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| An article on power to weight ratio in switched electronic motor control design. |
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| Circlotron:
--- Quote from: Zero999 on June 15, 2022, 09:42:36 am ---Why post the same crap again and expect a different result? https://www.eevblog.com/forum/chat/star-and-delta-motor-field-winding-configurations-are-not-efficient/ --- End quote --- In that post I can see what the author is saying. Not that I necessarily buy it though. Get a 3-phase 6-switch inverter so that each leg is either high or low, no dead time. With reference to the halfway point of the DC buss each output will be a square wave. Now get your scope with differential probes and measure across each winding of a delta connected motor. The winding voltage will be 2/3 high, 1/3 off, 2/3 low, 1/3 off, repeating. Now if we separate the windings so that all six ends are available and connect each winding to it's own individual H-bridge so that we now have 12 switching devices instead of 6 it will be possible to drive each winding with a proper square wave with 100% on time instead of 2/3 on time. That's the guts of the argument as I understand it. How the motor would behave with a square wave to each winding instead a 2/3 wave (which is in fact closer to a sine wave than the pure square wave) I don't know. With the foregoing there might be some difference in motor behavior if each H-bridge produced a pure square wave. If though they each produce sinewaves there would be no difference to a 6-switch inverter. |
| NiHaoMike:
--- Quote from: Circlotron on June 16, 2022, 03:03:40 am ---If though they each produce sinewaves there would be no difference to a 6-switch inverter. --- End quote --- As mentioned, with the sine waves 180 degrees apart instead of 120 degrees, you get about 15% more voltage for the same DC voltage. |
| Circlotron:
--- Quote from: NiHaoMike on June 16, 2022, 03:25:51 am --- --- Quote from: Circlotron on June 16, 2022, 03:03:40 am ---If though they each produce sinewaves there would be no difference to a 6-switch inverter. --- End quote --- As mentioned, with the sine waves 180 degrees apart instead of 120 degrees, you get about 15% more voltage for the same DC voltage. --- End quote --- So with opposite legs of each H-bridge producing sine waves 180 deg apart, and the resultant sine wave across the motor winding being 120 deg or 240 deg from the other windings. |
| andy3055:
There are people who come up with stupid ideas, post them in public forums and sit back, relax and laugh at all who are contributing and arguing about what he/she has written. Not to mention arguing with each other! Why does he not have any come backs to what is being said? |
| Miyuki:
--- Quote from: NiHaoMike on June 16, 2022, 02:03:43 am --- --- Quote from: rob77 on June 15, 2022, 04:17:41 pm ---i'm afraid i'm not following you there.... so how exactly the waveforms would look like and how would the rotating magnetic field look like ? isn't 180 degrees apart a single phase ? there is a 1:1 relation between waveforms and mechanical construction of an electric motor.. if the motor is constructed for 3 phases 120 degree apart then that's the only way how to feed it. --- End quote --- If you have the motor wired in delta, the inverter gives it 3 phases 120 degrees apart. If you have a 340V DC bus, the biggest undistorted sine wave you can get between two phases is 208V. If you have the motor wired with each winding to 3 separate single phase inverters, a 340V DC bus would get you a 240V undistorted sine wave between the ends of a winding. The 3 inverters are run 120 degrees apart so the phase relation between any two windings is still 120 degrees as was the case with the 3 phase inverter. --- End quote --- Only if you use simple modulation, when you add this order sine, you can get full 240V in a simple 3 wire configuration This is already solved and used You can reinvent the wheel but it will end up always the same Also, there is a reason why motors use 3 phases in symmetrical spacing (some can use more phases like stepper motor commonly have 4) Two phase/ 180 degree motor won't ever run smooth and efficient |
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