| Abstract |
Permanent magnet excitation is beneficial in a.c. machines in which the flux is required to remain substantially constant. However, in inverter-fed drives where it is necessary to reduce the flux in ordre to operate above base speed with limited supply voltage, constant rotor excitation becomes a serious drawback. The conventional method used to achieve flux-weakening in permanent magnet motors involves phase advancing the stator currents with respect to the back emf. This paper reviews the instantanious power theory and investigates the use of the imaginary power component as an alternative means of providing field weakening in brushless dc motors. This is shown to provide a wider speed range than the conventional method, without any significant current distortion. |
