Quote:
Originally Posted by Stubby79
I didn't know what a reluctance motor was until about a week ago. In my typical fashion, I didn't pay any attention to a technology that was out of my price range...none what so ever. Took one look at Paul's AC controller thread and assumed it was for induction...I mean, that's what Tesla runs as did a few others; assumed the rest were running a form of brushless DC. Oops. Very close, very similar, but not quite...
FWIW, the netgain, like most of the others these days, is not a simple reluctance motor...they call it a "Synchronous Reluctance Internal Permanent Magnet (SRIPM)" motor. The permanent magnets are equally important as the reluctance side of things.
And to make matters worse, there are other names for the same thing!
I can thank google for sniffing my searches and recommending a couple of youtube posts, including Tesla's "new" motor tech...which appears to have taken them a few years longer than everyone else to adopt, unless that was just on the model X which the video was about.
Anyway, just looked at the Netgain motors. The $4k US is prohibitive to me, at least for a just-for-the-fun-of-it project, but...nice efficiency map. You'd basically be running in the >85% area of the map most of the time, compared to a BLDC which would max out there. That's impressive. And all by hiding magnets inside of laminations...I wonder why it took so long to figure that out and bring it to the market. Ok, I know switching speeds/losses had something to do with it, but still...oh, and that Netgain controller only weighing 9lbs is also impressive, for the power output.
I gotta go, I'm drooling and this is making my head hurt to think about!
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These "HSG" "IPMSM" are the same thing...Tesla's IMPSynRM is the same thing...everyone does their rotor design a bit differently, all in the name of efficiency (or power-to weight or whatever their specific design is meant to do, but efficiency/range is where the money is, imo)...but they're all just the same thing in different flavors.
Vector control = field-oriented control = field weakening in a reluctance motor. Since these motors are a PM/Reluctance hybrid, it works on them, raising the rpm...while retaining the low-end grunt(torque) of a PM motor.
Super neat-o! (So much for sep-ex field weakening).
When I read "Interior Permanent Magnet" I was like..."Why???". Seemed at first thought it would make for weaker magnetism than having the magnets right on the outside of the rotor, second thought was simply to be able to contain the magnets safely at stupid high RPM.
I wasn't considering the iron - wasn't even considering what it was made out of, to be honest - and how it becomes magnetized when in a magnetic field. Duh! Didn't realize it was reluctance. I knew what reluctance was, electrically, didn't put it in context with magnetism and iron in a motor. Yeesh. Only because of youtube that I do now:
(gets really interesting at 9:38)
Wasn't
sure the HSG was the same. Makes sense that it would be, cuz this thing has to be able to hit 16000rpm...and if there was no field weakening, then you'd end up with a stupid high back EMF voltage, which you could compensate for, I suppose, and you'd not be able to feed any power in to it once it got above battery (or voltage multiplier) voltage, yet everyone (auto makers) claims their hybrid setups make power at higher RPM. Assumed induction...should have clued in then.
Anyway, back on topic...wasn't
sure, half the reason I wanted to pull one of these HSG apart, but they don't come apart easily...but you can just barely see down inside through the back:
First shot you can't really see the laminations -- dang it, another word to add to Firefox's "dictionary"; stop correcting me when I'm not wrong! -- but look at how tiny those stator (another word!) coils are! The whole rotating field makes more sense when you have a lot more coils...as does the smoothness of the motor.
Second shot, you can just make them out. The gnarled-look to the metal on the rotor right beneath the coils. Dang hard to take a picture of even that much, but you can see it with the naked eye. Laminations, between - presumably two - mirror-bright (you can see the reflection of the coils on it) end plates, which are presumably there to compress the laminations tight. So, yes, we have laminations, so we have reluctance and everything that goes with it.
The thickness (thinness?) of the copper windings makes sense as well, seeing how small said coils are. Why others cram bars through there instead of wire also makes sense, as small as they are.
The whole BLDC bit has tainted my assumptions of what it would be like inside quite a bit. Considerably fewer - therefore larger - coils, and equally large magnets. Not a lot of difference between the one in my insight and the ones on my ebikes. While similar, this is definitely different. A lot more switching going on to get higher speeds with more coils...then again, R/C motors spin at stupid high speeds, so not much reason for these not to translate that in to less speed and more torque.
Speaking of BLDC motors...which are fed via square-wave (or at least trapezoidal) rather than sine-wave...I would have thought that a magnet going past a coil would naturally result in a a sine-wave, but supposedly not...why not? is it trying to be a sine-wave, only saturation is cutting the rounded top off of it? That's what comes to mind...trapezoid = cut-off sine wave. Just a thought...
Yes, I use this thread as a sounding board. Helps me put my thoughts together, trying to explain them...often find details I've missed or assumed inside my head along the way.
Almost forgot...the whole synchronous bit about how the rotor follows the rotating field and stays in sync with it...and how using one of these as a generator creates a nice 3-phase sine wave output...well...that means you could use one to drive another one -- right up until it you hit breakdown torque (where the motor slips out of sync with the input) at least.
You couldn't start the motor with any load that way, but once it got going, if you didn't put so much load on it that it would fall out of sync, you'd be ok. It would be quite a mess if it did, mind you...anyway, it seemed like a potential way to transmit power electrically, rather than mechanically, if you had reason to. You could use a brushless controller to get it(both actually) started with a load on it, even, then switch over to driving one of them mechanically to drive the other one electrically.
I tested it, using my cordless drill again. It started the driven motor after an initial twitch as it synchronized, so no-load starting is fine. Hold the driven motor from spinning and it just twitches in your hand.
With the drill on low speed, I could stop it spinning by hand, despite having more torque on the driver motor. With the drill on high speed, it was the drill that gave out instead (the BMS on the battery cut out from over-current). That was rather as expected. No starting torque, but the faster it went, the more torque it could provide. I assume this is due to the peak voltage output being higher, therefore able to make a stronger push/pull on the coils.
I'm really left wondering what the breakdown torque would be at high speeds. I would hazard a guess that if it was being fed the full 270v, it would be dang hard to stop it...as in you might see that 10kw without much bother. Or it might fall flat on it's face. Going to have to experiment, get it up to a decent speed with plenty of power behind it and see if I can stop it turning. That treadmill motor with an alternator pulley is looking like a good place to start to spin the driver motor...
Could have it's uses, if it works...serial hybrid on something like a motorcycle...battery/controller for in-town speeds, engine driving a motor as a generator for higher speeds.
Nah, it will probably fall flat on it's face and blow up first.
Another thought...so, the motor synchronizes with the speed of the input wave form. So if I feed it off of 60hz 3-phase "mains", it should work...but...but...but...it's not going to turn very fast. If it doesn't turn very fast, the back EMF is not going to equal anything near the input...but it can't go faster than the 60hz will let it...is it just going to create an awful lot of heat? You'd be dissipating whatever the voltage difference between the two is, through the coils...so yeah, I think it would just get very angry and overheat. HMM...
I'm OK with that. "For science!" BOOM!