Design and analysis of a novel bounded nonlinear controller for three-phase ac/dc converters

A bounded nonlinear dynamic controller suitable for the regulation of the duty-ratio input of a three-phase AC/DC voltage source converter (VSC) is proposed. The controller design is based on the complete nonlinear average model of the power converter and takes into account that the controlled inputs -duty-ratio signals- should be saturated in a disk area on the input phase portrait while the grid voltages constitute the uncontrolled inputs. The proposed design approach fully satisfies the input constraint while simultaneously achieves precise DC bus voltage regulation and unity power factor operation. In addition, opposite to the conventional controllers, the present development is totally independent from the system parameters. A detailed nonlinear analysis shows that the closed-loop system operating under the uncontrolled external inputs has the input to state stability (ISS) property while the analysis is further extended to prove convergence to the desired nonzero equilibrium when constant external inputs act on the system. Simulation results verify the effectiveness of the controller under sudden DC bus voltage reference and load variations.