Electro-Thermal Modeling and Analysis of a Bidirectional Charger for Electric Vehicles

In recent years, the use of electric vehicles and their associated charging systems has seen significant improvements. This thesis focuses on the study of bidirectional chargers for electric vehicles. These systems are of particular interest because they are capable not only of charging the battery of the electric vehicle but also of utilizing it to support the electrical grid during periods of high demand. The primary objective is to investigate converter topologies and implement strategies for the thermal analysis of the active power components. The initial phase involved a theoretical study of the state-of-the-art architectures used in these converters, examining their characteristics, operating principles and respective advantages and disadvantages. Subsequently, a market analysis was conducted to examine evolutionary trends, including regional variations. The core of this thesis involved developing a model of a bidirectional charger within PLECS environment. Specifically, the system consists of two cascaded stages: an isolated DC/DC connected to the battery and an AC/DC connected to the three-phase grid. After constructing the circuit schematic, a thermal network was designed to describe device behavior based on energy dissipation during normal operation. At same time, specific thermal libraries for devices were created, incorporating the parameters necessary to evaluate losses and thermal behavior into the model. To reduce the computational cost of simulations, a methodology based on Look-Up Tables (LUTs) was developed. This approach minimizes the time required to calculate device thermal behavior, with the purpose to enabling the tracking of junction temperature of the active components with an acceptable timeframe. The developed model was used to evaluate various charge and discharge profiles. The objective was to analyze the switching losses, conduction losses and also the thermal cycles to which the devices are subjected. The results obtained serve as a basis for future reliability analyses and for estimating component aging. In particular, the junction temperature profiles and thermal cycles derived from the simulations can be used as inputs for degradation models. This will enable a correlation to be established between the charger's operating conditions and component reliability.