With the increasing emphasis on green and low-carbon initiatives, electric aircraft have become a focal point in the aviation industry. To investigate the air discharge mechanisms of onboard equipment under high-frequency voltage, this study analyzes the air discharge phenomena in a needle-plate gap under pulsed electric fields in high-altitude environments. The research considers factors such as temperature and air pressure at different altitudes, pulsed electric field parameters, and humidity. A simulation model of needle-plate electrode streamer discharge was constructed, and an experimental platform was developed for qualitative analysis. The results indicate that the streamer discharge characteristics obtained from simulations and experiments are highly consistent under variations in altitude, pulsed electric field parameters, and humidity. When the reduced field strength remains constant, the breakdown voltage values at different altitudes were quantitatively calculated. In addition, the effects of altitude, pulsed electric field parameters, and humidity on streamer discharge characteristics were studied. Furthermore, the study explains the underlying reasons for variations in electron density, electric field intensity distribution, and streamer development speed under different conditions.
The rise and fall of the internal temperature of power transformer will cause the moisture to change its distribution and aggregation position, and the local high moisture content will seriously affect the electrical strength of oil-paper insulation. Therefore, it is necessary to study the adsorption and desorption of moisture in cellulose insulation at different temperatures. In this paper, three oil-cellulose mixed systems (OCS) of 105 atoms with different moisture contents were established by molecular dynamics method, and temperature rise and temperature drop simulations were conducted respectively. The changes of the water molecule number (NW) in the interface domain and oil domain were obtained. By analyzing the solvent accessible surface area (SASA) and the microscopic scanning electron microscope (SEM) images of cellulose insulation, the effect of temperature changes and the deterioration of cellulose molecules on the moisture adsorption and desorption in cellulose insulation were studied. The results show that after the high-temperature system is reversely cooled, water molecules in the oil domain will migrate rapidly to the cellulose domain, while the irreversible deterioration of cellulose after high temperature leads to the weakening of its adsorption capacity. As a result, a large amount of water is retained at the interface. For the simulation of temperature rise, the higher the temperature is, the more water molecules accumulate in the oil domain and interface domain, and the stronger the desorption effect of cellulose on moisture. Notably, NW in the interface domain is not a simple increment trend, but an oscillatory increase and decrease trend that decreases first and then increases. The higher the temperature is, the more obvious the trend is. The research results have important theoretical value for the real-time monitoring of moisture in oil-immersed power equipment and the evaluation of its insulation performance
Abstract Due to the limitations imposed by urban power grid outages for maintenance, on‐line harmonic current detection technology for distribution network cables is expected to become an effective supplement to traditional offline diagnostic methods, enhancing the real‐time diagnosis of distribution network cable insulation conditions. This study established a 10 kV distribution network cable test platform and prepared typical defective cables subjected to moisture and long‐term thermal aging. Using COMSOL finite element electromagnetic simulation, the magnetic flux evolution laws of the cable insulation under typical defects were obtained. Experimental tests provided the harmonic current characteristics and statistical features of cables with typical defects. Based on these data, a method for analysing the degradation degree of distribution network cables was constructed using least absolute shrinkage and selection operator (LASSO) regression analysis. Furthermore, a defect‐type identification method based on cluster analysis was proposed. Results indicate that the odd harmonics and the 4th harmonic of the distribution network cable's harmonic current are closely related to the cable's degradation state. A model integrating principal component analysis (PCA) data dimensionality reduction and expectation‐maximization clustering analysis achieved a recognition accuracy of up to 75.64% in distinguishing between moisture‐affected and normal cable states. The proposed on‐line detection and evaluation methods can effectively identify high‐risk cables with latent defects.
An interleaved high step-up boost-zeta converter with resonant coupled inductors voltage multiplier cell is proposed in this article. The proposed converter achieves very high voltage gain by integrating the boost converter and the zeta converter and using coupled inductor voltage multiplier technique. Meanwhile, low input current ripple and continuous output current are realized, which is beneficial for photovoltaic, fuel cell, and dc-bus. Moreover, the zero-voltage switching (ZVS) and low voltage stress of the switches are achieved by utilizing the active clamp circuits. With the resonance between the leakage inductance and the resonant capacitor in the resonant coupled inductor multiplier cell, the zero-current switching (ZCS) of the diodes are achieved, leading to low reverse recovery losses. In addition, the main switches of the proposed converter can be operated in the full duty cycle range, which achieves a wide range of step-up regulation. The operation principles and steady-state performance of the proposed converter are analyzed in detail. A 400 W prototype with 30-40 V input, 400 V output is built to verify the theoretical analysis.
Gallium nitride high-electron-mobility transistor (GaN HEMT) power devices are favored in various scenarios due to their high-power density and efficiency. However, with the significant increase in the heat flux density, the junction temperature of GaN HEMT has become a crucial factor in device reliability. Since the junction temperature monitoring technology for GaN HEMT based on temperature-sensitive electrical parameters (TSEPs) is still in the exploratory stage, the TSEPs' characteristics of GaN HEMT have not been definitively established. In this paper, for the common steady-state TSEPs of GaN HEMT, the variation rules of the saturation voltage with low current injection, threshold voltage, and body-like diode voltage drop with temperature are investigated. The influences on the three TSEPs' characteristics are considered, and their stability is discussed. Through experimental comparison, it is found that the saturation voltage with low current injection retains favorable temperature-sensitive characteristics, which has potential application value in junction temperature measurement. However, the threshold voltage as a TSEP for certain GaN HEMT is not ideal in terms of linearity and stability.
As the core of conventional power electronics, the reliability problem of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) severely restricts the safe operation of the equipment. Accurate prediction of the remaining useful life (RUL) of MOSFETs is the key to achieve prognostic and health management (PHM) and condition-based maintenance (CBM). In this paper, long short-term memory (LSTM) networks are combined with adaptive moment estimation algorithm, Dropout techniques and Bayesian optimization methods to improve prediction accuracy and generalization by optimizing model parameters with continuously updated probability distributions. The results show that compared with exponential fitting and traditional LSTM methods, the method has the advantages of small prediction error, high prediction accuracy and good prediction stability, which is beneficial to practical engineering applications.
The double closed-loop control of single-phase PWM rectifier can achieve high power factor and stable output DC voltage, which has been widely used in industry. In the stage of designing controller parameters, the traditional approach based on small signal model cannot quantitatively evaluate and optimize the effect of control, resulting in deviating of design parameters from the actual used. Accordingly, this paper proposes a multi-objective design method that depends on discrete time domain model to realize quantitative design of controller parameters. Firstly, the design space is derived from the traditional small signal model, and it is positively mapped to the time domain dynamic and steady-state performance space of the controller by PLECS to evaluate the controller parameters quantitatively. On top of that, with the optimization algorithm, it is possible to find the design space that meets the requirements of multi-objective optimization. Finally, experiments are presented to verify the correctness and effectiveness of the proposed method.
IGBT parallel connections are an effective way to increase the capacity of power electronic converters. The junction temperature balance between IGBTs is one of the key factors in the safe and stable operation of parallel IGBTs system. Therefore, it is very important to study the influence of junction temperature on the power loss of parallel IGBTs system to improve their stability. However, existing research mainly focuses on the loss of a single IGBT or the optimal operating frequency range of parallel IGBTs. It does not involve research on the optimal operating duty cycle range (ODCR) of parallel IGBTs. When IGBT devices work in the positive temperature coefficient range, the on-state loss difference caused by the junction temperature difference and the switching loss difference have different temperature characteristics. Therefore, the concept of the inflection point duty cycle (IPDC) is proposed to evaluate the trend of the junction temperature mismatch between parallel IGBTs. In this paper, an inflection point duty cycle model (IPDCM) is established to analyze the influence of circuit design parameters, IGBT device parameters, and junction temperature differences on the ODCR of parallel IGBTs. Experimental results show that the IPDCM can provide a feasible reference for the reliability, circuit design parameters, and device selection of parallel power devices.
A novel high-power triple line-voltage cascaded three-phase unity power factor rectifier is proposed to address the complex topology and control of the three-phase rectifier stage in traditional high-power charging power supply modules. The topology is composed of three line-voltage cascaded traditional three-phase single-switch boost-type voltage rectifier modules. With the triple line-voltage cascaded structure, in the proposed topology, the number of the fully controlled power switches and the voltage stresses of each power switch are both effectively reduced. In addition, the proposed rectifier topology can operate at a unity power factor with a sinusoidal input current. In this paper, the circuit structure and the operation principle including the DC-link voltages output characteristics of the proposed topology are described, and a corresponding system control strategy based on one cycle control (OCC) is presented. Simulation and experimental results are given which verified the feasibility of the proposed topology and control strategy.
A large number of electric vehicles (EVs), distributed solar and/or wind turbine generators (WTGs) connected to distribution systems lead to frequent and sharp voltages fluctuations. The action rates of conventional adjustable devices and smart inverters are very different. In this context, a novel dual-timescale voltage control scheme is proposed by organically combining data-driven with physics-based optimization. On fast timescale, a quadratic programming (QP) for balanced and unbalanced distribution systems is developed based on branch flow equations. The optimal reactive power of renewable distributed generators (DGs) and static VAR compensators (SVCs) is configured on several minutes or seconds. Whereas, on slow timescale, a data-driven Markovian decision process (MDP) is developed, in which the charge/discharge power of energy storage systems (ESSs), statuses/ratios of switchable capacitors reactors (SCRs), and voltage regulators (VRs) are configured hourly to minimize long-term discounted squared voltages magnitudes deviations using an adapted deep deterministic policy gradient (DDPG) deep reinforcement learning (DRL) algorithm. The capabilities of the proposed method are validated with IEEE 33-bus balanced and 123-bus unbalanced distribution systems.
Summary The output current of the fast control power supply for the Experimental Advanced Superconducting Tokamak (EAST) excites the load coil. Magnetic field can be quickly generated by the fast output current to control the balance of plasma vertical displacement. In order to improve the output current speed of EAST fast control power supply and its ability to resist external disturbance, an improved discrete integral sliding mode control method combining gray prediction and variable gain sliding mode observer is proposed. A sliding mode disturbance observer is used to observe the total disturbance on the load side, and feedforward compensation control is performed on the total disturbance. To further suppress chattering and accelerate convergence speed, a high‐order term is added to the traditional discrete exponential reach law, and a gain adaptive observer is designed to adaptively adjust the observer gain based on the observed current error and the tracking current error. In the current sampling process, an improved gray prediction structure is added, and the original current sequence of gray prediction is improved based on the principle of new information priority, improving the accuracy of predicted current, compensating for the inherent delay in digital control, and further improving the output current response speed. Simulation and experimental verification show that the proposed disturbance suppression improved discrete integral sliding mode fast current tracking control strategy has faster output current response speed and strong antidisturbance performance.
The double stator high-temperature superconducting field modulated (DS-HTS-FM) machine with a dual-stator configuration and high-temperature superconducting materials includes numerous cryogenic components that establish the required operating temperature for superconducting magnets. This abundance of cryogenic elements introduces complexity to the process of conducting a modal analysis of the entire machine. However, the conventional trial-and-error approach employed to achieve precise modal analysis results for the entire-machine suffers from the drawback of lacking a clear direction for adjustment elastic modulus which has a great influence on the modal analysis results. Therefore, it is difficult to obtain accurate modal analysis results of the entire-machine. In response to this challenge, this study focuses on a 10 kW DS-HTS-FM machine as its subject and presents an elastic modulus adjustment method based on the entire-machine modal analysis, aiming to obtain accurate finite element (FE) modal analysis results of the entire-machine. Initially, the FE method is used to find the components that have a great influence on the outer stator modals while the components that have less influence on the outer stator modal are equivalent to the front and rear end cover in the form of additional mass, thus establishing an entire-machine equivalent model for elastic modulus adjustment. Subsequently, an examination is conducted to ascertain the relative impact proportions of the elastic modulus associated with the outer stator, casing, end cover, and armature windings on the natural frequencies of the outer stator, which can lead to a precise determination of the optimal direction for adjusting the elastic modulus parameters. Lastly, based on the entire-machine modal experiment, the elastic modulus of the equivalent model is modified in a definite direction. Consequently, the elastic modulus values for various components of the DS-HTS-FM machine can be accurately identified. Experimental outcomes affirm the efficacy of this approach in attaining precise FE modal results for the DS-HTS-FM machine and reducing the computational time required for FE analysis.
This paper addresses the position-estimation deviation issue of the sensorless drive method and a new algorithm for estimating position correction of surface-mounted permanent magnet synchronous motor (SPMSM) is proposed. To improve the estimation accuracy of sensorless methods, the estimated position correction algorithm based on variable gain steepest gradient descent position error observer is proposed in this paper. The position error is estimated by the flux observation, and the steepest gradient descent method is used to correct the integration process. In addition, the dynamic and accuracy performance of the position error observer are improved by variable gain cycle iterative optimization. Experimental evaluation validated the effectiveness of the proposed algorithm, and the results show that the proposed method has the characteristics of high position observation accuracy and strong robustness. (c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CCBY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Interior permanent magnet synchronous motors (IPMSMs) have some inherent disadvantages, such as high torque ripple and difficulty in optimizing design due to the complex rotor structure. To address these issues, this paper proposes a method for optimizing the rotor structure of IPMSMs to reduce torque ripple. The flux barriers in the rotor are abstracted as virtual slots, and the effect of the position of the virtual slots on torque ripple is studied. Based on this analysis, a general method for optimizing the rotor structure to reduce torque ripple is proposed. To demonstrate the proposed method's effectiveness, the original prototype's rotor structure is optimized using the proposed method. The electromagnetic performance of the prototype before and after optimization is calculated. The results show that the optimization can reduce the torque ripple without affecting other electromagnetic performance. Finally, the theoretical analysis and simulation results are validated by conducting a prototype test, which provides support for the proposed method of torque ripple reduction.
The natural transfer time of medium-voltage large-capacity hybrid DC circuit breaker is long or even fails. Therefore, this paper proposes a hybrid DC circuit breaker topology based on vacuum and gas integrated series switch, and analyzes the basic principle of vacuum and gas integrated series for current transfer performance. The experimental prototype of vacuum and gas integrated series switch in medium voltage field is designed by double over-range linkage operation structure. The influence of gas type, pressure, contact structure and contact material on arc voltage characteristics is studied. The W70 Cu bridge two contact structure, hydrogen and nitrogen mixed gas (H2: $\mathrm{N}_{2}=2:3$ ), pressure 0.3MPa and other related parameters are determined. The arc voltage can be increased from 20 V to 121 V, and the current transfer time is reduced to 1/6 of the original. The feasibility and effectiveness of vacuum and gas integrated series switch applied to medium voltage hybrid DC circuit breaker are verified.
Epoxy resin is one of the most commonly used insulating materials for electricians. Nevertheless, the emergence of localized damage or subtle microcracks within the material poses a formidable challenge in terms of detection and subsequent repair. The safe operation of power equipment is seriously jeopardized. In this study, driven by the need for self-healing insulating materials in power equipment applications, the successful synthesis of high-performance epoxy insulating materials featuring varying disulfide bond contents was achieved. Mechanical properties such as tensile strength and elongation at the break of epoxy insulations are enhanced by small amounts of disulfide bond. While an elevated content of disulfide bond diminishes the heat resistance and electrical characteristics of epoxy insulating materials, it is noteworthy that the prerequisites of epoxy resins for electrical applications remain adequately fulfilled. The results of the mechanical damage Self-healing test showed that the optimal repair efficiency reached 81.23 %. Simultaneously, the differentiation of electric tree branches can be inhibited by a disulfide bond. The diminishment of electric tree damage extent within epoxy resin is optimized, and the impairments of electric trees are repaired. Grounded in a disulfide bond, the viability of utilizing self-healing epoxy resins as insulating materials for electrical equipment is substantiated in this paper.
Constant on-time current mode (COTCM) Buck converters are widely used in power management integrated circuit (ICs) for microprocessors. Small-signal models are necessary tools to design high-quality controllers. Existing models neglect output voltage ripples (OVRs) and spectrum extension caused by switching, which makes significant errors under high control bandwidth. This article adopts Fourier series to describe OVRs precisely. Then, influences of OVRs on COTCM are analyzed. Finally, spectrum coupling from current loop and voltage loop is incorporated to obtain a high-frequency model, and four universal analytical expressions in frequency domain are obtained with the aid of matrix calculation. Based on the proposed model and genetic algorithm, an optimal controller design method is developed. Simulation and experiment validate the accuracy of proposed model and the effectiveness of proposed design method.
Model predictive current control (MPCC) is recognized to be a promising technology for multi-phase drive systems. Particularly when applied to dual three-phase permanent magnet synchronous motors (DT-PMSM), certain factors such as common-mode voltage (CMV), harmonic current and calculation burden need to be taken into account. Additionally, adjusting the weighting factor in the cost function poses a challenge due to the lack of a theoretical basis. Addressing these challenges, this paper proposes a MPCC method for DT-PMSM with CMV suppression. In this proposed method, the virtual voltage vectors (V 3 s) and equivalent zero V 3 s are synthesized using large voltage vectors that have small CMVs. Notably, the average voltage of V 3 s and equivalent zero V 3 s in the x–y subspace is zero. Consequently, the elimination of the weighting factor of the harmonic current term in the cost function becomes achievable. Furthermore, a method for optimal voltage vector selection is introduced, simplifying the process of candidate voltage vectors and circumventing the traversal prediction calculation process. The proposed method can effectively reduce the harmonic current, limit the peak-to-peak value of the CMV to 1/3 of the inverter DC bus voltage, and relieve the calculation burden. The effectiveness of the proposed method is verified by comparison with existing traditional MPCC methods.
Precise information on the current and back electromotive force is required to improve a brushless DC motor’s operational performance. For the dual-stage drive, a back electromotive force observer and a current observer corrected by the commutation signal based on the extended state observer were created. The properties of the classic nonlinear error gain function were theoretically investigated using mathematical analysis. By thoroughly researching the observer’s structure, a methodology for confirming optimal parameters through parameter traversal in experiments based on a digital control platform was developed. The ideal observer gain parameters were then found under various operating situations, such that the observer parameters match the constantly changing system at any moment. The experimental findings demonstrate that the output of the current observer and the back electromotive force observer may converge within the motor’s primary operating conditions of 2000 rpm to 3000 rpm, allowing the current, disturbance, and back electromotive force to be tracked efficiently. This work introduces an observation technique for the physical quantities of an ironless-stator permanent magnet brushless DC motor powered by a two-stage drive, as well as the optimization of extended state observer parameters for this architecture.
