CN114123288B - Method for determining optimal reactive power exchange quantity between converter station and alternating current power grid - Google Patents
Method for determining optimal reactive power exchange quantity between converter station and alternating current power grid Download PDFInfo
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Classifications
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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
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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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]
Abstract
The invention discloses a method for determining optimal reactive power exchange quantity between a converter station and an alternating current power grid, and belongs to the technical field of power transmission optimization. The invention provides a method for analyzing and determining the input number of optimal alternating current filters of a converter station and the optimal reactive power exchange quantity of the alternating current system under different control targets based on the idea of carrying out alternating current/direct current interconnection power system power flow calculation based on an alternate solution method. The calculation result provided by the invention can be used as a proper method for researching redundancy of the minimum filter and the absolute minimum filter set of the converter station under different transmission power levels and researching the optimal reactive exchange quantity between the converter station and an alternating current system under different transmission power levels.
Description
Technical Field
The invention belongs to the technical field of power transmission optimization, and particularly relates to a method for determining optimal reactive power exchange quantity between a converter station and an alternating current power grid.
Background
In the case of high-voltage direct current transmission, the converter for realizing the alternating-current-direct-current conversion becomes a nonlinear load of an alternating-current system due to the continuous change of the topological structure, the converters consume a large amount of reactive power, whether they are rectifying or inverting operations. I.e. for an ac system, the dc transmission system is a reactive load. Under rated power, the reactive power required to be consumed by the rectifier station is 40% -50% of the direct current transmission power, and the reactive power required to be consumed by the inverter station is huge and is about 50% -60%. In order to maintain the voltage safety of the AC/DC system, a reasonable reactive compensation and voltage control strategy of the converter station is necessary, and the reactive regulation and control characteristics of the converter station are coordinated with the reactive voltage requirement of the whole network from the perspective of a power grid; from the perspective of the converter station, reactive compensation and balance have own technical requirements, and are also coordinated with other technical problems of the direct current system.
The alternating current filter arranged at the alternating current bus of the converter station not only can filter harmonic waves and improve the electric energy quality, but also can provide a large amount of reactive power for the normal operation of the converter station. The operator should input the AC filter according to the dispatching command, and the safe and stable operation of the AC and DC system is maintained by selecting proper input quantity of the AC filter under different working conditions.
At present, the dynamic reactive power control of the converter station only considers that the reactive power exchange quantity of the system is zero, and does not consider the matching relation with reactive power compensation resources of an alternating current power grid in a nearby area of the converter station. The reactive compensation device in the converter station and the reactive compensation device in the near region of the converter station can be mutually matched in the actual operation process, so that the input quantity of the alternating current filters in the converter station and the proper reactive power exchange quantity among the alternating current systems can be determined under different power transmission levels through the adjustment of the general reactive control measures, the redundancy of the alternating current filters in the converter station can be increased, the voltage level of an alternating current bus of the converter station is optimized, and the safe and stable operation of the high-voltage direct current system during disturbance is ensured.
Disclosure of Invention
Based on the idea of alternating-current and direct-current interconnected power system power flow calculation based on an alternating-current solution, the invention provides a method for respectively solving the change curve of reactive power of an alternating-current system injected into a converter station to alternating-current bus voltage of the converter station after decoupling the alternating-current and direct-current system, and then analyzing and determining the input group numbers of the optimal alternating-current filters of the converter station and the optimal reactive power exchange quantity of the alternating-current and direct-current system under different control targets.
The invention is based on the principle and the deducing process:
the alternating-direct current series-parallel transmission system consists of a direct current system and an alternating current system, and the two systems are generally connected by a converter station. The AC part mainly comprises a power part, an AC line, a transformer, a load and the like, the DC part mainly comprises an inverter, a DC line, a smoothing reactor, a transformer, an AC filter, a switching capacitor and the like, and a characteristic equation of the HVDC under a steady-state working condition can be expressed as:
wherein V is acr And V aci The voltage amplitude values of the alternating current bus at the rectifying side and the inverting side are respectively; v (V) dr And V di Direct current voltages of the rectifier and the inverter respectively; i d Is a direct current line current; alpha and gamma are the advanced trigger angle of the rectifier and the arc-quenching angle of the inverter respectively; n is n r And n i The converter transformer transformation ratios of the rectifying side and the inverting side are respectively; x is X cr And X ci The single-bridge phase-change reactance is respectively a rectifying side and an inverting side; r is R d The resistor is a direct current line resistor;and->The power factor angles of the rectifier and inverter, respectively.
Using the 5 new variables V introduced in the above formula dr ，V di ，I d ，And->Other physical quantities in the steady state operation of HVDC can be calculated as
Wherein P is dcr And Q dcr Active power and reactive power absorbed by the rectifier respectively; p (P) dci And Q dci The inverter is respectively used for injecting active power into an alternating current power grid and reactive power absorbed from the alternating current power grid. θ Vr And theta Vi The voltage phase angles of the alternating current bus at the rectifying side and the inverting side are respectively; i acr And theta Ir The current amplitude and the phase angle of the rectifier side converter transformer are respectively; i aci And theta Ii The current amplitude and the phase angle of the inverter-side converter transformer are respectively.
The direct current control system can keep the controlled quantities such as direct current power, voltage, current and the trigger angle of the converter within a limited safety range while keeping the stable operation of the direct current line. In order to achieve the required control, a plurality of basic control devices are respectively arranged at the rectifying station and the inverting station. The rectifying station comprising constant current or constant power control (CC/CP), minimum trigger angle alpha min Restriction (CIA), low-voltage current limiting control (VDCOL), etc.; the inversion station comprises a fixed arc angle Control (CEA), a fixed voltage Control (CV), a maximum trigger angle limit, a low voltage current limiting control and the like. In general, in normal operation, the rectifying side is controlled by a constant power or a constant dc voltage, and the inverting side is controlled by a constant arc angle or a constant dc voltage. The DC transmission power and the running state depend on the control mode and the voltage of the converter bus, taking the common constant power-constant arc-extinguishing angle control mode as an example, the DC steady-state running characteristics meet the following conditions:
wherein P is order And gamma order The control value is the control value of rectifying and inverting sides.
Meanwhile, in a steady state condition, taking an inverter station as an example, the reactive power output by the alternating current filter connected in parallel to the alternating current bus of the converter station can be represented by the alternating current bus voltage of the inverter station and the input group number of the alternating current filter, so the reactive power injected into the converter station by the alternating current power grid can be represented as:
Q ex ＝Q dci -Q filt
in which Q filt And Q filtN Reactive power and rated capacity absorbed for the ac filter; n is the number of AC filter operation groups; u (U) aciN Rated voltage of an alternating current bus of the inversion station; q (Q) ex Reactive power is injected into the converter station by the ac grid.
From the characteristic equation of the HVDC system in steady state, the ac system acts on the dc system by just passing the primary side voltage V of the converter transformer acr And V aci And (3) generating. That is, if the ac voltages corresponding to all converters in the HVDC system are known, there are 5 equations in the equations of the dc system, including 5 to-be-calculated quantities: v (V) dr ,V di ,I d ,And->In addition, in combination with the control equation of the direct current system, these 5 direct current variables can be obtained by separately solving the direct current system equation.
Therefore, if the parameters and control modes of the direct current system are known, the reactive power injected into the inverter station by the alternating current power grid can be uniquely determined by the alternating current bus voltage of the inverter station, and can be expressed as follows in a compact form:
F(Q ex ,V ac )＝0
from the power equation corresponding to the AC bus of the converter, the effect of the DC system on the AC system is known to extract the power P from the AC system through the converter station ex +jQ ex And (3) generating. Therefore, if the power extracted or injected from the ac system by each converter is known, the voltage at each node of the ac system can be directly and independently solved regardless of the dc system, and the diagram of the ac-dc series-parallel system before and after decoupling is shown in fig. 1.
The idea of decoupling treatment between the alternating current system and the direct current system is just the basis for carrying out alternating current-direct current interconnection power system power flow calculation based on an alternating solution. Q-V change curves seen from alternating current buses of the converter station to the direct current system and the alternating current system under the condition of different input groups of alternating current filters are respectively made through decoupling analysis of the alternating current system and the direct current system, so that the optimal reactive power exchange quantity between the number of the alternating current filters required to be put into operation of the converter station and the alternating current system under different targets can be clearly determined according to the obtained intersection condition of the Q-V change curves of the alternating current system and the direct current system.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a method for determining the optimal reactive power exchange quantity between a converter station and an alternating current power grid comprises the following steps:
step 1: for the decoupled AC system, when the AC power grid injects reactive power Q with different levels into the converter station dci When the current is calculated, the alternating current bus voltage V of the converter station is obtained aci Thereby obtaining a Q-V change curve of the system when the alternating current bus of the converter station is seen into the alternating current system;
step 2: the absolute minimum number of alternating current filters of the switching station are put into operation, and a plurality of voltage values V are selected on the allowable range of alternating current bus voltage of the switching station aci According to a characteristic equation of the HVDC, 5 to-be-solved quantities of the direct current system are solved: DC voltage V of rectifier dr DC voltage V of inverter di Direct current line current I d Power factor angle of rectifierAnd the power factor angle of the inverter +.>And then, by combining with a control characteristic equation of the converter, calculating the reactive power Q absorbed by the inverter during normal operation dci The method comprises the steps of carrying out a first treatment on the surface of the At the same time, the reactive power value Q output by the AC filter at the moment is calculated according to the selected voltage value, the number of the AC filter groups put into operation at the moment and the rated capacity of the AC filter filt Then calculating the reactive power value Q of the alternating current power grid injected into the converter station ex The method comprises the steps of carrying out a first treatment on the surface of the The direct connection lines or interpolation is carried out on the multiple alternating voltage-reactive exchange data to obtain a Q-V change curve of the system when the alternating voltage bus of the converter station is seen into the direct current system;
step 3: adding a group of alternating current filters into a converter station, and repeating the step 2 until all the alternating current filters are put into operation, thereby obtaining a group of Q-V change curves Q ex,ac,min ，…，Q ex,ac,N ，…，Q ex,ac,max ；
Step 4: and (3) determining the quantity of the alternating current filters required to be put into operation of the converter station and the optimal reactive power exchange quantity between the alternating current and direct current systems according to the Q-V change curve of the alternating current system obtained in the step (1) and the intersection condition of the Q-V change curve of the direct current system obtained in the step (3).
Further, in step 2, V is solved according to the characteristic equation of the HVDC dr ，V di ，I d ，And->The formula of (2) is:
wherein V is acr And V aci The voltage amplitude values of the alternating current bus at the rectifying side and the inverting side are respectively; alpha and gamma are the advanced trigger angle of the rectifier and the arc-quenching angle of the inverter respectively; n is n r And n i The converter transformer transformation ratios of the rectifying side and the inverting side are respectively; x is X cr And X ci The single-bridge phase-change reactance is respectively a rectifying side and an inverting side; r is R d Is a direct current line resistance.
Further, in step 2, the reactive power Q absorbed by the inverter during normal operation is calculated in combination with the control characteristic equation of the inverter dci The formula of (2) is:
wherein P is dci The inverter is injected with active power of the ac power grid.
Further, in step 2, the reactive power value Q output by the ac filter filt And the reactive power value Q of the alternating current power grid injected into the converter station ex The calculation formula is as follows:
Q ex ＝Q dci -Q filt
in which Q filtN Is the rated capacity of the alternating current filter; n is the number of AC filter operation groups; u (U) aci And U aciN The voltage and rated voltage of the alternating current bus of the inversion station are respectively.
Further, in step 4, if the control of the ac bus voltage of the converter station is selected to be a control target in the vicinity of the rated value, the ac bus voltage of the converter station is selected to be an intersection in the vicinity of the rated value, the corresponding reactive power value is the optimum reactive power exchange amount between the ac/dc systems, and the corresponding number of ac filter groups to be input is the optimum number of groups.
The beneficial effects of the invention are as follows:
the invention provides a method for respectively solving a change curve of reactive power injected into a converter station by the AC system to the voltage of an AC bus of the converter station after decoupling the AC/DC system based on the concept of alternating current/DC interconnection power system power flow calculation by an alternating solution method, and analyzing and determining the input group number of an optimal AC filter of the converter station and the optimal reactive power exchange quantity of the AC/DC system.
The invention reduces the coupling calculation process of the AC-DC system, calculates the Q-V change curve of the system when the AC bus of the converter station is seen into the DC system, and calculates quickly and simply.
The calculation result provided by the invention can be used as a proper method for researching redundancy of the minimum filter and the absolute minimum filter set of the converter station under different transmission power levels and researching the optimal reactive exchange quantity between the converter station and an alternating current system under different transmission power levels.
Drawings
Fig. 1 is a schematic diagram of the structure of an ac/dc series-parallel system (for example, an inverter station) before and after decoupling when introducing the principles of the present invention;
FIG. 2 is a schematic diagram of an optimal reactive power exchange amount determination method in describing the principles of the present invention;
FIG. 3 shows a single-stage 1600MW (0.2P) transmission under a DC system employing a rectifying side fixed power and inverting side fixed quench angle control mode n ) Q-V curve at active power;
fig. 4 shows a single-stage transmission 3200MW (0.4P) of a direct current system adopting a rectifying side fixed power and an inverting side fixed arc angle control mode in accordance with an embodiment of the present invention n ) Q-V curve at active power.
FIG. 5 shows an example DC system employing a regulated side constant power and an inverted side constant quench angle controlTwo-stage transmission 4800MW (0.6P) in the manufacturing mode n ) Q-V curve at active power.
FIG. 6 shows a two-stage transmission 6800MW (0.8P) for an exemplary DC system employing a regulated side fixed power and an inverted side fixed quench angle control n ) Q-V curve at active power.
FIG. 7 shows a two-stage transmission 8000MW (P) of a DC system employing a rectifying side fixed power and inverting side fixed quench angle control mode according to an embodiment of the present invention n ) Q-V curve at active power.
FIG. 8 shows a single stage transmission of 1600MW (0.2P) in a DC system employing a DC side constant current and an DC side constant voltage control n ) Q-V curve at active power;
FIG. 9 shows a single-stage transmission 3200MW (0.4P) in a DC system employing a DC-side constant current and an DC-side constant voltage control n ) Q-V curve at active power;
FIG. 10 shows a two-stage transmission of 4800MW (0.6P) in a DC system employing a DC-side constant current and an DC-side constant voltage control n ) Q-V curve at active power;
FIG. 11 shows a two-stage transmission 6800MW (0.8P) of a DC system employing a DC-side constant current and an DC-side constant voltage control n ) Q-V curve at active power;
FIG. 12 shows a two-stage transmission 8000MW (P) of a DC system according to an embodiment of the present invention using a DC constant current on the rectifying side and a DC constant voltage control on the inverting side n ) Q-V curve at active power.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the invention, fall within the scope of protection of the invention.
A method for determining the optimal reactive power exchange quantity between a converter station and an alternating current power grid comprises the following steps:
step 1: for the decoupled AC system, when the AC power grid injects reactive power Q with different levels into the converter station dci When the current is calculated, the alternating current bus voltage V of the converter station is obtained aci Thereby obtaining a Q-V change curve of the system when looking into the AC system from the AC bus of the converter station, such as Q in FIG. 2 ex,ac As shown.
Step 2: the converter station operating with an absolute minimum of AC filters, over the permissible range of the voltage of the AC bus of the converter station, e.g. [0.95,1.05 ]]p.u. selecting several voltage values V aci According to a characteristic equation of the HVDC, 5 to-be-solved quantities of the direct current system are solved: DC voltage V of rectifier dr DC voltage V of inverter di Direct current line current I d Power factor angle of rectifierAnd the power factor angle of the inverter +.>And then, by combining with a control characteristic equation of the converter, calculating the reactive power Q absorbed by the inverter during normal operation dci The method comprises the steps of carrying out a first treatment on the surface of the At the same time, the reactive power value Q output by the AC filter at the moment is calculated according to the selected voltage value, the number of the AC filter groups put into operation at the moment and the rated capacity of the AC filter filt Then calculating the reactive power value Q of the alternating current power grid injected into the converter station ex The method comprises the steps of carrying out a first treatment on the surface of the And (3) interpolating the direct connection lines or the multiple alternating voltage-reactive exchange data to obtain a Q-V change curve of the system when the system is seen from the alternating current bus of the converter station to the direct current system. When N groups of alternating current filters are put into operation, the Q-V change curve of the obtained direct current system is shown as Q in figure 2 ex,ac,N As shown.
Step 3: adding a group of alternating current filters into a converter station, and repeating the step 2 until all the alternating current filters are put into operation, thereby obtaining a group of Q-V change curves Q ex,ac,min ，…，Q ex,ac,N ，…，Q ex,ac,max As shown in fig. 2.
Step 4: and (3) determining the quantity of the alternating current filters required to be put into operation of the converter station and the optimal reactive power exchange quantity between the alternating current and direct current systems according to the Q-V change curve of the alternating current system obtained in the step (1) and the intersection condition of the Q-V change curve of the direct current system obtained in the step (3). If the control of the ac bus voltage of the converter station is selected as the control target in the vicinity of the rated value, the ac bus voltage of the converter station is selected as the intersection point in the vicinity of the rated value, the corresponding reactive power value is the optimal reactive power exchange amount between the ac and dc systems, and the corresponding number of ac filter groups is the optimal number of groups.
Specifically, in step 2, V is solved according to the characteristic equation of HVDC dr ，V di ，I d ，And->The formula of (2) is:
wherein V is acr And V aci The voltage amplitude values of the alternating current bus at the rectifying side and the inverting side are respectively; alpha and gamma are the advanced trigger angle of the rectifier and the arc-quenching angle of the inverter respectively; n is n r And n i The converter transformer transformation ratios of the rectifying side and the inverting side are respectively; x is X cr And X ci The single-bridge phase-change reactance is respectively a rectifying side and an inverting side; r is R d Is a direct current line resistance.
Calculating the reactive power Q absorbed by the inverter during normal operation by combining the control characteristic equation of the inverter dci The formula of (2) is:
wherein P is dci The inverter is injected with active power of the ac power grid.
Reactive power value Q output by AC filter filt And the reactive power value Q of the alternating current power grid injected into the converter station ex The calculation formula is as follows:
Q ex ＝Q dci -Q filt
in which Q filtN Is the rated capacity of the alternating current filter; n is the number of AC filter operation groups; u (U) aci And U aciN The voltage and rated voltage of the alternating current bus of the inversion station are respectively.
Description of the preferred embodiments
The Tianshan-Zhongzhou + -800 kV direct current transmission project is the first extra-high voltage direct current transmission project for implementing the strategy of 'Jiang electric outgoing', and is also the first extra-high voltage project for bundling and sending large-scale thermal power and wind power base power in northwest areas. The method comprises the steps of setting up a power conversion station of Hami Tianshan of a Uygur autonomous region in Xinjiang of engineering, setting up a rated voltage of +/-800 kV, setting up a rated direct current of 5kA and setting up a rated transmission power of 8000MW in Zhengzhou of Henan province.
The extra-high voltage Zhongzhou converter station operates in a bipolar mode, and each pole is formed by connecting two groups of twelve pulsating converters in series. The alternating current filter is divided into 4 large groups 19 of groups WA.Z1, WA.Z2, WA.Z3 and WA.Z4, wherein the four groups comprise 10 groups of alternating current filters and 9 groups of parallel capacitors, each group provides 260Mvar reactive power, 4940Mvar is total, the large groups are provided with independent filter buses, and the groups can be independently put and taken back. In order to ensure safe and stable operation of Ha Zheng direct current engineering, the alternating current filter switching must consider requirements such as alternating current overvoltage limit, absolute filter minimum group number, alternating current bus voltage limit, reactive power limit and the like after switching.
The Henan power grid is stepped into the pattern of a provincial extra-high voltage alternating current-direct current series-parallel connection regional power grid, and the power grid voltage safety situation faces new challenges. At present, the dynamic reactive power control of the converter station only considers that the reactive power exchange quantity of the system is zero, and does not consider the matching relation with reactive power compensation resources of an alternating current power grid in a nearby area of the converter station. If the reactive power compensation device in the converter station and the reactive power compensation device in the near region of the converter station can be mutually matched in the actual operation process, the input quantity of the alternating current filters in the converter station and the proper reactive power exchange quantity between the alternating current and direct current systems can be determined under different power transmission levels through the adjustment of the reactive power control measures, the redundancy of the alternating current filters in the converter station can be increased, the alternating current bus voltage level of the converter station is optimized, and the safe and stable operation of the high-voltage direct current system during disturbance is ensured.
The verification example of the invention takes Tianshan-Zhongzhou +/-800 kV direct current transmission engineering as a background, adopts a Zhongzhou converter station and a Henan power grid practical model to implement the method provided by the invention, and gives the optimal input quantity of alternating current filters in the Zhongzhou converter station and the optimal reactive power exchange quantity between alternating current systems under three control targets under three common control modes of active power transmission levels when the Tianshan-Zhongzhou +/-800 kV direct current transmission engineering adopts a rectification side fixed power, an inversion side fixed arc angle control, a rectification side fixed direct current and an inversion side fixed direct current voltage control respectively.
When the method provided by the invention is used for determining the optimal input quantity of the alternating current filters in the Zhongzhou converter station and the optimal reactive power exchange quantity between the alternating current and direct current systems when the direct current systems respectively adopt two common control modes, the method specifically comprises the following steps:
step 1: for the decoupled Henan electric network alternating current system, when the Henan electric network injects reactive power Q with different levels into the Zhongzhou converter station ex When the current is calculated, the alternating current bus voltage V of the converter station is obtained aci In the embodiment, the flow calculation adopts Newton-Lapherson method flow calculation, so as to obtain a Q-V change curve of the system when the system is seen from an alternating current bus of the converter station to the alternating current system.
Step 2: the Zhongzhou converter station runs 3 groups of ac filters meeting the minimum filter capacity, in this example [0.95,1.05 ] over the allowable range of the ac bus voltage of the converter station]p.u. selecting several voltage values V aci At the same time respectivelySolving 5 to-be-solved quantities of the direct current system by combining a direct current control equation in a direct current side fixed power control mode, an inversion side fixed arc extinguishing angle control mode, a direct current side fixed direct current control mode and an inversion side fixed direct current voltage control mode: v (V) dr ,V di ,I d ,φ r And phi i Calculating reactive power Q absorbed by inverter in normal operation by combining control characteristic equation of direct current system dci . Meanwhile, the reactive power value output by the AC filter at the moment can be calculated according to the selected voltage value, the number of AC filter groups put into operation at the moment and the rated capacity of the AC filter, and then the reactive power value Q of the AC power grid injected into the converter station at the moment is calculated ex . And (3) interpolating the direct connection lines or the multiple alternating voltage-reactive exchange data to obtain a Q-V change curve of the system when the system is seen from the alternating current bus of the converter station to the direct current system.
Step 3: adding one group of alternating current filters in a Zhongzhou converter station, and repeating the step 2 until all 19 groups of alternating current filters are put into operation, thereby obtaining a family Q-V change curve Q ex,ac,min ，…，Q ex,ac,N ，…，Q ex,ac,max 。
Step 4: and (3) determining the quantity of the AC filters required to be put into operation by the Zhongzhou converter station and the optimal reactive power exchange quantity between the AC systems according to the Q-V change curve of the Henan power grid AC system obtained in the step (1) and the intersection condition of the Q-V change curve of the Zhongzhou converter station obtained in the step (3). If the control of the ac bus voltage of the converter station is selected as the control target in the vicinity of the rated value, the ac bus voltage of the converter station is selected as the intersection point in the vicinity of the rated value, the corresponding reactive power value is the optimal reactive power exchange amount between the ac and dc systems, and the corresponding number of ac filter groups is the optimal number of groups.
Fig. 3 to 7 show that the dc power transmission is controlled from 1600MW (0.2P) on the single pole when the dc power transmission engineering adopts the rectifying side fixed power and the inverting side fixed arc angle control mode n ) Rising to bipolar 8000MW (P n ) In the process, the Q-V change curve of the Henan power grid alternating current system manufactured by the step 1 of the method and the Q-V change of the Zhongzhou converter station obtained according to the step 2 and the step 3 are utilized at different power levelsAnd (5) a chemical curve. Fig. 8 to 12 show that the dc power is controlled from 1600MW (0.2P) on the single pole when the dc power transmission project uses the dc power control method on the rectifying side and the dc voltage control method on the inverting side n ) Rising to bipolar 8000MW (P n ) In the process, the Q-V change curve of the Henan power grid alternating current system and the Q-V change curve of the Zhongzhou converter station, which are obtained according to the steps 2 and 3, are manufactured by using the method in the step 1 under different power levels.
And (3) determining the quantity of the AC filters required to be put into operation by the Zhongzhou converter station and the optimal reactive power exchange quantity between the AC systems according to the Q-V change curve of the Henan power grid AC system obtained in the step (1) and the intersection condition of the Q-V change curve of the Zhongzhou converter station obtained in the step (3). In this example analysis, the following three ac filters were respectively cut into the target: (1) the converter station ac bus voltage is near the nominal value; (2) The reactive power exchange amount between the alternating current power grid and the converter station is near 0 Mvar; (3) The minimum number of ac filter input groups is used to determine the optimum number of ac filter input groups, the reactive power of the ac grid injected into the converter station, and the voltage level of the ac bus of the converter station at that time, and the obtained results are shown in tables 1 to 3 below.
Table 1 number of filter inputs and system operation status for ac filter switching target (1)
Table 2 number of filter inputs and system operation status for ac filter switching target (2)
TABLE 3 number of filter input groups and system operation status for AC filter switching target (3)
The analysis of the results obtained by the verification of the method example provided by the invention can be used for obtaining the following conclusion: with the increase of active power of direct current transmission, the number of the alternating current filter groups required to be input for maintaining the voltage stability of the alternating current bus of the Zhongzhou converter station is continuously increased under the premise of meeting the requirement of 3 groups of absolute minimum filtering. Under the same active power transmission level, the reactive power values absorbed by the Zhongzhou converter stations under the two control modes are different, and the optimal switching groups of the alternating current filter under various switching targets are different. Aiming at three different alternating current filter switching targets, the direct current control mode adopting the constant current inversion side fixed voltage at the rectifying side is adopted to have fewer alternating current filters than the alternating current filter needing to be input relative to the constant power inversion side fixed arc angle control mode at the rectifying side, and particularly when the converter station is at a higher active power transmission level, the number of alternating current filters needing to be input is obviously fewer than the direct current control mode adopting the constant current inversion side fixed voltage at the rectifying side, and the reactive compensation redundancy in the converter station is large.
When the voltage of the alternating current bus of the converter station is closest to the rated value and is used as an alternating current filter switching target, compared with other two control targets, the number of alternating current filters required to be put into is the largest under different power levels, the control effect of the voltage level of the alternating current bus of the converter station is best, but the requirement on the reactive power value of the alternating current power grid required to be injected into the converter station under the individual power transmission level is larger, so that the alternating current power grid in the nearby area of the converter station is required to have sufficient reactive power reserve to meet the reactive power exchange capacity requirement of an alternating current system, and the reactive power compensation capability requirement on the alternating current nearby area power grid of the converter station is higher; when the reactive power exchange quantity between the alternating current power grid and the converter station is about 0Mvar as an alternating current filter switching target, the absolute value of the reactive power exchanged between the alternating current and direct current systems is minimum, and at the moment, the reactive power compensation capability of the alternating current power grid is not excessively high, but the alternating current bus voltage of the converter station has a certain deviation from the rated value; when the input of the alternating current filter is the minimum, the alternating current power grid is required to always inject reactive power into the converter station under different active power transmission levels so as to maximize redundancy of the alternating current filter in the converter station, and the alternating current power grid in the nearby area of the converter station is required to have a certain reactive power supporting capability for the converter station.
In the embodiment, the invention is utilized to determine the quantity of the alternating current filters required to be put into operation by the Zhongzhou current converting station and the optimal reactive power exchange quantity between alternating current and direct current systems under different power transmission levels.
The invention provides a method for determining the input number of optimal alternating current filters of a converter station and the optimal reactive power exchange quantity of an alternating current-direct current system, and the method is realized according to the steps. It will be appreciated by those skilled in the art that the methods provided by the present invention may be used in example analysis, or in designing computer program products. The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. The method for determining the optimal reactive power exchange quantity between the converter station and the alternating current power grid is characterized by comprising the following steps of:
step 1: for the decoupled AC system, when the AC power grid injects reactive power Q with different levels into the converter station dci When the voltage amplitude V of the alternating current bus of the converter station is obtained through load flow calculation aci Thereby obtaining a Q-V change curve of the system when the alternating current bus of the converter station is seen into the alternating current system;
step 2: the absolute minimum number of alternating current filters of the converter station are put into operation, and a plurality of alternating current bus voltage amplitude values V of the converter station are selected on the allowable range of the alternating current bus voltage of the converter station aci According to a characteristic equation of the HVDC, 5 to-be-solved quantities of the direct current system are solved: DC voltage V of rectifier dr DC voltage V of inverter di Direct current line current I d Power factor angle of rectifierAnd the power factor angle of the inverter +.>And then, by combining with a control characteristic equation of the converter, calculating the reactive power Q absorbed by the inverter during normal operation dci The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, the reactive power value Q output by the alternating current filter at the moment is calculated according to the selected alternating current bus voltage amplitude of the converter station, the number of the alternating current filter groups put into operation at the moment and the rated capacity of the alternating current filter filt Then calculating the reactive power value Q of the alternating current power grid injected into the converter station ex The method comprises the steps of carrying out a first treatment on the surface of the The direct connection lines or interpolation is carried out on the multiple alternating voltage-reactive exchange data to obtain a Q-V change curve of the system when the alternating voltage bus of the converter station is seen into the direct current system;
step 3: adding a group of alternating current filters into a converter station, and repeating the step 2 until all the alternating current filters are put into operation, thereby obtaining a group of Q-V change curves Q ex,ac,min ，…，Q ex,ac,N ，…，Q ex,ac,max ；
Step 4: determining the quantity of alternating current filters required to be put into operation of a converter station and the optimal reactive power exchange quantity between alternating current and direct current systems according to the Q-V change curve of the alternating current system obtained in the step 1 and the intersection condition of the Q-V change curve of the direct current system obtained in the step 3;
in the step 2, V is solved according to the characteristic equation of the HVDC dr ，V di ，I d ，And->The formula of (2) is:
wherein V is acr And V aci The voltage amplitude values of the alternating current bus at the rectifying side and the inverting side are respectively; alpha and gamma are the lead firing angle of the rectifier and the inverter respectivelyArc extinguishing angle; n is n r And n i The converter transformer transformation ratios of the rectifying side and the inverting side are respectively; x is X cr And X ci The single-bridge phase-change reactance is respectively a rectifying side and an inverting side; r is R d The resistor is a direct current line resistor; in step 2, the reactive power Q absorbed by the inverter during normal operation is calculated by combining the control characteristic equation of the inverter dci The formula of (2) is:
wherein P is dci Injecting active power of an alternating current power grid into the inverter;
in step 2, the reactive power value Q output by the ac filter filt And the reactive power value Q of the alternating current power grid injected into the converter station ex The calculation formula is as follows:
Q ex ＝Q dci -Q filt
in which Q filtN Is the rated capacity of the alternating current filter; n is the number of AC filter operation groups; u (U) aci And U aciN The voltage and rated voltage of the alternating current bus of the inversion station are respectively;
in step 4, if the voltage of the ac bus of the converter station is selected to be a control target near the rated value, the ac bus voltage of the converter station is selected to be an intersection point near the rated value, the corresponding reactive power value is the optimal reactive power exchange amount between the ac-dc systems, and the corresponding input ac filter group number is the optimal group number;
wherein three ac filter switching targets are analyzed:
1) The voltage of the alternating current bus of the converter station is near the rated value;
2) The reactive power exchange amount between the alternating current power grid and the converter station is near 0 Mvar;
3) The number of ac filter input groups is minimized to determine the optimum number of ac filter input groups, the reactive power of the ac grid injected into the converter station, and the voltage level of the ac bus of the converter station at that time.
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