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 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 Ravens success with this simple and robust approach to generating steady 60 Hz AC power, at varying speeds is Ravens 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. The Blackbird: The first product developed utilizing this technology is the Blackbird, a compact 75 pound system that generates pure sine AC power across a wide range of shaft speeds. The system is available in 5kW-120V and 7kW-120/240V models. The Blackbird uses the power of a vehicles engine to generate auxiliary power incidental to normal operation where speed may vary widely. Raven has invested considerable engineering effort in proprietary design and manufacturing processes that result in robust performance and reasonable manufacturing costs. The system performs over a wide temperature range and has proven both capable and durable in the field. For a more complete discussion of the systems capabilities, please refer to the Spec sheet and the FAQ elsewhere on this site. A considerable additional amount of engineering has been devoted to developing complete well designed mounting kits for a broad assortment of vehicles. Both belt driven and gear drive PTO applications are available and a hydraulic drive application has been demonstrated. The system has received a warm reception from the emergency services and has demonstrated appeal in other mobile and field applications where off-grid power is used to run power tools and provide lighting in a wide variety of situations.
