tobewankenobi wrote:Someone here knows Ld, Lq, pole number and flux linkage for these ebike motors? Perhaps easiest to modell in femm directly or? Did someone mention flux2d? If so please send link to download?
This is what I wanted to evaluate, among others... so I don't have any Ld Lq or other data. Flux2D isn't free, but I think you can ask them for a demo @cedrat.com. Make it sound as official as you can, I don't think they give demo licenses to hobbyists
tobewankenobi wrote:drebikes wrote:About the winding, I suppose it's fractional slot, but it's not clear for me what's the throw. As a matter of fact it doesn't even seem the throw to be constant nor the number of slots per pole per phase (sometimes 3, sometimes 4). My background is more with concentrated non-overlapping stator windings and I'm having some trouble wrapping my head around this fractional varaible Nspp type of winding. Do you know of any published winding scheme of the 9C?
Fractional winding is common for high pole PM motors, it reduces cogging etc. Usually it is good idea to keep symmetry, both for noise and cost. Can link some document if you are interested.
About the fractional bit, that I have seen before. I have attached a scan of what I scribbled the other day: with 3 colors there are the 3 phases and I noted the number of slots per phase per pole.
The weird bit (for me) is that it's not constant, it's 2 times 4 and 3 times 3 slots per phase. I could caracterise this motor as actually 2 motors, one with 2 poles and 4 slots per pole and phase and another with 3 poles w/ 3 slots per pole and phase. These two motors are wound on the same stator, and they should be geometrically balanced.
Now, there may a point to this asymetry (I'm think BEMF shape), but I haven't seen this setup before. One thing is sure, the stator yoke must be more saturated behind the 4-slot zones. This means that either around the 4-slot zones it's over-saturated and lossy, or in the 3-slot zones it's under-used. I bet for the former.
tobewankenobi wrote:drebikes wrote:
Here's KF's FEMM sym (attached a B map), I don't know how to use FEMM except clicking on solve. It seems the motor is highly saturated @1.8T, while the material is rated for 1.5T before the permeability goes downhill. If this is how they're built and I haven't screwed up something in the sim, then I have some ideas on how to improve. It wouldn't cost the same amount, but they can be made better
http://www.cartech.com/ssalloysprod.aspx?id=2360
*EDIT: not dr, dre. I didn't want to imply I'm a doctor of ebikes, dam'... it just came up like this
Nice! Did you make the model? Saturation in teeth is nothing to worry about in such small machines, only problem is if they run closed loop control and parameters saturate. But the controllers arent that nice for ebikes. A real problem can be to high negative d-current which can cause demagnezation, or to high load angle and loss of synchronism. Gould you share the femm model?
I don't even think it's a synchronous motor in the "phases of the S and R are separated by the load angle" kind of way because the number of stator and rotor poles is different to reduce the cogging torque. I assume for this reason they're so woefully inefficient, a PMSM that tops at 80% isn't much to write home about.
Why doesn't tooth saturation matter, don't you loose torque if too saturated? The permeability for FeSi isn't great over 1.8T and this may not be the best FeSi in the world. There's also the iron loss aspect if too saturated.
About the Id... I don't know if we're talking about Id/Iq. I know far little about control than motors themselves, but I understood they're open loop BLDC command, so aside from the rise/fall time of the current we're in DC. For this reason Ld/Lq may not matter. I don't know how to do the park transformation on a square wave phase current, maybe taking the fundamental only?
I'm really curious to learn things about motor control, need to advance on that. I suggest you FEMM