The predominant form of wind power generation is asynchronous, using asynchronous (induction) generators. This is a robust and cost effective technology, but induction generators do not help regulate grid voltage, and are substantial absorbers of reactive power. Ideally, they need to be connected to strong grids so they will not reduce power quality, but this is not usually the case. On the contrary, wind power generation is usually connected at the far corners of a power grid, on sub-transmission or distribution levels. The grid was not originally designed to transfer power from these vulnerable extremities to the main network.
The reactive power balance of asynchronous generators can be improved to a certain extent by using the doubly-fed rotor concept. To keep this technology within reasonable cost margins, however, rotor converter ratings must be limited to steady-state requirements only. During transient occurrences in the grid, the performance of doubly-fed induction generators (DFIG) may well prove inadequate to safeguard the grid`s primarily voltage stability. Here, dynamic reactive power compensation plays an important role in supporting DFIG, and this is where FACTS technology comes in.
Sea cables: a key issue
For off-shore wind generation plants, comprehensive AC sea cable networks add another layer of complexity, requiring additional, elaborate reactive power control. The overall scope of reactive power control should encompass the wind farm as well as the sea cables, resulting in a well-regulated, reactive power balance of the whole system, answering to the same demands with respect to reactive power regulation as any other medium-to-large generator serving the grid.
FACTS for wind power comprises SVC, SVC Light and Dynamic Energy Storage.
>> More about SVC and SVC Light
>> More about Dynamic Energy Storage