DC traction networks that supply power to trolley-buses, tramcars and trains can be simultaneously used to integrate fast-charging stations for Electric Vehicles (EVs). This strategy improves the traction grid utilization of urban transportation systems. In addition, it offers a potential solution to the increasing requirement of charging infrastructure due to proliferation of plug-in EVs and the associated impact on the existing distribution network. This paper suggests that the use of multi-port converter based integration of EV chargers with dc trolley-bus network can be a preferred solution in terms of defined efficiency boundary. A sensitivity analysis to charging power, substation distance and section length of overhead contact system is performed in comparison to the conventional two-port dc/dc converter based EV integration.@en

The advent of rooftop photovoltaics (PV), energy storage systems like a battery (BESS) and high capacity electric vehicles (EVs) is changing the landscape of electrical distribution rapidly. Traditional electricity consumers like households, buildings (both commercial and residential) are augmented with these emerging technologies which are turning them into "Prosumers" (producer and consumer). This is beneficial to the current radial grid structure as Prosumers are inherently more self-sufficient in terms of energy and thus provide grid-relief from congestion and will potentially delay or obviate the need for expensive grid upgrades. To fully realize the potential of these multiple sources and loads as a single dispatch-able prosumer, this thesis focuses on developing electronic hardware to accurately control these individual elements which result in an intelligent, flexible and safe grid. @en

This paper aims to investigate the dynamic charging performance of an 11 kW dynamic inductive power transfer (DIPT) system. First, a multi-objective optimization (MOO) method is proposed to find the Pareto front of the DD charging pad. Then, the optimal design with a 96.82% efficiency is selected as the target design for the DIPT system. Based on the coupler mutual inductance at different misalignment, the orientation of the transmitter (Tx) and receiver (Rx) pads and the distance between Tx pads are studied and optimized. To obtain the dynamic characteristics of the DIPT system, the impact of mutual inductance variation is investigated, and a dynamic model using Laplace phasor transformation is built to solve the waveform amplitude of electrical variables. Finally, a time-variant circuit model is built. Based on the simulations, the dynamic model is proved to be accurate, and the proposed DIPT system displays a good dynamic charging performance.

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Multiactive bridge converters (MAB) have become a widely-researched candidate for the integration of multiple renewable sources, storage, and loads for a variety of applications, from robust smart grids to more-electric aircraft. Connecting multiple dc ports reduces power conversion stress, improves efficiency, reduces material billing, and increases power density. However, the power flows between the ports of an MAB converter are magnetically coupled via the high-frequency (HF) transformer, making it difficult to control. This article presents an MAB converter configuration with a rigid voltage source on the magnetizing inductance of the transformer resulting in inherently decoupled power flows. As a result, the configuration allows independent power flow control tuning of the rest of the ports. The theory behind the power flow decoupling of the proposed MAB configuration is analyzed in detail using a reduced-order model. A 2-kW, 100-kHz Si-C-based four-port MAB converter laboratory prototype is built and tested, showing completely decoupled control loops with fast transient response regardless of their control bandwidths. The proposed configuration therefore makes the operation and design of theMAB family of converters much more feasible for any number of ports and precludes the need for a high-performance dynamic decoupling controller @en

DC Microgrid with integrated photo-voltaics (PV) and battery storage system is a promising technology for future smart grid applications. This paper compares three battery storage technologies namely: lithium-ion (Li-ion), lead-acid, and vanadium redox flow battery (VRFB) in the residential low-voltage dc grids, to increase the penetration of PV to improve self-sufficiency and grid independence. A multi-objective optimisation method is proposed to visualise the trade-offs between four objective functions: cost of electricity, energy autonomy, peak power reduction, and lifetime capital cost. The method is applied to a near-future scenario, based on a real residential feeder. Pareto fronts of the dominant designs are used to compare different battery technologies for this PV-battery integrated dc microgrid application. Additionally, the results provide insight into the dimensioning the battery, the PV, and the front-end ac-dc converter.@en

Triple active bridge (TAB) as an isolated multiport converter is a promising integrated energy system for smart grids or electric vehicles. This article aims to derive and analyze zero voltage switching (ZVS) regions of TAB, in which both switching losses are reduced, and electromagnetic interference issues are mitigated. In the proposed closed-form solution of ZVS criteria, parameters such as the parasitic capacitance of the switches, the leakage inductance of the transformer, the switching frequency, the port voltage, the phase-shift inside and between the full-bridges are all taken into account. The analysis shows how the five degrees of freedom can be used to maintain ZVS operation in various operating points. The analysis and derived closed-form ZVS criteria are experimentally verified using a laboratory prototype. The derived analytical ZVS criteria are a powerful tool to study and optimize the operation of TAB converters.

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Multiactive bridge (MAB) converter is a promising solution for integrating multiple renewable sources, storage, and loads for various applications. However, the MAB converter is challenging to control due to the inherent coupling between the port power flows. To that end, this article presents a decoupling control strategy based on linear active disturbance rejection control. The proposed controller observes the coupling disturbance using a linear extended state observer and subsequently rejects the observed disturbance resulting in dynamic decoupling. Experiments conducted on a 2-kW 100-kHz Si-C-based four-port MAB converter laboratory prototype illustrate the decoupling performance of the proposed control strategy. Compared to the traditional decoupling control strategy, the proposed approach is decentralized and model independent, only requiring information regarding its order.

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This paper proposes a power flows decoupling controller for the triple active bridge converter. The controller is based on a full-order continuous-time model of the TAB converter derived using the generalized average modelling (GAM) technique. GAM uses the Fourier series expansion to decompose the state-space variables into two components, which represent the active power and the reactive power. The controller uses the active power components of the transformer currents to decouple the active power flows between converter ports. Additionally, the implementation of the decoupling controller in the digital domain is detailed in the paper. The decoupling performance of the proposed controller is validated in a hardware experiment.

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Microgrid with integrated photo-voltaics (PV) and battery storage system (BSS) is a promising technology for future residential applications. Optimally sizing the PV system and BSS can maximise self-sufficiency, grid relief, and at the same time can be cost-effective by exploiting tariff incentives. To that end, this paper presents a comprehensive optimisation model for the sizing of PV, battery, and grid converter for a microgrid system considering multiple objectives like energy autonomy, power autonomy, payback period, and capital costs. The proposed approach involves developing a holistic techno-economic microgrid model based on variables like PV system power, azimuth angle, battery size, converter ratings, capital investment and electricity tariffs. The proposed method is applied to determine the optimum capacity of a PV system and BSS for two case residential load profiles in the Netherlands and Texas, US to investigate the effect of meteorological conditions on the relative size of PV and battery. Based on the optimisation results, thumb rules for optimal system sizing are derived to facilitate microgrid design engineers during the initial design phase.

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This paper aims to identify the difference between foreign object (FO) and misalignment in terms of their influence on inductive power transfer (IPT) systems. This is performed through magnetic and equivalent circuit analysis of the mutual inductance, primary input impedance, charging pad terminal impedance and current harmonics. Experiment measurements on an IPT prototype are carried out to verify the analysis. It is found that: the charging pad terminal impedance under FO condition has a more pronounced decrement than that of misalignment; the mutual inductance under FO condition shows negative correlation with frequency, while positive for misalignment; the absolute value of the input impedance is decreased by FO and increased by misalignment; the influence of FO and misalignment on the THD of the input current is minimal. Finally, it is possible to detect FO and distinguish it from misalignment, through the variation of the primary pad terminal inductance, as well as the frequency dependence of the primary input impedance and the mutual inductance.@en

Inductive power transfer (IPT) is becoming increasingly popular in stationary electric vehicle charging systems. In this paper, the influence of the different IPT coupler geometries on the performance factors efficiency, power density, misalignment tolerance, and stray field is studied. Five different cou-pler topologies namely the circular, rectangular, double-D (DD-DD) and the double-D transmitter with double-D-Quadrature receiver (DD-DDQ) are considered in this study. The electromagnetic behavior of the couplers is modeled using three-dimensional finite element analysis. To ensure a fair quantitative comparison, a multi-objective optimization framework is developed to analyze the Pareto trade-offs between conflicting performance metrics like power densities, efficiencies, and misalignment tolerance for all the considered coupler topologies.

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With the rising popularity of the power electronic based systems with integrated energy storage, the multi-port isolated converter topologies are gaining popularity. In contemporary literature, the triple active bridge (TAB) converter is the most popular among these topologies. However, the TAB was not yet described with the continuous-time full-order model. In this paper, the continuous-time full-order model of the TAB converter is derived. The derived model is validated with the measurement of the control-to-output transfer functions. The derived model can provide useful insights into the operation of the converter and can be used for controller design.

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Inductive power transfer (IPT) is becoming increasingly popular in stationary electric vehicle (EV) charging systems. In this paper, the influence of the different IPT coupler geometries on the performance factors such as efficiency, power density, misalignment tolerance, and stray field is studied. Four different coupler topologies, namely the circular, rectangular, double-D (DD-DD), and the double-D transmitter with double-D-quadrature receiver (DD-DDQ) are considered in this study. The electromagnetic behavior of the couplers is modeled using three-dimensional finite-element method, which is validated by experiments on a laboratory prototype. A multi-objective optimization (MOO) framework is developed to analyze the Pareto tradeoffs between conflicting performance metrics for the couplers. Optimization results depict that the circular topology performs best among the selected topologies regarding higher coupling coefficient, and efficiency for similar active mass and coupler area. Circular and rectangular couplers perform better than the polarized couplers like DD-DD and DD-DDQ regarding stray field exposure in both vertical and lateral direction of the coupler position in the EV. However, polarized couplers show more tolerance toward misalignment compared to circular and rectangular couplers. Thus, this study provides information regarding the specific strengths and weaknesses of different coupler topologies, which can be used during the initial design phase.

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Autonomous operation of the dc grids with converter interfaced renewable energy sources and energy storage with droop based control can lead to instability. This paper analyzes the stability of droop based closed loop controllers in a dc nanogrid. Linear state space modeling approach is used to model the small signal model of the droop controlled dc-dc converters. The dominant eigenvalues are analyzed, and the effect of closed-loop gains of the converters are investigated. Detailed parametric sensitivity analysis and participation factor of the system parasitics and the controller gains are also presented. Based on that, a segmented droop strategy is proposed to divide the operating ranges into segments with adaptive controller gains to ensure system stability in all of them. A particle swarm optimization algorithm is used to optimize for the converter gains of individual segments.

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Inductive power transfer (IPT) is gaining popularity across a wide range of battery charging applications like biomedical, consumer electronics and electric vehicle (EV) charging. One of the major challenges in designing IPT charge pads is determining the optimal physical sizes of the magnetic couplers resulting in efficient power transfer and low cost of materials. In EV applications, it is especially difficult due to the variation in nominal air gap, required power levels associated with different vehicle classes, and charging locations that may be encountered. This paper aims to determine the relationship between optimal coupler sizes and the nominal air gap of an IPT system. Finite element analysis (FEA) is used to model the electromagnetic behavior of the magnetic couplers. A multi-objective optimization framework is built to reveal the Pareto fronts which show the trade-offs between the power transfer efficiencies and the coupler power densities at different air gaps. This method is applied on polarized double-D (DD) couplers for a 5 kW IPT system at different air gaps. Analyzing the power densities of the Pareto Optimal designs an approximate relation between optimal pad sizes and the air gap is derived. Results show that there is an exponential relationship between the optimal coupler sizes and the nominal air gap.

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Low voltage dc distribution grids face issues associated with arc faults, aggravated by the absence of current zero crossing. The focus of this paper is to comprehensively develop a method of series arc fault detection at the load side power electronics, based on the electrode dependent initial voltage drop occurring at the arc initiation. The proposed arc detection algorithm is described along with the structure and time constants of the designed bandpass filter. The operational boundaries of the arc detection algorithm are defined for copper electrodes depending on the set threshold voltage and the system parameters, like grid inductance, resistance, and the load capacitance. Further, the detection time and the zone of guaranteed positive detection are depicted. These are validated through test simulations on the state space model of the system. Finally, experimental validation of the proposed scheme is carried out, wherein, a series arc is generated in the dc circuit and the programmed micro-controller provides a real time signal upon detecting the arcing event. The results on variation in detection time with set threshold voltage are also presented experimentally.

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Misalignment during wireless charging of EVs can lead to low efficiencies (<85%) of power transfer which can lead to thermal issues and high leakage fields. This paper explores the most optimal solution towards a misalignment tolerant system. To that end, a DD-DDQ coil system with series-series compensation combined with an impedance matching control algorithm is explored. A multi-objective optimization approach is presented to visualize the trade-off between the design aspects which result in high misalignment tolerance. Finally, the results are compared with DD-DD coil designs to quantify the advantage of the proposed system.

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This paper deals with a generic methodology to evaluate the magnetic parameters of contactless power transfer systems. Neumann's integral has been used to create a matrix method that can model the magnetics of single coils (circle, square, rectangle). The principle of superposition has been utilized to extend the theory to multi-coil geometries, such as double circular, double rectangle and double rectangle quadrature. Numerical and experimental validation has been performed to validate the analytical models developed. A rigorous application of the analysis has been carried out to study misalignment and hence the efficacy of various geometries to misalignment tolerance. The comparison of single-coil and multi-coil inductive power transfer systems (MCIPT) considering coupling variation with misalignment, power transferred and maximum efficiency is carried out.

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Battery electric vehicles (BEVs) have the potential to replace conventional vehicles, but the short driving range is currently limiting their diffusion. Using analytical methods this paper compares two electric powertrains with respect to energy consumption and efficiency: the standard single-motor architecture, derived from conventional internal combustion engine vehicles and equipped with a high-speed electric motor and a mechanical reduction system, versus the novel in-wheel direct drive topology. The potential benefits of a two-speed transmission to improve the driving range of battery electric vehicles are also studied. A backwards-simulation model from the wheels (load) to the battery (source) has been developed to simulate an EV during representative drive cycles. The results show superior performance of the in-wheel powertrain, which can provide up to 14% energy saving vs. the single-motor configuration thanks to the absence of mechanical transmission components and related power losses. Furthermore, the adoption of a two-speed gearbox on a single-motor electric vehicle doesn’t provide any effective energy saving benefit versus a fixed reduction gear. On the contrary, it consumes more battery energy during urban driving, up to 7%, due to the lower efficiency of the multi-gear transmission compared to the single-speed type.@en

In general, PM machines with conventional integer slot distributed winding (ISDW) schemes exhibit significant cogging torque resulting in high torque ripple which makes them unsuitable for EV applications which require low torque pulsations. This paper presents detailed analysis of the performance of PM Synchronous motor (PMSM) with fractional slot distributed winding (FSDW) scheme which shows significant reduction in torque ripple compared ISDW PM machines. Effect of the fractional slot winding distribution on electromagnetic torque pulsations has been analysed using Finite element (FE) computation technique. For a fair quantitative comparison between the above machine types, a flexible optimisation approach is proposed in this paper which generates Pareto fronts of the individual machine types.@en