From August 3 to 6, 2020, the IEEE Power & Energy Society General Meeting was held online. At the meeting, the thesis "Exploiting Integrated Flexibility from a Local Smart Energy Hub" from the subject group of Professor Xia Qing and Professor Kang Chongqing of EEA, Tsinghua University won the best thesis award (Best-of-the-Best). The first author of this thesis is Tan Zhenfei, a doctoral student from EEA of Tsinghua University, and the communication author is Zhong Haiwang, an associate professor of EEA.

The best thesis award was selected by two rounds of evaluation. First of all, 66 best theses are selected in four technical fields from more than 800 published ones, and then one from each technical field is selected and granted the best thesis award (Best-of-the-Best) according to the presentation effect of an oral report. A total of 4 theses won this honor in 2020, and this thesis is the only award-winner in China.

This thesis focuses on the mode and method of terminal multi-energy microgrid to provide flexibility for power grid/ gas network/ heat network at the same time, creates the concept of integrated flexibility for the first time, and puts forward the mathematical model and solution method to describe the feasible region of integrated flexibility. SEH (Smart Energy Hub) refers to a local multi-energy system equipped with energy conversion equipment such as CHP (Combined Heat and Power), electric heating, gas-fired boilers and intelligent communication control devices. SEH is close to the load demand terminal, inputs energy from the centralized power grid/ gas network/ heating system, and supplies the terminal load through various energy conversion equipment. Typical SEH includes: intelligent building, industrial park, energy community and so on. Using energy conversion equipment, SEH can flexibly adjust the power absorbed from the centralized energy supply network without changing the terminal load demand, thus providing flexibility for the operation of the system. As an example of the SEH shown in the figure below, the power demand is provided by the local CHP unit and the power grid, and the heat load is provided by the CHP unit, the electric boiler and the heating network. When the power grid is blocked or an emergent fault occurs, the SEH can increase the power supply of the local CHP and reduce the local electric heating, thereby meeting the terminal power demand and reducing the power absorbed from the power grid at the same time; when the new energy output is more, the SEH directly will supply the local electricity and heat load from the network power supply, thereby increasing the consumption of new energy and reducing fossil energy consumption. This capability is called integrated flexibility. Integrated flexibility can change the load demand of centralized power grid/ gas network/ heating from rigid to elastic, expand the optimization space of a centralized system, and then improve the economy of system operation without influencing the energy demand of users.

To stimulate and utilize integrated flexibility, two key technical problems need to be solved:

First, how to define the range of integrated flexibility that SEH can provide?

Second, how to embed the integrated flexibility provided by SEH into the optimal operation of a centralized multi-energy system?

To solve the first problem, this thesis defines the IFR (Integrated Flexibility Region) of SEH, that is, the feasible region for energy input of SEH which can satisfy the terminal load without violating the constraints fir internal equipment operation. To calculate IFR in this thesis, firstly, the operational feasible region model of SEH is established based on the standard matrix model of energy hub, and the input-output equation, energy conversion equation and operational constraints of various energy conversion equipment are considered in the modeling process; secondly, the operational feasible region of SEH is projected from the state space to the input space, and the IFR model is obtained. To calculate IFR is a polyhedral projection problem, which can be solved by Fourier elimination, block elimination or vertex enumeration. Considering the IFR constraints of the demand-side energy hub in the coordinated and optimized operation of the power grid/ gas network/ heating network can ensure that the optimization decision result and scheduling instructions are executable for each local energy hub. Figure 2 shows the IFR of an energy hub. It can be seen that IFR is a closed area in the first quadrant of three-dimensional coordinate system, and it changes with the terminal load change of the energy hub.

In order to solve the problem of how to embed the integrated flexibility into the optimal operation of a centralized multi-energy system, a two-stage operation mode is proposed in this thesis, as shown in Fig. 3. In the first stage, each SEH evaluates the integrated flexible IFR which can be provided and submits it to the operating mechanism of the upper system; in the second stage, the operating mechanism of the upper system optimizes the energy input of each SEH with IFR as a constraint and makes the decision. The optimizing and decision-making problem of the operating mechanism is modeled as a linear programming problem, and the objective function is to minimize the total operating cost, and the constraints include: the IFR constraints of each SEH, the power/ gas/ heat supply and demand balance constraints of the system, and the equipment operation constraints of the centralized system.

The thesis constructed a regional multi-energy system containing 10 identical SEHs for numerical simulation and test. Two operation modes are compared: S1, without considering the integrated flexibility, that is, the terminal load demand of the regional multi-energy system is rigid; S2, considering the integrated flexibility provided by SEH. Figure 4 shows the energy input of SEH in the two operating modes. In the mode considering flexibility, SEH inputs less heat and natural gas most of the time; in the other mode, it inputs more electricity from external systems. This strategy promotes the use of renewable energy and reduces the consumption of fossil energy. Figure 5 compares the operating cost and non-wind and non-photovoltaic electricity of the system in different operating modes. With the introduction of integrated flexibility, the operating cost of the system is reduced by about 7% per day, and the consumption of non-wind and non-photovoltaic electricity is reduced by about 85%. In addition, it is worth mentioning that the integrated flexibility takes advantage of the complementary substitution between different energy carriers without influencing the terminal load demand and user satisfaction.

The IEEE PES General Meeting is the top international meeting in the field of power and energy, which is held once a year. The meeting provides the world largest power industry forums to share the latest technological developments in the power industry, develop standards to guide equipment and system development, and provide professional training for people in the industry and the general public. The meeting was originally scheduled to be held in Montreal, Canada, but affected by the COVID-19 epidemic, the meeting was held online this year.

This research was supported by the National Natural Science Foundation of China and the State Grid Science and Technology Project "Research on Multi-energy Conversion Simulation and Integrated Energy Efficiency Evaluation Technology of Integrated Energy Systems".

Citation format:

Z. Tan, H. Zhong, Q. Xia, C. Kang and H. Dai, "Exploiting Integrated Flexibility from a Local Smart Energy Hub,"

2020 IEEE Power & Energy Society General Meeting (PESGM), Montr茅al, Qu茅bec, Canada, 2020, pp. 1-5