Abstract
Global emissions must be reduced in order to slow down the planet degradation and achieve Climate Neutrality, which was set as an international objective for 2050 with the Paris Agreement. All the activities must contribute to this scope, even though there are still several sectors hard to mitigate; one of this is represented by agriculture machinery, which started to receive more attention only in the last decade. As a result, new and more restrictive emissions regulations have been introduced around the world to limit their emissions. ICE exhaust gas cleaning solutions are not enough to meet the current and future regulations, with particular reference to the carbon footprint. Electrified powertrains are a possible solution to this problem; their potential has been demonstrated with the automotive passenger vehicles. However, off-road machinery, in particular tractors, have more demanding and varied working conditions that make the design of an electrified powertrain very complicated. In fact, many manufacturers cannot afford the research costs required to develop this technology. Moreover, batteries working limits, high price and long term performance are additional factors that must be overcome for the widespread use of this technology. On this basis, this thesis presents a methodology capable of optimally sizing the different components of a hybrid powertrain for a tractor. The most important features of this approach are that: (i) it considers the energy management of the power sources during the optimization, (ii) the cost function includes economic and environmental aspects and (iii) the volume constraints for tractors powertrains have been considered; moreover, realistic data and validated models on the storage cells, thermal engines and machine loads were considered. The potential of this methodology has been demonstrated through the case study of a vineyard/orchard tractor. In particular, it was found that the best solution is a series hybrid configuration, which allows a 20% reduction in greenhouse emissions. Furthermore, it was found that hybrid tractors are already convenient with the current situation in different European countries and this trend is expected to increase with the further reduction of the battery price, the likely increase in the price of agrodiesel and more restrictive emissions standards. It was confirmed that the battery is the critical component of the powertrain, so this work also proposes several efforts to better understand batteries and facilitate their design and management. Equivalent electric circuits are the most used approach to model battery cells. In this Thesis, a technique has been developed to identify the parameters of a 1 RC cell model from a set of specific experimental data. Thanks to the innovative strategy suggested to cope with measurement noise, this method can be employed on-line to update the parameters and maintain the accuracy of the model. In fact, these parameters are strongly affected by aging. Therefore, aging and SOH estimation have been another focus of this work. In particular, the relationship between mechanical measurements and SOH was studied, obtaining that pressure is linearly related to cell resistance and with a third order polynomial to the SOH. Thus, embedding a pressure sensor in the battery module structure could improve the cells SOH estimation and, consequently, the vehicle autonomy, contributing to increase the reliability of the system. Finally, an open source tool for battery modules electro-thermal simulation has been developed. This can be used to support the design and control of battery modules, as it is easily configurable and it allows to study the electric performance of the cells and their interactions considering the heat flow and temperature distribution inside the module. The potential of this tool was demonstrated with the simulation of a battery module with a 18s2p configuration, to be used in a series hybrid tractor. All these contributions together create a new bridge that is intended to help the diffusion of hybrid tractors and, more generally, of electrified vehicles.