Use a VFD
i use a 2KW (max 3000hz) Talent Inverter VFD. See www.talent-hk.com
or more easily http://www.zgc168.org/user/talent/index_en.asp
Their spec on the name plate is BS at 4KW given the limited input current of 10A.
Once the acceleration ramp is set correctly, so that not too much voltage is output at the lower frequencies, I have been repairing and testing these motors using a VFD.
As a bonus (and overkill?) I run the 3 phase suds pump on my lathe with the VFD, so I don't have to fork out $huge$ for the 2 extra phases I don't get delivered to my meter.
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.