Unified Analysis of Induction Machine and Synchronous Machine Based on the General Airgap Field Modulation Theory

This paper investigates the natures of induction machine (IM) and synchronous machine (SM) from a new point of view based on the general airgap field modulation theory. The equivalent airgap model containing three critical elements is proposed to expound their modulation principles and common features in a unified way, thus the electromagnetic performance analysis, i.e., back-electromotive force (EMF) and torque, of IM and SM can be put together from the perspective of airgap field modulation principle while the only difference exists in the modulators. The modulators are optimized by considering the nonlinearities like rotor coils resistance and leakage inductance of IM and the actual magnetomotive force (MMF) distribution of SM. Theoretical expressions of airgap flux density distribution, flux linkage and EMF, general average torque, torque density comparison, and inductance characteristics are developed to reveal the relation between the performances and initial key topological parameters systematically and verify the model feasibility entirely. The iron saturation is treated as a constant discount on the airgap MMF to provide general mechanism comprehension and reasonable parameters calculation. All the theoretical predictions are verified by two-dimensional (2-D) finite element analysis together with experiment achieving good agreement.