Adaptive nonlinear control of a three-phase three-level Neutral Point Clamped rectifier

This paper presents a new control strategy for a three-phase three-level Neutral-Point-Clamped boost rectifier, which consists of applying an adaptive nonlinear control. The exact nonlinear Multiple-Input Multiple-Output state space model of the rectifier was obtained in (d,q,0) reference frame using the power balance between the input and output sides. Applying a change of coordinates and nonlinear feedback linearization technique to the nonlinear model results in a linear and decoupled model. Then a robust Model Reference Adaptive Control scheme is proposed for the feedback-linearized system in order to control line-currents, output and neutral point voltages and also to reduce the influence of the parameter uncertainty. This control uses a 3kHz Pulse Width Modulator. Computer simulations based on the use of Power System Blockset and Simulik/Matlab verify the robustness of the proposed control law in balanced output load conditions. The line-current THD and output voltage ripples are very low.