VFD of 200 kW Operation to 11kW

You will need to study the technical specs for any proposed VFD to see if its overcurrent and overload protection features can be "dialed down" low enough to protect the smaller motors, and without the VFD classifying such a small load as no load and thus shutting it off.

You might also be able to find a wide-range overload relay that can cover say 11-50 kW, while the large VFD continues to protect any larger motors. Even some schemes with simple fuses might work.

In my experience there is a limited functional range with the brand name (ABB, Rockwell or Allen Bradley) units. However since you appear to be using this as a test rig, one size may be the ticket. You may find you need to run the drive in V/HZ or scalar mode with the smaller motors, and the protection circuits may not scale well.

Check the spec sheets for any drive you contemplate and ask your local distributor and technical support for the unit you want.

Thanks for suggestions.

As a gross general rule, VFD mfrs generally say not to use a VFD for less than 50% of it's rated current. Mostly this is the result of newer designs using Sensorless Vector Control because the VFD must establish and maintain a mathematical model of the motor, then compare very subtle current signatures against that model in order to affect tight control regulation. As the current drops, the error rate in the sensors increases and the accuracy becomes more problematic.

But if you are planning to use simpler V/Hz control, it actually doesn't matter as much to the VFD. Yes, the same accuracy issues can become a problem for overload protection, but if you think about it, the accuracy gets worse at slower speeds, which means there is hardly any load on the motor, so it's highly unlikely that you can overload the motor. But a much BIGGER issue is the Short Circuit protection. Here in the US, UL started requiring all VFDs to provide the SC protection for the motor circuit, because there are rules for protecting the VFD that can end up not protecting the motor properly, So once UL required that the VFDs provide it, it affected VFD designs all over the world, and virtually any brand of VFD that is sold with a UL listing is going to have that, even if UL is not applicable to your location. What that means though is that if the motor is too small, the SC protection is again out of the acceptable range of protection for that motor.

So what to do...

I've built a lot of test stands similar to what you want to do, and to be safe, you set up a group of IEC "Motor Protection Switches" that are a combination of OL and SC protection, fed from the output of the VFD. Those have adjustable OLs, but are maybe only going to offer a 4:1 adjustment range. Still, that cuts down on the number of units you need. So what I would do for yours is to use the VFD alone for loads down to 100kW, then below that, set up a bank of maybe 5 or 6 MPS devices that cover your operating ranges. So when you want to test a motor smaller than 100kW, you connect it to the appropriate MPS sized for that motor, and run the VFD in V/Hz mode.