Energy-balancing AC and DC grid-forming control for power converters

Abstract

Control strategies for grid-connected power converters can be broadly categorized into (i) grid-forming strategies that form a stable AC voltage (i.e., magnitude and frequency) at the converter terminal but assume that the DC voltage is stabilized by a fully controllable power source, and (ii) grid-following controls that form a stable DC voltage but assume that the AC voltage is stabilized by other devices in the grid. Consequently, grid-following is often fragile and frequently fails when the power system is under stress. In contrast, grid-forming power converters are commonly seen as a robust solution that is envisioned to replace synchronous machines as the cornerstone of future power systems. However, requiring a stable DC voltage is a significant obstacle in several application scenarios such as highvoltage DC transmission, low-frequency AC networks with converter-based frequency conversion, flywheel energy storage systems, and grid-connected renewable generation with limited flexibility. Instead, we propose control strategies that simultaneously form the converter's DC side and AC side voltage while ensuring power balance between the two sides and discuss theoretical results and applications in power systems consisting of interconnected AC and DC grids and grid-connected renewable generation.