hmm... theoretical super EV car. I put much thought into that one myself!
I don't want a supercar, there are several of them already and they are way too expensive. I want to build something that is universal and inexpensive. I want flexibility most of all. This system seems to fit the bill. I love the idea of starting small, with two slaves and a few batteries so a car can drive around town. More power and/or range could be added at any time with a major redesign. Right now and EV will replace a whole string of batteries if just one is tired because replacing the one will unbalance the string. With this setup the batteries could be used until they were truly near the end. Also, the idea of adding different types of batteries is VERY appealing! I'd love to build all NiMH but there is no way I could afford it. With this type of system I could add NiMH incrementally, slowly replacing over time as the older LA batteries wore out.
AC motors have much more appeal than DC, but they are very expensive, as are the controllers. The smaller PMAC motors look great, but they can't power a car on their own. One for each wheel makes sense, but what about controllers? There are small PMAC controllers out there, and I have considered them. I want that max torque at start, since they won't be geared. The motors have to be oversized for the higher speed so they can perform well enough at the low speed. A 3-phase motor can do better at low end.
Well, I'm basically going way off course at this point, let me get back to the design.
What options are there for isolated gate control? I'd like something for the high side that didn't need its own power.
I've seen several options. I read about an optocoupler that could produce enough voltage at the output to drive a gate without additional power. There has to be a penalty though. Speed?
I've seen small transformers laid out with traces on the PCB to isolate a small gate signal. Seems tough to implement.
I've seen one module with an isolated internal DC-DC converter. Didn't get a price, but I figure it would be high.
What about having a small high-freq low-power transformer on board with a bunch of secondaries that could each power a high side gate driver? With a H bridge or 3-phase bridge is it possible to use one power source for all of the high-side gates or do they each need their own?
Anyone have any experience using a FET as an ideal diode? Can a simple circuit turn on the FET when the body diode becomes forward biased and turn it off when the current reaches zero? It would need power but it should be able to run autonomously, without central control. I'm using some high-current, low-voltage circuits for the batteries and the voltage drop across a read diode will really hurt efficiency and generate a lot of heat, both bad. The high-voltage DC stages won't suffer as much loss, but it can be done without a lot of hassle it makes sense to do it there as well.
That's enough rambling for now. Time to try and shut my brain off and go to bed.
Paul