A Bidirectional Soft-Switched DAB-Based Single-Stage Three-Phase AC–DC Converter for V2G Application

In vehicle-to-grid applications, the battery charger of the electric vehicle (EV) needs to have a bidirectional power flow capability. Galvanic isolation is necessary for safety. An ac-dc bidirectional power converter with high-frequency isolation results in high power density, a key requirement for an on-board charger of an EV. Dual-active-bridge (DAB) converters are preferred in medium power and high voltage isolated dc-dc converters due to high power density and better efficiency. This paper presents a DAB-based three-phase ac-dc isolated converter with a novel modulation strategy that results in: 1) single-stage power conversion with no electrolytic capacitor, improving the reliability and power density; 2) open-loop power factor correction; 3) soft-switching of all semiconductor devices; and 4) a simple linear relationship between the control variable and the transferred active power. This paper presents a detailed analysis of the proposed operation, along with simulation results and experimental verification

Power Electronic Architecture for Multi-Vehicle Extreme Fast Charging Stations

Electric vehicles (EV) are quickly gaining popularity but limited driving range and a lack of fast charging infrastructure are preventing widespread use when compared with gas powered vehicles. This gave rise to the concept of multi-vehicle extreme fast charging (XFC) stations. Extreme fast charging imposes challenges in the forms of power delivery, battery management, and energy dispatch. The extreme load demand must be handled in such a way that users may receive a timely charge with minimal impacts on the electric grid. Power electronics are implemented to address these challenges with highly power dense and efficient solutions. This work explores a power electronic architecture as one such solution. The system consists of three parts: a cascaded H-bridge (CHB) active rectifier that interfaces to a medium voltage (MV) grid, a dual active bridge (DAB) based solid state transformer (SST) that provides isolation and forms a low voltage DC (LVDC) bus, and full bridge DC-DC converters configured as partial power converters (PPC) that interface with the vehicle battery

Review of Electric Vehicle Charging Technologies, Configurations, and Architectures

Electric Vehicles (EVs) are projected to be one of the major contributors to energy transition in the global transportation due to their rapid expansion. The EVs will play a vital role in achieving a sustainable transportation system by reducing fossil fuel dependency and greenhouse gas (GHG) emissions. However, high level of EVs integration into the distribution grid has introduced many challenges for the power grid operation, safety, and network planning due to the increase in load demand, power quality impacts and power losses. An increasing fleet of electric mobility requires the advanced charging systems to enhance charging efficiency and utility grid support. Innovative EV charging technologies are obtaining much attention in recent research studies aimed at strengthening EV adoption while providing ancillary services. Therefore, analysis of the status of EV charging technologies is significant to accelerate EV adoption with advanced control strategies to discover a remedial solution for negative grid impacts, enhance desired charging efficiency and grid support. This paper presents a comprehensive review of the current deployment of EV charging systems, international standards, charging configurations, EV battery technologies, architecture of EV charging stations, and emerging technical challenges. The charging systems require a dedicated converter topology, a control strategy and international standards for charging and grid interconnection to ensure optimum operation and enhance grid support. An overview of different charging systems in terms of onboard and off-board chargers, AC-DC and DC-DC converter topologies, and AC and DC-based charging station architectures are evaluated

Power Conditioning for Plug-In Hybrid Electric Vehicles

Plugin Hybrid Electric Vehicles (PHEVs) propel from the electric energy stored in the batteries and gasoline stored in the fuel tank. PHEVs and Electric Vehicles (EVs) connect to external sources to charge the batteries. Moreover, PHEVs can supply stand-alone loads and inject power to the grid. Such functionalities have been defined as Vehicle to House (V2H) and Vehicle to Grid (V2G) and promoted by national and international policies such as the Energy Independency and Security Act (EISA) of 2007, enacted by the United States Congress. Exchanging energy between the vehicle and external sources is performed by the vehicular power conditioner (VPC). This dissertation proposes a design procedure for VPCs. The research mainly focuses on the VPC’s power converter design. A conceptual design approach is proposed to select the proper power converter topologies according to the determined power conditioning needs. The related standards and previous works are reviewed to determine the design guidelines. A set of specifications are introduced for a three port onboard VPC. This VPC is a reference for designs, simulations and experiments. The reference VPC is implemented with a modular three-stage isolated topology that utilizes voltage source ac-dc converters as the power conditioning stages. The multiport extension of this topology extends the vehicular power conditioning concept into a novel vehicular integrated power system. All the vehicle’s electric sources and loads can exchange energy in the described multiport integrated power system. Novel design methods are proposed for the power converter, filters, magnetic circuit and control of the VPC. The practical challenges of the VPC development are analyzed. The major contributions of this dissertation include a pioneer grounding scheme for VPC considering the vehicular standards, a novel modeling approach for the Snubberless Dual Active Bridge (DAB) commutation, an innovative integrated ac inductor, and a new experimental modeling method for multiwinding transformers. The contributions are supported by analyses, simulations, and practical experiments

Three-Phase Unfolding Based Soft DC-Link Converter Topologies for AC to DC Applications

Battery electric vehicles (BEVs) and plugin hybrid electric vehicles (PHEVs) are more efficient than internal combustion-based vehicles. Adaption of EVs will help reduce the carbon emissions produced by the transportation sector. The charging infrastructure has to grow at a rapid pace to encourage EV adaption. Installing higher capacity fast chargers will help alleviate the range anxiety of battery electric vehicle customers. More public charging stations are required for the full adaption of EVs. Utility power is distributed as ‘alternating current.’ A battery requires ‘direct current’ (DC) source to charge it. Hence a power converter that converts AC source to DC source is required to charge an electric vehicle battery. Public transportation is another sector that is adapting electric vehicles at a fast pace. These vehicles require more power to operate and hence have huge battery packs. These vehicles require ultra-high-power charger to keep the charging time reasonable. A 60 Hz stepdown transformer is required at the facility to use the power. The cost and time to install this heavy transformer will inhibit the setting up a charging station. Power converters than can connect to medium voltage directly will eliminate the need for the step-down transformer saving space and cost. Commercially available state-of-the-art fast charging converters are adapted from general purpose commercial and industrial application rectifiers. The efficiencies of these converters tend to be lower (around 94%) due to the two-stage power conversion architecture. All the power that flows from the AC utility grid to charge the battery will be processed and filtered through two power conversion stages. Due to the anticipated increase in demand, there is a renewed interest in developing power converter topologies specific to battery charging applications. The objective here is to develop cheaper and compact power converters for battery charging. This dissertation proposes an innovative quasi-single stage power converter topologies for battery charging applications and direct medium voltage connected converters. The proposed topology fundamentally can achieve higher efficiency and power density than the conventional two-stage based converters. Only one stage requires filtering and incurs power conversion losses. Control burden is usually higher for single stage topologies. Innovative control approaches are presented to simplify the control complexity

Soft-Switching Techniques of Power Conversion System in Automotive Chargers

abstract: This thesis investigates different unidirectional topologies for the on-board charger in an electric vehicle and proposes soft-switching solutions in both the AC/DC and DC/DC stage of the converter with a power rating of 3.3 kW. With an overview on different charger topologies and their applicability with respect to the target specification a soft-switching technique to reduce the switching losses of a single phase boost-type PFC is proposed. This work is followed by a modification to the popular soft-switching topology, the dual active bridge (DAB) converter for application requiring unidirectional power flow. The topology named as the semi-dual active bridge (S-DAB) is obtained by replacing the fully active (four switches) bridge on the load side of a DAB by a semi-active (two switches and two diodes) bridge. The operating principles, waveforms in different intervals and expression for power transfer, which differ significantly from the basic DAB topology, are presented in detail. The zero-voltage switching (ZVS) characteristics and requirements are analyzed in detail and compared to those of DAB. A small-signal model of the new configuration is also derived. The analysis and performance of S-DAB are validated through extensive simulation and experimental results from a hardware prototype. Secondly, a low-loss auxiliary circuit for a power factor correction (PFC) circuit to achieve zero voltage transition is also proposed to improve the efficiency and operating frequency of the converter. The high dynamic energy generated in the switching node during turn-on is diverted by providing a parallel path through an auxiliary inductor and a transistor placed across the main inductor. The paper discusses the operating principles, design, and merits of the proposed scheme with hardware validation on a 3.3 kW/ 500 kHz PFC prototype. Modifications to the proposed zero voltage transition (ZVT) circuit is also investigated by implementing two topological variations. Firstly, an integrated magnetic structure is built combining the main inductor and auxiliary inductor in a single core reducing the total footprint of the circuit board. This improvement also reduces the size of the auxiliary capacitor required in the ZVT operation. The second modification redirects the ZVT energy from the input end to the DC link through additional half-bridge circuit and inductor. The half-bridge operating at constant 50% duty cycle simulates a switching leg of the following DC/DC stage of the converter. A hardware prototype of the above-mentioned PFC and DC/DC stage was developed and the operating principles were verified using the same.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

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

Vehicle-to-grid (V2G) Reactive Power Operation Analysis of the EV/PHEV Bidirectional Battery Charger

More battery powered electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) will be introduced to the market in 2013 and beyond. Since these vehicles have large batteries that need to be charged from an external power source or directly from the grid, their charging circuits and grid interconnection issues are garnering more attention. It is possible to incorporate more than one operation mode in a charger by allowing the power to flow bidirectionally. Usually, the bidirectional power transfer stands for two-way transfer of active power between the charger and the grid. The general term of sending active power from the vehicle to the grid is called vehicle to grid (V2G). While plug-in electric vehicles (PEVs) potentially have the capability to fulfill the energy storage needs of the electric grid, the degradation on the battery during this operation makes it less preferable by the auto manufacturers and consumers. On the other hand, the on-board chargers can also supply energy storage system applications such as reactive power compensation, voltage regulation, and power factor correction without the need of engaging the battery with the grid and thereby preserving its lifetime. This study shows the effect of reactive power operation on the design and operation of single-phase on-board chargers that are suitable for reactive power support. It further introduces a classification of single-phase ac-dc converters that can be used in on-board PEV chargers based on their power transfer capabilities in addition to the currently available surveys. The cost of supplying reactive power is also important to effectively evaluate reactive power operation using chargers. There are two major impacts: one is on the converter design (incremental costs) and the other is on the operating electricity costs. Their combination shows the total effect and cost of reactive power operation and can be compared with other options of the utility grid to supply reactive power. Two customer scenarios are investigated to have two options of reactive power support. Level 1 and Level 2 reactive power support are evaluated separately

Power converters in WBG device technology for automotive applications and characterization setups for GaN power transistors

This PhD dissertation envisages the design of innovative power converters exploiting WBG devices to get state-of-the-art performance in products intended for industrial applications of automotive field. The collaborations with different specialized companies, provided the opportunity to access commercially-available state-of-the-art SiC and GaN technologies and the possibility to realize innovative converter prototypes. Concerning SiC technology, the complete design of a $350kW$ Battery Emulator instrument in collaboration with a company leader in the automotive testing sector, was carried out from scratch exploiting state-of-the-art SiC power-modules, planar magnetics and top-notch MCU technologies. Discrete high-voltage GaN switches were exploited in the Power Supplies design for automotive charger application to target improved performances compared to the market state-of-the-art. Specifically, two high-efficiency prototypes, an AC/DC converter and a DC/DC converter of $7.5kW$, have been realized for this purpose. To further investigate the characteristics of state-of-the-art GaN power devices two measurement set-ups have been designed. In particular, the trapping phenomenon causing the collapse of drain current during ON-state with a consequent degradation of ON-resistance has been analyzed

A review on power electronics technologies for electric mobility

Concerns about greenhouse gas emissions are a key topic addressed by modern societies worldwide. As a contribution to mitigate such effects caused by the transportation sector, the full adoption of electric mobility is increasingly being seen as the main alternative to conventional internal combustion engine (ICE) vehicles, which is supported by positive industry indicators, despite some identified hurdles. For such objective, power electronics technologies play an essential role and can be contextualized in different purposes to support the full adoption of electric mobility, including on-board and off-board battery charging systems, inductive wireless charging systems, unified traction and charging systems, new topologies with innovative operation modes for supporting the electrical power grid, and innovative solutions for electrified railways. Embracing all of these aspects, this paper presents a review on power electronics technologies for electric mobility where some of the main technologies and power electronics topologies are presented and explained. In order to address a broad scope of technologies, this paper covers road vehicles, lightweight vehicles and railway vehicles, among other electric vehicles.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UID/CEC/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017, and by the FCT Project new ERA4GRIDs PTDC/EEI-EEE/30283/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT