Pre-charger is a specific DC -DC converter application in the railway propulsion system. This study demonstrates the possible causes for output diode failures in the pre-charger. Overshoot voltage during diode reverse-recovery is a main reason for such failure. A test set-up is proposed to study the influence of reverse bias on the overshoot voltage. The method to mitigate the contact bounce in the control circuit, in the test set-up, is also introduced. The relationship between the overshoot and reverse bias is studied by means of applying different reverse biases. The parasitic capacitance and reverse-recovery characteristic of the diode is changed by the exceeding reverse bias. Reverse-recovery time is reduced when the reverse voltage is beyond a critical level. To overcome the overshoot problem, a snubber is applied, and experimentally verified. Overvoltage is dramatically reduced by applying this snubber. Current and voltage waveforms in different branches are recorded so as to give a better understanding of the working mechanism of the snubber.
There is an increasing demand for efficient and low-profile power converters in almost all industrial applications. Some require stable performance over a wide range of input voltages, whereas others require converters with a stable performance over a wide range of output voltages. In this regard, little work has been done to combine both requirements into one solution. This work suggests a unique solution that addresses both requirements at once. A power converter with 2x3 reconfigurable modes has been presented, able to operate with DC gains of 1, 2 and 4, which can be further extended to 8. The converter shows stable performance for the extended range of both input and output voltage. The flexible reconfigurable feature of the proposal can be applied in a variety of applications. Two reconfigurable modes on the input side can be configured following the variation in the line voltage to maintain a stable performance, and three reconfigurable modes for the output voltage, which raises the output voltage from 24V to 48V and 96V. The proposal is applied in an example application of a phase shifted full bridge converter. The converter is characterized for V in = 100-400V dc , P out = 1kW.
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