Low carbon emission transportation is attracting global attention where electric railway power systems (ERPS) and electric vehicles (EVs) act as a load. Besides the main utility grid, renewable energy sources (RES) including photovoltaic (PV) panels and wind turbines are implemented to supply the loads fully or partially. In this paper, a novel smart DC catenary system is proposed in which renewable sources, storage systems, and DC fast-charging stations are connected to the overhead DC catenary line of the high-speed railway power system. The generated power from renewable sources and consumed power by charging stations are processed by their dedicated DC-DC power electronics converters. Furthermore, a storage system is used as a backup system not only for the case of blackouts but also because of the intermittent nature of renewable energy sources to supply the loads continuously. The paper presents an optimal power control for various parts and a power management system (PMS) that manages the power flow from wind-PV-storage system to EV-ERPS system. The proposed system has been investigated using a real Italian Rome-Florence 3 kV high-speed line as a case study with real data of ERPS load. The EV fast-charging station power demand, wind speed, solar irradiance, and temperature were recorded for 24 h in order to provide us with realistic output data. The simulation results obtained by MATLAB/Simulink are presented to validate the effectiveness of the proposed system.

Modular Multilevel Converters (MMCs) find increasing applications in medium to high-voltage systems. In such systems, reliability-oriented selection of power electronic switches becomes essential because higher modularity implies an increased number of components. The trade-off between the impact of higher modularity on converter reliability is quantitatively established, corresponding to redundancy costs for the given lifetime requirements. Therefore, this paper proposes a method for an optimal choice among available market switch voltage rating for the MMC. It is shown that the sub-modules (SMs) based on 1.7 kV switches are the most suitable (instead of 1.2 kV and 3.3 kV switches) for two case studies adapting data from the medium voltage grid in The Netherlands. Moreover, the insights from these case studies are generalized to DC link voltage in the range of 10-220 kV and average loading of 1-100 %. The sensitivity analysis is performed for the different failure rates (FRs), required lifetime, components cost, and energy price. Sensitivity analysis is also performed to identify the impact of FIDES and Military Handbook (MIL-HDBK) methods. The impact of converter power capacity is studied under the variable current rating. Finally, a generalized form of the proposed method is presented and applied in the published works.

Modular multilevel converters are favorable for efficiently operating high-power usages. The required number of components significantly increases when higher modularity is introduced for the given voltage level, thus reducing the system's reliability. This article suggests a mixed redundancy strategy (MRS) that combines the operational concepts using active and spare redundant submodules. It is shown that more than 50% higher B10 lifetime (the point in time when the system has a 90% probability of survival) is achievable as compared to reliability improvement using fixed-level active redundancy strategy, load-sharing active redundancy strategy, and standby redundancy strategy with the same number of redundant submodules. The tradeoff between operational efficiency and investment cost is explored to define the boundary for selecting the MRS over other redundancy strategies with varying dc-link voltages and average converter loading, considering a ten-year payback period and equivalent B10 lifetime. The change in viability boundary for the MRS is established with increasing B10 lifetime and its sensitivity to power electronic component costs and assumed failure rate. The effect of power capacity with a higher switch current rating is evaluated. Also, the Monte Carlo simulation methodology is proposed to evaluate the practicality and effectiveness of the proposed MRS scheme. Finally, the insights of this study are applied to existing literature.

Power electronics converters will play a crucial role in power grid expansion. Superior advantages offered by MMC make it the most popular candidate amongst various converter topologies. However, due to a large number of components installed within MMC, reliability analysis is an unavoidable task that needs to be carried out to maximize the MMC's availability and positively affect the overall performance of the power system. To this end, applying redundancy at the converter level is one of the solutions to increase the reliability of the MMC. In this paper, the reliability of the MMC is evaluated during its useful lifetime according to various applied redundancy strategies. At the same time, it is proposed that optimal-decision making in redundancy strategy depends on the failure rate of which components are considered. It will be presented that the superiority of the applied redundancy can vary.

Installing new DC fast-charging stations especially alongside motorways is of great importance to meet the energy demand of a huge number of EVs in the near future. In this paper, a novel DC microgrid tied PV/storage system is purposed for EV fast chargers in which the power is supplied by large-scale PV arrays and storage systems through phase shift full bridge (PSFB) converter with minimum need of AC grid supplement. In this system, a phase shift full bridge (PSFB) is employed to boost the common voltage of the PV/storage system to higher values rather than connecting a large number of cells (PV and storage) in series to reach a high level of voltage which will consequently increase the reliability and redundancy of PV and storage system specifically for medium voltage (MV) DC grids. Moreover, the PSFB converter provides galvanic isolation between the storage and AC grid if there is a need to connect PV/storage system directly to the AC grid (without a line transformer). Due to uncertainties of solar irradiance generation, the power outputs of photovoltaic panels are not guaranteed which is the incentive to implement a storage system to certify adequate power supply to the DC fast charging station. Furthermore, the results are shown for a real 24-hour profile of solar irradiance and EV load. The performance of the system is evaluated in MATLAB/Simulink.