At present, wind turbine generators with gearboxes mainly include double-fed wind turbines and full-power variable-frequency wind turbines, of which the market share of doubly-fed wind turbines exceeds 90%. The following focuses on the characteristics, market applications and development trends of doubly-fed wind turbines.
First, the characteristics of doubly-fed wind turbines
The doubly-fed wind turbine has the following characteristics:
1. Mature technology and reliable quality. Since the industrial revolution, gear transmission has become the most mature and most mainstream transmission method, widely used in aviation, aerospace, shipbuilding, automobiles, watches and other industrial and living fields. Wind turbines have a harsh working environment and require high reliability. The high-power and large-speed gearbox technology adopted by the doubly-fed unit has been applied since the 1990s, and its failure rate in wind power is lower than that of electrical systems and generator systems. The impeller + gear box + generator has a simple transmission chain structure, reasonable distribution of various loads, and high overall quality reliability.
2. High efficiency and excellent cost performance. The technology effectively allocates the parameter configuration of the mechanical transmission system and the power generation system, and increases the motor speed through the high speed ratio gearbox, thereby greatly improving the efficiency of the generator. At the same time, the model only has a slip power of 1/5 to 1/3 of the rated power through the converter, and the energy loss of the converter is small. The machine has high efficiency and excellent cost performance.
3. Maintainability is good. The doubly-fed wind turbine generally adopts the transmission structure of the blade + hub + gear box + coupling + generator. The main components of this structure are relatively independent and can be separately maintained and repaired. On-site maintenance is easy and time response is timely.
4. Power quality is good, low voltage ride through ability. The doubly-fed wind turbine adopts the doubly-fed induction motor and part of the power converter technology, and more than 70% of the generated electric energy is sent to the grid through the stator, resulting in small harmonics and good power quality. At the same time, the technology has the characteristics of adjustable power factor, convenient control of active power and reactive power, and good low voltage ride-through performance, which can realize grid-friendly access.
However, in the actual operation of large wind turbines, the gearbox is a component with a high failure rate. Because wind turbines are generally installed in the wind, such as mountains, wilderness, beaches, islands, etc., they are subjected to the wind force of irregularly changing loads and the impact of strong gusts. They are often affected by the extreme cold and extreme temperature difference, and the natural environment. The traffic is inconvenient, the gear box is installed in the narrow space at the top of the tower. Once the fault occurs, the repair is very difficult, so the reliability and service life are much higher than the requirements of the general machinery. For example, the requirements of the material of the component, in addition to the mechanical properties under normal conditions, should also have the characteristics of cold and brittle resistance at low temperature; the gearbox should be operated smoothly to prevent vibration and shock; and sufficient lubrication conditions should be ensured. For areas with large temperature differences between winter and summer, appropriate heating and cooling devices should be provided. Also set up monitoring points to remotely control the operation and lubrication status.
