High-voltage System Research Articles

Special issue on all‐electric and hybrid‐electric flight

Special issue on all‐electric and hybrid‐electric flight

Modelling activity in support of MITICA high voltage system protections

MITICA, the full-scale prototype of ITER Heating Neutral Beam (HNBs), has challenging requirements on its power supplies. In particular its unconventional high voltage system is designed to operate at high power and voltage (up to -1 MV dc and about 54 MW), with many interfaces and high voltage insulation technologies co-existing in a single plant. Moreover, the electrical system must manage frequent breakdowns between the accelerator grids during the operation, creating electrical fast transients characterized by extremely high voltage and current peaks. In the conceptual design phase suitable design provisions were conceived to limit the energy in the grids and to limit the overvoltage on specific components in the case of grids-breakdown. The integration tests of the power supplies showed the capability of the system to generate and sustain voltage as high as 700 kV; at higher voltage the voltage withstanding capability was not confirmed as some breakdowns occurred in the plant. Although the location of the breakdowns has not been identified yet, an impact of such breakdowns was highlighted as a couple of the components of the plant suffered a damage. This paper is focused on the analyses performed for the understanding of the fault occurred on the secondary bushing of the 1 MV insulating transformer dedicated to the supply of the Ion Source and Extraction Power Supply system (ISEPS). An extensive activity of modelling and simulation has been developed for explaining the dynamic occurred. The model is based on the stray parameters of the components, which were not easy to be estimated in the design phase, but which turn out to have relevant effects in local fast transient phenomena. After reaching a full understanding of the phenomena, the models have been used to support the conceptual design of an additional protection system for the transformer, for MITICA but also in view of the ITER installation.

A New Modulation for Leakage Current Reduction of Modular Multilevel Converter

Leakage current is an important problem in non-isolated inverters, especially implemented in a medium- and high-voltage system. First, several analyses had carried out to reduce the high-frequency component of common-mode voltage (CMV) and the leakage current of a three-phase modular multilevel converter (MMC). Then, a new modulation method is proposed to keep CMV as the half of dc voltage and suppress the leakage current effectively. The peak value of leakage current can be suppressed under 5 mA, which complies with the VDE-0126-1-1 standard. Meanwhile, the parasitic capacitor voltage can be balanced automatically without the additional capacitor voltage control. Finally, the proposed scheme is verified in MATLAB/Simulink and tested on the hardware-in-loop platform. The effectiveness of the proposed scheme is verified by the experiment results.

Study on mechanical properties of the cross arm-insulator system under strong wind load

High-voltage transmission tower-line systems in coastal areas are often affected by strong winds, which leads to structural damage to the towers. Detailed analysis of the damage mechanism of towers is very useful to ensure the safety and stability of the power system. This paper examines the mechanical properties of the cross-insulator structure under horizontal wind load, and then the load-carrying capacity and deformation performance were analyzed based on ABAQUS. The results show that the structure is stable under the load, and the main structure is basically in the elastic working stage with insignificant flexural and torsional effects. On the contrary, the local stress of the combined link rod connected with the insulator is large; the bending deformation characteristics of the combined link rod are obvious under the maximum horizontal load the insulator can withstand. This result can provide a reference for cross-arms structural safety design.

Modeling of the Transient Electric Field in Multilayer Dielectric Composites Under Impulsive HV Energization

This article presents the theoretical analysis of composite electrical insulation, formed from layered dielectric materials and subjected to impulsive energization. The 1-D planar and cylindrical geometries were considered, consisting of an arbitrary number of layers with arbitrary relative permittivity and electrical conductivity. Analytical solutions have been successfully derived for the time-dependent electric field inside the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${i}$ </tex-math></inline-formula> th layer. To demonstrate the usage of the model under complex multilayer topologies where analytical solutions are nontrivial, the characteristics of a 20-layer-graded composite under microsecond and sub-microsecond impulses were analyzed and validated against a finite-element (FE) solver. Results indicate that the transient electric field response under impulsive energization is strongly dependent on the interplay between the composite relaxation time constants and the characteristic timescales associated with the applied impulse. The model is a further development for the design and coordination of functionally graded materials (FGMs) and composite insulation for high-voltage (HV) system design. This is particularly relevant under fast-rising impulsive conditions as often encountered in many pulsed power applications.

Replacement of LVDS to HVDS for Reduction in Distribution Losses, Improvement in Voltage Profiles and Economic Analysis for National Saving

Introduction: Rural electrification in India is planned with high-capacity distribution transformers which supply the isolated location loads of various categories like agricultural, household, small business, etc. This distribution system planning with non-optimal distribution transformers leads to poor voltage profiles and high power losses in the distribution network. This paper presents that a High-Voltage Distribution System (HVDS) is more suitable than a Low- Voltage Distribution System (LVDS). Methods: A model is developed to evaluate the technical losses, voltage profiles, and optimal payback period of the investments for the planned HVDS network. The replacement of LVDS with HVDS is achieved by replacing high-capacity distribution transformers with small-capacity at optimal locations. Results: The results of this study are validated on the real 11kV agricultural feeder of the Narshinghpur District of Madhya Pradesh, India. Conclusion: The results demonstrate improvement in voltage profiles, low power losses, and optimal payback period for the proposed problem. The obtained results proved that the replacement of LVDS with HVDS would be more beneficial for rural electric power distribution system planning.

An Improved Phase-Disposition Pulse Width Modulation Method for Hybrid Modular Multilevel Converter

The hybrid modular multilevel converter (MMC) consisting of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) is a promising solution for overhead lines high-voltage direct current systems (HVDC) due to the advantages of direct current short circuit fault ride-through (DC-FRT) capability. This paper proposes an improved phase-disposition pulse width modulation (PDPWM) method for the hybrid modular multilevel converter. The number of carriers can be reduced from 3N (N is the number of submodules in each arm) to 6. The theoretical harmonic analysis of the improved PDPWM method for hybrid MMC is performed by using double Fourier integral analysis. The influence of three carrier displacement angles between HBSMs and FBSMs in the upper and lower arms on harmonic characteristics is investigated. The output voltage harmonics minimization PDPWM scheme and circulating current harmonics cancellation PDPWM scheme can be achieved by selecting the optimum carrier displacement angles, respectively. The proposed method for hybrid MMC is verified by the simulation and experimental results.

Battery sizing of 48 V plug-in hybrids considering calendar and cycle degradation

Plug-in hybrid electric vehicles (PHEVs) with battery packs tailored to the driving use case can help to reduce the environmental footprint of the transportation sector. Compared to common high-voltage systems, PHEVs based on a low-voltage level show a higher fuel consumption, but in return benefit from lower component costs and allow the utilization of cheaper high-energy cells. In this paper, the battery size of a 48 V PHEV concept is optimized to minimize the operational costs while taking battery degradation into account and ensure a lifetime-robust system layout. To investigate the applicability of high-energy batteries, 31 automotive-grade cells were investigated experimentally in a calendar and cycle aging study. The results show that calendar aging has a significant contribution of 17.5 % to the overall capacity loss and should be considered during the battery design process. The cycle degradation model is integrated in a Dynamic Programming simulation environment with various real-driving speed and slope profiles, which are extracted from a measured year-round driving profile. The simulation results show, that considering the degradation in the energy management strategy reduces the capacity loss but results in higher operational costs throughout the vehicle lifetime. The extension of a mild hybrid vehicle to a PHEV can reduce the operational costs by 18.5 %. If the vehicle is not charged, the costs increase by 6 % highlighting the need for frequent charging of PHEVs.

A Low-Voltage AC, Low-Voltage DC, and High-Voltage DC Power Distribution System with Grid: Design and Analysis

Low-voltage (LV) and high-voltage (HV) DC distribution systems are being investigated as alternatives due to the growth of DC distribution energy resources (DER), DC loads such as solar and wind power systems, and energy storage sources (ESSs). Furthermore, an HV/LV DC distribution system offers various advantages, including lower conversion losses, an easier connecting strategy for DC DERs, and less complex power management techniques. As renewable energy sources are increasingly incorporated into the electrical grid, it is important to create novel, effective approaches for connecting such sources and loads. It would hence be effective to merge DC distribution with AC distribution to fulfill the energy demands of both DC and AC consumers. To this end, this study proposes a multizone design with four buses: low-voltage direct current (LVDC), high-voltage direct current (HVDC), low-voltage alternating current (LVAC), and an electrical grid. A model of this system that covers crucial elements, including power systems, DER systems, and power electronic devices, to serve as a foundation for the analysis and design of this architecture is proposed. MATLAB/Simulink is used to conduct a simulation study to verify the performance of the proposed design. In this study, a hybrid electrical grid with an LVDC, HVDC, and LVAC distribution network test is used and implemented. Additionally, a transient and steady-state characteristic analysis of the test system is performed.

A Fault-Tolerant Strategy for Three-Level Flying-Capacitor DC/DC Converter in Spacecraft Power System

With the development of space exploration, high-power and high-voltage power systems are essential for future spacecraft applications. Because of the effects of space radiation such as single event burnout (SEB), the rated voltage of power devices in converters for a spacecraft power system is limited to a level much lower than that for traditional ground applications. Thus, multi-level DC/DC converters are good choices for high-voltage applications in spacecraft. In this paper, a fault-tolerant strategy is proposed for a three-level flying capacitor DC/DC converter to increase the reliability with minimal cost. There is no extra hardware needed for the proposed strategy; the fault tolerance of the converter is only achieved by changing the software control strategy. A stage analysis of the proposed strategy is provided in detail for different fault locations and ratios between the input and output voltage. Finally, a simulation model and prototype are built to verify the effectiveness of the proposed strategy.

Fault Detection and Classification for Voltage source converter -High Voltage Systems by Using Different Swarm Optimization Algorithms-Based Neural Network

Fault Detection and Classification for Voltage source converter -High Voltage Systems by Using Different Swarm Optimization Algorithms-Based Neural Network

Stability Analysis and Control Design for Multiterminal HVDC Network With Power Flow Controller

The power flow control in high-voltage direct current (HVDC) grids can be improved by employing the interline dc power flow controller (IDCPFC). This article presents an improved control scheme using IDCPFC to balance power flow in the dc networks. In this work, a differential-mode transformer (DMT) is used in combination with a bidirectional buck converter to form a variable DMT. In comparison to the existing methods, the proposed system is scalable to higher voltages and powers, which makes it suitable for high-voltage dc transmission systems. Analysis of a small-signal model of the proposed method and design of compensator for improvement of transient behavior is performed. A simulation is performed with independent feed-forward and feedback control to show the effectiveness of the proposed method. The proposed method is also validated through a 600-W experimental prototype. The experimental results show that the current flow between lines is controlled for unbalance load conditions.

Support Vector Machine Parameters Optimization for 500 kV Long OHTL Fault Diagnosis

Faults can seriously damage high-voltage (HV) power systems, particularly if they occur on the long overhead transmission line (OHTL) that connects the nuclear power plant (NPP) to the electrical grid. Finding OHTL problems quickly and accurately is essential for the economy, safety, and dependability of the HV power systems. It is essential to pinpoint the problematic phase to avoid unneeded power outages. Thus, one of the most crucial research challenges is now how to identify, classify, and locate OHTL faults. In this study, transient current with high frequency oscillations that arise immediately after a defect at the sending end is investigated in a single-circuit, single-side fed Egyptian 500-kV HV long OHTL. Asymmetric and symmetric faults and locations are also represented in the Alternative Transients Program-Electro Magnetic Transients Program (ATP/EMTP) simulation model under varying fault resistance and inception angles. The proposed solution in this paper is an Optimized Support Vector Machine (OSVM), whose characteristics are optimized via a mutant particle swarm optimization (MPSO) method to detect 500 kV long OHTL faults. The localizer model is also built for practical applications, including power system noise contaminating fault signals. The findings prove that the suggested approach locates the fault in 0.012 seconds from the start of the event, with a 0.0098 percent average percentage error, and without being impacted by differences in fault distance, fault resistance, noise, or fault inception angle. Additionally, the optimised classifier reaches a 99.85% accuracy rate, enhancing line system dependability and advancing nuclear system development.

Мостовой резонансный источник питания электродугового двигателя малого космического аппарата

In this paper, the applied problems of designing a bridge resonant converter with a high-voltage arc ignition system in the channel of an electric arc motor is solved. The development of a bridge resonant power supply is presented, a review and analysis of power sources of arcjet thruster of various capacities is carried out. The theoretical aspects of calculating the main parameters of the source are considered. The transfer function describing the gain of the resonant circuit of the power supply is given. With the help of the transfer function, gain diagrams are constructed for various values of the Q-factor of the contour. A prototype of a power supply, a starting system and an arcjet thruster is presented. A series of experiments aimed at identifying the operability of the source is carried out. According to the experimental results, the maximum output power of the source wiz 182,4 watts, and the maximum efficiency is 87,5 %. Frequency spectra of the output current of the power supply are obtained. The current-voltage characteristics for the Ar and N2 are constructed. In the course of the study, phenomena related to the chaotic dynamics of the arc in the engine channel are discovered. Chaotic fluctuations are observed at the moment of starting the engine and disappeared after steady-state operation.

Debt crisis in the electricity market: causes and threats to the economic security of electricity companies

The article states that one of the main sector conditions for Ukraine's accession to the European Union is the launch of a full-fledged energy market, for which purpose a number of institutional, economic and regulatory reforms have been implemented since 2015. It is proved that despite the government’s conscientious efforts to make a transition to the European model of energy markets, Ukraine has failed to do so due to a large number of regulatory restrictions on wholesale prices (price caps), an unbalanced policy of supporting renewable energy industry, the absence of market prices for households and the existing mechanisms for imposing special obligations, which together have led to the formation of a chain of debts “all to all” in the electricity market. It is substantiated that the debt crisis currently observed in the energy sector of Ukraine requires urgent measures. Further ignoring it is unacceptable, as it poses significant threats to both the country’s energy security and the financial viability of electricity companies. The article considers the chain of debts of electric power enterprises formed through the Public Service Obligations (PSO) model. The causes of the debt crisis in the Ukrainian electricity market are identified, including: incorrect operation of the PSO mechanism; significant underfunding of tariffs for households, as well as tariffs for electricity transmission services via the high-voltage trunk network and power system management (dispatching); granting debtors a preference - depriving them of "punishment" for late payment of the cost of consumed services. The author analyses the proposed measures to mitigate the crisis by: compensation of debts at the expense of the State budget; attraction of loans from State and international banks; cancellation of price restrictions established by the National Commission for State Regulation of Energy and Public Utilities (NCSREPU), the so-called price caps; allocation of part of the excise tax revenues to repay the debts incurred in the electricity market; increasing the volume of clean electricity exports to the EU; introduction of a market for guarantees of origin, under which each renewable energy producer will receive guarantees, i.e. an asset that can be sold. The advantages and disadvantages of each of the proposed measures are indicated.

Current-Limiting Reactors Based Time-Domain Fault Location for High-Voltage DC Systems With Hybrid Transmission Corridors

Accurately locating the fault distance helps in the rapid restoration of the isolated line back into the system. This article proposes a novel time-domain-based algorithm to determine accurate fault location in high-voltage direct current (HVdc) systems with hybrid dc transmission corridors i.e., a combination of underground cables (UGCs) and overhead lines (OHLs). The work gives a fault location method for a two-segment and three-segment hybrid transmission corridor (HTC) and then generalizes the analysis for an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -segment HTC. The algorithm offers flexibility to locate faults ranging from the homogeneous transmission line to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -segment HTC. The algorithm uses a simplified unit resistance–inductance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$RL$ </tex-math></inline-formula> ) representation of transmission lines along with time-domain-based measurements i.e., terminal voltage, current, and voltage across current-limiting reactors (CLRs). Power systems computer-aided design/electromagnetic transients including dc (PSCAD/EMTDC)-based simulations are used to validate robust performance against variation of key implementation parameters like type of faults, fault resistance, fault location, sampling frequency, and white Gaussian noise (WGN) in measurement. Further, the fault location calculation is analyzed under parameter variation i.e., change in the true value of unit resistance and unit inductance of line or cable and the true value of dc link capacitance.

МОДЕЛИРОВАНИЕ ЭЛЕКТРОМАГНИТНЫХ ПРОЦЕССОВ В ФИЛЬТРОКОМПЕНСИРУЮЩЕМ УСТРОЙСТВЕ В СОСТАВЕ СИСТЕМЫ ЗАРЯДА ЕМКОСТНОГО НАКОПИТЕЛЯ

The relevance Secondary power supplies, frequency converters, and inverters are actively used in modern rapidly developing power engineering. The trend towards a decrease in the weight and size of devices and an increase in their power explains the need to use pulse modes of electrical energy converters. The oscillatory circuits of resonant inverters contain elements such as an inductor and a capacitor, i.e. electromagnetic elements, as a rule, constituting up to 85–90 % of the mass and dimensions of secondary power supplies. The main technical means of reducing the mass and dimensions of electromagnetic elements are increasing the conversion frequency and functional integration. Resonant modes of operation of inverters during switching can reduce interference and losses. Aim of research This article discusses the development of an efficient capacitive storage charging system and simulation of electromagnetic processes in a filtercompensating device as part of an efficient capacitive storage charging system. The main task is to develop an efficient capacitive storage charging system. Research methods Research methods. In this study, the following methods were used: the study of scientific literature and computer simulation in the Matlab environment. Results The authors have developed a computer model in MatLab of a capacitive storage charging system based on a half-bridge circuit of an inductivecapacitive converter. A multifunctional integrated electromagnetic component (MIEC) is used as a pre-absorber. Investigations of voltage levels at various points of the four-terminal network have been carried out. The voltage on the plates and capacitance MIEC was determined. The voltage in the diagonals of the inverter was measured to find the maximum voltage. Because of computer modeling and experimental research, graphs of voltages on the elements of the half-bridge circuit of the capacitive storage charging system were obtained. The developed computer model will allow the investigation of various modes of operation of a secondary power source based on the proposed component in high-voltage charging systems for energy storage devices. The developed model allows you to reduce the financial costs of experimental research. Also, this model allows you to explore more complex systems based on MIEC, which have different properties and indicators.

Comprehensive Review of Power Electronic Converters in Electric Vehicle Applications

Emerging electric vehicle (EV) technology requires high-voltage energy storage systems, efficient electric motors, electrified power trains, and power converters. If we consider forecasts for EV demand and driving applications, this article comprehensively reviewed power converter topologies, control schemes, output power, reliability, losses, switching frequency, operations, charging systems, advantages, and disadvantages. This article is intended to help engineers and researchers forecast typical recharging/discharging durations, the lifetime of energy storage with the help of control systems and machine learning, and the performance probability of using AlGaN/GaN heterojunction-based high-electron-mobility transistors (HEMTs) in EV systems. The analysis of this extensive review paper suggests that the Vienna rectifier provides significant performance among all AC–DC rectifier converters. Moreover, the multi-device interleaved DC–DC boost converter is best suited for the DC–DC conversion stage. Among DC–AC converters, the third harmonic injected seven-level inverter is found to be one of the best in EV driving. Furthermore, the utilization of multi-level inverters can terminate the requirement of the intermediate DC–DC converter. In addition, the current status, opportunities, challenges, and applications of wireless power transfer in hybrid and all-electric vehicles were also discussed in this paper. Moreover, the adoption of wide bandgap semiconductors was considered. Because of their higher power density, breakdown voltage, and switching frequency characteristics, a light yet efficient power converter design can be achieved for EVs. Finally, the article’s intent was to provide a reference for engineers and researchers in the automobile industry for forecasting calculations.

Partial Discharge Detection and Defect Location Method in GIS Cable Terminal

The complex structure of gas-insulated switchgear (GIS) cable terminals leads to serious electric field concentration, which is a frequent fault position of a high-voltage cable system. At present, due to the differences in the frequency bands of sensors, various partial discharge detection technologies have certain differences in their scope of application and anti-interference performance, resulting in a low defect detection rate in GIS cable terminals. In this paper, a comprehensive diagnosis scheme is proposed, which integrates transient earth voltage (TEV), ultra-high frequency (UHF), high frequency (HF), and ultrasonic methods. Two abnormal discharge defects of GIS terminals in two 220 kV substations in Tianjin were tracked and monitored, and the joint diagnosis was carried out using the proposed scheme; the type of discharge defect and the phase sequence of the defect were determined, and the UHV was employed to precisely locate and analyze the defect source. Finally, through the disassembly analysis and electric field simulation of the GIS cable terminal, the accuracy and effectiveness of the discharge detection and location method were verified, providing a typical detection demonstration for the defect diagnosis of a GIS cable terminal.

Robust Wavelet Transform Neural-Network-Based Short-Term Load Forecasting for Power Distribution Networks

A precise short-term load-forecasting model is vital for energy companies to create accurate supply plans to reduce carbon dioxide production, causing our lives to be more environmentally friendly. A variety of high-voltage-level load-forecasting approaches, such as linear regression (LR), autoregressive integrated moving average (ARIMA), and artificial neural network (ANN) models, have been proposed in recent decades. However, unlike load forecasting in high-voltage transmission systems, load forecasting at the distribution network level is more challenging since distribution networks are more variable and nonstationary. Moreover, existing load-forecasting models only consider the features of the time domain, while the demand load is highly correlated to the frequency-domain information. This paper introduces a robust wavelet transform neural network load-forecasting model. The proposed model utilizes both time- and frequency-domain information to improve the model’s prediction accuracy. Firstly, three wavelet transform methods, variational mode decomposition (VMD), empirical mode decomposition (EMD), and empirical wavelet transformation (EWT), were introduced to transform the time-domain demand load data into frequency-domain data. Then, neural network models were trained to predict all components simultaneously. Finally, all the predicted data were aggregated to form the predicted demand load. Three cases were simulated in the case study stage to evaluate the prediction accuracy under different layer numbers, weather information, and neural network types. The simulation results showed that the proposed robust time–frequency load-forecasting model performed better than the traditional time-domain forecasting models based on the comparison of the performance metrics, including the mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean squared error (RMSE).