Time delay-induced control cross-coupling in VSC-MMC systems: Implications in harmonic mitigation, passivity and stability

As renewable energy integration accelerates, so does the demand for voltage source converters, particularly Modular Multilevel Converters. However, control time delays –inherent to such converters– pose a significant challenge, threatening system stability. This paper investigates the impact of dq-frame time-delay-induced cross-coupling on AC-side control of MMCs. Traditional control designs in the dq-frame may overlook these cross-couplings arising from time-varying signals in the abc-frame, leading to unexpected performance outcomes. To address this challenge, we propose a method to compensate for time-delay-induced cross-coupling and validate it through comparative analysis between conventional high-frequency models and detailed MMC models. The analysis reveals the benefits of compensating for time-delay-induced cross-coupling to improve stability and performance. The paper elucidates the mechanism behind time-delay-induced cross-couplings, outlines the MMC model and control strategy, and introduces the compensation method. Additionally, it discusses a framework for the passivity-based design via a high-frequency model and presents results validating the compensation method.