Abstract:Energy internet has become the key technology for intelligent management of distributed devices and complementary applications of multiple forms of coupling energy. In order to solve the problem of multi-energy coordination optimization in energy, this paper proposes a multi-source and multi-level for the energy internet with renewable energy according to the idea of “layered control-collaborative optimization”. The distributed equipment is managed to realize coordinated and optimal scheduling of cold, heat, electricity and gas energy in the regional system. Finally, the genetic algorithm based on real number coding technology is used to simulate the optimization model. It is verified that the stratified optimization scheme can achieve regional energy Internet energy autonomy and multi-energy optimization with minimum cost as the optimization target, and solve the optimal scheduling between different regions problem.

Abstract:The harsh environment and poor communication conditions make it difficult for the operation and maintenance of island microgrid. Firstly, the architecture and function of the island microgrid monitoring system are analyzed. Based on the multi-time scale characteristics of microgrid control, combined with the geographical conditions of remote islands, the hybrid communication method is proposed to meet the communication requirements of the microgrid monitoring system. Secondly, based on the characteristics of communication, the preventive control and emergency control methods of the microgrid are proposed. When the microgrid is operating normally, the load and distributed power output are predicted based on the meteorological environment information monitored, and a microgrid energy scheduling strategy is formulated to implement preventive control measures in the microgrid. When the microgrid is in a state of emergency, the microgrid control center performs emergency load control measures based on the magnitude of the monitored disturbance and load power information. Finally, a microgrid is taken as an example for analysis to verify the validity of the proposed method.

Abstract:With UHVDC construction and renewable energy development, DC blocking faults bring challenge to fast frequency regulation of power system. To improve frequency stability of power system with energy storage technology, a demand assessment method is proposed for energy storage to participate in fast frequency regulation of power system. Firstly, bottleneck evaluation index and bottleneck scenario analysis method of fast frequency regulation are proposed to acquire scenario basis for capacity configuration of energy storage. Then an optimal configuration method on capacity of energy storage is proposed based on bottleneck boundary scenario, which eliminates bottleneck scenarios with the minimum cost of capacity configuration of energy storage. Finally, the effectiveness of the proposed method is verified via case studies based on actual data of Jiangsu grid.

Abstract:The open circuit fault of the direct-drive wind power system converter causes problems such as half-phase loss of AC current on the machine side, voltage fluctuation on the DC side, fluctuation of generator speed, etc., which seriously affects the operational stability of the wind power generation system. A fault diagnosis method for open-circuit fault of permanent magnet direct-drive wind power system based on real-time current amplitude is proposed. The real-time current amplitude is calculated by using the running characteristics of the motor, so that the fault diagnosis algorithm can diagnose and locate the fault in real time. Comparing the current amplitude in the fault state with the set current amplitude threshold eliminates the misdiagnosis caused by errors. The position of the abnormality of the current amplitude is used to determine the position of the fault switch tube. Experimental results verify the correctness of the theoretical analysis and the effectiveness of the fault diagnosis method. Compared with other methods, the detection speed of the method and the diagnostic capability of multiple switch faults are verified.

Abstract:To solve the high performance control grid-connected control problem of doubly fed induction generator(DFIG), we propose a predictive virtual torque control method for distributed DFIG grid connected inverter system. Virtual torque is derived from the concept of direct torque control in motor driven system. It is synthesized from the rotor flux of DFIG and the virtual flux of grid. On the basis of establishing the mathematical model of the DFIG grid-connected inverter system. The effects of voltage vectors in different sectors on virtual torque and rotor flux are analyzed. Sequence of three vectors containing two effective voltage vectors and a zero voltage vector are selected, and it also give a method to calculate the vector action time to make the power tracking. Finally, the performance of the proposed method is verified based on the 55 kW DFIG experimental prototype. The experimental results show that this method can achieve the DFIG system smooth and shock free grid-connection, and guarantee the dynamic and steady power quality of the grid-connection point.

Abstract:For the sake of easing the threat to the safe and stable operation of power system, control performance of static var compensator, widely used in cluster wind farms, and their triggering process of voltage overshoot are analyzed detailedly in this paper. The combined action of response lag and physical property defects, produces malposition compensation effect in SVC, which supports no effective reactive power output during voltage drip, while exports surplus reactive power during recovery process after fault resection. In order to overcome the limitations of SVC control performance, an additional locking control embedded in the SVC controller, is put forward, which comes into action merely under the condition of lower voltage.The judging criteria of SVC locking control and reoperating after shutting is given, to avoid malposition compensation, to effectively reduce high voltage threat triggered by SVC, thus ensuring the safety and stability of wind farm. Lastly, simulation has verified the effectiveness of the proposed control strategy. In addition, this tip offers some guidance for late construction and operation of wind farm.

Abstract:Accurate and rapid removal of transformer faults is related to the safe and stable operation of power system. The identification of magnetizing inrush current is a vital problem in transformer protection. In order to detect internal fault current from inrush current correctly and prevent incorrect operations of relays. By analyzing and summarizing the difference characteristics in frequency domain between fault current and inrush current, this paper proposed a novel inrush currents identification criterion based on least-square matrix pencil, using transformer differential current as detection signal. The matrix pencil algorithm is used to calculate the harmonic component of transformer current. And then entropy of current content and decay factor is computed to discriminate the inrush current. Simulation results show this scheme reliability and effective, can precisely identify the inrush current from the inner fault current. On this basis, key issues in the field are provided for the further research and engineering applications.

Abstract:In order to make full use of the reserve reactive power resources to improve the dynamic reactive power compensation capability of the receiving end of the power grid and improve the voltage stability better, this paper proposes the control strategy of the switching capacitor based on the automatic switching capacitor automatic device. The switching control strategy includes fault identification logic, low-voltage switching capacitor logic and over-voltage switching capacitor logic. The simulation platform builds a real-time simulation model of 220 kV and above based on RTDS, and connects DC protection devices and fast-switching capacitor automatic devices respectively, to form a double closed-loop real-time simulation system. By setting up a variety of test projects, an experimental study of basic switching strategies for automatic devices under different fault conditions is carried out to check the correctness and effectiveness of the switching strategy, which provides important technical guidance for the implementation and application of the device.

Abstract:Power flow calculation is the basis of power system calculation, and its core is LU decomposition calculation. Therefore, the key to power system power flow calculation acceleration is LU decomposition acceleration. Currently, parallel algorithms based on central processing units (CPU) have matured and limited space for performance improvement. As a coprocessor, the graphics processor (GPU) has powerful advantages in scientific computing and is widely used in power system power flow calculation. This paper first analyzes the GPU structure and parallel operation architecture, then introduces the LU decomposition principle, and selects the appropriate matrix sorting algorithm and sparse matrix storage model. The GPU-based single LU decomposition is realized by the unified computing device architecture (CUDA) programming model. Parallel acceleration with batch LU decomposition. Finally, five different cases were tested on the simulation device, and the acceleration effect of the parallel algorithm was compared and analyzed. The simulation test results show that the GPU-based batch sparse LU decomposition parallel algorithm can obtain an acceleration effect of 25~50 times on average.

Abstract:The primary frequency regulation of generator is import to frequency rapid recovery of power grid, this paper focuses on the ability of primary frequency regulation, an estimate scheme based on WAMS data is proposed. Based on enormous WAMS history statistic data, date and frequency difference two factors are considered. the ability of primary frequency regulation of single generator and power grid is estimated, the program is running in Jiangsu WAMS and providing decision support for power grid dispatching control.

Abstract:Parameter identification based time domain equivalent modeling method of wave farm is proposed. The wave data measured in any measuring point of the Archimedes wave swing (AWS)-based wave farm and the total output power of the wave farm are used to identify the parameters of the equivalent mechanical model by Particle swarm optimization(PSO) . The detailed model of the wave farm considering wake and time-lag effects are built via MATLAB/Simulink. Simulations are performed using multiple sets of measured wave data to validate the effectiveness of the proposed method. The simulation results show that the equivalent parameters identified under different measured data are stable and reasonable. For the equivalent model identified by the first set of measured data, the output power of the equivalent model and the detailed model fit well under the other three sets of measured wave data.

Abstract:In order to improve the security of scheduling decision and enhance its ability to deal with occasional line contingencies, a two-stage robust unit commitment model considering N-k network security constraints is proposed . Firstly, two kinds of N-k uncertainty sets used in the current research are introduced, and the characteristics of the set are described. Secondly, based on the two kinds of N-k uncertainty sets, a general form of two-stage robust unit commitment model is constructed. The formulation is divided into two stages, where the first stage is the unit commitment decision before the line contingency, and the second stage is the economic dispatching decision as the worst case of line contingencies are observed. The first and second stage problems are reformulated into a master problem and sub-problem, respectively, So that the column-and-constraint generation (C& CG) algorithm can be used to solve the proposed two-stage unit commitment model in an iterative manner. By using linearization techniques and duality theory, both the master problem and the sub-problem can be converted into mixed integer linear programming (MILP). Finally, the validity of the proposed model was verified by the calculation and analysis of the IEEE 14 bus and IEEE 118 bus systems.

Abstract:The current research and application status of last line protection in HVDC project are summarized. To overcome its disadvantages in existing engineering application, a modular LLP strategy is proposed. The module is equipped in the controller of each valve group, and it consists of input signals, output signals and corresponding LLP logic. When LLP is activated, if there is no power line connected to the valve group in service through the busbar and moreover certain auxiliary criterion is met, LLP would act and block the corresponding valve group immediately. Theoretical analysis and practical applications prove that the modular LLP can adapt to different kinds of HVDC and AC yard topology. The modular LLP is easier to configure , reuse and test. Without additional investment in hardware, the modular LLP can also achieve good performance in operating speed and reliability, and it will contribute to the safety and stability of the grid.

Abstract:The accuracy of load forecasting and the matching of planning are becoming more and more important. Due to the existence of forecasting errors, the results of different levels of load forecasting will be inconsistent and inconsistent in multilevel load forecasting. To solve this problem, a load coordination forecasting method based on information re-amendment is proposed. Firstly, the reliability of the prediction results is calculated by taking the prediction error of the prediction results one year before the prediction as the prior reference sequence, then the difference of load forecasting before and after the coordination of forecasting years under the same forecasting method is taken as a new reference sequence. Replace the original reference sequence, re-correct the information, and obtain new credibility. The coordination forecasting model is established by using this credibility, and then the coordination results are obtained. Finally, the correctness of the proposed method is verified by the analysis and calculation of an example.

Abstract:With presence of hybrid bad telemetry data and error parameter in power system, the validity of parameter identification and estimation methods of whole network cannot be guaranteed due to the fact that bad data will affect the parameter identification accuracy. It presents a detection and identification approach of bad-data based on augmented state estimation. First of all, the bad data are estimated whether they are bad telemetry data or parameters with error according to the residual balance degree. After deleting bad telemetry data, parameters with errors are kept within a certain area using node partition and then are modified according to augmented state estimation. The example results show that the proposed method can identify the bad telemetry data and parameters with error effectively, and interaction between the bad data can be avoid through parameter partition, so that the estimation accuracy of the suspicious parameters can be improved.

Abstract:In order to improve the working efficiency of Mach-Zehnder interference fiber optic sensing technology applied to the field of underground urban medium and low voltagecable anti-external force damage warning, it is necessary to clarify the relationship between the interference voltage signal and its vibration force. Firstly, the paper theoretically analyzes the relationship between the interference voltage and the vibration force, and points out that when the external environment is certain, the rate of change of the interference voltage is only related to the vibration force. On this basis, the design experiment is carried out to study the relationship between the vibration wave propagated on the rigid cement surface and the interference voltage signal, and the propagation and attenuation laws of the vibration wave and the interference voltage signal are compared and analyzed. The results show that the peak value of Mach-Zehnder′s interferometric voltage change has a positive correlation with the magnitude of the vibration force. The peak value of the voltage change speed can be used as the feature quantity to predict the distance or strength of the intrusive external force from the underground cable.

Abstract:Due to the accurate identification of wave front can improve accuracy of travelling wave fault location in distribution network, the paper used improved Hilbert-Huang transform to discern the travelling wave front, firstly, used the complete ensemble empirical mode decomposition with adaptive noise to decompose fault signal, then got instantaneous amplitude of high-frequency intrinsic mode function components by using Hilbert transform. The wave front could be recognized by the breakpoint of instantaneous amplitude. After using the above methods to discern the travelling wave front,for uniform line,used type D measuring distance technology to realize distance measurement, for hybrid line composed of overhead line and cable, fault location could be realized by utilized the two terminal method based on the difference of travelling wave propagation time at each connection point. Through simulations, the proposed method can be verified to locate the fault accurately and reliably in the case of different fault resistance, different fault location, different fault time and etc.

Abstract:In order to solve the problem that most of the existing network monitoring system can not support the display of process layer network topology and virtual connection circuit, this paper proposes a network monitoring online system based on the process layer switch. The system includes the host monitoring system and the process layer switch. The host monitoring system obtains the preset process level network topology and virtual connection logic circuit by parsing the SCD file. The process layer switch uses the ACL rule to capture and parse certain GOOSE and SV packets to obtain the device information connected to the switch. Then the host monitoring system obtains the actual process level network topology and the virtual connection physical circuit.Real-time monitoring and fault location of the process layer network are realized by comparing preset and catual network topology and virtual link loop. In practical applications, the system assists power system operation and maintenance personnel in real-time monitoring of network operation status and fault location, and improves the management level of power system automation operation and maintenance.

Abstract:In the process of manufacture, operation and maintenance of transformer, metal particles will inevitably be introduced into its internal insulation oil. In order to explore the influence of metal particles on the insulation performance of oil-paper, this paper builds a test platform for debugging lightning impulse discharge of oil-paper insulation, and carries out experimental research on the influence of metal particles on the development characteristics of oil-paper insulation. In this paper, the difference of initial voltage and development process of streamer with different concentrations of metal particles is studied and verified by COMSOL simulation platform. The results show that metal particles can promote the beginning and development of the streamer. The length and speed of stop and development of streamer are positively correlated with particle concentration, while the starting voltage and breakdown voltage of insulating oil streamer are negatively correlated with particle concentration. The analysis shows that the interaction between metal particles in oil and streamer is the main reason to reduce the starting voltage of streamer, accelerate the development of streamer, and then reduce the breakdown voltage of insulating oil.

Abstract:The complex electromagnetic environment in substation may disturb the electrical test in substation. By analyzing the interference signal, the basic principle of the adaptive filter is discussed. An adaptive signal separator are designed according to the minimum mean square error criterion and Least Mean Square (LMS) algorithm. The adaptive signal separator is used to analyze the suppression of low frequency narrow-band interference. With the help of the Fast Fourier Transformation (FFT) algorithm, frequency domain analysis is carried out. Moreover, the suppression of low frequency narrow-band interference is implemented and the practical electromagnetic clean space production device for substation is developed. The feasibility of the proposed design and the efficiency of the device are validated by the simulations in the lab. The field test results in 220 kV and above substations show that the electromagnetic clean space production device for substation based on this method can suppress the interference signal reliably and improve the test efficiency effectively.

Abstract:With the increase of urban development and energy demand, the electromagnetic influence of overhead alternating current (AC) transmission lines on buried steel pipelines is becoming more serious. Traditionally, the coupling voltage calculation methods mainly include electromagnetic simulation and calculation using earth loop equivalent model, which are complicated and time-consuming to get the pipeline coupled voltage. So, a method for calculating the coupled voltage on pipelines nearby the overhead transmission lines is proposed. Firstly, a calculation model for the unit-length pipeline coupling voltage under multiple factors is established. Secondly, by discussing the offset effect of insulation connection and pipeline breakage on the lowest point of inductive coupling voltage, the calculation method of the lowest point is given to determine the distribution form of pipeline coupling voltage. Finally, the calculation method of coupled voltage based on the increment of inductive coupling voltage per unit length pipeline and the distribution of coupling voltage is proposed. The example analysis shows that the error is less than 10% compared with simulated value and the measured value, and the coupling voltage can be reasonably calculated.

Abstract:In order to prevent the over heating defects of gas-insulated metal-enclosed switchgear(GIS) contacts and solve the problem of unable to measure the temperature of internal conductor in GIS by traditional temperature measurement, high-accuracy temperature detection of internal conductor in GIS based on infrared thermal imaging is proposed. Through a series of tests, the depth analysis of the optical path factors and the pressure of the SF₆ gas which have an impact on the accuracy of infrared temperature, the concrete relationship among the optical path factors, the pressure of the SF₆ gas and the measurement accuracy is gained. So is the compensation formula. According to the distance of the measured objects and the pressure of SF₆, a set of algorithm improving the measurement accuracy of infrared radiation thermometer to obtain the actual temperature of the contact measured is designed. It can combine with exact temperature compensation calculated by compensation formula. The final result of test shows that the infrared radiation thermometer with compensation algorithm can measure the temperature of the contacts in GIS more accurately.

Abstract:Excessive grounding current on metal sheath of single-core high-voltage cable will bring massive additional loss to the cable, which reduces the cable′s current-carrying capacity and safe operation lifetime. In order to analyze the grounding current in metal sheath, a mathematical model of grounding current calculation and relevant program are established aiming at single-core high-voltage cables in cross-bonding grounding mode. The calculation results prove that the program is competent to reflect actual grounding current. Furthermore, the relationship between grounding current and its influencing factors such as grounding resistance, sheath parameters and earth resistivity is analyzed. The results of analysis indicate that the grounding resistance has a great influence on the grounding current, while in actual engineering the parameters of metal sheath do not. Grounding current is sensitive to earth resistivity only when the value of earth resistivity is low. The research conclusions provide a theoretical basis for the operation and maintenance of high-voltage cables.

Abstract:In order to solve the problems in the design and implementation of current security access zone, such as poor universality, low transmission efficiency and lack of security, a design of power universal security access zone based on dual isolation is proposed. The design mainly includes the encryption and authentication device, the forward and reverse isolation devices and the universal access device. Based on the analysis of the structure and principle of the current security access zone, its shortcomings are given. By using universal access device, the design of security access zone is simplified, the no sense access of the two communication ends is realized, and the dual isolation of the security access zone and the encryption and authentication based on the state secret algorithm are realized. The results of test and verification prove the feasibility of the design and the test results of key communication and security parameters are given. Compared with the current schemes, the design has been improved in terms of universality, performance and security, and has good practicability.

Abstract:The 2×1 000 MW unit of Taizhou Phase II Power Plant is a demonstration project of energy saving and emission reduction technology in China during the 12th Five-Year Plan. It is also the first unit in the world applying supercritical secondary reheat power generation technology which was put into commercial operation in September 2015 and January 2016, respectively. Starting from the secondary reheat power generation technology, this paper systematically analyses the advantages of the boiler steel frame structure, heating surface tube arrangement, boiler temperature regulation and ten-stage extraction system in the unit of Taizhou Phase Ⅱ Project. It also analyses the operation of the unit in the past three years from three aspects of unit operation reliability, environmental emission index and economy, as well as the related units in domestic and foreign industries are compared. The results show that two Ultra Supercritical Secondary Reheating Units in the second phase of Taizhou Power Plant are stable in operation, excellent in environmental protection emission index and good in economic benefit index. Ultra supercritical secondary reheating power generation technology has been successfully realized in China.

Abstract:A fault location method for transmission line based on the weighting of reliability is proposed. First, reactance component is used to reduce the influence of transition resistance on single-ended impedance location algorithm. Second, using single-ended impedance location algorithm to determine the approximate range of the reflected traveling wave′s arrival time and solving the problem that single-ended traveling wave location algorithm can not accurately locate the fault in the second half of the line. Third, evaluating the reliability of single-ended impedance location algorithm, double-ended impedance location algorithm, single-ended traveling wave location algorithm and double-ended traveling wave location algorithm. The reliability evaluation criteria includes channel state, transition resistance, fault location and so on. Finally, the final fault location result is obtained based on the weighting of reliability. The simulation results show that the proposed fault location method has strong robustness and high accurate. It will not be affected by the factors such as fault type and line channel status.