Electricity Production from Renewables Energies

3.8. Variable speed wind turbine

3.8.1. Issues

The typical power characteristic of a turbine according to the wind speed and the speed ratio (β) is presented in Figure 3.39.

Figure 3.39. Example of the speed adjustment characteristic

The place of the point representing the maximum converted power (represented by the curve in dotted lines) can be followed by adapting the turbine speed (thick line). Thus, in order to maximize the converted power, the turbine speed must thus be adapted in relation to the wind speed. This is why the market share of the high power variable speed wind turbines is in constant development and tends towards 100%. The main advantages of the variable speed wind turbines in comparison to the fixed speed generators are as follows:

– They increase the recovery range, notably for small wind speeds, where the maximum recovery efficiency can be obtained. Indirectly, the availability and the generated power of the system are increased.

– The system of orientation of the blades is only used to deteriorate the turbine efficiency in the case of high-speed winds. Indeed, the possibility of controlling the generator speed via the electromagnetic torque helps to reduce the role of the orientation system of the blades, which will then mainly intervene to limit the turbine powers to high wind speeds. Consequently, for low wind speeds, the orientation angle of the blades ...