Efficient, High Power Density, Modular Wide Band-gap Based Converters for Medium Voltage Application

Recent advances in semiconductor technology have accelerated developments in medium-voltage direct-current (MVDC) power system transmission and distribution. A DC-DC converter is widely considered to be the most important technology for future DC networks. Wide band-gap (WBG) power devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) have paved the way for improving the efficiency and power density of power converters by means of higher switching frequencies with lower conduction and switching losses compared to their Silicon (Si) counterparts. However, due to rapid variation of the voltage and current, di/dt and dv/dt, to fully utilize the advantages of the Wide-bandgap semiconductors, more focus is needed to design the printed circuit boards (PCB) in terms of minimizing the parasitic components, which impacts efficiency. The aim of this dissertation is to study the technical challenges associated with the implementation of WBG devices and propose different power converter topologies for MVDC applications. Ship power system with MVDC distribution is attracting widespread interest due to higher reliability and reduced fuel consumption. Also, since the charging time is a barrier for adopting the electric vehicles, increasing the voltage level of the dc bus to achieve the fast charging is considered to be the most important solution to address this concern. Moreover, raising the voltage level reduces the size and cost of cables in the car. Employing MVDC system in the power grid offers secure, flexible and efficient power flow. It is shown that to reach optimal performance in terms of low package inductance and high slew rate of switches, designing a PCB with low common source inductance, power loop inductance, and gate-driver loop are essential. Compared with traditional power converters, the proposed circuits can reduce the voltage stress on switches and diodes, as well as the input current ripple. A lower voltage stress allows the designer to employ the switches and diodes with lower on-resistance RDS(ON) and forward voltage drop, respectively. Consequently, more efficient power conversion system can be achieved. Moreover, the proposed converters offer a high voltage gain that helps the power switches with smaller duty-cycle, which leads to lower current and voltage stress across them. To verify the proposed concept and prove the correctness of the theoretical analysis, the laboratory prototype of the converters using WBG devices were implemented. The proposed converters can provide energy conversion with an efficiency of 97% feeding the nominal load, which is 2% more than the efficiency of the-state-of-the-art converters. Besides the efficiency, shrinking the current ripple leads to 50% size reduction of the input filter inductors

Analysis and Design of a Soft Switching Z-Source Boost DC-DC Converter

This paper proposes a high step-up fully soft switched Z-source Boost DC-DC converter, which uses two resonant paths to create soft switching conditions for switches and diodes and also increases the voltage gain. The proposed converter only has one switch, so it has a simple structure. Furthermore, its control circuit remains pulse width modulation. Since soft switching conditions are provided for all switching elements, the converter efficiency is very high. This converter also has all advantages of Z-source converters. The converter is analyzed and simulated in PSPICE software. The results confirm the aforementioned advantages and features of the proposed converte

High efficiency and high gain non-isolated bidirectional dc-dc converter with soft switching capability

The non-isolated dc-dc power converters are considered as a unique option for flexible voltage control and adaptation in the modern energy conversion systems due to their simple and light configurations. To this date, these converters are primarily investigated to generate high efficiency and high gain with a sustained soft switching capability and a smaller footprint. On that account, this work proposes two effective solutions to address the aforementioned issues. First, a high-efficiency soft switching non-isolated bidirectional dc-dc converter with a simple configuration is proposed. The converter executes the zero voltage zero current switching (ZVZCS) over a wide operating region to ensure high efficiency. For verification, a 150 W experimental prototype is built and tested for soft switching performance by varying the input voltage, switching frequency and the loading. It is observed that the efficiency remains consistently high and has a full-load maximum of 98.2% in the boost mode and 97.5% in the buck mode. The analysis of the Electromagnetic Interference (EMI) performance of the converter also shows the improvement in the noise signature. Second, an improved high gain zero voltage switching (ZVS) nonisolated bidirectional dc-dc converter is proposed. The high gain is realized by using an intermediate energy storage cell with reduced size. Besides, the ZVS is implemented by two integrated auxiliary resonant networks. These networks ensure sustained ZVS operation over the entire duty ratio. A 200 W prototype is built to verify the concept. As a result, a full load efficiency of 97.5% (in boost mode) and 95.5% (in buck mode) is recorded at fs= 30 kHz. Also, these efficiencies are recorded as 97% (boost mode) and 94.5% (buck mode) at fs= 100 kHz. Moreover, it is observed that the efficiency (and so the soft switching) is consistent over the entire gain profile. However, there is a slight additional drop of 1.5% (boost mode) and 1% (buck mode) at extreme duty ratios. Both converters also implement soft switching for auxiliary switches and eliminate the reverse recovery loss

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

A comprehensive review on Bidirectional traction converter for Electric vehicles

In this fast-changing environmental condition, the effect of fossil fuel in vehicle is a significant concern. Many sustainable sources are being studied to replace the exhausting fossil fuel in most of the countries. This paper surveys the types of electric vehicle’s energy sources and current scenario of the on-road electric vehicle and its technical challenges. It summarizes the number of state-of-the-art research progresses in bidirectional dc-dc converters and its control strategies reported in last two decades. The performance of the various topologies of bidirectional dc-dc converters is also tabulated along with their references. Hence, this work will present a clear view on the development of state-of-the-art topologies in bidirectional dc-dc converters. This review paper will be a guide for the researchers for selecting suitable bidirectional traction dc-dc converters for electric vehicle and it gives the clear picture of this research field

Zero-voltage-switching buck converter with low-voltage stress using coupled inductor

This study presents a new zero-voltage-switching (ZVS) buck converter. The proposed converter utilises a coupled inductor to implement the output filter inductor as well as the auxiliary inductor which is commonly employed to realise ZVS for switches. Additional magnetic core for the auxiliary inductor in traditional ZVS converters is eliminated and hence reduced cost is achieved. Moreover, thanks to the series connection between the input and output, the switch voltage stress in the steady state is reduced and thus the ZVS operation can be easier achieved. Then the leakage inductor current circulating in the auxiliary switch is decreased, contributing to reduced conduction losses. In particular, low-voltage rating devices with low on-state resistance can be adopted to further improve efficiency in applications with non-zero output voltage all the time, such as the battery charger. Furthermore, the reverse-recovery problem of the diode is significantly alleviated by the leakage inductor of coupled inductor. In the study, operation principle and steady-state analysis of the proposed converter are presented in detail. Meanwhile, design considerations are given to obtain circuit parameters. Finally, simulations and experiments on a 200 W prototype circuit validate the advantages and effectiveness of the proposed converter

Development of Efficient Soft Switching Synchronous Buck Converter Topologies for Low Voltage High Current Applications

Switched mode power supplies (SMPS) have emerged as the popular candidate in all the power processing applications. The demand is soaring to design high power density converters. For reducing the size, weight, it is imperative to channelize the power at high switching frequency. High switching frequency converters insist upon soft switching techniques to curtail the switching losses. Several soft switching topologies have been evolved in the recent years. Nowadays, the soft switching converters are vastly applied modules and the demand is increasing for high power density and high efficiency modules by minimizing the conduction and switching losses. These modules are generally observed in many applications such as laptops, desktop processors for the enhancement of the battery life time. Apart from these applications, solar and spacecraft applications demand is increasing progressively for stressless and more efficient modules for maximizing the storage capacity which inturn enhances the power density that improves the battery life to supply in the uneven times. Modern trends in the consumer electronic market focus increases in the demand of lower voltage supplies. Conduction losses are significantly reduced by synchronous rectifiers i.e., MOSFET’s are essentially used in many of the low voltage power supplies. Active and passive auxiliary circuits are used in tandem with synchronous rectifier to diminish the crucial loss i.e., switching loss and also it minimizes the voltage and current stresses of the semiconductor devices. The rapid progress in the technology and emerging portable applications poses serious challenges to power supply design engineers for an efficient power converter design at high power density. The primary aim is to design and develop high efficiency, high power density topologies like: buck, synchronous buck and multiphase buck converters with the integration of soft switching techniques to minimize conduction and switching losses sustaining the voltage and current stresses within the tolerable range. In this work, two ZVT-ZCT PWM synchronous buck converters are introduced, one with active auxiliary circuit and the other one with passive auxiliary circuit. The operating principle and comprehensive steady state analysis of the ZVT-ZCT PWM synchronous buck converters are presented. The converters are designed to have high efficiency and low voltage that is suitable for high power density application. The semiconductor devices used in the topologies in addition to the main switch operate with soft switching conditions. The viii Abstract topologies proposed render a large overall efficiency in contrast to the contemporary topologies. In addition the circuit’s size is less, reliable and have high performance-cost ratio. The new generation microprocessor demands the features such as low voltage, high current, high power density and high efficiency etc., in the design of power supplies. The supply voltage for the future generation microprocessors must be low, in order to decrease the power consumption. The voltage levels are dripping to a level even less than 0.7V, and the power consumption increases as there is an increase in the current requirement for the processor. In order to meet the demands of the new generation microprocessor power supply, a soft switching multiphase PWM synchronous buck converter is proposed. The losses in the proposed topology due to increasing components are pared down by the proposed soft switching technique. The proposed converters in this research work are precisely described by the mathematical modelling and their operational modes. The practicality of the proposed converters for different applications is authenticated by their simulation and experimental results

Topology Derivation and Development of Non-Isolated Three-port Converters for DC Microgrids

Currently, three-port converters (TPCs) are gaining popularity in applications which integrate renewable energies, such as photovoltaics and wind, and energy storage elements, such as batteries and supercapacitors with load. This is due to the advantages of a single power conversion stage between any two ports for better conversion efficiency and a highly integrated structure for compactness. Most of the reported TPCs focus on the consuming load. However, there are applications such as hybrid-electric vehicle braking systems and DC microgrids which have power generating capability. A typical example is battery charging in a DC microgrid. When the photovoltaics has inadequate power to charge the battery, the TPCs that consider only consuming load need an extra DC/DC converter for the DC bus to charge the battery. Three-winding transformers associated with full-bridge configurations as the basis for TPCs can fulfill the purpose of bi-directional power flow between any two ports. However, bulkiness of transformers and the need for more switches and associated control mechanisms increases the converter complexity, volume and cost. Solutions for integrating a regenerative load in NITPCs are still limited. This research work focuses on the development of non-isolated three-port converters (NITPCs), as they are capable of driving a regenerative load while offering a compact solution. The study includes a systematic approach to deriving a family of NITPCs. They combine different commonly known power converters in an integrated manner while considering the voltage polarity, voltage levels among the ports and overall voltage conversion ratio. The derived converter topologies allow for all possible power flow combinations among the sources and load while preserving the single power processing feature of the TPC. A design example of a boost converter based TPC with a bi-directional buck converter is reported. In addition, a novel single-inductor NITPC is proposed. It is a further integrated topology according to the aforementioned design example where only one inductor is required instead of two, and the number of power transistors remains the same. The detailed topological derivation, operation principles, steady-state analysis, simulation results and experiment results are given to verify the proposed NITPCs

Survey on Photo-Voltaic Powered Interleaved Converter System

Renewable energy is the best solution to meet the growing demand for energy in the country. The solar energy is considered as the most promising energy by the researchers due to its abundant availability, eco-friendly nature, long lasting nature, wide range of application and above all it is a maintenance free system. The energy absorbed by the earth can satisfy 15000 times of today’s total energy demand and its hundred times more than that our conventional energy like coal and other fossil fuels. Though, there are overwhelming advantages in solar energy, It has few drawbacks as well such as its low conversion ratio, inconsistent supply of energy due to variation in the sun light, less efficiency due to ripples in the converter, time dependent and, above all, high capitation cost. These aforementioned flaws have been addressed by the researchers in order to extract maximum energy and attain hundred percentage benefits of this heavenly resource. So, this chapter presents a comprehensive investigation based on photo voltaic (PV) system requirements with the following constraints such as system efficiency, system gain, dynamic response, switching losses are investigated. The overview exhibits and identifies the requirements of a best PV power generation system