In this paper, a self-synchronization mechanism is embedded into the universal droop controllerud(UDC), which is applicable to inverters having an impedance angle between −π/2 rad and π/2 rad,udto form a self-synchronized UDC (SUDC). Both the voltage loop and the frequency loop of the UDC areudmodified to facilitate the standalone and grid-connected operation of inverters. Importantly, the dedicatedudphase-locked-loop that is often needed for grid-connected or parallel-operated converters is removed. Theudinverter is able to achieve synchronization before and after connection without the need of a dedicatedudsynchronization unit. Since the original structure of the UDC is kept in the SUDC, the properties of theudUDC, such as accurate power sharing and tight output voltage regulation, are well maintained. Extensiveudexperimental results are presented to demonstrate the performance of the proposed SUDC for a gridconnectedudsingle-phase inverter.
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