CN113761727B - Method for constructing optimal scheduling model of combined heat and power system containing distributed electric heat pump - Google Patents
Method for constructing optimal scheduling model of combined heat and power system containing distributed electric heat pump Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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Abstract
The invention discloses a method for constructing an optimal scheduling model of a combined heat and power system with a distributed electric heat pump, which comprises the following steps: the heating area under each primary heating station is regarded as the heat load at a heating station node, so that a heating network simplified topological structure is obtained; establishing a source load direct connection model considering heat medium transmission delay, heat medium dynamic temperature and heat load; calculating the water temperature of the heat source end when the electroless heat pump is used, and considering the temperature change degree of the heat medium at each load node and the temperature change at the outlet of the source end when the transmission delay is taken into consideration; establishing an operation power control model of the electric heating pump; the method comprises the steps of taking the minimum running cost of the whole system as a target, and taking the constraint condition of electrothermal coupling into consideration to establish an optimal scheduling model of the thermoelectric combined system; the middle process of the modeling of the heating power pipe network is properly simplified, and the dynamic mathematical relationship between the heat supply quantity of the heat source end and the heating demand quantity of the load end is directly expressed. This compact thermodynamic network model is more convenient to embed in the scheduling model of the power system.
Description
Technical Field
The invention relates to the technical fields of cogeneration unit operation, electric heat pump heating and wind power absorption, in particular to establishment of an optimal scheduling model of a cogeneration system by considering thermal inertia of a thermodynamic system and auxiliary heat supply of an electric heat pump.
Background
The wind power installation capacity of China is mainly distributed in the northern area, and meanwhile, the wind discarding problem in the northern area is most serious. In the power supply system in northern areas of China, large-scale coal-fired cogeneration units occupy the main position, and because the units are operated in a working mode of 'electricity by heat and electricity', the electric output cannot be flexibly regulated, the integral peak regulation capacity of the power system is weakened, and the problem of wind disposal is serious. According to the existing research results, constructing a combined heat and power system is considered to be an effective method for breaking the peak shaving bottleneck of the power system. On one hand, the thermodynamic system has larger thermal inertia, and the thermodynamic network can be equivalently regarded as a heat storage unit; on the other hand, an electric heat pump is arranged in the thermodynamic system, so that the cogeneration unit can be assisted to supply heat. The heat supply pressure of the cogeneration unit can be reduced in both aspects, so that the cogeneration unit can more flexibly adjust the electricity output, thereby improving the integral peak regulation capacity of the power system and promoting the wind power consumption.
In order to practically utilize the energy storage characteristics of the thermodynamic system in the optimal scheduling of the thermoelectric combined system, the key is to establish a reasonable thermodynamic system model: the energy storage characteristics of the heat supply network and the building are reserved, and the complexity of the model is simplified as much as possible, so that a concise and clear optimal scheduling model of the combined heat and power system is constructed. In a traditional thermodynamic system model, the heat medium flow and temperature variables at each pipe section and node of a primary heat supply network and a secondary heat supply network are generally included, the modeling process is biased to be complex, and the intermediate variables are numerous and are not suitable for scheduling modeling of a combined heat and power system. In addition, the addition of the electric heat pump also increases the modeling complexity, and the supply-demand balance relation between the source end and the load end of the thermodynamic network needs to be reconstructed.
In fact, key factors affecting the energy storage characteristics of the thermodynamic system are represented by transmission delay, transmission loss and dynamic temperature variation of the heating medium in the thermodynamic pipe network, and indoor temperature variation of the heating building. Therefore, the middle process of modeling the thermodynamic pipe network needs to be properly simplified, a source-load direct-connection model of the thermodynamic system is established, and the dynamic mathematical relationship between the heat supply quantity of the heat source end and the heating demand quantity of the load end is directly expressed. The compact thermodynamic network model is more convenient to embed into a scheduling model of the electric power system, and finally an optimal scheduling model of the thermoelectric combined system is built.
Summary of the invention
Aiming at the defects or improvement demands of the prior art, the invention aims to solve the problems that in the traditional thermodynamic system model in the prior art, the modeling process is biased to be complex, the intermediate variables are numerous, and the modeling method is not suitable for scheduling modeling of a combined heat and power system. In addition, the addition of the electric heat pump also increases the modeling complexity, and the problem of reconstructing the supply-demand balance relation between the source end and the load end of the thermal network is required.
The technical scheme of the invention is as follows: a method for constructing an optimal scheduling model of a combined heat and power system containing a distributed electric heat pump comprises the following steps:
step 1: the heating area under each primary heating station is regarded as the heat load at a heating station node, so that a heating network simplified topological structure is obtained; establishing a source load direct connection model considering heat medium transmission delay, heat medium dynamic temperature and heat load;
step 2: calculating the water temperature of the heat source end when the electroless heat pump is used, and considering the temperature change degree of the heat medium at each load node and the temperature change at the outlet of the source end when the transmission delay is taken into consideration; assuming that the energy conversion efficiency of the distributed electric heating pumps at each heating power station is the same, taking the transmission delay of a heating power network into consideration, and establishing an operation power control model of the electric heating pump;
step 3: and (3) taking the minimum running cost of the whole system as a target, and taking the constraint condition of electrothermal coupling into consideration to establish an optimal scheduling model of the thermoelectric combined system.
Further, in the step 1, the specific method for obtaining the simplified topological structure of the thermodynamic network is as follows:
in a dendritic topology thermodynamic network, the heating area under each primary thermodynamic station is regarded as the heat load at one thermodynamic station node, denoted by H m (m=1,., M) represents, M is the total number of nodes; the water supply pipe network and the water return pipe network are arranged in parallel under the ground, and each small section of water supply pipe network and the water return pipe network are marked as(n=1,..2M), in the water supply and return pipe networkThe nodes of (a) are respectively represented by letters S and R (the above label forms differ), resulting in a simplified topology of the thermodynamic network.
Further, the method for considering the transmission delay of the heating medium in the step 1 is as follows:
because the length of the pipeline in the primary pipe network can reach thousands of meters, a period of time is needed for the heat medium to be transferred to each load node after the heat exchange from the heat source, and the transfer delay can reach several times longer than the scheduling period of the electric power system; the transmission delay is determined by the length and the sectional area of the pipeline:
wherein ρ is w Is the density of water;and->Respectively corresponding pipelines->Length and cross section of (a); />Is the transmission delay;the mass flow of the heating medium in the pipeline is represented by M, which is a positive integer.
The water supply pipeline and the water return pipeline which are laid side by side in pairs have the same design parameters, namely, the length, the pipe diameter thickness, the heat insulation performance and other parameters of each pair of water supply pipeline and the water return pipeline are the same, so that the mass flow and the transmission delay in the paired pipelines are equal:
in the method, in the process of the invention,and->The mass flow and the transmission delay in the return water pipeline are respectively.
Further, the method for considering the dynamic temperature of the heating medium in the step 1 is as follows:
the heat output from the heat source is gradually reduced after passing through the transmission loss along the pipe network and being consumed by users, so that the temperature of the heat medium is continuously reduced along with the extension of the pipe network; the expression of temperature change and heat loss is:
wherein, in the formula,the temperature difference of heating medium is respectively the water supply pipe, the water return pipe and the input and output ports of the mth heating power station; />Is a water supply line connected to the mth heating station +.>The mass flow of the heating medium in the furnace; c w Is the specific heat capacity of water; h is a m Is the equivalent thermal load at the thermal station; />The heat power loss in the water supply and return pipelines is respectively;
because the number of nodes and pipelines in the thermodynamic network is numerous, if the temperature change of each pipeline is represented, a plurality of intermediate variables are generated, so that the establishment of a concise combined heat and power optimization scheduling model is not facilitated; in fact, since the losses in the pipe are substantially constant in the quality regulation mode, the temperature variation in the pipe is ultimately determined by the heat load level; if the relation between the heat load and the temperature of the heat source end water supply and return can be directly expressed, the calculation process of the intermediate temperature variable can be omitted, and the simplified modeling is realized;
according to the baseThe total flow of the heating media flowing into the same node from a plurality of pipelines is equal to the total flow flowing out of the node, and the energy of the heating media flowing into and out of the same node is the same; for any mixed flow node R 2m (m=1,., M) satisfying the energy conservation relation:
in the method, in the process of the invention,and->Respectively corresponding return water pipes->And->The mass flow of the heating medium; />Respectively corresponding return water pipes->The heat medium loss in the process; />Is the temperature of the heating medium flowing out of the mth heating station; />And->The temperature of the heat medium flowing out of the mixed flow nodes of the 2m and the 2 (m+1) th are respectively; thus, the mixed flow node R can be derived 2m The temperature expression of the outgoing heat medium is:
considering the transmission loss along the way from the heat source to the mth heating station, the temperature expression of the heat medium flowing out from the heating stationThe method comprises the following steps:
wherein T is 1 S 、Respectively water supply pipeline->The temperature of the heating medium, the loss of the heating medium and the mass flow of the heating medium;respectively water supply pipeline->Loss of heating medium, mass flow of heating medium, +.>For water supply pipe L s 2m The heat medium loss in the process;
according to formulas (5) - (7), the deductions are:
finally obtaining the return water temperature of the heat source portCan be expressed as:
substituting the transmission delay into the formula (9), and finally obtaining a dynamic relation between the temperature of the water supply and return at the heat source and the heat load:
in the method, in the process of the invention,and->The water supply and return temperatures of the heat source at the moment t are respectively; alpha m Is the total time required by the heat medium to be transmitted from the heat source to the mth heating power station, and takes integer times of the modulation time period delta t; />And->Is t-2 alpha m The water supply temperature at the heat source at the moment and the heat load at the mth heating station; />Is t-alpha m The thermal load at the mth thermal station at the moment,respectively corresponding water supply pipelines->Transmission delay in (a); />Is the maximum heating temperature born by the heating power pipe network, and round represents a rounding function.
Further, the transmission thermal power loss is determined by the thermal resistance and the length of the pipeline, and the power loss can be expressed as:
wherein, in the formula,and->The average temperatures of water supply, backwater and earth surface soil are respectively; gamma ray S 、γ R 、γ soil And gamma ad The thermal resistance and the additional thermal resistance of the water supply pipeline, the water return pipeline and the soil are respectively; />For corresponding pipe->Is a length of (2); the other parameters except the temperature are fixed parameters, so that the transmission loss of each section of pipeline can be estimated in advance according to the average temperature.
Further, the method for considering the thermal load in the step 1 is as follows: the load at each heat exchange station node is processed according to the building with the same heat conduction coefficient, and the outdoor temperature change of the same heat supply area is the same; according to the law of heat transfer, the transient thermal equilibrium expression of the indoor temperature is:
in the method, in the process of the invention,representing the indoor temperature of a building at an mth heating station at the moment t; t (T) t out The outdoor temperature is t time; h is a m,t The heat load at the mth heating station at the t moment; k (K) m 、A m 、V m The heat conduction coefficient, the surface area and the heating volume of the building are respectively; c air And ρ air Air specific heat capacity and density, respectively;
due to the heat preservation effect of the building wall, the temperature change in the building room is very slow, and the temperature outside the room is basically unchanged at intervals of a scheduling period, the steady-state expression of the temperature inside the room in each period can be obtained according to a first-order differential equation of the formula (11):
in the method, in the process of the invention,representing the indoor temperature of the building at the mth heating station at the time t-1; />Representing the indoor temperature of a building at an mth heating station at the moment t; x-shaped articles m Is a thermal coefficient;
the relation of the heating load power with respect to the indoor and outdoor temperatures can be simplified:
in the method, in the process of the invention,and->The upper limit and the lower limit of the indoor heating temperature are respectively +.>Representing the indoor temperature of the building at the mth heating station at the time t-1;
formulas (10) and (13) form a 'source-charge direct connection model' of the thermodynamic system, so that the temperature change characteristic and the transmission delay characteristic of the heat medium transmitted from a heat source end to a water return end are reserved, and a large number of temperature variables of intermediate nodes can be saved; the heat load demand is directly related to the hot water supply temperature of the source end, and the heat load demand is similar to the direct relation of the electric load and the unit electric output in the electric power system in form, so that a concise and clear combined heat and power dispatching model is conveniently generated.
Further, the step 2 specifically includes: the electric heating pump is arranged at the first-stage heat exchange station in a dispersing way, the operation of the electric heating pump does not change the flow of a pipe network, and only changes the inflowThe temperature of the load side heating medium; when the heat pump is in no-electricity state, the water supply temperature of the heat source end,satisfying the formula:
in the method, in the process of the invention,the heat power of the ith cogeneration unit CHP at the time t is used as the heat power; n1 is the number of thermoelectric units;
at the current backwater temperature of t period, if the thermal power plant reduces heat supply, the outlet water temperature of the heat source end is reduced, the temperature of the heat medium at the inlet of each heat load node is reduced, and the temperature change degree of the heat medium at each load node is the same as the temperature change at the outlet of the source end due to the unchanged flow of the pipeline, and the temperature change satisfies the following conditions in consideration of transmission delay:
in the method, in the process of the invention,the temperature of the heat medium at the heat source end and the heat load inlet end is reduced respectively; />A reduced total thermal power for the thermal power plant;
in order to meet the heating requirement, the reduced heating capacity of the thermal power plant should be supplemented by the electric heating pump, and assuming that the energy conversion efficiency of the electric heating pump dispersed at each thermal power station is the same, taking the transmission delay of the thermal network into consideration, the total heat power which should be provided by the electric heating pump in an auxiliary way is as follows:
in the method, in the process of the invention,and beta HP The total operation power and the conversion efficiency of the electric heat pump are respectively; />Is t+alpha m The operation power of the electric heating pump at the mth thermal load at the moment;
the reduction of heat supply at the heat source end reduces the water supply temperature at each thermodynamic loadThe electric heat pump heat supply at this point satisfies the condition:
by combining equations (15) - (17), it can be obtained that the heating power of the electric heat pump at each heat station should satisfy the following conditions:
in the method, in the process of the invention,is a water supply line connected to the mth heating station +.>The mass flow of the heating medium in the reactor is>The power capacity of the electric heat pump is installed for the mth heat load side.
Further, the method for establishing the optimal scheduling model of the thermoelectric combined system by taking the running cost of the whole system as the minimum and considering the constraint condition of the electrothermal coupling comprises the following steps:
the power supply unit in the combined heat and power system is a cogeneration unit, a pure condensing power unit, a wind power unit and other peak shaving units; the interaction of the electric power system and the thermodynamic system is realized through a cogeneration unit, the cogeneration unit takes heat supply as priority, and then peak regulation service is provided for the electric power system; the optimal scheduling of the combined heat and power system aims at minimizing the running cost of the whole system, and the running cost of the wind turbine generator set and the hydroelectric turbine generator set is very low, so that the running cost comprises the coal consumption cost of the coal-fired turbine generator set, and in addition, in order to consume wind power as much as possible, the abandoned wind is added into the cost in a penalty function mode; the objective function established is as follows:
wherein C is coal Is the total coal consumption;coal consumption of a thermoelectric unit and a pure thermal power unit; />A penalty function for wind abandoning; />The electric power output by the cogeneration unit and the pure condensing unit at the moment t respectively;is the coal consumption coefficient of the thermoelectric unit; /> The coal consumption coefficient of the pure condensing unit; n2 is the number of pure condensing units; />The wind power is produced and consumed respectively; epsilon w Is a penalty function coefficient; nt is the last scheduling period in the scheduling period, < >>The thermal power of the ith thermoelectric unit at the time t is obtained.
Further, the electrothermal coupling constraint condition in the step 3 includes:
(1) Electric power balance constraint
In the formula, the superscript CHP, CON, OTH, WF respectively represents a cogeneration unit, a pure fossil power unit, other types of units and a wind turbine generator; p (P) t OTH The total electric output of other types of units at the moment t; pe (Pe) t Is the electrical load power;
(2) Thermal power balance constraint
Wherein Ph is t In order to be able to carry out a thermal load power,and->Respectively t+alpha m The heat load and the running power of the electric heating pump at the mth heating station at the moment;
(3) Upper and lower limit constraint of unit output
In the method, in the process of the invention,the thermal power and the maximum thermal power output by the thermoelectric unit in the period t are respectively; /> The upper limit and the lower limit of the electric output of the ith thermoelectric unit are respectively; />The upper limit and the lower limit of the electric output force of the j-th pure condensing unit are respectively; />The upper limit and the lower limit of the electric output of other types of units are respectively; a, a i 、b i 、c i 、/>Is the operation characteristic parameter of the thermoelectric unit;
(4) Unit climbing constraint
In U CHP 、D CHP The upper limit and the lower limit of the climbing power of the thermoelectric unit are respectively; u (U) CON 、D CON The upper limit and the lower limit of climbing power of the pure condensing unit are respectively set; u (U) OTH 、D OTH The upper limit and the lower limit of climbing power of other types of units are respectively set;the electric power of the ith thermoelectric unit, the pure condensing unit and other types of units at the time t+1 is respectively; />The thermal power of the ith thermoelectric unit at the time t-1 is beta HP Respectively the conversion efficiency of the electric heating pump;
(5) Supply and return water temperature constraints
For time t-alpha m The electric heat pump operating power at the mth thermal load.
In general, the above technical solutions conceived by the present invention, compared with the prior art, enable the following beneficial effects to be obtained:
1. the method for constructing the optimal scheduling model of the combined heat and power system of the distributed electric heat pump not only maintains the temperature change characteristic and the transmission delay characteristic of the heat medium transmitted from the heat source end to the backwater end, but also can omit a large number of temperature variables of intermediate nodes. The heat load demand is directly related to the hot water supply temperature of the source end, and the heat load demand is similar to the direct relation of the electric load and the unit electric output in the electric power system in form, so that a concise and clear combined heat and power dispatching model is generated;
2. the invention relates to a construction method of a distributed electric heat pump combined heat and power system optimization scheduling model, which is used for properly simplifying the middle process of a heating power pipe network modeling, mainly taking the thermal inertia of the heating power network and the operation characteristics of an electric heat pump into consideration, and establishing a source load direct connection model of the heating power system, thereby directly expressing the dynamic mathematical relationship between the heat supply quantity of a heat source end and the heating demand quantity of a load end. This compact thermodynamic network model is more convenient to embed in the scheduling model of the power system.
Drawings
FIG. 1 is a simplified heat pipe network structure diagram of a preferred embodiment of the present invention;
FIG. 2 is a simplified topology of a cogeneration system according to a preferred embodiment of the invention;
FIG. 3 is a graph showing the comparison of wind power consumption curves before and after an electric heating pump is added in the preferred embodiment of the invention;
FIG. 4 is a graph of operating power of an electric heat pump in accordance with a preferred embodiment of the present invention;
FIG. 5 is a graph showing the change in heat output of thermoelectric units before and after the electric heat pump is installed in accordance with the preferred embodiment of the present invention;
FIG. 6 is a graph showing the temperature change of the water before and after the power-on heat pump according to the preferred embodiment of the present invention;
FIG. 7 is a graph showing the comparison of the power output of thermoelectric units before and after the electric heat pump is additionally installed in the preferred embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The invention relates to a method for constructing an optimal scheduling model of a combined heat and power system with a distributed electric heat pump, which specifically comprises the following steps:
step 1: and establishing a source load direct connection model of the thermodynamic system.
The central heating network with the dendritic topological structure is the most common network form of the central heating system in China, and the thermodynamic network related to the invention is the dendritic topological structure.
In a dendritic topology thermodynamic network, the heating area under each primary thermodynamic station is regarded as the heat load at one thermodynamic station node, denoted by H m (m=1.,), M) is represented by the formula (I), M is the total number of nodes. The water supply pipe network and the water return pipe network are arranged in parallel under the ground, and each small section of water supply pipe network and the water return pipe network are marked as(n=1,..2M.) nodes in the water supply and return network are denoted by letters S and R, respectively, resulting in a simplified topology of the thermodynamic network.
(1) Transmission delay
Because the length of the pipeline in the primary pipe network can reach thousands of meters, a period of time is required for the heat medium to be transferred to each load node after the heat exchange from the heat source, and the transfer delay can reach several times longer than the scheduling period of the power system. The transmission delay is mainly determined by the length and the sectional area of the pipeline:
wherein ρ is w Is the density of water;and->Respectively corresponding pipelines->Length and cross section of (a); />Is the transmission delay;is the mass flow of the heating medium in the pipeline.
The water supply pipeline and the water return pipeline which are laid side by side in pairs have the same design parameters, namely, the length, the pipe diameter thickness, the heat insulation performance and other parameters of each pair of water supply pipeline and the water return pipeline are the same, so that the mass flow and the transmission delay in the paired pipelines are equal:
in the method, in the process of the invention,and->The mass flow and the transmission delay in the return water pipeline are respectively.
(2) Dynamic temperature
The heat output from the heat source gradually decreases after passing through the pipe network and being consumed by users, so that the temperature of the heat medium is continuously reduced along with the extension of the pipe network. The expression of temperature change and heat loss is:
in the method, in the process of the invention,the temperature difference of heating medium is respectively the water supply pipe, the water return pipe and the input and output ports of the mth heating power station; />Is a water supply line connected to the mth heating station +.>The mass flow of the heating medium in the furnace; c w Is the specific heat capacity of water; h is a m Is the equivalent thermal load at the thermal station; />The heat power loss in the water supply pipeline and the water return pipeline are respectively. According to theory of heat transfer, transmission loss is mainly determined by thermal resistance and length of a pipeline, and power loss can be expressed as:
in the method, in the process of the invention,and->The average temperatures of water supply, backwater and earth surface soil are respectively; gamma ray S 、γ R 、γ soil And gamma ad Dividing into
The heat resistance and the additional heat resistance of a water supply pipeline, a water return pipeline and soil are respectively realized;for corresponding pipe->Is a length of (c). The other parameters except the temperature are fixed parameters, so that the transmission loss of each section of pipeline can be estimated in advance according to the average temperature.
Because of the number of nodes and pipelines in the thermodynamic network, if the temperature change of each pipeline is represented, a plurality of intermediate variables are generated, which is not beneficial to establishing a concise combined heat and power optimization scheduling model. In fact, since the losses in the pipe are substantially constant in the quality regulation mode, the temperature variation in the pipe is ultimately determined by the heat load level. If the relation between the heat load and the temperature of the heat source end water supply and return can be directly expressed, the calculation process of the intermediate temperature variable can be omitted, and the simplified modeling is realized.
According to kirchhoff flow law, the total flow of the heating medium flowing into the same node from a plurality of pipelines is equal to the total flow flowing out of the node, and the energy of the heating medium flowing into and out of the same node is the same. For any mixed flow node R 2m (m=1,., M-1) satisfying the energy conservation relation:
in the method, in the process of the invention,and->Respectively corresponding return water pipes->And->The mass flow of the heating medium; />Respectively corresponding return water pipes->The heat medium loss in the process; />Is the temperature of the heating medium flowing out of the mth heating station; />And->The temperature of the outgoing heating medium at the mixed flow nodes of the 2m and the 2 (m+1) th are respectively. Thus, the mixed flow node R can be derived 2m The temperature expression of the outgoing heat medium is:
considering the transmission loss along the way from the heat source to the mth heat station, the temperature expression of the heat medium flowing out from the heat station is:
wherein T is 1 S 、Respectively water supply pipeline->The temperature of the heating medium, the loss of the heating medium and the mass flow of the heating medium;respectively water supply pipeline->Loss of heating medium, mass flow of heating medium, +.>For water supply pipe L s 2m In (c) heat medium loss.
According to formulas (5) - (7), the deductions are:
finally obtaining the return water temperature of the heat source portCan be expressed as:
substituting the transmission delay into the formula (9), and finally obtaining a dynamic relation between the temperature of the water supply and return at the heat source and the heat load:
in the method, in the process of the invention,and->The water supply and return temperatures of the heat source at the moment t are respectively; alpha m Is the total time required by the heat medium to be transmitted from the heat source to the mth heating power station, and takes integer times of the modulation time period delta t; />And->Is t-2 alpha m The water supply temperature at the heat source at the moment and the heat load at the mth heating station; />Is t-alpha m The thermal load at the mth thermal station at the moment,respectively corresponding water supply pipelines->Transmission delay in (a); />Is the maximum heating temperature born by the heating power pipe network, and round represents a rounding function.
(3) Thermodynamic load
And (3) processing the load at each heat exchange station node according to the building with the same heat conduction coefficient, wherein the outdoor temperature change of the same heat supply area is the same. According to the law of heat transfer, the transient thermal equilibrium expression of the indoor temperature is:
in the method, in the process of the invention,representing the indoor temperature of a building at an mth heating station at the moment t; t (T) t out The outdoor temperature is t time; h is a m,t The heat load at the mth heating station at the t moment; k (K) m 、A m 、V m The heat conduction coefficient, the surface area and the heating volume of the building are respectively; c air And ρ air Air specific heat capacity and density, respectively.
Due to the heat preservation effect of the building wall, the temperature change in the building room is very slow, and the temperature outside the room is basically unchanged at intervals of a scheduling period, the steady-state expression of the temperature inside the room in each period can be obtained according to a first-order differential equation of the formula (11):
in the method, in the process of the invention,representing the indoor temperature of the building at the mth heating station at the time t-1; x-shaped articles m Is a thermal coefficient.
The relation of the heating load power with respect to the indoor and outdoor temperatures can be simplified:
in the method, in the process of the invention,and->The upper limit and the lower limit of the indoor heating temperature are respectively +.>Representing the indoor temperature of the building at the mth heating station at the time t-1;
the formulas (10) and (13) form a 'source-charge direct connection model' of the thermodynamic system, so that the temperature change characteristic and the transmission delay characteristic of the heat medium transmitted from a heat source end to a water return end are reserved, and a large number of temperature variables of intermediate nodes can be saved. The heat load demand is directly related to the hot water supply temperature of the source end, and the heat load demand is similar to the direct relation of the electric load and the unit electric output in the electric power system in form, so that a concise and clear combined heat and power dispatching model is conveniently generated.
Step 2: and establishing an operation power control model of the electric heating pump.
The electric heating pumps are arranged at the first-stage heat exchange station in a dispersing way, the operation of the electric heating pumps does not change the flow of a pipe network,
only the temperature of the heat medium flowing into the load side is changed. When the heat pump is in no electricity, the water supply temperature of the heat source end meets the formula:
in the method, in the process of the invention,the heat power of the ith cogeneration unit CHP at the time t is used as the heat power; n1 is the number of thermoelectric units.
At the current backwater temperature of t period, if the thermal power plant reduces heat supply, the outlet water temperature of the heat source end is reduced, the temperature of the heat medium at the inlet of each heat load node is reduced, and the temperature change degree of the heat medium at each load node is the same as the temperature change at the outlet of the source end due to the unchanged flow of the pipeline, and the temperature change satisfies the following conditions in consideration of transmission delay:
in the method, in the process of the invention,the temperature of the heat medium at the heat source end and the heat load inlet end is reduced respectively; />Is the total heat power reduced by the thermal power plant.
In order to meet the heating requirement, the reduced heating capacity of the thermal power plant should be supplemented by the electric heating pump, and assuming that the energy conversion efficiency of the electric heating pump dispersed at each thermal power station is the same, taking the transmission delay of the thermal network into consideration, the total heat power which should be provided by the electric heating pump in an auxiliary way is as follows:
in the method, in the process of the invention,and beta HP The total operation power and the conversion efficiency of the electric heat pump are respectively; />Is t+alpha m And the operation power of the electric heating pump at the mth thermal load at the moment.
The reduction of heat supply at the heat source end reduces the water supply temperature at each thermodynamic loadThe electric heat pump heat supply at this point satisfies the condition:
by combining equations (15) - (17), it can be obtained that the heating power of the electric heat pump at each heat station should satisfy the following conditions:
in the method, in the process of the invention,is a water supply line connected to the mth heating station +.>The mass flow of the heating medium in the reactor is>The power capacity of the electric heat pump is installed for the mth heat load side.
Step 3: and establishing an optimal scheduling model of the thermoelectric combined system.
The power supply unit in the combined heat and power system is a cogeneration unit, a pure condensing power unit, a wind power unit and other peak shaving units. The interaction between the electric power system and the thermodynamic system is mainly realized through a cogeneration unit, the cogeneration unit takes heat supply as priority, and then peak regulation service is provided for the electric power system. The optimal scheduling of the combined heat and power system aims at minimizing the running cost of the whole system, and the running cost of the wind turbine generator set and the hydroelectric turbine generator set is very low, so that the running cost mainly comprises the coal consumption cost of the coal-fired turbine generator set, and in addition, in order to consume wind power as much as possible, the abandoned wind is added into the cost in a penalty function mode. The objective function established is as follows:
wherein C is coal Is the total coal consumption;coal consumption of a thermoelectric unit and a pure thermal power unit; />A penalty function for wind abandoning; />The electric power output by the cogeneration unit and the pure condensing unit at the moment t respectively;is the coal consumption coefficient of the thermoelectric unit; />The coal consumption coefficient of the pure condensing unit; n2 is the number of pure condensing units; />The wind power is produced and consumed respectively; epsilon w Is a penalty function coefficient; nt is the last scheduling period in the scheduling period, < >>The thermal power of the ith thermoelectric unit at the time t is obtained.
The electrothermal coupling constraint conditions include:
(1) Electric power balance constraint
In the formula, the superscript CHP, CON, OTH, WF respectively represents a cogeneration unit, a pure fossil power unit, other types of units and a wind turbine generator; p (P) t OTH The total electric output of other types of units at the moment t; pe (Pe) t Is the electrical load power.
(2) Thermal power balance constraint
Wherein Ph is t Is the thermal load power;and->Respectively t+alpha m The thermal load and the electric heat pump operating power at the mth heating station at the moment.
(3) Upper and lower limit constraint of unit output
In the method, in the process of the invention,the thermal power and the maximum thermal power output by the thermoelectric unit in the period t are respectively; /> The upper limit and the lower limit of the electric output of the ith thermoelectric unit are respectively; />The upper limit and the lower limit of the electric output force of the j-th pure condensing unit are respectively; />The upper limit and the lower limit of the electric output of other types of units are respectively; a, a i 、b i 、c i 、/>Is an operating characteristic parameter of the thermoelectric unit.
(4) Unit climbing constraint
In U CHP 、D CHP The upper limit and the lower limit of the climbing power of the thermoelectric unit are respectively; u (U) CON 、D CON The upper limit and the lower limit of climbing power of the pure condensing unit are respectively set; u (U) OTH 、D OTH The upper limit and the lower limit of climbing power of other types of units are respectively set;the electric power of the ith thermoelectric unit, the pure condensing unit and other types of units at the time t+1 is respectively; />Is the ith thermoelectric unitThermal power at time t-1, beta HP Respectively the conversion efficiency of the electric heating pump.
(5) Supply and return water temperature constraints
For time t-alpha m The electric heat pump operating power at the mth thermal load.
It should be noted that the same symbols or parameters in all the different formulas in the present material have the same meaning.
The method of implementing the present invention is described in detail below in connection with an example of a cogeneration system topology. The unit composition in this embodiment is: the two cogeneration units are respectively 300MW and 200MW, the pure condensing power unit is 300MW, the wind power is 190MW, and the total capacity of other types of units is 260MW. The thermodynamic system comprises four primary heat exchange stations, and the electric power system is a six-node system. The scheduling period is one day, each scheduling period is 15 minutes, and 96 scheduling periods are total one day. The total power capacity of the electric heat pump is 66MW, the electric heat pump capacities at the No. 1-4 heating power stations are 14.64MW, 17.76MW, 13.14MW and 20.46MW respectively, and the thermoelectric ratio of the electric heat pumps is 3. The parameters of the machine set and the thermodynamic system are shown in tables 1-5.
FIG. 3 shows a comparison of wind power consumption before and after the addition of an electric heat pump. The air abandon time period is distributed in 1-20 and 87-96 time periods, and corresponds to 0 in the early morning: 00 to 5:45 and night 22:30 to the next morning 0:00, it can be seen from the figure that the wind power consumption is obviously improved under the condition of installing the electric heat pump.
The electroheat pumps dispersed at each thermodynamic station are labeled HP1, HP2, HP3 and HP4, respectively, and fig. 4 is a histogram of electroheat pump operating power. Compared with the abandoned wind generation period, the starting period of the electric heating pump has time delay, and the longer the electric heating pump is started from the heat source, the longer the electric heating pump is started. The method is characterized in that a demand instruction for starting the electric heat pump is sent out in a wind power surplus period, the thermoelectric unit simultaneously reduces heat output and electric output to operate, the reduced electric output takes effect on the improvement of the waste wind consumption in the current period, the reduced heat output can affect the water supply temperature at the inlet of the heating power station after a period of time due to the transmission delay of the heating power pipe network, and in order to keep the heat supply quantity at the heating power station, the electric heat pump responds to the start-stop demand only by taking the time of the heating medium reaching the heating power station as a reference. Fig. 5 and 6 are graphs showing the change in heat output and water supply and return temperatures of thermoelectric units before and after the electric heat pump is additionally installed. After the electric heat pump is installed, the thermal output of the thermoelectric unit is obviously reduced in the surplus wind power period, and when the electric heat pump is not used, the thermal output of the thermoelectric unit always needs to follow the thermal load change. The water supply temperature and the heat output have the same change trend, but because the electric heat pump heats, supplements and supplies heat, the heat actually provided for a heat user at the heat station is unchanged, and the backwater temperature is not changed along with the reduction of the heat output.
Fig. 7 is a graph comparing the power output of thermoelectric units before and after the electric heat pump is additionally installed and the power output of a pure thermal power unit. Under the condition of the electric heat pump, the electric output of the thermoelectric unit is obviously reduced in the wind power surplus period, but the electric output of the pure condensing unit is increased in the wind power surplus period, as shown by the red coil part in the figure. Because the surplus wind power is relatively less in the periods, the surplus wind power can be completely consumed by means of electricity consumption of the electric heating pump and power reduction of the thermoelectric unit, and the pure condensing unit still needs to keep the minimum power to consume the wind power when the heat pump is not used.
By means of the electric heat pump, the electric output of the thermal power plant can be reduced to a greater extent, and the purposes of improving the integral peak regulation capacity of the electric power system and absorbing more wind power are achieved.
Firstly, respectively deducing mathematical expressions of transmission delay, dynamic temperature and thermal load of a thermal network, and reasonably simplifying to obtain a source load direct-connection model of a thermal system; secondly, an operation power control model of the electric heating pump is established; and finally, listing the electrothermal coupling constraint conditions, and establishing an optimal scheduling model of the thermoelectric combined system.
The specific embodiments described in this specification are merely illustrative of the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (7)
1. A method for constructing an optimal scheduling model of a combined heat and power system containing a distributed electric heat pump comprises the following steps:
step 1: the heating area under each primary heating station is regarded as the heat load at a heating station node, so that a heating network simplified topological structure is obtained; establishing a source load direct connection model considering heat medium transmission delay, heat medium dynamic temperature and heat load;
step 2: calculating the water temperature of the heat source end when the electroless heat pump is used, and considering the temperature change degree of the heat medium at each load node and the temperature change at the outlet of the source end when the transmission delay is taken into consideration; assuming that the energy conversion efficiency of the distributed electric heating pumps at each heating power station is the same, taking the transmission delay of a heating power network into consideration, and establishing an operation power control model of the electric heating pump;
step 3: the method comprises the steps of taking the minimum running cost of the whole system as a target, and taking the constraint condition of electrothermal coupling into consideration to establish an optimal scheduling model of the thermoelectric combined system;
the method for considering the dynamic temperature of the heating medium in the step 1 is as follows:
the heat output from the heat source is gradually reduced after being consumed by a user through the transmission loss along the pipe network, so that the temperature of the heat medium is continuously reduced along with the extension of the pipe network; the expression of temperature change and heat loss is:
wherein, in the formula,ΔT n R 、/>the temperature difference of heating medium is respectively the water supply pipe, the water return pipe and the input and output ports of the mth heating power station; />Is a water supply line connected to the mth heating station +.>The mass flow of the heating medium in the furnace; c w Is the specific heat capacity of water; h is a m Is the equivalent thermal load at the thermal station; />The heat power loss in the water supply and return pipelines is respectively;
because the number of nodes and pipelines in the thermodynamic network is numerous, if the temperature change of each pipeline is represented, a plurality of intermediate variables are generated, so that the establishment of a concise combined heat and power optimization scheduling model is not facilitated; since the loss in the pipeline is basically unchanged in the quality adjustment mode, the temperature change in the pipeline is finally determined by the heat load level; if the relation between the heat load and the temperature of the heat source end water supply and return can be directly expressed, the calculation process of the intermediate temperature variable can be omitted, and the simplified modeling is realized;
according to kirchhoff flow law, the total flow of the heating medium flowing into the same node from a plurality of pipelines is equal to the total flow flowing out of the node, and the energy of the heating medium flowing into and out of the same node is the same; for any mixed flow node R 2m M=1,..m, M is the total number of nodes, satisfying the energy conservation relation:
in the method, in the process of the invention,and->Respectively corresponding return water pipes->And->The mass flow of the heating medium;respectively corresponding return water pipes->The heat medium loss in the process; />Is the temperature of the heating medium flowing out of the mth heating station; />And->The temperature of the heat medium flowing out of the mixed flow nodes of the 2m and the 2 (m+1) th are respectively; thus, the mixed flow node R can be derived 2m The temperature expression of the outgoing heat medium is:
considering the transmission loss along the way from the heat source to the mth heating station, the temperature expression of the heat medium flowing out from the heating stationThe method comprises the following steps:
wherein T is 1 S 、Respectively water supply pipeline->The temperature of the heating medium, the loss of the heating medium and the mass flow of the heating medium;respectively water supply pipeline->Loss of heating medium, mass flow of heating medium, +.>For water supply pipe L s 2m The heat medium loss in the process;
according to formulas (5) - (7), the deductions are:
finally obtaining the return water temperature of the heat source portCan be expressed as:
substituting the transmission delay into the formula (9), and finally obtaining a dynamic relation between the temperature of the water supply and return at the heat source and the heat load:
wherein, in the formula,and->The water supply and return temperatures of the heat source at the moment t are respectively; alpha m Is the total time required by the heat medium to be transmitted from the heat source to the mth heating power station, and takes integer times of the modulation time period delta t; />And->Is t-2 alpha m The water supply temperature at the heat source at the moment and the heat load at the mth heating station; />Is t-alpha m The thermal load at the mth thermal station at the moment,respectively corresponding water supply pipelines->Transmission delay in (a); />The maximum heating temperature born by the heating power pipe network is represented by round;
the transmission thermal power loss is determined by the thermal resistance and the length of the pipeline, and the power loss can be expressed as:
wherein, in the formula,and->The average temperatures of water supply, backwater and earth surface soil are respectively; gamma ray S 、γ R 、γ soil And gamma ad The thermal resistance and the additional thermal resistance of the water supply pipeline, the water return pipeline and the soil are respectively; />For corresponding pipe->Is a length of (2); the other parameters except the temperature are fixed parameters, so that the transmission loss of each section of pipeline can be estimated in advance according to the average temperature.
2. The method for constructing the optimal scheduling model of the combined heat and power system of the distributed electric heat pump according to claim 1, wherein the specific method for obtaining the simplified topological structure of the thermodynamic network in the step 1 is as follows:
in a dendritic topology thermodynamic network, the heating area under each primary thermodynamic station is regarded as the heat load at one thermodynamic station node, denoted by H m M, M is the total number of nodes; the water supply pipe network and the water return pipe network are arranged in parallel under the ground, and each small section of water supply pipe network and the water return pipe network are marked asn=1..2M, the nodes in the water supply and return network are respectively represented by letters S and R, and the above label forms are distinguished, so that the simplified topological structure of the thermodynamic network is obtained.
3. The method for constructing the optimal scheduling model of the combined heat and power system of the distributed electric heat pump according to claim 1, wherein the method for considering the transmission delay of the heating medium in the step 1 is as follows:
the length of a pipeline in the primary pipe network can reach thousands of meters, the heat medium is transmitted to each load node after heat exchange from a heat source, the transmission delay can reach several times of the scheduling period of the electric power system, and the transmission delay is determined by the length and the sectional area of the pipeline:
wherein ρ is w Is the density of water;and->Respectively corresponding pipelines->Length and cross section of (a); />Is the transmission delay; />The mass flow of the heating medium in the pipeline is represented by M, which is a positive integer;
the water supply pipeline and the water return pipeline which are laid side by side in pairs have the same design parameters, namely the length, the pipe diameter thickness and the heat preservation performance parameters of each pair of water supply pipeline and the water return pipeline are the same, so that the mass flow and the transmission delay in the paired pipelines are equal:
in the method, in the process of the invention,and->The mass flow and the transmission delay in the return water pipeline are respectively.
4. The method for constructing the optimal scheduling model of the combined heat and power system of the distributed electric heat pump according to claim 1, wherein the method for considering the thermal load in the step 1 is as follows: the load at each heat exchange station node is processed according to the building with the same heat conduction coefficient, and the outdoor temperature change of the same heat supply area is the same; according to the law of heat transfer, the transient thermal equilibrium expression of the indoor temperature is:
in the method, in the process of the invention,representing the indoor temperature of a building at an mth heating station at the moment t; t (T) t out The outdoor temperature is t time; h is a m,t The heat load at the mth heating station at the t moment; k (K) m 、A m 、V m The heat conduction coefficient, the surface area and the heating volume of the building are respectively; c air And ρ air Air specific heat capacity and density, respectively;
due to the thermal insulation effect of the building wall, the temperature in the building is very slow, and the temperature outside the building is considered to be basically unchanged at intervals of a scheduling period, a steady-state expression of the temperature inside the building in each period can be obtained according to a first-order differential equation of the formula (11):
in the method, in the process of the invention,representing the indoor temperature of the building at the mth heating station at the time t-1; />Representing the indoor temperature of a building at an mth heating station at the moment t; x-shaped articles m Is a thermal coefficient;
the relation of the heating load power with respect to the indoor and outdoor temperatures can be simplified:
in the method, in the process of the invention,and->The upper limit and the lower limit of the indoor heating temperature are respectively +.>And (3) representing the indoor temperature of the building at the mth heating station at the t-1 moment, wherein the formulas (10) and (13) form a source load direct connection model of the heating system.
5. The method for constructing the optimal scheduling model of the combined heat and power system of the distributed electric heat pump according to claim 1, wherein the step 2 is specifically as follows: the electric heating pump is arranged at the first-stage heat exchange station in a dispersing way, and the operation of the electric heating pump does not change the pipeNetwork flow, only changing the temperature of the heat medium flowing into the load side; when the heat pump is in no-electricity state, the water supply temperature of the heat source end,satisfying the formula:
in the method, in the process of the invention,the heat power of the ith cogeneration unit CHP at the time t is used as the heat power; n1 is the number of thermoelectric units;
at the current backwater temperature of t period, if the thermal power plant reduces heat supply, the outlet water temperature of the heat source end is reduced, the temperature of the heat medium at the inlet of each heat load node is reduced, and the temperature change degree of the heat medium at each load node is the same as the temperature change at the outlet of the source end due to the unchanged flow of the pipeline, and the temperature change satisfies the following conditions in consideration of transmission delay:
in the method, in the process of the invention,the temperature of the heat medium at the heat source end and the heat load inlet end is reduced respectively; />A reduced total thermal power for the thermal power plant;
in order to meet the heating requirement, the reduced heating capacity of the thermal power plant should be supplemented by the electric heating pump, and assuming that the energy conversion efficiency of the electric heating pump dispersed at each thermal power station is the same, taking the transmission delay of the thermal network into consideration, the total heat power which should be provided by the electric heating pump in an auxiliary way is as follows:
in the method, in the process of the invention,and beta HP The total operation power and the conversion efficiency of the electric heat pump are respectively; />Is t+alpha m The operation power of the electric heating pump at the mth thermal load at the moment;
the reduction of heat supply at the heat source end reduces the water supply temperature at each thermodynamic loadThe electric heat pump heat supply at this point satisfies the condition:
by combining equations (15) - (17), it can be obtained that the heating power of the electric heat pump at each heat station should satisfy the following conditions:
in the method, in the process of the invention,is a water supply line connected to the mth heating station +.>The mass flow of the heating medium in the reactor is>Is the mth heatLoad side mounted electric heat pump power capacity.
6. The method for constructing the optimal scheduling model of the thermoelectric combined system according to claim 1, wherein the method for constructing the optimal scheduling model of the thermoelectric combined system is characterized by taking the running cost of the whole system as a minimum and considering the constraint condition of electrothermal coupling as a target, and comprises the following steps:
the power supply unit in the combined heat and power system is a cogeneration unit, a pure condensing power unit, a wind power unit and other peak shaving units; the interaction of the electric power system and the thermodynamic system is realized through a cogeneration unit, the cogeneration unit takes heat supply as priority, and then peak regulation service is provided for the electric power system; the optimal scheduling of the combined heat and power system aims at minimizing the running cost of the whole system, and the running cost of the wind turbine generator set and the hydroelectric turbine generator set is very low, so that the running cost comprises the coal consumption cost of the coal-fired turbine generator set, and in addition, in order to consume wind power as much as possible, the abandoned wind is added into the cost in a penalty function mode; the objective function established is as follows:
wherein C is coal Is the total coal consumption;coal consumption of a thermoelectric unit and a pure thermal power unit; />A penalty function for wind abandoning; />The electric power output by the cogeneration unit and the pure condensing unit at the moment t respectively;is a thermoelectric machineGrouping coal consumption coefficients; /> The coal consumption coefficient of the pure condensing unit; n2 is the number of pure condensing units; />The wind power is produced and consumed respectively; epsilon w Is a penalty function coefficient; nt is the last scheduling period in the scheduling period, < >>The thermal power of the ith thermoelectric unit at the time t is obtained.
7. The method for constructing the optimal scheduling model of the combined heat and power system of the distributed electric heat pump according to claim 1, wherein the constraint condition of electric heating coupling in the step 3 comprises the following steps:
(1) Electric power balance constraint
In the formula, the superscript CHP, CON, OTH, WF respectively represents a cogeneration unit, a pure fossil power unit, other types of units and a wind turbine generator; p (P) t OTH The total electric output of other types of units at the moment t; pe (Pe) t Is the electrical load power;
(2) Thermal power balance constraint
Wherein Ph is t In order to be able to carry out a thermal load power,and->Respectively t+alpha m The heat load and the running power of the electric heating pump at the mth heating station at the moment;
(3) Upper and lower limit constraint of unit output
In the method, in the process of the invention,the thermal power and the maximum thermal power output by the thermoelectric unit in the period t are respectively; /> The upper limit and the lower limit of the electric output of the ith thermoelectric unit are respectively; />The upper limit and the lower limit of the electric output force of the j-th pure condensing unit are respectively;the upper limit and the lower limit of the electric output of other types of units are respectively; a, a i 、b i 、c i 、/>Is the operation characteristic parameter of the thermoelectric unit;
(4) Unit climbing constraint
In U CHP 、D CHP The upper limit and the lower limit of the climbing power of the thermoelectric unit are respectively; u (U) CON 、D CON The upper limit and the lower limit of climbing power of the pure condensing unit are respectively set; u (U) OTH 、D OTH The upper limit and the lower limit of climbing power of other types of units are respectively set;the electric power of the ith thermoelectric unit, the pure condensing unit and other types of units at the time t+1 is respectively; />The thermal power of the ith thermoelectric unit at the time t-1 is beta HP Respectively the conversion efficiency of the electric heating pump;
(5) Supply and return water temperature constraints
For time t-alpha m The electric heat pump operating power at the mth thermal load.
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| Optimal operation of the combined heat and power system equipped with power‐to‐heat devices for the improvement of wind energy utilization;Yanjuan Yu;《Energy Science & Engineering》;第1605-1620页 * |
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| CN113761727A (en) | 2021-12-07 |
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