Safety control method and system for alternating current and direct current system containing VSC-MTDC under electric heating coordination, electronic equipment and medium

Abstract

The invention relates to a VSC-MTDC-containing AC / DC system safety control method and system under electric heating coordination, electronic equipment and a medium, and belongs to the field of power system engineering, and the method comprises the steps: constructing a VSC converter station steady-state power model, and giving a control mode of a VSC converter station and a control mode of a DC power grid; constructing an overhead conductor heat balance equation under electric heating coordination; taking an alternating current node voltage amplitude and a phase angle, a direct current node voltage and an alternating current and direct current overhead conductor temperature as state variables, and constructing an alternating current and direct current power grid electrothermal coupling power flow model containing the VSC-MTDC according to node power balance; and constructing a VSC-MTDC-containing AC-DC system correction control model under electric heating coordination and an AC-DC system prevention control model considering correction, and solving. According to the method, the maximum allowable current constraint of the overhead conductor is relaxed, the real loading capacity of the overhead conductor is fully exerted, and the safety and the economical efficiency of the VSC-MTDC-containing alternating current and direct current system control are better met.

Description

Technical Field

[0001] This invention relates to a safety control method, system, electronic device, and medium for an AC / DC system with VSC-MTDC under electrothermal coordination, belonging to the field of power system engineering technology. Background Technology

[0002] With the rapid development of renewable energy sources such as offshore wind power and photovoltaics, the issue of large-scale renewable energy grid integration has become a research hotspot. Flexible DC transmission systems based on voltage source converters (VSCs) are one of the key technologies for solving the problem of large-scale renewable energy grid integration. Multi-terminal flexible DC transmission systems are DC transmission systems composed of three or more VSC converter stations connected in series, parallel, or hybrid configurations. Compared with traditional two-terminal DC transmission systems, multi-terminal DC transmission systems (MTDCs) can coordinate and control the power between individual converter stations, offering greater flexibility and reliability, and are more suitable for scenarios such as offshore wind power grid integration, urban power supply, and asynchronous interconnection of AC systems.

[0003] Currently, driven by economic development and the clean energy transformation, social electricity demand is constantly rising, and the grid-connected capacity of new energy power generation is growing rapidly. This has led to complex and variable power grid operation modes, a decrease in grid load safety margin, and frequent occurrences of power flow exceeding limits caused by faults. Improper handling can result in costly safety control measures at best, and at worst, trigger cascading failures and large-scale power outages. Therefore, leveraging current smart grid technology for online monitoring of transmission components, exploring the load potential of transmission components (overhead conductors) in emergency situations, expanding the feasible domain for safety control decisions, and implementing more economical and effective safety control measures are urgent problems to be solved in power system safety control.

[0004] Initially, researchers used Static Thermal Rating (STR) to measure the load capacity of transmission components. However, STR is based on conservative conditions of harsh weather and thermal stability, and cannot reflect the true load capacity of transmission components. Later, in the 1970s, scholars proposed the concept of Dynamic Thermal Rating (DTR), which enabled real-time monitoring of environmental factors and operating status of transmission components. This aligns with the requirements of modern smart grids and the power Internet of Things, revealing the external manifestation of the load capacity of transmission components (the correlation between load and temperature). The true load capacity is inherent in the slow dynamic process of temperature relative to load (thermal inertia). This asynchronous relationship indicates that, over a considerable period, the essence characterizing the load capacity of transmission components should be the maximum permissible temperature, rather than the load value. Based on the aforementioned research on dynamic thermal setpoints, the Electrothermal Coordination (ETC) theory further elucidates the relationship between electrical quantities and physical quantities of transmission components in the power grid. It incorporates the operating temperature of transmission components as a key state quantity into the load capacity criterion, making it possible for the load capacity of transmission components to play a role in power flow and optimization decisions. This allows the operating current to exceed the maximum allowable operating current (short-term overload capacity) for short periods while ensuring safe and reliable operation. Therefore, with the continuous development and application of DTR technology in the power Internet of Things, the consideration of the load capacity of transmission components has gradually transitioned from conservative constraints based on static thermal setpoints to dynamic thermal setpoints under DTR technology, and further to the ETC theoretical framework with the maximum allowable temperature of transmission components as a constraint. However, current research has not organically integrated flexible transmission technology with electrothermal coordination. In the safety control of AC / DC systems containing VSC-MTDC, it has not considered the inherent load characteristics of transmission components from the perspective of their load nature, nor has it refined the short-term overload capacity inherent in thermal inertia. Consequently, the load potential of transmission components needs to be further actively explored in safety control decisions.

[0005] To address the shortcomings of existing technologies, this invention provides a safety control method, system, electronic equipment, and medium for AC / DC systems with VSC-MTDC under electrothermal coordination. First, an electrothermal coupled power flow model of the AC / DC system with VSC-MTDC is constructed. Based on this model, research is conducted on safety correction control and preventive control methods for AC / DC systems that take correction into account. The invention focuses on the essential thermal load capacity of overhead conductors, explores the short-time overload capacity in the thermal inertia of transmission components, and uses overhead conductor temperature as a safety control decision variable. This allows for the formulation of superior control measures while ensuring system safety, demonstrating significant theoretical value and promising engineering applications.

[0006] The technical solution of the present invention is as follows:

[0007] A safety control method for an AC / DC system with VSC-MTDC under electrothermal coordination includes the following steps:

[0008] S1: Construct a steady-state power model of the VSC converter station based on the equivalent circuit of the VSC converter station, and give the control method of the VSC converter station and the control method of the DC grid.

[0009] S2: Based on the laws of heat transfer, and using the overhead conductor current and meteorological data of the power system, construct the heat balance equation of the overhead conductor under electrothermal coordination.

[0010] S3: Using AC node voltage amplitude and phase angle, DC node voltage and AC / DC overhead conductor temperature as state variables, construct an AC / DC power grid electrothermal coupling power flow model with VSC-MTDC based on node power balance;

[0011] S4: Based on the definitions of the correction control model and the preventive control model that takes correction into account, list the corresponding electrical constraints, temperature constraints, and objective functions, construct the correction control model and the preventive control model that takes correction into account for the VSC-MTDC AC / DC system under electrothermal coordination, and solve them.

[0012] Preferably, the steady-state power model of the VSC converter station in step S1 includes:

[0013]

[0014] In the formula, express Figure 2 Active power is injected at point s on the AC side of the VSC converter station shown. This indicates that reactive power is injected at point f on the AC side of the VSC converter station; These represent the voltage amplitudes at AC nodes s and f, respectively; g sf and b sf These are the real and imaginary parts of the equivalent line admittance sf within the converter station, respectively, g sg and b sg They are respectively Figure 3 The point s shown in the diagram is resisted by the ground group z. sg The real and imaginary parts of the reciprocal (earth-oriented admittance); These are the phase angles of the corresponding node voltages;

[0015]

[0016] In the formula, Inject active power from VSC into node c; Inject active power into DC node d of VSC; P vsc ,loss For the active power loss of VSC;

[0017]

[0018] In the formula, P sfc,loss Let the sum of the active power losses of the converter transformer, filter, and converter reactor be:

[0019]

[0020] In the formula, r is the square of the current flowing through the converter transformer. sf This represents the equivalent line resistance of the converter transformer; g fg express Figure 3 The point f shown in the diagram is resisted by the ground group z. fg The real part of the reciprocal (earth admittance); The square of the current flowing through the converter reactor. g c b represents the real part of the admittance of the commutator reactor; c The imaginary part of the admittance of the commutator reactor; r c This indicates the resistance of the commutator reactor.

[0021] Preferably, the control methods of the VSC converter station include two types: active power control and reactive power control. Among them, active power control includes constant AC side active power control, constant DC side voltage control, DC voltage-power droop control, and DC voltage-current droop control. The DC voltage-power droop control and DC voltage-current droop control are shown in formulas (5) and (6), respectively:

[0022]

[0023] In the formula, the superscript "^" on the parameter represents the reference value of the corresponding control quantity. Inject DC current into the DC node d of VSC; k P k is the droop coefficient for DC voltage-power droop control. I This is the droop coefficient for DC voltage-current droop control;

[0024] Reactive power control includes constant-s point reactive power control and constant-s point voltage control;

[0025] The DC grid includes multiple VSC converter stations. The control methods of the DC grid include master-slave control and droop control. Under master-slave control and droop control, the reactive power control method of each VSC converter station is constant-s point reactive power control or constant-s point voltage control. In master-slave control, the active power control method of the master station of the VSC converter station is constant DC side voltage control, and the active power control method of the slave station is constant AC side active power control. In droop control, there are VSC converter stations with at least one active power control method of DC voltage-power droop control or DC voltage-current droop control, and the active power control method of the remaining VSC converter stations is selected from constant AC side active power control, DC voltage-power droop control, or DC voltage-current droop control.

[0026] Preferably, in step S2, let Δt be the discretization step size (s), and the study time period [t0, t...] f The total number of discretized units is n. k After discretization, the heat balance equations for the AC and DC overhead conductors l in the k-th time period are:

[0027]

[0028] In equations (11) and (12), the variable subscripts k and k-1 represent the k-th and k-1th time periods, respectively. and These represent the mismatch (°C) in the thermal balance equations for AC and DC overhead conductors l during the k-th time period; and For AC and DC overhead conductors, l represents the mass per unit length of conductor (kg / m). and Specific heat capacity of AC and DC overhead conductors (J / (kg·℃)); n al and n dl These represent the number of AC and DC overhead lines, respectively.

[0029] Preferably, in step S3, the AC system power flow model is as follows:

[0030]

[0031] In the formula, and These represent the injected active power and reactive power (pu) at AC node i, respectively. Specifically, for VSC AC-side node c, the injected power includes... and (These two variables are the optimization variables for VSC active power control and reactive power control, respectively). and These are the voltage amplitudes (pu) at AC nodes i and j, respectively. and Let be the voltage phase angles (rad) at AC nodes i and j, respectively. and These are the elements (pu) in the i-th row and j-th column of the real part G and imaginary part B of the AC node admittance matrix, respectively. Let i be the temperature vector of the AC overhead conductor. When i ≠ j, l∈(i,j); when i=j S represents the temperature vector of the AC overhead line conductor connected to node i; ac,bus For the set of communication nodes; n a Indicates the number of communication nodes;

[0032] The DC system power flow model is as follows:

[0033]

[0034] In the formula, The injected active power (pu) is for DC node i. Specifically, for VSC DC-side node d, the injected power includes... and Let be the voltages (pu) at nodes i and j in the k-th time period, respectively. Let be the element (pu) in the i-th row and j-th column of the DC grid node admittance matrix Y. Considering the temperature effect of conductor resistance, the elements in Y are functions of conductor temperature. Let i be the temperature vector of the DC overhead conductor during the k-th time period. When i ≠ j, l∈(i,j); when i=j, T dc S represents the temperature vector of the DC overhead conductor connected to node i; dc,bus n is the set of DC nodes; d Indicates the number of DC nodes;

[0035] The electro-thermal coupling power flow model of AC / DC power grids including VSC-MTDC is as follows:

[0036]

[0037] In the formula, The injected power (pu) is the AC side node c of the VSC converter station. V-loss (pu) of VSC converter station; The injected power (pu) is the DC-side node d of the VSC converter station.

[0038] Preferably, in step S4, the AC / DC system optimization power flow model including VSC-MTDC is as follows:

[0039]

[0040] In the formula, the first term f is the objective function; x is the system state variable, including the AC node voltage amplitude and phase angle, the DC node voltage, and the AC / DC overhead conductor temperature; u is the system control variable, mainly including generator output, load shedding, curtailment of solar power, and converter power of the converter station; the second term g is the equality constraint function; the third term h is the inequality constraint condition; and the fourth term r is the generator output rate regulation inequality constraint. This represents the active power generated by the AC generator during time period k. This represents the active power generated by the AC generator during time period k-1;

[0041] When the voltage of a transmission line or bus exceeds the limit in the power grid, corrective control is required to restore the system to a safe operating state. The corrective control model for an AC / DC system including VSC-MTDC is as follows:

[0042]

[0043] In the formula, the first term is the generator output adjustment cost of process-oriented safety correction control, the second term is the load shedding cost, and the third term is the curtailment cost; n k n represents the number of study periods. PH S represents the number of photovoltaic power plants. ac,G Let S be the set of generator nodes. ac,CL A set of controllable load nodes; and Let be the cost coefficients for the second and first power outputs of generator node i during time period k. γ is the load shedding cost coefficient for load node i during time period k. i Let i be the curtailment penalty coefficient for photovoltaic unit node i; and These represent the output of generator node i before and after correction during time period k. and These represent the active power loads of load node i before and after correction during time period k. Adjust the curtailment power for photovoltaic unit node i.

[0044] Preferably, in step S4, the generator regulation output rate constraint of the corrected AC / DC system preventive control model is taken into account. The constraints include the normal-state generator output rate regulation constraint formula and the fault-state generator output rate constraint formula, as shown in formulas (25) and (26) respectively:

[0045]

[0046] In the formula, the subscript w represents the variable of system operation under the expected accident, w = 0, 1, ..., n outage ;n outageThe number of critical anticipated accidents; where, and These represent the active and reactive power outputs of the generator at AC node i, respectively. To adjust the maximum speed of output regulation at AC generator node i;

[0047] The AC / DC system preventive control model that takes into account correction is as follows:

[0048]

[0049] In the formula, is the cost constant coefficient of generator node i during time period k; the subscript 0 indicates a variable indicating normal system operation.

[0050] A safety control system for an AC / DC system with VSC-MTDC under electrothermal coordination, used to implement the above-mentioned safety control method for an AC / DC system with VSC-MTDC under electrothermal coordination, includes:

[0051] The VSC converter station steady-state power model construction module is configured to construct a VSC converter station steady-state power model based on the equivalent circuit of the VSC converter station, and to provide the control mode of the VSC converter station and the control mode of the DC grid.

[0052] The heat balance equation construction module is configured to construct the heat balance equation of the overhead conductor under electrothermal coordination based on the laws of heat transfer and the current of the overhead conductor and the meteorological data of the power system.

[0053] The AC / DC power grid electrothermal coupling power flow model construction module is configured to construct an AC / DC power grid electrothermal coupling power flow model containing VSC-MTDC based on the node power balance, using AC node voltage amplitude and phase angle, DC node voltage and AC / DC overhead conductor temperature as state variables.

[0054] The AC / DC system safety control model construction and solution module is configured to, based on the definitions of the correction control model and the prevention control model considering correction, list the corresponding electrical constraints, temperature constraints, and objective functions, construct and solve the correction control model of the AC / DC system with VSC-MTDC under electrothermal coordination and the prevention control model of the AC / DC system considering correction.

[0055] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described above.

[0056] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the above-described method.

[0057] The beneficial effects of this invention are as follows:

[0058] Traditional safety correction control uses the maximum allowable current of overhead conductors as the load constraint. This method ignores the short-term overload capacity due to thermal inertia, and the true load capacity of overhead conductors needs to be further explored, resulting in high control costs. The safety correction control model for AC / DC systems with VSC-MTDC proposed in this invention relaxes the maximum allowable current constraint of overhead conductors, fully utilizes their true load capacity, improves the system's renewable energy absorption level, and better meets the safety and economy requirements of control.

[0059] Preventive control of AC / DC systems with overhead conductor temperature as a constraint and correction has a wider safety control domain, providing greater slack for decision-making in AC / DC systems including VSC-MTDC, making it easier to determine a more economical operating state while meeting system safety requirements. Attached Figure Description

[0060] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0061] Figure 1 This is a schematic flowchart of a safety control method for an AC / DC system with VSC-MTDC under electrothermal coordination, provided in Embodiment 1 of the present invention.

[0062] Figure 2 This is a structural diagram of the VSC converter station provided in Embodiment 1 of the present invention;

[0063] Figure 3 The equivalent circuit diagram of the VSC converter station provided in Embodiment 1 of the present invention;

[0064] Figure 4 This is a diagram of the retrofit system of IEEE 39 node with 8-terminal VSC converter stations provided in Embodiment 1 of the present invention;

[0065] Figure 5 The current carrying capacity and temperature curves of the critical circuit (DC branch 7-10) under master-slave control during the entire research period provided in Embodiment 1 of the present invention;

[0066] Figure 6 The current and temperature of the critical circuit after correction during the research period provided in Embodiment 1 of the present invention;

[0067] Figure 7 The current carrying capacity and temperature change curves of the critical circuit (AC branch 6-7) after an accident under master-slave control during the entire research period provided in Embodiment 1 of the present invention;

[0068] Figure 8 The current and temperature diagram of the critical circuit after constraint I and T correction is provided in Embodiment 1 of the present invention. Detailed Implementation

[0069] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. However, this is not the only description; all aspects not described in detail herein are based on conventional techniques in the art.

[0070] Example 1

[0071] A safety control method for an AC / DC system with VSC-MTDC under electrothermal coordination includes the following steps:

[0072] S1: Construct a steady-state power model of the VSC converter station based on the equivalent circuit of the VSC converter station, and give the control method of the VSC converter station and the control method of the DC grid.

[0073] S2: Based on the laws of heat transfer, and using the overhead conductor current and meteorological data of the power system, construct the heat balance equation of the overhead conductor under electrothermal coordination.

[0074] S3: Using AC node voltage amplitude and phase angle, DC node voltage and AC / DC overhead conductor temperature as state variables, construct an AC / DC power grid electrothermal coupling power flow model with VSC-MTDC based on node power balance;

[0075] S4: Based on the definitions of the correction control model and the preventive control model that takes correction into account, list the corresponding electrical constraints, temperature constraints, and objective functions, construct the correction control model and the preventive control model that takes correction into account for the VSC-MTDC AC / DC system under electrothermal coordination, and solve them.

[0076] 1. Steady-state power model and control method of VSC converter station

[0077] In AC / DC systems containing VSC-MTDC converters, the VSC converter station is the core of AC / DC power conversion and control. This section introduces the steady-state power model and control method of the VSC converter station, laying the foundation for the subsequent construction of the ETCPF-FDCG model.

[0078] 1.1 Steady-state power model of VSC converter station

[0079] The structure of the VSC converter station is as follows: Figure 2 As shown, the equipment includes an AC bus (i.e., refers to...) Figure 2 AC power grid), converter transformers, filters, converter reactors, VSCs and DC buses (i.e., referring to...) Figure 2 (DC power grid). Using VSC as the dividing line, the converter station can be divided into AC and DC parts. The equivalent circuit of the converter station is as follows: Figure 3 As shown.

[0080] Figure 3 In the converter station, nodes s, f, and c belong to the AC section, serving as the connection node to the AC grid, the filter connection node, and the VSC AC side node, respectively. Node d belongs to the DC section and is the VSC DC side node. t z c =r c +jx c and z f These are the converter transformer impedance (referencing to the AC grid side), the converter reactor impedance, and the filter impedance, respectively. c Indicates the reactance of the commutator reactor; K t For the converter transformer ratio; z sg =r sg +jx sg Z represents the equivalent grounding impedance of the converter transformer on the s-side of node; sf =r sf +jx sf For the equivalent line impedance of the converter transformer, x sf This represents the equivalent line reactance of the converter transformer; z fg =r fg +jx fg The equivalent grounding impedance of the converter transformer at node f and z f The sum of, r fg Represents resistance, x fg Indicates reactance. and These represent the voltage amplitudes at AC nodes s, f, and c, respectively. and These are the phase angles of the corresponding node voltages. Inject the power of the converter station into node s, i.e., the power at the beginning of branch sf; Inject complex power from VSC into node c; P vsc,loss This refers to the active power loss of the VSC. Inject active power into DC node d of VSC; Let be the voltage at DC node d. According to Kirchhoff's laws and the law of conservation of power, the complex power of the converter station... (In the field of power systems, P represents the corresponding active power and Q represents the corresponding reactive power.) and It can be expressed by formulas (1) to (2);

[0081] The steady-state power model of the VSC converter station in step S1 includes:

[0082]

[0083] In the formula, express Figure 2 Active power is injected at point s on the AC side of the VSC converter station shown. This indicates that reactive power is injected at point f on the AC side of the VSC converter station; These represent the voltage amplitudes at AC nodes s and f, respectively; g sf and b sf These are the real and imaginary parts of the equivalent line admittance sf within the converter station, respectively, g sg and b sg They are respectively Figure 3 The point s shown in the diagram is resisted by the ground group z. sg The real and imaginary parts of the reciprocal (earth-oriented admittance); These are the phase angles of the corresponding node voltages;

[0084]

[0085] In the formula, Inject active power from VSC into node c; Inject active power into DC node d of VSC; P vsc ,loss This refers to the active power loss of VSC. a', b', and c' are the loss coefficients of the VSC; 1 / z c =g c +jb c For the admittance of the commutator reactor (g) c +jb c These are the real and imaginary parts of the commutator reactor admittance, respectively. It represents the difference between the phase angles of two voltages;

[0086]

[0087] In the formula, P sfc,loss Let the sum of the active power losses of the converter transformer, filter, and converter reactor be:

[0088]

[0089] In the formula, The square of the current flowing through the converter transformer; r sf This represents the equivalent line resistance of the converter transformer; g fg express Figure 3 The point f shown in the diagram is resisted by the ground group z. fg The real part of the reciprocal (earth admittance); The square of the current flowing through the converter reactor. g c b represents the real part of the admittance of the commutator reactor; c The imaginary part of the admittance of the commutator reactor; r c This indicates the resistance of the commutator reactor.

[0090] 1.2 Control methods for VSC and DC power grid

[0091] The control methods of VSC converter stations include two categories: active power control and reactive power control. Active power control includes constant AC side (…). Figure 3 Active power control at midpoint (S) #1 control method For AC active power control target value), constant DC side ( Figure 3 Voltage control at point d (middle d point) #2 control method The DC voltage control target value), DC voltage-power (VP) droop control (#3 control mode) and DC voltage-current (VI) droop control (#4 control mode) are shown in formulas (5) and (6), respectively:

[0092]

[0093] In the formula, the superscript "^" on the parameter represents the reference value of the corresponding control quantity. Inject DC current into the DC node d of VSC; k P k is the droop coefficient for DC voltage-power droop control. I This is the droop coefficient for DC voltage-current droop control;

[0094] Reactive power control includes constant-s-point reactive power control ( #5 Control method For AC reactive power control target value) and fixed-s point voltage control ( #6 Control method (Target value for AC voltage control);

[0095] The DC grid includes multiple VSC converter stations. The control methods of the DC grid include master-slave control and droop control. Under master-slave control and droop control, the reactive power control method of each VSC converter station is constant-s point reactive power control or constant-s point voltage control (i.e., #5 or #6). In master-slave control, the active power control method of the master station of the VSC converter station is constant DC side voltage control (i.e., #2), and the active power control method of the slave station is constant AC side active power control (i.e., #1). In droop control, there is at least one VSC converter station with DC voltage-power droop control or DC voltage-current droop control (i.e., #3 or #4), and the active power control method of the remaining VSC converter stations is selected from constant AC side active power control, DC voltage-power droop control, or DC voltage-current droop control (i.e., #1, #3, or #4).

[0096] 2. Electrothermal Coupled Power Flow Model of AC / DC System

[0097] 2.1 Heat balance equations for AC and DC overhead conductors

[0098] In step S2, according to the IEEE standard, the thermal balance equation for overhead conductors is expressed as:

[0099]

[0100] In the formula, m l C is the mass per unit length of the overhead conductor l (kg / m). l Specific heat capacity of the conductor (J / (kg·℃)); T l t represents the conductor temperature (°C); t represents time (s). Joule heat (W / m) generated per unit length of conductor carrying current; The amount of heat absorbed by the conductor per unit length under sunlight (W / m); The convective heat dissipation per unit length of conductor (W / m); The radiative heat dissipation per unit length of conductor (W / m);

[0101] For AC and DC overhead conductors, the above formulas for calculating heat absorption and dissipation are shown in (8) and (10):

[0102]

[0103] In the formula, The Joule heat (W / m) generated per unit length of AC and DC overhead conductors is respectively. The conductor temperatures (°C) of AC and DC overhead conductors l are respectively. These represent the AC and DC overhead conductor currents (pu), respectively. and S represents the length (m) of the AC and DC overhead conductors l, respectively; B This represents the system's baseline capacity (VA). and Let be the resistance (pu) of the AC and DC overhead conductor l, respectively. Their expressions are as follows:

[0104]

[0105] In the formula, R dc,ref To be at the reference temperature T dc,ref Resistance of a DC overhead conductor (pu) at (20℃), α dc The DC resistance temperature coefficient (for aluminum conductors, α) dc Approximately 0.004℃ -1 Temperature coefficient of resistance α of AC overhead conductors acα is estimated from the actual measured values ​​of the wire resistance at different temperatures. ac =(R ac,high -R ac,low ) / ((T ac,high -T ac,low )R ac,low ), where R ac ,low To achieve the specified lower conductor temperature T ac,low Resistance (pu) of AC overhead conductor at (20℃), R ac,high To achieve the specified higher conductor temperature T ac,high Resistance (pu) of AC overhead conductor at 80℃; The calculation formulas for solar heat absorption, convective heat dissipation and thermal radiation heat dissipation in the heat balance equations of AC and DC overhead conductors are the same, as shown in equation (10):

[0106]

[0107] In the formula, The superscript 'ac' indicates the variable value of AC overhead conductors, and the superscript 'dc' indicates the variable value of AC / DC overhead conductors; β l The solar absorption rate of conductor l in the overhead wire; Solar radiation power density (W / m) 2 ); The diameter (m) of the conductor; The convective heat dissipation coefficient (W / (m·℃)) is related to wind speed and wind direction; The radiative heat dissipation coefficient (W / (m·℃)) 4 ));T am The ambient temperature (°C) is the temperature around the conductor.

[0108] To facilitate the solution, this embodiment uses the implicit trapezoidal rule to discretize the differential form of the overhead conductor heat balance equation shown in equation (7). Let Δt be the discretization step size (s), and the study time period [t0, t... f The total number of discretized units is n. k After discretization, the heat balance equations for the AC and DC overhead conductors l in the k-th time period are:

[0109]

[0110] In equations (11) and (12), the variable subscripts k and k-1 represent the k-th and k-1th time periods, respectively. and These represent the mismatch (°C) in the thermal balance equations for AC and DC overhead conductors l during the k-th time period; and For AC and DC overhead conductors, l represents the mass per unit length of conductor (kg / m). and Specific heat capacity of AC and DC overhead conductors (J / (kg·℃)); n al and n dl These represent the number of AC and DC overhead lines, respectively.

[0111] 2.2 Power Flow Equations for Electrothermal Coupling in AC and DC Systems

[0112] In step S3, the AC system power flow model is as follows:

[0113] (13)

[0115] In the formula, and These represent the injected active power and reactive power (pu) at AC node i, respectively. Specifically, for VSC AC-side node c, the injected power includes... and (These two variables are the optimization variables for VSC active power control and reactive power control, respectively). and These are the voltage amplitudes (pu) at AC nodes i and j, respectively. and Let be the voltage phase angles (rad) at AC nodes i and j, respectively. and These are the elements (pu) in the i-th row and j-th column of the real part G and imaginary part B of the AC node admittance matrix, respectively. Let i be the temperature vector of the AC overhead conductor. When i ≠ j, l∈(i,j); when i=j S represents the temperature vector of the AC overhead line conductor connected to node i; ac bus is the set of communication nodes; n a Indicates the number of communication nodes;

[0116] The DC system power flow model is as follows:

[0117]

[0118] In the formula, The injected active power (pu) is for DC node i. Specifically, for VSC DC-side node d, the injected power includes... and Let be the voltages (pu) at nodes i and j in the k-th time period, respectively. Let be the element (pu) in the i-th row and j-th column of the DC grid node admittance matrix Y. Considering the temperature effect of conductor resistance, the elements in Y are functions of conductor temperature. Let i be the temperature vector of the DC overhead conductor during the k-th time period. When i ≠ j, l∈(i,j); when i=j, T dc S represents the temperature vector of the DC overhead conductor connected to node i; dc ,bus is the set of DC nodes; n d Indicates the number of DC nodes;

[0119] The electro-thermal coupling power flow model of AC / DC power grids including VSC-MTDC is as follows:

[0120]

[0121] In the formula, The injected power (pu) is the AC side node c of the VSC converter station. V-loss (pu) of VSC converter station; The injected power (pu) is the DC-side node d of the VSC converter station.

[0122] 3. Safety control model of AC / DC system with VSC-MTDC under electrothermal coordination

[0123] The safety control described in this invention includes safety correction control and preventive control models that take correction into account, both of which are essentially optimization power flow models. Therefore, the basic concepts of optimization power flow are introduced first, and then the two safety control models mentioned above are constructed.

[0124] 3.1 In step S4, the optimized power flow model for the AC / DC system containing VSC-MTDC is as follows:

[0125]

[0126] In the formula, the first term f is the objective function; x is the system state variable, including the AC node voltage amplitude and phase angle, the DC node voltage, and the AC / DC overhead conductor temperature; u is the system control variable, mainly including generator output, load shedding, curtailment of solar power, and converter power of the converter station; the second term g is the equality constraint function; the third term h is the inequality constraint condition; and the fourth term r is the generator output rate regulation inequality constraint. This represents the active power generated by the AC generator during time period k. This represents the active power generated by the AC generator during time period k-1;

[0127] The equality constraint function g includes the AC system electrothermal coupling power flow model (13), the DC system electrothermal coupling power flow model (14), the AC / DC system active power coupling relationship (15), and the AC / DC overhead conductor heat balance equations (11) to (12). In particular, for the DC grid with droop control, g also includes the VSC droop control equations (5) to (6).

[0128] The inequality constraint h includes equations (17) to (21), as follows:

[0129] Generator output constraints:

[0130]

[0131] In the formula, and These represent the active and reactive power outputs of the generator at AC node i, respectively. and These are the upper and lower limits (pu) of the active power output at node i of the AC generator, respectively. For the set of alternator nodes; and These represent the upper and lower limits (pu) of reactive power output at AC generator node i.

[0132] Operational constraints of VSC converter stations:

[0133]

[0134] In the formula, and The maximum active and reactive power (pu) of converter station v are respectively.

[0135] AC and DC node voltage constraints:

[0136]

[0137] In the formula, and These are the upper and lower limits (pu) of the voltage amplitude at AC node i, respectively; and These are the upper and lower limits (pu) of the voltage amplitude at DC node i, respectively.

[0138] Maximum allowable operating current constraints for AC and DC transmission lines:

[0139]

[0140] In the formula, and These are the maximum allowable operating current values ​​(pu) for AC and DC transmission lines, respectively, i.e., DTR; S ac,line and S dc,line The set of AC and DC transmission lines (pu) are respectively. This represents the current in the AC overhead conductor l during time period k; This represents the current in the DC overhead conductor l during time period k.

[0141] Maximum allowable operating temperature constraints for AC and DC overhead transmission lines:

[0142]

[0143] In the formula, and These are the maximum allowable operating temperatures (°C) for AC and DC overhead transmission lines, respectively.

[0144] The generator output rate regulation constraint r is as follows:

[0145]

[0146] In the formula, The maximum speed for adjusting the output of AC generator node i.

[0147] 3.2 Safety Correction Control Model for AC / DC Systems

[0148] When the voltage of a transmission line or busbar exceeds the limit in the power grid, corrective control measures are required to restore the system to a safe operating state. This embodiment adopts corrective control measures of adjusting generator output, load shedding, and controlling the consumption of new energy sources. The control costs of these three measures are shown in equation (23).

[0149] The AC / DC system correction control model including VSC-MTDC is as follows:

[0150]

[0151] In the formula, the first term is the generator output adjustment cost of process-oriented safety correction control, the second term is the load shedding cost, and the third term is the curtailment cost; n k n represents the number of study periods. PH S represents the number of photovoltaic power plants. ac,G Let S be the set of generator nodes. ac,CL A set of controllable load nodes; and Let be the cost coefficients for the second and first power outputs of generator node i during time period k. γ is the load shedding cost coefficient for load node i during time period k. i Let i be the curtailment penalty coefficient for photovoltaic unit node i; and These represent the output of generator node i before and after correction during time period k. and These represent the active power loads of load node i before and after correction during time period k. Adjust the curtailment power for photovoltaic unit node i.

[0152] It is worth noting that the droop control coefficient k P and k IThis is achieved by pre-setting conditions such as rated capacity and operating status to ensure that multiple converter stations share the power fluctuations of the power grid. In actual operation, these settings are not repeatedly configured. Therefore, this paper selects the vertical control converter station method. and As a control optimization variable. In summary, the active power control optimization variable of VCS. and All can be transformed into VCS reactive power control optimization quantity and All can be transformed into This lays the foundation for subsequent simplified modeling.

[0153] During the period of process-oriented safety correction control, the equality constraint g(x) k ,u k ), inequality constraint h(x) k ,u k ), Generator output rate regulation constraint The correction control model constructed with objective function (23) uses the traditional dynamic thermal setpoint as the line load constraint, which is the most widely used in practice, but it ignores the potential load capacity in the thermal inertia of the overhead conductor. The correction control model that ignores the overhead conductor current constraint in equation (20) uses the overhead conductor temperature as the load constraint, which to some extent releases the short-term load capacity of the overhead conductor and helps to improve the flexibility of safety correction control. Both are complex nonlinear programming models, and this paper uses mature commercial computer numerical analysis software to solve them.

[0154] 3.3 AC / DC system preventive control model considering correction

[0155] The objective function for AC / DC system preventive control, which takes into account corrections, includes the generator operating cost in the normal state, the load shedding cost in the fault state, and the curtailment cost.

[0156]

[0157] In the formula, Here is the cost constant coefficient for generator node i during time period k; the subscript 0 indicates a variable indicating normal system operation.

[0158] In step S4, the generator regulation output rate constraint of the AC / DC system preventive control model is taken into account. The constraints include the normal-state generator output rate regulation constraint formula and the fault-state generator output rate constraint formula, as shown in formulas (25) and (26) respectively:

[0159]

[0160] In the formula, the subscript w represents the variable of system operation under the expected accident, w = 0, 1, ..., n outage ;n outage The number of critical anticipated accidents; where, and These represent the active and reactive power outputs of the generator at AC node i, respectively. To adjust the maximum speed of output regulation at AC generator node i;

[0161] The AC / DC system preventive control model that takes into account correction is as follows:

[0162]

[0163] In the formula, is the cost constant coefficient of generator node i during time period k; the subscript 0 indicates a variable indicating normal system operation.

[0164] During the period of preventive control of AC / DC systems involving process calculation and correction, the objective function (24) and the equality constraint g(x) are... k,w ,u k,w ), inequality constraint h(x) k,w ,u k,w ) and generator output rate regulation constraints The constructed control model uses traditional dynamic thermal setpoints as line load constraints, while the control model that ignores overhead conductor current constraints uses overhead conductor temperature as load constraints. Both are complex nonlinear programming models, and this embodiment uses mature commercial computer numerical analysis software to solve them.

[0165] Example 2

[0166] A safety control method for AC / DC systems with VSC-MTDC under electrothermal coordination is presented in this embodiment, which combines specific algorithm analysis.

[0167] This embodiment includes the retrofit system for the IEEE 39 node with 8 VSC converter stations (see...). Figure 4 Taking [example 36] as an example, the effectiveness of the safety control method proposed in this chapter is verified. The upper and lower limits of the AC / DC node voltage are set to 0.95 pu and 1.05 pu, respectively. The initial voltage amplitude of generator node 36 is 1.05 pu. The load shedding cost coefficient for each AC node is 10000, and the curtailment penalty coefficient is 5000. According to the solution of the overhead conductor thermal dynamics process, the thermal inertia time of the overhead conductor under normal operating conditions does not exceed 30 min. Therefore, the study period for the example analysis in this chapter is 0–30 min. Environmental parameters are shown in Table 1, generator parameters are shown in Table 2, VSC operating constraints are shown in Table 3, and the distance step length is Δt = 5 min.

[0168] Table 1 Meteorological and environmental data from 0 to 30 minutes

[0169]

[0170] Table 2 Generator Set Output Constraints and Cost Factors

[0171]

[0172]

[0173] Table 3 VSC converter power constraints

[0174]

[0175] 1) AC / DC system correction analysis

[0176] Under the parameters of the above example, assuming that DC line 7-8 is interrupted at time 0, a safety analysis is performed on this scenario. If load and voltage exceedances occur, the model proposed in this example is used for safety correction.

[0177] Figure 5 The current carrying capacity and temperature curves of the critical circuit (DC branch 7-10) under master-slave control are shown throughout the entire study period.

[0178] Depend on Figure 5 It is known that the current in the DC overhead conductors 7-10 exceeded their maximum allowable current throughout the entire study period, and exceeded their maximum allowable temperature at approximately 10 minutes. Apart from this, no other transmission component loads or node voltages in the AC / DC system exceeded their limits. Therefore, safety correction control is required for this system scenario to ensure its safe operation.

[0179] The safety correction control model for line load constraints was solved using the maximum allowable current (constraint I) and the maximum allowable temperature (constraint T) as constraints, respectively. The corrected current and temperature of the critical line during the study period are shown in the figure. Figure 6 Table 4 shows the amount of solar power curtailment from photovoltaic power plants; Control variables for VSC7 converter stations. and commutation power See Table 5 for the converter power of converter stations VSC1 to VSC6 and VSC8. The value represents the maximum inverter power throughout the entire study period.

[0180] Throughout the study period, converter stations VSC1–VSC6 and VSC8 operated at maximum inverter conversion active power, while the converter power of converter station VSC7 remained a relaxed variable. The newly generated photovoltaic power was only transmitted to the VSC7 main converter station for consumption via the critical line (DC branch 7-10). Analysis Figure 6It can be seen that during the period from 0 to 20 minutes, the critical circuit under constraint I operates at its maximum allowable current, reaching the upper limit of the constraint to ensure that the amount of abandoned light is minimized. However, during this period, due to the thermal inertia characteristics of the overhead conductor, its temperature rises slowly during the correction control period, and the temperature of the critical circuit does not reach its maximum thermal limit. Its true load capacity needs to be further explored. The green shaded area in Figure (a) represents the maximum thermal load capacity to be explored. During the period from 0 to 15 minutes, the critical circuit under constraint T operates at a current greater than the maximum allowable current while ensuring that its temperature does not exceed the maximum allowable temperature. The load capacity of the critical circuit has been further explored.

[0181] Table 4. Curtailment of Solar Power Plants

[0182]

[0183] Table 5 Control Variables for VSC7 Converter Station and commutation power

[0184]

[0185] Table 4 shows that the total curtailment of solar power under constraint I was 0.963 pu during the entire study period, while it was 0.453 pu under constraint T, a difference of 0.51 pu. Compared to the total curtailment under constraint I, the curtailment under constraint T was reduced by 53.0%. Furthermore, Table 5 shows that the corrective control decision results under different constraints also varied depending on the system operating state. During the 5–10 min period, the control voltage of the VSC7 main converter station under constraint I... The power consumption is 1.035 pu under constraint T and 1.033 pu under constraint T, a difference of 0.002 pu; the VSC7 converter power under both constraints. The maximum difference is 0.234 pu.

[0186] The total system adjustment cost under constraint I is 3132, while the total system adjustment cost under constraint T is 517, a reduction of 83.5% compared to constraint I. In summary, using constraint T as the line load constraint takes into account the short-term overload capacity caused by the thermal inertia of overhead conductors, alleviates the congestion pressure on transmission components, and improves the system's renewable energy absorption level.

[0187] 2) Analysis of the results of AC / DC system prevention and control taking correction into account

[0188] Under the parameters of the above example, the safety analysis method is used to screen out the more serious expected accidents in the master-slave controlled AC / DC system, namely disconnecting AC branch 5-8. Figure 7The current carrying capacity and temperature change curves of the critical circuit (AC branch 6-7) after the accident under master-slave control throughout the entire study period are shown.

[0189] Depend on Figure 7 It is known that after AC branch 5-8 was disconnected, AC overhead line 6-7 exceeded its maximum allowable current throughout the entire study period and exceeded its maximum allowable temperature approximately 10 minutes later. Apart from this, no other transmission component loads or node voltages in the AC / DC system exceeded their limits under this contingency scenario.

[0190] Therefore, considering the safety constraints of the aforementioned anticipated accidents, the preventive control models taking into account corrections, with constraints I and T as line load constraints respectively, were solved. The corrected generator output plans under constraints I and T during the study period are shown in Tables 6 and 7 respectively; VSC7 converter station control variables and commutation power See Table 8; the current and temperature of the critical circuit after constraint I and T correction are shown in Table 8. Figure 8 There was no waste of light.

[0191] analyze Figure 8 It can be seen that after the line break, the generator output adjustment, VSC control setpoint adjustment, and load shedding coordination alleviated the load pressure on AC branch 6-7, correcting the system to a safe operating state. After the anticipated accident, the current of the critical line (AC branch 6-7) under constraint I reached the upper limit of current during the 0-10 minute period due to power flow transfer. However, due to the temperature lag of the overhead conductor in the current change characteristic, its temperature rose slowly and did not reach the conductor thermal limit. After the power flow transfer, the current of the critical line under constraint T during the 0-5 minute period (8.57 pu) was still greater than the maximum allowable current (8.03 pu), but its temperature was less than its thermal limit throughout the entire study period, meeting the line operation safety constraints.

[0192] Table 6. Corrected generator output plan (pu) under constraint I

[0193]

[0194] Table 7. Corrected generator output plan (pu) under constraint T

[0195]

[0196] After the anticipated accident (disconnection of AC branch 5-8) occurs, the generating power will no longer supply AC load node 7 via AC branches 5-8 and 8-7, causing the power flow to shift to AC branch 6-7, increasing the load on AC branch 6-7. Analysis of Tables 6 and 7 shows that during the 0-5 minute period, on the one hand, the system under constraint I ignores the thermal inertia of the overhead line, causing blockage of AC branch 6-7; on the other hand, the maximum ramp rate limitation of the generator set under constraint I prevents it from supplying a large amount of power to node 7 via AC branches 9-8 and 8-7, resulting in load shedding in the system under constraint I during this period, i.e., cutting off 0.492 pu of active load from AC node 7. However, the system under constraint T fully utilizes the load potential of the overhead line; AC branch 6-7 is not blocked, and the generator set can still supply power to load node 7 via AC branch 6-7 without needing to shed the load at load node 7.

[0197] Table 8 Control Variables for VSC7 Converter Station and commutation power

[0198]

[0199] Analysis of Table 8 shows that the VSC decision results for preventive control vary depending on the load constraints of different lines. Throughout the entire study period, the control voltage of the VSC7 main converter station under constraint I is... The maximum difference from constraint T is 0.09 pu. Furthermore, the total generator cost under constraint I is 36533, while under constraint T it is 34072, a reduction of 6.7%. In summary, the load potential inherent in the thermal inertia of the overhead lines under constraint T provides greater relaxation for system decision-making, making it easier to determine a more economical operating state while ensuring system safety. Based on electrothermal coordination, the system achieves its optimal balance between safety and economy.

[0200] Example 3

[0201] A safety control system for an AC / DC system with VSC-MTDC under electrothermal coordination, used to implement the safety control method for an AC / DC system with VSC-MTDC under electrothermal coordination in Embodiment 1, comprising:

[0202] The VSC converter station steady-state power model construction module is configured to construct a VSC converter station steady-state power model based on the equivalent circuit of the VSC converter station, and to provide the control mode of the VSC converter station and the control mode of the DC grid.

[0203] The heat balance equation construction module is configured to construct the heat balance equation of the overhead conductor under electrothermal coordination based on the laws of heat transfer and the current of the overhead conductor and the meteorological data of the power system.

[0204] The AC / DC power grid electrothermal coupling power flow model construction module is configured to construct an AC / DC power grid electrothermal coupling power flow model containing VSC-MTDC based on the node power balance, using AC node voltage amplitude and phase angle, DC node voltage and AC / DC overhead conductor temperature as state variables.

[0205] The AC / DC system safety control model construction and solution module is configured to, based on the definitions of the correction control model and the prevention control model considering correction, list the corresponding electrical constraints, temperature constraints, and objective functions, construct and solve the correction control model of the AC / DC system with VSC-MTDC under electrothermal coordination and the prevention control model of the AC / DC system considering correction.

[0206] Example 4

[0207] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method of Embodiment 1.

[0208] Example 5

[0209] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, complete the method of Embodiment 1.

[0210] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A safety control method for an AC / DC system containing VSC-MTDC under electric-heat coordination, characterized in that: The steps include: S1: Based on the VSC converter station equivalent circuit, a steady-state power model of the VSC converter station is constructed, and the control method of the VSC converter station and the control method of the DC power grid are given; S2: Based on the laws of heat transfer, the overhead conductor current and the meteorological data of the power system, the thermal balance equation of the overhead conductor under electric-thermal coordination is constructed; S3: Taking the AC node voltage amplitude and phase angle, DC node voltage and AC and DC overhead conductor temperature as state variables, an AC / DC power grid electrothermal coupling power flow model containing VSC-MTDC is constructed based on node power balance; S4: According to the definitions of the correction control model and the preventive control model taking correction into account, list the power constraints, temperature constraints and objective functions, and construct and solve the correction control model of the AC / DC system containing VSC-MTDC under electric-heat coordination and the preventive control model taking correction into account.

2. The method for safe control of AC / DC systems containing VSC-MTDC under electric-thermal coordination according to claim 1 is characterized in that: The steady-state power model of the VSC converter station in step S1 includes: In the formula, It represents the active power injected into point s on the AC side of the VSC converter station; It represents the reactive power injected into point f on the AC side of the VSC converter station; are the voltage amplitudes of the AC nodes s and f respectively; g sf and b sf are the real and imaginary parts of the equivalent line admittance sf in the converter station, respectively, and g sg and b sg The resistance of point s to the ground is z sg The real and imaginary parts of the reciprocal; δ are the corresponding node voltage phase angles respectively; In the formula, Inject the active power of VSC into node c; The active power injected into the DC node d by the VSC; P vsc,loss is the active power loss of VSC; Where P sfc,loss is the sum of the active losses of the converter transformer, filter and converter reactor, and is: In the formula, is the square of the current flowing through the converter transformer; r sf Indicates the equivalent line resistance of the commutation transformer; g fg The resistance of point f to the ground is z fg The real part of the reciprocal; is the square of the current flowing through the commutation reactor, g c represents the real part of the commutation reactor admittance; b c represents the imaginary part of the commutation reactor admittance; r c Indicates the resistance of the commutation reactor.

3. The method for safe control of AC / DC systems containing VSC-MTDC under electric-thermal coordination according to claim 2 is characterized in that: The control methods of the VSC converter station include active power control and reactive power control. Among them, active power control includes constant AC side active power control, constant DC side voltage control, DC voltage-power droop control and DC voltage-current droop control. The DC voltage-power droop control and DC voltage-current droop control are shown in formulas (5) and (6) respectively: In the formula, the parameter superscript "^" represents the reference value of the corresponding control quantity. k is the DC current injected into the DC node d by the VSC; P is the droop coefficient of DC voltage-power droop control, k I is the droop coefficient of DC voltage-current droop control; Reactive power control includes fixed-point reactive power control and fixed-point voltage control; The DC power grid includes multiple VSC converter stations. The control modes of the DC power grid include master-slave control and droop control. Under the master-slave control and droop control modes, the reactive power control mode of each VSC converter station is fixed-point reactive power control or fixed-point voltage control. In the master-slave control, the active power control mode of the master VSC converter station is fixed DC side voltage control, and the active power control mode of the slave station is fixed AC side active power control. In the droop control, there is at least one VSC converter station with an active control mode of DC voltage-power droop control or DC voltage-current droop control, and the active power control modes of the remaining VSC converter stations are selected to be fixed AC side active power control, DC voltage-power droop control or DC voltage-current droop control.

4. The method for safe control of AC / DC systems containing VSC-MTDC under electric-thermal coordination according to claim 3 is characterized in that: In step S2, let Δt be the discretization step size, and study the time period [t0,t f ] is discretized into n k After discretization, the heat balance equation of AC and DC overhead conductors in the kth period is: In formulas (11) and (12), the variable subscripts k and k-1 represent the kth and k-1th time periods, respectively. and are the mismatch of the heat balance equation of AC and DC overhead conductor l in the kth period (℃); and is the mass per unit length of AC and DC overhead wires (kg / m), and is the specific heat capacity of AC and DC overhead conductors (J / (kg·℃)); n al and n dl are the numbers of AC and DC overhead lines, respectively.

5. The method for safe control of AC / DC systems containing VSC-MTDC under electric-thermal coordination according to claim 4 is characterized in that: In step S3, the AC system power flow model is: In the formula, and are the injected active power and reactive power of AC node i respectively. At the AC side node c of VSC, the injected power includes and and are the voltage amplitudes (pu) of AC nodes i and j respectively; and are the voltage phase angles (rad) at AC nodes i and j respectively, and are the corresponding elements (pu) in the ith row and jth column of the real part G and imaginary part B of the AC node admittance matrix respectively; is the AC overhead conductor temperature vector, when i≠j, When i=j, represents the temperature vector of the AC overhead line conductor connected to node i; S ac,bus is the set of communication nodes; n a Indicates the number of communication nodes; The DC system power flow model is: In the formula, is the injected active power of DC node i. For VSC DC side node d, the injected power includes and are the voltages of nodes i and j at the kth time period (pu); is the element in the i-th row and j-th column of the DC grid node admittance matrix Y (pu). When considering the temperature effect of the conductor resistance, the elements in Y are functions of the conductor temperature. is the temperature vector of the DC overhead wire in the kth period, when i≠j, l∈(i,j); when i=j, T dc represents the temperature vector of the DC overhead wire connected to node i; S dc,bus is the DC node set; n d Indicates the number of DC nodes; The electrothermal coupled power flow model of the AC / DC power grid containing VSC-MTDC is: In the formula, is the injected power (pu) of the node c on the AC side of the VSC converter station v; is the VSC converter station v loss (pu); is the injected power (pu) of node d on the DC side of the VSC converter station v.

6. The method for safe control of AC / DC systems containing VSC-MTDC under electric-thermal coordination according to claim 5 is characterized in that: In step S4, the optimized power flow model of the AC / DC system including VSC-MTDC is: In the formula, the first term f is the objective function; x is the state variable of the system, including the AC node voltage amplitude and phase angle, DC node voltage and AC and DC overhead conductor temperature; u is the control variable of the system, mainly including the output of the generator set, load shedding, abandoned light and the commutation power of the converter station; the second term g is the equality constraint function; the third term h is the inequality constraint; the fourth term r is the inequality constraint of the generator output rate; represents the active power generated by the AC generator in period k; represents the active power generated by the AC generator in period k-1; When the transmission line or bus voltage of the power grid exceeds the limit, correction control is required to restore the system to a safe operating state. The correction control model of the AC / DC system including VSC-MTDC is: Where, the first term is the generator output adjustment cost of process-based safety correction control, the second term is the load shedding cost, and the third term is the solar abandonment cost; n k is the number of study periods, n PH is the number of photovoltaic power stations; S ac,G is the set of generator nodes, S ac,CL is a set of controllable load nodes; and is the secondary and primary output cost coefficient of generator node i in period k, is the load shedding cost coefficient of load node i in period k, γ i is the penalty coefficient for abandoned light at PV unit node i; and are the output before and after correction of generator node i in period k, and are the active loads before and after correction of load node i in period k, Adjust the power for photovoltaic unit node i to abandon light.

7. The method for safe control of AC / DC systems containing VSC-MTDC under electric-thermal coordination according to claim 6 is characterized in that: In step S4, the generator output rate constraint of the corrected AC / DC system preventive control model is taken into account It includes the normal state generator output rate constraint formula and the fault state generator output rate constraint formula, as shown in formulas (25) and (26) respectively: Where, the subscript w represents the variable of system operation under the expected accident, w = 0, 1, ..., n outage ;n outage is the number of critical anticipated accidents; where, and are the active and reactive outputs of the generator at AC node i, The maximum rate of output regulation for the AC generator node i; The preventive control model of AC / DC system taking into account correction is: In the formula, is the cost constant coefficient of generator node i in period k; subscript 0 indicates the variable of normal operation of the system.

8. A safety control system for an AC / DC system containing VSC-MTDC under electric-heat coordination, used to implement the safety control method for an AC / DC system containing VSC-MTDC under electric-heat coordination as claimed in claim 7, characterized in that: include: A VSC converter station steady-state power model building module is configured to build a VSC converter station steady-state power model according to an equivalent circuit of the VSC converter station, and provide a control method of the VSC converter station and a control method of the DC power grid; The heat balance equation building module is configured to build the overhead conductor heat balance equation under electric-heat coordination according to the laws of heat transfer, the overhead conductor current and the meteorological data of the power system; The AC / DC grid electrothermal coupling power flow model building module is configured to use the AC node voltage amplitude and phase angle, DC node voltage and AC / DC overhead conductor temperature as state variables, and build an AC / DC grid electrothermal coupling power flow model containing VSC-MTDC based on node power balance; The AC / DC system safety control model construction and solution module is configured to list the power constraints, temperature constraints and objective functions according to the definitions of the correction control model and the preventive control model taking correction into account, and to construct and solve the correction control model of the AC / DC system containing VSC-MTDC under electric-heat coordination and the preventive control model of the AC / DC system taking correction into account.

9. An electronic device, characterized in that: The method comprises a memory and a processor and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the method according to any one of claims 1 to 7 is completed.

10. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, complete the method described in any one of claims 1 to 7.

Images