A Precise Analytical Model of the Grid Connected Cascaded Doubly Fed Induction Machine

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 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. Each term of the derived relationship is classified into the possible types of torque based on the term's nature and then is discussed in detail. Then, the steady state and dynamic behavior of these terms are presented and explained individually. The total output torque dynamic response is calculated both analytically and numerically in a simulation environment, and the results are compared.