Studyo n the Frequencyo fV oltageF licker Caused byth e FrequencyF eedback Method with StepI njection ofR eactive Power

This paper examines the oscillation frequency of the volage flicker caused by the frequency feedback method with step injection of reactive power. It has recently been reported that the oscillation frequency has shifted from around 6 Hz to around 3 Hz. This paper derives the transfer function of the inverter and the distribution system. Based on the open-loop transfer function of the system, it is demonstrated that the system becomes unstable around 6 Hz and 3 Hz. It is clarified that flicker occurs at the frequency at which the system becomes unstable. Furthermore, both 6-Hz flicker and 3-Hz flicker are caused by the same mechanism, but changes in line impedance and PLL parameters cause the flicker frequency to shift from 6 Hz to 3 Hz.