This study presents a practical method to construct a high-frequency equivalent circuit model for AC motors in Spicelike simulation software. This model can be used to analyse the characteristics of the motor and predict the conducted electromagnetic noise in an adjustable speed drive system. The modelling is based on measured data of the impedance and vector fitting technique. The procedure of the modelling is elaborated in this study and verified by comparing simulated data with experimental data on a 200 kW induction motor in the frequency range from 10 kHz to 10 MHz. This modelling method can be extended to model other types of motors irrespective of the power rating of the motors. Applications of the motor modelling to study common mode voltage in the system and current oscillation in motor winding are presented.
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.
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