Frequency-fixed grid-forming control for less-dynamic and safer renewable power systems

Grid-forming (GFM) control is a key technology for ensuring the safe and stable operation of renewable power systems dominated by converter-interfaced generation (CIG), including wind power, photovoltaic, and battery energy storage. In this paper, we challenge the traditional approach of emulating a synchronous generator by proposing a frequency-fixed GFM control strategy. The CIG endeavors to regulate itself as a constant voltage source without control dynamics due to its capability limitation, denoted as the frequency-fixed zone. With the proposed strategy, the system frequency is almost always fixed at its rated value, achieving system active power balance independent of frequency, and intentional power flow adjustments are implemented through direct phase angle control. This approach significantly reduces the frequency dynamics and safety issues associated with frequency variations. Furthermore, synchronization dynamics are significantly diminished, and synchronization stability is enhanced. The proposed strategy has the potential to realize a renewable power system with a fixed frequency and robust stability.