Raven Technology LLC has developed a breakthrough in mobile AC power. Raven’s AC-Direct™ technology provides 60 Hz 120 VAC power directly from a special high frequency alternator regardless of engine speed and without the costs or limitations of inverter systems.
The overall system is described in US Patent 6,051,959. The output of a three-phase high frequency alternator is rectified into a single output voltage by natural commutation of diodes-devices similar to the operation of a typical automobile alternator. The output level of the alternator is controlled by modulating the field coil magnetism with a 60 Hz sine wave. This produces a 60 Hz rectified sine wave output which is then “unfolded” into a full sine wave by soft-switching as the current passes through zero. The result is a 60-Hz AC sine wave (fig 3 below). We refer to the combination of natural commutation and soft switching as “Soft Commutation™.”
Key to Raven’s success with this simple and robust approach to generating steady 60 Hz AC power, at varying speeds is Raven’s patented technique for “Resonant Excitation” of the alternator field. Use of resonant circuit techniques efficiently provides the high driving voltages needed to force the magnetic energy into and out of the alternator field 60 times per second. Typical automotive alternator designs are not suitable for this resonant excitation because the quickly changing magnetic field would produce high losses from eddy currents. Raven has designed a special low core-loss alternator design, described in US Patent 6,177,746 B1, which enables the resonant excitation technique. Raven also holds US Patent 6,570,370 B2 for a technique which allows for automatic tuning of the system for peak resonant behavior at 60 Hz. This is important because the resonant frequency is subject to dynamic effects from varying output loads.