There is an increasing interest among utilities to perform real time simulation of large power systems. If the entire power system is simulated using real time simulators, the cost of hardware can be prohibitive to many utilities. There has been many efforts to perform real time co-simulation where the part of the network that needs to be modelled with details is modelled using Electromagnetic Transient (EMT) models while the remaining part modelled using conventional Transient Stability (TS) models. The established approach of interfacing the two networks (EMT and TS) is to have a Frequency Dependent Network Equivalent at the boundary between the EMT and TS parts of the network.
We investigated an alternative approach that eliminates the need of an FDNE. In the proposed co-simulation model the interface between the two models is a portion of the network (buffer zone) modelled using Dynamic Phasors (DP). This requires two interfaces, namely, EMT to DP and DP to TS. The challenges of interfacing EMT-DP and DP-TS and the proposed solutions will be presented. A data prediction method is used to overcome the time-step delay between EMT and DP models. Since high frequency dynamics in the TS part are of no interest, the TS part of the simulation uses a relatively larger time-step than DP and EMT. The challenges associated with using two different time steps will be discussed and the proposed solutions will be presented. The numerical stability and accuracy of the proposed EMT-DP-TS co-simulation tested on the IEEE 68 bus system with an LCC HVDC in-feed will also be presented to conclude that the proposed approach has the potential to replace FDNE at interfaces.
Harshani Konara, U.D. Annakkage, C. Karawita, University of Manitoba