Review on unidirectional non-isolated high gain DC-DC converters for EV sustainable DC fast charging applications

Modern electrical transportation systems require eco-friendly refueling stations worldwide. This has attracted the interest of researchers toward a feasible optimal solution for electric vehicle (EV) charging stations. EV charging can be simply classified as Slow charging (domestic use), Fast charging and Ultrafast charging (commercial use). This study highlights recent advancements in commercial DC charging. The battery voltage varies widely from 36V to 900V according to the EVs. This study focuses on non-isolated unidirectional converters for off-board charging. Various standards and references for fast off-board charging have been proposed. Complete transportation is changed to EVs, which are charged by the grid supply obtained by burning natural fuels, contributing to environmental concerns. Sustainable charging from sustainable energy sources will make future EV completely eco-friendly transportation. The research gap in complete eco-friendly transit is located in interfacing sustainable energy sources and fast DC EV charging. The first step towards clean, eco-friendly transportation is identifying a suitable converter for bridging the research gap in this locality. A simple approach has been made to identify the suitable DC-DC converter for DC fast-charging EVs. This article carefully selected suitable topologies derived from Boost, SEPIC, Cuk, Luo, and Zeta converters for clean EV charging applications. A detailed study on the components count, voltage stress on the controlled and uncontrolled switches, voltage gain obtained, output voltage, power rating of the converters, switching frequency, efficiency obtained, and issues associated with the selected topologies are presented. The outcome of this study is presented as the research challenges or expectations of future converter topologies for charging

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

Development of novel non-isolated unidirectional DCDC multistage power converter configurations for renewable energy applications- hardware implementation and investigation studies

Abstract: In the last decades, there is a rapid development towards new energy sources due to the increasing demand of energy and cost of the fossil fuels. Renewable energy sources getting more popular day by day due to government support and carbon dioxide (CO2) emission reduction policy to reduce greenhouse gas emissions. Photovoltaic energy generation is the excellent example of energy generation through various serious parallel arrangement of a small voltage generating cells or modules. There are directly use of synchronous generators to transfer power to grid from hydro energy plant, geothermal energy plant, bio-fuel energy plants. However, the photovoltaic energy generation systems requires the power electronic converters system to satisfy the demand of realtime application or electric grid. Therefore, for real-time applications or before feeding energy to the grid via inverter, photovoltaic systems linked with DC-DC converters, which have high-voltage conversion ratio capability. Thus, DC-DC power converter is the paramount constituent in the photovoltaic power conversion stage. This research work carried out in focusing on hardware implementation and investigation studies of novel non-isolated unidirectional DC-DC multistage power converter configurations for renewable energy application. The comprehensive review of various unidirectional non-isolated DC-DC multistage power converters are presented and it is found that not all of them have the capability to convert low voltage into high voltage, thus not suitable for photovoltaic energy applications. It is investigated that there is a scope to design new DC-DC multistage power converter topologies configurations with high voltage conversion ratio by employing a new arrangement of reactive elements and semiconductor devices. A new breed of DC-DC multistage power converters called “X-Y converter family” proposed for photovoltaic application by utilizing the switchedinductor, the switched capacitor, the voltage lift switch capacitor and modified voltage lift switched capacitor, voltage doubler and multiplier boosting techniques. The derivation of voltage conversion ratio, advantage of each converter of X-Y family and hierarchy of X-Y family is discussed. The research work also proposed a new DC-DC multistage power converter without a magnetic component for photovoltaic application by utilizing the concept of switched capacitors. An original Transformer and Switched Capacitor (T-SC) based multistage power converter proposed for high-voltage/lowcurrent photovoltaic applications by combining the feature of the boost converter, transformer and switched capacitor. New Nx IMBC (Nx Interleaved Multilevel Boost Converter) or Cockcroft Walton (CW) Voltage Multiplier based Multistage/Multilevel Power Converter (CW-VM-MPC) converter topologies are presented to achieve maximum voltage conversion ratio by utilizing the feature of Cockcroft Walton (CW) voltage multiplier. Moreover, the proposed multistage power converter compared with each other as well as recently proposed multistage power converters in term of voltage conversion ratio, number of devices and costs.D.Eng. (Electrical and Electronic Engineering