A filtering technique to solve flicker problems due to use of induction machines in wind power generation

Squirrel cage induction machines represent a common solution widely adopted in wind generation. In fact, the induction machine is simple, reliable, cheap and requires very little maintenance. The employment of induction machines in wind power generation system needs, however, particular care and braininess. It is well known, in fact, that generator operating conditions can imply saturation of magnetic circuits of the machine. The saturation phenomenon has to be taken into account when the capacitance necessary for the power factor correction is chosen. Moreover, wind energy conversion system can produce torque fluctuations at the generator shaft. These fluctuations represent a serious limitation for weak networks in which flicker effect can emerge. In the paper a full modelling of the induction machine used in wind energy systems and of the flicker phenomenon is done. Moreover, the problem of connection of the induction generator to a weak network is analysed. In particular, guidelines to design an electrical filter suitable to avoid flicker effect are given.