Study on the impact of the complex impedance on the droop control method for the parallel inverters

In this paper, a new droop controller for parallel connected UPS inverters is presented. The proposed controller is based on the droop method in order to avoid the using of communication signals between the modules. The paper studies the control of the active and reactive power flow through the analysis of the output impedance of inverters and its impact on power sharing. As a consequence, we propose a novel control scheme which is based on virtual complex impedances. As opposed to the conventional methods, the controller proposed can achieve accurate power sharing, good dynamic performance and be more adaptive to the different line impedance situations. Design method and experimental results are presented in order to show the validity of the proposed control technique.