Performance Evaluation of Four Grid-Forming Control Techniques with Soft Black-Start Capabilities

Grid-Forming Converters (GFC) can be controlled as independent, self-starting, voltage sources. This feature is essential for power converters to achieve successful black-start sequence initiation. Conventional grid-following converters are not capable of self-starting an islanded network. GFC control thus exploits wider grid support and network restart potential. This study analyzes and compares four GFC controllers to assess their generic and soft black-start (ramping voltage) capabilities. The compared techniques are: Droop Control, Power Synchronizing Control (PSC), Virtual Synchronous Machine (VSM), and Matching control. These techniques are selected based on their direct voltage reference control flexibility. Various simulations are performed with common parameters to assess the response of each technique under similar conditions against load, DC voltage and active power reference disturbances, in addition to their soft-start readiness. The results demonstrate the high-level compatibility of these four controllers with soft black-start through successful and timely ramping voltage reference tracking. Moreover, the four considered control techniques achieve satisfactory performance, with VSM demonstrating more flexibility due to its tunable virtual inertia parameter (J).