PhD student helps advance wind-produced energy

Wind-produced energy is an idea that dates back to the development of windmills in Persia, but there are still obstacles keeping wind turbines from being heavily relied upon today.

While working on his PhD at the Public University of Navarre in Spain, Jesús López Taberna began researching solutions for problems wind turbines experience during dips in voltage in a part of the electric grid. 

A dip in voltage occurs when there is a sudden reduction in potential in the grid that is followed by a quick return to normal value. Causes of these voltage dips can be lightning, trees fallen on power lines, or a company consuming a lot of energy at once. The drop only lasts milliseconds, but for a machine, a half-second interruption can cause a productive process to become blocked and need to be re-initiated. 

In normal operation the flux in the stator rotates at grid frequency, inducing a small voltage. The dips in voltage cause the appearance of a new flux in the stator that doesn’t rotate. Therefore, it’s speed relative to the rotor is larger, so it induces voltages greater than in normal operation. Sometimes the electronic converter connected to the rotor will lose control of the currents at these voltages, which can damage the converter.

An industrial engineer and member of the INGEPER Research Team at the university, López said the current protection solution to this problem, called Crowbar, does protect the machine, but stops the wind turbine in the process. This makes it difficult to get the voltage back up to normal operating value after the dip.

Wind power is important in Spain, as, at times, a third of the electricity is being produced by wind energy, so these outages can be costly. Thus it is important for engineers to find new ways for the turbines to not disconnect during voltage dips, and instead help bring the grid voltage up.

By building a rotor model, López and other researchers were able to propose a solution that modifies the control of a computer that controls the electrical machinery of the turbine. López proposed a protection system that changes the control of the machine converter in his PhD thesis, and it has now been transferred to a manufacturer for introduction into wind farms. Another system he proposed that changes elements in the machine is still being developed in new wind generators.