New motor design

Found this article interesting about a new motor design. Most goes over my head. I do find it crazy that they are talking about a 4% increase. Not mind blowing, but I guess an extra 4 miles out of a hundred is worth it.
https://www.google.com/amp/spectrum...tter-electric-car-is-a-lighter-motor.amp.html

Interesting. Most of what he relates is well known and currently used. Slip rings and winding on the rotor of a motor operating in reluctance mode is a new one on me. Typically they rely on rotor salient steel shape with stator only excitation. Another strange point is the force/angle graph. I assume he means reluctance force where he states inductance force. Why use force and not torque? Anyway most perplexing is his 2 gray traces; one being Lorentz force and other is reluctance force. One shows a period of pi radians and the other a period of two pi. That's like a 2-pole and 4-pole acting together.

But the main problem I see with that graph is his summation of the two force curves. Yes, as he claims, a phase shift can increase the positive peak of the sum. However at the same time it decrease the magnitude of the negative peak. Motors using pole pairs utilize both positive and negative for the N & S poles. So I think the proper way to sum the two forces is to use RMS values. In this case the sum is the same regardless of his phase shift. And this shift of rotor excitation between Lorentz and reluctance is his claim to fame.

I'm not saying this angle is unimportant. I just don't like the explanation. I believe current IPM motors for EVs use a combination of torque from the magnets and from reluctance torque. Those use shaft position feedback and vector algorithms to maximize performance.

We'll see if slip rings starts showing up in EV traction motors. I doubt it. But I do appreciate such research coming from universities especially ones having EV race programs.

Thanks for the article. Maybe another member can enlighten me about that graph.

major

Maybe another member can enlighten me about that graph.

Click to expand...

Not sure why he uses force instead of torque but it doesn't really matter for the point he is making. The 2 force vs angle graphs are a bit different than the standard ones you generally see in the literature but the bottom graph is force vs current vector phase angle with respect to the d-axis for an IPM (most graphs I've seen are with respect to the q-axis).

For a surface mounted rotor, there is zero reluctance torque so all you have is the "lower frequency" grey line. This tells you that to get maximum torque out of a surface mounted PMSM, you need to have your current vector on your q-axis (90 electrical degrees from your d-axis).

For an IPM, you now have reluctance torque added in (the second "higher frequency" grey line). Reluctance torque only depends on the phase current and the change in inductance with respect to rotor angle. Because of this, the reluctance torque in IPM's is always twice the electrical frequency of the motor. So if you had an IPM with no magnets in it you could still generate reluctance torque if you changed your current vector phase angle to 45 degrees from your d-axis.

So for an IPM when you add the torque from the magnets and the torque from reluctance your maximum torque occurs when your current vector angle is somewhere between 45 and 90 degrees from the d-axis (depending on the design of the rotor and the load).

The problem with this is that those 2 peaks don't occur at the same current vector angle. Their new motor design with slip rings allows them to align the PM and reluctance torque peaks so they occur at the same angle.

learningrc said:

Maybe another member can enlighten me about that graph.

Click to expand...

Not sure why he uses force instead of torque but it doesn't really matter for the point he is making. The 2 force vs angle graphs are a bit different than the standard ones you generally see in the literature but the bottom graph is force vs current vector phase angle with respect to the d-axis for an IPM (most graphs I've seen are with respect to the q-axis).

For a surface mounted rotor, there is zero reluctance torque so all you have is the "lower frequency" grey line. This tells you that to get maximum torque out of a surface mounted PMSM, you need to have your current vector on your q-axis (90 electrical degrees from your d-axis).

For an IPM, you now have reluctance torque added in (the second "higher frequency" grey line). Reluctance torque only depends on the phase current and the change in inductance with respect to rotor angle. Because of this, the reluctance torque in IPM's is always twice the electrical frequency of the motor. So if you had an IPM with no magnets in it you could still generate reluctance torque if you changed your current vector phase angle to 45 degrees from your d-axis.

So for an IPM when you add the torque from the magnets and the torque from reluctance your maximum torque occurs when your current vector angle is somewhere between 45 and 90 degrees from the d-axis (depending on the design of the rotor and the load).

The problem with this is that those 2 peaks don't occur at the same current vector angle. Their new motor design with slip rings allows them to align the PM and reluctance torque peaks so they occur at the same angle.

Click to expand...

Thanks. Helps a lot. Nice explanation.

Regards,

major

Interesting.

The long & thin rotor design seems to diverge from many modern motor designs but I guess that's irrelevant to the principle they're demonstrating.

The 2% gain in peak efficiency they're claiming might not sound like much, but if that's going from, say 96% to 98% then the waste head load just halved. That's got to add up to increased power rating somewhere, or a smaller, lighter motor.

Each year, the team built a new car with improved motors, gearboxes, and power electronics. There are four motors per car, one for each wheel. Each motor is:

• 8 centimeters in diameter,
• 12 cm in length,
• 4.1 kg in weight,
• produces 30 kW of continuous power
• peaks at 50 kW.

Click to expand...

Nice!