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Method to Reduce Harmonic Voltage Distortion and Improve Harmonic Current Sharing in an islanded AC Microgrid

One of the key challenges in an islanded microgrid is fundamental and harmonic power sharing by the inverters in proportion to their ratings. Emulating virtual impedance much larger than the line impedance at the output of the inverters ensures proportional sharing of harmonic currents at the cost of increase in voltage harmonic distortion. This may violate the voltage harmonic limits specified by IEEE 519 standard. These limits are even more stringent when the loads are highly voltage sensitive. A novel method is proposed in this work to ensure proportional harmonic current sharing while maintaining the harmonic voltage distortion within the limit. Increase in harmonics in the output voltage due to high virtual impedance is estimated and compensated. A low bandwidth communication (LBC) is used to compensate the harmonic voltage which utilizes only two bits per harmonic frequency. A detailed simulation study is done in MATLAB-Simulink to validate the proposed technique.