Enhanced Finite Control Set MPC for Parallel NPC Inverters in Standalone Microgrids with Diverse Load Conditions

In grid-forming inverter topologies, droop control typically generates the reference voltage for the capacitor in inverter-based LC filters. However, nonlinear and unbalanced loads often introduce inaccuracies in power calculation, compromising voltage waveform quality. To address this challenge and improve both voltage and current control, precise reference inductor current generation is essential. The proposed method innovatively employs multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL) to accurately extract positive-sequence load current components, which are used to generate the reference inductor filter current. Furthermore, an enhanced finite control set model predictive control (FCS-MPC) is introduced for the parallel operation of neutral point clamped (NPC) inverters within AC islanded microgrids. The cost function design within the FCS-MPC framework incorporates multiple control objectives, optimizing the performance of the inverter system. The effectiveness of the proposed control strategy is validated using MATLAB Simulink under various load conditions. Compared to the conventional approach, the proposed FCS-MPC control reduces response time by up to 47%, settling time by nearly 60%, and overshoot by approximately 50%, while achieving a THD load voltage of 0.89%. These quantified improvements demonstrate the efficacy of the proposed control strategy.