SLCC direct-current power transmission system based on six pulse converter valves

Abstract

The invention discloses an SLCC direct-current power transmission system based on six pulse converter valves, which comprises a sending-end power grid, a rectification-side converter station, an inversion-side converter station and a receiving-end power grid, and at least comprises a first SVG, a first converter, a second SVG and a second converter, the rectification side converter station is at least composed of a first SVG and a first current converter, the inversion side converter station is at least composed of a second SVG and a second current converter, the first current converter comprises a rectification unit composed of a plurality of six-pulse thyristor rectification units, and the second current converter comprises an inversion unit composed of a plurality of six-pulse thyristor rectification units. The first SVG is configured between the rectification unit and the first converter transformer in parallel, the second SVG is configured between the inversion unit and the second converter transformer in parallel, the SVGs are connected in parallel on the valve side on the basis of a conventional LCC to form an SLCC, and the capacity of reactive compensation, voltage supporting and the like is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current transmission, and in particular to a SLCC direct current transmission system based on six-pulse converter valves. Background Art

[0002] The system support capacity of new energy units is relatively weak. Conventional DC transmission technology is no longer applicable in scenarios with a high proportion of new energy over long distances. SVG is configured on the valve side of the transformer. The converter composed of SVG and LCC is called SLCC, which can compensate for reactive power consumption and harmonic current during the operation of LCC. The system does not need to be additionally configured with AC filters / parallel capacitors. It can effectively solve problems such as AC overvoltage / low voltage ride-through and receiving-end commutation failure. It has a smaller footprint and stronger economy than flexible DC transmission. SLCC has received widespread attention in recent years and has been applied in engineering. However, the LCC valve side configuration in the existing SLCC is a three-phase star-connected SVG, which is not conducive to the formation of a zero-sequence current path on this side under transient conditions. In addition, as a converter with multiple functions such as reactive power compensation, harmonic suppression, and voltage support, the topological structure with only a single bridge arm per phase limits the full play of the above functions. Summary of the invention

[0003] In order to solve the above technical problems, an embodiment of the present invention provides an SLCC DC transmission system based on a six-pulse converter valve. By making improvements on the conventional SLCC, the SLCC reactive power compensation, voltage support and other functions can be better exerted, and a local path is provided for the zero-sequence current during a fault, which is suitable for large-scale new energy transmission scenarios.

[0004] The embodiment of the present invention provides an SLCC DC transmission system based on six-pulsation converter valves, the system 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 includes at least a first SVG, a first converter, a second SVG and a second converter;

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

[0006] The sending-end power grid is connected to the AC side of the rectifier-side converter station through an AC line, and the DC side of the rectifier-side converter station is connected to the inverter-side converter station through a DC line. The rectifier-side converter station is used to receive the AC power transmitted by the sending-end power grid, convert the AC power into DC power, and then send it to the inverter-side converter station;

[0007] The inverter-side converter station is connected to the receiving-end power grid. The inverter-side converter station is used to receive the direct current sent by the rectifier-side converter station, and convert the direct current into alternating current and send it to the receiving-end power grid.

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

[0009] In a possible implementation manner of the embodiment, the snubber reactor is configured on the grid-connected side of the first SVG and / or the second SVG.

[0010] In a possible implementation manner of the embodiment, the first SVG and / or the second SVG further includes a starting circuit, and the starting circuit is arranged at a connection point between 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 manner of the embodiment, the starting circuit includes at least a current measuring device, a starting resistor and a single-pole isolating switch.

[0012] In a possible implementation manner of the embodiment, the rectifier unit in the rectifier-side converter station is configured to be controlled by a fixed DC voltage, and the rectifier unit in the inverter-side converter station is configured to be controlled by a fixed AC voltage or a fixed reactive power.

[0013] In a possible implementation manner of the embodiment, when the first SVG and / or the second SVG is configured to perform harmonic supplement 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 utilizing the power supply of the rectifier side converter station and the inverter side converter station, or to be charged by pre-charging the rectifier side converter station and the inverter side converter station.

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

[0016] In a possible implementation manner of the embodiment, when the first SVG or the second SVG is configured to have a reactive control variable on the grid side of the converter transformer, 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 THE DRAWINGS

[0017] Figure 1A schematic structural diagram of an SLCC DC power transmission system according to an embodiment of the SLCC DC power transmission system based on six-pulsation converter valves provided by the present invention;

[0018] Figure 2 Another structural schematic diagram of an SLCC DC power transmission system according to an embodiment of the SLCC DC power transmission system based on six-pulsation converter valves provided by the present invention;

[0019] Figure 3 Another structural schematic diagram of an SLCC direct current transmission system according to an embodiment of the SLCC direct current transmission system based on six-pulsation converter valves provided by the present invention;

[0020] Figure 4 A schematic diagram of the structure of an SVG unit based on a full-bridge submodule in an embodiment of an SLCC DC power transmission system based on six-pulsation converter valves provided by the present invention;

[0021] Figure 5 A schematic diagram of SLCC control functions of an embodiment of an SLCC DC power transmission system based on six-pulsation converter valves provided by the present invention;

[0022] Among them, 1 is the new energy station; 2 is the transmission line; 3 is the rectifier side converter station; 4 is the inverter side converter station; 5 is the receiving end power grid; 6 is SVG; 7 is the starting circuit. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be understood that the step numbers used in this article are only for convenience of description and are not intended to limit the order in which the steps are executed.

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

[0026] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

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

[0028] See also Figure 1 A certain embodiment of the present invention provides a schematic diagram of the system structure connection of an embodiment of a SLCC DC transmission system based on six-pulsation converter valves, as shown in FIG. Figure 1 As shown, it includes a sending-end power grid, a rectifier-side converter station, an inverter-side converter station and a receiving-end power grid, and at least includes a first SVG, a first converter, a second SVG and a second converter;

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

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

[0031] The inverter-side converter station is connected to the receiving-end power grid. The inverter-side converter station is used to receive the direct current sent by the rectifier-side converter station, and convert the direct current into alternating current and send it to the receiving-end power grid.

[0032] In this embodiment, if Figure 1-Figure 3 As shown in FIG. 1 , the SLCC DC transmission system based on six-pulsation converter valves 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 to the AC side of the rectifier-side converter station via a transmission line, the rectifier-side converter station is connected to the inverter-side converter station via a DC line, and the inverter-side converter station is connected to the receiving-end power grid.

[0033] The converter station on the rectifier side and the converter station on the inverter side are SLCC, which consists of three-phase six-bridge arm SVG and traditional LCC converter. According to the engineering requirements, the SLCC DC transmission system based on six-pulse converter valves can use six-pulse converter valves SLCC at either end and six-pulse converter valves SLCC, conventional SLCC, LCC or MMC at the other end. The SLCC converter LCC on the rectifier side uses a twelve-pulse rectifier unit composed of two six-pulse thyristor rectifier units. The SVG is arranged in parallel between the twelve-pulse rectifier unit and the converter transformer. Each twelve-pulse rectifier unit is equipped with a set of SVG, and the SVG and LCC unit form a whole. The SLCC converter LCC on the inverter side uses a twelve-pulse inverter unit composed of two six-pulse thyristor rectifier units. The SVG is arranged in parallel between the twelve-pulse rectifier unit and the converter transformer. Each twelve-pulse rectifier unit is equipped with a set of SVG, and the SVG and LCC unit form a whole.

[0034] SVG has functions such as voltage support, reactive power compensation, active filtering and amplitude and phase correction. There is no need to install an AC filter on the SLCC side, and LCC is responsible for active power transmission. SVG is connected in parallel on the valve side on the basis of conventional LCC to form SLCC, which has the capabilities of reactive power compensation and voltage support.

[0035] It should be noted that the first SVG refers to the SVG in the rectifier side converter station, 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 refers to a static VAR generator, which is an advanced power electronic device mainly used for dynamic reactive power compensation.

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

[0037] In this embodiment, if Figure 4 As shown, Figure 4 The schematic diagram of the structure of the SVG unit based on the full-bridge submodule is shown in Figure 1. The SVG adopts the full-bridge submodule or half-bridge submodule in series, and the three-phase branches are connected in a bridge-like manner. The SVG consists of three-phase six-bridge branches, and each bridge arm is composed of a large number of half-bridge or full-bridge submodules cascaded and connected in series with a buffer reactor.

[0038] The upper and lower bridge arms of the six-pulse converter valve can be controlled separately according to the system requirements, with the same or different control objectives such as voltage support, reactive power compensation, and harmonic suppression, so as to achieve better overall control effect. The upper and lower three-phase bridge arms of the SVG are connected at the ports of the converter valve to form a neutral point. Under the condition of three-phase symmetry, the neutral point voltage is zero, and there is no electrical connection between the neutral points of the upper and lower bridge arms. The use of three-phase six-bridge arm SVG increases the zero-sequence current path of the system. During a fault, the zero-sequence current can be consumed by the interphase circulating current, reducing the zero-sequence current in the LCC during the transient process. And without increasing the number of sub-modules, each phase can compensate for reactive power, support system voltage, and suppress harmonics by controlling the upper and lower bridge arms, which has higher flexibility and can give full play to the performance of the equipment.

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

[0040] In this embodiment, the buffer reactor is configured on the grid-connected side of the SVG, and a total of six buffer reactors are configured for the three-phase six-bridge-arm SVG.

[0041] In some embodiments, the first SVG and / or the second SVG further comprises a starting circuit, which is arranged at a connection point between 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 in the SLCC converter is not provided with a starting circuit, and the SVG is provided with a starting circuit alone. The starting circuit is configured between the SVG on the valve side of the converter transformer and the connection point between the converter transformer and the LCC.

[0043] In some embodiments, the starting circuit includes at least a current measuring device, a starting resistor, and a single-pole isolating switch.

[0044] In this embodiment, the starting circuit preferably integrates a current measuring device, a starting resistor and a complete starting device with a single-pole disconnector, wherein the starting resistor can preferably replace the closing resistor of the incoming circuit breaker.

[0045] In some embodiments, the rectifier unit in the rectifier-side converter station is configured to be controlled by a fixed DC voltage, and the rectifier unit in the inverter-side converter station is configured to be controlled by a fixed AC voltage or a fixed reactive power.

[0046] In this embodiment, if Figure 5 As shown, Figure 5Schematic diagram of SLCC control function. When the SLCC DC transmission system based on six-pulse converter valves operates normally, the LCC thyristor rectifier unit in the rectifier side converter station adopts fixed DC voltage control, and the LCC thyristor rectifier unit in the inverter side converter station adopts fixed reactive power or fixed AC voltage control.

[0047] In some embodiments, when the first SVG and / or the second SVG is configured to perform harmonic complement control, the filtering order is 12n±1.

[0048] In this embodiment, if the SVG in the rectifier-side converter station and the SVG in the inverter-side converter station perform harmonic compensation control, according to system requirements, the filtering order can be preferably set to 12n±1 times, of which 6(2n)±1 can be offset by the upper and lower six-pulse unit transformers.

[0049] In some embodiments, the first SVG and / or the second SVG is configured to be charged by utilizing 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 this embodiment, there are two pre-charging methods for SVG, one is to charge the SVG through the power supply of the station, and the other is to start the station by pre-charging. For the method of pre-charging and starting the SVG through the power supply of the station, as the startup process of the SLCC converter station, it should be carried out in the state where the circuit breaker between the LCC and the converter transformer and SVG of the station is disconnected. The charging process should include two steps: passive charging and active charging. The SLCC converter station is located at the rectifier side converter station and the inverter side converter station.

[0051] The station power pre-charging start-up method should be carried out when the circuit breakers between the station LCC and SVG are closed, that is, the converter station on the power supply side does not need to be charged or the charging is completed. At this time, the circuit breaker between the station SLCC and the low-frequency / power frequency AC power supply / grid of the station should be in the open state.

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

[0053] In this embodiment, when SVG realizes functions such as voltage support, reactive power compensation, and harmonic suppression, its reactive power control quantity can be the valve side of the converter transformer where the SVG access point is located, or the grid side of the converter transformer connected to the AC system.

[0054] In some embodiments, when the first SVG or the second SVG is configured to have a reactive control variable on the grid side of the converter transformer, the current of the first converter or the second converter is introduced into the control loop of the first SVG or the second SVG.

[0055] In this embodiment, when the controlled variable is the grid-side reactive power of the converter transformer, it is necessary to introduce the LCC current into the SVG control loop to offset its influence on the SVG control link.

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

[0057] The SLCC DC transmission system based on six-pulse converter valves includes 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 a first SVG and a first converter, and the inverter-side converter station is composed of at least a second SVG and a second converter, wherein the first converter and / or the second converter include a rectifier unit composed of a plurality of six-pulse thyristor rectifier units, and the first SVG and / or the second SVG are configured in parallel in the rectifier unit. and the converter transformer, the converter transformer includes a first converter transformer and / or 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, and 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 used to receive the AC power transmitted by the sending-end power grid, and convert the AC power into DC power and send it 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 used to receive the DC power sent by the rectifier-side converter station, and convert the DC power into AC power and send it to the receiving-end power grid. By combining the two transmission technologies of conventional DC transmission and flexible DC transmission, complementary advantages are achieved, and the organic unity of technical economy and flexibility in the existing large-scale new energy transmission scenario is effectively achieved. The technology used is relatively mature, the pressure of technical research and development is relatively small, and engineering applications can be quickly realized, which has a strong promotion value. Therefore, the present invention can be widely used in large-scale new energy transmission scenarios.

[0058] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

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

Claims

1. A SLCC DC transmission system based on six-pulsation converter valves, 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 a 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 rectifier unit composed of a plurality of six-pulse thyristor rectifier units, the second converter includes an inverter unit composed of a plurality of six-pulse thyristor rectifier units, the first SVG is arranged in parallel between the rectifier unit and the first converter transformer, and the second SVG is arranged in parallel between the inverter unit and the second converter transformer; The sending-end power grid is connected to the AC side of the rectifier-side converter station through an AC line, and the DC side of the rectifier-side converter station is connected to the inverter-side converter station through a DC line. The rectifier-side converter station is used to receive the AC power transmitted by the sending-end power grid, and convert the AC power into DC power and then send it to the inverter-side converter station; The inverter-side converter station is connected to the receiving-end power grid, and is used to receive the direct current sent by the rectifier-side converter station, and convert the direct current into alternating current and send it to the receiving-end power grid.

2. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 1 is characterized in that: The first SVG and / or the second SVG is composed of three-phase six-bridge arm branches, and each of the bridge arms is connected to a buffer reactor after a plurality of half-bridge sub-modules or full-bridge sub-modules are cascaded.

3. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 2 is characterized in that: The snubber reactor is configured on the grid-connected side of the first SVG and / or the second SVG.

4. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 1, characterized in that: The first SVG and / or the second SVG further comprises a starting circuit, which is arranged at a connection point among the first SVG and / or the second SVG, the converter transformer and a converter, wherein the converter comprises a first converter and / or a second converter.

5. The SLCC DC power transmission system based on six-pulsation converter valves as claimed in claim 4 is characterized in that: The starting circuit at least comprises a current measuring device, a starting resistor and a single-pole isolating switch.

6. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 1, characterized in that: The rectifier unit in the rectifier-side converter station is configured to be controlled by a fixed DC voltage, and the rectifier unit in the inverter-side converter station is configured to be controlled by a fixed AC voltage or a fixed reactive power.

7. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 1, characterized in that: When the first SVG and / or the second SVG is configured to perform harmonic supplement control, the filtering order is 12n±1.

8. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 1, characterized in that: The first SVG and / or the second SVG is configured to be charged by utilizing the power supply of the rectifier-side converter station and the inverter-side converter station, or to be charged by pre-charging the rectifier-side converter station and the inverter-side converter station.

9. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 7, characterized in that: When the first SVG or the second SVG is configured to perform control through reactive power, the monitoring point of the reactive control amount is the grid side of the converter transformer of the station where the first SVG or the second SVG is located.

10. The SLCC DC power transmission system based on six-pulsation converter valves according to claim 9, characterized in that: When the reactive control variable monitoring point of the first SVG or the second SVG is configured as the grid side of the converter transformer, 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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