Abstract
The centering guidance forces in self-bearing permanent magnet motors are magnetically integrated with the torque generation windings, and can take place in a single multifunction winding. This radial guidance is usually actively controlled as a function of the rotor position, with the drawbacks associated to actively controlled devices. This article describes how multifunction windings can passively generate electrodynamic centering forces without the need for specific additional electronics, and simultaneously a driving torque if fed by a power supply. It shows the experimental electromotive force (EMF) measures, both for the electrodynamic centering and for the motor functions, obtained on a prototype, operating in quasistatic conditions. It also shows the measured radial forces generated by the electrodynamic bearing and the measured drive torque in these conditions. These measures show a good agreement with model predictions. These measures also confirm the theoretical conclusions stating that it is possible to generate passive guidance forces and torque simultaneously in a single winding. The effect of adding external inductors on the coils of the prototype is also investigated by experimental measures and model predictions on the bearing radial forces, and on the motor driving torque. It is shown that these external inductors mainly affect the radial guidance forces with minor impact on the torque.
Highlights
Self-bearing motors are an attractive solution to issues related to compactness and maximum spin speed
The windings are left in open circuit, and the induced electromotive forces are measured on the two coils of each of the three phases (m (t) and m2 (t)), which correspond to the phasors M1 and M2 on the coils of each of the three phases (m11(t) and m2(t)), which correspond to the phasors and on the equivalent circuit, in Figure 8, for one phase
The windings are left in open circuit, and the induced electromotive forces are measured on the two coils of each of the three phases (m1(t) and m2(t)), which correspond to the phasors and on the equivalent circuit, in Figure 8, for one phase
Summary
Self-bearing motors are an attractive solution to issues related to compactness and maximum spin speed. Various kinds of electric machines have been studied for self-bearing operation, where self-bearing operation means a system in which the drive function and the bearing function are magnetically integrated. This bearing function is always achieved, at least for one degree of freedom, by the generation of guidance forces controlled by modulating a current as a function of the rotor position. Active guidance in self-bearing-motors can be related to active magnetic bearings (AMBs), which allow reaching relatively high stiffness values, high positioning precision, and have reached a certain level of industrial maturity. The complexity, cost, and overall dimensions associated with this control system can be prohibitive, e.g., for low-rated power applications
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