A slack bus-like grid-forming wind turbine node for flexible power sharing in microgrids facing uneven wind speeds

The typical power synchronization-controlled (PSC) grid-forming permanent magnet synchronous generators (PMSGs) simulate the P-f and Q-V droop characteristics for power sharing through the grid-side converter. This scheme decouples the rotor speed and the grid frequency by regulating the DC-link voltage to a constant value. However, the output powers of multiple units are solely dictated by the droop setting, limiting the power sharing flexibility in both islanded and grid-connected wind power microgrids, particularly in scenarios with unevenly distributed wind speeds. This paper proposes a grid-forming strategy based on rotor speed coupled DC-link voltage-synchronized control, which couples the grid frequency and rotor speed using variable DC-link voltage. It enables each wind turbine node act as slack bus to share power under uneven wind speeds without communication, improving the flexibility of power sharing performance. Within the physical constraints of power balancing, the maximum power point can be reached by adjusting rotor speed setpoint without switching control modes. Moreover, the wide-rotor speed range operation ability is equipped throughout the droop range in response to fluctuations in wind speed or load demand. The dynamic model of the wind power microgrid is established, demonstrating improved damping and small-signal stability over the typical DC-link voltage synchronized approach and the power synchronization-controlled grid-forming approach. The theoretical analysis and the hardware-in-the-loop experimental results verify the feasibility of the proposed strategy.