Modeling and laboratory research on brushless DFIG

Purpose – Doubly fed induction generator DFIG applied in over 50 percent of modern variable speed wind power systems and interesting also for adjustable speed diesel generation sets or multimegawatt water turbines is troublesome in the mean of maintenance of sliprings and brushes. Especially, it concerns isolated power systems and offshore wind turbines. Application of brushless DFIG in such cases eliminates the mentioned problem. Constructions of the machine and consequently the model and mathematical description is more complicated than classical slipring DFIG, therefore it is still developed in several scientific institutions to obtain adequate performance. The following work is dedicated to mathematical description, modelling and implementation of the control method for autonomous operation in the laboratory model of brushless DFIG. Design/methodology/approach – Analysis and simulation of the machine model and laboratory tests on a small scale prototype of brushless DFIG. Findings – It has been proven that sensorless direct voltage control of DFIG can be applied for both slipring and brushless machines, as it does not require machine parameters. Research limitations/implications – Brushless DFIG development is far from the performance needed by industrial implementation. Lower efficiency and higher reactive power needed by the machine, in comparison to classical DFIG of the same power range, result from double air gap seen by magnetic flux. However, the constructions of prototype machines are better and better, and their capabilities become closer to DFIG. Practical implications – Variable and adjustable speed generation systems such as wind turbines, diesel generation sets, water turbines. Originality/value – Standalone power systems with DFIG described in several papers require quite complicated control methods based on the mathematical equations of the machine model. Thus, these methods have to be significantly modified for the brushless version of this machine type, due to the fact of a much more complicated model. The proposed sensorless method of the output voltage control requires only redesign (tuning) of the PI controllers responsible for control of the rotor current, stator voltage amplitude and frequency. © 2012, Emerald Group Publishing Limited