interior permanent magnet synchronous motor (ipmsm) is highly appreciated by researchers in variable speed drive applications due to some of its advantageous features such as small size, high power density, simple maintenance, high output torque, high power factor, low noise and robustness as compared to the conventional im and other ac motors. although these motor drives are well known for their relatively high efficiency, improvement margins still exist in their operating efficiency. particularly, the reduction of power loss for ipmsm still remains a challenge for researchers. improvement of motor drives efficiency is important not only from the viewpoints of energy loss and hence cost saving, but also from the perspective of environmental pollution. the thesis presents development of a fuzzy logic based efficiency and speed control system of an ipmsm drive. in order to maximize the efficiency in steady state operation while meeting the speed and load torque demands a search based fuzzy efficiency controller is designed to minimize the drive power losses to achieve higher efficiency by reducing the flux. the air gap flux level can be reduced by controlling the d-axis armature current as it is supplied by rotor permanent magnet. in order for the drive to track the reference speed in transient operation another fuzzy logic based controller is designed to increase the flux depending on the speed error and its derivative. the torque component of stator current (q-axis component of stator current) is generated by fuzzy logic based speed controller for different dynamic operation depending on speed error and its derivative. in this work a torque compensation algorithm is also introduced to reduce the torque and speed fluctuations.