Grid-forming VSM control for black-start applications with experimental PHiL validation

The rising penetration of power converters interfaced generation into the electrical grid is leading to a paradigm shift where distributed resources are expected to provide ancillary services. The voltage-source behavior of grid-forming converter (GFC) makes it an attractive black-start provision alternative. This paper thus proposes a modified grid-forming virtual synchronous machine (VSM) control that is tailored for black-start applications. Voltage and power loops in the proposed controller are modified to provide soft energization to mitigate transformers inrush current, in addition to improved voltage support for the restored AC network and a smooth synchronization with neighboring islands or the main grid after a black-start event. The VSM control performance is first validated through simulations. Then, Power Hardware-in-the-Loop (PHiL) technique is used to validate the ability of a hardware GFC equipped with the modified VSM controller to restore a simulated network in a digital real-time simulator (DRTS) platform. Current-type Ideal Transformer Model (I-ITM) interface technique is successfully used in the experiment with time-delay impact compensation in the synchronous dq0 frame. The novel presented PHiL demonstration in this paper paves the way for similar testing of industrial GFCs for black-start and ancillary services provision under flexible network restoration conditions and complexity.