Simplified Finite-Control-Set Model Predictive Control for Grid-Connected Inverters with LCL Filters: Reduced Prediction Horizon and Weighting Factors-Free Design

Adel Tatish, Kanchapogu Vaisakh

Abstract


Finite-Control-Set Model Predictive Control (FCS-MPC) has shown great promise for controlling microgrid converters. However, conventional FCS-MPC approaches applied to high-order dynamic systems, such as grid-connected converters with LCL filters, require a long prediction horizon to achieve accurate grid current tracking, resulting in increased computational burden. This paper proposes a simplified FCS-MPC strategy for grid-connected inverters with LCL filters, addressing the computational complexity and tuning challenges of conventional methods. By tracking the filter capacitor voltage instead of directly regulating grid-side or converter-side currents, the proposed approach reduces the required prediction horizon from six steps (Np=6) to three steps (Np=3), significantly lowering computational burden. This reduction, coupled with a single-objective cost function, slashes the computational time by over 300 times, from 7.8 ms to 25.3 µs on embedded hardware (400 MHz CPU), making real-time implementation feasible. A single-objective cost function eliminates the need for weighting factors, simplifying controller design and tuning. The method ensures sinusoidal current injection even under unbalanced grid conditions by exclusively utilizing the positive sequence of the PCC voltage, extracted via a discrete-time quadrature signal generator. The effectiveness of the proposed strategy is validated through both MATLAB/Simulink simulations and experimental testing. The results demonstrate that the proposed controller achieves performance comparable to conventional FCS-MPC approaches with longer prediction horizons, maintaining a low grid-current THD of 1.7%, while offering the distinct advantages of reduced computational complexity, improved robustness against grid harmonics and voltage sags, and simpler implementation without the need for tuning weighting factors.


Keywords


Grid following inverter; LCL filter; Finite-control-set model predictive control (FCS-MPC); Prediction horizon.

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References


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DOI (PDF): https://doi.org/10.20508/ijsmartgrid.v10i1.594.g417

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