A Simple and Practical PLL for Single-Phase Grid-Tied Inverters Facing with Abnormal Grid Voltage Conditions

As the number of distributed generation (DG)systems connected to the utility grid is increasing the issueof synchronization between the DGs and the grid isbecoming more profound. This paper presents a simplephase-locked loop (PLL) for the proper operation of theinverters even when the utility grid voltage is subjected toconsiderable abnormal conditions, such as changes infrequency and voltage amplitude or the presence of gridvoltage harmonics. The proposed PLL is based on zero crossing points, which makes it robust and compatible invarious grid voltage frequencies and amplitudes. Since inthe proposed PLL the grid voltage phase and amplitude areextracted without Park matrix and notch filter, it demandslower number of clocks for the calculations with respect to theexisting methods. This feature is practically desired sincethe proposed PLL can be executed on a simple and low-costmicrocontroller. The performance of the proposed PLL hasbeen evaluated by simulation and experimental tests. Theresults demonstrate the functionality of the proposed PLLon a 1.6 kW single-phase inverter.