A Novel Hybrid DC Traction Power Supply System Integrating PV and Reversible Converters

Abstract

A novel hybrid traction power supply system (HTPSS) integrating PV and reversible converter (RC) is proposed. PV is introduced to reduce the energy cost and increase the reliability of power systems. A reversible converter can achieve multiple objectives including regenerative braking energy recovery, PV energy inverting, DC voltage regulation and power factor improvement. In this paper, the topology and operating modes of the HTPSS are first introduced. Three-level boost converter (TLBC) is employed in the PV system. A double closed-loop control scheme considering both maximum power point tracking (MPPT) and midpoint potential balancing (MPB) is recommended. The reversible converter adopts a multi-modular topology and the independent control for active power and reactive power has been achieved by a current decoupling control. According to the working characteristic of each device, a coordinated control strategy is designed, and four basic principles are given. A system simulation model containing a hybrid traction substation and a train was built, and comprehensive simulations under multi-scenario were carried out. The results show that the reversible converter can accomplish PV energy inversion, DC voltage regulation, regenerative braking energy recovery and power factor improvement, by which a high utilization rate and energy-saving effect can be obtained.Energies 2018, 11, 1661 2 of 24 train runs between two substations, the braking time is only 10-15 s under normal circumstances. The relatively low utilization rate, in addition to the single function (just inverting), result in a long investment payback period. It is becoming the main obstacle for the massive application of inverters.Urban rail transit is becoming a big energy consumer and has significant impacts on energy consumption at a regional scale [15]. It turns out to be more and more urgent to reduce system energy consumption through all possible means. As a clean energy, photovoltaic has had rapid development all over the world recently, and the installed capacity has been increasing year by year [16,17]. Large-scale PV plants are mainly located in the desert regions due to the high solar irradiance and vast area, but the output power is usually constrained by the transmission capacity of the grid [18]. Future development will focus on the distributed PV system, which is located as close to the user as possible [19]. Railway companies have much potential to introduce PV system around railway premises, such as the roof of platforms, substations, vehicle depots, sound walls and other buildings or openings along the line [20]. It is reported that the PV system installed on platform roof of Tokyo station generates 340 MWh electric energy annually [20]. The possibility of introducing PV technologies into traction power supply system is discussed in [21], but solar energy is just used for air conditioning and lighting. In [22], a grid-connected PV system is introduced in TPSS. However, it is not an optimal scheme for the transmission and distribution of...

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