Integrated Topologies And Digital Control For Satellite Power Management And Distribution Systems

This work is focused on exploring advanced solutions for space power management and distribution (PMAD) systems. As spacecraft power requirements continue to increase, paralleled by the pressures for reducing cost and overall system weight, power electronics engineers will continue to face major redesigns of the space power systems in order to meet such challenges. Front-end PMAD systems, used to interface the solar sources and battery backup to the distribution bus, need to be designed with increased efficiency, reliability, and power density. A new family of integrated single-stage power converter structures is introduced here. This family allows the interface and control of multiple power sources and storage devices in order to optimize utilization of available resources. Employing single-stage power topologies, these converters control power flow efficiently and cost-effectively. This is achieved by modifying the operation and control strategies of isolated soft-switched half-bridge and full-bridge converters--two of the most popular two-port converter topologies. These topologies are reconfigured and utilized to realize three power processing paths. These paths simultaneously utilize the power devices, allowing increased functionality while promising reduced losses and enhanced power densities. Each of the proposed topologies is capable of performing simultaneous control of two of its three ports. Control objectives include battery or ultra-capacitor charge regulation, solar array maximum power point tracking (MPPT), and/or bus voltage regulation. Another advantage of the proposed power structure is that current engineering design concepts can be used to optimize the new topologies in a fashion similar to the mother topologies. This includes component selection and magnetic design procedures, as well as achieving soft-switching for increased efficiency at higher switching frequencies. Galvanic isolation of the load port through high-frequency transformers provides design flexibility for high step-up/step-down conversion ratios. It further allows the converters to be used as power electronics building blocks (PEBB) with outputs connected in different series/parallel combinations to meet different load requirements. Utilizing such converters promises significant savings in size, weight, and costs of the power management system as well as the devices it manages. Chapter 1 of this dissertation provides an introduction to the requirements, challenges, and trends of space PMAD. A review of existing multi-port converter technologies and digital control techniques is given in Chapter 2. Chapter 3 discusses different PMAD system architectures. It outlines the basic concepts used for PMAD integration and discusses the potential for improvement. Chapters 4 and 5 present and discuss the operation and characteristics of three different integrated multi-port converters. Chapter 6 presents improved methods for practical digital control of switching converters, which are especially useful in complex multi-objective controllers used for PMAD. This is followed by conclusions and suggested future work

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

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Design and implementation of multi-port DC-DC converters for electrical power systems

The thesis proposes developing, analysing, and verifying these DC-DC converters to improve the current state-of-the-art topology. Four new DC-DC converters for applications like light emitting diode, lighting microgrids DC, PV applications, and electric vehicles are as follows. In this study, the two-input converter is presented. The two-input converter that has been proposed serves as the interface between the two input sources and load. Using two switches and two diodes, the proposed converter minimises switching losses and contains eight components in total, making it compact and low volume. As a result, the highest average efficiency is 92.5%, and the lowest is 89.6%. In this research, the new three-port converter that has been proposed serves as the interface between the input source, a battery, and a load. In addition, the converter is suitable for use in standalone systems or satellite applications. A low-volume converter is designed with three switches and two diodes, thereby minimizing switching losses and ten components in total. Regarding efficiency, the highest average is 92.5%, and the lowest is 90.9%. Also, this study proposes a single-switch high-step-up converter for LED drivers and PV applications. A further benefit of the proposed converter over conventional classical converters is that it utilises only one active switch. These results align with simulation results, and its gain is 6.8 times greater than classical converters. Furthermore, stress across switches and diodes is smaller than the output voltage, approximately 50%. Semiconductor losses were limited with a low duty cycle of 0.7. This makes the highest average efficiency 95% and the lowest 93.9%. The new four-port converter is presented for applications such as microgrid structures and electric vehicles. As part of the integrated converter, two or three converters are combined by sharing some components, such as switches, inductors, and capacitors, to form a single integrated converter. As a result of the four-port converter proposed, battery power can be managed, and output voltage can be regulated simultaneously

A review on power electronics technologies for electric mobility

Concerns about greenhouse gas emissions are a key topic addressed by modern societies worldwide. As a contribution to mitigate such effects caused by the transportation sector, the full adoption of electric mobility is increasingly being seen as the main alternative to conventional internal combustion engine (ICE) vehicles, which is supported by positive industry indicators, despite some identified hurdles. For such objective, power electronics technologies play an essential role and can be contextualized in different purposes to support the full adoption of electric mobility, including on-board and off-board battery charging systems, inductive wireless charging systems, unified traction and charging systems, new topologies with innovative operation modes for supporting the electrical power grid, and innovative solutions for electrified railways. Embracing all of these aspects, this paper presents a review on power electronics technologies for electric mobility where some of the main technologies and power electronics topologies are presented and explained. In order to address a broad scope of technologies, this paper covers road vehicles, lightweight vehicles and railway vehicles, among other electric vehicles.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UID/CEC/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017, and by the FCT Project new ERA4GRIDs PTDC/EEI-EEE/30283/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT

A Novel Single-Phase Grid-connected PV Inverter System

Renewable energy sources, especially solar energy, continue to gain popularity and are ready to become a significant part of global energy portfolio. Grid-connected inverter based distributed generator is becoming increasingly popular due to its advanced control flexibility. Power quality and reliability are attracting much attention in such systems. In order to meet requirements of future applications and maximize the value of inverter system, advanced inverter functions are expected to provide more functionalities. This dissertation proposes a novel single phase inverter system combining proposed advanced control schemes and active power decoupling technique. This dissertation firstly investigates the existing power control schemes for single phase grid-connected inverter and then proposed an independent power control scheme, which is implemented in stationary reference frame. The synchronization function is combined in power loop directly to eliminate the use of conventional phase locked loop. The proposed controller with double-loop current controller based on proportional resonant compensator is proved to achieve good power tracking performance even under distorted grid conditions. Active damping function for resonant peak problem is also implemented in controller. Inverter based distributed generators may operate in different conditions and transition between different operating conditions may result into voltage spikes across the local loads and inrush currents into the grid due to the failure of synchronization on point of common coupling voltage. In this dissertation, a novel control scheme based on model predictive control is proposed for grid connected inverter to enable the capability to operate in both grid-connected and island conditions and the capability to seamless transfer between different conditions through proposed synchronization and phase adjustment algorithm. The auto-tuning strategy of weight factor is presented as well as the stability analysis on the system. Compared with the conventional methods, the proposed seamless transfer control strategy has simpler structure and exhibits good transient performance. Double line frequency ripple power is inherent in single phase rectifiers and inverters and can be adverse to system performance. Therefore, numerous active power decoupling techniques have been introduced to decouple that. All existing active topologies are investigated. Comprehensive comparison is conducted on the minimum required capacitance for power decoupling, the dc voltage utilizations, the current stresses, the modulation complexity and even application evaluations except for power rating and component counts. Based on the investigations and generalized comparison results, a new active power decoupling circuit composed of dual buck converters is proposed together with its control and modulation strategy. The ripple power is stored in split dc link capacitors with high energy utilization. The proposed power decoupling circuit could reduce the storage capacitance needed. The proposed power decoupling circuit does not have shoot-through concern, thus it could enhance the overall system reliability and decoupling performance