Optimal Dispatching of Energy Hub for New Energy Consumption

In recent years, with the continuous increase of wind power installed capacity, due to insufficient flexibility of the system, there has been a serious problem of wind power abandonment. In response to this phenomenon, this article improves the flexibility of the regional energy system by adding various flexible devices. Based on the concept of an energy hub, an energy hub model including wind power, CHP, heat pumps, heat storage, and other equipment is established. On this basis, considering system operating costs, wind abandonment penalty costs, and electricity purchase costs, a multi-objective regional energy system flexibility configuration model based on energy hubs was established to explore the feasibility of this model in improving wind power consumption. Finally, specific examples were combined in two different cases for analysis. The results indicate that the model has a very good effect on improving system flexibility and improving wind power consumption rate.


Introduction
Recently, the stable operation of the power system has been affected by uncertainty due to the largescale application of wind power generation.Therefore, in order to ensure supply-demand balance, the power system needs to have a certain degree of adaptability and response capability, namely system flexibility, to eliminate or reduce the negative impact of uncertain factors on the power system to the greatest extent and ensure its safe and stable operation [1] .
Based on different flexibility solutions, the utilization of wind resources can be improved by providing flexibility in various aspects, including source network load storage, electricity market, etc. [2].In different solutions, people are increasingly concerned about exploring different flexible options in integrated energy systems.Due to the severe shortage of flexibility resources in the past, there was a significant waste of resources such as wind, water, and light.Therefore, it is necessary to expand to the interconnection of multiple energy sources and find new flexible resources from them to support the large-scale consumption of renewable energy.[3] - [6] describe a specific example based on the Danish integrated energy system, which investigates the importance of using different flexibility options in the thermal sector to support a high proportion of wind power generation and smart grid integration.
From the perspective of flexibility measures, the main utilization of integrated energy systems is the separate or combined use of heat storage devices and thermoelectric conversion devices [7,8] to improve system flexibility and absorb more abandoned wind.The thermal storage device reduces the forced power generation of the thermal power plant under the principle of "heat to electricity" by shifting the thermal load; Heat pumps, electric boilers, and other thermoelectric conversion devices achieve the effect of reducing heat load peaks and filling electricity load valleys through electric load conversion.
The energy hub achieves coupling between different energy sources, abstracting the integrated energy system into a multi-input and multi-output system, with the core equipment inside being the CHP unit.In terms of optimizing the operation of energy hubs, [9] summarizes the optimization planning and operation of energy hubs, including the optimization of energy hubs themselves and the interactions between different energy hubs.[10] incorporated flexible loads into the optimization scheduling model of energy hubs and constructed a multi-objective energy hub optimization model.
Building upon previous research, this article focuses on improving the flexibility of integrated energy systems and applies an energy hub model to develop a flexibility configuration model for wind power curtailment.Additionally, through case analysis, the impact of incorporating flexible equipment on wind power curtailment in the system is discussed.

Energy Hub
An Energy Hub refers to a multiple-input multiple-output (MIMO) port model used to describe the energy production, load form, energy network exchange, and coupling relationships in a multi-energy system.The coupling matrix in this model clearly illustrates the various conversion, storage, and transmission relationships between different forms of energy such as electricity, heat, and gas.There are three types of equipment within the Energy Hub: 1) Energy transmission equipment, such as power lines, natural gas pipelines, and hot water pipelines; 2) Energy conversion equipment, such as electric boilers, CHP units, gas turbines, and gas boilers; 3) Energy storage equipment, such as energy storage batteries, gas storage equipment, and thermal storage tanks.The essence of an energy hub is to describe the functional relationship between multiple energy inputs and outputs in a system containing multiple energy sources, which can be expressed using a coupling matrix.Assuming that there are m types of energy sources at the input end and n types of energy sources at the output end, the energy hub can be described using the following mathematical model, as shown in Equation (1).

Typical Energy Hub Structure
The energy hub structure of the integrated energy system established in this article includes CHP, wind turbines, electric boilers (EB), heat pumps (HP), heat storage devices (HS), and demand side response (DSM).
In the structure of the energy hub in this article, the input expression for the energy hub is The heat storage is placed at the output port of the system, which is equivalent to correcting the output matrix.The expression for the energy conversion matrix of the energy hub is where eb  L and h t L represent the power and heat load demand taking into account demand response.

Objective function
The focus of this article is to optimize the operation of the system with the goal of minimizing daily operating costs.In order to improve the flexibility of the system, this article does not consider the use of thermal power plants.Daily operating costs mainly include the operating costs of cogeneration and the cost of purchasing electricity.In order to increase the amount of wind power consumption, we have added a penalty cost for wind power curtailment in the objective function.Taking into account the above factors, we can establish the following objective function.

 
where chp  , and t ex P , respectively represent the cost of coal consumption per unit, 24 hours in a day, number of simultaneously operated CHP devices, the total amount of coal consumed by CHP devices during operation, cost incurred by wind power abandonment behavior, penalty factor for wind power abandonment, wind power abandonment quantity which is the amount of untapped wind energy generated by wind turbines, cost of purchasing electricity from external sources, the unit price of purchased and sold power, energy consumed or generated within a given period of time.

Equality constraint
The constraints of energy hubs mainly include electrical power balance constraints, thermal power balance constraints, and constraints on the production, conversion, and storage equipment of energy hubs.Equation (3) shows the details.

Equipment constraints and load constraints
Equations ( 8)-( 12) are equipment constraints and load constraints, respectively wind turbine constraints, CHP constraints, heat storage constraints, heat pump constraints, electric boiler constraints, and flexible demand response.

Example Settings
This article selects a typical industrial park in the northwest region as a research case, which includes various forms of flexible equipment, such as wind turbines, CHP, electric boilers, and thermal energy storage systems.The industrial park will be scheduled for 24 hours, with each hour being a time unit.We investigate various flexibility options and their combinations, including CHP/EB/HP, CHP/EB/HS/DSM, and all other comprehensive flexibility means options, to study the different combinations of flexibility options in thermal systems and coordinate control with thermal power plants and wind farms to support integrated wind power consumption.We consider the following two cases: Case 1: CHP/EB/HP scenario.To study the effects of electric boilers and heat pumps on the absorption of abandoned wind and to compare the effects of heat pumps and electric boilers on the absorption of abandoned wind, it is divided into four situations: CHP, CHP/EB, CHP/HP, and CHP/EB/HP.
Cast 2: CHP/EB/HS/DSM scenario.We research the impact of heat storage devices and demand side response on waste wind absorption, which is divided into two cases: CHP/EB/HS and CHP/EB/DSM.

Analysis of calculation results
In Case 1, the CHP mode is used as a reference scenario for research, with only CHP in the system and connected to the wind farm remotely.The goal of coordinated control is to consume wind power as much as possible.Without any additional flexibility options, using CHP alone to meet heat demand while maintaining electricity balance will result in only a relatively low share of wind power usage.Correspondingly, the wind power waste wind volume is 789.73MWh, and the total operating cost is 560.74kCNY.important means to break the CHP thermoelectric coupling and improve the flexibility of the heating system.At the same capacity, heat pumps are better as a means of flexibility regulation, as their thermal efficiency is much higher than that of electric boilers.Consider adding a 10 MW EB and a 10 MW HP simultaneously, and the wind utilization curve is represented by a blue dashed line.It can be seen that the combined effect of EB and HP is significantly better than a single flexibility method under the studied conditions.
In Case 2, after optimizing the addition of heat storage devices, the wind power consumption curve is shown as a light red dashed line in Figure 3.The flexibility of the system can not only be adjusted by means of power sources such as electric boilers, heat pumps, and heat storage but also be considered the flexibility adjustment on the load side, that is, the time delay of the thermal load.The results of the abandoned wind volume and operating costs for the two flexible methods are shown in Table 2.When a maximum 10% change in heat load is allowed, performance similar to HS can also be achieved.Under current research conditions, DSM is not as effective as HS, and it will play a better role when the heat load fluctuates greatly.

Conclusion
This article constructs a multi-objective regional energy system flexibility configuration model based on energy hubs, comprehensively considers operating costs, wind abandonment penalty costs, and electricity purchase costs, and optimizes the output of each piece of equipment.The following conclusions are drawn: Improving the flexibility of the system can increase its ability to absorb wind power, thereby reducing the operating costs of the system.At the same capacity, heat pumps are better as a means of flexibility regulation, as their thermal efficiency is much higher than that of electric boilers.Although the response effect of the load demand side is not as good as that of heat storage, the capital investment is almost zero, and the demand side response will play a better role when the heat load fluctuates greatly.

Fig. 1
Fig. 1 Input-output port model for Energy Hub


and hp COP represent the efficiency value of the electric boiler and the efficiency value of the heat pump,  and  represent the proportion coefficient of the input electric power consumed by the electric boiler and the heat pump, t s Q , represents the heat absorption and release of heat storage.

F
respectively represent the operating cost, penalty cost for wind abandonment, and electricity purchase cost of CHP during the scheduling period.

Fig. 2
Fig. 2 Case 1 wind power consumption Fig. 3 Case 2 wind power consumption International Conference on Energy Systems and Electrical Power

Table 1
Case 1 wind curtailment and operation cost