A new Auxiliary Converter Topology with SiC Components for Railway Applications
Abstract: Smaller size and lower weight are always the targets of the power electronic product development. This work introduces two new topologies of auxiliary converters which have the feature of fewer components and fewer number of energy conversion stages comparing with the conventional auxiliary converter used in railway applications. The initial proposal of the proposed new topology is based on the idea which converts the high frequency current pulses into low frequency AC voltages without rectification stages. This thesis starts with theoretical analysis of the initial ideas with the conclusion of two versions of new topology converter proposal: inductive link auxiliary converter and resonant link auxiliary converter. The modulation method strategy for both of those two versions of auxiliary converters are developed within this thesis, the equations for dimensioning the passive components are also given. Simulation shows that the output voltage waveform has very low THD (Less than 3%).The output waveform is similar to a multilevel converter with ‘infinite’ number of levels. The inductive link auxiliary converter is able to deliver power with unsymmetrical load due there is no energy stored in the inductive link circuit between two adjacent current pulses. The semiconductor switches have to turn off at high current peaks which introduce high switching losses. To solve this issue the resonant link auxiliary converter is proposed. Due to the added resonant capacitor the resonant link converter is able to store energy in the resonant link circuit between two adjacent current pulses which reduce the total numbers of hard turn off in the semiconductor switches which will reduce the switching losses. On the other hand the resonant link auxiliary converter suffers with output voltage distortion with unsymmetrical load. In order to verify the theory which is developed by the theoretical analysis step, prototypes are designed and tested for the inductive link auxiliary converter. A scaled down version prototype is designed to develop the control software and validate the idea of generating low frequency AC voltage from high frequency current pulses. A three phase 80 kW inductive link auxiliary converter is designed and tested. The measured waveforms agree with the simulation model. The measured THD is less than 1% at all measured output power range. The measured efficiency on the complete system is 86% at 50kW output power.
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