Abstract
This paper studies and presents a series-connected high frequency DC/DC converter connected to a DC microgrid system to provide auxiliary power for lighting, control and communication in a DC light rail vehicle. Three converters with low voltage and current stresses of power devices are series-connected with single transformers to convert a high voltage input to a low voltage output for a DC light rail vehicle. Thus, Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) with a low voltage rating and a turn-on resistance are adopted in the proposed circuit topology in order to decrease power losses on power switches and copper losses on transformer windings. A duty cycle control with an asymmetric pulse-width modulation is adopted to control the output voltage at the desired voltage level. It is also adopted to reduce switching losses on MOSFETs due to the resonant behavior from a leakage inductor of an isolated transformer and output capacitor of MOSFETs at the turn-on instant. The feasibility and effectiveness of the proposed circuit have been verified by a laboratory prototype with a 760 V input and a 24 V/60 A output.
Highlights
Direct current (DC) microgrids are studied to combine alternative current (AC) utility power, renewable energy sources, energy storage units and local DC and AC loads in order to reduce global warming and climbing temperature issues
This paper presents a series-connected soft switching converter using a single transformer for light rail vehicle applications
A laboratory prototype with 1.44 kW rated power was constructed and tested in order to verify the feasibility of the studied converter to supply the auxiliary power in a light rail vehicle from the DC microgrid system
Summary
Direct current (DC) microgrids are studied to combine alternative current (AC) utility power, renewable energy sources, energy storage units and local DC and AC loads in order to reduce global warming and climbing temperature issues. To avoid using bulky line frequency transformers, transformerless converter topologies [4–8] with primary-series and secondary-parallel connections have been proposed to lessen the blocking-voltage capability of active devices on the high voltage side and the current stress of power components on the low voltage side. Half-bridge (HB) or full-bridge (FB) converters have been widely adopted for medium power applications to provide a stable and low voltage output. The high switching frequency will increase core losses on magnetic components and switching losses on power MOSFETs. Zero-voltage switching converters [12–15] have been proposed to achieve a low switching loss. This paper presents a series-connected soft switching converter using a single transformer for light rail vehicle applications. The mechanism of the zero-voltage turn-on switching is realized and the electromagnetic interference can be reduced.
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