Ahmed T. Elsayed

Advanced Battery Management and Diagnostic System for Smart Grid Infrastructure

This paper presents the design and implementation of an advanced battery management system (BMS). The basic concept is to divide each series battery array into sub-arrays where each battery is individually monitored and managed. The proposed BMS continuously monitors the voltage, current, and energy of each battery. Based on these measurements, the BMS can calculate individual state of charge (SoC) levels and C-rates. Furthermore, the system has the capability to isolate each individual battery to apply different charging profiles and advanced diagnostics to detect the correct problems. Pulsed charging is deployed using different duty cycles for SoC balancing. The isolated battery is bypassed to maintain uninterrupted supply to the load despite reduced series array voltage. An unidirectional dc-dc boost converter maintains a constant output voltage level to the load, regardless of the number of batteries connected, until the problem is corrected. A hardware implementation of the proposed BMS is explained in detail. The performance of the system is tested experimentally under different loading conditions, including heavy pulsed loads.

Frequency and voltage control of microgrids upon unintentional cascading islanding

Microgrids are small scale electricity networks comprising diverse distributed resources (DER) which can operate in grid-connected or islanded mode. An islanding situation may occur in a cascading way, where the DER types inside the islanded area have substantial impacts by means of control schemes. This paper presents a comprehensive study of the islanding process and the subsequent frequency and voltage control of different island schemes that comply with the IEEE 1547.4 grid code. Grid-connected operation, transition-to-island and islanded-mode operation of three different forms of cascading islanding were investigated. Studied islanding forms were a synchronous generator, inverter-based DER and a hybrid type. Experimental results are given in addition to simulation studies.

Microgrid automation assisted by synchrophasors

This paper presents synchrophasor deployment for microgrid automation applications. A microgrid, which is the main component of future smart grids, requires sophisticated measurement and control capabilities. Conventional RTU based automation approaches suffer from slow measurement update and lack of time-stamp values. In this study, a time-synchronized control approach is proposed for a deployable hardware-based microgrid involving a synchronous generator and an inverter based DER. Protection event analysis, islanding detection, re-synchronization, and online remote generation unit dispatch studies are realistically demonstrated in hardware in a laboratory based test-bed.

A comparative study on the optimal combination of hybrid energy storage system for ship power systems

This paper presents a comparative study to determine the optimal combination of hybrid energy storage system used on Shipboard Power System (SPS). The hybrid energy storage comprises two or more types of energy storage elements (Batteries, Ultra-Capacitors and Flywheels). In this research work, the optimal combination of these three types is determined to minimize the voltage and frequency fluctuations caused by the connection of pulsed loads on the AC or DC sides of the system. A model for hybrid AC/DC SPS with zonal distribution architecture was built in DIgSILENT PowerFactory software. Several case studies are carried out and their results are compared and analyzed.

A Computational Approach for a Wireless Power Transfer Link Design Optimization Considering Electromagnetic Compatibility

This paper presents an electromagnetic-artificial intelligence design optimization approach of a wireless power transfer link (WPTL). Electromagnetic solutions from a 3-DFE model of the WPTL were utilized to minimize the field signature around each design while maintaining high efficiency. The reduced field signatures around the WPTL would enable the achievement of designs that are in accordance with international electromagnetic compatibility (EMC) standards such as international commission on nonionizing radiation protection guidelines with respect to public exposure levels of EM signatures below 27 μT. As the optimization process involved utilizing a large number of fitness function evaluations, numerous 3-DFE solutions were required increasing the computational burden. Artificial neural networks were developed, trained, and used to produce the required equivalent 3-DFE solutions to evaluate the fitness function. As a result, this process significantly reduced the computational time by nearly 90%. The genetic algorithm-based optimization process yielded the desired results of electromagnetically compatible WPTL designs at the early development stage satisfying EMC standards.

Modeling and control of a low speed flywheel driving system for pulsed load mitigation in DC distribution networks

This paper details the modeling and development of an improved controller design for a dc flywheel energy storage system (FESS) driving circuit. The driving system is based on a bidirectional buck-boost converter. The modeling of this converter including the parasitic resistances for all the components was carried out. In this model, the equivalent circuit of the machine was integrated in the converter state-space model for improved accuracy and controllability. The system has two operating modes; when the FESS is charging, the converter operates in the buck mode. A controller was designed to regulate the charging rate through controlling the machines terminal voltage. In the discharging mode, the converter operates in the boost mode. A current controller takes over to control the injected current from the machine to the dc bus. The detailed design of both control loops was identified. Simulation results show the accuracy of the derived model and the enhanced performance of the FESS. Further, it is shown that the reversal of power-flow direction was performed seamlessly. A hardware prototype of the converter was implemented and the effectiveness of the developed system was experimentally verified. The experimental results are in excellent agreement with the simulation.

Improved design of controlled rectifier for reduced ripple resulting from integration of DC loads to AC systems

In this paper, an improved methodology for the design and precise parameter selection for a controlled rectifier (CR) is presented. We propose an improvement over the existing techniques for inductor and capacitor design based on current ripple, error analysis and switching state analysis. Furthermore, an equation for the design of the DC link capacitor considering the voltage ripple and the switching state analysis is derived. The analysis for the inductor is based on the estimation of the current error area using pulse width modulation (PWM) center and left aligned. This methodology is extendible to Active Power Filters (APF). The proposed methodology is verified through Matlab/ SIMULINK simulation using a predictive current control scheme over the voltage source converter (VSC). In order to show the effectiveness and validity of the proposed methodology; calculations are verified numerically and a comparison with other techniques in the literature is presented.

Modeling and Control of a Low-Speed Flywheel Driving System for Pulsed-Load Mitigation in DC Distribution Networks

This paper introduces the modeling and an improved controller design for a driving system for a DC Flywheel Energy Storage System (FESS). The Driving system is based on a Bi-directional Buck-Boost converter, the accurate modeling of the system including the parasitic resistances for all the components is carried out. In this model, the equivalent circuit of the machine is integrated in the converter state space model for improved accuracy and controllability. The system has two operating modes; when the machine is charging, the converter is operated in the buck mode. A controller is designed to regulate the charging rate through controlling the machine terminal voltage. In the discharging mode, the converter is operating in the boost mode, a current controller is taking over to control the injected current from the machine to the DC bus. The detailed design of both control loops is explained. Simulation results show the accuracy of the derived model and the enhanced performance of the FESS. Further, it is shown that the reversal of power flow direction is done seamlessly.

An Integrated Characterization Model and Multiobjective Optimization for the Design of an EV Charger’s Circular Wireless Power Transfer Pads

A good magnetic design of a wireless electric vehicle (EV) charging system requires accurate characterization of the equivalent circuit parameters. This is while considering the effect of the magnetic core and the conductive shielding layers. In the literature, such an analysis is done using 3-D finite element analysis, which makes the design and optimization process time-consuming and computationally expensive. In this paper, an integrated analytical model for the characterization of a circular wireless power transfer EV pads is utilized. This analytical model provides a valuable tool to optimize the design process. This model is utilized when evaluating the objective function for each individual in the multiobjective Pareto Optimality optimization algorithm. The objective is optimizing the pads with three decision variables and four constraints.

DC voltage ripple quantification for a flywheel-battery based Hybrid Energy Storage System

Flywheel energy storage has started attracting more attention as an energy storage means, but certain impediments face their deployment such as a high self-discharging rate and power quality issues. A potential solution is to combine flywheels with another energy storage types to form a Hybrid Energy Storage System (HESS). In this paper, a new method is established to perform power quality analysis and DC voltage ripple quantification in an HESS connected solely to a DC bus. Previous efforts have analyzed voltage and current ripple using an AC frequency reference, but these techniques are ineffective when the system does not contain an AC connection. Extensive laboratory testing and verification is conducted to characterize a flywheel-battery based HESS with different battery contribution levels. A correlation is made between the required battery support and resulting DC voltage ripple. Due to the nature of a flywheel operating at various speeds, a new Machine Speed Multiple (MSM) frequency reference is used as a profiling tool corresponding to the harmonic number in AC systems. Using the MSM in conjunction with the Discrete Fourier Transform, a voltage ripple frequency table is produced to highlight the target frequencies which must be reduced. A quantitative analysis identifies an overall reduction of voltage ripple magnitudes as a result of current injection from the battery.