Modelling a Rotor Bar of an Induction Motor for Improving Electromagnetic Torque and Efficiency Using Permeance-Based Equivalent Circuit Model and FEA.

Induction machines (IMs) are attracting the automotive industries’ focus due to remunerative benefits striving researchers to improve electromagnetic performance characteristics. Enhancing the electromagnetic capabilities of an IM is a challenging task, given the obstacles posed by an elevated rotor copper loss which leads to a rise in rotor temperature, and a low torque density. This paper presents a permeance–based equivalent circuit model (PECM) considering the impact of the rotor temperature in rotor resistance to model a proposed rotor cage structure, by formulating the link between the geometry of the rotor cage and the electrical parameters of the machine. The variation in electrical parameters including rotor resistance and reactance for various rotor structures resulted in the changes of the electromagnetic performances, such as torque production, rotor copper loss, and efficiency. Therefore, the significant impact of the proposed rotor cage dimensions is investigated using sensitivity analysis for finite element analysis (FEA)–based optimization under a fixed volume of the IM. To validate the improvement of the optimal rotor cage over a wide range of frequencies and loading levels, a laboratory–prototyped $11\mathrm{~kW}\mathrm{IM}$ is used as a reference rotor structure. The optimal rotor structure offers improved torque and reduced rotor copper loss resulting in a decreased rotor temperature and higher efficiency.