Abstract
In an autonomous ac microgrid system, a peer-to-peer decentralized solution would be a preferred choice for the coordinative control of distributed generation units. However, due to the dispersed sources and loads, and mismatched line impedances, it is hard to achieve satisfactory power sharing performance and power quality without communication links. Therefore, a comprehensive decentralized solution based on dual-frequency-droop is proposed in this article. With only local information, appropriate virtual impedances could be obtained to compensate the mismatched complex line impedances in the required frequency range, and hence active, reactive, unbalanced, and harmonic powers could be shared accurately among parallel inverters under various load conditions. Then, the frequency deviation caused by the droop control is effectively attenuated without affecting power sharing through a dynamic droop-slope regulator. Moreover, the causes of steady-state ripples on virtual impedance waveforms are carefully analyzed, and the design criterions to eliminate these ripples are provided. Finally, case studies are provided in simulations and experiments to validate the effectiveness of this method.
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