You want continuity to 150v and a voltage limiter after that.
Assuming smooth DC at first, the equivalent circuit would be a 150v Zener with a dropping resistor that varies from zero up to whatever is necessary to dissipate the extra power.
One way is to have a comparator that senses the 150v and switches in series resistors using one or more relays.
This gets a little tricky, Very.
Let's say the invertor draws constant power over a range of input voltages. And, it "likes" voltages between 120v and 150v.
Is there a single value of resistance that, when switched in, drops the invertor voltage from 180v to 120v?
If not, you need more than one value of resistance.
You can also use this circuit to switch in energy storage that can use from zero to 30v.
You've given us some center values and some limits; what are reasonable limits for invertor input voltages?
I think the whole design can fall out of this single interval, once known.