Permanent magnet brushless dc (PMBDC) and synchronous machines (PMSM) drives are favored in variable speed applications for their high efficiency operation. Energy efficiency improvement in such motor drives is of interest in recent times because of rising cost of energy. Accordingly, two current control options for improving efficiency of these drives are taken for study and they are; (i) injecting sinusoidal and non-sinusoidal currents in PMBDC machines and (ii) lowering switching frequency of inverter driving the PMSM but without having significant low ordered sidebands of currents. Both these methods are applicable to existing types of permanent magnet motors and hence do not upset their existing optimized designs. / Ph. D.