# Wind Turbine Technology Trends
## 3 Discussion
### Onshore Wind Turbine Development
#### 3.1.3 The Drivetrain  
The gearbox is the part of the turbine that requires the most maintenance. So, if you remove it, the reliability of the turbine will be increased. It is also the most massive element in the nacelle of the turbine, so removing it will also improve this aspect of the turbine. For this reason, research has been conducted for years to optimize direct-drive turbines [25] to make them more competitive than turbines with gearboxes. This type of power generator has no gearbox and operates at the same speed as the rotor of a wind turbine. These generators are very large and the electrical energy output is converted to a constant frequency and voltage using power electronics. Direct drive, on the other hand, eliminates two-thirds of the conventional drive: gearbox, coupling and high-speed generator. In addition, direct-drive turbines are more practical at higher wind speeds. Until recently, however, the size and price of the generator prevented them from becoming a major competitor to geared turbines. The development of direct-drive turbines and the drop in the price of permanent magnets led to a more affordable and lightweight direct-drive model. It should be remembered that thousands of turbines with gearboxes are in operation and will continue to function for a long time. For this reason, gear technology continues to be refined to reduce costs and increase reliability.  
Experts place the two technologies side by side, which can be interpreted in two ways: Either both technologies will evolve until one prevails, or both technologies will find enough users to coexist in the marketplace. Other experts believe that direct-drive technology will prevail over time. They support this with three arguments:  
1. The cost of offshore support structures for direct-drive wind turbines is lower because of their lighter mass.
2. While the geared wind turbine has almost reached maximum efficiency, direct drive offers more potential for further enhancement.
3. Direct drive is more efficient at higher wind speeds, as geared wind turbines require additional gear stages, resulting in higher losses in the gearbox. There is also the possibility of a hybrid design, which combines elements of a gearbox and a direct drive [14].  
Development has resulted in wind turbine electromagnetic systems containing less copper and being lighter. The rotor contains components that generate a magnetic field and therefore represent rotating poles. There are two types of components that can perform this task: synchronous and asynchronous generators. So-called synchronous generators have simple permanent magnets similar to ordinary horseshoe magnets. In a synchronous generator, the rotor and the magnetic field rotate at the same speed (synchronously). These generators are increasingly used in wind turbines due to their high power density and low mass. The challenges these generators face are demagnetization of the permanent magnets when extreme heat is generated, rendering the generator unusable, and the inability to generate power at a fixed frequency. This is due to the variability of wind speeds and rotation at the same speed. Therefore, these generators require rectifier power converters. An alternative to the synchronous generator is an asynchronous generator. It generates an electric field with the help of additional coils. According to [PERSON]'s law, electric current and magnetic field always exist together. So a magnetic field can be used to induce an electric current, but a magnetic field can also be created by sending current through the coil. This is exactly what asynchronous generators do. This type of generator requires a special power supply for the magnets, but in return, damage is less and reliability is higher. In addition, fluctuations in rotor speed are much easier to absorb because of the higher degree of damping. The design of the asynchronous generator no longer plays a major role, and permanent magnet synchronous generators are considered the best for wind turbines [26].