Analysis and Design of High Voltage Gain Three-Elements Resonant Soft-Switching Current-fed DC/DC Converters

Transportation electrification and distributed generation are proven effective strategies to counter climate change. Modern generation and transportation aim to bring down the carbon footprint by transforming the fossil fuel-driven society with alternate energy sources and electric propulsion, respectively. However, harnessing energy from renewable sources is not straight forward but demands a suitable power electronic interface. Similarly, electric transportation propulsion system demands for specific power conversion stages. These power electronic conversion systems include dc-dc converter and dc-ac inverter. Cost, efficiency, power density, and weight are the major requirements of these converters. To obtain these merits, high-frequency soft-switching converters are selected and designed. Resonant converters with a suitable resonance have been usually explored for voltage-fed switching converters to obtain soft-switching of the semiconductor devices at high-frequency. However, owing to the high voltage gain requirements of the solar/fuel cells/batteries, this thesis explores current-fed topologies with different resonant circuits with natural voltage gain. In traditional voltage-fed resonant converters, it is observed that the converter characteristics can be fine-tuned to design the requirements by proper selection of resonant tank. In addition, the resonant tank can integrate the transformer non-idealities and circuit/device parasitic in circuit operation thereby suppressing the consequent voltage spikes across the semiconductor devices. Since voltage-fed converters is fundamentally not suitable for high voltage gain and low voltage applications, this thesis attempts to improve current-fed dc/dc converter characteristics with resonant tanks. In this thesis, a current-fed load resonant DC/DC converter topology is proposed whose characteristics are tuneable with the adopted resonant tank. Further, this thesis proposes a simple technique to ease and improve accuracy of the Fundamental Harmonic Analysis (FHA), which would have been complex otherwise due to capacitive termination of proposed converter. Initially, the characteristics of the proposed converter topology with a parallel resonance derived LCC-T resonant tank is studied to implement zero voltage switching (ZVS) and zero current switching (ZCS) of the semiconductor devices. Three-phase topology of the same has been investigated and analysed. Following the study and a need to further improve the characteristics of resonant dc/dc converter, a series resonance based LCL resonant converter, a dual of the parallel resonance tank is studied and analysed. The load resonant converters are redeemed for integration of PV/fuel cells. Further, for high power applications, suitability of load resonant converters is verified by adopting resonant tank in three-phase topology. Proof-of-concept hardware prototypes are designed and developed in the laboratory to demonstrate the performance and the merits of the proposed soft-switching resonant converter topologies as well as to prove the proposed theory and the claims

Power electronic converter design handbook

Nowadays, power electronic converters play an essential role in the majority of consumer electronic devices and are widely used in industrial applications. Since most of these applications are supplied through the AC grid, the use of rectifiers and DC-DC conveters are mandatory to adapt the grid voltage to the application requirements. In this book, most used AC-DC rectifier topologies and DC-DC converter topologies are thoroughly discussed. Basics of each converter, equations for the power losses evaluation and passive elements design are described. Moreover, the medium frequency transformer required by several of the studied DC-DC converters is analysed in depth. Therefore, this book pretends to be a handbook with a wide scope, which could be used for academic purposes or even by engineers

Analysis and design of a dual series-resonant DC-DC converter

DC-DC conversion systems are vital components in DC distribution systems, renewable energy generation systems, telecommunication systems, and portable electronics devices. The extensive applications of DC-DC converter have resulted in continuous improvement in the topologies and control methods in these converters. The challenge is to build a converter that improves factors such as efficiency of conversion and power density with a simple topology, which incorporates simplified switching and control schemes and fewer numbers of active and passive components to reduce the manufacturing cost. This thesis addresses this challenge by proposing an alternative topology of a DC-DC converter based on dual series-resonant circuits. The proposed topology operates under zero voltage switching (ZVS) and zero current switching (ZCS) conditions to reduce the switching losses. It achieves two degrees of freedom (i.e., duty ratio and switching frequency) to control the output voltage of the converter, which results in both step-down and step-up voltage conversions. The number of active components is limited to two semiconductor switches and two rectifying diodes, which reduces the manufacturing cost of the converter. Detailed analytical analysis is carried out using the extended describing function methodology to characterize the steady state and small signal operation of the converter. Small-signal transfer functions are developed and used to propose a simple closed-loop control scheme to control the output voltage of the converter. An experimental 10 V, 40 W prototype of the proposed converter is built and tested to investigate its operation and confirm its features. The improvement in the efficiency of the converter and power transfer capability of the proposed dual series-resonant converter compared with the traditional single series-resonant circuit, which is used in the interleaved topologies are experimentally verified. In addition, soft switching operation of the converter is realized and a simple control scheme is developed to control the output voltage of the converter. A detailed and step-by-step design procedure is developed, which can be used to customize the design of the converter for different levels of power and voltage. It is shown that the proposed dual series-resonant DC-DC converter provides significant improvement regarding power density, efficiency of power conversion, simplicity of switching and control schemes, and reduced number of converter components resulting in a low cost and compact converter

A Comprehensive Review of DC-DC Converters for EV Applications

DC-DC converters in Electric vehicles (EVs) have the role of interfacing power sources to the DC-link and the DC-link to the required voltage levels for usage of different systems in EVs like DC drive, electric traction, entertainment, safety and etc. Improvement of gain and performance in these converters has a huge impact on the overall performance and future of EVs. So, different configurations have been suggested by many researches. In this paper, bidirectional DC-DC converters (BDCs) are divided into four categories as isolated-soft, isolated-hard, non-isolated-soft and non-isolated-hard depending on the isolation and type of switching. Moreover, the control strategies, comparative factors, selection for a specific application and recent trends are reviewed completely. As a matter of fact, over than 200 papers have been categorized and considered to help the researchers who work on BDCs for EV application

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

Soft-switching current-fed power converters for low voltage high current applications

Ph.DDOCTOR OF PHILOSOPH

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

Analysis and Design of Series LC Resonant-Pulse Assisted Soft-Switching Current-Fed DC/DC Converters

The accelerating pace of electrification via renewable energy sources is shifting focus towards de-carbonization and distributed generation with the potential to combat increasing environmental crisis and to promote sustainable development. Renewable technologies have the potential to fulfil the electricity demand locally which eliminates the unwanted conversion stages, promoting DC microgrid concept, ultimately lowering the energy costs and easy energy access. Alternative energy sources such as solar photovoltaic (PV) and fuel cell along with energy storage systems are promising for DC microgrid applications. However, the effective integration of these alternative energy sources still remains a challenge due to their low voltage output, unregulated and intermittent characteristics issuing a requirement of a dedicated power conditioning unit. To revolutionize the way these alternative sources are interfaced with a high voltage DC microgrid or to the conventional ac grid, dc/dc converters are expected to be power-dense, compact and extremely efficient. Current-fed dc/dc converters have strong application potential owing to their inherent merits. Accomplishing the abovementioned objectives together with distinct merits offered by current-fed circuits, this thesis aims to exploit the quasi-resonance concept for achieving soft-switching and smooth commutation of the semiconductor switching devices. The proposed quasi resonant approach that utilizes the leakage inductance of transformer and a high frequency series resonant capacitor for a short period also termed as ‘resonant-pulse’, has been investigated in various current-fed converter topologies. Proposed converter class emphasize on simple and efficient design, without the use of additional snubber circuits and eliminates device turn-off voltage spike, which is a historical problem with traditional current-fed converters. In this thesis, at first the proposed series resonant-pulse concept is implemented in single-phase current-fed push-pull and half-bridge configuration. The converter operation, control and performance are investigated for low voltage high current specifications. These converter configurations demonstrate good efficiency and compact structure with only two switching devices and simpler gate control requirement because devices having common ground with power supply. The idea has then been extended to modular current-fed full-bridge topology. The proposed series resonant-pulse assisted converter enables wide range ZCS and turn-off spike elimination across the semiconductor switches. Modularity of this converter allows easy scalability for high power and voltage levels with significantly lower current and voltage stress, making it suitable for relatively higher power industrial applications. Lastly, to achieve high power capability with high density, three-phase current sharing current-fed topology utilizing series resonant-pulse feature has been studied and investigated in detail. The proposed three-phase topology combines the benefits of current-sharing primary and load adaptive series resonant-pulse. As a result, these converters demonstrate promising attributes such as wide ZCS operation, reduced filtering requirement, lower component count, lower conduction losses etc

Inductive Wireless Power Transfer Charging for Electric vehicles - A Review

Considering a future scenario in which a driverless Electric Vehicle (EV) needs an automatic charging system without human intervention. In this regard, there is a requirement for a fully automatable, fast, safe, cost-effective, and reliable charging infrastructure that provides a profitable business model and fast adoption in the electrified transportation systems. These qualities can be comprehended through wireless charging systems. Wireless Power Transfer (WPT) is a futuristic technology with the advantage of flexibility, convenience, safety, and the capability of becoming fully automated. In WPT methods resonant inductive wireless charging has to gain more attention compared to other wireless power transfer methods due to high efficiency and easy maintenance. This literature presents a review of the status of Resonant Inductive Wireless Power Transfer Charging technology also highlighting the present status and its future of the wireless EV market. First, the paper delivers a brief history throw lights on wireless charging methods, highlighting the pros and cons. Then, the paper aids a comparative review of different type’s inductive pads, rails, and compensations technologies done so far. The static and dynamic charging techniques and their characteristics are also illustrated. The role and importance of power electronics and converter types used in various applications are discussed. The batteries and their management systems as well as various problems involved in WPT are also addressed. Different trades like cyber security economic effects, health and safety, foreign object detection, and the effect and impact on the distribution grid are explored. Prospects and challenges involved in wireless charging systems are also highlighting in this work. We believe that this work could help further the research and development of WPT systems.publishedVersio