Dynamic Response of Grid-following and Grid-forming Inverters when encountering disturbances

The integration of renewable energy sources leads to the increase of inverter-based generators, causing a decrease in grid strength and stability issues. To deal with this problem, researchers proposed different control structures of the grid-forming (GFM) control strategy, which can automatically provide active and reactive energy support when the power network encounters disturbances during operation. This paper focuses on the capability of different types of inverters to recover from disturbances when encountering balanced load disturbance and different depths of voltage fault. The theoretical assessment and PSCAD simulations of different control strategies have been conducted. The results indicate that when encountering a fault under weak grid conditions, large frequency and voltage variations will occur in the power network connected with the grid-following (GFL) inverter, while these variations are much smaller in the power network connected with the grid-forming inverter, which demonstrates better dynamic response to disturbance.

I. Introduction

The integration of renewable energy like wind and solar generation as well as battery energy storage systems leads to an increase of inverter-based generators in power systems, causing the reduction of the rotating reserve capacity [1] in the grid, making them become weak grid and face fault ride-through issues [2]. The typical fault ride-through capability refers to, when a load disturbance or voltage fault occurs at the POC point and causes system frequency and voltage to exceed the rated operating range, generators should stay uninterrupted and provide extra power within a certain duration to support the grid and back to regular operation after the removal of fault [3]. Traditional power network has been dominated by synchronous generators and recognized as strong power grids, which is the result of the rotational kinetic energy stored in the physical rotor of synchronous generator and the ability to provide extra current that is several times over the normal operating current when a fault occurs [4]. Yet, in a power network with a large amount of inverter-based resources, the maximum current provided by the inverter is limited by the capacity of electronic components, which reduces the strength provision to the system [5].