Energy-efficient operation of vapor compression systems applied to the battery thermal management of electric buses

In this research, an energy-efficient operating strategy of a battery thermal management system (BTMS) of electric buses is investigated. This is accomplished by addressing both liquid-based battery temperature control and ideal set-point operation of vapor compression systems in general. To examine the thermal behavior of the battery and the required cooling load, a novel transient calculation method of the thermal battery system is proposed. The results indicate a sufficient regulation of the cell temperature via quasi-stationary control. Consequently, the battery cooling unit can operate at steady-state conditions to meet the battery temperature requirements. To optimize the energy efficiency of the battery cooling unit, detailed theoretical and experimental analysis of the ideal steady-state operation of VCS are carried out for a serial cooling unit of the Mahle GmbH. Based on the results, a new model-based set-point optimization method is proposed to drive the VCS to ideal settings. For quasi-stationary applications, the proposed method represents a promising alternative to extremum seeking control or other advanced methods that may be more accurate but have a high convergence time.