OK, I've been quiet. Now for my two cents worth.
If the individual power units need information from each other, then we loose the advantage of separate units and may as well do it the "old" way.
I think each unit needs a CAN-Do if for no other reason than to gather telemetry about what that unit is doing and the state of the batteries (or whatever the storage technology) it manages. The IHU could provide input over the CAN bus this way as well, but I very much dislike the idea of *any* computer being involved in the power management system.
I don't think we should carry this distributed system to an extreme (one cell per unit) but should have a smaller number of units each managing a string of batteries. Perhaps 4 to 8 units total.
Chuck
Bdale Garbee wrote:
On Wed, 2006-10-11 at 09:41 -0700, Louis McFadin wrote:
One of the ways we planned to manage the system is to have deadbands on the buss voltage. Another way is to have a simple way that the units can communicate to each other as to their state.
As we've discussed, this all needs to be designed very carefully, and deserves careful review by a broad team. Adding another bus of some type to pass state information around between the various power management devices seems attractive, but the more I've thought about it the more I think we should try to minimize the amount of shared state information and complexity. If we can do it all with voltages on the DC bus and suitable dead band definitions, that seems like a big win to me. I'm certainly open to being convinced otherwise, though!
I have also been thinking of using a common system such as the IHU to send out a number which is it's opinion as to the voltage of the bus.
That's an interesting thought. The immediate difficulty I see is how all these devices would be connected to the IHU... putting a CAN controller on each certainly seems to be driving the complexity equation the wrong way, and yet we really don't have any other communications path to/from the IHU. Perhaps some intermediate flavor where there's an overall power management controller coordinating all these little devices and interacting with the IHU makes sense, but keeping each of the little units completely independent may be lower risk overall?
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle