Analysis and Design of Voltage-controller Based on Single-state Feedback Active Damping for Grid-forming Converters

Abstract

This paper investigates the analysis and design of digital single-loop voltage-controller for grid-forming voltage source converters with LC-filters. Inspired by the structure diagram of the passive damping method, the virtual resistance concept based on only capacitor voltage feedback is used to realize active damping without the need of any current sensor, reducing thus the system costs. It is revealed from the controller closed-loop analysis that the insertion of an integrator in series with a proportional and resonant controller can significantly improve stability margin and dynamic performance of the system, then only the proportional controller need to be determined for system stability and the resonant controller is merely used for zero steady-state tracking error, which facilitates the controller parameter tuning. A systematic design based on the root contours in the discrete z-domain is proposed to optimize the parameters of the controller. The largest distance between the poles of the closed-loop system and the unit circle is achieved, which indicates the fastest dynamic performance under desired stability margins. Meanwhile, a simple differentiator constructed by backward-Euler plus lead-compensator is used to replace the noise-sensitive derivative term. In order to evaluate the proposed control approach performance, the system is tested in laboratory setup under different load conditions. The obtained results verify the effectiveness of the proposed design method and validate the analysis.