CN114362234A - Improved parallel capacitor commutation converter and parameter design method thereof - Google Patents
Improved parallel capacitor commutation converter and parameter design method thereof Download PDFInfo
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- CN114362234A CN114362234A CN202210014639.XA CN202210014639A CN114362234A CN 114362234 A CN114362234 A CN 114362234A CN 202210014639 A CN202210014639 A CN 202210014639A CN 114362234 A CN114362234 A CN 114362234A
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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- 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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
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- 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 an improved parallel capacitor commutation converter and a parameter design method thereof. The converter comprises a converter transformer, a filter inductor, a parallel capacitor and a converter, wherein the high-voltage side of the converter transformer is connected with an alternating current bus, the filter inductor is connected to the low-voltage side of the converter transformer in series, the parallel capacitor is connected between the filter inductor and the outlet of an alternating current side valve of the converter in parallel, and the parallel capacitor is connected in a star shape or a triangular shape. The parameter design method considers the resonance characteristic and the reactive characteristic and designs parameters such as filter inductance, parallel capacitance and the like. The technical scheme provided by the invention has the advantages that: an additional filter and a reactive power compensation device are not needed on the side of the alternating current bus; the commutation characteristics of rectification and an inverter can be improved, and the capability of resisting commutation failure is enhanced; the provided parameter design method can not only meet the reactive power requirement of the system, but also improve the AC and DC harmonic characteristics of the system.
Description
Technical Field
The invention relates to the field of high-voltage direct-current power transmission and power electronics, in particular to an improved parallel capacitor phase-change converter and a parameter design method thereof.
Background
In the existing high-voltage direct-current transmission system, the structure and parameters of the converter transformer are determined and are difficult to change, the system may have resonance risk due to unreasonable structure and parameters, obvious oscillation occurs on a direct-current side, and harmonic characteristics on an alternating-current side are poor.
A high-voltage direct-current transmission system adopting a Line Communtated Converter (LCC) needs to rely on a power grid for phase change because of adopting a thyristor device without automatic turn-off, so that phase change failure is easy to occur when an alternating-current fault occurs in an inverter station; because the short-circuit impedance of the converter transformer of the alternating-current line is large, the commutation overlap angle is large, the LCC converter station needs to absorb a large amount of reactive power due to the existence of the commutation overlap angle and the turn-off angle, and a large amount of reactive compensation equipment and filter devices need to be installed on the alternating-current side, which accounts for about 40% of the total area of the converter station. Harmonic currents of 5 th order and 7 th order generated by the converter can be filtered out on the network side by means of a 12-pulse converter structure, and still filters of 11 th order, 13 th order and higher order need to be additionally arranged on the alternating current bus side to ensure that the harmonic content on the network side meets the requirement. The reactive power required by the converter transformer and the converter is provided by the reactive power compensation device.
For a high-voltage direct-current power transmission system adopting a series Capacitor Commutated Converter (CCC) and a controllable capacitor commutated converter (CSCC), partial defects of the LCC can be overcome, the reactive power of the converter can be compensated through the series capacitor, the risk of phase commutation failure is reduced, but overvoltage possibly caused during asymmetric fault can aggravate the occurrence of the phase commutation failure. Improved power grid commutation converter (ELCC) and Enhanced Capacitor Commutation Converter (ECCC) which are connected into a novel sub-module in series can promote commutation through the sub-module, reduce commutation failure risk, but the sub-module has limited forced commutation capacity and cannot filter and compensate a large amount of idle work.
The researchers also proposed a high voltage dc transmission system using an absorption and shunt capacitance phase change converter (ASCCC), which can provide the reactive power required by a converter transformer and a converter by connecting a capacitor in parallel at the outlet side of the converter valve, without connecting a large number of filters and reactive compensation devices in parallel at the ac bus side, and at the same time, the shunt capacitance accelerates the phase change process, so that the phase change overlap angle is almost zero, and the reactive power requirement of the system and the risk of phase change failure are reduced. However, ASCCC has a risk of resonance when the structure and parameters are unreasonable, and the direct current side has obvious oscillation and the alternating current side has poor harmonic characteristics.
Disclosure of Invention
In order to solve the technical problems of the existing direct current transmission system, the invention provides an improved parallel capacitor phase-change converter and a parameter design method thereof, wherein the improved parallel capacitor phase-change converter is convenient for converter structure modification, improves the alternating current-direct current harmonic characteristic and improves the capability of resisting phase-change failure. The method is characterized in that: the parallel capacitor at the outlet side of the converter can form a filter with an inductor connected in series with the valve side of the converter transformer to filter alternating current, the parallel capacitor can also compensate reactive power, the alternating current side does not need an additional filter and a reactive power compensation device, the phase change process is accelerated, the phase change of the converter can be improved, and particularly the risk of phase change failure at the inverter side is reduced. The parameter design method can effectively filter out higher harmonics of 11 times and above, optimize the characteristics of alternating current and direct current harmonics, avoid resonance caused by characteristic harmonics, meet the reactive power requirement of the system and realize that the system operates under the conditions of specific active power and reactive power.
The topology adopted by the invention to solve the technical problems is as follows: an improved parallel capacitor commutation converter comprises a converter transformer, a filter inductor, a parallel capacitor and a converter, wherein the high-voltage side of the converter transformer is connected with an alternating current bus, the filter inductor is connected to the low-voltage side of the converter transformer in series, and the parallel capacitor is connected between the filter inductor and the outlet side of the converter.
The parallel capacitors are connected in star or triangle.
The parameter design method of the invention comprises the following steps:
n-th harmonic current content index k after capacitance filteringnThe calculation method comprises the following steps:
wherein, I0h,j,nAnd Ih,j,nAnd j-phase n-order harmonic waves of alternating current on the outlet side of the high valve group converter and j-phase n-order harmonic waves of the alternating current after passing through the filter capacitor are respectively obtained.
The calculation formula of j-phase n-order harmonic of alternating current after passing through the filter capacitor is as follows:
where, ω is the angular frequency of the system, C is the capacitance of the parallel capacitor at the outlet side of the converter, Up,j,nThe amplitude of the j-phase n-th harmonic voltage of the alternating current bus is shown, and L is the sum of the leakage inductance and the filter inductance of the converter transformer.
Under reasonable parameters, harmonic wave Up,j,nShould be approximately 0 and can be ignored. By combining formulae (1) to (2), k can be obtainednThe calculation formula is as follows:
|knthe smaller the | is, the smaller the amplitude of the nth harmonic is. As the characteristic harmonic frequency of the alternating current side of a single valve bank is 6k +/-1, only k is needed5<0，kn(n>5) Will be smaller and the harmonic amplitudes will be less, so k5Is an important indicator of resonance. In addition, k5Also affects the harmonics flowing through the transformer, | k to avoid ferroresonance5L cannot be too large.
For 12-pulse ESCCC, the harmonic order of the incoming AC system is 12k + -1, and the lowest harmonic order is 11. The content of higher order harmonics is much lower than the 11 th harmonic content. Therefore | k11And | is an important index for evaluating the alternating current harmonic.
The calculation formula of the active power and the reactive power flowing into the alternating current system is as follows:
p, Q therein are respectively the active power flowing into the AC system andreactive power, UpmIs the AC bus voltage amplitude, kTTo change the transformer ratio of the converter, IdcIs direct current and alpha is converter trigger angle.
The specific parameter design method comprises the following steps: (1) to ensure good AC/DC harmonic characteristics, | knS%, n and s are determined by actual engineering, for example, n may be 11, and s may be 1; (2) selecting an active power P and a reactive power Q according to the actual engineering requirements, wherein for example, P can be 1000MW, and Q can be 0 Mvar; (3) aiming at the requirement of an inversion side, a proper large turn-off angle is needed, and meanwhile, a large amount of reactive power consumption is avoided, for example, the turn-off angle is required to be 15 degrees, and other reasonable values can also be taken according to the operation requirement; (4) LC should not be too large in view of volume and cost. Wherein (1) and (2) are main limiting conditions, and (3) and (4) are secondary limiting conditions, the main limiting conditions need to be met first, and the secondary limiting conditions can be met as far as possible under the premise so as to improve the system performance.
The invention has the beneficial effects that: the improved parallel capacitor commutation converter is adopted, the existing power grid commutation converter can be conveniently transformed, the filter inductor and the parallel capacitor can filter harmonic voltage or current on a circuit on the valve side of the converter transformer, the parallel capacitor provides reactive compensation, an additional filter and a reactive compensation device are not needed, the commutation of the converter can be improved, and particularly the commutation failure risk on the inversion side is reduced; by adopting the parameter design method suitable for the improved parallel capacitor commutation converter, the reactive power requirement of a system can be met, the AC/DC harmonic characteristic is improved, and the resonance caused by characteristic harmonic is avoided.
Drawings
FIG. 1 is a schematic diagram of an improved parallel capacitor commutation converter topology according to the present invention;
the components in fig. 1 are illustrated as follows:
1: alternating current transmission system, 2: converter transformer, 3: filter inductance, 4: parallel capacitor, 5: 6 pulsating current converter, 6: smoothing reactor
FIG. 2 is a schematic diagram of a star-coupled parallel capacitor configuration.
Fig. 3 is a schematic diagram of a delta-coupled parallel capacitor structure.
FIG. 4 is an equivalent circuit diagram of an improved parallel capacitor commutated converter provided by the present invention;
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Referring to fig. 1, the improved parallel capacitor commutated converter comprises an ac power transmission system 1, a converter transformer 2, a filter inductor 3, parallel capacitors 4, 6, a ripple converter 5 and a smoothing reactor 6. Wherein, converter transformer 2 adopts Yd connection mode, filter inductance 3 connects in series between converter transformer 2 valve side and transverter 5, shunt capacitance 4 connects in parallel between filter inductance 3 and transverter 5; the converter transformer 2, the filter inductor 3, the parallel capacitor 4 and the converter 5 jointly form a 6-pulse converter unit, and the converter transformer and the other group of converter transformers jointly form a 12-pulse converter by adopting the 6-pulse converter unit connected by Yy; the two 6-pulse converters are connected in series on the direct current side and in parallel on the alternating current side, and the two 6-pulse converters are connected into the alternating current transmission system 1 through a common alternating current bus on the alternating current side respectively. The 12-pulse converter can be used as a rectifier to convert alternating current into direct current, the direct current is transmitted to the outside through a direct current cable or an overhead wire after passing through a smoothing reactor 5, and can also be used as an inverter to receive power transmitted from a rectifying side and convert the direct current into alternating current to be injected into an alternating current transmission system. The parallel capacitors 4 are connected in a star shape or a triangular shape, referring to fig. 2 and 3, and the specific connection mode, the grouping number and the like are determined by actual engineering.
Referring to fig. 4, taking the inverter side high valve bank and the parallel capacitor in star connection as an example, the outlet side alternating current j phase n harmonic of the high valve bank converter is i0h,nThe j phase n harmonic of the alternating current after passing through the filter capacitor is ih,n，|knThe meaning expressed by s% of | is ih,nAccount for i0h,nThe proportion of (a) and (b), n and s are determined by actual engineering; p, Q respectively representing the active power and the reactive power flowing into the AC transmission system, and the values of the active power and the reactive power are set according to the operation requirement, for example, P is 1000MW, and Q is 1000MWMvar, substituted for formula (4), in combination with | knAnd the parameters such as filter inductance, parallel capacitance, converter transformer transformation ratio and the like can be obtained by solving the equation set through the expression of | the formula.
The above-mentioned examples are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person skilled in the art can modify the specific embodiments of the present invention or substitute the same with reference to the above-mentioned examples, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention is within the scope of the claims of the present invention as filed.
Claims (5)
1. An improved generation parallel capacitance commutation transverter which characterized in that: the high-voltage side of the converter transformer is connected with an alternating current bus, the filter inductor is connected to the low-voltage side of the converter transformer in series, and the parallel capacitor is connected between the filter inductor and the outlet side of the converter.
2. The improved parallel capacitor commutated converter according to claim 1, wherein: the parallel capacitors are connected in a star shape.
3. The improved parallel capacitor commutated converter according to claim 1, wherein: the parallel capacitors are connected in a triangular mode.
4. A parameter design method suitable for an improved parallel capacitor commutation converter is characterized by comprising the following steps: the resonance characteristic and the reactive characteristic are considered.
5. The parameter design method suitable for the improved parallel capacitor commutation converter according to claim 4, wherein: the harmonic distortion rate after capacitance filtering is limited to a specific value, and the inverter side parameter design is ensured to leave enough turn-off angle margin to prevent commutation failure; the active and reactive power flowing into the ac transmission system can be controlled according to a parametric design.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115149563A (en) * | 2022-07-13 | 2022-10-04 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Filtering optimization method, device, equipment and storage medium for converter output harmonic |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115149563A (en) * | 2022-07-13 | 2022-10-04 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Filtering optimization method, device, equipment and storage medium for converter output harmonic |
| CN115149563B (en) * | 2022-07-13 | 2024-06-28 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Filter optimization method, device, equipment and storage medium for converter output harmonic wave |
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