2-DOF decoupled discrete current control for AC drives at low sampling-to-fundamental frequency ratios

In high performance drive systems, wide bandwidth and reference tracking accuracy of current control loop are fundamental requirements. The conventional PI controller provides robustness against the machine parameter mismatching and zero steady-state error, but its dynamic performance degrades at high-speed due to the bandwidth limitation. In this paper, a new control structure of discrete PI controller with a deadbeat response is proposed, which combines the advantage of conventional PI controller with deadbeat characteristic. The proposed controller shows a decoupled tracking performance of up to 15% of the switching frequency, while also providing an extra control freedom of the disturbance rejection, which effectively improves the system stability. Experiments show a reduction of oscillation by 30% compared to the conventional PI and the validity and applicability of the proposed control method for high-speed applications with low sampling to fundamental frequency ratios.