CN110797917A - Scheduling model of electric heating combined system - Google Patents

Abstract

The invention discloses a scheduling model of an electric heating combined system, which models the influence of the thermal inertia of a building at a user side on the operation cost of the electric heating combined system, and the established objective function is expressed as:the objective function is to minimize the total system cost, which is made up of the fuel cost of the conventional unit, the startup cost, and the wind or light penalty cost of the new energy unit. The model considers the thermal inertia of a building, realizes the delay satisfaction of the load of a thermodynamic system, improves the flexibility of the operation of the CHP unit and obviously reduces the operation cost of the system.

Description

A Scheduling Model of Combined Electric and Heating System

technical field

The invention relates to the technical field of electric heating systems, in particular to a scheduling model of an electric heating combined system.

Background technique

In winter in northern China, combined heat and power (CHP) units tend to generate electricity at night at their technical minimum output due to the unsynchronized power and heat loads, also known as the heat constant power mode. This inflexible cogeneration model is an important factor in reducing the utilization of wind or solar energy. In response to this problem, the current plans are mainly divided into two categories: (1) Install flexible heat sources or heat storage devices, including heat storage tanks, electric boilers, water (gas) source heat pumps, and pumped storage power stations. These devices can Adjusting the distribution of electricity and heat loads within a day, decoupling the limitation of CHP units in the heat-fixing mode, thereby increasing the consumption rate of new energy, but a big disadvantage is that additional investment and maintenance are required. (2) Another solution is to fully consider the heat storage effect and transmission delay of the heating pipe network, because the transmission of hot water in the heating pipe network takes time, and the longer the transmission distance, the greater the delay effect. By fully considering this dynamic process, it is possible to realize the delayed satisfaction of thermal load and smooth the change of thermal load, which can significantly reduce the operating cost of the system and reduce the loss of abandoned wind and abandoned light.

In addition, the response potential of the demand side has received increasing attention in recent years. In the category of thermal demand, the structure of the building directly affects the actual thermal demand of users. The research of the prior art mainly focuses on modeling the thermal demand of the building, including (1) a white box model, that is, the heat exchange of the building is studied through a specific physical process (2) a gray box model, which is simplified by the specific physical process. As a result, the mainstream model is the RC model (3) black-box model, which breaks away from the limitation of the physical model and simulates the thermal demand of the building based on historical data or machine learning. These methods can accurately simulate the thermal demand of users, but most of the current technical solutions do not connect the user side with the energy side, and do not deeply explore the impact of user demand response on the operating cost of large systems and new energy consumption.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a scheduling model of an electric-heating combined system, which takes into account the thermal inertia of the building, realizes the delayed satisfaction of the thermal system load, improves the flexibility of the CHP unit operation, and makes the operating cost of the system significantly decline.

The purpose of this invention is to realize through the following technical solutions:

A dispatching model of an electric-heating combined system, the dispatching model is modeled on the influence of the thermal inertia of the user-side building on the operation cost of the electric-heating combined system, and the established objective function is expressed as:

The objective function is to minimize the total cost of the system, which is composed of the fuel cost, startup cost of traditional units, and wind curtailment and light penalty costs of new energy units;

表示纯凝火电机组函数，其中p_it表示火电机组的出力，a_i、b_i、c_i表示与火电机组类型相关的成本参数，

表示火电机组的集合；in,

represents the pure condensing thermal power unit function, where p _it represents the output of the thermal power unit, a _i , b _i , c _i represent the cost parameters related to the type of thermal power unit,

Represents a collection of thermal power units;

表示热电联产CHP机组的成本函数，其中p_it、h_it分别表示CHP的电热出力，

表示与CHP机组类型相关的成本参数，

表示CHP机组的集合；

represents the cost function of the CHP unit, where p _it and h _it represent the electrothermal output of CHP, respectively,

represents the cost parameter associated with the CHP unit type,

Represents a collection of CHP units;

为风电机组的可发电出力上限，p_it为风电机组的实际电出力，表示风电机组的集合； represents the wind abandonment penalty function, where λ _i wind abandonment penalty term coefficient,

is the upper limit of the power generation output of the wind turbine, p _it is the actual electric output of the wind turbine, Represents a collection of wind turbines;

表示弃光惩罚函数，其中λ_i弃光惩罚项系数，为光伏机组的可发电出力上限，p_it为光伏机组的实际电出力，

表示光伏机组的集合。

represents the light rejection penalty function, where λ _i is the light rejection penalty term coefficient, is the upper limit of the power generation output of the photovoltaic unit, p _it is the actual power output of the photovoltaic unit,

Represents a collection of PV units.

It can be seen from the technical solution provided by the present invention that the above model considers the thermal inertia of the building, realizes the delayed satisfaction of the thermal system load, improves the flexibility of the CHP unit operation, and significantly reduces the operating cost of the system.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a structural diagram of an electric heating combined power supply energy system according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a test system in an example of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. FIG. 1 is a structural diagram of a combined electricity and heat power supply energy system according to an embodiment of the present invention. For the combined electricity and heat energy system, based on this FIG. 1 , an embodiment of the present invention provides a scheduling model of the combined electricity and heat system. The established objective function is expressed as:

The objective function is to minimize the total cost of the system, which is composed of the fuel cost, startup cost of traditional units, and wind curtailment and light penalty costs of new energy units;

表示纯凝火电机组函数，其中p_it表示火电机组的出力，a_i、b_i、c_i表示与火电机组类型相关的成本参数，

表示火电机组的集合；

represents the pure condensing thermal power unit function, where p _it represents the output of the thermal power unit, a _i , b _i , c _i represent the cost parameters related to the type of thermal power unit,

Represents a collection of thermal power units;

表示热电联产CHP机组的成本函数，其中p_it、h_it分别表示CHP的电热出力，表示与CHP机组类型相关的成本参数，

表示CHP机组的集合；

represents the cost function of the CHP unit, where p _it and h _it represent the electrothermal output of CHP, respectively, represents the cost parameter associated with the CHP unit type,

Represents a collection of CHP units;

表示弃风惩罚函数，其中λ_i弃风惩罚项系数，

为风电机组的可发电出力上限，p_it为风电机组的实际电出力，

表示风电机组的集合；

represents the wind abandonment penalty function, where λ _i wind abandonment penalty term coefficient,

is the upper limit of the power generation output of the wind turbine, p _it is the actual electric output of the wind turbine,

Represents a collection of wind turbines;

表示弃光惩罚函数，其中λ_i弃光惩罚项系数，

为光伏机组的可发电出力上限，p_it为光伏机组的实际电出力，

表示光伏机组的集合。

represents the light rejection penalty function, where λ _i is the light rejection penalty term coefficient,

is the upper limit of the power generation output of the photovoltaic unit, p _it is the actual power output of the photovoltaic unit,

Represents a collection of PV units.

In the specific implementation, the constraints of the above scheduling model in the thermal system include:

1) The combined electric and heat distribution interval of the CHP unit is a convex interval surrounded by several poles connected by line segments, and the corresponding constraints are as follows:

表示CHP机组的集合；

表示时段的集合；公式(3)表示CHP机组与热网之间的传热过程，表示CHP机组在单位时间内的流量；

表示CHP机组在热网中的供、回水温度；Φ_n(i)表示CHP机组所连接的热网节点的集合；Among them, formulas (1)-(2) are used to describe the feasible range of the CHP unit; p _it and h _it are the electrical and thermal outputs of the CHP unit, respectively; P _i ^j , respectively represent the electric and thermal output of each pole corresponding to the feasible region of the CHP unit; NJ _c is the number of poles;

Represents a collection of CHP units;

represents the set of time periods; formula (3) represents the heat transfer process between the CHP unit and the heat network, Indicates the flow rate of CHP unit in unit time;

Represents the supply and return water temperatures of the CHP unit in the heat network; Φ _n (i) represents the set of heat network nodes connected to the CHP unit;

2) The electric boiler generates heat energy by consuming electric energy, which is used to decouple the limitation of the CHP unit in the heat constant electricity mode. The relevant constraints are as follows:

为电锅炉的消耗电功率的上下限值；

为电锅炉的电热转换效率；

表示电锅炉的集合；Among them, p _it and h _it respectively represent the electric power consumed by the electric boiler and the output heat;

is the upper and lower limit of the electric power consumption of the electric boiler;

is the electric heat conversion efficiency of the electric boiler;

Represents a collection of electric boilers;

3) The heat exchange station is a transfer station in the thermal system, which is equivalent to the heat load in the heat transmission network, and acts as a heat source to heat the lower-level user group in the heat distribution network. The corresponding constraints are as follows:

为流经换热站的热水流量；

分别为流经换热站的供、回水温度；h_it为换热站的热交换量；

为回水温度上、下限；Φ_n(i)表示换热站所连接的节点的集合；表示换热站的集合；in,

is the hot water flow through the heat exchange station;

are the temperature of supply and return water flowing through the heat exchange station respectively; h _it is the heat exchange amount of the heat exchange station;

are the upper and lower limits of the return water temperature; Φ _n (i) represents the set of nodes connected to the heat exchange station; Represents a collection of heat exchange stations;

4) Due to the low flow rate of the pipes in the thermal network, the hot water can be fully mixed at the nodes, that is, the transient process of hot water mixing is ignored, and the constraint of temperature mixing is expressed as:

分别表示在供、回水管道中热水的温度；

分别表示在供、回水管道中热水的流量；

分别表示离开和通往节点的管道的集合；表示热网中的节点集合；in,

Represent the temperature of hot water in the supply and return pipes, respectively;

Represent the flow of hot water in the supply and return pipes, respectively;

represents the set of pipes leaving and leading to a node, respectively; Represents the set of nodes in the thermal network;

The constraint on pressure loss is expressed as:

表示供、回水管道始末两节点的压强；n₁、n₂分别表示管道的起始节点和终止节点；μ_b表示管道的粗糙程度；为热网中管道的集合。in,

represents the pressure at the beginning and end of the supply and return pipes; n ₁ and n ₂ represent the starting and ending nodes of the pipeline respectively; μ _b represents the roughness of the pipeline; is a collection of pipes in the heat network.

The constraints on the demand side of the scheduling model include:

In this technical solution, the heat load parameter is not derived from the forecast curve of the heat load a day before, but is obtained from the actual wind speed, temperature and other parameters on the demand side. The model considers the heat exchange of the building wall, the heat exchange of the window and the ventilation consumption. To simplify the problem, the necessary approximation conditions are described as follows:

a) The heat transmission medium (ie air) is evenly distributed in the room.

b) The applicable object in this technical solution is set as a building cluster, so the heat transfer process between the walls inside the building is ignored.

1) Heat exchange of building walls

Due to the thickness of the wall, the change of the external temperature does not immediately act on the inside of the building, and the heat exchange between the exterior and interior surfaces of the building wall is as follows:

分别表示墙体外、内表面以及室内温度变量；

表示墙体内表面的平均温度；Among them, λ _env,out , λ _env,in represent the thermal conductivity of the exterior and interior surfaces of the building wall, respectively; α _env,out , α _env,in are the composite heat transfer coefficients of the exterior and interior surfaces of the wall; T _t ^env is the temperature of the wall; x ^env represents the displacement variable inside the wall (0≤x ^env ≤δ _env ); β ^solar represents the solar radiation absorption ratio of the outer surface of the wall; T _t ^out represents the external temperature parameter;

Represent the external, internal surface and indoor temperature variables of the wall, respectively;

Indicates the average temperature of the inner surface of the wall;

2) Heat exchange of building windows

Compared with the wall, the windows of the building are much thinner, so the dynamic heat transfer process inside the window glass can be ignored. The heat balance equation of the building window is expressed as:

表示由建筑物窗户热交换总量，其可分为与两部分，

为通过太阳辐射获得的热量，

为由室内外温差的导致的传导热损；A^wg是窗户玻璃的散射面积；A^sg是窗户玻璃的直射面积；

表示单位时间单位面积太阳的直射、散射量；C₁是窗户的类型系数；C₂是窗户的颜色系数；C₃是窗户的材料系数；M表示热量积累系数；in,

Represents the total amount of heat exchange by building windows, which can be divided into and two parts,

for the heat obtained by solar radiation,

is the conduction heat loss caused by the temperature difference between indoor and outdoor; A ^wg is the scattering area of the window glass; A ^sg is the direct area of the window glass;

Indicates the direct and scattered amount of the sun per unit time and unit area; _C1 is the type coefficient of the window; _C2 is the color coefficient of the window; C3 is the material coefficient of the window; _M is the heat accumulation coefficient;

3) Heat dissipation of buildings

The dissipation of ventilation caused by these gaps is unavoidable as the wall and window are not perfectly fitted.

表示建筑物的通风热耗散，Ven是每小时通风量，与外界风速相关。in,

Representing the ventilation heat dissipation of the building, Ven is the ventilation volume per hour, which is related to the outside wind speed.

4) Heat balance equation

The regional total heat balance equation is of the form:

由上述公式获得；H_t表示由供热管网供应的热量；C_in表示室内空气的比热容；M_K表示室内空气的总体积。in,

Obtained by the above formula; H _t represents the heat supplied by the heating pipe network; C _in represents the specific heat capacity of indoor air; M _K represents the total volume of indoor air.

In addition, the constraints of the dispatch model power system further include:

Among them, Equation 25 is the node power balance constraint; Equation 26-28 is the generator output constraint; Equation 29-30 is the unit climbing constraint; Equation 31-32 is the line capacity limit constraint.

In order to verify the validity of the model described in the embodiment of the present invention, a combined system composed of an improved IEEE six-node power system and a six-node thermal system is used for analysis. Figure 2 shows the structure of the test system in the example of the present invention. Schematic, Table 1 lists the capacities of the equipment involved in this example:

Table 1 Capacity of main equipment

A. Thermal inertia of the building

The following two cases are used to test the influence of the thermal inertia of the building:

Case 1: The dynamic process of heat transfer inside the building wall is not considered, that is, the traditional economic dispatch mode.

Case 2: Consider the thermal dynamic process inside the building wall and compare it with the traditional economic model.

As shown in Table 2, the running cost of Case 2 is lower than that of Case 1. The operating cost of the pure condensing unit is almost the same in the two cases, while for the CHP unit operating cost and wind abandonment penalty cost, Case2 is significantly lower than Case1, so the wind energy utilization rate is different in the two cases. It can be seen that in Case 2, the limitation of the CHP unit in the heat constant power mode is relaxed, so that the amount of abandoned air is significantly reduced.

Table 2 Costs of Case 1 and Case 2 ($)

B. Influence of wind speed and light parameters

Take wind speed as an example to test the impact on system cost.

Case 3: On the basis of Case 2, set the wind speed to 75% of the typical value.

Case 4: On the basis of Case2, set the wind speed to 125% of the typical value.

Table 3 Costs of Case 2-Case 4 ($)

As shown in the data in Table 3 above: the total cost of the system of Case 3 is reduced by 3.9% compared with that of Case 2, while the total cost of the system of Case 4 is increased by 1.4% compared with that of Case 2, and when the proportion of wind power access is doubled , the difference of system cost can exceed ±5%, indicating that the change of wind speed will have a significant impact on the change of system energy cost.

It should be noted that the content not described in detail in the embodiments of the present invention belongs to the prior art known to those skilled in the art.

To sum up, the model provided by the embodiment of the present invention has the following advantages:

1) In addition to considering the heat storage effect of the heating pipe network, this embodiment also models the thermal inertia of the building on the user side.

2) The traditional thermal scheduling model only predicts the thermal load based on the temperature difference, ignoring the wind speed and solar radiation. This embodiment quantifies the influence of wind speed and solar radiation on the heat demand on the load side, and visualizes the effects of wind speed and illumination. For areas with large changes in wind speed and illumination, the accuracy of prediction and the flexibility of adjustment can still be guaranteed.

3) In addition to the wall of the building, this embodiment also models the heat exchange model of the window of the building, so that the proposed solution has stronger accuracy and applicability.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (4)

1. a dispatching model of an electric-heating combined system, it is characterized in that, described dispatching model is modeled with the thermal inertia of user side building on the influence of electric-heating combined system operating cost, and the established objective function is expressed as:

The objective function is to minimize the total cost of the system, which is composed of the fuel cost, startup cost of traditional units, and wind curtailment and light penalty costs of new energy units; in,

represents the pure condensing thermal power unit function, where p _it represents the output of the thermal power unit, a _i , b _i , c _i represent the cost parameters related to the type of thermal power unit,

Represents a collection of thermal power units;

represents the cost function of the CHP unit, where p _it and h _it represent the electrothermal output of CHP, respectively,

represents the cost parameter associated with the CHP unit type,

Represents a collection of CHP units;

represents the wind abandonment penalty function, where λ _i wind abandonment penalty term coefficient,

is the upper limit of the power generation output of the wind turbine, p _it is the actual electric output of the wind turbine,

Represents a collection of wind turbines;

represents the light rejection penalty function, where λ _i is the light rejection penalty term coefficient,

is the upper limit of the power generation output of the photovoltaic unit, p _it is the actual power output of the photovoltaic unit,

Represents a collection of PV units. 2. The scheduling model of the combined electric and heating system according to claim 1, wherein the constraints of the scheduling model in the thermal system include: 1) The combined electric and heat distribution interval of the CHP unit is a convex interval surrounded by several poles connected by line segments, and the corresponding constraints are as follows:

Among them, formulas (1)-(2) are used to describe the feasible range of the CHP unit; p _it and h _it are the electrical and thermal outputs of the CHP unit, respectively; P _i ^j ,

respectively represent the electric and thermal output of each pole corresponding to the feasible region of the CHP unit; NJ _c is the number of poles;

Represents a collection of CHP units;

represents the set of time periods; formula (3) represents the heat transfer process between the CHP unit and the heat network,

Indicates the flow rate of CHP unit in unit time; Represents the supply and return water temperatures of the CHP unit in the heat network; Φ _n (i) represents the set of heat network nodes connected to the CHP unit; 2) The electric boiler generates heat energy by consuming electric energy, which is used to decouple the limitation of the CHP unit in the heat constant electricity mode. The relevant constraints are as follows:

Among them, p _it and h _it respectively represent the electric power consumed by the electric boiler and the output heat;

is the upper and lower limit of the electric power consumption of the electric boiler;

is the electric heat conversion efficiency of the electric boiler; Represents a collection of electric boilers; 3) The heat exchange station is a transfer station in the thermal system, and its corresponding constraints are as follows:

in,

is the hot water flow through the heat exchange station;

are the temperature of supply and return water flowing through the heat exchange station respectively; h _it is the heat exchange amount of the heat exchange station;

are the upper and lower limits of the return water temperature; Φ _n (i) represents the set of nodes connected to the heat exchange station;

Represents a collection of heat exchange stations; 4) The constraint of temperature mixing is expressed as:

in,

Represent the temperature of hot water in the supply and return pipes, respectively;

Represent the flow of hot water in the supply and return pipes, respectively;

represents the set of pipes leaving and leading to a node, respectively;

Represents the set of nodes in the thermal network; The constraint on pressure loss is expressed as:

in, represents the pressure at the beginning and end of the supply and return pipes; n ₁ and n ₂ represent the starting and ending nodes of the pipeline respectively; μ _b represents the roughness of the pipeline;

is a collection of pipes in the heat network. 3. The scheduling model of the combined electric and heating system according to claim 1, wherein the constraints of the scheduling model on the demand side include: 1) Heat exchange of building walls The heat exchange between the exterior and interior surfaces of a building wall is as follows:

Among them, λ _env,out , λ _env,in represent the thermal conductivity of the exterior and interior surfaces of the building wall, respectively; α _env,out , α _env,in are the composite heat transfer coefficients of the exterior and interior surfaces of the wall; T _t ^env is the temperature of the wall; x ^env represents the displacement variable inside the wall (0≤x ^env ≤δ _env ); β ^solar represents the solar radiation absorption ratio of the outer surface of the wall; T _t ^out represents the external temperature parameter;

T _t ⁱⁿ represents the external, internal surface and indoor temperature variables of the wall, respectively;

Indicates the average temperature of the inner surface of the wall; 2) Heat exchange of building windows The heat balance equation for a building window is expressed as:

in,

Represents the total amount of heat exchange by building windows, which can be divided into

and two parts,

for the heat obtained by solar radiation,

is the conduction heat loss caused by the temperature difference between indoor and outdoor; A ^wg is the scattering area of the window glass; A ^sg is the direct area of the window glass; Indicates the direct and scattered amount of the sun per unit time and unit area; _C1 is the type coefficient of the window; _C2 is the color coefficient of the window; C3 is the material coefficient of the window; _M is the heat accumulation coefficient; 3) Heat dissipation of buildings Specifically expressed as: in,

Represents the ventilation heat dissipation of the building, Ven is the ventilation volume per hour, which is related to the outside wind speed; 4) Heat balance equation The regional total heat balance equation is of the form:

in, Obtained by the above formula; H _t represents the heat supplied by the heating pipe network; C _in represents the specific heat capacity of indoor air; M _K represents the total volume of indoor air. 4. The dispatch model of the combined electric and heat system according to claim 1, wherein the constraints of the dispatch model power system include:

Among them, Equation 25 is the node power balance constraint; Equation 26-28 is the generator output constraint; Equation 29-30 is the unit climbing constraint; Equation 31-32 is the line capacity limit constraint.

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