Rare-earth free motor with field poles excited by space harmonics — Current phase-torque characteristics of self-excitation synchronous motor

This paper describes a synchronous motor in which space harmonics power is utilized for field magnetization instead of permanent magnets. The stator has a concentrated winding structure, and the rotor has two sorts of windings, i.e., an induction pole (I-pole) winding that retrieves mainly the third space harmonics power and an excitation pole (E-pole) winding for the field magnetization. The both coils are connected via a diode rectifying circuit. The optimum placement of the I-pole on the rotor is mathematically discussed and is analytically determined through FEM based computer simulations. In addition, it is clarified that the E-pole torque becomes larger as the fundamental synchronous speed rises and that the MTPA control angle advances with increase of the speed.