The wind energy, which is known as “blue sky and white coalâ€, is an inexhaustible, clean and pollution-free renewable energy source. Its good development and utilization prospects have been widely recognized by countries all over the world. In particular, with the application of computer technology and advanced control technology to the field of wind power, the design and manufacturing technology of wind power generation has become more and more complete, and it has quickly entered into commercialization and industrialization. As one of the countries with abundant wind resources, China has made rapid progress in the localization of wind turbines. During the "Eighth Five-Year Plan" period, 200kW/250kW wind turbines were successfully developed and 600kW stall-type wind turbines were developed during the "Ninth Five-Year Plan" period. The key technology of wind turbine control system was successfully developed. During the "10th Five-Year Plan" period, the 600kW stall-type wind turbines began to be industrialized, and the megawatt-type stall-type and megawatt-speed variable-speed constant frequency have been listed as national scientific and technological projects. This paper introduces the industrialization project of the 600kW stall-type wind turbine of the “10th Five-Year†scientific and technological project. On the basis of introducing the control system, several major aspects of this key technology research of the wind turbine control system are highlighted.
2 Control system composition and function control system is the core of the normal operation of wind turbines. Its control technology is one of the key technologies of wind turbines. It is closely related to other parts of wind turbines. Its precise control and perfect functions will directly affect the unit. Safety and efficiency. Therefore, the control system is a reliable guarantee for the normal and reliable operation of the entire unit and for optimal operation. The components of the control system mainly include: main circuit, control circuit, sensor and interface circuit.
2.1 System Components 2.1.1 Main Circuit The main circuit is the main distribution system of the wind turbine. It mainly completes the connection between the generator and the grid, the reactive power compensation device, the soft grid-connected control device and the actuators and the control loop. The main circuit provides more power levels (such as 690VAC, 400VAC, engine, power supply, etc.) or feedback signals sent to the central controller for monitoring.
2.1.2 Control Circuit The control circuit consists of the central controller and its functional extensions. It mainly realizes the input, output signal processing and logic function judgment, and issues control commands to the peripheral actuators. According to the signal processing and logic judgment, the reliable operation of each part of the unit is guaranteed. At the same time, the data record is read through the configured man-machine interface, and the operation is modified. Parameters and manual operation, the configured communication interface communicates with the central monitoring system in real time.
2.1.3 Sensors and Interface Circuits Sensors mainly include current transformers and voltage transformers for monitoring power parameters; wind speed anemometers, wind vanes and Hall proximity switches, platinum thermal resistance, vibration acceleration sensors, and yaw counting sensors. A sensor that monitors the status parameters of the unit, such as a travel switch, a level switch, and a pressure switch.
The interface circuit converts the signals collected by some of the sensors into a unified standard signal through the interface circuit or sends them to the central controller for processing by means of communication.
2.2 System function control system mainly realizes three functions of normal operation control, parameter monitoring and monitoring, and safety protection and processing.
The normal operation control includes wind turbine automatic starting soft grid connection, large/small generator automatic switching, generator heating, automatic yaw to wind, hydraulic oil pump automatic start and stop, gear oil pump automatic start and stop, gear oil heater, cooling Start and stop, automatic yaw unwinding, capacitor compensation automatic group switching and negative power automatic shutdown.
Parameter monitoring and monitoring include power, wind parameters and hydraulic system conditions, yaw system conditions, soft grid connection and other working conditions; configuration of communication interface for central control room monitoring and remote monitoring, monitoring of operating status and fault conditions, collection of fan operating data , the control command issued to the fan.
The safety protection and treatment system ensures the safety and reliability of the operation process, including braking protection when the unit fails, safety chain protection independent of the computer, protection of the device itself, grounding protection and lightning protection.
3 The key technology of the control system The control system of the wind turbine is a comprehensive control system. The control system not only monitors the grid, wind conditions and unit operating parameters, but also controls the grid connection and off-grid, and also changes according to wind speed and wind direction. , optimize control of the unit. Therefore, the key technologies of the control system include the following main aspects: soft grid-connected control, yaw system control, reactive power compensation control, braking and safety protection, operating state parameter monitoring, local monitoring and remote monitoring.
3.1 Soft grid-connected control Soft grid-connected control technology is an important part of the control system.
Since the wind turbine adopts the squirrel-cage double-winding asynchronous generator and the power grid, if the current limiting measures are not taken, it will have a strong impact on the wind turbine and the power grid. When the impact is severe, it will not only cause the system voltage to drop, but also may Generators and mechanical components (such as towers, gearboxes) cause damage. Therefore, the use of soft grid-connected control can limit the transient current of the generator when it is connected to the grid and switch between large and small motors to avoid excessive impact on the grid.
The soft grid-connected control device adopts a bidirectional thyristor or a thyristor anti-parallel mode, and the control method thereof adopts a voltage ramp soft grid control method. This method is derived from the step-down startup. Through the thyristor phase shift trigger control, the conduction angle of the thyristor is changed, so that the voltage applied to the stator of the motor is gradually increased from a small initial value to a step wave. Full pressure state, to achieve the purpose of pressure limiting current limit. The specific method is that when the generator speed is close to the synchronous speed, the two-way thyristor directly connected to the power grid is turned on according to the gate trigger pulse, and the grid-connected inrush current is limited to 2 times the rated current of the motor. After the thyristor is fully turned on, the speed exceeds the synchronous speed and enters the power generation state. The bypass contactor short-circuits the two-way thyristor, and the wind turbine enters the steady-state operation phase.
Soft grid-connected control mainly includes small motor soft grid connection, large motor soft grid connection, small motor switch to large motor, large motor to small motor switch, small motor static electric start grid.
3.2 Yaw system control The yaw system is a unique control system for wind turbines. The yaw control system is mainly composed of three parts: yaw measurement, yaw drive transmission part and new line protection device. It mainly realizes two functions: one is to make the cabin track the stable wind direction; the other is to automatically unwind the cable inside the cabin due to the yaw effect.
The wind direction is used to track the change of wind direction to design automatic yaw and design 90* crosswind according to specific control requirements, central control room to control yaw, control panel yaw and top cabin yaw. The yaw control sets the priority. The order of priority from small to large is: automatic yaw of wind vane control, yaw control of central control room, yaw of control panel and yaw of top cabin.
The cable unwinding system automatically unwinds the cable according to the signal of the cable sensor when the cable is wound. The cable unwinding system is divided into two types: automatic cable unwinding controlled by the button sensor and safety chain protection controlled by the button switch. When the cable winding reaches the set value, the control system controls the yaw system to perform cable unwinding according to the signal from the cable sensor. If the control system does not automatically untie the cable, when the cable winding reaches the allowable limit, the safety chain protection of the new cable switch is triggered, and the unit is shut down urgently, waiting for manual processing.
3.3 Reactive Power Compensation Control Wind turbines use asynchronous generators, which must absorb backward reactive power from the grid for excitation, while stator and rotor leakage also consume reactive power. For power systems, reactive power primarily affects grid voltage and increases line losses. When the reactive power provided by the grid is insufficient, it will affect the quality of the grid. Therefore, reactive power compensation can improve the power factor and improve the power quality of wind turbines.
The specific control idea is: using parallel capacitors for reactive power compensation. It is compensated in four levels. The four-level capacity is 87.5kvar, 50kvar, 25kvar and 12.5kvar. The switching of the capacitor can be switched according to the active power generated by the generator, and the frequent switching of the compensation capacitor is prevented. In the process of switching, the delay setting is set, and a certain difference value is set for the input and cut power values.
3.4 Brake and safety protection Brake system and safety protection are the guarantee for the safe operation of wind turbines. The brake system is mainly composed of two parts: the tip pneumatic brake and the disc high speed brake.
The control system judges the alarm, normal shutdown, safety shutdown and emergency shutdown according to the type of fault of the wind turbine, and realizes the automatic restart or manual start of the wind turbine for the self-reset fault and the non-resettable fault. Safety and efficiency of the unit to improve the efficiency; k independent of the computer's safety chain is the use of anti-logic design, the extraordinary faults that may cause fatal damage to the wind turbine, such as computer system out of control, etc. in series, once one action Will cause an emergency stop and the system will lose power. After an emergency stop occurs, it can be restarted after a manual reset operation.
The protection measures of the device itself mainly adopt hardware protection measures, such as adding RC absorption circuit, hardware interlock circuit, over-voltage and over-current protection at both ends of the coil; grounding protection mainly directly grounds the control cabinet and the shielded cable layer; The protection mainly adopts lightning protection measures for the output end of the main circuit, the input end of the electronic circuit, and the communication line, and is generally protected by a transient absorption circuit.
3.S operating state parameters Monitoring and monitoring Various operating parameters of the wind turbine during operation include power parameters, wind parameters and state parameter monitoring.
The power parameters that wind turbines need to continuously monitor mainly include the three-phase voltage of the power grid, the three-phase current of the generator output, the grid frequency, the generator power factor, the active power, and the reactive power. When measuring voltage, it mainly detects grid shock, overvoltage, overcurrent, grid voltage drop, etc. When measuring current, it mainly detects current drop and three-phase unbalance; the wind parameters that wind turbine needs to monitor are mainly wind speed and wind direction. The state parameters to be monitored mainly include temperature, cabin vibration, new cable, system pressure, tip pressure, gear oil pressure, gear oil filter and feedback signal from the actuator; wherein the speed includes the speed including the generator speed and the impeller speed; Mainly include gearbox oil temperature, large generator temperature, small generator temperature, front bearing temperature, rear bearing temperature, ambient temperature and control cabinet temperature.
3.6 Local monitoring and remote monitoring The central control room PC is used as the upper computer, and multiple lower computer control systems (central controllers) are networked, and communication is realized with the PC through dedicated communication devices and interface circuits. Real-time monitoring Wind turbine operation status, operation data, accumulated data storage, recording fault conditions, statistical printing reports, yaw, reset, start, stop, etc.
Remote monitoring is to communicate with the central control room PC through Modem or Industrial Ethernet, collect monitoring data of the PC in the central control room, and remotely monitor multiple wind turbines in different places (such as fan manufacturers).
4 System reliability design Wind resources rich areas are usually remote areas or islands or even offshore, the natural environment is harsh, need unattended and remote monitoring, the reliability and security requirements of the control system is higher. Therefore, when designing the control system, the central controller generally chooses to use more in the industrial control field, especially to work in the harsh natural environment, and has strong real-time, reliability and anti-interference ability; Signal isolation measures and shielding protection should be adopted for signal processing; hardware interlocking and instantaneous induced overvoltage protection measures are adopted for hardware circuit design; in software design, software permission design, task coordination design, fault tolerance design, Anti-jamming design and program infinite loops need to be considered.
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