Wind turbine power capability is an essential set of data for both wind turbine manufacturers/operators and transmission system operators since the power capability determines whether a wind turbine is able to fulfill transmission system reactive power requirements and how much it is able to provide reactive power support as an ancillary service. For multimegawatt full-scale wind turbines, power capability depends on converter topology and semiconductor switch technology. As power capability limiting factors, switch current, semiconductor junction temperature, and converter output voltage are addressed in this study for the three-level neutral-point-clamped voltage source converter (3L-NPC-VSC) and 3L Active NPC VSC (3L-ANPC-VSC) with press-pack insulated gate bipolar transistors employed as a grid-side converter. In order to investigate these VSCs' power capabilities under various operating conditions with respect to these limiting factors, a power capability generation algorithm based on the converter electrothermal model is developed. Built considering the VSCs' operation principles and physical structure, the model is validated by a 2 MV·A single-phase 3L-ANPC-VSC test setup. The power capability investigations regarding a sample grid code's reactive power requirement show that 3L-ANPC-VSC results in 32% better power capability than 3L-NPC-VSC at the switching frequency of 1050 Hz. Furthermore, 3L-ANPC-VSC with 57% higher switching frequency (1650 Hz) and 33% smaller switching ripple filter can yield close power capability compared to 3L-NPC-VSC with 1050 Hz.