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Topic: BLDC Current Control: L6234 (Read 163 times) previous topic - next topic

NonConformalMapping

Jun 15, 2016, 03:48 pm Last Edit: Jun 15, 2016, 05:40 pm by NonConformalMapping
Hi everyone,

I tried searching for this topic but nothing relevant came up.

So, I want to drive a BLDC (22 poles, 24 coils) using field-oriented control. I have a rotary encoder and a L6234 driver.

The L6234 has two SENSE outputs, that enable measuring the voltage drop across resistors and acquiring the current from that.

These two SENSE outputs are connected in such a way that the first one can measure the voltage (or current) in phases 1 and 2 (combined! not either one), and the other measures phase 3. That's it.

Now the thing is - in order to implement FOC, I kinda need two separate phase currents... (e.g. phases 1 and 3, 1 and 2, etc.)

(Technically, three phase currents are needed, but Kirchhoff's law handles the 3rd one)

So, is there a way to make this possible? Or something similar to it?

I would appreciate any kind of help.

MarkT

#1
Jun 15, 2016, 07:25 pm Last Edit: Jun 15, 2016, 07:26 pm by MarkT
The sense pins are probably intended to be commoned, they come out on separate pins because you can't
route high-current signals across the rest of the chip sensibly.

The chip is designed for trapezoidal drive I suspect, for sinsoidal FOC I'd suggest measuring
2 of the the winding currents directly with isolated hall sensors.  The chip clearly cannot handle
the case where an arbitrary two phases are switched to ground and then measure the current
separately for each...

Current sensing is a prerequisite for any torque control, whether field-oriented or not.

When I've driven a BLDC for control loops I stick a couple of ACS71 or ACS712's in two of the phases,
which high-speed SPI ADC's monitoring them both.  Then you can get a decent update rate on the
current control loop (20kHz upwards is good).

It would be nice if someone made a 2 or 3 channel isolated current sensor with built-in fast ADC,
but I've not noticed one...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

NonConformalMapping

Oh, I see. I guess I should've checked before ordering a bunch of those for testing... You live, you learn.

Thanks for the reply, I appreciate it.

MarkT

You still need a 3-phase bridge whatever you do, those chips do that for you.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

NonConformalMapping

Cool, I'll be sure to check for that before my next purchase. Thanks again.

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