Saggowski island new energy positive and negative electrode addressing direct current delivery topological structure

Abstract

The invention discloses a new energy positive and negative pole addressing direct-current delivery topological structure of a Saggowski island, and relates to the technical field of new energy delivery and direct-current power transmission. The topological sending end of the topological structure is photovoltaic and wind power, new energy wind and light complementation of all areas is collected through short-distance collection lines, converted into direct current through respective modularized multi-level current converters, transmitted to the receiving end MMC current converters through direct-current overhead lines, inverted into alternating current and then merged into an alternating-current power grid. The conditions of large distribution scale and wide region of multi-type new energy such as wind, light and the like are fully considered, an original grounding line is flexibly utilized, optimization of system strength, fault occurrence rate and economical efficiency is realized, and large-scale transmission of the new energy of the wide-area Sgogong island is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy transmission and direct current power transmission, and in particular to a wide-area deserted island new energy positive and negative pole separated direct current transmission topology structure. Background Art

[0002] With the proposal of the "dual carbon" goal, Shagohuang Island has become the main transmission end of renewable energy power due to its abundant renewable energy. The large-scale Shagohuang Island new energy transmission scenario has the following characteristics: larger scale, the installed capacity of the new energy base will reach thousands to tens of thousands of megawatts; wider region, the area is as high as thousands to tens of thousands of square kilometers; without the support of conventional power supply, networking is difficult. This means that the transmission of new energy on Shagohuang Island faces the following challenges: the networking principles and grid structure of the sending-end power grid considering the characteristics of DC are unknown. Existing new energy island DC transmission projects mostly use energy bases to centrally gather and then transmit them through flexible DC converter stations, without considering the scenario of multi-type and large-scale new energy distributed in a wide area.

[0003] Flexible direct current transmission has a good development prospect. The hybrid MMC composed of half-bridge and full-bridge sub-modules not only has two control dimensions that can be used for network construction, but also has the ability to ride through direct current faults, which is suitable for scenarios where new energy is transmitted from isolated islands. At present, most flexible direct current converter stations are built at a unified site (positive and negative poles are arranged at the same site). However, this solution has the following problems: it does not take into account the large-scale and wide geographical distribution of various types of new energy such as wind and solar power, and the long AC electrical distance affects the strength of the system. To address this problem, the Jinshang DC project adopts a high-low valve address construction structure, but its high-low valve address needs to rely on long-distance overhead lines, and the DC fault rate is high and fault handling is difficult.

[0004] In order to solve the above problems, the present invention proposes a wide-area deserted island new energy positive and negative pole separated DC transmission topology structure. Summary of the invention

[0005] The purpose of the present invention is to propose a positive and negative pole separated DC transmission topology structure of new energy on the isolated island of Shagohuang to solve the problems raised in the background technology. The present invention fully considers the scenario in which multiple types of large-scale new energy are distributed in a wide area in the Shagohuang area, and proposes positive and negative pole separated construction using the original grounding line, which can realize short-distance collection line collection, improve the system strength, and can realize partial power transmission when there is a fault at the sending end, reducing the power shortage of the receiving end power grid.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The Shago Desert Island New Energy has a positive and negative pole separated DC transmission topology structure. The sending end of the topology structure is new energy, which is collected through multi-voltage AC and then converted into DC using their own modular multi-level converters. It is then transmitted to the receiving end MMC converter through DC overhead lines, inverted into AC and then incorporated into the AC power grid.

[0008] Preferably, the new energy sources are photovoltaic and wind power, and the new energy photovoltaic and wind power in each area are complementary.

[0009] Preferably, the topological structure is divided into area 1, area 2, area 3, and area 4. The wind power and photovoltaic power in area 1 and area 2 are complementary, flow into the positive sending-end converter station through the collecting line, are converted into direct current through rectification, and are sent out through the positive overhead line; the wind power and photovoltaic power in area 3 and area 4 are complementary, flow into the negative sending-end converter station through the collecting line, are converted into direct current through rectification, and are sent out through the negative overhead line.

[0010] Preferably, the modular multilevel converter is a half-bridge-full-bridge hybrid structure, composed of IGBTs and sub-module capacitors, for networking and handling DC faults.

[0011] Preferably, the modular multilevel converter comprises a positive converter and a negative converter, each area of ​​the topological structure is connected to the positive converter or the negative converter respectively, and the positive converter is connected to the negative converter via a 30-50 km grounding line.

[0012] Compared with the prior art, the present invention provides a Shago Desert Island new energy positive and negative pole addressing DC transmission topology structure, which has the following beneficial effects:

[0013] The present invention proposes a wide-area Shago deserted island new energy positive and negative pole separated address DC transmission topology structure, the positive and negative pole separated address DC transmission structure, compared with the positive and negative poles at the same address, has more independent system control rights, better fault characteristics, for high and low valve addressing, cancels the DC overhead line in the addressing process, improves economy, reduces the occurrence rate of DC faults, and has great application value to actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the topological structure of the wide-area Shago deserted island new energy positive and negative pole separate address direct current transmission proposed in Example 1 of the present invention;

[0015] Figure 2 It is a simulation waveform diagram of the AC side fault at the sending end when the positive and negative poles are arranged at the same location as proposed in Embodiment 1 of the present invention;

[0016] Figure 3 This is a simulation waveform diagram of the AC side fault at the sending end under the positive and negative pole addressing arrangement proposed in Example 1 of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0018] Embodiment 1:

[0019] The present invention proposes a Shagohuang isolated island new energy positive and negative pole separated DC transmission topology structure, which fully considers the scenario of multi-type and large-scale new energy distributed in a wide area in the Shagohuang area, and proposes positive and negative pole separated construction using the original grounding line, which can realize short-distance collection line collection, improve system strength, and can realize partial power transmission when a fault occurs at the sending end, reducing the power shortage of the receiving-end power grid.

[0020] Since a major feature of a DC converter station is that a grounding line of more than 30 km is required between the positive and negative poles, and the wind and solar resources in Shagohuang are concentrated, the original grounding line can be flexibly utilized to increase the distance between the positive and negative poles, form a single-pole network, increase the distance of the DC line, and reduce the electrical distance from the collection station to the converter station, thereby reducing the voltage level and achieving stability and economic optimization. Therefore, a positive and negative pole address layout is proposed, such as Figure 1 As shown:

[0021] The sending end of the wide-area Shago Desert Island new energy positive and negative pole separate address DC transmission topology is photovoltaic and wind power. The new energy in areas 1 and 3 are respectively collected through multi-voltage level AC, converted into DC through their own modular multi-level converters, and transmitted to the receiving end MMC converter through DC overhead lines. After being inverted into AC, they are integrated into the AC power grid.

[0022] Considering the characteristics of photovoltaic and wind power, the areas corresponding to the positive and negative poles need to complement each other. For the Shagohuang area with a diameter of about 100 kilometers, the wind and solar characteristics of the new energy stations corresponding to the two sub-site converter stations are basically the same, so the mutual assistance between the positive and negative poles is not considered during steady-state operation.

[0023] To simplify the analysis, it is assumed that the voltage of each node is equal to the rated voltage, and the nominal voltage of node i and the rated capacity of the equipment connected to this point are taken as the reference voltage and reference capacity. Then the multi-infeed short-circuit ratio of the flexible DC converter station with the positive and negative poles at the same location can be simplified to formula (1):

[0024]

[0025] In the formula, They represent the self-impedance and mutual impedance of the nodes in the equivalent impedance matrix of the positive and negative co-located system respectively.

[0026] Similarly, we can get Figure 1 Under the arrangement of positive and negative pole addresses shown, the short circuit ratio is as shown in formula (2):

[0027]

[0028] In the formula, Respectively Figure 1 Self-impedance and mutual impedance in the equivalent impedance matrix of the system shown.

[0029] After the positive and negative poles are arranged separately, the distance of the AC collection line can be shortened. The AC equivalent impedance in formula (2) will be further reduced compared with formula (1). After the positive and negative poles are arranged separately, the short-circuit ratio of the new energy grid connection point can be further improved.

[0030] The following further describes the Shago Desert Island New Energy positive and negative pole separated DC transmission topology structure proposed by the present invention in conjunction with the accompanying drawings, and the specific reasons are as follows.

[0031] Figure 1 This is a schematic diagram of the DC transmission topology of the wide-area deserted island new energy with positive and negative polarity. Figure 1 As shown in the figure, wind power and photovoltaic power in Area 1 and Area 2 complement each other, flow into the positive sending-end converter station through the collection line, and are sent out through the positive overhead line after being rectified into DC power. Wind power and photovoltaic power in Area 3 and Area 4 complement each other, flow into the negative sending-end converter station through the collection line, and are sent out through the negative overhead line after being rectified into DC power. Among them, the positive converter station and the negative converter station are connected by a 30-50km grounding line.

[0032] The converter station is a hybrid modular multi-level converter composed of half-bridge and full-bridge sub-modules. It is composed of IGBTs and sub-module capacitors, can form a grid to form voltage, and has the ability to ride through DC faults. New energy only needs to follow the grid to operate.

[0033] Figure 2 The system waveform when a fault occurs in the AC system at the sending end with the positive and negative poles arranged at the same location. Figure 2 It can be seen from (a) and 2(b) that for the sending-end converter station with the positive and negative poles co-located, the fault causes a sharp drop in the AC voltage, and the active power also drops rapidly. The voltage drop caused by the fault causes the voltage outer loop control output of the steady-state control strategy of the sending-end converter station to saturate, making it impossible to effectively control the AC voltage. The sudden increase in short-circuit current cannot be effectively suppressed, and the rapid increase in bridge arm current will cause overcurrent in the power devices of the converter. To prevent the sub-module from discharging for a long time, when the sub-module capacitor voltage is detected to be low, the overcurrent protection of the converter is triggered, and the limit value is set to ±0.1pu, thereby suppressing the bridge arm current, such as Figure 2 In addition, the short-circuit current and active power contributed by the sending-end converter station come from the MMC submodule capacitor, which causes the submodule capacitor voltage to decrease, as shown in Figure 2 (d) as shown.

[0034] When a new UHV flexible DC transmission system is constructed with positive and negative poles separated, the AC voltage at the non-fault pole can still remain stable. Figure 3 (a) As shown; the non-faulty pole can still deliver at rated power, such as Figure 3 (b) as shown; Figure 2 Compared with (c) and (d), the bridge arm current and submodule average capacitor voltage of the non-fault pole can still maintain the rated value and are not affected by the fault pole AC system. In summary, the topological structure of cluster networking and positive and negative pole address construction improves system reliability, reduces the power shortage of the receiving end grid, and is conducive to improving economic benefits.

[0035] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. The positive and negative poles of the Shago Desert Island New Energy DC transmission topology structure is characterized by: The sending end of the topological structure is new energy, which is collected through multi-voltage AC, converted into DC by respective modular multi-level converters, and transmitted to the receiving end MMC converter through DC overhead lines, and then inverted into AC and incorporated into the AC power grid.

2. The Shago Desert Island new energy positive and negative pole separate address direct current transmission topology structure according to claim 1 is characterized in that: The new energy sources specifically include photovoltaic power and wind power, and the new energy photovoltaic power and wind power in each area are complementary.

3. The Shago Desert Island new energy positive and negative pole separate address direct current transmission topology structure according to claim 2 is characterized in that: The topological structure is divided into area 1, area 2, area 3, and area 4. The wind power and photovoltaic power in area 1 and area 2 complement each other, flow into the positive sending-end converter station through the collecting line, are converted into direct current through rectification, and then are sent out through the positive overhead line; the wind power and photovoltaic power in area 3 and area 4 complement each other, flow into the negative sending-end converter station through the collecting line, are converted into direct current through rectification, and then are sent out through the negative overhead line.

4. The Shago Desert Island new energy positive and negative pole separate address direct current transmission topology structure according to claim 1 is characterized in that: The modular multi-level converter is a half-bridge-full-bridge hybrid structure, composed of IGBTs and sub-module capacitors, and is used to form a network and handle DC faults.

5. The Shago Desert Island new energy positive and negative pole separate address direct current transmission topology structure according to claim 4 is characterized in that: The modular multilevel converter includes a positive converter and a negative converter. Each area of ​​the topological structure is connected to the positive converter or the negative converter to realize short-distance collection line collection. The positive converter and the negative converter are connected through a 30-50km grounding line.

Images