Modeling and analysis of electric machines with asymmetric rotor poles using a reluctance based, magnetic equivalent circuit

In this research, magnetic equivalent circuit (MEC) techniques are applied to model the behavior of claw-pole alternators. As a first step, a model has been created using a magnetic circuit composed of elements that represent magnetic permeance. The flux throughout the machine is determined from stator and rotor winding flux linkages using nodal analysis techniques. The permeance-based model implements an approach proposed in existing literature, and is shown to accurately predict the behavior of the machine in the linear magnetic region. However, in saturation, measured and simulated results show poor agreement, most notably in the harmonic content of open-circuit voltage. To improve accuracy, an alternative formulation is considered wherein the magnetic paths in the machine are modeled using a reluctance network and solved using mesh circuit analysis. It is observed that a solution procedure based upon mesh formulation results in a more stable numerical algorithm. Additionally, using the mesh approach, saturation is modeled through the relationship between magnetic flux and permeability. This is shown to be more accurate than a permeance model wherein saturation is modeled using the relationship between magnetic potential and permeability. For a two-dimensional rotor structure, the mesh-formulated MEC model is shown to accurately predict the spatial distribution of air gap flux density over a wide range of operating points. A three-dimensional MEC model of the claw structure is also derived. To implement the model, novel algorithms have been developed to generate the set of loop equations and modify the set to incorporate rotation. Predicted results compare favorably with those obtained using three-dimensional finite element analysis.