The comprehensive assessment of the investment and development status of county distribution system is an important part in distribution system planning and investment demanding analysis, and is also an important problem to be addressed. Considering that the assessment indices for county distribution system have the feature of multiple attributes, we firstly present an object-based comprehensive assessment index system. Then, we use the combination weighting method and the self-adaptive weighting correction to determine the weights of indices. The index weights are divided into ranking weights and classification weights in the combination weighting method, in order to respectively reflect the influence degrees of the overall difference of index sample values with different properties and evaluation objects on the evaluation results, which are determined by order relation analysis method and projection pursuit principle respectively, to determine the combination weight according to the principle of minimum identification information. Next, we adopt self-adaptive weighting correction for evaluation object weight whose indicator values seriously deviate from the normal range. Finally, we employ 5 county distribution systems in a province to demonstrate the proposed method, and use radar chart to find the weak links of power grid construction. The simulation results show that the proposed evaluation method can reasonably reflect the investment and development status of county power distribution system.
This paper introduces the Gini coefficient widely used in the national income allocation and environmental governance into the investment allocation scheme design of power network. Firstly, we use three indexes including the return on total assets, future forecasted electricity consumption in a given period and the ratio between investment and electricity sale, to determine the initial allocation scheme of future investment in a given power network under the premise of preferentially considering the efficiency/benefits. Then, we choose capacity-load ratio, reliability and other control indexes to develop the investment allocation model based on the Gini coefficient. And we determine the final optimal investment allocation scheme from the perspective of improving the allocation fairness, based on the initial allocation scheme of future investment. Finally, a provincial power company is taken as an example to demonstrate the feasibility of the proposed investment allocation model.
The reasonable and accurate prediction of energy consumption is of great significance for scientifically making energy plan and optimizing the structure of energy and industry. Aiming at the shortcomings of the traditional energy forecasting method, which has low prediction accuracy and not be fully accounted for the influence of environmental policies, this paper presents a combined forecasting and scene correction model based on the Shapley value theory. Firstly, according to the requirements and characteristics of energy consumption forecasting, we select three single forecasting models, and determine the weight of the single model in the combined model through the Shapley value theory to obtain the basic forecasting result. Then, three main aspects of technological progress, economic development and policy change are quantified as the correction term and coefficient to further improve the model function and obtain the modified prediction results under different scenes. Finally, the case of life energy consumption in T City is studied. The results show that the forecasted value curve and actual value curve are highly fitted in the proposed method, which can improve the accuracy of energy forecasting based on the full consideration of environmental policy influence and provide decision basis for the energy planning of related departments.
This paper studies the supply and demand optimization method of urban energy systems. Firstly, taking the minimum total cost of energy system as the target, we establish the supply and demand optimization model of urban energy system with considering multiclass energy planning constraints. Secondly, we introduce the improved multispecies hybrid evolutionary algorithm to determine the optimal process of the model. Finally, we use the related results of the terminal energy consumption forecast model as demand constraints, and apply the model to the example analysis of T city. The results show that the optimal energy supply results during the future planning period obtained in the model can meet the requirements of urban energy relative policy documents, which will guide the energy supply of T city to clean and sustainable development direction.
According to the operation of electric vehicle charging/swapping station, we construct a systematic model for the cost benefit structure of charging/swapping station, and propose the cost benefit evaluation method of electric vehicle charging/swapping station based on life cycle analysis, with considering the charging/swapping infrastructure construction, the operations of charging station and swapping station, and the operation of monitoring and intelligent scheduling etc. Taking the planning data of charging/swapping infrastructure in Guangdong Province as example, we compare and analyze the cost benefits of electric vehicle charging/swapping station, and further analyze the influences of charging/swapping tariff, government subsidy, charging spots unit price and other factors on the profit and loss level of electric vehicle charging/swapping station.
Active distribution network (ADN) with more autonomy in dispatching is able to control distributed generators, energy storage equipments and active load, which can realize the efficient operation of distribution network. The dispatching schedule of main network and distribution network influences each other. Besides the operating cost, the coordination of main network and distribution network should be considered when we make the optimal schedule of ADN. This paper provides a real-time information interaction mode, carries out modeling analysis on active load and energy storage equipments, and proposes a coordinative dispatching model based on real-time pricing. In addition, a parallel optimization algorithm is presented aiming at the scheduling model. Simulation results on the IEEE 9 node system connected with a distribution network verify the validity of the model and the algorithm. Finally, we analyze the influences of demand response, energy storage equipments and power limit in interconnecting lines on the dispatching schedule.
To reduce the use of fossil fuels, more and more renewable distributed power is applied in power grid. Micro-Grid is an effective utilization mode for distributed generation；however, during the grid-connected operation of micro-grid, the frequency and voltage fluctuation of distributed generation will have great influence on main power grid. DC micro-grid can suppress the interference of these fluctuations. At the same time, the DC load of user terminal is increasing, and the DC grid will be the development trend of the future grid. Therefore, we construct a local network with using DC, and use the information of power for dispatching and routing DC power. The digital packet should be carried out for DC power in the DC local network. Then, the power supply and demand balance between distributed generation and load can be realized by transferring the power and its information through power routers. Finally, we present the power routing algorithm based on continuous shortest path, and carry out the simulation and analysis of this algorithm.
With the continuous improvement of the voltage level of transmission line, people pay more and more attention to the power frequency electromagnetic field problems. This paper analyzes the power frequency electric field effects of simplified human body model in 750kV AC transmission lines. In order to compare the distribution of induced electric field of human body with different postures, prolapsing and lifting of hands, taking an umbrella and walking human body model is built. Taking both hands prolapse model as an example, we study the influence of the height from the ground to the overhead transmission line on human electric field effect. The simulation calculation results show that the existence of human body will change the distribution of the electric field near the ground. There will be the maximum local field strength near the head, ear and shoulder of human body. The change of body posture will affect the distribution of induced electric field and the maximum local field strength always appears in the contour parts of human body. The higher the wire above the ground is, the smaller the electric field value on human body is. It can be concluded that the maximum local field strength of human body model in different postures is still within the numerical range of health and the power frequency electric field of 750 kV UHV transmission line won't cause harm to human body health.
To comprehensively evaluate the rationality and advantage of UHV AC-DC project timing programs during the whole construction period, this paper establishes the evaluation index system including economy, technology, security and stability, social environment and other factors. Considering the development characteristics of UHV AC-DC power grid, we suggest using transmission congestion fees, structure balancing, social environmental influence and other some conventional transmission network planning evaluation indexes such as steady-state security, to compose the comprehensive evaluation index system, in order to compare and analyze clean energy development adaptability, power grid structure balancing, the effect of energy-saving and emission reduction, etc. in different UHVAC and UHVDC project construction timing programs.
Considering the power system development in China, this paper summarizes the problems and solutions of the security and stability control for UHV AC/DC hybrid power system. Firstly, according to the structure of AC/DC hybrid system, we present a normal method of preliminary evaluation for the system, and analyze the stability problems and control requirements in the AC/DC hybrid system. Then, in combination with the AC/DC hybrid system in China power grid planning, we discuss the methods which use DC power emergency control, power modulation, frequency modulation, etc. to improve the stability of AC/DC system, and present study cases to verify the validity of the proposed methods. Finally, we discuss the future research direction according to the deficiency in the study of AC/DC hybrid system.
Integrated community energy system (ICES) can make full use of renewable energy and improve the energy efficiency of ICES. This paper focuses on the optimal dispatching problem of ICES. Firstly, we construct the optimal dispatching model of ICES with electricity as the core, whose optimization objectives include the economic optimum criterion and the environmental optimum criterion. Based on the typical equipment models of renewable energy technique, energy-saving technique and power substitution technique, the operation constraint model and demand balancing constraint model on electrical and cool/heat are established for the periods of heating and cooling respectively. Particle swarm optimization (PSO) algorithm with good global search capacity is applied to solve the optimal dispatching problem. The model and the algorithm are verified through a case study to produce optimal dispatching plans of ICES under the economic and environmental criterion respectively. Meanwhile, the reasons of the similarity and contradiction in the dispatching plans under different objectives are compared and analyzed.
To make sure the safe and reliable operation of echelon-use battery energy storage system, this paper proposes a safe battery management system for 100 kW·h echelon-use energy storage battery system. Firstly, we analyze the characteristics of 100 kW·h echelon-use power battery for energy storage, including the battery capacity distribution analysis, SOC-OCV characteristics analysis of battery module with different capacities under certain conditions, the charge and discharge capacity test of system, the inconsistency analysis of battery capacity, etc. And the key parameters used in the echelon-use battery manage system have been decided. Then, we analyze the system safety and reliability of echelon-use battery characteristics in order to ensure the safe and reliable operation of echelon-use battery energy storage system, and adopt the system-level fault diagnosis method and multilevel fault alarm strategy. Finally, we use the developed battery management system prototype to test and verify the system capacity. The experimental results show that this battery management system can meet the application requirements of the echelon-use battery energy storage system.
With the development of interconnected grids and the increase of trans-regional transmission trading, the power outside sending to large area is faced with the problem of electric energy consumption optimization configuration. Based on this, we propose four electric power consumption modes of the power outside sending to large area by UHV DC: placement consumption, consumption according to the thermal power installed capacity ratio of each province, consumption according to the load ratio of each province, and consumption according to the ratio of the load to the electrical distance between load centers and placement of UHV in each province. Then, we define the comprehensive economic index with considering electricity price and carbon emission, and use thermal power replacement rate and thermal power output rate for the quantitative assessment of the consumption modes. An example of the power outside sending to central China power grid as large area by the Hami-Zhengzhou UHV DC is taken to be analyzed. Finally, we propose the corresponding consumption mode among the respective provinces based on different transmission capacity, wet and dry conditions and load space, which can provide an effective basis and a quantitative means of decision-making for regional power grid dispatching sector.
The accurate identification of the fault conditions of steam turbine rotor has been the research focus in the field of engineering. In the process of fault diagnosis by using support vector machine (SVM), extracting the signal characteristic parameters, which can clearly distinguish different fault signals to construct high-quality samples, plays a significant role in improving the classification accuracy of SVM model. To solve these problems, we propose a multiple fault diagnosis method for steam turbine rotor based on ensemble empirical mode decomposition (EEMD), permutation entropy and SVM. Firstly, this method applies directed acyclic graph to establish multiple faults diagnosis model, and uses EEMD to decompose the vibration signals into single and unmixed IMF components. Then, the permutation entropy of IMF component, which is very sensitive to the changes in vibration signal, is calculated as eigenvectors, and applied in directed acyclic graph SVM for multiple fault state recognition. The experimental results show that this method can realize the multiple faults diagnosis of turbine rotor vibration. Meanwhile, compared with the extracted eigenvectors based on EEMD energy method, the experiment proves that this method has more accurate recognition rate.
To further discuss the effect of steam on the sulfation characteristics under oxygen-enriched atmosphere, this paper implements the simultaneous calcination and sulfation experiment for limestone in oxygen-enriched combustion with using isothermal thermogravimetric experiment device, and studies the influences of steam concentration, temperature, particle size and limestone type on the simultaneous calcination/sulfation characteristics of limestone. The calcination rate is increased by the presence of H2O, which results in a shorter time needed for the complete decomposing of limestone. There is an obvious promotion by H2O in the diffusion controlled stage；however the influence is hardly detected in the dynamic controlled stage. The influence of steam is highlighted with the increase of temperature (within experimental range) under oxygen-enriched atmosphere, and the finally calcium conversion rate increases with the temperature increasing. The effect of particle size is significant, and the ultimate calcium conversion rate increases significantly with the decrease of limestone particle size. The influences of steam on the simultaneous calcination/sulfation characteristics of different types of limestone are basically the same.
To alleviate the influence of wind power uncertainty on the wind power accommodation of systemand improve the utilization efficiency of wind power, we introducethe robust stochastic optimization theory, employ wind power and heat storage electric boilers to set up heating supply system, and construct the heating scheduling optimization model of wind power with taking the uncertainty of wind power into consideration. First of all, we build the model of wind power output and the load demand model of heat storage electric boilers；then, we use the theory of robust stochastic optimization to describe the uncertainty of wind power output, and construct the heating scheduling optimization models of wind power and heat storage electric boilers respectively under the uncertainty and randomness conditions of wind power output. Finally, we choose a wind power heating project in a certain city in the north of China for example analysis. The results show that the robust stochastic optimization theory can effectively describe the uncertainty output of wind power and provide the decision-making tool for different risk attitude decision-makers. The heating system composed of wind power and heat storage electric boiler can realize the heating load flexibly in power system dispatching, increase the accommodation capacity of wind power, and reduce abandoned wind power, which has remarkable economic and environmental benefits.
The reasonable demand-side price is the key factor to promote and guide the users demand response. Considering geographical dispersion and large number of controllable load in difference demand response of marginal cost and consumption preferences, this paper presents a controllable load menu-pricing method based on discrete choice theory. Considering the different preferences of the user in a wide variety of electricity price, this method establishes the discrete choice model for users menu price, which is based on the three factors: the marginal cost of load, the load reduction and the compensation price, and calculates the discrete choice probability of users menu price. Then we take the price of demand response and the load reduction for the menu options, the minimum cost of system power supply as the target, and construct the menu-pricing model for controllable load which can reflect the different consumption preference of users. Finally, through numerical example, we analyze the power supply cost and users total load reduction with or without discrete choice, as well as the sensitivity of affecting users selection factor. The results show that menu-pricing considering discrete choice can effectively reflect the users preferences for different electricity price, and induce its intrinsic demand elasticity, so that the menu price can meet the users consumption preference, promote the user to participate in and cut more load, save the system power supply cost, and realize the optimal allocation of power resources.
In the north of China, water freezing phenomenon occurs easily during the operation of natural draft counter-flow wet cooling towers in winter. It is necessary to install windshield boards at the air inlet of cooling tower. During the actual operation of power plants, it often appears the situation that the number of windshield boards is over large in order to avoid water freezing in cooling tower, which decreases the economics of unit. In order to improve the feasibility of installing windshield boards to avoid water freezing, we propose a new installation method of spaced longitudinal windshield board, and establish a heat and mass transfer model of cooling tower in a 600 MW unit. With using Fluent, we simulate and analyze the influence of the installing area of windshield boards on the minimum water droplet temperature on different characteristic planes after windshield board installation, and find the optimal installing area of windshield boards at different ambient temperatures. The results indicate that, the lowest water droplet temperature in the tower increase with the installing area increase of windshield boards；when the ambient temperatures are 264.15 K, 261.15 K and 258.15 K respectively；the cooling tower can avoid water freezing with windshield boards installed at a regular longitudinal spacing at the first layer with 45 longitudinal air inlets, the first two layers with 72 longitudinal air inlets and the first three layers with 90 longitudinal air inlets respectively, the corresponding optimal installing area of windshield boards are 848.95 m2, 1578.79 m2 and 1864.16 m2 respectively.
With the expansion of the scale of wind power, the timely and accurate prediction of wind power output is of great significance. However, due to the uncertainty of wind speed, the wind power is difficult to control. Through the trend analysis of wind speed and power, we establish a mathematical model of wind power based on wind speed. Then, taking the wind speed forecasting as a breakthrough point, the irregular history of wind speed is pattern decomposed based on wavelet decomposition mode. We analyzed the decomposed historical series, adopted the appropriate forecasting model to forecast respectively, reduced the series to the original series to obtained the predicted wind speed, finally obtained the predicted wind power through calculation. Through the calculation at a certain place, the accuracy and reliability of wind power forecasting with using wavelet decomposition and time series model are proved.
Aimed at damage accidents of box-type transformer outside wind turbine when the top of wind tower being struck by lightning, an ATP/EMTP simulation model is established according to wind turbine-box type transformer system lightning protection, which is based on the mechanism analysis of the lightning overvoltage of box-type transformer at low-voltage side. We use this model to calculate the lightning overvoltage of box-type transformer at low-voltage side when surge protective device (SPD) is connected and disconnected, and analyze the influences of the waveform and peak of lightning current, impulse grounding resistance on the voltage on the low voltage side of box-type transformer. Meanwhile, we calculate the power frequency current after the low-voltage side short circuit of transformer. The calculation result shows that the potential differences of low-voltage side of transformer when SPD is disconnected exceed the impulse withstand voltage 12kV, and the power frequency current at low-voltage side is 4.50-8.75 kA. Because switch-type SPD cannot cut off power frequency current, it is suggested that switch-type SPD should be replaced by zinc oxide arrester (YH10W-0.8/3.0) without follow current, whose lightning protection effect is verified by simulating calculation.
With the distributed photovoltaic generation connected to distribution network gradually increases, its consumptive ability has been paid more and more attention. This paper studies the consumptive ability of distributed photovoltaic generation with considering active management, and proposes the maximum consumption calculation method of distributed photovoltaic generation in active distribution network. Based on the analysis on the timing characteristics of distributed photovoltaic generation and load, we propose the improved particle swarm optimization algorithm with comprehensively considering chaos theory and adaptive adjustment, and study the influence of some active management measures on the maximum consumption of distributed photovoltaic generation, such as distributed power output curtailment, on-load tap changing transformer regulation, reactive power compensation and so on. IEEE 33 node distribution network system verifies the rationality of the proposed model and the effectiveness of the algorithm, and the three active management measures can effectively improve the maximum consumption of distributed photovoltaic generation.
