Dave.

It’s ok, that 1500 watt output is only for a microsecond before all the 3 cent “power” MOSFETs inside act as fuses.

More likely, there is enough internal capacitance for the inverter to sustain one (1) half of a full-wave AC cycle at 1500W, after which the overload/low voltage cutout triggers.

Possibly your motor is having an insulation breakdown when 220v is applied. Looks fine when testing with an ordinary multimeter and it’s low supply voltage.

So everything looks fine until it powers up and then you get a failure of the insulation on your motor windings, either failing to ground/frame or across windings in the motor. This flashover would likely fry whatever control components are in your main board, and it’s possible that your safety capacitor has a set of polyfuses in it that temporarily go high resistance when excess load is applied.

To check for an insulation breakdown you’d really need a megger which can apply 250/500v to the motor windings to check the leakage to ground/between windings.