Stability analysis of grid-forming converters under hybrid synchronous control mode

This study examines the dynamic responses of grid-forming converters operating under a hybrid synchronous control strategy, which integrates a power-frequency loop with phase-locked loop like technology. This control strategy aims to enhance the converter's responsiveness to current thresholds, thereby minimizing or shortening periods of synchronization losses. In this paper, a mathematical model is developed, and an analytical investigation is conducted to analyze the dynamic behavior of these converters under the influence of the hybrid synchronous control strategy, particularly after abrupt grid condition changes. The findings indicate that the hybrid synchronous control may prompt erroneous control actions under certain grid conditions and current thresholds. These erroneous actions can occur due to the specific characteristics of the system. As a result, the converter may become trapped in a state of current saturation. These theoretical predictions have been verified through controller hardware-in-the-loop experiments.