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.