This　article　investigates　the　generation　mechanism　of　electromagnetic　torque,　particularly　the　reluctance　torque　in　FSCW　V-IPM　machine.　Based　on　the　air-gap　field　modulation　theory,　the　modulation　process　of　the　PM　field　and　armature　reaction　field　is　elucidated　by　establishing　a　MMF　and　permeance　model　considering　the　magnetic　saturation　of　rotor　magnetic　bridge.　Through　analyzing　the　conditions　for　effective　coupling　of　air-gap　field　harmonics,　studying　the　time　domain　modulation　effect　resulting　from　the　magnetic　saturation　of　rotor　magnetic　bridge,　and　establishing　the　mapping　relationship　between　inductance　harmonic　and　single-phase　winding　field　harmonic,　the　generation　mechanism　of　electromagnetic　torque,　including　both　the　PM　torque　and　reluctance　torque　in　FSCW　V-IPM　machine　is　firstly　revealed.　Then,　a　harmonic　restoration　method　based　on　frozen　permeability　is　adopted　to　quantitatively　analyze　the　contribution　of　the　armature　reaction　MMF　harmonics　to　the　PM　torque　and　reluctance　torque.　Moreover,　the　reluctance　torque　ratio,　defined　as　the　ratio　of　reluctance　torque　to　electromagnetic　torque,　is　additionally　presented　from　the　aspect　of　armature　reaction　MMF　harmonics.　Finally,　the　analysis　is　verified　numerically　by　an　exist　well-developed　FSCW　V-IPM　machine.　©　2015　IEEE.