The application relates to an AC side main wiring structure of a symmetric bipolar flexible DC power transmission system considering single-pole blocking post-power transfer of offshore wind power

Abstract

The application relates to an offshore wind power symmetrical bipolar flexible DC power transmission system AC side main wiring structure considering single pole blocking power transfer. Compared with a traditional wiring mode, a sectional switch is additionally arranged between positive and negative high-voltage AC buses in a connecting area, that is, the positive and negative poles of the AC connecting area adopt a single-mother sectional wiring type. In a normal operation condition, the sectional switch is turned off, and each pole AC bus is connected with a corresponding pole converter transformer incoming line and a converter valve incoming line; when single pole blocking occurs, the switch between the fault pole AC bus and the fault pole blocking converter valve is turned off, the sectional switch between the positive and negative pole AC buses is turned on, and the fault pole offshore wind power is transferred to the normal pole for transmission. Compared with the traditional scheme, the scheme provided by the application is simple in wiring, easy to control, and the power transfer capacity is not limited by the rated capacity of a low-voltage power distribution device.

Description

Technical Field

[0001] This invention belongs to the field of offshore wind power flexible DC transmission technology, specifically relating to an AC side main wiring structure of an offshore wind power symmetrical bipolar flexible DC transmission system that considers power transfer after unipolar blocking. Technical Background

[0002] With the continuous increase in the scale and distance of offshore wind power installations, traditional power frequency AC transmission schemes are no longer suitable. Flexible DC transmission schemes based on fully controllable devices are becoming the mainstream solution for large-scale deep-sea wind power transmission. For the main wiring topology of flexible DC transmission systems, there are generally two forms: symmetrical monopolar and symmetrical bipolar. The former has a relatively simple wiring, but will lose all transmitted power in the event of a monopolar fault; the latter has more electrical equipment and operating modes, more complex wiring, and a higher cost for the same transmission capacity, but can still transmit half the power in the event of a monopolar fault. Therefore, for large-scale deep-sea wind power transmission projects, considering system reliability and stability, the symmetrical bipolar flexible DC transmission scheme is more suitable.

[0003] For offshore wind power using symmetrical bipolar flexible DC transmission, the design of its AC-side main wiring structure is crucial, directly affecting the system's steady-state operation and the switching between different operating modes, especially the transfer of offshore wind power to the normal pole after a fault pole is blocked. Traditional symmetrical bipolar flexible DC transmission systems employ dual-bus segmented wiring or more complex wiring configurations on the low-voltage side. By changing the low-voltage side wiring, power transfer and operation mode changes after unipolar blocking are achieved. However, this method is complex, and the power transfer capacity is significantly limited by the rated capacity of the low-voltage side distribution equipment. Therefore, it is necessary to consider the power transfer condition after unipolar blocking and optimize the design of the AC-side main wiring of the symmetrical bipolar flexible DC transmission system for offshore wind power. Summary of the Invention

[0004] The purpose of this invention is to provide an AC side main wiring structure for a symmetrical bipolar flexible DC transmission system for offshore wind power that considers power transfer after unipolar blocking. By setting a sectional switch on the high-voltage side bus in the AC connection area (forming a single bus sectional wiring type), the power transfer of offshore wind power after unipolar blocking can be realized. The wiring is simple and easy to control.

[0005] For the AC main wiring structure of the offshore wind power symmetrical bipolar flexible DC transmission system considering power transfer after unipolar blocking, including the AC wiring scheme of the connection area, the converter transformer wiring scheme, and the low-voltage AC wiring scheme, the specific composition of each system is as follows: (1) AC wiring scheme for connection area The connection zone refers to the AC area between the high-voltage side of the converter transformer and the converter valve. For a symmetrical bipolar flexible DC transmission system, there are positive and negative connection zones, and the wiring schemes for the two connection zones are the same. Compared with the traditional wiring method, this invention adds a sectionalizing switch between the positive and negative high-voltage AC buses in the connection zone. That is, the positive and negative AC connection zones adopt a single bus sectionalizing wiring type. Under normal operating conditions, the sectionalizing switch is open, and each pole's AC bus is connected to its respective pole's converter transformer inlet and converter valve inlet. When a single pole is blocked, the switch between the faulty pole's AC bus and the faulty pole's blocked converter valve is opened, and the sectionalizing switch between the positive and negative AC buses is closed, transferring the offshore wind power from the faulty pole to the normal pole for transmission.

[0006] (2) Converter transformer wiring scheme The low-voltage side (wind turbine inlet side) of the converter transformer adopts a double-split type and star connection method. The neutral point is grounded through a small resistor (the value of which can be calculated based on the charging current when a single-phase grounding occurs in the collector submarine cable); the high-voltage side adopts a delta connection method.

[0007] (3) Low-voltage AC wiring scheme The low-voltage AC wiring scheme refers to the wiring scheme of the low-voltage power distribution equipment. The low-voltage power distribution equipment is mainly used to collect incoming lines from offshore wind power collection cables, station service transformers, and other auxiliary equipment. In this invention, the low-voltage AC wiring adopts several sets of single-bus segmented wiring types, which are connected to the low-voltage side of the converter transformer in an interleaved manner. Interleaving means that the busbars on each set of single-bus segments are connected to the low-voltage side of two different converter transformers.

[0008] Compared with traditional solutions, the present invention has the following advantages: (1) Compared with the traditional symmetrical bipolar flexible DC transmission system main wiring structure, the present invention abandons the complex wiring method on the low-voltage side and adopts the AC bus section switch method of the newly added connection area. The offshore wind power transfer after single-pole blocking is realized by the opening and closing of the section switch. The wiring is simple and easy to control.

[0009] (2) Compared with the traditional symmetrical bipolar flexible DC transmission system main wiring structure, the present invention overcomes the limitation of power transfer by the rated capacity of the low-voltage side distribution device. After single-pole blocking, power transfer is realized by using the AC bus section switch in the closed connection area, which greatly improves the power transfer capability. Attached Figure Description

[0010] Figure 1 This invention provides a schematic diagram of the AC side main wiring structure of a symmetrical bipolar flexible DC transmission system for offshore wind power, considering power transfer after unipolar blocking.

[0011] Figure 2 This is a schematic diagram illustrating the principle of offshore wind power transfer after a single-pole blockage occurs in the main wiring structure provided by this invention. Detailed Implementation

[0012] The following is in conjunction with the appendix Figure 1 and 1 A 3GW offshore wind power case study is provided to illustrate the technical solution of this invention in detail: This invention proposes an AC-side main wiring structure for a symmetrical bipolar flexible DC transmission system for offshore wind power that considers power transfer after unipolar blocking, such as... Figure 1 As shown, it includes AC wiring 1 for the connection area, AC wiring 2 for the converter transformer, and AC wiring 3 for the low voltage area.

[0013] In this case, the AC connection 1 in the connection area includes AC connection 11 in the positive connection area and AC connection 12 in the negative connection area. The AC connection in the connection area adopts a single busbar segmented connection form, with one busbar for each of the positive and negative poles, and a disconnecting switch added between the positive and negative busbars. Specifically, the positive busbar is connected to the positive converter valve, positive converter transformer 21, and positive converter transformer 22 through circuit breakers Q11, Q12, and Q13, respectively. The negative busbar is connected to the negative converter valve, negative converter transformer 23, and negative converter transformer 24 through circuit breakers Q14, Q15, and Q16, respectively. The positive and negative busbars are connected by the segmented switch Q17. Under normal operating conditions, the segmented switch Q17 is open; under single-pole blocking conditions, the segmented switch Q17 is closed, used to realize the transfer of offshore wind power.

[0014] The converter transformer connection 2 includes the connections of a total of 4 converter transformers 21, 22, 23 and 24. The low-voltage side of the four converter transformers 21, 22, 23 and 24 all adopt a double split type and star connection method. The neutral point is grounded through a small resistor (the value of the small resistor can be calculated based on the charging current when the collector submarine cable is grounded in a single phase). The high-voltage side all adopt a delta connection method.

[0015] The low-voltage AC wiring 3 includes a total of 4 sets of single bus sectional wiring 31, 32, 33 and 34, which are connected to the low-voltage side of the converter transformer in an alternating manner. Specifically, the single bus sectional converter transformer output line 31 is connected to the positive converter transformer 21 and the positive converter transformer 22 respectively; the single bus sectional converter transformer output line 32 is connected to the positive converter transformer 22 and the negative converter transformer 23 respectively; the single bus sectional converter transformer output line 33 is connected to the negative converter transformer 23 and the negative converter transformer 24 respectively; and the single bus sectional converter transformer output line 34 is connected to the negative converter transformer 24 and the positive converter transformer 21 respectively.

[0016] Furthermore, the following is in conjunction with the appendix Figure 2 This explains how offshore wind power transfer can be achieved through the main wiring structure of the present invention after a single-pole blockage occurs.

[0017] Under normal operating conditions, Q11~Q16 are closed and Q17 is open. When a single pole fails and causes the positive pole converter valve to lock up, Q11 is open and Q17 is closed. The offshore wind power originally transmitted by the faulty positive pole will be transmitted to the normal negative pole converter valve through the AC bus of the connection area, thus realizing the transfer of offshore wind power after the single pole is locked up.

[0018] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. The AC-side main wiring structure of a symmetrical bipolar flexible DC transmission system for offshore wind power considering power transfer after unipolar blocking, characterized in that, A sectionalizing switch is added between the positive and negative high-voltage AC busbars in the connection area. That is, the positive and negative AC connection area adopts a single busbar sectionalizing connection type. Under normal operating conditions, the sectionalizing switch is open, and each AC busbar is connected to its respective converter transformer inlet and converter valve inlet. When a single pole is blocked, the switch between the AC busbar of the faulty pole and the blocked converter valve of the faulty pole is opened, and the sectionalizing switch between the positive and negative AC busbars is closed, transferring the offshore wind power of the faulty pole to the normal pole for transmission.

2. The AC side main wiring structure according to claim 1, characterized in that, The converter transformer adopts a double-split type and star connection on the low-voltage side, with the neutral point grounded through a small resistor; the high-voltage side adopts a delta connection.

3. The AC side main wiring structure according to claim 1, characterized in that, The low-voltage AC wiring adopts several sets of single bus section wiring types, and is connected to the low-voltage side of the converter transformer in an interleaved manner. Interleaving means that the busbars on each set of single bus sections are connected to the low-voltage side of two different converter transformers.

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