A design methodology and a feasible equivalent circuit are proposed to test the reliability of insulated gate bipolar transistors (IGBT) in actual modular multilevel converter (MMC) conditions

which is impossible for existing IGBT test platforms due to unexplicit equivalent indexes and low reliability of test platforms. Characteristics of IGBT devices are extracted during MMC operation

and turn-off transient and effective current are highlighted as key indexes for the equivalent test. A feasible equivalent timing diagram and a corresponding test circuit are proposed

as well as the circuit's operation concept. The proposed equivalent test method is verified by a back-to-back experiment with twenty-four submodules

and results indicate the proposed method has good equivalence. Between the proposed circuit waveform and the back-to-back experiment waveform

all indexes have errors of less than 5.9%. Furthermore

the proposed circuit components have losses less than 0.7 times those of the device under test

making them reliable and suitable for long-term operation tests for IGBT devices in MMC.