Differently, the double-drive wind turbine is composed of a three-phase asynchronous winding motor and a permanent magnet synchronous motor connected coaxially, and there are two wind turbines: a main wind turbine and an auxiliary wind turbine, where the name. Double drive motor, also called double wind wheel motor. Among them, the main wind wheel directly drives the rotor of the asynchronous motor and the stator of the permanent magnet motor to rotate together, and the auxiliary wind wheel directly drives the rotor of the permanent magnet motor to rotate in the opposite direction. This is a direct drive structure. The stator winding of the permanent magnet motor is connected to the rotor winding of the asynchronous motor in reverse phase sequence. Its main function is to excite the asynchronous motor. The entire generator produces electrical energy on the stator side. the asynchronous motor.
What we call the double power supply can be understood as the stator and rotor can emit electrical energy at the same time. The generator principle theoretically says that as long as there is power to drive the motor, the stator side of the motor can directly output electrical energy. The working principle of a modern dual-powered variable speed wind turbine is to convert wind energy into mechanical torque (i.e. the rotational inertia of the wind wheel) via the turbine, increase speed via main shaft transmission chain and gearbox. , then rotate the generator rotor to produce electricity.
The differences between horizontal axis and vertical axis wind turbines lie in the following aspects:
1. Design method
The design of horizontal axis wind turbine blades, The theory of impulse-leaf elements is commonly used and the main methodsThese include the Glauert method, the Wilson method, etc. However, because the blade element theory ignores the flow interference between each blade element, and at the same time ignores the airfoil resistance when designing blades using blade element theory, this simplification inevitably leads to inaccuracy in the results. This simplification has little impact. on the design of the blade shape, but has a greater impact on the wind energy utilization rate of the wind wheel. At the same time, the interference between the blades of the wind wheel is also very strong, and the entire flow is very complex. It is impossible to obtain accurate results based on blade element theory alone.
The design of vertical-axis wind turbine blades was formerly based on the horizontal-axis design method and relied on blade element theory. ESince the flow of vertical axis wind turbine is more complex than that of horizontal axis, it is a typical large separation unsteady flow and is not suitable for analysis and design using blade element theory. This is also an important reason for the vertical axis. The wind turbine has not been developed for a long time.
2. Wind power utilization rate
The wind power utilization rate of large horizontal axis wind turbines is mainly calculated by blade designers and is generally above 40%. As mentioned earlier, due to flaws in the design method itself, the accuracy of wind energy usage calculated in this way is highly questionable. Of course, wind turbines at wind power plants will plot wind power curves based on measured wind speed and power output. However, the wind speed at that timeis the wind speed measured by the anemometer at the back of the wind wheel. as the speed and power of the incoming wind. The curve is too high and needs to be corrected. After applying the correction method, the wind energy utilization rate of the horizontal axis will be reduced by 30-50%. Regarding the wind energy utilization rate of small horizontal axis wind turbines, the China Aerodynamic Research and Development Center has conducted relevant wind tunnel experiments, and the measured utilization rate is between 23% and 29%. %.
3. Structural characteristics
When the blades of the horizontal axis wind turbine rotate, they are subject to the combined effects of the force of inertia and gravity. The direction of the inertial force changes at any time, while the direction of gravity thus remains unchanged. The blades experience a variable load, which is very detrimental to the fatigue resistance of the blade.a blade. In addition, horizontal axis generators are placed at an altitude of tens of meters, which brings a lot of inconvenience to the installation, maintenance and inspection of generators.
The blades of the vertical axis wind turbine are much better stressed during rotation than those of the horizontal axis. Since the direction of the force of inertia and gravity always remains unchanged, the blades are subjected to a constant load. The fatigue life is longer than that of horizontal axis wind rotors. At the same time, the vertical axis generator can be placed under the wind wheel or on the ground for easy installation and maintenance.
4. Start-up wind speed
There is a consensus that the start-up performance of horizontal axis wind turbines is good. However, depending on the wind speed of small horizontal axis wind turbines driven. the aé research and development centerrodynamics of China According to tunnel experiments, the starting wind speed is generally between 4-5 m/s, and the maximum reaches 5.9 m/s. Such startup performance is obviously unsatisfactory. There is also an industry consensus that the starting performance of vertical axis wind turbines is poor, especially for Darrieus Ф-type wind turbines, which have no self-starting capability, which is also a reason which limits the application of the vertical wind turbine. axis wind turbines. However, for the Darrieus type H wind wheel, the conclusion is the opposite. According to the author's research, as long as the aerodynamic profile and installation angle are correctly selected, fairly good starting performance can be achieved. Judging from tunnel experiments, the starting wind speed of this Darrieus type H-shaped wind rotor only needs 2 m/s. , whatis better than the horizontal axis wind turbine mentioned above.