Milestone@UM, Volume 6, Number 2, 2017

The editor rearranged the sequence of volume's number

New SR drive with integrated charging capacity for plug-in hybrid electric vehicles (PHEVs)

Plug-in hybrid electric vehicles (PHEVs) provide much promise in reducing greenhouse gas emissions and, thus, are a focal point of research and development. Existing on-board charging capacity is effective but requires the use of several power conversion devices and power converters, which reduce reliability and cost efficiency. This paper presents a novel three-phase switched reluctance (SR) motor drive with integrated charging functions (including internal combustion engine and grid charging). The electrical energy flow within the drivetrain is controlled by a power electronic converter with less power switching devices and magnetic devices. It allows the desired energy conversion between the engine generator, the battery, and the SR motor under different operation modes. Battery-charging techniques are developed to operate under both motor-driving mode and standstill-charging mode. During the magnetization mode, the machine's phase windings are energized by the dc-link voltage. The power converter and the machine phase windings are controlled with a three-phase relay to enable the use of the ac-dc rectifier. The power converter can work as a buck-boost-type or a buck-type dc-dc converter for charging the battery. Simulation results in MATLAB/Simulink and experiments on a 3-kW SR motor validate the effectiveness of the proposed technologies, which may have significant economic implications and improve the PHEVs' market acceptance

Technical Challenges and Solutions of a three-phase bidirectional two stage Electric Vehicle charger

The sustainability of the power grid owing to the building strain of the ever-growing demand for electrical energy urges innovative and more practical solutions that enable active participation of end-users in stable and reliable management of power systems. One of the emerging projections of such a two-way exchange of electrical power between the grid and consumers is the developing field of bidirectional energy trade between power providers and electric vehicle owners. A bidirectional, three-phase, two-stage off-board electric vehicle EV charger design is proposed in this research. The first stage acts as alternating current AC to direct current DC converter during charging operation and behaves as three phase inverter and power factor corrector when energy exchange is from vehicle to grid. The second stage is a bidirectional DC-DC level converter linked to the first stage by a DC bus. The grid side filter is designed to enable the grid interfacing without any significant power quality problems. The proposed design, topology and the devised control infrastructure are tested through simulations on MATLAB/Simulink platform by interfacing the charger to a three-phase AC microgrid and the results approve the performance of the proposed charging topology

Split converter-fed SRM drive for flexible charging in EV/HEV applications

Electric vehicles (EVs) and hybrid EVs are the way forward for green transportation and for establishing low-carbon economy. This paper presents a split converter-fed four-phase switched reluctance motor (SRM) drive to realize flexible integrated charging functions (dc and ac sources). The machine is featured with a central-tapped winding node, eight stator slots, and six rotor poles (8/6). In the driving mode, the developed topology has the same characteristics as the traditional asymmetric bridge topology but better fault tolerance. The proposed system supports battery energy balance and on-board dc and ac charging. When connecting with an ac power grid, the proposed topology has a merit of the multilevel converter; the charging current control can be achieved by the improved hysteresis control. The energy flow between the two batteries is balanced by the hysteresis control based on their state-of-charge conditions. Simulation results in MATLAB/Simulink and experiments on a 150-W prototype SRM validate the effectiveness of the proposed technologies, which may provide a solution to EV charging issues associated with significant infrastructure requirements

A Transformerless PCB Based Medium-Voltage Multilevel Power Converter with A DC Capacitor Balancing Circuit and Algorithm

This dissertation presents a new method of constructing a transformerless, voltage-sourced, medium-voltage multilevel converter using existing discrete power semiconductor devices and printed circuit board technology. While the approach is general, it is particularly well-suited for medium-voltage converters and motor-drives in the 4.16 kV, 500 - 1000 kW range. A novel way of visualizing the power stage topology is developed which allows simplified mechanical layouts while managing the commutation paths. Using so many discrete devices typically drives cost and complexity of the gate-drive system including its control and isolation; a gate-drive circuit is presented to address this problem. As with most multilevel topologies, the dc-link voltages must be balanced during operation. This is accomplished using an auxiliary circuit made up of the same power stage and an associated control algorithm. Experimental results are presented for a 4.16 kV, 746 kW, five-level power converter prototype. This dissertation also analyzes a new capacitor voltage-balancing converter along with a novel capacitor voltage balancing control algorithm. Analysis of the inverter system provides a new description of capacitor voltage stability as a function of system operating conditions

CONVERTIDOR CD/CD MULTI-ENTRADA CON RESPALDO DE BATERÍAS PARA APLICACIONES RENOVABLES

ResumenLos paneles fotovoltaicos (PV por sus siglas en inglés) se conectan, tradicionalmente, en módulos para incrementar la potencia del sistema; y para obtener el punto de máxima potencia se puede utilizar ya sea un convertidor en cada panel o un convertidor de múltiples entradas en el que puede controlarse de manera independiente cada una de ellas. En este artículo se propone una topología multi-entradas, basada en el convertidor Flyback, el cual podría regular de manera independiente cada una de las entradas, además de permitir la carga/descarga de una batería para funcionar en modo respaldo.El convertidor propuesto es descrito y simulado con el propósito de demostrar su factibilidad.Palabra(s) Clave(s): Cargador/descargador de baterías, Convertidor Flyback, Fuente de energía renovable, Topología multi-entrada. MULTI-INPUT CD/CD CONVERTER WITH BATTERY BACKUP FOR RENEWABLE APPLICATIONSAbstractPhotovoltaic PV panels are traditionally arranged in more than one modules in order to increase the power system; however in this configuration with the purpose of obtain the maximum power point a converter for each panel could be used, or a multi-input converter that is able to control independently each input. In this paper is proposed a multi-input topology based on the Flyback converter, which should have the capability of regulate independently each input, but also the proposal provides the battery charger/discharger function as backup.The proposed converter is described and simulated, showing its feasibility.Keywords: Battery Charger/discharger, Flyback converter, Multi-input topology, Renewable energy source

Contributions to the efficiency and safety of stand-alone DC microgrids

Currently, the distributed generation based on renewable energy sources is mainly DC. Those DC systems are used diverse applications such as airplanes, automobiles, ships, spaceships, computers, servers, telecommunications stations, among others. This thesis considers an isolated DC microgrid architecture composed of a renewable source, an energy storage system, and a DC load. The thesis is aimed at identifying and solving efficiency and safety problems at the source, the DC bus, and the load. During the development of this Thesis, six contributions to the state-of-the-art of DC microgrids were obtained. The first contribution is the mathematical model of a distributed maximum power point platform formed by multiple module-converter sets connected in series, which can be implemented in different programming languages and deployed on multiple platforms to evaluate optimization strategies. The second contribution is a vectorial MPPT algorithm for a distributed photovoltaic system, based in the perturb and observe algorithm. This algorithm provides a satisfactory trade-off between implementation cost and energy production since it uses a single I/V sensor. The third contribution is a reconfiguration algorithm that optimizes the electrical connections of a commercial photovoltaic array, which enables to maximize the energy extraction under arbitrary shading conditions. The fourth and fifth contributions are two control strategies, based on sliding-modes, designed for a charger/discharger DC/DC converter. Those solutions enable to regulate the voltage on the DC-bus of the microgrid to improve the microgrid safety. One of the strategies considers the current of the DC-bus into the sliding surface, which gives a better performance in terms of overshoot and settling time of the DC bus voltage. The final contribution concerns a control strategy, also based on sliding modes, to regulate a point-of-load DC/DC converter. Such a contribution enables to improve the conversion efficiency, and at the same time, to improve the load safety by reducing the current and voltage ripples delivered by the converter. Finally, those contributions improve the electrical efficiency and operational safety of DC microgrids based on renewable sources. The results obtained in this thesis were published in five journals articles and three communications to conferences. From those, three articles were published in Q1 journals, one article was published in Q3 journal, and another one was published in a Colombian journalResumen: Actualmente, la generación distribuida basada en fuentes de energía renovable es principalmente DC. Estos sistemas DC son utilizados en aviones, automóviles, barcos, naves espaciales, computadores, servidores, estaciones de telecomunicaciones, etc. Esta Tesis considera una arquitectura de microrred DC aislada compuesta por una fuente renovable, un sistema de almacenamiento de energía y una carga DC. La tesis tiene como objetivo identificar y solucionar problemas de eficiencia y seguridad de operación en la fuente, en el bus DC y en la carga. Durante el desarrollo de esta Tesis se obtuvieron seis aportes al estado del arte en microrredes DC. La primera contribución es el modelo matemático de una plataforma de seguimiento del punto de máxima potencia formada por múltiples conjuntos panel-convertidor conectados en serie, el cual se puede implementar en diferentes lenguajes de programación y desplegar en múltiples plataformas para evaluar estrategias de optimización. La segunda contribución es un algoritmo MPPT vectorial para un sistema fotovoltaico distribuido, basado en el algoritmo de perturbar y observar. Este algoritmo proporciona una compensación satisfactoria entre el costo de implementación y la producción de energía, ya que utiliza un solo sensor de I/V. La tercera contribución es un algoritmo de reconfiguración que optimiza las conexiones eléctricas de un arreglo de paneles fotovoltaicos comercial, el cual permite maximizar la extracción de energía bajo condiciones arbitrarias de sombreado. La cuarta y quinta contribución son dos estrategias de control, basadas en modos deslizantes, diseñadas para un convertidor DC/DC cargador/descargador. Estas soluciones permiten regular el voltaje del bus DC de la microrred para mejorar la seguridad de su operación. Una de las estrategias considera la corriente del bus DC en la superficie deslizante, lo cual da un mejor desempeño en cuanto al sobreimpulso y el tiempo de establecimiento del voltaje del bus DC. La contribución final es una estrategia de control, también basada en modos deslizantes, para regular un convertidor DC/DC point-of-load. Esta contribución permite mejorar la eficiencia de la conversión y al mismo tiempo mejorar la seguridad operativa de la carga reduciendo el rizado de voltaje y corriente entregado por el convertidor. Finalmente, estas contribuciones mejoran la eficiencia eléctrica y la seguridad operativa de microrredes DC basadas en fuentes de energía renovable. Los resultados obtenidos en esta Tesis fueron publicados en cinco artículo de revista y tres ponencias en conferencias. De estos, tres artículos fueron publicados en revistas clasificadas en Q1, un artículo fue publicado en una revista con clasificación Q3 y otro en una revista colombianaDoctorad

Integrated DC-DC Charger Powertrain Converter Design for Electric Vehicles Using Wide Bandgap Semiconductors

Electric vehicles (EVs) adoption is growing due to environmental concerns, government subsidies, and cheaper battery packs. The main power electronics design challenges for next-generation EV power converters are power converter weight, volume, cost, and loss reduction. In conventional EVs, the traction boost and the onboard charger (OBC) have separate power modules, passives, and heat sinks. An integrated converter, combining and re-using some charging and powertrain components together, can reduce converter cost, volume, and weight. However, efficiency is often reduced to obtain the advantage of cost, volume, and weight reduction.An integrated converter topology is proposed to combine the functionality of the traction boost converter and isolated DC-DC converter of the OBC using a hybrid transformer where the same core is used for both converters. The reconfiguration between charging and traction operation is performed by the existing Battery Management System (BMS) contactors. The proposed converter is operated in both boost and dual active bridge (DAB) mode during traction operation. The loss mechanisms of the proposed integrated converter are modeled for different operating modes for design optimization. An aggregated drive cycle is considered for optimizing the integrated converter design parameters to reduce energy loss during traction operation, weight, and cost. By operating the integrated converter in DAB mode at light-load and boost mode at high-speed heavy-load, the traction efficiency is improved. An online mode transition algorithm is also developed to ensure stable output voltage and eliminate current oscillation during the mode transition. A high-power prototype is developed to verify the integrated converter functionality, validate the loss model, and demonstrate the online transition algorithm. An automated closed-loop controller is developed to implement the transition algorithm which can automatically make the transition between modes based on embedded efficiency mapping. The closed-loop control system also regulates the integrated converter output voltage to improve the overall traction efficiency of the integrated converter. Using the targeted design approach, the proposed integrated converter performs better in all three aspects including efficiency, weight, and cost than comparable discrete solutions for each converter

A DUAL INPUT BIDIRECTIONAL POWER CONVERTER FOR CHARGING AND DISCHARGING A PHEV BATTERY

This thesis looks at a new design for a dual input bidirectional power converter (DIBPC) for charging and discharging a PHEV battery. The design incorporates a power factor correcting rectifier aimed at optimizing the battery charging efficiency from either a 120 VAC or 240 VAC source or discharging the battery to a usable AC voltage at 120 VAC. For simplicity and cost-effectiveness, the DIBPC is constructed using a standard IGBT 6-pack intended for motor control. The DIBPC is designed specifically to provide efficient operation with 120 VAC and 240 VAC inputs while achieving a very low THDI. The DIBPC also needs to be able to provide AC output power at 120 VAC with the flexibility to output at 240 VAC in the future. The DIBPC was tested first in simulation, and then in experimentation. The DIBPC consists of two portions, an AC/DC converter and a DC/DC converter. Although both were simulated, only the AC/DC converter was constructed. Testing under various load values and in each mode of operation provided ample data to show the DIBPC can meet all design goals. When operating as a rectifier, the DIBPC produces between 7.4% and 13.35% THDI and a DC voltage ripple of 8 VP-P or less at 400 VDC. At 120 VAC and 240 VAC an efficiency of 84.5% and 94.6% was achieved, respectively. When operating as an inverter, the DIBPC produces less than 6% THDV and 7% THDI, while outputting a voltage between 114 and 128 VRMS. Overall, the THDI in the charging mode easily meets and exceeds all standards and design constraints set forth, including IEC 61000-3-4. The efficiency with a 120 VAC input, however, is less than expected - about 84%

Design, Modeling, And Control Of Three-port Converters For Solar Power Applications

This paper describes the results of research into multi-port converter design and control, specifically a pair of three-port topologies based on the half-bridge and full-bridge topologies. These converters are capable of simultaneous and independent regulation of two out of their three ports, while the third port provides the power balance in the system. A dynamic model was developed for each topology to aid in testing and for designing the control loops. The models were then used to design the control structures, and the results were tested in Simulink. In addition, a basic outline of a system level architecture to control multiple converters working in parallel is presented. To improve the reliability of this system, output current sharing controls were also developed. Finally, one of the topologies is analyzed in detail in order to obtain a set of design equations that can be used to improve the efficiency, weight, and cost of the converter for a specific application