Flexible Grid Research Articles

A Flexible DC Ranging Scheme Based on Variational Mode Decomposition and Teager Energy Operator

In this paper, a new Cable fault location scheme is proposed for the existing flexible DC Cable fault location methods, in which the fault signal is mixed with noise and the traveling wave speed is affected by line parameters. This scheme is based on the propagation characteristics of fault line mode voltage traveling waves in flexible DC transmission. Firstly, the fault voltage is effectively decomposed using Variational Mode Decomposition (VMD). Then, the decomposed intrinsic mode functions (IMF) are reconstructed to obtain the high-frequency components of the recorded fault information. Finally, the traveling wave head is calibrated using the Teager Energy Operator (TEO). A dual terminal ranging algorithm that is not affected by wave velocity has been proposed, which can effectively avoid the impact of fault traveling wave velocity uncertainty on the ranging results. A dual ended flexible DC power grid model was built in PSCAD/EMTDC, and a large number of simulation results show that the algorithm proposed in this paper can accurately calibrate the fault traveling wave head, has little interference from transition resistance, strong noise resistance, and can obtain high-precision fault location results in different fault locations.

New pilot protection method based on the current fault component waveform similarity

AbstractIn order to improve the ability of the modular multi‐level converter to quickly clear and isolate faults in the multi‐terminal flexible DC grid, this paper analyzes the characteristics of current faults in the multi‐terminal flexible direct current grid, introduces the comprehensive distance of current fault waveform, and proposes a line protection method based on the similarity of current fault waveform. This protection method firstly uses Euclid Dynamic Time Warping (DTW) distance and entropy weight method to process electrical quantity signals, calculates the comprehensive distance of current fault waveform of two converter stations, and builds the protection criterion based on the similarity of current fault waveform. Then, the fault identification is realized by using the calculated comprehensive distance, and the fault pole identification is realized by using the ratio of comprehensive distance between positive and negative poles. Finally, PSCAD was used to build a simulation model to output the fault data under different fault conditions, and MATLAB was used to process the fault data to verify the protection algorithm. The simulation results show that the proposed method has good resistance to high resistance, and its rapidity and adaptability are further improved. Compared with other similarity methods, this method combines Euclidean DTW distance and entropy method to process the signal, realizes the fault pole identification, and can still operate correctly under the interference of 500 Ω transition resistance and 20 dB noise ratio. The research results will provide a theoretical basis for the safe and reliable operation of flexible DC power grid.

Operational flexibility analysis of alkaline electrolyzers integrated with a temperature-stabilizing control

Alkaline electrolyzers (AELs) have emerged as promising candidates for providing flexible grid services. However, a comprehensive understanding of their operational flexibility has been hindered by a lack of consideration of their thermodynamics in previous studies. To address this limitation, this paper presents comprehensive models that analyze the impact of AEL thermodynamics on their operational flexibility. Specifically, a closed-loop thermal model with temperature-stabilizing control is established to capture the temperature evolution, followed by the development of a temperature-dependent U–I model to characterize the influence of temperature on electrical performance. Case studies are conducted to simulate a practical 26 kW AEL facility using Matlab/Simulink. The results demonstrate that the proposed temperature-stabilizing control effectively maintains the temperature at the setpoint when adjusting the power consumed by AELs. Consequently, the power regulation range of AELs increases from 7.4 kW to 16 kW, compared to a simple control that fixes the cooling water flow at 0.02 m3/h. While increasing the fixed water flow to 0.05 m3/h can also enhance the regulation capacity, the proposed control ensures higher system efficiency than that of the fixed flow control. Moreover, the temperature-stabilizing performance of the controller is influenced by the cooling system’s parameters. Hence, a coordinated design approach between the cooling system and temperature controller is recommended to achieve favorable temperature-stabilizing performance.

FIELDimageR.Extra: Advancing user experience and computational efficiency for analysis of orthomosaic from agricultural field trials

AbstractFieldimageR.Extra is an advanced R package that enhances user experience and computational efficiency in analyzing orthomosaic images from agricultural field trials. Through the integration of modern GIS libraries like terra, stars, and sf, it surpasses traditional packages like raster and sp. The FieldimageR.Extra offers interactive visualization, vector feature creation, and spatial data editing within the R environment through the integration of mapview and mapedit packages. Notably, FieldimageR.Extra introduces new functions like fieldShape_render and fieldShape_edit, enabling flexible plot grid generation and editing capabilities. Comparative evaluations demonstrate the superior performance of FieldimageR.Extra in handling spatial data, crop and extract operations, and plot grid generation. With its comprehensive features, FieldimageR.Extra stands as a valuable addition to the FieldimageR R package, offering researchers efficient tools for unmanned aerial vehicle‐based orthomosaic image analysis in agricultural research. FIELDimageR.Extra is publicly available as a GitHub repository (https://github.com/filipematias23/FIELDimageR.Extra).

Multi-Port Hybrid DC Circuit Breaker Based on Bridge Commutation Branch

Flexible DC grids have become an important means to support large-scale new energy integration utilization due to their advantages of flexible power control and high efficiency. Flexible DC grids generally consist of multiple converter stations and DC lines. Therefore, there are multiple line intersection points, and DC circuit breakers (DCCBs) need to be installed at the intersection to isolate faults. Multi-port hybrid DCCBs (MPHCBs) based on topology optimization can greatly reduce the cost by replacing multiple two-port DCCBs with one multi-port DCCB at the intersection. However, currently researched multi-port DCCBs still have a high cost and large volume while lacking engineering verification. This paper proposes a hybrid multi-port DCCB based on a bridge commutation branch that greatly reduces the number of power electronic devices used and the cost and volume of the DCCB. First, the topology and control method of the proposed MPHCB are studied, and its cost and reliability are analyzed. Then, the breaking test of the proposed MPHCB based on the bridge commutation branch is carried out at a 15 kV voltage level. The results show that the proposed MPHCB can interrupt a 15 kA current in 3 ms, which verifies the feasibility of the scheme.

An Improved Decentralized Control of Cascaded Inverters With Robust Stability Against Grid-Voltage Variation

The existing decentralized control method for grid-connected cascaded inverters has the problem that the system stability is sensitive to grid-voltage variation. As a result, the system would lose stability when the grid-voltage amplitude is abnormal. To address this issue, this letter proposes a novel decentralized -sin and V-P power control scheme. The robust stability condition against grid-voltage variation is proved. Moreover, the power-factor-angle consistency of inherent synchronization mechanism is clearly revealed for cascaded inverters, and the flexible grid power factor is enabled. For future practical applications, the proposed primary control of this letter explores a promising control idea for low-voltage cascaded PV/storage systems. Finally, the performance of the proposed method is compared with the existing method by simulations under small and large grid disturbances.

Fault protection scheme of flexible DC grid based on transient power instantaneous energy difference

The DC line protection is the key to the stable operation of the multi-terminal flexible DC grid, and the current limiting reactor (CLR) as the boundary condition provides great convenience for the design of the flexible DC grid fault protection scheme. Using the boundary condition characteristics of the CLR, the paper proposes a fault protection method for flexible DC grid based on transient power instantaneous energy (IE) difference. First, the equivalent circuit of the DC line of the flexible DC grid under different faults is established. On this basis, the conclusion that the transient power amplitude of internal fault is much larger than the external is deduced from the full-power in the time-domain. The Teager energy operator is used to calculate the maximum IE of the transient power, and then the internal and external faults are identified. Secondly, according to the difference of the transient power amplitude of the CLR on the fault pole and the healthy pole, the ratio of the IE of the positive and negative CLR transient power is used to construct the fault pole selection. The scheme is simple and easy to implement, and does not need to consider the synchronization problem of data at both sides. Finally, the simulation results show that the proposed method can better satisfy the speediness and selectivity requirements of DC grid protection. The scheme can accurately detect faults under different working conditions, and has strong fault resistances capability.

Social construction of fire accidents in battery energy storage systems in Korea

Renewable energy (RE) has the potential to become an essential part of the national policy for energy transition. The government of the Republic of Korea has sought to solve the problem of RE intermittency and achieve flexible grid management by leveraging a powerful policy drive for battery energy storage system (B-ESS) technology. However, from 2017 to 2019, over two dozen B-ESS fire accidents occurred across Korea. Consecutive fires in B-ESSs, which were expected to be game-changers in energy transition, have instead become an issue of social concern. This study aims to analyze the influence of various social factors on fire accidents, for which previous studies could not provide sufficient explanation. A literature analysis and qualitative interviews revealed the social construction process of B-ESS fires through stakeholder interaction. The economic incentive schemes of B-ESS and insufficient safety regulations has had a significant influence on the interactions of relevant social groups (RSGs), and several factors in the environment, organizations, and cognition/choice of RSGs have exacerbated fire risks. This research provides a clearer understanding of the adverse outcomes of adopting new energy technologies.

A branch-and-cut algorithm for the routing and spectrum allocation problem

One of the most promising solutions to deal with huge data traffic demands in large communication networks is given by flexible optical networking, in particular the flexible grid (flexgrid) technology specified in the ITU-T standard G.694.1. In this specification, the frequency spectrum of an optical fiber link is divided into narrow frequency slots. Any sequence of consecutive slots can be used as a simple channel, and such a channel can be switched in the network nodes to create a lightpath. In this kind of networks, the problem of establishing lightpaths for a set of end-to-end demands that compete for spectrum resources is called the routing and spectrum allocation problem (RSA). Due to its relevance, RSA has been intensively studied in the last years. It has been shown to be NP-hard and different solution approaches have been proposed for this problem. In this paper we present several families of valid inequalities, valid equations, and optimality cuts for a natural integer programming formulation of RSA and, based on these results, we develop a branch-and-cut algorithm for this problem. Our computational experiments suggest that such an approach is effective at tackling this problem.

On-chip non-uniformly spaced multi-channel microwave photonic signal processor based on an ultrahigh-Q multimode micro-disk resonator.

Multi-channel microwave photonic (MWP) signal processing can simultaneously perform different task operations on multiple signals carried by multiple wavelengths, which holds great potential for ultrafast signal processing and characterization in a wavelength-division-multiplexed (WDM) network. As emerging telecommunication services create more data, an elastic optical network, which has a flexible and non-uniform spectrum channel spacing, is an alternative architecture to meet the ever-increasing data transfer need. Here, for the multi-channel ultra-fast signal processing in the elastic optical network, we propose and demonstrate an on-chip non-uniformly spaced multi-channel microwave photonic signal processor based on an ultrahigh-Q multimode micro-disk resonator (MDR). In the proposed signal processor, an MDR supporting multiple different order whispering-gallery modes (WGMs) with an ultrahigh Q-factor is specifically designed. Benefiting from the large and different free spectral ranges (FSRs) provided by the different order WGMs, a non-uniformly spaced multi-channel microwave photonic signal processor is realized, and various processing functions are experimentally demonstrated including bandpass filtering with a narrow passband of 103 MHz, a rejection ratio of 22.3 dB and a frequency tuning range from 1 to 30 GHz, multiple frequency measurement with a frequency measurement range from 1 to 30 GHz, a frequency resolution better than 200 MHz and a measurement accuracy of 91.3 MHz, and phase shifting with a phase tuning range from -170°∼160°, an operational bandwidth of 26 GHz from 6 GHz to 32 GHz and a small power variation of 0.43 dB. Thanks to the coexistence of different order WGMs supported by the MDR, non-uniformly spaced multi-channel signal processing is enabled with the key advantages including a broad operation bandwidth, an ultra-narrow frequency selectivity, and a large phase tuning range with a small power variation. The proposed signal processor is promising to be widely used in future elastic optical networks with flexible spectrum grids.

Quantifying Hand Strength and Isometric Pinch Individuation Using a Flexible Pressure Sensor Grid.

Modulating force between the thumb and another digit, or isometric pinch individuation, is critical for daily tasks and can be impaired due to central or peripheral nervous system injury. Because surgical and rehabilitative efforts often focus on regaining this dexterous ability, we need to be able to consistently quantify pinch individuation across time and facilities. Currently, a standardized metric for such an assessment does not exist. Therefore, we tested whether we could use a commercially available flexible pressure sensor grid (Tekscan F-Socket [Tekscan Inc., Norwood, MA, USA]) to repeatedly measure isometric pinch individuation and maximum voluntary contraction (MVC) in twenty right-handed healthy volunteers at two visits. We developed a novel equation informed by the prior literature to calculate isometric individuation scores that quantified percentage of force on the grid generated by the indicated digit. MVC intra-class correlation coefficients (ICCs) for the left and right hands were 0.86 (p < 0.0001) and 0.88 (p < 0.0001), respectively, suggesting MVC measurements were consistent over time. However, individuation score ICCs, were poorer (left index ICC 0.41, p = 0.28; right index ICC -0.02, p = 0.51), indicating that this protocol did not provide a sufficiently repeatable individuation assessment. These data support the need to develop novel platforms specifically for repeatable and objective isometric hand dexterity assessments.

High-Frequency Oscillation Suppression Strategy for Flexible DC Transmission Systems Based on Additional Joint Damping

Flexible DC transmission systems experience negative damping characteristics in the high-frequency range due to the delay in the system control link. This can lead to interactions between the impedance of modular multilevel converters (MMCs) and AC transmission lines, resulting in high-frequency oscillation (HFO) issues. To resolve this problem, a simplified MMC control model was developed, taking into account the current inner loop control link. The Sobol method was employed to analyze the factors influencing the impedance characteristics of MMC. Additionally, a combined approach involving a virtual passive filtering method and an equivalent current sampling method was proposed to provide additional damping. The study compared and analyzed the impact of additional damping control on the impedance characteristics and system stability of MMCs. Lastly, a flexible direct current grid connection simulation model was constructed using PSCAD to validate the effectiveness of the proposed additional damping control strategy.

A flexibility-based multi-objective model for contingency-constrained transmission expansion planning incorporating large-scale hydrogen/compressed-air energy storage systems and wind/solar farms

The remarkable arrival of uncertainties given by the fluctuations in the output of renewable energy sources (RESs) calls for a more flexible power grid. In confronting this issue, large-scale energy storage systems play a vital role in achieving higher flexibility. In this regard, the authors of this study present here a new multi-objective model for contingency-constrained transmission expansion planning that incorporates large-scale hydrogen/compressed-air energy storage systems and wind/solar farms to simultaneously boost both supply-demand-related flexibility (SDFX) and grid-related flexibility (GDFX). The proposed model is formulated as a non-convex mixed-integer nonlinear master-slave optimization problem. The planning objectives, modeled through the master problem, are intended to minimize the investment and operation costs, while maximizing the SDFX enhancement metric minus the GDFX degradation metric. The slave problem, however, aims to maximize the community welfare function (CIWF) and microgrid welfare function (MIWF) under both normal and N-1 operating conditions. To solve the resulting non-convex mixed-integer nonlinear master-slave optimization problem, a potent symphony orchestra search algorithm (SOSA)—empowered with a multi-computational-step, multi-dimensional, multiple-homogeneous structure—is employed to allow better diversification and exploration. Following the determination of optimal solutions, a conservative-based fuzzy satisfying approach is applied to characterize the best trade-off solution that suits cost-effectiveness and flexibility requirements. The newly developed model was implemented on the IEEE 24-bus and IEEE 118-bus test grids, and the simulation results proved its effectiveness and practicality.

Fabrication of submicron linewidth silver grid/ionogel hybrid films for highly stable flexible transparent electrodes via asymmetric wettability template-assisted self-assembly

High-performance flexible transparent electrodes are the basis for the continuous upgrading of optoelectronic devices. Silver grids are attractive for replacing traditional indium tin oxide (ITO) as the premier transparent electrode materials, due to their high transmittance, excellent conductivity, and low cost. However, large linewidth and oxidation of silver grids are limiting the practical application of the resulting optoelectronic devices. Here, we report an effective and scalable solution-based method to prepare highly stable flexible transparent silver grid electrodes with submicron linewidth by the asymmetric wettability template-assisted self-assembly of silver nanoparticles (AgNPs), which is then encapsulated by a thin transparent conductive ionogel as protective layer. It is demonstrated that the linewidth of silver grids can be precisely controlled by the concentration of the AgNP dispersion. Wrapping with the ionogel nanolayer have no deterioration for conductivity and transmittance of the grid electrodes. The optimized hybrid grid electrodes exhibit low sheet resistance of 24.6 Ω sq−1 and high transparency of 99%. More importantly, the introduction of the iongel nanolayer endows the hybrid grid electrodes with excellent mechanical flexibility and thermal, electrical, and chemical stability. As a proof of concept demonstration, the submicron linewidth silver grid/ionogel hybrid films are successfully used to fabricate flexible smart windows and transparent touch panel. We envision that this work will shed new light on the development of next-generation optoelectronic applications which need ultrahigh resolution displays.

DA-LSTM: A dynamic drift-adaptive learning framework for interval load forecasting with LSTM networks

Load forecasting is a crucial topic in energy management systems (EMS) due to its vital role in optimizing energy scheduling and enabling more flexible and intelligent power grid systems. As a result, these systems allow power utility companies to respond promptly to demands in the electricity market. Deep learning (DL) models have been commonly employed in load forecasting problems supported by adaptation mechanisms to cope with the changing pattern of consumption by customers, known as concept drift. A drift magnitude threshold should be defined to design change detection methods to identify drifts. While the drift magnitude in load forecasting problems can vary significantly over time, existing literature often assumes a fixed drift magnitude threshold, which should be dynamically adjusted rather than fixed during system evolution. To address this gap, in this paper, we propose a dynamic drift-adaptive Long Short-Term Memory (DA-LSTM) framework that can improve the performance of load forecasting models without requiring a drift threshold setting. We integrate several strategies into the framework based on active and passive adaptation approaches. To evaluate DA-LSTM in real-life settings, we thoroughly analyze the proposed framework and deploy it in a real-world problem through a cloud-based environment. Efficiency is evaluated in terms of the prediction performance of each approach and computational cost. The experiments show performance improvements on multiple evaluation metrics achieved by our framework compared to baseline methods from the literature. Finally, we present a trade-off analysis between prediction performance and computational costs.

112. Utilizing a Flexible Pressure Grid to Quantify, Map, and Track Hand Grip Strength

112. Utilizing a Flexible Pressure Grid to Quantify, Map, and Track Hand Grip Strength

Experimental Study of the Mechanical Properties of a Flexible Grid Filling Body

The fill mining method has become more widely used due to its advantages of a high resource recovery rate, reliability and safety, and reduced surface tailings storage. However, the mechanical properties of the cemented fillings in fill mining are similar to those of ultra-low strength plain concrete, and there are problems such as high brittleness, low bending and tensile strength, and sudden failure. Using a flexible grid as reinforcement material, uniaxial compression, tensile, and shear tests of a flexible grid filling body were carried out, and the results were compared with the mechanical properties of the filling body without the flexible grid. We drew the following main conclusions: the uniaxial compressive strength of the flexible grid filling body gradually increased with the decrease in the grid spacing (the increase in the grid density); the grid dimension had little effect on the uniaxial compressive strength of the flexible grid filling body. The uniaxial tensile strength and shear strength of the flexible grid filling body increased with the increase in the grid dimension; and they first increased and then decreased with the increase in the grid spacing, and there was an optimal grid spacing. From the perspective of the macroscopic failure mode, the flexible grid filling body specimen after the uniaxial compression test had a conjugate shear failure, forming a “dumbbell shape” with two large ends and a small middle. After the uniaxial tensile test, the macroscopic failure mode of the specimen was tensile failure. After the shear test, the macroscopic failure mode of the specimen was shear slip failure. It is proposed that the tensile strength, shear strength, cohesion, and internal friction angle strengthening coefficients of the flexible grid filling body with different dimensions and spacing are higher than the elastic modulus strengthening coefficients. The experimental results can provide a certain reference and guidance for mine filling.

Used vs. new: Does it have consequences for the performance of fishing gear?

Sea trials to test size selectivity equipment in trawls are often limited in time because they are costly, and the results can be influenced by multiple factors that are often overlooked. In the Barents Sea gadoid trawl fishery, the use of a size sorting grid in front of the codend is compulsory. The flexigrid, a netting section containing two flexible grids, is the most widely used grid section in this fishery. However, earlier selectivity studies with this device have shown inconclusive results. It has been speculated that the differences observed resulted from the difference in age and usage of the grid sections in the studies compared. To reveal whether potential changes in the device construction over time can lead to differences in size selection properties, we performed comparative fishing trials where we compared a brand new flexigrid section and a well-used flexigrid section used continuously by a commercial trawler for approximately four years. The results showed that the new flexigrid released significantly more cod below ∼60 cm than the used flexigrid. However, when the grids were fished with a subsequent diamond mesh codend, there was no difference in the overall selectivity of the two gears, meaning that the size selectivity in the codend compensates for the potential reduction in selectivity performance of the grids. This study shows the importance of considering the age and earlier use of size selection devices like sorting grids before they are compared with other devices, as their size selection properties can change significantly over time and with use.

A single‐ended protection method for flexible DC distribution grid

AbstractConsidering that no current limiting inductances (CLIs) are installed at the end of the DC line in the flexible DC distribution grid, the protections relying on line boundary are no longer applicable. To overcome this problem, the paper proposes a single‐ended protection method independent of line boundary. Firstly, the Peterson equivalent circuit is applied to analyze the amplitude‐time ratio of initial voltage travelling wave (ARIVTW) under internal and external faults. Secondly, the fault direction criterion based on the fault component current and the fault type criterion based on the pole voltage are built. Subsequently, the fault identification criterion is constructed by using the ARIVTW, and the corresponding protection method is formed. Finally, the flexible DC distribution grid is built in PSCAD to verify the proposed method. The simulation results show that the method is robust to fault resistance and noise. Besides, the method realizes the protection of the whole line, which has good selectivity and engineering applicability.

Machine learning aided optimization for balanced resource allocations in SDM-EONs

A fine-grained flexible frequency grid for elastic optical transmission and space division multiplexing in conjunction with spectrally efficient modulations is an excellent solution to the coming capacity crunch. In space division multiplexed elastic optical networks (SDM-EONs), the routing, modulation, core, and spectrum assignment (RMCSA) problem is an important lightpath resource assignment problem. Intercore cross talk (XT) reduces the quality of parallel transmissions on separate cores, and the RMCSA algorithm must ensure that XT requirements are satisfied while optimizing network performance. There is an indirect trade-off between spectrum utilization and XT tolerance; while higher modulations are more spectrum efficient, they are also less tolerant of XT since they permit fewer connections on neighboring cores on the overlapping spectra. Numerous XT-aware RMCSA algorithms restrict the number of litcores, cores on which overlapping spectra are occupied, to guarantee XT constraints are met. In this paper, we present a machine learning (ML) aided threshold optimization strategy that enhances the performance of any RMCSA algorithm for any network model. We show that our strategy applied to a few algorithms from the literature improves the bandwidth blocking probability by up to three orders of magnitude. We also present the RMCSA algorithm called spectrum-wastage-avoidance-based resource allocation (SWARM), which is based on the idea of spectrum wastage due to spectrum requirements and XT constraints. We note that SWARM not only outperforms other RMCSA algorithms, but also its ML-optimized variant outperforms other ML-optimized RMCSA algorithms.