TIDA-01606: On load output waveform distortion of inverter

When I tested tida-01606, I encountered the same problem: the sine wave distortion of inverter output after load.

Due to the limitation of conditions, safety is also considered. At present, my DC bus voltage is 48VDC, output three-phase 17vac, with 5.1 ohm pure resistive load.

Waveform distortion found. I don't know what the problem is? Is it because my DC bus voltage is too low or something else.

            Hope to get your answer,

Thanks and regards,

No load

15R 

5.1R