Standardized Assessment Framework for Design and Operation of Weak AC Grid-Connected VSC Controllers

Abstract

Significant research attention is focused on the stability and control of voltage-source converters (VSCs) in weak ac grids. However, the assessment of VSC control strategies has never been standardized, such that novel solutions proposed in the literature are not objectively evaluated against current best-practice. This paper establishes a comprehensive, standardized assessment framework for grid-connected VSC controllers, which allows objective comparison of novel controllers under development and established methods already in operation. The assessment consists of a tuning stage, time-domain analysis and frequency-domain analysis to form a complete evaluation that can be applied in its full aggregated form or as individual assessment steps. Three VSC controllers, namely vector current control, power-synchronization control and a virtual synchronous machine, are compared in this paper using small-signal models, time-domain simulations and control hardware-in-the-loop Real-Time Digital Simulation (RTDS) experiments to demonstrate the versatility and robustness of the proposed framework for controllers with very different structures.

Keywords

• Voltage-source converters
• weak ac grids
• vector current control
• virtual synchronous machine
• power-synchronization control