Brushless motor question - consequences when mechanically driven

Op vrijdag 6 oktober 2017 12:19:21 UTC+2 schreef unk:

Most controllers use an EMF brake to limit the windmilling. Specially useful for electric sailplanes: the prop has to fold in non-power assisted flight.

It?s normally sensorless PMSM motor, and I don?t think they have detection for turbine mode

But, the efficiency of turbine mode is low, so do you even think that it wi ll be able to draw the rotor out of the motor control loop?

Cheers

Klaus

Don't know what is exactly "windmilling" meaning.

Sensorless BLDC application are quite useless in the majority (fan application with stable Torque param may be ...)

I'm on a EPS (electric power steering) project for vehicle.

FOC(Field Oriented Control) and Flux weakening are the two major methods implemented in a modern PMSM control. It is mandatory to know the rotor position/speed to run the algos. Not so hard to master BTW anyway.

Sensorless scheme based on back EMF stator windings is very uncertain on low rotor rpm.

Please explain what is windmilling in PMSM or BLDC motor.

H.

Remember this dude...

for the Mercedes air circulation system. I designed a chip for Bosch

I actually breadboarded the chip circuit. I had issues with windmilling running it backwards from desired... and it not starting forward upon command... it wanted to continue backwards.

So I used a leaf-blower to simulate windmilling, watched the commutation waveforms and came up with a scheme to overcome that mis-commutation.

Whether your particular motor controller can handle that... who knows?

Get a leaf blower ;-) ...Jim Thompson

It's the prop that windmills.

Windmill is what you call it when the air moving through the prop makes it turn a shaft (which in this case is the BLDC motor shaft); they were invented many centuries ago.

Oh I see thanks to Jim post.

The power driving stage of the stator (3 windings) is almost always build with 6 MOSFETS so when rotors turning "windmilling by the prop on rotor shaft" then i think the energy will be absorbed by the power source if it is a battery otherwise it depends.

You're right the reverse mechanical energy absorbtion shall be implemented in real electronics ECU for PMS Motor drive. In that sort of things it is not always supported by motor test benches ... We have smoke some ECU (1KW PMSM on EPS) weeks ago ...

Nope. Y-winding, tap to battery plus, 3 NMOS switches to ground.

Superbly easy to decipher commutation signal.

...Jim Thompson

Jim,

We are using this GDU for EPS Vehicle

Please see pp.19

For weird "ASIL" reasons from "Safety Guys" we have to switch to the new Allegro A4916.

Oh no. The hard thing is to accomplish a clean SVPWM with the 6 dedicated PWMs outputs of the uC (an RH850 from Renesas) in order to

mostly in Y but Delta works fine also)

I've never see 3 MOSFET only drive structure. I'll see. Thx.

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Error alert... error alert... "BLDC Motors... need Hall sensors".

Wrong, with my Y-winding, tap to + approach, with only 3-FET's to ground, the "flying" end of a disconnected winding gives a very nice commutation signal... ensuring direction control.

That design is so old it's in OrCAD Crapture format. I'll see if I can figure out how to print it out. ...Jim Thompson

On Saturday, October 7, 2017 at 5:28:51 PM UTC-7, Jim Thompson wrote: ...

...

All of the RC model motors I know about use a 3 wire connection. So there is no connection to the centre junction of the windings.

Typically aircraft use sensorless operation with 6 MOSFETs. They don't generally need to change direction for aircraft of course which makes things easier.

It seems that model cars can use sensors or not.

kevin

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and right underneath it say "sensorless possible"

the point was the BLDC is wound to be driven with square waves, PMSM are wo und to be driven with sinewaves

sure, and that is also how all the sensorless six transistor drives do it

e is no connection to the centre junction of the windings.

enerally need to change direction for aircraft of course which makes things easier.

it is harder to start from zero speed under load without sensors but it is possible,

I used a ring oscillator for starting, which was then "over-powered" by the commutation. Don't ask for details... 20+ years ago :-]

It's own paper, probably in my archive storage facility. I'll look for it next time I'm there. ...Jim Thompson

In 3 phase sensorless Field Oriented Control (FOC) which are used for the higher end aircrafts, you start in open loop, closing the loop at rev up

You can easily load the motor during rev up

The other direction control is just a bit in SW

BLDC is not cheaper for the motor, but the control can be easily done in an 8bit micro

FOC can be crammed into an 8bit also, so I hear, but I think THD numbers are then allowed to rise

Cheers

Klaus

Please Jim explain me how commutations of 3 MOSFETs (or BJTs) is sequenced with respect of hall sensors. Please.

As someone here has explained, there is some differences between BLDC and PMSM. We are using a 12 slots(stator)/4 pair pole(rotor) PMSM from Allied Motion. I've never thought before it could be exists such a thing ! Even now I hardly believe it ... They did it on our specs (Torque/rpm, Vbattery, ...etc). Incroyable !

Why is it incredible?

We design our own motors and produce them in-house

For high volume standard 3 phase 4 pole is hard to beat

High Torque 4 mN, 4000rpm rated, low ripple torque, low volume, relatively low mass ... that's what is incredible ! Mainly because of using Dy and other rare earth materials. What makes you think you can do the same in house without knowing anything on ours ?

Cheers, H