Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

[MPaulHolmes]

I'm so excited! I just finished routing and ordered a 4 ounce copper (each side) pcb from pcbcart.com for a low voltage (144v? or 200v if you use 300v mosfets) AC controller. It is mosfet based. I figure about 300 amps per phase is what the mosfets can safely handle. It uses 18 of those TO-264 gigamos 7.5mOhm 200v 230amp mosfets. 3 mosfets per "thingy". YOu know, how there are 6 of those things. What are they called?! dang it! I sound like a friggen idiot now. Also, I routed and ordered a single through-hole AC control board. 12v control power. It powers the 6 "things" with 6 ISOLATED supplies. IT's a little excessive to have all 6 be isolated, but that makes it very open ended for extremely high power power sections. What's more, it can be used as a standard DC control board, or a SR control board, or a sepex control board, or a PMSM control board, or an ACIM board. hahaha. Just leave some stuff unpopulated. Every other motor controller is a special case of the 3 phase controllers. I've been super sneaky! The software is also mostly done.

I got off school on the 20th of August, and have been spending a LOT of time doing that stuff. I had the EVTECH list check the control board, and I added a few really good additions, so if there are mistakes, I think they will be very minor. I hope. duh duh duhhhhhhhh.

The plan is to test my AC motor with V/Hz, then PMSM with field oriented control, and then AC motor with field oriented control (the grand pooba). The low voltage (like up to 144v) power board won't get here for a couple weeks, since it's being worked on in a friggen slave labor camp in China.

[sawickm]

What's more, it can be used as a standard DC control board, or a SR control board, or a sepex control board, or a PMSM control board, or an ACIM board. I've been super sneaky! The software is also mostly done.

Hey Paul,

Great and exciting stuff !!!

Questions:

1. Could you also use this controller for your bulk DC charger ?
2. Are any plans in the works for a program like RTD Explore for this controller ?
3. Are you planning modular firmware for the different configurations ?
4. Would your controller work with the other “SR” ??? could it drive a Switched Reluctance Motor (SRM).

Thanks,

-Mark

[MPaulHolmes]

Oops I forgot, yes it can be used as a charger too. RTD explorer would work the same if I make the serial output the same. The problem is there are 6 pwm outputs now, and 3 currents, so modifications would be needed. Right now my serial output is just random numbers for debugging. It also has CANbus, so I could send data at a much higher rate to another "thing" that has CAN.

I used to do a lot of DirectX programming in C/C++, but I haven't done any recently. It would take me probably a couple months of only doing that if I wanted to do something like RTD.

Modular firmware would be possible I think. Actually, now that you mention it, the code could be written with all the variables there, and just different configurations, and maybe just different conditional compiler directives.

The charger is a constant current/constant voltage algorithm right now, set up for Thundersky batteries, and expects communication with a BMS through CAN, so it would be the most different of all the code I think, but still is really similar. You have a "throttle" to set the charge current.

It would work with a 500 amp SR, since it only has a single 12amp driver for each of the 6 pwm channels, so I need to modify the board for 2 drivers per pwm channel, and only have 2 pwm channels. That should allow for 1000 amp. The current capability isn't the problem, it's the load capacitance capability of the driver. 10 of those gigamos mosfets have too high of a capacitance for just that one driver.

Yes, it could also do a switched reluctance motor as far as I know. The stator magnetic field rotates just like normal I think.

[Automcdonough]

I've found that those driver chips tend to get hot, I prefer to use them just for the logic and offload the gruntwork to a NPN+PNP pair of transistors to drive the gates. I ran them with no bias resistors for the bases, collectors, emitters.. just a pure saturation buffer. But each FET should have it's own gate resistor.

[thingstodo]

Originally Posted by Automcdonough

...
Part of this decision was also rooted in arc-flash safety, I just don't want the battery voltage any higher than this from a liability perspective. (does everyone here know about arc-flash hazards? If not look it up, it's a very big deal!!)

I know that there are standard calculations for arc flash hazard on AC for the various voltages and short circuit currents. We (day job) were using the same calculations for DC with a couple of 'best practice' rules. They don't really fit well since DC does not 'turn off' 120 times per second and extinguish the arc.

I guess I'd better re-READ the info I have

[Automcdonough]

well, I'm not sure how separate they are in that situation.. and that is a lot of the problem is that the conduit of superheated gas and vaporized metal doesn't need to wait out 8.3ms for peak voltage when 50% of peak is still enough to maintain the arc. Also if the current was such that the heat generated can just wait out a few ms and still be maintained. That is why the instantaneous energy present is such a big deal, the breakers can kill the power but an explosion still happened.

[dcb]

Is this a long winded way of saying put your controller in a box?

[Automcdonough]

If said box would do any good to protect you from an unstable stick of dynamite, then yes. But it could occure anywhere in the system, off the batteries, failed wire insulation, etc.

Basically the safety factor is much more serious when you have stored energy at high voltages. On a 48V pack a short will give you some fireworks and perhaps a fire, but not a full-on EXPLOSION.

Sorry for the derail, I'm done w/ this, just wanted to point out that it is a factor I consider when choosing voltage. The average DIY hobbyist may not even realize what they are getting into.. some reading on wiki or something on arc-flash should clear up any questions or we could start a seperate thread on it.

[ElectricZX2]

So....does 300amps per phase mean a total of 900amps and 144 (or 200) volts?

Luke

[MPaulHolmes]

I was wondering about that myself. The 3 phases are 120 degrees out of phase, so it wouldn't be 300 amps on all of them at the same instant. Also, the sum of the currents in the 3 phases add up to zero. Like Phase 1 + phase 2 = -Phase 3. There's probably some sort of root mean square thing going on. Maybe it's 300*sqrt(3) haha. I have no idea what I'm talking about.