Enhancing Large Disturbance Stability of Direct Voltage Grid-Forming Converters Through Integration of the Virtual Power Method

Grid-Forming control (GFM) plays an increasingly crucial role in modern power grids by ensuring stability and providing inertia, keeping the voltage waveform steady and preventing rapid changes. One of the main challenges in GFM is that it operates as a voltage source, making current control challenging. Since power electronics converters have limited capacity, managing current limitation becomes critical. To address this, certain types of grid-forming embed a current loop (CCGFM); therefore, limiting the current reference can effectively control the current. Despite its effectiveness, a significant issue arises in post-fault states, where current limitation can decrease the stability margin and restrict synchronization. To overcome this challenge, a virtual power-based method has been proposed, which decouples synchronization angle control from current limitation by employing unsaturated current references for power measurement. While effective, continuous current control has been found to reduce the small-signal stability of the system. This paper presents a novel hybrid architecture of Voltage Control Grid-Forming (VCGFM) that improves stability under large disturbances by incorporating the virtual power approach from CCGFM while taking advantage of the small-signal stability superiority of the classical VCGFM by eliminating the impact of current control during normal operation. The proposed method is further validated through experimental testing.