Doubly Fed Wind Turbine Features, Market Application and Development Trend

At present, wind turbines with gearboxes mainly include double-fed wind turbines and full-power inverter wind turbines. The market share of doubly-fed wind turbines exceeds 90%. The following focuses on the characteristics of double-fed wind turbines, market applications and development trends.

First, the characteristics of double-fed wind turbines Doubly-fed wind turbines have the following characteristics:

1. Mature technology and reliable quality. Since the industrial revolution, gear transmission has become the most mature and the most popular transmission method, and is widely used in aviation, aerospace, shipbuilding, automobiles, watches and other industrial and living areas. The harsh working environment of wind turbines requires high reliability of the turbines. The high-power, high-speed ratio gearbox technology used by the double-fed unit has been used since the 1990s, and its failure rate in wind power is lower than that of electrical systems and generator systems. The drive chain of the impeller + gearbox + generator is simple, all kinds of load distribution are reasonable, and the overall quality and reliability are high.

2. High efficiency and excellent price/performance ratio. This technology effectively distributes the parameter configuration of the mechanical transmission system and the power generation system, and increases the motor speed through the high-speed ratio gearbox, which greatly improves the generator efficiency. At the same time, this model only has a power of 1/5 to 1/3 of the rated power through the converter, and the energy loss of the converter is small. The whole machine has high efficiency and excellent cost performance.

3. Maintainability is good. Doubly-fed wind turbines generally adopt the transmission structure of the blade + hub + gear box + coupling + generator. The main components of this structure are relatively independent and can be maintained and maintained separately. On-site maintenance is easy and time response is timely.

4. Power quality is good, low voltage ride through ability. Doubly-fed wind turbines use doubly-fed induction motors and some power conversion technologies. More than 70% of the electrical energy emitted by the wind turbines is sent to the grid through the stator. The resulting harmonics are small and the power quality is good. At the same time, the technology has the advantages 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-scale wind turbines, the gearbox is a component with a high failure rate. Because wind turbines are generally installed at the outlets of mountains, wilderness, beaches, islands, etc., and are subjected to irregular wind load changes and the impact of strong gusts, they are often exposed to the effects of extreme heat and extreme temperature, combined with their natural environment. With inconvenient traffic, the gearbox is installed in a narrow space on the top of the tower. Once a failure occurs, repair is very difficult. Therefore, the reliability and service life of the gearbox are much higher than those of general machinery. For example, the requirements for component materials, in addition to the mechanical properties under normal conditions, should also have the characteristics of resistance to cold and brittleness at low temperatures; the gearbox should be guaranteed to work smoothly to prevent vibration and shock; ensure adequate lubrication conditions. For areas where the temperature difference between winter and summer is huge, appropriate heating and cooling devices must be configured. Also set up monitoring points to remotely control the operation and lubrication status.

Second, market applications The world's leading wind energy industry research institute BTM's latest global wind power industry report released in 2009 shows that in 2009 the world's new wind power installed capacity of 13.8 million kilowatts, in installed wind turbines, 86% of wind turbines used Wind turbine with gear box. Among the world's top ten wind power equipment manufacturers, eight companies, VESTAS, GE WIND, Huarui Wind Power, GAMESA, Dongqi, SUZLON, SIEMENS, and REPOWER, have adopted gearbox technology. In direct-drive wind power products, about 8.5% of the units are powered by direct excitation, while permanent-magnet direct drives are less than 5%. At present, there are more than 800 offshore wind turbines that have been connected to the grid in the world and all use gearboxes.

Judging from the current domestic situation, the proportion of the installed capacity of gearbox unit variable-speed double-fed wind turbines with gearbox units is the largest. Representative manufacturers include Huarui Wind Power, Dongqi, Guodian United Power, Mingyang, Shanghai Electric and Beizhong etc. The market share exceeds 80%; the direct-drive variable pitch fan also has a certain installed capacity, representing manufacturers including Goldwind Technology, Xiangdian Wind Energy and so on.

III. Development Trends The maturity of wind turbine technology, the stability and reliability of quality, and timely and low-cost maintenance will be the most important criteria for market selection. Gearbox unit technology has become the mainstream technology of large-scale wind turbines in the past ten years; permanent magnet direct drive technology has not yet been tested by the market for a long time. Judging from the current situation in China, gearbox units occupy the mainstream of wind power technology. Some companies think that gearboxes are components that have high failure rates. The use of a gearless box structure can greatly increase the reliability of wind turbines, reduce the failure rate, and increase the lifespan of wind turbines. Therefore, these enterprises are optimistic about the future development potential and market demand of direct-drive generators. The number of manufacturers with direct drive wind turbine production technology is gradually increasing, including Enercon, Goldwind, Siemens, GE, Xiangdian Wind Energy, Aerospace Wanyuan and Dongfang Electric.

The development of different wind power technology routes needs to be tested through the market. The choice of market is the best standard, which will be more conducive to promoting the healthy development and technological progress of the wind power industry.