Highly Efficient SiC Based Onboard Chargers for Plug-in Electric Vehicles

Grid-enabled plug-in electrified vehicles (PEVs) are deemed as one of the most sustainable solutions to profoundly reduce both oil consumption and greenhouse gas emissions. One of the most important realities, which will facilitate the adoption of PEVs is the method by which these vehicles will be charged. This dissertation focuses on the research of highly efficient onboard charging solutions for next generation PEVs. This dissertation designs a two-stage onboard battery charger to charge a 360 V lithium-ion battery pack. An interleaved boost topology is employed in the first stage for power factor correction (PFC) and to reduce total harmonic distortion (THD). In the second stage, a full bridge inductor-inductor-capacitor (LLC) multi-resonant converter is adopted for galvanic isolation and dc/dc conversion. Design considerations focusing on reducing the charger volume, and optimizing the conversion efficiency over the wide battery pack voltage range are investigated. The designed 1 kW Silicon based charger prototype is able to charge the battery with an output voltage range of 320 V to 420 V from 110 V, 60 Hz single-phase grid. Unity power factor, low THD, and high peak conversion efficiency have been demonstrated experimentally. This dissertation proposes a new technique to track the maximum efficiency point of LLC converter over a wide battery state-of-charge range. With the proposed variable dc link control approach, dc link voltage follows the battery pack voltage. The operating point of the LLC converter is always constrained to the proximity of the primary resonant frequency, so that the circulating losses and the turning off losses are minimized. The proposed variable dc link voltage methodology, demonstrates efficiency improvement across the wide state-of-charge range. An efficiency improvement of 2.1% at the heaviest load condition and 9.1% at the lightest load condition for LLC conversion stage are demonstrated experimentally. This dissertation proposes a novel PEV charger based on single-ended primary-inductor converter (SEPIC) and the maximum efficiency point tracking technique of an LLC converter. The proposed charger architecture demonstrates attracting features such as (1) compatible with universal grid inputs; (2) able to charge the fully depleted battery pack; (3) pulse width modulation and simplified control algorithm; and (4) the advantages of Silicon Carbide MOSFETs can be fully manifested. A 3.3 kW all Silicon Carbide based PEV charger prototype is designed to validate the proposed idea

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

High-Frequency Bidirectional DC-DC Converters for Electric Vehicle Applications

As a part of an electric vehicle (EV) onboard charger, a highly efficient, highly compact, lightweight and isolated DC-DC converter is required to enable battery charging through voltage/current regulation. In addition, a bidirectional on-board charger requires the DC-DC converter to achieve bidirectional power flow: grid-to-vehicle (G2V) and vehicle-to-grid (V2G). In this work, performance characteristics of two popular DC-DC topologies, CLLC and dual active bridge (DAB), are analyzed and compared for EV charging applications. The CLLC topology is selected due to its wide gain range, soft-switching capability over the full load range, and potential for a smaller and more compact size. This dissertation outlines the feasibility, analyses, and performance of a CLLC converter investigated and designed to operate at 1 MHz and 3.3 kW for EV onboard chargers. The proposed design utilizes the emerging wide bandgap (WBG) gallium nitride (GaN) based MOSFETs to enable high-frequency switching without sacrificing the conversion efficiency. One of the major challenges in MHz-level power converter design is to reduce the parasitic components of printed circuit boards (PCBs), which can cause faulty triggering of switches leading to circuit failure. An innovative gate driver is designed and optimized to minimize the effect of parasitic components, which includes a +6/-3 V driving logic enhancing the noise immunity of the system. Another challenge is the efficient design of magnetic components, which requires minimizing the impacts of skin and proximity effects on the transformer winding to reduce the conduction loss at high frequencies. A novel MHz-level planar transformer with adjustable leakage inductance is modeled, designed, and developed for the proposed converter. A comprehensive system level power loss analysis is completed and confirmed with the help of experimental results. This is the first prototype of a 3.3 kW power bidirectional CLLC converter operating at 1 MHz operating frequency with 400-450 V input voltage range, 250-420 V output voltage range. The experiment results have successfully validated the feasibility of the proposed converter conforming to the analysis carried out during the design phase. With an appropriate design of driving circuit and control signal, the prototype achieves a peak efficiency of 97.2% with 9.22 W/cm3 (151.1 W/in3) power density which is twice more power dense than other state-of-the-art isolated DC-DC converters

Review on classification of resonant converters for electric vehicle application

The conventional hard-switching converters suffer from the limitations like the upper limit on switching frequency, high electromagnetic interference (EMI), more switching losses, large size, increased weight and low efficiency. To overcome these limitations, resonant converters are popularly used in chargers of electric vehicles (EVs). However, the detailed classification of resonant converters used in EVs is not sufficiently discussed in the literature. The guideline to select a resonant converter based topology required to charge an EV on the basis of its rating is not mentioned. To fill this gap, this paper presents a state-of-art literature survey of various resonant converter based topologies used in chargers of EVs. This paper focuses on a detailed classification of resonant converters used in the second stage of EV chargers. Further, it provides a guideline to designers to choose a converter topology used in the first stage and the second stage of EV charger required based on wattage, unidirectional and bidirectional power flow. Depending on the number of reactive elements present in a given resonant converter topology, these are classified as two-element, three-element, and multi-element resonant converters. Depending upon the connection of inductive (L) and capacitive (C) elements with respect to transformer winding, these converter topologies are further categorized as series, parallel (two-elements), inductor–inductor–capacitor (LLC) (three-element) and capacitor–inductor–inductor–capacitor (CLLC) (Multi-elements). However, the LLC type resonant converters offer high efficiency, zero-voltage switching (ZVS turn-on, turn-off) and low voltage stress on switches and high power density. Therefore, this paper mainly focuses on LLC type resonant converter topology. In addition, various modulation schemes and control schemes for LLC, CLLC resonant converter along with control of active power and reactive power are discussed for vehicle-2-grid (V2G) mode of operation

Analysis and Development of Multiple Phase Shift Modulation in A SiC-Based Dual Active Bridge Converter

Renewable energy adoption is a popular topic to release the stress of climate change caused by greenhouse gas. Electricity is ideal secondary energy for clean primary energy such as nuclear, wind, photovoltaic, and so on. To extend the application of electricity and reduce fossil energy consumption by transportation sectors, electric vehicles (EVs) become promising technology that can further inspire the development of renewable energy. Battery as the core in an EV provides the energy to the motor and all on-board electric equipment. The battery charger is mainly composed of a power factor correction (PFC) and isolated DC-DC converter. Therefore, power electronics equipment plays an important role in automotive products. Meanwhile, in recent years, the market capacity for wide band-gap devices, SiC MOSFET, continues to increase in EV applications. Dual active bridge (DAB) is an excellent candidate for isolated DC-DC converter in EV battery charger. The characteristics include an easy control algorithm, galvanic isolation and adjustable voltage gain. Different modulation strategies are developed to improve the performance and stability by using multiple phase shift (MPS) control. This thesis focuses on the utilization of different modulation strategies to realize smooth transition among MPS control in full operational range with securing zero-voltage-switching (ZVS) to eliminate the crosstalk in the hard-switching process. The influence of MPS control on ZVS resonance transient is also addressed to find out the accurate minimum required energy of the inductor to finish the ZVS transition. Furthermore, a general common-mode voltage model for DAB is proposed to analyze the impact of MPS control on the common-mode performance

E-Mobility -- Advancements and Challenges

Mobile platforms cover a broad range of applications from small portable electric devices, drones, and robots to electric transportation, which influence the quality of modern life. The end-to-end energy systems of these platforms are moving toward more electrification. Despite their wide range of power ratings and diverse applications, the electrification of these systems shares several technical requirements. Electrified mobile energy systems have minimal or no access to the power grid, and thus, to achieve long operating time, ultrafast charging or charging during motion as well as advanced battery technologies are needed. Mobile platforms are space-, shape-, and weight-constrained, and therefore, their onboard energy technologies such as the power electronic converters and magnetic components must be compact and lightweight. These systems should also demonstrate improved efficiency and cost-effectiveness compared to traditional designs. This paper discusses some technical challenges that the industry currently faces moving toward more electrification of energy conversion systems in mobile platforms, herein referred to as E-Mobility, and reviews the recent advancements reported in literature

A critical review on charging technologies of electric vehicles

The enormous number of automobiles across the world has caused a significant increase in emissions of greenhouse gases, which pose a grave and mounting threat to modern life by escalating global warming and polluting air quality. These adverse effects of climate change have motivated the automotive sector to reform and have pushed the drive towards the transformation to fully electric. Charging time has been identified as one of the key barriers in large-scale applications of Electric Vehicles (EVs). In addition, various challenges are associated with the formulation of a safe charging scheme, which is concerned with appropriate charging converter architecture, with the aim of ensuring a safe charging protocol within a range of 5–10 min. This paper provides a systematic review of thharging technologies and their impacts on battery systems, including charger converter design and associated limitations. Furthermore, the knowledge gap and research directions are provided with regard to the challenges associated with the charger converter architecture design at the systems level

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

A Review of Power Converters for Ships Electrification

Fully electric ships have become popular to meet the demand for emission-free transportation and improve ships' functionality, reliability, and efficiency. Previous studies reviewed the shipboard power systems, the different types of shipboard energy storage devices, and the influences of the shore-to-ship connection on ports' electrical grid. However, the converter topologies used in the electrification of ships have received very little attention. This article presents a comprehensive topological review of currently available shore-to-ship and shipboard power converters in the literature and on the market. The main goal is to anticipate future trends and potential challenges to stimulate research to accelerate more efficient and reliable electric ships

Single-Sensor DCM PFC Based Onboard Chargers for Low Voltage Electric Vehicles

Grid-connected plug-in electric vehicles (PEVs) are considered as one of the most sustainable solutions to substantially reduce both the oil consumption and greenhouse gas emissions. Electric vehicles (EVs) are broadly categorized into low power EVs (48/72 V battery) and high power EVs (450/650 V battery). Low power EVs comprise two-wheelers, three-wheelers (rickshaws), golf carts, intra-logistics equipment and short-range EVs whereas high power EVs consist of passenger cars, trucks and electric buses. Charger, which is a power electronic converter, is an important component of EV infrastructures. These chargers consist of power converters to convert AC voltage (grid) to constant DC voltage (battery). The existing chargers are bulky, have high components’ count, complex control system and poor input power quality. Henceforth, to overcome these drawbacks, this thesis focuses on the onboard charging solutions (two-stage isolated and single-stage non-isolated) for the low voltage battery EVs. Power factor correction (PFC) is the fundamental component in the EV charger. Considering the specific boundaries of the continuous conduction mode (CCM) operation for AC-DC power conversion and their complexity, the proposed chargers are designed to operate in discontinuous conduction mode (DCM) and benefiting from the characteristics like built-in PFC, single sensor, simple control, easy implementation, inherent zero-current turn-on of the switches, and inherent zero diode reverse recovery losses. Proposed converters can operate for the wide input voltage range and the output voltage is controlled by a single sensor-based single voltage control loop making the control simple and easy to implement, and improves the system reliability and robustness. This thesis studies and designs both single-stage non-isolated and two-stage isolated onboard battery chargers to charge a 48 V lead-acid battery pack. At first, a non-isolated single-stage single-cell buck-boost PFC AC-DC converter is studied and analyzed that offers reduced components’ count and is cost-effective, compact in size and illustrates high efficiency. While the DCM operation ensures unity power factor (UPF) operation at AC mains without the use of input voltage and current sensors. However, they employ high current rated semiconductor devices and the use of diode bridge rectifier suffers from higher conduction losses. To overcome these issues, a new front-end bridgeless AC-DC PFC topology is proposed and analyzed. With this new bridgeless front-end topology, the conduction losses are significantly reduced resulting in improved efficiency. The low voltage stress on the semiconductor devices are observed because of the voltage doubler configuration. Later, an isolated two-stage topology is proposed. The previously proposed bridgeless buck-boost derived PFC converter is employed followed by an isolated half-bridge LLC resonant converter. Loss analysis is done to determine optimal DC-link voltage for the efficient operation of the proposed conversion. The converters' steady-state operation, DCM condition, and design equations are reported in detail. The small-signal models for all the proposed topologies using the average current injected equivalent circuit approach are developed, and detailed closed-loop controller design is illustrated. The simulation results from PSIM 11.1 software and the experimental results from proof-of-concept laboratory hardware prototypes are provided in order to validate the reported analysis, design, and performance