2020, 35(1):3-13. DOI: 10.19781/j.issn.16739140.2020.01.001
Abstract:Coordinated planning for an integrated energy system (IES) could promote its operational security and economics, implement complementation among various kinds of energy systems, and improve the overall energy utilization efficiency. Given this background, the optimal planning problem of an IES with natural gas and heating networks is addressed. First, the mathematical model of an IES based on multiple energy hubs (EHs) is established, with the line pack of the concerned natural gas network, the heat loss and timedelay of the concerned heating network considered. Then, the optimal coordinated planning problem of an IES is addressed and a mixed integer nonlinear programming model attained, with an objective of minimizing its overall cost including investment and operation ones, so as to achieve the optimal placements of EH devices and energy networks. The optimal coordinated planning model is next transformed into a mixed integer linear programming problem by applying the incremental method, and then solved by the commercial solver Yalmip/Gurobi. Finally, an IES with six EHs is employed to demonstrate the proposed coordinated planning method. It is shown by simulation results that it is necessary to consider the characteristics of natural gas and heating networks in the IES planning, and the presented method is feasible.
2020, 35(1):14-23. DOI: 10.19781/j.issn.16739140.2020.01.002
Abstract:The integrated energy system can integrate multiple kinds of energy sources and effectively improve the utilization efficiency of renewable energy generation, and represents a significant means to promote the sustainable development of energy. The research on the impacts of multienergy connected on the power system has become an essential part for the development of the integrated energy system. In this paper, the damping characteristics of an integrated energy system with hybrid windfuel cells integrated are studied. The mathematical models of wind turbines and fuel cells are constructed and the stability analysis model of small disturbance then derived. The damping characteristics of the interconnected power system with wind power units and fuel cells under different operating conditions are studied for a sample power system, including different capacity ratios, different access modes, and different levels of tieline transmission power, using the eigenvalue analysis and timedomain simulation. The research results can provide a reference for the integrated energy system to accommodate renewable energy and operate stably.
2020, 35(1):24-30. DOI: 10.19781/j.issn.16739140.2020.01.003
Abstract:The cost prediction of an overhead line reconstruction project represents an important part of management and control of the project, and to improve the prediction accuracy, a combinational forecasting method is presented. An overhead line reconstruction project is first decomposed into several subprojects depending on the characteristics of the project, and the cost prediction could be made first for each subproject and then integrated. The principal component analysis and expertise of domain experts are combined to get the key factors of the subprojects. The genetic algorithm based support vector machine and extreme gradient boosting algorithm are then used for cost prediction respectively. The Shapley value theory in game theory is next employed to determine the weights of combinational forecasting so as to attain an appropriate combinational forecasting model. Finally, an actual overhead line reconstruction project is employed to demonstrate the presented combinatorial forecasting model, and more accurate prediction result is attained, compared with those attained by the genetic algorithm based support vector machine and extreme gradient boosting system independently.
2020, 35(1):31-39. DOI: 10.19781/j.issn.16739140.2020.01.004
Abstract:Before the spot electricity market is established, electrical energy is traded through forward contracts in the current medium and longterm electricity market in China. A reasonable balancing and settlement mechanism for electrical energy deviation is conducive to the smooth transition from the mediumand longterm electricity market to the spot market. Given this background, an assessment mechanism is presented for contract energy deviation in a mediumand longterm electricity market. First, the deviation settlement mechanism of the basic rules for the mediumand longterm electricity market is examined, and a generationside deviation balancing mechanism suitable for the current electricity market environment proposed. Then, considering the differences of the marketoriented electricity proportion and the differences in the capabilities of various users in controlling contract deviations, the risk of the electrical energy deviation penalty imposed on demand customers is analyzed. A fixedratio energy deviation settlement method is next designed for nontotal electrical energy transaction, and a staged assessment mechanism of demandside energy deviation proposed. Simulations based on actual deviation assessment data from a provincial electricity market in China show that the proposed energy deviation assessment mechanism is effective in the mediumand longterm electricity market.
2020, 35(1):40-49. DOI: 10.19781/j.issn.16739140.2020.01.005
Abstract:The wellestablished contract for difference (CfD) is a middleor longterm financial contract. When the CfD is applied in the electricity market, the electricity price can be fixed and the risk associated with the fluctuated electricity price in the spot market avoided. In recent years, with the advance of the power industry restructuring and the expansion of the pilot scope in China, the electrical energy CfD is included in the designed electricity market mechanisms in several provinces. Currently the implemented CfD contracts for electricity in provincial electricity markets in China are actually electrical energy contracts rather than electrical power ones, and hence it is necessary to decompose the contracted electricity energy into dispatchable electrical power demand curves. A brief overview of the electrical CfD is first presented, and the existing theories and methods from the perspectives of the rolling correction and optimization models based decomposition algorithms for definite contracted electrical energy are presented and compared. Finally, some problems associated with the decomposition of the contracted electrical energy in this round of power industry restructuring are prospected, and possible solved methods addressed.
2020, 35(1):50-60. DOI: 10.19781/j.issn.16739140.2020.01.006
Abstract:This paper proposes a transmissiondistribution interaction multiobjective dynamic random fuzzy optimal power flow method for wind integrated power system. It is a breakthrough of the traditional independent optimal power flow method for transmission and distribution network and that the distribution network is seen as load. Considering bidirectional power interaction between active distribution network (ADN) and transmission system (TS) and the randomfuzzy nature of wind power injection, with multiobjectives of economic lowcarbon and lossreduction, with respect to steadystate security and based on randomfuzzy chance constraint programming, transmissiondistribution interaction multiobjective dynamic randomfuzzy optimal power flow model is established. Randomfuzzy power flow of transmissiondistribution system is calculated through the randomfuzzy simulation, Newton Ralph method and forwardbackward sweep method. Based on this and considering transmissiondistribution interaction power and voltage, Pareto optimal frontier of each time period is obtained through lookahead and NASAII, and the maximizingsatisfaction method is adopted in decisionmaking. An illustration case based on modified IEEE 30 transmission system and IEEE 33 distribution system verifies the feasibility and superiority of the proposed method.
2020, 35(1):61-67. DOI: 10.19781/j.issn.16739140.2020.01.007
Abstract:The distribution network has inherent characteristics of long supply radius and complex structure. With the increasing of strong wave from load and DGs, the uncertainty of distribution network power flow is also increased and might causes the voltage quality deterioration in the distribution network. Therefore, it is necessary to rationally configure the DSTATCOM to improve the economic benefit of distribution network, ensure the voltage quality, and improve the DG accommodation. In this paper, a multiobjective coordinated optimization method are proposed for the DSTATCOM configuration and its setting in distribution networks, which considers the operation of DSTATCOM and the parameters setting problem in the process of optimal configuration. For distribution networks with DG, the optimization model of target system involves losses, a total investment of equipment, equipment idle rate and abandoned power generation of DG. The Pareto solution sets are obtained based on the NSGAII, and the weighted ideal point method is employed for decisionmaking. The outstanding characteristic of those methods is that it considers the configuration and operation of the DSTATCOM synthetically and the proposed method is verified by the example of IEEE33 bus sample system.
2020, 35(1):68-74. DOI: 10.19781/j.issn.16739140.2020.01.008
Abstract:If a power grid signal is analyzed by the FFT algorithm in the case of nonsynchronous sampling, it will cause the spectral leakage, and calculation precision reduction of active electric energy. In order to ensure calculation accuracy of fundamental and harmonic active electric energy, a timedomain calculation method for fundamental and harmonic parameters is proposed. Fundamental parameters are calculated by the integral of fundamental signal. On this basis, voltage and current signal models are established based on Fourier series. Fundamental and their harmonic parameters are then identified by using the RLS algorithm to match the sample data of voltage and current signals. As a result, the measured values of fundamental and harmonic active electric energy are obtained. The numerical simulation results show that the proposed method has high measurement accuracy of active electric energy. The optimal parameters of fundamental and harmonic are obtained by the sample data in only three rated cycle windows in working frequency. In this way, the active electric energy of the ten rated operating frequency period can be obtained in advance. Hence, it is an effective measurement method of active electric energy.
2020, 35(1):75-82. DOI: 10.19781/j.issn.16739140.2020.01.009
Abstract:The optimal allocation of SNOP considering operation efficiency and investment of distribution network is a multiobjective problem. In this paper, a multiattribute utility mergence method is proposed. Firstly, mergence rules are identified to achieve the aggregate utility according to the internal characteristic and logic relation of optimization indexes. Then, a SNOP allocation optimization model is built with the max aggregate utility value as the object. Finally, a case study of IEEE 33bus system is included to verify the effectiveness of the proposed model and method. It is shown that the multiattribute utility method for SNOP allocation can decrease active power losses, improve the system voltage level and load balancing level and increase the distributed generation penetration with a reasonable SNOP capacity.
2020, 35(1):83-89. DOI: 10.19781/j.issn.16739140.2020.01.010
Abstract:The problem of voltage safety and stability might occur when the wind power is connected to the power grid. In order to improve the voltage stability of the wind farm's grid connection point, this paper proposes a reactive configuration of the doublyfed wind farms on the basis of the calculation of load's safe domain. In addition, a collector line selection method is also proposed. Firstly, the P-Q characteristic curve of the wind turbine unit is derived, and the stable operation domain of the doublyfed wind turbine is obtained. Then, the P-Q characteristic curve and the boundary coordination problem of the safety end of collector line are analyzed to determine the collector line type, so as to fully utilize the nonfunctionality of the wind turbine. Finally, the reactive power allocation capacity of the wind farm is calculated through the security domain boundary of the grid connection point. The results of the example show that the proposed reactive power configuration method can ensure the grid voltage within the safe range.
2020, 35(1):90-95. DOI: 10.19781/j.issn.16739140.2020.01.011
Abstract:Cloud energy storage can aggregate a large amount of distributed energy storage and centralized energy storage control information. The wind farm can realize the controllability of the output power by renting cloud energy storage and selfbuilt physical energy storage. In order to extend the service life of selfbuilt energy storage equipment, a power allocation strategy is designed. Based on the life cycle cost of selfbuilt energy storage equipment, cloud energy storage energy lease cost, abandoned wind penalty cost, and minimum power shortage penalty cost, the optimal configuration model of the selfbuilt energy storage and the leased cloud energy storage capacity is established for a wind farm. Simulation analysis shows that the energy rental unit prices of different cloud energy storage will affect the cloud energy storage energy utilization, charge and discharge results, thus affecting the optimal configuration capacity of selfbuiltenergy storage. The reasonable allocation of cloud energy storage energy lease and selfbuilt physical energy storage has good economy and practicality.
2020, 35(1):96-101. DOI: 10.19781/j.issn.16739140.2020.01.012
Abstract:With the popularization of electric vehicles, the impact of electric vehicle charging is becoming prominent for power grids, and disorderly charging of largescale electric vehicles also have severe negative influences on the safety and reliability of the power grid and economic dispatch. On this background, considering the behavior characteristics of electric vehicle users, the economic dispatch of power systems is studied. Firstly, on the basis of the measured data, the uncertainty of electric vehicle charging is considered and the charging start time and duration are analyzed to obtain the time distribution of electric vehicle charging load. Secondly, the minimum sum of the coal consumption cost and the valve point effect cost of the system is taken as the objective function, and the penalty function method is applied to add function constraints. An economic dispatch model of power system is then established with the impacts of electric vehicle charging in consideration. Finally, the different charging behaviors of electric vehicles are simulated with cuckoo search algorithms respectively to verify the correctness of the proposed model, and the effects of different electric vehicles charging behaviors are analyzed for power systems.
2020, 35(1):102-108. DOI: 10.19781/j.issn.16739140.2020.01.013
Abstract:DC power distribution technology greatly reduces the use of converters. After applying this technology, the cost of power grid operation can be significantly reduced and the system reliability and stability is improved also. Under this background, a DC distribution network with both ends is considered, and a typical urban mediumvoltage DC distribution network topology is proposed and simulated. Firstly, the technical advantages of the DC distribution network is explored and compared with the traditional AC distribution network. Then, the feasibility is analyzed for structure of DC distribution network with both ends. Secondly, the power and voltage control model of AC / DC converter and the control model of DC / DC converter is established. Furthermore, the characteristics of photovoltaic and energy storage batteries are analyzed. It is found that the DC distribution network can reduces the converter's Investment and has the advantage of high efficiency and low cost. Finally, the DC distribution network system with both ends is modeled and simulated on the PSCAD / EMTDC platform. It is shown that stable operation of the DC distribution network is achieved by the effective control when photovoltaic, energy storage, and load power fluctuations exist.
2020, 35(1):109-114. DOI: 10.19781/j.issn.16739140.2020.01.014
Abstract:The accurate measurement of system capacitance current is the precondition and key factor for the correct tuning of the arc suppression coil in the resonance grounding system. On the basis of analyzing the existing problems in the capacitor current measurement method of distribution network, a new method for capacitor current measurement is proposed. By changing the inductance value of the arc suppression coil, the amplitude and phase of the neutral point displacement voltage and neutral point current of the system are measured before and after changing the inductance value. According to the formula, the total capacitance and conductance of the system are calculated. And then the rated capacitor current of the system is calculated. Finally, the MATLAB simulation proves that the method can achieve high measurement accuracy. The method is easy to operate and simple to calculate, and it can be used for the tuning calculation of arc suppression coil.
2020, 35(1):115-121. DOI: 10.19781/j.issn.16739140.2020.01.015
Abstract:More and more attentions are paid to the protection strategy for the MMC-HVDC. Due to the difference between the mmchvdc and traditional HVDC, a new flexible DC line protection scheme is proposed based on the boundary current. Firstly, transient characteristics of both ends of current waveforms are analyzed when various types of faults in HVDC lines occur in different positions. It is noticed that the line current in the rectifier is significantly greater than that in the inverter side during the transient process of internal fault. Comparably, there are no significant differences between the two ends of current value at external faults. Secondly, a DC line protection strategy for MMC-HVDC is proposed based on boundary current distance. Finally, the simulation and verification of protection strategy are carried out on the 21level MMC-HVDC system. It is shown that the proposed protection strategy can correctly distinguish the internal fault from the external fault, thus has high reliability.
2020, 35(1):122-129. DOI: 10.19781/j.issn.16739140.2020.01.016
Abstract:The VSC-HVDC system has a nice selfcommutated ability and can supply power to the passive network and weak AC network directly. In this paper, an adaptive control strategy is proposed for the inverter side of a VSC-HVDC system to overcome the problems of PI parameter tuning difficulties and the poor dynamic response of traditional double closedloop control. Firstly, the mathematical model of the VSC-HVDC system in the dq0 coordinate system is deduced with a discrete format. The prediction model of AC voltage control on the inverter side and the corresponding multiobjective optimization performance function are given. Then, the improved multistep strategy of model predictive control is designed by introducing the an incremental operator and the feedback correction link, which improves the parameter robustness of the prediction model. Finally, the VSC-HVDC power supplying system under different operating conditions is simulated to demonstrate the reliability and efficiency of the proposed control strategy.
2020, 35(1):130-136. DOI: 10.19781/j.issn.16739140.2020.01.017
Abstract:On the basis of the fuzzy mathematics theory and the evidence theory, an assessment model of bushing condition of transformers is proposed in this paper. Firstly, the hierarchical evaluation index system is constructed from the perspectives of qualitative and quantitative, which is based on experimental data and also considering the inspection tour program. Then, considering the shortages of single weighting in transformer condition assessment, this paper introduces a method to obtain the optimal weight. The subjective and objective factors are combined through solving the minimum deviation optimal function. Meanwhile, for the fuzziness and uncertainty of index information, the original reliability allocation of state variables are calculated and updated by adopting the fuzzy evaluation method. And then the modified evidence sources and combination rules are utilized to evaluate the bushing condition level. Finally, the results of case study show that this method is accurate and effective.
2020, 35(1):137-143. DOI: 10.19781/j.issn.16739140.2020.01.018
Abstract:In order to assess the insulation condition of transformer accurately, a comprehensive evaluation method is proposed on the basis of the grey matterelement analysis method. First of all, measurement results of insulation parameters and the actual operating condition of transformers are selected as evaluation indices to establish a multiindices evaluation system. Then, the grey matterelements are utilized to quantify eigenvalues of indices and then the condition of transformer more can be evaluated qualitatively and quantitatively. Meanwhile, the independence among indices is taken into account and correlation functions are constructed based on the matterelement theory. The multiindices evaluation problem is then transformed into a singleobjective assessment. However, the correlation between indices would bring duplicate information. To solve this problem, two objective weighting methods, which are the variation coefficient method and the multiple correlation coefficient method, are employed to calculate weights according to the importance of the indices. Finally, the improved method is applied to calculate the degree of grey correlation and the aging level of transformer insulation is evaluated. It is shown that this method is reasonable and feasible.
2020, 35(1):144-150. DOI: 10.19781/j.issn.16739140.2020.01.019
Abstract:The rolling bearing is a widely used mechanical part, but the existing technology has limitations on the fault diagnosis of rolling bearing. In order to improve the accuracy of rolling bearing fault diagnosis, a method of confidence rule base is proposed on the basis of fault samples by using historical data. Firstly, the typical faults of rolling bearing are analyzed, and their vibration data are obtained as samples to extract. The timedomain and timefrequency parameters are then fused and symptom parameters are extracted to build the confidence rule base of fault diagnosis. Finally, the abnormal data of rolling bearing are obtained through the experimental platform, which verifies the validity and accuracy of the established confidence rule base.
2020, 35(1):151-156. DOI: 10.19781/j.issn.16739140.2020.01.020
Abstract:Economic distribution (ED) is a typical optimization problem of power grid and it is also very important for power system energy saving. However, the optimization method based on the traditional particle swarm algorithm only considers speed and position parameters, which easily leads to local optimization. Under this background, taking into account the valvepoint effect of generators, an improved particle swarm algorithm is proposed for the active power distribution of power systems. The perspective parameter is introduced, and then the moving state of particle is decided by the new highdimensional parameters. The proposed algorithm can avoid the local optimal, reduce the search randomness and improve the optimization accuracy. Simulation results shows that the improved particle swarm algorithm with viewing angle parameters has a more efficient global search capability and a more reliable optimal solution, which provides an effective new algorithm for the power system economic distribution problem.
2020, 35(1):157-162. DOI: 10.19781/j.issn.16739140.2020.01.021
Abstract:110 kV flashover limiter has two kinds of installation method depending on the lower discharge electrode installed lower or higher than grading ring. In this paper, a finite element model is established for a 110 kV doublecircuit transmission line and the influence of installation type for the electric field distribution of glass insulator and grading ring is compared. It is shown that the lower electrode which is installed lower than the grading ring reduces the uniformity of electric field along the glass insulator, whereas the other installation method uniform the electric field along the glass insulator. Both two types of installation reduce the electric field at the outer surface of the grading ring. It is better that the lower discharge electrode is installed higher than grading ring when installing 110 kV flashover limiter on glass insulator.
2020, 35(1):163-168. DOI: 10.19781/j.issn.16739140.2020.01.022
Abstract:Nowadays, the manual inspection is considered as a low efficiency way for substation inspection. The potential abnormal for equipments might not be warned since. The temperature measurement of electrical equipments is inaccurate. Therefore, an temperature early warning system for substation equipments is proposed based on the mobile infrared temperature measurement in this paper. This system takes the inspection robot as a mobile platform and new technologies such as infrared temperature measurement, WiFi communications and remote monitoring display, etc are incorporated. It is able to conduct temperature measurement early warning. In addition, the effects factors of infrared temperature measurement error are analyzed and the BP neural network is employed to modify the infrared temperature measurement errors. The proposed system combines the absolute and relative temperature measurements early warning method so as to achieve the ideal early warning effect. It has been run successfully in Deqing substation to verify its rationality and reliability.
2020, 35(1):169-175. DOI: 10.19781/j.issn.16739140.2020.01.023
Abstract:According to the existing problems in the supervision of onsite operation in electrical power systems, an onsite operation monitoring and command system is designed. The onsite video is transmitted to command center via servicers by wireless networks. However, the realtime transmission of video can't be guaranteed due to the instability of wireless network bandwidth. The video transmission delay is long and the frames are lost seriously. In order to make the video transmission realtime and integrity, a video optimal transmission method considering the frame similarity is proposed in this paper. Firstly, on the basis of the characteristics of H.264 video coding mode, the frame similarity parameter is marked to distinguish the frame importance. The network bandwidth changes are then monitored in realtime and the PrioDrop scheduling algorithm is employed, so the important frames can be transmitted in advance. Finally, a test is included for verification. It is shown that the proposed optimal transmission method can improve the decoding quality of transmitted video, and achieve the requirements of realtime video transmission. It also provides a technical guidance to enhance the power supervision and strengthen the emergency command.
2020, 35(1):176-180. DOI: 10.19781/j.issn.16739140.2020.01.024
Abstract:The DC grounding system is one of important parts in DC transmission system. In order to ensure the reliable operation of DC transmission systems, it is necessary to develop live working tools for UHV grounding systems. In this paper, the overvoltage of grounding faults on BP and GR modes is calculated firstly and the maximum amplitude is 288 kV. Then, the switching impulse flashover tests are carried out in live working air gaps of a simulation tower. The routine method is employed and the live working safety distance is calculated as 0.65m. In addition, for the electric field strength at the surface of live working workers is generally less than 240 kV/m, the additional protection is not required for such electric field. Nevertheless, thermal insulation measures should be adopted due to the influence of hightemperature wire on the operating personnel and insulation tools. It is recommended to use the insulated rod operation method. Otherwise, necessary measures should be taken to ensure the safety distance when the direct work method is selected.
2020, 35(1):181-186. DOI: 10.19781/j.issn.16739140.2020.01.025
Abstract:Power transmission lines in the coastal areas of South China are often threatened by typhoons. This paper aims to study windresistance and windmonitoring technologies for typical cement poleline structures in 10kV distribution lines. Firstly, a windresistant monitoring system for poleline structures is established. Then, a method is proposed to determine the threshold in the monitoring system. A finite element model for a whole rodline is established. By using the fluidstructure coupling model to calculate the windrod system, the value of wind speed is transformed into the wind load which is generally used as the threshold of wind speed in early warning stage. Finally, the windresistant monitoring technology of polelines is verified by the monitoring results in practical operation. It is shown that the wind load at the surface of conductors is inhomogeneous. The wind load can be accurately calculated through the fluidsolid coupling model of the windpole system. And The structural response obtained by the model accurately reflects the actual stress state of the structure, which can be used to determine the threshold of wind speed in the early warning stage. The windresistant monitoring system of poleslines proposed in this paper has been verified by practical projects.