| Summary: | [Objective] Multiple incidents of overvoltage chopping IGBT (insulated gate bipolar transistor) faults are observed during train main line operation of Chongqing Rail Transit Line 2, significantly impacting the line normal operation. It is aimed to analyze the root causes of these faults and put forward resolution measures. [Method] Based on the overvoltage chopping principle, the fault phenomena and mechanisms are analyzed, fault causes are further obtained, and a physical test unit is built to validate the identified causes through tests, thus targeted resolution measures are proposed. [Result & Conclusion] The reported OVT-IGBT faults are traced back to breakdowns in driver board, adapter board and chopper IGBT. Furthermore, the overvoltage chopping circuit remained in conducting state due to the IGBT breakdown, leading to prolonged service time and damage of overvoltage absorption resistor at elevated temperature, triggering GR (ground relay) faults. Test results further confirm that the peak voltage generated at the instance of chopper shutdown is the primary cause of IGBT faults. Improvement measures include optimizing the active discharge function of the overvoltage absorption circuit to reduce the working frequency of overvoltage absorption circuit chopper; enhancing VVVF (variable voltage variable frequency) control program by introducing the fault logic of chopping without current, the fault logic with current but no chopping, and immediate isolation of the faulty unit logic once a fault occurs; optimizing relevant parameters of driver board to reduce the switching frequency of IGBT. The practical results demonstrate that these improvement measures can effectively resolve the OVT-IGBT fault issues, leading to significant reduction in traction faults and ensuring the normal operation of Chongqing Rail Transit Line 2.
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