  In this work we present a novel dual-port grid-forming control strategy, for
permanent magnet synchronous generator wind turbines with back-to-back voltage
source converters, that unifies the entire range of functions from maximum
power point tracking (MPPT) to providing inertia and fast frequency response
without explicit mode switching between grid-following and grid-forming
control. The controls impose a well-defined AC voltage at the grid-side
converter (GSC) and the machine-side converter (MSC) AC terminals and
explicitly stabilize the DC-link capacitor voltage through both GSC and MSC.
The wind turbine's kinetic energy storage and curtailment are adjusted through
a combination of implicit rotor speed control and pitch angle control and
directly determine the operating mode and level of grid support. Moreover, we
provide analytical small-signal stability conditions for a simplified system
and explicitly characterize the relationship between control gains,
curtailment, and the wind turbines steady-state response. Finally, a detailed
simulation study is used to validate the results and compared the proposed
control with state-of-the-art MPPT control.
