For the construction of electric vehicle （EV） charging station, the sitting of EV charging station is very important to the operation benefit, the service quality, etc. So it is necessary to use scientific method for the evaluation and decision of EV charging station sitting. Comprehensively considering the related factors of the charging station sitting, this paper constructed the evaluation index system for the sitting of EV charging station, proposed the planning evaluation method based on the cloud focus theory, and used quantitative index and qualitative index to process and build corresponding cloud models, respectively. The weighting deviation degree was introduced to judge the deviation degree of EV charging station from the ideal position, and the assessment results could be obtained according to the remark set. Taking ten alternative locations of EV charging station as examples, the calculation results show that the proposed method can comprehensively consider the related factors of the charging station sitting and process quantitative index and qualitative index, then, determine the optimal location of charging station, which can provide scientific basis for charging station sitting planning.
Research on the impact of wind power integration on transmission loss is beneficial to the safe and economic operation of wind power system. However, the existing sensitivity index of transmission loss cannot directly reflect the influence of wind speed fluctuation. Under the maximum power point tracking （MPPT） strategy, active power output of doubly-fed induction generator （DFIG） is dependent on the stator voltage, and unknown before power flow solution due to its power loss. Based on power flow model of DFIGs, transmission loss sensitivity model was extended to propose new model for the sensitivity of active power loss to wind speed, which could reflect the influence of wind speed on active power loss and its tendency. The influence of var control modes for DFIGs on transmission loss and wind speed sensitivity was quantified. With considering wind speed probability interval distribution, the auxiliary criterions of sensitivity results on the location of wind farm and the var control modes of DFIGs were compositely analyzed. The results validate the feasibility and accuracy of the proposed sensitivity model.
To match users’ actual electricity load with transmission and distribution capacity planning, and improve the utilization efficiency of grid equipments as well as the scientific nature and rationality of transmission and distribution capacity planning projects, this paper first built the evaluation index system for new transmission and distribution capacity planning projects with considering the comprehensive demand-side resources. The impact of demand-side integrated resources on users’ actual electrical load was included in the evaluation system of planning projects in order to evaluate the planning projects from three aspects: project investment, project planning and comprehensive demand-side resources. Second, this paper built the evaluation model for transmission and distribution capacity planning projects based on gray correlation and TOPSIS method. Finally, the effectiveness of this model was verified through the actual data of three transmission and distribution capacity planning projects in a province of North China. The results show that the calculation of this model is accurate and scientific, which can provide data support and decision suggestion for transmission and distribution capacity planning projects.
Under the condition that the development and utilization of new energy are vigorously advocated in China, the construction of small hydropower has developed rapidly. However, due to the lack of standardized management, the operation of small hydropower often leads to overvoltage in regional power network. Therefore, combined with the characteristics of small hydropower, this paper constructed the equivalent analysis model of power grid with small hydropower. On this basis, the theoretical analysis was carried out on the serious overvoltage process occurred in three situations: the isolated operation of small hydropower, transferring power supply and going into the wet season. The generation mechanism of overvoltage was studied； and the restrain measures were proposed for the overvoltage from the technical and management level, according to different overvoltage conditions. Finally, based on simulation software DIgSILENT/PowerFactory, this paper constructed the model for actual power grid with small hydropower, and verified the correctness of theoretical analysis and the effect of restrain measures.
To solve the randomness of photovoltaic （PV） system and low voltage tolerance ability under fault, the over voltage of DC bus, the low efficiency of PV power generation and so on, this paper brought energy storage technology into PV system, and formed solar-battery hybrid system. Detailed modeling of solar-battery co-generation system was studied, and a PV grid model was constructed based on improved maximum power tracking technology and the decoupling control of active and reactive power. The third-order dynamic model of lead-acid batteries had been simplified. In PSCAD/EMTDC, the simulation model of solar-battery hybrid system was established and the simulation results verified the correctness of the model. Furthermore, the impact of energy storage capacity on the low voltage tolerance ability of PV grid was compared. The simulation results show that reasonable storage configurations can effectively improve the low voltage tolerance ability of PV system.
This paper proposed an optimal control strategy for photovoltaic （PV）-wind-storage coordination based on variable weight adaptive filtering to smooth the fluctuations of the output power in the PV-wind-storage hybrid power system. Based on traditional weighted moving filtering algorithm, the relationship of the output of energy storage system, the fluctuation rates and the filtering bandwidth was analyzed； the balance index of the state of charge （SOC） of energy storage system and the fluctuation rates of the output power connected to the grid were used as constraint conditions to optimize the weight of the weighted moving filtering algorithm and the filtering bandwidth. Under the given constraint of fluctuation rate, the coordination optimal control of hybrid power system including PV, wind power and energy storage system was achieved. The example results show that the smoothing performance of PV-wind power of the proposed variable weight adaptive filtering method is better than that of traditional first-order low-pass filtering method. Under the premise of maintaining a reasonable level of SOC, the fluctuation of PV-wind output power is smoothed significantly, the charging or discharging times of energy storage system are reduced and the service life of energy storage system is improved.
When connected into the distribution network, distributed energy storage system （DESS） can be coordinated with distributed generations （DGs）, make up for the negative effects on network safety and economic operation because of DGs’ random outputs, and regulate the power exchange between distribution and main network for peak load shifting. The optimal allocation of DESS connected in distribution network is the basis to bring all these benefits. Therefore, this paper proposed the optimal allocation method for DESS in distribution network. Firstly, the load curve, wind power curve and photovoltaic power curve of typical days were obtained with clustering algorithm to consider the randomness of all the three curves. Secondly, considering the constraints of location, power and the safe operation of distribution network, the multi-period mixed-integer nonlinear optimization model was established with the objective of minimum total investment and operation cost of DESS. Then a two-level optimization method was proposed to solve the model, which used improved genetic algorithm to optimize the DESS allocation scheme at outer layer and optimal power flow algorithm to optimize energy storage charging/discharging of the allocation scheme at inner layer. Finally, a distribution system with wind and photovoltaic power was tested to prove the effectiveness of the proposed method； and the impact of wind and photovoltaic power rating, load demand changes and other factors on the allocation results of DESS were analyzed.
To solve the problems that traditional Fuzzy C-means algorithm （FCM） was unsuitable for the clustering of non-normal distribution data set and sensitive to the noise, and its convergence speed for high dimensional dataset treatment was slow, a clustering hierarchy process based on kernel Fuzzy C-means algorithm was proposed for power load classification, which was composed of two modules and a algorithm: improved quick sort module, kernel function module and FCM. Firstly, an improved quick sort module was used to divide the large dataset into several subspaces with significant characteristics, then it could complete the clustering of subspaces combined with kernel function module and FCM algorithm. Based on the investigation data of load in Guangdong, the classification result of clustering hierarchy algorithm based on kernel Fuzzy C-means was compared with that of FCM on MATLAB platform. The results show that: the proposed method can improve the efficiency and accuracy of classification, and has higher convergence rate； moreover, the accuracy controllability of its classification results is benefited to grid engineering planning.
DC grids based on voltage source converters （VSCs） have been proposed for integrating large wind farms and delivering remote energy source power through long distance. A number of DC voltage control and power dispatch strategies have been presented by researchers to guarantee the power transmission’s flexibility and capacity of such DC grids. Based on the analysis on the advantages and disadvantages of DC voltage margin control strategy and DC voltage droop control strategy, a novel control strategy was proposed to achieve the goal of both precise DC voltage tracking under normal operation and steady control mode conversion after slack-bus terminal loss. Based on PSCAD/EMTDC simulation platform, a mean value model of a five-terminal VSC-based DC grid with four onshore AC systems and one offshore DC system was built. Through the comparison on the steady-state and dynamic-state characteristics of the DC grid under wind power variation, main converter station tripping and other conditions, the validity and advantages of the proposed control strategy were verified.
The magnetic properties of 30Q105 grain-oriented silicon steels at home and abroad were tested under invigorative magnetic field of sine wave, as well as the core loss under power grid complicated conditions with DC bias and harmonic wave. The results show that, the core loss （P1.7/50） of domestic sample is lower than that of imported sample by 0.03 W/kg under sine wave magnetic field. However, the core loss of domestic grain-oriented silicon steel is higher than that of imported sample by different degrees under DC bias or third, fifth harmonic wave with DC bias. The reasons for core loss diversity of the same grade 30Q105 grain oriented silicon steels at home and abroad under different working conditions were analyzed by optical microscope, electron back scattered diffraction, and X-ray diffraction technique. The results show that, the above differences are attributed to the inhomogeneity in grain size distribution and the existence of {110}<112> Brass orientation grains.
According to the actual operating condition of the converter valve and valve control system in UHVDC transmission project in recent years, this paper designed a complete simulation test system for valve control equipment （VCE） in UHVDC transmission project, including converter valve and VCE of rectifier and inverter, and control and monitoring systems. The engineering-used thyristor was used to build miniature converter valve in this test system, so as to reduce the thyristor number of each valve compared with the converter valve used in practical engineering, while the design parameters of other converter valves was the same as that of practical engineering. Compared with the mode that used real-time digital simulator （RTDS） to simulate the parameters of converter valves, this system is more beneficial to the accurate acquisition and processing of the parameters of converter valve and transmission lines, and more effective for the verification of valve control function. Finally, the VCE800 valve control equipment made by XJ Group Corporation was tested. The result shows that the dynamic simulation test system of the VCE can meet the joint debugging test needs of VCE in UHVDC project.
According to the present situation of ice cover of power system in China, combined with the practical experience of ice melting at home and abroad, this paper analyzed the mechanism of ground wire ice melting. On this basis, an elliptic mathematical calculation model was set up for ice-melting, combined with the theory of heat transfer. In the light of the engineering application, the calculation method of minimum ice-melting current was studied. Through the ice-melting current calculation of three kinds of aluminum clad steel wires （LBGJ-100-20AC,LBGJ-120-20AC, LBGJ-150-40AC）, this paper analyzed the impact of ice thickness, wind speed, ambient temperature, ice melting time and other factors on ground wire ice-melting； calculated the relationship between different wire materials and ice melting current. Finally, the proposed calculation model was used to calculate the minimum ice-melting current of ground wire materials commonly used in transmission line engineering. Through the comparison of the calculation results with those results of Bauers Dolf ice-melting current calculation formula which was commonly used in transmission line engineering, it shows that two kinds of calculation results are in good agreement. The analysis and calculation results show that the ice-melting current is determined collaboratively by ice thickness, ambient temperature, wind speed and ground wire material； ambient temperature, ice thickness and ground wire material all have obvious influences on the ground wire ice-melting current, but the influence of wind speed is relatively small. The proposed calculation model of ice-melting current can provide useful and valid reference for the selection of ground wires ice-melting current and the design of defroster.
Icing flashover is an important cause of icing transmission lines’ trip fault. In China, the relatively high elevation areas, especially in the mountain areas with developed river basin and complex terrain, has a relatively high rate of icing flashover accident. According to the icing flashover of transmission lines in existing UHVAC demonstration project and the relevant test data of scientific research units, this paper summarized the characteristics of icing flashover and the technical points of anti-icing flashover in UHVAC demonstration projects. According to the icing flashover test, the configuration principle of icing insulation was proposed, which could provide reference data for icing insulation configuration, strengthen the tower design in UHVAC transmission lines, and improve the reliability of safe operation of UHV power grid.
To accurately calculate the hybrid electric field under AC-DC parallel transmission lines, this paper analyzed the impact of AC transmission lines on the surface electric field of DC conductor, used optimization algorithm to optimize and simulate the charge location, and analyzed the change of the surface electric field of DC conductor with the voltage of AC conductor. Considering with the impact of AC transmission lines on the space ion trajectory of DC transmission lines, the maximum instantaneous value of total electric field under DC transmission lines was calculated based on Deutsch hypothesis, and a reasonable assumption was proposed to accurately calculate the hybrid electric field under AC-DC parallel transmission line. Finally, this paper analyzed the impact of line spacing on the hybrid electric field. The results show that AC transmission lines have a great influence on the corona and space ion flow field of DC conductor, which should be considered in the calculation； the spacing of AC/DC transmission lines also has a great influence on the hybrid electric field of DC transmission lines, which should be considered in the line design.
The de-NOx catalyst developed for the high-dust flue gas in power plant was successfully applied in denitration system for 2×600 MW units in a power plant. The characteristics of denitration system and the conditions of flue gas in this power plant were introduced, as well as the design and selection of the de-NOx catalyst, the acceptance of denitration engineering and the changes of various performance parameters of de-NOx catalyst used for 18 months. The results show that the application of de-NOx catalyst developed for the high-dust flue gas for 3 months is very well. The denitration efficiency which reaches about 83.9% is significant, and the NOx concentration is reduced to about 73.7 mg/m3 in the flue gas. Simultaneously, the amount of ammonia slip, SO2/SO3 conversion rate, and the loss of system pressure are better than the design value. In addition, after used in the high-dust flue gas for 18 months, various performance of the de-NOx catalyst is normal, and wear resistance is excellent.
This paper analyzes the subsynchronous resonance （SSR） phenomena in DFIG-based （doubly-fed induction generator） wind farms interconnected with series compensated networks. The study system was derived from IEEE first benchmark model. Small-signal stability analysis was conducted on the basis of detailed mathematical model of wind farm. The model of power system was constructed by power system analysis software DIgSILENT/Power Factory, and time domain simulations were performed to confirm the results of small-signal eigenvalue analysis. The results show that IGE （induction generator effect） instead of TI （torsional interaction） is the major reason for SSR in such systems. Finally, this paper analyzes the influence of controller parameters on the characteristics of SSR.
The data format of existing commercial softwares for power system is not unified, which leads to the existence of a large number of heterogeneous data sources, and difficult data exchange among simulation softwares. To solve this problem, a data conversion method based on particle swarm optimization-genetic algorithm （PSO_GA） was proposed for power system simulation softwares. The differences of component model and control model in simulation software BPA, PSASP were dissected, and then the conversion relationship between corresponding models was established, as well as the objective function and associated constraints of intelligent optimization algorithm （PSO_GA）. The parameters of each model in objective conversion software were corrected based on PSO_GA to achieve the data conversion of power system simulation software BPA to PSASP. By the example of IEEE 43 system, the data conversion process of BPA to PSASP was validated, the effectiveness of the method for the data conversion of power system simulation software was demonstrated, and the accuracy of data conversion and the speed of the algorithm were improved.
Demand response （DR） has important significance to energy and economic development, resource and energy saving, as well as environmental protection； however how to realize Auto-DR still need further study. First, the influence factors of DR were analyzed from three aspects of response cost, enterprise production characteristics, and response time. Second, on the basis of the variable analysis and the user division according to sustainable interruption time of power supply, the models of Auto-DR in 2 cases were proposed with using the idea ‘from simple to complex’, in which the power enterprises that were chosen to participate in DR were set as variables, and the minimum total outage cost was set as the objective function, with the constraint conditions of power outage time and active power. Finally, according to different outage time, two cases were chosen to verify the validities of these two models.
Power demand and distribution prediction is the first link of the power planning. There are less systemic researches on middle and long-term electric power demand and the ‘Thirteenth Five-Year Development Planning’ of Chongqing in existing power planning achievements, and the traditional analysis of load distribution is difficult to adapt to the functional location of the new ‘five major functional areas’ in Chongqing. Therefore, medium and long-term power demand and distribution in Chongqing were comprehensively studied and forecasted； the power demand and national economic development situation in Chongqing were summarized； the major indicators during the development of power load in Chongqing: power consumption per capita, electric elasticity coefficient and production value per unit consumption, were analyzed； the electric power development indicators of developed countries and the eastern developed areas in China were researched. Then, by way of transverse comparison, this paper analyzed the development stage and rising trend of electric power industry in Chongqing； three forecasting schemes of total medium and long-term electrical energy demand in different levels were proposed with using electric elasticity coefficient method, electricity consumption per unit output method and power consumption per capita method. Finally, combined with the prediction results of load characteristics and energy needs of whole society, the maximum power loads of Chongqing in 2020, 2030 were forecasted, as well as the future regional growth in electricity and weight function according to the functional location of the ‘five major functional areas’ in Chongqing. Power demand forecasting can reflect a variety of situations of citys future economic development. The comprehensive analysis based on various methods can make the prediction results have good inclusiveness, which has important guiding significance for the electric power planning and power construction scheme in Chongqing. So the power demand and distribution prediction can be used as important reference for the layout of new power supply.
At present, the offshore wind power in China is in the initial stage of construction. Along with the gradually clear policy of the offshore wind power in China, the offshore wind power in China will usher in a new round of large-scale development. Based on the comprehensive consideration and analysis of the related factors affecting the grid connection of offshore wind power: the installed capacity, the transmission distance, the grid connected mode, the transmission capacity of submarine cable, the grid structure, the reactive power configuration of wind power and so on, this paper proposed 4 typical grid connected solutions for offshore wind farm, through economic and technical comparison. The proposed grid connected solutions can provide a complete solution for grid connected schemes of offshore wind farm in building or planning, standardize the system scheme, clear the design principle and idea of wind power transmission scheme, effectively improve the design level and efficiency, ensure the safe and stable operation of power grid, and realize the coordinated development of wind power and grid.
Along with the further deepening of the national new-energy strategy, offshore wind farm will step into a period of great development. Due to far away from the land, offshore wind farm has characteristics of complex environment, bad weather, difficult construction, inconvenient operation and maintenance, etc., and its secondary key technologies are different from those of wind farm on land, such as operation and duty mode, relay protection configuration, network scheme, information transmission, equipment condition monitoring, modular design and so on. This paper studied related design technologies of secondary system in offshore wind farm, further standardized and optimized the design scheme, which had very important significance to ensure the reliability of the running of offshore wind farm, enhance the levels of automation and construction, and promote the healthy development of offshore wind farm in China.
To predict the development scale of offshore wind power under current electricity price policy in China, the supply model had been built through the following procedures. More than 100 planned offshore wind power projects in coastal provinces of China were investigated and annual electricity generation of which was calculated with using Weibull model. The generation cost of each project was calculated with using the investment model based on top-down and data fitting research methods. On the basis of the definition of basic return rate of project, the supply curve of offshore wind power in China based on planned projects was issued for the first time. According to the supply curve of offshore wind power, its development scale in China was predicted, with considering the price level in current fixed tariff policy. According to the electricity tariff of offshore wind power in China and its difference from the electricity tariff of local desulfurized coal, this paper calculated the related total annual subsidies and electricity price addition corresponding to the predicted scale of offshore wind power in China, and first used four dimensional coordinate including total installed capacity, total annual generated energy, total annual subsidies and electricity price addition, to measure the development scale and subsidy situation of offshore wind power in China under the condition of different electricity price.
