An In-Situ On-Board Offline Diagnostic Method of IGBT Modules for Bond Wire Degradation Within High-Power 3L-NPC Converters

Performing in-situ diagnosis is a crucial task during routine inspections of high-power converter systems, such as mine hoist. This paper presents an on-board offline condition assessment method for bond wire degradation of high-power IGBT modules within three-level neutral-point clamped (3L-NPC) converter. This method is based on the increment of the on-state voltage $V_{\mathrm {on}}$ during series short-circuit (SSC). The SSC is formed by the conduction of the IGBT modules to be tested and the external constant current switch (CCS). In CCS circuits, a PI-controlled gate drive circuit is employed to achieve high constant short-circuit current and maintain the stability of the $V_{\mathrm {on}}$ . The improved $V_{\mathrm {on}}$ detection circuit takes the decrement of charging time $t_{\mathrm {cp}}$ of the capacitor as the parameter for aging assessment. It simplifies the data processing of $V_{\mathrm {on}}$ , while increasing the aging sensitivity. To validate the effectiveness of this method in practical applications, a single-phase 3L-NPC experimental platform was built to simulate the aging state of IGBTs by cutting off the bonding wires. The feasibility of the detection circuit, the influence of short-circuit current and ambient temperature on $t_{\mathrm {cp}}$ , and the reliability of the CCS circuit are analyzed in detail.