Two-dimensional hexagonal boron nitride (hBN) has attracted large attentions as platforms for realizations for integrated nanophotonics and collective effort has been focused on the spin defect centers. Here, the temperature dependence of the resonance spectrum in the range of 5-600 K is investigated. The zero-field splitting (ZFS) parameter D is found to decrease monotonicly with increasing temperature and can be described by Varshni empirical equation perfectly, while E almost does not change. We systematically study the differences among different hBN nanopowders and provide an evidence of edge effects on ODMR of V − B defects. Considering the proportional relation between D and reciprocal of lattice volume (V −1 ), the thermal expansion might be the dominant reason for energy-level shifts. We also demonstrate that the V − B defects still exist stably at least at 600 K. Moreover, we propose a scheme for detecting laser intensity using the V − B defects in hBN nanopowders, which is based on the obvious dependence of its D value on laser intensity. Our results are helpful to gain insight into the spin properties of V − B and for the realizations of miniaturized, integrated thermal sensor.
Reactive power control through the static compensator (STATCOM) has gained wide attentions due to its outstanding performance. But for a STATCOM with traditional control strategies, unbalanced utility voltages will greatly affect the performance of the STATCOM and, in severe cases, may even cause the shutdown of the STATCOM for overcurrent protection. This paper proposes novel control strategies to ensure normal operation of STATCOM in three-phase three-wire systems when severe system voltage unbalance occurs and, furthermore, to mitigate voltage unbalance at the point of common coupling (PCC) whether it is caused by the utility or load. The control laws, operation principles, compensation characteristics, and operating point optimization of the proposed control strategies are analyzed and compared in detail. The power flow in the STATCOM and corresponding dc-side voltage-control schemes for these control strategies are also introduced. It is shown that the proposed voltage-controlled current source (VCCS) strategy and modified voltage-controlled voltage source strategy are valid for voltage unbalance compensation, especially the VCCS strategy for low rating under the same performance. Finally, the simulation and experimental investigations were carried out with these three parameter-optimized control strategies, respectively, for light and heavy load conditions. The results verified that the current passing through the STATCOM is under control and the voltage at the PCC is more balanced than before compensation. The compensation performance of the STATCOM is thus proven satisfactory.Index Terms-Control strategy, point of common coupling (PCC), static compensator (STATCOM), voltage-controlled current source (VCCS), voltage-controlled voltage source (VCVS), voltage unbalance.
Abstract-A novel current-detection algorithm based on the time-domain approach for three-phase shunt active power filters (APFs) to eliminate harmonics, and/or correct power factor, and/or balance asymmetrical loads is analyzed in this paper. A basic overview and evaluation of the performance of existing current-detection algorithms for active power filters are presented. According to different complicated power quality issues and various compensation purposes, a novel current-detection algorithm is then proposed. Comparing with existing algorithms, this algorithm has shorter response time delay and clearer physical meaning. Different compensating current references can, thus, be accurately and easily obtained by adopting the proposed algorithm. It ensures that the shunt APF can very well achieve different compensation purposes. Moreover, it is very easy to implement this algorithm in a digital signal processor (DSP). Simulation results obtained with MATLAB and testing results on an experimental shunt APF are presented to validate the proposed algorithm.
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