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- Improvement of DC microgrid voltage regulation based on bidirectional intelligent charging systemsPublication . Santos, Pedro; Fonte, Pedro M; Luís, RicardoIn several cities, there are existing DC tram/subway grids. These existing grids in some cases cover a big part of the city and create the opportunity to install EV charging infrastructures. Such implementation could be built in order to contribute to the DC grid stability, enhancing the DC grid voltage regulation, through vehicle-to-tram concept. This can be reached with bidirectional DC/DC converters which enable energy transfer from vehicles to the DC grid to support such starts. Hereafter, the energy may flow normally from the grid to the vehicles. However, these improvements come with certain challenges in terms of power conversion, voltage regulation, grid coordination and intelligence. This paper defines the design principles of a tram DC-microgrid, which enables fast-charging, supported by fuzzy controllers that follow dynamically the overhead line voltages and the charging/discharging conditions of the proposed EV charging infrastructure. A discussion and conclusion about the practical applicability of the tram DC microgrid and its the complementarity with the EV charging infrastructure are demonstrated evaluating the results of DCmicrogrid voltage regulation with the proposed methodology.
- Li-NMC batteries model evaluation with experimental data for electric vehicle applicationPublication . Baczynska, Aleksandra; Niewiadomski, Waldemar; Gonçalves, Ana; Almeida, Paulo; Luís, RicardoThe aim of the paper is to present the battery equivalent circuit for electric vehicle application. Moreover, the model described below is dedicated to lithium-ion types of batteries. The purpose of this paper is to introduce an efficient and transparent method to develop a battery equivalent circuit model. Battery modeling requires, depending on the chosen method, either significant calculations or a highly developed mathematical model for optimization. The model is evaluated in comparison to the real data measurements, to present the performance of the method. Battery measurements based on charge/discharge tests at a fixed C-rate are presented to show the relation of the output voltage profiles with the battery state of charge. The pulse discharge test is presented to obtain the electric parameters of the battery equivalent circuit model, using a Thevenin circuit. According to the Reverse Trike Ecologic Electric Vehicle (VEECO RT) characteristics used as a case study in this work, new values for vehicle autonomy and battery pack volume based on lithium nickel manganese cobalt oxide cells are evaluated.
- Powertrain test bench systemPublication . Fonte, Pedro M; Almeida, Paulo; Luís, Ricardo; Pereira, Rita; Chaves, MiguelIn parallel with major automotive manufacturers, some smaller companies are trying to launch their own electric or hybrid-propulsion models. During the development of these prototypes some tests must be done, namely consumption, autonomy, batteries state-of-charge, gradability, among others. The results of these tests can lead changes in design, motorization or battery packages. This paper presents a powertrain test bench system in order to test electrical vehicles. Regarding the automobile sector, and due to EU ruling, it is intended to enable the test bench to apply the Worldwide Harmonized Light Vehicles Test Cycle. Having a laboratorial test bench that can emulate vehicle dynamics under a specific drive cycle will allow small automotive manufacturers to confirm compliance with the mandatory drive cycles during different stages of their development. Nevertheless, other electric vehicles (EV) like boats or trains, can also be tested since the mathematical models of their dynamics are available.
- Novel design of the converter for an active UPS application based on Marx modulator concept with supercapacitorsPublication . Pestana, Celso; Canacsinh, Hiren; Chaves, Miguel; Gamboa, Paulo; Cordeiro, Armando; Luís, Ricardo; Martins, Ana Alexandra; Encarnação, Luís; Pereira, Fernando; Silva, José Fernando; Santos, NunoA new Marx modulator 4-leg multilevel converter is proposed to replace the well-known 4-leg inverter fed from batteries in Uninterruptible Power Supply (UPS) applications. The novel design concept for the Marx modulator based multilevel converter is presented and described. Each leg uses 2 Marx modulator modules, each one using an Electrochemical Double-Layer Capacitor (EDLC) (also known as supercapacitor (SC)) energy storage bank. The new topology concept enables multilevel operation with five voltage level per phase, allowing high quality voltage and current waveforms, distributed supercapacitor storage and reduction of supercapacitor bank voltage. The proposed converter can operate as UPS or as Active Power Filter (APF), powering non-linear or/and unbalanced loads, while balancing each leg supercapacitor voltage. A control strategy to choose the redundant vector configuration to balance the supercapacitor voltages is explained. Simulation results are presented for a Marx modulator based interactive 40 kVA UPS.
- Optimal brake specific fuel consumption trajectory for stand-alone variable speed Diesel Gen-SetPublication . Luís, Ricardo; Quadrado, Jose Carlos; Silva, José FernandoEnergy efficiency plays an important role to the CO2 emissions reduction, combating climate change and improving the competitiveness of the economy. The problem presented here is related to the use of stand-alone diesel gen-sets and its high specific fuel consumptions when operates at low loads. The variable speed gen-set concept is explained as an energy-saving solution to improve this system efficiency. This paper details how an optimum fuel consumption trajectory based on experimentally Diesel engine power map is obtained.
- Design of single phase SiC bidirectional DC-AC converter with low-cost PLL for power factor correctionPublication . Bento, Alexandre; André, Sérgio; Luís, Ricardo; Silva, J. FernandoThe paper presents the design stages of a single-phase Silicon Carbide bidirectional DC-AC converter. This includes the LCL filter design responsible to meet grid connection requirements. A 3kW laboratory prototype of the power converter is built employing a low-cost phase locked loop and its results are presented. The design of the low-cost phase locked loop and its implementation are depicted in some detail.
- Transformerless ultra-high gain buck-boost DC-DC converter with single-switch of reduced voltage stressPublication . Cordeiro, Armando; Gamboa, Paulo; Luís, Ricardo; Fonte, Pedro M; Monteiro, Joaquim; Martins, João F.; Silva, J. Fernando; Foito, Daniel; Fernao Pires, VitorThis paper introduces a new DC-DC power converter topology capable of both step-up and step-down voltage conversion, with an exceptionally high voltage gain ratio.. Besides the high extension of the voltage gain range, the converter is also characterized by the use of a single switch. Moreover, the stress imposed on the switch's voltage is minimized, enabling the utilization of low-voltage, low RDS-ON MOSFETs. Consequently, this modification leads to reduced costs and losses associated with switch conduction and turn ON. Another aspect concerning the proposed converter is that the input current exhibits a continuous behavior, which can be significant for various applications. The paper provides insights into the operational performance, steady state behavior, and mathematical underpinnings of the proposed dc-dc converter. Comparative evaluation of the static voltage gain of the proposed converter and other topologies with comparable characteristics will also be shown. Verification of the presented converter's key features are conducted through both simulation and experimental assessments using a 440-W laboratory prototype. Through these analyses, the efficacy and viability of the modified coupled-inductor SEPIC converter with enhanced voltage gain capability are confirmed.
- Output voltage quality evaluation of stand-alone four-leg inverters using linear and non-linear controllersPublication . Luís, Ricardo; Silva, José Fernando; Quadrado, José CarlosThis paper presents the design and experimental voltage quality evaluation of controllers for the output voltages of 3-phase four-leg voltage source inverters. These inverters are needed in stand-alone power systems to supply linear and non-linear, balanced or unbalanced loads with constant RMS value voltages at fixed frequency. Comparisons include closed loop outer voltage controllers based on predictive, sliding mode and decoupled proportional-integral controllers in dqo synchronous space, fitted with an inner hysteretic current loop vector controller in alpha beta gamma space. The 3-phase four-leg VSI output voltages waveform quality is analysed under unbalanced and non-linear loads.
- A Novel Multilevel T-Type Indirect Matrix Converter for Three-phase Open-end AC LoadsPublication . Bento, Alexandre; Luís, Ricardo; Pinto, Sonia; Silva, J. FernandoIn this work a novel topology featuring an Indirect Matrix Converter (IMC) supplying a three-phase openend load is proposed to allow multiple levels of voltage while reducing common mode voltages (CMV) at load terminals. The topology features a T-Type three phase inverter connected to the grid neutral terminal, allowing phase to phase or phase to neutral voltages to be supplied to the load. A comparison with the already known IMC open-end load scheme, based on two voltage source inverters (VSI), is performed achieving promising results in terms of Common Mode Voltage reduction at the load terminals, while achieving current waveforms with lower distortion. The improvement of CMV waveforms is useful for motor drives, reducing drive bearing currents and increasing overall lifespan.
- ESS design and management considering solar PV to fed off-grid EV chargerPublication . Santos, Diogo; Fonte, Pedro M; Pereira, Rita; Barata, Filipe; Almeida, Paulo; Cordeiro, Armando; Luís, Ricardo; Fernao Pires, VitorThe increase of electric vehicles creates several challenges to the electric grid, mainly in those with weak power or off-grid. DC microgrids are becoming more and more important in the context of renewable energy sources, where solar PV systems are dominant. In this paper is proposed the design of a DC system to charge electric vehicles using PV generation and a battery storage system. A single DC-DC converter is used to operate the solar PV array with maximum power point tracking method and controls power flow from PV to storage battery and to the EV, operating as DC EV charger. The operation under various loading conditions is discussed. The performance of the proposed solution was simulated using MATLAB/Simulink software.