A Comparative Study of PI and PDF Controllers for DVR Under Distorted Grid Conditions

In this paper the enhancement of power quality related issue is dealt by using Dynamic Voltage Restorer (DVR). There are mainly two aspects with DVR injection voltages one is reference generation and the other is control of DVR. Under unbalanced grid conditions negative sequence components will appear in the grid voltage and causes continuous oscillations in the estimated dq - voltages, which makes sag detection difficult with conventional SRF-PLL. In this paper Double Second Order Generalized Integrator (DSOGI) prefilter based PLL is used for extracting the symmetrical components of grid voltage and further mitigate the harmonic ripple in estimated dq quantities. Further a Pseudo Derivative Feedback (PDF) controller is proposed for single loop voltage feedback control for DVR. The robustness of the proposed controller is verified through comparative studies with PI controller using time response analysis. It is observed that the proposed PDF controller improves the system dynamics i.e., eliminates oscillations and overshoot compared to PI controller. MATLAB/SIMULINK platform is used to perform simulation studies for the 10 kV system subjected to different disturbances viz balanced and unbalanced voltage sags for both PI and PDF based controller. Finally, the experimental studies are carried out for low voltage DVR of 0.5 kVA, 100 V laboratory prototype.