Hey www,
the unreliability of Huanyang VFDs is known. If you read the cnc forums, you find often that they fail and no one knows why. And get replaced.
But like all electronics, bad grounding can destroy it. Be sure to have your machine correctly grounded.
A VFD is a device intended to be enclosed into a grounded VFD control cabinet, the spindle motor cable must be shielded and properly terminated, and the machine must be correctly bonded and grounded.