Control method and control device of series voltage source converter valve group

Abstract

The present application proposes a control method and a control device for a series voltage source converter valve group, wherein the series voltage source converter valve group includes at least two series voltage source converter valve groups, and the control method includes determining a voltage source converter valve group that performs balance control in the series voltage source converter valve group, and marking the voltage source converter valve group that performs balance control as a selected operating valve group; obtaining a DC voltage operating value of the selected operating valve group; determining a DC voltage reference value of the selected operating valve group; determining a phase compensation amount of the selected operating valve group using the DC voltage operating value and the DC voltage reference value; and determining a final phase reference value of the selected operating valve group using the phase compensation amount. According to an embodiment of the present application, by obtaining the final phase reference value of the operating valve group participating in the balance control, the DC voltage of the voltage source converter valve group is balanced, thereby ensuring the stable operation of the DC system.

Description

Technical Field

[0001] The present application relates to the field of direct current power transmission, and in particular to a control method and a control device for a series voltage source converter valve group. Background Art

[0002] The UHV flexible DC transmission system has the key technical advantages of long transmission distance, large transmission capacity, no charging power limit for DC lines, decoupling of new energy electric fields and AC power grids, and suitable for building a multi-energy complementary new energy DC power grid transmission system. It is an important technical means for large-scale centralized transmission of new energy. In the process of building a new power system in the future, large-scale new energy UHV flexible DC transmission will surely play an important role.

[0003] With the increasing penetration of new energy and power electronic equipment, the power system has a tendency to reduce inertia and weaken system strength, and the stability problem is becoming more serious. Grid-forming (GFM) control technology can improve the voltage and frequency support capabilities of the converter, enhance the stability of the power system, and can effectively solve the problems of weak system access, low inertia and weak voltage support in the "double high" power system.

[0004] Due to the large capacity and high voltage level of the UHV flexible DC transmission system, the use of a single voltage source converter valve group solution will make it difficult to manufacture and transport equipment such as converter transformers; when multiple voltage source converter valve groups are connected in series, equipment manufacturing and transportation are easy to achieve. Therefore, the series voltage source converter valve group solution is generally used in UHV flexible DC transmission. At the same time, in order to achieve the independence of control between valve groups, an independent valve control system is configured between each pole series voltage source converter valve group. However, unlike a single valve group, the converter station of the series voltage source converter valve group has an unbalanced DC voltage between valve groups, which will result in a higher voltage in the submodule of one valve group and reactive circulating current of the series voltage source converter valve group. In severe cases, the valve group overvoltage protection will be activated, resulting in a tripping event.

[0005] Grid-type control can be divided into two control modes, closed-loop and open-loop, according to whether there is inner-loop current control. For the closed-loop control mode of grid-type control, the active current compensation amount of the existing grid-following (GFL) control can be used to solve the voltage balancing problem of the series voltage source converter valve group through inner-loop current control. However, for the open-loop control mode of grid-type control, there is currently no voltage balancing method for the series voltage source converter valve group. Summary of the invention

[0006] The present application aims to propose a control method and a control device for a series voltage source converter valve group, so as to solve the problem of DC voltage balancing of each voltage source converter valve group when the DC pole of a grid-type DC transmission system adopts two or more voltage source converter valve groups to operate in series.

[0007] According to one aspect of the present application, a control method for a series voltage source converter valve group is proposed, wherein the series voltage source converter valve group includes at least two series-connected voltage source converter valve groups, and the control method includes: determining a voltage source converter valve group that performs balancing control among the series voltage source converter valve groups, and marking the voltage source converter valve group that performs balancing control as a selected operating valve group; obtaining a DC voltage operating value of the selected operating valve group; determining a DC voltage reference value of the selected operating valve group; determining a phase compensation amount of the selected operating valve group using the DC voltage operating value and the DC voltage reference value; and determining a final phase reference value of the selected operating valve group using the phase compensation amount.

[0008] According to some embodiments, the series voltage source converter valve group adopts a grid-type control strategy, wherein the grid-type control strategy includes: VF control, droop control, virtual synchronization control, matching control, virtual oscillator control and / or DC voltage synchronization control.

[0009] According to some embodiments, the phase output process or voltage amplitude output process of the series voltage source converter valve group includes master-slave control, wherein, when the master-slave control is adopted, one of the voltage source converter valve groups in the series voltage source converter valve group is selected as the master control valve group, and the other voltage source converter valve groups are selected as slave control valve groups, wherein the phase and voltage amplitude of the slave control valve group change with the master control valve group; and after the phase and voltage amplitude of the series voltage source converter valve group are output, the control mode of the networked control strategy includes a closed-loop control mode with voltage and current control or an open-loop control mode without voltage and current control.

[0010] According to some embodiments, determining the voltage source converter valve group for balancing control in the series voltage source converter valve group includes: selecting all operating voltage source converter valve groups in the series voltage source converter valve group for balancing control; selecting a slave control valve group in the series voltage source converter valve group for balancing control; or when only two voltage source converter valve groups in the series voltage source converter valve group are operating, selecting any voltage source converter valve group for balancing control.

[0011] According to some embodiments, obtaining the DC voltage operating value of the selected operating valve group includes: obtaining the output voltage measurement value of both ends of the selected operating valve group; and obtaining the DC voltage operating value of the selected operating valve group using the output voltage measurement value of both ends.

[0012] According to some embodiments, determining the DC voltage reference value of the selected operating valve group includes: obtaining the pole DC voltage operating value of the series voltage source converter valve group; and determining the DC voltage reference value of the selected operating valve group using the pole DC voltage operating value.

[0013] According to some embodiments, obtaining the pole DC voltage operating value of the series voltage source converter valve group includes: obtaining the DC voltage operating values ​​of all operating voltage source converter valve groups in the series voltage source converter valve group; and adding the DC voltage operating values ​​of all operating voltage source converter valve groups as the pole DC voltage operating value.

[0014] According to some embodiments, obtaining the pole DC voltage operating value of the series voltage source converter valve group includes: obtaining the DC voltage measurement value across the pole of the series voltage source converter valve group; and obtaining the pole DC voltage operating value of the series voltage source converter valve group using the DC voltage measurement value across the pole.

[0015] According to some embodiments, the control method further includes: determining a DC bias value of a bridge arm voltage of all operating valve groups; and performing DC voltage balancing control on the selected operating valve group using the phase compensation value and the bridge arm voltage DC bias value.

[0016] According to some embodiments, determining the DC bias of the bridge arm voltage of all operating valve groups includes: obtaining the pole DC voltage target value of the series voltage source converter valve group; equally dividing the pole DC voltage operating value according to the total number of voltage source converter valve groups operating in series at the pole where the series voltage source converter valve group is located, and using the equally divided value as the DC voltage target value of all operating valve groups; and using 1 / 2 of the DC voltage target value of all operating valve groups as the bridge arm voltage DC bias of all operating valve groups.

[0017] According to some embodiments, obtaining the target value of the polar DC voltage of the series voltage source converter valve group includes: when the series voltage source converter valve group is the farthest sending-end converter station, the target value of the polar DC voltage is the rated value of the DC line voltage; or when the series voltage source converter valve group is not the farthest sending-end converter station, the target value of the polar DC voltage is the rated voltage of the DC line minus the DC line voltage drop from the farthest sending-end converter station to the current station, wherein the DC line voltage drop is obtained by multiplying the DC current by the theoretical line impedance value.

[0018] According to some embodiments, the phase compensation amount of the selected operating valve group is determined using the DC voltage operating value and the DC voltage reference value, including: determining the DC voltage deviation amount of the selected operating valve group using the DC voltage operating value and the DC voltage reference value; and obtaining the phase compensation amount of the selected operating valve group using the DC voltage deviation amount.

[0019] According to some embodiments, the operating valve group includes only two voltage source converter valve groups connected in series, and the two voltage source converter valve groups connected in series are both the selected operating valve group, the two voltage source converter valve groups connected in series include a first voltage source converter valve group and a second voltage source converter valve group, and the phase compensation amount of the selected operating valve group is determined using the DC voltage operating value and the DC voltage reference value, including: respectively obtaining the DC voltage measurement values ​​of the first voltage source converter valve group and the second voltage source converter valve group; using the DC voltage measurement values ​​of the first voltage source converter valve group and the second voltage source converter valve group to calculate the DC voltage deviation of the first voltage source converter valve group; and using the DC voltage deviation to calculate the phase compensation amount of the selected operating valve group.

[0020] According to some embodiments, the phase compensation of the selected operating valve group is calculated using the DC voltage deviation, including: calculating the DC voltage deviation by proportional, integral, or proportional plus integral method to obtain the phase compensation of the selected operating valve group.

[0021] According to some embodiments, the control method further comprises: determining a phase reference quantity output by the selected operating valve group using a networked control strategy;

[0022] Determining a final phase reference value of the selected operating valve group using the phase compensation amount includes: determining a final phase reference value of the selected operating valve group using the phase compensation amount and the phase reference amount.

[0023] According to one aspect of the present application, a control device for a series voltage source converter valve group is proposed, wherein the series voltage source converter valve group includes at least two voltage source converter valve groups connected in series, and the control device includes: a voltage source converter valve group determination unit, used to determine the voltage source converter valve group that performs balance control in the series voltage source converter valve group, and mark the voltage source converter valve group that performs balance control as a selected operating valve group; a DC voltage operating value acquisition unit, used to acquire the DC voltage operating value of the selected operating valve group; a DC voltage reference value determination unit, used to determine the DC voltage reference value of the selected operating valve group; a phase compensation amount determination unit, used to determine the phase compensation amount of the selected operating valve group using the DC voltage operating value and the DC voltage reference value; and a final phase reference amount determination unit, used to determine the final phase reference value of the selected operating valve group using the phase compensation amount.

[0024] According to the embodiments of the present application, by obtaining the final phase reference value of the operating valve group participating in the balancing control, the final phase reference value can be used to control the voltage of the selected operating valve group, thereby balancing the DC voltage of the voltage source converter valve group, ensuring the stable operation of the DC system, and meeting the operating needs of the grid-type series flexible DC transmission system.

[0025] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. By describing the exemplary embodiments in detail with reference to the drawings, the above and other objectives, features and advantages of the present application will become more apparent.

[0027] Figure 1 A flow chart of a control method for a series voltage source converter valve group according to an exemplary embodiment of the present application is shown.

[0028] Figure 2 A flow chart of another control method of a series voltage source converter valve group according to an exemplary embodiment of the present application is shown.

[0029] Figure 3 A topological schematic diagram of a series voltage source converter valve group according to an exemplary embodiment of the present application is shown.

[0030] Figure 4 A schematic diagram showing the principle of a coordinated control method for a grid-type series voltage source converter valve group according to an exemplary embodiment of the present application is shown.

[0031] Figure 5 A block diagram of a control device for a series voltage source converter valve group according to an exemplary embodiment of the present application is shown.

[0032] Figure 6 A block diagram of a control device for another series voltage source converter valve group according to an exemplary embodiment of the present application is shown. DETAILED DESCRIPTION

[0033] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. In the figures, the same figures show the same or similar parts, and thus their repeated description will be omitted.

[0034] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices or operations may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0035] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0036] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0037] The specific embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0038] Figure 1 A flow chart of a control method for a series voltage source converter valve group according to an exemplary embodiment of the present application is shown. Figure 1 The illustrated embodiment includes step S101 , step S103 , step S105 , step S107 , and step S109 .

[0039] According to an embodiment of the present application, Figure 1 The series voltage source converter valve group includes at least two series voltage source converter valve groups. The series voltage source converter valve group adopts a grid-type control strategy, wherein the grid-type control strategy includes: VF control, droop control, virtual synchronization control, matching control, virtual oscillator control and / or DC voltage synchronization control.

[0040] The control process of the output phase reference value of the network control strategy is called the phase output link, and the control process of the output voltage amplitude reference value of the network control strategy is called the voltage amplitude output link. The phase and voltage amplitude output links of the series voltage source converter valve group can adopt master-slave control or independent control. When master-slave control is adopted, one voltage source converter valve group in the series voltage source converter valve group is selected as the master control valve group, and the other voltage source converter valve groups are selected as slave control valve groups. The phase and voltage amplitude of the slave control valve group change with the master control valve group. After the phase output link and the voltage amplitude link are output, either a closed-loop control method with voltage and current control or an open-loop control method without voltage and current control can be adopted.

[0041] like Figure 1 As shown, in step S101, the voltage source converter valve group performing balancing control in the series voltage source converter valve group is determined, and the voltage source converter valve group performing balancing control is marked as a selected operating valve group.

[0042] The series voltage source converter valve group includes a plurality of operating valve groups. In step S101, part of the operating valve groups may be selected for balancing control, or all of the operating valve groups may be selected for balancing control, which is not limited here.

[0043] For example, all operating voltage source converter valve groups in the series voltage source converter valve group are selected for balancing control; a slave control valve group in the series voltage source converter valve group is selected for balancing control; or

[0044] When only two of the series-connected voltage source converter valve groups are in operation, any one of the voltage source converter valve groups is selected for balancing control.

[0045] According to some embodiments, the selected operating valve group is marked as a selected operating valve group.

[0046] In step S103, the DC voltage operating value of the selected operating valve group is obtained.

[0047] According to an embodiment of the application, in step S103, first, the output voltage measurement value at both ends of the selected operating valve group is obtained; then, the DC voltage operating value of the selected operating valve group is obtained using the output voltage measurement value at both ends.

[0048] For example, first obtain the output voltage measurement value U of each valve group at both ends of the selected operating valve group for balancing control of the series voltage source converter valve group. dVH-i and U dVL-i Then, the difference between the two is calculated to obtain the DC voltage operating value U of the operating valve group selected for balancing control. dV-i , as shown in formula (1).

[0049] U dV-i =U dVH-i -U dVL-i ,i∈(1,…,N) (1)

[0050] Where N is a positive integer, U dVH-i and U dVL-i The output voltage measurement value across the selected operating valve group.

[0051] In step S105, a DC voltage reference value of the selected operating valve group is determined.

[0052] According to an embodiment of the present application, in step S105, first, the pole DC voltage operating value of the series voltage source converter valve group is obtained; and the DC voltage reference value of the selected operating valve group is determined using the pole DC voltage operating value.

[0053] In a specific embodiment, first, the DC voltage operation value U of the pole where the series voltage source converter valve group is located is obtained. dcP , and distribute the pole DC voltage operation value according to the total number N of voltage source converter valve groups operating in series at the pole, for example, according to average distribution, and use the averaged value as the DC voltage reference value U of each selected operating valve group for balancing control dVref-i , as shown in formula (2).

[0054]

[0055] Where N is a positive integer, U dVref-i is the DC voltage reference value, U dcP It is the DC voltage operating value.

[0056] According to some embodiments, first, the DC voltage operating values ​​of all operating voltage source converter valve groups in the series voltage source converter valve group are obtained; then, the DC voltage operating values ​​of all operating voltage source converter valve groups are added up to serve as the pole DC voltage operating value.

[0057] For example, in a specific embodiment, the DC voltage operating value U of the pole where the series voltage source converter valve group is located dcP How to obtain:

[0058] Firstly, the DC voltage operating values ​​of all the operating series voltage source converter valve groups are obtained;

[0059] Then, sum the DC voltage operating values ​​of all operating valve groups to obtain the DC operating voltage U of the pole where the series valve group is located. dcP , as shown in formula (3).

[0060]

[0061] Where N is a positive integer, UdcP is the pole DC voltage operating value, U dV-i It is the DC voltage operating value of the series voltage source converter valve group.

[0062] In some other embodiments, first, the DC voltage measurement values ​​across the poles of the series voltage source converter valve group are obtained; then, the DC voltage measurement values ​​across the poles are used to obtain the DC voltage operating values ​​of the poles of the series voltage source converter valve group.

[0063] For example, in a specific embodiment, the DC voltage operating value U of the pole where the series voltage source converter valve group is located dcP How to obtain:

[0064] First, obtain the DC voltage measurement value U at both ends of the series voltage source converter valve group dcPH and U dcPL ;

[0065] Then, the difference between the two is calculated to obtain the DC voltage operating value U of the pole where the series valve group is located. dcP , as shown in formula (4).

[0066] U dcP =U dcPH -U dcPL (4)

[0067] Among them, U dcP is the pole DC voltage operating value, U dcPH and U dcPL It is the measured value of the DC voltage at both ends of the series voltage source converter valve group.

[0068] In step S107, the phase compensation amount of the selected operating valve group is determined by using the DC voltage operating value and the DC voltage reference value.

[0069] In some embodiments, in order to obtain the phase compensation amount, first, the DC voltage deviation of the selected operating valve group is determined using the DC voltage operating value and the DC voltage reference value; then, the phase compensation amount of the selected operating valve group is obtained using the DC voltage deviation.

[0070] In a specific embodiment, the phase compensation amount acquisition step includes:

[0071] First, each valve group selected for balancing control is set to the DC voltage reference value U dVref-i The DC voltage operating value U of this valve group dV-i Make a difference and get the DC voltage deviation of this valve group ΔU dV-i ;

[0072] Then, each valve group selected for balance control will calculate the DC voltage deviation ΔU of the valve group.dV-i Input the valve group equalizing pressure compensator of this valve group, the valve group equalizing pressure compensator of this valve group has a DC voltage deviation of ΔU dV-i The phase compensation value Δθ of this valve group is calculated by proportional or integral or proportional plus integral. UV-i .

[0073] According to some other embodiments of the present application, the operating valve group only includes two voltage source converter valve groups connected in series, and the two voltage source converter valve groups connected in series are both the selected operating valve groups, and the two voltage source converter valve groups connected in series include a first voltage source converter valve group and a second voltage source converter valve group.

[0074] In step S107, the phase compensation amount is obtained by the following steps, for example:

[0075] First, obtaining DC voltage measurement values ​​of the first voltage source converter valve group and the second voltage source converter valve group respectively;

[0076] Then, the DC voltage deviation of the first voltage source converter valve group is calculated using the DC voltage measurement values ​​of the first voltage source converter valve group and the second voltage source converter valve group;

[0077] Finally, the phase compensation amount of the selected operating valve group is calculated using the DC voltage deviation amount.

[0078] For example, in a specific embodiment, when there are only two operating valve groups, any one valve group can be selected for balance control or all operating valve groups can be selected for balance control. Accordingly, the phase compensation amount acquisition method includes:

[0079] First, each valve group selected for balancing control subtracts the DC voltage operation value of the valve group obtained in step S103 from the DC voltage operation value of another valve group to obtain the DC voltage deviation ΔU of the valve group. dV2-i ;in,

[0080] Then, each valve group selected for balance control will have its DC voltage deviation ΔU dV2-i Input the valve group equalizing pressure compensator of this valve group, the valve group equalizing pressure compensator of this valve group has a DC voltage deviation of ΔU dV2-i The phase compensation value Δθ of this valve group is calculated by proportional or integral or proportional plus integral. UV2-i .

[0081] In step S109, a final phase reference value of the selected operating valve group is determined using the phase compensation amount.

[0082] According to an embodiment of the present application, after step S109, Figure 1The method shown also includes determining a phase reference value output by the selected operating valve group using a meshed control strategy, and in step S109, determining a final phase reference value of the selected operating valve group using the phase compensation value and the phase reference value.

[0083] according to Figure 1 In the embodiment shown, by obtaining the final phase reference value of the operating valve group participating in the balancing control, the final phase reference value can be used to control the voltage of the selected operating valve group, thereby balancing the DC voltage of the voltage source converter valve group and ensuring the stable operation of the DC system.

[0084] Figure 2 A flow chart of another control method of a series voltage source converter valve group according to an exemplary embodiment of the present application is shown. Figure 2 As shown, except for steps S101 to S109, Figure 2 The control method shown also includes steps S111 and S113. For the sake of brevity, only the following will describe Figure 2 The embodiment shown is similar to Figure 1 The differences are described below, and detailed description of the similarities will be omitted.

[0085] like Figure 2 As shown, in step S111, the DC bias of the bridge arm voltage of all operating valve groups is determined.

[0086] According to an embodiment of the present application, in step S111, first, the pole DC voltage target value of the series voltage source converter valve group is obtained; then, the pole DC voltage operating value is evenly divided according to the total number of voltage source converter valve groups operating in series at the pole where the series voltage source converter valve group is located, and the evenly divided value is used as the DC voltage target value of all operating valve groups; finally, 1 / 2 of the DC voltage target value of all operating valve groups is used as the DC bias of the bridge arm voltage of all operating valve groups.

[0087] For example, in a specific embodiment, first, the DC voltage target value U of the pole where the series voltage source converter valve group is located is obtained. dcPN Then, the voltage source converter valve groups N in series operation are evenly distributed according to the total number of the poles, and the average value is used as the DC voltage target value U of all operating valve groups. dvNop , as shown in formula (5).

[0088]

[0089] Where N is a positive integer, U dvNop is the DC voltage target value of all operating valve groups, U dcPN It is the target value of DC voltage at the pole where the series voltage source converter valve group is located.

[0090] Finally, the target value U dvNop 1 / 2 of the DC bias value is used as the bridge arm voltage DC bias value of all running valve groups.

[0091] In a specific embodiment, a method for obtaining a target value of a pole DC voltage of the series voltage source converter valve group includes:

[0092] When the series voltage source converter valve group is the farthest sending-end converter station, the pole DC voltage target value is the DC line voltage rated value; or

[0093] When the series voltage source converter valve group is not the farthest sending-end converter station, the pole DC voltage target value is the rated voltage of the DC line minus the DC line voltage drop from the farthest sending-end converter station to the current station, wherein the DC line voltage drop is obtained by multiplying the DC current by the theoretical line impedance value.

[0094] In step S113, the phase compensation amount and the bridge arm voltage DC bias amount are used to perform DC voltage balancing control on the selected operating valve group.

[0095] according to Figure 2 In the embodiment shown, the bridge arm voltage DC bias of all valve groups and the final phase reference value of the selected valve group are used to obtain the upper and lower bridge arm reference voltages of the selected operating valve group. By controlling the bridge arm voltages of the upper and lower bridge arms of each phase of the selected valve group, the DC voltage of each operating valve group at the DC voltage control end is balanced.

[0096] Figure 3 A topological diagram of a series voltage source converter valve group according to an exemplary embodiment of the present application is shown. Figure 4 The schematic diagram of the principle of a coordinated control method of a grid-type series voltage source converter valve group in an exemplary embodiment of the present application is shown. Figure 3 and Figure 4 , the control process of the series voltage source converter valve group in the exemplary embodiment of the present application is described in detail.

[0097] like Figure 3 As shown in the figure, 301 is the series voltage source converter valve group, 302 is the voltage measurement value at both ends of each series voltage source converter valve group, 303 is the DC voltage operation value of each series voltage source converter valve group, 304 is the DC voltage measurement value at both ends of the pole where the series voltage source converter valve group is located, 305 is the DC voltage operation value of the pole where the series voltage source converter valve group is located, and 306 is the DC current operation value of the pole where the series voltage source converter valve group is located.

[0098] like Figure 4As shown, 401 is the phase compensation amount for obtaining the valve group voltage balancing effect of each selected operating valve group of the series voltage source converter valve group, 402 is the phase reference value output by the grid-type control phase output link, 403 is the superposition of the phase compensation amount and the grid-type control phase reference value, 404 is the voltage and current dual closed-loop control, 405 is the open-loop control, 406 is the grid-type control using a closed-loop control or open-loop control selector, 407 is the bridge arm voltage control, 408 is the grid-type control voltage amplitude output link, and 409 is the bridge arm voltage DC bias amount for obtaining each valve group.

[0099] First, select Figure 3 The series voltage source converter valve group 303 includes an operating valve group for balancing control. The operating valve group for balancing control may be all operating valve groups, all slave control valve groups, or any valve group when only two valve groups are in operation.

[0100] Then, the DC voltage operation value U of the operating valve group for balancing control is obtained. dv-i The methods for obtaining the DC voltage operating value of the operating valve group for balancing control include:

[0101] Obtain the output voltage measurement value U of each valve group at both ends of the selected operating valve group for balancing control of the series voltage source converter valve group dVH-i and U dVL-i , the difference between the two is calculated to obtain the DC voltage operating value U of the operating valve group selected for balancing control dV-i , as shown in formula (1).

[0102] Then, obtain the DC voltage operating value U of the pole where the series voltage source converter valve group is located dcP like Figure 3 As shown in 305 in the figure, the voltage source converter valve groups N are distributed according to the total number of voltage source converter valve groups in series operation at the pole, and the averaged value is used as the DC voltage reference value U of each selected operating valve group for balancing control. dVref-i , as shown in formula (2).

[0103] Specifically, the total operating voltage U across the series voltage source converter valve group is dcP How to obtain:

[0104] Get the DC voltage operating value U of all running series voltage source converter valve groups dV-i Then sum the DC voltage operating values ​​of all running valve groups to obtain the DC operating voltage U of the pole where the series valve group is located. dcP , as shown in formula (3).

[0105] Alternatively, obtain the DC voltage measurement value U at both ends of the series voltage source converter valve group. dcPH and U dcPL, the difference between the two is calculated to obtain the DC voltage operating value U of the pole where the series valve group is located dcP , as shown in formula (4).

[0106] For the voltage source converter valve group, its operating characteristics are shown in formula (6):

[0107]

[0108] Among them, u pj and u nj are the upper and lower bridge arm voltages of the voltage source converter valve group j (j = a, b, c) phase, is the DC bias of the bridge arm voltage, u jref is the AC voltage reference wave of phase j.

[0109] It can be seen that the control of the voltage source converter valve group is achieved by controlling the bridge arm voltage of the upper and lower bridge arms of each phase. As shown in formula (6), the bridge arm voltage includes two parts: the DC bias and the AC voltage reference wave. Therefore, the control process of the series voltage source converter valve group specifically includes:

[0110] First, obtain the DC voltage target value U of the pole where the series voltage source converter valve group is located dcPN , and as Figure 4 As shown in 409, the voltage source converter valve groups N operating in series are evenly distributed according to the total number of the voltage source converter valve groups in the pole, and the evenly distributed value is used as the DC voltage target value U of all operating valve groups. dvNop , as shown in formula (5). Figure 4 As shown in 407, the target value U dvNop 1 / 2 of the DC bias value is used as the bridge arm voltage DC bias value of all running valve groups.

[0111] Then, if Figure 4 As shown in 401, each valve group selected for balancing control is operated according to the DC voltage operation value U of the valve group. dV-i The DC voltage reference value U of this valve group dVref-i Obtain the phase compensation value Δθ of the valve group for equalizing pressure UV-i .

[0112] Finally, if Figure 4 As shown in 403, each selected operating valve group for balancing control will play a phase compensation amount Δθ of the pressure equalization function. UV-i The phase reference value θ output by the valve group network control strategy GFMV-i Superposition, to obtain the final phase reference value θ of the selected valve group V-i .

[0113] Specifically, Figure 4The network-type control strategy described in the above may be a network-type control strategy such as VF control, droop control, virtual synchronization control, matching control, virtual oscillator control, DC voltage synchronization control, etc. The control process of the network-type control strategy outputting the phase reference value is called the phase output link, such as Figure 4 As shown in 402 in FIG. The control process of the output voltage amplitude reference value of the network control strategy is called the voltage amplitude output link, such as Figure 4 As shown in 408.

[0114] The phase and voltage amplitude output links of the series voltage source converter valve group can adopt master-slave control or independent control. When master-slave control is adopted, one valve group is selected as the master control valve group, and the phase and voltage amplitude of other slave control valve groups follow the master control valve group. After the phase output link and voltage amplitude link are output, it can be adopted Figure 4 The closed-loop control method with voltage and current control shown in 404 can also be Figure 4 The open-loop control method shown in 405 in FIG. 4 is a voltage-free current control method. Figure 4 As shown, when CHOOSE in Figure 406 is 1, the closed-loop control mode is selected, and when it is 0, the open-loop mode is selected.

[0115] In some embodiments, the DC voltage target value U of the pole where the series voltage source converter valve group is located dcPN How to obtain:

[0116] When the grid-type series voltage source converter valve group is the farthest sending-end converter station, the pole DC voltage operation target value U dcPN is the DC line voltage rating;

[0117] When the grid-type series voltage source converter valve group is not the farthest sending-end converter station, the pole DC voltage operation target value U dcPN It is the rated voltage of the DC line minus the voltage drop of the DC line from the farthest sending converter station to the station. The voltage drop of the DC line can be obtained by multiplying the DC current by the theoretical line impedance value.

[0118] According to the embodiments of the present application, Figure 4 As shown in 401, each operating valve group selected for balancing control obtains the phase compensation amount Δθ of the valve group for equalizing pressure UV-i The acquisition steps include:

[0119] First, each valve group selected for balancing control sets the DC voltage reference value U dVref-i The DC voltage operating value U of this valve group dV-i Make a difference and get the DC voltage deviation of this valve group ΔU dV-i ;

[0120] Then, each valve group selected for balance control will calculate the DC voltage deviation ΔU of the valve group.dV-i Input the valve group equalizing pressure compensator of this valve group, the valve group equalizing pressure compensator of this valve group has a DC voltage deviation of ΔU dV-i The phase compensation value Δθ of this valve group is calculated by proportional or integral or proportional plus integral. UV-i .

[0121] When there are only two operating valve groups, each operating valve group selected for balancing control can obtain the phase compensation amount of the valve group for pressure equalization in the following ways:

[0122] First, each valve group selected for balancing control sets the DC voltage operating value U dV-fov With another valve group DC voltage operating value U dV-own Make a difference and get the DC voltage deviation of this valve group ΔU dV2-i ;

[0123] Then, each valve group selected for balance control will calculate the DC voltage deviation ΔU of the valve group. dV2-i Input the valve group equalizing pressure compensator of this valve group, the valve group equalizing pressure compensator of this valve group has a DC voltage deviation of ΔU dV2-i The phase compensation value Δθ of this valve group is calculated by proportional or integral or proportional plus integral. UV2-i .

[0124] Using the bridge arm voltage DC bias of all valve groups and the final phase reference value θ of the selected valve group V-i And the network type control voltage amplitude output link, using Figure 4 The open-loop or closed-loop control method shown can obtain the upper and lower bridge arm reference voltages of the voltage source converter valve group selected for balancing control, and control the bridge arm voltages of the upper and lower bridge arms of each phase of the selected valve group, thereby achieving the balance of the DC voltage of each operating valve group at the DC voltage control end.

[0125] The above mainly introduces the embodiments of the present application from the perspective of the method. Those skilled in the art should easily appreciate that, in combination with the operations or steps of each example described in the embodiments disclosed herein, the present application can be implemented in the form of hardware or a combination of hardware and computer software. Those skilled in the art can use different ways to implement the described functions for each specific operation or method, and such implementation should not be considered to be beyond the scope of the present application.

[0126] The following describes the device embodiments of the present application. For details not described in the device embodiments of the present application, reference can be made to the method embodiments of the present application.

[0127] Figure 5A block diagram of a control device of a series voltage source converter valve group according to an exemplary embodiment of the present application is shown. According to an embodiment of the present application, the series voltage source converter valve group includes at least two series-connected voltage source converter valve groups.

[0128] like Figure 5 The control device comprises a voltage source converter valve group determination unit 501, a DC voltage operation value acquisition unit 503, a DC voltage reference value determination unit 505, a phase compensation amount determination unit 507 and a final phase reference value determination unit 509. The voltage source converter valve group determination unit 501 is used to determine the voltage source converter valve group that performs balance control in the series voltage source converter valve group, and mark the voltage source converter valve group that performs balance control as a selected operation valve group; the DC voltage operation value acquisition unit 503 is used to acquire the DC voltage operation value of the selected operation valve group; the DC voltage reference value determination unit 505 is used to determine the DC voltage reference value of the selected operation valve group; the phase compensation amount determination unit 507 is used to determine the phase compensation amount of the selected operation valve group using the DC voltage operation value and the DC voltage reference value; and the final phase reference value determination unit 509 is used to determine the final phase reference value of the selected operation valve group using the phase compensation amount.

[0129] Figure 6 A block diagram of a control device for another series voltage source converter valve group according to an exemplary embodiment of the present application is shown. Figure 6 The control device shown includes a data collection and distribution unit 601 , a networking control unit 603 and a DC voltage balance control unit 605 .

[0130] The acquisition allocation unit 601 is used to obtain Figure 3 The voltage measurement value U at both ends of each series voltage source converter valve group shown in 302 is dVH-i and U dVL-i , and obtain Figure 3 The DC voltage measurement value U at both ends of the series voltage source converter valve group shown in 304 is dcPH and U dcPL , and thereby obtain Figure 3 The DC voltage operating value U of each selected operating valve group for balancing control shown in 303 dV-i He Ru Figure 3 The DC voltage operating value U of the pole where the series voltage source converter valve group shown in 305 is located dcP . Then if Figure 4 As shown in 401, the total number of voltage source converter valve groups N in series operation is U dcP The average value is used as the DC voltage reference value U of each valve group selected for balance control. dVref-iIn addition, when the grid-type converter valve is not the farthest sending-end converter station, the acquisition and distribution unit obtains Figure 3 The DC current value I shown in 306 dcH , and as Figure 4 409 shows the calculation of the DC voltage operation target value U of all operating valve groups. dvNop .

[0131] The mesh control unit 603 is used to generate a phase reference value and an amplitude reference value. The mesh control method is arbitrary. The control process of the mesh control strategy outputting the phase reference value is called the phase output link. According to the embodiment of the present application, each operating valve group selected for balancing control superimposes the phase compensation amount for equalizing pressure with the phase reference value output by the mesh control strategy of the valve group to obtain the final phase reference value of the selected valve group, such as Figure 4 The output phase reference value θ shown in 402 GFMV-i Because the three-phase AC reference wave that controls the final output is generated using the final phase reference value and the network output amplitude, the amplitude indirectly participates in the voltage balancing, and there is no additional voltage balancing strategy. The amplitude reference value is provided by the network control unit, such as Figure 4 E shown in 408 dref-i According to an embodiment of the present application, the meshing control strategy adopted by the meshing control unit includes but is not limited to VF control, droop control, virtual synchronization control, matching control, virtual oscillator control and / or DC voltage synchronization control.

[0132] The DC voltage balance control unit 605 is used for each selected operating valve group for balance control according to Figure 4 According to the DC voltage reference value U of the valve group shown in 401 dVref-i And the DC voltage measurement value U of this valve group dV-i Get the phase compensation value Δθ of this valve group UV-i , and as Figure 4 As shown in 403, the phase compensation amount Δθ of the valve group UV-i The phase reference value θ of the network output GFMV-i Superposition, to obtain the final phase reference value θ of this valve group V-i , thereby performing DC voltage balancing control on the series voltage source converter valve group.

[0133] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application. At the same time, changes or deformations made by those skilled in the art based on the ideas of the present application, the specific implementation methods and the scope of application of the present application, all belong to the scope of protection of the present application. In summary, the content of this specification should not be construed as a limitation on the present application.

Claims

1. A control method for a series voltage source converter valve group, wherein the series voltage source converter valve group comprises at least two series-connected voltage source converter valve groups, characterized in that: The control method comprises: Determine a voltage source converter valve group that performs balancing control among the series voltage source converter valve groups, and mark the voltage source converter valve group that performs balancing control as a selected operating valve group; Obtaining a DC voltage operating value of the selected operating valve group; Determining a DC voltage reference value of the selected operating valve group; Determining a phase compensation amount of the selected operating valve group using the DC voltage operating value and the DC voltage reference value; Determining a final phase reference value of the selected operating valve group using the phase compensation amount; Determine the DC bias of the bridge arm voltage of all operating valve groups; Using the phase compensation amount and the bridge arm voltage DC bias amount, an open-loop control method without voltage and current control or a closed-loop control method with voltage and current control is used to perform DC voltage balancing control on the selected operating valve group; Among them, determining the DC bias of the bridge arm voltage of all operating valve groups includes: Obtaining a target value of a direct current voltage of the series voltage source converter valve group; Dividing the pole DC voltage target value equally according to the total number of voltage source converter valve groups operating in series at the pole where the series voltage source converter valve group is located, and using the equally divided value as the DC voltage target value of all operating valve groups; 1 / 2 of the DC voltage target value of all operating valve groups is used as the DC bias value of the bridge arm voltage of all operating valve groups; Wherein, obtaining the target value of the pole DC voltage of the series voltage source converter valve group includes: When the series voltage source converter valve group is the farthest sending-end converter station, the pole DC voltage target value is the DC line voltage rated value; or When the series voltage source converter valve group is not the farthest sending-end converter station, the pole DC voltage target value is the DC line rated voltage minus the DC line voltage drop from the farthest sending-end converter station to the station, wherein the DC line voltage drop is obtained by multiplying the DC current by the theoretical line impedance value; Wherein, the series voltage source converter valve group adopts a grid-type control strategy, and the method further includes: Determining a phase reference quantity output by the selected operating valve group using a network control strategy; Wherein, determining the final phase reference value of the selected operating valve group by using the phase compensation amount includes: The final phase reference value of the selected operating valve group is determined by using the phase compensation amount and the phase reference amount.

2. The control method according to claim 1, characterized in that: The networked control strategy includes: VF control, droop control, virtual synchronization control, matching control, virtual oscillator control and / or DC voltage synchronization control.

3. The control method according to claim 2, characterized in that: The phase output process or voltage amplitude output process of the series voltage source converter valve group includes master-slave control, wherein: When the master-slave control is adopted, one of the series voltage source converter valve groups is selected as the master control valve group, and the other voltage source converter valve groups are selected as slave control valve groups, wherein the phase and voltage amplitude of the slave control valve group change with the master control valve group; and After the phase and voltage amplitude of the series voltage source converter valve group are output, the control method of the network control strategy includes a closed-loop control method with voltage and current control or an open-loop control method without voltage and current control.

4. The control method according to claim 3, characterized in that: Determining the voltage source converter valve group for balancing control in the series voltage source converter valve group includes: Selecting all operating voltage source converter valve groups in the series voltage source converter valve group for balancing control; Selecting a slave control valve group in the series voltage source converter valve group to perform balancing control; or When only two of the series-connected voltage source converter valve groups are in operation, any one of the voltage source converter valve groups is selected for balancing control.

5. The control method according to claim 1, characterized in that: Obtaining the DC voltage operating value of the selected operating valve group includes: Obtaining output voltage measurement values ​​at both ends of the selected operating valve group; The DC voltage operating value of the selected operating valve group is obtained by using the output voltage measurement value of the two ends.

6. The control method according to claim 1, characterized in that: Determining a DC voltage reference value of the selected operating valve group includes: Obtaining a polar direct current voltage operating value of the series voltage source converter valve group; The DC voltage reference value of the selected operating valve group is determined using the pole DC voltage operating value.

7. The control method according to claim 6, characterized in that: Obtaining the pole DC voltage operation value of the series voltage source converter valve group includes: Obtaining the DC voltage operating values ​​of all operating voltage source converter valve groups in the series voltage source converter valve group; The DC voltage operating values ​​of all the operating voltage source converter valve groups are summed up to serve as the pole DC voltage operating value.

8. The control method according to claim 6, characterized in that: Obtaining the pole DC voltage operation value of the series voltage source converter valve group includes: Obtaining a DC voltage measurement value across the poles of the series voltage source converter valve group; The pole DC voltage operating value of the series voltage source converter valve group is obtained by using the DC voltage measurement value across the pole.

9. The control method according to claim 1, characterized in that: Determining the phase compensation amount of the selected operating valve group by using the DC voltage operating value and the DC voltage reference value includes: Determining a DC voltage deviation of the selected operating valve group using the DC voltage operating value and the DC voltage reference value; The phase compensation amount of the selected operating valve group is obtained by using the DC voltage deviation amount.

10. The control method according to claim 1, characterized in that: The operating valve group includes only two voltage source converter valve groups connected in series, and the two voltage source converter valve groups connected in series are both the selected operating valve groups, the two voltage source converter valve groups connected in series include a first voltage source converter valve group and a second voltage source converter valve group, and the phase compensation amount of the selected operating valve group is determined by using the DC voltage operating value and the DC voltage reference value, including: Respectively obtaining DC voltage measurement values ​​of the first voltage source converter valve group and the second voltage source converter valve group; The DC voltage deviation of the first voltage source converter valve group is calculated by using the DC voltage measurement values ​​of the first voltage source converter valve group and the second voltage source converter valve group; The phase compensation amount of the selected operating valve group is calculated using the DC voltage deviation amount.

11. The control method according to claim 9 or 10, characterized in that: Calculating the phase compensation amount of the selected operating valve group using the DC voltage deviation amount includes: The DC voltage deviation is calculated in a proportional, integral or proportional plus integral manner to obtain a phase compensation amount for the selected operating valve group.

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