If money’s really tight, you can do a lot with a variac as follows:
- make sure you’ve got good protection: undervoltage, overvoltage, overcurrent etc. If possible I like to do it in hardware for my development units
- think about safety! You have dangerous voltages, large capacitors, risk of debris flying into your eyes, risk of small fires etc
- internally disconnect output inductors from AC line and short term together (models 3 phase grid with zero voltage)
- connect line voltage sensors to 3 phase line so PLL can lock
- set line voltage feedforward term to zero
- you can now test current loop stability against a low impedance and verify that the phase current aligns with the voltage as you expect. Note that some PLLs can lock to the negative sequence component of the 3 phase line, so check phase rotation too (ie measure at 2 line voltages and 2 line currents)
- once control loops stable you can return the inductor connection to normal
- use three phase variac to begin testing at low voltage
- use variac to test over varying line voltage (efficiency, VAR injection )