Flexible distribution network voltage and power coordinated control method and system

Abstract

The present invention belongs to the field of flexible distribution network optimization and scheduling, and provides a flexible distribution network voltage and power coordinated control method and system. First, according to the multi-port SOP control strategy and the linear power flow model, the voltage and power coordinated control principle of the flexible interconnected distribution network based on the multi-port SOP is analyzed; secondly, a discrete-time state-space model of the flexible distribution network based on the multi-port SOP is constructed, and then the voltage and transformer load coordinated optimal control model is established, and a linear quadratic regulator is used to solve it; finally, simulation tests prove that the proposed control method can quickly and effectively optimize the power flow distribution of the interconnected distribution network, improve the node voltage and transformer overload, and solve the problems of distribution network voltage exceeding the limit and transformer overload caused by the access of a high proportion of distributed power sources.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible distribution network optimization and scheduling, and particularly relates to a method and system for coordinated control of voltage and power in a flexible distribution network. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The growing demand for electricity from vehicles, cars, and air conditioners has led to increasingly unbalanced loads on distribution networks. Furthermore, distributed photovoltaics and electric vehicles exhibit significant stochastic characteristics, which can easily lead to voltage overshoots and transformer overloads, impacting the safe and reliable operation of distribution networks. Multi-port soft openpoints (SOPs), typically consisting of multiple back-to-back voltage source converters (VSCs), optimize power flows across distribution networks by interconnecting the DC sides of these converters. This improves voltage levels, alleviates transformer overload, and enhances the capacity of distributed photovoltaics. These SOPs are a key development direction for intelligent distribution systems.

[0004] Depending on the implementation method, the control methods of SOP include optimization scheduling and real-time control. The SOP control method based on master station optimization scheduling obtains the status information of the distribution network, optimizes and solves the transmission power of SOP, and sends it to the multi-port SOP for execution. In the prior art, a SOP real-time optimization strategy based on mixed integer second-order cone is proposed to solve the voltage over-limit problem caused by a high proportion of distributed photovoltaic access; a distribution network optimization model that coordinates SOP with multiple devices such as static VAR compensators and energy storage is also constructed, and the model is relaxed and solved through second-order cone programming and large M method; at the same time, the Pareto frontier method and hierarchical analysis method are used to optimize multiple objectives such as network loss, voltage quality, and feeder load balance, effectively playing the role of SOP in improving the economy and safety of distribution network operation.

[0005] The above-mentioned static optimization method requires the control master station to have strong computing power, but it also places high demands on system communication and measurement conditions. In addition, the random changes in distributed photovoltaic output between two optimization dispatches can easily cause voltage over-limit problems. In order to improve the rapidity of optimization and control of flexible interconnected distribution networks, research on real-time optimization control of SOP continues to deepen. There are also existing technologies that propose a practical power coordination control strategy for multi-terminal flexible interconnected systems, including overload limit control to reasonably distribute power when some feeders are overloaded, and power balancing control to optimize power flow distribution when all feeders are overloaded. To solve the problem of unbalanced feeder loads in distribution networks, a dynamic adjustment model for the economic load rate of feeders based on flexible interconnected devices is proposed, and the controller design is implemented through a consistency algorithm and load balancing control strategy. At the same time, there are existing technical solutions that propose a power coordination control strategy for a three-port DC energy router based on droop-shifting to achieve reasonable energy distribution between multiple DC stations, but do not consider the power distribution between AC distribution networks. The high proportion of distributed power generation access leads to transformer overload and node voltage over-limit in flexible interconnected distribution networks, which cannot meet the needs of multi-port SOP multi-objective rapid control under weak communication conditions. Summary of the Invention

[0006] In order to solve the above problems, the present invention proposes a method and system for coordinated control of voltage and power in a flexible distribution network. According to the multi-port SOP control strategy and the linear power flow model, the present invention analyzes the coordinated control principle of voltage and power in a flexible interconnected distribution network based on the multi-port SOP; constructs a discrete-time state-space model of the flexible distribution network based on the multi-port SOP, and then establishes an optimal control model for coordinated voltage and transformer load, which is solved by a linear quadratic regulator; the effectiveness of the proposed control method is proved through simulation tests.

[0007] According to some embodiments, a first solution of the present invention provides a method for coordinated control of voltage and power in a flexible distribution network, which adopts the following technical solution:

[0008] The flexible distribution network voltage and power coordinated control method includes:

[0009] Based on the voltage and power control principle of the multi-port soft switching steady-state model, the discrete-time state space model of the flexible distribution network is constructed using the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer.

[0010] By setting weights for different objective functions, an optimal control model for voltage and transformer load coordination is constructed.

[0011] A linear quadratic regulator is used to solve the optimal control model of voltage and transformer load coordination to obtain control variables, and control instructions are issued to the voltage source converter using constant power control based on the control variables.

[0012] Furthermore, the voltage and power control principle based on the multi-port soft switching steady-state model utilizes the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer to construct a discrete-time state space model of the flexible distribution network, specifically:

[0013] Determining a discrete-time state transition equation for a voltage state variable based on a difference between a voltage amplitude increment at an AC-side node of a voltage source converter using constant power control and a voltage amplitude increment at an AC-side node of a voltage source converter using constant DC voltage control;

[0014] Determine the discrete-time state transition equation of the load factor state variable based on the difference between the feeder transformer load increment of the voltage source converter using constant power control and the feeder transformer load factor increment of the voltage source converter using constant DC voltage control;

[0015] The discrete-time state transfer equations of N-1 voltage state variables and the discrete-time state transfer equations of N-1 load rate state variables are combined to establish a discrete-time state space model of the flexible distribution network, where N is the number of voltage source converters.

[0016] Furthermore, the voltage amplitude increment of the AC side node of the voltage source converter using constant power control is determined according to the product of the injection power increment of the voltage source converter using constant power control and the voltage sensitivity coefficient;

[0017] According to the power balance relationship of the multi-port soft switching steady-state model and the branch resistance, the AC side node voltage increment of the voltage source converter using constant DC voltage control is determined.

[0018] Furthermore, the voltage and transformer load coordinated optimal control model is specifically:

[0019]

[0020] Where: diagonal matrix is the weight matrix, x is the system state variable vector, u is the control variable, and t is the discrete sampling time; are the system state variables and control variables at the tth time step respectively.

[0021] Furthermore, the linear quadratic regulator is used to solve the optimal control model for voltage and transformer load coordination to obtain control variables, specifically:

[0022] Input the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer at the current moment;

[0023] Establish the current discrete-time state space model of the flexible distribution network and the optimal control model for voltage and transformer load coordination;

[0024] By solving the Riccati equation, we can determine the matrix in the optimal feedback gain matrix. P ;

[0025] Based on the solved matrix P Determine the optimal feedback gain that minimizes the optimal control model for voltage and transformer load coordination;

[0026] The optimal feedback gain and the system state variables at the current moment are used to determine the control variables at the current moment.

[0027] Furthermore, the control variables are specifically:

[0028] u(t)=Kx(t);

[0029] in: are the system state variables and control variables at the tth time step respectively; is the optimal feedback gain matrix, that is, the feedback gain that minimizes the optimal control model for voltage and transformer load coordination, which is given by the following formula:

[0030] K=-(R+B T PB) -1 B T PA;

[0031] in, is the weight matrix, P is the matrix solved by the Riccati equation, is the system state transfer matrix; is the system control matrix.

[0032] Furthermore, the matrix P in the optimal feedback gain matrix is ​​determined by solving the Riccati equation, specifically:

[0033] P=A T PA+QA T PB(R+B T PB) -1 B T PA;

[0034] Where P is the matrix solved by the Riccati equation. When P is the only positive solution of the above Riccati equation, the system (A+BK) is stable.

[0035] According to some embodiments, a second solution of the present invention provides a flexible distribution network voltage and power coordinated control system, which adopts the following technical solutions:

[0036] Flexible distribution network voltage and power coordinated control system, including:

[0037] The discrete-time state-space model building module is configured to build a discrete-time state-space model of the flexible distribution network based on the voltage and power control principle of the multi-port soft switching steady-state model and the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer;

[0038] An optimal control model building module is configured to construct an optimal control model for voltage and transformer load coordination by setting weights for different objective functions;

[0039] The control variable solving module is configured to use a linear quadratic regulator to solve the optimal control model for voltage and transformer load coordination to obtain control variables, and issue control instructions to the voltage source converter using constant power control based on the control variables.

[0040] According to some embodiments, a third aspect of the present invention provides a computer-readable storage medium.

[0041] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the flexible distribution network voltage and power coordinated control method as described in the first aspect above.

[0042] According to some embodiments, a fourth aspect of the present invention provides a computer device.

[0043] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the method for coordinated control of voltage and power of a flexible distribution network as described in the first aspect above are implemented.

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

[0045] In order to solve the problems of voltage over-limit and transformer overload in distribution networks caused by the access of a high proportion of distributed power sources, the present invention proposes a method for coordinated control of voltage and power in flexible distribution networks based on linear quadratic regulators. First, according to the multi-port SOP control strategy and the linear power flow model, the principle of coordinated control of voltage and power in flexible interconnected distribution networks based on multi-port SOPs is analyzed; secondly, a discrete-time state-space model of the flexible distribution network based on multi-port SOPs is constructed, and then an optimal control model for coordinated voltage and transformer load is established, which is solved using a linear quadratic regulator; finally, simulation tests prove that the proposed control method can quickly and effectively optimize the power flow distribution of the interconnected distribution network, improve node voltage and transformer overload.

[0046] The present invention adopts state feedback control and does not rely on the system master station. It can quickly and effectively optimize the power flow distribution of the flexible interconnected distribution network, improve the voltage level and balance the transformer load. It can be effectively applied to different situations such as large photovoltaic power generation during the day and multiple transformers overloaded at night, and has good applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0048] Figure 1 This is a flow chart of a method for coordinated control of voltage and power in a flexible distribution network according to an embodiment of the present invention;

[0049] Figure 2 1 is a schematic diagram of a multi-port SOP steady-state model according to an embodiment of the present invention;

[0050] Figure 3 is a flow chart of a linear quadratic regulator (LQR) in an embodiment of the present invention;

[0051] Figure 4 Schematic diagram of a flexible interconnected distribution network according to an embodiment of the present invention;

[0052] Figure 5 1 is a schematic diagram of a VSC injection power curve (case 1) according to an embodiment of the present invention;

[0053] Figure 6 1 is a schematic diagram of node voltage comparison before and after adjustment (case 1) in an embodiment of the present invention;

[0054] Figure 7 1 is a schematic diagram comparing the AC side voltage of the VSC before and after adjustment (Case 1) in an embodiment of the present invention;

[0055] Figure 8 1 is a schematic diagram of a transformer load rate curve (case 1) according to an embodiment of the present invention;

[0056] Figure 9 2 is a schematic diagram of a VSC injection power curve (case 2) according to an embodiment of the present invention;

[0057] Figure 10 2 is a schematic diagram of node voltage comparison before and after adjustment (Case 2) in an embodiment of the present invention;

[0058] Figure 11 2 is a schematic diagram showing a comparison of the AC side voltage of the VSC before and after adjustment (Case 2) in an embodiment of the present invention;

[0059] Figure 12 2 is a schematic diagram of a transformer load rate curve (case 2) in an embodiment of the present invention. DETAILED DESCRIPTION

[0060] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0061] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0062] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0063] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0064] Example 1

[0065] like Figure 1 As shown, this embodiment provides a method for coordinated control of voltage and power of a flexible distribution network. This embodiment uses the method applied to a server as an example for illustration. It is understandable that the method can also be applied to a terminal, and can also be applied to a system including a terminal, a server, and a server, and is implemented through the interaction between the terminal and the server. The server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network servers, cloud communications, middleware services, domain name services, security services CDN, and big data and artificial intelligence platforms. The terminal can be a smart phone, tablet computer, laptop computer, desktop computer, smart speaker, smart watch, etc., but is not limited to this. The terminal and the server can be directly or indirectly connected via wired or wireless communication, and this application does not limit this. In this embodiment, the method includes the following steps:

[0066] Based on the voltage and power control principle of the multi-port soft switching steady-state model, the discrete-time state space model of the flexible distribution network is constructed using the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer.

[0067] By setting weights for different objective functions, an optimal control model for voltage and transformer load coordination is constructed.

[0068] A linear quadratic regulator is used to solve the optimal control model of voltage and transformer load coordination to obtain control variables, and control instructions are issued to the voltage source converter using constant power control based on the control variables.

[0069] Multi-port flexible soft switch (soft openpoint, SOP) can realize the power intercommunication between different distribution networks, which is of great significance to optimizing power flow distribution and improving power quality. In order to solve the problem of voltage exceeding the limit and transformer overload in the distribution network caused by the access of a high proportion of distributed power sources, this embodiment proposes a flexible distribution network voltage and power coordination control method based on a linear quadratic regulator. First, according to the multi-port SOP control strategy and the linear power flow model, the voltage and power coordination control principle of the flexible interconnected distribution network based on the multi-port SOP is analyzed; secondly, a discrete time state space model of the flexible distribution network based on the multi-port SOP is constructed, and then the voltage and transformer load coordination optimal control model is established, and a linear quadratic regulator is used for solution; finally, through simulation tests, it is proved that the proposed control method can quickly and effectively optimize the power flow distribution of the interconnected distribution network, improve the node voltage and transformer overload.

[0070] Flexible interconnected distribution network model

[0071] like Figure 1 As shown in the figure, the N-port SOP of the multi-port soft switch (SOP) steady-state model consists of N VSCs (voltage source converters) connected to M feeders, where M = N; a transformer is configured at the head end of each feeder. The VSC at one end adopts a constant DC voltage control (V dc The VSCs on the other ports use constant power control (PQ control); all VSCs on the AC side use constant reactive power control. Figure 2 When the VSC power loss is not considered, the multi-port SOP power balance relationship is:

[0072]

[0073] Where: P a is the power injected into the AC grid by the ath VSC, and N is the number of VSCs in the multi-port SOP.

[0074] Voltage and power control principles of multi-port SOP

[0075] Based on the DistFlow power flow model of the radial distribution network, the linear relationship between the voltage amplitude of each node and the injected power of each node under the standard system is:

[0076]

[0077] Where: P ij , Qij is the active and reactive power of branch ij; r jk is the resistance of branch jk; P jk , Q jk is the active and reactive power of branch jk; P j , Q j is the injected active and reactive power of node j; V i is the voltage amplitude of node i; V0 is the voltage amplitude of the root node; x jk is the reactance of branch ij; r ij is the resistance of branch ij; Ω is the set of all nodes; is the set of branches on the path from the root node to node i; R ij and X ij Size

[0078]

[0079] Among them, x hk is the reactance of branch hk; r hk is the resistance of branch hk.

[0080] When the injection power of a node i increases by ΔP i When , the voltage amplitude increment of node j is:

[0081]

[0082] Where: r l is the resistance of branch l.

[0083] Determining a voltage amplitude increment of an AC-side node of a voltage source converter using constant power control according to a product of an injection power increment of the voltage source converter using constant power control and a voltage sensitivity coefficient;

[0084] According to the power balance relationship of the multi-port soft switching steady-state model and the branch resistance, the AC side node voltage increment of the voltage source converter using constant DC voltage control is determined.

[0085] For N-port SOP, assuming VSC1 uses V dc Control to maintain the DC voltage stability inside the SOP, and its transmission power is determined by the transmission power of the other VSCs. a Injection power increases by ΔP a When the injection power of the ath VSC increases ΔP a , the voltage amplitude increment of the AC side node is:

[0086]

[0087] Where: ΔVVSCa For VSC a Voltage increment of AC side node; For VSC a The set of lines on the path from the AC side node to the feeder root node; S a For VSC a The voltage sensitivity coefficient.

[0088] According to formula (1), V dc The voltage increment of the controlled VSC1 AC side node is:

[0089]

[0090] Active load increment ΔP of the feeder transformer where the PQ-controlled VSCa is located Ta for:

[0091] ΔP Ta =-ΔP a (7);

[0092] V dc Active load increment ΔP of the feeder transformer where VSC1 is controlled T1 for:

[0093]

[0094] The voltage and power control principle based on the multi-port soft switching steady-state model is used to construct a discrete-time state space model of the flexible distribution network using the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer. Specifically,

[0095] Determining a discrete-time state transition equation for a voltage state variable based on a difference between a voltage amplitude increment at an AC-side node of a voltage source converter using constant power control and a voltage amplitude increment at an AC-side node of a voltage source converter using constant DC voltage control;

[0096] Determine the discrete-time state transition equation of the load factor state variable based on the difference between the feeder transformer load increment of the voltage source converter using constant power control and the feeder transformer load factor increment of the voltage source converter using constant DC voltage control;

[0097] The discrete-time state transfer equations of N-1 voltage state variables and the discrete-time state transfer equations of N-1 load rate state variables are combined to establish a discrete-time state space model of the flexible distribution network, where N is the number of voltage source converters.

[0098] Specifically, the discrete-time state-space model construction process is as follows:

[0099] Select the active power increment injected by all constant power controlled VSCs as the control variable:

[0100]

[0101] Where ΔP VSC2 is the active power increment injected by VSC2 into its AC side node; ΔP VSCN is the increase in active power injected by VSCN into its AC side nodes.

[0102] Taking the VSC1 AC side node voltage as a reference, the deviation between the other N-1 VSC AC side node voltages and the VSC1 AC side node voltage amplitude is defined as:

[0103] V deva =V VSCa -V VSC1 ,a=2,…,N (10);

[0104] Similarly, taking the feeder transformer where VSC1 is located as a reference, the deviation between the load factor of the feeder transformers where the other N-1 VSCs are located and the load factor of the feeder transformer where VSC1 is located can be defined as:

[0105] T devb =T b -T1,b=2,…,M (11);

[0106] Where: T b is the load factor of the transformer on feeder b, and T1 is the load factor of the transformer on feeder 1.

[0107] According to equations (10) and (11), the system state variable vector is composed of the voltage amplitude deviation vector of the AC side node of each constant power controlled VSC and the load rate deviation vector of the feeder transformer where each constant power controlled VSC is located:

[0108]

[0109] When the VSCa injection power of a certain power control increases by ΔP a When the reactive load of each node is small, the feeder transformer load factor increment ΔT can be obtained by combining formula (7) without considering the reactive load. i for:

[0110]

[0111] Where: S Tb is the rated apparent power of the transformer on feeder b, ΔP VSCa is the increase in active power injected by VSCa into its AC side node; ΔP Ta It is the active load increment of the feeder transformer where VSCa is located.

[0112] State variable V deva The increment is:

[0113]

[0114] Where ΔP VSCc It is the increase in active power injected by VSCc into its AC side node.

[0115] The above formula can be rewritten as discrete time state transfer form:

[0116]

[0117] Where t is the discrete sampling time.

[0118] State variable T devb The increment is:

[0119]

[0120] Where ΔT1 is the load factor of the transformer of feeder 1; S T1 is the rated apparent power of feeder 1 transformer;

[0121] The above formula can be rewritten as discrete time state transfer form:

[0122]

[0123] By combining the N-1 state transfer equations (15) and the N-1 state transfer equations (17) and rewriting them into matrix-vector form, a linear time-invariant discrete-time state space model can be established:

[0124]

[0125] in, are the system state variables and control variables at the t-th time step, is the system state variable at the t+1th time step.

[0126] In order to simultaneously achieve the goals of improving voltage levels and balancing transformer load rates, a voltage and transformer load coordinated optimal control model is constructed by setting weights for different objective functions. Specifically,

[0127]

[0128] Where: diagonal matrix is the weight matrix, are the system state variables and control variables at the tth time step, respectively, and t is the discrete sampling moment.

[0129] Solving the above optimal control model can obtain the control variables, which are specifically:

[0130] u(t)=Kx(t) (20);

[0131] in: is the optimal feedback gain matrix, are the system state variables and control variables at the t-th time step, respectively, and t is the discrete sampling moment; is the optimal feedback gain matrix, that is, the feedback gain that minimizes the optimal control model for voltage and transformer load coordination, which is given by the following formula:

[0132] K=-(R+B T PB) -1 B T PA (21);

[0133] in, is the weight matrix, P is the matrix solved by the Riccati equation, is the system state transfer matrix; is the system control matrix.

[0134] The matrix P in the optimal feedback gain matrix is ​​determined by solving the Riccati equation, specifically:

[0135] P=A T PA+QA T PB(R+B T PB) -1 B T PA (22);

[0136] Where P is the matrix solved by the Riccati equation, is the system state transfer matrix; is the system control matrix; when P is the only positive solution of the above Riccati equation, the system (A+BK) is stable.

[0137] The above control objectives can not only realize the power flow distribution between the feeders where the constant power control VSC is located and the feeders where the constant DC voltage control VSC is located, but also realize the power flow distribution between the feeders by leveraging the power coupling relationship between the VSCs.

[0138] The control flow diagram is as follows Figure 3 As shown, the linear quadratic regulator is used to solve the optimal control model of voltage and transformer load coordination to obtain the control variables, which are specifically:

[0139] Input the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer at the current moment;

[0140] Establish the current discrete-time state space model of the flexible distribution network and the optimal control model for voltage and transformer load coordination;

[0141] By solving the Riccati equation, we can determine the matrix in the optimal feedback gain matrix. P ;

[0142] Based on the solved matrix P Determine the optimal feedback gain that minimizes the optimal control model for voltage and transformer load coordination;

[0143] The optimal feedback gain and the system state variables at the current moment are used to determine the control variables at the current moment.

[0144] Simulation Results

[0145] use Figure 4 The proposed method is tested on a three-terminal flexible interconnected distribution network with a voltage level of 10 kV. Node 1 in each feeder is the root node, with a voltage of 1.0 pu. The impedance parameters of each line are shown in Table 1. The transformer capacity is 5 MW.

[0146] Table 1 Line impedance

[0147]

[0148]

[0149] 3.1 Scenario 1

[0150] This section analyzes the control effect of the proposed SOP voltage and power coordinated control method when the photovoltaic output is high during the day. The injected power of each node at this time is shown in Table 2.

[0151] Table 2 Injection power of each node (case 1)

[0152] node Feeder 1 Feeder 2 Feeder 3 2 -100-j60 -100-j60 -100-j60 3 2000+j1000 -900-j400 -90-j40 4 -200-j80 -120-j80 -60-j30 5 600+j300 -1500-j700 -60-j30

[0153] Assuming that the power of each port is 0 before SOP participates in regulation, the transmission power of each port of SOP during regulation is as follows: Figure 5 As shown in the figure, before regulation, due to the high PV output power on feeder 1, the node voltage increased, and the transformer was reversely overloaded. Meanwhile, due to the high load power on feeder 2, the node voltage was low, and the transformer was overloaded. There is potential for power flow optimization between different distribution networks. The SOP begins power regulation at 0.5s, with a sampling period of 10ms. This increases the power injected by VSC2 and the power absorbed by VSC1 from feeder 1, achieving optimal power regulation between feeders 1 and 2.

[0154] The node voltage of each feeder and the AC side voltage of each port VSC before and after SOP coordinated control are as follows: Figure 6 、 Figure 7 As shown in the figure, by adjusting the input and output power of each VSC through SOP, the AC side voltage of VSC1 is reduced from 1.04pu to 0.98pu, and the AC side voltage of VSC2 is increased from 0.94pu to 0.99pu, and the system voltage level is improved.

[0155] The transformer load rate of each feeder before and after the implementation of SOP coordinated control is as follows: Figure 8 As shown in the figure, through SOP coordinated control, the transformer load factors of feeder 1 and feeder 2 were reduced from 32% and 52% to 18% and 28%, respectively, effectively avoiding transformer overload. Simulation results show that the proposed SOP coordinated control strategy effectively improves voltage levels and balances transformer loads during periods of high photovoltaic power generation, effectively addressing the challenges posed by the intermittent and variable nature of solar power generation.

[0156] 3.2 Scenario 2

[0157] This section analyzes the control effect of the proposed SOP voltage and power coordinated control method when there is no photovoltaic output at night and the distribution network is heavily loaded. The injected power of each load node at this time is shown in Table 3.

[0158] Table 3 Injection power of each node (case 1)

[0159] node Feeder 1(kW) Feeder 2(kW) Feeder 3(kW) 2 0+j0 0+j0 -100-j60 3 -2000-j700 -1700-j400 -90-j40 4 -1300-j500 -2500-j800 -60-j30 5 0+j0 0+j0 -60-j30

[0160] Assuming that the power of each port is 0 before SOP is involved in regulation, the SOP power of each port during SOP regulation is as follows: Figure 9 As shown in the figure, after SOP regulation, the power absorbed by VSC1 and VSC2 from feeder 1 and feeder 2 increases, and the power injected into feeder 3 by VSC3 increases, thus achieving optimal regulation of power between different feeders.

[0161] The changes of each node voltage and VSC AC side voltage before and after adjustment are as follows: Figure 10 、 Figure 11 As shown in the figure, before SOP control, the AC side voltages of VSC1 and VSC2 were 0.938 pu and 0.922 pu, respectively. After control, the AC side voltages of VSC1 and VSC2 increased to 0.952 pu and 0.955 pu, respectively. Simulation results show that the proposed SOP coordinated control method can still effectively improve system voltage even when multiple interconnected feeders are heavily loaded.

[0162] Comparison of transformer load rate changes before and after implementing SOP voltage coordinated control Figure 12As shown in the figure, before SOP regulation, the transformer load factors of feeder 1 and feeder 2 were 66% and 84%, respectively, and both transformers 1 and 2 were overloaded. Through SOP voltage coordination control, the load factors of transformer 1 and transformer 2 were reduced to 62.94% and 68.48%, respectively, effectively reducing the degree of transformer overload.

[0163] Comparative Analysis

[0164] Compare the multi-objective control method proposed in this paper with the single-objective control method:

[0165] Control mode 1: voltage control only;

[0166] Control mode 2: Transformer load balancing control only;

[0167] Control mode 3: Coordinated control of voltage and transformer load.

[0168] Table 4 shows a comparison of the control effects of different control methods. It can be seen that in Scenario 1, Control Method 2 causes the voltage on Feeder 1 to exceed the limit, indicating that the control method aimed at balancing transformer load factors cannot effectively improve the system voltage level during periods of high photovoltaic power generation. In Scenario 2, when multiple transformers are overloaded, Control Method 1, which aims to improve voltage, cannot effectively balance transformer load factors. Compared with Control Methods 1 and 2, the proposed coordinated control method for voltage and transformer load can effectively avoid both node voltage exceeding the limit and transformer overloading, demonstrating excellent control effectiveness.

[0169] Table 4 Node voltage and transformer load under three control modes

[0170]

[0171]

[0172] To address the voltage over-limit and transformer overload issues caused by a high proportion of distributed generation (DGs) connected, this embodiment proposes a voltage and power coordinated control method for a flexible interconnected distribution network based on a linear quadratic regulator. Simulation tests yield the following conclusions:

[0173] 1) The proposed SOP coordinated control strategy adopts state feedback control and does not rely on the system master station. It can quickly and effectively optimize the power flow distribution of the flexible interconnected distribution network, improve the voltage level and balance the transformer load.

[0174] 2) The proposed SOP coordinated control strategy can be effectively applied to different situations such as large photovoltaic power generation during the day and multiple transformers overloaded at night, and has good applicability.

[0175] Example 2

[0176] This embodiment provides a flexible distribution network voltage and power coordinated control system, including:

[0177] The discrete-time state-space model building module is configured to build a discrete-time state-space model of the flexible distribution network based on the voltage and power control principle of the multi-port soft switching steady-state model and the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer;

[0178] An optimal control model building module is configured to construct an optimal control model for voltage and transformer load coordination by setting weights for different objective functions;

[0179] The control variable solving module is configured to use a linear quadratic regulator to solve the optimal control model for voltage and transformer load coordination to obtain control variables, and issue control instructions to the voltage source converter using constant power control based on the control variables.

[0180] The examples and application scenarios implemented by the above modules and corresponding steps are the same, but are not limited to the contents disclosed in the above embodiment 1. It should be noted that the above modules as part of the system can be executed in a computer system such as a set of computer executable instructions.

[0181] The descriptions of the various embodiments in the above embodiments have different focuses. For parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0182] The proposed system can be implemented in other ways. For example, the system embodiment described above is merely illustrative. For example, the above module division is only a logical function division. In actual implementation, other division methods may be used. For example, multiple modules can be combined or integrated into another system, or some features can be ignored or not implemented.

[0183] Example 3

[0184] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the steps of the method for coordinated control of voltage and power in a flexible distribution network as described in the first embodiment above are implemented.

[0185] Example 4

[0186] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps in the flexible distribution network voltage and power coordinated control method as described in the first embodiment are implemented.

[0187] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of hardware embodiments, software embodiments, or embodiments combining software and hardware. Furthermore, 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 magnetic disk storage and optical storage, etc.) containing computer-usable program code.

[0188] 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 flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, 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 flowcharts and / or block diagrams. 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.

[0189] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work 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 The function specified in one or more boxes.

[0190] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0191] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware through a computer program. The program can be stored in a computer-readable storage medium, and when executed, the program can include the processes in the above-described method embodiments. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0192] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for coordinated control of voltage and power in a flexible distribution network, characterized in that: include: Based on the voltage and power control principle of the multi-port soft switching steady-state model, the discrete-time state space model of the flexible distribution network is constructed using the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer. Specifically, Determining a discrete-time state transition equation for a voltage state variable based on a difference between a voltage amplitude increment at an AC-side node of a voltage source converter using constant power control and a voltage amplitude increment at an AC-side node of a voltage source converter using constant DC voltage control; Determine the discrete-time state transition equation of the load factor state variable based on the difference between the feeder transformer load increment of the voltage source converter using constant power control and the feeder transformer load factor increment of the voltage source converter using constant DC voltage control; The discrete-time state-space model of the flexible distribution network is established by simultaneously formulating the discrete-time state-transfer equations of N-1 voltage state variables and N-1 load rate state variables, where N is the number of voltage source converters. By setting weights for different objective functions, an optimal control model for voltage and transformer load coordination is constructed. The optimal control model for voltage and transformer load coordination is specifically: ； Where: diagonal matrix 、 is the weight matrix, 、 Respectively t The system state variables and control variables of each time step, t is the discrete sampling instant; A linear quadratic regulator is used to solve the optimal control model of voltage and transformer load coordination to obtain control variables, and control instructions are issued to the voltage source converter using constant power control based on the control variables.

2. The method for coordinated control of voltage and power in a flexible distribution network according to claim 1, wherein: Determining a voltage amplitude increment of an AC-side node of a voltage source converter using constant power control according to an increase in the injected power of the voltage source converter using constant power control and a product of a voltage sensitivity coefficient; According to the power balance relationship of the multi-port soft switching steady-state model and the branch resistance, the AC side node voltage increment of the voltage source converter using constant DC voltage control is determined.

3. The method for coordinated control of voltage and power in a flexible distribution network according to claim 1, wherein: The linear quadratic regulator is used to solve the optimal control model for voltage and transformer load coordination to obtain the control variables, specifically: Input the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer at the current moment; Establish the current discrete-time state space model of the flexible distribution network and the optimal control model for voltage and transformer load coordination; By solving the Riccati equation, we can determine the matrix in the optimal feedback gain matrix. ; Based on the solved matrix Determine the optimal feedback gain that minimizes the optimal control model for voltage and transformer load coordination; The optimal feedback gain and the system state variables at the current moment are used to determine the control variables at the current moment.

4. The method for coordinated control of voltage and power in a flexible distribution network according to claim 3, wherein: The control variables are specifically: ； in: 、 Respectively t The system state variables and control variables of each time step, t is the discrete sampling instant; is the optimal feedback gain matrix, that is, the feedback gain that minimizes the optimal control model for voltage and transformer load coordination, which is given by the following formula: ； in, is the weight matrix, is the matrix solved by the Riccati equation, is the system state transfer matrix; is the system control matrix.

5. The method for coordinated control of voltage and power in a flexible distribution network according to claim 3, wherein: The matrix in the optimal feedback gain matrix is ​​determined by solving the Riccati equation , specifically: ； in, is the matrix solved by the Riccati equation, is the system state transfer matrix; is the system control matrix; when is the only positive solution of the above Riccati equation is stable.

6. Flexible distribution network voltage and power coordinated control system, characterized in that: include: The discrete-time state-space model construction module is configured to build a discrete-time state-space model of the flexible distribution network based on the voltage and power control principle of the multi-port soft switching steady-state model, using the AC side voltage amplitude of each voltage source converter and the load factor of each feeder transformer. Specifically: Determining a discrete-time state transition equation for a voltage state variable based on a difference between a voltage amplitude increment at an AC-side node of a voltage source converter using constant power control and a voltage amplitude increment at an AC-side node of a voltage source converter using constant DC voltage control; Determine the discrete-time state transition equation of the load factor state variable based on the difference between the feeder transformer load increment of the voltage source converter using constant power control and the feeder transformer load factor increment of the voltage source converter using constant DC voltage control; The discrete-time state-space model of the flexible distribution network is established by simultaneously formulating the discrete-time state-transfer equations of N-1 voltage state variables and N-1 load rate state variables, where N is the number of voltage source converters. An optimal control model building module is configured to construct an optimal control model for voltage and transformer load coordination by setting weights for different objective functions; The optimal control model for voltage and transformer load coordination is specifically: ； Where: diagonal matrix 、 is the weight matrix, 、 Respectively t The system state variables and control variables of each time step, t is the discrete sampling instant; The control variable solving module is configured to use a linear quadratic regulator to solve the optimal control model for voltage and transformer load coordination to obtain control variables, and issue control instructions to the voltage source converter using constant power control based on the control variables.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the flexible distribution network voltage and power coordinated control method as described in any one of claims 1 to 5 are implemented.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the flexible distribution network voltage and power coordinated control method according to any one of claims 1 to 5 are implemented.

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