Equipment Optimization Scheme for High Failure Rate Auxiliary Converter of Metro Train in High Temperature and High Humidity Environment

Objective Over high humidity in the operating environment of metro train auxiliary power supply system will lead to high leakage current of IGBT (insulated gate bipolar transistor), which may further cause the auxiliary converter failure. Therefore, it is necessary to optimize the internal environment of the auxiliary converter box based on the high temperature and high humidity environment to reduce the failure rate of IGBT. Method Based on a case study of the train auxiliary converter failure on Ningbo Metro Line 4, causes of IGBT failure are investigated, and four equipment optimization schemes are proposed, including reducing the speed regulation voltage of the auxiliary converter cooling fan, adjusting the direction of internal circulation fan to reduce the humidity around IGBT, improving the sealing between cabinet and the external part, and optimizing the cooling fan control logic. Simulation and on-site tests verify that the four optimization schemes are effective and operable. Result & Conclusion IGBT failure causes are as follows: on Ningbo Metro Line 4, the low on-site operation load of the train auxiliary converter, the low operating temperature of the components, the undischarged moisture inside the IGBT, while the fast air exchange rate in the auxiliary converter box results in rapid increase of humidity in the cabinet, further leading to the over high leakage current of IGBT module. The four optimization schemes can reduce the relative humidity in the auxiliary converter cabinet and improve the reliability of the IGBT operation.