Re: Production EVs

[XURQ03A@prodigy.com ( LEE A HART)]

> All the newer, more modern contollers for EVs use at least one
> micoprocessor. Auburn, DCP, DAX, and Godzilla all are computer-controlled.

Except that total sales of all of them don't amount to 1% of the market. I
don't mean to be critical of the effort and enthusiasm of the people in these
companies; they are to be applauded for pushing the state of the art. But they
are all garage shop operations.

> It would be hard to imagine a software failure that would result
> in a ramp up to full throttle in an AC controller.

Then you have never tried to design a fault-tolerant micro. Here is just a
sample of the things you have to think about:

 - a reset can occur at any time, between any two instructions, and in
   most micros, the reset process takes many clock cycles to complete.
 - a bit in any memory location or register can flip or stick at any
   time. You have to consider what this will do to program execution
   and data validity.
 - the clocks can fail, freezing the outputs, or run at the wrong frequency.
 - input and output bits can spontaneously change states or modes,
   due to design defects in the chip (essentially all chips have them)
   or external EMI or noise.
 - undetected software bugs that arise when the right conditions occur.
 - self-test and diagnostic modes that get entered inadvertently.
 - the I/O channels blindly keep generating some output (like a PWM)
   even if the micro is distracted and off doing some unimportant task.

You might say "that can't happen", but they DO! So you have to examine each
one in detail, and be sure your design has protection.

>> Do not suppose a problem cannot be solved just because you don't
>> know how to do it.

> Excuse me. There is no known way to avoid this problem.

Oh, there isn't, eh?

 - overdesign the switch so the chance of a failure is negligible.
 - use another topology; boost converter, or buck-boost converter.
 - use redundant switches; if one fails, the other immediately turns off
   and won't turn on again until the problem is fixed.
 - use an electronic circuit breaker; microsecond response when fault
   is detected.
 - crowbar the motor with an SCR; forces a slow fuse or circuit breaker
   to clear.
 - mechanical solutions, like a shear pin in the drive line.

> An AC controller is likely less expensive (or at least more practical)
> than these other types of DC controllers.

No; all the DC/DC converter topologies use just one transistor and one diode.

> Inherently, plug braking does not present the degree of hazard that
> uncommanded full-throttle does. That is why OEM EVs have AC drives.

If the EV-1 with its 100 HP drive goes into full braking or reverse on the
freeway, you don't think that's a "degree of hazard"? No transmission or
clutch, no emergency stop button; what are you going to do, my friend?

Lee Hart                     If you would not be forgotten
4209 France Ave. N.          Soon as you are dead and rotten
Robbinsdale, MN 55422 USA    Either write things worth the reading
phone (612) 533-3226         Or do things worthy of the writing
e-mail XURQ03A@prodigy.com   (Ben Franklin, Poor Richard's Almanac)