In practice, it is common for AHU VFD fans to have some set minimum motor frequency. I've been trying to implement this is an OS/E+ model but seem to be stuck (i.e. you need to fix the fan so it never goes below 30 Hz)
@KyleBenne seems to be asking about this as well...but not sure if he ever got any satisfaction. https://unmethours.com/question/11631/fanvariablevolume-minimum-flow-input/
Anyone know how to accomplish this?