| In the DC-traction substations, the diode rectifi-ers are commonly used to provide the needed DC-voltage for vehicles. Unfortunately, they attract important issues of power quality, of which the most significant is the injection of harmonic currents into the AC power supply. Withal, the feedback of the recovered braking energy into the power supply is not possible. This paper is focused on the trans-forming a DC-traction substation with six-pulse uncon-trolled rectifier into an active substation, leading to substan-tially improved power quality and energy efficiency. These effects are obtained through an IGBT-based voltage source inverter with a proper control, connected between the DC-traction line and the power supply via a dedicated trans-former and specific interfacing circuits. The indirect current control is based on the concepts of the p-q theory of the powers and intermediate use of the synchronous reference frame, so that perfect harmonic cancellation is imposed even under distorted supply voltages. The conceived Matlab-Simulink model of the system for active filtering and regen-eration is presented and the simulation results illustrate very good performance in both operating regimes of the system. Experiments on a 30 kVA reduced-scale laboratory setup controlled and monitored by a dSPACE 1103 based platform verify the feasibility and effectiveness of the pro-posed scheme. Both the harmonic distortion of the current upstream the point of common coupling and the power fac-tor are significantly improved. |
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