Abstract
This paper addresses the operation of parallel interlinking converters (ICs) in hybrid AC-DC microgrids from different perspectives, then proposes a unified mitigation technique. Firstly, the influence of the system nonlinearity on circulating currents between parallel ICs is investigated. Secondly, it is shown that ICs might induce voltage harmonics due to the antiparallel diodes of the power electronic switches which are seen by the AC subgrid as nonlinear diode rectifiers. Lastly, the synchronization of ICs following abnormal operating conditions is discussed and new findings are presented. In order to enhance the operation of ICs and overcome the preceding challenges, a modified virtual synchronous machine (VSM) strategy with a dual-droop (DD) controller is proposed. The positive influence of the proposed VSM-DD controller on the overall system dynamics is clearly justified. Small-signal state-space modeling for the entire system is conducted to verify the results analytically. A nonlinear time-domain simulation model is developed using PSCAD/EMTDC to validate the impact of the VSM-DD controller experimentally.