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• Accordingly, a flexible traction power supply system (FTPSS) composed of a TT and multi-port power hub and its coordinated control strategy are proposed for VU compensation and energy conservation in this paper. The main contributions can be summarized as follows: • Different from previous research, a power hub is installed in the TPSS to achieve power flow control among the utility grid, traction network, and DC grid. The FTPPS with the power hub can enable VU compensation for the utility grid, which also offers a friendly interface with distributed PV and ESS for on-site access. • A three-port VU compensation method based on active power flow control and reactive power injection is presented, which divides the system demand compensation capacity and reduces the performance requirements for power electronics, compared with traditional compensation methods. • A coordinated control strategy with a hierarchical structure is designed for FTPSS. The control strategy enables real-time power management to enhance energy utilization and mitigate VU in the system layer and coordinates multiple converters to realize the multi-function operation of the system in the converter layer. To mitigate voltage unbalance (VU) and eliminate the neutral sections while reducing the energy consumption of railways, a flexible traction power supply system (FTPSS) with the power hub is proposed. Different from conventional schemes, the proposed system provides a friendly interface to realize the on-site access of distributed photovoltaic (PV) generation along the railway line and concentrated integration of energy storage systems. The power flow is centrally managed by the power hub to reduce energy consumption and the proposed three-port VU compensation method is coupled with the power hub to suppress negative sequence current caused by trains. Considering the volatility of PV generation and traction loads, four operation modes including grid-connected, valley filling, VU compensation, and peak clipping mode, are proposed to dynamically regulate the operation of FTPSS. Moreover, a coordinated control strategy with a hierarchical structure is developed to enable the operation modes. The strategy is implemented with a global controller and multiple local controllers, which can realize real-time power management and flexible transition among different modes. Finally, different simulation and experimental case studies based on the field data are carried out to comprehensively verify the feasibility and effectiveness of the proposed FTPSS and control strategy. [ABSTRACT FROM AUTHOR]

In DC electric railways, energy storage systems (ESSs) have been addressed to assist in the energy efficiency improvement, which is achieved by exploiting the captured excess braking energy of decelerating trains in order to reduce the traction energy demand of the accelerating trains. Conventionally, stationary ESSs are assumed to have access to the substations and grid, which is being a significant shortcoming since the ESS in many locations such as the London Underground has neither access to the traction substations nor external sources. Since ESSs cannot have infinite capacity and have practical restrictions on the state of charge (SOC), much of the regenerative energies during braking are being lost, which reduces the benefits of ESSs in enhancing energy efficiency of electric railways. In this paper, boosting the energy efficiency of the system is achieved by proposing a new adaptive control method based on fuzzy logic control (FLC) to dynamically control a stationary ESS connected to a DC track system. Therefore, the power flow between the track and the ESS with respect to the storage capacity is managed without affecting the benefits yielded by the system. The proposed control method is simulated and tested experimentally on a real prototype including a supercapacitor ESS. Three traffic scenarios are applied to evaluate the feasibility and the performance of the proposed controller with respect to the undefined traffic scenarios matching the case in the London Underground. The proposed control method applied to three traffic scenarios have achieved energy savings of 39.2–41.4%. The experimental results are compared against the simulation results, showing a percentage error ranging from 1.8 to 3.6%. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

Renewable energy generation is inherently unpredictable and may contain unacceptably significant variations. In particular, high solar photovoltaic (PV) penetration makes it difficult for utility companies to coordinate production and consumption on the grid. PV generation with an energy storage element flattens the duck curve and eliminates the PV curtailment during the mid-day hours. This paper proposes a novel improved Gamma (Γ -) type Y-source inverter for rooftop photovoltaic (PV)-grid applications with battery storage ability. The proposed inverter can maintain high voltage gain even under partial shading conditions, where the PV voltage at the maximum power point is far away from the open circuit PV voltage. The proposed inverter allows plant owners to charge the battery from PV source during low-peak loading hours and can reduce power import during high-peak loading hours (or) export the excess power to the distribution grid, which increases the return on investment. The operation of the proposed inverter is analysed in three modes (a) stand-alone operational mode without battery, (b) stand-alone operational mode with battery, and (c) stand-alone operational mode with PV and battery. A scaled-down laboratory prototype of 70 W is created to test the functionality of the proposed inverter and validate the simulation results. Experiments show that the proposed Improved Gamma type YSI can generate a boosted ac voltage using independent PV and battery sources, as well as their combination. • A novel improved Gamma (Γ -) type Y-source inverter is proposed for rooftop PV-grid applications with battery storage ability. • The proposed inverter can maintain high voltage gain even under partial shading conditions. • The proposed system flattens the duck curve energy demand and stores excess energy during the over-generation period, avoiding the curtailment operation. • The proposed system aids in the tracking of MPP power from PV modules when partial shading is present. • Experiments show that the proposed inverter can generate a boosted AC voltage using independent PV and battery sources, as well as their combination. [ABSTRACT FROM AUTHOR]