Energy storage systems (ESSs) play a very important role in recent years. Flywheel is one of the oldest storage energy devices and it has several benefits. Flywheel Energy Storage System (FESS) can be applied from very small micro-satellites to huge power networks. A comprehensive review of FESS for hybrid vehicle, railway, wind power system, hybrid power generation system, power network, marine, space and other applications are presented in this paper. There are three main devices in FESS, including machine, bearing, and Power Electronic Interface (PEI). Furthermore, advantages and disadvantages all of them have been presented. In addition a brief review of new and conventional power electronic converters used in FESS, have been discussed. Finally, practical ways to develop this technology in the future are presented.

A comprehensive review of Flywheel Energy Storage System technology

Today, conventional power systems are evolving to smart grids, which encompass clusters of AC/DC microgrids, interfaced through power electronics converters. In such systems, increasing penetration of the power electronics-based distributed generations, energy storages, and modern loads provide a great opportunity for power quality control. In this paper, an overview of the power quality control of smart hybrid AC/DC microgrids is presented. Different types of power quality issues are studied first, with consideration of real-world hybrid microgrid examples, including data centers, electric railway systems, and electric vehicles charging stations. It shows that compared to traditional centralized power quality compensations, smart interfacing power converters from distributed generations, energy storages, and loads, and the AC and DC subgrids interfacing converters are promising candidates for power quality control. To realize the smart interfacing converters' power quality control, both primary converters control and secondary system coordination are required. In this paper, a thorough review of the primary control of interfacing converters to integrate the power quality compensation are presented, with a focus on the hybrid AC/DC microgrid harmonics compensation and unbalance compensation. For multiple interfacing converters, the secondary control with system-level coordination and optimization for harmonics and unbalance compensation (considering both unbalance and harmonics in single-phase and three-phase systems) are also presented. Challenges like low switching frequency of interfacing converters, parallel interfacing converters operation, and interfacing converters communications are discussed, and typical solutions for primary and secondary controls to deal with them are presented. The paper also includes rich case study results.

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Power Quality Control of Smart Hybrid AC/DC Microgrids: An Overview

With the development of high-speed and high-power electrified railway, power quality of traction power grid becomes more serious. In order to achieve three-phase balance of traction power grid, a modular multilevel converter (MMC)-based railway traction power conditioner (RTPC) is studied, which is characterized by modular multilevel cascaded structure. The RTPC consists of four H-Bridge links and output filter inductors, which can be connected to 27.5-kV traction feeders in co-phase supply system directly. This conditioner can be used for different kinds of traction system, especially suited to Scott traction system. According to the analysis of equivalent electrical model and power balance of RTPC, a hierarchical control strategy is put forward aiming to balance the submodule capacitor voltages, which ensures the safety and stability of system. Finally, the structure and its control strategy are verified by the simulation and experiment effectively.

A Railway Traction Power Conditioner Using Modular Multilevel Converter and Its Control Strategy for High-Speed Railway System

With the rapid development of modern electrified railway, negative-sequence current minimization is one of the most important considerations in the high-speed railway traction system. In the past, many multiple or multilevel topologies with high compensation capacity have been introduced for railway power conditioner (RPC). This paper presents a simplified quantitative comparison of five previous modular RPC topologies for negative sequence compensation in V/V and SCOTT traction systems, aiming for an optimal selection of the compensators. Performance criteria such as transformer requirement, voltage stress and current stress of a power switch, numbers of the power switches and capacitor are derived by analytical methods. Moreover, the numerical comparison of operating controllers is completed for modular RPCs. In addition, power losses of five modular RPCs are obtained by theoretical analysis, IPOSIM calculation as well as PSIM simulation. These calculations are validated via simulations results in PSIM. The main conclusion is that presented modular RPCs can be divided into general purpose RPC and special purpose RPC in terms of the behavior and efficiency. It is helpful to choose the appropriate topology for specific applications.

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Analysis and Comparison of Modular Railway Power Conditioner for High-Speed Railway Traction System

Electrical railway power supply systems: Current situation and future trends

Since the beginning of railway electrification, power quality has been a main problem in railway networks because of their special characteristics. Many ways of power quality improvement have been investigated and applied to ac and dc traction systems through railway electrification history. This paper presents a perspective on power quality issues through railway electrification development and investigates the necessity of power quality and system requirements for appropriate power quality. Compensation strategies are classified and compared. This aims to provide a comprehensive perspective of the power quality issue in railway power/distribution networks for researchers and engineers working on railway electrification. Less than 100 research articles are referenced for researchers to obtain good background information.

Power Quality Issues in Railway Electrification: A Comprehensive Perspective

In order to decrease the noise and vibration of operation in railway tracks, it is necessary to inspect the status of them frequently. A main task in inspection of railway tracks is measurement of rail corrugation. The rail corrugation occurs during operation due to wear. The dynamic component of the vertical wheel-rail contact force, as induced by rail corrugation is an important source to vibration. Also, according to the corrugation wavelength and railway vehicle speed, a dynamic excitation is generated which is an important source to noise. It is essential to utilize a system to check the rail corrugation. In this article, a new measurement system based on image processing is proposed to perform the corrugation measurement in a reliable manner, while traditional measurement systems are based on acceleration measurement or chord measurement and they are not reliable due to physical contact or need for knowing the characteristics of the track. The proposed system is based on laser triangulation principle using image processing to measure the rail corrugation precisely and quickly. This approach is an efficient technique for high-speed and high-accurate rail corrugation measurement. Experimental results show the capability of the system for practical usages.

A High Accuracy and High Speed Imaging and Measurement System for Rail Corrugation Inspection

Due to economic and environmental problems of fossil fuels and drawbacks of single implementation of renewable resources systems, Hybrid Renewable Energy Sources (HRESs) have been introduced. Thus, in this paper, a PV/wind source with various backups including battery/grid/diesel generator for an educational load with 35kW peak in Tehran city are proposed in order to reach the minimum lifecycle cost (NPC) by HOMER. The results show that grid-connected 150kW PV-110kW converter system is the most economical option among all 36 feasible systems due to supportive policies and subsidizing for renewable retailers in Iran. Not only could this system make the emissions produced by educational load equal to zero, but also it reduces other loads' emissions by helping the grid to meet surrounding loads. The other results of this paper show that in grid-battery and diesel-battery backup systems, Cycle Charging (CC) dispatch strategy has more economical result than Load following (LF) dispatch strategy. Furthermore, wind turbines in Tehran region is not economical, but if they were used, it would be better to implement small 1kW XL.1 wind turbine rather than a 10kW XLS one. In the end, according to the economic turbulence in Iran, a sensitivity analysis on the inflation rate shows that increasing the inflation rate could dramatically decrease the NPC of the system.

Techno-economic evaluation of a hybrid PV/wind system with grid/DG/Battery backups for an educational department in Tehran

Any reduction in the cross-sectional area of wires (RCSAW) in the stator or rotor (field or damper) windings of synchronous generators (SGs) is considered as a fault in SGs. In this article, a signal-model-based fault detection, isolation, and estimation approach based on the eigenvalues estimation of SGs is presented to diagnose RCSAW fault. The subspace identification method is employed to estimate the state matrix eigenvalues. A form of the characteristic equation in the faulty condition is introduced for fault diagnosis of SGs in the presence of linear and nonlinear loads. The stator and field currents and voltages, and the rotor speed are used for fault diagnosis. The effectiveness of the introduced fault diagnosis method is shown using simulation and experimental results on a salient-pole SG in Iran-Safir (ER24) diesel-electric locomotives.

Signal-Model-Based Fault Diagnosis in Windings of Synchronous Generator

Air-gap eccentricity fault causes rotor-stator rub and consequently damage to Synchronous Generators (SGs). In this paper, a fault diagnosis approach to diagnose the eccentricity fault for SGs is presented. In this approach, the state matrix eigenvalues based on the subspace identification are estimated, and those are used for fault diagnosis. Two dq models of SGs in faulty and healthy conditions are employed to present the theoretical foundation of the method. As the main advantage, the introduced fault diagnosis method is working properly for either linear or nonlinear loads of SGs. The stator and field currents and voltages, and rotor rotational speed are required signals in the introduced approach. The method is validated using experimental data of SGs in Iran-Safir (ER24) diesel-electric locomotives. 

Sayed Mohammad Mousavi Gazafrudi

Papers

Power Quality Issues in Railway Electrification: A Comprehensive Perspective

A High Accuracy and High Speed Imaging and Measurement System for Rail Corrugation Inspection

Techno-economic evaluation of a hybrid PV/wind system with grid/DG/Battery backups for an educational department in Tehran

Signal-Model-Based Fault Diagnosis in Windings of Synchronous Generator

Air-gap eccentricity fault detection, isolation, and estimation for synchronous generators based on eigenvalues analysis.