The three-phase variable frequency drive inverter controls the AC motor, which has significant energy saving effect and excellent performance. It is widely used in industrial, commercial, aviation, military and other fields. Due to the fragility of power electronic devices and the complexity of their control, the inverter part, especially the inverter part that implements various PWM control strategies, is a weak link in the system that is prone to failure. Once the inverter fails, the entire drive system will lose the ability to work normally, which will affect the normal production and bring economic losses in general occasions, and will cause catastrophic accidents in important occasions such as aviation and military. Therefore, it is of great practical significance to study how to improve the reliability of the three-phase variable frequency drive system and avoid the shutdown due to failure. To solve this problem, in 1980, someone proposed a multi-phase redundant motor structure that uses multiple independent drive units to supply power, but this method is too wasteful and cumbersome. Since 1990, domestic and foreign experts, especially European and American experts, have conducted more fault diagnosis and fault tolerance research on inverters. The so-called fault tolerance refers to the fact that the system can still complete the task safely according to the original performance index or the performance index is reduced (but acceptable) in the case of some component failures, while the fault diagnosis technology is the important guaranteee to achieve the system fault tolerance performance.
When the inverter fails, different phenomena will occur. The voltage and current in the circuit will change compared with the normal operating conditions. These phenomena or changes are used as fault characteristic signals. The existing diagnosis methods mainly include knowledge-based expert systems nethod, current detection method and voltage detection method.