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Event location in power systems is quite essential information for system operators to enhance control-room situational awareness capability. Therefore, it is of great importance to develop an event location estimation algorithm for transmission systems with high accuracy. With the development of wide-area measurement system (WAMS) such as FNET/GridEye, and the synchrophasor measurement devices (SMDs) such as frequency disturbance recorders (FDRs), the synchronous measurement data including frequency, voltage amplitude and phase angle can be collected and used for event location estimation. First, the phase angle and rate of change of frequency (RoCoF) trajectories are respectively used for determining two sets of wave arrival time associated with each FDR. Then, a convolutional neural network (CNN) is utilized to determine the wave arrival order to select the more suitable set of wave arrival times for a given case and to perform corresponding modifications. Next, the oscillation intensity associated with each FDR is determined based on phase angle trajectories in the center of inertia (COI) coordinate system. Finally, the multiple criteria for event location estimation are represented. Case studies and comparisons between the proposed and previous algorithms using actual and confirmed cases in U.S. power systems are performed to demonstrate the effectiveness and improvement of the proposed algorithm in practical applications. [ABSTRACT FROM AUTHOR]

This article introduces a new scheme for suburban renewable energies, hydrogen plant, and logistics (SRE-HP-LC) integration scheme and dispatching. The objective of the proposed SRE-HP-LC integration scheme aims at coordinating the operation of renewable energies, hydrogen production, and storage and logistic transportation. In order to take advantages of various energy conversion techniques to enhance the energy utilization rate and improves the financial revenue of the integration scheme, a completed dispatching and operating scheme for the proposed SRE-HP-LC integration scheme is introduced in the scheme stage. A multiple-demand response objective function is developed in the operation stage to coordinate the hydrogen energy usage in the SRE-HP-LC integration scheme. The proposed SRE-HP-LC integration scheme considers the uncertainties of renewable energy output and truck demand so that it improves the revenue of every component in the integration scheme. Case studies on a general integration system verify the effectiveness and economic value of the proposed SRE-HP-LC integration scheme. [ABSTRACT FROM AUTHOR]

Due to the independent controllability and fast power regulation capability, the High Voltage Direct Current (HVDC) system could be a prospective technology to provide multiple ancillary services to the system besides conventional bulk power transmission. However, with the increase of False Data Injection Attacks (FDIAs) on PMU data, the HVDC system could have the wrong response once the collected data that the HVDC system relied on is attacked, thus threatening the system operating security. How to ensure the security of the PMU-based HVDC ancillary service control become an urgent issue. To mitigate the risk, this paper proposed an HVDC attack-defense control based on the FDIAs detection method. Firstly, the Squeeze-Excitation based Double Convolutional Neural Networks (SE-DCNN) is proposed to realize fast identification of the attacking frequency type based on the time and frequency domain signals. The duration time of FDIAs is detected by the local outlier factor. Then, utilizing the results from SE-DCNN, HVDC ancillary service control framework is reorganized and an HVDC attack defense control is proposed for suppressing the potential influence of various types of FDIAs on the HVDC system ancillary service. Different experiments results demonstrate that the proposed method has the ability to significantly mitigate the frequency deviation and oscillation under the FDIA. [ABSTRACT FROM AUTHOR]

Urban power grids are facing many operational and expansion challenges to meet further demand growth and increased reliability requirements. Advanced transmission technologies have been considered by the electric utilities to effectively increase the utilization of existing infrastructure and operational flexibility. The focus of this paper is on VSC-HVDC technologies for urban power grid enhancement and modernization. First, a potential technical scheme is proposed for converting an existing AC circuit to DC operation, which could boost the power transfer capability of the critical transmission corridor and increase network operational flexibility. Second, this paper proposes three operation modes for the VSC-HVDC interties in urban power grids corresponding to normal, emergency and island operating conditions, respectively. An integrated, adaptive emergency control strategy (AEC) is proposed that can enable adaptive power flow responses of the VSC-HVDC intertie under varying system operating conditions and critical contingencies. The flexibility and effectiveness of the proposed operational principles of urban VSC-HVDC intertie and the corresponding control strategies are verified in PSCAD/EMTDC using a realistic urban power grid in China. [ABSTRACT FROM AUTHOR]

In this study, a new kind of hybrid high‐voltage direct current (HVDC) system is proposed. Each terminal of the proposed system consists of one line commutated converter (LCC) and one full‐bridge modular multilevel converter (FB‐MMC). The LCC and FB‐MMC are connected in parallel so that they can share the same transmission line. The active–reactive power capability of the hybrid HVDC system is extended compared with the conventional LCC‐HVDC system, and power reversal control without power interruption can be achieved by the coordination control of LCC and FB‐MMC. Besides, the proposed hybrid HVDC system is capable of handling DC fault, because both LCC and FB‐MMC have DC fault blocking capability. Moreover, the power rating of FB‐MMC can be designed to low value while keeping the bulk‐power transmission capability of LCC. A two‐terminal bipolar hybrid HVDC system is built in PSCAD/EMTDC. The simulation results verify the effectiveness and feasibility of the proposed hybrid topology and corresponding control strategies. [ABSTRACT FROM AUTHOR]

• 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]

As the typical clean and renewable energy, wind energy has witnessed a continuous annual increase in the last few decades. Due to the random and intermittent characteristics, the wind producers in the electric market meet serious financial losses caused by the deviation between the actual power output and forecasting result. It is difficult to increase the accuracy of forecasting in a short time. How to improve the financial income has become a major task to wind producers and academia. Being the backbone network of the offshore wind farms (OWFs), voltage source converter-based multi-terminal HVdc system (VSC-MTdc) has been regarded as one of the effective solutions to transport wind power. In this paper, an optimal distribution method is proposed for VSC-MTdc system integrating OWFs to reduce the financial loss due to wind power output deviation. The proposed method could be divided into two optimizing functions. The first optimizing function of the proposed method is to analyze the onshore external system according to the historical system operation data and adjust the droop coefficient with the analytic hierarchy process. The second optimizing function of the proposed method is to do further adjusting with the regulating price. With the case study, the proposed optimal distribution method has proved that it can bring more benefit to wind producers. [ABSTRACT FROM AUTHOR]

With the development of urban economy and the growing integration of renewable energy, there are increasing challenges on the urban power grid. Due to the transmission stress and short-circuit current limitation, the traditional urban power grid cannot satisfy the new requirements. Multivoltage-level dc grid (MDCG) is an alternative approach to the urban power grid upgrade. This paper presents an MDCG topology, which can be used in a future urban power grid. Three operation modes of an urban MDCG are proposed: auto operation mode, power-limited operation mode, and stand-alone operation mode. The auto operation mode is the normal one for urban MDCG. The power-limited operation mode is designed to keep the capability to support urban high voltage ac transmission grid in emergencies. The stand-alone operation mode is used to keep stability in case the dc–dc converter system outage occurs. The combination control of three operation modes is put forward to enhance the reliability of urban MDCG in various operating conditions. The simulation results show that the proposed operation modes and combination control are effective and have good performance. [ABSTRACT FROM PUBLISHER]

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]

Erythrocyte possesses high sphingosine kinase 1 (SphK1) activity and is the major cell type supplying plasma sphingosine-1-phosphate, a signaling lipid regulating multiple physiological and pathological functions. Recent studies revealed that erythrocyte SphK1 activity is upregulated in sickle cell disease (SCD) and contributes to sickling and disease progression. However, how erythrocyte SphK1 activity is regulated remains unknown. Here we report that adenosine induces SphK1 activity in human and mouse sickle and normal erythrocytes in vitro. Next, using 4 adenosine receptor-deficient mice and pharmacological approaches, we determined that the A2B adenosine receptor (ADORA2B) is essential for adenosine-induced SphK1 activity in human and mouse normal and sickle erythrocytes in vitro. Subsequently, we provide in vivo genetic evidence that adenosine deaminase (ADA) deficiency leads to excess plasma adenosine and elevated erythrocyte SphK1 activity. Lowering adenosine by ADA enzyme therapy or genetic deletion of ADORA2B significantly reduced excess adenosine-induced erythrocyte SphK1 activity in ADA-deficient mice. Finally, we revealed that protein kinase A-mediated extracellular signal-regulated kinase 1/2 activation functioning downstream of ADORA2B underlies adenosine-induced erythrocyte SphK1 activity. Overall, our findings reveal a novel signaling network regulating erythrocyte SphK1 and highlight innovative mechanisms regulating SphK1 activity in normal and SCD. [ABSTRACT FROM AUTHOR]

Background: Preeclampsia is a prevalent hypertensive disorder of pregnancy and a leading cause of maternal and neonatal morbidity and mortality worldwide. This pathogenic condition is speculated to be caused by placental abnormalities that contribute to the maternal syndrome. However, the specific factors and signaling pathways that lead to impaired placentas and maternal disease development remain elusive.Methods and Results: Using 2 independent animal models of preeclampsia (genetically engineered pregnant mice with elevated adenosine exclusively in placentas and a pathogenic autoantibody-induced preeclampsia mouse model), we demonstrated that chronically elevated placental adenosine was sufficient to induce hallmark features of preeclampsia, including hypertension, proteinuria, small fetuses, and impaired placental vasculature. Genetic and pharmacological approaches revealed that elevated placental adenosine coupled with excessive A₂B adenosine receptor (ADORA2B) signaling contributed to the development of these features of preeclampsia. Mechanistically, we provided both human and mouse evidence that elevated placental CD73 is a key enzyme causing increased placental adenosine, thereby contributing to preeclampsia.Conclusions: We determined that elevated placental adenosine signaling is a previously unrecognized pathogenic factor for preeclampsia. Moreover, our findings revealed the molecular basis underlying the elevation of placental adenosine and the detrimental role of excess placental adenosine in the pathophysiology of preeclampsia, and thereby, we highlight novel therapeutic targets. [ABSTRACT FROM AUTHOR]

• 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]

Grounding fault analysis is of vital importance for low voltage direct current (LVDC) supply and utilization systems. However, the existing DC grounding fault model is inappropriate for LVDC supply and utilization system. In order to provide an appropriate assessment model for the DC grounding fault impact on the LVDC supply and utilization system, an LVDC supply and utilization system grounding fault model is proposed in this paper. Firstly, the model is derived by utilizing capacitor current and voltage as the system state variable, which considers the impact of the converter switch state on the topology of the fault circuit. The variation of system state parameters under various fault conditions can be easily obtained by inputting system state data in normal conditions as the initial value. Then, a model solution algorithm for the proposed model is utilized to calculated the maximum fault current, the system maximum fault current with different grounding resistance is simple to acquired based on the solution algorithm. The calculation results demonstrate that grounding resistance and structure of LVDC supply and utilization system have remarkable impacts on the transient current. The effectiveness of the proposed model is verified in PSCAD/EMTDC. The simulation results indicate that the proposed method is appropriate for the system fault analysis under various fault conditions with different grounding resistance and the proposed model can offer theoretical guidance for system fault protection. [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]

Presents a study which uses in vitro extracellular single-unit recording techniques to investigate the responsiveness of area postrema (AP) neurons to cholecyctokinin (CCK).

Examines the effects of arginine vasopressin (AVP) on area postrema (AP) neurons with the use of extracellular single unit recordings in vitro. Electrophysiological recordings; Slice preparation; Histology; Data analysis; Perspectives.

Investigates the responsiveness of the area postrema (AP) neurons in the brain stem to cholecystokinin. Demonstration of a direct and dose-dependent excitatory action of CCK on AP neurons; Evidence for the potential of role of AP in processing afferent information derived from circulating peptide concentrations that could be involved in food intake regulation.

With the development of dc renewable power generation and dc power consumption, more and more attention has been paid to residential low-voltage dc (RLVDC) power systems in recent years because of their advantages in conversion efficiency and control flexibility. Meanwhile, there are still some obstacles and challenges in the practical application of RLVdc due to the lack of standardization. One of the most important issues in RLVdc standardization progress is the voltage level standard. In this article, a comparative study on the performance of different RLVdc system voltage levels is presented. The main purpose of the article is to provide a voltage level selection guidance for energy prosumers and equipment manufacturers interested in RLVdc systems. The voltage levels commonly used in academia and industry, from 220 to 750 V, are compared and analyzed considering their influence on compatibility, topology, power supply capability, and safety. The article contains a research surveys, market statistics, power system simulations, and calculations with simplified models. The results of the comparative study show that ±375 V is optimal for the RLVdc system in cases with large power ratings and voltage levels below 240 V are suitable for RLVdc systems with special safety requirements. [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]

• An improved hybrid Isolated modular multilevel converter (IM2C) and a medium-voltage DC (MVDC) fault ride-through (FRT) control method for three-port modular multilevel converters are proposed. • With the utilization of isolated matrix submodules, the improved IM2C can regulate its MVDC voltage much lower than the rate value, even negative. • During MVDC fault, the proposed FRT control method protect the normal operation of IM2C by the suppression of the surging arm currents and the LVDC voltage fluctuation. • The fault characteristic of split capacitor grounding is improved by an energy dissipation branch. Modular solid-state transformers (SSTs) are the core devices of the medium-voltage DC (MVDC) distribution network, interlinking the MVDC system with medium-voltage AC (MVAC) system and low-voltage DC (LVDC) system. With the adoption of the modular multilevel converter (MMC) topology, the isolated MMC (IM2C) is a three-port SST sharing one common LVDC-link capacitor. The IM2C saves the cost of sub-converter capacitors. However, the existing IM2C topology is vulnerable under MVDC fault, with the overcurrent risk of power switches and the malfunction danger of LVDC and MVAC ports. In this paper, an improved hybrid IM2C topology is proposed to provide the MVDC fault ride-through (FRT) capability. Using matrix converter topology for sub-converters, the improved IM2C is able to generate negative MVDC voltage. An improved FRT control method for three-port modular multilevel converters is also proposed. With the proposed method, the hybrid IM2C can control the arm currents and maintain the operation of the LVDC and LVAC ports during the MVDC fault. The simulation results with different MVDC fault locations, fault types and system parameters prove the validity of the proposed topology. [ABSTRACT FROM AUTHOR]

Programmable logic controllers (PLCs) are used to control devices throughout the power system since they have fast control capabilities and can utilize multiple types of communication interfaces. Therefore, studying and mitigating their vulnerabilities to electromagnetic pulse is important for the reliability of PLC operations. In this article, an effective impedance measurement scheme is proposed and demonstrated for three PLCs to estimate their susceptibility to an electromagnetic pulse. The equivalent nonuniform transmission line model is established to eliminate the impact of the fixture in the de-embedding process. Then, different parameters of the impedance measurement setup are explored. Based on the measured impedance, the equivalent circuit is established to calculate the response of the device when subjected to the electromagnetic pulse. The voltage and current responses of different interfaces are compared utilizing the developed pulsed current injection (CI) method. Finally, the impedance measurement scheme is verified through testing using three measuring instruments. And the CI simulation experiments reveal the characteristics and susceptibilities of different PLCs interfaces, indicating that some protection measures are required for the reliable operation of the PLC. [ABSTRACT FROM AUTHOR]

The front-end circuit used in the pulsar acquisition of the radio telescope determines the availability of the entire pulsar-based timing framework. However, it would be expensive and resource consuming to use a real radio telescope in the circuit design process. To address this issue, in this article, the hardware-in-the-loop simulation solution is proposed to generate, sample, and extract pulse signals in real time. The artificial pulse generation method is first proposed to generate the pulses that are close to real pulsar signals. Then, three analog front-end circuit architectures (AFCAs) are proposed to generate the analog pulses, including the superposition, attenuator, and attenuator-based superposition structures. The generated pulses are close to the real pulsar signal in shape, amplitude, and noise level. Next, a pulsar-based timing synchronization framework that can be used to improve the timing accuracy of the wide-area monitoring systems is developed to process the sampled data. Multiple experiments are conducted to verify the effectiveness of the analog front-end and the pulsar-based timing synchronization framework using the simulated pulse and real pulsar signals. The results demonstrated that the designed AFCAs can generate effective analog pulses, and is convenient and flexible. [ABSTRACT FROM AUTHOR]

With the increasing penetration of renewable energy into the power system, the voltage source converter (VSC) for integrating renewable energy has become the most common device in the electric network. However, the operating stability of the VSC is strongly dependent on its operating control strategy, which is also highly related to the strength of the AC system. Choosing the control strategy of VSC for different strengths of AC systems becomes an essential issue for maintaining the symmetry between high proportion of renewable energy integration and stable operation of AC system. In order to obtain the operation zones of the control strategies of the VSC under different strengths of AC system, in this paper, the two common VSC control strategies, vector current control (VCC) and power synchronization control (PSC), are compared. Firstly, the principle of VCC and PSC are introduced. Then, based on the short circuit ratio (SCR) and the power limit calculation under steady-state conditions of the VSC, the operation zones of the vector current control and power synchronization control are proposed. Finally, a medium voltage modular multilevel converter (MMC) system was built in PSCAD/EMTDC and the proposed operation zones of the VCC and PSC were tested by changing the SCR of the modified IEEE 33 bus system and analyzed via the critical short circuit ratio (CSCR) analysis, the small-signal stability analysis, and transient stability analysis. The results indicate that, as the SCR decreases, the VSC based on VCC is gradually worked into unstable conditions, while the stability of VSC based on PSC gradually increases. The analysis results provide a criterion for the converter operation strategy change that could significantly improve the operating stability of the VSC in the power system and realize the symmetry of the stability of the converter and the change of the strength of the AC system. [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]

The capacitance of sub-module capacitor has a great impact on the cost, size, and operation of the modular multi-level converter (MMC). However, the capacitance selected by the existing methods does not always meet the requirement in practice. To find out the reasons for this improper selection, the existing selection methods are analyzed in this paper. Based on the analysis, a new capacitance-selection method is proposed. In the new method, the problems of the existing methods are solved, and the calculation of capacitor voltage is based on a proposed capacitor-voltage model whose calculation error can be smaller than 0.1%. Furthermore, the Secant Method is used in the capacitance selection to quickly calculate the required capacitance. The new capacitance-selection method can be applicable to the MMC not having a circular operating region. In addition, this paper found that the capacitor voltage and the capacitor-voltage ripple reach their maximum values when the power-factor angles of the MMC are –π/2 and π/2, respectively, and the dc component in the capacitor voltage changes according to the operating condition of the MMC. Finally, the proposed selection method and theoretical analyses are verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) have shown great potential in the area of multimegawatt wind energy conversion system (WECS) based on permanent magnet synchronous generators (PMSGs). However, the studies in this area are few, and most of them refer to the MMC used in high-voltage direct current (HVDC) systems, and hence the characteristics of the PMSG are not considered. This paper proposes a steady-state analysis method for MMCs connected to a PMSG-based WECS. In the proposed method, only the wind speed (operating condition) is required as input, and all the electrical quantities in the MMC, including the amplitudes, phase angles and their harmonics, can be calculated step by step. The analysis method is built on the proposed d-q frame mathematical model. Interactions of electrical quantities between the MMC and PMSG are comprehensively considered. Moreover, a new way to calculate the average switching functions are adopted in order to improve the accuracy of the analysis method. Applications of the proposed method are also presented, which includes the characteristic analysis of capacitor voltage ripples and the capacitor sizing. Finally, the accuracy of the method and the correctness of the analysis are verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

With the increasing demand of electricity, the development of the urban power grid has drawn a lot of attention in China. In order to focus on the analysis of an urban power grid, the remaining part of the large-scale power grid used is to be reduced. The accuracy of the equivalence is key to urban power grid research. In this paper, a multistep dynamic equivalent method based on district dividing is proposed. Based on the electrical distance, voltage level, and geographic location, the external system is divided into outer layer, inner layer, and buffer subsystem. Each district is separately reduced by different methods. The proposed technique is illustrated by a real large-scale power grid in the south of China. [ABSTRACT FROM PUBLISHER]

• 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]

• A mode switch control and reactive power support strategy are proposed. • Voltage sags are mitigated or eliminated with proposed control. • The real-time local control enables inverters to respond to voltage drops swiftly. • The probability of AC voltage sag impact on windfarm is reduced with proposed control. In recent years, VSC-HVDC has been widely used in windfarm integration owing to its ability of connecting the weak AC system. And the hybrid modular multilevel converter based HVDC(MMC-HVDC) has attracted more attention because of its DC fault blocking capability. However, most of the researches about MMC-HVDC connected to windfarm are focused on frequency response and wind farm fault ride through, without assisting AC system to maintain the voltage via the converter's reactive power control capacity. Based on this, this paper proposes a mode switch control and reactive power support control scheme for the grid connected inverter connected to windfarms. The switch mode control scheme provides three operation modes for MMC to adapt to different operation situations. The reactive power support coordination control scheme is an advanced control scheme for cooperating converter, unloading resistor and wind farm. With the cooperating control, the PCC voltage sag due to the fault is alleviated while reducing the impact of grid failures on the wind farm. Finally, the presented control strategy is simulated in PSCAD/ EMTDC, which verifies the effectiveness of the scheme proposed. [ABSTRACT FROM AUTHOR]

• The proposed DC line protection scheme based on the amplitude ratio of dual-frequency traveling wave can identify the internal and external faults reliably. • The sensibility under the internal fault with fault resistance of 1500Ω is still high. • The required time window is only 1.2ms after the traveling wave propagates to the protection device, which satisfies the fast protection requirement of MMC-MTDC grids. • The method of calculating h and the criterion for selecting the sampling frequency can be applied to any system. Fast and reliable DC line protection is an essential challenge for the modular multilevel converter (MMC) based multi-terminal direct current (MTDC) grid. This paper proposed a novel single-ended protection scheme for DC lines in MMC-MTDC grids. Firstly, the values of the initial voltage traveling wave (IVTW) generated by internal and external faults are calculated by using the equivalent model of the MTDC grid, respectively. Then a criterion for identifying internal and external faults is constructed based on the amplitude ratio of the low-frequency component of the IVTW to its high-frequency component. The amplitude of the IVTW in both frequency bands is concisely expressed by the modulus maximums of stationary wavelet transform (SWT). Additionally, the criteria for discriminating the fault direction and the faulted pole are also proposed, which are both based on the integral values of the fault component currents on positive- and negative-pole lines. Lastly, simulation results verify the effectiveness of the proposed protection scheme. [ABSTRACT FROM AUTHOR]

A response from the authors of the article "Elevated placental adenosine signaling contributes to the pathogenesis of preeclampsia" in the 2015 issue is presented. [ABSTRACT FROM AUTHOR]