Limitations of voltage source converter in weak ac networks from voltage stability point of view

A weak ac grid could be envisioned as a voltage source behind a large synchronous impedance; thus the phase and magnitude of its terminal voltage vary significantly with the magnitudes of active and reactive powers it sinks or sources. Such characteristics present formidable challenges to control and stability of voltage source converters in weak ac grids. Therefore, this paper presents a theoretical analysis which establishes the maximum active power transfer that the voltage source converter (VSC) can exchange with a weak ac grid. The presented analysis reveals that the maximum active power that the VSC can exchange with a weak ac grid is determined by voltage stability limit. The validity of the presented theoretical analysis is confirmed by simplified simulation, and further corroborated by detailed simulations from a VSC model, developed in MATLAB-SIMULINK that incorporates all necessary control systems.