Not so Harmonious?
This article describes an aspect of wind turbine operation related to control instability which may result in excessive harmonic currents injection from wind turbines, well above the typical level. This phenomenon and has been reported for a number of wind plants. The excessive harmonic currents were the result of the interactions between harmonic currents on the power systems and turbine controls under particular operating conditions. These conditions can be summarised as follows: (1) the presence of background harmonics and resonance conditions in the power system and (2) undampened turbine control response at frequencies coinciding with one or more of the harmonic currents in the power system. Both these conditions will be explained in this article, and the resulting control interaction will be clarified. Harmonic interaction is a known problem among power electronics engineers and control designers, and mitigating solutions are available.By Grazia Todeschini, EnerNex, USA