Expressway network and power grid coupling method based on field-to-road deduction methodology

Abstract

The invention discloses an expressway network and power grid coupling method based on a field-to-road deduction methodology, and belongs to the field of power and traffic network coupling. The method comprises the following steps: establishing an equivalent road model of an expressway network based on the field-to-road deduction methodology in a circuit theory; establishing constraints of an equivalent road model of the expressway network according to the operation characteristics of the electric vehicle on the expressway and the characteristics of the expressway; according to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established, and load flow calculation of the unified energy circuit model is achieved. The method solves the problems that the existing method does not consider that the highway network and the power grid are mutually separated at the model and method levels during actual calculation, and complex interaction between the highway network and the power grid cannot be accurately simulated.

Description

Technical Field

[0001] The present invention belongs to the field of coupling of electric power and traffic network, and in particular to a method for coupling a highway network and a power grid based on field-to-road deduction methodology. Background Art

[0002] With the development of the transportation system, highways have gradually become an indispensable transportation hub. Electric vehicles are both a traffic load on the transportation network and a power load on the power grid. Their charging demand depends to a certain extent on traffic flow, and their demand fluctuations directly affect the power grid load, forming a complex coupling relationship between the transportation network and the power grid.

[0003] In the coupling scenario of highways and power grids, traffic flow characteristics are closely related to grid operation characteristics. During peak travel periods, the concentrated charging demand of electric vehicles in highway service areas may significantly increase the power load in a short period of time, bringing the risk of grid fluctuations or even overload. At the same time, problems such as grid load fluctuations and local voltage instability also affect the traffic flow on highways. This complex interaction shows that the dynamic interaction between the two cannot be fully revealed by a single-field analysis method. Therefore, it is of great significance to study the complex dynamic coupling relationship between highways and power grids.

[0004] Most existing technologies focus on the prediction of electric vehicle charging demand and grid load, or the short-term impact of traffic flow on the grid. In actual calculations, the highway network and the grid are still regarded as independent systems, and the two are separated from each other at the model and method levels. In addition, due to the heterogeneity of the network and the complexity of the interdependencies, it is still challenging to accurately simulate the complex interaction between the highway network and the grid. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a highway network and power grid coupling method based on field-to-road deduction methodology, which solves the problem that the prior methods do not take into account that in actual calculations, the highway network and the power grid are separated from each other at the model and method levels, and cannot accurately simulate the complex interaction between the highway network and the power grid.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a highway network and power grid coupling method based on field-to-road deduction methodology, comprising:

[0007] Based on the mid-field to road deduction methodology in circuit theory, an equivalent road model of the expressway network is established;

[0008] According to the running characteristics of electric vehicles on the highway and the characteristics of the highway itself, the constraints of the equivalent road model of the highway network are established;

[0009] According to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established to complete the coupling of the expressway network and the power grid.

[0010] Furthermore, the equivalent road model of the expressway network is established based on the deduction methodology from field to road in circuit theory, specifically:

[0011] Based on the deduction methodology from field to road in circuit theory, the traffic volume of vehicles passing through a certain cross-sectional area per unit time is defined as road flow. Taking the vehicle starting point as the potential reference point, the energy demand per unit time passing through the cross-sectional area is defined as road pressure, and the relationship between road flow and road pressure is obtained:

[0012]

[0013] The energy consumption of vehicles due to ground friction and wind resistance between any two cross sections on the highway is defined as the road potential difference:

[0014]

[0015] Combining the relationship between road flow and road pressure as well as road potential difference, the one-dimensional flow process of vehicles on the highway is described as follows:

[0016] Q(x+Δx,t)-Q(x,t)=-(mgf+f w v 2 (x,t))·q(x,t)Δx

[0017]

[0018]

[0019] According to the one-dimensional flow process of vehicles on the highway, the energy demand at different positions x is calculated as the traffic volume changes, and the energy transmission model is obtained:

[0020]

[0021] Abstracting the path resistance R from the energy transfer model h 、Road Sense L h 、Road guide h And road capacity C h Road components, defined as distributed parameter road models:

[0022] R h =(mgf+f w v 2 )

[0023] L h =αmv

[0024] g h=(mgf+f w v 2 ) / λ 2

[0025] C h =αmv / λ 2

[0026] According to the power system analysis method, the distributed parameter road model is mapped to the frequency domain, and the ordinary differential equations in the frequency domain are obtained:

[0027] dq=-(g h +jωC h )dx·Q

[0028] dQ=-(R h +jωL h )dx·q

[0029] Solving the system of ordinary differential equations in the frequency domain, we obtain the state variables at the end of the road, which are defined as the equivalent road model of the highway network:

[0030] Q 1 =A'Q 0 +Bq 0

[0031] q 1 =CQ 0 +Dq 0

[0032] Where Q(x+Δx,t) is the energy demand of the vehicle at the distance x+Δx at time t; x is the position; Δx is the distance between any two cross sections on the highway; t is the time series; Q(x,t) is the energy demand of the vehicle at the distance x at time t; m is the vehicle weight; g is the acceleration of gravity; f is the rolling resistance coefficient; f w is the total wind resistance parameter on the highway; v(x,t) is the speed of the vehicle at the distance x at time t; q(x,t) is the traffic flow of the vehicle at the distance x at time t; Δ is the difference sign; α is Δx a The ratio of the total distance Δx; a is the vehicle acceleration; Δx a is the distance traveled by the vehicle at an accelerated speed; ρ is the air density; C d is the drag coefficient; A is the frontal area of ​​the vehicle; is the symbol of partial derivative; Q is the energy demand per unit time for passing through a cross-sectional area; v is the speed of vehicles passing through a certain cross-sectional area per unit time; q is the traffic volume of vehicles passing through a certain cross-sectional area per unit time; λ is With E n The product of E is the state of charge that needs to be replenished; nis the battery capacity; ΔQ is the potential difference between two points; d is the differential sign; g h is the path guide; j is the imaginary unit; ω is the angular frequency; C h R h For road obstruction; L h For road feel; Q 1 is the energy demand at the end of the road; Q 0 is the energy demand at the beginning of the road; q 0 is the traffic volume at the beginning of the road; q 1 is the traffic flow at the end of the road; A', B, C and D are the transmission coefficients of the two-port network.

[0033] Furthermore, the constraint expression of the equivalent road model of the expressway network is:

[0034] Q t =K t Q f +E t

[0035] q t =K t q f

[0036]

[0037]

[0038]

[0039] Q f =A t T Q node

[0040] q node =A f q t +q n

[0041]

[0042] Among them, Q t is the column vector composed of the energy requirements at the end of each road; K t is a diagonal matrix consisting of the energy transfer factors of each road; Q f is the column vector composed of the energy demand at the head end of each road; E t is the column vector of energy difference at the end of the road; q t is the column vector composed of the traffic flow at the end of each road; q f is the column vector composed of the traffic flow at the head end of each road; Q 1 is the energy demand at the end of the road; Q0 is the energy demand at the beginning of the road; e is the base of the natural logarithm; R tc is the equivalent road resistance from the beginning to the end of the road; j is the imaginary unit; ω is the angular frequency; L tc is the equivalent road inductance from the beginning to the end of the road; tc The total distance from the beginning to the end of the road With E n The product of E is the state of charge that needs to be replenished; n is the battery capacity; x is the position; E c is the energy difference generated by the vehicle after charging; q 0 is the traffic volume at the beginning of the road; q 1 is the traffic volume at the end of the road; l is the distance between the beginning and the end of the road; Q node is the column vector composed of the road pressure at each node; is the weighted node-inflow branch association matrix; is a column vector composed of the weighted injection energy demand of each charging station equivalent node. The weighted injection energy demand is the injection energy demand multiplied by the proportion of the injection flow to the total inflow flow. node When it is the equivalent node of the starting point of the expressway section, =0; Q f A is the energy demand at the head end of each outflow branch, that is, the node road pressure; t is the node-outflow branch association matrix; q node is the column vector of the total flow through each node; A f is the node-inflow branch association matrix; q n A column vector consisting of the flow injected into each node; is the weighted node-outflow branch association matrix.

[0043] Furthermore, the node-outflow branch association matrix A t The element in row i and column j in (A t ) i,j Indicates: If branch j flows out from node i, the element is 1, otherwise it is 0;

[0044] Node-inflow branch association matrix A f The element in row i and column j in (A f ) i,j Indicates: if branch j flows into node i, then the element is 1, otherwise it is 0;

[0045] Weighted node-outflow branch association matrix The element in row i and column j Means: If branch j flows out from node i, then this element is the ratio of the flow of branch j to the total flow out of node i, otherwise it is 0;

[0046] Weighted node-inflow branch association matrix The element in row i and column j Indicates: If branch j flows into node i, then this element is the ratio of the flow of branch j to the total flow of node i, otherwise it is 0.

[0047] Furthermore, according to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established to complete the coupling of the expressway network and the power grid, specifically:

[0048] According to the equivalent road model of the expressway network, vehicles charging at charging stations are connected as loads of the power grid, charging piles are used as direct coupling devices between the expressway network and the power grid, charging stations are used as coupling nodes connected to the power grid nodes, and vehicles flowing into the charging stations and the sections of the expressways through which the vehicles pass form an equivalent road network connecting the coupling nodes; the entrance of the expressway is connected to the power grid as the starting node, and the equivalent road network corresponding to each vehicle flowing into the charging station is connected to the power grid, so as to obtain a unified energy circuit model of the expressway network and the power grid, and complete the coupling of the expressway network and the power grid.

[0049] Furthermore, the equivalent road network corresponding to each vehicle flowing into the charging station is connected to the power grid to obtain a unified energy circuit model of the highway network and the power grid, which is specifically:

[0050] Obtain a power grid topology, where there are several power grid nodes;

[0051] If the starting and ending points of the vehicle are the entrance of the expressway and the charging station, the entrance of the expressway is taken as the starting node, the energy demand of the vehicle at the starting node is obtained, and the energy demand of the vehicle at the starting node is taken as the starting load, and the starting load is connected to the starting node;

[0052] The charging stations that the vehicle passes through on the way from the starting node to the destination charging station are regarded as intermediate nodes and are not connected to the load;

[0053] The destination charging station is used as a coupling node. Based on the equivalent road model of the vehicle's highway network, the energy loss of each section along the route is calculated respectively, and the energy loss of each section is superimposed to obtain the loss energy. The loss energy and the starting load are added to obtain the charging load; and the charging load is connected to the coupling node; the starting node, the intermediate node and the coupling node are connected in sequence based on the starting and ending points of the vehicle to obtain the equivalent road network of the vehicle; and the equivalent road network of the vehicle is connected to the grid node through the coupling node to obtain a unified energy circuit model of the highway network and the grid;

[0054] If the starting and ending points of the vehicle are both charging stations, the starting charging station and the charging stations that the vehicle passes through on the way from the starting charging station to the destination charging station are regarded as intermediate nodes and no load is connected;

[0055] The destination charging station is used as a coupling node. Based on the equivalent road model of the vehicle's highway network, the energy loss of each section along the route is calculated separately, and the energy loss of each section is superimposed to obtain the loss energy. The loss energy is used as the charging load, and the charging load is connected to the coupling node. Based on the vehicle's starting and ending points, the intermediate nodes and coupling nodes are connected in sequence to obtain the vehicle's equivalent road network; and the vehicle's equivalent road network is connected to the power grid node through the coupling node to obtain a unified energy circuit model of the highway network and the power grid.

[0056] The beneficial effects of the present invention are as follows: an equivalent road model of the highway network is established, which explicitly considers the energy loss and delay in the time domain during the migration of vehicles on the highway and the energy replenishment of vehicles in the charging station, and lays the foundation for the subsequent coupling of the highway network and the power grid. Constraints are established based on the actual operating characteristics of electric vehicles on the highway and the characteristics of the highway itself, thereby ensuring the equivalent constraints of the highway network. A unified energy circuit model of the highway network and the power grid is established, which reduces the computational complexity of highway network analysis while meeting the computational accuracy. The introduction of coupling nodes allows the changes in the energy demand of vehicles on the highway to be reflected in the voltage fluctuations of the coupling nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The present invention is a flow chart of the method.

[0058] Figure 2 This is a unified energy circuit model diagram of the highway network and the power grid coupled according to the present invention.

[0059] Figure 3 Schematic diagram of the output of photovoltaic and vehicle clusters in an embodiment of the present invention.

[0060] Figure 4 Schematic diagram of a 20-node power system in an embodiment of the present invention.

[0061] Figure 5 Schematic diagram of energy demand variation curves of each charging station and voltage curves of each coupling node in an embodiment of the present invention. DETAILED DESCRIPTION

[0062] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0063] Example 1

[0064] like Figure 1 As shown, in one embodiment of the present invention, a method for coupling a highway network and a power grid based on field-to-road deduction methodology includes:

[0065] Based on the mid-field to road deduction methodology in circuit theory, an equivalent road model of the expressway network is established;

[0066] According to the running characteristics of electric vehicles on the highway and the characteristics of the highway itself, the constraints of the equivalent road model of the highway network are established;

[0067] According to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established to complete the coupling of the expressway network and the power grid.

[0068] The equivalent road model of the expressway network is established based on the deduction methodology of mid-field to road in circuit theory, which is specifically as follows:

[0069] Based on the deduction methodology from field to road in circuit theory, the traffic volume of vehicles passing through a certain cross-sectional area per unit time is defined as road flow. Taking the vehicle starting point as the potential reference point, the energy demand per unit time passing through the cross-sectional area is defined as road pressure, and the relationship between road flow and road pressure is obtained:

[0070]

[0071] The energy consumption of vehicles due to ground friction and wind resistance between any two cross sections on the highway is defined as the road potential difference:

[0072]

[0073]

[0074] Combining the relationship between road flow and road pressure as well as road potential difference, the one-dimensional flow process of vehicles on the highway is described as follows:

[0075] Q(x+Δx,t)-Q(x,t)=-(mgf+f w v 2 (x,t))·q(x,t)Δx

[0076]

[0077]

[0078] According to the one-dimensional flow process of vehicles on the highway, the energy demand at different positions x is calculated as the traffic volume changes, and the energy transmission model is obtained:

[0079]

[0080] Abstracting the path resistance R from the energy transfer model h 、Road Sense L h 、Road guide h And road capacity C h Road components, defined as distributed parameter road models:

[0081] R h =(mgf+f w v 2 )

[0082] L h =αmv

[0083] g h =(mgf+f w v 2 ) / λ 2

[0084] C h =αmv / λ 2

[0085] According to the power system analysis method, the distributed parameter road model is mapped to the frequency domain, and the ordinary differential equations in the frequency domain are obtained:

[0086] dq=-(g h +jωC h )dx·Q

[0087] dQ=-(R h +jωL h )dx·q

[0088] Solving the system of ordinary differential equations in the frequency domain, we obtain the state variables at the end of the road, which are defined as the equivalent road model of the highway network:

[0089] Q 1 =A'Q 0 +Bq 0

[0090] q 1 =CQ 0 +Dq 0

[0091] Where Q(x+Δx,t) is the energy demand of the vehicle at the distance x+Δx at time t; x is the position; Δx is the distance between any two cross sections on the highway; t is the time series; Q(x,t) is the energy demand of the vehicle at the distance x at time t; m is the vehicle weight; g is the acceleration of gravity; f is the rolling resistance coefficient; f w is the total wind resistance parameter on the highway; v(x,t) is the speed of the vehicle at the distance x at time t; q(x,t) is the traffic flow of the vehicle at the distance x at time t; Δ is the difference sign; α is Δx a The ratio of the total distance Δx; a is the vehicle acceleration; Δx a is the distance traveled by the vehicle at an accelerated speed; ρ is the air density; C d is the drag coefficient; A is the frontal area of ​​the vehicle; is the symbol of partial derivative; Q is the energy demand per unit time for passing through a cross-sectional area; v is the speed of vehicles passing through a certain cross-sectional area per unit time; q is the traffic volume of vehicles passing through a certain cross-sectional area per unit time; λ is With E n The product of E is the state of charge that needs to be replenished; n is the battery capacity; ΔQ is the potential difference between two points; d is the differential sign; g h is the path guide; j is the imaginary unit; ω is the angular frequency; C h R h For road obstruction; L h For road feel; Q 1 is the energy demand at the end of the road; Q 0 is the energy demand at the beginning of the road; q 0 is the traffic volume at the beginning of the road; q 1 is the traffic flow at the end of the road; A', B, C and D are the transmission coefficients of the two-port network.

[0092] The constraint expression of the equivalent road model of the expressway network is:

[0093] Q t =K t Q f +E t

[0094] q t =K t q f

[0095]

[0096]

[0097]

[0098] Q f =A t T Q node

[0099] q node =A f q t +q n

[0100]

[0101] Among them, Q t is the column vector composed of the energy requirements at the end of each road; K t is a diagonal matrix consisting of the energy transfer factors of each road; Q f is the column vector composed of the energy demand at the head end of each road; E t is the column vector of energy difference at the end of the road; q t is the column vector composed of the traffic flow at the end of each road; q f is the column vector composed of the traffic flow at the head end of each road; Q 1 is the energy demand at the end of the road; Q 0 is the energy demand at the beginning of the road; e is the base of the natural logarithm; R tc is the equivalent road resistance from the beginning to the end of the road; j is the imaginary unit; ω is the angular frequency; L tc is the equivalent road inductance from the beginning to the end of the road; tc The total distance from the beginning to the end of the road With E n The product of E is the state of charge that needs to be replenished; n is the battery capacity; x is the position; E c is the energy difference generated by the vehicle after charging; q 0 is the traffic volume at the beginning of the road; q 1 is the traffic volume at the end of the road; l is the distance between the beginning and the end of the road; Q node is the column vector composed of the road pressure at each node; is the weighted node-inflow branch association matrix; is a column vector composed of the weighted injection energy demand of each charging station equivalent node. The weighted injection energy demand is the injection energy demand multiplied by the proportion of the injection flow to the total inflow flow. node When it is the equivalent node of the starting point of the expressway section, =0; Q f A is the energy demand at the head end of each outflow branch, that is, the node road pressure; t is the node-outflow branch association matrix; q nodeis the column vector of the total flow through each node; A f is the node-inflow branch association matrix; q n A column vector consisting of the flow injected into each node; is the weighted node-outflow branch association matrix.

[0102] Node-outflow branch association matrix A t The element in row i and column j in (A t ) i,j Indicates: If branch j flows out from node i, the element is 1, otherwise it is 0;

[0103] Node-inflow branch association matrix A f The element in row i and column j in (A f ) i,j Indicates: if branch j flows into node i, then the element is 1, otherwise it is 0;

[0104] Weighted node-outflow branch association matrix The element in row i and column j Means: If branch j flows out from node i, then this element is the ratio of the flow of branch j to the total flow out of node i, otherwise it is 0;

[0105] Weighted node-inflow branch association matrix The element in row i and column j Indicates: If branch j flows into node i, then this element is the ratio of the flow of branch j to the total flow of node i, otherwise it is 0.

[0106] According to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established to complete the coupling of the expressway network and the power grid, specifically:

[0107] According to the equivalent road model of the expressway network, vehicles charging at charging stations are connected as loads of the power grid, charging piles are used as direct coupling devices between the expressway network and the power grid, charging stations are used as coupling nodes connected to the power grid nodes, and vehicles flowing into the charging stations and the sections of the expressways through which the vehicles pass form an equivalent road network connecting the coupling nodes; the entrance of the expressway is connected to the power grid as the starting node, and the equivalent road network corresponding to each vehicle flowing into the charging station is connected to the power grid, so as to obtain a unified energy circuit model of the expressway network and the power grid, and complete the coupling of the expressway network and the power grid.

[0108] The equivalent road network corresponding to each vehicle flowing into the charging station is connected to the power grid to obtain a unified energy circuit model of the highway network and the power grid, which is specifically:

[0109] Obtain a power grid topology, where there are several power grid nodes;

[0110] If the starting and ending points of the vehicle are the entrance of the expressway and the charging station, the entrance of the expressway is taken as the starting node, the energy demand of the vehicle at the starting node is obtained, and the energy demand of the vehicle at the starting node is taken as the starting load, and the starting load is connected to the starting node;

[0111] The charging stations that the vehicle passes through on the way from the starting node to the destination charging station are regarded as intermediate nodes and are not connected to the load;

[0112] The destination charging station is used as a coupling node. Based on the equivalent road model of the vehicle's highway network, the energy loss of each section along the route is calculated respectively, and the energy loss of each section is superimposed to obtain the loss energy. The loss energy and the starting load are added to obtain the charging load; and the charging load is connected to the coupling node; the starting node, the intermediate node and the coupling node are connected in sequence based on the starting and ending points of the vehicle to obtain the equivalent road network of the vehicle; and the equivalent road network of the vehicle is connected to the grid node through the coupling node to obtain a unified energy circuit model of the highway network and the grid;

[0113] If the starting and ending points of the vehicle are both charging stations, the starting charging station and the charging stations that the vehicle passes through on the way from the starting charging station to the destination charging station are regarded as intermediate nodes and are not connected to the load;

[0114] The destination charging station is used as a coupling node. Based on the equivalent road model of the vehicle's highway network, the energy loss of each section along the route is calculated separately, and the energy loss of each section is superimposed to obtain the loss energy. The loss energy is used as the charging load, and the charging load is connected to the coupling node. Based on the vehicle's starting and ending points, the intermediate nodes and coupling nodes are connected in sequence to obtain the vehicle's equivalent road network; and the vehicle's equivalent road network is connected to the power grid node through the coupling node to obtain a unified energy circuit model of the highway network and the power grid.

[0115] Example 2

[0116] like Figure 1 As shown, in one embodiment of the present invention, a unified energy circuit model method for coupling a highway network with a power grid includes the following steps:

[0117] S1. Based on the deduction methodology from "field" to "road" in circuit theory, an energy circuit method for modeling highway networks in the frequency domain is proposed;

[0118] S2. By using "potential" and "flow" to describe the characteristics of equivalent highway network branches, the characteristics and topological constraints of highway network branches are characterized;

[0119] S3. Establish a unified energy circuit model that couples the expressway network with the power grid and implement power flow calculation of the unified energy circuit model.

[0120] The step S1 is specifically as follows:

[0121] S101. On a highway, assuming that vehicles are traveling continuously, the process of a cluster of vehicles traveling continuously in one direction can be approximately regarded as the one-dimensional flow process of free electrons in a circuit. At this time, the highway can be equivalent to a wire in the circuit, and the vehicles are equivalent to electrons in the wire. Similarly, the traffic volume q of vehicles passing through a certain cross-sectional area per unit time is analogous to the current in the circuit, which is defined as road flow in the present invention; taking the vehicle starting point as the potential reference point, the energy demand Q passing through the cross-sectional area per unit time is analogous to the voltage in the circuit, which is defined as road pressure in the present invention. The physical relationship between the two state quantities is:

[0122]

[0123] in, is the state of charge that needs to be replenished, E n is the battery capacity, Q is the energy demand per unit time through the cross-sectional area, and q is the traffic volume of vehicles passing through a certain cross-sectional area per unit time. With E n The product of is set to be λ.

[0124] Between any two cross sections on the highway, vehicles will consume energy due to the influence of ground friction and wind resistance. Analogous to the potential difference between two points in a circuit, the present invention defines it as the road potential difference between the two points, and the expression is as follows:

[0125]

[0126] Where ΔQ is the road potential difference between two points; m is the vehicle weight; g is the acceleration of gravity; f is the rolling resistance coefficient; v is the speed of the electric vehicle; a is the vehicle acceleration; Δx is the distance between any two cross sections on the highway; dx is the unit distance on the highway; f w is the total wind resistance parameter on the highway, which can be described as:

[0127]

[0128] Where ρ is the air density; A is the frontal area of ​​the vehicle; C d is the drag coefficient.

[0129] Combining (1) and (2), the one-dimensional flow process of vehicles on the highway can be described as:

[0130]

[0131] Where t is the time series; Q(x+Δx,t) is the energy demand of the vehicle at the distance x+Δx at time t; Q(x,t) is the energy demand of the vehicle at the distance x at time t; q(x,t) is the traffic volume of the vehicle at the distance x at time t; v(x+Δx,t) is the speed of the vehicle at the distance x+Δx at time t; v(x,t) is the speed of the vehicle at the distance x at time t; Δx a Let Δx be the distance travelled by the vehicle at an accelerated speed. a The ratio of α to the total distance Δx is α, then (4) can be described as:

[0132]

[0133] S102. Take a microelement of length dx from the highway. At this time, Δx approaches 0. Then the energy transmission on the road can be expressed as the energy demand at different positions x changes with the traffic flow, satisfying a set of spatiotemporal partial differential equations:

[0134]

[0135] in, and are the partial derivatives of energy demand and vehicle flow, respectively; and are the partial derivatives of distance and time respectively.

[0136] This simplified transmission model has several assumptions. First, the slope of the road and the energy conversion efficiency of the motor are ignored. Second, the length of the vehicle is not considered when it is traveling on the road. The road resistance R is abstracted from formula (6): h 、Road Sense L h 、Road guide h And road capacity C h Road elements, as shown in equations (7)-(10).

[0137] R h =(mgf+f w v 2 ) (7)

[0138] L h =αmv (8)

[0139] g h =(mgf+f w v 2 ) / λ 2 (9)

[0140] C h =αmv / λ 2 (10)

[0141] It should be pointed out that the above-mentioned resistance, conduction, inductance and capacitance elements are mathematical representations introduced to describe physical phenomena such as energy loss and time delay that occur during the migration of vehicles on highways, and are not real impedances.

[0142] S103, mapping the above distributed parameter road model to the frequency domain according to the power system analysis method:

[0143] dq=-(g h +jωC h )dx·Q (11)

[0144] dQ=-(R h +jωL h )dx·q (12)

[0145] Where, dQ and dq are the differential energy demand and differential vehicle flow respectively; ω is the angular frequency; j is the imaginary unit.

[0146] Then, given the state variable of the road head end is q 0 and Q 0 As boundary conditions, solving the above ordinary differential equations in the frequency domain, the state variables at the end of the road are obtained as follows:

[0147] Q 1 =AQ 0 +Bq 0 (13)

[0148] q 1 =CQ 0 +Dq 0 (14)

[0149] Where: Q 0 and q 0 are the energy demand and traffic volume at the road head end; Q 1 and q 1 are the energy demand and traffic volume at the end of the road respectively; A, B, C, and D are the transmission coefficients of the two-port network respectively.

[0150] The step S2 is specifically as follows:

[0151] S201. In the road model, there is a physical relationship between road pressure and road flow as shown in (1), which means that the binary equations shown in (13) and (14) can be simplified into an expression that uses only one of them to describe the characteristics of the equivalent highway network branch. Substituting (1) into (13) and (14), the characteristics of the equivalent highway network branch described by "potential" and the characteristics of the equivalent highway network branch described by "flow" can be derived respectively:

[0152]

[0153]

[0154] In the formula, the negative exponential term describes the energy loss and delay of the vehicle from the beginning to the end of the highway, which is called the energy transfer factor and is represented by kt. tc The total distance from the beginning to the end of the road With E n The product of ; e is the base of natural logarithms.

[0155] Considering that there is energy transfer when vehicles enter the charging station to charge, it can be used as the road pressure source at the end of the branch in the "potential" analysis. Therefore, the "potential" is used to describe the characteristics of general road branches as follows:

[0156]

[0157] Where: E c is the energy difference generated by the vehicle after charging, which is a simplified description of the vehicle charging process; the branch equations of all road branches in the equivalent highway network are written in matrix form:

[0158] Q t =K t Q f +E t (18)

[0159] q t =K t q f (19)

[0160] Where: Q f , Q t is the column vector composed of the energy requirements at the beginning and end of each road; q f ,q t is the column vector composed of the traffic flow at the beginning and end of each road; K t is the diagonal matrix composed of the energy transfer factors of each road; E t is a column vector consisting of the energy differences at the end of the road.

[0161] S202. Since there are hub interchanges and landing interchanges on highways, a highway can intersect with other highways at one point, or connect to the entrance and exit of ordinary roads on local roads. This causes vehicles to merge and diverge when passing the starting point and end point of a section of highway. In addition, vehicles at the entrance of the charging station may include vehicles flowing into the charging station and vehicles directly entering the next section of the road. Similarly, vehicles at the exit of the charging station may include vehicles flowing out of the charging station and vehicles directly entering the next section of the road. The charging station can be regarded as a special interchange point, and its confluence and divergence can be considered. Therefore, the equivalent highway network topology constraints can be analyzed from the two perspectives of "convergence" and "divergence" at equivalent nodes.

[0162] In order to describe the confluence and diversion processes, the node-outflow branch association matrix A is introduced t , node-inflow branch association matrix A f , weighted node-outflow branch association matrix and weighted node-inflow branch association matrix

[0163] For the node-outflow branch association matrix A t The element in row i and column j in (A t ) i,j , if branch j flows out from node i, then this element is 1, otherwise it is 0; for the node-inflow branch association matrix A f The element in row i and column j in (A f ) i,j , if branch j flows into node i, then the element is 1, otherwise it is 0.

[0164] For the weighted node-outflow branch association matrix The element in row i and column j If branch j flows out from node i, then this element is the ratio of branch j flow to the total flow out of node i, otherwise it is 0; for the weighted node-inflow branch association matrix The element in row i and column j If branch j flows into node i, then this element is the ratio of the flow of branch j to the total flow of node i, otherwise it is 0.

[0165] S203. For the confluence process, the flow of each branch is mixed, and the node road pressure after mixing is the average value of the energy demand of different branches weighted by the flow. The charging station is a special confluence point, and the traffic flow formed by the exiting vehicles in the charging station is used as the injection flow. The node road pressure after mixing is the average value of the energy demand of different traffic flows weighted by the flow. The general expression of the confluence process is as follows:

[0166]

[0167] Where: Q node is the column vector composed of the road pressure at each node; is a column vector composed of the weighted injection energy demand (injection energy demand multiplied by the proportion of injection flow to total inflow flow) of each charging station equivalent node. It is worth noting that when Q node When it is the equivalent node of the starting point of the expressway section, is equal to 0.

[0168] For the diversion process, the energy demand at the head end of each outflow branch, i.e., the node road pressure, is:

[0169] Q f =At T Q node (twenty one)

[0170] S204. As with potential analysis, for the confluence process, the total flow through a node is the sum of the flow into each branch and the injection flow:

[0171] q node =A f q t +q n (twenty two)

[0172] Where: q node is the column vector of the total flow through each node; q n A column vector consisting of the flow injected into each node.

[0173]

[0174] The step S3 is specifically as follows:

[0175] S301, when the highway network is coupled with the power grid, the energy demand trend of vehicles on the highway is converted into a process of load transfer. For the power grid, vehicles charging at charging stations should be connected as loads. For charging stations, regardless of charging losses, the electric power required by the vehicle is equal to the electric power generated by the power grid. Charging piles are introduced as direct coupling devices between the highway network and the power grid, and charging stations are introduced as coupling nodes to be directly connected to the power grid nodes. The vehicles flowing into the charging station and the sections of the highway they pass through form a road model of an equivalent highway connecting the coupling node. The road models of all equivalent highways form an equivalent highway network. Since the energy demand of all vehicles flowing into the charging station initially comes from the entrance of the highway, the entrance can be connected to the power grid as the starting node, and the sections of the highway passed through can be connected to the power grid according to the equivalent method in the second subsection. In this way, the flow process of the energy demand of vehicles on the highway can be directly reflected in the voltage of the power grid coupling node.

[0176] S302. Based on the conditions in S301, two situations are considered:

[0177] ① If the vehicle goes directly from the starting point to the charging station for charging, the total energy that the vehicle needs to replenish in the charging station is the starting energy demand plus the energy loss of the vehicle during driving on the highway. At the starting moment, the vehicle departs from the entrance of the highway, and the starting load is connected to the starting node. After t time, the vehicle arrives at the charging station Sn, and the charging load is connected to the coupling node Sn. From the equivalent model of the highway above, it can be known that the equivalent impedance of the road section between the two charging stations will be different due to changes in traffic volume. Therefore, in the process of the vehicle arriving at the charging station Sn from the starting point, the energy loss of the vehicle in each section needs to be superimposed. In order to better reflect this feature, the charging station that the vehicle passes through from the starting point to the charging station Sn is regarded as an intermediate node, and no load is connected. Only the impact of the equivalent impedance of each section between the two nodes is considered.

[0178] ② If the vehicle is charged at one charging station first and then goes to another charging station for charging. The total energy that the vehicle needs to replenish in the charging station is the energy loss between the vehicle from the previous charging station to the other charging station. At the starting time, the vehicle departs from the entrance of the highway, and the starting load is connected to the starting node. After t1 time, the vehicle arrives at the charging station Sn, at which time the charging load 1 is connected to the coupling node Sn. After t2 time, the vehicle arrives at the charging station Sm, at which time the charging load 2 is connected to the coupling node Sm. The charging station Sn is an intermediate node and is not connected to the load. Only the impact of the equivalent impedance of each section between the two nodes is considered.

[0179] The load of a charging station may come from the starting location or other charging stations, so the topologies of the above two cases need to be superimposed. The unified energy circuit model of the highway network coupled with the power grid is obtained as follows:

[0180] It is worth noting that although the starting nodes on the branches corresponding to different coupling nodes all represent the entrances of the highway, the starting loads they carry are different, which are determined by the load that eventually flows into the coupling node.

[0181] Based on the establishment of the equivalent model of the highway network in steps S1 and S2, the dynamic behavior of the parameters of the unified energy circuit model is obtained. In order to realize its dynamic power flow calculation, a steady-state power flow calculation can be performed at each moment, and then the calculation results at each moment are superimposed to finally obtain the result of the dynamic power flow calculation.

[0182] Similar to the solution of the traditional power system flow model, for a system with 1 balance node and N PV PV nodes and N PQ The power flow equation of the N-node road-electric coupling system with PQ nodes is:

[0183]

[0184] in, For Node The active power of; j is the imaginary unit; For Node Reactive power; For Node Voltage; For Node and the mutual admittance of node τ conjugation of; is the voltage of node τ; N is the total number of nodes;

[0185] The Newton-Raphson method is used to calculate and the correction equation in polar coordinate form is as follows:

[0186]

[0187] Where: H, N, J, L are the block sub-matrices of the Jacobian matrix, expressed as:

[0188]

[0189] Wherein, ΔP is the active power correction; ΔQ is the reactive power correction; H, N, J, L are all block sub-matrices of the Jacobian matrix; Δθ is the voltage phase angle correction; θ is the voltage phase angle; ΔU is the voltage correction; U is the voltage amplitude; for θ τ is the voltage phase angle of node τ; for U τ is the voltage amplitude of node τ; for for

[0190] According to the coupling network structure and network parameters, the node admittance matrix is ​​formed. Given the initial value of each node voltage, the correction amount of the k+1th iteration can be obtained by equation (25), thereby obtaining a new solution. The iterative formula is as follows:

[0191]

[0192]

[0193] In the formula, ΔP k is the kth active power correction, ΔQ k is the kth reactive power correction, H k 、N k , J k , L k are the block sub-matrices of the k-th Jacobian matrix. k+1 ΔUk+1 are the phase angle and voltage amplitude of the kth system node, respectively. k ,θ k+1 are the phase angles of the kth and k+1th system nodes, respectively, U k , U k+1 are the voltage amplitudes of the kth and k+1th system nodes respectively, and x is the phase angle and voltage of the system node: x=[θ,U] T Δx is the phase angle and voltage correction of the system node: Δx=[Δθ,ΔU] T ΔF is the deviation between the active power and reactive power of the node: ΔF = [ΔP, ΔQ] T .

[0194] In this embodiment, the test is conducted on a highway without an interchange. Each charging station is equipped with 150 charging piles, and the entrance and exit of the highway are close to the charging station. The average speed is used for the speed of each vehicle on the same equivalent branch road on the highway, and the battery capacity is 60kwh. The time when the starting vehicle enters the highway obeys the normal distribution, and the required SOC is 0.4. There are 4,000 vehicles entering the highway in working condition 1 throughout the day, and 7,000 vehicles entering the highway in working condition 2 throughout the day. The sampling time is 1min. The vehicle parameters are shown in Table 1, and the environmental coefficients are shown in Table 2.

[0195] Table 1 Vehicle parameters

[0196] Cd M / kg A / m2 C / (kwh) 0.23 2000 2.8774 78.4

[0197] Table 2 Environmental coefficients

[0198] parameter Value Gravity acceleration 9.81m / s2 Air density 1.29kg / m3 Rolling resistance coefficient 0.014

[0199] Under the boundary conditions set at the entrance of the expressway, the road pressure at the end of the expressway and the road potential difference between the beginning and the end of the expressway network equivalent road model are calculated, and the results of the expressway network equivalent road model are compared with the simulation results of the Van Aerde model. Figure 3 It can be seen that the calculation results of the proposed highway network equivalent road model are highly consistent with the actual results, and the error range is less than 0.5%, which fully verifies the accuracy and effectiveness of the equivalent road model in the solution. Figure 3 In (a), the time delay at the beginning and the end clearly shows the process of vehicle migration on the highway, and the change in energy demand reflects the energy loss in the process. Figure 2The energy demand at some moments in the process is lower than that at the beginning because some vehicles are replenished with energy at the charging station, and this energy is superimposed on the road model by injecting road pressure. In addition, the solution time of the equivalent road model of the proposed highway network is only 0.06 seconds, while the Van Aerde model takes 6.39 seconds, which shows the significant advantage of the proposed equivalent road model of the highway network in computational performance, which is mainly due to the simplification process from partial differential equations to algebraic equations.

[0200] The unified energy circuit model of a highway without an interchange coupled with a 20-node power system was tested. The voltage fluctuations at each node were analyzed to explore the impact of vehicle energy demand on the power grid. Figure 4 The 20-node power system shown has a basic capacity of 100 MVA and a basic voltage of 23 kV.

[0201] Depend on Figure 5 It can be seen that, from the overall point of view, the energy demand change curve of each charging station is opposite to the voltage curve of each coupling node. At the starting moment, the vehicle enters the highway, the starting load begins to connect to the coupling network, and the voltage of the corresponding coupling node decreases. When the vehicle enters charging station S1, the voltage drops faster, and the coupling node corresponding to S1 changes most significantly. Similarly, when the vehicle demand for a certain charging station increases, the voltage of each coupling node will decrease as a whole. And the voltage of the coupling node corresponding to the charging station decreases more, and the impact is greater. Therefore, the change in the energy demand of vehicles on the highway can be reflected through the voltage curve. The effectiveness of the coupling network model is further verified.

[0202] In summary, the proposed method of coupling the highway network with the power grid is analogous to the circuit analysis method, and an equivalent highway road model under realistic road conditions and speed limit conditions is established, which can not only reflect the behavioral characteristics of vehicles on the highway, but also reduce the analysis complexity of the highway network. The coupling nodes connecting the equivalent highway network and the power grid are defined, and a unified energy circuit model of the coupling of the highway network and the power grid is established, which can not only simulate the complex interaction between the highway network and the power grid, but also facilitate the subsequent better coordination of the operation of the power grid and the highway network.

Claims

1. A highway network and power grid coupling method based on field-to-road deduction methodology, characterized in that: include: Based on the mid-field to road deduction methodology in circuit theory, an equivalent road model of the expressway network is established; According to the running characteristics of electric vehicles on the highway and the characteristics of the highway itself, the constraints of the equivalent road model of the highway network are established; According to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established to complete the coupling of the expressway network and the power grid.

2. The highway network and power grid coupling method based on field-to-road deduction methodology according to claim 1 is characterized in that: The equivalent road model of the expressway network is established based on the deduction methodology of mid-field to road in circuit theory, which is specifically as follows: Based on the deduction methodology from field to road in circuit theory, the traffic volume of vehicles passing through a certain cross-sectional area per unit time is defined as road flow. Taking the vehicle starting point as the potential reference point, the energy demand per unit time passing through the cross-sectional area is defined as road pressure, and the relationship between road flow and road pressure is obtained: The energy consumption of vehicles due to ground friction and wind resistance between any two cross sections on the highway is defined as the road potential difference: Combining the relationship between road flow and road pressure as well as road potential difference, the one-dimensional flow process of vehicles on the highway is described as follows: According to the one-dimensional flow process of vehicles on the highway, the energy demand at different positions x is calculated as the traffic volume changes, and the energy transmission model is obtained: Abstracting the path resistance R from the energy transfer model h 、Road Sense L h 、Road guide h And road capacity C h Road components, defined as distributed parameter road models: R h =(mgf+f w v 2 ) L h =αmv g h =(mgf+f w v 2 ) / λ 2 C h =αmv / λ 2 According to the power system analysis method, the distributed parameter road model is mapped to the frequency domain, and the ordinary differential equations in the frequency domain are obtained: dq=-(g h +jωC h )dx·Q dQ=-(R h +jωL h )dx·q Solving the system of ordinary differential equations in the frequency domain, we obtain the state variables at the end of the road, which are defined as the equivalent road model of the highway network: Q1=A'Q0+Bq0 q1=CQ0+Dq0 Where Q(x+Δx,t) is the energy demand of the vehicle at the distance x+Δx at time t; x is the position; Δx is the distance between any two cross sections on the highway; t is the time series; Q(x,t) is the energy demand of the vehicle at the distance x at time t; m is the vehicle weight; g is the acceleration of gravity; f is the rolling resistance coefficient; f w is the total wind resistance parameter on the highway; v(x,t) is the speed of the vehicle at the distance x at time t; q(x,t) is the traffic flow of the vehicle at the distance x at time t; Δ is the difference sign; α is Δx a The ratio of the total distance Δx; a is the vehicle acceleration; Δx a is the distance traveled by the vehicle at an accelerated speed; ρ is the air density; C d is the drag coefficient; A is the frontal area of ​​the vehicle; is the symbol of partial derivative; Q is the energy demand per unit time for passing through a cross-sectional area; v is the speed of vehicles passing through a certain cross-sectional area per unit time; q is the traffic volume of vehicles passing through a certain cross-sectional area per unit time; λ is With E n The product of E is the state of charge that needs to be replenished; n is the battery capacity; ΔQ is the potential difference between two points; d is the differential sign; g h is the path guide; j is the imaginary unit; ω is the angular frequency; C h R h For road obstruction; L h is the road feeling; Q1 is the energy demand at the end of the road; Q0 is the energy demand at the beginning of the road; q0 is the traffic flow at the beginning of the road; q1 is the traffic flow at the end of the road; A', B, C and D are all dual-port network transmission coefficients.

3. The highway network and power grid coupling method based on field-to-road deduction methodology according to claim 1 is characterized in that: The constraint expression of the equivalent road model of the expressway network is: Q t =K t Q f +E t q t =K t q f Q f =A t T Q node q node =A f q t +q n Among them, Q t is the column vector composed of the energy requirements at the end of each road; K t is a diagonal matrix consisting of the energy transfer factors of each road; Q f is the column vector composed of the energy demand at the head end of each road; E t is the column vector of energy difference at the end of the road; q t is the column vector composed of the traffic flow at the end of each road; q f is the column vector of the traffic flow at the beginning of each road; Q1 is the energy demand at the end of the road; Q0 is the energy demand at the beginning of the road; e is the base of the natural logarithm; R tc is the equivalent road resistance from the beginning to the end of the road; j is the imaginary unit; ω is the angular frequency; L tc is the equivalent road inductance from the beginning to the end of the road; tc The total distance from the beginning to the end of the road With E n The product of E is the state of charge that needs to be replenished; n is the battery capacity; x is the position; E c is the energy difference generated by the vehicle after charging; q0 is the traffic flow at the beginning of the road; q1 is the traffic flow at the end of the road; l is the distance between the beginning and the end of the road; Q node is the column vector composed of the road pressure at each node; is the weighted node-inflow branch association matrix; is a column vector composed of the weighted injection energy demand of each charging station equivalent node. The weighted injection energy demand is the injection energy demand multiplied by the proportion of the injection flow to the total inflow flow. node When it is the equivalent node of the starting point of the expressway section, =0; Q f A is the energy demand at the head end of each outflow branch, that is, the node road pressure; t is the node-outflow branch association matrix; q node is the column vector of the total flow through each node; A f is the node-inflow branch association matrix; q n A column vector consisting of the flow injected into each node; is the weighted node-outflow branch association matrix.

4. The highway network and power grid coupling method based on field-to-road deduction methodology according to claim 3 is characterized in that: Node-outflow branch association matrix A t The element in row i and column j (A t ) i,j Indicates: If branch j flows out from node i, the element is 1, otherwise it is 0; Node-inflow branch association matrix A f The element in row i and column j (A f ) i,j Indicates: if branch j flows into node i, then the element is 1, otherwise it is 0; Weighted node-outflow branch association matrix The element in row i and column j Means: If branch j flows out from node i, then this element is the ratio of the flow of branch j to the total flow out of node i, otherwise it is 0; Weighted node-inflow branch association matrix The element in row i and column j Indicates: If branch j flows into node i, then this element is the ratio of the flow of branch j to the total flow of node i, otherwise it is 0.

5. The highway network and power grid coupling method based on field-to-road deduction methodology according to claim 1 is characterized in that: According to the equivalent road model of the expressway network, a unified energy circuit model of the expressway network and the power grid is established to complete the coupling of the expressway network and the power grid, specifically: According to the equivalent road model of the expressway network, vehicles charging at charging stations are connected as loads of the power grid, charging piles are used as direct coupling devices between the expressway network and the power grid, charging stations are used as coupling nodes connected to the power grid nodes, and vehicles flowing into the charging stations and the sections of the expressways through which the vehicles pass form an equivalent road network connecting the coupling nodes; the entrance of the expressway is connected to the power grid as the starting node, and the equivalent road network corresponding to each vehicle flowing into the charging station is connected to the power grid, so as to obtain a unified energy circuit model of the expressway network and the power grid, and complete the coupling of the expressway network and the power grid.

6. The highway network and power grid coupling method based on field-to-road deduction methodology according to claim 5 is characterized in that: The equivalent road network corresponding to each vehicle flowing into the charging station is connected to the power grid to obtain a unified energy circuit model of the highway network and the power grid, which is specifically: Obtain a power grid topology, where there are several power grid nodes; If the starting and ending points of the vehicle are the entrance of the expressway and the charging station, the entrance of the expressway is taken as the starting node, the energy demand of the vehicle at the starting node is obtained, and the energy demand of the vehicle at the starting node is taken as the starting load, and the starting load is connected to the starting node; The charging stations that the vehicle passes through on the way from the starting node to the destination charging station are regarded as intermediate nodes and are not connected to the load; The destination charging station is used as a coupling node. Based on the equivalent road model of the vehicle's highway network, the energy loss of each section is calculated separately, and the energy loss of each section is superimposed to obtain the loss energy. The loss energy is added to the initial load to obtain the charging load. and connecting the charging load to the coupling node; Based on the starting and ending points of the vehicle, the starting node, the intermediate node and the coupling node are connected in sequence to obtain the equivalent road network of the vehicle; and the equivalent road network of the vehicle is connected to the power grid node through the coupling node to obtain a unified energy circuit model of the highway network and the power grid; If the starting and ending points of the vehicle are both charging stations, the starting charging station and the charging stations that the vehicle passes through on the way from the starting charging station to the destination charging station are regarded as intermediate nodes and no load is connected; The destination charging station is used as a coupling node. Based on the equivalent road model of the vehicle's highway network, the energy loss of each section along the route is calculated separately, and the energy loss of each section is superimposed to obtain the loss energy. The loss energy is used as the charging load, and the charging load is connected to the coupling node. Based on the vehicle's starting and ending points, the intermediate nodes and coupling nodes are connected in sequence to obtain the vehicle's equivalent road network. The equivalent road network of the vehicle is connected to the grid nodes through coupling nodes to obtain a unified energy circuit model of the highway network and the grid.

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