INTEGRATED INDUCTIVE AND CONDUCTIVE CHARGING SYSTEM FOR ELECTRIC VEHICLES

The global electric vehicle (EV) market acceleration is facilitated by supporting policies deployed by governments and cities to reap multiple benefits in the fields of transport decarbonization, air pollution reduction, energy efficiency, and security. Currently, conductive chargers are a customary method of storing electric energy into the storage elements present onboard of an EV which is inadequate in supporting complete autonomy. The thriving inclination towards the design of autonomous vehicles has shaped wireless charging as an attractive solution in favor of complete autonomy. As long as the wireless charging infrastructure, as well as interoperability standards, are not completely developed, wired and wireless chargers have to co-exist onboard the vehicles for user convenience. Incorporation of an entire parallel wireless charging system on-board an EV, either during manufacturing or after-market increases size, weight, or cost while declining the electric range of the vehicle. The current requisite for multiple on-board charging options motivate the necessity for a solution for efficiently integrating wired and wireless charging systems. In this Ph.D. research, we propose multiple charging architectures capable of integrating inductive and conductive charging systems. The proposed architectures merge the output rectifying stage of an inductive charging system to the existing on-board charger eliminating the additional weight and volume associated with a wireless charger. Since the proposed system involves multiple power conversion stages, a system level study is carried out to select feasible topologies capable of maximizing the efficiency of an integrated system. Additionally, an extended harmonic approximation (EHA) technique is introduced to increase the accuracy of a resonant converter model facilitating the optimized design parameter selection of an inductive charging system. Furthermore, a novel analog synchronous rectification circuit is proposed and designed to enable active rectification maximizing power transfer efficiency. For proof of concept verification, a laboratory prototype of a 3.3kW Silicon Carbide (SiC) based integrated wireless charger is developed that can be interfaced to a variable input voltage (85-265 Vrms) 50/60Hz AC grid. According to the experimental measurements, the charger draws an input current with a total harmonic distortion of 1.3% while achieving an overall efficiency of 92.77% at rated output power

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

An Integrated Single-phase On-board Charger

With the growing demand for transportation electrification, plug-in electric vehicles (PEVs), and plug-in hybrid electric vehicles (PHEVs), cumulatively called electric vehicles (EVs) are drawing more and more attention. The on-board charger (OBC), which is the power electronics interface between the power grid and the high voltage traction battery, is an important part for charging EVs. Besides the OBC, every EV is equipped with another separate power unit called the auxiliary power module (APM) to charge the low voltage (LV) auxiliary battery, which supplies all the electronics on car including audio, air conditioner, lights and controllers. The main target of this work is a novel way to integrate both units together to achieve a charger design that is not only capable of bi-directional operation with high efficiency, but also higher gravimetric and volumetric power density, as compared with those of the existing OBCs and APMs combined. To achieve this target, following contributions are made: (i) a three-port integrated DC/DC converter, which combines OBC and APM together through an innovative integration method; (ii) an innovative zero-crossing current spike compensation for interleaved totem pole power factor correction (PFC) and (iii) a new phase-shift based control strategy to achieve a regulated power flow management with minimum circulating losses

A GALLIUM NITRIDE INTEGRATED ONBOARD CHARGER

Compared to Silicon metal–oxide–semiconductor field-effect transistors (MOSFETs), Gallium Nitride (GaN) devices have a significant reduction in gate charge, output capacitance, and zero reverse recovery charge, enabling higher switching frequency operation and efficient power conversion. GaN devices are gaining momentum in power electronic systems such as electric vehicle (EV) charging system, due to their promises to significantly enhance the power density and efficiency. In this dissertation, a GaN-based integrated onboard charger (OBC) and auxiliary power module (APM) is proposed for EVs to ensure high efficiency, high frequency, high power density, and capability of bidirectional operation. The high switching frequency operation enabled by the GaN devices and the integration of OBC and APM bring many unique challenges, which are addressed in this dissertation. An important challenge is the optimal design of high-frequency magnetics for a high-frequency GaN-based power electronic interface. Another challenge is to achieve power flow management among three active ports while minimizing the circulating power. Furthermore, the impact of circuit layout parasitics could significantly deteriorate the system interface, due to the sensitivity of GaN device switching characteristics. In this work, the aforementioned challenges have been addressed. First, a comprehensive analysis of the front-end AC-DC power factor correction stage is presented, covering a detailed magnetic modeling technique to address the high-frequency magnetics challenge. Second, the modeling and control of a three-port DC-DC converter, interfacing the AC-DC stage, high-voltage traction battery and low-voltage battery, are discussed to address the power flow challenge. Advanced control methodologies are developed to realize power flow management while maintaining minimum circulating power and soft switching. Furthermore, a new three-winding high-frequency transformer design with improved power density and efficiency is achieved using a genetic-algorithm-based optimization approach. Finally, a GaN-based integrated charger prototype is developed to validate the proposed theoretical hypothesis. The experimental results showed that the GaN-based charging system has the capability of achieving simultaneous charging (G2B) of both HV and LV batteries with a peak efficiency of 95%

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