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

High step up DC-DC converter topology for PV systems and electric vehicles

This thesis presents new high step-up DC-DC converters for photovoltaic and electric vehicle applications. An asymmetric flyback-forward DC-DC converter is proposed for the PV system controlled by the MPPT algorithm. The second converter is a modular switched-capacitor DC-DC converter, it has the capability to operate with transistor and capacitor open-circuit faults in every module. The results from simulations and tests of the asymmetric DC-DC converters have suggested that the proposed converter has a 5% to 10% voltage gain ratio increased to the symmetric structures among 100W – 300W power (such as [3]) range while maintaining efficiency of 89%-93% when input voltage is in the range of 25 – 30 V. they also indicated that the softswitching technique has been achieved, which significantly reduce the power loss by 1.7%, which exceeds the same topology of the proposed converter without the softswitching technique. Moreover, the converters can maintain rated outputs under main transistor open circuit fault situation or capacitor open circuit faults. The simulation and test results of the proposed modularized switched-capacitor DC-DC converters indicate that the proposed converter has the potential of extension, it can be embedded with infinite module in simulation results, however, during experiment. The sign open circuit fault to the transistors and capacitors would have low impact to the proposed converters, only the current ripple on the input source would increase around 25% for 4-module switched-capacitor DC-DC converters. The developed converters can be applied to many applications where DC-DC voltage conversion is alighted. In addition to PVs and EVs. Since they can ride through some electrical faults in the devices, the developed converter will have economic implications to improve the system efficiency and reliability

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

Analysis of a new family of DC-DC converters with input-parallel output-series structure

There is an increasing trend of development and installation of switching power supplies due to their highly efficient power conversion, fast power control and high quality power conditioning for applications such as renewable energy integration and energy storage management systems. In most of these applications, high voltage conversion ratio is required. However, basic switching converters have limited voltage conversion ratio. There has been much research into development of high gain power converters. While most of the reported topologies focus on high gain and high efficiency, in this thesis, the input and output ripple currents and reliability are also considered to derive a new converter structure suitable for high step-up voltage conversion applications. High ripple currents and voltages at the input and output of dc-dc converters are not desirable because they may affect the operation of the dc source or the load. A number of converters operating in an interleaved manner can reduce these ripples. This thesis proposes a dc/dc switching converter structure which is capable of reducing the ripple problem through interleaved action, in addition to high gain and high efficiency voltage conversion. The thesis analyses the proposed converter structure through a dual buck-boost converter topology. The structure allows different converter topologies and combinations of them for different applications to be configured. The study begins with a motivation and a literature review of dc/dc converters. The new family of high step-up converters is introduced with an interleaved buck-boost as an example, followed by small-signal analysis. Experimental verifications, conclusions and future work are discussed

Analysis of a new family of DC-DC converters with input-parallel output-series structure

There is an increasing trend of development and installation of switching power supplies due to their highly efficient power conversion, fast power control and high quality power conditioning for applications such as renewable energy integration and energy storage management systems. In most of these applications, high voltage conversion ratio is required. However, basic switching converters have limited voltage conversion ratio. There has been much research into development of high gain power converters. While most of the reported topologies focus on high gain and high efficiency, in this thesis, the input and output ripple currents and reliability are also considered to derive a new converter structure suitable for high step-up voltage conversion applications. High ripple currents and voltages at the input and output of dc-dc converters are not desirable because they may affect the operation of the dc source or the load. A number of converters operating in an interleaved manner can reduce these ripples. This thesis proposes a dc/dc switching converter structure which is capable of reducing the ripple problem through interleaved action, in addition to high gain and high efficiency voltage conversion. The thesis analyses the proposed converter structure through a dual buck-boost converter topology. The structure allows different converter topologies and combinations of them for different applications to be configured. The study begins with a motivation and a literature review of dc/dc converters. The new family of high step-up converters is introduced with an interleaved buck-boost as an example, followed by small-signal analysis. Experimental verifications, conclusions and future work are discussed

ANALYSIS AND DESIGN OF IMPULSE COMMUTATED SOFT-SWITCHING CURRENT-FED CONVERTERS

Ph.DDOCTOR OF PHILOSOPH

Improved Dual-Output Step-Down Soft-Switching Current-Fed Push-Pull DC-DC Converter

Multi-port DC-DC converters are gaining more significance in modern power system environments by enabling the connection of multiple renewable energy sources, so the efficient operation of these converters is paramount. Soft switching methods increase efficiency in DC-DC converters and increase the reliability and lifespan of devices by relieving stress on components. This paper proposes a method for soft-switching of a dual-output step-down current-fed full-bridge push-pull DC-DC converter. The converter enables two independent outputs to supply different loads. The topology achieves zero-current switching on the primary side and zero-voltage switching on the secondary side, eliminating the need for active-clamp circuits and passive snubbers to absorb surge voltage. This reduces switching losses and lower voltage and current stresses on power electronic devices. The paper thoroughly investigates the proposed converter's operation principle, control strategy, and characteristics. Equations for the voltage and current of all components are derived, and the conditions for achieving soft switching are calculated. Simulation results in EMTDC/PSCAD software validate the accuracy of the proposed method.Comment: 2023 55th North American Power Symposium (NAPS

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