RPM Wide-speed-range DC Generators --
Description & Specifications
Main Features of RPM Generators
Power generation efficiency exceeds 95% over a 10-to-1 speed range, with current and voltage regulation by integral power interface electronics.
Modular disk assembly affords wide power range selection, to maximize yield from various rotary power drive sources.
Zero cogging torque and no gearing, plus boost regulation integral power interface electronics, provides useful current and voltage regulated generator output DC (direct current) power over a very wide speed and torque range. So energy yields are 2 to 10 times more than other generators, in addition to delivering far higher power quality.
No gears and hence no gear friction or stiction and far less periodic maintenance, no disconnect switchgear, and no cooling systems for gear lubricants or generator coolants.
The RPM Generator's current regulation facilitates parallel connection of like generator power interface electronics. And it facilitates parallel electronics power interfaces, connected to stacks of stator disks of the same generator assembly, thus accommodating a wide power range with a small inventory of different parts.
Its DC output power is uniquely compatible with RPM's flywheel batteries as well as chemical batteries.
Another version installed in electric vehicles (EVs) or electric power water-craft would augment onboard battery power while affording a healthy exercise option. This version could also produce electric power from health club exercise equipment.
Customized Models for specific applications
Left: Vertical axis version, mainly for coupling to vertical axis wind
turbines, over a wide range of power ratings to optimize yield from a wide
variety of wind turbine sizes. We have built and tested 2 prototypes that each
generate 500 watts at about 1000 rpm, with useful power down to about 85 rpm,
that charge a 48 vdc battery pack.
The vertical axis version has a relatively large diameter and large number of axial-field poles, to accommodate direct shaft connection by a flexible coupling to relatively low speed vertical axis wind turbines, and does not need the normal speed-up gearing of conventional generators (which would include drawbacks like friction and stiction and need for periodic maintenance, lubricants and additional bearings).
Left: Horizontal axis version, mainly for coupling to horizontal axis wind
turbines, over a wide range of power ratings to optimize
yield from a wide variety of wind turbine sizes.
Another version, with foot pedals attached to the shaft at each side, can be installed in an ultra-light electric vehicle, to augment onboard battery charge by generating electric power from a recumbent cyclist driver and/or passenger. This would extend the range of the EV while affording a healthy and convenient exercise option.
Both the vertical and horizontal axis versions provide regulated DC current and voltage to their loads through boost regulators in their power interface electronics. Both are self-starting, and never need to be disconnected from their loads. So they deliver far better power quality, at regulated voltage, optimized for the normally varying mechanical power driving their shaft.
Early applications for the Broad-speed-range RPM Generators, with mechanical shaft input power supplied by wind turbines, will supply regulated DC current and voltage to a 48-volt DC power bus, connected to 48vdc chemical batteries.
Later version Broad-speed-range RPM Generator versions will accommodate higher DC voltages. For example, generator versions that will supply DC power to poly-phase AC inverters, can provide relatively very high quality power synchronized to poly-phase power grids.
Test Setup to Demonstrate Controlled DC Output Current and Voltage over a Wide Speed Range
Testing the RPM Wide-speed-range Generator output current and voltage over variable selected shaft speed and torque is illustrated by the photo below.
Electric output power and electromechanical power conversion efficiency as a function of shaft speed, for a representative RPM Wide-speed-range DC generator for use with wind turbines, is shown in the figure below.
Its extraordinarily high DC electric energy yield from wind turbines, and the high power quality (well regulated and with no disconnect switchgear), of the RPM Wide-speed-range DC generator, is best understood by examining the Rayleigh Statistical Distribution illustrated below.
The curve showing Mean Hours at MPH for a 10 MPH average wind speed is determined for a representative location by compiling anemometer and/or Pitot tube recordings, typically available for many locations over decades. If a specific location has a different average wind speed from the 10 MPH average shown above, its Wind Speed axis for the above graph would accordingly reflect the Average Wind Speed for that location, with the same ratios of Mean Hours at MPH to Average Wind Speed, and following the same statistical distribution except for different Wind Speed parameters.
The curve of KW at MPH shows available shaft power from a wind turbine as a function of wind speed. Shaft power varies as the third power of wind speed. Hence the RPM Wide-speed-range generator power interface electronics control output current so that power generated is also proportional to the third power of wind speed. This attribute extracts and produces maximum available power from the turbine shaft over a far wider wind speed range than other generators.
The curve of Mean KWH at MPH is plotted from the product of Mean Hours at MPH and KW at MPH. Energy yield available from a wind turbine is thus the area under this curve.
Fradella's US Patent Pending 12/463,295 "Broad-Speed-Range Generator" fully describes and illustrates its many details.
Conventional Generator Drawbacks
Widely used induction generators can only generate power when their shaft speed exceeds the synchronous speed of the power grid connected to them, to augment grid power. At shaft speeds below synchronous, they would consume grid power, and so must be disconnected as wind speed fluctuates. At shaft speeds where induction generator losses are very high, the grid connection must also be disconnected, because power exchanged fluctuates excessively and internal generator losses can cause generator overheating. Although these shortcomings are widely recognized, induction generators are widely used in wind farms, directly connected to 3-phase power grids with no power interface electronics.
Common alternator output voltages substantially vary proportional to
shaft speed. Hence they cannot reach output voltage levels high enough
to charge batteries or drive DC-to-AC power inverters, until wind speed
is relatively high. And if connected to loads with no current regulation,
internal losses may cause generator overheating and/or excessive load currents
if shaft speed is not limited.
RPM Flywheel Battery, to store power as kinetic energy of its spinning rotor, from the RPM Broad-speed-range Generator and other power sources, and regenerate electric power as needed
A photo that illustrates early laboratory prototype testing, with descriptions
of main elements of RPM's prototype flywheel battery that has magnetic bearings
stabilized by ceramic ball bearings, is shown below.
Its integral regenerative motor is inside the rim and its top and bottom
rim holders.
The motor stator is fixed to the center shaft. Its four 2-phase stator wires and four connections to two aligned Hall sensors are accessed by a center bore that can be seen at the top of the center shaft.
Main rotor axial lift is provided by the ring magnet shown and an identical ring magnet in the bottom rim holder. These magnets are radially aligned to axially repel each other, by a ceramic ball bearing in the top rim holder and another in the bottom rim holder. Their axially free inner races are centered by the center shaft.
An axial preload spring under the top ball bearing and another under the bottom ball bearing prevent ball skipping and sliding, and provide consistent additional rotor lift force to each inner race. The main rotor axial support is provided by the magnets.
The 4 power (from 2-phase stator windings) and 4 sensor (from 2 Hall-effect devices each aligned to a respective stator winding, that sense regenerative motor magnetic field) conductors of the assembly shown in the above photo, connects to power interface electronics, which exchanges DC current with a 48vdc power bus.
Follow-up development tasks include: Replacing the aluminum rotor rim with a carbon fiber composite rim (that will provide over 4 times the energy storage capacity for the same weight flywheel battery); mounting the completed flywheel assembly, centered in a vacuum enclosure; purging the enclosure at elevated temperature under high vacuum, to remove contaminants that may otherwise be released during the flywheel service life; sealing the vacuum enclosure; mounting the flywheel in its vacuum enclosure within a self-leveling structure; and finally installing the complete flywheel battery system preferably in an underground site that can safely absorb the stored flywheel energy in the unlikely event it may explode.
Fradella's US Patent Pending 12/463,275 "Low-Cost Minimal-Loss Flywheel Battery" fully describes and illustrates its many details.
A flywheel battery prototype we built and tested, having a non-contacting rotor whose axial and radial position is stabilized by servos, is shown below. It is described in Fradella's U.S. Patent 6,794,777. Its manufacturing cost would be considerably more than the flywheel battery shown above. While its rotor balancing is not critical, and its probable service life is virtually unlimited, its many rotor position and rate sensors and need for close proximity magnetic bearing servo electronics with high sensitivity to ground loops, difficult to stabilize magnetic bearing servos, and high servo startup power, are challenging problems that we learned how to circumvent in a successor flywheel battery we are now developing.
The flywheel battery we are now developing, that we expect will supersede the very complex flywheel shown in the photo below, has passive magnetic bearings that inherently maintain radial centering for the rotor and provide rotor lift force that is stabilized by a single axial servo. Startup power for the successor flywheel battery is a small fraction of that needed for the flywheel prototype shown below. Axial forces needed from the new flywheel battery top and bottom electromagnets are a fraction of the axial forces needed to position the rotor for spinning, and can achieve desired rotor position in about one second. The successor flywheel battery is expected to cost about the same as the flywheel shown above, and will not have its size, speed, and service lifetime limitations.
Status of the RPM Broad-speed-range Generator and Flywheel Battery
RPM (Regenerative Power & Motion) and EES (Excellent Energy Solutions, LLC) are jointly developing the Broad-speed-range Generator and Low-cost Minimal-loss Flywheel Battery described here. Prototype tests and demonstrations have been conducted for 2 generator versions and 2 flywheel versions.
The technology shown and described above is covered by U.S. Patents
4085355, 4520300, 6566775, and 6794777, plus 2 pending patents.
RPM Generator and Flywheel Battery in Solar/Wind-Powered Building
Left:
Building-integral solar and wind power generation with flywheel battery
power storage and regeneration to provide uninterrupted electric power
as needed.
Advantages of building-integral RPM Generator installations are:
The building exterior walls channel wind to the turbines driving the generators, which increases wind speed. Doubling wind speed increases generated power 8x.
The generators and wind turbines do not need towers to support them.
Screens around the generators and wind turbines can prevent birds from colliding with turbine blades.
Movable louvers around the generators and wind turbines can limit wind speed at the turbines, to provide steady and regulated generator output power during wind storms and to prevent turbine damage.
The building can protect the wind turbines and
generators from rain and sun.
Horizontal Axis Broad-speed-range Generator Version for Ultra-light EV
Left:
A "see-through" view of a personal, 4-wheel ultra-light "Fitness EV" that
seats 2. PV can be applied on all top surfaces, that would collect
about 500 watts for several hours daily. Thin-film amorphous PV in
window glass can reduce glare and interior heat load from sunlight, comparable
to conventional tinted glass or reflective coatings that don't provide
electric power.
Intelligent power electronics can enhance this EV, by providing infinitely variable speed control, with synchronized non-conflicting proportional regenerative braking.
With power electronics, its 2 rear wheels are each driven by a brushless regenerative motor-in-wheel, a special version of the motor described in US Patent 4520300. Instead of conventional connection to tire rims, it has S-shape springs between the motor housing and rear wheel rim, and between the front wheel hubs and rims. So unsprung mass (only its tires and rims) is very low, and the motor-in-wheel is cushioned from road shock.
This EV weighs 800 pounds or so. Its ultra-efficient motor has cruise control for any speed from zero to maximum. It also controls downhill speed, and regenerates power to charge the battery whenever braking or decelerating.
Optional pedal power supplied by a driver in a recumbent position (where we output the most power without tiring) to the RPM EV version generator (shown in red) can augment solar power. Effort level is selectable, like cardio workout gym equipment. As can be seen from the graphs below, a champion athlete can generate 370 watts almost indefinitely, a physically fit person 180 watts. So a driver, pedaling in daylight with 500 watts from PV, could travel indefinitely at about 35 mph. This EV would be capable of traveling at speeds up to 60 mph, on mostly battery power, recharged by plugging into a garage power outlet.
Left:
Block diagram of ultralight EV with onboard battery power, charged by ac
or dc plug-in sources, probably in owner's garage.
Batteries are essential for regenerative braking, whenever the EV's 2 motor-in-wheel brushless regenerative motors decelerate the EV.
While driving, power can be augmented by about 500 watts from thin-film amorphous photovoltaics on all upper EV exterior surfaces, including its front and rear windows. Also, power can be augmented at any speed, by the pedal-powered generator. A second generator can be easily included for a passenger who might also want the exercise it affords, while extending the EV's range. Pedal effort level can be selected by the user. Depending on the user's fitness level, each generator can output up to 1.5 hp (1100 watts) for brief periods and 0.5 hp (370 watts) for over an hour, as can be seen in the graph below. Total sustained power, from 1 generator and the EV's PV, can thus average about 870 watts. So the EV can thus be driven for extended durations at speeds averaging 35 mph, without discharging the batteries. At such speeds, aero drag would be negligible, even with open windows, for ventilation.
If provided in-transit power, via the 2 red extendable contacts shown, on electrified highways, it could maintain 60 mph indefinitely. We need to make the public aware of this simple, clean, very low-cost option, so politicians will come onboard, and permit the highway infrastructure for it.
Main motor and braking effort may be applied to the two rear wheels, by regenerative bi-directional motor drive and braking, plus a friction brake (as a parking brake, and backup mechanical brake). No motor clutch or gearshift or differential gear is needed. With 2 large diameter motors in the 2 rear rear wheels, no speed reducer is needed. If the batteries ever fail (and must be disconnected), the EV may be driven powered only by PV and/or pedal power. It can be driven forward or reverse at 0-15 mph on pedal power only.
Two red stripes are shown at the EV's rear left side. Early versions may have only an extension cord, to plug into 60 Hz outlets. Until we have electrified highways for EVs, the 2 red extendable contacts shown could be used as charging contacts, automatically extending to engage recessed electrified conductive charging strips, in a future home's garage.
PV and sustained pedaling power can sustain ~35 mph without discharging
the batteries. Considerable data from cyclists is available. It's compiled
in the chart at right:
Note that the time scale is logarithmic. Also note that a champion 160-pound athlete can output 1.5-hp for several seconds, while a physically fit person can output about 1-hp.
The athlete can sustain about 0.5-hp for well over an hour, while the fit person can sustain about 0.25-hp. A driver wanting to power his vehicle more from his pedaling will probably choose to have 4 onboard 600 watt-hour batteries or less.
This lightweight "fitness EV" might have only 2.5 kwh onboard battery capacity. Its aero drag coefficient could be 0.1 (large area, sloped PV windows, and narrow large-diameter tires, help achieve this), but aero drag is higher when side windows are open for ventilation. Its frontal area could be 12 square feet (with a bit less head-room, and a bit more reclining recumbent driver sitting position than shown in the image at the top of this page). With less batteries, there would be more dependence on PV power. Nickel-metal-hydride, lithium-ion batteries, and ultracaps may soon cost less, and higher efficiency PV with 800 watts output may be worth the higher cost for this market segment.
On battery power only, its cruising range would be about 70 miles at 45 mph -- and 55 miles at 60 mph. This range is not reduced much, for night driving, with ultra-efficient LED head-lights and tail-lights. In daylight, on PV and pedal power only, a fit driver could maintain 35 mph, and achieve occasional 45 mph bursts.
With 10-kw peak motor power, this EV can accelerate to 15 mph in 2 seconds, 30 mph in 7 seconds, and 45 mph in 20 seconds (mostly on battery power).
Aero drag will increase when interior ventilation is needed, during high driver pedal effort. But that's no problem at speeds up to about 35 mph (where rolling friction considerably exceeds aero drag).
The images below are from 3D CAD models. Analysis shows RPM's generator, with electronics that includes selectable effort level; plus a motor-wheel version of RPM's regenerative motor having a tubular non-rotating shaft that supports its motor-wheel ball bearings and is a conduit for its 8 electrical connections to its power interface electronics, can enable a very low cost no-gas "fitness-EV". Spring connections between the motor and wheel rim enable very low unsprung mass; and with its large diameter/width ratio tires, to low rolling friction and smooth ride.
While applications for the "cleantech" electric power products we hope to manufacture and distribute shown above may seem diverse, their technologies are related. And the generator, flywheel battery, plus the ultra-light EV shown above are very compatible with each other and with solar power.
RPM's other 11 webpages also cover sustainable technology we are developing; to improve our environment; increase building and vehicle safety; lessen global dependence on fossil fuels and nuclear energy (and their serious negative consequences); and provide far more convenient and reliable UPS (Uninterruptible Power Supplies). To view them, please click on any of the links below.
Comparison of RPM's flywheel battery with others -- a somewhat detailed study
Brief Summary of RPM's Business Plan -- what we've done and plan to do for the future
RPM's Resources -- our people, tangible properties, office and lab facilities, etc.
Technology: Public and Business Policy
RPM's UPS can enable future distributed on-site solar/wind power, and more
RPM's brushless regenerative
motor and generator in ultralight EVs
RPM greatly values your interest in this exciting venture, and welcomes your participation.
If you have comments or suggestions, email Dick Fradella at fradella@earthlink.net
Edited November 2009
