Analysis About Overshoot Peaks Appearing in the Current Loop With Resonant Controller

Resonant controller is considered ideal for harmonics current control, with advantages of zero steady-state error and computation efficiency. The commonly employed proportional-resonant (PR) controller is widely accepted, but its limited ability in dealing with higher order harmonics, or named limited regulation bandwidth, is also recognized from practical applications. This paper points out that regulation bandwidth of resonant controller is related to the overshoot peaks around resonant frequency in the current loop. The overshoot peaks are caused by open-loop phase lag around resonant frequency, which comes from delay link and R-L plant. The phase lag from delay link could be canceled by the proposed delay-compensated forms for both PR and vector resonant (VR) controller; but toward phase lag from R-L plant, the two types resonant controller perform different: PR controller does not give full consideration about R-L plant, leading to inherent obvious overshoot peaks in current loop, whereas VR controller provides proper leading phase to cancel the phase lag from R-L plant, greatly reducing the overshoot peaks and promising wider regulation bandwidth. The comparisons and analysis reveal the principle and relations of PR and VR controllers, which help to deepen the understanding for further improving the resonant controller.