Voltage Sag/Swell Detection Based on Decoupled Stationary Reference Frame PLL in DVR

The voltage detection process is a basic task for the control system in the Dynamic Voltage Restorer (DVR). This detection has great importance because it is responsible for calculating the reference voltage and consequently the compensating voltage values. The stationary reference frame Phase Locked Loop (αβ-PLL) is widely used in three-phase grid-connected power converters because of its simple implementation and accurate estimation of the phase angle of the grid. The αβ-PLL works excellent in the case of ideal grid conditions without unbalance, DC offset, or any grid disturbance. However, it is not a good solution in the presence of unbalanced grid voltages. Decoupled stationary reference frame (Dαβ-PLL) overcomes the limitations of αβ-PLL by decoupling the positive and the negative sequences of the grid voltage. In this proposed study, the Dαβ-PLL is implemented as a voltage detection method applied in the control system of the DVR. The control system combined a feedforward control signal and a closed-loop feedback control signal. The Proportion Integral (PI) controller is implemented in the dq synchronous rotating reference frame. The system is simulated using MATLAB/Simulink. The results show that the Daß-PLL success in synchronizing with the grid voltage even if in the case of unbalance and superior to the αβ-PLL.