Adaptive FRT Improvement of DC-Link Voltage-based VSGs in Weak Power Grids

Abstract

The integration of renewable energy sources (RESs) in modern power systems (MPSs) has been increased. This integration has led to a quick shift in the control approaches of grid connected power converters (GCPCs). Traditionally, Grid-Following Inverters (GFLIs) have been widely employed for integrating in MPSs, because of their simplicity and reliance on external grid signals for synchronization. However, in recent years, Grid-Forming Inverters (GFMIs) have emerged as a promising control architecture for integrating of RESs. GFMIs are capable of emulating the dynamics of synchronous generators (SGs). GFMIs mainly establishes their voltage and frequency references independently, to form a grid. This feature enables GFMIs to have an actively contribution on the system inertia, damping, and voltage support; which makes them suitable for MPSs with high RES penetration. This work formulates and develops a fault ride through (FRT) mechanism for Virtual Synchronous Generator (VSG) GFMIs. The proposed scheme has been developed according to the current limiter dynamics and presents a novel power deceleration scheme. During current saturation scheme, the proposed scheme modifies the active power swing loop structured on d-axes current. By a set of tests and simulations results,  the effectiveness of the proposed adaptive FRT has been shown under both strong (with SCR 20) and weak grid (with SCR 2) conditions. Under symmetrical and asymmetrical fault types with different durations, the performance of the proposed scheme has been checked. The results validate the merits of proposed scheme and its compatibility with GFMI objectives. It has been shown that the proposed architecture enhances the FRT capability of DC-link VSGs; in addition, it supports stable operation in weak MPSs, and provides a robust solution for grids with high share of RESs.