher than the set value, the heater stops. When the temperature is higher than a certain set value, the gear oil cooler starts; when the temperature drops to the set value, the gear oil cooler stops.
The lubricating oil pump is controlled so that it starts when the lubricating oil pressure is lower than the set value and stops when the oil pressure is higher than the set value.
(6) Yaw system control
Based on the current nacelle angle, the measured low-frequency average wind direction signal value, and the current operating status and load signal of the unit, the CW (clockwise) and CCW (counterclockwise) motors are adjusted to achieve automatic wind and cable unwinding control.
Automatic wind alignment: When the unit is in operation or standby mode, the CW and CCW motors are adjusted according to the deviation value of the nacelle angle and the measured wind direction to achieve automatic wind alignment. (Yawing is performed at the set yaw speed, and the operating status of the yaw motor needs to be monitored.)
Automatic unmooring control: When the unit is in a suspended state, if the nacelle twists more than 720 degrees in a certain direction, the automatic unmooring procedure is initiated; or when the unit is in operation, if the twist exceeds 1024 degrees, the unmooring procedure is implemented.
(7) Communication of high-power converters
The main controller communicates with the converter via the CANOPEN communication bus. The converter performs grid-connection/disconnection control, generator speed regulation, active power control, and reactive power control.
Grid connection and grid disconnection: According to the master control instructions, the converter system excites the generator rotor and controls the generator stator output power to be in the same frequency, phase and amplitude, and then drives the stator output contactor to close to achieve grid connection; when the generator power is less than a certain value for several seconds or when the wind turbine or the grid has an operating fault, the converter drives the generator stator output contactor to open to achieve grid disconnection of the unit.
Generator speed regulation: When the unit is running below the rated load after grid connection, the generator speed is controlled to make the unit run on the optimal λ curve. The wind turbine is used as an anemometer to measure the real-time torque value and adjust the unit to the optimal state of operation.
Power control: When the unit enters the constant power zone, it maintains the unit's output power according to the communication command with the frequency converter.
Reactive power control: Reactive power control or power factor adjustment is achieved through communication commands with the frequency converter.
8) Safety chain loop
The safety chain loop is independent of the main control system and executes emergency shutdown logic in parallel. All related drive loops are powered by backup batteries to ensure reliable system operation in emergency situations.
III. Current Technical Status and Countermeasures
Currently, our factory possesses generator technology, and the converter system is under development, having been completed in early 2010. Other technologies are still lacking. To quickly enter the market, we should adopt a two-pronged approach: independent research and development, and technology import. Domestic manufacturers currently possessing this technology include Nanjing Keyuan Automation Group Co., Ltd., and Beijing Jingxin also possesses this technology and has conducted trial operations on a 1MW unit.
In terms of independent research and development, given the complexity of wind power control systems, it is necessary to collaborate with reputable universities. Multiple sub-projects need to be established during the research and development process, as these projects include technologies such as computer hardware, power electronics, software, and communications, which are also distributed throughout the wind turbine unit according to their functions.
IV. Conclusion
The main directions of wind power generation at present:
1. The land-based wind turbine generator set adopts a 1.5/2M doubly fed asynchronous generator set.
2. The offshore wind turbine generator set adopts a 4/5M permanent magnet synchronous fully fed generator set.
3. Construct large or super-large wind farms (consisting of hundreds of wind turbine units).
4. The wind turbine control system has a voltage penetration protection function.
5. Wind turbine generators can adjust the power factor when generating electricity online, and can also adjust the power factor when not generating electricity to perform reactive power compensation and purify the power grid.
