Design and analysis of topologies and control algorithms used in ev fast charging systems

Abstract

Because of rising carbon emissions, there is a growing trend toward alternative fuels for vehicles instead of gasoline and diesel fuel. Different studies have been conducted, such as on full electric vehicles with batteries as the main powertrain, hydrogen-fueled vehicles, and hybrid vehicles with both an internal combustion engine and an electric motor. Today, many automotive manufacturers such as Renault, Volkswagen, Citroen and Porsche have released electric variants of some of their models, while some manufacturers have produced electric vehicles with new model names. There are also companies, such as Tesla, that were established just for the production of electric vehicles. Each vehicle has its own on-board charging system for charging the battery packs in each vehicle. However, due to limited space inside the vehicle, this charging system is typically low-powered, and charging the battery packs in a low state of charge takes a very long time. Fast charging stations, which we can think of as fuel stations for charging in a short time, have been developed. On-board charging systems usually have power below 20 kW due to size constraints. However, because the size of the fast-charging station is larger, there are charging stations with power greater than 300 kW. Rather than designing the structure with a single high-power system, many manufacturers prefer a modular structure. The charging station's wide output voltage range is also one of the criteria considered in its design. Over time, with the increase in studies on electric vehicles and charging stations, different standards, such as CHAdeMO and CCS, have emerged in different regions. Even if each standard differs from the other in certain aspects, some standards are globally applicable. The IEEE 519 standard is a general standard for grid-connected power electronic devices, while the IEC 61851 standard is the general standard for conduction charging. In the sub-sections of this standard, rules are also set for different issues such as DC charging stations, insulation types, and communication protocols. First, the structures of various DC fast charging systems and the configurations used are examined in this thesis. The topologies and structures that can be used for each subsystem are then compared, and the DC fast charging system is designed in the topologies of the chosen structure. The design is for the one module that will be located in a modular charging station. A three-level neutral point clamped rectifier topology is chosen as the rectifier. In the grid-connection filter, an LCL filter with a damping resistor and a trap filter tuned to the switching frequency is designed. Isolation between the grid and the vehicle battery pack is provided by a high frequency transformer in the DC/DC converter. A phase-shifted full bridge DC/DC converter is used in this part. However, in order to reduce the switching losses, improve system performance, and increase efficiency, design modifications have been made to the topology for switching at zero voltage transition.