The work presented in this thesis has been modelling , simulation and detailed analysis of the operation characteristics of a surface mounted PMmotor supplied by a voltage inverter and operating in the 120° conduction mode . a detailed mathematical model for predicting , in the steady-state and transient operation , of a PM BDCM system has been presented , the model was formulated entirely operation , of a frame of reference , to facilite the comparison of simulation and experimental results .a novel approach is based on the subdivision of the motor operation of the BDCM has been presented .this approach is based on the subdivision of the motor operation into two conduction modes ; conduction and commutation periods .this has simplified further the mathematical model and provided a value in gaining insight into the operation of the motor .also a simulation model for the prediction for the prediction of the duration of commutation has been presented .the very good agreement between the measured and computer simulation program to accurately predict the performance of the brushless DC motor used .the devloped model was further used to investigate the impact of advancing the instant of current commutation , relative to the position of the rotor , on the performance of the BDCM system , it has been shown that advancing the commutation allows a more rapid build-up of current under constant speed operation and heavy load .the results also showed that phase advance can alter considerably the torque-speed characteristics and the average torque may be maximised.the theorecal analysis and the subsequent simulation resuts , obtained on the BDCM model , showed that the motor operating characteristics are similar , to the extent of current and torque ripple , to the conventional DC motor .