PLL Control Design for Voltage Source Converters with Frequency and Current Limiting Properties

A novel phase locked loop (PLL) control scheme is introduced for a voltage source converter (VSC) that is connected to the main grid through an LR filter; also, new suitable inner-loop current controllers are implemented. This new approach enables us to accurately limit the ac current value of the VSC, even under hard abnormal conditions whereas its robust synchronizing operation additionally provides en-hanced frequency limiting properties. The whole analysis is implemented in the well-known d-q synchronously rotating reference frame which is widely used in modern power grid studies, especially when distributed generation (DG) from renewable energy sources exists. A fundamental advantage of the proposed methodology constitutes the fact that it allows to prove asymptotic stability and convergence to an equilibrium through large signal analysis. To verify the theoretical results and to evaluate the expected performance, the system under consideration with the proposed controllers is simulated under cumbersome scenarios featuring large current flows and frequency deviations. In all cases, both the current and frequency limiting properties and the improved system dynamic response are fully confirmed.