Hybrid control of multiple inverters in an island-mode distribution system

Inverter-interfaced distributed generation offers the possibility of introducing power quality functions such as suppression of harmonic distortion. However, the traditional voltage- and frequency-droop methods of achieving load sharing work on average values and do not address waveform quality. This paper proposes a hybrid scheme for an island-mode system with many inverters. Inverters in close proximity operate in master-salve mode whereas load sharing between distant groups uses frequency droop. Communication between inverters is used where it can improve performance but not where such links are impractical. The master inverter uses repetitive voltage control at the common node to suppress harmonic distortion. Slave inverters within a group also use repetitive control but in current mode. The performance has been assessed through simulation.