Performance Verification of a New Integrated Droop Controller with a Novel Virtual-Impedance Based PLL for Parallel Operation of Inverters

Abstract

This paper presents a novel droop control method for decentralized paralleling of inverters in distributed generation (DG) system. The controller satisfies two basic objectives simultaneously: It provides active power ($P$) and reactive power ($Q$) based droops on voltage and frequency references using d-axis and q-axis currents, respectively and also incorporates virtual impedance loop. A novel PLL (Phase Locked Loop) structure and an integrated droop control (IDC) strategy are devised to achieve the same. This control method enables parallel inverters to share any type of load viz. linear and nonlinear proportional to the inverter power ratings under any transmission line condition namely resistive and resistive-inductive type. Performance of the proposed control method is verified through experimental results.