Isolated Single-stage Power Electronic Building Blocks Using Medium Voltage Series-stacked Wide-bandgap Switches

The demand for efficient power conversion systems that can process the energy at high power and voltage levels is increasing every day. These systems are to be used in microgrid applications. Wide-bandgap semiconductor devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) are very promising candidates due to their lower conduction and switching losses compared to the state-of-the-art Silicon (Si) devices. The main challenge for these devices is that their breakdown voltages are relatively lower compared to their Si counterpart. In addition, the high frequency operation of the wide-bandgap devices are impeded in many cases by the magnetic core losses of the magnetic coupling components (i.e. coupled inductors and/or high frequency transformers) utilized in the power converter circuit. Six new dc-dc converter topologies are propose. The converters have reduced voltage stresses on the switches. Three of them are unidirectional step-up converters with universal input voltage which make them excellent candidates for photovoltaic and fuel cell applications. The other three converters are bidirectional dc-dc converters with wide voltage conversion ratios. These converters are very good candidates for the applications that require bidirectional power flow capability. In addition, the wide voltage conversion ratios of these converters can be utilized for applications such as energy storage systems with wide voltage swings

MODELING, DESIGN, AND IMPLEMENTATION OF HIGH GAIN POWER ELECTRONIC DC-DC CONVERTERS FOR NANOGRID APPLICATIONS

Nanogrids are nothing but power distribution systems that are based on renewable energy sources and are apt for low-power home applications. Nanogrids are considered to be the building cells of a Microgrid. Nanogrid is intended for feeding domestic loads (of the order of 100 W to 5 kW) from renewable energy sources such as wind farms, roof-top solar photovoltaic, biomass, and fuel cell, etc. Nonetheless, the voltages produced by these renewable energy sources are small and not sufficient enough to be utilized in all the applications. Hence, it is necessary to include high gain and high-efficiency DC-DC converters in the system. To interface the generators and the loads, power electronic converters are employed within a Nanogrid. The power system grid is also linked to the Nanogrid using these converters. The most fundamental characteristics of the high-gain DC-DC converters are high efficiency, high-voltage gain, and low voltage/current stress on switching components. A comprehensive literature review of various boosting methods is disseminated in this research work. After a detailed investigation, five new DC-DC power converter topologies have been designed and developed to achieve high gain factors with reduced switch ratings and low cost for use in Nanogrids. The proposed converters cannot only reduce voltage/current stresses across the switching components significantly but also achieve a higher voltage gain at moderate duty cycles with a lesser number of components. Moreover, the proposed converters are designed in such a way that they can maintain a continuous input current, and hence making them useful for power conversion in the battery, fuel cell, and solar PV applications. By using boosting technique five novel high voltage gain DC-DC converters are developed and presented in the dissertation, namely: 1. modified Switched Inductor Boost Converter (mSIBC) with reduced switch voltage stress, 2. Transformer-less Boost Converter (TBC) with reduced voltage stress, 3. Switched-Inductor based DC-DC Converter with reduced switch current stress, 4. Novel High Gain Active Switched Network-Based Converter, and 5. Double Stage Converter with low current stress for Nanogrid The detailed theoretical analysis of the voltage conversion ratio, parameter design, continuous and discontinuous conduction mode, and advantages are presented. In addition, a detailed comparative study of each converter topology is also given. The functionality of the proposed power converters is tested in real-time by developing Laboratory prototypes of the proposed converters and the theoretical analysis is validated by obtaining the experimental results. The proposed converter configurations are simulated in MATLAB as well, to verify the theoretical analysis. Simulation results of all the proposed converters are presented indicating clear evidence of the expected predictions in close proximity with experimental results

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