I. Introduction
With the fast development and expansion of cities, high-speed trains have become one of the most convenient and necessary transportations in the past decades. Inevitably, the associated railway accidents have happened unexpectedly in many countries [1]–[4]. Therefore, safety and reliability should be the most vital requirement for high-speed trains. As well known, the traction system is the most important core in high-speed trains, so early and effective fault detection and diagnosis (FDD) of traction system gives a very important significance for safety guarantee and reliable operation of high-speed trains [5].