Instant Transformer Energization for Inverter Based Resources Based on Pre-fluxing and Virtual Resistance Control

In this paper, an instant approach to energize power transformers with inverter-based resources (IBRs) is proposed. According to the excitation mechanism of the transformer, an inrush current-free transformer energization process can be achieved by applying pre-fluxing and virtual resistance control based on direct current detection. The transformer flux is brought to a predefined state by controlling the inverter switching state. Then the inverter is started at a phase angle corresponding to the predefined core flux. A virtual resistance in the control loop is employed to generate active damping due to the matching deviation of the core flux to the starting angle. Transformer energization that can be achieved in milliseconds without inrush current is verified by simulation. The current transient characteristics of the transformer energization process are tested experimentally the effectiveness of the proposed method is validated. With the proposed approach, an ultra-fast black start can be achieved for IBRs to pick up local critical loads and ultimately support the bulk power system recovery from blackouts.