Recovery Voltage Research Articles

A Novel Synchronization Strategy for Distributed Energy Resources in Weak Grids Using Remote Strong Grid Sensing

This paper proposes a novel strategy for the current injection-based control of distributed energy resources connected to weak grids via a voltage source converter. The current injection controller is no longer synchronized with the point of common coupling but with the strong grid point voltage. The strong grid synchronization control strategy improves the output dynamics of the voltage source converter and recovery after faults in weak grids. The phase difference between the voltage source converter and the strong grid voltages caused by the long power lines does not affect the power control. Furthermore, a time delay-compensation method is proposed which tolerates the communication time delay introduced by the transmission of the synchronization signal from the strong grid point. The performance of the proposed control strategy is verified in detail using MATLAB 2023b simulations and real-time digital simulations on a medium voltage model and also validated in an experiment on a low-voltage grid-feeding inverter setup.

A cooperative control strategy for balancing SoC and power sharing in multiple energy storage unit within DC microgrids

AbstractThis paper proposes a distributed cooperative control scheme for multiple energy storage unit (ESU) in DC microgrids to achieve the control objectives of SoC balancing, power sharing, and bus voltage recovery. In the primary control part, the proposed scheme constructs a control function between the SoC values of each ESU and the droop coefficients to dynamically adjust the droop coefficients. Through a communication network, information is exchanged with neighbouring ESUs to achieve SoC convergence. In the secondary control part, by exchanging power information with neighbouring ESUs, precise power distribution is achieved. Additionally, the proposed scheme maintains bus voltage stability. Finally, a DC microgrid simulation model and experimental platform were developed, demonstrating the feasibility and plug‐and‐play capability of the proposed control strategy through both simulation and experimental case tests.

Low Pass Filter Based Lithium‐ion Battery Equivalent Circuit Model With High Accuracy

AbstractThe equivalent circuit model (ECM) of lithium batteries provides a simplified way to describe their output behaviors. In this paper, a low pass filter‐based ECM of lithium battery is proposed with high accuracy. A voltage source is employed to represent the capability of the lithium battery to store energy chemically, a RC branch paralleled with the voltage source represents the charge transfer process. This RC branch acts as a low pass filter, and the capacitance buffers the charges during charging or discharging process, and this explains the dynamic voltage recovery process. However, with the traditional RC branches‐based ECM, the dynamic voltage is realized by the resistance in parallel with the capacitor, which discharges the capacitor and the RC branch is series‐connected with the voltage source. The proposed ECM is compared with the 1‐RC Thevenin model, which has the same number of model parameters with the proposed model. The parameters are obtained by the hybrid pulse power characterization (HPPC) test. The output voltage accuracy of the 1‐RC Thevenin model and the proposed model with LFP battery and NCM battery is verified with different test conditions. The experimental results show that the proposed ECM has higher accuracy, this validates the correctness of the proposed model.

A proton exchange membrane fuel cells degradation prediction method based on multi-scale temporal information merging network

Performance degradation prediction is considered as an effective method to improve the service life of proton exchange membrane fuel cells (PEMFCs). A hybrid method Multi-scale Temporal Information Merging Network (MTIMN) is then proposed for PEMFC degradation prediction, which is designed to merge information from both macro and micro perspectives in PEMFC historical working data. Firstly, a data preprocessing method based on P-M scores and min-max wavelet denoising is designed to eliminate redundant variables and noise considering the structure of PEMFC and data statistics. Secondly, aiming at the voltage recovery phenomenon during the aging process, a Multi-scale Exponential Decomposition Encoding Module (MEDEM) is presented to extract and encode different time scales of sequences from the PEMFC degradation data. Thirdly, a two-layer Historical Information Integration Module (HIIM) is established, which consists of the trend extraction module and the local extraction module, to extract deep dynamic nonlinear characteristics. Finally, the Merging Prediction Module (MPM) merges information from trend and local modules for the final output. The experimental results show that Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) are 0.0107 and 0.0079, respectively. Therefore, MTIMN can effectively extract deep dynamic nonlinear characteristics in PEMFC degradation data and improve prediction accuracy greatly.

Threshold Voltage Recovery Time Measurement Technique Post VTH Instability in Normally-Off p-Gate GaN High Electron Mobility Transistors

In this study, we propose a simple measurement technique to quantitatively measure the time taken by threshold voltage of normally-off p-GaN AlGaN/GaN HEMTs to recover from a nominal operational gate stress-induced instability. The proposed technique eliminates the requirement to perform a full transfer characteristic sweep post-stress, thereby eliminating the measurement-induced instability effect, often colluding precise recovery time measurement. The rate of recovery and extracted recovery times hold significance in empirically correlating the location of traps in the p-GaN or AlGaN barrier region causing VTH instability. The gate of the HEMT is stressed at nominal operational drive voltages 1.5 V, 2 V, and 4 V for various time intervals from 500 μs to 100 s, and the time taken for the drain current to recover to prestress levels measured at near-threshold voltage (~1.1 VTH) is measured as the threshold voltage recovery time. With increasing gate stress voltages, 2DEG gets trapped at relatively deeper trap energy levels at the AlGaN/GaN interface requiring more emission time during the process of recovery, mandating larger recovery times. At higher stress voltage of 4 V, the Schottky gate leakage current is high enough enabling injected holes to cross the AlGaN barrier and counter-compensate for the deeply trapped 2DEG, requiring relatively the same recovery times as lower stress voltages where the gate leakage is negligibly small. With increasing stress time, the amount of 2DEG trapped increases, requiring more recovery time to de-trap and beyond a certain time, saturation of the trap density occurs causing the recovery time to plateau.

Influence of Cable and Overhead Lines Parameters on the of Transient Recovery Voltages of High-voltage Circuit Breakers

Influence of Cable and Overhead Lines Parameters on the of Transient Recovery Voltages of High-voltage Circuit Breakers

Lyapunov-based distributed secondary frequency and voltage control for distributed energy resources in islanded microgrids with expected dynamic performance improvement

Microgrids (MGs) can effectively integrate the high penetration distributed energy resources (DERs) for the energy and environmental crisis. Still, fluctuations in intermittent DERs may lead to severe frequency and voltage deviations or even the instability of islanded MGs. Secondary control has successfully compensated for the frequency and voltage deviations. Research on secondary control mainly focused on steady-state operating objectives, i.e., frequency and voltage recovery and power sharing. Still, improving the dynamic responses of secondary control is crucial for system-stable operation, especially in the presence of synchronous DERs. This is because these units can cause undesired oscillatory modes, leading to system instability. In addition, because of the line impedance effect, accurate reactive power sharing is usually ignored when voltage recovery is considered. This will lead to an overload of MGs. To improve the dynamics of secondary control while trading off voltage regulation and reactive power sharing, we propose a Lyapunov-Function (LF)–based distributed secondary control strategy. In the proposed LF-based control strategy, the frequency, voltage, and power information are introduced into feedback control based on the Lyapunov stability theorem. Therefore, the improved frequency and voltage deviations and accurate power sharing can be guaranteed when the Lyapunov function asymptotically attenuates to zero. The inherent conflict between voltage regulation and reactive power sharing is addressed by converging the average voltage to the rated reference. Besides, the improved dynamic performance of secondary control is achieved by considering global power variations, which are obtained by distribution-level phasor measurement units. Global power variations can establish control actions to dampen system oscillations and accelerate system restoration. Furthermore, the controller design method based on the Lyapunov stability theorem can naturally promise the stability of the proposed secondary frequency and voltage controllers. Numerical simulations on the IEEE 34-bus system validate that the proposed control strategy can ensure the significantly improved dynamic performance of secondary control while achieving steady-state operation objectives.

Adaptive control strategy for microgrid inverters based on Narendra model

In recent years, microgrid technology has been widely studied and applied. However, with times developing, the installed capacity of distributed power generation devices has been improved, and work is being carried out in increasingly complex situations, resulting in a decline in the control performance of microgrids. In view of this, to effectively improve inverter’s control performance, research is conducted on the fusion of Narendra model and adaptive control strategies for real-time voltage correction and compensation in complex situations. Compared to traditional inverters, inverters under research methods have faster voltage recovery speed when encountering load switching, and can recover in about one cycle, with good control performance. In the comparison between the improved inverter adaptive control system and the inverter adaptive system, the improved inverter voltage recovery speed is faster, can be restored within one cycle, and the control effect of the inverter is better. The harmonic rate of the port voltage has decreased from 10.43 to 1.92%. The applicability of the research method was verified. It indicats that the research method can improve inverter’s control effect and solve problems such as voltage deviation, three-phase asymmetry, harmonic pollution, etc. that are easily generated by the output terminal voltage. Simultaneously, research has provided theoretical basis and data support for the research of microgrids.

Optimal‐droop voltage‐restorer for zonal dc distribution system with simultaneous consideration of dynamic current balance and power loss reduction

AbstractA dc voltage restorer (dc‐VR) with optimal droop control is developed to reduce the power loss and solve the dynamic current imbalance simultaneously of the zonal dc distribution system integrating multi‐parallel energy storage. Firstly, the power loss model composed of line loss and converter loss is built and it is proved to be a strictly convex function with respect to droop coefficients, which indicates the power loss can be mitigated by optimizing the current distribution. Thus, an image‐based droop optimization method is proposed to search for the optimal droop coefficients. Then, the economy of voltage compensation on power loss reduction is investigated and an ESS‐combined dc‐VR is designed, including an interleaved parallel architecture and a capacitor‐integrated electric spring (C‐ES). Unified virtual inertia is proposed for interleaved parallel bridge arms to make their dynamic performance consistent. And the newly introduced C‐ES can keep the bus voltage at the rated level to reduce the system cost. Therefore, the problem of dynamic currents imbalance is addressed from the points of converter structure (dc‐VR) and control system (unified inertia), and the power loss can be reduced by voltage recovery (C‐ES) and optimizing the current reallocation which is achieved by updating sharing coefficients from the image‐based droop optimization method. Finally, the simulation cases validate the effectiveness of the proposed optimal‐droop dc‐VR on dynamic current balance and power loss reduction, and hardware in the loop experiment results prove the consistent dynamic characteristics of the dc‐VR's arms.

Analysis of different test techniques of DC circuit breaker

Abstract Amidst the escalating demand for energy and the proliferation of renewable energy sources, direct current (DC) systems have garnered increasing interest. As pivotal for the safety and reliability of DC systems, testing DC circuit breakers is a critical step to evaluate their performance and dependability. This study focuses on the breaking test method for medium and high-voltage DC circuit breakers. It compares and evaluates the current waveform, recovery voltage, and energy dissipation across various test circuit methodologies during the breaking process of DC circuit breakers and assesses the suitability of test methods across different voltage levels.

Phase sequence selection method of double-circuit transmission lines on the same tower based on a comprehensive index

Abstract The non-transposition erection of transmission lines will lead to the imbalance of electrical parameters, which will affect the protection and automatic reclosing. The best phase sequence arrangement is determined by comprehensively considering the comprehensive indexes (current imbalance, secondary current, and recovery voltage) of double transmission un-transposed lines with shared towers. PSCAD/EMTDC electromagnetic transient simulation software is applied to build a typical 750kV transmission line model for simulation analysis, and the comprehensive indexes under different phase sequence arrangements are studied. The analysis reveals that the arrangement of phase sequence exerts a significant consequence of the comprehensive index. The findings indicate that the margin and different secondary current and recovery voltage indexes, double transmission un-transposed lines with shared towers can be erected in the same direction or in different phase sequences to reduce the current imbalance.

Data-Driven Distributed Predictive Control for Voltage Regulation and Current Sharing in DC Microgrids With Communication Constraints.

The use of nonideal communication networks makes communication constraints become a topical issue in the research of dc microgrids. How to design a distributed secondary control scheme for voltage recovery and accurate current sharing in islanded dc microgrids subject to communication constraints is of interest in this article. In order to restore the bus voltage to the rated value, a nonlinear element is first introduced into the primary control layer. Then, the closed-loop system of primary control is modeled as a data-driven time-varying linear system. Based on the established model, considering communication constraints, a distributed secondary predictive control strategy is developed to achieve accurate current sharing. While actively compensating for network delays and packet losses, the proposed method renders mathematical physical models unnecessary for the traditional predictive control, and simultaneously completes the multitask in dc microgrids. Finally, several case studies are conducted on a hardware microgrid experimental platform, which not only verifies the effectiveness of the designed data-driven predictive control strategy but also tests microgrid properties such as the plug-and-play ability.

Design of Recovery Voltage Injected Method Equipment for Post-Arc Explosion Interrupt Rating Test

Design of Recovery Voltage Injected Method Equipment for Post-Arc Explosion Interrupt Rating Test

Conceptional design for a universal HVDC-HVAC vacuum-interrupter-based circuit breaker

Modern power systems high voltage transmission systems either HVDC or HVAC has mandated the presence of two types of circuit breakers (CB), HVAC-CB and HVDC-CB. That required two different production lines, higher costs and more complicated manufacturing process. A solution is proposed in this paper which is a concept design for a universal HVCB (UHVCB) that is applicable to both HVDC and HVAC system. Such a concept would allow a faster, easier production and more economical unit cost for CBs that would benefit the entire industry from manufacturers to utilities. The design of HVDC-CB was used as the foundation the proposed UHVCB such that L–C branches are used. The UHVCB was tested in both HVAC and HVDC transmission systems. The results showed the reliable performance of UHVCB in both systems. The recorded transient recovery voltage (TRV) was reduced from 750 to 430 kV when UHVCB was used instead of conventional HVCB. The testing included both technical and economic aspects. The performance of the UHVCB was tested by varying the parameters for L–C shunt branches in both systems. That included varying the value of L in range 0.3–1 mH and 10–30 µF for C. The most important conclusion from this paper that a UHVCB that is applicable in HVDC and HVAC systems is achievable and this paper is only an initial step in achieving this goal.

Quantum coupling and self-heating impacts on threshold voltages of GaN metal–insulator-semiconductor high-electron-mobility transistors

A transient heat conduction equation has been proposed to describe the cooling process of a hot two-dimensional electron gas layer in a GaN-based transistor. This equation serves as the basis for a physical analytical model that explains the impacts of hot electrons in the hot two-dimensional electron gas layer via quantum coupling on the threshold voltage of GaN-based transistors. The temperature of the two-dimensional electron gas layer decreases to ambient temperature as time increases, and the threshold voltage shifts caused by such a temperature will recover with time. The proposed model accurately reflects the observed recovery of threshold voltage over time in experiments. At the same time, it offers insight into how the gate voltage, the source-drain voltage, and the ambient temperature can shift the threshold voltage in these transistors. The simplicity and analytic nature of this proposed model not only provide a physical origin of the threshold voltage instability in GaN-based devices but also offer the possibility for improving device reliability by selecting appropriate device physical parameters.

Bio-based polyurethane triboelectric nanogenerator with superior low-temperature self-healing performance for unmanned surveillance

Damaged flexible triboelectric nanogenerators face difficulties in autonomous healing at low temperatures, limiting their application range. Impeded dynamic network reconstruction presents a challenge in developing materials for autonomous low-temperature healing. This study constructed a multi-dynamic network utilizing both strong and weak hydrogen and disulfide bonds to develop a biobased polyurethane elastomer (PBES-U, prepared from biobased monomers such as itaconic acid, sebacic acid, etc.), featuring a cross-linked network capable of cryogenic self-healing, superior toughness, and reprocessability. This elastomer extends to 1100 % of its original length, achieving 90 % self-healing efficiency at temperatures down to −10 °C due to the low glass transition temperature (Tg, −30 ℃) achieved by modulating the flexibility of chain segments. Consequently, a bio-based TENG (LS-TENG) was produced using this elastomer as a positive friction layer through a dynamic interfacial interlocking method. The results reveal that LS-TENG achieves a notable power density of 12.2 mW/m2, an output voltage reaching 160 V, and a 98 % output voltage recovery post-low-temperature self-healing. Furthermore, a non-contact LS-TENG-based monitoring system was developed with significant potential for applications in battlefield sensing, wildlife monitoring, and intelligent driving.

Security-constrained unit commitment model considering frequency and voltage stabilities with multiresource participation

The rapidly increasing proportion of renewable energy sources has led to a reduction in the relative share of synchronous units, which has resulted in a decline in the inertia of the power system and a decrease in its voltage support capacity. This has led to several issues related to the frequency and voltage stabilities of the power system. To ensure these frequency and voltage stabilities, it is necessary to maintain a number of synchronous units online in the day-ahead generation schedule. First, the dynamic frequency change process after a power system fault is discussed, and a linear expression is derived for the frequency stability constraints involving energy storage systems and wind turbines. Second, the short-circuit capacity of the bus is characterized to describe the strength of voltage support, and the minimum short-circuit capacity requirement of the bus is solved based on the transient voltage recovery problem after clearance of the short-circuit faults. The total short-circuit capacity provided by the unit to the bus is then calculated through the network reactance matrix to establish the voltage stability constraint. Subsequently, the security-constrained unit commitment model considering frequency and voltage stabilities (FVS-SCUC) is established. Finally, the effectiveness of the proposed model is demonstrated through a numerical simulation of the IEEE-39 system comprising storage and wind turbines. The model ensures the frequency and voltage securities of the system, and the renewable energy output is improved upon considering energy storage. Thus, the overall system cost was reduced by nearly 30% by considering the frequency regulation effects of the energy storage system and wind turbine as well as the voltage regulation effects of the energy storage system.

Ensembled methodology for the comtrade analysis regarding medium voltage side in wind park

This research proposes a methodology for automated COMTRADE analysis using ensembled algorithms for fault analysis in medium voltage circuits, specifically for wind park feeders. Traditional fault detection methods face significant limitations, such as CT saturation and DC offset, underscoring the need for improved approaches. The proposed methodology integrates Random Committee, XGBoost (XGB), and Light XGB algorithms, optimized through grid search, achieving an accuracy of 99.397 %. This ensemble approach significantly reduces classification errors, false positives, and false negatives compared to single algorithm methods. This research has the analysis of 3929 events for training and 829 fault events for test, it revealed a high correlation between current and fault spectra; the methodology demonstrated superior performance in fault location analysis, with terminal faults showing the most severe transient recovery voltage (TRV) peak values, while kilometer faults exhibited higher transient recovery restoration voltage growth rates. The fault location analysis was conducted by comparing simulation-derived overvoltage with standard TRV graphs, aligned with IEC 62271-100 standards. Circuit breakers exhibited higher TRV tolerance with lower fault currents. Terminal faults, particularly symmetrical three-phase faults, were identified as the most severe, typically occurring at peak TRV values. Its findings reduced classification errors, from 41 to 5 events, and decreased the false negative rate from 1.81 % to 0.24 % compared to Random Forest. Validation with virtual relays showed a reduction in RCE from 5.3 % to 0.63 %.

A Study on Analysis of Voltage Recovery Impact of Smart Inverter Based on Distribution System Characteristics

A Study on Analysis of Voltage Recovery Impact of Smart Inverter Based on Distribution System Characteristics

The consequence of ignoring load modeling on the circuit breaker selection in densely-meshed sub-transmission systems

In this paper, the selection of circuit breakers for a densely-meshed sub-transmission system with relatively short transmission lines is investigated. The results highlight the significance of modeling the load at the end of lines for accurately calculating the transient recovery voltage (TRV) following the short-circuit current interruption. According to IEEE standards, assuming load modeling at the end of the transmission lines can result in a maximum discrepancy of 20 % in the calculated TRV. Supposing that the load modeling leads to a moderating effect on the calculated TRV, the difference is considered as a safety margin, and load modeling is ignored. Nevertheless, the results presented here illustrate that this assumption strongly depends on characteristics of the studied network and the load type. In a network possessing the characteristics outlined in this paper, even a passive load as small as 15 % of the nominal capacity can significantly moderate the calculated TRV, with impacts reaching up to 38 %. Conversely, modeling an active load may result in a more severe TRV than if it were disregarded. The simulation results indicate that for networks with transmission lines longer than 70 km, neglecting to model passive loads on the transmission lines still yields sufficiently accurate calculations of TRV.