Influence of output impedance of an inverter on its droop control strategies in a microgrid

Abstract

The objective of this paper is to present a comprehensive review of the various droop control strategies employed tocontrol the operation of the parallel inverters present in a microgrid, based onits output impedance. Predominantly, theoutput impedances of the inverters are inductive due to the line impedance and filter but in low power systems, the inverterhas a resistive output impedance. The various categories under which the droop control strategies of inverters with inductiveoutput impedance fall have been reviewed, along with its pros and cons. Although most of the inverters have inductiveoutput impedance, inverters with resistive output impedance are superior due to the easier compensation of harmonics.Along with their advantages the various disadvantages present in the droop control strategies utilized for inverters withresistive output impedance and the solutions to overcome these problems are presented. Recent studies have shown thatinverters with capacitive output impedance provide the lowest Total Harmonic Distortion along with reliable regulation ofvoltage and accurate power sharing. The technique of obtaining an inverter with capacitive output impedance along with itsvarious advantages has also been presented. The universal droop strategy utilized for all types of inverters without priorknowledge of their output impedances is reviewed along with an example, to overcome the problem of having to change thedroop equations according to the output impedance of the inverter. Lastly a few case studies related to microgridimplementation have been analyzed along with its challenges as well as standards and policies