Series-Connected High Frequency Converters in a DC Microgrid System for DC Light Rail Transit

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.

Single-Ended Protection Scheme for VSC-Based DC Microgrid Lines

“…For a DC microgrid system, the resistance of DC lines is relatively small enough to fulfill the underdamping condition R < 2 √ L/C. In this case, the eigenvalues of the nonlinear Equation (1) are a pair of conjugate complex numbers in Equation (2). Supposing the pole-to-pole fault happens at t = 0 with the initial conditions U 0 and I 0 , the fault voltage and current can be solved as follows:…”

“…Compared with AC microgrid systems, the voltage source converter (VSC)-based DC microgrids show many advantages, including a high power-converting efficiency, greater power capacity, better power quality, and thus a lower discarding rate of distributed energies [1,2]. The converters in a microgrid allow the power flow to be bidirectional, catering for the flexible locations of loads and renewable energy.…”