This paper proposes a novel optimal current given (OCG) maximum power point tracking (MPPT) control strategy based on the theory of power feedback and hill climb searching (HCS) for a permanent magnet direct drive wind energy conversion system (WECS). The presented strategy not only has the advantages of not needing the wind speed and wind turbine characteristics of the traditional HCS method, but it also improves the stability and accuracy of MPPT by estimating the exact loss torque. The OCG MPPT control strategy is first carried out by simulation, then an experimental platform based on the dSPACE1103 controller is built and a 5.5 kW permanent magnet synchronous generator (PMSG) is tested. Furthermore, the proposed method is compared experimentally with the traditional optimum tip speed ratio (TSR) MPPT control. The experiments verify the effectiveness of the proposed OCG MPPT strategy and demonstrate its better performance than the traditional TSR MPPT control.
Engineering spontaneous emission by means of photonic crystals (PHC) is under extensive study. However PHC modification of line emissions of rare earth (RE) ions has not been thoroughly understood, especially in cases of weak opal PHCs and while emitters are well dispersed into dielectric media. In this study, poly-methyl methacrylate (PMMA) opal PHCs containing uniformly dispersed europium chelate were fabricated with finely controlled photonic stop band (PSB) positions. Measurements of luminescent dynamics and angle resolved/integrated emission spectra as well as numerical calculations of total densities of states (DOS) were performed. We determined that in weak opals, the total spontaneous emission rate (SER) of Σ(5)D(0)-(7)F(J) for Eu(3+) was independent of PSB positions but was higher than that of the disordered powder sample, which was attributed to higher effective refractive indices in the PHC rather than PSB effect. Branch SER of (5)D(0)-(7)F(2) for Eu(3+) in the PHCs, on the other hand, was spatially redistributed, suppressed or enhanced in directions of elevated or reduced optical modes, keeping the angle-integrated total unchanged. All the results are in agreement with total DOS approximation. Our paper addressed two unstudied issues regarding modified narrow line emission in weak opal PHCs: firstly whether PSB could change the SER of emitters and whether there exist, apart from PSB, other reasons to change SERs; secondly, while directional enhancement and suppression by PSB has been confirmed, whether the angle-integrated overall effect is enhancing or suppressing.
A one-step synthesis of water soluble and pH-responsive trypsin-stabilized fluorescent copper nanoclusters (CuNCs) was reported without using additional protective or reducing agents, and the as-prepared CuNCs exhibited highly stable properties including oxidation resistance, thermal stability and photostability.
In cloud radio access networks (C-RANs), the baseband units and radio units of base stations are separated, which requires high-capacity fronthaul links connecting both parts. In this paper, we consider the delay-aware fronthaul allocation problem for C-RANs. The stochastic optimization problem is formulated as an infinite horizon average cost Markov decision process. To deal with the curse of dimensionality, we derive a closed-form approximate priority function and the associated error bound using perturbation analysis. Based on the closed-form approximate priority function, we propose a lowcomplexity delay-aware fronthaul allocation algorithm solving the per-stage optimization problem. The proposed solution is further shown to be asymptotically optimal for sufficiently small cross link path gains. Finally, the proposed fronthaul allocation algorithm is compared with various baselines through simulations, and it is shown that significant performance gain can be achieved.
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