Abstract:Forced power oscillations in the power system are likely to trigger a wide range of power fluctuations.When new energy such as wind power is connected to the power grid,the fluctuation of output power is random.When the power fluctuation causes the forced oscillation in the system,the oscillation will also show random characteristics and it is difficult to locate the disturbance source.Therefore,a method of locating forced oscillation disturbance source caused by wind farm is proposed.The method uses the oscillation bispectrum to obtain the center frequency and obtains the initial phase at the oscillation center frequency by wavelet transform.According to this,the disturbance source can be located by the energy function.The actual example verifies the feasibility and effectiveness of the proposed method.

Abstract:Power system is facing growing challenges in maintaining a secure and reliable energy supply.Part of the growing challenge is the possibility of significant levels of uncertain wind generation being installed on power system.Hence the wind power forecasting approaches have drawn to our attention.This paper gives a comprehensive overview of the state-of-the-art wind power forecasting approaches at home and abroad.The basic theory and approaches of wind power forecast,and hot issues are concerned.This paper mainly introduces the research progress of deterministic wind power forecast,probabilistic wind power forecast,wind power ramp events,big data and deep learning approaches.

Abstract:The Wind turbine simulator (WTS) generally uses a simplified aerodynamic model (i.e.C_p-λ-βcurved surface) to simulate the aerodynamic characteristics of the rotor,which will not only affect the accuracy of aerodynamic torque,but also cannot reproduce the aero-elastic coupling characteristics of a large wind turbine.This paper analyzes the operating principle and program structure of FAST (Fatigue,Aerodynamics,Structures,and Turbulence),which is an open source wind turbine simulation software developed by the National Renewable Energy Laboratory (NREL).Then,the pneumatic calculation code in FAST is extracted and packaged,combined with the speed measured from WTS,the aero-elastic coupling simulation based on FAST is finally realized on WTS.As a result,the aerodynamic torque given by WTS is more credible and more data about aerodynamic loads can be achieved.At the end of this paper,experiments show that the WTS combined with FAST code can achieve a more realistic and comprehensive aerodynamic simulation.

Abstract:In light of poor regularity and predictability of RMS value of node voltage in power distribution networks,this paper proposes to apply the ARMA model to predict the RMS value,which mainly comprises of data preprocessing,fitting training of AMRA,fitting review of AMRA,and forecasted application of ARMA.This method is realized through using Python.ARMA fitting training is performed on two randomly selected 10 kV RMS value monitoring sequences,before conducting analysis with the model generated by the training,which demonstrates that root-mean-square errors between the two predicted sequences and actual values are 9.57 and 5.05 respectively.Therefore,method proposed in this paper is applicable in performing voltage RMS value predictions,with reliable effectiveness and practicality.

Abstract:This paper presents an accurate model to forecast voltage deviation with improved BP neural network,which concerns with the meteorological factors.The proposed method is a combination of PCA dimension reduction,AP clustering and BP neural network.The proposed method is successfully applied to actual data and the practical application results proved that the mean absolute percentage error (MAPE) of the proposed method is 3.06%,which is obviously better than that of other methods.

Abstract:A two-step method to improve the sparse representation is proposed to estimate the dynamic harmonic impedance matrix under the underdetermined model.First measured on bus node harmonic voltage value,based on the two-dimensional sparse domain minimum deviation Angle of the change of the harmonic impedance matrix moment,and then estimates the dynamic change of the harmonic impedance matrix and obtain the real-time harmonic source number.Simulation verification of IEEE-14 node system was carried out through MATLAB simulation software to verify the accuracy and rationality of two-step algorithm for estimating harmonic impedance improved sparse representation.

Abstract:On the basis of the research on the load characteristics,the model of the inverter air conditioner is established.In circumstances that could satisfy the requirement of the users'comfort,design a control method of the single inverter air conditioning,and design a direct and easy aggregation control algorithm.At the same time,depending on the different order of air conditioning control,two goals are respectively to make full use of the load reduction potential or economy optimal.A power grid planning model is established considering the cost of the demand response,and the effectiveness of the control method and the planning scheme are proved by the case study.

Abstract:Droop control makes power electronic interface have some external characteristics of synchronous generator,such as realizing droop curve,but still cannot provide damping and inertia for power grid.In order to simulate the synchronous generator damping and inertia,this paper explains how from the evolution of droop control virtual synchronous machine control,through the establishment of similar mechanical equations of synchronous generator model,characteristic of the power electronic converter with synchronous generator damping and inertia.Simulation and experimental results verify the feasibility and correctness of the proposed method.

Abstract:The factory test or acceptance test should be done before putting into operation to ensure the MOA's quality,where the impulse current generator is often used to simulate the impulse current and test the stability of withstanding the impulse current.But in the simulation analysis,the lightning current function model was used to study MOA's nonlinear characteristics instead of the impulse current test circuit,and the influence of the difference between the current waveform on the load characteristics was ignored.The lightning current model research status was introduced in this paper,and three models,including double exponential model,Heidler model and Pulse model,were carried out by MATLAB/Simulink.Then simulation results and experimental results were compared and analyzed according to the relative error of residual voltage and energy absorption.Then parameter in Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) is determined.The research results can provide reference for the following MOA research on the characteristics of the very fast transient overvoltage (VFTO),the simulation analysis of the circuit model and the lightning protection research.

Abstract:Due to the volatility of renewable energy output,the power grid with high proportion of renewable energy integration frequently faces the power quality declining.This reduces the operation efficiency of sensitive load and further leads to abnormal operation or even malfunction of equipment.In this background,the load loss may occur when the voltage falls to the uncertain region of the sensitive load voltage tolerance curve,which should not be neglected.Such load mode possibility should be considered for the distribution network planning in order to improve the security and economy of the power grid.In this paper,the frequency variable motor is taken as a typical load to model and analyze in terms of its voltage sensitivity.First,the fault probability of the frequency converter in the uncertain region of the voltage tolerance curve is estimated,and then the loss of voltage sensitive load is calculated and incorporated into the distribution network risk planning model to improve the adaptability of the existing method.The results of the test example verify the feasibility and effectiveness of the proposed method,which will be a reference for the future distribution network planning.

Abstract:With the development of smart grid,the interconnection level of power systems is being enhanced so that it is very important to strengthen the security and stability analysis to prevent blackouts.Power system vulnerability identification is the prerequisite and foundation of power system security and stability assessment.Based on the complex network theory,we establish a comprehensive vulnerability index combining with the actual power grid operation,improve the line-efficiency definition using active value of transmission power flow,and identify vulnerable buses and transmission lines through calculating global efficiency variation when network topology or operation status changes.Simulations show that the transmission lines which are closely related to the power sources and key hub buses have great impacts on the overall vulnerability index of power systems.

Abstract:There are two popular practical models of synchronous generator used in power system transient simulation,both of them are based on Park equations and can be defined as assumed A and assumed B,according to the different assumptions.In order to study the influence of different models on the calculation precision of transient stability,single-machine infinite system is taken for example to compare the transient stability calculated by two practical models,and the simulation results are verified by time-step finite element model (T-S FEM).The results show that the transient stability calculated by assumed A is close to that calculated by T-S FEM,thus the transient stability limit calculated by assumed A is more accurate.

Abstract:Sulfur corrosion is widespread in transformer oil.The generation of corrosive sulfide can affect the performance of insulation winding and cause equipment failure.In this paper,the influence of corrosive sulfide in transformer oil on the partial discharge characteristics of insulation winding is studied.Through partial discharge test of insulation winding samples with different corrosion conditions,the influence of the corrosive sulfide deposition on the partial discharge characteristics of winding is obtained.The results show that the deposition of corrosive sulfide reduces the initial discharge voltage of the insulation winding,which makes the insulation winding easy to discharge,and the discharge density and discharge repetition rate are proportional to the deposition of corrosive sulfide.

Abstract:In the valve-side busing of the UHV converter transformer,a capacitor-type bushing tap voltage divider is installed.In order to transmit the valve-side voltage to the control and protection equipment,after the converter is charged,a voltage transformer is connected to the bushing tap.During the actual operation,it was found that the ferro-magnetic resonance phenomenon occurred between the bushing tap capacitor and the voltage transformer of the converter valve side bushing,which may lead to the malfunction of the converter transformer in charging state.The article carries on the harmonic analysis based on the actual transiet fault recording,and obtains the characteristic frequency of the resonance.By analyzing the electrical principle of the voltage divider and voltage transmitter of the bushing tap,a transient simulation model is built,and the working condition of the ferroresonance is reproduced by using PSCAD/EMTDC simulation.Based on the theoretical analysis,the concrete measures of improving the voltage divider to avoid the resonance are put forward.

Abstract:Aiming at the problem of commutation failure in high voltage direct current (HVDC) transmission system,the unified power flow controller (UPFC) is applied to reduce the probability of commutation failure of HVDC system,and improve the original control strategy of the unified power flow controller.When the AC side faults,UPFC shunt control strategy using AC bus voltage reference value adjustment method to suppress commutation failure.The severity of fault is introduced into the fault level FL to characterize the HVDC system,through theoretical analysis and simulation verification of PSCAD/EMTDC:When the fault level of F_L=18.7%,which can control the original control strategy and improvement strategy of UPFC inhibition after commutation failure;fault level F_L=23.1%,only the improved control strategy can effectively inhibit the occurrence of commutation failure;failure is more serious,when the fault level reached F_L=93.56%,the improved control strategy can effectively reduce the probability of occurrence of continuous commutation failure.Reactive power compensation can be affected by AC system strength enhanced HVDC system using UPFC dynamic,improve the commutation failure resistance,thereby effectively improving the operation performance of HVDC system.

Abstract:In view of the fact that the spectral resolution of the sub (super) synchronous component of the engineering site is sparse,this paper summarizes the inadaptability of the existing algorithm engineering application and proposes an engineering method of FFT calculation.The effect of spectral aliasing is first eliminated by combining the low-pass filter and the FFT data window length,and then eliminating the interference of fundamental frequency spectrum leakage to harmonic calculation through the decreasing characteristic of FFT calculation results.Finally,using the FFT correction algorithm to eliminate the influence of the fence effect to accurately calculate the frequency and amplitude of sub (super) synchronous oscillation harmonics.Meanwhile,according to the FFT spectrum amplitude of the number of extreme occurrences to distinguish between the sudden changes in the operating conditions of the amplitude,as a basis for the development of monitoring devices to meet the grid sub (super) synchronous oscillation of the precise monitoring of functional requirements.

Abstract:For a long time,tariff recovery risk of large power customers is a hot spot for electric power company.But because of the lack of external data support and efficient early warning model,tariff recovery risk early warning has become a difficult problem.Based on electricity consumption and electricity charge data,combining with the relevant business,tax and court information of the enterprise,the paper established a serial of tariff recovery risk indexes for large power customers.Secondly,the entropy method (EM) is adopted to evaluate tariff recovery risk assessment of customers'electricity bills,and the customer risk level is divided according to the distribution of risk score.Weak influence indexes were filtered by weight coefficients and overlapping indexes were dropped by correlation analysis.Tariff recovery risk early warning model was carried out by Long Short-Term Memory (LSTM) network.Numerical example results show that the proposed risk early warning model was accurate and effective,and the result gained by LSTM is better than Logistic regression in accuracy,precision and recall.The tariff recovery risk early warning results can accurately locate high risk customers and improve tariff recovery efficiency.

Abstract:This paper discusses the complex situation and characteristics of the new energy centralized control curve.In view of this phenomenon,this paper introduces the power-changed factor as well as the variable state marker variables and presents a complete set of strategy,which uses real-time dynamic closed-loop correction to eliminate the macro-data transition and microscopic data anomalies,to amend the power data.It not only guarantees the second-level refresh and data accuracy features required for big data presentations,but also takes into account the statistical demand that the statistical calculation of any time period must avoid the untrust worthy interval and the statistical loss.This strategy is also suitable for data corrections of other project cumulative quantity.

Abstract:As a kind of important means for DC frequency stability,frequency limit controller has been used widely in HVDC projects.DXB UHVDC project is faced with the problems of increasing frequency instability of the Yunnan power grid,as it runs asynchronously from the main grid,and the shortage of the opening unit in the initial stage of production.The configuration of FLC is very important.It analyzes two kinds of FLC control logic used in current DC project of China Southern Power Grid and compares the results of two kinds of control logic response through simulation test.The FLC configuration and parameter selection of DXB UHVDC are explained,and the response characteristics of FLC under the typical fault under the isolated island system are verified through simulation.And verify its function in DXB RTDS simulation platform as well as field test.

Abstract:In order to effectively analyze the economic benefits of investment of the electricity distribution network from the perspective of the characteristics of the public transformer industry,it is necessary to classify the industry of public transformers.In this paper,the use of big data technology to analyze the industry load characteristics,and then the improved K-means algorithm based on canopy is used to analyze the characteristics of the public transformer load.After that,according to the cosine similarity algorithm,from the perspective of the characteristics of the four seasons load and the characteristics of holiday load,he analysis of public transformers belong to which industry.Finally,the industry fitting method from different dimensions is used to match the industry which public transformers belong.For public transformers in Jiangsu province,the use of the method has been achieved after the high accuracy rate,to achieve a more accurate analytical method of the public transformers industry.The analytical method of the industry which public transformers belong based on load data mining provide a strong support for the evaluation of economic benefits of investment of the electricity distribution network.

Abstract:As a powerful flexible AC transmission equipment,Unified Power Flow Controller (UPFC) has been further extended in the domestic power system and gradually applied in the 500 kV level system,circuit breaker protection in the 3/2 connecting mode of transmission line with UPFC will face new application problems.Based on the Southern SuZhou power grid 500 kV UPFC demonstration project,this paper analysis the circuit breaker protection device's special functional requirements in power system with UPFC.According to different connecting modes,the adaptability of circuit breaker protection and the combination strategy of circuit breaker protection and UPFC control protection in three phase inconsistent operation are proposed.All of this can effectively avoid the reclosing of circuit breaker protection with UPFC.The research improves operation reliability of UPFC system.

Abstract:The hydrophobic condition of composite insulators has an important influence on the security and stability of power system.In order to identify hydrophobicity of composite insulators accurately,fast and conveniently,with the tools of MATLAB image processing and GUI developing composite insulators hydrophobicity analysis software.The software was developed using a modular thinking,the establishment of image processing,the amount of drops of water feature extraction,hydrophobicity detection methods and database management modules.The improved Canny operator was used for image segmentation,extraction characteristics of water drop (or water stains),finally the improved RBF neural network was used to analyse the insulators hydrophobicity grade.The results of experiment show that the software was able to identify insulators hydrophobicity grade accurately and objectively and its accurate recognition rate is as high as 92%.The software can avoid the influence of artificial factors,improve the work efficiency and provide data support and reference for field operation personnel.

Abstract:With the advancement of the global energy interconnection strategy,many domestic scientific institutions have already done researches on the series multi-terminal HVDC systems applied into the cross-sea interconnection,LCC and VSC hybrid transmission and other area.However,the inherent characteristic that series converter can't be grounded in normal operation determines its reliability should be improved higher.Therefore,this paper analyzes the requirement of electrode topology for series multi-terminal HVDC transmission system in different operating modes and proposes an electrode topology of series multi-terminal HVDC system and its control method.At last,it is concluded that the electrode topology can effectively avoid the overall outage of the series multi-terminal HVDC system in the case of any equipment overhaul.

Abstract:In order to improve the design quality and efficiency of the hanger and support in the thermal power plant,the characteristics of the design process of the pipe hanger and support are studied in this paper,and a solution for the digital design of the pipe support hanger is present.Through establish the logic rules and algorithms to automatically identify the rooting conditions of the hanger and support,combined with the selection requirements of common hanger and supports in thermal power plants,the 3D digital design of pipe supports and hangers was successfully realized with redeveloping plug-in on plant design management system (PDMS) software platform,improved the process of digital design.

Abstract:The fault repair work of distribution network is an important part of distribution network operation.The quality and efficiency of repair work are of great significance to the improvement of the power supply reliability and service quality of distribution network.However,there are some difficulties in the evaluation of fault repair work at present.This paper takes fault repair as the entry point,and investigates and analyzes 95598 fault repair work orders from 3 dimensions of time,space and fault type;on this basis,the evaluation indexes that can accurately reflect the quality and efficiency of fault repair of distribution network are determined,the indexes are compared and evaluated by the way of scoring,and the weights are determined by using the analytic hierarchy process and entropy method,and the comprehensive score is obtained by weighted sum,thus a set of clear and practical evaluation system for the quality and efficiency of fault repair of distribution network is established.Finally,taking Nanjing as an example to evaluate the quality and efficiency of distribution network fault repair in each area,and the weak points of repair work are excavated by comparison and evaluation,and the operation management level and the high quality service level of distribution network are improved.

Abstract:Hybrid HVDC can take full advantage of the thyristor converter and voltage source converter,and it has a good development prospects.In order to analysis the control strategy and operating characteristic of hybrid DC grid,a four terminal bipolar's hybrid grid structure is established,whose rectifier side is modular multilevel converter and inverter side is thyristor converter,the mathematical model is derived and corresponding control strategy is designed.The start-up process and operating characteristic of hybrid DC grid are simulated and analyzed in PSCAD/EMTDC,which demonstrates the effectiveness of the proposed control strategy.

Abstract:The blooming HVDC links has caused a serious frequency problem for the multi-infeed grid.To make full use of the interruptible load,reduce the risk of under-frequency load shedding and the risk of triggering a serious accident,an interruptible load shedding scheme according to the frequency and the value setting method is proposed.An equivalent model is adopted for the interruptible load shedding study considering the load frequency characteristics.The reasonable frequency setting values and load shedding percentage are analyzed.The completed scheme is checked by the detailed grid model.The simulation results show that the proposed scheme is effective.In case of large power loss which may cause the under-frequency load shedding,the scheme can remove the interruptible load.As a result,the risk of under-frequency load shedding is reduced and the frequency stability of the grid is improved.