Design of a cooperative voltage harmonic compensation strategy for islanded microgrids combining virtual admittance and Repetitive Controller

Non-linear loads (NLLs) in three-phase systems areknown to produce current harmonics at -5, 7, -11, 13… times thefundamental frequency; harmonics of the same frequencies areinduced in microgrid voltage, reducing therefore the powerquality. Dedicated equipment like active power filters can be usedto compensate the microgrid harmonics; alternatively, eachdistributed generation (DG) unit present in the microgrid can bepotentially used to compensate for those harmonics. The use of thevirtual admittance concept combined with a PI-RES controlstructure has been previously proposed as a harmoniccompensation sharing strategy when multiple DGs operate inparallel. The drawback of this methodology is that a large numberof RES controllers might be required to compensate for allharmonic components induced by NLLs, increasing the tuningcomplexity as well as the execution time. This paper proposes thecombined use of virtual admittance control loop and repetitivecontroller (RC) for harmonic compensation. The main advantageof the proposed method is that only one RC is required tocompensate for all the harmonic components, significantlyreducing the computational burden and the design complexity.The dynamic performance of the whole system is tested undervariable NLL