Numerical Investigation of an Optimal Thermal Management Strategy for a Plug-In Hybrid Electric Vehicle

Recent UE legislations requires that CO2 emissions of newly registered passenger cars should reduce by 55% in 2030. The widespread adoption of electrification powertrains will be needed to achieve these targets. Moreover, the thermal management of the vehicle will play a fundamental role to guarantee that the powertrain will operate with high efficiency. The object of this thesis, made in collaboration with POWERTECH Engineering S.r.l., is therefore the development of a control strategy aimed to optimize both the thermal management and the fuel efficiency of a Plug-in Hybrid Electric Vehicle (PHEV). First, a physical vehicle model, representative of a C-SUV passenger car, is built on the commercial software GT-SUITE. This vehicle model is composed by different subsystems: the driveline and the powertrain (electric motor and battery pack, engine), the thermal circuits for the thermal management and the controllers. The driveline contains all the hybrid powertrain components, for example engine, electric motor, clutches, battery, and the controllers linked to these components. The thermal one includes the cooling circuit with radiators, heat exchangers, oil circuit, among the others. The controller overseeing the Energy Management Strategy of the entire powertrain is developed in Simulink. As a starting point, an online Equivalent Consumption Minimization Strategy (ECMS) is used. Then, the ECMS controller is updated in order to account for the engine thermal state. In this way the controller at each time interval receives different powertrain inputs, such as the driver power demand and the engine temperature and computes the optimal split between engine and electric motor power. The vehicle model featuring the ECMS accounting for the engine thermal state is tested in charge sustaining operation along two different driving cycles: the New European Driving Cycle (NEDC) and the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). Moreover, two different environment temperatures have been considered: -10 °C and 20 °C. The controller showed an improved fuel consumption for both the starting temperatures: 1.5% (-10 °C) and 1.6% (20 °C) along the NEDC and 1.1% (-10 °C) and 1.5% (20 °C) along the WLTC, demonstrating that the integration and knowledge of the thermal state of the powertrain allows to improve the energy management strategy of hybrid vehicles.