Steady state of the cascaded doubly-fed induction machine

A cascaded doubly-fed induction machine (CDFM) is a connection of two wound rotor induction machines. The rotors of the two individual machines are electrically and mechanically coupled so that brushes for the rotor slip-rings are no longer required. This paper describes the steady state behaviour of such a cascaded machine arrangement. Frequency and slip values are defined. A per-phase equivalent circuit, based on the common induction machine equivalent circuit, helps to gain understanding of the machine quantities. Measurements on a CDFM confirm simulations with the equivalent circuit experimentally. Saturation effects are discussed to show the limitation of the simple equivalent circuit model. By studying the power flow within the CDFM and taking machine utilisation into consideration allows to suggest that a CDFM has to consist of two identical machines.