The attached project is based on the medium voltage distribution network benchmark developed by Cigré (European configuration) [1]. The MV network includes two points of connection to the upstream HV network, but in the operation scenario used for the analysis, the MV network operates islanded.

Three diesel gensets, each with a nominal power of approximately 5 MVA, are added and connected to the MV network through step-up transformers. Their simulation model is based on the template available in the PowerFactory global library “Diesel Genset 3.8MW Islanded Operation”. The sudden trip of generator #1, which causes a deviation in the network frequency, is simulated. The impact of different configurations of a Battery Energy Storage System (BESS) with converter is evaluated.

The following study cases were prepared:

• 00_Comparison: This case shows a comparison of results from all study cases. It is recommended to execute the preconfigured Task Automation command (ComTasks) to run the dynamic simulations across all study cases. Subsequently, individual study cases can be activated to facilitate a detailed analysis of the results.
• 01_No BESS: This case corresponds to the initial configuration of the network, with no BESS. The simulation results (see “Plot Generators”) show that the frequency reaches a nadir of 47.6 Hz and then stabilizes successfully at 48.7 Hz after the action of the primary controllers in the diesel gensets, configured with a droop of 5%.
• 02_BESS GFL - ramp rate 0.1 p.u./s: This case analyses the impact of a BESS with a grid-following (GFL) converter. The BESS is meant to replace the primary control power of diesel genset #3, which is deactivated. The simulation model of the BESS is based on the template available in the PowerFactory global library “WECC DER Storage 14.25MW 50Hz[BW1] ”. The nominal rating and the droop are adjusted to be consistent with those used in the diesel genset models. In addition, the maximum power-up ramp rate is set to 10%/s. The simulation results show that the system is not capable to stabilize successfully after the event, and there is a frequency collapse in the network.
• 03_BESS GFL - ramp rate 0.5 p.u./s: This case is similar to the previous, but the BESS is adjusted with a maximum power-up ramp rate of 50%/s. This higher ramp-up capabilities improve the frequency stability of the system, and the simulation results indicate that the system is now capable to stabilize successfully after the event, with a nadir of 47.7 Hz.
• 04_BESS GFM VSM: This case analyses the impact of a BESS with a grid-forming (GFM) converter, implemented as a virtual synchronous machine. The simulation model of the BESS is based on the template available in the PowerFactory global library “Virtual Synchronous Machine”. The nominal rating, acceleration time constant and damping are adjusted to be consistent with the diesel genset models. The simulation results show that the system is capable to stabilize successfully after the event.
• 05_BESS GFM Droop: This case analyses the impact of a BESS with a grid-forming (GFM) converter, implemented as a droop controller. The simulation model of the BESS is based on the template available in the PowerFactory global library “Droop Controlled Converter”. The nominal rating and the active power droop coefficient are adjusted to be consistent with the diesel genset models. The simulation results show that the system is capable to stabilize successfully after the event.

Notes:

1. The grid-forming converter models used in this example are valid for positive sequence (balanced) RMS simulations and for EMT simulation. They do not consider possible inner control loops. You can find examples for grid-forming converters with inner control loops in the "MV Microgrid" application example in PowerFactory.
2. The WECC models are only valid for RMS simulation, not generally suitable in EMT simulation. Consequently, they were excluded from the EMT simulation study cases.

References:

[1] Cigré Task Force C6.04, "Benchmark systems for network integration of renewable and distributed energy resources," 2014.