A robust adaptive controller for a three-phase three-level neutral-point clamped rectifier

This paper presents a new adaptive strategy to control the DC output voltage and the power factor of a three-phase, three-level, neutral point clamped (NPC) boost rectifier. The proposed controller combines three sub-controllers. The zero-sequence controller maintains the difference between the upper and the lower DC output voltages equal to zero. The q-axis controller keeps the power factor equal to 1. The d-axis controller is used to meet active power and DC output voltage specifications, despite balanced or unbalanced load conditions. Converter and AC voltage source parameters (amplitude and frequency) are assumed unknown. A robust adaptive nonlinear control law is derived from a backstepping procedure and helps to stabilize the system and attenuate unknown parameters effects. The adaptation laws are based on the projection method and guarantee that estimated parameters converge and remain inside predefined domains. The main advantage of the proposed design approach is its simplicity due to the fact that sub-controller designs are decoupled, and their gains are independently tuned. Simulation results demonstrate the effectiveness and the performance of the new robust adaptive controller.