A Study on DC-Link Voltage Variation Characteristics of Power Conversion Systems in Electric Locomotives

This paper comparatively investigates the DC-link pre-charging and voltage formation characteristics of 8200-series and 8500-series electric locomotives using field data acquired under actual operating conditions. DC-link voltage and contactor operating signals were simultaneously analyzed to identify the relationship between the pre-charging sequence and voltage rise characteristics. The results show that the 8200-series locomotive exhibits a relatively gradual DC-link voltage rise, whereas the 8500-series locomotive shows a rapid change in voltage slope near the main contactor closing point. These differences may be associated not only with the operating characteristics of the contactors but also with the parameters and operating sequence of the pre-charging circuit, including pre-charge resistance and DC-link capacitance. Since the charging current was not directly measured in this study, the magnitude of inrush current and its quantitative effects on component lifetime were not evaluated. The results provide a comparative characterization of the DC-link pre-charging and voltage formation behavior of the two locomotive series and can serve as a basis for further studies involving simultaneous voltage and current measurements.