CN106655236B

CN106655236B - High-voltage direct-current transmission system adopting absorption and parallel capacitor commutation

Info

Publication number: CN106655236B
Application number: CN201611069035.6A
Authority: CN
Inventors: 罗隆福; 周冠东; 张志文; 赵亮; 梁崇淦; 欧阳志国
Original assignee: Hunan Huada Electrician Hi Tech Co ltd; Hunan University
Current assignee: Hunan Huada Electrician Hi Tech Co ltd; Hunan University
Priority date: 2016-10-18
Filing date: 2016-11-29
Publication date: 2023-07-21
Anticipated expiration: 2036-11-29
Also published as: CN106655236A

Abstract

The invention discloses a high-voltage direct-current transmission system adopting absorption and parallel capacitor commutation. The high-voltage winding side of the converter transformer is connected with a high-voltage power grid, the absorption and parallel capacitor is connected with the low-voltage winding side of the converter transformer after being connected with the converter in parallel, and the absorption and parallel capacitor is connected in a triangular mode or a star mode. The invention can absorb the high frequency component of the voltage or current on the valve side winding of the converter transformer, filter out the harmonic voltage or current, realize reactive compensation and replace the passive filter device arranged on the network side winding of the converter transformer; noise of the converter transformer is reduced, and a BOX-IN noise reduction device is canceled; commutation of the rectifier and inverter can be improved; the operation loss of the converter transformer is reduced, and the service lives of the wall bushing and the converter transformer are prolonged. The method can be suitable for ultra-high voltage and ultra-high voltage direct current transmission.

Description

High-voltage direct-current transmission system adopting absorption and parallel capacitor commutation

Technical Field

The invention relates to a high-voltage direct-current transmission system, in particular to a high-voltage direct-current transmission system adopting absorption and parallel capacitor commutation.

Background

In a high-voltage direct-current transmission system, as the short-circuit impedance of the converter transformer is between 18 and 22 percent, the commutation overlap angle is large, and in order to avoid commutation failure, the arc extinguishing angle gamma is always ensured to have a margin of 15 degrees or more. This results in a dc power converter station consuming a large amount of reactive power.

For a traditional direct current transmission system adopting a grid commutation converter (LCC) technology, since the commutation voltage is all provided by an alternating current grid, a weak alternating current system is easy to cause commutation failure; and all reactive power of about 50% of direct current power is provided by a network side compensation system through a converter transformer, so that the capacity requirement and loss of the converter transformer are increased. And 5 times and 7 times of characteristic harmonic currents caused by the converter are subjected to converging filtering on the network side by a 12-pulse converter system, and 11 times, 13 times and higher filters are additionally arranged, so that the harmonic content of the network side is ensured to meet the requirement. Reactive power required by the converter and the converter transformer is partially compensated by the filter, and the rest is provided by a parallel capacitor SC on the network side alternating current bus.

For high voltage direct current transmission using series Capacitor Commutated Converter (CCC) technology, the above-mentioned disadvantages of grid commutated converters can be overcome. The fixed capacitor is connected in series between the converter transformer and the converter of the traditional converter system, and reactive power consumption of the converter is compensated by the capacitor connected in series, so that the system can still operate stably when the alpha (rectification) and gamma (inversion) angles of the converter are close to 0 and even negative. The reactive power is reduced, so that the reactive power consumption is greatly reduced, and the occurrence of commutation failure is avoided. However, the problem of transient overvoltage limits the engineering applications of CCC technology.

In ultra-high voltage and extra-high voltage direct current transmission systems, during converter (rectifying and inverting) commutation, voltage waveforms with severe burrs are generated on the valve side windings of the converter transformer, and fourier decomposition shows that the voltage contains a large n=6k±1 (k=1, 2, 3.) low order characteristic harmonic wave, and also contains a rich high order component.

Experimental studies conducted by the applicant have shown that: it is because this severely distorted voltage causes converter transformer noise to exceed the power transformer noise of the same capacity by more than 80 db, so that expensive BOX-IN technology has to be employed to meet environmental requirements.

Disclosure of Invention

In order to solve the technical problems of the existing direct current transmission system, the invention provides the high-voltage direct current transmission system which is low in harmonic wave, low in loss, long in service life and low in noise and adopts absorption and parallel capacitor commutation. The system is connected with an absorption capacitor in parallel on an alternating current bus of a valve side winding outgoing line of the converter transformer to realize the conversion of the converter, and replaces a filtering and compensating device (FC+SC) connected with the alternating current bus on the network side of the traditional direct current transmission system in parallel. Compared with LCC and CCC, ASCC not only can compensate reactive power and improve commutation, but also can effectively filter out 7 times and more harmonic waves of a 6 pulse wave system (12 pulse wave system, 5 times and 7 times harmonic currents on the net side are filtered after being converged by two 6 pulse wave systems), and the noise of the converter transformer is reduced.

The technical scheme adopted by the invention for solving the technical problems is as follows: the high-voltage direct-current transmission system adopting absorption and parallel capacitor commutation comprises a converter transformer, an absorption and parallel capacitor and a converter, wherein the high-voltage winding side of the converter transformer is connected with a high-voltage power grid, and the absorption and parallel capacitor is connected with the converter in parallel at the low-voltage winding side of the converter transformer.

The absorption and parallel capacitor adopts triangle connection.

The absorption and parallel capacitors may also be star-coupled.

The beneficial effects of the invention are as follows:

1) The noise of the converter transformer is greatly reduced, and a BOX IN noise reduction device is canceled;

2) The system replaces the traditional network side filtering and power factor compensation system of high-voltage direct-current transmission, and meets the requirements of filtering (the network side current distortion rate can be realized to be less than 5%) and power factor compensation of a (special) high-voltage direct-current transmission system;

3) The operation capacity and loss of the converter transformer are reduced;

4) Electromagnetic stress born by the converter transformer and the wall bushing can be greatly reduced, so that the service life is prolonged;

5) The running loss of the converter transformer is reduced, so that the starting frequency of the cooling fan is reduced, and the noise of the converter transformer is further reduced;

6) Commutation of the converter can be improved, in particular to reduce the inverter failure. And the alpha (rectification) and gamma (inversion) angles of the converter are lower than the traditional 15 DEG, so that reactive power requirements and harmonic current content are reduced.

Drawings

Fig. 1 is a block diagram of a conventional dc power transmission system.

The components in fig. 1 are described as follows:

1: ac power transmission system, 2: converter transformer 3: filtering and compensating means (fc+sc), 3: converter transformer, 4:6 pulsating current converter, 5: smoothing reactor. Wherein the filtering and compensating device (FC+SC) comprises a BP11/13 filter, a HP24/36 filter, a HP3 filter and a SC parallel filter.

Fig. 2 is a block diagram of the structure of the present invention.

The components in fig. 2 are described as follows:

1: ac power transmission system, 2: converter transformer, 3: absorption and parallel capacitor (ASC), 4:6 pulsating current converter, 5: smoothing reactor.

Fig. 3 is a schematic diagram of a star-connected absorption and parallel capacitor structure.

Fig. 4 is a schematic diagram of a delta-connected absorption and parallel capacitor structure.

Detailed Description

The invention is further described below with reference to the drawings and examples.

Referring to fig. 2, the present invention includes an ac power transmission system 1, a converter transformer 2, an absorption and parallel capacitor 3, 6, a pulsating converter 4 and a smoothing reactor 5. The converter transformer 2 is a converter transformer adopting Yy connection; the absorption and parallel capacitor 3 and 6 pulse converter 4 are connected in parallel and then are directly connected with the valve side of the converter transformer 2; the converter transformer 2, the absorption and parallel capacitor 3 and the 6 pulsation converter 4 form a 6 pulsation converter unit, and the 6 pulsation converter unit connected with the other converter transformer for Yd forms a 12 pulsation converter unit; the alternating current sides of the two 6-pulse converter stations are respectively connected with the alternating current power transmission system 1 through a public alternating current bus, and are used for converting alternating current in the alternating current power transmission system 1 into direct current, and the direct current is transmitted to a receiving place through an overhead line or a cable after passing through the smoothing reactor 5, and is restored into alternating current through an inversion side and is transmitted to another alternating current power transmission system. The absorption and parallel capacitor 3 is an absorption capacitor adopting star-shaped or triangle-shaped connection, see fig. 3 and 4, and the specific connection mode, capacitance capacity and grouping number are determined by practical engineering.

The above examples illustrate only one embodiment of the invention, which is described in more detail and is not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. A high-voltage direct-current transmission system adopting absorption and parallel capacitor commutation is characterized in that: the converter comprises an alternating current transmission system, a converter transformer, a capacitor, a pulse converter and a smoothing reactor, wherein the converter transformer adopts Yy connection; the capacitor is directly connected with the valve side of the converter transformer after being connected with the 6-pulse converter in parallel; the converter transformer, the capacitor and the 6 pulse converter form a 6 pulse converter unit, and the 6 pulse converter unit connected with the other converter transformer for Yd forms a 12 pulse converter unit; the alternating current sides of the two 6-pulse converter stations are respectively connected with an alternating current transmission system through a public alternating current bus, and the capacitors are absorption capacitors adopting triangular connection or absorption capacitors adopting star connection.