Using a 3-phase Transformer After a Variable Frequency Drive for Voltage Reduction
A transformer will work with variable frequency, but there are some design challenges involved. VFDs generally do not maintain constant V/Hz down to the minimum operating frequency. V/Hz is increased because the voltage drop in the motor winding resistance becomes more significant at lower operating voltages. Rather than using a 380:24 volt transformer with a 380 V VFD, you should use 480:48 V transformer with a 240 V VFD. The transformer should also be sized to provide more secondary current than the motor requires to compensate for additional heating due to the waveform. The VFD rating will need to be increased to supply the transformer losses and magnetizing current.

Early in the history of VFDs, this was done to control 480 V motors with 240 V VFDs prior to the availability of semiconductors suitable to build 480 V VFDs.