I am designing a three phase inverter (SPWM) for Motor drive. As part of the protection circuit, I would like to use 3 shunt resistors (one in every phase), which will measure the AC current. The output voltage of the current sensor will go to a comparator, which in case of over-current will send a high output signal.
The voltage of my DC source is 48Volts, that means that each phase will take ±2*Vdc/3=±32Volts, but just to be sure lets assume ±48Volts! The maximum current, at which I want the comparator to send the high output signal is at 15Amps. The switching frequency of the Mosfets will be at 5Khz and the frequency of my current will be very low at 40Hz...
Note that accuracy is of high importance. I don’t want because of some noise to have a faulty output signal, because that signal will be used to disable the whole circuit. Adding to that, I would like the shunt resistor (or generally the resistance which will be added to the line) to be as small as possible (if possible to be less than 3mOhms). Finally the signal circuit is galvanically isolated from the power circuit. So if possible, it will be better to find an isolated sensing solution.
Thank you very much, in advance.