Control algorithm based on limit cycle oscillator-FLL for UPQC-S with optimized PI gains

This paper involves a limit cycle oscillator-frequency lock loop (LCO-FLL) based control algorithm for unified power quality controllers-S type (UPQC-S) for compensation of reactive power, to maintain a unity power factor, regulate constant voltage at the PCC, mitigate sag, swell and to eliminate harmonics. In this approach, an extraction of fundamental in-phase and quadrature components for the estimation of reference signals are taken from the LCO-FLL circuit. The control LCO-FLL provides a high grade of protection against sag-swell voltages, unbalance loading and harmonics present in the utility grid. In addition to that, it has advantageous characteristics of synchronization with the grid frequency at any previously mentioned conditions without use of phase locked loops or trigonometric functions. Other advantages of the LCO-FLL are to give useful information to estimate fundamental components from a highly polluted grid scenario. The values obtained from the JAYA optimization algorithm are used to fine-tune the proportional integral (PI) controller gains, so that it maintains DC link voltage to the desired level. The mean square error (MSE) is employed as an objective function for optimizing the error between actual and reference values. The control algorithm based on LCO-FLL is developed in MATLAB/Simulink software and it is tested for power conditioning features .