A Solution for Energy-Efficient Operation of Urban Electric Trains: Integrating Rooftop PV with the Active Rectifier in the Traction Substation

The utilization of renewable sources connected to a grid to reduce traction substation installation costs and electrified trains' operation energy is a highly promising solution in the electric transportation field. This study proposes a DC traction power supply system integrated with a solar energy system using a DC-DC boost converter and an active rectifier replacing a diode located at the traction substation. The active rectifier not only recovers regenerative braking energy when electric trains operate in braking mode but also transfers solar energy from the DC bus to the grid. With the characteristics of urban railway lines utilizing high-power traction motors and high-voltage DC bus, this paper presents the structure of the Modular Multilevel DC-DC boost converter in the solar energy system employing the Maximum Power Point Tracking (MPPT) algorithm, whereas the modular multilevel active rectifier utilizes the Voltage Oriented Control (VOC) algorithm with three loop circuits: phase-lock loop, current loop, and voltage loop. Simulation results in Matlab/Simulink with parameters collected from the Nhon-Hanoi station urban railway line in Vietnam demonstrate that the PV system produces almost 37% of the energy in the accelerating phase of electric trains.