Hi, and thank you for that excellent and detailed explanation. I think I understand most of it but I’d like to take you up on your offer to clarify, if you don’t mind!
The STSPIN830 is a pretty cool driver, but it’s just a driver. It doesn’t have a MCU, so it can’t do FOC by itself, and it uses the current sense input only to limit the motor current (for things like low resistance windings or stall situations I assume). But it can be configured for either 3-PWM or 6-PWM driving, and has some other cool features. It’s very small though, and the PCB layout is (for me) challenging.
I understand fully the argument that sensing the individual phase currents for the purposes of FOC control with just one low side shunt is very difficult, as you describe and illustrate with the table.
But for the purpose of current limiting, when you’re only trying to understand the total current flowing through the system and don’t care about individual phase currents, why would the 1-shunt setup not work?
When T1,T2,T3==0 then the current flowing through the system is also 0, or am I wrong? I guess this state is not a normal state in terms of motor commutation, but can occur due to the PWM?
I would assume that – for the purposes of current limiting --, a single high-side or a single low-side shunt should read the same value?
Isn’t the reason single shunt sensing is ok for current limiting purposes, because the whole system current is flowing through the shunt, regardless of which path it takes through the windings?
Regards from Vienna,
Richard