Transient Angle and Voltage Stability of Grid-Forming Converters with Typical Reactive Power Control Schemes

Grid-forming converters have been identified as an enabling technology in more-electronic power systems. Nevertheless, the reactive power control of grid-forming converters has often been ignored during transients. This article innovatively points out the transient angle and/or voltage instability of grid-forming converters with typical reactive power control schemes, comprising voltage, reactive power droop, and reactive power PI control schemes. We disclose that the grid-forming converter with the voltage, reactive power droop, or other zero-order reactive control schemes faces only the transient angle stability problem yet with a limited capacity for reactive power/power factor regulation. In contrast, the reactive power PI control scheme, as a first-order reactive control scheme, allows for constant reactive power/power factor operation. However, this control scheme or other first-order reactive control schemes may destabilize grid-forming converters through three transient stability problems—transient angle, voltage, and mixed stability problems. Moreover, we disclose the mechanisms behind these transient stability problems. Furthermore, we present a thorough comparison of typical reactive power control schemes. Finally, experimental results verify theoretical analyses.