The Impact of Detailed Distribution System Representation in Dynamic Sub-Transmission-Distribution Co-Simulation

There has been a significant growth in the distributed energy resources (DERs) connected to the distribution networks in recent years, increasing the need for modeling the distribution networks in detail in conjunction with the sub-transmission/transmission networks. This paper models a real distribution/ sub-transmission network using a three-phase/three-sequence co-simulation. One of the modeled distribution feeders has a high penetration of DERs with significant reverse power flow and is modeled including the secondary network. Custom user-defined models are used to represent the solar photovoltaic (PV) units on the feeder including advanced controls and abnormal voltage responses from IEEE 1547–2018 standard. The co-simulation framework developed supports power flow/steady state as well as dynamic analysis. Using this developed framework, this paper studies the impact of balanced and unbalanced faults applied to the distribution and sub-transmission networks. The impacts of the faults on the feeder with the high penetration of DERs are studied in terms of the solar PV units tripping due to under/overvoltages and the resulting change in the feeder-head flow. It is seen that the detailed modeling of the distribution network is needed for accurately capturing the response from the distribution-connected DERs during fault events both on the distribution as well as sub-transmission networks.