2022(4):3-12. DOI: 10.19781/j.issn.1673-9140.2022.04.001
Abstract:The phenomenon of resigning annual contracts in China medium-term and long-term electricity market highlights the theoretical and policy issues of optimal power combination decision making by multiple investors considering risk factors in 2021. Based on the independent decision making for power purchase in wholesale market and tariff packages in retail market, the decision making model of optimal power ratio of power salez business based on conditional value at risk (CVaR) is constructed for power companies, numerical calculation and analysis are carried out. According to the typical power purchase and sales business scenario for power companies based on the current provincial power market, this paper proposes a corresponding revenue or cost calculation method; uses CVaR as the risk assessment index, and takes the purchase ratio of different trading varieties in the wholesale market and the sales ratio of different tariff packages in the retail market as the decision variables. The optimal revenue-risk decision model aims to maximize the revenues. The impact of typical power transaction combinations and different confidence levels on the structure, revenue and risks of power transactions by power companies is calculated by combining the actual data of Guangdong power market. The paper analyzes the reasons for resigning contracts based on the objective models and simulation, and provides a basis for investors, including power companies, to make decisions on power purchase and sales considering risk management and the government's annual market trading scheme.
2022(4):13-19. DOI: 10.19781/j.issn.1673-9140.2022.04.002
Abstract:As distributed power sources connected to the distribution network, the magnitude of the fault current and the direction of the power flow have been changed, and the relay protection setting of the distribution network has become more difficult. Aiming at the optimization problem of inverse time overcurrent protection setting for the distribution network containing DG, the uncertain factors of distribution network failure, the inherent properties of relays and the four requirements of relay protection is considered. The concept of "global historical average optimal solution" and dynamic inertia weight is introduced in the update process of particle swarm optimization. Finally a fixed value optimization method for inverse time overcurrent protection in the distribution network containing DG based on improved particle swarm optimization is proposed. The conclusion shows that the improved particle swarm algorithm can effectively prevent the fixed value solution from falling into the local optimal dilemma, and it is suitable for the fixed value optimization problem of the inverse time overcurrent protection in the distribution network containing DG.
2022(4):20-28. DOI: 10.19781/j.issn.1673-9140.2022.04.003
Abstract:This paper proposes a pulse power topology and its prototype implementation for power tower defect detection. The pulse power topology adopts new switching devices, which can meet the requirements of fast and adjustable pulse Defect detection of power poles and towers requires the generation of pulsed power supplies with sub-nanosecond rise times at voltages of tens of kilovolts. To achieve this, traditional pulsed power supplies are introduced into solid-state switching devices. The proposed pulsed power supply is designed as the topology structure which consists of multiple stacked coaxial layers, where each layer consists of a printed circuit board (PCB) containing multiple switching devices. Then, the 3D electromagnetic simulation analysis of the proposed pulse power supply is carried out, and a 5 kV pulse power supply prototype is designed. The test prototype can achieve a pulse rise time of 6 ns under a load of 2.5 kV and 50 Ω, verifying that the proposed power supply can generate flexible pulse waveforms, verifying the effectiveness of the proposed design method.
2022(4):29-37. DOI: 10.19781/j.issn.1673-9140.2022.04.004
Abstract:The frequent occurrence of natural disasters make a serious threat to the reliability and safety of power supply in distribution network. Under the background, the distribution network elasticity improvement technology for the medium and low voltage power system considering user demand response is studied to enhance its fault recovery capability. Firstly, the demand of reliability for user's differentiated power supply and the operation characteristics of demand response is considered, and then an index to measure the resilience of distribution network is established-outage loss. Secondly, a demand response control strategy is proposed on the basis of the power supply priority. In th end, an optimization model of distribution network resilience enhancement considering demand response is developed. The IEEE 33-bus system is simulated to verify the index and the model. It is shown that the optimization model of resilience enhancement can significantly reduce the outage loss in the whole process of resilience restoration in distribution network and improve its resilience under disaster scenarios.
2022(4):38-44. DOI: 10.19781/j.issn.1673-9140.2022.04.005
Abstract:The frequent occurrence of forest fires in recent years has led to major casualties and significant losses of the national economy, affecting the operational safety of the power grid. Besides lightning, human and other factors, whether the power line tree failure triggered is also a highly controversial issue in the investigation of the cause of the occurrence of forest fires. This paper takes the medium-voltage line as the main research object, a flame and tree-line discharge test platform is built. The fault characteristics of tree discharge near the line, tree discharge due to external factors hitching on the line and line discharge when the flame appears below are studied, and the identification basis of line fault causes by mountain fire or tree is proposed. Finally a theoretical model of tree grounding fault, which can predict the amplitude of electrical parameters such as leakage current is proposed. This study can provide ideas to the prevention of tree line faults in the power grid caused by mountain fire.
2022(4):45-56. DOI: 10.19781/j.issn.1673-9140.2022.04.006
Abstract:The integration of distributed generation (DG) to the distribution network and the random characteristic of DGs and load fluctuations increase the complexity of system optimization and control. In this paper, an adjustment strategy for partitioning is proposed considering the influence of DG integration on system voltage and reactive power partitioning based on the temporal characteristics of "source-load". Firstly, based on the principle of voltage and reactive power partitioning, four indexes containing regional reactive power balance, inter-regional coupling, intra-regional coupling, and regional reactive power reserve are selected as, and a fuzzy clustering partitioning model is established based on the augmented voltage and reactive power sensitivity matrix. Secondly, the characteristics of time series output of wind power and PV power, and typical daily load curve is analyzed to select the typical scenarios based on "source-load" time series. Then, a partitioning adjustment method is proposed considering the variations of the four regional evaluation indexes in multiple "source-load" scenarios. Finally, the simulation is conducted based on the modified IEEE 33-node system. And the results show that the sequential variation of the "source-load" affects the voltage and reactive power partitioning. Besides, the evaluation indexes of each partition can be controlled in a reasonable range based on the proposed partitioning adjustment method.
2022(4):57-64. DOI: 10.19781/j.issn.1673-9140.2022.04.007
Abstract:Due to the fact of insufficient peaking capacity in power grid, the wind curtailment becomes prominent in recent years. However, the regulation potential from a large number of coal-fired self-supply power plants is not fully valued and utilized. Under the background of current market policy, a short time-scale trading mode of power generation rights is designed with the consideration of captive power plants participating in transactions and promoting wind power consumption. The unit price of the transaction uses the hour as the time scale, and the settlement uses the day as the time scale. In addtion, in the self-supplied power plant, the electric heating device is employed to absorb wind power and participate in the joint heating. Thus, the thermoelectric coupling constraints of the unit is decoupled, and the power output of the unit is reduced. Finally, The lowest cost is selected as the objective, and a clean alternative cogeneration dispatch model is constructed for wind power plants. Simulation results show that this method effectively improves the level of wind power consumption, reduces the operating cost of captive power plants, reduces coal consumption, and realizes clean replacement of electric energy.
2022(4):65-77. DOI: 10.19781/j.issn.1673-9140.2022.04.008
Abstract:The movement and parking of electric vehicles between different types of planned land have regular patterns. Based on the different charging and discharging needs of residential areas, industrial areas, and commercial areas, a mobile energy storage model for electric vehicles has been established. In addition, in order to better reflect the advantages of mobile energy storage for electric vehicles in load management, the power grid, vehicle owners and charging/discharging places are comprehensively considered, and a multi-objective optimization model is constructed with the goal of minimizing the load standard deviation and maximizing economic benefits. The Pareto optimal front surface is obtained through the fast non-dominated sorting genetic algorithm (NSGA-II), and the fuzzy membership method is used to find the compromise optimal solution. Finally, a simulation of the charging and discharging case of mobile energy storage for electric vehicles consisting of three residential areas, one industrial area and one commercial area is carried out to verify the effectiveness of the proposed model and strategy.
2022(4):78-87. DOI: 10.19781/j.issn.1673-9140.2022.04.009
Abstract:The location and capacity planning of electric vehicle charging stations are closely related to the travel characteristics of electric vehicle loads. Therefore, only when the charging load demand is reasonably predicted can an effective charging station planning result be obtained. To this end, this paper firstly defines the state space of electric vehicle charging load in multiple dimensions, and the probability matrix of state transfer of charging load can be established consequently. Furthermore, a Markov Chain Monte Carlo (MCMC) load forecasting model based on the multi-dimensional state space of electric vehicles travelling is proposed, the spatial-temporal prediction distribution of charging load is obtained by combining the real-time sample data. Then, a two-level programming model considering the economic benefits and user satisfaction of enterprise station construction is established. With the variable weight particle swarm optimization, the optimal site and scale of charging station can be determined. Finally, the simulation results can demonstrate the rationality and effectiveness of the model and method.
2022(4):88-96. DOI: 10.19781/j.issn.1673-9140.2022.04.010
Abstract:Many wind and hydropower stations are connected to the grid in mountainous areas, which brings excellent reactive power resources to the grid in the mountainous areas. The traditional regional optimization control method of Automatic Voltage Control (AVC) relies on state estimation data. The state estimation data of the grid in the mountainous area cannot frequently meet the real-time control requirements. The traditional AVC regional optimization control method can not be implemented generally in the grid in the mountainous area. Moreover, these wind and hydropower reactive power resources can not play an effective role. As a result, the voltage control of the grid in mountainous areas is difficult, the voltage qualification rate is low, and the power loss is high. To solve this problem, this paper proposed a novel regional optimization control method of reactive power & voltage for the grid in the mountainous areas based on the existing AVC system. It does not rely on state estimation data. According to the mountainous area grid's different voltage and reactive power control objectives, the corresponding optimal control strategy is presented and sorted by priority. An accurate selection method of 10 kV bus voltage control target value is proposed and the control target value of 10 kV bus voltage is corrected periodically according to the station voltage in the power supply area. The feasibility and effectiveness of the proposed method are verified by the practical application of a typical mountainous power grid. Without relying on the state estimation data, the proposed method can significantly improve the voltage qualification rate of the applied mountainous power grid, reduce the power loss of the grid and, provide a large amount of reactive dynamic support power as well.
2022(4):97-104. DOI: 10.19781/j.issn.1673-9140.2022.04.011
Abstract:Travelling-wave location method which can locate transmission faults precisely is widely used in transmission networks. However, only the electrical distance is given generally during practical applications. If the influence of span and sag is not taken into account, notable deviation between the calculation result and the actual fault location especially in long-distance transmission line will impact. In complex terrain areas, this misjudgment of fault locations will greatly affect the efficiency of inspection and overhaul. To handle this, an accurate fault location method considering the influence of span and sag is proposed in this paper. Firstly, the Haversine formula is used to compensate the transmission line span. Then, considering the structural parameters of the tower and the actual temperature, a catenary model is built, and the electrical distance can be compensated via the compensated span length. Finally, a double-terminal traveling wave positioning method is utilized to obtain the precise location of the fault. According to the actual parameters, a 500 kV transmission line is built in PSCAD/EMTDC, and different faults are set at different positions. Multiple sets of experimental results show that this method can improve the accuracy of the traveling wave location method.
2022(4):105-113. DOI: 10.19781/j.issn.1673-9140.2022.04.012
Abstract:In order to solve the low accuracy of high-resistance grounding fault selection in small-current grounding systems, a multi-criteria grounding fault selection method based on the changing amount of zero-sequence current is proposed from the perspective of active regulation of neutral point voltage. Multiple grounding levels are uniformly set on the system side of the special grounding transformer. When a single-phase ground fault occurs in the system, the grounding level size is flexibly adjusted to suppress the fault phase voltage until no higher than the fault arc reignition voltage. If the fault arc can not be extinguished, the line will be judgedas a permanent ground fault line. In that case, the transformer grounding level will be decreased to amplify the fault feeder zero sequence currentand the non-fault feeder zero sequence current. The difference between the zero sequence current increase and decrease of each feeder before and after the lowering gear level can then be incorporated for line selection. Next, in the case of large transition resistance, the non-faulted feeder zero sequence current has a linear trend and the faulted feeder zero sequence current has a non-linear trend, and the degree of this non-linear distortion of each feeder zero sequence current can be exploited in line selection. Simulation results show that the method can achieve rapid extinguishing of the fault arc for transient grounding faults, can accurately identify ten kilo-ohm grounding fault feeders for permanent grounding faults, and effectively improving the accuracy of high resistance fault selection for small current grounding systems.
2022(4):114-124. DOI: 10.19781/j.issn.1673-9140.2022.04.013
Abstract:The transition from passive power distribution network to active power distribution leads to the change of network structure, which results in the significant increase of risk in operation and maintenance work. This paper proposes a verification method about the safety of grounding wire in medium-voltage active distribution network based on Ondendonks formula. Considering the situation that the staff in the medium voltage side for maintenance, the distributed generators are divided into two types, which are rotating machine-based generator and inverter-based generator. On this basis, the short-circuit current generated at the grounding device due to mis-operation and device reasons is calculated according to the superposition theorem. The cross-sectional area of the grounding device is selected by using the Ondendonks formula preliminarily, and then the secondary check is carried out by calculating the single-phase and three-phase residual voltage. Finally, reliable grounding measures can be obtained on the basis of the actual topology. The feasibility and effectiveness of this method are validated by the application in a practical case.
2022(4):125-133. DOI: 10.19781/j.issn.1673-9140.2022.04.014
Abstract:The cyber physical distribution system (CPDS) is designed to realize the interoperability and deep integration of physical and cyber systems, so that it can obtain better operating effects beyond the traditional distribution system. At the same time, it also brings potential negative impact on the reliability and security of distribution systems’ operation. Therefore, it is of great significance to study the vulnerability of the CPDS considering cyber-physical interactions. Considering the islanded operation of power grids, this paper analyzes the influence of network topology and coupling mode under different attack strategies on CPDS, and explores the strong robustness of the CPDS network topology based on the theory of interdependent networks. The simulation results show that: high-betweenness node attack is the most destructive to CPDS network model, and the CPDS with small-world characteristic cyber network has the strongest robustness. Different network coupling modes have different vulnerabilities to different attack modes. Compared with random coupling mode, assortative coupling mode has stronger robustness to random attack, but assortative coupling mode has worse robustness to target attack mode.
2022(4):134-142. DOI: 10.19781/j.issn.1673-9140.2022.04.015
Abstract:In distribution network, the application of distributed power resources such as photovoltaics and battery energy storage systems can achieve flexible and efficient reactive power compensation.Therefore, the reactive power dispatch and energy storage optimization considering distributed power sources is proposed.The operating cost is selected as the objective function, and thebackward-forward sweep algorithm and approximate fitting method are combined to optimize the reactive power dispatch and energy storage method of distributed network. In the end, the actual solar radiation data and system operating data are employed to verify the effectiveness of the proposed method in two power distribution systems. It is shown that this method does not depend on the initial solution and parameter tuning. Its solution speed is 50 times faster than the existing common algorithms, and can be utilized for real-time scheduling.
2022(4):143-151. DOI: 10.19781/j.issn.1673-9140.2022.04.016
Abstract:In order to solve the problem that the number of charging piles is insufficient and the platforms of each charging pile operator are independent, a strategy of sharing platform of EV charging piles based on block chain is proposed in this paper. Firstly, the feasibility of building platform with block chain is anaylzed, then the electric vehicle charging pile sharing platform is established on the basis of block chain and the workflow of the trading platform and user utility function is designed. Secondly, a three-layer charging pile strategy is constructed to find the optimal charging pile for EV users by introducing the particle swarm optimization (PSO) algorithm. Finally, the simulation results show that the platform security can be improved by utilzing block chain, and the user utility function is improved at the same time. The three-layer charging pile strategy can find the optimal charging pile in terms of different needs of users. With the proposed stratrgy, the charging cost of users is reduced, the utilization ratio of charging post is increased and the collective charging number of EVs is reduced at night.
2022(4):152-160. DOI: 10.19781/j.issn.1673-9140.2022.04.017
Abstract:Deploying energy storage is an effective way to solve the problem of negative peak regulation and random fluctuation of wind power output. The impact of the actual service life of energy storage on the cost of energy storage and the integration of the day-day and day-day scheduling demands of wind power grid connection are seldom taken into account into the energy storage configuration of wind farms. This paper establishes the actual service life annual value model with the consideration of the characteristics of the service life loss of electric energy storage to. According to the scheduling demand characteristics of wind power in the day-day and day-day phases, battery and supercapacitor are preliminarily determined to meet the scheduling demand of day-day and day-day phases. In order to meet the requirements of wind power grid-connected technology, the energy storage allocation strategy was carried out with the goal of annual operating income of wind farm as the target, which take into account the integrity of wind power dispatching demand in the day-day and day-day phases. An optimal allocation model of integrated energy storage for wind farm was further established, which considers the annual service life of energy storage. An actual wind farm is taken as an example for simulation analysis, and the effectiveness of the proposed energy storage configuration method is verified. The configuration method in this paper can effectively utilize the integrality of day-day and day-day demand correlation in the process of wind power grid connection, and can provide some guidance for the application of energy storage configuration in actual wind power projects.
2022(4):161-168. DOI: 10.19781/j.issn.1673-9140.2022.04.018
Abstract:Driving intention is an important factor affecting the energy distribution of hybrid energy vehicles. Considering that the low-frequency part of the demanded power has less impact, which can be borne by the battery first, and the high-frequency part has more impact, which can be borne by the supercapacitor first. A hybrid electric vehicle power distribution control method based on driving intention recognition is proposed, which increases the consideration of the "human" factor based on of only considering the "vehicle" factor in the traditional control strategy. Compared with the traditional control strategy, the battery's output current in the proposed strategy is smoother, the power fluctuation is reduced by 23.72%, and the output power fluctuation of the supercapacitor is enhanced. Under this strategy, the average energy consumption per unit mileage of the whole vehicle is 32.61 Wh/km. The simulation results show that the proposed strategy can make full use of the dynamic characteristics of the energy storage system and effectively prolong the battery life.
2022(4):169-174. DOI: 10.19781/j.issn.1673-9140.2022.04.019
Abstract:The thermal effect of current is the main cause of cable service life and aging failure. It is very important to establish the cable temperature characteristic model. Power enterprises should be able to correctly estimate the related aging failure rate of distribution network cables. However, the existing cable failure rate estimations are calculated at the rated temperature and do not take into account the effect of actual operating temperature changes. Therefore, a method based on artificial neural network is used to estimate the maximum temperature of the cable. This temperature variation is in good agreement with the daily load curve in some extent. The artificial neural network only needs four easily obtained input variables, and the life loss at each stage of the predicted temperature curve is estimated by using the combined electric heating life model of cable insulation. Finally, the life model and probability failure model are used to predict the failure rate of power cables in the future. The results show that the estimation of failure probability is in good agreement with the actual results, which indicates that the three-stage gradual change curve of cable temperature can truly reflect the cable transient temperature change.
2022(4):175-182. DOI: 10.19781/j.issn.1673-9140.2022.04.020
Abstract:The gas distributed energy system (GDES) is becoming a new and important field of clean energy utilization. Considering different environmental characteristics according to local conditions is an important premise for the orderly promotion and healthy development of GDES. It is necessary to establish a systematic and scientific index system to evaluate and compare GDES in different regions. This paper identified the influencing factors of GDES developments through a literature review. Total 16 quantifiable indicators were concluded from 4 aspects involving resource conditions, energy environments, economic environments, and social environments. An evaluation index system of regional GDES development environments is established. Then, a combined weighting determination method was applied to evaluate and rank the GDES development environments of 31 provincial administrative regions in China. According to the evaluation results, the development environments were divided into five categories, and the differences in resource conditions, energy, economic, and social environments were compared. According to the different environmental characteristics of the five categories, a series of development strategies was suggested.
2022(4):183-188. DOI: 10.19781/j.issn.1673-9140.2022.04.021
Abstract:Considering the security authentication requirements due to the massive power terminals in the smart grid scenario, the problem of safe and convenient storage and use of keys in power terminals is studied, and a power terminal security authentication scheme is proposed based on SM9 threshold signature.First of all, the certificateless identity-based cryptographic technology is applied to the power terminal and it can solve the defect that certificate management in the original PKI protection system is relatively complex. Then, the threshold cryptography is introduced to improve the standard SM9 digital signature algorithm.The SM9 private key is split and then stored separately.When using the private key signature, a synthesizing signature is generated via an interactive calculation between the power terminal and the server. Based on this algorithm, a power terminal security authentication scheme is proposed.Finally, an example is analyzed to verify the correctness and security of the scheme.
2022(4):189-197. DOI: 10.19781/j.issn.1673-9140.2022.04.022
Abstract:To solve the problem of few PD defects detected by narrowband acquisition, it is necessary to study the active integrated sensor system with wide dynamic range. In this paper, according to the attenuation analysis of local electromagnetic propagation in GIS under coaxial waveguide model and HFSS simulation, it is found that a dynamic range of at least 40 dB is required for the effective detection of PD signal in long GIS. Secondly, through comparative analysis, the dynamic range of the system can be increased by logarithmic domain transformation, and the butterfly antenna with the optimized size is selected as the antenna for partial discharge detection. The standing wave ratio of the butterfly antenna is less than 2 in the frequency range of 730 MHz~ 1.05 GHz. Finally, a wide dynamic range of frequency-reduction analog circuit is designed, and logarithmic detection technology is developed for GIS partial discharge detection. This paper realized the antenna, detection circuit, signal conditioning and transmission highly integrated UHF local discharge detection sensor system. It not only has excellent signal-to-noise ratio but also greatly reduces the cost of the whole collection system, which has practical significance for PD detection and accurate operation and maintenance.
2022(4):198-208. DOI: 10.19781/j.issn.1673-9140.2022.04.023
Abstract:Influenced by the cannabis legalization of USA and EU, the illegal indoor cannabis cultivation got popular in China in recent years. Since indoor cultivation of cannabis has a large number of electricity consumption with distinct feature of electricity usage, A dectecting methed based on the relative entropy of the frequency distribution of electricity usage is developed to identify abnormal users in this paper. Firstly, the electricity usage data of indoor cultivate cannabis is generated from the laboratary simulation. Then, the electricity usage feature difference between the indoor cultivation of cannabis users and the normal residential users are compared in terms of the temporal, frequency domain and specific indicitors. Thereafter, the identification process of obnormal users of indoor cultivation of cannabis is proposed. In the end, a numerical analysis of electricity usage data from Irish residents suggests that the proposed approach can seperate residential users and anomaly users. It is helpful to identify the illegal user with the indoor cultivating cannabis.
2022(4):209-216. DOI: 10.19781/j.issn.1673-9140.2022.04.024
Abstract:The project configuration file in the intelligent substation has multi versions in multi-terminal applications and it brings problems that the archive configuration file might be different with that running set in the on-site intelligent substation. It has negative impacts on the power system operation since a lot of time is necessary for the revision of file setting. On the background, a mirror image management and control technology for smart substation engineering configuration is proposed in this paper. Firstly, a mirror management and control system for smart substation project configuration is designed and it is suitable for multi-terminal applications. And then, a whole process management process of smart substation engineering configuration files is established. Secondly, the intelligent substation engineering configuration verification and comparison are carried out utilizing the cyclic neural network algorithm and the Markov clustering algorithm. Thirdly, the image debugging is run for the intelligent substation engineering configuration file. Finally, a substation reconstruction and expansion project is included to verify that the proposed method can reduce the on-site transmission of reconstruction and expansion, and reduce the period and scope of power outages.
2022(4):217-226. DOI: 10.19781/j.issn.1673-9140.2022.04.025
Abstract:As the intelligent of substation is continuously improved, the power equipment is updated fast. The security risk of substation maintenance is gradually increasing. Under the background, a smart bracelet for the maintenance work of substations is designed to reduce the security risk in the maintenance work. The main functions of bracelet are heart rate monitoring, exercise detection and near-electricity alarm. Firstly, the overall function of the wearable bracelet is designed and involved key technologies are briefly summarized. Then, the chip selection, debugging and software flow design of the key functional modules such as the main control chip of the bracelet, the heart rate detection module, the fall detection module, and the near power alarm module are completed. In the end, the hand ring is tesed to verify the practicability of each function. The wearable device can improve the security of maintenance operations and the intelligence of substation safety monitoring system.