Does a 3-phase VFD work if one phase is reduced (e.g. with a dimmer)?
A VFD will work in the way described. The increased ripple in the DC bus capacitors could cause them to overheat. Also the increased current in the two phases with increased current could overheat the rectifier diodes in those phases. The input harmonic current content would increase. A VFD may have phase-loss protection to prevent that use. The VFD manufacturer may be able to provide a specification stating the maximum output current and power for operating the VFD with a missing input phase. There is some demand for VFDs that accept single-phase input power.