Suleiman Sharkh | University of Southampton (original) (raw)

Papers by Suleiman Sharkh

Journal of Power Electronics, 2016

The unequal impedances of the interconnecting cables between paralleled inverters in the island m... more The unequal impedances of the interconnecting cables between paralleled inverters in the island mode of microgrids cause inaccurate reactive power sharing when the traditional droop control is used. Many studies in the literature adopt low speed communications between the inverters and the central control unit to overcome this problem. However, the losses of this communication link can be very detrimental to the performance of the controller. This paper proposes an improved reactive power-sharing control method. It employs infrequent measurements of the voltage at the point of common coupling (PCC) to estimate the output impedance between the inverters and the PCC and then readjust the voltage droop controller gains accordingly. The controller then reverts to being a traditional droop controller using the newly calculated gains. This increases the immunity of the controller against any losses in the communication links between the central control unit and the inverters. The capability of the proposed control method has been demonstrated by simulation and experimental results using a laboratory scale microgrid.

IEEE Transactions on Power Electronics, 2015

In inverter-based microgrids, the paralleled inverters need to work in grid-connected mode and st... more In inverter-based microgrids, the paralleled inverters need to work in grid-connected mode and stand-alone mode and to transfer seamlessly between the two modes. In grid-connected mode, the inverters control the amount of power injected into the grid. In stand-alone mode, however, the inverters control the island voltage while the output power is dictated by the load. This can be achieved using the droop control. Inverters can have different power set-points during grid-connected mode but in stand-alone mode they all need their power set-points to be adjusted according to their power ratings. However, during sudden unintentional islanding (due to loss of mains), transient power can flow from inverters with high power setpoints to inverters with low power set-points, which can raise the DC link voltage of the inverters causing them to shut down. This paper investigates the transient circulating power between paralleled inverters during unintentional islanding and proposes a controller to limit it. The controller monitors the DC link voltage and adjusts the power set-point in proportion to the rise in the voltage. A small signal model of an islanded microgrid is developed and used to design the controller. Simulation and experimental results are presented to validate the design. Index Termsmicrogrid, droop control, power sharing, unintentional islanding. NOMENCLATURE * , * Active and reactive power set-points , Instantaneous active and reactive power Load resistance Inverter output inductance , Frequency and voltage drooping gains , Voltage and frequency set points Measurement filter time constant * Nominal DC link voltage DC link capacitor , Voltage and phase equilibrium points I.

IEEE Transactions on Industrial Electronics, 2014

Line interactive Uninterruptable Power Supply (UPS) systems are good candidates for providing ene... more Line interactive Uninterruptable Power Supply (UPS) systems are good candidates for providing energy storage within a microgrid to help improve its reliability, economy and efficiency. In grid-connected mode, power can be imported from the grid by the UPS to charge its battery. Power can also be exported when required, e.g., when the tariffs are advantageous. In stand-alone mode, the UPS supplies local distributed loads in parallel with other sources. In this paper, a line interactive UPS and its control system are presented and discussed. Power flow is controlled using the frequency and voltage drooping technique to ensure seamless transfer between grid-connected and stand-alone parallel modes of operation. The drooping coefficients are chosen to limit the energy imported by the USP when reconnecting to the grid and to give good transient response. Experimental results of a microgrid consisting of two 60kW line interactive UPS systems are provided to validate the design. Index Terms-Line interactive UPS, microgird, distributed generation. I. INTRODUCTION O INCREASE reliability, energy storage systems within a microgrid are essential. Energy is stored while in grid-connected mode, when the microgrid's Distributed Generation (DG) systems produce excess power, to be used later to supply critical loads during power outages. In stand-alone mode, they can be used to boost the power supplied by the microgrid if the DG systems cannot meet the expected level of power. To meet these demands, the energy storage system needs to be able to work in grid-connected and stand-alone modes. In the latter mode of operation, the system needs to operate in parallel with other DG systems to meet the variable power demand of the load. More importantly, it needs to switch seamlessly between the two modes. Line interactive UPS systems are good candidates for providing energy storage within microgrids as they can be connected in parallel with both the main grid and local load. The classical topology of line interactive UPS systems [1],[2] is simpler, cheaper, more efficient and more reliable than the on-line double conversion UPS. This topology, however, does not provide voltage regulation to the load. Voltage regulation is M. A.

2020 2nd International Conference on Smart Power & Internet Energy Systems (SPIES)

This paper discusses the sizing and control of a hybrid energy storage system comprising a batter... more This paper discusses the sizing and control of a hybrid energy storage system comprising a battery and a compressed air energy storage (CAES) system. The CAES system is connected to the load through a boost converter that controls the air motor's speed to achieve maximum power point tracking (MPPT). A bidirectional converter is used to connect a battery to the load and maintain the output voltage constant. The air motor and battery sizes are estimated for a typical house in the Southern region of the UK. The battery is sized to buffer load fluctuations. All system models have been simulated using MATLAB/Simulink. Two scenarios are considered: a CAES only system controlled in constant voltage mode and a hybrid system comprising CAES with an MPPT controller and a battery with a voltage controller. The results demonstrate that the power rate of air motor is estimated properly by considering the difference between the generated power and demand power. The power difference called energy deficit is used to size the battery. The performance of CAES system is improved by hybridizing with a battery; the system maintains constant voltage when the CAES operates at maximum power point (MPP). The air motor in hybrid system controlled in MPPT mode has approximately 47% greater efficiency than that of air motor controlled in voltage mode.

Energies, 2021

For integrating large batteries in the medium voltage grid, current fed solid-state transformers ... more For integrating large batteries in the medium voltage grid, current fed solid-state transformers offer galvanic isolation and a significant weight and size reduction. While the power losses increase with frequency and flux density, the core volume is contrariwise. Therefore, a design optimisation to achieve minimum losses and/or a minimum volume is essential. An optimisation strategy is proposed in this paper to find the optimum operating frequency and core flux density under certain practical constraints such as winding voltage per turn, clearance between transformer windings, saturation flux density and minimum efficiency. Differently from previous works, the proposed strategy provides a holistic approach for the design considering all main power losses from all main components using nonsinusoidal voltage waveforms and different operating conditions. Analytical equations for the power losses calculation and the cores design are derived and validated using ANSYS and MATLAB Simulink...

Advanced Energy and Sustainability Research, 2021

Figure 11. Layers of protection against TR in a high-power lithium-ion battery. The layers are or... more Figure 11. Layers of protection against TR in a high-power lithium-ion battery. The layers are ordered to how close they are to the internal protection of the cell.

Electronics, 2020

A transformer-less Buck-Boost direct current–direct current (DC–DC) converter in use for the fast... more A transformer-less Buck-Boost direct current–direct current (DC–DC) converter in use for the fast charge of electric vehicles, based on powerful high-voltage isolated gate bipolar transistor (IGBT) modules is analyzed, designed and experimentally verified. The main advantages of this topology are: simple structure on the converter’s power stage; a wide range of the output voltage, capable of supporting contemporary vehicles’ on-board battery packs; efficiency; and power density accepted to be high enough for such a class of hard-switched converters. A precise estimation of the loss, dissipated in the converter’s basic modes of operation Buck, Boost, and Buck-Boost is presented. The analysis shows an approach of loss minimization, based on switching frequency reduction during the Buck-Boost operation mode. Such a technique guarantees stable thermal characteristics during the entire operation, i.e., battery charge cycle. As the Buck-Boost mode takes place when Buck and Boost modes can...

Energies, 2018

This editorial summarizes the content of the Special Issue entitled "The International Symposium ... more This editorial summarizes the content of the Special Issue entitled "The International Symposium on Electric Vehicles (ISEV2017)", which was published in MDPI's Energies journal. The Special Issue was compiled in 2017 and accepted a total of 26 papers. Lithium-ion battery, energy management of electric vehicles, and motor control in electric vehicles were the most discussed topics, introducing brand new methods with very sound results.

IEEE Transactions on Vehicular Technology, 2017

The number of electric vehicles (EVs) is expected to increase significantly in the future to comb... more The number of electric vehicles (EVs) is expected to increase significantly in the future to combat air pollution and reduce reliance on fossil fuels. This will impact on the power system. However, appropriate charging and discharging of EVs through vehicle-to-grid operations could also provide support for the power system and benefits for the EV owners. This raises the questions of when and how EV battery storage should be dispatched, taking into account both vehicle users' and power system's requirements and priorities, as well as the constraints of the battery system. This paper proposes a novel decentralized dispatch strategy based on the Analytic Hierarchy Process (AHP) taking into account the relative importance of the different criteria including cost, battery state of charge, power system contingency and load levelling. The proposed AHP-based dispatch strategy was tested on an IEEE Reliability Test System with different EV numbers and capacities to investigate the efficacy of such an approach. The simulation results demonstrate the feasibility and benefits of this dispatch strategy.

IET Power Electronics, 2019

Achieving an accurate steady-state averaged active power sharing between parallel inverters in is... more Achieving an accurate steady-state averaged active power sharing between parallel inverters in islanded AC microgrids could be realized by a traditional droop control. For identical inverters having the same droop gains, it is assumed that the transient average power responses will be similar, and no circulating current will flow between the units. However, different line impedances could influence the instantaneous power significantly and thus circulating power flows among the inverters particularly during sudden disturbances such as load changes. This power, if absorbed by an inverter, will lead the DC link voltage to rise abruptly and trip the inverter, thus, degrading the performance of the whole microgrid. The problem becomes worse when hybrid generators are serving as unidirectional power source. This paper assesses the performance of hybrid generators within an islanded microgrid against the mismatch in line impedances. Two schemes to stabilize the microgrid are proposed. In addition, a participation factor analysis is developed to select the most effective controller scheme to bound the DC link voltage and minimize the circulating power. Simulation and experimental results are presented to verify the analysis and the capability of the proposed controller.

IEEE Transactions on Industry Applications, 2017

Despite transverse flux machines (TFMs) being intrinsically three-dimensional, it is still possib... more Despite transverse flux machines (TFMs) being intrinsically three-dimensional, it is still possible to model them analytically using relatively simple models. This paper aims to provide an insight into the behaviour of TFMs using a compact equation, which relates torque to the electric and magnetic loadings of the machine and a flux factor. The flux factor is also used to estimate the flux linkage and therefore the power factor of this kind of machines. It is shown that the low power factor of TFMs is not only due to leakage but also due to the nature of the electromagnetic interaction that takes place. The TFM developed at the University of Southampton is used as the basis of a case study to illustrate the trade-off between torque density and power factor, and to provide some design guidelines. The analytical results are verified using finite elements analysis and experimental data. Index Terms-Analytical models, permanent magnet machines, power factor, torque, transverse-flux machines.

This paper discusses the analysis and design of a very thin slotless PM brushless motor whose sta... more This paper discusses the analysis and design of a very thin slotless PM brushless motor whose stator laminations are manufactured from a single strip of steel that is edge wound into a spiral (like a "Slinky") and then fitted over the windings that are preformed on the outside surface of a non-conducting former. Analytical and finite element analysis (FEA) are used to determine the constrained optimum dimensions of a motor used to drive a rim driven thruster in which the motor rotor is fitted onto the rim of the propeller and the stator is encapsulated in the thin Kort nozzle of the thruster. The paper describes the fabrication of a demonstrator motor and presents experimental results to validate the theoretical calculations. Experimental motor performance results are also reported and compared with those of a slotted motor that fits within the same active radial dimensions as the slotless motor. The slotless motor, which has longer active length and endwindings, and thicker magnets than the slotted motor, was found to be less efficient and more expensive (prototype cost) than the slotted machine.

Journal of Modern Power Systems and Clean Energy, 2015

The storage capacity of the batteries in an electric vehicle (EV) could be utilised to store elec... more The storage capacity of the batteries in an electric vehicle (EV) could be utilised to store electrical energy and give it back to the grid when needed by participating in vehicle to grid (V2G) schemes. This participation could be a source of revenue for vehicle owners thus reducing the total charging cost of their EVs. A V2G simulator has been developed using MATLAB to find out the potential cost saving from participation of EVs in V2G schemes. A standard IEEE30 network has been modelled in the simulator which uses the MATPOWER engine to undertake power flow analysis. A novel control algorithm has been developed to take advantage of the difference between the selling and buying electricity prices by charging and discharging EVs at the appropriate time. Two scenarios are simulated to compare the total charging cost of EVs with or without the utilisation of V2G technology within the power system assuming a total of 5000 EVs. The results of the simulation show that the applied control strategy with V2G is able to reduce the charging cost of EVs by 13.6 % while satisfying the minimum requirement for state of charge (SoC) of the EV batteries to complete their next journey.

TheScientificWorldJournal, 2015

Proceedings. Biological sciences / The Royal Society, Jan 7, 2015

Natural and anthropogenic static electric fields are commonly found in the environment and can ha... more Natural and anthropogenic static electric fields are commonly found in the environment and can have both beneficial and harmful effects on many animals. Here, we asked how the fruitfly responds to these fields and what the consequences of exposure are on the levels of biogenic amines in the brain. When given a choice in a Y-tube bioassay Drosophila avoided electric fields, and the greater the field strength the more likely Drosophila were to avoid it. By comparing wild-type flies, flies with wings surgically removed and vestigial winged flies we found that the presence of intact wings was necessary to produce avoidance behaviour. We also show that Coulomb forces produced by electric fields physically lift excised wings, with the smaller wings of males being raised by lower field strengths than larger female wings. An analysis of neurochemical changes in the brains showed that a suite of changes in biogenic amine levels occurs following chronic exposure. Taken together we conclude th...

3rd IET International Conference on Power Electronics, Machines and Drives (PEMD 2006), 2006

Rim driven thrusters with structurally integrated brushless PM motors are now an established tech... more Rim driven thrusters with structurally integrated brushless PM motors are now an established technology with an increasing range of applications. In these thrusters, the stator of the motor is housed within the thruster duct, and the rotor forms a ring around the tips of the propeller. Such high pole number motors tend to be very thin radialy, have very small length to diameter ratios, and have relatively large airgaps to accommodate corrosion protection layers on the surfaces of the rotor and stator. The relatively large diameter stator laminations of such machines tend therefore to have very thin back of core and narrow teeth, which make them expensive and difficult to manufacture. This paper proposes an alternative potentially lower cost motor topology featuring a slotless stator whose laminations are manufactured from a single strip of steel that is edge wound into a spiral (like a "slinky" and then fitted over the windings that are preformed on the outside surface of a non-conducting former. The former is also part of the sealed housing that protects the stator from corrosion in seawater. The paper discusses the design optimisation of such a motor using analytical and finite element analysis (FEA), describes a demonstrator motor and reports experimental and FEA results.

Journal of Experimental Biology, 2011

SUMMARYStatic electric fields are found throughout the environment and there is growing interest ... more SUMMARYStatic electric fields are found throughout the environment and there is growing interest in how electric fields influence insect behaviour. Here we have analysed the locomotory behaviour of cockroaches (Periplaneta americana) in response to static electric fields at levels equal to and above those found in the natural environment. Walking behaviour (including velocity, distance moved, turn angle and time spent walking) were analysed as cockroaches approached an electric field boundary in an open arena, and also when continuously exposed to an electric field. On approaching an electric field boundary, the greater the electric field strength the more likely a cockroach would be to turn away from, or be repulsed by, the electric field. Cockroaches completely exposed to electric fields showed significant changes in locomotion by covering less distance, walking slowly and turning more often. This study highlights the importance of electric fields on the normal locomotory behaviou...

Energies, 2014

Fast capacity estimation is a key enabling technique for second-life of lithium-ion batteries due... more Fast capacity estimation is a key enabling technique for second-life of lithium-ion batteries due to the hard work involved in determining the capacity of a large number of used electric vehicle (EV) batteries. This paper tries to make three contributions to the existing literature through a robust and advanced algorithm: (1) a three layer back propagation artificial neural network (BP ANN) model is developed to estimate the battery capacity. The model employs internal resistance expressing the battery's kinetics as the model input, which can realize fast capacity estimation; (2) an estimation error model is established to investigate the relationship between the robustness coefficient and regression coefficient. It is revealed that commonly used ANN capacity estimation algorithm is flawed in providing robustness of parameter measurement uncertainties; (3) the law of large numbers is used as the basis for a proposed robust estimation approach, which optimally balances the relationship between estimation accuracy and disturbance rejection. An optimal range of the threshold for robustness coefficient is also discussed and proposed. Experimental results demonstrate the efficacy and the robustness of the BP ANN model together with the

5th IEEE Vehicle Power and Propulsion Conference, VPPC '09, 2009

Electric vehicles have been the focus of much research over the last two decades as the world has... more Electric vehicles have been the focus of much research over the last two decades as the world has sought improved energy utilization and reduced emissions. However, the lengthy charging time, modest range and relatively sluggish performance of batteries have restricted the commercialization of electric vehicles. Hybrid propulsion can overcome most of these shortcomings, with improved energy efficiency and reduced emissions compared to conventional internal combustion engine vehicles (ICEVs). Nonetheless, energy storage issues are still critical. Redox flow batteries (RFB), which continue to mature, have the potential to be fast recharging contenders. Refuelling is possible by rapid pumping of the reactants into the batteries' tanks. Another feature of RFBs that makes them attractive for EV applications is the separation, in terms of physical location and sizing, of the energy and power components. This adds a degree of flexibility that allows the optimization of the power and energy components for a specific vehicle configuration and performance. This paper concisely reviews RFBs and assesses their potential as a power source for hybrid electric vehicles. Experimental performance data from a 100 cm 2 laboratory, unit cell, allvanadium redox flow battery (V-RFB) are presented. Based on these results, the size and performance of a V-RFB, suitable for a series hybrid electric vehicle, are estimated and compared with lithium-ion and conventional lead-acid alternatives. The results suggest that V-RFB performance could be improved to match that of the conventional lead-acid, with the added advantage of very rapid recharging. Index Terms-Redox flow battery, Road vehicle electric propulsion, Road vehicle power systems Abbreviations AER All electric range BEV Battery-powered electric vehicle EV Electric vehicle EGM Electric generator / motor FC Fuel cell HEV Hybrid electric vehicle ICEV Internal combustion engine vehicle PHEV Plug-in hybrid electric vehicle RFB Redox flow battery V-RFB All-vanadium redox flow battery Symbols Δc Change in reactant concentration in the electrolyte η C Charge efficiency η E Energy efficiency η P Power efficiency η V Voltage efficiency E Energy F Faraday constant I Current j Current density M Molar mass q Electrical charge V Volume of electrolyte V cell Cell voltage V reference Open-circuit cell voltage of the monitoring cell z No. of electrons transferred during redox reaction