A Study of Commercial Frequency Component and Doubled Component at DC-side of Three-phase Rectifiers and Their Influence on Electric Railways

Abstract

This paper discusses non-theoretical harmonics at the DC-side of a 12-pulse rectifier in DC railway systems. These harmonics are the commercial frequency component and the doubled component. The cause of these harmonics are (a) diode forward voltage drop difference, (b) transformer secondary inductance difference, (c) voltage harmonics at the AC-side of the rectifier, and (d) effects of the voltage induced by adjacent high-voltage power transmission lines. We evaluated cases (a), (b), and (c), as case (d) has been previously studied⁽⁴⁾. The results of the evaluation were as follows:  ·The effects of both the transformer secondary inductance difference and the voltage harmonics inside the electric power system are not negligible in some cases on the discussion of the EMC problem among railway equipments.  ·If there are several traction circuits in parallel each of which consists of an input filter, an inverter and several traction motors, the harmonic reduction effect of the filters weakens significantly.