Effect of PLL Bandwidth on Stability of Grid-Tied Inverter under Grid Impedance Variations

The stability of grid-tied inverter (GTI) is a critical concern in microgrid environments, particularly under varying grid conditions where impedance mismatches and control dynamics significantly impact performance. phase-locked loop (PLL) bandwidth emerges as a key parameter influencing GTI stability, as it directly affects the inverter’s output impedance and overall system dynamics. This paper investigates the impact of PLL bandwidth on the stability of an LCL-filtered grid tied inverter (LCL-GTI) using impedance-based stability analysis. A comprehensive small-signal model is developed to derive the output impedance of GTI by considering the power stage, current controller, and PLL dynamics. The stability is evaluated using the generalized Nyquist criterion (GNC) to analyze the system's behavior across different PLL bandwidths. Experimental validation is conducted using a 3.8 kW LCL-GTI, demonstrates the critical influence of PLL bandwidth on GTI stability, offering practical insights for designing robust synchronization mechanisms to enhance GTI reliability in microgrid applications.