A Novel Method for Synchronization with Unbalanced Grid: An Experimental Investigation

A major issue for the grid connected renewable energy system specifically during unbalance grid condition is the grid synchronization. Under unbalance grid condition, in order to implement stable operation, it is necessity to determine the grid parameter accurately and rapidly. Algorithms used for Grid synchronization plays an important role in the control and steady operation of grid-connected converters. To implement stable and steady control strategy under unbalance grid condition, the detection of grid parameter accurately and rapidly are also crucial. Synchronous Reference Frame Phase Locked Loop (SRF-PLL) works satisfactory for balance grid condition but its performance deteriorates with unbalance grid condition. However, Dual Second Order generalized Integrator (DSOGI)-PLL performs reasonably well in grid synchronization during unbalance grid condition. DSOGI consists of a low pass lter (LPF) and band pass filter to attenuate harmonic of the unbalance grid. In SRF-PLL, the angle is tracked in such a way that the maximum phase voltage is reflected on d-axis while component voltage along q-axis is zero. Hence taking the advantages of DSOGI and SRF-PLL, the DSOGI-PLL architecture has been proposed in this paper. The proposed DSOGI-PLL has better performance in grid synchronization under unbalance grid conditions.