Small-signal stability enhancement of communicationless parallel connected inverters

In this paper, small-signal stability issues of parallel-connected voltage source inverters without control interconnections are addressed. The dynamic analysis performed showed that the system stability margin is reduced when the composition of the inverter connection impedance is neither purely inductive nor purely resistive, which are two common approximations found in the literature. Based on a multivariable approach, this paper proposes the application of decoupling to the control of parallel inverters in order to increase the stability range concerning the connection impedance composition R/X. It is shown that decoupling can significantly improve the system damping even without precise knowledge of actual R/X. Experimental results are presented and corroborate the presented ideas.