The partial shading of a photovoltaic array repeatedly occurs in the natural environment, which can cause a failure of a conventional maximum power point tracking (MPPT) algorithm. In this paper, the convergence conditions of the standard particle swarm optimization (PSO) algorithm are deduced by the functional analysis, and then the influence of the random variables and inertia factor of the algorithm on the trajectory in the particle swarm optimization is analyzed. Based on the analysis results, an improved particle swarm optimization (IPSO) algorithm, which adopts both global and local modes to locate the maximum power point, is proposed. Compared to the standard PSO algorithm, in the improved PSO algorithm, many random and interfered variables are removed, and the structure is optimized significantly. The proposed algorithm is first simulated in MATLAB to ensure its capability. The feasibility of the approach is validated through physical implementation and experimentation. Results demonstrate that the proposed algorithm has the capability to track the global maximum power point within 3.3 s with an accuracy of 99%. Compared with five recently developed Global MPPT algorithms, the proposed IPSO algorithm achieved better performance in the maximum power tracking in the partial shading conditions. INDEX TERMS Maximum power point tracking, partial shade, particle swarm optimization, photovoltaic array.
We numerically and experimentally demonstrated double Fano resonances in a simple S-shaped plasmonic metasurface in the terahertz frequency range. Apart from the electric-LC resonance and electric dipole (ED) resonance, two trapped modes are excited in two different types of asymmetric S-shaped structures in the frequency range 0.2-1.4 THz, which are mainly attributed to a magnetic dipole (MD) and an electric quadrupole (EQ). Thereafter, double Fano resonances [one Fano and one electromagnetically induced transparency (EIT) resonance] are achieved via the coupling of the two dark trapped modes and a broad bright ED at normal incidence of the metasurfaces. Furthermore, under oblique incidence, strong Fano responses can be observed; they are considerably enhanced in asymmetric structures, and even in a symmetric structure. The proposed S-shaped plasmonic metasurfaces are easy to fabricate and have potential applications in multi-wavelength optical switches, filters, and sensors.
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