#$%@$#@ <--- (insert favorite swearword here), IT WORKS !!!!

[Gordo]

I'm impressed by your work Lebowski, and looking forward to follow your progress.

One thing is bugging me, though. You say the motor is driven with true three-phase sinusoidal currents. I like that. But I don't understand how it can be sensorless at the same time. If all phases are continuously driven, then there is never an undriven phase to measure the back-EMF on. Would you like to explain how this works? (or is it part of the secret sauce that you don't want to give away for free?)

The question does not make sense to me. The current and voltage are switched, (AC) going from zero to maximum and back to zero. Therefore there is back-EMF to measure. Where does the conclusion that true three-phase current is a DC state come from? The phases are driven one at a time, the same as with all BLDC motors. The motor/controller waveform is identical to a sensored setup. The difference is that Lebo does it with an algorithym which takes over at a very low rpm.

[c_a]

three phase sinus:

[Arlo1]

three phase sinus:

It is impossible to replicate that with 3 H bridges. You only actualy get one peak at a time. Other wise you would get a blown H bridge

[Alan B]

My present understanding:

Sensorless BLDC motor control is generally done with current driven in one motor connection, out another and the third floating connection is used to measure back EMF and determine the commutation point. The drive current could be DC or sinusoidal. It is most efficient if the drive waveform matches the motor waveform which for BLDC is generally DC. A permanent magnet brushless motor that has sinusoidal back EMF is generally not called a BLDC motor but is instead called a PMSM (permanent magnet synchronous motor).

In three phase sensorless drive the phase current/voltage relationships are used to determine the rotor position since all three phases have driven current and back EMF is obscured by the drive voltages.

[Gordo]

My present understanding:
In three phase sensorless drive the phase current/voltage relationships are used to determine the rotor position since all three phases have driven current and back EMF is obscured by the drive voltages.

Are the SOIC ACS714-20 current sensors used because the back EMF can't be seen?

[bearing]

It is impossible to replicate that with 3 H bridges. You only actualy get one peak at a time. Other wise you would get a blown H bridge

Here is one way to do it (sensored). (With three half bridges.)
http://www.atmel.com/dyn/resources/prod ... oc8010.pdf

Where does the conclusion that true three-phase current is a DC state come from?

I never stated DC. With "driven" I meant "PWM-driven with a sinusodial shape to the duty cycle".

The current and voltage are switched, (AC) going from zero to maximum and back to zero. Therefore there is back-EMF to measure.

I'm not sure if you are trying to explain something simple to me here, or if there was something in depth in there. In that case I missed the point. I have a good understanding of electronics and the many ways to implement motor drives.

In three phase sensorless drive the phase current/voltage relationships are used to determine the rotor position since all three phases have driven current and back EMF is obscured by the drive voltages.

That may be the case. I think I have some reading to do about this, because I don't immediately see how you could determine position that way.

[Gordo]

Perhaps you have not read this entire post?
My answer to you was a simple one, nothing complex. I was leading off your assumption of no back-EMF being present, not Allan's point that the EMF is masked by the motor current. Under what conditions do you have a fluctuating current and no back-EMF? I'm not a motor guy, just trying to learn from ancient experience in analog VHF/UHF.

[bearing]

I wasn't saying it didn't have an EMF, just that I couldn't see how you would measure it at the same time as driving it. When you drive a BLDC the "normal way", you have one phase floating, which makes you able to measure EMF on that phase.

I linked the wrong AN in the last post. This is the one I was thinking of.
http://www.atmel.com/dyn/resources/prod ... oc7671.pdf

Atmel has quite a few Application Notes on BLDC control on their website.
http://www.atmel.com/dyn/general/docume ... chhome.y=7

I may have understood Lebowski wrong about the driving method. It may be sinusoidal, but with two phases at a time (like in Alans post). Sorry about the confusion.

[Alan B]

My present understanding:
In three phase sensorless drive the phase current/voltage relationships are used to determine the rotor position since all three phases have driven current and back EMF is obscured by the drive voltages.

Are the SOIC ACS714-20 current sensors used because the back EMF can't be seen?

Yes. Here is one example of how this is done, though this one uses a single battery current monitor rather than phase current monitors:

http://www.infineon.com/dgdl/AP0805910_ ... 2c3cff002f

Here is another that uses the phase current measurements. Three are shown but two is sufficient since the third can be calculated from the two measured currents.

http://cache.freescale.com/files/microc ... DRM109.pdf

There are other techniques and one can find papers on even more sophisticated systems that can, for example, significantly exceed the back EMF voltage limit of motor speed with timing changes and other tricks.

[Gordo]

Thank you Alan. I'm not sure how many of the few neurons I have left, that I wish to burn out on this puzzle, but I will try to follow the thread. My hope is to build a controller by scabbing Lebowski's 30F onto a chinee power section.
Arlo1 will be jumping on me for this haywire route to a working controller.

[Arlo1]

Hey lebowski. At low rpm can we program a max on time for both fets??? I am wondering how this all works... If the max on time was say 20uS then they both shit off for ~5 uS to cool down its not the same as the PWM of the one side... Maybe I need to studie the center aligned up down PWM control to understand this all better.

[Lebowski]

Hey lebowski. At low rpm can we program a max on time for both fets??? I am wondering how this all works... If the max on time was say 20uS then they both shit off for ~5 uS to cool down its not the same as the PWM of the one side... Maybe I need to studie the center aligned up down PWM control to understand this all better.

The nasty bit is that the FET's don't determine the current, the inductors do. So you can shut off the FET's but then the current
will just take the path through the protection diodes, dissipating more than if you would have just kept the FET switched on.
So, to answer your question, no this option is not there as it does not make sense...

[Lebowski]

Sorry for the slow reporting, I've been very busy with adding the setup menu's and swapping my current sensing
resistors out for proper current sensors. I'm thinking about spending this (rainy windy snowy) weekend swapping
around all the analog channels and adding 'room' for a third current sensor so that I have sensors in all motor phases.

I have to see whether the third current sensor makes sense... theoretically you would say 'no' but practically, the
third sensor makes it possible to compensate for the common-mode voltage offset (which may be temperature
dependent) and common mode voltage spikes on the sensor outputs / ADC reference voltage. If i put in the third
sensor it'll be an option in a setup menu, you can choose whether you have 2 or 3 sensors.

I also just got myself a present, my GF for some reason 's been comparing me to Sheldon from Big Bang Theory
after i showed her this

DSC00705.JPG (169.72 KiB) Viewed 335 times

[Arlo1]

Hey lebowski. At low rpm can we program a max on time for both fets??? I am wondering how this all works... If the max on time was say 20uS then they both shit off for ~5 uS to cool down its not the same as the PWM of the one side... Maybe I need to studie the center aligned up down PWM control to understand this all better.

The nasty bit is that the FET's don't determine the current, the inductors do. So you can shut off the FET's but then the current
will just take the path through the protection diodes, dissipating more than if you would have just kept the FET switched on.
So, to answer your question, no this option is not there as it does not make sense...

If the fets are shut off for long enough then yes they stop the current from flowing other wise my bike which has had a powered up controller for 6 months without use would be dead. When the fets are on the current climbs but when they are off the current falls and the inductance determins how fast!

[bearing]

the third sensor makes it possible to compensate for the common-mode voltage offset (which may be temperature
dependent)

These Allegro sensors (at least the bigger ones that I have been playing with) have a built in ferrite core. Remanence in the core makes the voltage at 0 amps differ from 0.5Vdd. If the last direction of magnetization was positive, sensor will output some mV in the positive direction at rest. This makes it hard, or maybe even impossible, to measure small currents. If you are integrating current over time (like I did) it will accumulate to a big error.

[c_a]

We need a quick solution because my 135-50 inrunner is on the way:
http://www.powerditto.de/monster.html

We will run it at 24s lipo @450amps = 40kW

[c_a]

Is one enough or should I buy two?
http://www.mitsubishielectric.com/semic ... u-3a_e.pdf

[Arlo1]

We need a quick solution because my 135-50 inrunner is on the way:
http://www.powerditto.de/monster.html

We will run it at 24s lipo @450amps = 40kW

Good luck man i have needed something fast for 2 years!!!

[Arlo1]

Is one enough or should I buy two?
http://www.mitsubishielectric.com/semic ... u-3a_e.pdf

You will be lucky to get 1/4 there rating so... Get 6. How much are they?

[c_a]

I trust in mitsubishi spec sheets, found them for 347€ each in germany. I really like the big blocks

[bearing]

Is one enough or should I buy two?
http://www.mitsubishielectric.com/semic ... u-3a_e.pdf

Do you know if anyone have used those for high frequency switching? They have a pretty big gate capacitance, so you'll need a stiff gate drive.
Spec says it can handle 1kW of losses, but since thermal resistance is 0.1°C/W, that means the junctions will be 100°C above case temperature. So, I don't think you can use them close to their power rating.

I wonder if every "transistor" is made of several chips in the "normal" power mosfet size, or if it's one giant chip per transistor.

[Arlo1]

I trust in mitsubishi spec sheets, found them for 347€ each in germany. I really like the big blocks

IR and ixys have the best fets most have us have tested so far and their spec sheets are very optimistic. Remember when the fet is on it can only touch the max ratings then you have to turn them off and wait till the current falls enough so you can turn them on again so you wont see 300 amps 150 v from each unit more likely ~80amps at ~130v each unit and thats 80 phase amps!

[Arlo1]

I wonder if every "transistor" is made of several chips in the "normal" power mosfet size, or if it's one giant chip per transistor.

I took some big ixys fets apart and they were 8 smaller fets inside.

[Lebowski]

the third sensor makes it possible to compensate for the common-mode voltage offset (which may be temperature
dependent)

These Allegro sensors (at least the bigger ones that I have been playing with) have a built in ferrite core. Remanence in the core makes the voltage at 0 amps differ from 0.5Vdd. If the last direction of magnetization was positive, sensor will output some mV in the positive direction at rest. This makes it hard, or maybe even impossible, to measure small currents. If you are integrating current over time (like I did) it will accumulate to a big error.

The small Allegro current sensor work in the same way as the big ones. I'm not integrating currents over a long time so it's not a big issue, it's more that I want to build the best controller IC possible, and for this reason I am considering adding the option to use 3 current sensors. It adds the cost of a 3rd sensor but makes it more robust against (drifting, maybe temperature dependent) offsets. The effect of offset is that, because the throttle is current based, at throttle closed you get a tiny bit of either regen or power. Not a big issue but something I want to fix.

[Alan B]

Phase currents are AC so compensating for DC offset should be possible.