The high freq signal has to be lower than the switching frequency - otherwise you end up with harmonic interference from the PWM like you mentioned. For high performance servo control in the 5-200kW range with switching frequencies up to 20kHz I typically see high frequency injection in the 1-4kHz range. This is high enough to produce negligible torque ripple and minimal estimation error, but low enough to be synthesizable without an ultra high PWM frequency. Of course for smaller systems switching at 100s of kHz or even MHz a higher high frequency signal could be injected.
I suspect that this type of sensorless strategy will become more popular with the rise of GaN and SiC devices, but it is currently implemented with good results today using only standard Si IGBTs and MOSFETs.
I suspect that this type of sensorless strategy will become more popular with the rise of GaN and SiC devices, but it is currently implemented with good results today using only standard Si IGBTs and MOSFETs.