Transient Performance Optimization of Grid Forming Converter

Abstract

With the increased penetration of renewable energy sources (RES), the power system is emerging a lower inertial characteristic. This can lead to a higher rate-of-change of frequency (RoCoF) and the voltage instability issue during grid disturbance conditions, thus threatening the security of the power grid. Accordingly, researchers have recently proposed a novel grid-forming (GFM) control strategy. Compared to the traditional grid-following (GFL) control method, the GFM control can emulate the dynamic behaviors of the synchronous generator (SG), inherently providing inertial support to stabilize the grid frequency and transient AC voltage. However, it may lead to abnormal transient stress, such as over/under DC voltage and AC overcurrent, raising the risk of unexpected tripping. The paper will present the operating principles of multiple types of GFM and GFL control strategies, and evaluate their dynamic performance during the grid voltage variation events. To address the issue of transient stress, the paper will propose a novel control strategy for suppressing the over/under DC voltage and AC overcurrent so that prevented disconnection of the GFM converters. The proposed method is validated with an example of PV generation scenario, and the effectiveness in improving the dynamic performance has been demonstrated by studying the frequency variation cases.