Control and optimization of multifunctional and multilevel solar active filter

Abstract

Different configurations of double-stage solar active filters are available in the literature. They differ in either the type of the inverter, the maximum power point tracking (MPPT) algorithm, the number of sensors, the validation strategy, the achieved performance indices, etc. Each configuration can be evaluated as better from one aspect or/and many aspects, particularly the performance indices such as total harmonic distortion (THD) and power factor. However, there is always room for improvement. This research presents a novel architecture to enhance the performance of grid-connected photovoltaic (PV) systems through the introduction of several key novelties. Firstly, a packed U-cell seven-level (PUC7)-based single-phase solar active filter is implemented, offering a comprehensive solution for harmonics mitigation, reactive power compensation, and efficient power extraction from the PV source while facilitating the injection of real power into the grid. Secondly, the P-Q power injection algorithm is modified to accommodate the extraction of solar power from the PV generator to the grid, simultaneously addressing the need for harmonic current injection to improve power quality. This modification ensures dynamic performance by extracting reference current with harmonic content and solar power information, thereby enhancing the system's overall efficiency. Additionally, the Model Predictive Control (MPC) strategy employed in this system is enhanced through the integration of the 4th-order Runge-Kutta (4oRK) method. Unlike conventional MPC approaches that rely on Euler integration and suffer from diminished accuracy at larger sampling intervals, the 4oRK-based MPC achieves a significantly lower computational error, ensuring precise trajectory predictions and corrections. Comparative analysis shows that the 4oRK-based MPC consistently maintains a THD below 5% under nonlinear load and voltage sag conditions, surpassing the Euler-based method. Furthermore, this improvement is realized without increasing computational complexity or task execution times. Lastly, the proposed architecture undergoes real outdoor testing, validating its performance in various key aspects, including maximum power tracking, reduction of THD in comparison with previous work, operation at unity power factor, and testing the effective operation of the multifunction feature. Extensive MATLAB/Simulink simulations and physical prototype experiments further validate the proposed 4oRK-based MPC, showing its ability to minimize THD, reduce switching losses, and maintain robust control performance at lower switching frequencies. These contributions collectively demonstrate the effectiveness of the proposed system in enhancing power injection quality, reactive power compensation, and overall control precision under real outdoor conditions of PV systems connected to the grid, making it an effective solution in the field of renewable energy systems.