adaptive backstepping control of an autonomous multi-bus ‎microgrid based on grid-forming/grid-following strategy ‎under unbalanced load conditions

In this article, in order to maintain the voltage and frequency of a multi-bus island microgrid, a robust control strategy ‎is proposed. the microgrid under study is a medium voltage distribution system consisting of several inverter-based ‎distributed generation (dg) units, and a combination of balanced and unbalanced local loads. based on the grid- ‎forming/grid-following structure, a robust voltage controller is designed based on the adaptive backstepping control ‎method to keep the voltage and frequency of the grid-forming unit at predefined values.  in addition, to adjust the ‎active/reactive powers of the grid-following units, a direct power controller based on adaptive input-output feedback ‎linearization control method is proposed.  the negative sequence component of unbalanced local loads current is ‎compensated by the proposed power controller. only local measurements are used in designing of the controllers; ‎therefore, the proposed method is independent of the topology of microgrid, the parameters of the system, and the ‎dynamics of loads. the controllers presented in this article are robust and stable against various disturbances and ‎parameter uncertainties. after outage of grid-following unit, the power generated by the grid-forming unit is adaptively ‎adjusted so that the absence of generation at pc2 is offset. in addition, despite the mismatched filter resistance and ‎accidental outage of grid-following unit, even under non-local unbalanced load condition the proposed voltage ‎controller robustly regulates the voltage waveform of mg with a reasonable transient. validity and effectiveness of the ‎proposed control strategy are shown based on time domain studies in matlab/simulink environment‎.