An integrated starter-generator (ISG) system includes a flux-regulated permanent magnet machine (PMM), a wound-field synchronous machine, and a control coil controller. The flux-regulated PMM includes a stationary portion having a control coil and a plurality of permanent magnets, and a rotating portion that includes rotating armature windings. The wound-field synchronous machine includes a stationary portion that includes a main armature winding and a rotating portion that includes a main field winding that receives excitation from the flux-regulated PMM. The control coil controller controls current supplied to the control coil of the flux-regulated PMM to selectively control magnetic flux presented to the rotating armature windings.