PR Based Indirect Current Control for Seamless Transfer of Grid-Connected Inverter

This paper describes the PR control based indirect current control for seamless transfer of three-phase grid connected inverter. DG based inverter is defined as a current source in the grid-connected mode and a voltage source in the islanded mode, respectively. Hence, it needs a robust control to supply the high quality power under both modes. Therefore, PR based indirect current control which can be used under both modes, has been proposed here. In this paper, firstly, the PR based control methods under the steady state of each mode and under the transient state of mode change are considered. And then, the PR based proposed mode transfer technique is described in detail when the PLL mode is located between the islanded mode and the grid-connected mode. Additionally, a simple voltage restoration technique is added to solve the magnitude degradation of output voltage tracking due to the practical PR control tracking limitation. Finally, the PR based proposed control method for supplying the reliable power to the local load and grid is verified with seamless mode transfer through the PSIM simulation.