Speed regulation of a wind turbine with current source or matrix converter: Tuning procedure

In DC series-connection of wind turbines the common variable for the turbines is the DC current and thus the simplest control approach is to use current source type converter to perform the speed control of the generators for maximum power extraction. When using current source type converters like the Current Source or the matrix converter, LC filters are needed at the input of the generator to remove switching harmonics. Thus resonance can be an issue and special care needs to be taken when designing controllers. In this article a wind farm topology with series connected turbines is presented along with the wind energy conversion system inside in which a matrix converter performs speed control of the generator. To counteract resonance, three nested loops controlling respectively the turbine rotational speed, the stator current and the filter capacitor voltage are implemented. The tuning should be performed carefully so that the control is fast, stable and tracking the maximum power point. The system model is analyzed in the dq reference frame to find appropriate controllers for each loop and a method is presented to tune each controller in a systematic manner for a satisfactory system response. Simulation results are presented.