Optimal Design of Current Loop for Permanent Magnet AC Servo System

There are two major factors restricting current loop bandwidth, switching frequency and digital delay. Digital delay includes A/D sampling time and PWM duty cycle update. The calculating delay is the major source of delay in the loop. The bandwidth expansion strategy was proposed. Double stator current sampling and double PWM duty cycle update were achieved in a carrier period. This paper chooses the optimum switching frequencies and reduces the delay effects of current sampling. The dynamic performances of servo system are improved. Simulation and experimental results verify the validity of the proposed scheme.