Search

• The small-signal stability of current vector control and power synchronization control under different system strengths is studied. • The key factors of disturbance in the process of control mode switching are analyzed. • Based on the principles of current vector control and power synchronization control, a smooth switching control strategy for PV grid-connected converter is proposed. • An advanced smooth switching control strategy with complete process frequency support by the power correction is proposed. The continuous increase in the penetration of renewable energy sources such as photovoltaics (PV) brings operational challenges to the traditional distribution network. With a large-scale PV integration, the power system behaves as a weak grid, which leads to more frequent and wider changes in system strength. In order to improve the system stability, the PV system is required to operate stably while providing necessary system support under different operating conditions. However, there are two issues for the PV system needs to address to satisfy this requirement. Nowadays, there are two types of control strategies for PV systems: the grid-following (GFL) control and the grid-forming (GFM) control. The two control strategies differ in inertia support capability and control stability under different operating conditions. To guarantee the grid connection stability as well as the operating stability under AC systems with different strengths, the smooth switching between the GFL and GFM is an urgent topic. In addition, how to maintain the system frequency support performance during the control switching of the PV system is also a challenge. In this paper, an advanced smooth switching control strategy is proposed to enhance the operational stability and flexibility of the PV system while maintaining the frequency support performance during the switching process. Firstly, the small-signal stability of typical control strategies of GFL and GFM under different system strengths is compared to analyze the necessity of the control switching between the two control modes. Then, a smooth switching control strategy is proposed to realize the smooth switching when AC grid strength changes. More importantly, to improve the system frequency performance and realize continuous frequency support during the switching process, a power correction function is developed on the smooth switching control strategy. The effectiveness and universality of the proposed control strategy are verified by case studies on a modified IEEE 33 bus distribution network with high PV system integration. [ABSTRACT FROM AUTHOR]

• An optimal combined operation scheme for pump storage and wind-pv system is proposed. • Real-time coordinated control enabling automatic dispatch of the pump storage. • The power production fluctuations of wind-pv system is reduced with proposed scheme. • The revenue of hydro wind-pv system is significantly improved with proposed scheme. Because of the steady increase of wind and solar capacity installations in recent years, the goal of the Paris Agreement is expected to be reached. However, due to the intermittent characteristics of renewable generation, challenges are presented for the power grid to operate reliably and economically under the high uncertainty of wind and solar power productions. Sufficient responsive reserves must be available for the power grid to maintain the balance between the supply and demand. To be fair to the market participants, the renewable generation companies should pay for the received grid ancillary services. In this paper, an optimal combined operation scheme is proposed for pumped storage hydro and hybrid wind-photovoltaic complementary power generation system interconnected by a Voltage Source Converter-based multi-terminal HVDC system. The optimal combined operation scheme has two real-time control functions. The pumped storage hydro control function enables automatic dispatch of the pumped storage hydro to effectively suppress or compensate for the output deviations of wind and solar generation from the forecasted production; and the output control function is able to distribute the non-compensated production surplus or deficit to different ac systems based on the market regulating service prices. A Case study is provided to demonstrate the improved power generation profile and reduced revenue losses of the pumped storage hydro and hybrid wind-photovoltaic complementary power generation system. [ABSTRACT FROM AUTHOR]

Simply supported purlins inter braced by one line of sagrods in a parallel purlin system under wind suction are analyzed. The sagrods are assumed to be zigzag placed with 30–50 mm offset in adjacent spacing. The effect of this offset and the local deformation on the effectiveness of sagrod is analyzed. A purlin is divided into 3 segments by offsetted sagrods, and the general solution is found for such a purlin under wind suction. The solution is then extended to a parallel purlin system to determine the deformations of all purlins in the system. Examples are given to reveal the bracing effect of sagrods to purlins away from the sagrod anchor spacing. It is found that the sagrod bracing effect drops quickly as the number of spacings to the sagrod anchor spacing increases. The deformation of the last purlin in the 10 purlin system is close to a purlin without sagrod if the purlin thickness is 1.5 mm. FE analysis is carried out to verify the analytic results and excellent agreement is found. Simplified equations are proposed to find the tensile forces in sagrods, purlin deformations and internal forces easily. Practical meaning of this study may be formulated as follows: (1) the distance of two diagonally braced spacing should be smaller if the purlin thickness is small. (2) It is welcome to take measures to reduce the local deformation of purlin web at the sagrod points. [ABSTRACT FROM AUTHOR]

Summary The molecular mechanisms of chronic pain are poorly understood and effective mechanism-based treatments are lacking. Here, we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected chronic mechanical and thermal hypersensitivity due to sustained elevated circulating adenosine. Extending from Ada −/− mice, we further discovered that prolonged elevated adenosine contributed to chronic pain behaviors in two additional independent animal models: sickle cell disease mice, a model of severe pain with limited treatment, and complete Freund’s adjuvant paw-injected mice, a well-accepted inflammatory model of chronic pain. Mechanistically, we revealed that activation of adenosine A2B receptors on myeloid cells caused nociceptor hyperexcitability and promoted chronic pain via soluble IL-6 receptor trans-signaling, and our findings determined that prolonged accumulated circulating adenosine contributes to chronic pain by promoting immune-neuronal interaction and revealed multiple therapeutic targets. [ABSTRACT FROM AUTHOR]

Abstract: Objective: This study investigated if central sensitization is induced in the trigeminal subnucleus caudalis (also termed the medullary dorsal horn) and C1 and C2 dorsal horns by noxious stimulation of deep upper cervical paraspinal tissues in a preparation relatively free of surgical trauma. Methods: Adult male Sprague-Dawley rats (275-450 g) were anesthetized intraperitoneally. Animals were then placed in a stereotaxic frame; a small cutaneous incision was made 3 to 4 mm near the bregma in the midline, and an opening into the skull was prepared by a 1/32-inch drill, 1 mm to the left from the midline. An epoxylite-coated tungsten microelectrode was introduced at an 18° angle to enter this small opening on the skull and was then carefully advanced about 16 mm through cortex, cerebellum, and brainstem to reach subsequently histologically confirmed sites in the Vc and upper cervical (C1 and C2) dorsal horn region. Thirty-three, 27, and 15 neurons recorded in medullary, C1, and C2 dorsal horns, respectively, of chloralose/urethane-anesthetized rats were activated by noxious stimulation of mechanoreceptive fields involving V1, V2, and/or V3 trigeminal nerve territories. The inflammatory irritant mustard oil was injected into the deep paraspinal tissues at the level of the left C1-C2 joint. Pre and postinjection receptive field (RF) sizes were mapped by nonnoxious mechanical stimuli and noxious mechanical and heat stimuli. Results: A 30- to 50-minute increase (mean, 165% ± 38.1%) in RF size postinjection for 62% of neurons tested was demonstrated, suggesting central sensitization; for most (>70%) neurons, the RF expanded caudally into cervically innervated tissues. Conclusions: These findings provide the first documentation that deep cervical nociceptive inputs can induce central sensitization in medullary and C1/C2 dorsal horns and suggest that these effects may reflect mechanisms contributing to deep cervical pain and its referral. [Copyright &y& Elsevier]

• Impact and threat of cyber security are analyzed in WAMS-based FFR control system. • Novel dual-frequency scale CNN for processing the spoofing data from two scales. • Time-frequency based cyber security defense framework for WAMS-based FFR system. • The result shows higher accuracy and robustness with actual synchrophasor data. Global power systems are transiting from conventional fossil fuel energy to renewable energies due to their environmental benefits. The increasing penetration of renewable energies presents challenges for power system operation. The efficiency and sufficiency of responsive reserves have become increasingly important for power systems with a high proportion of renewable energies. The Fast Frequency Reserve (FFR), especially the Wide-area Monitoring System (WAMS)-based FFR, is a promising and effective solution to secure and enhance the stability of power systems. However, cyber security has become a new challenge for the WAMS-based FFR system. Cyber attacks on the FFR control system may threaten the safety of power system operation due to the rapid power controllability requirement of FFR. To address this problem, a time-frequency based cyber security defense framework is proposed to detect the cyber spoofing of synchrophasor data in WAMS-based FFR control systems. This paper first introduces the Continuous Wavelet Transforms (CWTs) to decompose spoofing signals. Then, the Dual-frequency Scale Convolutional Neural Networks (DSCNN) is proposed to identify the time-frequency domains matrix from two frequency scales. Integrating CWTs and DSCNN, an identification framework called CWTs-DSCNN is further proposed to detect the spoofing attacks in the WAMS-based FFR system. Multiple experiments using the actual data from FNET/GridEye are performed to verify the effectiveness of the framework in securing WAMS-based FFR systems. [ABSTRACT FROM AUTHOR]

• A review of four LCC-VSC hybrid HVDC topologies is proposed. • The PQ operating zone of the four hybrid HVDC topologies is investigated. • The power flow reversal comparison of the four hybrid HVDC topologies are achieved. • The DC fault ride-through strategy of the four hybrid HVDC topologies are studied. Hybrid HVDC system, which consists of the advantages of line commutated converter (LCC) and voltage source converter (VSC), is an emerging power transmission system. This paper presents a review of four LCC-VSC hybrid HVDC topologies. The first topology is the pole-hybrid HVDC system, in which the LCC and VSC form the positive- and negative-pole respectively. The second one is the terminal-hybrid HVDC system; in this topology one terminal adopts LCC and the other terminal adopts VSC. The series converter-hybrid HVDC system is the third topology wherein each terminal is formed by LCC and VSC in series. The fourth hybrid topology under consideration is a parallel converter-hybrid HVDC system with LCC and VSC connected in parallel in each terminal. The main contribution of this paper is a comprehensive analysis and comparison of the four mentioned hybrid topologies in terms of PQ operating zone, power flow reversal method, and DC fault ride-through strategy. [ABSTRACT FROM AUTHOR]

• A coordinated frequency regulation scheme for asynchronous AC grids is proposed. • The proposed scheme is a communication-free method. • A sample and hold component is implemented to enhance the inertia response. • A frequency safety control is proposed to improve the system security. • Two measures are used to reduce the coupling effect among asynchronous AC grids. With the increasing penetration level of renewable power, the power systems' inertias are decreasing. To ensure that the frequency is above the threshold of the under frequency load shedding, one effective way is to share the spinning reserves among asynchronous AC grids through HVDC systems. In this paper, a coordinated frequency regulation scheme that enables spinning reserves sharing is proposed for such hybrid AC/DC grids. This scheme is a communication-free method that consists of the droop control, the inertia emulation control and the frequency safety control. The combined response of the three controls can increase not only the frequency nadir but also the settled frequency of the disturbed grid. In addition, the hysteresis comparators and the power injection limits are adopted in the frequency regulation scheme to reduce the coupling effect among AC grids. Thus, under small and harmless disturbance, the frequency regulation scheme will be inactive; the disturbance in strong AC grids would not affect the weak AC systems. The frequency regulation scheme coordinates well with the automatic generation control of the grids. The feasibility and effectiveness of the proposed frequency regulation scheme are verified through simulation studies. [ABSTRACT FROM AUTHOR]

With the rise of user energy consumption data as a significant data asset, data privacy has emerged as a critical concern. To address users' diverse attitudes towards data sharing and their varied usage requirements, this paper introduces an adaptive privacy protection framework for user energy data based on dictionary learning and watermarking techniques. Central to this framework is an innovative digital watermark anonymization method designed to meet the dual objectives of encryption and anonymous data sharing. This method employs sparse dictionary decomposition to embed confidential user information within sparse coefficients, significantly enhancing computational efficiency while minimally impacting the integrity of the original data. Additionally, through sparse data representation, the framework achieves effective data compression, addressing the challenges of extensive storage requirements inherent in maintaining original energy consumption data, encryption results, and the data sharing process. Security analysis and case studies demonstrate the proposed method's robustness against eavesdropping, unauthorized access, and other security threats. • A hierarchical privacy-preserving scheme considering diverse use of smart meter data. • An efficient compression and secure sharing method based on cloud storage. • Flexible anonymous control for energy consumption data based on blind watermark. • The adaptive blind watermark method has lower distortion and controllable capacity. • The scheme robustness against eavesdropping and unauthorized access. [ABSTRACT FROM AUTHOR]

• A back-up frequency response control based on the HVDC link is proposed. • To avoid a second frequency drop, a frequency compensation control is proposed. • A response distribution optimization strategy is proposed to reduce the event cost. With the increasing penetration of wind energy into power grids, the frequency regulation capability of the system tends to deteriorate. Wind generators (WGs) could provide fast frequency response when the system suffers from disturbances. However, due to the randomness and intermittence of WG, its emergency support is not stable. The spinning reserves of the asynchronous power grids can be shared through the high voltage direct current (HVDC) links. Under a large disturbance, the HVDC link could provide fast frequency response support to maintain the operating frequency of the disturbed power grid within a secure range. In this paper, a frequency secure control strategy is proposed for the HVDC link connected to a power system with high penetration of wind energy. The proposed frequency secure control strategy has three control functions: (1) back-up frequency response control, (2) frequency compensation control, and (3) response distribution optimization. The objective of this control strategy is to improve the synthetic frequency response performance of the system under severe frequency disturbance while avoiding possible subsequent frequency drop caused by rotor speed recovery of wind turbines. Besides, the cost of ancillary service for obtaining frequency response support from interconnected power systems could be reduced. Simulation verifications are conducted on a reduced equivalent ERCOT system which is interconnected to equivalent Western and Eastern Interconnections by HVDC links. The simulation results verify the feasibility and effectiveness of the proposed frequency secure control strategy. [ABSTRACT FROM AUTHOR]

• A switch mode control and a dc–dc coordination control for dc–dc converters' coordinated operation is proposed. • Real-time coordinated control enabling automatic dispatch of the dc–dc converters. • The unbalanced power from one dc grid could be optimally distributed with proposed control. • The serious power fluctuation events could be prevented with proposed control. Dc–dc converters are emerging as a key device for future dc transmission networks. This paper develops a switch mode control and a dc–dc coordination control for dc–dc converters' coordinated operation in the multi-voltage-level dc grid. The switch mode control is a local controller on the dc–dc converter to enable the automatic switch of the dc–dc operation mode. The dc–dc coordination control is an advanced control based on the switch mode control. With the dc–dc coordination control, unbalanced power from one dc grid could be optimally distributed to other grids, in order to avoid serious power fluctuation events. Simulation results are provided to demonstrate the performance of the switch mode control and dc–dc coordination control. [ABSTRACT FROM AUTHOR]

In order to improve the utilization of industrial lignin as an effective component for ultraviolet (UV) shielding, organic solvent (methanol, ethanol, and acetone) fractionation was applied to improve its UV absorption performance and reduce its apparent color. Physicochemical properties of lignin and lignin-based sunscreens, such as molar mass fraction, functional group content, color change and UV shielding properties, were characterized in detail by GPC, UV spectroscopy, 31P NMR and HSQC-NMR spectroscopy. The results showed that the color and UV-shielding properties of the soluble fraction were significantly superior to those of the original and insoluble fractions. Different lignin fractions were acted as the only active substance in the pure cream and its UV-shielding properties were compared. Among them, the composite sunscreen by adding 5 wt% acetone fractionated lignin had highest sun protection factor (SPF) value of 6.6, approximately 4.5 times higher than those sunscreens mixed with pristine lignin. Overall, this work offers the potential of industrial lignin in value-added applications such as UV protection and cosmetics. • Alkali lignin was separated by solvent fractionation to obtain soluble fraction. • The soluble fraction of lignin had more phenolic hydroxyl groups and lighter color. • Lignin-based sunscreen exhibited higher sun protection factor value. • This work provides a convenient pathway for the value-added utilization of lignin. [ABSTRACT FROM AUTHOR]

• The framework combines a cloud-edge-end structure to break the information barriers of multi-source measured data. • The method executes different strategies according to voltage levels based on interaction of edge computing is proposed. • Harmonic source identification and evaluation are achieved through the multi-level interaction of edge computing. • TVE, CMHSE and HHSE method for cloud-edge-end collaborative computing strategy are developed into the system. With the increase of power electronic devices such as distributed renewable energies, energy storage, and flexible loads, the disturbance sources are rapidly raised and distributed in multiple voltage levels in the distributed network. The harmonics they produce are random and uncertain, and the massive amounts of data propose high demands on server computing capability, which restrict harmonic sources evaluation and significantly influence the judgments of the power quality in the distribution network. In order to improve the power quality and the harmonic source evaluation function of the distribution network, in this paper, a framework for multi-harmonic source identification and evaluation based on cloud-edge-end collaboration is proposed. Firstly, based on the analysis of the functional requirements harmonic sources evaluation in multiple voltage levels, a novel framework of cloud-edge-end collaboration is proposed. Secondly, the cloud-edge-end collaborative harmonic sources evaluation method which executes different service strategies according to voltage levels and grid operation based on the multi-level interaction of edge computing is proposed. Further, the working principle of the proposed novel framework with multiple evaluation methods including the dominant harmonic source identification, concentrated multiple harmonic sources evaluation (CMHSE) and hierarchical harmonic sources evaluation (HHSE) is described in detail in order to show the completed work processes of the proposed framework. Finally, the performance of the proposed method is verified based on the real data measured from different realistic urban power grids in China. The proposed method can effectively evaluate harmonic contributions in distribution systems and in turn provide a basis for harmonic mitigation measures. [ABSTRACT FROM AUTHOR]

• A novel generalized admittance criterion is proposed, significantly reducing the requirement for synchronous phasor measurements. • Harmonic contribution evaluation is simplified based on the proposed generalized admittance criterion. • The fluctuation characteristic of harmonics is considered for the harmonic admittance estimation. • The proposed method has comprehensive applicability and high harmonic source location accuracy. The widespread integration of various nonlinear power electronic devices in modern power systems has made harmonic distortion more serious than ever before. Given the urgent need to improve power quality, the harmonic contribution evaluation (HCE) is of great importance since it can provide a strong basis for harmonic mitigation measures. However, the conventional HCE methods are not effective due to the lack of synchronous voltage and current phasor information in real-field practice. To overcome the phasor limitation, an HCE method based on a generalized admittance criterion (GAC) is proposed in this paper. The proposed GAC aims to determine the dominant harmonic source at the point of common coupling (PCC) from the utility side and customer side. Compared to the conventional method, the developed method only needs the RMS values of the PCC voltage, current, and phase angle difference. Therefore, the synchronous phasor information of voltage and current is no longer required. Meanwhile, a threshold to determine the dominant harmonic source is established by using the equivalent admittance ratio on both sides of PCC. The evaluation process of the proposed method is significantly simplified by comparing the generalized admittance limit with the proposed threshold, which also greatly improves the method evaluation accuracy. Moreover, the interference of background harmonic fluctuation is excluded by using the linear calibration-based harmonic admittance estimation method. Finally, multiple scenarios with various admittance characteristics were simulated to verify the performance of the proposed criterion, and the real-field measurement is also used to demonstrate the accuracy and validity of the proposed method. [ABSTRACT FROM AUTHOR]

• Widespread use of power-electronic devices leadsto serious harmonic distortion. • Harmonic forecasting cansupport system operating and strategy designing. • Strong time-varying uncertain features are described with less computing burden. • Correlation of multiple variables is considered to reduce the estimated deviation. • Probabilistic harmonic with statistical feature hascomprehensive applicability. Distributed energy resources (DER) and electrical loads have grown rapidly in response to concerns about energy sustainability and rising energy demand. However, to realize energy conversion, a large number of power electronic converters are used, resulting in serious harmonic issues in the distribution system. Meanwhile, the random and intermittent characteristics of DER and electrical load bring strong uncertainties to the distribution system. It not only affects the safe and stable operation but also leads to the new stochastic characteristics of harmonics. The study proposes a novel probabilistic harmonic power flow method that takes into account DER and electrical load uncertainties in order to effectively forecast and analyze the uncertain harmonic distortion. Firstly, the time-varying states with stochastic characteristics are determined to represent the uncertainties of electrical load, distributed photovoltaic power, and distributed wind power. The proposed method adapts to time-varying uncertain variable analysis while requiring less computation. Then, a novel constant-weight point estimate method based on the Nataf transformation is proposed to obtain the statistical features of the uncertainties. By simplifying the approximation process, the uncertain variable can be estimated more rapidly and effectively. Moreover, the interaction between multiple uncertain variables is also considered with the correlation coefficient matrix, which can analyze the harmonic coupling interaction in the system. Finally, the probabilistic harmonic power flow is developed considering the time-varying stochastic characteristic of uncertainties. On this basis, the proposed method can be used to forecast the harmonic distortion and also analyze the daily or seasonal statistical features. The proposed probabilistic harmonic power flow method's effectiveness is validated using real-field measured data. [ABSTRACT FROM AUTHOR]