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Old 05-14-2012, 03:39 AM   #721 (permalink)
nlc
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Quote:
Originally Posted by thingstodo View Post
I think that what Paul said is that he's measuring 2 currents at the same time and that this is enough information.
Yes absolutely, I do the same on my FOC PMAC controller


Quote:
Originally Posted by thingstodo View Post
- the hall effect current sensors are on the three output phases, after the IGBTs
- phase to phase issues can be detected in the motor by comparing phase currents
- phase to ground issues can be detected in the motor by having the currents not add to 0
In my case, for short circuit detection I don't use software, because the current measurement is done on the middle of the voltage pulse, and it can be really too long to protect the mosfet/igbt. Thus my 2 current sensor outputs are connected to my 2 ADC input, but also each current sensor output enters in two op amp comparators : if the sensor current signal go above a high threshold (positive current) or go below a low threshold (negative current), the comparator output (all outputs are /ORed) trigger the /fault entry of the microcontroller, which instantaneously shut down the PWM signals.
Thus in my case short circuit detection is done in hardware. With 2 current sensors 2 phases are completely protected, the third is not hardware protected against phase to V+ or V- short circuit (only phase to phase short circuit).
But it's easy to add the third sensor to do that, can be useful for big and expensive controller. But it's not mandatory to connect the third current sensor output to an adc input (can be only connected to the hardware comparators), except if it's also needed to do software verification (3 currents sums to zero), to detect motor or current sensor problem.

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