US Patent 7106030 Field excitation for an alternator

A system for controlling the excitation of an alternator field coil. The system comprises a capacitor forming a charge reservoir, a first and a second selectively operable switch connected to opposing ends of a field coil of the alternator, a first catch diode, and a second catch diode. At least one of the first and second switches are operated at a variable duty cycle and the capacitor both absorbs energy from the field coil and supplies energy to the field coil to regulate the magnetic field of the field coil, effective to regulate the output voltage of the alternator and rapidly compensate for changes in at least one load connected to the alternator.