Method, device and equipment for controlling dynamic power distribution of flexible direct-current power transmission system

Abstract

The invention relates to a control method, device and equipment for dynamic power distribution of a flexible direct current transmission system, and the method comprises the steps: setting a centralized control center and sub-control centers which are in communication connection with the centralized control center, and enabling each shore converter station to be provided with the sub-control center; acquiring a voltage reference value, electrical quantity data and a topological equivalent circuit diagram of the multi-terminal direct current power transmission system; according to the voltage reference value and the electrical quantity data, PI control processing is adopted to obtain total d-axis current; according to the electrical quantity data and the topological equivalent circuit diagram, processing to obtain a power distribution coefficient by adopting an optimal power flow; and distributing active power to the corresponding shore converter station according to the total d-axis current and the power distribution coefficient. According to the method, the active power is distributed to the corresponding shore converter station through the total d-axis current and the power distribution coefficient, and flexible distribution control of the active power is realized for the shore converter station; and the sub-control center controls the operation of the corresponding shore converter stations according to the active power, so that the plurality of shore converter stations jointly control the DC voltage.

Description

Technical Field

[0001] The present application relates to the field of direct current transmission technology, and in particular to a control method, device and equipment for dynamic power distribution of a flexible direct current transmission system. Background Art

[0002] The power distribution control of existing multi-terminal DC transmission generally adopts the master-slave control mode and the voltage droop control mode. However, the master-slave control mode places high demands on the power grid to which the master station is connected. The lack of power control capability of the master station often cannot meet the access standards of the local power grid, especially the weak power grid, which requires the master station to have sufficient capacity. For complex multi-terminal DC networks with a large number of grid-side converter stations, it will be very difficult to set a simple power distribution relationship between different converter stations. Summary of the invention

[0003] The present application provides a control method, device and equipment for dynamic power distribution of a flexible direct current transmission system, which is used to solve the technical problem that the power distribution control of existing multi-terminal direct current transmission uses a master-slave control method or a voltage droop control method, and there is difficulty in controlling power distribution.

[0004] In order to achieve the above objectives, this application provides the following technical solutions:

[0005] On the one hand, a control method for dynamic power distribution of a flexible direct current transmission system is provided, comprising the following steps:

[0006] A central control center and a sub-control center in communication with the central control center are provided in the coordinated DC voltage control strategy of the multi-terminal DC transmission system, and each onshore converter station of the multi-terminal DC transmission system is provided with the sub-control center;

[0007] Obtaining a voltage reference value, electrical quantity data and a topological equivalent circuit diagram of the multi-terminal direct current transmission system;

[0008] The centralized control center adopts PI control processing according to the voltage reference value and the electrical quantity data to obtain the total d-axis current; and the centralized control center adopts optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power distribution coefficient allocated to each of the onshore converter stations;

[0009] The centralized control center allocates active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient;

[0010] The sum of the power allocation coefficients of all the onshore converter stations is 1.

[0011] Preferably, the content of obtaining the power allocation coefficient allocated to each of the onshore converter stations by using optimal power flow processing according to the electrical quantity data and the topological equivalent circuit includes:

[0012] Obtaining the line resistance of each of the onshore converter stations according to the topological equivalent circuit diagram;

[0013] Determine the current ratio of each of the onshore converter stations according to the total current of the electrical quantity parameter and the line resistance of each of the onshore converter stations using the minimum transmission loss principle of the optimal power flow;

[0014] Determining a power allocation coefficient of each of the onshore converter stations according to the current ratio;

[0015] The current ratio is used as the ratio of the power allocation coefficients in each of the onshore converter stations.

[0016] Preferably, the expression of the minimum transmission loss principle is:

[0017]

[0018]

[0019] Where n is the total number of onshore converter stations in the multi-terminal DC transmission system, I dci is the current of the i-th onshore converter station, R i is the line resistance of the i-th onshore converter station, I dc The total current is an electrical quantity parameter.

[0020] Preferably, the content of obtaining the total d-axis current by adopting PI control processing according to the voltage reference value and the electrical quantity data includes: calculating the total voltage according to the voltage reference value and the electrical quantity data to obtain the voltage difference; and adopting PI control processing on the voltage difference to obtain the total d-axis current.

[0021] Preferably, the content of allocating active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient includes:

[0022] Calculating according to the power allocation coefficient and the total d-axis current of each of the onshore converter stations to obtain an operating current corresponding to each of the onshore converter stations;

[0023] Determining the operating power of the corresponding onshore converter station according to the operating current and the line resistance of each onshore converter station;

[0024] Active power is allocated to the corresponding onshore converter station according to the operating power to control the DC voltage of the corresponding onshore converter station.

[0025] In another aspect, a control device for dynamic power distribution of a flexible direct current transmission system is provided, comprising a control setting module, a data acquisition module, a processing and calculation module, and a power distribution module;

[0026] The control setting module is used to set a central control center and a sub-control center in communication connection with the central control center in a coordinated DC voltage control strategy of a multi-terminal DC transmission system, and each onshore converter station of the multi-terminal DC transmission system is provided with the sub-control center;

[0027] The data acquisition module is used to acquire the voltage reference value, electrical quantity data and topological equivalent circuit diagram of the multi-terminal direct current transmission system;

[0028] The processing and calculation module is used to adopt PI control processing according to the voltage reference value and the electrical quantity data to obtain the total d-axis current; and the centralized control center adopts optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power distribution coefficient allocated to each of the onshore converter stations;

[0029] The power allocation module is used to allocate active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient;

[0030] The sum of the power allocation coefficients of all the onshore converter stations is 1.

[0031] Preferably, the power allocation module includes a first calculation submodule and a second calculation submodule;

[0032] The first calculation submodule is used to calculate the voltage difference according to the voltage reference value and the total voltage of the electrical quantity data; and to obtain the total d-axis current by applying PI control to the voltage difference;

[0033] The second calculation submodule is used to obtain the line resistance at each of the onshore converter stations according to the topological equivalent circuit diagram; determine the current ratio of each of the onshore converter stations according to the total current of the electrical quantity parameters and the line resistance at each of the onshore converter stations using the minimum transmission loss principle of the optimal power flow; determine the power distribution coefficient of each of the onshore converter stations according to the current ratio; and the current ratio is used as the ratio of the power distribution coefficients in each of the onshore converter stations.

[0034] Preferably, the expression of the minimum transmission loss principle is:

[0035]

[0036]

[0037] Where n is the total number of onshore converter stations in the multi-terminal DC transmission system, Idci is the current of the i-th onshore converter station, R i is the line resistance of the i-th onshore converter station, I dc The total current is an electrical quantity parameter.

[0038] Preferably, the power distribution module is also used to calculate the operating current corresponding to each of the onshore converter stations based on the power distribution coefficient and the total d-axis current of each of the onshore converter stations; determine the operating power corresponding to the onshore converter station based on the operating current and the line resistance of each of the onshore converter stations; and allocate active power to the corresponding onshore converter station according to the operating power to control the DC voltage of the corresponding onshore converter station.

[0039] In another aspect, a terminal device is provided, comprising a processor and a memory;

[0040] The memory is used to store program codes and transmit the program codes to the processor;

[0041] The processor is used to execute the above-mentioned control method for dynamic power distribution of the flexible direct current transmission system according to the instructions in the program code.

[0042] The control method, device and equipment for dynamic power distribution of the flexible direct current transmission system, the control method for dynamic power distribution of the flexible direct current transmission system, including setting a central control center and a sub-control center connected to the central control center in communication with the central control center in the coordinated direct current voltage control strategy of the multi-terminal direct current transmission system, each onshore converter station of the multi-terminal direct current transmission system is provided with a sub-control center; obtaining the voltage reference value, electrical quantity data and topological equivalent circuit diagram of the multi-terminal direct current transmission system; the central control center adopts PI control processing according to the voltage reference value and the electrical quantity data to obtain the total d-axis current; and the central control center adopts optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power distribution coefficient distributed to each onshore converter station; the central control center distributes active power to the corresponding onshore converter station according to the total d-axis current and the power distribution coefficient.

[0043] It can be seen from the above technical scheme that the present application has the following advantages: the control method for dynamic power distribution of the flexible direct current transmission system obtains the total d-axis current and the power distribution coefficient distributed to each onshore converter station by analyzing the data of the multi-terminal direct current transmission system through the centralized control center, distributes active power to the corresponding onshore converter station, and realizes flexible distribution control of active power for the onshore converter station; the sub-control center controls the operation of the corresponding onshore converter station according to the active power, so that the centralized control center and the sub-control center cooperate with each other to realize the joint control of the DC voltage by multiple onshore converter stations; the technical problem of difficulty in controlling power distribution in the existing multi-terminal direct current transmission power distribution control using the master-slave control mode or the voltage droop control mode is solved.

[0044] The control device for dynamic power distribution of the flexible DC transmission system realizes the joint control of DC voltage by multiple onshore converter stations through the cooperation of the control setting module, the data acquisition module, the processing and calculation module and the power distribution module. At the same time, under the premise of ensuring accurate voltage control, the flexible distribution control of active power of the onshore converter stations is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0046] Figure 1 A flowchart of the steps of the control method for dynamic power distribution of a flexible direct current transmission system according to an embodiment of the present application;

[0047] Figure 2 A framework diagram of coordinated DC voltage control in a control method for dynamic power distribution of a flexible DC power transmission system described in an embodiment of the present application;

[0048] Figure 3 A topological equivalent circuit diagram of a multi-terminal direct current transmission system in a control method for dynamic power distribution of a flexible direct current transmission system described in an embodiment of the present application;

[0049] Figure 4 A voltage and current characteristic curve diagram of controlling an onshore converter station by coordinating a DC voltage control strategy in a control method for dynamic power distribution of a flexible DC transmission system described in an embodiment of the present application;

[0050] Figure 5 It is a curve diagram of electrical quantities of an onshore converter station in the control method for dynamic power distribution of a flexible direct current transmission system described in an embodiment of the present application;

[0051] Figure 6 In the control method for dynamic power distribution of the flexible direct current transmission system described in the embodiment of the present application, when the power distribution ratio K i The electrical quantity curve of the onshore converter station changes;

[0052] Figure 7 It is a curve diagram of electrical quantities of an onshore converter station with wind speed variation in the control method for dynamic power distribution of a flexible direct current transmission system described in an embodiment of the present application;

[0053] Figure 8 A schematic diagram of a framework of a control device for dynamic power distribution of a flexible direct current transmission system according to an embodiment of the present application;

[0054] Fig. 9 A schematic diagram of a terminal device according to an embodiment of the present application;

[0055] Fig.10 This is the control block diagram of the existing master station;

[0056] Fig.11 This is the control block diagram of the existing slave station;

[0057] Fig.12 The power distribution characteristic diagram of the existing grid-side converter station power master-slave control;

[0058] Fig.13 The power distribution characteristic diagram of the power voltage droop control of the existing grid-side converter station;

[0059] Fig.14 This is the DC voltage droop control block diagram of the existing grid-side converter station. DETAILED DESCRIPTION

[0060] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0061] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0062] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0063] In the embodiment of the present application, for the power distribution of multi-terminal DC transmission in the master-slave control mode, if a converter station on the grid side is used as the master station to control the DC grid voltage, and the remaining converter stations are used as slave stations to control their respective output powers; wherein the master station adopts a control strategy of fixed DC voltage, the control block diagram is as follows: Fig.10 As shown; the slave station adopts a fixed active power control strategy, and the control block diagram is as follows Fig.11 As shown. The communication system ensures that there is only one converter station as the master station. When the master station fails, another master station that controls the DC voltage can be quickly found. As a balancing node, the master station emits or absorbs enough active power to maintain the power balance in the multi-terminal DC network. When the slave station adopts constant power control, the master station will bear all wind power fluctuations. This is similar to the balancing node control in the AC power grid, which places high demands on the power grid to which the master station is connected. The master station lacks power control capabilities and often cannot meet the access standards of the local power grid, especially the weak power grid. Fig.12 As shown, according to the voltage and current characteristic curve of the above control strategy, if the master station has sufficient capacity, flexible allocation of the active power of the slave stations can be achieved.

[0064] For the power distribution of multi-terminal DC transmission in voltage droop control mode, the power transmitted by each grid-side converter station can be obtained by Fig.13 The DC voltage droop curve shown in the figure can be used to control the DC network. It can also be understood as exchanging the DC voltage deviation of the DC network for power balance in the network. Each grid-side converter station has its own linear relationship between DC voltage and current. This coordinated control method is similar to the frequency droop control in the AC power grid, except that the control target becomes the DC voltage. The control strategy of each grid-side converter station is as follows: Fig.14 As shown, the reference value of the DC voltage outer loop is From the DC voltage-current droop equation However, for a complex multi-terminal DC network with a large number of grid-side converter stations, it becomes very difficult to set a simple power distribution relationship between different converter stations.

[0065] Multi-terminal DC transmission systems have important application prospects for offshore wind farms. The requirements for DC voltage control and dynamic allocation of active power are very important for multi-terminal DC transmission control systems. However, the disadvantage of conventional voltage droop control methods is that it is difficult to control the DC voltage to a fixed value when the active power fluctuates. The voltage margin method actually only uses one converter station to control the DC voltage at a time.

[0066] The embodiments of the present application provide a control method, device and equipment for dynamic power distribution of a flexible direct current transmission system, which solves the technical problem that the power distribution control of existing multi-terminal direct current transmission uses a master-slave control method or a voltage droop control method, and there is difficulty in controlling power distribution.

[0067] Embodiment 1:

[0068] Figure 1 This is a flowchart of the steps of the control method for dynamic power distribution of a flexible direct current transmission system according to an embodiment of the present application. Figure 2 A framework diagram of coordinated DC voltage control in a control method for dynamic power distribution in a flexible DC power transmission system described in an embodiment of the present application.

[0069] like Figure 1 As shown, the embodiment of the present application provides a control method for dynamic power distribution of a flexible direct current transmission system, comprising the following steps:

[0070] S1. In the coordinated DC voltage control strategy of the multi-terminal DC transmission system, a central control center and a sub-control center connected to the central control center are set, and each onshore converter station of the multi-terminal DC transmission system is provided with a sub-control center.

[0071] It should be noted that if Figure 2 As shown, in step S1, a coordinated DC voltage control strategy is set on the multi-terminal DC transmission system. The coordinated DC voltage control strategy means that the multi-terminal DC transmission system should have a centralized control center, which controls the operation of all onshore converter stations on the multi-terminal DC transmission system. At the same time, each onshore converter station should have its own local control center (such as a sub-control center).

[0072] In the embodiment of the present application, the disadvantage of the master-slave control mode that only one converter station actually controls the DC voltage is taken into account, and the deficiency that the automatic distribution of power in the voltage droop control mode is at the expense of voltage deviation. The coordinated DC voltage control strategy proposed by the control method for dynamic power distribution of the flexible DC transmission system combines the advantages of the two, and realizes the joint control of DC voltage by multiple onshore converter stations. At the same time, under the premise of ensuring accurate voltage control, the flexible distribution control of active power is realized for the onshore converter stations. The coordinated DC voltage control strategy requires the use of communication equipment to perform global and local control of multiple onshore converter stations on the grid side. By placing the control loop of the DC voltage in the centralized control center of global control, other parts of the control system (such as the control strategy for fixed active power) still remain in the sub-control center in each converter station.

[0073] It should be noted that the coordinated DC voltage control strategy requires communication, and it is necessary to consider the way to transmit information. The communication of the coordinated DC voltage control strategy can be achieved through microwave, satellite and optical fiber. Although communication is necessary, the loss of a signal at an onshore converter station will not affect the stability of the DC cable. The probability of communication failure can be reduced by installing monitoring equipment.

[0074] S2. Obtain the voltage reference value V of the multi-terminal DC transmission system dc*, electrical quantity data and topological equivalent circuit diagram.

[0075] It should be noted that in step S2, data of the multi-terminal DC power transmission system is obtained to provide data for subsequent steps. In this embodiment, the electrical quantity data includes the total current and total voltage outputted from the multi-terminal DC power transmission system to the grid side.

[0076] S3. The centralized control center uses PI control processing according to the voltage reference value and electrical quantity data to obtain the total d-axis current; and the centralized control center uses optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power allocation coefficient allocated to each onshore converter station. The sum of the power allocation coefficients of all onshore converter stations is 1.

[0077] It should be noted that in step S3, the coordinated DC voltage control strategy set in step S1 processes the data obtained according to step S2 to obtain the power distribution coefficient allocated to each onshore converter station and the total d-axis current output to each onshore converter station on the grid side.

[0078] In the embodiments of the present application, the Optimal Power Flow (OPF) refers to finding the power flow distribution that satisfies all operating constraints and makes a certain performance indicator of the system (such as power generation cost or network loss) reach the optimal value by adjusting the available control variables (such as generator output power, adjustable transformer taps, etc.) under given power system structural parameters and load conditions. The optimal power flow not only considers the active load of the system, but also the optimal distribution of reactive load, while considering the upper and lower limits of active and reactive power of each power generation unit, the upper and lower limits of the voltage of each node, etc.

[0079] S4. The centralized control center allocates active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient.

[0080] It should be noted that in step S4, active power is allocated to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient of each onshore converter station obtained in step S3, and the sub-control center controls the operation of the corresponding onshore converter station according to the active power, thereby realizing the joint control of the DC voltage by multiple onshore converter stations. At the same time, under the premise of ensuring precise voltage control, flexible distribution control of active power is realized for the onshore converter station.

[0081] The present application provides a control method for dynamic power distribution of a flexible direct current transmission system, comprising setting a central control center and a sub-control center in communication with the central control center in a coordinated direct current voltage control strategy of a multi-terminal direct current transmission system, wherein each onshore converter station of the multi-terminal direct current transmission system is provided with a sub-control center; obtaining a voltage reference value, electrical quantity data and a topological equivalent circuit diagram of the multi-terminal direct current transmission system; the central control center adopts PI control processing according to the voltage reference value and the electrical quantity data to obtain a total d-axis current; and the central control center adopts optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain a power distribution coefficient distributed to each onshore converter station; the central control center distributes active power to the corresponding onshore converter station according to the total d-axis current and the power distribution coefficient. The control method for dynamic power distribution of the flexible direct current transmission system obtains the total d-axis current and the power distribution coefficient distributed to each onshore converter station by analyzing the data of the multi-terminal direct current transmission system through the centralized control center, distributes active power to the corresponding onshore converter station, and realizes flexible distribution control of active power for the onshore converter station; the sub-control center controls the operation of the corresponding onshore converter station according to the active power, so that the centralized control center and the sub-control center cooperate with each other to realize the joint control of the direct current voltage by multiple onshore converter stations; the technical problem of the difficulty in controlling power distribution in the existing multi-terminal direct current transmission power distribution control using the master-slave control mode or the voltage droop control mode is solved.

[0082] Figure 3 It is a topological equivalent circuit diagram of a multi-terminal direct current transmission system in a control method for dynamic power distribution of a flexible direct current transmission system described in an embodiment of the present application. Figure 3 It is an equivalent circuit of a five-terminal DC transmission system, where R1, R2, and R3 are the line resistances of the DC cables connected to the onshore converter station on the grid side, and R4 and R5 are the line resistances of the DC cables connected to the converter stations on the two wind farm sides. dc1 -V dc5 and I dc1 -I dc5 is the DC voltage and DC current of the corresponding converter station. V dc0 It is the total voltage output by the multi-terminal DC transmission system, which can also be understood as the bus voltage, which is detected and monitored by the distribution center. dc0 is the total current output by the multi-terminal DC transmission system.

[0083] In one embodiment of the present application, the content of obtaining the power distribution coefficient allocated to each onshore converter station by using the optimal power flow processing according to the electrical quantity data and the topological equivalent circuit includes:

[0084] Obtain the line resistance at each onshore converter station according to the topological equivalent circuit diagram;

[0085] According to the total current of the electrical quantity parameters and the line resistance at each onshore converter station, the current ratio of each onshore converter station is determined by adopting the minimum transmission loss principle of the optimal power flow;

[0086] Determine the power allocation coefficient of each onshore converter station based on the current ratio;

[0087] Among them, the current ratio is used as the ratio of the power allocation coefficients in each onshore converter station;

[0088] The expression of the minimum transmission loss principle is:

[0089]

[0090]

[0091] Where n is the total number of onshore converter stations in the multi-terminal DC transmission system, I dci is the current of the i-th onshore converter station, R i is the line resistance of the i-th onshore converter station, I dc The total current is an electrical quantity parameter.

[0092] It should be noted that the proportion of active power transmitted to each grid-side onshore converter station is determined by the coefficient K i The coefficient K can be selected according to the principle of minimum transmission loss. i .by Figure 3 As an example, the minimum transmission loss principle is min{I dc1 2 *R1+I dc2 2 *R2+I dc3 2 *R3},I dc0 =I dc1 +I dc2 +I dc3 From this, the current ratio of the onshore converter station 1, onshore converter station 2 and onshore converter station 3 can be deduced, and the current ratio is I dc1 :I dc2 :I dc3 =The ratio of power distribution coefficient K1:K2:K3. V dc0 *I dc0 =V dc4 *I dc4 +V dc5 *I dc5 =V dc1 *I dc1 +V dc2 *I dc2 +V dc3 *I dc3; The sum of the power allocation coefficients of all onshore converter stations is 1. Derived: V dc0 *I dc0 =V dc1 *K1*I dc0 +V dc2 *K2*I dc0 +V dc3 *K3*I dc0 , K1+K2+K3=1.

[0093] like Figure 2 As shown, in one embodiment of the present application, the content of obtaining the total d-axis current by using PI control processing according to the voltage reference value and the electrical quantity data includes: calculating the total voltage according to the voltage reference value and the electrical quantity data to obtain the voltage difference; and using PI control processing on the voltage difference to obtain the total d-axis current i d .

[0094] It should be noted that the voltage difference refers to the voltage reference value V dc *Total voltage V with electrical quantity data dc In this embodiment, the voltage difference is processed by a PI controller to obtain the total d-axis current.

[0095] Figure 4 This is a voltage and current characteristic curve diagram of controlling the onshore converter station by coordinating the DC voltage control strategy in the control method for dynamic power distribution of the flexible DC transmission system described in an embodiment of the present application.

[0096] In one embodiment of the present application, the content of allocating active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient includes:

[0097] According to the power allocation coefficient and the total d-axis current of each onshore converter station, the operating current corresponding to each onshore converter station is obtained;

[0098] Determine the operating power of the corresponding onshore converter station according to the operating current and line resistance of each onshore converter station;

[0099] Active power is distributed to the corresponding onshore converter station according to the operating power to control the DC voltage of the corresponding onshore converter station.

[0100] It should be noted that the operating current i dc =Power distribution coefficient K i ×Total d-axis current i d . Operating power P = operating current i dc 2 × line resistance. In this embodiment, the operating current i of each onshore converter station is dc It can be given by the sub-control center, such as Figure 4As shown. In the normal state, each onshore converter station plays a certain role in controlling the DC voltage.

[0101] Figure 5 It is the electrical quantity curve diagram of the onshore converter station in the control method for power dynamic distribution of the flexible DC transmission system described in the embodiments of the present application. Figure 6 It is the electrical quantity curve diagram of the onshore converter station when the power distribution ratio K i changes in the control method for power dynamic distribution of the flexible DC transmission system described in the embodiments of the present application. Figure 7 It is the electrical quantity curve diagram of the onshore converter station when the wind speed changes in the control method for power dynamic distribution of the flexible DC transmission system described in the embodiments of the present application.

[0102] In the embodiments of the present application, the control method for power dynamic distribution of the flexible DC transmission system is described by taking a five-terminal DC transmission system as an example. The rated powers of wind farm 1 and wind farm 2 based on doubly-fed induction generators are 200 MW and 150 MW respectively, and the rated powers of the three onshore converter stations on the grid side are all 200 MW, and the rated DC voltage is 320 kV. The parameters of the DC cable are shown in Table 1.

[0103] Table 1 shows the parameters of the DC cable in the five-terminal DC transmission system.

[0104]

[0105] According to the above parameters, the control effect of the control method for power dynamic distribution of the flexible DC transmission system is verified in the five-terminal DC transmission system under different operating conditions, and the operating conditions include system startup, steady-state operation, and wind speed fluctuation, etc.

[0106] It should be noted that the control effect of the control method for power dynamic distribution of the flexible DC transmission system is verified by starting the five-terminal DC transmission system (0 < t < 1.5 s). Specifically: According to Figure 3 The five-terminal DC transmission system shown is composed of 5 converter stations and two wind farms. Initially, the three onshore converter stations on the grid side start first at 0.5 s to establish a stable DC voltage of 320 kV, and then the two converter stations on the wind farm side start at 1 s to establish a stable AC voltage. At 1.1 s, the two wind farms are connected to the DC transmission system and operate at the rated wind speed of 12 m / s to generate the rated power. From Figure 5 It can be seen that after the entire five-terminal DC transmission system starts at 1.1 s, the active powers absorbed by the three onshore converter stations on the grid side are different, and they are actually distributed in a ratio of 6:4:3 according to the ratio of the power distribution coefficients. This is the initial power distribution ratio set by the sub-control center.

[0107] The control effect of the control method for power dynamic distribution of the flexible DC transmission system is verified by the active power dynamic distribution (1.5 s < t < 2.3 s) of the five-terminal DC transmission system in the steady state. Specifically, by changing the power distribution coefficient K i to change the operating current or the d-axis current reference value of each onshore converter station, the purpose of regulating the active power can be achieved; this function of flexibly controlling the active power is very valuable because in this way, the active power can be distributed according to the power market, and power trading can be realized in this way. At 2 s, the power distribution coefficient K i of the active power changes from 6:4:3 to 1:1:1. Obviously, the process of power change is smooth and rapid. At the same time, from Figure 6 it can be seen that the DC voltage remains unchanged at the rated value during the process of power redistribution. Due to the influence of the line resistance, the active power does not flow precisely into different onshore converter stations according to the ratio of the power distribution coefficients in all onshore converter stations. If necessary, this difference can also be compensated by fine-tuning the power distribution coefficient K i because this regulation is independent of the line resistance.

[0108] The control effect of the control method for power dynamic distribution of the flexible DC transmission system is verified by the wind speed mutation (2.5 s < t < 4 s) of the five-terminal DC transmission system. Specifically, under the influence of the wind speed mutation, the stability performance of the five-terminal DC transmission system. At 2.5 s, the wind speed changes from 12 m / s to 8 m / s, and the wind power correspondingly changes from 350 MW to 180 MW. From Figure 7 it can be seen that the DC current changes with the decrease of the wind power. However, coordinating the DC voltage control strategy can keep the DC voltage unchanged at the rated value, and at the same time, the distribution ratio of the active power remains unchanged. If the voltage droop control strategy is adopted, the DC voltage will inevitably fluctuate due to the change of the active power. Even if this fluctuation range is controlled within ±10%, this change in the DC voltage cannot be ignored for the damage of power electronic devices.

[0109] Embodiment 2:

[0110] Figure 8 It is a schematic framework diagram of a control device for power dynamic distribution of a flexible DC transmission system described in an embodiment of the present application.

[0111] As Figure 8 shown, an embodiment of the present application provides a control device for power dynamic distribution of a flexible DC transmission system, including a control setting module 100, a data acquisition module 200, a processing and calculation module 300, and a power distribution module 400;

[0112] A control setting module 100 is used to set a central control center and a sub-control center in communication with the central control center in a coordinated DC voltage control strategy of a multi-terminal DC transmission system, and each onshore converter station of the multi-terminal DC transmission system is provided with a sub-control center;

[0113] The data acquisition module 200 is used to acquire the voltage reference value, electrical quantity data and topological equivalent circuit diagram of the multi-terminal direct current transmission system;

[0114] The processing and calculation module 300 is used to obtain the total d-axis current by using PI control processing according to the voltage reference value and the electrical quantity data; and the centralized control center uses the optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power distribution coefficient allocated to each onshore converter station;

[0115] A power distribution module 400, configured to distribute active power to a corresponding onshore converter station according to the total d-axis current and the power distribution coefficient;

[0116] Among them, the sum of the power allocation coefficients of all onshore converter stations is 1.

[0117] It should be noted that the content of the module in the control device for dynamic power distribution of the flexible direct current transmission system corresponds to the step content of the control method for dynamic power distribution of the flexible direct current transmission system. The step content of the control method for dynamic power distribution of the flexible direct current transmission system has been described in the first embodiment, and the content of the module in the control device for dynamic power distribution of the flexible direct current transmission system will not be repeated in this embodiment. The control device for dynamic power distribution of the flexible direct current transmission system realizes the joint control of the DC voltage by multiple onshore converter stations through the cooperation of the control setting module, the data acquisition module, the processing and calculation module and the power distribution module, and at the same time, realizes the flexible distribution control of active power of the onshore converter stations under the premise of ensuring accurate voltage control.

[0118] In one embodiment of the present application, the processing calculation module 300 includes a first calculation submodule and a second calculation submodule;

[0119] The first calculation submodule is used to calculate the total voltage according to the voltage reference value and the electrical quantity data to obtain the voltage difference; the voltage difference is processed by PI control to obtain the total d-axis current;

[0120] The second calculation submodule is used to obtain the line resistance at each onshore converter station according to the topological equivalent circuit diagram; determine the current ratio of each onshore converter station according to the total current of the electrical quantity parameters and the line resistance at each onshore converter station using the minimum transmission loss principle of the optimal power flow; determine the power distribution coefficient of each onshore converter station according to the current ratio; the current ratio is used as the ratio of the power distribution coefficients in each onshore converter station.

[0121] In one embodiment of the present application, the expression of the minimum transmission loss principle is:

[0122]

[0123]

[0124] Where n is the total number of onshore converter stations in the multi-terminal DC transmission system, I dci is the current of the i-th onshore converter station, R i is the line resistance of the i-th onshore converter station, I dc The total current is an electrical quantity parameter.

[0125] In one embodiment of the present application, the power distribution module 400 is also used to obtain the operating current corresponding to each shore converter station based on the power distribution coefficient and the total d-axis current of each shore converter station; determine the operating power of the corresponding shore converter station based on the operating current and line resistance of each shore converter station; and allocate active power to the corresponding shore converter station according to the operating power to control the DC voltage of the corresponding shore converter station.

[0126] Embodiment three:

[0127] Fig. 9 A schematic diagram of a terminal device described in an embodiment of the present application.

[0128] like Fig. 9 As shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0129] A memory, used for storing program codes and transmitting the program codes to a processor;

[0130] The processor is used to execute the above-mentioned control method for dynamic power distribution of the flexible direct current transmission system according to the instructions in the program code.

[0131] It should be noted that the processor is used to execute the steps in the above-mentioned control method for dynamic power allocation of a flexible DC transmission system according to the instructions in the program code. Alternatively, the processor implements the functions of each module / unit in the above-mentioned system / device embodiments when executing the computer program.

[0132] Exemplarily, the computer program may be divided into one or more modules / units, one or more modules / units are stored in a memory and executed by a processor to complete the present application. One or more modules / units may be a series of computer program instruction segments capable of completing a specific function, and the instruction segments are used to describe the execution process of the computer program in a terminal device.

[0133] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The terminal device may include, but is not limited to, a processor and a memory. Those skilled in the art will appreciate that this does not constitute a limitation on the terminal device, and may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal device may also include input and output devices, network access devices, buses, etc.

[0134] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (dSIC), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0135] The memory may be an internal storage unit of the terminal device, such as a hard disk or memory of the terminal device. The memory may also be an external storage device of the terminal device, such as a plug-in hard disk, a smart memory card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the terminal device. Furthermore, the memory may include both an internal storage unit of the terminal device and an external storage device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory may also be used to temporarily store data that has been output or is to be output.

[0136] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0137] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0138] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0139] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0140] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0141] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A control method for dynamic power distribution of a flexible direct current transmission system, characterized in that: The following steps are involved: A central control center and a sub-control center in communication with the central control center are provided in the coordinated DC voltage control strategy of the multi-terminal DC transmission system, and each onshore converter station of the multi-terminal DC transmission system is provided with the sub-control center; Obtaining a voltage reference value, electrical quantity data and a topological equivalent circuit diagram of the multi-terminal direct current transmission system; The centralized control center adopts PI control processing according to the voltage reference value and the electrical quantity data to obtain the total d-axis current; and the centralized control center adopts optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power distribution coefficient allocated to each of the onshore converter stations; The centralized control center allocates active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient; The sum of the power allocation coefficients of all the onshore converter stations is 1.

2. The control method for dynamic power distribution of a flexible direct current transmission system according to claim 1, characterized in that: The content of obtaining the power distribution coefficient allocated to each of the onshore converter stations by using the optimal power flow processing according to the electrical quantity data and the topological equivalent circuit includes: Obtaining the line resistance of each of the onshore converter stations according to the topological equivalent circuit diagram; Determine the current ratio of each of the onshore converter stations according to the total current of the electrical quantity parameter and the line resistance of each of the onshore converter stations using the minimum transmission loss principle of the optimal power flow; Determining a power allocation coefficient of each of the onshore converter stations according to the current ratio; The current ratio is used as the ratio of the power allocation coefficients in each of the onshore converter stations.

3. The control method for dynamic power distribution of a flexible direct current transmission system according to claim 2, characterized in that: The expression of the minimum transmission loss principle is: Where n is the total number of onshore converter stations in the multi-terminal DC transmission system, I dci is the current of the i-th onshore converter station, R i is the line resistance of the i-th onshore converter station, I dc The total current is an electrical quantity parameter.

4. The control method for dynamic power distribution of a flexible direct current transmission system according to claim 1, characterized in that: The content of obtaining the total d-axis current by using PI control processing according to the voltage reference value and the electrical quantity data includes: calculating the total voltage according to the voltage reference value and the electrical quantity data to obtain the voltage difference; and obtaining the total d-axis current by using PI control processing on the voltage difference.

5. The control method for dynamic power distribution of a flexible direct current transmission system according to claim 2 or 3, characterized in that: The content of allocating active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient includes: Calculating according to the power allocation coefficient and the total d-axis current of each of the onshore converter stations to obtain an operating current corresponding to each of the onshore converter stations; Determining the operating power of the corresponding onshore converter station according to the operating current and the line resistance of each onshore converter station; Active power is allocated to the corresponding onshore converter station according to the operating power to control the DC voltage of the corresponding onshore converter station.

6. A control device for dynamic power distribution of a flexible direct current transmission system, characterized in that: It includes a control setting module, a data acquisition module, a processing and calculation module and a power distribution module; The control setting module is used to set a central control center and a sub-control center in communication connection with the central control center in a coordinated DC voltage control strategy of a multi-terminal DC transmission system, and each onshore converter station of the multi-terminal DC transmission system is provided with the sub-control center; The data acquisition module is used to acquire the voltage reference value, electrical quantity data and topological equivalent circuit diagram of the multi-terminal direct current transmission system; The processing and calculation module is used to adopt PI control processing according to the voltage reference value and the electrical quantity data to obtain the total d-axis current; and the centralized control center adopts optimal power flow processing according to the electrical quantity data and the topological equivalent circuit diagram to obtain the power distribution coefficient allocated to each of the onshore converter stations; The power allocation module is used to allocate active power to the corresponding onshore converter station according to the total d-axis current and the power allocation coefficient; The sum of the power allocation coefficients of all the onshore converter stations is 1.

7. The control device for dynamic power distribution of a flexible direct current transmission system according to claim 6, characterized in that: The processing and computing module includes a first computing submodule and a second computing submodule; The first calculation submodule is used to calculate the voltage difference according to the voltage reference value and the total voltage of the electrical quantity data; and to obtain the total d-axis current by applying PI control to the voltage difference; The second calculation submodule is used to obtain the line resistance of each of the onshore converter stations according to the topological equivalent circuit diagram; determine the current ratio of each of the onshore converter stations according to the total current of the electrical quantity parameter and the line resistance of each of the onshore converter stations using the minimum transmission loss principle of the optimal power flow; The power allocation coefficient of each of the onshore converter stations is determined according to the current ratio; the current ratio is used as the ratio of the power allocation coefficients in each of the onshore converter stations.

8. The control device for dynamic power distribution of a flexible direct current transmission system according to claim 7, characterized in that: The expression of the minimum transmission loss principle is: Where n is the total number of onshore converter stations in the multi-terminal DC transmission system, I dci is the current of the i-th onshore converter station, R i is the line resistance of the i-th onshore converter station, I dc The total current is an electrical quantity parameter.

9. The control device for dynamic power distribution of a flexible direct current transmission system according to claim 7, characterized in that: The power distribution module is also used to calculate the operating current corresponding to each of the onshore converter stations based on the power distribution coefficient and the total d-axis current of each of the onshore converter stations; determine the operating power corresponding to the onshore converter station based on the operating current and the line resistance of each of the onshore converter stations; and allocate active power to the corresponding onshore converter station according to the operating power to control the DC voltage of the corresponding onshore converter station.

10. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program codes and transmit the program codes to the processor; The processor is used to execute the control method for dynamic power distribution of a flexible direct current transmission system according to any one of claims 1 to 5 according to the instructions in the program code.

Images