Abstract
•This paper has established that the voltage stability limit is the main factor that restricts the Voltage Source Converter (VSC) active power exchange with weak ac grids.•The factors that restrict VSC active power capability in weak ac grids have been established with aid of static voltage stability analysis.•Approximate expressions that define VSC and corresponding ac voltage before system collapse have been established.•The presented theoretical analysis, detailed discussions and observations have been corroborated quantitatively, using simulations.
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.