Ph.D. Thesis Modular Multiport Power Converter Topologies for Electric Vehicle Charging Stations by Ngoc Dat Dao-Graduate School of Yeungnam University Department of Electrical Engineering-

 Ph.D. Thesis Modular Multiport Power Converter Topologies for
Electric Vehicle Charging Stations
Graduate School of Yeungnam University
Department of Electrical Engineering
Major in Control and Electric Machinery  Power Conversion
by Ngoc Dat Dao

Advisor: Professor Dong-Choon Lee

August 2021

Abstract 

The main objective of this thesis is to develop converter topologies with high efficiency and low cost for fast charging stations. Based on the investigation of different power conversion structures for fast charging stations, new topologies have been derived, which can offer additional benefits to EV fast charging stations. Firstly, a novel isolated three-port DC/DC converter is proposed, which is based on a series resonant converter (SRC) and a dual active bridge (DAB) converter for electricvehicle (EV) charging stations with fast and slow charging functions. With this three-port structure, the proposed converter has fewer components, which results in lower system cost and volume compared with separate charger systems. A simple control method using phase shift and frequency modulations was developed to control the output power of the fast and slow charging ports simultaneously. An optimal phase shift angle was also derived to minimize the transformer current for when only the DAB converter is operated for slow charging. To verify the converter operation, a 5-kW SiC-based prototype with a power density of 2.74-kW/dm3 was built and tested with an input voltage of 600-V. A high efficiency performance over a wide output voltage range has been achieved, and the peak efficiency is 98.2% at the rated conditions Secondly, a half-bridge bidirectional isolated matrix-based AC/DC converter is proposed for compact AC/DC power stages in fast charging stations. The converter can control not only the DC voltage or current, but also the power factor of the AC current with a single conversion stage, which helps to achieve a higher power density with a lower complexity. The converter operates with zero-voltage switching (ZVS) or zero-current switching (ZCS) in all switches. Hence, the switching frequency of the converter can be increased higher, leading to smaller passive components. Besides the simple circuit, the modulation scheme derived from time domain analyses is also easy to implement. The proposed topology has been verified by experimental results for a 2-kW SiC-based prototype. A high efficiency of 96.8 % was achieved at a full load condition. The current THD is lower than 4 % and the power density is 1.8-kW/dm3. Furthermore, an experiment for two modules has been carried out to demonstrate the feasible of the proposed converter for modular SST-based charging stations. Finally, a novel semi-modular three-phase AC/DC structure is proposed for SST-based fast charging stations. The proposed system employs single-stage indirect matrix-based AC/DC converters. A single full-bridge rectifier is used for each phase of the medium voltage (MV) grid so that each AC/DC module does not need a voltage rectifier. As a result, the number of semiconductor devices in the proposed system is reduced significantly compared with other existing SST-based systems. A decentralized control scheme without high-speed communication has been developed to regulate the input and output currents while keeping the voltages of each module balance. A design of a 360-kW system has been carried out to evaluate the efficiency of the proposed system, which is 97.7 % at rated power. With delta connection in three-phase system, a third harmonic current can be injected to the phase currents to increase the output current and power by 15 %. Simulation results for a 360-kW 3.3-kV system are provided to verify the performance of the proposed system. Finally, a 3-kW hardware prototype has been built and tested to demonstrate the feasibility of the proposed system.

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Isolated DC-DC Power Converters for Simultaneous Charging of Electric Vehicle Batteries: Research Review, Design, High-Frequency Transformer Testing, Power Quality Concerns, and Future-----Srinath Belakavadi Sudarshan and Gopal Arunkumar

Isolated DC-DC Power Converters for Simultaneous Charging of Electric Vehicle Batteries: Research Review, Design, High-Frequency Transformer Testing, Power Quality Concerns, and Future-----Srinath Belakavadi Sudarshan and Gopal Arunkumar 

 Abstract: 

The transportation industry is transitioning from conventional Internal Combustion Engine Vehicles (ICVs) to Electric Vehicles (EVs) due to the depletion of fossil fuels and the rise in nontraditional energy sources. EVs are emerging as the new leaders in the industry. Some essential requirements necessary for the widespread adoption of EVs include sufficient charging stations with numerous chargers, less to no wait time before charging, quick charging, and better range. To enable a quicker transition from ICVs to EVs, commercial organizations and governments would have to put in a mammoth effort, given the low number of installed chargers in developing nations such as India. One solution to lower the waiting time is to have multiple vehicles charging simultaneously, which might involve charging two- and four-wheelers simultaneously, even though their battery voltage ratings differ. This paper begins by providing the details of the power sources for EV charging, the charging levels and connector types, along with the specifications of some of the commercial chargers. The necessity of AC-DC converters in EV charging systems is addressed along with the power quality concerns due to the increased penetration of EVs. Next, a review of the existing research and technology of isolated DC-DC converters for simultaneous charging of EV batteries is provided. Further, several potential isolated DC-DC converter topologies for simultaneous charging are described with their design and loss estimation. A summary of the existing products and projects with simultaneous charging features is provided. Finally, insight is given into the future of simultaneous charging.

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https://www.mdpi.com/2071-1050/15/3/2813

Power Electronics Converters and Regulators (Language: English) Authors: Branko L. Dokic , Branko Blanusa

 

Novos desafios para a Eletrônica de Potência com o advento das redes inteligentes-Dr. JOSE NTENOR POMILI-UNICAMP-SÃO PAULO-BRASIL

 

Técnicas de control para la conexión en paralelo de inversores aplicadas a convertidores de interconexión entre los buses de CC y CA de microrredes híbridas e inversores fotovoltaicos centralizados de alta potencia---DEPARTAMENTO DE INGENIERÍA ELECTRÓNICA Grupo de Sistemas Electrónicos Industriales

Técnicas de control para la conexión en paralelo de inversores aplicadas a convertidores de interconexión entre los buses de CC y CA de microrredes híbridas e inversores fotovoltaicos centralizados de alta potencia-

DEPARTAMENTO DE INGENIERÍA ELECTRÓNICA Grupo de Sistemas Electrónicos Industriales

 Tesis Doctoral Presentada por: Marian Liberos Mascarell 

Dirigida por: Dr. Emilio Figueres Amorós Dr. Gabriel Garcerá Sanfelíu Valencia, Abril 2021 UNIVERSIDAD POLITECNICA DE VALENCIA 

 Resumen 

En este trabajo se proponen técnicas de control específicas para la paralelización de inversores sin transformador conectados a red, en aplicaciones de interconexión de buses de microrredes híbridas e instalaciones fotovoltaicas de gran potencia. La paralelización de inversores presenta múltiples ventajas como la modularidad, la redundancia o la flexibilidad para ampliar la potencia de un sistema o de una instalación. En el caso de inversores fotovoltaicos centralizados, también permite la conexión/desconexión de módulos inversores conectados en paralelo permitiendo una mayor eficiencia global cuando se trabaja a bajas potencias. Sin embargo, la paralelización de inversores provoca la aparición de corrientes de circulación que pueden provocar efectos indeseables en el sistema o en la instalación. Las contribuciones que se llevan a cabo en esta tesis están todas ellas orientadas a la mejora de la operación de inversores en paralelo en las aplicaciones descritas y son las siguientes: 1) Se presenta un modelo preciso en pequeña señal de n inversores conectados en paralelo con filtro de conexión a red LCL, en el cual se tienen en consideración los términos de acoplamiento entre fases de los inductores trifásicos. 2) Se propone una técnica de control en la que se emplean n-1 lazos de regulación que controlan la componente homopolar de las corrientes e imponen un valor nulo en régimen permanente, a fin de eliminar las corrientes de circulación. 3) Se propone el uso de moduladores en espacio vectorial de tres dimensiones (3D-SVM) para implementar el control de la componente homopolar de las corrientes. 4) Se muestran resultados analíticos, de simulación y experimentales que validan el esquema de control propuesto considerando la aparición de corrientes de circulación debido a distintos factores: desbalanceo de inductancias entre las fases de un inversor y de distintos inversores, desbalanceo de potencia entre inversores y empleo de modulaciones distintas en los inversores conectados en paralelo. Los ensayos experimentales se realizan sobre un convertidor trifásico de 10 kW formado por la conexión en paralelo de dos módulos de 5 kW cada uno. 5) Se muestran resultados de simulación y experimentales de la aplicación de las técnicas de reducción de corrientes de circulación a convertidores de interconexión entre los buses de alterna y continua de microrredes híbridas. Los ensayos experimentales se particularizan a un convertidor trifásico de 7.5 kW formado por un módulo de 5 kW y otro de 2.5 kW conectados en paralelo, emulando una eventual ampliación de potencia del 50 %. 6) Se lleva a cabo el estudio por simulación de un sistema fotovoltaico de 2 MW compuesto por cuatro inversores de 500 kW conectados en paralelo, demostrando que el control de las componentes homopolares de las corrientes reduce en gran medida el valor de las corrientes de circulación y mejora el desempeño de la instalación. 7) Por último, se propone una técnica de control para mejorar la eficiencia global de inversores fotovoltaicos centralizados de potencia elevada, el cual se basa en la utilización de modelos funcionales bidimensionales de eficiencia para activar/desactivar los módulos de potencia en función del punto de operación del campo fotovoltaico.

 Abstract 

In this work they have been proposed specific control techniques for the parallelization of transformerless inverters connected to the grid in two specific applications: i) the interlinking converter between ac and dc bus of hybrid microgrids and ii) high power photovoltaic farms. Paralleling of inverters presents some advantages as modularity, redundancy or flexibility for increasing the power of a system or of a plant. In photovoltaic centralized inverters, the parallel inverters can be connected and disconnected in order to improve the global efficiency when the system works at low power. However, the inverters paralleling causes the appearance of circulating currents which can produce undesirable effects in the system or in the plant. The contributions that are carried out in this thesis are all of them aimed at improving the operation of parallel inverters in the described applications and they are as follows: 1) It has been presented an accurate small signal model of n parallel inverters with an LCL grid filter, in which the mutual coupling terms of the three-phase inductors has been considered. 2) It has been proposed a control technique with n-1 control loops that control the zero-sequence current component by setting a zero value in steady state, looking for eliminating the circulating currents. 3) It has been proposed the use of three-dimension space vector modulator (3D-SVM) to implement the zero-sequence currents control. 4) The analytical results have been validated by means of simulation and experimental results, showing the performance of the proposed control scheme considering the appearance of circulating currents due to different factors: i) inductor imbalances between the phases of an inverter or ii) between different inverters, iii) power imbalances between inverters and iv) the use of different modulation techniques in the parallel inverters. The experimental tests have been carried out on a 10 kW three-phase converter composed by the parallel connection of two 5 kW modules. 5) They have been shown both simulation and experimental results of the application of circulating current reduction techniques to interlinking converters between the DC and the AC buses of hybrid microgrids. The experimental tests have been particularized to a 7.5 kW three-phase converter

composed by a 5 kW and a 2.5 kW module connected in parallel, emulating an eventual 50 % power expansion. 6) Is has been carried out the simulation study of a 2 MW photovoltaic system composed by four 500 kW inverters connected in parallel, showing that the control of the zero-sequence currents greatly reduces the value of the circulating currents and improve the system performance. 7) Finally, it has been proposed a control technique for the improvement of the global efficiency of high power photovoltaic centralized inverters, which is based in the use of bidimensional functional efficiency models to activate/deactivate the power modules according to the operation point of the photovoltaic farm.

VIEW FULL TEXT:https://riunet.upv.es/handle/10251/168190