Power Electronic Autotransformer Based 3×25 kV Network for Power Quality Enhancement In Railway Supply Systems

State of the art single-phase AC traction systems are based on a split-phase 2×25kV supply network with multiple regularly spaced auto-transformers. The main drawbacks of this arrangement are the unbalanced currents in the three-phase grid and reactive power flow due to transformers and auto-transformers. This paper proposes to solve these issues with a completely new 3×25 kV railway power supply supported by a power electronic autotransformer (PEAT). The PEAT circuit comprises of single-phase back-to-back voltage source converters, connected across different phase pairs of the three-phase network. These voltage-source converters balance the three-phase grid current for all traction load conditions, ensuring grid compliant power quality performance. Over and above that, the PEAT system enables reactive power control and ensure unity power factor at the point of connection. Besides detailing the control algorithm for the PEAT system, this paper also discusses various design aspects and optimal positioning of the PEAT unit along the railway line. The efficacy of the PEAT topology is illustrated through extensive simulations carried out in Matlab/Simulink environment. These are further validated via real time hardware-in-the-loop (HIL) results obtained from a Typhoon HIL 404 device together with a C2000 microcontroller based interface card.