The attached project includes a PV plant model connected to an external grid in a single-machine infinite-bus (SMIB) configuration. The template “WECC Large-scale PV Plant 110MVA 50Hz”, available in the global library of PowerFactory, was used for the PV plant model. It includes the converter model type WECC REGC_C, which was originally developed to reproduce small-signal and large-signal oscillatory instabilities associated with converters interfaced at low short circuit locations.

One of the main objectives of this model is, according to the developers, “to bridge the gap between positive sequence simulation platforms and point on wave simulation platforms, to provide system planners with an intermediate step to help further screen locations where a detailed electromagnetic simulation would be required”. It is implemented as a RMS model but validated against EMT simulations [1].

In the project, the dynamic behavior of the plant is evaluated from a small-signal and large-signal stability standpoint. The small signal stability is analysed by means of step response tests and eigenvalue plots. The large signal stability is analysed by simulating a solid three-phase short-circuit at the point of connection (POC), cleared after 150 ms.

Five different study cases are included in the project, with variations in the parameters of converter model, the output power of the PV plant and the short-circuit power of the external grid, as shown in the following table:

The new set of converter parameters refer to the converter model REGC_C, where the parameters Kii (integral gain of the inner current loop) and Kipll (integral gain of the PLL) were increased from 70 and 1400 (default) to 150 and 2000 (new), respectively. The new parametrization represents a more aggressive tuning which, in weak grid conditions, can lead to instability.

The study case “00_Comparison” includes plots comparing the results from all study cases. It is recommended to execute the preconfigured Task Automation command (ComTasks) to run the dynamic simulations and modal analysis across all study cases. Subsequently, individual study cases can be activated to facilitate a detailed analysis of the results.

References:

[1] D. Ramasubramanian, W. Wang, P. Pourbeik, E. Farantatos, A. Gaikwad, S. Soni and V. Chadliev, "Positive sequence voltage source converter mathematical model for use in low short circuit systems," IET Generation, Transmission & Distribution, vol. 14, no. 1, pp. 87-97, 2020.