Synchronous and asynchronous secondary power generation wind power system

Wind turbine technology evolved from the original low-power synchronous generators to the constant-speed squirrel-cage generators used in large-scale wind turbines in the 1980s. Constant-speed squirrel-cage generator with a speed-increasing gearbox belongs to asynchronous generator technology. The advantage is that the structure of the squirrel cage generator is simple, maintenance is convenient, the price is cheap, and the grid connection is easy. The gear box is used to increase the rotation speed of the wind turbine and the light and inexpensive high-speed squirrel cage generator is economical and reasonable, and has a relatively high cost performance. Due to its simple technology and high economic efficiency, the aircraft has been widely used in many countries since the end of the last century. At present, China has built large-scale wind turbines in operation, and most of them belong to this type of technology.

However, the disadvantages of fixed-speed squirrel-cage generators are also obvious. First of all, it is difficult for fixed-speed wind turbines to obtain suitable tip speed ratios at different wind speeds, resulting in a decrease in the efficiency of intercepting wind energy. Second, gearboxes are subject to variable load shocks, disparities in temperature differences, harsh operating conditions, and maintenance in wind conditions and environmental changes. The maintenance cost is very high and becomes the weak link in the wind turbine; third, the efficiency of the squirrel-cage generator is not high, the slip power cannot be used, the slip ratio is slightly high and the heat is severe, and the excitation must also be absorbed from the power grid. Power, low power factor.

In view of the shortcomings of the constant-speed squirrel-cage generator, the technical solution of the variable-speed doubly-fed wind generator was adopted. Variable-speed doubly-fed wind generators are also asynchronous generators. Variable-speed doubly-fed wind generators are the same as fixed-speed squirrel-cage generators. The generator stators are directly connected to the grid, and most of the energy can be input to the grid and the excitation power can be absorbed from the grid. The difference is that with the wind turbine speed The change of the double-fed rotor winding can convert the slip power generated by the rotor into a power-frequency current through the inverter and return it to the power grid. At the same time, this part of the power-frequency current can also adjust the power factor, thus making the total of the unit Power factor is improved. At present, many wind turbine generators from GE Energy and Fuhrländer in the United States use variable-speed double-fed wind power generation technology solutions.

The wind motor manufacturer headed by Germany's Enercon Company focused on removing the gearbox and introducing a gearbox-free variable speed permanent magnet wind generator. Permanent-magnet wind generator is a kind of synchronous generator, which belongs to the same type as the generator in large power grid. The difference is that it replaces the excitation of ordinary generators with permanent magnets, eliminating the brush slip ring, and the structure is simple and reliable. At the same time, it also saves excitation power and improves generator efficiency. As the speed of the wind turbine changes, the frequency of the power generated by the permanent magnet wind power generator is constantly changing. Therefore, a full-power inverter must be used to change these powers into constant-frequency constant-voltage AC power before entering the power grid. . Dedicated to the development of permanent-magnet wind turbines without gearboxes, Germany’s Siemens, Vensys, Sweden’s ABB and other companies are also involved.

At present, the typical technical solutions in advanced wind turbine products are nothing more than variable-speed double-fed asynchronous wind turbines and gear-box permanent-magnet synchronous wind turbines, both of which have their advantages and disadvantages. Variable-speed double-fed asynchronous wind turbine frequency converter, power is about one quarter of the unit power, the unit's total price is lower, but there is a gear box, its maintenance costs are much higher than the gearbox variable-speed permanent magnet synchronous wind power machine. Some people may ask, if gear-shifting a variable-speed doubly-fed asynchronous wind turbine, it will not be able to take into account the advantages of both. It will not only save unit costs but also reduce maintenance costs. However, no one has yet made such an improvement because the manufacturing cost of a low-speed double-fed gearless wind turbine suitable for direct drive is much higher than that of current gearless permanent magnet generators of the same power. Therefore, Such an improvement will undoubtedly offset the price advantage of doubly-fed asynchronous wind turbines.

To obtain the most wind energy, and to achieve the goal of technological innovation with the lowest equipment manufacturing cost and the lowest maintenance cost, it should be the direction and power of any advanced wind turbine technology improvement and improvement. Then, in the course of improving and improving the current two advanced models of variable-speed doubly-fed asynchronous wind turbines or gear-box permanent-magnet synchronous wind turbines, whether it can find the third advanced wind turbine technology, it can not only integrate the current two What are the advantages of the big advanced models while also overcoming the disadvantages of both?

The answer is very certain, that is, synchronous asynchronous secondary wind power system, referred to as synchronous asynchronous secondary wind turbine.

As the name suggests, synchronous secondary asynchronous wind turbines have a secondary power generation process. The first is synchronous power generation and the second is asynchronous power generation. The principle is that firstly, a gearless permanent magnet synchronous generator is used to realize primary power generation, and the technical scheme of the gearless permanent magnet synchronous generator is basically the same; in the second step, the permanent magnet wind generator is replaced by a PCT asynchronous generator system. The full-power inverter of the machine does not need to be rectified into direct current and then converted. Most of the power is directly generated by frequency-raising and frequency-doubling power generation to obtain constant-frequency constant-voltage piezoelectric energy and transmitted to the power grid. Why does it not simply use the existing permanent magnet synchronous power generation method to generate secondary power? The purpose is to minimize the weight and manufacturing cost of the wind turbine engine room. The permanent magnet generator in the secondary power generation system is lighter and cheaper than the existing permanent magnet generator; and it sends low-frequency three-phase alternating current, and then it will The low-frequency three-phase alternating current introduced the PCT asynchronous generator for secondary power generation, and the frequency up-conversion and frequency stabilization became constant-frequency constant-voltage power-frequency current input to the power grid. The secondary power generation of this system originated from the permanent magnet synchronous power generation without a gearbox, so the advantage of the gearless box of permanent magnet synchronous power generation has been preserved. At the same time, the PCT asynchronous generator and its configured frequency converter can be reasonably estimated. The combined cost of the two is not as high as that of a full-power inverter in the original permanent magnet generator set. Therefore, the cost of generators and inverters for synchronous and asynchronous secondary wind turbines has decreased, and the total cost performance has also been reduced. Better than gearless permanent magnet synchronous generator.

Further discuss the similarities and differences between the second generation and doubly-fed asynchronous wind turbines. The working process of the quadratic generator and the doubly-fed asynchronous wind generator is actually the same. Both can change the inverter-converted current to a constant-frequency constant-voltage current. The other similarity is the PCT during the secondary generation. Induction generators are also equipped with a quarter-power inverter, which is the same point. The difference is that the PCT secondary generator has the dual functions of up-scaling and frequency stabilization, while the existing doubly-fed asynchronous wind generator only has the frequency stabilization function but no up-conversion function unless the frequency converter of the double-fed asynchronous generator is used. When the power is increased from a quarter to more than two-thirds, the doubly-fed asynchronous generator only has an up-converting function, and in this way, it will offset the economic advantages of the low-cost double-fed asynchronous generator equipment, so the synchronous asynchronous two In the secondary wind turbine system, a DF asynchronous generator cannot be replaced by a doubly-fed asynchronous generator. Although the cost of motor equipment for synchronous and asynchronous secondary wind turbines may be higher than that of doubly-fed asynchronous generators, the cost of eliminating gearboxes, and the costly maintenance of gearboxes, as well as the gearless technology, can all be achieved. Better than double-fed induction generators.

In summary, currently the most advanced two major wind power technology solutions, variable-speed doubly-fed asynchronous wind turbines and gearbox-variable permanent-magnet synchronous wind turbines, have their own advantages and are in a difficult position to compete with each other. In the structure, the synchronous and asynchronous secondary wind turbine can have both advantages, and at the same time overcome the shortcomings of both, it can reduce the equipment manufacturing cost of the gearbox-free variable-speed permanent magnet synchronous wind turbine, and can solve the double-fed asynchronous wind generator. Difficult to achieve gear-free technology and the resulting high maintenance costs, its technical advantages are obvious. It can be foreseen that the market potential brought about by the technological advantages of synchronous and asynchronous secondary wind turbine generators is very high. Through this basic technology plan, other supporting technologies for absorbing mature products from home and abroad are put into practical development, and fundamentally significant. To improve the manufacturing technology of wind turbines in China and change the backwardness of China’s wind turbine manufacturing industry relying heavily on imported machine products and imported machine technology, it is a shortcut to rapidly develop China’s wind turbine manufacturing industry.