from MIT Technology Review
直驅式渦輪使用永久磁鐵代替銅線圈和齒輪箱，永久磁鐵需要稀土金屬，目前大部分稀土金屬來源為中國，供給問題 價格成為一大隱憂
1. Direct drive will always require power electronics, because the generator will always be driven at variable speed, producing wild AC that must be conditioned by power electronics before it enters the grid. With geared drive, the power electronics can be eliminated by using the gearbox to convert the variable speed of the rotor to constant speed for the generator, as in the DeWind 8.2. The power quality improves, the generator is more robust and proven over a century of use in central power stations, it is easier to control and it does not require permanent magnets (rare earths).
2. Direct drive requires mounting the generator in the nacelle. With a geared drive, the rotor power can be transferred to the base of the tower through a low speed drive shaft. A gearbox at the base can be used to increase the speed to allow for a small generator, and to convert the variable speed to constant as discussed above. Furthermore, with most of the equipment at the base of the tower, erection and maintenance will be much easier, especially offshore. The tower top weight is greatly reduced. This allows lighter towers and greater stability, especially if the tower is mounted on a floating platform offshore.
3. One reason that direct drive is presently gaining favor is the difficulty of protecting the gearbox from shock loading, or wind gusts, and from distortions caused by the weight of the rotor, which is often partially supported by the gearbox. These distortions misalign the shafts and cause premature failure of gears and bearings. If the gearbox is mounted at the base of the turbine and driven by a vertical drive shaft, the shaft will act as a torsional spring, eliminating the shock from wind gusts by absorbing the overloads and then returning them to the system as the gust subsides. Also, since the gearbox is not supporting any part of the rotor, the stresses that cause distortion are eliminated. In this alternative geared drive arrangement, the gearbox is protected and there is no justification for direct drive.
直驅更容易受到雷擊損壞電路
4. Some will say that geared drive has more parts, so it will be less reliable. How many parts does an electronic power converter have? Eliminate it and the part count of the turbine drops drastically. It would also greatly reduce the chance that a lightning strike would disable the turbine.
5. The huge direct drive generator will be very difficult to protect from the weather offshore. It will be easier to protect the smaller geared drive generator, especially if it is mounted at the base of the turbine. At best, the interest in direct drive is the result of timid, conventional thinking. At worst it is like a financial mania - not supported by rational thought. This bubble will burst, but not after an enormous waste of money and time and resources. What about Enercon? They seem to be doing alright. But as the turbines get larger and larger for offshore use, we will see that direct drive was never the best way, because competitors will appear with new geared drive turbines, possibly in the arrangement described here, and they will prove to be superior to direct drive for any turbine above 1 MW.
2. Direct drive requires mounting the generator in the nacelle. With a geared drive, the rotor power can be transferred to the base of the tower through a low speed drive shaft. A gearbox at the base can be used to increase the speed to allow for a small generator, and to convert the variable speed to constant as discussed above. Furthermore, with most of the equipment at the base of the tower, erection and maintenance will be much easier, especially offshore. The tower top weight is greatly reduced. This allows lighter towers and greater stability, especially if the tower is mounted on a floating platform offshore.
3. One reason that direct drive is presently gaining favor is the difficulty of protecting the gearbox from shock loading, or wind gusts, and from distortions caused by the weight of the rotor, which is often partially supported by the gearbox. These distortions misalign the shafts and cause premature failure of gears and bearings. If the gearbox is mounted at the base of the turbine and driven by a vertical drive shaft, the shaft will act as a torsional spring, eliminating the shock from wind gusts by absorbing the overloads and then returning them to the system as the gust subsides. Also, since the gearbox is not supporting any part of the rotor, the stresses that cause distortion are eliminated. In this alternative geared drive arrangement, the gearbox is protected and there is no justification for direct drive.
直驅更容易受到雷擊損壞電路
4. Some will say that geared drive has more parts, so it will be less reliable. How many parts does an electronic power converter have? Eliminate it and the part count of the turbine drops drastically. It would also greatly reduce the chance that a lightning strike would disable the turbine.
5. The huge direct drive generator will be very difficult to protect from the weather offshore. It will be easier to protect the smaller geared drive generator, especially if it is mounted at the base of the turbine. At best, the interest in direct drive is the result of timid, conventional thinking. At worst it is like a financial mania - not supported by rational thought. This bubble will burst, but not after an enormous waste of money and time and resources. What about Enercon? They seem to be doing alright. But as the turbines get larger and larger for offshore use, we will see that direct drive was never the best way, because competitors will appear with new geared drive turbines, possibly in the arrangement described here, and they will prove to be superior to direct drive for any turbine above 1 MW.
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