LQR with integral action controller applied to a three-phase three-switch three-level AC/DC converter

This paper presents a Linear Quadratic Regulator with Integral action (LQIR) applied to the three-phase three-switch three-level boost-type Vienna rectifier. The design of the controller is based on the small-signal model of the converter, which is developed in the dq0 rotating reference frame using the state-space averaging technique along with the linearization process. This controller is designed to regulate the DC bus voltages, ensure low THD of line currents and compensate the reactive power. While the standard linear quadratic regulator provides only proportional gains, the integral action is added to cancel the steady-state errors in the control loop. This is done by extending the state vector to include the integral of the source currents dq0 components, the overall output voltage and the DC load unbalance. The controller is tested using Matlab/Simulink, considering successively the cases of a balanced load, an unbalanced load and mains voltages disturbances. The obtained results have shown high performance compared to other control techniques applied to this same topology.