Detailed Model of the Grid-Connected Cascaded Doubly Fed Induction Machine

Abstract

The Cascaded (Brushless) Doubly-Fed Induction Machine (CDFIM) is a promising substitute for the commonly used Doubly-Fed Induction Machines (DFIM) for wind power application. The CDFIM offers reliable performance and low maintenance due to the absence of slip rings and graphite brushes. In this study, a detailed analytical model for the CDFIM is proposed in order to clearly show the controllable input (i.e., current from inverter side) and output (i.e., total output torque) relationship. The proposed model is expressed in the frequency (Laplace) domain. Field oriented (i.e., vector) control approach is adopted in order to achieve a precise dynamic model for the grid connected CDFIM. The steady-state and dynamic behavior of derived torque terms are presented and explained individually. Dynamic response of the total output torque is calculated, both analytically and numerically in a simulation and the results are shown to be consistent. Next, the torque-sharing and power-sharing concepts of the CDFIM are presented to further study the system behavior under different rotor velocities. Finally, to verify the proposed model, an experimental setup, using a cascaded DFIM was used, and the results are reported.