Page 403 - Power Electronics Handbook

392 Power semiconductor circuit applications
To obtain a high power factor with good pull-in and pull-out torques it is
essential to increase the ratio of the direct axis to the quadrature axis
magnetising reactance of the motor. Figure 14.42 shows a conventional
reluctance motor and indicates the paths of the direct and quadrature
fluxes. To achieve a large value of direct axis reactance and a small value of
quadrature axis reactance it is necessary to reduce the salient pole arc to as
low a value as possible. Although this now increases the power factor it
leads to greatly increased magnetising currents and reduces torques. A
form of segmental motor which overcomes these disadvantages is shown in
Figure 14.43 for a two-pole motor. Since all the torque is experienced by the
salient poles and none by the central rotor cylinder, this has been eliminated
to give a motor with reduced inertia. In Figure 14.43 only the quadrature axis
flux crosses the relatively large interpolar space so that its reactance is
greatly reduced.

I Quadrature

Figure 14.43 Segmental two-pole reluctance motor

Figure 14.44 Flux barriers in reluctance motors