Comprehensive Analysis of Proportional-Resonant Controller for Grid-Connected Inverters

Proportional–resonant (PR) controllers are widely adopted in single-phase grid-connected inverters for tracking sinusoidal references with zero steady-state error and satisfactory dynamic performance. However, in practical digital implementations, discretization delays modify the stability characteristics, while grid-frequency deviations degrade tracking accuracy. To mitigate these issues, three techniques, namely delay compensation, resonance damping, and resonant frequency adaptation are commonly employed. Nevertheless, this article, through comprehensive theoretical, simulation, and experimental studies, demonstrates that these conventional implementations have important limitations when an inverter with an inductor-capacitor-inductor filter regulates the grid-side current. The passivity of the inverter admittance is analyzed as a theoretical criterion, revealing that the real part of the admittance can become negative even with delay compensation. Furthermore, it is shown that resonance damping introduces a steady-state error in the grid current amplitude. Moreover, a comprehensive analysis reveals that directly updating the resonant frequencies to maintain accurate tracking under grid-frequency deviations introduces substantial interharmonic distortion. Accordingly, this article proposes retaining the standard PR structure without delay compensation or resonance damping, while updating the resonant frequencies based on the output of a moving average filter.