EVDL Administrator wrote:
http://www.chorusmotors.gi/technology/chorus_motor.php
That's an interesting website. I was especially gratified to learn that,
according to their page on wind machines, "Chorus's high-phase order drive
eliminates single points of failure and reduces power electronics costs
by X%." I take it that's the Roman numeral 10?
Naa... it lets the Marketeers change the specs depending on who they are
trying to impress today. An engineer? Only claim 10% because he
understands physics. A journalist? Claim 90%; he won't know it's
impossible! :-)
Here's a crude way to understand what the Chorus motor is doing: First,
consider a conventional 3-phase AC motor. It has 3 windings, and needs 6
big transistors in its inverter. Each transistor has to be big enough to
carry the peak motor current.
Now consider a DC motor's armature. It has lots more than 3 phases. If
it has 30 commutator bars, it has 30 windings. The commutator functions
as a 2-pole 30-position rotary switch. It powers each winding with a
square wave, but these square waves are each 360/30 = 12 degrees apart.
It is running as a 12-phase AC motor, with a square wave on each phase.
Suppose you replace the commutator with a set of transistors. You'll
need four transistors per winding; that's 30 windings x 4 = 120
transistors! You can see why we don't normally build motors this way.
However, each of these transistors only needs to carry 1/30th of the
motor's full load current. You can build a 300 amp motor controller with
cheap little mass-produced 10 amp transistors. These (might) be cheaper
than 6 big special high-power transistors.
Also, you don't need a sophisticated controller that can synthesize
three good sinewaves. You can use lots of simple squarewave controllers
for each of the 30 windings. That (might) be cheaper.
Over the years, we've had quite a few discussions here about the
practicality of wheel motors for road EVs. There seem to be some
significant obstacles. The only really successful road EV application of
them I've yet heard of was Luciole, though I suspect there've been others.
http://www.gaura.net/ev/luciole/index_e.html
The Luciole was a lovely little EV. I saw it at EVS-14 many years ago.
Kind of a forerunner of the Commutercar' Tango.
Its wheel motors did have gear reducers in each wheel. It used a small
high-RPM motor to get its size and weight within reason, and reduced it
down with gears to get reasonable torque and low-speed performance.
This made the wheels rather heavy, so it had the handling problems often
found with wheel motors (high unsprung weight).
--
Don't worry about people stealing your ideas. If your ideas are any
good, you'll have to ram them down people's throats. -- Howard Aiken
--
Lee Hart -- See my Xmas projects at www.sunrise-ev.com/projects.htm
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