A New Robust Controller for a Three-Phase Three-Level NPC Rectifier

This paper presents a new control strategy for a three-phase, three-level, neutral point clamped (NPC) rectifier. The controller is a combination of three sub-controllers, one for each of the d-axis, q-axis and zero-sequence components of the converter dynamic model In the proposed control strategy, the zero-sequence and the q-axis sub-controllers are inner loop controllers, whereas the d-axis sub-controller acts as an outer controller. Controller gains are selected in such a way that the zero-sequence controller is faster than the q-axis controller. Converter and AC voltage source parameters (amplitude and frequency) are assumed unknown. A robust nonlinear control law is derived from a backstepping procedure. It considerably attenuates unknown parameters effects. The advantage of the proposed design approach is its simplicity due to the fact that sub- controllers are decoupled, and gains are independently tuned. Simulation results show the effectiveness and the performance of the new robust controller.