Flexible power distribution network voltage and power coordination control method and system

Abstract

The invention belongs to the field of flexible power distribution network optimization scheduling, and provides a flexible power distribution network voltage and power coordination control method and system.The method comprises the steps that firstly, according to a multi-port SOP control strategy and a linear power flow model, a flexible interconnection power distribution network voltage and power coordination control principle based on a multi-port SOP is analyzed; secondly, constructing a discrete time state space model of the flexible power distribution network based on a multi-port SOP, further establishing a voltage and transformer load coordination optimal control model, and adopting a linear quadratic regulator for solving; finally, simulation tests prove that the control method can quickly and effectively optimize the power flow distribution of the interconnected power distribution network, node voltage and transformer heavy load are improved, and the problems of power distribution network voltage out-of-limit and transformer heavy overload caused by high-proportion distributed power supply access are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible distribution network optimization and dispatching, and in particular relates to a method and system for coordinated control of voltage and power of 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] With the continuous growth of electricity demand for cars, air conditioners, etc., the imbalance of distribution network load is becoming increasingly prominent. At the same time, distributed photovoltaic and electric vehicles have significant random characteristics, which are prone to cause problems such as voltage over-limit and transformer overload, affecting the safe and reliable operation of the distribution network. Multi-port soft switch (soft openpoint, SOP) is usually composed of multiple back-to-back voltage source converters (voltage source converter, VSC). Through the interconnection of the DC side of different converters, the power flow between different distribution networks is optimized, the voltage level is improved, the transformer load is relieved, and the acceptance capacity of distributed photovoltaic is improved. It is an important direction for the development of intelligent distribution system.

[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 optimizes and solves the transmission power of SOP by obtaining the status information of the distribution network, and issues 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 high-proportion 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 by 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, so as to effectively play the role of SOP in improving the economy and safety of distribution network operation.

[0005] The above static optimization method requires the control master station to have strong computing power, but has high requirements for system communication and measurement conditions; in addition, between two optimization dispatches, the random changes in distributed photovoltaic output are also prone to cause voltage over-limit and other problems. In order to improve the rapidity of optimization and control of flexible interconnected distribution networks, the real-time optimization control of SOP is continuously deepened. There are also existing technologies that propose a practical power coordination control strategy for multi-terminal flexible interconnection systems, including overload limit control for reasonable power distribution when some feeders are overloaded, and power balancing control for optimizing power flow distribution when all feeders are overloaded; in order to solve the problem of unbalanced load on distribution network feeders, a dynamic adjustment model for feeder economic load rate based on flexible interconnection devices is proposed, and the controller design is realized through 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-shift 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 access leads to overload of transformers and over-limit of node voltage in flexible interconnected distribution networks, which cannot meet the needs of multi-port SOP multi-objective rapid regulation 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 multi-port SOP; a discrete-time state-space model of a flexible distribution network based on multi-port SOP is constructed, and then an optimal control model of coordinated voltage and transformer load is established, 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] A voltage and power coordinated control method for a flexible distribution network, comprising:

[0009] Based on the voltage and power control principle of the multi-port soft switch steady-state model, the discrete time state space model of the flexible distribution network is constructed using the voltage amplitude of the AC side of each voltage source converter and the load rate 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 switch steady-state model uses the voltage amplitude on the AC side of each voltage source converter and the load rate of each feeder transformer to construct a discrete time state space model of the flexible distribution network, specifically:

[0013] Determine a discrete time state transfer equation of a voltage state variable according to a difference between a voltage amplitude increment of an AC side node of a voltage source converter using constant power control and a voltage amplitude increment of an AC side node of a voltage source converter using constant DC voltage control;

[0014] Determine the discrete time state transfer equation of the load factor state variable based on the difference between the load increment of the feeder transformer of the voltage source converter using constant power control and the load factor increment of the feeder transformer 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] Further, according to the product of the injection power increment of the voltage source converter using constant power control and the voltage sensitivity coefficient, the voltage amplitude increment of the AC side node of the voltage source converter using constant power control is determined;

[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 of voltage and transformer load coordination to obtain control variables, specifically:

[0022] Input the voltage amplitude of the AC side of each voltage source converter and the load rate 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 optimal feedback gain matrix. P ;

[0025] Based on the matrix of the solution 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 variable at the current moment are used to determine the control variable 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, which is the minimum feedback gain of the optimal control model for voltage and transformer load coordination, and is given by the following formula:

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

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

[0032] Furthermore, the matrix P in the optimal feedback gain matrix is ​​determined by solving the Riccati equation, which is 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 coordination control system, which adopts the following technical solution:

[0036] Flexible distribution network voltage and power coordination 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 switch steady-state model and using the voltage amplitude of the AC side of each voltage source converter and the load rate 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 in the method for coordinated control of voltage and power in a flexible distribution network 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 in 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 problem of voltage over-limit and transformer overload in distribution network caused by high proportion of distributed power access, the present invention proposes a method for coordinated control of voltage and power in flexible distribution network based on linear quadratic regulator. Firstly, according to the multi-port SOP control strategy and linear power flow model, the principle of coordinated control of voltage and power in flexible interconnected distribution network based on multi-port SOP is analyzed; secondly, a discrete time state space model of flexible distribution network based on multi-port SOP is constructed, and then the optimal control model of voltage and transformer load coordination is established, and a linear quadratic regulator is used for solution; finally, it is proved through simulation test that the proposed control method can quickly and effectively optimize the power flow distribution of interconnected distribution network, improve node voltage and transformer overload.

[0046] The present invention adopts state feedback control, does not rely on the system master station, 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 in the specification, 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 It 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 Schematic diagram of a multi-port SOP steady-state model in 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 is a schematic diagram of a flexible interconnected distribution network in an embodiment of the present invention;

[0052] Figure 5 is a schematic diagram of a VSC injection power curve (case 1) in 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 is a schematic diagram of comparison of the AC side voltage of the VSC before and after adjustment (case 1) in an embodiment of the present invention;

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

[0056] Fig. 9 is a schematic diagram of a VSC injection power curve (case 2) in an embodiment of the present invention;

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

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

[0059] Fig.12 Schematic diagram of transformer load rate curve (case 2) in an embodiment of the present invention. DETAILED DESCRIPTION

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

[0061] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those 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 exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates 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 of the embodiments may be combined with each other.

[0064] Embodiment 1

[0065] like Figure 1 As shown, this embodiment provides a method for coordinated control of voltage and power in 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 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, a tablet computer, a laptop computer, a desktop computer, a smart speaker, a 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, which is not limited in this application. In this embodiment, the method includes the following steps:

[0066] Based on the voltage and power control principle of the multi-port soft switch steady-state model, the discrete time state space model of the flexible distribution network is constructed using the voltage amplitude of the AC side of each voltage source converter and the load rate 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 optimize the power flow distribution and improve the power quality. In order to solve the problem of voltage over-limit and transformer overload in the distribution network caused by the access of high-proportion distributed power sources, this embodiment proposes a flexible distribution network voltage and power coordination control method based on linear quadratic regulator. First, according to the multi-port SOP control strategy and linear power flow model, the voltage and power coordination control principle of the flexible interconnected distribution network based on multi-port SOP is analyzed; secondly, a discrete time state space model of the flexible distribution network based on 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, it is proved through simulation tests 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.

[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 principle 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 injected 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 an increment of an injected power of the voltage source converter using constant power control and a product of 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 internal DC voltage of SOP stable, and its transmission power is determined by the transmission power of other VSCs. a Injection power increases by ΔP a When the injection power of the ath VSC increases by ΔP a , the voltage amplitude increment of the AC side node is:

[0086]

[0087] Where: ΔVVSCa For VSC a Voltage increment of the AC side node; For VSC a The line set 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 AC side node of VSC1 is controlled as follows:

[0089]

[0090] Active load increment ΔP of the feeder transformer where VSCa is located under PQ control 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 switch steady-state model uses the voltage amplitude of the AC side of each voltage source converter and the load rate of each feeder transformer to construct a discrete time state space model of the flexible distribution network, which is specifically:

[0095] Determine a discrete time state transfer equation of a voltage state variable according to a difference between a voltage amplitude increment of an AC side node of a voltage source converter using constant power control and a voltage amplitude increment of an AC side node of a voltage source converter using constant DC voltage control;

[0096] Determine the discrete time state transfer equation of the load factor state variable based on the difference between the load increment of the feeder transformer of the voltage source converter using constant power control and the load factor increment of the feeder transformer 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 VSCs with constant power control as the control variable:

[0100]

[0101] Among them, 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 rate of the feeder transformers where the other N-1 VSCs are located and the load rate 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 of 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] Among them, 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 tth time step, is the system state variable at the t+1th time step.

[0126] In order to achieve the goals of improving the voltage level and balancing the transformer load rate at the same time, the optimal control model of voltage and transformer load coordination 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 time.

[0129] The control variables can be obtained by solving the above optimal control model. The control variables 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 time; is the optimal feedback gain matrix, which is the minimum feedback gain of the optimal control model for voltage and transformer load coordination, and 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; It is the system control matrix.

[0134] The matrix P in the optimal feedback gain matrix is ​​determined by solving the Riccati equation, which is 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 of the feeder where the constant power control VSC is located and the feeder where the constant DC voltage control VSC is located, but also realize the power flow distribution between the feeders by means of the power coupling relationship between the VSCs.

[0138] The control flow chart 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 voltage amplitude of the AC side of each voltage source converter and the load rate 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 optimal feedback gain matrix. P ;

[0142] Based on the matrix of the solution 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 variable at the current moment are used to determine the control variable at the current moment.

[0144] Simulation Results

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

[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. At this time, the injected power of each node 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 large photovoltaic output power of feeder 1, the node voltage increased and the transformer was reversely overloaded; the load power of feeder 2 was large, the node voltage was low, and the transformer was overloaded. There is potential for power flow optimization between different distribution networks. SOP starts power regulation at 0.5s, with a sampling period of 10ms. The power injected by VSC2 increases, and the power absorbed by VSC1 from feeder 1 increases, realizing the optimal regulation of power between feeder 1 and feeder 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 rate of feeder 1 and feeder 2 is reduced from 32% and 52% to 18% and 28% respectively, effectively avoiding transformer overload. The simulation results show that the proposed SOP coordinated control strategy effectively improves the voltage level and balances the transformer load during the period of photovoltaic power generation, effectively coping with the challenges brought by the intermittent and variability 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 load is heavy. At this time, the injected power of each load node 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 before SOP is involved in regulation, the power of each port is 0, the SOP power of each port during SOP regulation is as follows: Fig. 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, thereby achieving optimal regulation of power between different feeders.

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

[0162] Comparison of transformer load rate changes before and after implementing SOP voltage coordination control Fig.12As shown in the figure, before SOP regulation, the transformer load rates of feeder 1 and feeder 2 were 66% and 84% respectively, and both transformer 1 and transformer 2 were overloaded; through SOP voltage coordination control, the load rates 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] The comparison results of the control effects of different control methods are shown in Table 4. It can be seen that in situation 1, control method 2 causes the voltage of feeder 1 to exceed the limit. It can be seen that the control method with the transformer load rate balance as the goal cannot effectively improve the system voltage level during the photovoltaic power generation period. In situation 2, when multiple transformers are overloaded, control method 1 with the goal of improving voltage cannot effectively balance the transformer load rate. Compared with control methods 1 and 2, the proposed voltage and transformer load coordinated control method can effectively avoid node voltage over-limit and transformer overload at the same time, and has a good control effect.

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

[0170]

[0171]

[0172] In order to solve the voltage over-limit and transformer overload problems caused by the access of a high proportion of distributed power sources, this embodiment proposes a voltage and power coordinated control method for a flexible interconnected distribution network based on a linear quadratic regulator, and obtains the following conclusions through simulation tests:

[0173] 1) The proposed SOP coordinated control strategy adopts state feedback control, does not rely on the system master station, and 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] Embodiment 2

[0176] This embodiment provides a flexible distribution network voltage and power coordination 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 switch steady-state model and using the voltage amplitude of the AC side of each voltage source converter and the load rate 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 description of each embodiment in the above embodiments has different emphases. 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 only illustrative, and the division of the modules is only a logical function division. In actual implementation, there may be other division methods, such as multiple modules can be combined or integrated into another system, or some features can be ignored or not executed.

[0183] Embodiment 3

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

[0185] Embodiment 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 method for coordinated control of voltage and power of a flexible distribution network 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. Therefore, the present invention may take the form of hardware embodiments, software embodiments, or embodiments 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 and optical storage, etc.) containing computer-usable program codes.

[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 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.

[0189] 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.

[0190] 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 in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0191] A person skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0192] Although the above describes the specific implementation mode 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 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 switch steady-state model, the discrete time state space model of the flexible distribution network is constructed using the voltage amplitude of the AC side of each voltage source converter and the load rate of each feeder transformer. By setting weights for different objective functions, an optimal control model for voltage and transformer load coordination is constructed; 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, characterized in that: The voltage and power control principle based on the multi-port soft switch steady-state model uses the voltage amplitude of the AC side of each voltage source converter and the load rate of each feeder transformer to construct a discrete time state space model of the flexible distribution network, which is specifically: Determine a discrete time state transfer equation of a voltage state variable according to a difference between a voltage amplitude increment of an AC side node of a voltage source converter using constant power control and a voltage amplitude increment of an AC side node of a voltage source converter using constant DC voltage control; Determine the discrete time state transfer equation of the load factor state variable based on the difference between the load increment of the feeder transformer of the voltage source converter using constant power control and the load factor increment of the feeder transformer of the voltage source converter using constant DC voltage control; 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.

3. The method for coordinated control of voltage and power in a flexible distribution network according to claim 2, characterized in that: Determine the voltage amplitude increment of the AC side node of the voltage source converter using constant power control according to the increase of the injected power of the voltage source converter using constant power control and the product of the 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.

4. The method for coordinated control of voltage and power in a flexible distribution network according to claim 1, characterized in that: The optimal control model for voltage and transformer load coordination is specifically: 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 time.

5. The method for coordinated control of voltage and power in a flexible distribution network according to claim 1, characterized in that: The linear quadratic regulator is used to solve the optimal control model of voltage and transformer load coordination to obtain control variables, specifically: Input the voltage amplitude of the AC side of each voltage source converter and the load rate 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 optimal feedback gain matrix. P ; Based on the matrix of the solution P 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 variable at the current moment are used to determine the control variable at the current moment.

6. The method for coordinated control of voltage and power in a flexible distribution network according to claim 5, characterized in that: The control variables are specifically: u(t)=Kx(t); in: are the system state variables and control variables at the t-th time step, respectively, and t is the discrete sampling time; is the optimal feedback gain matrix, which is the minimum feedback gain of the optimal control model for voltage and transformer load coordination, and is given by the following formula: K=-(R+B T PB) -1 B T PA; in, is the weight matrix, P is the matrix solved by the Riccati equation, is the system state transfer matrix; It is the system control matrix.

7. The method for coordinated control of voltage and power in a flexible distribution network according to claim 5, characterized in that: The matrix in the optimal feedback gain matrix is ​​determined by solving the Riccati equation P , specifically: P=A T PA+Q-A T PB(R+B T PB) -1 B T PA; where P is the matrix solved by the Riccati equation, is the system state transfer matrix; is the system control matrix; when P The system (A+BK) is stable when is the only positive solution of the above Riccati equation.

8. Flexible distribution network voltage and power coordination control system, characterized in that: include: 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 switch steady-state model and using the voltage amplitude of the AC side of each voltage source converter and the load rate of each feeder transformer; 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 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.

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

10. A computer 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 program, the steps in the flexible distribution network voltage and power coordinated control method as described in any one of claims 1-7 are implemented.

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