A Riding-through Technique for Seamless Transition between Islanded and Grid-Connected Modes of Droop-Controlled Inverters

Shang-Hung Hu,Chun-Yi Kuo,Josep Guerrero,Tzung-Lin Lee

doi:10.3390/en9090732

Abstract

This paper presents a seamless transition method for a droop-controlled inverter. The droop control is suitable to make the inverter work as a voltage source in both islanded and grid-connected modes, however, the transfer between theses modes can result in a big inrush current that may damage the system. The proposed method allows the droop-controlled inverter to improve the transient response when transferring between modes, by detecting the inrush current, activating a current control loop during transients, and then transferring back to droop-controlled mode smoothly by using a virtual inductance loop. In addition, a local phase-locked-loop (PLL) is proposed to align the inverter voltage with the grid in order to reduce the transient current during the transition. Therefore, the droop-controlled inverter is able to operate in both grid-connected and islanded modes, providing as well a smooth transition between them, requiring neither synchronization signals nor grid-side information. The control algorithm and design procedure are presented. Experimental results from a laboratory prototype validate the effectiveness of the proposed method.

Highlights

Inverter-based distributed power generation systems (DPGSs) have received much attention recently due to their flexible power-control capability [1,2]
The droop control is suitable to make the inverter work as a voltage source in both islanded and grid-connected modes
The proposed method will allow the droop-controlled inverter to improve the transient response when transferring between modes, by detecting the inrush current, activating a current control loop during the transient, and transferring back to the droop-controlled mode smoothly by using a virtual inductance loop

Summary

Introduction

Inverter-based distributed power generation systems (DPGSs) have received much attention recently due to their flexible power-control capability [1,2]. To the grid-following inverter, the grid-forming one is preferred due to its ability to provide many ancillary services defined in IEEE Std. 1547 [3], such as load regulation, reactive power compensation, and power quality improvement. IEEE Std. 1547 does not define the operation of distributed resources (DRs) in intentionally islanded electric power systems (EPSs). The term “DR Island System” has been defined by IEEE Std. 1547.4 [4] in order to integrate various DRs into EPSs with the possibility of operating as a microgrid [5,6]. The first mode referred to as the DR operation described in the original IEEE Std

Methods

Results

Conclusion