Because of its fast response, high power density, no strict installation location specification, battery energy storage is one of the most promising energy storage technologies. When a cascaded converter is used in a large capacity battery energy storage system, it can be directly connected to the medium/ high voltage power system without a transformer, i.e. high voltage battery energy storage system without transformer, having the advantages of moduling, connecting to high-voltage system without a transformer, single-machine high capacity, multi-level output, etc. However, there is still a lack of model development and control strategy research based on real-time simulation in the study of such a system considering the battery’s external characteristics. The first CPU-FPGA real-time simulation model in the world of such a storage system is developed. Taking a typical 35 kV system as an example, the corresponding real-time simulation system is built based on RT-LAB platform developed by OPAL-RT. It is verified that control and protection close access is feasible. Finally, the test results in different conditions shows the effectiveness of the simulation model and the relevant control and protection strategy. It can provide technical support for the design and control development of a high-voltage large capacity battery storage system.