CN109066760B - Hybrid direct-current power transmission and current sharing control method for high-medium-voltage side-to-side direct-current line - Google Patents

Hybrid direct-current power transmission and current sharing control method for high-medium-voltage side-to-side direct-current line Download PDF

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CN109066760B
CN109066760B CN201810993139.9A CN201810993139A CN109066760B CN 109066760 B CN109066760 B CN 109066760B CN 201810993139 A CN201810993139 A CN 201810993139A CN 109066760 B CN109066760 B CN 109066760B
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高丙团
杨志超
胡正阳
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Southeast University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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Abstract

The invention discloses a mixed direct-current power transmission and current sharing control method for a direct-current line with a high-medium voltage side and a uniform-current side, which comprises the following steps of: s1: establishing a hybrid direct-current transmission system topology of a direct-current line on a high-medium voltage side and a uniform-output direct-current line on the basis of direct-current flexible transformation and the parallel operation characteristics of 400kV and 800kV submarine cables; s2: on the basis of the topology of the hybrid direct-current power transmission system, considering the constraint conditions including the through-current capacity of a current converter and a direct-current power instruction, and establishing a submarine cable power loss model; s3: and performing optimization calculation on the submarine cable power loss model to obtain the optimal current values of 400kV and 800kV submarine cables, and calculating direct current instructions of high-end and low-end converters according to the optimal current values to further realize current sharing control. The invention combines the advantages of the conventional converter and the flexible converter on one hand, and ensures the current coordination control of the high-low end converter at the rectifying side on the other hand, thereby realizing the reliable operation of the topology.

Description

Hybrid direct-current power transmission and current sharing control method for high-medium-voltage side-to-side direct-current line
Technical Field
The invention relates to the technical field of power transmission and distribution, in particular to a hybrid direct-current power transmission and current sharing control method for a direct-current line with a uniform output at a high and medium voltage side.
Background
According to the concept proposed by Liu Zhen Suan of the Global energy Internet research institute, the global power grid interconnection is completed in three steps: interconnection of power grids in continents, interconnection of power grids across continents and interconnection of power grids all over the world. With the development of the high-voltage direct-current technology and the increase of the power demand of each country, a series of predecessor projects are planned and implemented. At present, the direct-current voltage grade of cross-country interconnection engineering is not suitable to exceed 500kV due to the highest voltage grade of the direct-current submarine cable. Based on a planning scheme of certain transnational engineering, a 400kV domestic converter station is planned recently, and electric energy of China (a sending end LCC converter station) is transmitted to abroad (a receiving end MMC converter station) through a 400kV submarine cable; on the basis of the recent 400kV direct current project, the long-term project raises the direct current voltage to 800kV to realize the transmission of more electric energy. In order to avoid circuit waste, the 400kV submarine cable is reserved in the long-term project, and therefore hybrid direct-current transmission of direct-current circuits on the high and medium voltage sides is formed.
The hybrid direct-current transmission topology not only retains the advantages of a conventional converter and a flexible converter, but also supports the output of two voltage classes (400kV and 800 kV). Different from the control mode of the traditional double 12-pulse converter, the high-low end 12-pulse converter of the topology is connected with different direct current lines, and corresponding direct current controllers are required to be respectively configured for the high-low end converter. Because the resistance values of the submarine cables of the two voltage classes are different, and the resistance value of the 800kV submarine cable is smaller, the situation that more direct current flows through the 800kV submarine cable is considered, but the direct current of the 800kV submarine cable cannot be increased without limit due to the current capacity and power limitation of the current converter. Therefore, how to effectively configure the direct current of 400kV and 800kV submarine cables is crucial to the stable operation of the topology.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems in the prior art, the invention provides a hybrid direct-current power transmission and current sharing control method for a direct-current line with a high-medium voltage side and a uniform-current side, which combines the advantages of a conventional converter and a flexible converter on the one hand, and ensures the current coordination control of the high-low side converter on the rectification side on the other hand, thereby realizing the reliable operation of the topology.
The technical scheme is as follows: the invention relates to a hybrid direct-current power transmission and current sharing control method of a direct-current line with a high and medium voltage side output, which comprises the following steps:
s1: establishing a hybrid direct-current transmission system topology of a direct-current line on a high-medium voltage side and a uniform-output direct-current line on the basis of a direct-current flexible transformation idea and the parallel operation characteristics of 400kV submarine cables and 800kV submarine cables;
s2: on the basis of the topology of the hybrid direct-current power transmission system, considering the constraint conditions including the through-current capacity of a current converter and a direct-current power instruction, and establishing a submarine cable power loss model;
s3: and performing optimization calculation on the submarine cable power loss model to obtain the optimal current values of 400kV and 800kV submarine cables, and calculating direct current instructions of high-end and low-end converters according to the optimal current values to further realize current sharing control.
Further, the hybrid dc power transmission system topology established in step S1 includes a plurality of LCC converters located on the rectifying side, a plurality of MMC converters located on the inverting side, a plurality of 400kV submarine cables, and a 800kV submarine cable, where a high-end converter of the LCC converters is connected to the MMC converters through the 800kV submarine cables, and a low-end converter is connected to the MMC converters through the 400kV submarine cables. Specifically, the rectifying side comprises 4 double 12-pulse LCC converters which adopt constant-direct-current control; the inversion side comprises an MMC current converter integrated by 4 half-bridge type sub-modules, and a constant direct current voltage and constant alternating current voltage control mode or a constant direct current voltage and constant reactive power control mode is adopted.
Further, the submarine cable power loss model established in step S2 specifically includes:
Figure BDA0001781260730000021
Figure BDA0001781260730000022
in the formula, PLossFor total power loss, R, of submarine cable1、R2Resistance values of 400kV and 800kV submarine cables respectively; i is1、I2Direct currents respectively flowing through 400kV submarine cables and 800kV submarine cables; i is1max、I2maxThe maximum current values of the submarine cables flowing through 400kV and 800kV are respectively; prefThe power instruction value of the direct current system; u shape2、U1The DC voltages of the high-side converter and the low-side converter are respectively; i isLCCmaxThe maximum current value of the low-side inverter.
Further, in step S3, the dc current command values of the high-side and low-side inverters are specifically:
Figure BDA0001781260730000023
in the formula ILCC high end、ILCC low endDirect current instruction values of the high-side inverter and the low-side inverter respectively,
Figure BDA0001781260730000024
the optimum direct current for passing through 400kV and 800kV submarine cables, respectively.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the invention discloses a mixed direct-current power transmission and current sharing control method of a direct-current line with a high and medium voltage side, wherein the topology not only takes the advantages of a conventional converter and a flexible converter into account, but also can realize the output of two direct-current voltages; analyzing a simplified equivalent circuit diagram of the monopole system, and establishing a submarine cable power loss model by taking parameters of the current capacity, the power level, the voltage grade and the like of the two converters as constraint conditions; and analyzing the power loss model of the submarine cable through an optimization algorithm to obtain the direct current optimized values of the submarine cables with different voltage grades, further calculating the direct current instruction value of the high-low end converter at the rectifying side, and further reasonably configuring the high-low end converter controller. On the basis of the control idea of the traditional double 12-pulse converter, the design idea of independent configuration of a high-low end converter controller is provided, a current sharing control strategy is optimized based on the principle of minimum power loss of submarine cables, and stable operation and minimum line loss of the high-low end converter and two submarine cables with different voltage levels are realized.
Drawings
FIG. 1 is a topology diagram of a hybrid DC power transmission system with DC lines on the high and medium voltage side;
FIG. 2 is a simplified equivalent circuit diagram of a unipolar system;
fig. 3 is a block diagram of a current sharing controller configuration of a high-side converter and a low-side converter.
Detailed Description
The embodiment discloses a hybrid direct-current power transmission and current sharing control method for a direct-current line with a high-medium voltage side and a uniform-current side, which comprises the following steps of:
s1: based on the idea of direct current flexible transformation and the parallel operation characteristics of 400kV and 800kV submarine cables, the topology of a hybrid direct current transmission system with direct current lines on the high and medium voltage sides is established.
As shown in fig. 1, the hybrid dc transmission system topology includes a plurality of LCC converters located on the rectifying side, a plurality of MMC converters located on the inverting side, and a plurality of 400kV and 800kV submarine cables, wherein a high-end converter of the LCC converters is connected to the MMC converter through the 800kV submarine cable, and a low-end converter is connected to the MMC converter through the 400kV submarine cable. Specifically, the rectifying side comprises 4 double 12-pulse LCC converters which adopt constant-direct-current control; the contravariant side includes 4 half-bridge type submodule piece integrated MMC transverters, adopts and decides DC voltage and decides alternating voltage control mode, perhaps adopts and decides DC voltage and decides reactive power control mode, and every utmost point of bipolar system all has two direct current circuit, is 400kV and 800kV respectively.
S2: on the basis of the topology of the hybrid direct-current transmission system, a submarine cable power loss model is established by considering the constraint conditions including the through-current capacity of the converter and the direct-current power instruction.
Considering that the 400kV submarine cable and the 800kV submarine cable have different resistance values, the direct current values of the two submarine cables are reasonably distributed, the topology of the figure 1 is simplified, and an equivalent circuit diagram of a single-pole system is established, as shown in figure 2. Taking parameters such as the through-current capacity, the power level, the voltage grade and the like of the two converters as constraint conditions, and establishing a submarine cable power loss model as follows:
Figure BDA0001781260730000031
Figure BDA0001781260730000032
in the formula, PLossFor total power loss, R, of submarine cable1、R2Resistance values of 400kV and 800kV submarine cables respectively; i is1、I2Direct currents respectively flowing through 400kV submarine cables and 800kV submarine cables; i is1max、I2maxThe maximum current values of the submarine cables flowing through 400kV and 800kV are respectively; prefThe power instruction value of the direct current system; u shape2、U1The DC voltages of the high-side converter and the low-side converter are respectively; i isLCCmaxThe maximum current value of the low-side inverter.
S3: and performing optimization calculation on the submarine cable power loss model to obtain the optimal current values of 400kV and 800kV submarine cables, and calculating direct current instructions of high-end and low-end converters according to the optimal current values to further realize current sharing control.
The direct current instruction values of the high-side converter and the low-side converter are specifically as follows:
Figure BDA0001781260730000041
in the formula ILCC high end、ILCC low endDirect current instruction values of the high-side inverter and the low-side inverter respectively,
Figure BDA0001781260730000042
the optimum direct current for passing through 400kV and 800kV submarine cables, respectively.
Inputting the dc current instruction values of the high-side and low-side inverter controllers into the current sharing controller, the current sharing controller is as shown in fig. 3, and specifically includes: firstly, the controller obtains direct current setting values I of the high-end LCC converter and the low-end LCC converter through a submarine cable power loss optimization modelHigh end refAnd ILow end refThen collecting the direct current I from the rectifying sideLCC high endAnd ILCC low endAnd passing through a filtering element, and then combining IHigh end refAnd ILCC high end、ILow end refAnd ILCC low endMaking a difference, and making the difference signal pass through PI link to obtain βLCC high endAnd βLCC low end(radian), subtracting β from pi to obtain firing angle commands α of high and low end convertersLCC high endAnd αLCC low end。
By introducing the current-sharing controller, the independent control of the submarine cables with different voltage classes can be realized, namely the single-pole double-valve group is respectively controlled, and the minimum total power loss of the submarine cables is realized on the economic level.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (3)

1. A mixed direct current transmission and current sharing control method of a direct current line with a high and medium voltage side being output is characterized in that: the method comprises the following steps:
s1: establishing a hybrid direct-current transmission system topology with direct-current lines on the high and medium voltage sides on the basis of a direct-current flexible transformation idea and the parallel operation characteristics of 400kV and 800kV submarine cables, wherein the topology comprises a plurality of LCC converters on the rectifying side, a plurality of MMC converters on the inverting side, a plurality of 400kV submarine cables and 800kV submarine cables, a high-end converter in each LCC converter is connected with one MMC converter through one 800kV submarine cable, and a low-end converter in each LCC converter is connected with one MMC converter through one 400kV submarine cable;
s2: on the basis of the topology of the hybrid direct-current transmission system, a submarine cable power loss model is established by considering the constraint conditions including the through-current capacity of a current converter and a direct-current power instruction, and specifically comprises the following steps:
Figure FDA0002487628170000011
Figure FDA0002487628170000012
in the formula, PLossFor total power loss, R, of submarine cable1、R2Resistance values of 400kV and 800kV submarine cables respectively; i is1、I2Direct currents respectively flowing through 400kV submarine cables and 800kV submarine cables; i is1max、I2maxThe maximum current values of the submarine cables flowing through 400kV and 800kV are respectively; prefThe power instruction value of the hybrid direct current power transmission system is obtained; u shape2、U1The DC voltages of the high-side converter and the low-side converter are respectively; i isLCCmaxThe maximum current value of the low-end converter;
s3: and performing optimization calculation on the submarine cable power loss model to obtain the optimal current values of 400kV and 800kV submarine cables, and calculating direct current instructions of high-end and low-end converters according to the optimal current values to further realize current sharing control.
2. The hybrid direct-current power transmission and current sharing control method of the high-medium voltage side-sharing direct-current line according to claim 1, characterized in that: the rectifying side comprises 4 double 12-pulse LCC converters which adopt constant direct current control; the inversion side comprises an MMC current converter integrated by 4 half-bridge type sub-modules, and a constant direct current voltage and constant alternating current voltage control mode or a constant direct current voltage and constant reactive power control mode is adopted.
3. The hybrid direct-current power transmission and current sharing control method of the high-medium voltage side-sharing direct-current line according to claim 1, characterized in that: in step S3, the dc current command values of the high-side and low-side inverters are specifically:
Figure FDA0002487628170000013
in the formula ILCC high end、ILCC low endDirect current instruction values of the high-side inverter and the low-side inverter respectively,
Figure FDA0002487628170000014
the optimum direct current for passing through 400kV and 800kV submarine cables, respectively.
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