<![CDATA[This paper presents an experimental comparison of two control strategies for mitigating three-phase current unbalance in Scott-transformer-fed railway power systems. Both methods employ the same single-phase three-level back-to-back converter, but they differ in the variable used to generate the compensation command. The first strategy derives the reference from load-side active and reactive power, whereas the second generates the reference directly from the Scott-transformer secondary current, thereby targeting the source-side balance condition more directly. To ensure reliable synchronization under low-switching-frequency operation and notch-distorted secondary voltage, an observer-assisted synchronous reference frame phase-locked loop is adopted ahead of the control stage. The proposed approaches are validated experimentally on a 5 kVA laboratory prototype. The measured results show that the three-phase current-unbalance ratio is reduced from 34.2% before compensation to 2.8% with the power-based strategy and to 1.2% with the current-based strategy. In addition, both methods maintain stable DC-link operation and exhibit comparable harmonic and current-tracking performance. These results demonstrate that source-current-oriented compensation based on Scott-transformer secondary current provides superior balancing performance for railway applications with strongly varying single-phase loads.]]>
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