Passivity-Based Analysis and Performance Enhancement of a Vector Controlled VSC Connected to a Weak AC Grid

Despite attempts to increase the active power capability of vector-controlled voltage source converters (VSCs) connected to very weak grids, the interaction between the control dynamics and physical system is not completely understood. The result is often complex strategies that are difficult to implement. This paper proposes an intuitive modification of the VSC control based on physical considerations and dynamics of existing control. Several physical variables as seen from the point of common coupling (PCC) are found to contribute to the detrimental behavior of the VSC under weak connections. Hence, eliminating the impacts of these variables through feedforward eliminates their influence and significantly improves the active power capability. Notably, the basic structure of the vector controlled VSC is kept and its output-impedance is effectively reshaped. The proposed modification is validated through nonlinear time-domain simulations in MATLAB/Simulink Simscape Power System and results demonstrate the simplicity and intuitiveness of the modified structure.