RMS Model of MMC-VSC-HVDC System with Grid-Forming Control Concept

This paper presents a RMS model for a Voltage Source Converter High Voltage Direct Current system in modular multilevel converter topology (MMC-VSC-HVDC), incorporating a grid-forming control strategy. The converter stations are represented by two controlled voltage sources on both the AC and DC sides. The coupling between the AC and DC sides of the converter station is achieved through power balance control, which is integrated into the control system governing the two voltage sources. Detailed descriptions of the control systems behind each voltage source are provided, including the grid-forming control concept utilizing swing equation emulation and virtual admittance control for reference current limitation. The proposed model's accuracy is validated through time-domain simulations, comparing its performance against a detailed Electromagnetic Transient (EMT) model under various typical disturbance scenarios in time domain simulation. The impact of AC network strength and time step simulation on model accuracy is also examined.