Under partial shading conditions (PSCs), the I‐V curve of PV systems consist of multiple local maximum power points (MPP's) and one global MPP which is required to extract the peak power of solar PV. ...In this article, an improved variable step size‐radial basis function algorithm (VSS‐RBFA) based MPPT controller is implemented to track the MPP with high speed. The advantages of proposed MPPT controller are high convergence speed, reduced oscillations across MPP, and takes less time to track MPP. Also, a universal high step‐up boost converter (HSBC) is proposed in this work to step up the PV voltage. The attractive features of HSBC are continuous input current, high voltage gain, less voltage stress on switches, and wide input and output operation. The proposed converter continuous conduction mode (CCM) and discontinuous conduction mode (DCM) of operations are compared successfully at the steady‐state operating condition. The simulation results of the proposed PV fed HSBC system is validated under uniform and PSC's of solar PV. In addition, the proposed converter results are verified experimentally by using a programmable DC source.
An improved VSS‐RBFA based MPPT controller.
Agricultural expansion is the main driver of forest and biodiversity loss. As a countermeasure, Voluntary Sustainability Standards (VSS) try to enhance sustainability in agricultural production but ...evidence if VSS reduce deforestation at country level is lacking. We used annual certification data of seven VSS (Fairtrade, Rainforest Alliance, UTZ, 4C, Round Table on Sustainable Palm Oil (RSPO), GlobalGAP, Organic) certifying five food commodities (cocoa, coffee, tea, palm oil, banana) and data on tree cover loss in humid tropical primary forest to study the impact of VSS on primary forest loss in 67 tropical countries. Using two generalised additive models (GAMs), one with VSS separately and one with VSS coverage aggregated, we found only Fairtrade to coincide with lower tree cover loss in primary forests at country level while we observed higher tree cover loss with higher certification for UTZ, RSPO and Organic. Using spatially explicit certification data in Google Earth Engine, we did not observe an effect of VSS on tree cover loss, thereby raising doubts on the potential of VSS to govern deforestation free supply chains. Reasons for this might be, among others, certification displacing unsustainable agriculture to other regions (leakage), weak or insufficiently enforced VSS criteria, and outcomes being context specific depending on, for example, institutional factors.
•Impact of Voluntary Sustainability Standards (VSS) on primary forests at country level.•Study covers seven VSS, five food commodities and 67 tropical countries.•VSS coverage in general has no effect on tree cover loss in primary forests.•Several VSS coincide with higher forest loss; lower forest loss observed for Fairtrade.•Leakage, weak VSS criteria and low enforcement might explain limited effects.
This paper demonstrates an integration of wind-solar fed microgrid enabled with improved power quality (PQ) performance and seamless operational mode transition capability. Wind turbine is a variable ...speed type realized by a doubly fed induction generator (DFIG). Solar photovoltaic (SPV) array is integrated to DC-link of DFIG's back-to-back converters via a maximum power extraction DC/DC converter. DC-link is also supported by battery-energy-storage to maintain voltage level and continuity of power during low generation and grid outage. An adaptive variable step size gradient descent total least squares (VSS-GDTLS) based power injection control is implemented for grid-side-converter during grid-tied operation to improve PQ performance. VSS is sum of square of active unit-template and instantaneous fundamental weight. This approach improves convergence compared to conventional fixed step approach. Seamless transition is achieved by using a pre-filter enabled frequency and phase angle estimation tool. A complex band-pass filter (CBF) enabled second-order generalized-integrator type frequency locked loop (SOGI-FLL) technique is used for frequency and phase angle estimations. Microgrid laced with control techniques is tested on a laboratory setup and various dynamic conditions are emulated to validate satisfactory performance of microgrid.
•A novel auxiliary active noise control system based on signal reconstruction is proposed.•A signal reconstruction model for multi-networks based on decomposition optimization is design.•The Bat ...Algorithm is used to optimize the weights of online AANC controller.•Results demonstrate that proposed system can balance modeling efficiency and accuracy.
Faced with the problem of existing active control systems failing to obtain a reference signal and reducing or deteriorating the effectiveness of interior noise control, an Auxiliary Active Noise Control system (AANC) based on signal reconstruction technology is proposed, which main contains offline update of multi-network weights and online AANC controller. Firstly, considering the non-linear and non-stationary of the interior noise, and aiming to balance the modeling efficiency and accuracy of algorithms, based on the data fusion and compression sensing technology, a signal reconstruction model for multi-networks based on decomposition optimization is design; Then, in the online AANC controller, the offline calculation of the weight of signal reconstruction model is used to obtain the reconstruction reference signal of the control position, and based on the reconstructed signal, the controller achieves adaptive suppression of passenger ear-sides noise through the VSS-LMS algorithm. Finally, the effectiveness of the proposed AANC is verified using real vehicle data. The results show that the proposed system achieves the balance the modeling efficiency and accuracy, and is superior to existing ANC system in terms of robustness, guaranteeing the stable operation of the interior noise control.
To improve the signal-to-noise ratio (SNR) of vibration signals in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) system, a principal component analysis variable step-size normalized ...least mean square (PCA-VSS-NLMS) denoising method was proposed in this study. First, the mathematical principle of the PCA-VSS-NLMS algorithm was constructed. This algorithm can adjust the input signal to achieve the best filter effect. Second, the effectiveness of the algorithm was verified via simulation, and the simulation results show that compared with the wavelet denoising (WD), Wiener filtering, variational mode decomposition (VMD), and variable step-size normalized least mean square (VSS-NLMS) algorithms, the PCA-VSS-NLMS algorithm can improve the SNR to 30.68 dB when the initial SNR is −1.23 dB. Finally, the PCA-VSS-NLMS algorithm was embedded into the built Φ-OTDR system, an 11.22 km fiber was measured, and PZT was added at 10.19–10.24 km to impose multiple sets of fixed-frequency disturbances. The experimental results show that the SNR of the vibration signal is 8.77 dB at 100 Hz and 0.07 s, and the SNR is improved to 26.17 dB after PCA-VSS-NLMS filtering; thus, the SNR is improved by 17.40 dB. This method can improve the SNR of the system’s position information without the need to change the existing hardware conditions, and it provides a new scheme for the detection and recognition of long-distance vibration signals.
•Nonpolar direction Ga2O3 Nanowires catalyzed by Cu3As: insights into As layer epitaxy.•Control composition and interfacial abruptness in vapor-solid-solid nanowires.•Influences of growth temperature ...on the structural and growth mechanism of the Ga2O3 NWs were investigated via unique ternary alloy phase diagram.
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To accurately control semiconductor nanowires’ (NW) physical characteristics defining electronic, optical and sensor applications, it is necessary to understand their potential growth mechanism. In this study, the Ga2O3 NW growth orientation is found to be dependent on their Cu3As catalyst structure via vapor-solid-solid (VSS) mechanism. The Ga2O3 NWs are synthesized by vapor transport method at 700 °C below the Cu3As alloy eutectic temperature, which forms a solid structure on top of the NWs. The NWs have relatively uniform diameter of 40–60 nm and prefer to grow along direction. Energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscope (HRTEM) data provide strong evidence that the harvested Ga2O3 NWs are epitaxially grown from Cu3As-based (cubic and hexagonal) catalyst seeds. And Ga2O3{110} |Cubic Cu3As {210}, Ga2O3{110} |Cubic Cu3As {110} and Ga2O3 {110} | hexagonal Cu3As {110} have relatively low mismatch compared to other interface lattice planes, providing a key insight into the growth process according to the VSS mechanism. The thermodynamics driven composition changes in the growth process are elaborated in detail.
In Visual Cryptography Schemes (VCSs), for message n transparencies are generated, such that the original message is visible if any k of them are stacked. VCS especially for large values of k and n, ...the pixel expansion’s reduction and enhancement of the recovered images’ display quality continue to be critical issues. In addition to this, it is challenging to develop a practical and systematic approach to threshold VCSs. An optimization-based pixel-expansion-free threshold VCSs approach has been proposed for binary secret images’ encryption. Along with contrast, blackness is also treated as a performance metric for assessing the recovered images’ display quality. An ideally secure technique for a secret image’s protection through its partition into shadow images (known as shadows) is the Visual Secret Sharing (VSS) scheme. Acquirement of a smaller shadow size or a higher contrast is the VSS schemes’ latest focus. The white pixels’ frequency has been utilized to demonstrate the recovered image’s contrast in this work. While the Probabilistic VSS (ProbVSS) scheme is non-expansible, it can also be readily deployed depending upon the traditional VSS scheme. Initially, this work has defined the problem as a mathematical optimization model such that, while contingent on blackness and density-balance constraints, there is the maximization of the recovered images’ contrast. Afterward, an algorithm dependent on the Tabu Search (TS) is devised in this work for this problem’s resolution. Multiple complicated combinatorial problems have been successfully resolved with the powerful TS algorithm. Moreover, this work has attempted to bolster the contrast through the density-balance constraint’s slight relaxation. Compared to the older techniques, the proposed optimization-based approach is superior regarding the recovered images’ display quality and the pixel expansion factor from the experimental outcomes.
•This paper proposes a cluster sparsity-induced affine projection algorithm for clustersparse system identification.•A variable step-size is developed to address the problem of tradeoff between ...convergence rate and steady-state misalignment.•Simulation results are provided to verify the effectiveness of the proposed algorithm and the variable step-size strategy.
The affine projection algorithm (APA) is widely used in various applications of adaptive filtering due to its decorrelating property. However, when the unknown system to be estimated is a cluster-sparse one, the APA cannot make full use of its cluster-sparsity characteristic to accelerate convergence rate. In this paper we propose a cluster-sparsity-induced APA (CSI-APA) to promote the performance of the adaptive filter for estimating cluster-sparse systems. When the number of elements in each cluster of the adaptive filter weights is set to one, the CSI-APA reduces to a sparsity-induced APA (SI-APA). Like other fixed step-size adaptive filtering algorithms, the proposed CSI-APA needs to make a trade-off between convergence rate and steady-state misalignment. To address this problem, the step-size of the CSI-APA is optimized by minimizing the mean-square deviation (MSD) at each iteration and a variable step-size CSI-APA (VSS-CSI-APA) is developed. Simulation results are provided to show the superior performance of the proposed algorithms.
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