Reversible substation modelling with regenerative braking in DC traction power supply systems

Compared to traditional unidirectional substations, a reversible substation (RSS) permitting bidirectional power flows is an efficient approach to recovering the braking energy of trains and increasing the energy efficiency of DC traction power supply systems (TPSS). This paper develops two models to reflect the role of an RSS under high and low fidelities, focusing on the converter- and TPSS-level simulation respectively. A particular RSS topology consisting of a 12-pulse diode rectifier and an antiparallel active neutral point clamped voltage source inverter (VSI) is replicated in a high-fidelity model where the VSI is controlled to maintain a constant DC voltage in the braking mode. To reduce computation burden, a low-fidelity model simplifies the rectifier into a diode in series with a controlled voltage source (CVS) that reflects its nonlinear output characteristics, and connects a DC voltage source in parallel with the CVS branch, permitting the delivery of braking power to the RSS under the constant DC voltage control. The two models are tested based on a simplified 1.5 kV TPSS and discussed alongside the consistency in the simulation of the power exchange and voltage transients at the RSS in traction and braking modes.