The development patterns of over reliance on fossil energy are changing, accelerating the construction of energy internet with clean energy transmission as the core has become the inevitable trend of energy development. This paper analyzed the basic connotation and characteristics of energy internet, and expounded the basic idea of its framework system construction and top-level design. Finally, taking the power system development as the core, this paper proposed the task and challenge in the development of energy internet, and discussed the development path of the energy internet.
With the rapid progress in information technology, a novel concept—“Energy Internet”, that concentrates on the coordination and optimization of multi-type energy flows via advanced communication and internet technology, has received a lot of attention. The result of such an inevitable trend is that a fundamental technique—Big Data Analytics—must be developed to handle massive influx of data from multiple heterogeneous sources, as well as utilize the data to swiftly derive an economic value. The paper gives an overview on research works conducted at SGRI North America big data lab with highlights on hardware configuration and software deployment of the cluster environment. The paper reviews several ongoing research topics performed in the lab with an emphasis on customer segmentation and response targeting （collaboration with Stanford University）；and energy disaggregation. These works are built on an integrated power system data model that is supported by open source technology. Preliminary results show that our research will benefit both utility companies and customers.
Energy internet technology can achieve the efficient utilization and long-distance transmission of large-scale renewable energy. The DC grid based on modular multilevel converter （MMC） technology is an important component and effective technical mean of energy internet and renewable energy transmission. However, limited to the existing development of power electronic technology, the rated voltage and rated current of single MMC are hard to increase, which will hamper the large-scale renewable energy transmission over countries or over states. To solve the above challenges, the topological structures of MMCs sub-modules, arms and converters in series and parallel were studied, whose technology advantages and disadvantages applied in large-scale wind power integration transmission were analyzed. Moreover, in order to combine the advantages of line commutated converter （LCC） and MMC and meet the need of future energy internet, the series, parallel structures of LCC and MMC were also studied. At last, the voltage balancing problem for series structure and current balancing problem for parallel structure were simulated and analyzed. Through the comparison on the capacity enlarging methods of various series, parallel structure, it can be concluded that either the series of MMC or the series of MMC and LCC is applicable for high voltage and power application. The research results can provide reference for the construction method and engineering application of high-power converter station.
In independent micro grid, ensuring energy supply and demand balance, as well as enough system backup is very important to meet customer demand and maintain the secure operation of micro grid. So battery energy storage system （BESS） is indispensable. However, due to the high cost of BESS at the present stage, the reasonable planning is necessary for deciding the optimal system scale. Based on this, this paper firstly constructs the planning objective function of BESS for independent micro grid, and presented constraint conditions from the aspects of supply and demand balance, as well as reserve requirements. Then, the optimal planning of the installation year, rated power and capacity of BESS is carried out by improved harmony search algorithm. Finally, the effectiveness of proposed model and algorithm will be verified through three different kinds of micro grid operating scenes.
The concept of constant voltage operation was proposed, and it was demonstrated as the ultimate goal of power grid development. The topic was expanded from three aspects, including constant voltage operations benefit, realization way, and cost. The benefit of constant voltage operation includes four facets: constant voltage operation is the ultimate presentation of the strong smart grid；constant voltage operation can resist fault disturbance in the most powerful manner and improve the stability of power system greatly；constant voltage operation can completely eliminate the voltage fluctuation problem caused by the integration of large-scale renewable energy；constant voltage operation can minimize the grid loss. The realization way of constant voltage operation is mainly the static synchronous compensator based on modular multilevel converter （MMC-STATCOM）, whose appropriate single unit capacity at present technology level is about 500 MVA. The cost of constant voltage operation was estimated on a typical receiving system of 20 000 km 500 kV transmission line. The result shows that the capacity of the needed MMC-STATCOM is less than 30 GVA and the investment cost is less than 10 billion Yuan.
European power grid is the largest regional interconnected power network in the world, and a rare multi-national interconnected power network in the world. The total installed capacity of European power grid is the largest in the world, its acceptance and utilization for renewable energy is a learning model for every country to promote energy transformation and high-proportion renewable energy accommodation. Based on the analysis on the European power grid and the power source structure, load characteristics and network interconnection status of every country, this paper summarized the development situation of power grid of several countries in European and the main features of the interconnection with neighbouring countries. In addition, on the basis of analyzing the specific data of power gird, this paper analyzed the construction demand of building energy internet in 3 aspects: physical platform, information platform and financing mechanism, and summarized three implications of European power grid development for the construction of energy internet. The analysis and conclusion of this paper have certain reference value for deep research on energy internet.
Combined with the demand of large-scale wind power integration, this paper put forward a two-step coordinated planning comprehensive model between wind farm construction and transmission network expansion, based on the multi-scenario probability model with wind power. Both wind power integration and grid construction were taken into consideration in this model. The model also took into account the technicality, economy, coordination and adaptability of the planning scheme, and realized the comprehensive benefit optimization of the planning scheme. Finally, the test case with wind power integration verified the effectiveness of the proposed model.
There are rich renewable energy reserves in five provinces in Southern China and its offshore areas. The large-scale development of renewable energy, such as wind power and solar power, can help to alleviate the problems of energy shortage and environment pollution in Southern China. On the other hand, as an important component of Chinas western development strategy, west-east power transmission is an effective measure to optimize the allocation of electric power resources and promote the adjustment of economic structure for five provinces in Southern China. Based on the interaction mechanism of west-east power transmission characteristics in China Southern Power Grid and renewable energy generation characteristics, this paper uses the mid-long term production simulation method of China Southern Power Grid to analyze the impacts of west-east power transmission characteristics in China Southern Power Grid on the renewable energy acceptability, which could provide references for the reasonable determination of west-east power supply level and the reasonable arrangement of the exploiting priority scheduling of renewable energy in each province.
UHVDC combined wind-thermal power transmission can resolve the long-distance transmission of wind power from western and north, and expand the accommodation range of wind power. This paper presented research method for the auxiliary power supply scale optimization of UHVDC wind-thermal power bundled transmission. First of all, this paper studied the technical constraints of wind-thermal power transmission through UHVDC, including the operation mode of UHVDC transmission and its influence on the scale of wind-thermal power, as well as proposed the research principles and ideas of auxiliary power supply. Secondly, the optimization method for auxiliary power supply scale of UHVDC combined wind-thermal power transmission was studied. Finally, taking the Jiuquan-Hunan ±800 kV UHVDC project as an example, this paper presented the wind-thermal power scale in Jiuquan-Hunan UHVDC, and verified the scientificity of the proposed method. The proposed method has great significance for expanding the accommodation range of wind power in the north of our country and improving the transmission efficiency of UHVDC transmission.
Both the output of hydropower and photovoltaic （PV） are related to weather conditions. Hydropower is able to quickly adjust and has the capacity of energy storage, which can be complementary with the PV operation and compensate the intermittent of solar energy. At present, the papers that study the complementary characteristics of these 2 kinds of power supply in different time dimension are less. This paper proposed the analysis method for the complementary characteristics of hydropower and PV power, established the evaluation index for the synergy between hydropower and PV power based on the thermal generation load factor and PV curtailment ratio, and calculated the evaluation index for the synergy between hydropower and PV power with using the chronological simulation of PV output and the operation simulation of the power system with hydropower. Taking the planning data of power system in Qinghai Province in 2020 as example, the characteristics of the synergy between hydropower and PV power in Qinghai Province in 2020 were studied, and some suggestions were proposed for the synergy operation between hydropower and photovoltaic power in Qinghai Province in the future according to the calculation results.
The rapid development of large-scale wind farms results in some new problems for the secure and economic operation of the power system associated. In making transmission system planning, sufficient available transfer capability （ATC） is required so as to accommodate large-scale wind farms, while excessive transmission capacity must be avoided so as to save investment. Given this background, a stochastic optimization model for transmission system planning is presented for a power system with the integration of large-scale wind farms with the following contributions: 1） a probabilistic ATC model is developed with the correlations among random input variables such as wind speed and loads as well as the outage probabilities of generators and transmission lines taken into account；2） a method is employed to solve the probabilistic ATC model by the combined use of the Latin hypercube sampling based Monte Carlo simulation and sensitivity analysis；3） a bi-objective transmission system planning model is presented with transmission investment cost minimized and the expected value of ATC maximized, subject to the acceptable overload probability constraints, and in this way the economics and operation risks associated with a transmission planning scheme could be compromised. Finally, the developed transmission system planning model is solved by the well-established genetic algorithm, and demonstrated by a 18-bus and a 46-bus sample power systems.
With the policies supported by national and local governments, the distributed photovoltaic power generation achieves rapid development in recent years. The relatively high penetration of distributed photovoltaic system in some areas leads to the requirement of grid reinforcement. And the distributed photovoltaic system also faces the risk of power ration. According to the grid reinforcement cost, loss reduction and grid investment delay and other cost benefits caused by distributed photovoltaic system with high permeability, this paper proposed a comprehensive cost benefit analysis method with considering grid reinforcement. Then, based on the analysis results of 8 760 hours in typical planning scenario, the optimal planning research on integration of high penetration distributed photovoltaic system was carried out, whose results could provide references for the scientific planning of high penetration distributed photovoltaic system.
The implementation of power grid planning facing low-carbon development is important basis for power grid enterprises and power industry to deal with the carbon lock-in effect and achieve the transition to the low-carbon power system. The low-carbon factors of power grid planning were firstly analyzed comprehensively from both the space and time dimension. Based on the process of conventional power grid planning, the novel mode of low-carbon power grid planning was analyzed, and the influences of the low-carbon factors on the power grid planning process were studied in detail. On this basis, some suggestions were proposed for the low-carbon power grid planning based on the characteristics and development status of the power industry in China.
Energy internet is an important development direction of future energy supply systems, and combined cooling, heating and power （CCHP）, which is one of the fundamental elements of energy internet, builds a conversation relationship between heating/cooling and power. When considering the operation of concentrated CCHP, the unit startup and shutdown method of gas-steam combined cycles and its operating state will impact the running efficiency and operating income of concentrated CCHP. So the reasonable unit startup strategy is the promise and foundation for the economic operation of CCHP. This paper analyzed the CCHP that used gas-steam combined cycle as power plant, lithium bromide absorption refrigeration technology and phase-change energy storage devices. According to relevant operating parameters of CCHP units, the economy objective function of concentrated CCHP operating was established based on the investigation of cooling-heating-power load in a region；and a unit startup and shutdown strategy of CCHP under economic operation was proposed, in order to improve the work efficiency and increase the operating income.
The energy internet is gradually impacting the planning and construction way of power grid, which puts harder request on the prediction technology of related factors. Due to the huge differences between holidays and weekdays and the lack of historic data, the results of load prediction for holidays are not so good. Weather, date and other related factors were corrected by the unified correction model of related factor, and then the data for normal weekdays impacted by unified related factors was obtained. Considering the principle of ‘emphasizing the near and belittling the long’, the relevance of load curves between normal weekdays and holidays was analyzed, and the load forecasting model was proposed based on the point-to-point analogy, which could reduce the prediction error caused by the abnormal historic data automatically. The proposed prediction method was applied to the holiday load forecasting in one of the northern cities and districts in China. The example analysis results show that the prediction accuracy can satisfy the actual requirements, which can provide a certain reference value for the holiday load forecasting of related power sector.
The saturated load forecasting of power demand can determine the ultimate size of a regions future grid development and power demand, and the forward power grid planning goals can be used to guide recent grid construction, which can effectively reduce the cost of the reconstruction of power grid, contribute to the work of gradual and methodical renovation and construction of the regional power grid, and has great significance for the regional planning, and the coordinated development between regional economy and power grid. This paper presented the stages division theory of load development based on improved Logistic model, proposed a new definition and meaning for saturated load, and amended and improved the quantified index system for judging power saturated load. Finally, the improved Logistic model was applied to study and analyze the case, the prediction and analysis work of the power saturation scale and saturation time point in the case was completed, and its feasibility was validated.
There are different evaluation indexes and methods for the development scheme selection of transmission network between development department and dispatch department of power grid based on different emphasis points. So it is difficult to form an objective, comprehensive, unified development scheme, which will cause contradiction among transmission networks planning, construction, operation and other aspects. In view of the above problems, this paper presented a selection method for transmission network development scheme based on fitness and evidence theory. The concept of fitness was established to quantitatively evaluate the development degree of power grid, and the evidence theory was used to integrate the aspects of safety, economy and other fitness indexes；the obtained parameters could provide the basis for the development scheme selection of transmission network. The proposed method can solve the coordinate problem of transmission network development scheme selection in different developments. The simulation of actual power grid development scheme selection shows the feasibility and validity of this method.
With the deepening of the power market, the users reliability has been paid much attention. In order to fully reflect the different reliability requirements of users, the emergency control strategies which take the power outage cost of users as economic index in optimization objective function have been widely used. However, these decision models do not consider the transient stability of the system, so the system may be unable to withstand failure again and cause transient instability after the execution of generator re-scheduling and load shedding. In view of this problem, this paper proposed an optimal emergency control strategy with considering transient stability constrains. The relevant constraints were used in this model could indicate that the system satisfied the transient stability at the new operating point. Therefore, the system could still maintain transient stability after the execution of generator re-scheduling and load shedding. Finally, taking IEEE-RBTS 6-nodes system and new-England 39-nodes system as example, the proposed strategy was described in detail, and its result was compared with that of the strategy without considering transient stability constrains.
The operation efficiency of power grid reflects the fine level of power system operation, which has significant influence on the revenue of power grid enterprises. The scientific evaluation on the operation efficiency of future-proofed power grid planning scheme provides significant guidance for the construction of power grid. The evaluation index set of power grid operation efficiency was designed from two aspects: generation and transmission. The calculation method for the evaluation index of power grid operation efficiency was proposed based on the sequential operation simulation technology of power system, which could fully consider the complex boundary conditions and various operating scenarios of power system operation, and comprehensively accurately reflect the operation efficiency of power system. The empirical analysis was carried out on the actual data of Jiangsu power grid planning scheme in 2018, and the impacts of Jinbei-Nanjing UHVDC project and 10 GW wind power base in Jiangsu province on the operation efficiency of power grid were studied. The results show that the construction of Jinbei-Nanjing DC project will increase the network loss and transmission congestion of the power system to some extent, and have a negative effect on the operation efficiency. The integration of wind power will increase the line blocking near the wind farm and thus reduce the operation efficiency of power grid.
Accurate accommodation evaluation is important for the development planning of wind power. However, it is difficult to obtain the detailed time-sequence data of wind power output during planning stage and the typical evaluation method of time-sequence accommodation is difficult to be applied, so it is necessary to research the evaluation method of accommodation capacity based on the limited wind resource probabilistic characteristic data. This paper proposed a functional minimization model which took maximum wind power accommodation as target based on probability production simulation and a practical evaluation algorithm based on heuristic method. This method only needed the probability distribution information of wind resource and could solve the problem of lacking detailed wind power data during planning stage, which also had a fast computation speed. Based on the actual running data in 2014 and planning data in 2020 of a large wind power base in northern China, the simulation analysis was carried out. The actual wind power accommodation results in 2014 were compared with the simulation results, which could validity the correctness of the proposed method. Finally, according to the planning data in 2020, this paper analyzed the saturation trend of wind power accommodation and installed capacity, and quantitatively studied the promoting effect of flexible measures on wind power accommodation, which could provide some suggestions for wind power planning.
As the increases of power grid size and external influence factors, it is worth thinking and research on whether the existing evaluation theory can be used to provide effective technical support for power grid development direction and development mode. In addition to improve safety evaluation system and economy evaluation system, the evaluation system was proposed and established for the adaptability of large power grid. The characteristics of existing power grid evaluation system and its application scopes were summarized. Combined with the characteristics and development trend of large power grid, the adaptability evaluation theory and its system framework were proposed. Problems solved by adaptability evaluation system of large power grid were analysis, and the important significance of adaptability evaluation system of large power grid was discussed. Finally, the key theories, implementation technology and other issues of the adaptability evaluation system were studied.
This paper firstly summarized the achievements and experiences of power system planning evaluation in countries with leading development in wind power and photovoltaic power. Then, the interactions between grid-connected intermittent generations（IGs） with high penetration and power network planning were analyzed, and on this basis, the comprehensive evaluation index system of power network planning was preliminarily studied, which could characterize large-scale IGs after grid-connected. Based on traditional index system, some indicators such as the risk assessment, the maximum integration capacity of IGs, the transmission capability, the credible capacity of IGs, and the pollutants emission reduction, were used to evaluate the power network planning schemes of IGs after large-scale grid-connected from aspects of economics, power supply quality, flexibility, environmental friendliness, etc. Finally, two alternative power network planning schemes in southern Brazil 46-node system were applied to demonstrate the proposed evaluation index system. The analysis results show that the adaptability degree of IGs integrations into a power system has significant impact on the IGs accommodation capability and operation risk of the power system. Therefore, during determining power network planning scheme, it is necessary to make a compromise between the economics and adaptability of grid-connected IGs.
According to the uncertainty of comprehensive decision-making and the strong subjectivity of index weight determining method in power transmission network planning, a comprehensive decision-making method for transmission network planning schemes was proposed based on the combined weight and cloud model. Firstly, based on the subjective weights calculated by analytic hierarchy process （AHP） and order relation method as well as the objective weights calculated by entropy method and variation coefficient method, the combined weight of each evaluation index was obtained by particle swarm optimization （PSO） algorithm, in order to remedy the insufficiency of experts assigned index weight and objective weight. Then the cloud model was adapted to determine the comprehensive evaluation results of each network planning scheme, which could fully reflect the fuzziness and randomness of index information. Finally, a simulation analysis of IEEE Garver-6 system was given to verify the effectiveness of the proposed decision-making method.
This paper introduces equivalent no-wind scenarios and uses Monte Carlo method to evaluate the influence of wind power intermittent on system reliability, with considering the reliability of generators and transmission lines at the same time. Based on this scenario, the calculation method of wind power reserve requirement under reliability was proposed to quantize the influence of wind power intermittent characteristics on system reliability. Meanwhile, along with the gradual increase of wind power permeability in CSG, it is necessary to evaluate the capacity benefit of wind power in system planning and the contribution of system capacity adequacy, in order to reduce the deviation caused by power supply and demand forecasting and reduce excessive investment, which can also provide data reference and support for the capacity market development in future electric market reform. Based on the reliability evaluation model, this paper evaluates the credible capacity and capacity credit of wind power in CSG by using sequence operation. Finally, taking a practical case in CSG as example, the influence of wind power output characteristics, penetration factor and wind area relativity on capacity credit are studied.
