Hybrid current loop timing control method for permanent magnet AC servo systems

The relationship between current loop bandwidth and time delay was analyzed on the basis of the mathematical model of a current loop. The time delays generated by double sampling and pulse-width modulation (PWM) duty cycle double update (DSDU) and immediate sampling and PWM duty cycle immediate update (ISIU) and their effects on the current loop bandwidth were compared. Combining DSDU and ISIU, a novel hybrid current loop timing control method was proposed to solve the problems of insufficient bandwidth expansion and low voltage output capability. ISIU was used when calculation delay is less than or equal to the action time of the zero voltage vector to expand the bandwidth. Meanwhile, DSDU was adopted when calculation delay is greater than the action time of the zero voltage vector to improve voltage output capability. Experimental results proved that the proposed method can reduce current loop delay to increase bandwidth without changing switching frequency and limiting output voltage.