Transient Voltage Research Articles

Real-time monitoring method for power system voltage based on optical voltage sensors

Abstract A real-time monitoring method for power system voltage based on optical voltage sensors is proposed to obtain transient voltage signals and achieve real-time tracking of instantaneous changes in electrical parameters of the power system accurately and effectively. Analyzing the topology principle of power system transformers clarifies the installation location of optical voltage sensors. By combining the measurement principle of optical voltage sensors, the electrical, optical modulation, and optical-electrical conversion of voltage signals are achieved, and the voltage signal of the power system is output. Using the short-time Fourier transform method to perform temporal processing on the output signal and obtaining a voltage signal sliding window based on wavelet packet decomposition, we set the normal range threshold of the voltage signal in the sliding window, combined with information entropy theory to extract key features of the voltage signal and achieve real-time monitoring of the power system voltage. The experimental results show that the proposed method can effectively obtain transient voltage signals of the power system, with an average detection accuracy of 92.61%, and the output voltage can be adjusted promptly to reflect the instantaneous changes in the power system voltage.

A Rapidly Reconfigurable DC Battery for Increasing Flexibility and Efficiency of Electric Vehicle Drive Trains

Traditional electric vehicle (EV) battery drive trains comprise hard-wired batteries forming a fixed high-voltage DC link, and a main inverter. This paper proposes a novel topology to break hard-wired batteries into smaller subunits interfaced by low-voltage field effect transistors (FET). The new DC link, named <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">reconfigurable DC battery</i> , can offload a great portion of the switching duty from the main inverter. Several benefits follow: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1)</i> The proposed topology reduces the total loss despite the added components. The net loss is reduced because the reconfigurable DC battery can generate an optimal high-frequency voltage waveform to spare up to 2/3 of the switching actions of the main inverter—i.e., delegating the modulation duty from the main inverter to the reconfigurable DC battery. The added semiconductor loss is negligible compared to that of the main inverter, thanks to small voltage steps of multilevel conversion and the latest low-voltage transistors. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2)</i> The main inverter’s output waveform has less distortion, e.g., down to 50% compared to conventional space-vector modulation. This distortion reduction is a consequence of large segments of the overall output voltage (particularly the apex) being entirely formed by the reconfigurable DC battery with multilevel precision. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3)</i> The multilevel output qualities substantially reduce the voltage transients d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> of the inverter output, which is known to reduce insulation and bearing stress in motors. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4)</i> The topology eliminates the vulnerability of large hard-wired battery packs to the weakest cells. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5)</i> The constant presence of the high voltage in conventional hard-wired batteries and the associated issues, e.g., during manufacturing, maintenance, and crashs are avoided because of normally-off FETs. We demonstrate the proposed motor drive on a 3-kW setup with eight battery modules.

Small Signal Modelling and Stability Analysis of a Grid Connected Inverted Based Microgrid

Objectives: This work focuses on the stability analysis of grid connected microgrids. It considers the impact of load disturbance and grid voltage change on voltage and current levels, as well as reactive and active power responses, is analysed. Methods: A comprehensive small-signal state-space model is developed for an inverter-based microgrid, incorporating submodules of inverters, phase-locked loops (PLLs), and LCL filters. The model is linearized around a stable operating point, and eigenvalue analysis is performed and validated through MATLAB/Simulink simulations. A current controller operating in the d-q frame is proposed to enhance stable power conversion and maintain microgrid stability. Findings: The proposed model and control strategy demonstrate the microgrid's ability to maintain transient voltage stability under severe dynamic conditions. During a 10% grid voltage fluctuation, the microgrid exhibits stable active and reactive power responses, with currents and voltages at the point of common coupling stabilizing within 0.2 seconds. Furthermore, when a 25 kVA active load is disconnected, the microgrid effectively manages the power transition, maintaining stable operation with minimal deviations in key parameters. The current controller simplifies AC current control, integrating active power management from solar input, DC-link voltage stability, and reactive power control. Novelty: The novelty lies in the comprehensive analysis of transient voltage stability in grid-connected microgrids under grid voltage fluctuations and load disturbances, areas that have received limited attention in previous research. By developing a detailed small-signal state-space model incorporating PLL and LCL filter dynamics and proposing a robust control strategy with the current controller, this study offers new insights into enhancing the resilience and reliability of grid-connected microgrids during transient events. Keywords: Microgrid, Small Signal Stability, Voltage Source Inverter, State Space model, Eigen Values

A Novel Direct Current Circuit Breaker with a Gradually Increasing Counter-Current

A reliable and cost-effective mechanical direct current circuit breaker (DCCB) is a promising solution for DC interruption. However, the typical mechanical DCCB has difficulty in interrupting a rated current, because the high oscillating current superimposed on the rated current generates a steep current slope at current zero-crossing (CZC) points, which makes it difficult for the vacuum interrupter to extinguish the arc. The objective of this paper is to present a novel DCCB topology with a gradually increasing counter-current. It utilizes a full-controlled converter, a semi-controlled full bridge, and an LC oscillation branch to generate a gradually increasing counter-current, which is superimposed on any fault current and generates a smooth current slope at CZC points. The proposed DCCB topology is modeled with PSCAD, and the current slope and the initial transient interruption voltage (ITIV) at CZC are analyzed and compared with the typical mechanical DCCB. The results indicate that the current slope at CZC decreases by 57–84% in full-range current interruptions, and the ITIV can be reduced by the same extent. Additionally, the performance of the proposed DCCB is evaluated in a four-terminal HVDC system. A cost and performance comparison is conducted among the main topologies. The obtained results show that the proposed DCCB is a reliable solution for the multi-terminal HVDC system.

A green approach to synthesis of Ag-doped CeO2 nanorods embedded reduced graphene oxide nanocomposite for excellent photocatalytic and antimicrobial activity

In this paper, the Ag-doped cerium oxide nanorods embedded reduced graphene oxide (Ag@CeO2/rGO) nanocomposite was synthesized via Punica Granatum peel extract for for photocatalytic degradation of methylene blue (MB) and 4-nitrophenol (4-NP). The microstructural results confirmed the successful decoration of Ag-doped CeO2 nanorods on rGO matrix. The photocatalytic properties, including photocatalytic degradation, charge transfer kinetics and photocurrent generation, are systematically investigated using electrochemical impedance spectroscopy (EIS), photocurrent transient response (PCTR) and open circuit voltage decay (OCVD). The results of photocatalytic dye degradation measurements indicated that Ag@CeO2/rGO nanocomposite is more effective than pristine CeO2 to degrade the MB dye, and the degradation rate reached 100 % in 60 min. The decomposition of MB with Ag@CeO2/rGO nanostructure followed first-order reaction kinetics with a reaction rate constant (Ka) of 0.0198 min−1. The EIS and OCVD measurements revealed that the Ag doping and incorporation of rGO could suppress the recombination probability in CeO2 by the separation of photo-generated electron–hole pairs, which leads to the enhanced photocurrent generation and photocatalytic activity. The photocurrent density of Ag@CeO2/rGO, CeO2/rGO and pristine CeO2 are 215, 167.4 and 98.8 mAcm−2, respectively.

Transient overvoltage suppression of LCC‐HVDC sending‐end system based on DC current control optimisation

AbstractThe receiving‐end system AC fault of the line‐commutated‐converter‐based high voltage direct current (LCC‐HVDC) will lead to commutation failure of the inverter side. During the fault and its recovery, AC transient low voltage and transient overvoltage (TOV) will occur in the sending‐end system. The TOV has the risk of triggering the disorderly off‐grid of the nearby renewable power generations. Besides, in a serious situation, it will threaten the power system to maintain a secure and steady operation. Therefore, the authors analyse the mechanism involved in the AC transient voltage during the AC fault and the recovery period first. It reveals that the key factor causing the TOV of the sending‐end system is the setting of the DC current reference value. Then, a DC current reference value limit method based on the AC TOV sampling value is proposed, which is used to accelerate DC current recovery and suppress the TOV of the sending‐end system. Finally, the effectiveness of the designed control method has been confirmed through electromagnetic transient simulations using the CIGRE HVDC benchmark model and a ±800 kV HVDC transmission system model situated in Northwest China.

An Improved Suppression Method of AC Transient Overvoltage for Line Commuted Converter Based High Voltage Direct Current Considering AC-DC System Coupling

Commutation failures in line commuted converter-based high voltage direct current (LCC-HVDC) transmission systems leads to an increase in the converter bus voltage of the rectifier station, thus resulting in AC transient overvoltage in the sending-end grid. The transient overvoltage could lead to the disconnection of renewable energy generation and threaten the stable operation of the sending-end grid. However, the influences of the coupling between AC and DC systems caused by the interaction between the active and reactive power of the sending-end grid, the AC bus voltage of the rectifier station, and the DC current are ignored. The AC transient overvoltage cannot be accurately suppressed. Therefore, in this study, the transient voltage characteristics of the rectifier station under a commutation failure of the inverter station are analyzed. The influence of LCC-HVDC control on the AC bus voltage of a rectifier station through the active and reactive power of the rectifier station is analyzed. A dynamic model of the AC bus voltage of a rectifier station under an AC-DC system coupling is established. The calculation method of the command value of the DC current of the rectifier station is proposed by a predictive control model, and an improved suppression method for AC transient overvoltage is proposed. The case studies show that the accuracy and effectiveness of the suppression of AC transient overvoltage are improved by considering the coupling between AC and DC systems.

Regional Evaluation Study of VFTO Interference to Secondary Side Cables Based on Cloud Model and MARCOS.

With the advent of the data era, most power secondary side equipment tends to be digitized. The power system needs more accurate numerical results to further improve its operating efficiency. Therefore, it is important to study the electromagnetic interferences of very fast transient overvoltage (VFTO) generated by gas-insulated switchgear (GIS). To protect the secondary side cable from interferences, the secondary side cable is wrapped with an outer shield and the shield is grounded. When the interference of VFTO comes, it will couple the interference current and interference voltage on the shield of the cable. By grounding, the interference is greatly discharged. However, due to the grounding resistance, there will be a potential difference between the grounding points at the two ends of the shield of the cable. This causes a corresponding interference current to flow through the shield, which will affect the transmission of signals inside the cable. In the actual substation, the resistivity of the soil, the ambient temperature and humidity of the area, and so on will have impacts on the grounding resistance. In addition, the irregularity of the cable arrangement and the time of the use of the cable will have impacts on the signal transmission of the cable. Based on the abovementioned issues, this article proposed a comprehensive assessment method based on the combination of the cloud model and measurement of alternatives and ranking according to compromise solution (MARCOS). The method brings the cloud model into MARCOS by the algorithm of the contribution of the cloud droplets. It overcomes the difficulty of cloud model quantification. By comparing the results of the proposed method with the actual conditions at the substation and the results of the common MARCOS assessment method, the validity of the method is verified, and a reference scheme is provided for substation optimization.

Transient Voltage Propagation in Bifilar Coils of a 380 kV Resistive Type SFCL

Transient Voltage Propagation in Bifilar Coils of a 380 kV Resistive Type SFCL

Simulation study of electromagnetic protection of ignition chip

The purpose of this paper is to study the adaptability and enhancement methods of ignition chips in complex electromagnetic environments. In this paper, combined with simulation and calculation technology, we first establish the electromagnetic–electrical–thermal coupling simulation model of ignition chips and analyze the influence of two electromagnetic environments, continuous electromagnetic wave and nuclear electromagnetic pulse, on the electrical–thermal coupling in the bridge area of the ignition chip. The results show that a continuous electromagnetic wave field strength of 1200 V/m, irradiated for 5 s, a nuclear electromagnetic pulse with a rise time of 5 ns, a half-height width of 24 ns, and a leg wire length of 350 mm will cause the ignition chip to fire accidently. In order to suppress its accidental firing, the electromagnetic protection is enhanced by using parallel Transient Voltage Suppressor (TVS) diodes. It has been shown that parallel TVS diodes provide good protection against both continuous electromagnetic waves and nuclear electromagnetic pulses. In particular, the peak induced current decreases by more than 64.7% during the action of continuous electromagnetic waves, and the maximum temperature in the bridge area decreases by 54.34% during the action of nuclear electromagnetic pulses.

Dynamic Improvement of a UPQC System Operating Under Grid Voltage Sag/Swell Disturbances

This paper proposes feed-forward control loops that accelerate the dynamic responses of both the dc-bus voltage and the compensated grid/input currents of a three-phase unified power quality conditioner (UPQC) under the occurrence of voltage sags/swells. The strategy adopted in this paper to control the UPQC is implemented by controlling the input currents and the output voltages for being in phase with their respective input voltages (grid voltages). Since the input currents and voltages are in phase, the UPQC series converter will furnish active power to the system during voltage sags. Thus, to maintain the system power balance, this active power is absorbed by the UPQC parallel converter. In contrast, under a voltage swell event, the series converter absorbs active power and furnishes it to the load through the parallel converter. Therefore, in both mentioned power quality events, the amplitudes of the UPQC input currents must be controlled appropriately to regulate the dc-bus voltage, prevent sudden dc-bus voltage transients, and perform the system power balance as fast as possible. Simulation and experimental results are achieved to present the effectiveness of the proposed feed-forward control loops.

Seamless Switching Control Strategy for a Power Conversion System in a Microgrid Based on Extended State Observer and Super-Twisting Algorithm

Microgrids can operate stably in both islanded and grid-connected modes, and the transition between these modes enhances system reliability and flexibility, enabling microgrids to adapt to diverse operational requirements and environmental conditions. The switching process, however, may introduce transient voltage and frequency fluctuations, causing voltage and current shocks to the grid and potentially damaging devices and systems connected to the microgrid. To address this issue, this study introduces a novel approach based on the Extended State Observer (ESO) and the Super-Twisting Algorithm (STA). Power conversion systems use Virtual Synchronous Generator (VSG) control and Power-Quality (PQ) control when they are connected to the grid or when the microgrid is not connected to the grid. VSG and PQ share a current loop. Transitioning the reference current generated by the outer loop achieves the switching of control strategies. A real-time observer is designed to estimate and compensate for current fluctuations, disturbances, and variations in id, iq, and system parameters during the switching process to facilitate a smooth transition of control strategies. Furthermore, to enhance the dynamic response and robustness of the system, the Proportional–Integral (PI) controller in the ESO is replaced with a novel super-twisting sliding mode controller based on a boundary layer. The Lyapunov stability principle is applied to ensure asymptotic stability under disturbances. The proposed control strategy is validated through simulation using a seamless switching model of the power conversion system developed on the Matlab/Simulink (R2021b) platform. Simulation results demonstrate that the optimized control strategy enables smooth microgrid transitions, thereby improving the overall reliability of grid operations.

Boundary Protection Based on S-Transform Considering Fault Factors

Boundary protection is a protection that takes advantage of the characteristic that signals will be attenuated when passing through the “line boundary”. The location of the traps and current transformers in the structure of extra-high voltage (EHV) transmission lines makes it difficult to apply current-based travelling wave protection in engineering practice. If the protection is put into use, it is necessary to carry out a large number of engineering modifications to the existing transmission lines, which greatly increases the economic cost. And after simulation, the protection will be misjudged under weak fault conditions, and it has low reliability. After analyzing the influence of fault factors, a boundary protection method using high-frequency voltage component energy is proposed. The fault signal is processed by S-transform, and the transient voltage energy is normalized with the initial fault phase and transition resistance. The reduced characteristic quantity is used to construct a criterion to judge the fault condition of the protection line. This protection eliminates the influence of fault factors on transient protection. The ATP-Draw 6.0 simulation results based on the proposed protection scheme show that the protection scheme can distinguish internal and external faults, and can work normally under weak faults with high reliability.

Rapid optical switching of latched electrical resistance in a high-T c superconducting tape

We report microsecond timescale switching between the superconducting and normal states of commercially manufactured high-Tc superconducting wires using optical radiation to heat the conductor above Tc. The achieved voltages and switching times have significant implications for a new class of thermal switches. The report contains experimental data for photo-induced microsecond scale voltage transients as well as numerical analysis of heat propagation through the material in response to optical radiation. The microbridges are etched into commercially manufactured coated conductors and submerged in liquid nitrogen. By varying the magnitude of the transport current, two different optical responses are identified. At low transport currents, short-lived voltage transients occur, transitioning to persistent latching once the current is increased above a threshold value. The microbridge, therefore, behaves as a fast opening and closing switch when carrying low currents or an optically latched thyristor at high currents. This is understood to occur due to critical current suppression as a result of heating from the optical pulse. Optically induced heating reduces the superconducting volume fraction, and Joule heating due to the transport current interaction with the high temperature superconducting occurs, which either causes short-lived or stable self-heating normal regions dependent on the magnitude of the transport current. This study is concluded with an estimate of the energy necessary to drive the microbridge into the resistive state. The observed behavior can potentially be utilized as a switching element in superconducting transformer rectifiers where high frequency switch operation is required.

Positive Rail Voltage Rise Behavior and Inhibition Analysis of Regenerative Braking of Medium–Low-Speed Maglev Train

When a medium–low-speed (MLS) maglev train is braking, part of its regenerative braking (RB) power consumption may cause a significant rise in the positive rail (PR) voltage. For RB energy re-utilization, an RB energy feedback system (RBEFS) is a promising application, but there is still no specific research in the field of MLS maglev trains. From this perspective, this article focuses on identifying the PR voltage rise behavior and investigating the application of an RBEFS on the over-voltage inhibition. Some development trends of the MLS maglev train, including the DC 3 kV traction grid system and the speed being raised to 160~200 km/h, are also considered in the analyzed scenarios. At first, a modeling scheme of a detailed vehicle–grid electrical power model with the RBEFS is established. On this basis, the PR voltage rise characteristics are analyzed with consideration of three pivotal influencing factors: RB power, PR impedance and supply voltage level. Subsequently, to stabilize the PR voltage fluctuations, the influence rules of the RBEFS on the voltage rise and the mutual transient voltage influences under the operating status switching for multiple vehicles running on the same power supply section are analyzed.

Hybrid Power System Design and Dynamic Modeling for Enhanced Reliability in Remote Natural Gas Pipeline Control Stations

The most rapid and efficient method to transport natural gas from its source to its destination is through a pipeline network. The optimal functioning of control stations for natural gas pipelines depends on the use of electrical devices, including data loggers, communication devices, control systems, surveillance equipment, and more. Ensuring a reliable and consistent power supply proves to be challenging due to the remote locations of these control stations. This research article presents a case study detailing the design and dynamic modeling of a hybrid power system (HPS) to address the specific energy needs of a particular natural gas pipeline control station. The HOMER Pro 3.17.1 software is used to design an optimal HPS for the specified location. The designed system combines a photovoltaic (PV) system with natural gas generators as a backup to ensure a reliable and consistent power supply for the control station. Furthermore, it provides significant cost savings, reducing the cost of energy (COE) by USD 0.148 and the annual operating costs by USD 87,321, all while integrating a renewable energy fraction of 79.2%. Dynamic modeling of the designed system is performed in MATLAB/Simulink R2022a to analyze the system’s response, including its power quality, harmonics, voltage transients, load impact, etc. The experimental results are validated using hardware in the loop (HIL) and OPAL-RT Technologies’ real-time OP5707XG simulator.

Diagnosis of Li-ion battery degradation based on resistive and diffusion-related transient voltage changes at early stage of discharge

Lithium-ion batteries degradation can be classified into capacity reduction and increase of the internal resistance. Accurate estimation of the degradation is important to determine the economic value and the remaining useful life of the battery. This paper proposes a method which analyzes the transient voltage response at the early stage of discharge, starting from the fully charged state. An equivalent circuit composed by a series resistance and a Warburg element is adopted to fit the transient voltage. The Warburg element is modeled as a transmission line composed by a ladder of resistances and capacitances. The method is validated with data obtained before and after aging cycles performed at 1.4 C charge and 2.0 C discharge rates, at 25 °C, 10 °C and −5 °C. The loss of cyclable lithium is deemed to be the main reason behind the battery degradation at all the tested temperatures. The dependency of the Warburg parameter to the remaining cell capacity is the same regardless of the aging temperature, suggesting that estimation of the Warburg parameter provides information about the state of health of the cell. On the other hand, the relationship between the capacity reduction and the increase of resistance has a temperature-dependent slope with low increase at lower temperatures where lithium plating is likely to occur. Accordingly, a relatively low resistance increase is deemed to be the sign of lithium plating.

Revealing the critical role of low voltage excursions in enhancing PEM fuel cell catalyst degradation by automotive hydrogen/air potential cycling experiments

The durability of Polymer Electrolyte Membrane Fuel Cells under dynamic operation still needs to be improved. To understand the automotive voltage cycling-induced catalyst degradation, the loss of the electrochemically active surface area (ECSA) is investigated through an experimental campaign on Membrane Electrode Assemblies. Ad-hoc hydrogen/air accelerated protocols were designed to evaluate the voltage profile impact in a range relevant for both automotive and heavy duty transport application (<0.90 V). Besides the well-known aging dependence on the upper potential limit, this work evidences the critical role of the short-stops, characterized by low voltage transients. Effort was spent in studying this procedure parameters (voltage level, duration, scan rate, humidification). The accelerated ECSA loss is due to Pt nanoparticles coarsening as proved by transmission electron microscopy and is suspected dominated by Pt cathodic dissolution, incentivized during excursions towards very low potentials (<0.4 V). These findings help the development of system mitigation strategies.

Safety hysteresis comparator design for transient overvoltage detection

This research introduces a safety hysteresis comparator that detects transient overvoltage in the track circuit relay interlocking of railway signaling system. This overvoltage is caused by voltage faults transmitted through the electric conductor on the track feed unit to the receiver equipped with the track relay, which acts as the occupied track circuit controller. The circuit was designed using safety system design principles and concepts. Findings illustrated that the transient overvoltage detection of the safety hysteresis comparator in the track circuit activated when the input voltage (Vin) was higher than the high hysteresis signal level (Vhyst_H). When Vin was less than low hysteresis signal level (VVhyst_L), the output voltage (Vo) state was low. Otherwise, it was high. The hysteresis voltage was 4.4 V. The installation of the transient overvoltage detector in the track circuit was to monitor the transient overvoltage fault in the track circuit and to confirm that the hysteresis comparator was in the safety failure mode, which was the safety function for the track circuit to be compliant with the IEC 61800-5-2 standard to ensure the system stability and reliability. It would maximize the performance of the controlling function and commanding of train arrangement of State Railway of Thailand (SRT).

An on-chip soft-start pseudo-current hysteresis-controlled buck converter for automotive applications

This paper introduces a novel direct current to direct current (DC-DC) buck converter that uses a pseudo-current hysteresis controller and an on-chip soft start circuit for improved transient performance in automotive applications. The proposed converter, implemented with Taiwan semiconductor manufacturing company (TSMC) 0.18 µm complementary metal oxide semiconductor (CMOS) one-poly-six-metal (1P6M) technology, includes a rail-to-rail current detection circuit and an on-chip soft start circuit to handle transient responses and improve efficiency. Transient response analysis shows fast settling times of 28 µs for both load current changes from 100 mA to 1 A and reversals with consistent transient voltages of approximately 190 mV and peak power efficiency of 99.32% at 5 V output voltage and 100 mA load current. Additionally, the converter maintains a constant output voltage of approximately 5 V across the entire load current range with an average accuracy of 90.41%. A comparative analysis with previous work shows superior performance in terms of figure of merit (FOM). Overall, the proposed pseudo-current hysteresis controlled buck converter exhibits remarkable transient response, load regulation and power efficiency, positioning it as a promising solution for demanding applications, particularly in automotive systems where precise voltage regulation is crucial.