System Harmonic Stability Analysis of Grid-Tied Interlinking Converters Operating Under AC Voltage Control Mode

The hybrid AC/DC admittance of interlinking converters operating under AC voltage control mode may contain right half-plane (RHP) pole(s), and thus, the existing harmonic stability analyses on grid-tied interlinking converter systems may become inapplicable as well. Aiming at addressing this deficiency, this letter modifies the hybrid AC/DC admittance definition and re-studies the harmonic stability of a grid-tied interlinking converter operating under AC voltage control mode. The results reveal that when the control mode of an interlinking converter changes from $P/Q$ control to AC voltage control, the system minor-loop gain utilized to assess the AC-side stability evolves to its inverse matrix. In contrast, the stability assessment related to the DC side (and the coupling interaction between the AC and DC sides) remains unchanged. Furthermore, the DC- and AC-side stabilities can also be regulated independently and are dominated by the $d$ -axis and the $q$ -axis controllers, respectively.