Abstract—AC motors are more rugged and have much simpler construction as compare to DC motors and after introducing field oriented control, it has been made possible for the AC motors to achieve high dynamic performance similar to DC motors. This paper focus on the discussion about vector control principles and how it solved the problems of controlling AC motors, particularly synchronous machine such as decoupling control of torque and speed. Starting with the brief history about the evolution of motor drives then discuss about the significance of FOC including mechanism of torque production in synchronous motor, importance of phase transformation and advancing it to a simplified DQ model of PM synchronous motor. Finally combining altogether to elaborate the proposed model of complete FOC drive system. This paper adopted a different approach to describe these concepts in a lucid manner that many literatures lacking.