DC Voltage Control and DC Fault Protection Scheme for Multi-Voltage Level DC Grids with High Voltage DC/DC Transformer

With the rapid expansion of new energy sources like photovoltaics, aggregating and transmitting power from these energy bases has become a critical challenge. The multi-voltage level DC scheme holds significant potential for addressing this. In such a DC grid, high-voltage DC/DC transformers play a vital role, though practical engineering experience is still limited. Key technologies for operation, control, and protection are essential, but current feasible solutions are scarce. This paper explores DC voltage control and fault protection strategies for multi-voltage level DC grids using high-voltage DC/DC transformers. Case studies based on a modified Zhoushan 5-terminal MMC-HVDC system demonstrate the effectiveness of the proposed strategies.