Research on the longitudinal protection of a through-type cophase traction direct power supply system based on the empirical wavelet transform

This paper proposes a longitudinal protection scheme utilizing empirical wavelet transform(EWT)for a through-type cophase traction direct power supply system,where both sides of a traction network line exhibit a distinctive boundary structure.This approach capitalizes on the boundary’s capacity to attenuate the high-frequency component of fault signals,resulting in a variation in the high-frequency transient energy ratio when faults occur inside or outside the line.During internal line faults,the high-frequency transient energy at the checkpoints located at both ends surpasses that of its neighboring lines.Conversely,for faults external to the line,the energy is lower compared to adjacent lines.EWT is employed to decompose the collected fault current signals,allowing access to the high-frequency transient energy.The longitudinal protection for the traction network line is established based on disparities between both ends of the traction network line and the high-frequency transient energy on either side of the boundary.Moreover,simulation verification through experimental results demonstrates the effectiveness of the proposed protection scheme across various initial fault angles,distances to faults,and fault transition resistances.

Effect of power parameter and induction coil on magnetic field in cold crucible during continuous melting and directional solidification

Bottomless electromagnetic cold crucible is a new apparatus for continuous melting and directional solidification;however,improving its power efficiency and optimizing the configuration are important for experiment and production.In this study,a 3-D finite element (FE) method based on experimental verification was applied to calculate the magnetic flux density (Bz).The effects of the power parameters and the induction coil on the magnetic field distribution in the cold crucible were investigated.The results show that higher current intensity and lower frequency are beneficial to the increase of Bz at both the segment midpoint and the slit location.The induction coil with racetrack section can induce greater Bz,and a larger gap between the induction coil and the shield ring increases Bz.The mechanism for this effect is also discussed.

Directed Acyclic Graph Blockchain for Secure Spectrum Sharing and Energy Trading in Power IoT

Peer-to-peer(P2P)spectrum sharing and energy trading are promising solutions to locally satisfy spectrum and energy demands in power Internet of Things(IoT).However,implementation of largescale P2P spectrum sharing and energy trading confronts security and privacy challenges.In this paper,we exploit consortium blockchain and Directed Acyclic Graph(DAG)to propose a new secure and distributed spectrum sharing and energy trading framework in power IoT,named spectrum-energy chain,where a set of local aggregators(LAGs)cooperatively confirm the identity of the power devices by utilizing consortium blockchain,so as to form a main chain.Then,the local power devices verify spectrum and energy micro-transactions simultaneously but asynchronously to form local spectrum tangle and local energy tangle,respectively.Moreover,an iterative double auction based micro transactions scheme is designed to solve the spectrum and energy pricing and the amount of shared spectrum and energy among power devices.Security analysis and numerical results illustrate that the developed spectrum-energy chain and the designed iterative double auction based microtransactions scheme are secure and efficient for spectrum sharing and energy trading in power IoT.

Analysis on Output Power for Multi-direction Piezoelectric Vibration Energy Harvester

To predict the performance of multi-direction piezoelectric vibration energy harvester,an equation for calculating its output power is obtained based on elastic mechanics theory and piezoelectricity theory.Experiments are performed to verify theoretical analysis.When the excitation direction is along Y direction,a maximal output power about 0.139 mW can be harvested at a resistive load of 65kΩ and an excitation frequency of 136 Hz.Theoretical analysis agrees well with experimental results.Furthermore,the performance of multi-direction vibration energy harvester is experimentally tested.The results show that the multi-direction vibration energy harvester can harvest perfect energy as the excitation direction changes in XY plane,YZ plane,XZ plane and body diagonal plane of the harvester.

Two stages power generation test of the hot dry rock exploration and production demonstration project in the Gonghe Basin,northeastern Qinghai-Tibet plateau,China

The Hot Dry Rock(HDR)is considered as a clean and renewable energy,poised to significantly contribute to the global energy decarbonization agenda.Many HDR projects worldwide have accumulated valuable experience in efficient drilling and completion,reservoir construction,and fracture simulation.In 2019,China Geological Survey(CGS)initiated a demonstration project of HDR exploration and production in the Gonghe Basin,aiming to overcome the setbacks faced by HDR projects.Over the ensuing four years,the Gonghe HDR project achieved the first power generation in 2021,followed by the second power generation test in 2022.After establishing the primary well group in the initial phase,two directional wells and one branch well were drilled.Noteworthy progress was made in successfully constructing the targeted reservoir,realizing inter-well connectivity,power generation and grid connection,implementing of the real-time micro-seismic monitoring.A closed-loop technical validation of the HDR exploration and production was completed.However,many technical challenges remain in the process of HDR industrialization,such as reservoir fracture network characterization,efficient drilling and completion,multiple fracturing treatment,continuous injection and production,as well as mitigation of induced seismicity and numerical simulation technology.

Investigation on the multi-hole directional coupler for power measurement of the J-TEXT ECRH system

Power measurement is necessary for an electron cyclotron resonance heating(ECRH)system.The directional coupler method has been put forward to monitor high-power microwave from gyrotrons in real time.A multi-hole directional coupler has been designed and manufactured for the 105 GHz/500 kW ECRH system on the J-TEXT tokamak.During the design process,we established the relationships between hole parameters and coupling characteristics based on the multi-hole coupling method and small-hole coupling theory.High-power tests have been carried out.The results indicated the reasonability of the theoretical design and practicality of the fabricated directional coupler.Sources of test errors have been discussed in detail,and the influences of spurious modes on the directional couplers have been emphatically analyzed.

Improved direct power injection model of 16-bit microcontroller for electromagnetic immunity prediction

To promote the modeling standardization process of the integrated circuits, an improved electrical simulation model for a direct power injection （DPI） setup which was used to measure the conducted immunity of a 16-bit microcontroller to radio frequency aggression was investigated. Based on the existing model of the same microcontroller, the PDN module was modified by adding the core, PLL and MD network models, which could reflect the actual electric distribution situation within the microcontroller more accurately. By comparing the simulation results with the measurement results, the effectiveness of the modified model can be improved to 500 MHz, and its uncertainty is within ＋1.8 dB （＋2 dB is acceptable）. Then, to improve the simulation accuracy of the complete model in the high frequency range, the I/O model which contained the dynamic and nonlinear characteristics reflecting the variation of the internal impedance of the microcontroller with increasing the frequency of the external noise was introduced. By comparing the simulation results with the measurement results, the effectiveness of the second modified model can be improved up to 1.4 GHz with the uncertainty of ~1.8 dB. Thus, a conclusion can be reached that the proposed model can be applied to a much wider frequency range with a smaller uncertainty than the latest model of the similar type. Furthermore, associated with the electromagnetic emission testing platform model, the PDN module can also be used to predict the electromagnetic conducted and radiated emission characteristics. This modeling method can also be applied to other integrated circuits, which is very helpful to the standardization of the IC electromagnetic compatibility （EMC） modeling process.

COMPUTATIONALLY EFFICIENT ESPRIT METHOD FOR DIRECTION FINDING

In this paper,a low complexity ESPRIT algorithm based on power method and Orthogo- nal-triangular (QR) decomposition is presented for direction finding,which does not require a priori knowledge of source number and the predetermined threshold (separates the signal and noise ei- gen-values).Firstly,according to the estimation of noise subspace obtained by the power method,a novel source number detection method without eigen-decomposition is proposed based on QR de- composition.Furthermore,the eigenvectors of signal subspace can be determined according to Q matrix and then the directions of signals could be computed by the ESPRIT algorithm.To determine the source number and subspace,the computation complexity of the proposed algorithm is approximated as (2log_2 n+2.67)M^3,where n is the power of covariance matrix and M is the number of array ele- ments.Compared with the Single Vector Decomposition (SVD) based algorithm,it has a substantial computational saving with the approximation performance.The simulation results demonstrate its effectiveness and robustness.

Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability

An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current(HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.

Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage conditions

This paper proposes an analysis and a direct power control (DPC) design of a wind turbine driven doubly-fed induction generator (DFIG) under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions.

The Security Correction of Large Consumers Long-Term Direct Power Trading Based on DC Power Transfer Distribution Factor

The experiments of large consumers direct power trading is conducting in china nationwide, and it’s important to the reform of electricity market. To compensated efficiencies in security correction of large consumers direct power trading, a novel security correction method based on DC power transfer distribution factor was proposed. Using the presented method to comply security correction, all the transactions that satisfy the specific requirements of maximizing social welfare are able to enter security correction process, and when the power of transmission line is out of limit, this method avoid the transaction which causes this problem is abandoned directly by introducing supplement transactions. The simulation has shown that the proposed security correction method of large consumers direct power trading based on DC power transfer distribution factor is effective.

RECENT DEVELOPMENTS OF DIRECT BONDED COPPER(DBC)SUBSTRATES FOR POWER MODULES

DBC substrates are the standard circuit boardsfor power modules. Using the DBC technologythick copper foils (0.125mm - 0.Tmm) arecladded to Alumina or Aluminum Nitride,The strong adhesion of the copper to ceramicbond reduces the thermal expansion coefficientin horizontal direction only slightly above theTEC of the ceramic itself. This allows directsilicon attach of large dies without using TECcontrolling layers.As DBC technology is using copper foils,integralleads overhanging the ceramic can be realized...

Advances and challenges of methanol-tolerant oxygen reduction reaction electrocatalysts for the direct methanol fuel cell

Methanol cross-over effects from the anode to the cathode are important parameters for reducing catalytic performance in direct methanol fuel cells.A promising candidate catalyst for the cathode in direct methanol fuel cells must have excellent activity toward oxygen reduction reaction and resistance to methanol oxidation reaction.This review focuses on the methanol tolerant noble metal-based electrocatalysts,including platinum and palladium-based alloys,noble metal–carbon based composites,transition metal-based catalysts,carbon-based metal catalysts,and metal-free catalysts.The understanding of the correlation between the activity and the synthesis method,electrolyte environment and stability issues are highlighted.For the transition metal-based catalyst,their activity,stability and methanol tolerance in direct methanol fuel cells and comparisons with those of platinum are particularly discussed.Finally,strategies to enhance the methanol tolerance and hinder the generation of mixed potential in direct methanol fuel cells are also presented.This review provides a perspective for future developments for the scientist in selecting suitable methanol tolerate catalyst for oxygen reduction reaction and designing high-performance practical direct methanol fuel cells.

Evaporative Cooling Applied in Thermal Power Plants:A Review of the State-ofthe-Art and Typical Case Studies

A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

Bias Correction in Wind Direction Forecasting Using the Circular-Circular Regression Method

Wind direction forecasting plays an important role in wind power prediction and air pollution management. Weather quantities such as temperature, precipitation, and wind speed are linear variables in which traditional model output statistics and bias correction methods are applied. However, wind direction is an angular variable; therefore, such traditional methods are ineffective for its evaluation. This paper proposes an effective bias correction technique for wind direction forecasting of turbine height from numerical weather prediction models, which is based on a circular-circular regression approach. The technique is applied to a 24-h forecast of 65-m wind directions observed at Yangmeishan wind farm, Yunnan Province, China, which consistently yields improvements in forecast performance parameters such as smaller absolute mean error and stronger similarity in wind rose diagram pattern.

A Direct Liquid Fuel Cell with High Power Density Using Reduced Phosphotungstic Acid as Redox Fuel

Direct liquid fuel cells(DLFCs)are proposed to address the problems of high cost and complex storage and transportation of hydrogen in traditional hydrogen-oxygen proton exchange membrane fuel cells.However,present fuels of organic small molecules used in DLFCs are restricted to problems of sluggish electrochemical kinetics and easily poisoning of precious metal catalysts.Herein,we demonstrate reduced phosphotungstic acid as a liquid fuel for DLFCs based on its advantages of high chemical and electrochemical stability,high electrochemical activity on common carbon material electrodes,and low permeability through proton exchange membranes.The application of phosphotungstic acid fuel effectively solves the problems of high cost of anode catalysts and serious fuel permeation loss in traditional DLFCs.A phosphotungstic acid fuel cell achieves a peak power density of466 mW cm^(-2)at a cell voltage of 0.42 V and good stability at current densities in the range from 20 to 200 mA cm^(-2).

Predictive direct power control of three-phase PWM rectifier based on TOGI grid voltage sensor free algorithm

In predictive direct power control(PDPC)system of three-phase pulse width modulation(PWM)rectifier,grid voltage sensor makes the whole system more complex and costly.Therefore,third-order generalized integrator(TOGI)is used to generate orthogonal signals with the same frequency to estimate the grid voltage.In addition,in view of the deviation between actual and reference power in the three-phase PWM rectifier traditional PDPC strategy,a power correction link is designed to correct the power reference value.The grid voltage sensor free algorithm based on TOGI and the corrected PDPC strategy are applied to three-phase PWM rectifier and simulated on the simulation platform.Simulation results show that the proposed method can effectively eliminate the power tracking deviation and the grid voltage.The effectiveness of the proposed method is verified by comparing the simulation results.

Research and Demonstration of Direct Air-Cooling System for 600-MW Fossil-Fired Power Plants

Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.

Direct Power Control of Variable Wind Speed Based on the Doubly Fed Asynchronous Machine

In this work, the authors propose the study of a wind speed variable based on the DFAM （double fed asynchronous machine）. The model of the turbine is drawn from the classical equations describing the operation of a variable wind speed. The torque generated by the turbine is applied to the DFAM directly connected on the network side and the stator via a bidirectional converter side rotor. This configuration allows velocity variations of ±30% around the synchronous speed and the converter is then sized to one third of the rated power of the machine. The DFAM is controlled by a control vector ensuring operation of the wind turbine power coefficient maximum.