(National Institute of Thermal Power Institute of Thermal Power Research Institute, Xi'an 710032, China) Xu Jue-rong has achieved the maximum value of the ratio of the blade speed to the wind speed of the M blade. The wind speed of the constant-speed constant-frequency unit remains unchanged, and the wind speed changes frequently. Obviously Cp cannot be maintained at the optimal value. The characteristic of the variable speed constant frequency unit is that the rotation speed of the windmill and the generator can be varied within a wide range without affecting the frequency of the output electrical energy. Because the rotational speed of the windmill is variable, the peripheral speed ratio of the wind turbine can be set at or near the optimum value through appropriate control, thereby maximizing the use of wind energy for power generation. 2.3 Characteristics of constant speed constant frequency units At present, the most frequently used asynchronous generators in wind power generation systems are constant speed constant frequency generators. In order to meet the requirements of large wind speeds, two asynchronous generators with different capacities and different poles are generally used. When the wind speed is low, small-capacity generators are used to generate electricity. When the wind speed is high, large-capacity generators are used to generate electricity. At the same time, the pitch system is usually adopted. Change the blade's angle of attack to adjust the output power. However, this only allows the asynchronous generator to have a better output coefficient at two wind speeds and cannot effectively use the wind energy at different wind speeds. 2.4 Realization of Variable Speed ​​Constant Frequency System There are many kinds of variable speed constant frequency systems that can be used in wind power generation, such as AC-DC-AC frequency conversion system, AC excitation generator system, brushless double-fed motor system, switched-reluctance generator system, magnetic field. Modulation generator system and synchronous asynchronous variable speed constant frequency generator system. Some of the variable speed constant-frequency systems are realized by changing the structure of the generator itself to realize variable speed constant frequency, and some are combined with a power electronic device and a microcomputer control system to achieve variable speed constant frequency. Each of them has its own characteristics and different application occasions. 3 Control of constant-speed constant-frequency wind turbine 3.1 Soft-start grid-connected wind turbine When the wind turbine starts, the control system continuously monitors the change of wind speed. When the 10-minute average wind speed is greater than the starting wind speed, the wind turbine is controlled. All the preparations for a good cut into the grid: Loosen the mechanical brakes and retract the blade tip damper plate. The wind turbine is in the windward direction. The control system continuously detects whether each sensor signal is normal, such as whether the hydraulic system pressure is normal, whether the wind direction deviates, and whether the grid parameters are normal. If the 10-minute average wind speed is still greater than the start-up wind speed, check whether the wind wheel has started to turn and turn on the thyristor current limiting soft-start equipment, China Automation Yellow Pages, the industry's first public welfare large-scale tool book, read the book and donate books, invite advertising to join us! The Automation Expo will quickly start the wind turbine and control the starting current so that it does not exceed the maximum limit. When the generator reaches synchronous speed, the current drops suddenly and the controller issues a command to bypass the thyristor. Asynchronous wind turbines can also be off-grid when the speed is lower than the synchronous speed during start-up, and cut into the grid when the synchronous speed is approached or reached, which can avoid inrush current and can also save the thyristor current-limiting soft starter. 3.2 Switching control of generator size When the output power of the generator changes due to the change of wind speed during the operation of the wind turbine generator, the control system should be able to automatically switch between the generator and the generator according to the change of the output power of the generator, thereby increasing the Wind turbine efficiency. The specific control method is: switching from small generators to large generators. During the period of small generators connected to the grid, the control system detects the output power of the generators. If the instantaneous power within 1 second exceeds 20% or 2 minutes of the rated power of the small generators. When the average power inside is greater than a certain value, switching from a small generator to a large generator is realized. Switching of large generators to small generators detects the output power of large generators, if the average power within 2 minutes is less than a certain set value (this value should be less than the rated power of small generators) or the instantaneous power is less than 50 seconds With a smaller setpoint, it immediately switches to a small generator run. 3.3 pitch control method and its improvement After the wind generator is connected to the grid, the control system changes the blade angle of attack to adjust the output power according to the change of the wind speed, so as to use the wind energy more effectively. Below the rated wind speed, when the blade angle of attack is near zero, it can be considered equal to a fixed pitch wind turbine, and the output power of the generator changes with the change of wind speed. When the wind speed reaches above the rated wind speed, the pitch-raising mechanism plays a role in adjusting the angle of attack of the blades to ensure that the output power of the generator is within the permissible range. In order to reduce the adverse effect of the pitch adjustment method on the power grid, a new power-assisted adjustment method, Rotor Current Control (RCC) method, can be used in conjunction with the variable pitch mechanism to jointly accomplish the adjustment of the output power of the generator. . The RCC control must use an in-line asynchronous generator, control the rotor current of the generator through power electronic devices, and make the ordinary asynchronous generator a variable slip generator. RCC control is a fast electrical control method used to overcome rapid changes in wind speed. 3.4 Reactive power compensation control Since the asynchronous generator needs to absorb reactive power from the grid, the power factor of the wind turbine is reduced, and the wind turbine generating unit that is connected to the grid generally requires a power factor of 0.99 or higher, so the capacitor bank must be used for reactive power. make up. Because of the randomness of the wind speed changes, the output power of the generator is randomly changed before the rated power is reached. Therefore, the input and removal of the compensation capacitor needs to be controlled. There are four sets of compensation capacitors with different capacities in the control system. The computer controls the compensation capacitors to be put in or cut out in stages according to the change of the output reactive power to ensure that the power factor at the half power point is above 0.99. 3.5 Yaw and automatic cable unwinding control The yaw control system has three main functions: When the vehicle is normally transported, the control system sends an instruction to adjust to the left or right when the cabin deviates from the wind direction, and the cabin starts to wind. When it reaches the allowable error range, the wind stops automatically. Automatic cable unwinding when cable winding When the nacelle is accumulated and deflected for 2.3 laps in the same direction, if the wind speed is less than the wind speed of the wind turbine and there is no power output, it will stop and the control system will rotate the nacelle in the opposite direction for 2.3 laps. If there is a power output, it will not be automatically unwound temporarily; if the nacelle continues to deflect in the same direction for a total of 3 turns, the control will be stopped and unwound; if the unwinding is not successful due to a fault, the twisted cable will reach 4 turns, the twisted cable The mechanical switch will act. At this time, the cable fault will be reported and the machine will automatically stop and wait for the manual cable unplugging operation. Off-wind direction during stall protection When an oversize wind occurs, stop and release the tip damper plate, adjust the pitch to the maximum and yaw 90 leeward to protect the wind turbine from damage. 3.6 Stop Control The stop process is divided into normal stop and emergency stop. When the controller issues a normal stop command, the wind turbine will stop according to the following procedure: 1Remove the compensation capacitor; 2Release the blade tip damping plate; 3The generator is disconnected from the grid; 4Measurement after the generator speed drops to the set value, put into the mechanical brake ;5 If there is a brake failure, then the propeller is received and the nacelle is yawing 90 leeward. When an emergency shutdown fault occurs, the following shutdown operations are performed: first the compensation capacitor is removed, the blade tip damping plate is actuated, and the caliper brake action is performed after a delay of 0.3 seconds. When detecting the instantaneous power is negative or the generator speed is less than the synchronous speed, the generator is disengaged (off the net), if the braking time exceeds 20s, the speed has not dropped to a certain set value, then the propeller is received, and the cabin is yawing 90* ​​leeward . 4 Control of Variable Speed ​​Constant Frequency Generator Set 4.1 Synchronous Generator AC-DC-AC System Control This type of wind turbine adopts synchronous generator. The frequency, voltage, and electric power of the generator's electrical energy all change with the wind speed. However, it is beneficial to maximize the use of wind energy resources, and the task of constant-frequency constant-voltage grid-connection is accomplished by the AC-DC-AC system. Wind turbine start-up, control and protection functions are basically similar to constant-speed constant-frequency units. The difference is that this type of unit generally adopts a fixed-pitch wind automation expo "fieldbus technology collection" in May 2002 a grand publication of the field bus set The essence, on the hot topics in the industry! 21 rounds, so the pitch control mechanism is eliminated. The generator's output power is controlled by excitation. When the output power is less than the rated power, it is operated with fixed excitation. When the output power exceeds the rated power, the output power of the generator is adjusted to operate within the allowable safety range by adjusting the excitation. The adjustment of the excitation is achieved by the controller adjusting the conduction angle of the thyristor of the excitation system. The frequency and voltage of the alternating current are rectified into direct current, and then the microcomputer is used to control the power electronic devices to convert the direct current into a frequency and voltage alternating current. The basic principle is as shown. The three-phase alternating current generated by the wind generator is rectified by a diode three-phase full-bridge into a direct current and then by six insulated gate bipolar power transistors (IGBTs) under the control of the control and drive circuits. Inverted into three-phase AC into the power grid. Inverter control generally adopts SPWM*VWF method, that is, sine wave pulse width modulation type transformer voltage conversion method. The capacity of the frequency conversion device adopting the AC-DC-AC system is relatively large, and it is generally required to select 120% or more of the rated power of the generator. 4.2 Doubly-fed generator control Current wind turbines often use constant-speed constant-frequency systems. Generators use synchronous motors or asynchronous induction motors. When the wind turbine sends power to the constant-frequency grid, no speed regulation is required because the grid frequency will force the control of the rotor speed. In this case, the wind turbine maintains or approximately maintains the same speed at different wind speeds. The decline in efficiency, forced reduction in output, and even downtime are clearly undesirable. In contrast, double-fed generators, whether at sub-synchronous or hypersynchronous speeds, can operate at different wind speeds, and their speeds can be adjusted accordingly to changes in wind speed so that the operation of the wind turbine is always at its best. State, unit efficiency increased. At the same time, the voltage and frequency of the stator output power can be maintained unchanged, which can not only adjust the power factor of the power grid, but also improve the stability of the system. The structure of the doubly-fed motor is similar to that of a wound-type induction motor, and the stator winding is also excited by a symmetrical three-phase power source with a fixed frequency. The difference is that the rotor winding has a three-phase power supply with adjustable frequency, and the AC-AC frequency converter is generally used. Or AC-DC-AC frequency converters provide low frequency currents. Compared with synchronous motors, there are three adjustable amounts of excitation for doubly-fed machines: one is the same as synchronous motors, which can adjust the amplitude of excitation current; the other is that the frequency of excitation current can be changed; and third, the phase of excitation current can be changed. By changing the excitation frequency, the speed can be adjusted. In this way, when the load suddenly changes, the speed of the motor is rapidly changed, and the kinetic energy of the rotor is fully utilized to release and absorb the load. The disturbance to the power grid is much smaller than that of the conventional motor. In addition, active power and reactive power are adjusted by adjusting the amplitude and phase of the rotor excitation current. However, there is only one adjustable amount of synchronous motor, that is, the amplitude of the excitation current, so adjusting the excitation of the synchronous motor generally can only compensate the reactive power. The excitation of a doubly-fed machine not only can adjust the current amplitude, but also can adjust its phase. When the phase of the rotor current changes, the rotor magnetic field generated by the rotor current generates a displacement in the air gap space, which changes the double feed. The relative position of the motor potential and the grid voltage vector also changes the power angle of the motor. Therefore, the doubly-fed motor can not only adjust the reactive power, but also adjust the active power. (2) Doubly-fed motor control in wind power Doubly-fed motor control system diagram for wind power generation In wind power generation, due to the unpredictable wind speed, there are certain difficulties in using it. Therefore, it is of great significance to improve wind power generation technology, increase the efficiency of wind turbines, and make full use of wind energy resources. Through the inverter controller's control of the power device in the inverter circuit, the amplitude, frequency and phase angle of the excitation current of the doubly-fed generator rotor can be changed to achieve the purpose of adjusting the rotational speed, active power and reactive power of the double-fed generator, which improves the The efficiency of the unit also plays a role in stabilizing the frequency and regulating the power grid. It is a block diagram of a wind power double-fed motor control system designed according to this control concept. The entire control system can be divided into: speed adjustment unit, active power adjustment unit and voltage adjustment unit (reactive power adjustment). They respectively receive wind speed and speed, active power, and reactive power commands, and generate a comprehensive signal, which is sent to the excitation control device to change the amplitude, frequency and phase angle of the excitation current to meet the requirements of the system. Since doubly-fed machines can adjust active power as well as reactive power, the unit can be connected to the grid for power generation when there is wind, and it can also be used as a compensation device for suppressing grid frequency and voltage fluctuations when there is no wind. 22 "China Automation Yellow Pages" The industry's first large-scale public-weapons tool books, books, gifts, invites advertising to join! Automation Expo Doubly-fed Wind Turbine has broad application prospects In summary, the application of doubly-fed machines in wind power generation can solve problems such as the non-adjustable speed of the wind turbine and the low efficiency of the unit. At the same time, since the doubly-fed electric machine has adjustable reactive power and active power, it can play a role of voltage regulation and frequency stabilization for the power grid and improve the quality of power generation. Compared with the synchronous-AC-AC system of the synchronous machine, it also has the advantages of small capacity of the inverter (generally 10% of the rated capacity of the generator 20%) and light weight, and is more suitable for the use of the wind turbine. The idea of ​​applying a doubly-fed machine to wind power generation is not only theoretically established but also technically feasible. Compared with the existing wind power generation technology, both in terms of economy and reliability, they have irreplaceable advantages, have strong competitiveness, and are conducive to the localization process of wind turbines, and their development prospects are very broad. . Wind power generation technology has matured and it has occupied a prominent position in the field of renewable green energy development and has important development and utilization value. Especially in remote mountainous areas, pastoral areas and islands, wind power generation can provide clean energy for local residents' lives and production, and ease the tension of energy supply. It is worth promoting. Non Slip Floor Mats are a smart choice for any bathroom that wants to offer both durability and security. These luxurious floor mats have the durability and performance you expect from high-quality materials, and they're backed by a year-long warranty. 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