The overall design and operation strategy of the wind generator should ensure he safe of operation, in the meanwhile, to make p C keep within the maximum during the operation area, to maximize the output power. We can
know from formula (1) that, the output power of the wind generators is a cube function of the wind speed, that is to say, the bigger the wind speed, the higher the output power, but there are two limitations in the actual system: firstly, the maximum limitation of the electrical installations and electrical components, secondly, there is a rotate speed limit of the turbine components, especially the wind wheel. Thus, there are three typical run states: low wind speed phase operates in shift state, to maintain p C be a constant value (to the extent possible, the best is to achieve the Betz limit), we can control the rotate speed of the generator according to the changes of the wind speed, to make_ unchanged until the rotate speed
get to the limit. When rotate speed get to the limit, the wind speed increased further, control the operation at constant rotate speed until get to the maximum output power. At this point, p C is not necessarily the maximum.
When excess the rating speed, the output power gets to the limitation regulates the generators in constant output power. Figure 3 plots these three typical operating conditions. Figure 4 plots the control curve of maximum
wind energy capturing.