불평형 계통에서의 유효전력 리플 저감을 위한 새로운 그리드 포밍 컨버터 제어기법

Abstract

As global electricity demand rises and the transition to clean energy accelerates, inverter-based resources (IBRs) are becoming an increasingly dominant presence in modern power grids. Consequently, the proportion of synchronous generators— traditionally responsible for providing rotational inertia and frequency stability—has been decreasing, undermining the robustness of overall grid stability. Recently, Grid-Forming (GFM) converter technology has received significant attention due to its capability to provide virtual inertia through Virtual Synchronous Generator (VSG) control methods, which mimic the characteristics of conventional synchronous generators. GFM converters are particularly important for establishing reference voltages in weak grids or microgrids, and robust operation under fault conditions is essential. If active power ripple and frequency fluctuations under unbalanced grid conditions are not properly controlled, the stability of the entire system could be severely compromised. Specifically, a large amount of active power ripple can cause fluctuations in DC-link voltage, degrading inverter performance and potentially threatening the stability of the overall power system. Existing studies for reducing active power ripple primarily focus on grid-following (GFL) inverters using Phase-Locked Loops (PLLs). However, these techniques are not directly applicable to GFM inverters because they connect to the grid based on power synchronization. On the other hand, conventional approaches for reducing active power ripple based on negative-sequence current control in GFM converters involve complex control structures, demanding processes for sequence extraction, and intricate current reference calculations, with insufficient validation in weak grid conditions. This paper proposes a simplified control strategy for reducing active power ripple in GFM converters by avoiding negative-sequence current control and minimizing reliance on sequence extraction methods. Additionally, unlike conventional methods, the proposed strategy was verified to effectively reduce active power ripples while preserving the transient response of the active power as designed by the external control unit. The effectiveness of the proposed approach has been validated through PLECS offline simulations and Hardware-in-the-Loop (HIL) experiments, demonstrating robust operation even in very weak grid conditions.