Vcommon mode, first, from which reference should be measured? Usual reference seems to be: midpoint of DC bus Comments about Vcommon mode: I understand that it is of special interest measure Vcm referenced to VFD real ground connection, due to it is the main cause of leak currents etc. etc.. After reviewing some manuals and from my practical experience, ground in VFDs usually seems to be connected to: 1) midpoint of DC bus directly or through coupling network (seems the usual). In this case the mean Vcm is zero (red waveform below). 2) negative of DC bus directly (if IT distribution) or through coupling network. This seem to cause a mean voltage to ground Vcm=Vbus/2, that don´t know if can be dangerous (see blue waveform below). I.e. direct connection of DC bus negative to ground is the actual case in railway traction inverters. 3) Connection to ground through star-connected capacitor network in output phases (this sometimes is the case with dettachable EMI filters). 4) No connection to ground at all, in this case it is not clear to me from which reference makes sense measure Vcm….