Dynamic modeling, simulation and stability analysis of brushless doubly fed machines

A brushless doubly-fed machine (BDFM) is a single-frame, self-cascaded induction machine capable of operating in both the induction and the synchronous modes. This thesis presents some important advances concerning dynamic modeling, simulation and analysis of the BDFM.; Initially, a two-axis model and its associated parameters are developed and calculated. The development of the model is not subject to the commonly made assumption that the BDFM is electromagnetically equivalent to two wound rotor induction motors in cascade connection. Instead, the model is derived from a rigorous mathematical transformation of a detailed machine design model. This novel approach emphasizes not only the analysis of the machine performance in both dynamic and steady state conditions, but also the design aspects of the machine by correlating the machine performance with the actual machine parameters computed from machine geometry.; Using the two-axis model, simulation of the machine dynamic performance in all conceivable modes of operation is carried out and the results are compared with test data available with good correlation.; Steady state models, under certain assumptions, are derived based on the two-axis model. For the synchronous mode, motoring operation, a solution technique is developed and utilized to perform steady state performance analysis of the BDFM.; Finally, stability analysis of the machine is examined using the linearized version of the two-axis model. Since the linearized two-axis model of the BDFM is time-varying, commonly used eigenvalue analysis techniques cannot be employed directly to investigate the stability characteristics of the machine. However, since the system matrix is a periodic function of time, the theory of Floquet is introduced so that the original linear time-varying system of equations are transformed into a set of equivalent system of equations with a constant system matrix. Eigenvalue analysis is then applied to analyze the stability of the BDFM system over a wide speed range. Predictions by the eigenvalue analysis are correlated with test data.; The study concludes that the proposed two-axis model is a good representation of the BDFM for dynamics, steady state, stability investigations of the machine and further development of control strategies for the proposed BDFM system for adjustable speed drive and variable speed generation applications.