This paper presents a modified power supply system based on the current alternating current (AC)-fed railways with neutral zones that can further improve the eco-friendliness and smart level of railways. The modified system complements the existing infrastructure with additional energy-storage-based smart electrical infrastructure. This infrastructure comprises power electronic devices with energy storage system connected in parallel to both sides of each neutral zone in the traction substations, power electronic devices connected in parallel to both sides of each neutral zone in section posts, and an energy management system. The description and functions of such a modified system are outlined in this paper. The system allows for the centralized-and distributed-control of different functions via an energy management system. In addition, a control algorithm is proposed, based on the modified system for regenerative braking energy utilization. This would ensure that all the regenerative braking energy in the whole railway electrical system is used more efficiently. Finally, a modified power supply system with eight power supply sections is considered to be a case study; furthermore, the advantages of the proposed system and the effectiveness of the proposed control algorithm are verified.The installation of equipment that provide clean energy from renewable sources (e.g., solar panels and wind generators) to feed the traction loads in rail may have a significant impact in the energy costs and CO 2 emissions of a railway system, increasing the environment friendliness of the railway [4][5][6]. The introduction of renewable energy is to partially reduce the depletion of non-renewable energy resources and thus reduce CO 2 emissions. These outcomes have been favored by scholars and many countries, such as North American, European, China, and Japan [6,7]. But in practice, the traction energy consumption of railways has not been reduced.By contrast, the efficient driving and regenerative braking schemes differ the renewable energy scheme. They can essentially reduce the traction energy consumption of railways.Efficient driving is an effective way to reduce the traction energy consumption of rolling stock. Typically, the running state of vehicles comprises three phases: braking, speed-holding (cruising) and acceleration. At present, many literatures have studied the efficient driving and realize the traction energy savings through the optimum combination of these phases [8][9][10][11][12][13]. To implement such trajectories and maximize savings, some auxiliary systems, such as driver advisory systems (DAS) [10,11] and automatic train operation (ATO) [12,13], must be provided to drivers. The trials of such systems have shown savings of 5-18%. However, with efficient driving, the savings of energy consumption may sacrifice service quality, such as the train speed, stopping time, etc. [1].Regenerative braking energy (RBE) recovery is a simple and efficient way to reduce energy consumption, which cannot influence the operati...
In a cascaded H-bridge rectifier (CHBR), the dc capacitor voltages need to be controlled to balance by the voltage balance controller when the loads are unbalanced. However, the voltage balance controller will fail to balance the dc capacitor voltages when the load unbalancing range exceeds a certain limit under unity power factor; that limit is constrained by the AC voltage and transmission power of each H-bridge. First, the relationships in CHBR were analyzed. Then, the expression between AC voltage and the power of each H-bridge was derived. Then the load unbalancing limits to maintain the dc capacitor voltage balance of each H-bridge were further deduced. In addition, the influence of ripple power and total load power on the load unbalancing limits was investigated. Finally, an experimental prototype of a single-phase threecell cascaded H-bridge rectifier was built and the correctness of the proposed load unbalancing limits was verified by the experiment. The proposed load unbalancing limits are universal, which provides theoretical support for the stable operation and power transmission of CHBR.INDEX TERMS Cascaded H-bridge rectifier (CHBR), unity power factor, dc capacitor voltage, load unbalancing limits.
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