  We prove that the popular grid-forming control, i.e., dispatchable virtual
oscillator control (dVOC), also termed complex droop control, exhibits
output-feedback passivity in its large-signal model, featuring an explicit and
physically meaningful passivity index. Using this passivity property, we derive
decentralized stability conditions for the transient stability of dVOC in
multi-converter grid-connected systems, beyond prior small-signal stability
results. The decentralized conditions are of practical significance,
particularly for ensuring the transient stability of renewable power plants
under grid disturbances.
