Development of Amplitude Equations Model and Assessment of Performance Limits for Brushless Doubly-Fed Reluctance Machines

The brushless doubly-fed reluctance machine (BDFRM) has received increasing attention as a cost-effective alternative for wind power and large pump applications due to the high reliability of brushless structure besides competitive performance to the commercial doubly-fed induction generator. In this research, a novel amplitude equation model has been presented for the BDFRM. The proposed model is an electrical circuit-based model, like existing space vector models, and therefore has a fast nature. Although the space vector models are suitable for modeling in dynamic conditions, they cannot introduce a straightforward way to determine the performance limits. To fill this gap, the amplitude equations have been derived to describe the BDFRM operation in steady-state, instead of vector models. The proposed amplitude equations describe the relationship between the BDFRM variables, directly. They are also employed to obtain the BDFRM feasible operational area of active and reactive power in both motoring and generating modes, which is important to determine reactive power reference for the control systems, reactive power capability supported by the primary in fault-ride-through conditions, and determining the ratings for the partially sized converter. An automated MATLAB script has been generated to implement the proposed model. In addition, an existing space vector model of the BDFRM has been simulated in MATLAB/Simulink Software to validate the results of the proposed model. A comparison of the results shows good agreement between the models, while the proposed model has the superiority in directly describing the relation between the BDFRM variables and determining the feasible operational area.