This paper analyzes the necessity of developing energy internet from the perspective of the analysis of electric power utility, then discusses the basic features and demonstration prospect of energy internet.Reasonably restricting the scale of synchronized power systems, using VSC back-to-back HVDC to separate multiple AC regional power systems, and constructing multi-terminal flexible HVDC meshed network among multiple AC regional power system are the features of energy internet on the level of power transmission.The local active distribution system and VSC-DC distribution system with multi-energy interconversion is the physical foundation of energy internet on the level of power distribution, in which the generalized demand response and local energy trading platform can achieve the commercial operation of energy internet.This paper proposes that constructing the advanced information communication network and new energy trading system and using them as ties of brand-new energy comprehensive utilization architecture are the demonstration roadmap of energy internet.

Energy internet is an important infrastructure for large-scale distributed renewable energy access and energy sharing in the future. Considering the fundamental goal of energy internet construction, the characteristics of energy internet are presented, and an energy internet structure based on energy router is proposed. An energy router with hierarchical function modules is proposed, which is capable of supporting the access of distributed sources, electric vehicles, and loads. The detailed introduction of the function modules are presented. A modularized main circuit with multiple power interfaces of the energy router is also proposed. An energy trading mode based on the energy router is proposed, which can not only realize the free and fair energy trade, but also realize the local or nearest consumption of the distributed energy automatically. The energy trading process is also presented.

As the concept of energy internet develops rapidly, the top-level design in different areas of energy internet has become one of the important tasks among energy field research. The discussion aiming at the transaction characteristics and business management modes of energy internet has been led to economical and technical fields of energy economics. Based on the idea that energy internet consists of multi-level systems, the concept of EIBM (energy internet based microgrid) has been proposed. This paper reviews the basic frame of EIBM, and proposes its transaction characteristics and business management modes. Distribution company, individual investors, sub-microgrids are the three main parts in EIBM operation, and their roles, rights and responsibilities are analized specifically in operation mode of EIBM. Operation principle, government role and advantages of EIBM are discussed respectively in detail. The suggestions on EIBM business management mode and operation mode are helpful to the design and construction of energy internet.

By controlling the magnitude and direction of load flow at the PCC (point of common coupling), a grid-connected microgrid can provide load shifting service for utility. However, the variability and randomness of loads and renewable energy sources bring in great fluctuation of exchanging power at the PCC, which is harmful to the operation safety of the grid. To solve this problem, a multi-time scale energy optimization method for microgrid is proposed aiming at load shifting. Firstly, the optimal preseting exchanging power curve is obtained by fuzzy control. Secondly, in order to satisfy the energy control target of microgrid with load shifting, a three time scale multi-energy optimization method is proposed including hourly schedule, regulative schedule and real-time schedule. Finally, the proposed method is applied to a typical microgrid with wind turbine (WT), photovoltaic (PV) generation, batteries and loads, simulation and analysis results verify the efficiency of the proposed multi-time scale method on the spression of the pwer flutuationat PCC.

For a combined cooling heating and power (CCHP) microgrid including photovoltaic, storage battery and CCHP, and under the conditions of fulfilling the multiple energy demand for subscribers and interacting with the distribution system, and based on part load ratio models of the principal components in the microgrid including the micro turbine, heat recovery steam generator (HRSG) and refrigerating machines as well as the combined cooling heating and power (CCHP), a 0-1 mixed integer nonlinear programming (MINLP) model for day-ahead CCHP microgrid dynamic economic dispatch is established with the target of minimizing the total operating energy cost. Furthermore, the differences between the part load ratio based model and the constant efficiency model of the components are compared in dispatch scheme optimizing and total operating cost via solution of a residence building CCHP-type microgrid during a typical summer day. It turns out that the error between these two models cannot be ignored in dispatch scheme optimizing, and the result of part load ratio model is more precise. What’s more, the model error from the cooling load is more considerable.

With the development of energy internet, various technologies will be firstly applied to user-side microgrid so as to change the traditional power generation, transmission and operation mode. With various distributed energy, energy storage devices and controllable loads integrated into user-side microgrid, it can provide high flexibility and efficiency for energy conversion and consumption under energy internet environment. The form, key technologies and business mode of user-side microgrid in energy internet environment are envisioned, coordinated operations within a microgrid or among microgrids are studied. Based on forecasting technologies of distributed energy supply and user demand, an optimal operation model for user-side microgrid is proposed. A distributed model predictive control technology is applied to online updating forecasting information and operation status of microgrids so as to optimize the operation strategies of upper and lower layer to converge to an equilibrium point. The proposed optimal operation strategy provides reference for dispatch and operation of user-side microgrids.

Based on the characteristics analysis of industrial type user-side microgrid, the microgrid energy storage capacity and power allocation principles are summarized. Considering the diversity of investors in industrial type user-side microgrid, in the case of the power grid investing energy storage system, the optimal operation principles and processes of microgrid and energy storage are proposed to promote local consumption of photovoltaic energy, to optimize the power exchange of microgrid with the outside grid, and to balance the economic benefits. A business mode suitable for industrial type user-side microgrid is also proposed. Taking a real microgrid project as example, the energy storage selection process is introduced, the profit gained by the energy storage and the distribution proportions of each investors are calculated in detail based on the proposed operation modes of energy storage. The example provides a business mode refference for the large-scale development of the industrial type user-side microgrid.

Microgrid’s internal renewable energy output fluctuation may damage the grid, so energy storage devices are needed to smooth the fluctuation. As a kind of temperature control load, air conditioning (AC) load has thermal storage capacity, it can be regarded as energy storage device. This paper considers the energy storage characteristics of AC load, establishes the microgrid tie-line power fluctuation smoothing model considering the air conditioning load. The proposed model uses imbalance electricity price to punish the power fluctuation of microgrid tie-line. Under the premise of meeting user’s thermal comfort, through reasonable arrangements for AC to start and stop, the microgrid’s tie-line power fluctuation is smoothed. The model aims at getting the minimum of the summation of tie-line power purchase cost, tie-line power imbalance settlement cost and AC user incentive cost by the optimal dispatching of microgrid’s AC load. The simulation of tie-line power fluctuation smoothing effect demonstrate the effectiveness of the proposed model.

EV (electric vehicle) route selection and charging navigation optimization can improve EV user’s travel efficiency and alleviate the influence of large-scale disorder charging on the safe operation of distribution system. Considering the constraints of path selection, battery capacity and mutually exclusive charge/discharge state, two optimization models for electric vehicle route selection and charging navigation with two different decision-making objectives of optimal travel time and optimal charging cost of EV user are constructed respectively under time-of-use price mechanism. Numerical simulations are carried out to a transportation network containing 4 fast charging stations within a 20 km×20 km zone and its distribution system. The influence of various decision goals on user’s travel path and the influence of electric vehicles’ charging or discharging state on distribution system are analyzed, the results verify the feasibility and effectiveness of the proposed model and solution.

Energy internet has been highly promoted in most recent years, whose most obvious advantage is to provide bi-directional power flow and intellectual power sharing. Based on Benders decomposition (BD), a security constrained optimal power flow (SCOPF) model for corrective control in energy internet by using multi-microgrids is presented in this paper. Then an incentive control strategy that can effectively coordinate multi-microgrids and system generators to relieve post-contingency overflows is proposed. Comparing with the direct load control, the proposed control strategycan better encourage the bi-directional energy flow between the main grid and microgrids for post-contingency recovery. Numerical simulations on IEEE118-bus system demonstrate the effectiveness and efficiency of the proposed control strategy.

Load aggregator (LA) can supply system reserve by aggregating middle and small demand-side response resources. This paper discusses the contents of different types of interruptible load constract between LA and users based on different load characteristics of users. The operation modes of LA are presented, including the compensation scheme for interruption, prophase subsidy for users and participating in system supply-demand balance. The cost-benefit models of user, LA and power system are established, and the interaction between them is analyzed. Finally, based on the cases,the characteristics of different cost-benefit perspectives are analyzed, and the coordination of extra subsidy on each cost-benefit, the effect of compensation scheme on LA cost-benefit and the effect of participating in system supply-demand balance on each side are demonstrated. Some suggestions on implementing the program are given.

When a photovoltaic system is used as black-start unit, it can be considered as a special islanding condition. This paper simulates the output characteristics of photovoltaic array under various temperature and intensity of illumination, based on which a control strategy for black start is proposed and then the influence of the battery configuration and environment variation are analyzed. Results indicate that the control strategy can adapt to different environment condition. Moreover, battery capacity and environment variation will affect the stability of frequency and voltage as well as the time duration of black-start process. Based on the simulation results, application prerequisite for using photovoltaic system as black-start unit is proposed, which can be a reference for restoration planning and field testing.

Reactive power optimization is a nonconvex, nonlinear and mixed integer programming problem, and it is difficult to obtain the optimal solution. In this paper, the problem of reactive power optimization of distribution network is transformed into a convex semi-definite programming( SDP) based on the consideration of three-phase unbalance in distribution network, and the convex problem can obtain the optimal solution. By using the method of sensitivity analysis and the combination of the branch and bound, the mixed programming problem with discrete-continuous variable is soluted. Finally, taking the modified IEEE 33 three-phase power distribution system as an example, analysis results show that the proposed method can accurately solve the nonconvex and nonlinear programming problem.

In order to meet the requirements of cost management of power transmission and transformation projects and look for the deep level factors influencing the cost, the multiple regression method is used to find the scale factors influencing the cost of power transmission and transformation projects, based on these scale factors, the projects are classified reasonably, then the direct contrast among projects of different scales can be realized. Through the analysis of influencing factors, the scale factor, market factor, external environmental factor, the design techniques and construction standards are distinguished, and the key factors of the cost reasonability evaluation are also determined. Through building the influencing factor index and total index, the regional cost index system is built to provide criteria for cost reasonability evaluation. By building the cost reasonability evaluation index system, the costs are quantitatively evaluated from three aspects including regions comparison, annual cost comparison and concentration degree. Some research results of this paper have been applied to the 2015 cost analysis report of China Southern Power Grid.