Analysis and Tuning of Dual-loop Control for Grid-forming Converters in the Discrete-time Domain

Effective voltage regulation is of utmost essence for grid-connected converters. The dual-loop voltage-current control approach have a preference for preferred for its excellent performance of providing active damping for the undamped equipment to avoid filter resonance. However, the tuning of the controller is commonly performed in the continues-time domain, which is not suitable for applications with a low pulse ratio, that is, the ratio of the switching frequency to the switching frequency of the reference signal. Therefore, this work focuses on the analysis and tuning the dual-loop control in the discrete-time domain. The discrete model of the plant is firstly developed, and then the tuning of the inner-loop gain is discussed based on the discrete root locus analysis, to achieve the maximum active damping for the equivalent plant. The experimental results have verified the validity of the methods proposed above for grid connected converter regulation.