The application of resonant-mode techniques to off-line converters for the commercial market

This thesis presents the work performed by the author on the application of resonantmode techniques to commercially-orientated off-line converters. An extensive review of resonant-mode topologies leads to the development of a method of categorisation of these topologies which allows a greater comprehension of their properties. The categories of converter thus obtained are the conventional resonant converter, the quasi-resonant converter, and the gap-resonant converter. The gap-resonant converter is selected for further investigation. An analysis reveals the limited load and input voltage capabilities of this converter, and hence leads to the introduction of a pre-regulating converter to improve reliability and commercial viability. High-frequency techniques are explored and reported, and new techniques are developed in several areas in order to extend the concept of the gap-resonant converter to a realworld practical design. Subjects explored include the high speed driving of power MOSFETs, MOSFET and diode switching losses, high frequency magnetic materials and core losses, and skin and proximity effects. The techniques developed are used in the design of a 30OW, off-line converter with an input voltage range of 165V to 380V after rectification, and a ten-to-one output load range

An Adaptable Interleaved DC-DC Boost Converter

A.H. Weinberg presented his classic boost topology in his 1974 publication intended for use in satellites. It comprises minimal external components and uses multiple coupled coil systems to provide a boost of up to 2x. Its simplicity makes it inherently robust and reliable as minimal components means lower chance of failure. While its simplicity makes it attractive it has limited boost capability which makes it unsuitable for many modern day applications. No significant investigation has been carried out on adapting the Weinberg topology for high boost operation so far as can be ascertained. An investigation into adapting the Weinberg converter for high boost operation is presented in this thesis. A novel topology is developed which preserves the simplicity, reliability and efficiency of the Weinberg design while achieving boost ratios >2x. An analysis of the proposed topology is provided and mathematical expressions are derived to quantify the voltages and currents in relevant component for a given set of operating conditions. All coupled windings share a single core and are arranged so the magnetic flux does not reverse direction which further reduces loss in the magnetic core material. The coupled coils clamp the MOSFET drain voltage to an amount much lower than the output voltage which allows lower breakdown versions with lower intrinsic ON-resistance to be used leading to reduced conduction losses. Modelling of circuit losses and their sources allows optimal selection and positioning of components and finds wound component and MOSFET conduction losses contribute around 70% of the total circuit loss. Modelling and trialling of wound component geometries is carried out to optimise magnetic coupling and reduce leakage inductance. Working prototypes are developed and used to verify the mathematical claims through experimentation. Overall system efficiency of 94.1% is achieved at a boost ratio of 8.8x and an output power of 257W. Overall system losses are reduced from 11% to 6% by simply optimising the magnetic assembly. However optimisation of the magnetic assembly is more involved and may be less tolerant to variation which may hinder repeatability but the results are very positive despite crude, hand-wound magnetic coils and standard quality silicon components being used; which is a promising sign

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

Miniaturized Ultraviolet Imager High Voltage Power Supply

Sending satellites into orbit becomes exponentially more expensive with weight and size, so designing high-voltage DC-DC converters that can achieve kilovolt level outputs in a small form factor is crucial to reducing costs. The Miniaturized Ultraviolet Imager (MUVI) aims to monitor Earth’s ionosphere and report weather patterns to climate scientists within a 2U cube satellite footprint. The imaging equipment consists of a microchannel plate and phosphor screen that require 2.5kV and 5.5kV respectively at microamp level currents. This report explains the implementation of a high voltage boost cascaded flyback converter to meet all of the MUVI satellite output voltage requirements. The small mechanical footprint of a cube satellite severely limits board size and component heights. This design further expands the power electronics field and provides inspiration for future space-rated voltage converters in small form factors. The results from circuit simulations validated the design as a viable solution for MUVI’s imaging equipment. A boost-flyback converter can achieve the required high voltage DC output while remaining within the 7ppm ripple specification. This report summarizes all of the circuit simulation results for both the power stage and analog circuitry that monitor and control the output voltage. The analog circuitry was hardware tested and validated for the monitoring and control signals. The power stage testing is scheduled for the Summer of 2021 so those results are not included in this report

Dynamic modeling of pwm and single-switch single-stage power factor correction converters

The concept of averaging has been used extensively in the modeling of power electronic circuits to overcome their inherent time-variant nature. Among various methods, the PWM switch modeling approach is most widely accepted in the study of closed-loop stability and transient response because of its accuracy and simplicity. However, a non-ideal PWM switch model considering conduction losses is not available except for converters operating in continuous conduction mode (CCM) and under small ripple conditions. Modeling of conductor losses under large ripple conditions has not been reported in the open literature, especially when the converter operates in discontinuous conduction mode (DCM). In this dissertation, new models are developed to include conduction losses in the non-ideal PWM switch model under CCM and DCM conditions. The developed model is verified through two converter examples and the effect of conduction losses on the steady state and dynamic responses of the converter is also studied. Another major constraint of the PWM switch modeling approach is that it heavily relies on finding the three-terminal PWM switch. This requirement severely limits its application in modeling single-switch single-stage power factor correction (PFC) converters, where more complex topological structures and switching actions are often encountered. In this work, we developed a new modeling approach which extends the PWM switch concept by identifying the charging and discharging voltages applied to the inductors. The new method can be easily applied to derive large-signal models for a large group of PFC converters and the procedure is elaborated through a specific example. Finally, analytical results regarding harmonic contents and power factors of various PWM converters in PFC applications are also presented here

High Temperature Boost (HTB) Power Processing Unit (PPU) Formulation Study

This technical memorandum is to summarize the Formulation Study conducted during fiscal year 2012 on the High Temperature Boost (HTB) Power Processing Unit (PPU). The effort is authorized and supported by the Game Changing Technology Division, NASA Office of the Chief Technologist. NASA center participation during the formulation includes LaRC, KSC and JPL. The Formulation Study continues into fiscal year 2013. The formulation study has focused on the power processing unit. The team has proposed a modular, power scalable, and new technology enabled High Temperature Boost (HTB) PPU, which has 5-10X improvement in PPU specific power/mass and over 30% in-space solar electric system mass saving

Double Resonant High-Frequency Converters for Wireless Power Transfer

This thesis describes novel techniques and developments in the design and implementation of a low power radio frequency (40kHz to 1MHz) wireless power transfer (WPT) system, with an application in the wireless charging of autonomous drones without physical connection to its on-board Battery Management System (BMS). The WPT system is developed around a matrix converter exploiting the benefits such as a small footprint (DC-link free), high efficiency and high power density. The overall WPT system topology discussed in this thesis is based on the current state-of-the-art found in literature, but enhancements are made through novel methods to further improve the converter’s stability, reduce control complexity and improve the wireless power efficiency. In this work, each part of the system is analysed and novel techniques are proposed to achieve improvements. The WPT system design methodology presented in this thesis commences with the use of a conventional full-bridge converter. For cost-efficiency and to improve the converters stability, a novel gate drive circuit is presented which provides self-generated negative bias such that a bipolar MOSFET drive can be driven without an additional voltage source or magnetic component. The switching control sequences for both a full-bridge and single phase to single phase matrix converter are analysed which show that the switching of a matrix converter can be considered to be the same as a full-bridge converter under certain conditions. A middleware is then presented that reduces the complexity of the control required for a matrix converter and enables control by a conventional full-bridge controller (i.e. linear controller or microcontroller). A novel technique that can maximise and maintain in real-time the WPT efficiency is presented using a maximum efficiency point tracking approach. A detailed study of potential issues that may affect the implementation of this novel approach are presented and new solutions are proposed. A novel wireless pseudo-synchronous sampling method is presented and implemented on a prototype system to realise the maximum efficiency point tracking approach. Finally, a new hybrid wireless phase-locked loop is presented and implemented to minimise the bandwidth requirements of the maximum efficiency point tracking approach. The performance and methods for implementation of the novel concepts introduced in this thesis are demonstrated through a number of prototypes that were built. These include a matrix converter and two full WPT systems with operating frequencies ranging from sub-megahertz to megahertz level. Moreover, the final prototype is applied to the charging of a quadcopter battery pack to successfully charge the pack wirelessly whilst actively balancing the cells. Hence, fast battery charging and cell balancing, which conventionally requires battery removal, can be achieved without re-balance the weight of the UAV

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