A multirate approach to combine electromagnetic transients and fundamental-frequency simulations

Abstract--- A new multi-rate technique is proposed to combine fundamental-frequency simulation (typical of stability studies) with electromagnetic transients simulation. The objective of this hybrid approach is to obtain more accurate simulations than with the fundamental-frequency approximation, while saving computing time by applying the detailed model to a subsystem only, in some neighbourhood of the disturbance. It also allows to remove some limitations of fundamental-frequency simulation, such as the difficulty of simulating unbalanced faults. A relaxation technique is used to iterate between both models with simple interfacing. Preliminary results obtained with a 74-bus test system are presented, together with a comparison with full electromagnetic transients simulation.