Stable power supply thanks to wind turbines

October 08, 2001

Wind turbines can help keep the voltage in the electricity network at a constant level. The power electronics in the turbines can effectively correct peaks and dips in the mains voltage. This is the conclusion reached by NWO-funded researchers.

Modern wind turbines are a good means of coping with fluctuations in the mains voltage. Such fluctuations occur when the demand for energy increases suddenly (for example when a factory turns on heavy machinery) or the supply decreases (for example if a nearby power station suddenly goes off line).

The electrical engineers at Delft University of Technology base their conclusion on a model which they developed to study fluctuations in the electricity network on a time scale running from seconds to minutes. At the moment, the task of maintaining the stability of the mains voltage is left entirely to power stations. In future, sustainable energy will become more important. Wind turbines and other sustainable energy sources will then need to help stabilise the mains voltage.

A large number of modern wind turbines are equipped with a power electronics converter that ensures that they produce the same voltage at all times, regardless of the rotor speed. Minor alterations to the power electronics and the controller can also ensure that the mains voltage is adjusted. The electronic system makes clever use of the properties of alternating current. In alternating current, the voltage crosses zero a hundred times a second. By sending electricity into the network at that moment, the power electronics can boost the voltage. Strangely enough, this does not need to cost much energy. 'Reactive power compensation', to give it its proper technical name, even works when there is no wind and the rotor blades are not rotating. In that case, the power electronics can extract the necessary energy from the network, precisely between two zero-axis crossings.

Not all types of wind turbine can help stabilise the mains voltage. One type is not equipped with the power electronics converter which is necessary. The principle behind this type of turbine is that the rotational speed of the rotor is constant and independent of the wind speed.

The NWO research team intend extending their model of fluctuations in the electricity network so as to have it model the influence of other sustainable energy sources, such as solar cells. The energy sector will be able to use the model to calculate what the maximum contribution of various sustainable energy sources can be without endangering the stability of the power supply. The model can also indicate what additional technology is necessary to ensure stability.

Netherlands Organization for Scientific Research

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