2020, 35(3):3-11. DOI: 10.19781/j.issn.16739140.2020.03.001
Abstract:In the distribution power system with its neutral point grounded by an arc suppression coil connected with the damping resistance in series, the existing method for the grounded parameter measurement is not accurate enough. Therefore, an improved resonance measurement method of grounded parameters is proposed for distribution power systems. In this paper, the influence from the damping resistance on the arcsuppression coil compensation is analyzed. And then, the equivalent circuit of resonance measurement is constructed respectively for two grounding modes whose arc suppression coils connect a damping resistance in series and parallel. In addition, the mathematical expressions of the distribution power system's grounded capacitance and grounded leakage conductance are derived respectively. A current signal with characteristic frequency is directly injected into the distribution network through the neutral point connected to the constant current signal source with the variable frequency, and the characteristic voltage signal is measured through the triangular side of zerosequence voltage transformer. In terms of the grounded parameter expressions, the fast and accurate grounded parameter measurement in distribution power system is realized by exploring the system resonance frequency. The correctness of proposed method is verified by PSCAD/EMTDC simulation. It is shown that this method has the high precision and wide application.
2020, 35(3):12-18. DOI: 10.19781/j.issn.16739140.2020.03.002
Abstract:Due to the complex structure and changeable operation mode, the distribution network frequently suffers from various types of damage such as a line break fault. It is reliability is relatively low since the feature of singleline break fault is not obvious and the conventional detection method is difficult to monitor effectively. In order to solve this problem, a real time monitoring method for the singleline break fault based on dualterminal information in distribution network is proposed in this paper. Firstly, the singleline break fault feature information is extracted by monitoring the relevant voltage and current signals on the power supply side and load side in real time. A comprehensive criterion is established for the identifying singleline break fault to realize the realtime monitoring of singleline break fault. This method can greatly improve the recognition accuracy of singleline break fault. Finally, the simulation is carried out on PSCAD/EMTDC. It is shown that the proposed method is not affected by the distribution line parameters and operation mode. It can effectively eliminates other faults and reliable and accurately identify the singleline break fault. Moreover, the monitoring process is accurate and fast to meet the realtime monitoring requirements for the safe operation of distribution network. It is valuable for engineering applications.
2020, 35(3):19-28. DOI: 10.19781/j.issn.16739140.2020.03.003
Abstract:In order to improve the stability and signal tracking ability of existing flexible grounding devices to suppress the threephase unbalance in distribution networks, a flexible grounding control method is proposed based on the improved double closedloop control strategy. Firstly, the control system is modeled and analyzed, and an injection current control strategy is proposed. This strategy is based on the double closedloop control and it adopts the current innerloop PI control and voltage outerloop hysteresis network control. By setting the reference value of neutral point voltage to zero and taking it as the control target, the difference between the reference value and the feedback value of neutral point voltage is compared in real time. And then the difference goes through the series lag correction. Thus, it can be treated as a reference current in the current inner loop. The deviation between the theoretical reference current and the actual measurement current is taken as the input of PI correction link. For the outer loop output, the target control for the output current is realized, the stability margin of current is effectively improved and the tracking time of output and input signals is shorten. The good performance of proposed method in threephase unbalanced overvoltage suppression is verified by a system simulation analysis. Neutral point voltage in distribution network is accurately suppressed to zero.
2020, 35(3):29-35. DOI: 10.19781/j.issn.16739140.2020.03.004
Abstract:Aiming at the problem of low accuracy of current line selection technology in distribution network protection, A method of line selection protection based on power angle clustering analysis is proposed in this paper. A variety of fault characteristics of each feeder under different operation conditions are collected, and the historical database is formed. Through fuzzy clustering analysis, the clustering centers of fault and nonfault classes are obtained. The realtime data of each feeder is collected to form the characteristic samples to be tested. The power angle similarity is used to analyze the similarity between the characteristic samples to be tested and the historical characteristic samples, and the samples to be tested are classified into fault or non fault categories, so as to realize the accurate selection of fault feeders in distribution network. The effectiveness of the proposed protection method is verified by PSCAD. The simulation results shows that the misjudgment of single fault feature caused by external interference can be effectively eliminated by the proposed method. No need to set the setting value during the line selection process, which can accurately realize the fault line selection of the small current grounding system.
2020, 35(3):36-45. DOI: 10.19781/j.issn.16739140.2020.03.005
Abstract:In recent years, the development of P2G technique has succeed a bidirectional energy flow between electricity and natural gas. It also enhances the coupling between the power and gas systems. P2G technique is a new approach which can rise up wind power accommodation. Under this circumstance, the economic dispatch model is proposed with the consideration of the electric and gas network constraints and energy transform equation of P2G. Its objective function aims to minimize the system operation costs of integrated electricitygas network embedded P2G. Besides, based on the interior point algorithm, Matlab simulation is included for this model. The test consists of an IEEE 39bus electric network and a Belgian 20bus gas network. Based on the proposed model, the wind power accommodation and low carbon effects is analyzed by considering the carbon captured by P2G under the given 5 scenarios. It is shown that the feasibility and availability is verified for the increasing wind power accommodation and low carbon effects in network with an embedded P2G.
2020, 35(3):46-54. DOI: 10.19781/j.issn.16739140.2020.03.006
Abstract:In order to refine the power dispatching plan, a load situational awareness method is proposed for the bus in the basis of the kmeans clustering and fuzzy neural networks. Firstly, the concept for the static dynamic potential of bus load is proposed. It characterizes the bus load state parameter and the trend of its state parameter change, and then the bus load situational awareness method is established. This method collects and processes the historical load situation information of the bus in the situational awareness stage. In the situation understanding stage, it adopts the kmeans clustering algorithm based on the elbow method which clusters the historical load situation information of the busbar considering the bus environmental factors and load factors. In the situation prediction stage, the Fisher discriminant analysis is utilized to classify the dynamic information of the day to be measured and predict its category of historical data clustering. Then, the historical static potential data of the category is substituted into the fuzzy neural network prediction model to predict the situation of the perceived daily bus load. Finally, a simulation is included to verify the effectiveness and feasibility of the proposed method. It is shown that comparing with the traditional fuzzy neural network prediction, the proposed bus load situational awareness method has the higher situation prediction accuracy.
2020, 35(3):55-60. DOI: 10.19781/j.issn.16739140.2020.03.007
Abstract:The iterative algorithm is widely used in determining the parameters of photovoltaic models. In order to study the convergence speed of using the different iterative to solve the PV parameters, on the basis of brief introduction on the characteristics of NewtonRaphson and GaussSeidel iterative algorithms, combining with nonlinear transcendental equation for the output characteristics of photovoltaic models, the equations of the output parameters for the photovoltaic models are deduced in detail with NewtonRaphson and GaussSeidel iterative method. We use the equations to derive the PV parameters of three different photovoltaic modules and analyze and test these results. The results show that NewtonRaphson iterative method is insensitive to the selection of initial values and has faster convergence rate under the same precision. Such method is more suitable for the calculation of photovoltaic model parameters.
2020, 35(3):61-67. DOI: 10.19781/j.issn.16739140.2020.03.008
Abstract:Aiming at the aggregation of coherent generator groups, based on an artificial fish swarm algorithm, a method is proposed to optimize parameters of the equivalent generator through the simulation of fish group behavior under the principle that the aggregate functions of generator group should be consistent with the transfer functions of equivalent generators in frequency domain. The proposed method can effectively solve the limitations of traditional aggregation methods in initial value setting, optimization direction constraint, local extremum, etc. The validation results of generator aggregation in New England 39bus system show the optimal parameters derived by the new method can better ensure that the frequency response and system transient characteristics of the generator before and after aggregation are basically the same and improve the accuracy of generator aggregation.
2020, 35(3):68-73. DOI: 10.19781/j.issn.16739140.2020.03.009
Abstract:The photovoltaic power generation depends on the uncertain external environment, therefore, the generated power has a relatively high fluctuation resulting a low ratio power access. The accurate forecasting of photovoltaic power can raise up its penetration and also keep a safe operation and dispatching of the power grid.In this paper, a prediction method for photovoltaic power is proposed based on information fusion theory. The dynamic neural network model is adopted. Then, the influence factors, which limit the photovoltaic power generation, are fully considered and a comprehensive influence factor lambda is proposed. After that, the gradient algorithm is utilized for optimization. For the period with high fluctuation, the forecast time interval is shorted and the number of layers is increased to improve the prediction accuracy. Finally, the feasible and effective of the proposed theory is verified at Yueyang photovoltaic power plant in practice.
2020, 35(3):74-82. DOI: 10.19781/j.issn.16739140.2020.03.010
Abstract:With the rapid increase and wide usage of distributed generation (DG), isolated island detection becomes an unignorable research problem. At present, most of the research on island detection focuses on the isolated island situation of the single inverter grid connection. The study on the island detection of multiinverter is relatively scarce. This paper analyzes the inverter interactions in multiinverter grid connection. In view of the problem that the line impedance angle between the inverters produces a dilution effect on the disturbance signal and leads to the failure of island detection, this paper proposes a sinusoidal droop control (SDC) island detection method. The nondetection zone (NDZ) of the method and its impact on the power quality of the power grid is analyzed. Experimental simulation results in Matlab/Simulink show that this method can effectively reduce the NDZ, reduce the impact of power quality to the grid, and can effectively avoid the dilution effect of line impedance NDZ.
2020, 35(3):83-91. DOI: 10.19781/j.issn.16739140.2020.03.011
Abstract:Under the circumstances of development for scaled electric vehicles (EVs), it is of great significance to rationally control and optimize the EV charging load and carry out the structure planning of the active distribution network. This paper establishes a bilevel model for structure planning of active distribution networks based on the regulation of the EV charging load. Firstly, taking the uncertainties of distributed generation and load into consideration, the main process framework for EV charging load forecasting is constructed, and then the dispatching method of the charging load is described and the mathematical model of structure planning for active distribution networks is build up. In such a mathematical model, the planning layer aims at the lowest comprehensive economic cost for kilowatthour of electricity and the operational layer is targeted at minimizing the load curve variance. Secondly, in the process of model solving, the Prim algorithm is utilized to improve the population generation process of particle swarm optimization (PSO) and constraints are processed by a penalty function so as to improve the efficiency and precision of algorithm. Finally, the rationality and validity of the model are verified by an actual distribution network.
2020, 35(3):92-98. DOI: 10.19781/j.issn.16739140.2020.03.012
Abstract:In the background of power market reformation, the new power supply and demand service mode are emerging. A dispatching strategy of the intelligent electricity equipment group is proposed on the basis of the load resource reservation under those new modes. In order to meet the energy consumption demand of the renewable energy generation, such as the wind power, the main idea of regulating load is to reserve a part of the demand. The reserved resources are applied when there is demand for renewable energy consumption. Besides, under the mode of user's demand reservation, the load group control strategy is proposed based on genetic algorithm which guarantees the normal power consumption as the priority. Finally, a situation is included for verification. It is shown that the proposed algorithm effectively consumes the renewable energy generation while guaranteeing the user's electricity consumption demand, and the load curve is optimized at the same time.
2020, 35(3):99-106. DOI: 10.19781/j.issn.16739140.2020.03.013
Abstract:The traditional method is based on Weibull distribution fitting, which does not consider the difference of different circuit modules in the smart meter affected by different external stress, and lacks the influence of different stress factors on the life of the smart meter. So, an intelligent meter life prediction method based on adaptive weighting coefficient is proposed in the paper, which realizes an improvement of the whole meter prediction algorithm . This method starts from the historical data of product failure, finds out the relationship between the stress and the historical original failure rate, and obtains the stress adjustment coefficient K and the weighting coefficient R based on the historical original failure rate respectively. The stress adjustment coefficient K and the weighting coefficient R is utilized to modify the obtained predicted failure rate and achieve higher accuracy. The case study shows that this method can reduce the miscalculation rate of remaining life of batch electric energy meters, In the actual application process, the proposed method can provide the useful information for purchasing electric energy meters in advance for batch rotation, and avoid largescale failure of electric energy meters.
2020, 35(3):107-113. DOI: 10.19781/j.issn.16739140.2020.03.014
Abstract:The power system reformation changes the power market operation mode and deeply influences on the planning and operation of the power supply company. Under this circumstacne, the new planning requirement from the reformation is analyzed, and a bilevel distribution network planning model is established by considering DG and ILR under the environment of deregulated retailer market. The objective of upper level is to minimize the cost of investment and maximize power supply reliability and power quality. While the lower level make optimally decision to the DG output and ILR in the operation stage of distribution network. Besides, the upper level model is the mixed integer nonlinear planning and the genetic algorithm is employed. The lower level model is continuous nonlinear planning and it is solved by utilizing the prime dual interior point method. Finally, a modified IEEE33 bus system is included to verify the proposed model. The income of power supply company is analyzed. It is shown that introducing the power sales side market competition into the lower level of distribution network planning can suit to the change of profit pattern.
2020, 35(3):114-119. DOI: 10.19781/j.issn.16739140.2020.03.015
Abstract:In order to improve the power network stability involving the wind power, a twostage price adjustment strategy is proposed for electric vehicles based on the wind power prediction. This strategy promotes the wind power accommodation by predicting wind power and then regulating the price of electric vehicles. In the prediction stage, the LSTM neural network with a memory ability of time series is utilized to predict the wind power. At the pricing stage, an optimization model of price adjustment is established with an objective function of the high similarity between the predicted wind power curve and the charging load curve, and the small charging cost. The price is set based on the forecast wind power and then it is utilized to adjust the load so that the charging load is close to the wind power over time. Finally, a simulation is included to verify the effectiveness of the strategy. The charging load before and after optimization is compared. It is shown that the latter is closer to the prediction of wind power.
2020, 35(3):120-126. DOI: 10.19781/j.issn.16739140.2020.03.016
Abstract:As a new scheme of the distribution networks, the DC distribution network should be compared in detail with the AC distribution network in planning and design stage. Mean while, the voltage sags problems are also dominated in resent years. Under this circumstance, this paper studies the effect of DC distribution network which can relieve voltage sags occurs of the sensitive customers. Then, the life cycle cost (LCC) model of AC/DC distribution network is established by considering the economic and reliability impacts. It is shown that, in the case of 50% DC loads, even the DC distribution network has more initial cost and lower reliability, the LCC of DC distribution networks is better due to its ability to mitigation voltage sags and less loss. At last, the optimization method of AC/DC distribution network under different DC load ratios and power electronic device failure rate is proposed.
2020, 35(3):127-134. DOI: 10.19781/j.issn.16739140.2020.03.017
Abstract:Voltage transmission characteristics of power line communication (PLC) channel are asymmetric in medium voltage distribution networks. It is found that the asymmetry reduces the efficiency of establishing connection when the PLC device is tested at the medium voltage distribution network. In this paper, a PLC channel model is established based on the partial reflection theory. Then the forward and backward voltage transmission characteristics are analyzed in typical topologies of medium voltage distribution networks. The results show that under the condition of homogeneous trunk channel or overheadcableoverhead trunk channel, channel characteristics can be only analyzed in either direction of forward or backward. And for the condition of overheadcable trunk channel, only the channel characteristic of overhead to cable needs to be analyzed. The lateral network among trunk channels has a shunt effect on PLC signals. The channel quality is poorer when the signal is transferred from the terminal with a stronger shunt effect. In addition, the PLC device can select a better communication frequency by detecting the reactance component of the online input impedance.
2020, 35(3):135-140. DOI: 10.19781/j.issn.16739140.2020.03.018
Abstract:In order to reduce the induced voltage at the metal sheath of cables, as well as the circulation current of sheath in the cross interconnected grounding mode, the grounding mode of sheath is modified for the reconstruction of cable lines. Based on the defects of cross interconnection grounding in t he practical application, three kinds of the optimization scheme for grounding protection are proposed. There are the grounding of one side of the protective layer through the compensating inductance, single terminal grounding through the cross connection, and grounding at each section. The simulation models are built by utilizing PSCAD simulation software to study the voltage and circulation current at sheaths under different schemes. Theoretical analysis and simulation results show that those three kinds of cable sheath grounding can effectively suppress the metal sheath end induction high voltage. The sheath circulation current produced after the line reconstruction can be reduced. The optimization schemes for cable sheath grounding can be utilized as the engineering practice in the future direction of promotion.
2020, 35(3):141-147. DOI: 10.19781/j.issn.16739140.2020.03.019
Abstract:The wind power penetration of power system is increasing rapidly, while the wind abandoning phenomenon is getting more serious. The lack of thermal power and hydropower's peaking and frequency regulation ability is one of the main reasons to restrict the utilization efficiency of wind power. Under this circumstance, the wind generator vector control, rotor kinetic energy control strategy principle and rotor kinetic energy control strategy process are analyzed in this paper.Firstly, based on the analysis of the range of wind generator operating area and rotor kinetic energy control, a frequency regulation scheme is proposed to match the wind generator's frequency control capability. According to the running condition, DFIGs are controlled reasonably to participate in system frequency regulation. Control parameters could be optimized by the wind speed, which can effectively give full play to the frequency regulation ability of wind power without any additional investment, avoiding the risk of wind generators excessive participating in frequency regulation and improving the operational efficiency of wind power. Finally, the validity of the scheme are verified by a simulation in DIgSILENT/PowerFactory.
2020, 35(3):148-154. DOI: 10.19781/j.issn.16739140.2020.03.020
Abstract:Regarding to the lowfrequency oscillation problem brought by AC/DC hybrid system involving the wind power, the characteristics of weak or negative damp lowfrequency oscillation for AC/DC hybrid system with permanent magnetic synchronous generator (PSMG)based wind farms are studied in this paper. Firstly, a DC transmission dynamic model of is analyzed by considering direct drive wind turbines, full power ACDC converters, as well as the constant current at the rectified side and constant voltage at the inverter side. Then, a differential equation model is established to study the stability of small interference in PSMGbased wind farms. The stability of small interference of a DC transmission system with CEPRI 36 nodes is also analyzed under four different connection modes. In addition, the effects of two operation modes of wind farms participating active and reactive power dispatching on the characteristics of weak or negative damp lowfrequency oscillation are analyzed. The results show that the weak or negative damp lowfrequency oscillation of the system is better when the DC transmission system works under the mode of bipolar neutral grounding at both ends.
2020, 35(3):155-161. DOI: 10.19781/j.issn.16739140.2020.03.021
Abstract:Based on the theory of uniform transmission line, an equivalent circuit model and an equivalent distributionparameter circuit model are established respectively for studying the deicing process of transmission lines. The determinizing method for the optimal frequency and voltage of the deicing power supply is then given. A transmission line with the rated voltage of 110 kV is adopted as an example. Combinations of frequency and voltage are obtained at several dielectric loss angles. Finally, the effects from the frequency and voltage on the thermal power and power factor along the transmission line are analyzed by utilizing MATLAB/Simulink. The research results show that both frequency and voltage of the deicing power supply play a decisive role in deicing process of transmission lines. The proposed method can not only realize reliable and efficient deicing effects for icecovered lines, but also reduce the requirements of the deicing power supply on its power electronics selection in terms of switching frequency and withstand voltage level.
2020, 35(3):162-165. DOI: 10.19781/j.issn.16739140.2020.03.022
Abstract:A faulttolerant drive circuit for two phase hybrid stepping motor is designed. Although the hardware cost raises, the double Hbridge driving circuits have largely improved ability of permitting the mistakes by adding redundant bridge arm. This paper analyzes the topology of the main circuit in detail, and gives the block diagram of its normal operation. In order to verify the feasibility of the proposed scheme, the test bench is built with TI controller TMS320F28335. A part of function of the designed circuits is validated by the prototype.
2020, 35(3):166-172. DOI: 10.19781/j.issn.16739140.2020.03.023
Abstract:According to the characteristics of distribution automation system, such as wide range of points and wide distribution, a dual protection scheme based on "network layer + application layer" is designed. A password authentication protocol based on the combination of SM2, SM3, SM4 national secret algorithm and message authentication code (MAC) onetime password authentication is proposed to realize twoway authentication and encryption of service data between distribution master station and distribution terminal. Therefore, this protocol ensures the integrity and confidentiality of communication data, solves the problem of network security protection of distribution automation system. Once the multicore heterogeneous independent security chip is applied for hardware acceleration, the speed and efficiency of encryption algorithm will be improved.
2020, 35(3):173-178. DOI: 10.19781/j.issn.16739140.2020.03.024
Abstract:Aiming at the problem of how to effectively and reliably isolate the relevant secondary equipment during the expansion, rebuilding and overhaul of the smart substation, this paper presents a method of security measures online rehearsal and antierror warning of intelligent substation secondary equipment. This method establishes substation graphics files through the SCD model file, and correlates the information collected by the data acquisition unit and the substation graphics file, to get the initial state of substation safety measures while conducting rehearsal of secondary equipment safety measures and dynamically previewing the safety process rehearsal process. The example validation shows that the method can automatically warn against the incomplete safety isolation and provide an effective technical means for the maintenance personnel in the intelligent substation.
2020, 35(3):179-184. DOI: 10.19781/j.issn.16739140.2020.03.025
Abstract:Due to the lack of corresponding test equipment, key technologies and test procedures, the field accuracy calibration test is not fully carried out for the DC electronic voltage transformer (DCEVT) which is widely used in the power grid at present. Under this circumstance, its theory, transmission mechanism and error source are completely analyzed firstly. Then, for the fact that there is no synchronous signal port accessing in the converter station merging unit. A scheme of synchronous field calibration in different places is proposed, and the development of high accuracy field calibration system and uncertainty analysis is carried out. The proposed method is verified in Yongfu DC project, which provides a reference for the field calibration of DC electronic voltage transformer in converter station in China.