Intermediate-frequency net-following type symmetrical monopole offshore converter station
By increasing the operating frequency of the offshore converter station to the intermediate frequency, the size and weight of transformers, reactors, and converter valves are reduced, solving the problem of excessive equipment size and weight, achieving compactness and lightweight design of the offshore converter station, and reducing engineering costs.
Patent Information
- Application Number
- CN202410576012.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-10
- Publication Date
- 2025-11-11
AI Technical Summary
Existing offshore converter station equipment is too large and heavy, resulting in wasted space and high engineering costs.
The medium-frequency grid-type symmetrical single-pole offshore converter station adopts a design that increases the operating frequency to 100-200Hz, thereby reducing the leakage reactance of the transformer, the inductance of the bridge arm reactor, and the capacitance of the converter valve, thus achieving equipment compactness and lightweight design.
This effectively reduced the size and weight of offshore converter station equipment, lowered construction costs, and improved the project's economic efficiency.
Smart Images
Figure CN120934048A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of water conservancy and hydropower engineering technology, specifically to a medium-frequency grid-type symmetrical single-pole offshore converter station. Background Technology
[0002] With the large-scale and deep-sea development of offshore wind power in my country, the investment in the power transmission portion of offshore wind power is increasing, and it also plays an important role in power transmission. Flexible DC transmission technology has many advantages, such as system stability, decoupling between AC and DC systems, independent control of active and reactive power, and flexible regulation methods. It is especially suitable for grid connection and power transmission of long-distance, large-capacity deep-sea offshore wind farms.
[0003] In existing projects, the operating frequency of offshore AC systems is the same as that of onshore AC systems, using the power frequency of 50Hz. However, an offshore wind farm system is actually an independent system, and its operating frequency can be freely chosen. Furthermore, at the aforementioned power frequency, due to spatial design and equipment placement issues, there is room for optimization in the weight and size of converter transformers, converter valves, and bridge arm reactors. This leads to wasted space and a large overall footprint for the converter station, thus increasing the design and construction difficulty under marine environmental load conditions and significantly raising project costs. Summary of the Invention
[0004] The purpose of this invention is to provide a disassembly tool that can easily and conveniently separate the rotary wheel and the rotary wheel spindle.
[0005] Therefore, the present invention adopts the following technical solution:
[0006] A medium-frequency grid-connected symmetrical monopole offshore converter station operates its DC transmission system at a frequency of 100-200Hz. This operating frequency reduces the leakage reactance of the transformer, the inductance of the bridge arm reactor, and the capacitance of the converter valve submodules compared to conventional power frequency-connected offshore wind farms. (That is, based on the principle of electromagnetic induction, increasing the operating frequency directly reduces the leakage reactance of the transformer, the inductance of the bridge arm reactor, and the capacitance of the converter valve submodules, thereby compressing the volume and weight of the equipment within the offshore converter station.) Compared to conventional power frequency-connected offshore wind farms, this reduces the impact of power frequency on the offshore converter station. The station's equipment and the spaces between them are designed for compact use. The offshore converter station includes a lower through-level platform and an upper through-level platform. A valve hall is installed in the central section of the lower through-level platform, and a DC field is installed in the side section of the upper through-level platform. The AC field of the offshore converter station includes a 66kV AC GIS room and a 330kV AC GIS room. The 66kV AC GIS room is located in the side section of the lower through-level platform, and the 330kV AC GIS room is located in the central section of the upper through-level platform. A connecting transformer room adjacent to the 330kV AC GIS room is also installed in the central section of the upper through-level platform.
[0007] Furthermore: the grid-side frequency design frequency for both offshore wind farms and offshore converter stations adopts the intermediate frequency f. m =n·f0 (n = 2, 3, 4...), which can reduce the transformer leakage reactance ratio to 1 / n of the conventional scheme, reduce the converter valve capacitance value to 1 / n of the conventional scheme, and reduce the bridge arm reactor inductance value to 1 / n of the conventional scheme. 2 This effectively reduces the size and weight of key equipment in offshore converter stations.
[0008] Furthermore, the 66kV AC GIS room and the DC field are respectively located on opposite sides of the central area.
[0009] Furthermore, the offshore converter station is also equipped with an auxiliary equipment room, which includes a lower auxiliary equipment room and an upper auxiliary equipment room. The lower auxiliary equipment room is located in the side area opposite to the 66kV AC GIS room.
[0010] Furthermore, the upper auxiliary equipment room is located in the middle area of the upper through-level platform, adjacent to the connecting transformer room and the 330kV AC GIS room.
[0011] Furthermore, a communication relay protection room is also provided on the upper through-level platform. The area where the communication relay protection room is located is opposite in direction to the 66kV AC GIS room relative to the central area.
[0012] Furthermore: the high-voltage side and low-voltage side of the connecting transformer room are electrically connected to the 330kV AC GIS room and the 66kV AC GIS room, respectively; the AC side of the converter valve in the valve hall is electrically connected to the outgoing cable of the 330kV AC GIS power distribution device; and the DC side of the converter valve is led to the DC field.
[0013] Compared with the prior art, the present invention has the following beneficial effects:
[0014] This invention employs a medium-frequency grid-connected offshore wind power DC transmission system. Based on the principle of electromagnetic induction, increasing the operating frequency can reduce the size and weight of transformers and reactors, and decrease the capacitance value of MMC submodule capacitors, thereby achieving miniaturization and lightweighting of the offshore converter station platform and reducing the construction cost of long-distance offshore wind power DC transmission systems. As a result, the external dimensions of equipment such as transformers and reactors in the offshore converter station decrease with increasing frequency. Therefore, the size of each major equipment room can be effectively reduced, thus solving the problem of the large size and excessive weight of the offshore converter station platform, reducing the procurement and manufacturing costs of steel structures, and achieving higher engineering economics. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the lower through-layer platform of the present invention;
[0016] Figure 2 This is a schematic diagram of the upper through-layer platform of the present invention;
[0017] Figure 3 This is a comparison diagram of the lower through-layer platform (bottom) of the converter station of the present invention and the lower through-layer platform (top) of a conventional power frequency converter station;
[0018] Figure 4 This is a comparison diagram of the upper through-layer platform (lower) of the converter station of the present invention and the upper through-layer platform (upper) of a conventional power frequency converter station.
[0019] The markings in the attached diagram are as follows: 110-66kV AC GIS room; 120-connection transformer room; 130-330kV AC GIS room; 200-valve hall; 300-DC field; 400-lower auxiliary equipment room; 500-upper auxiliary equipment room. Detailed Implementation
[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.
[0021] This embodiment increases the operating frequency of the offshore wind farm system to the medium frequency range (100-200Hz, generally n times the power frequency). Based on the offshore converter station operating in a constant AC voltage amplitude and frequency (V / f) control mode, it provides supporting voltage for the entire offshore AC system. Therefore, using the medium frequency on the wind farm side of the flexible DC transmission system will not affect the operational performance of the flexible DC transmission system, creating an independent medium frequency power grid for offshore wind power.
[0022] Therefore, the converter valves and grid-side equipment of the offshore converter station all use medium-frequency equipment; the wiring and control strategies of the remaining systems are equivalent to those of a conventional symmetrical single-pole converter station. In this embodiment, f is selected. m The equipment parameters and manufacturing are designed based on the frequency of n·f0, with the frequency selection range being typical mid-frequency parameters within 100-200Hz, such as 100Hz, 150Hz, 180Hz, and 200Hz. Based on this optimal frequency, the core equipment such as transformers, converter valves, and bridge arm reactors have significantly reduced footprint and size compared to conventional 50Hz power frequency equipment, thus drastically reducing the footprint and weight of the offshore converter station.
[0023] like Figure 1-4 As shown, a medium-frequency grid-type symmetrical single-pole offshore converter station arranges the interconnecting transformers, converter valves, and bridge arm reactors—which can be optimized in terms of size and weight—in corresponding rooms. The offshore converter station includes a lower through-level platform and an upper through-level platform. The middle section of the lower through-level platform is equipped with a valve hall 200 mm high. Figure 3 The shaded area in the lower through-level platform of a conventional power frequency converter station represents the reduced area of the valve hall 200. A DC field 300 is installed on the side area of the upper through-level platform. Figure 4 The shaded area in the upper through-level platform of the conventional power frequency converter station represents the reduced area of the DC field 300. The valve hall 200 and the DC field 300 are arranged adjacent to each other vertically. The AC field of the offshore converter station includes a 66kV AC GIS room 110 and a 330kV AC GIS room 130. The 66kV AC GIS room 110 is located in the side area of the lower through-level platform, and the 330kV AC GIS room 130 is located in the middle area of the upper through-level platform. A connecting transformer room 120 adjacent to the 330kV AC GIS room 130 is also set in the middle area of the upper through-level platform.
[0024] In this embodiment, the valve hall 200 has a height of approximately 20m within the lower through-level platform (divided into 1 to 3 levels). The DC field 300 has a height of approximately 15m within the upper through-level platform (divided into 4 to 6 levels).
[0025] Specifically, the offshore converter station is also equipped with auxiliary equipment rooms, including a lower auxiliary equipment room 400 and an upper auxiliary equipment room 500. The lower auxiliary equipment room 400 is located in the side area opposite to the 66kV AC GIS room 110. The upper auxiliary equipment room 500 is located in the middle area of the upper through platform, adjacent to the connecting transformer room 120 and the 330kV AC GIS room 130. There are two upper auxiliary equipment rooms 500, which are separated on both sides of the 330kV AC GIS room 130.
[0026] The lower auxiliary equipment room 400 includes a cooling room, seawater pump room, valve cooling room, fresh air handling unit room, refrigeration room, spare parts room, offices, rest room, and other equipment rooms. The upper auxiliary equipment room 500 includes a secondary equipment room, communication equipment room, battery room, station power supply room, air conditioning equipment room, and other equipment rooms.
[0027] In this embodiment, it should be noted that the 330kV AC GIS room 130 is located between the connecting transformer room 120 and the DC field 300. This allows the equipment rooms included in the upper auxiliary equipment room 500 to be separated and filled into the empty space around the 330kV AC GIS room 130. Therefore, placing the DC field 300 in the side area can effectively save the overall platform size. Furthermore, the overall electrical process flow of this embodiment is the same as that of the prior art, with the sequence being from connecting transformer room 120 - 330kV AC GIS room 130 - valve hall 200 - DC field 300.
[0028] The 66kV AC GIS room 110 and the DC field 300 are located on opposite sides of the central area. A communication relay protection room is also located on the upper through-level platform, with its location opposite to that of the 66kV AC GIS room 110 relative to the central area. Correspondingly, the 66kV AC GIS room 110 is located below the communication relay protection room, and the lower auxiliary equipment room 400 is located below the DC field 300.
[0029] Specifically, the 66kV AC submarine cable is directly connected from the offshore wind farm to the offshore converter station, and is led through a cable shaft to the 66kV AC GIS distribution device in the 66kV AC GIS room 110. The high-voltage side of the connecting transformer room 120 is electrically connected to the 330kV AC GIS room 130, and the low-voltage side of the connecting transformer room 120 is electrically connected to the 66kV AC GIS distribution device using split windings. The 330kV AC GIS distribution device in the 330kV AC GIS room 130 adopts a "two-in, one-out" single busbar connection, and the 330kV AC outgoing cable is connected to the AC side of the converter valve. The DC side of the converter valve is led through a wall bushing to the DC field 300, and the DC submarine cable is led down through a cable shaft and then out.
[0030] In this embodiment, the impact of using a medium-frequency converter station on key equipment parameters, as well as its dimensions and weight, is analyzed as follows:
[0031] In this embodiment, the transformer parameters of the main circuit design of the offshore converter station adopt a medium-frequency connected transformer, and the transformer capacity is selected based on the total capacity of the transmission circuit. Under the premise of constant transformer capacity, due to the increase in frequency, the transformer leakage reactance parameter Lt, which has a decisive influence on the size and weight of the transformer equipment, is shown in equation (1) below. According to f m = n·f0, therefore, compared to conventional power frequency equipment, the transformer leakage reactance can be directly reduced inversely:
[0032]
[0033] In equation (1) above: U tN The rated voltage of the connection transformer; X t S represents the percentage of the short-circuit impedance of the connecting transformer. tN For the capacity of the connecting transformer; f m This refers to the intermediate frequency (IF) of the AC system.
[0034] Correspondingly, since the reactance of the transformer is inversely proportional to the frequency, according to formula (1), the transformer inductance is reduced to about 1 / 3 of that of the power frequency transformer when calculated at a frequency of 150Hz. Ideally, the transformer coil can be reduced to 1 / 3 of the conventional scheme. However, since the transformer insulation level has not changed, the transformer's external dimensions are limited by the voltage insulation level and have not been significantly adjusted. Only the coil material is optimized, but the weight can still be reduced to about 60% of that of the power frequency transformer.
[0035] The converter valve capacitor parameters for the main circuit design of the offshore converter station in this embodiment are designed according to the following formula (2):
[0036]
[0037] In equation (2) above: U dc The rated voltage of the DC system; Nc is determined by the number of cascaded submodules in each bridge arm; S VN The rated capacity of the converter valve; ε c The voltage fluctuation rate of the submodule capacitor is determined by the voltage fluctuation amplitude of the submodule capacitor and the DC component of the submodule capacitor voltage.
[0038] According to equation (2), under the premise that the rated DC voltage, rated capacity of the converter valve, and number of bridge arm submodules of the flexible DC transmission system are constant, based on f m =n·f0, therefore the capacity of the sub-module of the converter valve can be reduced inversely, thus providing a prerequisite for the miniaturization and lightweight design of the converter valve.
[0039] Correspondingly, since the capacitance of the converter valve is inversely proportional to the frequency, the capacitance value for a 150Hz intermediate frequency can be reduced to 1 / 3 of the conventional solution according to formula (2). Similarly, since the insulation level has not changed, the reduction in the size of the equipment is slightly limited. Therefore, the capacitance can be reduced to about 60% of the power frequency parameter. The width dimension of the converter valve can be reduced to about 75% of the original equipment. The overall weight of the converter valve can be reduced to about 75% of the original equipment. Therefore, the size and weight of the valve hall 200 can be greatly optimized.
[0040] The bridge arm reactor parameters for the main circuit design of the offshore converter station in this embodiment are designed using the following formula:
[0041]
[0042] In equation (3) above: Nc is determined by the number of cascaded sub-modules in each bridge arm; C0 is the calculated result of the converter valve capacitor parameter, as shown in equation (2).
[0043] Correspondingly, since the reactance value of the bridge arm reactor is inversely proportional to the frequency, the size and weight of the bridge arm reactor can be reduced. According to formula (3), for a mid-frequency of 150Hz, the inductive reactance of the bridge arm reactor can be reduced to about 1 / 9 of the original equipment. Since the insulation level of the reactor has not changed, the size reduction of the bridge arm reactor is limited, but the weight can be reduced due to the reactance value. The reactor's external dimensions can be reduced to about 60% of the conventional solution, and the weight can be reduced to about 70% of the conventional solution.
[0044] The above embodiments are merely preferred technical solutions of the present invention. Those skilled in the art should understand that modifications or substitutions to the technical solutions or parameters in the embodiments can be made without departing from the principles and essence of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.
Claims
1. A medium-frequency grid-type symmetrical single-pole offshore converter station, characterized in that: The DC transmission system of the offshore converter station operates at a frequency of 100-200Hz. This operating frequency reduces the leakage reactance of the transformer, the inductance of the bridge arm reactor, and the capacitance of the converter valve submodule compared to offshore wind farms that use conventional power frequency, thus enabling a more compact use of space for each piece of equipment in the offshore converter station and between them. The offshore converter station includes a lower through-level platform and an upper through-level platform. A valve hall (200) is provided in the middle section of the lower through-level platform, and a DC field (300) is provided in the side section of the upper through-level platform. The AC field of the offshore converter station includes a 66kV AC GIS room (110) and a 330kV AC GIS room (130). The 66kV AC GIS room (110) is located in the side section of the lower through-level platform, and the 330kV AC GIS room (130) is located in the middle section of the upper through-level platform. A connecting transformer room (120) adjacent to the 330kV AC GIS room (130) is also provided in the middle section of the upper through-level platform.
2. The medium-frequency grid-type symmetrical single-pole offshore converter station according to claim 1, characterized in that: The 66kV AC GIS room (110) and the DC field (300) are respectively located on opposite sides of the middle zone.
3. A medium-frequency grid-type symmetrical single-pole offshore converter station according to claim 1, characterized in that: The offshore converter station is also equipped with an auxiliary equipment room, which includes a lower auxiliary equipment room (400) and an upper auxiliary equipment room (500). The lower auxiliary equipment room (400) is located in the side area opposite to the 66kV AC GIS room (110).
4. A medium-frequency grid-type symmetrical single-pole offshore converter station according to claim 3, characterized in that: The upper auxiliary equipment room (500) is located in the middle area of the upper through-floor platform, adjacent to the connecting transformer room (120) and the 330kV AC GIS room (130).
5. A medium-frequency grid-type symmetrical single-pole offshore converter station according to claim 1, characterized in that: A communication relay protection room is also provided on the upper through-layer platform. The area where the communication relay protection room is located is opposite to the central area of the 66kV AC GIS room (110).
6. A medium-frequency grid-type symmetrical single-pole offshore converter station according to claim 1, characterized in that: The high-voltage side and low-voltage side of the connecting transformer room (120) are electrically connected to the 330kV AC GIS room (130) and the 66kV AC GIS room (110) respectively. The AC side of the converter valve in the valve hall (200) is electrically connected to the outgoing cable of the 330kV AC GIS power distribution device. The DC side of the converter valve is led to the DC field (300).