180 degree commutation with sensors vs standard 120

General topics and discussions about the VESC and its development.
Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: 180 degree commutation with sensors vs standard 120

Postby Hummie » 03 Dec 2017, 17:34

I don't see 180 commutation shortening electrical pathways just when they were fed

rew with two coils being powered instead of one I see the motor would have two iron teeth being magnetized and on a slow moving heavily loaded skateboard the motor would maybe even have double the torque output before magnetic saturation of the iron as there's now double the amount of iron, no? And this follows the same logic that a delta motor would be able to produce more torque before saturation as it seems to have all teeth electrified while the wye is just 2/3. Everyone says they perform the same but if the amount of teeth is truly different it makes sense. But maybe isn't really the case and black transformer magic is going on and ...how many teeth are magnetized?

devin
Posts: 253
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: 180 degree commutation with sensors vs standard 120

Postby devin » 03 Dec 2017, 18:06

In theory:
Image

Image

Hummie wrote:I don't see 180 commutation shortening electrical pathways just when they were fed

rew with two coils being powered instead of one I see the motor would have two iron teeth being magnetized and on a slow moving heavily loaded skateboard the motor would maybe even have double the torque output before magnetic saturation of the iron as there's now double the amount of iron, no? And this follows the same logic that a delta motor would be able to produce more torque before saturation as it seems to have all teeth electrified while the wye is just 2/3. Everyone says they perform the same but if the amount of teeth is truly different it makes sense. But maybe isn't really the case and black transformer magic is going on and ...how many teeth are magnetized?


devin wrote:@rew wrote:

No, From what I read above, the "180 deg commutation" is simply BLDC but with an extra motor coil powered up. (Y or Delta does not matter).

But if we think about what we want to achieve.... We have a permanent magnet in an electromagnetic field. We want to set up that magnetic field that has creates the most torque on that permanent magnet. Well... That's exactly what FOC does: It optimizes the D field vector to be just enough, minimizes the Q component. (the D causes the maximum torque per applied current, the Q field vector does not cause any torque).

This way of commutating would improve performance if the motor amp rating of say 15A would mean: The motor wires blow up at 15.1A. That is not the case. So running two coils at slightly less current instead of just one is going to win you very little.


@rew do you suspect running either delta or wye in bldc 180 degree commutation mode vs 120 degree would cause any change in the “apparent kv” max rpm per volt of either delta or wye, considering 180 degree commutation with delta (but not wye) would effectively “shorten” one of the 2 simultaneous pathways the electricity takes through the delta in bldc mode? shortening (halving the length of) this electical path would have the effect of doubling the drift velocity at stall for a given effective voltage in that section of the conductor, and as we have previously discussed... i have observed that doubling the drift velocity at stall in a wye motor either by doubling the battery voltage or halving the winding length doubles the max rpm of the wye motor.

it also seems 2 outputs instead of one would lower the apparent positive-to-negative winding resistance of the motor, in theory leading to more motor amps for the same battery amps and electical wattage at the same rpm.

Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: 180 degree commutation with sensors vs standard 120

Postby Hummie » 03 Dec 2017, 18:52

the D and Q field vectors of a spinning motor must be seen to know whats going on. need a moving diagram to visualize and then we can talk about something for sure.

devin
Posts: 253
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: 180 degree commutation with sensors vs standard 120

Postby devin » 03 Dec 2017, 19:11

Hummie wrote:the D and Q field vectors of a spinning motor must be seen to know whats going on. need a moving diagram to visualize and then we can talk about something for sure.


Wikipedia wrote:Source: https://en.wikipedia.org/wiki/Vector_control_(motor)
"Projections associated with the (d,q) coordinate system typically involve:[19][22][23]

Forward projection from instantaneous currents to (a,b,c) complex stator current space vector representation of the three-phase sinusoidal system.

Forward three-to-two phase, (a,b,c)-to-(α\alpha, β\beta ) projection using the Clarke transformation."
Source: https://en.wikipedia.org/wiki/Vector_control_(motor)

Clarke Transformation: https://en.wikipedia.org/wiki/Alpha–beta_transformation


certainly at stall, the electron drift velocity of "path 2" is doubled with 180-degree-commutation-delta, compared to 120-degree-commutation-delta. by contrast the electron drift velocity at stall remains unchanged with 180 vs 120 degree commutation wye.


Return to “General”

Who is online

Users browsing this forum: Bing [Bot] and 2 guests