The software has the following features.
- Capable of launching sub-processes for individual feeders. The parallelization helps improves the scalability of the software.
- Capable of configuring each feeder with different DER penetration levels, ratings, and voltage ride through settings (compatible with IEEE Std 1547-2018).
- Capable of introducing fault events during simulation.
- Captures and reports data from both transmission and distribution system for the entirety of the co-simulation.
TDcoSim comprise interface modules and a synchronization module. There are separate interface modules with sockets and interaction protocols for both the T & D and D & DER co-simulations.
1. T&D interface: A Python program that exchanges and iterates information (voltages, currents, and powers) between T&D simulators through synchronization protocols (loosely or tightly-coupled). The Python-based T&D interface is easy to use and adds minimal overhead.
2. D&DER interface: A Python program that exchanges information between the distribution system simulator and the dynamic DER model.
3. Configuration file: It is the main user interface where the user can configure a T+D or T+D+DER co-simulation.
1.PSS®E It is an off-the-shelf positive-sequence transmission system simulator.
2.OpenDSS It is a three-phase unbalanced distribution system simulator.
3.Solar PV-DER simulation utility It is Python utility than can simulate dynamics of grid connected solar PV-DER systems. It uses dynamic phasor models and has single and three-phase PV-DERs.
A schematic showing the software architecture of the TDcoSim package is shown in the Fig. 1.
Fig. 1. Highlevel software architecture
TDcoSim runs with multiple processes. The main process runs the transmission network simulation with PSSE and generates a report of the simulation. Each sub-processes runs the distribution network simulation with OpenDSS and PV-DER. The tool uses the TCP sockets to exchange the data between main and sub-processes. The detailed simulation architecture is shown in the Fig.2.
Fig. 2. Detailed simulation architecture
The simulation is managed by procedures for each model. The procedures define the simulation orders between multiple simulation objects. Each model represent a single simulation object that represents a specific component of T&D system. The procedures have hierarchical one-to-many relationships. The simulation type procedures are connected to multiple OpenDSS procedures via OpenDSS model, and the OpenDSS procedures are connected to multiple PVDER procedures via PVDER Aggregation model.
The sequence of operations within the program is listed below:
- Open TCP server sockets
- Create a transmission network object
- Create transmission network bus objects
- Create distribution network objects
- Create sub-processes
- Establish TCP connection
- Connect to OpenDSS via COM-Interface
- Run the distribution network simulation
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