Direct power flow modeling and simple controller design for ac/dc voltage-source converters

In this paper, instead of using traditional cascaded control structures, a model-based simple controller scheme is proposed. This scheme, developed on the synchronously rotating dq reference frame, enables the direct active and reactive power regulation in contrast to the usually applied schemes that utilize inner-loops to regulate the d and q current components at a reference, as it is provided by outer-loop active and reactive power controllers. Extracting the suitable model and adopting the grid voltage orientation, decoupling of the control inputs is immediately observed that permits for each input to separately regulate the active and reactive power, respectively. However the main contribution of this study, with respect to other existing direct power control methods, is its theoretical analysis that proves a stable operation and convergence to the desired equilibrium. The analysis and the performance of the nonlinear closed-loop system are verified through simulation results.