A SLCC DC power transmission system based on a six-pulse converter valve

Abstract

The application discloses a SLCC direct current power transmission system based on a six-pulse converter valve, which comprises a sending-end power grid, a rectification-side converter station, an inversion-side converter station and a receiving-end power grid, wherein at least a first SVG, a first converter, a second SVG and a second converter are included; the rectification-side converter station is at least composed of the first SVG and the first converter, the inversion-side converter station is at least composed of the second SVG and the second converter, the first converter comprises a plurality of six-pulse thyristor rectification units to form a rectification unit, the second converter comprises a plurality of six-pulse thyristor rectification units to form an inversion unit, the first SVG is configured in parallel between the rectification unit and a first converter transformer, and the second SVG is configured in parallel between the inversion unit and a second converter transformer; the SLCC is formed by configuring the SVG in parallel at the valve side on the basis of a conventional LCC, and has the ability of reactive power compensation, voltage support and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current transmission, in particular to a SLCC direct current transmission system based on a six-pulse converter valve. BACKGROUND

[0002] The system support capability of new energy units is weak, and in the scenario of high proportion of new energy long-distance transmission, the conventional direct current transmission technology is no longer applicable. The SVG is configured on the valve side of the transformer, and the converter composed of the SVG and the LCC is called SLCC, which can compensate the reactive power consumption and harmonic current in the operation process of the LCC, and the system does not need to additionally configure an AC filter / parallel capacitor, which can effectively solve the problems of AC overvoltage / low voltage ride through and commutation failure at the receiving end, and the SLCC has smaller occupation area and stronger economy compared with the flexible direct current transmission. The SLCC has been widely concerned in recent years and has been applied in engineering, but the LCC valve side configuration in the existing SLCC is a three-phase star-connected SVG, which is not conducive to the formation of the zero sequence current local path in the transient state, and as a converter with functions of reactive power compensation, harmonic suppression and voltage support, the topology structure of only a single bridge arm in each phase limits the full play of the above functions. SUMMARY

[0003] In order to solve the above technical problems, the present application provides a SLCC direct current transmission system based on a six-pulse converter valve, which can better play the functions of reactive power compensation, voltage support and the like of the SLCC by improving the conventional SLCC, and provides a local path for the zero sequence current in the fault, which is suitable for large-scale new energy external transmission scenarios.

[0004] The present application provides a SLCC direct current transmission system based on a six-pulse converter valve, which includes a sending end power grid, a rectifier side converter station, an inverter side converter station and a receiving end power grid, and is characterized in that it at least includes a first SVG, a first converter, a second SVG and a second converter.

[0005] The rectifier side converter station is composed of at least the first SVG and the first converter, and the inverter side converter station is composed of at least the second SVG and the second converter, wherein the first converter includes a plurality of six-pulse thyristor rectifier units to form a rectifier unit, the second converter includes a plurality of six-pulse thyristor rectifier units to form an inverter unit, the first SVG is configured in parallel between the rectifier unit and the first converter transformer, and the second SVG is configured in parallel between the inverter unit and the second converter transformer.

[0006] The sending end power grid is connected with the AC side of the rectifier side converter station through an AC line, the DC side of the rectifier side converter station is connected with the inverter side converter station through a DC line, and the rectifier side converter station is used for receiving the AC power transmitted by the sending end power grid and converting the AC power into DC power and sending the DC power to the inverter side converter station.

[0007] The inverter side converter station is connected with the receiving end power grid, and is configured to receive the direct current transmitted by the rectifier side converter station and convert the direct current into alternating current to transmit to the receiving end power grid.

[0008] In a possible implementation of the embodiment, the first SVG and / or the second SVG is composed of three-phase six-bridge-arm branches, and each bridge arm is connected with a buffer reactor after cascading a plurality of half-bridge sub-modules or full-bridge sub-modules.

[0009] In a possible implementation of the embodiment, the buffer reactor is arranged at the grid-connected side in the first SVG and / or the second SVG.

[0010] In a possible implementation of the embodiment, the first SVG and / or the second SVG further includes a start-up loop arranged at the connection point of the first SVG and / or the second SVG, the converter transformer and the converter, wherein the converter includes the first converter and / or the second converter.

[0011] In a possible implementation of the embodiment, the start-up loop at least includes a current measuring device, a start-up resistor and a single-knife disconnector.

[0012] In a possible implementation of the embodiment, the rectifier units in the rectifier side converter station are configured to be controlled by a fixed direct current voltage, and the rectifier units in the inverter side converter station are configured to be controlled by a fixed alternating current voltage or a fixed reactive power.

[0013] In a possible implementation of the embodiment, when the first SVG and / or the second SVG is configured to perform harmonic supplementary control, the filtering order is 12n±1.

[0014] In a possible implementation of the embodiment, the first SVG and / or the second SVG is configured to be charged by means of the power supply of the rectifier side converter station and the inverter side converter station, or to be pre-charged by the rectifier side converter station and the inverter side converter station.

[0015] In a possible implementation of the embodiment, when the first SVG or the second SVG is configured to be controlled by reactive power, the monitoring point of the reactive control quantity is the converter transformer grid side of the station where the first SVG or the second SVG is located.

[0016] In a possible implementation of the embodiment, when the first SVG or the second SVG is configured to control the reactive control quantity at the converter transformer grid side, the current of the first converter or the second converter is introduced into the control loop of the first SVG or the second SVG. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1A structural schematic diagram of the SLCC DC power transmission system of one embodiment of the SLCC DC power transmission system based on the six-pulse converter valve provided by the present application;

[0018] Figure 2 Another structural schematic diagram of the SLCC DC power transmission system of one embodiment of the SLCC DC power transmission system based on the six-pulse converter valve provided by the present application;

[0019] Figure 3 Still another structural schematic diagram of the SLCC DC power transmission system of one embodiment of the SLCC DC power transmission system based on the six-pulse converter valve provided by the present application;

[0020] Figure 4 A structural schematic diagram of the SVG unit based on the full-bridge sub-module of one embodiment of the SLCC DC power transmission system based on the six-pulse converter valve provided by the present application;

[0021] Figure 5 A control function schematic diagram of one embodiment of the SLCC DC power transmission system based on the six-pulse converter valve provided by the present application;

[0022] In the figure, 1 is a new energy station; 2 is a power transmission line; 3 is a rectifier side converter station; 4 is an inverter side converter station; 5 is a receiving end power grid; 6 is an SVG; and 7 is a starting loop. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0024] It should be understood that the step numbers used herein are only for the convenience of description, and are not limited to the execution sequence of the steps.

[0025] It should be understood that the terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the present application specification and the appended claims, unless otherwise clearly indicated by the context, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0026] The terms "comprise" and "include" indicate the presence of the described features, whole, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, whole, steps, operations, elements, components and / or sets thereof.

[0027] The term "and / or" means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0028] Referring to Figure 1 , the present embodiment provides a system structure connection diagram of an embodiment of a SLCC DC power transmission system based on a six-pulse converter valve, as Figure 1 shown, including a sending end power grid, a rectifier side converter station, an inverter side converter station and a receiving end power grid, at least including a first SVG, a first converter, a second SVG and a second converter;

[0029] The rectifier side converter station is composed of at least the first SVG and the first converter, and the inverter side converter station is composed of at least the second SVG and the second converter, wherein the first converter and / or the second converter includes a plurality of six-pulse thyristor rectifier units to form a rectifier unit, the second converter includes a plurality of six-pulse thyristor rectifier units to form an inverter unit, the first SVG is configured in parallel between the rectifier unit and the first converter transformer, and the second SVG is configured in parallel between the inverter unit and the second converter transformer;

[0030] The sending end power grid is connected with the AC side of the rectifier side converter station through an AC line, the DC side of the rectifier side converter station is connected with the inverter side converter station through a DC line, and the rectifier side converter station is used to receive AC power transmitted by the sending end power grid and convert the AC power into DC power and send the DC power to the inverter side converter station;

[0031] The inverter side converter station is connected with the receiving end power grid, and the inverter side converter station is used to receive DC power sent by the rectifier side converter station and convert the DC power into AC power and send the AC power to the receiving end power grid.

[0032] In the present embodiment, as Figures 1-3 shown, the SLCC DC power transmission system based on a six-pulse converter valve includes a sending end power grid, a receiving end power grid, a rectifier side converter station and an inverter side converter station. The sending end power grid is connected with the AC side of the rectifier side converter station through a transmission line, the rectifier side converter station is connected with the inverter side converter station through a DC line, and the inverter side converter station is connected with the receiving end power grid.

[0033] The rectifier-side converter station and inverter-side converter station are SLCCs, composed of three-phase six-arm SVGs and conventional LCC converters. Depending on project requirements, the SLCC DC transmission system based on six-pulse converter valves can use a six-pulse converter valve SLCC at one end and a six-pulse converter valve SLCC, conventional SLCC, LCC, or MMC at the other end. The rectifier-side SLCC converter LCC uses a twelve-pulse rectifier unit composed of two six-pulse thyristor rectifier units. SVGs are connected in parallel between the twelve-pulse rectifier units and the converter transformer. Each twelve-pulse rectifier unit is equipped with one SVG, and the SVG and LCC unit form a whole. The inverter-side SLCC converter LCC uses a twelve-pulse inverter unit composed of two six-pulse thyristor rectifier units. SVGs are connected in parallel between the twelve-pulse rectifier units and the converter transformer. Each twelve-pulse rectifier unit is equipped with one SVG, and the SVG and LCC unit form a whole.

[0034] The SVG (Static Var Generator) provides voltage support, reactive power compensation, active filtering, and amplitude-phase correction. No AC filter is needed on the SLCC (Signal-Standard Capacitor) side, and the LCC (Low Voltage Controller) handles active power transmission. By connecting an SVG in parallel on the valve side to form an SLCC based on a conventional LCC, reactive power compensation and voltage support capabilities are achieved.

[0035] It should be noted that the first SVG refers to the SVG in the rectifier-side converter station, and the first converter refers to the LCC converter in the rectifier-side converter station. The second SVG refers to the SVG in the inverter-side converter station, and the second converter refers to the LCC converter in the inverter-side converter station. SVG stands for Static Var Generator, an advanced power electronic device mainly used for dynamic reactive power compensation.

[0036] In some embodiments, the first SVG and / or the second SVG are composed of three-phase six-arm branches, and each arm is connected to a buffer reactor after being cascaded by multiple half-bridge sub-modules or full-bridge sub-modules.

[0037] In this embodiment, as Figure 4 As shown, Figure 4 This is a schematic diagram of an SVG unit based on a full-bridge submodule. The SVG uses full-bridge or half-bridge submodules connected in series, with the three-phase branches connected in a bridge configuration. The SVG consists of three-phase six-arm branches, with each arm composed of a large number of cascaded half-bridge or full-bridge submodules connected in series with a buffer reactor.

[0038] The upper and lower bridge arms of the six-pulse converter valve can be set with different control strategies according to system requirements, such as voltage support, reactive power compensation, harmonic suppression, and the like, to achieve better overall control effect. The upper and lower three-phase bridge arms of the SVG are connected to form a neutral point through the converter valve ports, and the neutral point voltage is zero under three-phase symmetry, and there is no electrical connection between the neutral points of the upper and lower bridge arms. The three-phase six-bridge-arm SVG increases the zero-sequence current path of the system, and the zero-sequence current can be consumed through inter-phase circulation during the fault process, thereby reducing the zero-sequence current in the LCC during the transient process. Moreover, without increasing the number of sub-modules, each phase can compensate reactive power, support system voltage, and suppress harmonics through control of the upper and lower two bridge arms, thereby having higher flexibility and being able to fully exert the performance of the device.

[0039] In some embodiments, the buffer reactor is configured at the grid-connected side of the first SVG and / or the second SVG.

[0040] In this embodiment, the buffer reactor is configured at the grid-connected side of the SVG, and the three-phase six-bridge-arm SVG is configured with six buffer reactors.

[0041] In some embodiments, the first SVG and / or the second SVG further comprises a starting loop, which is arranged at the connection point of the first SVG and / or the second SVG, the converter transformer and the converter, wherein the converter comprises the first converter and / or the second converter.

[0042] In this embodiment, the LCC part of the SLCC converter is not provided with a starting loop, and the SVG is separately provided with a starting loop, which is arranged between the valve-side SVG of the converter transformer and the connection point of the converter transformer and the LCC.

[0043] In some embodiments, the starting loop at least comprises a current measuring device, a starting resistor and a single-knife disconnector.

[0044] In this embodiment, the starting loop is preferably integrated with a complete starting device comprising a current measuring device, a starting resistor and a single-knife disconnector, wherein the starting resistor can preferably replace the closing resistor of the incoming line circuit breaker.

[0045] In some embodiments, the rectification units in the rectification-side converter station are configured to be controlled with a fixed DC voltage, and the rectification units in the inversion-side converter station are configured to be controlled with a fixed AC voltage or a fixed reactive power.

[0046] In this embodiment, as shown in FIG. 1, Figure 5 Figure 5 ​The schematic diagram of the SLCC control function is shown in the figure. When the SLCC DC power transmission system based on the six-pulse converter valve is in normal operation, the LCC thyristor rectifier unit in the rectifier side converter station adopts the constant DC voltage control, and the LCC thyristor rectifier unit in the inverter side converter station adopts the constant reactive power or constant AC voltage control.

[0047] In some embodiments, when the first SVG and / or the second SVG are configured for harmonic compensation control, the filter order is 12n±1.

[0048] In the present embodiment, when the SVG in the rectifier side converter station and the SVG in the inverter side converter station are configured for harmonic compensation control, the filter order can be 12n±1 according to the system requirement, wherein 6(2n)±1 can be offset by the two six-pulse unit transformers above and below.

[0049] In some embodiments, the first SVG and / or the second SVG are configured to be charged by using the power supply of the rectifier side converter station and the inverter side converter station, or by pre-charging the rectifier side converter station and the inverter side converter station.

[0050] In the present embodiment, there are two pre-charging methods for the SVG. One is to charge the SVG by using the power supply of the station, and the other is to start by pre-charging the station. For the method of starting by pre-charging the SVG by using the power supply of the station, the starting process of the SLCC converter station should be performed in the state that the breakers between the LCC and the converter transformer and the SVG of the station are disconnected. The charging process should include two steps of passive charging and active charging, and the SLCC converter station is in the same condition in the rectifier side converter station and the inverter side converter station.

[0051] The method of starting by pre-charging the station should be performed in the state that the breakers between the LCC and the SVG of the station are closed, i.e. the power supply side converter station does not need to be charged or the charging is completed, at this time, the breakers between the SLCC of the station and the low-frequency / working-frequency AC power supply / grid of the station should be in the disconnected state.

[0052] In some embodiments, when the first SVG or the second SVG are configured to be controlled by using the reactive power, the access point of the reactive control quantity is the converter transformer grid side of the station where the first SVG or the second SVG is located.

[0053] In the present embodiment, in the process of realizing the functions of voltage support, reactive power compensation, harmonic suppression, etc. by the SVG, the reactive control quantity of the SVG can be the converter transformer valve side of the access point of the SVG, or the converter transformer grid side connected with the AC system.

[0054] In some embodiments, the first SVG or the second SVG is configured to introduce the current of the first converter or the second converter in the control loop of the first SVG or the second SVG when the control quantity of the first SVG or the second SVG is the reactive power of the grid side of the converter transformer.

[0055] In the embodiment, when the control quantity thereof is the reactive power of the grid side of the converter transformer, the current of the LCC needs to be introduced in the control loop of the SVG to offset the influence of the LCC on the control loop of the SVG.

[0056] Compared with the prior art, the present application has the following beneficial effects:

[0057] The SLCC DC power transmission system based on the six-pulse converter valve comprises a sending-end power grid, a rectifier-side converter station, an inverter-side converter station and a receiving-end power grid, wherein at least a first SVG, a first converter, a second SVG and a second converter are included; the rectifier-side converter station is composed of at least the first SVG and the first converter, and the inverter-side converter station is composed of at least the second SVG and the second converter, wherein the first converter and / or the second converter comprises a plurality of rectification units composed of six-pulse thyristor rectification units, the first SVG and / or the second SVG are configured in parallel between the rectification unit and a converter transformer, the converter transformer comprises a first converter transformer and / or a second converter transformer; the sending-end power grid is connected with the alternating current side of the rectifier-side converter station through an alternating current line, the direct current side of the rectifier-side converter station is connected with the inverter-side converter station through a direct current line, the rectifier-side converter station is used for receiving alternating current transmitted by the sending-end power grid and converting the alternating current into direct current to send to the inverter-side converter station; the inverter-side converter station is connected with the receiving-end power grid, and the inverter-side converter station is used for receiving direct current sent by the rectifier-side converter station and converting the direct current into alternating current to send to the receiving-end power grid. By combining the conventional DC power transmission and the flexible DC power transmission, the advantages are complementary, the technical economy and flexibility in the existing large-scale new energy power transmission scene are effectively realized, the technology is relatively mature, the technical research and development pressure is relatively small, the engineering application can be quickly realized, and the application has strong popularization value. Therefore, the application can be widely applied to the large-scale new energy power transmission scene.

[0058] The technical features of the above embodiments can be combined in any manner, and to make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application.

[0059] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only for specific embodiments of the present application and is not used to limit the protection scope of the present application. It is particularly pointed out that any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A SLCC DC power transmission system based on a six-pulse converter valve, comprising a sending-end power grid, a rectifier-side converter station, an inverter-side converter station and a receiving-end power grid, characterized in that, at least comprising a first SVG, a first converter, a second SVG and a second converter; the rectifier side converter station is composed of at least the first SVG and the first converter, and the inverter side converter station is composed of at least the second SVG and the second converter, wherein the first converter comprises a plurality of six-pulse thyristor rectifier units, the second converter comprises a plurality of six-pulse thyristor inverter units, the first SVG is connected in parallel between the rectifier units and a first converter transformer, and the second SVG is connected in parallel between the inverter units and a second converter transformer; the sending end power grid is connected to the AC side of the rectifier side converter station through an AC line, the DC side of the rectifier side converter station is connected to the inverter side converter station through a DC line, and the rectifier side converter station is configured to receive AC power transmitted by the sending end power grid and convert the AC power into DC power and send the DC power to the inverter side converter station. the inverter side converter station is connected to the receiving end power grid, and the inverter side converter station is configured to receive DC power sent by the rectifier side converter station and convert the DC power into AC power and send the AC power to the receiving end power grid.

2. A six-pulse converter valve based SLCC HVDC power transmission system as claimed in claim 1, characterized in that, the first SVG and / or the second SVG is composed of three-phase six-bridge-arm branches, each bridge arm is connected to a buffer reactor after cascading a plurality of half-bridge sub-modules or full-bridge sub-modules.

3. A six-pulse converter valve based SLCC HVDC power transmission system as claimed in claim 2, characterized in that, the buffer reactor is arranged at the grid-connected side of the first SVG and / or the second SVG.

4. The six-pulse converter valve based SLCC HVDC power transmission system of claim 1, wherein, the first SVG and / or the second SVG further comprises a start-up loop arranged at a connection point of the first SVG and / or the second SVG, a converter transformer and a converter, wherein the converter comprises the first converter and / or the second converter.

5. A six-pulse converter valve based SLCC HVDC power transmission system as claimed in claim 4, characterized in that, the start-up loop comprises at least a current measuring device, a start-up resistor and a single-knife disconnector.

6. The six-pulse converter valve based SLCC HVDC power transmission system of claim 1, wherein, the rectifier units in the rectifier side converter station are configured to be controlled by a fixed DC voltage, and the rectifier units in the inverter side converter station are configured to be controlled by a fixed AC voltage or a fixed reactive power.

7. A six-pulse converter valve based SLCC HVDC power transmission system as claimed in claim 1, wherein, when the first SVG and / or the second SVG is configured to perform harmonic supplementary control, the filtering order is 12n±1.

8. The six-pulse converter valve based SLCC HVDC power transmission system of claim 1, wherein, the first SVG and / or the second SVG is configured to be charged by using power sources of the rectifier side converter station and the inverter side converter station, or to be pre-charged by the rectifier side converter station and the inverter side converter station.

9. A six-pulse converter valve based SLCC HVDC power transmission system as claimed in claim 7, characterized in that, when the first SVG or the second SVG is configured to be controlled by reactive power, the monitoring point of the reactive control quantity is the converter transformer grid side of the station where the first SVG or the second SVG is located.

10. A six-pulse converter valve based SLCC HVDC power transmission system as claimed in claim 9, characterized in that, when the monitoring point of the reactive control quantity of the first SVG or the second SVG is configured as the converter transformer grid side, the current of the first converter or the second converter is introduced into the control loop of the first SVG or the second SVG.

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