The difference between single and series-connected insulated gate bipolar transistor (IGBTs) during short circuit II (SC II) is analyzed contrastively, and requirements for an improved protection have been advanced to solve the SC II problem of series-connected IGBTs. A new principle of short circuit protection based on the logic of SC II fault processing used by the main control unit was proposed, using an active voltage clamping circuit to balance the dynamic voltage during breakdown, using an RC circuit to balance the voltage during tail current stage, and a formula to estimate the absorption capacitance and the selection principle of static voltage balancing resistance was proposed. The parameters under the actual test condition was given, the short circuit test system of series-connected IGBTs established, and the experimental verification carried out under the actual conditions. The result shows that under a Vbus of 1400V (2.65kV maximum peak voltage for each IGBT), the new protection method can provide synchronization of protect operation and voltage balancing during turning-off process, and the unbalance of steady stage voltage is under 5%.
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