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

Abstract

The invention discloses an urban power grid dynamic voltage reactive power control method and a related device, and the method comprises the steps: building a state equation of each flexible DC converter, and building an output equation of each flexible DC converter through employing a track sensitivity method; 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 converter is minimum as targets, and determining constraint conditions of the target function by combining a state equation and an output equation of the flexible direct-current converter to ensure that the output reactive power of the flexible direct-current converter does not exceed a capacity upper limit; the voltage reactive power control problem of the flexible direct current converter is further formed; solving the voltage reactive power control problem of the flexible direct-current converters by adopting a model prediction control method to obtain a reactive power output instruction sequence of each flexible direct-current converter; according to the model prediction control method, a recursive relation between output matrixes and control matrixes of all the flexible direct current converters is determined according to a state equation and an output equation of each flexible direct current converter; and performing reactive power control on each flexible direct current converter by using a first instruction in the reactive power output instruction sequence of each flexible direct current converter. The method is suitable for the flexible direct-current traction power supply system, the voltage stability of the power grid is improved by optimizing the control strategy, and the reliability of power supply is ensured.

Description

Technical Field

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

[0002] In the load center areas of megacities, with the acceleration of urbanization and the improvement of residents' living standards, residential electricity consumption has become the main body of electricity consumption in the region, resulting in a continuous increase in electricity load. In particular, in recent years, the proportion of motor loads represented by air-conditioning compressors has increased year by year, bringing unprecedented challenges to the voltage stability of regional distribution networks. Motor loads, especially induction motors, due to their dynamic characteristics, often cause slow voltage recovery when the power grid encounters disturbances and causes voltage fluctuations. In severe cases, it may even cause voltage collapse, posing a serious threat to the voltage stability of the power grid.

[0003] In order to deal with this problem, the flexible DC traction power supply system came into being. The system uses the voltage source converter (VSC) as the core equipment, and realizes the bidirectional four-quadrant operation of active and reactive power through the dq decoupling control technology. This feature enables the flexible DC traction power supply system to provide the necessary reactive power compensation for the power grid without affecting the normal power supply. Especially when the power grid voltage drops due to faults and other reasons, the system can respond quickly, provide reactive power support for the power grid, effectively maintain the stability of the power grid voltage, and thus improve the reliability of the power grid.

[0004] In terms of control strategy, model predictive control, as a method based on modern control theory, has attracted much attention because of its ability to handle constraint problems well. Model predictive control achieves the effect of closed-loop control through three key links: prediction model, rolling optimization, and feedback correction. Its rolling solution method not only improves the real-time performance of control, but also enhances the system's ability to resist disturbances and overcome uncertainty. Therefore, model predictive control has been widely used in engineering practice. However, the commonly used voltage control methods still have certain limitations. Local voltage control methods represented by droop control and constant voltage PI control have the advantages of no need for communication and fast control speed. However, in flexible DC traction power supply systems, these methods cannot guarantee stable reactive output due to the strong randomness of loads caused by the acceleration and deceleration of subway trains, and the control effect is seriously affected. On the other hand, although the linear quadratic regulator (LQR) is a classic optimal control method, it cannot handle control problems with constraints and is not applicable to flexible DC traction power supply systems whose output reactive capacity is limited by load levels. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method and related devices for dynamic voltage reactive power control of an urban power grid, which is applicable to a flexible DC traction power supply system. By optimizing the control strategy, the voltage stability of the power grid is improved, thereby ensuring the reliability of power supply.

[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 dynamic voltage and reactive power control of 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 comprises:

[0008] Establishing a state equation for each flexible DC converter, and using a trajectory sensitivity method to establish an output equation for each flexible DC converter;

[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, and the output reactive power of the flexible DC converter does not exceed the capacity upper limit. The constraint conditions of the objective function are determined by combining the state equation and output equation of the flexible DC converter, thereby forming a voltage reactive power control problem of the flexible DC converter.

[0010] A model predictive control method is used to solve the voltage reactive power control problem of the flexible DC converter, and a reactive power output instruction sequence of each flexible DC converter is obtained; wherein, in the model predictive control method, a recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter;

[0011] Reactive power control is performed on each flexible DC converter using the first instruction in the reactive power output instruction sequence of each flexible DC converter.

[0012] In a possible implementation manner of the first aspect, the state equation of the flexible DC converter is:

[0013]

[0014] In the formula, is the change of the q-axis current derivative of the flexible DC converter; is the change of the derivative of the intermediate variable; T q is the q-axis inertia time constant of the flexible DC converter; Δi q is the change in the q-axis current of the flexible DC converter; Δx b is the change of the intermediate variable; k p and k i is the PI parameter of the reactive power control loop; ΔQ refis the change in the reactive power command output by the flexible DC converter; ΔQ is the change in the actual reactive power output by the flexible DC converter.

[0015] In a possible implementation manner of the first aspect, an output equation of the flexible DC converter is:

[0016]

[0017] Where V i (t+1) is the voltage value of the grid node i at time t+1 after control; V i,0 (t+1) is the voltage value of grid node i at time t+1 before control; s i,j (t) is the trajectory sensitivity between the voltage of grid node i and the q-axis current output by flexible DC converter j at time t; is the q-axis current output by the flexible DC converter j at time t.

[0018] In a possible implementation manner of the first aspect, the objective function is:

[0019] minJ=(Y t -Y) T Q(Y t -Y)+ΔU T RΔU

[0020] The constraints are:

[0021] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T

[0022]

[0023] V i (t+1)=V i,0 (t+1)+s i,j (t)Δu j (t)

[0024] Where Y t is the voltage reference value column vector; Y is the output column vector; Q is the control error matrix; ΔU is the control matrix; R is the input weight matrix; ΔQ max (k+i) is the remaining reactive capacity of the flexible DC converter at time section k+i; N c For the control domain.

[0025] In a possible implementation manner of the first aspect, the state equation and the output equation of each flexible DC converter determine a recursive relationship between output matrices and control matrices of all flexible DC converters, including:

[0026] The state equation and the output equation are combined to obtain the state space equation;

[0027] The state space equation is discretized by using a zero-order hold method to obtain a discrete state space equation;

[0028] The recursive relationship between the output matrix and the control matrix of all flexible DC converters is obtained by recursion according to the discrete state space equation, which is specifically:

[0029] Y=Y0+HΔx(k)+KΔU

[0030] Where Y0 is the output column vector without control; H and K are coefficient matrices; Δx(k) is the change in the state variable.

[0031] In a possible implementation manner of the first aspect, the adopting of a model predictive control method to solve the voltage reactive power control problem of the flexible DC converter is specifically:

[0032] The voltage reactive power control problem of the flexible DC converter is transformed into a quadratic programming structure as follows:

[0033] minJ=ΔU T (K T QK+R)ΔU-2M T KΔU+M T QM

[0034] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T M=Y t -Y0-HΔx(k)

[0035] The quadratic programming structure is solved by using an interior point method to obtain a reactive power output instruction sequence for each flexible DC converter.

[0036] According to a second aspect of the present invention, a dynamic 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 device includes:

[0037] Establishing a module for establishing a state equation of each flexible DC converter and establishing an output equation of each flexible DC converter by using a trajectory sensitivity method;

[0038] A 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 with the reactive power output of the flexible DC converter not exceeding the capacity upper limit, and combining the state equation and output equation of the flexible DC converter, thereby forming a voltage reactive power control problem of the flexible DC converter;

[0039] A solution module is used to solve the voltage reactive power control problem of the flexible DC converter by using a model predictive control method to obtain a reactive power output instruction sequence of each flexible DC converter; wherein, in the model predictive control method, a recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter;

[0040] The control module is used to perform reactive power control on each flexible DC converter by utilizing the first instruction in the reactive power output instruction sequence of each flexible DC converter.

[0041] 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 dynamic voltage and reactive power control of an urban power grid when executing the computer program.

[0042] 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 dynamic voltage and reactive power control of a city power grid.

[0043] 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 dynamic voltage and reactive power control of a city power grid.

[0044] Compared with the prior art, the present invention has at least the following beneficial effects:

[0045] The present invention provides a method for dynamic voltage reactive power control of an urban power grid. Based on a flexible DC traction power supply system, the method realizes precise reactive power control of a flexible DC converter by introducing a model predictive control method. The method not only considers the requirement of maintaining the grid voltage at a reference value, but also takes into account the minimization of the reactive power output of the flexible DC converter. Thus, while ensuring the stability of the grid voltage, the reactive power utilization rate of the flexible DC traction power supply system is improved. The present invention establishes the output equation of each flexible DC converter by using the trajectory sensitivity method, which can more accurately reflect the transient state of the system state when it changes rapidly, thereby improving the accuracy of the control model. The dynamic voltage reactive power control method proposed by the present invention overcomes the problem of strong randomness of the reactive power capacity of the flexible DC converter by collaboratively controlling multiple flexible DC converters. The collaborative control strategy not only realizes the rapid recovery of the global voltage after a grid fault, but also improves the overall reactive power output capacity of the flexible DC traction power supply system, thereby enhancing the stability of the grid.

[0046] 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

[0047] 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.

[0048] Figure 1 This is a flow chart of a method for controlling dynamic voltage and reactive power of a city power grid according to an embodiment of the present invention;

[0049] Figure 2 is a schematic diagram of the control loop of the flexible DC converter;

[0050] Figure 3 This is the schematic diagram of the model predictive control process;

[0051] Figure 4 Voltage control effect of different control strategies. DETAILED DESCRIPTION

[0052] 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.

[0053] like Figure 1 As shown, an embodiment of the present invention provides a method for controlling the dynamic voltage and reactive power of 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 applicable to the flexible DC traction power supply system, and improves the grid voltage stability and ensures the reliability of power supply by optimizing the control strategy. The control method specifically includes the following steps:

[0054] Step 1: Establish a state equation for each flexible DC converter, and use a trajectory sensitivity method to establish an output equation for each flexible DC converter.

[0055] It should be understood that the state equation describes the dynamic change process of the internal state variables of the flexible DC converter, including the change of electrical quantities such as current and voltage. The output equation defines the interaction between these state variables and the external power grid, especially the output of reactive power. These equations are established based on the working principle and circuit characteristics of the flexible DC converter.

[0056] Specifically, the state equation of the flexible DC converter is:

[0057]

[0058] In the formula, is the change of the q-axis current derivative of the flexible DC converter; is the change of the derivative of the intermediate variable; T q is the q-axis inertia time constant of the flexible DC converter; Δi q is the change in the q-axis current of the flexible DC converter; Δx b is the change of the intermediate variable; k p and k i is the PI parameter of the reactive power control loop; ΔQ ref is the change in the reactive power command output by the flexible DC converter; ΔQ is the change in the actual reactive power output by the flexible DC converter.

[0059] More specifically, the control loop of the flexible DC converter is shown in the attached Figure 2 As shown. Because the dynamic time of the current loop (10ms) is much smaller than the dynamic time of the power outer loop (100ms), when studying the dynamics of the power loop, the dynamics of the current loop can be ignored and simplified to a delay link. That is:

[0060]

[0061] Among them, i d and i q are the d-axis and q-axis currents of the flexible DC converter respectively; T d and T qare the d-axis and q-axis inertia time constants of the flexible DC converter respectively; i dref and i qref are the d-axis and q-axis current reference values ​​of the flexible DC converter respectively.

[0062] Then the q-axis control equation can be written as:

[0063]

[0064] Among them, k p and k i is the PI parameter of the reactive power control loop; Q ref is the output reactive power instruction of the flexible DC converter; Q is the reactive power actually output by the flexible DC converter.

[0065] Introduce intermediate variable x b :

[0066]

[0067] The state equation of the flexible DC converter can be obtained:

[0068]

[0069] Among them, i q and x b is the state variable, and is the derivative of the state variable, (Q ref -Q) is the input variable. The q-axis of the flexible DC converter is modeled with small signals. During the modeling process, the inner current loop is replaced by a first-order delay link, and we have:

[0070]

[0071] Specifically, the output equation of the flexible DC converter is:

[0072]

[0073] Where V i (t+1) is the voltage value of the grid node i at time t+1 after control; V i,0 (t+1) is the voltage value of grid node i at time t+1 before control; s i,j (t) is the trajectory sensitivity between the voltage of grid node i and the q-axis current output by flexible DC converter j at time t; is the q-axis current output by the flexible DC converter j at time t.

[0074] More specifically, after obtaining the state equation, it is necessary to establish the output equation. Since the control purpose is to achieve rapid recovery of voltage after disturbance, voltage is selected as the output variable. Therefore, the output equation is the relationship between the node voltage and the reactive current output by the flexible DC converter. However, the flexible DC traction power supply system is a nonlinear system, that is, the relationship between the node voltage and the reactive current is nonlinear. The most commonly used linearization method is the sensitivity method. The sensitivity calculated by the power flow equation is only applicable near the steady-state operating point. For transient processes, the traditional sensitivity method is no longer feasible, so trajectory sensitivity is introduced. The trajectory sensitivity changes with time, reflecting the impact of small changes in parameters on the operating state of the flexible DC traction power supply system. The dynamic process of the flexible DC traction power supply system can be expressed as:

[0075]

[0076] Among them, x(t) and They represent the system state variables and their derivatives respectively. y(t) is the algebraic variable of the flexible DC traction power supply system, and u represents the control variable of the flexible DC traction power supply system.

[0077] Carry out Taylor series expansion of x(t) and y(t) at u=u0 and ignore the higher-order terms, then the relationship between the changes of state variables and algebraic variables and the control variables can be written as:

[0078]

[0079] Among them, Φ x (u,t) and Φ y (u, t) represents the change trajectory of state variables and algebraic variables. When Δu is small enough, the trajectory sensitivity can be calculated as follows:

[0080]

[0081] It can be seen from the above formula that when the control variable changes Δu, the trajectory sensitivity can be used to obtain the trajectory of the state variable and the algebraic variable. The trajectory sensitivity can be solved by analytical method and perturbation method. Due to the complex structure and high dimension of the flexible DC traction power supply system, it is difficult to calculate the trajectory sensitivity by analytical method. Therefore, the perturbation method is widely used. The perturbation method can easily obtain the approximate value of the trajectory sensitivity through time domain simulation. Combined with the trajectory sensitivity, the output equation is expressed as:

[0082]

[0083] 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, and determine the constraints of the objective function by ensuring that the reactive power output of the flexible DC converter does not exceed the capacity upper limit, and combining the state equation and output equation of the flexible DC converter, thereby forming a voltage reactive power control problem for the flexible DC converter.

[0084] That is to say, considering the physical limitations of the flexible DC converter's output reactive power (i.e., not exceeding the capacity upper limit) and the working state of the flexible DC converter itself (determined by the state equation and the output equation), these factors are added as constraints to the objective function to form a complete flexible DC converter voltage reactive power control problem.

[0085] It should be noted that the voltage reference value is an ideal voltage value set according to the grid operation requirements and is used to measure the stability of the grid voltage.

[0086] Specifically, the objective function is:

[0087] minJ=(Y t -Y) T Q(Y t -Y)+ΔU T RΔU

[0088] The constraints are:

[0089] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T

[0090]

[0091] V i (t+1)=V i,0 (t+1)+s i,j (t)Δu j (t)

[0092] Where Y t is the voltage reference value column vector; Y is the output column vector; Q is the control error matrix; ΔU is the control matrix; R is the input weight matrix; ΔQ max (k+i) is the remaining reactive capacity of the flexible DC converter at time section k+i; N c For the control domain.

[0093] More specifically, the objectives of dynamic voltage control include two parts: 1) the node voltage tracks its reference value; 2) the flexible DC converter outputs reactive power as small as possible. Therefore, the objective function can be expressed as follows:

[0094] minJ=(Y t -Y) T Q(Y t -Y)+ΔU T RΔU

[0095] Among them, the voltage reference value Y t Normally set to rated voltage.

[0096] In the dynamic voltage control process, the reactive power output of the flexible DC converter must not exceed the upper capacity limit, so:

[0097] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T

[0098] Step 3, using a model predictive control (MPC) method to solve the voltage reactive power control problem of the flexible DC converter, and obtain a reactive power output instruction sequence for each flexible DC converter; wherein, in the model predictive control method, the recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter.

[0099] That is to say, in each control cycle, the current state information and prediction model are used to predict the state in the future, and rolling optimization is performed based on the objective function and constraints to solve the reactive power output instruction sequence of each flexible DC converter. The reactive power output instruction sequence contains reactive power output instructions in multiple future control cycles, which is used to guide the real-time control of the flexible DC converter.

[0100] Specifically, the recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter, as follows:

[0101] The state equation and the output equation are combined to obtain the state space equation;

[0102] The state space equation is discretized by using a zero-order hold method to obtain a discrete state space equation;

[0103] The recursive relationship between the output matrix and the control matrix of all flexible DC converters is obtained by recursion according to the discrete state space equation, which is specifically:

[0104] Y=Y0+HΔx(k)+KΔU

[0105] Where Y0 is the output column vector without control; H and K are coefficient matrices; Δx(k) is the change in the state variable.

[0106] More specifically, assuming a grid with K nodes connected to L flexible DC converters, the complete state space equation is:

[0107]

[0108] Among them, the state variable Δx=[Di q1 ,Δx b1 ,...,Δi qL ,Δx bL ] T ∈R 2L′1 Including the flexible DC converter output reactive current and intermediate variables. Control variable Δu = [ΔQ ref1 -ΔQ1,...,ΔQ refL -ΔQ L [ T ∈R L×1 In the ref is the output reactive power command of the flexible DC converter, ΔQ is the output reactive power change value of the flexible DC converter, which can be measured by PMU. Output variable y = [V i ,...,V N ] T ∈R N×1 To control the node voltage afterwards, y0 = [V 0i ,...,V 0N ] T ∈R N ×1 is the node voltage without control. Coefficient matrix A c (t), B c (t), C c (t) is:

[0109]

[0110] Among them, A c (t)∈R 2L×2L ,B c (t)∈R 2L×L ,C c (t)∈R N×2L . T qi is the q-axis inertia time constant of flexible DC converter i, k pi and k ii is the PI parameter of the q-axis current, sj,i (t) is the trajectory sensitivity of the voltage at node j to the output reactive current of flexible DC converter i.

[0111] However, due to the intermittent nature of measurement and data communication in actual systems, the dynamic voltage reactive power control system can be regarded as a sampling control system. The zero-order hold method is used for discretization to obtain the discrete time state space equation:

[0112]

[0113] The coefficient matrix is ​​calculated as:

[0114]

[0115] C d (k) = C c (t)

[0116] Among them, T s is the sampling time interval.

[0117] The coefficient matrix in the state space equation is time-varying, which means that the control model is linear and time-varying. Since the update of the above coefficient matrix only involves basic matrix operations, the calculation speed is fast and does not affect the real-time performance of dynamic voltage and reactive power control.

[0118] For time instant k, define the vector:

[0119] ΔU=[Δu(k),Δu(k+1),...,Δu(k+N c -1)] T

[0120] Y=[y(k+1|k),y(k+2|k),...,y(k+N p |k)] T

[0121] Y0=[y0(k+1),y0(k+2),...,y0(k+N p )] T

[0122] Among them, N p and N c are the prediction domain and control domain respectively, Δu(k+i) is the output variable at time k+i, y(k+i|k) and y0(k+1) are the output with control and without control at time k+i respectively.

[0123] The state variable at time k+i is:

[0124]

[0125] The output prediction value is:

[0126]

[0127] Among them, the matrix E, matrix F and matrix G are defined as follows:

[0128]

[0129] Therefore, the relationship between the output matrix Y and the control matrix ΔU can be expressed as:

[0130] Y=Y0+HΔx(k)+KΔU

[0131] Among them, the coefficient matrices H and K are defined as follows:

[0132]

[0133] Specifically, the model predictive control method is used to solve the voltage reactive power control problem of the flexible DC converter, specifically:

[0134] The voltage reactive power control problem of the flexible DC converter is transformed into a quadratic programming structure as follows:

[0135] min J=ΔU T (K T QK+R)ΔU-2M T KΔU+M T QM

[0136] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T

[0137] The matrix M is defined as follows:

[0138] M=Y t -Y0-HΔx(k)

[0139] The quadratic programming structure is solved by using an interior point method to obtain a reactive power output instruction sequence for each flexible DC converter.

[0140] Step 4: Use the first instruction in the reactive power output instruction sequence of each flexible DC converter to perform reactive power control on each flexible DC converter.

[0141] In other words, the real-time adjustment of the reactive output of the flexible DC converter is finally achieved, thereby ensuring the stability of the grid voltage. After each control cycle, steps 3 and 4 are repeated according to the new state information and prediction model to form a closed-loop control process, that is, updating the system state and resolving the control instructions. The control process is shown in the attached Figure 3 .

[0142] Compared with the traditional local voltage control strategy, the dynamic voltage reactive power control method proposed in the present invention can realize the rapid recovery of global voltage after power grid failure by coordinating the flexible DC converter, and at the same time improve the overall reactive power utilization rate of the flexible DC traction power supply system. Figure 4 As shown in Table 1. In the process of establishing the control model, the trajectory sensitivity method is used to establish a linear relationship between the grid voltage and the reactive current output by the flexible DC converter, eliminating the nonlinearity of the model. Compared with the conventional power flow sensitivity, the trajectory sensitivity adopted can be applied to transient conditions where the system state is changing rapidly, rather than just being limited to the vicinity of the steady-state operating point.

[0143] Table 1 Comparison of control situations under different control strategies

[0144]

[0145] The embodiment of the present invention provides a dynamic 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:

[0146] A module is established to establish a state equation of each flexible DC converter, and an output equation of each flexible DC converter is established by using a trajectory sensitivity method.

[0147] In one possible implementation, the state equation of the flexible DC converter is:

[0148]

[0149] In the formula, is the change of the q-axis current derivative of the flexible DC converter; is the change of the derivative of the intermediate variable; T q is the q-axis inertia time constant of the flexible DC converter; Δi q is the change in the q-axis current of the flexible DC converter; Δx b is the change of the intermediate variable; k p and k i is the PI parameter of the reactive power control loop; ΔQ ref is the change in the reactive power command output by the flexible DC converter; ΔQ is the change in the actual reactive power output by the flexible DC converter.

[0150] In one possible implementation, the output equation of the flexible DC converter is:

[0151]

[0152] Where V i (t+1) is the voltage value of the grid node i at time t+1 after control; V i,0 (t+1) is the voltage value of grid node i at time t+1 before control; s i,j (t) is the trajectory sensitivity between the voltage of grid node i and the q-axis current output by flexible DC converter j at time t; is the q-axis current output by the flexible DC converter j at time t.

[0153] 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 ensuring that the reactive power output of the flexible DC converter does not exceed the capacity upper limit, and combining the state equation and output equation of the flexible DC converter, thereby forming a voltage reactive power control problem of the flexible DC converter.

[0154] In one possible implementation, the objective function is:

[0155] minJ=(Y t -Y) T Q(Y t -Y)+ΔU T RΔU

[0156] The constraints are:

[0157] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T

[0158]

[0159] V i (t+1)=V i,0 (t+1)+s i,j (t)Δu j (t)

[0160] Where Y t is the voltage reference value column vector; Y is the output column vector; Q is the control error matrix; ΔU is the control matrix; R is the input weight matrix; ΔQ max(k+i) is the remaining reactive capacity of the flexible DC converter at time section k+i; N c For the control domain.

[0161] A solution module is used to solve the voltage reactive power control problem of the flexible DC converter by using a model predictive control method to obtain a reactive power output instruction sequence for each flexible DC converter; wherein, in the model predictive control method, a recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter.

[0162] In one implementable manner, the recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and the output equation of each flexible DC converter, as follows:

[0163] The state equation and the output equation are combined to obtain the state space equation;

[0164] The state space equation is discretized by using a zero-order hold method to obtain a discrete state space equation;

[0165] The recursive relationship between the output matrix and the control matrix of all flexible DC converters is obtained by recursion according to the discrete state space equation, which is specifically:

[0166] Y=Y0+HΔx(k)+KΔU

[0167] Where Y0 is the output column vector without control; H and K are coefficient matrices; Δx(k) is the change in the state variable.

[0168] In one achievable manner, the model predictive control method is used to solve the voltage reactive power control problem of the flexible DC converter, specifically:

[0169] The voltage reactive power control problem of the flexible DC converter is transformed into a quadratic programming structure as follows:

[0170] minJ=ΔU T (K T QK+R)ΔU-2M T KΔU+M T QM

[0171] ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T

[0172] The matrix M is defined as follows:

[0173] M=Yt -Y0-HΔx(k)

[0174] The quadratic programming structure is solved by using an interior point method to obtain a reactive power output instruction sequence for each flexible DC converter.

[0175] The control module is used to perform reactive power control on each flexible DC converter by utilizing the first instruction in the reactive power output instruction sequence of each flexible DC converter.

[0176] All relevant contents of each step involved in the aforementioned embodiment of a method for dynamic voltage and reactive power control of a city power grid can be referred to the functional description of a functional module corresponding to a device for dynamic voltage and reactive power control of a city power grid in an embodiment of the present invention, and will not be repeated here. The division of modules in the embodiment of the present invention is schematic, and 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 may be integrated into a processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules can be implemented in the form of hardware or in the form of software functional modules.

[0177] 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 method for dynamic voltage reactive power control of an urban power grid.

[0178] In another embodiment of the present invention, the present invention also 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 can be understood that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media 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 a method for dynamic voltage and reactive power control of a city power grid in the above embodiment.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] The present invention also provides a computer program product, which is used to execute any one of the above-mentioned methods for controlling the dynamic voltage and reactive power of a city power grid. Since the computer program product provided by the present invention and the above-mentioned method for controlling the dynamic voltage and reactive power of a city 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 the dynamic voltage and reactive power of a city 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.

[0184] 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.

[0185] 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 method for controlling dynamic voltage and reactive power of 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: Establishing a state equation for each flexible DC converter, and using a trajectory sensitivity method to establish an output equation for each flexible DC converter; 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, and the output reactive power of the flexible DC converter does not exceed the capacity upper limit. The constraint conditions of the objective function are determined by combining the state equation and output equation of the flexible DC converter, thereby forming a voltage reactive power control problem of the flexible DC converter. A model predictive control method is used to solve the voltage reactive power control problem of the flexible DC converter, and a reactive power output instruction sequence of each flexible DC converter is obtained; wherein, in the model predictive control method, a recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter; Reactive power control is performed on each flexible DC converter using the first instruction in the reactive power output instruction sequence of each flexible DC converter.

2. A method for controlling dynamic voltage and reactive power of a city power grid according to claim 1, characterized in that: The state equation of the flexible DC converter is: In the formula, is the change of the q-axis current derivative of the flexible DC converter; is the change of the derivative of the intermediate variable; T q is the q-axis inertia time constant of the flexible DC converter; Δi q is the change in the q-axis current of the flexible DC converter; Δx b is the change of the intermediate variable; k p and k i is the PI parameter of the reactive power control loop; ΔQ ref is the change in the reactive power command output by the flexible DC converter; ΔQ is the change in the actual reactive power output by the flexible DC converter.

3. A method for controlling dynamic voltage and reactive power of a city power grid according to claim 2, characterized in that: The output equation of the flexible DC converter is: Where V i (t+1) is the voltage value of the grid node i at time t+1 after control; V i,0 (t+1) is the voltage value of grid node i at time t+1 before control; s i,j (t) is the trajectory sensitivity between the voltage of grid node i and the q-axis current output by flexible DC converter j at time t; is the q-axis current output by the flexible DC converter j at time t.

4. A method for controlling dynamic voltage and reactive power of a city power grid according to claim 3, characterized in that: The objective function is: minJ=(Y t -Y) T Q(Y t −Y)+ΔU T RΔU The constraints are: ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T V i (t+1)=V i,0 (t+1)+s i,j (t)Δu j (t) Where Y t is the voltage reference value column vector; Y is the output column vector; Q is the control error matrix; ΔU is the control matrix; R is the input weight matrix; ΔQ max (k+i) is the remaining reactive capacity of the flexible DC converter at time section k+i; N c For the control domain.

5. A method for controlling dynamic voltage and reactive power of a city power grid according to claim 4, characterized in that: The state equation and output equation of each flexible DC converter determine the recursive relationship between the output matrix and the control matrix of all flexible DC converters, including: The state equation and the output equation are combined to obtain the state space equation; The state space equation is discretized by using a zero-order hold method to obtain a discrete state space equation; The recursive relationship between the output matrix and the control matrix of all flexible DC converters is obtained by recursion according to the discrete state space equation, which is specifically: Y=Y0+HΔx(k)+KΔU Where Y0 is the output column vector without control; H and K are coefficient matrices; Δx(k) is the change in the state variable.

6. A method for controlling dynamic voltage and reactive power of a city power grid according to claim 5, characterized in that: The model predictive control method is used to solve the voltage reactive power control problem of the flexible DC converter, specifically: The voltage reactive power control problem of the flexible DC converter is transformed into a quadratic programming structure as follows: minJ=ΔU T (K T QK+R)ΔU-2M T KΔU+M T QM ΔU≤[ΔQ max (k),ΔQ max (k+1),...,ΔQ max (k+N c -1)] T M=Y t -Y0-HΔx(k) The quadratic programming structure is solved by using an interior point method to obtain a reactive power output instruction sequence for each flexible DC converter.

7. A dynamic 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 device includes: Establishing a module for establishing a state equation of each flexible DC converter and establishing an output equation of each flexible DC converter by using a trajectory sensitivity method; A 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 with the reactive power output of the flexible DC converter not exceeding the capacity upper limit, and combining the state equation and output equation of the flexible DC converter, thereby forming a voltage reactive power control problem of the flexible DC converter; A solution module is used to solve the voltage reactive power control problem of the flexible DC converter by using a model predictive control method to obtain a reactive power output instruction sequence of each flexible DC converter; wherein, in the model predictive control method, a recursive relationship between the output matrix and the control matrix of all flexible DC converters is determined according to the state equation and output equation of each flexible DC converter; The control module is used to perform reactive power control on each flexible DC converter by utilizing the first instruction in the reactive power output instruction sequence 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 dynamic 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, the method for dynamic voltage and reactive power control of a city power grid as claimed 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 method for dynamic voltage and reactive power control of a city power grid as described in any one of claims 1 to 6.

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