Criterion for Continuous Oscillation of Reactive Power caused by the Frequency Feedback Method with Step Injection of Reactive Power

Abstract

This paper focuses on the continuous oscillation of reactive power caused by the frequency feedback method in the grid-connected inverters. The transfer functions of inverter and ac system are derived. Then the stability of the system is analyzed according to the transfer functions. The analysis clarified that the system becomes unstable if the product of line impedance, inverter capacity, and frequency feedback characteristic exceeds a specific threshold value. Then it results in the continuous oscillation of reactive power.