Dear All,
My apologize if similar topic has been discussed here before, I just haven't found any. I'm designing my own hardware based on vesc_75_300 with some changes like low side current sensing instead of phase current sensing, I'm using INA181 for this purpose. INA181 has a REF pin which I'm planning to connect with GND so when there is no positive current through shunt the output of INA181 will be near zero Volts. I do not need regen braking and it seems to me quite attractive to increase dynamic range of current measurement by getting rid of negative current sensing and give the full ADC scale for positive currents only. Based on this, I have a few questions/concerns:
1. Is it ok to have no information for VESC software about negative currents? So when there will be negative current through shunt, the ouput of INA181 will be just near zero?
2. How should I setup things around that in VESC tool? Is it enough to set Current Offsets accordingly (near 0V), set Allow Braking to False, set Motor Current Max Brake to 0A?
3. What limitations (except absence of regen braking), issues, drawbacks my idea of using "single polarity" low side current sensing causes?
4. Have I missed smth principal which prevents me from ignoring negative currents sensing?
Thanks!
Well, answering to myself: No, it's not possible to skip negative currents sensing. It wasn't really obvious that low side shunts can see negative currents because deadtime is assumed as pretty small and constant value comparing to duty cycle. But, as it appears, it depends... It depends on a modulation schema mainly, so all of FOC guides which I've seen and which uselow side current sensing use bidirectional one. Sad but true... Thanks to everyone!