Core Technology

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, (see diagram), 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.

 

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 vehicle’s 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 system’s 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. 

 

Technology Extensions

 

“Global Power”

 

The Blackbird’s success in the US emergency services (est. 10,000 vehicles per year) confirms the value the product brings to this industry.  The global market for comparable mobile power applications is as much as 5x the US market making this market an obvious next step.  Raven’s current design produces the 60 Hz  120 volt power which is standard in the US and Canada but is not compatible with the 50hz  230 volt standard in the EU and most of the rest of the world.  An EU product would use essentially the same generator section as the present US product, but would require redesigned electronics to handle the higher voltages.  Raven engineers have developed the fundamental design for this product extension. 

Raven is seeking to partner with a non-US manufacturer to attack this market, because such a partner could much more readily design and market an “EU” ( aka “Global”) version.  EU design standards for electronics are both different from those in the US and restrictive, but familiar to companies active in that market.  European vehicles also have different under-hood engine arrangements and it makes more sense for a partner active in that space to develop necessary bracketing and exploit existing relationships with vehicle manufacturers and upfitters.

Raven’s core resonant circuit technology is patented in Canada, Great Britain, France, Germany and Italy, Korea and Singapore.

Alternative Energy

 

Raven’s engineers recently filed for patent protection for special generator configurations that extend the benefits of its patented speed independent generating technology to large three phase generating systems suitable for use in the growing alternative energy field.  At present, the power produced by these variable speed sources requires manipulation of the generated energy to produce constant AC voltage and frequency output, more often than not at a substantial efficiency penalty.

Read a white paper that describes the benefits and applications of this technology in detail.

Raven’s technology, which allows generators to produce 60 Hz Ac regardless of shaft speed, has particular relevance in several important areas:

 

• Wind power is the fastest growing sector of the world power supply.  It is projected to provide 1.5% of the world’s electricity needs by 2020 as reported by the World Energy Council - an enormous market.  Raven’s patented speed independent technology offers significant advantages over current approaches including:
• Buffers output from speed fluctuations- eliminates surge and flicker
• Reduces system stresses due to wind pulsing
• Eliminates inverters – high system efficiency
• Eliminates the need for grid excitation power and VAR support
• Reduces gearing
• Optimizes prime mover efficiency
• Reduces electronic losses

 

•  In many co-generation projects users generate power from industrial waste heat.  “Downstream” heat flow varies as control efforts focus on the primary process.  Raven’s speed independent power technology can enhance these systems’ ability to efficiently utilize this variable energy flow.

 

 

Micro turbines

Raven was recently issued a patent for use of its field modulation techniques in conjunction with special single-pole type generators which offer significant advantages when coupled with a class of very high speed micro turbines:

 

• Direct generation of high quality AC output without any rectification, filtering or electronic processing of the output current.
• Elimination of inverters which are problematic at high power levels.
• Elimination of diode rectifiers and associated heat loss.
• Inherent capability for handling reactive loads without complicating electronics.
• Output frequency and amplitude are field controlled and not a function of shaft speed.
• Provides the flexibility of variable speed engine operation supporting strategies around fuel efficiency, noise, weight, absence of gearing.

 

Military Gen Set efficiency

This was the rationale behind the original DoD support for the technology under the SBIR program.  For the present, the DoD has moved along the path of traditional inverter based products for the 3-5kW level.  Future power-source development programs, targeted toward larger units, will focus on weight, size and “signature” issues which play toward the demonstrated strengths of Raven’s technology.

Patent Protection

 

Five patents have been granted on this technology.  Raven Technology holds exclusive license rights to this technology and these patents.  International patents are pending.  (The US Government has a stated interest and royalty-free-right in those patents marked with a (*).)

• (*) US Patent 6,051,959 “Apparatus for Resonant Excitation of High Frequency Alternator Field” – Christopher N. Tupper April 18, 2000.
• US Patent 6,133,699 “Low-Loss Magnet Core for High Frequency Claw-Pole-Type Alternator” – Christopher N. Tupper, October 17, 2000.
• US Patent 6,177,746 B1 “Low Inductance Electrical Machine” – Christopher N. Tupper and Duncan G. Wood, January 23, 2001.
• US Patent 6,175,178 B1 “Low Inductance Electrical Machine for Flywheel Energy Storage” Christopher N. Tupper and Duncan G. Wood, Jan 16, 2001.
• (*)US Patent  6,570,370 B2 “Apparatus for Automatic Tuning and Control of Series Resonant Circuit”  - Christopher N. Tupper and Duncan G. Wood, May 27, 2003.
• US Patent 7,071,657 B2 “Method and Apparatus for the Production of Power Frequency Alternating current Directly form the Output of a Single-Pole Type Generator” - Christopher N. Tupper and Duncan G. Wood, July 4, 2006.

 

As noted above, Raven recently filed an additional patent covering generator configurations that will produce three phase grid quality power from variable speed inputs.