The InterBDL joint project, funded by the Federal Ministry for Economic Affairs and Energy and led by Ulm University of Applied Sciences (THU), is investigating the interoperability of bidirectional charging of electric vehicles. The central research goal is the seamless integration of electric vehicles into existing energy supply systems through systematic analysis of the entire charging and discharging process chain. The innovative research approach comprises a comprehensive investigation using a multi-level test environment: simulations, laboratory experiments and field tests. Particular focus is placed on the use of open standards at system interfaces to ensure optimal communication between electric vehicles and energy systems. The research analyses technical, economic, regulatory and socio-cultural aspects. The aim is to develop concrete recommendations for action for stakeholders from politics, regulation, standardisation, industry and research. To this end, THU is developing a comprehensive system test that holistically evaluates all project functions. This integration test checks bidirectional charging power, energy flow control and communication protocols, and also compares the performance of different charging technologies.