Modelling and Operating Characteristics of Air-Cored Resonant Induction Machines

The performance of a high-speed air-cored induction machine (IMs) using capacitors to provide resonant operation is analyzed in this paper. Resonance can be obtained using the stator and rotor capacitors appropriately tuned with the machine inductances, though alternative options may be considered instead of rotor capacitors. The aim is to develop a simple analytical model for air-cored resonant induction machines and to use this to obtain an understanding of the operating principles and the limitations and issues. The analysis is based on the classical IM equivalent circuit supplemented with stator and rotor capacitors and considers different control scenarios to derive key expressions for resonance conditions, capacitor values, peak torque and efficiency and related slip values. The aim of this paper is to provide a full understanding of air-cored resonant IMs to assess the practicality of these machines.