Urban power grid distributed voltage reactive power control method and related device

Abstract

The invention discloses an urban power grid distributed voltage reactive power control method and a related device, and the method comprises the steps: determining a reactive power sensitivity coefficient between a power grid voltage and each flexible DC converter according to a network topology formed by a flexible DC traction power supply system and a power grid; the method comprises the following steps of: constructing a target function by taking a condition that the power grid voltage is maintained at a voltage reference value and the output reactive power of the flexible direct-current converters is minimum as targets, and determining constraint conditions of the target function by combining a reactive sensitivity coefficient between the power grid voltage and each flexible direct-current converter and a condition that the output reactive power of the flexible direct-current converters does not exceed a capacity upper limit; therefore, the problem of coordinated voltage reactive power control of the flexible direct-current converter is solved; the method comprises the following steps: firstly, decoupling a flexible direct current converter coordinated voltage reactive power control problem into a voltage reactive power control problem of each flexible direct current converter, and then independently solving the voltage reactive power control problem of each flexible direct current converter to obtain a reactive power output instruction of each flexible direct current converter; and performing reactive power control on each flexible DC converter according to the reactive power output instruction of each flexible DC converter. According to the invention, the stability of the power grid voltage can be effectively maintained under new energy fluctuation or other disturbances.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid voltage control, and in particular relates to a distributed voltage reactive power control method and related devices for a city power grid. Background Art

[0002] With the transformation of energy structure, the proportion of distributed renewable energy access in power system has increased significantly. At the same time, the popularity of electric vehicles has further aggravated the volatility of system power. This trend is particularly evident in urban power grids. The uncertainty of renewable energy and the changes in power demand caused by large-scale charging of electric vehicles have jointly caused frequent fluctuations in grid voltage, which has brought many impacts on the normal operation of urban rail transit. More seriously, emergencies such as grid failures or sudden switching of loads often cause more serious voltage problems. In extreme cases, these problems may even cause the flexible DC traction power supply system to be forced to cut off due to voltage exceeding the limit, resulting in the suspension of subway operations, which brings great inconvenience to citizens' travel. Therefore, how to effectively maintain the stability of urban power grid voltage and ensure the normal operation of urban rail transit system has become a technical problem that needs to be solved urgently.

[0003] In response to the above problems, voltage reactive power control technology is widely used in urban power grids to achieve effective regulation of grid voltage. For example, the Technical Specifications for Photovoltaic Grid-connected Inverters (NB / T 32004-2018) issued by the National Energy Administration clearly require that distributed renewable energy must have certain voltage reactive power control capabilities. In recent years, with the rapid development of flexible DC traction power supply technology, urban rail transit systems have gradually shifted from traditional diode converters to voltage source inverters (VSCs). VSCs have bidirectional four-quadrant operation capabilities, which can not only provide active power supply for urban rail transit systems, but also provide reactive power compensation to the grid when necessary, thereby effectively maintaining the stability of grid voltage.

[0004] At present, the most commonly used voltage reactive power control strategy is the local voltage control strategy represented by droop control and PI control. However, the droop coefficient of droop control must be small enough to ensure the stability of the system, which has brought great restrictions on the reactive power output capacity of the converter; the selection of PI parameters in PI control needs to be selected based on experience, resulting in the inability to guarantee the control effect. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a distributed voltage and reactive power control method and related devices for a city power grid, which ensure that the grid voltage can effectively maintain grid voltage stability under fluctuations in renewable energy or other disturbances.

[0006] In order to solve the above technical problems, the present invention is implemented by the following technical solutions:

[0007] According to a first aspect of the present invention, a method for controlling voltage and reactive power in a distributed manner in a city power grid is provided. The method is based on a flexible DC traction power supply system, wherein the flexible DC traction power supply system includes a plurality of flexible DC converters. The control method includes:

[0008] According to the network topology formed by the flexible DC traction power supply system and the power grid, the reactive sensitivity coefficient between the grid voltage and each flexible DC converter is determined;

[0009] The objective function is constructed with the goal of maintaining the grid voltage at the voltage reference value and minimizing the reactive power output of the flexible DC converter. The constraints of the objective function are determined by combining the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the reactive power output of the flexible DC converter not exceeding the capacity upper limit, thereby forming a coordinated voltage-reactive power control problem of the flexible DC converter.

[0010] Firstly, the coordinated voltage-reactive power control problem of the flexible DC converter is decoupled into the voltage-reactive power control problem of each flexible DC converter, and then each flexible DC converter voltage-reactive power control problem is solved independently to obtain the reactive power output instruction of each flexible DC converter;

[0011] Reactive power control is performed on each flexible DC converter according to the reactive power output instruction of each flexible DC converter.

[0012] In a possible implementation manner of the first aspect, determining the reactive sensitivity coefficient between the grid voltage and each flexible DC converter according to the network topology formed by the flexible DC traction power supply system and the grid is specifically:

[0013]

[0014] In the formula, S i is the reactive sensitivity coefficient between the grid voltage and the flexible DC converter i; Q i is the reactive power output of flexible DC converter i; V ci B is the AC side voltage of flexible DC converter i; i is the susceptance of the cable connecting the flexible DC converter i and the grid; V pcc is the grid voltage; G i is the conductance of the cable connecting the flexible DC converter i and the grid.

[0015] In a possible implementation manner of the first aspect, the flexible DC converter coordinated voltage and reactive power control problem is specifically:

[0016] min J=(V pcc -V ref ) 2 +Q TRQ

[0017]

[0018] Where V pcc is the grid voltage; V ref is the voltage reference value; Q=[Q1,Q2,...,Q n ] T ∈R n×1 is the reactive power output of the flexible DC converter; R=diag[R1,R2,...,R n ]∈R n×n is the weight matrix; S = [S1, S2, ..., S n ]∈R 1×n is the reactive sensitivity coefficient between the grid voltage and each flexible DC converter; V0 is the initial voltage value; Q i max is the upper limit of reactive capacity of flexible DC converter i.

[0019] In a possible implementation of the first aspect, the flexible DC converter coordinated voltage reactive power control problem is first decoupled into each flexible DC converter voltage reactive power control problem, and then each flexible DC converter voltage reactive power control problem is independently solved, specifically:

[0020] Using the gradient descent method, the coordinated voltage-reactive power control problem of the flexible DC converter is first decoupled into each flexible DC converter voltage-reactive power control problem, and then each flexible DC converter voltage-reactive power control problem is solved independently, as follows:

[0021] Q i (k+1)=Q i (k)-γ[2(V pcc (k)-V ref )S i +2R i Q i (k)]

[0022] In the formula, Q i (k+1) is the reactive power output instruction corresponding to the flexible DC converter i at time section k+1; Q i (k) is the reactive power output instruction corresponding to the flexible DC converter i at time section k; V pcc (k) is the grid voltage at time section k; γ is the step size.

[0023] In a possible implementation manner of the first aspect, before independently solving the voltage reactive power control problem of each flexible DC converter, the method further includes:

[0024] The output reactive power of each flexible DC converter is evenly distributed according to their respective capacities.

[0025] In a possible implementation manner of the first aspect, the output reactive power of each flexible DC converter is evenly divided according to their respective capacities, specifically as follows:

[0026]

[0027] Where m is a constant.

[0028] According to a second aspect of the present invention, a distributed voltage and reactive power control device for a city power grid is provided, based on a flexible DC traction power supply system, wherein the flexible DC traction power supply system includes a plurality of flexible DC converters, and the control method includes:

[0029] A reactive sensitivity coefficient determination module is used to determine the reactive sensitivity coefficient between the grid voltage and each flexible DC converter according to the network topology formed by the flexible DC traction power supply system and the grid;

[0030] The problem construction module is used to construct an objective function with the goal of maintaining the grid voltage at a voltage reference value and minimizing the reactive power output of the flexible DC converter, and to determine the constraint conditions of the objective function by combining the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the reactive power output of the flexible DC converter not exceeding the capacity upper limit, thereby forming a coordinated voltage reactive power control problem of the flexible DC converter;

[0031] A decoupling solution module is used to first decouple the coordinated voltage-reactive power control problem of the flexible DC converter into the voltage-reactive power control problem of each flexible DC converter, and then independently solve each flexible DC converter voltage-reactive power control problem to obtain the reactive power output instruction of each flexible DC converter;

[0032] The control module is used to perform reactive power control on each flexible DC converter according to the reactive power output instruction of each flexible DC converter.

[0033] According to a third aspect of the present invention, there is provided a device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the method for distributed voltage and reactive power control of a city power grid when executing the computer program.

[0034] According to a fourth aspect of the present invention, there is provided a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the method for distributed voltage and reactive power control of a city power grid.

[0035] According to a fifth aspect of the present invention, a computer program product is provided, which, when executed by a processor, implements the method for distributed voltage and reactive power control of a city power grid.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] The present invention provides a method for controlling the voltage and reactive power of a distributed urban power grid, which realizes effective and stable control of the voltage of the urban power grid under fluctuations of new energy or other disturbances. By calculating the reactive sensitivity coefficient between the power grid voltage and each flexible DC converter, the influence of each flexible DC converter on the power grid voltage can be accurately evaluated, thereby formulating a more accurate reactive power control strategy, which is helpful to maintain the stability of the power grid voltage and reduce the influence of voltage fluctuations on urban rail transit under complex working conditions such as the increase in the proportion of new energy access and the change in the charging demand of electric vehicles. The objective function is constructed with the goal of maintaining the power grid voltage at the voltage reference value and the flexible DC converter outputting the minimum reactive power as the goal, and combined with the reactive sensitivity coefficient and the flexible DC converter output reactive power not exceeding the capacity upper limit constraint condition, the flexible DC converter coordinated voltage and reactive power control problem is formed, which can optimize the distribution of reactive power, ensure that the reactive output of the converter is minimized as much as possible while meeting the power grid voltage stability requirements, and improve energy utilization efficiency. In particular, it is proposed to decouple the problem of coordinated voltage-reactive control of flexible DC converters into the problem of voltage-reactive control of each flexible DC converter, and solve them independently, thereby realizing decentralized reactive control. Compared with droop control and PI control, the control of the present invention is unrestricted and flexible, and can also adapt to power grids of different sizes and structures. Through precise reactive control and optimized reactive power distribution, the present invention can enhance the adaptability of urban power grids to external disturbances such as fluctuations in renewable energy and changes in loads, effectively reduce the impact of emergencies such as grid failures or sudden load switching on grid voltage, reduce the risk of forced cutting of flexible DC traction power supply systems due to voltage exceeding the limit, and ensure the normal operation and of urban rail transit systems.

[0038] Furthermore, the present invention automatically realizes global power sharing during the self-update process of the voltage reactive power instruction of the flexible DC converter. Without any communication, only local information is required. It can automatically adjust the output reactive power according to its own real-time load level to realize power sharing. It has a faster response rate and a higher reactive power utilization rate, and meets the requirements of real-time control.

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the specific implementation modes of the present invention, the drawings required for use in the description of the specific implementation modes will be briefly introduced below. Obviously, the drawings described below are some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 This is a flow chart of a method for distributed voltage and reactive power control of a city power grid according to an embodiment of the present invention;

[0042] Figure 2 A connection relationship diagram of a flexible DC converter in a distributed voltage and reactive power control method for a city power grid according to an embodiment of the present invention;

[0043] Figure 3 A comparison of voltage control effects with and without power sharing in a distributed voltage and reactive power control method for a city power grid according to an embodiment of the present invention;

[0044] Figure 4 The present invention provides a method for controlling voltage and reactive power of a city power grid in a distributed manner and a comparison of reactive power output with and without power balancing, wherein (a) is with power balancing and (b) is without power balancing. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] like Figure 1 As shown, the embodiment of the present invention provides a method for controlling voltage and reactive power in a distributed manner in a city power grid, based on a flexible DC traction power supply system, wherein the flexible DC traction power supply system includes multiple flexible DC converters. The method is particularly suitable for a city power grid including a large number of distributed new energy sources and electric vehicle charging stations, especially in the scenario where flexible DC traction power supply technology is used in an urban rail transit system. The method for controlling voltage and reactive power in a distributed manner in a city power grid specifically includes the following steps:

[0047] Step 1: According to the network topology formed by the flexible DC traction power supply system and the power grid, determine the reactive sensitivity coefficient between the grid voltage and each flexible DC converter.

[0048] That is to say, based on the network topology formed by the flexible DC traction power supply system and the power grid, the reactive sensitivity coefficient between the grid voltage and each flexible DC converter (VSC) is calculated. By establishing an equivalent circuit model of the power grid and using the sensitivity analysis method, the influence of each VSC on the grid voltage change is calculated. The reactive sensitivity coefficient reflects the responsiveness of the VSC output reactive power change to the grid voltage fluctuation.

[0049] In one achievable manner, the calculation of the reactive sensitivity coefficient between the grid voltage and each flexible DC converter is specifically as follows:

[0050]

[0051] In the formula, S i is the reactive sensitivity coefficient between the grid voltage and the flexible DC converter i; Q i is the reactive power output of flexible DC converter i; V ci B is the AC side voltage of flexible DC converter i; i is the susceptance of the cable connecting the flexible DC converter i and the grid; V pcc is the grid voltage; G i is the conductance of the cable connecting the flexible DC converter i and the grid.

[0052] More specifically, the flexible DC traction power supply system can be divided into centralized and distributed power supply systems. In the distributed power supply system, the 10kV distribution network supplies power to all flexible DC converters in a power supply area through the main distribution station, see Appendix Figure 2 As shown. That is to say, the flexible DC converters in the same power supply section have the same AC bus, which means that they can cooperate with each other in the voltage control process. For example, when the output reactive power of the first flexible DC converter decreases due to the acceleration or deceleration of the subway train, other flexible DC converters at low load levels can increase their reactive power output to ensure the balance of the total output reactive power, that is, power sharing.

[0053] For the flexible DC converter i, its external output power is:

[0054]

[0055] Where P i is the active power output of flexible DC converter i; δ ci is the AC side voltage phase of flexible DC converter i.

[0056] The relationship between its output active and reactive power is:

[0057]

[0058] If its output reactive power changes by ΔQ i , the grid voltage will also change accordingly ΔV pcc , through sensitivity analysis, the linear relationship between the output reactive power and voltage of the flexible DC converter is established:

[0059] ΔV pcc =S i ΔQ i

[0060] Then, the reactive sensitivity coefficient S between the grid voltage and the flexible DC converter i is i The calculation method is:

[0061]

[0062] Step 2: Construct an objective function with the goal of maintaining the grid voltage at the voltage reference value and minimizing the reactive power output of the flexible DC converter. Combined with the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the reactive power output of the flexible DC converter not exceeding the capacity upper limit, determine the constraints of the objective function, and then form a flexible DC converter coordinated voltage reactive power control problem.

[0063] That is to say, the objective function is constructed with the goal of maintaining the grid voltage within the preset voltage reference value range and minimizing the reactive power output of the flexible DC converter. At the same time, the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the constraint that the reactive power output of the VSC does not exceed its capacity upper limit are combined to form a complete flexible DC converter coordinated voltage reactive control problem.

[0064] In one achievable manner, the flexible DC converter coordinated voltage and reactive power control problem is specifically:

[0065] min J=(V pcc -V ref ) 2 +Q T RQ

[0066]

[0067] Where V pcc is the grid voltage; V ref is the voltage reference value; Q=[Q1,Q2,...,Q n ] T ∈R n×1 is the reactive power output of the flexible DC converter; R=diag[R1,R2,...,R n ]∈R n×n is the weight matrix; S = [S1, S2, ..., S n]∈R 1×n is the reactive sensitivity coefficient between the grid voltage and each flexible DC converter; V0 is the initial voltage value; Q i max is the upper limit of reactive capacity of flexible DC converter i.

[0068] Step 3: first decouple the flexible DC converter coordinated voltage-reactive power control problem into each flexible DC converter voltage-reactive power control problem, then independently solve each flexible DC converter voltage-reactive power control problem to obtain the reactive power output instruction of each flexible DC converter.

[0069] That is to say, in order to simplify calculation and improve control efficiency, the complex coordinated voltage reactive power control problem is decoupled into multiple independent VSC reactive power control problems. By utilizing the relative independence between VSCs, the global optimization problem is transformed into a local optimization problem. Then, the reactive power control problem of each VSC is solved independently to obtain their respective reactive power output instructions.

[0070] In one feasible method, the gradient descent method is used to first decouple the flexible DC converter coordinated voltage reactive power control problem into each flexible DC converter voltage reactive power control problem, and then each flexible DC converter voltage reactive power control problem is solved independently, as follows:

[0071] Q i (k+1)=Q i (k)-γ[2(V pcc (k)-V ref )S i +2R i Q i (k)]

[0072] In the formula, Q i (k+1) is the reactive power output instruction corresponding to the flexible DC converter i at time section k+1; Q i (k) is the reactive power output instruction corresponding to the flexible DC converter i at time section k; V pcc (k) is the grid voltage at time section k; γ is the step size.

[0073] More specifically, since the voltage control problem is a linear programming problem, it can be solved using the gradient descent method, and the iterative formula is:

[0074] Q(k+1)=Q(k)-γ▽J(Q(k))

[0075] where γ is the step size, is the gradient of the objective function with respect to the reactive power output of the flexible DC converter:

[0076]

[0077] Grid voltage V pcc can be measured by all flexible DC converters, so the global gradient can be decoupled into local gradients, namely:

[0078]

[0079] In the formula, is the gradient of the objective function with respect to the reactive power output of flexible DC converter i.

[0080] Thus, the update formula of the reactive power output command of the flexible DC converter can be obtained:

[0081] Q i (k+1)=Q i (k)-γ[2(V pcc (k)-V ref )S i +2R i Q i (k)]

[0082] This means that the flexible DC converter only needs local measurement information to achieve global coordinated control, that is, it achieves the same effect as centralized control through distributed control logic.

[0083] As a more preferred implementation, before independently solving the voltage reactive power control problem of each flexible DC converter, the method further includes:

[0084] The output reactive power of each flexible DC converter is evenly divided according to their respective capacities, specifically:

[0085]

[0086] Where m is a constant.

[0087] To expand on this, when the linear programming converges to the optimal value point, if the reactive capacity upper limit is not reached at this time, then ▽J(Q)=0,

[0088] Right now:

[0089] in, and It indicates the grid voltage and the output reactive power of the flexible DC converter when they reach the optimal value point.

[0090]

[0091] In order to make the reactive power output of the flexible DC converter proportional to its reactive capacity, that is, power equalization, it is necessary to meet the following requirements:

[0092]

[0093] Introducing the constant m, we have:

[0094]

[0095] Therefore, the sufficient condition for power sharing is:

[0096]

[0097] During the voltage control process, the flexible DC converter can independently adjust its input weight coefficient according to its own real-time reactive capacity, thereby achieving a global power sharing effect.

[0098] Step 4: Perform reactive power control on each flexible DC converter according to the reactive power output instruction of each flexible DC converter.

[0099] The urban power grid distributed voltage reactive power control method provided by the present invention effectively solves the problem of grid voltage fluctuation caused by new energy access and electric vehicle charging by calculating the reactive sensitivity coefficient, constructing the optimization objective function, realizing problem decoupling and independent solution, and performing reactive power control on VSC, thereby ensuring the stable operation of the urban rail transit system.

[0100] This embodiment verifies the optimality and stability of the above-mentioned distributed reactive power control method of the present invention, as follows:

[0101] Assumption 1: As long as the sufficient conditions for power sharing are met, the upper limit of the reactive capacity of the flexible DC converter is reached together.

[0102] Proof: By using the proof by contradiction, assuming that when the flexible DC converter i reaches the upper limit of reactive capacity, the flexible DC converter j does not reach the upper limit, then:

[0103]

[0104] Right now:

[0105]

[0106] Because the flexible DC converter i has reached the upper limit of reactive capacity therefore:

[0107]

[0108] The flexible DC converter j has not reached the upper limit of reactive capacity therefore:

[0109]

[0110] The two are contradictory, so the assumption is not valid. The upper limit of the reactive capacity of the flexible DC converter is reached together, that is, as long as the sufficient conditions for power sharing are met, power sharing can be achieved under any circumstances.

[0111] Assumption 2: The matrix S'S+R is positive definite

[0112] Proof: For any non-zero vector x, we have:

[0113] x'S'Sx=(Sx)'(Sx)=(Sx) 2 >0

[0114] That is, the matrix S'S is positive definite, and the matrix R is a nonzero diagonal matrix, so the matrix R is positive definite, and the matrix S'S+R is also positive definite.

[0115] Assumption 3: If γ < 1 / λ max (S'S+R) holds true, then the urban power grid distributed voltage and reactive power control strategy of the present invention can ensure stability.

[0116] Proof: Because the iteration formula can be written as:

[0117] Q(k+1)=[I-2γ(S'S+R)]Q(k)-2γS'(V0-V ref )

[0118] In order to ensure iterative convergence, the following conditions must be met:

[0119] ||I-2γ(S'S+R)||<1

[0120] According to the principle that the Euclidean norm of a matrix is ​​equal to its maximum singular value, we have:

[0121] |1-2γλ i (S'S+R)| max <1,i=1,2,...,n

[0122] Among them, λ i Represents the eigenvalues ​​of a matrix.

[0123] Because γ>0, the necessary and sufficient conditions for the control algorithm to ensure stability are:

[0124]

[0125] Among them, λ max Represents the largest eigenvalue of a matrix.

[0126] In the implementation mode of the present invention, based on the gradient descent method, the problem of coordinated voltage-reactive control of the flexible DC converter is decoupled into the problem of voltage-reactive control of each flexible DC converter, that is, the local voltage control problem, so that it can be achieved by self-updating the reactive power output of the flexible DC converter. Existing studies have proposed to adjust the droop coefficient according to the real-time active load of the converter to achieve uniform distribution of reactive responsibility, but this adjustment is based on communication and requires obtaining the real-time load conditions of all converters, which is not feasible for urban rail systems with sub-second power changes. Compared with existing studies, the present invention automatically realizes global power sharing during the self-update process of the voltage-reactive command of the flexible DC converter. Without any communication, only local information is required to automatically adjust the output reactive power according to its own real-time load level to achieve power sharing. It has a faster response rate and a higher reactive utilization rate, and meets the requirements of real-time control. The urban power grid distributed voltage-reactive control strategy of the present invention can effectively suppress voltage fluctuations and maintain voltage stability. As shown in the attached figure Figure 3 Voltage balancing not only reduces the loss of the flexible DC converter, but also improves the overall reactive power utilization rate, as shown in the attached figure. Figure 4 As shown, this is very important for the flexible DC traction power supply system where the reactive capacity changes rapidly due to sudden acceleration or deceleration of the train.

[0127] The embodiment of the present invention provides a distributed voltage and reactive power control device for a city power grid, based on a flexible DC traction power supply system, wherein the flexible DC traction power supply system includes a plurality of flexible DC converters, and the control device includes:

[0128] The reactive sensitivity coefficient determination module is used to determine the reactive sensitivity coefficient between the grid voltage and each flexible DC converter according to the network topology formed by the flexible DC traction power supply system and the grid.

[0129] In one achievable manner, the calculation of the reactive sensitivity coefficient between the grid voltage and each flexible DC converter is specifically as follows:

[0130]

[0131] In the formula, S i is the reactive sensitivity coefficient between the grid voltage and the flexible DC converter i; Q i is the reactive power output of flexible DC converter i; V ci B is the AC side voltage of flexible DC converter i; i is the susceptance of the cable connecting the flexible DC converter i and the grid; V pcc is the grid voltage; G i is the conductance of the cable connecting the flexible DC converter i and the grid.

[0132] The problem construction module is used to construct an objective function with the goal of maintaining the grid voltage at a voltage reference value and minimizing the reactive power output of the flexible DC converter, and to determine the constraints of the objective function by combining the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the reactive power output of the flexible DC converter not exceeding the capacity upper limit, thereby forming a flexible DC converter coordinated voltage reactive power control problem.

[0133] In one achievable manner, the flexible DC converter coordinated voltage and reactive power control problem is specifically:

[0134] min J=(V pcc -V ref ) 2 +Q T RQ

[0135]

[0136] Where V pcc is the grid voltage; V ref is the voltage reference value; Q=[Q1,Q2,...,Q n ] T ∈R n×1 is the reactive power output of the flexible DC converter; R=diag[R1,R2,...,R n ]∈R n×n is the weight matrix; S = [S1, S2, ..., S n ]∈R 1×n is the reactive sensitivity coefficient between the grid voltage and each flexible DC converter; V0 is the initial voltage value; Q i max is the upper limit of reactive capacity of flexible DC converter i.

[0137] The decoupling solution module is used to first decouple the flexible DC converter coordinated voltage reactive power control problem into each flexible DC converter voltage reactive power control problem, and then independently solve each flexible DC converter voltage reactive power control problem to obtain the reactive power output instruction of each flexible DC converter.

[0138] In one feasible method, the gradient descent method is used to first decouple the flexible DC converter coordinated voltage reactive power control problem into each flexible DC converter voltage reactive power control problem, and then each flexible DC converter voltage reactive power control problem is solved independently, as follows:

[0139] Q i (k+1)=Q i (k)-γ[2(V pcc (k)-V ref )S i +2Ri Q i (k)]

[0140] In the formula, Q i (k+1) is the reactive power output instruction corresponding to the flexible DC converter i at time section k+1; Q i (k) is the reactive power output instruction corresponding to the flexible DC converter i at time section k; V pcc (k) is the grid voltage at time section k; γ is the step size.

[0141] The control module is used to perform reactive power control on each flexible DC converter according to the reactive power output instruction of each flexible DC converter.

[0142] All relevant contents of each step involved in the aforementioned embodiment of a city power grid distributed voltage reactive power control method can be referred to the functional description of the functional module corresponding to a city power grid distributed voltage reactive power control device in the embodiment of the present invention, and will not be repeated here. The division of modules in the embodiment of the present invention is schematic, which is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention can be integrated into a processor, or it can exist physically separately, or two or more modules can be integrated into one module. The above-mentioned integrated module can be implemented in the form of hardware or in the form of software functional modules.

[0143] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in a computer storage medium to implement a corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a distributed voltage reactive power control method for an urban power grid.

[0144] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the computer device and the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the above-mentioned embodiment of a method for controlling voltage and reactive power of a distributed urban power grid.

[0145] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0146] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0147] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0148] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0149] The present invention also provides a computer program product, which is used to execute any one of the above-mentioned methods for controlling voltage and reactive power in a distributed urban power grid. Since the computer program product provided by the present invention and the above-mentioned method for controlling voltage and reactive power in a distributed urban power grid belong to the same inventive concept, the computer program product provided by the present invention has all the advantages of the above-mentioned method for controlling voltage and reactive power in a distributed urban power grid, and therefore, the beneficial effects of the computer program product provided by the present invention will not be described one by one here.

[0150] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0151] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A distributed voltage and reactive power control method for a city power grid, characterized in that: Based on a flexible DC traction power supply system, the flexible DC traction power supply system includes a plurality of flexible DC converters, and the control method includes: According to the network topology formed by the flexible DC traction power supply system and the power grid, the reactive sensitivity coefficient between the grid voltage and each flexible DC converter is determined; The objective function is constructed with the goal of maintaining the grid voltage at the voltage reference value and minimizing the reactive power output of the flexible DC converter. The constraints of the objective function are determined by combining the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the reactive power output of the flexible DC converter not exceeding the capacity upper limit, thereby forming a coordinated voltage-reactive power control problem of the flexible DC converter. Firstly, the coordinated voltage-reactive power control problem of the flexible DC converter is decoupled into the voltage-reactive power control problem of each flexible DC converter, and then each flexible DC converter voltage-reactive power control problem is solved independently to obtain the reactive power output instruction of each flexible DC converter; Reactive power control is performed on each flexible DC converter according to the reactive power output instruction of each flexible DC converter.

2. A distributed voltage and reactive power control method for a city power grid according to claim 1, characterized in that: The reactive sensitivity coefficient between the grid voltage and each flexible DC converter is determined according to the network topology formed by the flexible DC traction power supply system and the grid, specifically: In the formula, S i is the reactive sensitivity coefficient between the grid voltage and the flexible DC converter i; Q i is the reactive power output of flexible DC converter i; V ci B is the AC side voltage of flexible DC converter i; i is the susceptance of the cable connecting the flexible DC converter i and the grid; V pcc is the grid voltage; G i is the conductance of the cable connecting the flexible DC converter i and the grid.

3. A distributed voltage and reactive power control method for a city power grid according to claim 1, characterized in that: The problem of coordinated voltage and reactive power control of the flexible DC converter is specifically as follows: minJ=(V pcc -V ref ) 2 +Q T RQ Where V pcc is the grid voltage; V ref is the voltage reference value; Q=[Q1,Q2,...,Q n ] T ∈R n×1 is the reactive power output of the flexible DC converter; R=diag[R1,R2,...,R n ]∈R n×n is the weight matrix; S = [S1, S2, ..., S n ]∈R 1×n is the reactive sensitivity coefficient between the grid voltage and each flexible DC converter; V0 is the initial voltage value; is the upper limit of reactive capacity of flexible DC converter i.

4. A distributed voltage and reactive power control method for urban power grid according to claim 3, characterized in that: The flexible DC converter coordinated voltage reactive power control problem is first decoupled into each flexible DC converter voltage reactive power control problem, and then each flexible DC converter voltage reactive power control problem is solved independently, specifically: Using the gradient descent method, the coordinated voltage-reactive power control problem of the flexible DC converter is first decoupled into each flexible DC converter voltage-reactive power control problem, and then each flexible DC converter voltage-reactive power control problem is solved independently, as follows: Q i (k+1)=Q i (k)-γ[2(V pcc (k)-V ref )S i +2R i Q i (k)] In the formula, Q i (k+1) is the reactive power output instruction corresponding to the flexible DC converter i at time section k+1; Q i (k) is the reactive power output instruction corresponding to the flexible DC converter i at time section k; V pcc (k) is the grid voltage at time section k; γ is the step size.

5. A distributed voltage and reactive power control method for a city power grid according to claim 4, characterized in that: Before independently solving the voltage reactive power control problem of each flexible DC converter, the method further includes: The output reactive power of each flexible DC converter is evenly distributed according to their respective capacities.

6. A distributed voltage and reactive power control method for a city power grid according to claim 5, characterized in that: The output reactive power of each flexible DC converter is evenly divided according to its capacity, specifically: Where m is a constant.

7. A distributed voltage and reactive power control device for a city power grid, characterized in that: Based on a flexible DC traction power supply system, the flexible DC traction power supply system includes a plurality of flexible DC converters, and the control method includes: A reactive sensitivity coefficient determination module is used to determine the reactive sensitivity coefficient between the grid voltage and each flexible DC converter according to the network topology formed by the flexible DC traction power supply system and the grid; The problem construction module is used to construct an objective function with the goal of maintaining the grid voltage at a voltage reference value and minimizing the reactive power output of the flexible DC converter, and to determine the constraint conditions of the objective function by combining the reactive sensitivity coefficient between the grid voltage and each flexible DC converter and the reactive power output of the flexible DC converter not exceeding the capacity upper limit, thereby forming a coordinated voltage reactive power control problem of the flexible DC converter; A decoupling solution module is used to first decouple the coordinated voltage-reactive power control problem of the flexible DC converter into the voltage-reactive power control problem of each flexible DC converter, and then independently solve each flexible DC converter voltage-reactive power control problem to obtain the reactive power output instruction of each flexible DC converter; The control module is used to perform reactive power control on each flexible DC converter according to the reactive power output instruction of each flexible DC converter.

8. A device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method for distributed voltage and reactive power control of a city power grid as described in any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, a distributed voltage and reactive power control method for a city power grid as described in any one of claims 1 to 6 is implemented.

10. A computer program product, characterized in that When the computer program product is executed by a processor, it implements a distributed voltage and reactive power control method for a city power grid as described in any one of claims 1 to 6.

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