I. Introduction
Wind energy, as a renewable and clean source of energy, is a growing contributor to the world's energy markets [1]. Wind turbine is a device converting wind energy into electricity efficiently. However, due to the complexity of its structure and the diversity of control methods, it has a high failure rate leading to the increase of capital investment in wind farm equipment operation and maintenance year by year. Monitoring the operating status and incipient fault detection, and providing appropriate repair and replacement strategies in time can effectively reduce the operation and maintenance costs of wind turbines and prolong their service life [2].