wind power generation

Brushless doubly-fed generator, its stator has two sets of windings, one is called power winding, which is directly connected to the power grid; The other is called control winding, which is connected to the power grid through bidirectional frequency converter. Its rotor is a cage or reluctance structure, without brushes and slip rings, and the number of poles of the rotor should be the sum of the pole pairs of the two windings of the stator. The rotor of the brushless doubly-fed generator is connected with the windmill, and the rotating speed of the windmill can change with the wind speed. When the generator speed changes, the frequency converter can change the frequency of the stator control winding, which brings inconvenience to the output frequency of the generator power winding. Although this variable speed constant frequency control scheme is realized in the stator circuit, the power flowing through the stator winding is only a small part of the total power of brushless doubly-fed generator. This control scheme using brushless doubly-fed generator can not only realize variable speed constant frequency control and reduce the capacity of inverter, but also realize flexible control of active and reactive power, which plays a role in reactive power compensation for power grid. At the same time, the generator itself has no slip ring and brush, which not only reduces the cost of the motor, but also improves the reliability of the system operation. In addition, the brushless generator can operate at different wind speeds, and its rotation speed can be modulated accordingly with the change of wind speed, so that the operation of the wind turbine is in the best working condition and the efficiency of the unit is improved. The disadvantage is that the stator needs two motors, which increases the complexity and cost of the system and is still difficult to realize.

Let's talk about permanent magnet synchronous power generation. Now it is generally said that direct-drive permanent magnet synchronous starting. The electromagnetic mechanical system of traditional wind turbine usually includes three main parts: wind turbine, gear box and generator. Due to the limitation of the speed range of traditional wind turbines, it is necessary to use a speed-increasing gearbox to connect wind turbines and generators. However, on the one hand, the speed-up gearbox has some shortcomings, such as increasing the weight of the unit, generating noise, requiring regular maintenance, increasing the loss, etc., and at the same time it also reduces the utilization efficiency of wind energy. The new direct-drive wind power generation system adopts low-speed permanent magnet synchronous generator, which is directly connected to the power grid through power conversion circuit, greatly improving the system efficiency. Its working principle is that the wind acts on the blades of the wind turbine at a certain speed and angle of attack, so that the wind turbine generates a rotating torque and rotates, and the wind energy is converted into mechanical energy. The wind generator drives the permanent magnet synchronous generator coaxially connected with it to rotate, converts mechanical energy into electrical energy, and emits alternating current varying with wind speed and frequency. The alternating current generated by the generator cannot be directly connected to the power grid. It needs to be converted into alternating current with the same frequency as the power grid through a converter, and then connected to the power grid through a transformer. The disadvantage of direct-drive permanent magnet wind power generation point is that the converter in direct-drive wind power generation system is the full power of the unit, which is limited by the current level of power electronic devices, and it is very difficult to realize large capacity. However, with the improvement of power electronics technology, it will be widely used in megawatt wind power generation systems.