Comparative analysis involving PI and state-feedback multi-resonant controllers applied to the grid voltage disturbances rejection of a unified power quality conditioner

This paper presents a detailed evaluation of the grid voltage disturbance rejection capability using three kinds of controllers inserted into the current control loop of the series converter that composes a single-phase unified power quality conditioner (UPQC). The mentioned controllers are evaluated and compared to each other to give subsidies to the designer in choosing the one that performs better, since static behaviour of the UPQC is directly affected with the presence of grid voltage disturbances. Firstly, the classical proportional-integral (PI) controller is discussed. After that, in order to improve the performance of the conventional PI controller, multi-resonant (MR) terms are added resulting in the PI-MR controller. Finally, a state-feedback controller composed of an error integrator and multi-resonant terms, named SF-MR controller is employed, where the state-feedback controller gains are calculated using an increased model of the controlled system. Independent of the three current controllers implemented in the series converter, the parallel converter of the UPQC will always be controlled to operate using the SF-MR controller. Mathematical models, stability and sensitivity analyses are presented and discussed in detail. Furthermore, experimental results are presented to comparatively evaluate the static UPQC performance involving the PI-MR and SF-MR controllers, as well as the well-known conventional PI controller.