High Voltage Direct Current (HVDC) grid concept has recently been introduced as the next step to the point-to-point HVDC links to maximise the benefits of more power flow share, and reduce the impact of renewables intermittency. However, the integration of DC grid within existing AC systems is complex and very challenging. The compatibility between the two systems under different operating conditions needs to be fully understood. This will require sophisticated models and analysis of their behaviour using powerful tools. This paper presents a representative dynamic model of a hybrid AC-DC gird, and investigates the transient and dynamic interaction between the AC and DC grids under different fault conditions. The model represents a reduced AC UK power system interfaced to a detailed four-terminal DC grid. The developed mode is built in Real Time Digital Simulation (RTDS) using dual time steps simulation techniques
