Communication system and communication method for flexible DC modular multi-level converter valve

Abstract

A communication system and communication method for a flexible DC modular multi-level converter valve, comprising: a plurality of power submodules, a valve base bridge arm control device and an optical fiber pair; the plurality of power submodules are respectively connected horizontally and vertically through the optical fiber pair to form a matrix optical fiber communication network; the power submodules in the matrix optical fiber communication network are connected to the valve base bridge arm control device through the optical fiber pair and then connected to the converter valve. The technical solution provided by the present invention connects multiple pairs of optical fibers to the same power submodule as backup for each other, avoiding the risk of submodule bypass caused by a single optical fiber failure under the traditional communication mode, improving the overall operation reliability and stability of the converter valve, and reducing the optical fiber connecting the valve base bridge arm controller and the converter valve power submodule network, further reducing the overall cost.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current power transmission, and in particular to a communication system and a communication method for a flexible direct current modular multi-level converter valve. Background Art

[0002] Modular flexible DC systems are increasingly widely used in engineering because of their flexible regulation, low harmonic content, and ability to operate in high-voltage, high-capacity transmission systems. Among them, the converter valve is the core component of the modular multilevel converter, and is mainly responsible for energy exchange and power transmission. The converter valve requires hundreds or even thousands of power sub-modules to be connected in series, and each power sub-module must be controlled, protected, and monitored individually. When the converter valve is running, the valve based controller (VBC) controls the operating status of each power sub-module according to the required output voltage; at the same time, the power sub-module's own control device, the sub-module controller (SMC), also needs to feedback its own working status to the valve based controller VBC. Therefore, the communication networking method connecting the valve based controller VBC and the converter valve also provides necessary guarantees for flexible DC transmission projects.

[0003] At present, the project mainly adopts the form of optical fiber communication. Each submodule is connected to a pair of optical ports of the VBC interface device through a pair of optical fibers. The communication data is transmitted through the optical fiber and the optical port, that is, the traditional valve control and the converter valve are connected in a point-to-point communication mode. With the increase of the voltage level of the flexible direct current project, more and more submodules are required for a single bridge arm. Taking the 500kV flexible direct current project as an example, the number of power submodules in a single bridge arm reaches more than 250. Since the valve base bridge arm control equipment is in the control and protection room of the ground potential, the distance from each converter valve is far, which can reach more than 300m. The sharp increase in the length and number of optical fibers has become one of the important reasons affecting the cost of flexible direct current projects. At the same time, it also greatly increases the cost of installation, operation and maintenance of converter valves. Summary of the invention

[0004] Aiming at the shortcomings of traditional point-to-point optical fiber communication, the present invention provides a communication system for flexible DC modular multi-level converter valve, including: multiple power sub-modules, valve base bridge arm control equipment and optical fiber pairs;

[0005] The multiple power submodules are connected horizontally and vertically through optical fiber pairs to form a matrix optical fiber communication network;

[0006] The power submodule in the matrix optical fiber communication network is connected to the valve base bridge arm control device through an optical fiber pair and then connected to the flow conversion valve.

[0007] Preferably, the valve base bridge arm control device comprises: a plurality of transceiver interfaces;

[0008] The power submodules in the matrix optical fiber communication network are connected to different transceiver interfaces on the valve base bridge arm control device through optical fiber pairs according to the pre-programmed first and last rows of power submodules.

[0009] Preferably, the plurality of power submodules are laterally connected through optical fiber pairs, specifically comprising:

[0010] Each power submodule in the horizontal direction is connected head to tail in sequence through an optical fiber pair, and the head and tail optical fiber submodules in each row are connected respectively to form a horizontal power submodule communication network.

[0011] Preferably, the plurality of power submodules are longitudinally connected through optical fibers, specifically comprising:

[0012] Each power sub-module in the vertical direction is connected end to end in sequence through optical fiber pairs to form a vertical power sub-module communication network.

[0013] Preferably, it also includes: a sub-fiber optical communication network;

[0014] The sub-fiber communication network is formed by connecting the plurality of power sub-modules horizontally and vertically via optical fiber pairs;

[0015] The sub-fiber optic communication network is connected to the matrix fiber optic communication network in the form of a power sub-module and then connected to the valve base bridge arm control device.

[0016] Preferably, the sub-fiber communication network is formed by the plurality of power sub-modules being laterally connected through optical fiber pairs, specifically comprising:

[0017] The power submodules added to the communication path between each valve base bridge arm control device and the longitudinal power submodules are connected head to tail via a pair of optical fibers in the transverse direction, and the head and tail power submodules in each row are connected via another pair of optical fibers.

[0018] Preferably, the sub-fiber communication network is longitudinally connected by the plurality of power sub-modules through optical fiber pairs, specifically comprising:

[0019] Based on the power sub-modules added to the communication path between each valve base bridge arm control device and the longitudinal power sub-modules, each of the power sub-modules in the longitudinal direction is connected end to end in sequence through optical fiber pairs.

[0020] Preferably, the power submodule includes a number;

[0021] The numbering is performed based on the rows and columns in which the power submodules are located in the matrix communication network or the sub-optical fiber communication network.

[0022] Based on the same inventive concept, the present invention also provides a communication method of a communication system based on a flexible DC modular multi-level converter valve, comprising:

[0023] When the communication system is started, the valve base bridge arm control device sends information to the power submodule through the optical fibers arranged horizontally and vertically;

[0024] The information of the power submodule is fed back to the valve base bridge arm control device through the optical fiber pairs arranged transversely and longitudinally.

[0025] Preferably, the valve base bridge arm control device sends information to the power submodule through optical fibers arranged horizontally and vertically, including:

[0026] The valve base bridge arm control device sends information to the power submodule and the sub-optical fiber communication network connected in the form of the power submodule through the optical fibers arranged horizontally and vertically.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention provides a communication system for a flexible DC modular multi-level converter valve, comprising: a plurality of power sub-modules, a valve base bridge arm control device and an optical fiber pair; the plurality of power sub-modules are respectively connected horizontally and vertically through optical fiber pairs to form a matrix optical fiber communication network; the power sub-modules in the matrix optical fiber communication network are connected to the valve base bridge arm control device through the optical fiber pair and then connected to the converter valve; in the matrix communication networking mode provided by the present invention, multiple pairs of optical fibers connected to the same power sub-module serve as backup for each other, thereby increasing the redundancy of the communication network, avoiding the risk of sub-module bypass caused by a single optical fiber failure under traditional communication methods, and improving the overall operation reliability and stability of the converter valve.

[0029] 2. The present invention is different from the traditional communication method. When the longitudinal length of the power submodules in the converter valve power submodule network is too long, a nested method can be selected to reduce the long-distance use of optical fibers and reduce the overall cost. While ensuring the reliable and stable operation of the converter valve, the optical fibers connecting the valve base bridge arm control device and the converter valve power submodule network can be reduced, further reducing the overall cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of a communication method of a communication system based on a flexible DC modular multi-level converter valve of the present invention;

[0031] Figure 2 It is a lateral power submodule communication network of the matrix optical fiber communication system of the present invention;

[0032] Figure 3A longitudinal power submodule communication network of a matrix optical fiber communication system of the present invention;

[0033] Figure 4 It is a schematic diagram of optical fiber connection between the matrix optical fiber communication system of the present invention and the valve base bridge arm control device;

[0034] Figure 5 A schematic diagram of network connection after a longitudinal optical fiber connection failure of a transverse power submodule communication network of a matrix optical fiber communication system of the present invention;

[0035] Figure 6 A schematic diagram of network connection after a transverse optical fiber connection failure of a longitudinal power submodule communication system of a matrix optical fiber communication network of the present invention;

[0036] Figure 7 A 2-level nested communication network group of the matrix optical fiber communication network of the present invention;

[0037] Figure 8 The number of optical fibers of the matrix optical fiber communication network and valve base bridge arm control device of the present invention;

[0038] Fig. 9 It is a three-level nested communication network group of the matrix optical fiber communication network of the present invention. DETAILED DESCRIPTION

[0039] In view of the shortcomings of traditional point-to-point optical fiber communication, the present invention provides a communication network and networking method for a flexible DC modular multi-level converter valve. This communication networking method reduces the optical fiber cost problem caused by the long distance from the valve hall to the control room, reduces the communication failure rate, and reduces the overall project cost while ensuring the stable and reliable operation of the converter valve.

[0040] An overall flexible direct current system is three-phase, each phase has two upper and lower bridge arms, and each bridge arm has many sub-modules connected in series. By changing the operating status of the sub-modules, different voltages can be output. In practice, many sub-modules are placed on the valve tower of the converter valve.

[0041] Embodiment 1:

[0042] The present invention proposes that the communication network of the converter valve can adopt a matrix communication network mode, such as Figure 4 As shown, optical fibers are used to connect each submodule and the VBC, wherein N is the number of columns and M is the number of rows, that is, 2*N pairs of optical fibers are used to control M*N groups of submodules in the converter valve, so that each submodule can be accurately positioned.

[0043] like Figure 4 and Figure 8As shown, a communication system for a flexible DC modular multi-level converter valve includes a valve base bridge arm controller, multiple pairs of transceiver optical fibers, and multiple power sub-modules;

[0044] The multiple power submodules are connected horizontally and vertically through optical fiber pairs to form a matrix optical fiber communication network;

[0045] A matrix optical fiber communication network and a valve base bridge arm control device are connected by multiple pairs of optical fibers; wherein, in the same matrix optical fiber communication network, each power submodule is connected to all surrounding power submodules by multiple pairs of optical fibers.

[0046] All power sub-modules in each bridge arm of the converter valve are numbered in matrix form according to M*N, where N≥1 and M≥1; the M*N power sub-modules are numbered in sequence according to SM{1,1}, SM{1,2}, SM{1,3}, …, SM{1,N}, SM{2,1}, SM{2,2}, SM{2,3}, …, SM{2,N}, …, SM{M,1}, SM{M,2}, SM{M,3}, …, SM{M,N}.

[0047] The power submodule SM{m,1} and the power submodule SM{m,2}, the power submodule SM{m,2} and the power submodule SM{m,3}, until the power submodule SM{m,(N-1)} and the power submodule SM{m,N}, the power submodule SM{m,N} and the power submodule SM{m,1} are interconnected by a pair of transceiver communication optical fibers, wherein m={1, 2, 3, ..., M}, so that the M*N power submodules form M "horizontal communication networks of power submodules with bidirectional ring communication", wherein the horizontal communication network of power submodules with bidirectional ring communication refers to the horizontal power submodule communication network; Figure 2 shown.

[0048] The power submodule SM{1,n} and the power submodule SM{2,n}, the power submodule SM{2,n} and the power submodule SM{3,n}, and finally the power submodule SM{(M-1),n} and the power submodule SM{M,n} are connected by a pair of transceiver communication optical fibers, wherein n={1, 2, 3, ..., N}, so that the M*N power submodules form N "vertical power submodule communication networks with two-way communication", wherein the vertical power submodule communication network with two-way communication refers to the vertical power submodule communication network; Figure 3 shown.

[0049] Thus, M*N power sub-modules are connected through two modes, namely, a horizontal power sub-module communication network and a vertical power sub-module communication network, to form a matrix optical fiber communication network, which is defined as a converter valve power sub-module matrix network.

[0050] The power submodules SM{1,n} and the power submodules SM{M,n} of the converter valve power submodule matrix network can be connected to the valve base bridge arm control device through a pair of communication optical fibers, respectively, to realize the communication connection between the valve base bridge arm control device and the converter valve power submodule matrix network, wherein n={1, 2, 3, ..., N}; the number of optical fiber pairs between the valve base bridge arm control device and a converter valve power submodule matrix network is j, and at most j=2N pairs of optical fibers can be connected; the communication networking method is defined as a matrix communication networking scheme for modular flexible DC converter valves, which is referred to as "matrix communication networking scheme" in this article; such as Figure 4 shown.

[0051] In each pair of optical fibers interconnecting the valve base bridge arm control device and the converter valve power submodule matrix network, the transmitted information includes the information sent by the valve base bridge arm control device to all power submodules in the converter valve power submodule matrix network, and the information received by the valve base bridge arm control device includes the information sent by all power submodules in the converter valve power submodule matrix network to the valve base bridge arm control device; the j=2N pairs of optical fibers interconnecting the valve base bridge arm control device and the converter valve power submodule matrix network are completely backup for each other.

[0052] For any horizontal power submodule communication network with a bidirectional ring in the converter valve power submodule matrix network, as long as one pair of optical fibers in all the vertical communication optical fibers communicates normally, and the adjacent power submodule networks in the horizontal network communicate normally, all power submodules and valve base bridge arm control devices in the converter valve power submodule network can maintain normal communication, such as Figure 5 shown.

[0053] For any longitudinal power submodule communication network with bidirectional communication in the converter valve power submodule matrix network, as long as one pair of optical fibers in all transverse communication optical fibers communicates normally, and the adjacent power submodule networks in the longitudinal network communicate normally, all power submodules and valve base bridge arm control devices in the converter valve power submodule network can maintain normal communication, such as Figure 6 Shown

[0054] For any power submodule in the converter valve power submodule matrix network, it has at least four pairs of optical ports that can communicate with the communication network, and the four pairs of transmitting and receiving communication optical fibers are backup for each other; as long as one pair of optical fibers communicates normally, the power submodule can be in a normal communication state.

[0055] The valve base bridge arm control device and a converter valve power submodule matrix network are connected through j=2N pairs of redundant optical fibers. When the N value is large, and while ensuring the reliable operation of the entire converter valve power submodule communication network group and the valve base bridge arm control device, the number of j pairs of optical fibers connecting the valve base bridge arm control device and the converter valve power submodule matrix network can be reduced, thereby further reducing the number of optical fibers used and reducing the project cost.

[0056] One valve base bridge arm control device can communicate with k (k>=1) converter valve power submodule matrix networks.

[0057] In a power submodule matrix network of a converter valve composed of M*N power submodules, for a vertical power submodule communication network with bidirectional communication, the maximum length of the communication path from the valve base bridge arm control device to the power submodule is M; because the length of the communication path determines the length of the information delay, when M is large, the communication path length can be reduced to avoid a long information delay, that is, a nested manner is used for matrix communication networking. Figure 7 and Fig. 9 As shown. The nested power submodule number becomes SM{(x,y),m,n}, where (x,y) is the matrix network number, x is the network level number, y is the matrix network number under the level, m is the row number of the power submodule in the network, and n is the column number of the power submodule in the network. In order to increase the redundancy of the lower-level network communication, the two pairs of external transceiver optical fibers in the same lower-level network and the same vertical network can be connected to two different power submodules in the upper-level network respectively. The two pairs of optical fibers serve as backup for each other, avoiding the risk of overall bypass of the lower-level network due to optical fiber failure or upper-level power submodule failure. Among them, each network has the above-mentioned matrix communication, including horizontal ring bidirectional and vertical bidirectional communication networks. Unlike ordinary power submodules with four transceiver optical ports, the power submodule that can be connected to the lower-level network has six transceiver optical ports, and the two newly added transceiver optical ports can be defined as "dry node optical ports." That is to say, when there are Y converter valve power sub-module matrix networks in the lower-level network, and the maximum number of columns in each lower-level network is N, it means that there should be at least Y*N power sub-modules with dry node optical ports in the upper-level network, and the two dry node optical ports on the same power sub-module should be connected to two different lower-level networks respectively. For example, Figure 7It is a 2-level nested network. The lower level network 1 is connected to different power submodules in the same vertical network of the upper level network 1 through SM{(2,1),1,n} and SM{(2,1),2,n} respectively: SM{(1,1),1,n} and SM{(1,1),2,n}. The same is true for the lower level network 2. When the vertical column in the converter valve power submodule matrix network is too long, multiple nesting methods can be further used for matrix communication networking.

[0058] The beneficial effects of the present invention are:

[0059] (1) The present invention proposes a matrix communication networking method, in which multiple pairs of optical fibers connected to the same power submodule serve as backup for each other, thereby increasing the redundancy of the communication network, avoiding the risk of submodule bypass caused by a single optical fiber failure under traditional communication methods, and improving the overall operating reliability and stability of the converter valve.

[0060] (2) Different from traditional communication methods, the present invention can reduce the long-distance use of optical fibers and reduce the overall cost. While ensuring the reliable and stable operation of the converter valve, the optical fibers connecting the valve base bridge arm control device and the converter valve power submodule network can be reduced, further reducing the overall cost.

[0061] When the longitudinal length of the power sub-module arrangement in the converter valve power sub-module network is too long, a nested approach can be selected to reduce the length of the communication path and the delay length of the information.

[0062] Example 2

[0063] The present invention based on the same inventive concept also provides a communication networking method applicable to a flexible DC modular multi-level converter valve, comprising:

[0064] Step 1: Multiple power sub-modules are connected horizontally and vertically through optical fiber pairs to form a matrix optical fiber communication network;

[0065] Step 2: The power submodule in the matrix optical fiber communication network is connected to the valve base bridge arm control device via an optical fiber pair.

[0066] The power submodule in the matrix optical fiber communication network is connected to the valve base bridge arm control device through an optical fiber pair and then connected to the converter valve, including:

[0067] The power submodules in the matrix optical fiber communication network are connected to different transceiver interfaces on the valve base bridge arm control device through optical fiber pairs according to the pre-programmed first and last rows of power submodules to send and receive information.

[0068] The plurality of power submodules are laterally connected via optical fiber pairs, including:

[0069] Each power submodule in the horizontal direction is connected head to tail in sequence through an optical fiber pair, and the head and tail optical fiber submodules in each row are connected respectively to form a horizontal power submodule communication network.

[0070] The plurality of power submodules are longitudinally connected via optical fiber pairs, including:

[0071] Each power sub-module in the vertical direction is connected end to end in sequence through optical fiber pairs to form a vertical power sub-module communication network.

[0072] Also includes:

[0073] When the communication path length between the valve base bridge arm control device and the longitudinal power submodule in the matrix optical fiber communication network is greater than a preset threshold, a nested manner is used to perform matrix communication networking.

[0074] The matrix communication networking is performed in a nested manner, including:

[0075] The multiple power sub-modules are connected horizontally and vertically through optical fiber pairs to form a sub-optical fiber communication network;

[0076] The sub-fiber optic communication network is connected to the matrix fiber optic communication network in the form of a power sub-module and then connected to the converter valve.

[0077] The plurality of power sub-modules are respectively connected horizontally and vertically through optical fiber pairs to form a sub-optical fiber communication network, including:

[0078] Based on the power submodules added on the communication path between each valve base bridge arm control device and the longitudinal power submodules, each power submodule is connected head to tail through an optical fiber pair in the transverse direction, and the head and tail power submodules of each row are connected through another pair of optical fibers to form a nested transverse power submodule network;

[0079] Each of the power sub-modules in the longitudinal direction is sequentially connected end to end through optical fiber pairs to form a nested longitudinal power sub-module communication network;

[0080] The sub-optical fiber communication network is composed of a nested transverse power sub-module network and a nested longitudinal power sub-module communication network.

[0081] Embodiment 3:

[0082] Based on the same inventive concept, the present invention also provides a communication method based on a communication system of a flexible DC modular multi-level converter valve. Figure 1 As shown, including:

[0083] Step 1: When the communication system is started, the valve base bridge arm control device sends information to the power submodule through the optical fibers arranged horizontally and vertically;

[0084] Step 2: Feedback the information of the power submodule to the valve base bridge arm control device through the optical fiber pairs arranged transversely and longitudinally.

[0085] The valve base bridge arm control device sends information to the power submodule through optical fibers arranged horizontally and vertically, including:

[0086] The valve base bridge arm control device sends information to the power submodule and the sub-optical fiber communication network connected in the form of the power submodule through the optical fibers arranged horizontally and vertically.

[0087] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0088] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0089] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0090] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1The steps for the functions specified in one or more boxes.

[0091] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A communication system for a flexible DC modular multi-level converter valve, characterized in that: include: Multiple power submodules, valve base bridge arm control equipment and optical fiber pairs; The multiple power submodules are connected horizontally and vertically through optical fiber pairs to form a matrix optical fiber communication network; The power submodule in the matrix optical fiber communication network is connected to the valve base bridge arm control device through an optical fiber pair and then connected to the converter valve; The valve base bridge arm control device comprises: a plurality of transceiver interfaces; The power submodules in the matrix optical fiber communication network are connected to different transceiver interfaces on the valve base bridge arm control device through optical fiber pairs according to the pre-compiled first and last rows of power submodules.

2. The communication system according to claim 1, characterized in that The multiple power sub-modules are horizontally connected through optical fiber pairs, specifically including: Each power submodule in the horizontal direction is connected head to tail in sequence through an optical fiber pair, and the head and tail optical fiber submodules in each row are connected respectively to form a horizontal power submodule communication network.

3. The communication system according to claim 1, characterized in that The multiple power sub-modules are longitudinally connected through optical fiber pairs specifically including: Each power sub-module in the vertical direction is connected end to end in sequence through optical fiber pairs to form a vertical power sub-module communication network.

4. The communication system according to claim 1, wherein: Also includes: Sub-fiber optic communication network; The sub-fiber communication network is formed by connecting the plurality of power sub-modules horizontally and vertically via optical fiber pairs; The sub-fiber optic communication network is connected to the matrix fiber optic communication network in the form of a power sub-module and then connected to the valve base bridge arm control device.

5. The communication system according to claim 4, characterized in that The sub-fiber communication network is formed by the plurality of power sub-modules being laterally connected through optical fiber pairs and specifically includes: The power submodules added to the communication path between each valve base bridge arm control device and the longitudinal power submodules are connected head to tail via a pair of optical fibers in the transverse direction, and the head and tail power submodules in each row are connected via another pair of optical fibers.

6. The communication system according to claim 5, characterized in that The sub-fiber communication network is composed of the plurality of power sub-modules connected longitudinally through optical fiber pairs, and specifically includes: Based on the power sub-modules added to the communication path between each valve base bridge arm control device and the longitudinal power sub-modules, each of the power sub-modules in the longitudinal direction is connected end to end in sequence through optical fiber pairs.

7. The communication system according to claim 6, characterized in that The power submodule includes a number; The numbering is performed based on the rows and columns in which the power submodules are located in the matrix communication network or the sub-optical fiber communication network.

8. A communication method based on the communication system according to any one of claims 1 to 7, characterized in that: include: When the communication system is started, the valve base bridge arm control device sends information to the power submodule through the optical fibers arranged horizontally and vertically; The information of the power submodule is fed back to the valve base bridge arm control device through the optical fiber pairs arranged transversely and longitudinally.

9. The communication method according to claim 8, characterized in that: The valve base bridge arm control device sends information to the power submodule through optical fibers arranged horizontally and vertically, including: The valve base bridge arm control device sends information to the power submodule and the sub-optical fiber communication network connected in the form of the power submodule through the optical fibers arranged horizontally and vertically.

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