A Lyapunov-based nonlinear direct power control for grid-side converters interfacing renewable energy in weak grids

This paper presents a nonlinear direct power control (DPC) strategy for grid-connected voltage source converters based on adopting instantaneous active and reactive power as dynamic variables. A general uniform expression with the instantaneous magnitude and phase for arbitrary three-phase signals has been established in this paper. The proposed model gives instantaneous relationships between the variables and no restrictions are imposed on the voltage or current waveform, i.e., the model is valid in the entire state space. A higher control layer, i.e., the power plant centralized controller, generates the reactive power command to support the point of common coupling voltage. A dynamic current limitation mechanism is included to protect the converter during grid faults. The stability of the control system is analyzed via the Lyapunov theory, and the system states are proven to converge to the desired equilibrium point asymptotically. Simulation results using PSCAD/EMTDC demonstrate that the grid-side converter using the proposed DPC approach has a fast response (less than 40 ms) along with very small power variation even with low SCR and is demonstrably superior to the latest DPC scheme in the literature under various grid conditions.