Current-loop bandwidth expansion strategy for permanent magnet synchronous motor drives

The dynamic response of the permanent magnet AC servo system is restricted by the bandwidth of current loop, which is the innermost loop. In digital control AC servo system, there are two major limiting factors for current-loop bandwidth, switching frequency and digital delay which means sum of A/D sampling time, algorithm execution time and PWM duty cycle update delay. The bandwidth expansion of current-loop without changing the switching frequency of power devices is necessary, as the increasing of switching frequency will raise the losses. Based on the synchronous rotating frame current decoupled control, the delay effects of current sampling and PWM duty cycle update in the permanent magnet synchronous motor drive systems were analyzed. The bandwidth expansion strategy was proposed, to achieve the stator current double sampling and PWM duty cycle double update in a carrier period. The current-loop bandwidth can be extended more than one times theoretically while the switching frequency remaining unchanged, so that the dynamic performance of permanent magnet synchronous motor drive systems was improved. Simulation and experimental results verified the theoretical analysis and effectiveness of the method.