CN107809118B - Design method of ring-opening scheme of electromagnetic ring network - Google Patents
Design method of ring-opening scheme of electromagnetic ring network Download PDFInfo
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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
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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
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- 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
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Abstract
The invention discloses a design method of an electromagnetic looped network ring-releasing scheme, relates to the technical field of direct-current transmission, and aims to solve the problems that in the prior art, when an electromagnetic looped network is positioned in a delivery channel of a delivery-end power grid, the construction difficulty of operators is high, and the ring-releasing cost is high. The design method of the electromagnetic looped network ring-opening scheme comprises the following steps: acquiring a ring-opening point of the electromagnetic looped network, and additionally arranging a flexible direct-current back-to-back system for ring opening at the ring-opening point to construct a virtual ring-opening scheme; under the condition of ensuring stable isolated network operation frequency of a power grid at a sending end, obtaining a critical active power value of a flexible direct current back-to-back system; determining the ring-opening cost for additionally arranging the flexible direct current back-to-back system according to the critical active power value of the flexible direct current back-to-back system; and determining whether to adopt the virtual ring-opening scheme as a target ring-opening scheme or not according to the relationship between the ring-opening cost and the estimated ring-opening cost of the electromagnetic ring network. The design method of the ring-opening scheme of the electromagnetic ring network is used for an outgoing channel of a sending-end power grid.
Description
Technical Field
The invention relates to the technical field of direct current transmission, in particular to a design method of an electromagnetic looped network ring-opening scheme.
Background
With the continuous development of power grid systems, one or more electromagnetic ring networks are mostly present in the power grid systems, and the electromagnetic ring networks are also called high-low voltage electromagnetic ring networks, which refer to two groups of lines running at different voltage levels and run in parallel through the connection of transformer magnetic loops at two ends.
When the electromagnetic ring network is positioned in an outgoing channel of a sending-end power grid, once a high-voltage line in the electromagnetic ring network trips, the power grid system tide transfers to a low-voltage line in the electromagnetic ring network, and the low-voltage line in the electromagnetic ring network is easily tripped in an overload mode, so that local power grid blackout is caused. Therefore, in order to ensure the stable operation of the transmission-end power grid, complete power grid operation control regulations and corresponding safety measures must be made to deal with sudden severe accidents, and the ring-opening of the electromagnetic ring network becomes a conventional choice for dealing with the sudden accidents.
At present, for an electromagnetic ring network located in a delivery channel of a delivery-end power grid, a commonly used ring-opening method is as follows: the grid structure of the high-voltage line is reinforced in the outgoing channel of the sending-end power grid, so that the high-voltage line is prevented from tripping completely; or, a standby high-voltage transmission line is additionally arranged in the existing delivery channel, and when all high-voltage lines in the electromagnetic ring network trip, the standby high-voltage transmission line is started to keep the open-loop operation of the delivery-end power grid.
However, when the electromagnetic ring network is looped off by the loop-opening method of reinforcing the grid structure of the high-voltage line or adding the spare high-voltage transmission line, because the coverage range of the outgoing channel of the sending-end power grid is wider, the grid structure of the reinforcing high-voltage line or adding the spare high-voltage transmission line needs to cover a larger construction range and occupy a longer construction period, the construction is difficult, a larger loop-opening cost is consumed, and great inconvenience is brought to operators.
Disclosure of Invention
The invention aims to provide a design method of an electromagnetic looped network ring-releasing scheme, which aims to solve the problems that in the prior art, when an electromagnetic looped network is positioned in a delivery channel of a delivery-end power grid, the construction difficulty of operators is high, and the ring-releasing cost is high.
In order to achieve the above purpose, the invention provides the following technical scheme:
a design method of an electromagnetic ring network loop-opening scheme is provided, wherein an electromagnetic ring network is positioned in an outgoing channel of a sending-end power grid, and the design method of the electromagnetic ring network loop-opening scheme comprises the following steps:
step 1, acquiring a ring-opening point of an electromagnetic looped network, and additionally arranging a flexible direct-current back-to-back system for ring opening at the ring-opening point to construct a virtual ring-opening scheme;
step 2, the electromagnetic looped network is looped off through a virtual looping-off scheme, and a critical active power value of the flexible direct current back-to-back system is obtained under the condition that the isolated network operation frequency of a power grid at a sending end is stable;
step 3, determining the ring-opening cost for additionally arranging the flexible direct current back-to-back system according to the critical active power value of the flexible direct current back-to-back system;
and 4, determining whether a virtual ring-opening scheme is adopted as a target ring-opening scheme or not according to the relationship between the ring-opening cost and the estimated ring-opening cost of the electromagnetic ring network.
Compared with the prior art, the design method of the ring-opening scheme of the electromagnetic ring network has the following beneficial effects:
in the design method of the ring-opening scheme of the electromagnetic ring network, a flexible direct-current back-to-back system for ring opening is additionally arranged at the ring-opening point of the electromagnetic ring network to construct a virtual ring-opening scheme, meanwhile, the critical active power value of the flexible direct-current back-to-back system in the virtual ring-opening scheme is utilized to determine the ring-opening cost for additionally arranging the flexible direct-current back-to-back system, and the ring-opening cost is compared with the estimated ring-opening cost to control the ring-opening cost of the electromagnetic ring network; therefore, when the estimated ring-opening cost of the existing ring-opening scheme is too high, the electromagnetic ring network can be opened by selecting the virtual ring-opening scheme as a target ring-opening scheme, so that the ring-opening cost of the electromagnetic ring network is reduced;
moreover, the virtual ring-opening scheme is that the flexible direct-current back-to-back system for opening the ring is additionally arranged at the ring-opening point of the electromagnetic ring network, so that the construction position of the flexible direct-current back-to-back system on the electromagnetic ring network is uniquely determined, and the flexible direct-current back-to-back system does not need additional reactive compensation filters and other equipment for auxiliary operation, the flexible direct-current back-to-back system occupies a small area, and the construction period occupied by construction and installation is short, so that after the virtual ring-opening scheme is selected as the target ring-opening scheme, the difficulty in operating the electromagnetic ring network for opening the ring is greatly reduced by using the target ring-opening scheme.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a first flowchart of a design method of an electromagnetic ring network looping-off scheme according to an embodiment of the present invention;
fig. 2 is a flowchart of a second method for designing an electromagnetic ring network looping-off scheme according to an embodiment of the present invention;
fig. 3 is a schematic view of a rack structure of an electromagnetic ring network according to an embodiment of the present invention;
fig. 4 is a schematic view of a net rack structure of an electromagnetic ring network ring-opening point according to an embodiment of the present invention;
fig. 5 is a schematic frequency curve diagram of isolated grid operation of the transmission-side power grid according to the embodiment of the present invention.
Reference numerals:
a first delivery channel of 1-500kV, a second delivery channel of 2-500kV,
a first sending channel of 3-220kV, a second sending channel of 4-220kV,
5-a transmitting end power grid, 6-a main network,
7-flexible direct current back-to-back system.
Detailed Description
For the convenience of understanding, the method for looping an electromagnetic ring network provided by the embodiment of the invention is described in detail below with reference to the drawings in the specification.
Referring to fig. 1-2, the electromagnetic ring network is located in the outgoing channel of the sending-end power grid, and the method for disconnecting the electromagnetic ring network provided by the embodiment of the invention includes the following steps:
step 1, acquiring a ring-opening point of an electromagnetic looped network, and additionally arranging a flexible direct-current back-to-back system for ring opening at the ring-opening point to construct a virtual ring-opening scheme;
step 2, the electromagnetic looped network is looped off through a virtual looping-off scheme, and a critical active power value of the flexible direct current back-to-back system is obtained under the condition that the isolated network operation frequency of a power grid at a sending end is stable;
step 3, determining the ring-opening cost for additionally arranging the flexible direct current back-to-back system according to the critical active power value of the flexible direct current back-to-back system;
and 4, determining whether the virtual ring-opening scheme is adopted as a target ring-opening scheme or not according to the relationship between the ring-opening cost and the estimated ring-opening cost of the electromagnetic ring network.
In specific implementation, in the design method of the electromagnetic ring network ring-opening scheme provided in the embodiment of the present invention, a virtual ring-opening scheme is constructed by adding a flexible direct-current back-to-back system for ring opening at a ring-opening point, a ring-opening cost required for adding the flexible direct-current back-to-back system can be obtained by determining a critical active power value that the flexible direct-current back-to-back system should have in the virtual ring-opening scheme, and then whether the virtual ring-opening scheme for adding the flexible direct-current back-to-back system is feasible is considered by comparing the ring-opening cost required for adding the flexible direct-current back-to-back system with the estimated ring-opening cost of the electromagnetic ring network; specifically, when the solution ring cost of the virtual solution ring scheme is less than or equal to the estimated solution ring cost of the electromagnetic ring network, the virtual solution ring scheme is determined to be a target solution ring scheme, that is, the virtual solution ring scheme is feasible; when the ring-opening cost of the virtual ring-opening scheme is greater than the estimated ring-opening cost of the electromagnetic ring network, the virtual ring-opening scheme is not feasible, and the electromagnetic ring network can only be opened through other existing ring-opening schemes. The estimated ring-opening cost of the electromagnetic ring network refers to the lowest ring-opening cost estimated when the same electromagnetic ring network is opened through other conventional ring-opening schemes.
As can be seen from the above specific implementation process, in the design method of the ring opening scheme of the electromagnetic ring network provided in the embodiment of the present invention, a flexible dc back-to-back system for ring opening is added at a ring opening point of the electromagnetic ring network to construct a virtual ring opening scheme, and meanwhile, a critical active power value of the flexible dc back-to-back system in the virtual ring opening scheme is used to determine a ring opening cost for adding the flexible dc back-to-back system, and the ring opening cost is compared with an estimated ring opening cost to control the ring opening cost of the electromagnetic ring network; therefore, when the estimated ring-opening cost of the existing ring-opening scheme is too high, the electromagnetic ring network can be opened by selecting the virtual ring-opening scheme as a target ring-opening scheme, so that the ring-opening cost of the electromagnetic ring network is reduced;
moreover, the virtual ring-opening scheme is that the flexible direct-current back-to-back system for opening the ring is additionally arranged at the ring-opening point of the electromagnetic ring network, so that the construction position of the flexible direct-current back-to-back system on the electromagnetic ring network is uniquely determined, and the flexible direct-current back-to-back system does not need additional reactive compensation filters and other equipment for auxiliary operation, the flexible direct-current back-to-back system occupies a small area, and the construction period occupied by construction and installation is short, so that after the virtual ring-opening scheme is selected as the target ring-opening scheme, the difficulty in operating the electromagnetic ring network for opening the ring is greatly reduced by using the target ring-opening scheme.
In addition, when the virtual ring-opening scheme is determined to be feasible, namely the virtual ring-opening scheme is adopted as a target ring-opening scheme, a flexible direct-current back-to-back system is additionally arranged at a ring-opening point to open a ring of the electromagnetic ring network, the current of the power grid system can be conveniently reversed through the change of the flexible direct-current back-to-back system to the direction of direct current, the existence of the flexible direct-current back-to-back system does not need to limit the output active power of a sending-end power grid outgoing channel, and the flexible direct-current back-to-back system can realize the flexible scheduling and control of the power grid system current; and moreover, the flexible direct-current back-to-back system can provide rapid and independent dynamic reactive compensation and active power regulation for the power grid at the sending end, and simultaneously and independently control the active power and the reactive power of the power grid at the sending end, so that the frequency stability of the power grid at the sending end in isolated network operation is improved.
It should be noted that, in step 2, the method for obtaining the critical active power value of the flexible direct current back-to-back system includes:
step 201, determining a rated frequency value when the isolated network operation frequency of the power grid at the sending end is stable, wherein the rated frequency value comprises a steady-state rated frequency value fWAnd a transient nominal frequency value fZ. The rated frequency value of the power grid isolated grid operation frequency at the sending end is determined by the technical experience of the power related standards such as 'safety and stability of power system' and the like, wherein the steady-state frequency value is generally 49.2 Hz-50.5 Hz, and the transient frequency value is 47.5 Hz-51.5 Hz.
Step 202, obtaining a first steady state critical active power value P of the flexible direct current back-to-back systemVSC1-W；
The obtaining formula of the first steady-state critical active power value is as follows:
wherein, PLFor the value of the active power of the outgoing channel of the transmitting-end network, PGThe total active power value for generating power of the power grid unit at the sending end, R is the single frequency modulation difference adjustment coefficient of the power grid unit at the sending end, and delta fWAnd (4) a steady-state frequency deviation value allowed for isolated grid operation of the power grid at the sending end.
Step 203, obtain a first transient critical active power value P of the flexible dc back-to-back systemVSC1-Z；
Obtaining that the isolated network transient state operation frequency of the power grid at the sending end is equal to the transient state rated frequency value fZTransient active power value delta P of power generation of sending-end power grid unitZ(ii) a And transient active power value delta P of power generation of sending end power grid unitZThe method comprises the following steps:
establishing a relation function between a frequency variable delta f of a transmission-end power grid after correction through a first-order lag link and an active power variable delta P generated by a transmission-end power grid unit:
in the formula,
the value range of active power variable delta P generated by the sending end power grid unit is 0-PG；
M is an inertia time constant of a sending-end power grid unit, T is a first-order lag link time constant, and T is a time variable;
when the frequency variable delta f of the sending-end power grid after being corrected through a first-order lag link is equal to the transient rated frequency value fZThen, the active power variable Δ P of the sending-end power grid unit generated by the relation function is the transient active power value Δ P of the sending-end power grid unit generated by the sending-end power grid unitZ。
Then, according to the active power value P of the outgoing channel of the sending-end power gridLTransient active power value delta P for generating power by sending-end power grid unitZPassing through the first transient critical active power value PVSC1-ZThe obtaining formula of (1): pVSC1-Z＝PL-ΔPZObtaining a first transient critical active power value PVSC1-Z。
Step 204, according to the first steady critical active power value P of the flexible direct current back-to-back systemVSC1-WAnd a first transient critical active power value P of the flexible direct current back-to-back systemVSC1-ZComparing the two power values to obtain a critical active power value of the flexible direct current back-to-back system, namely the critical active power value of the flexible direct current back-to-back system is Max (PVSC1-W，PVSC1-Z)。
In order to ensure that the flexible direct-current back-to-back system can have the lowest ring-opening cost on the premise of ensuring the stable isolated network operation frequency of the sending-end power grid, the ring-opening method provided by the embodiment of the invention can also determine the critical active power value of the flexible direct-current back-to-back system again by comparing the second critical active power value of the flexible direct-current back-to-back system when the safety control assistance of the high-frequency generator tripping is adopted with the first critical active power value of the flexible direct-current back-to-back system when the safety control assistance of the high-frequency generator tripping is not adopted by means of the high-frequency generator tripping in the sending-end power grid.
The critical active power value of the flexible dc back-to-back system determined in step 204 is a first critical active power value PVSC1I.e. PVSC1＝Max(PVSC1-W，PVSC1-Z)；
Step 205, obtaining a second steady-state critical active power value P of the flexible direct current back-to-back system after the high-cycle generator is used by the transmission-end power gridVSC2-M；
Second steady state critical active power value
Wherein, Δ PCThe cutting amount of the high-circumference cutting machine.
And the cutting amount delta P of the high-circumference cutting machineCThe specific value of (b) should be estimated by those skilled in the art according to conventional methods for calculating the amount of the machine cutting. The embodiment of the invention provides a specific estimation method, namely the cutting amount of a high-frequency cutting machineWherein, Δ P1And Δ P2The method for obtaining the transient active power value delta P of the power generation of the sending-end power grid unitZThe obtaining method is the same, and the relation function of the frequency variable delta f after the correction of the first-order lag link of the sending-end power grid and the active power variable delta P generated by the sending-end power grid unit is as follows:determining;
when the frequency variable delta f of the sending-end power grid after being corrected through a first-order lag link is equal to the transient frequency value fZ1In time, the active power variable delta P of the sending-end power grid unit power generation obtained through the relation function is delta P1(ii) a When the frequency variable delta f of the sending-end power grid after being corrected through a first-order lag link is equal to the transient frequency value fZ2The power generation of the sending-end power grid unit is obtained through the relation functionWork power variable Δ P is Δ P2(ii) a Value of the transient frequency fZ1And a transient frequency value fZ2And two groups of maximum frequency values allowed when the isolated network transient operation frequency of the power grid at the sending end is stable are respectively obtained.
Step 206, obtaining a second transient critical active power value P of the flexible direct current back-to-back system after the high cycle generator is used by the transmission-end power gridVSC2-ZAnd a second transient critical active power value PVSC2-Z＝PL-ΔPZ-ΔPC；
Step 207, according to the second steady critical active power value P of the flexible dc back-to-back systemVSC2-WAnd a second transient critical active power value P of the flexible direct current back-to-back systemVSC2-ZThe comparison is larger to obtain a second critical active power value P of the flexible direct current back-to-back systemVSC2I.e. PVSC2＝Max(PVSC2-W，PVSC2-Z)；
Step 208, according to the first critical active power value PVSC1And a second critical active power value PVSC2The comparison is smaller to obtain a critical active power value of the flexible direct current back-to-back system, that is, the critical active power value of the flexible direct current back-to-back system is Min (P)VSC1，PVSC2)。
The design method of the electromagnetic looped network looping-off scheme provided by the embodiment of the invention determines the minimum critical active power value of the flexible direct current back-to-back system again by comparing the second critical active power value of the flexible direct current back-to-back system when the safety control assistance of the high-frequency cutting machine is adopted with the first critical active power value of the flexible direct current back-to-back system when the safety control assistance of the high-frequency cutting machine is not adopted, so that the looping-off cost required by additionally arranging the flexible direct current back-to-back system can be further reduced.
In order to ensure that the isolated network operating frequency of the sending-end power grid can be kept stable when the flexible direct-current back-to-back system has the minimum critical active power value, in the design method of the electromagnetic ring network looping splitting scheme provided in this embodiment, when the determination condition of the target looping splitting scheme is that the looping cost is less than or equal to the estimated looping cost of the electromagnetic ring network, that is, when the looping cost of the virtual looping splitting scheme is less than or equal to the estimated looping cost of the electromagnetic ring network, and it is determined that the virtual looping splitting scheme is the target looping splitting scheme, the design method of the electromagnetic ring network looping splitting scheme further includes:
step 5, constructing a simulation model according to the target loop-opening scheme, and setting a critical active power value of the flexible direct current back-to-back system as an active power simulation parameter of the flexible direct current back-to-back system;
step 6, carrying out simulation analysis on the simulation model so as to verify whether the flexible direct-current back-to-back system can stabilize the isolated network operation frequency of the power grid at the sending end according to a target ring-opening scheme;
determining whether a target ring-opening scheme is adopted as a ring-opening scheme or not according to the stability of the isolated network operation frequency of the power grid at the sending end; specifically, if after simulation analysis of the target ring-opening scheme, it is verified that the flexible direct-current back-to-back system can stabilize the isolated network operation frequency of the power grid at the sending end, the target ring-opening scheme is used as the ring-opening scheme, the flexible direct-current back-to-back system is additionally arranged at a ring-opening point, and the electromagnetic ring network is opened; if the target ring-opening scheme is subjected to simulation analysis, and it is verified that the flexible direct-current back-to-back system cannot enable isolated network operation frequency of the power grid at the sending end to be stable, the target ring-opening scheme is abandoned to be adopted as the ring-opening scheme, and other existing ring-opening schemes need to be selected again to perform ring-opening on the electromagnetic ring network.
In order to obtain the balance between the economy and the loop-separating stability of the flexible direct-current back-to-back system, in the design method of the electromagnetic ring network loop-separating scheme provided in this embodiment, when the target loop-separating scheme is determined according to the stability of the isolated operation frequency of the power grid at the sending end and the isolated operation frequency of the power grid at the sending end is not stable, the design method of the electromagnetic ring network loop-separating scheme further includes:
step 7, debugging active power simulation parameters of the flexible direct current back-to-back system until the flexible direct current back-to-back system enables isolated grid operation frequency of a power grid at a sending end to be stable in a simulation model, and obtaining a simulation active power value of the flexible direct current back-to-back system;
step 8, determining the simulation loop-opening cost for additionally arranging the flexible direct current back-to-back system according to the simulation active power value of the flexible direct current back-to-back system;
step 9, determining whether a debugged target ring-opening scheme is adopted as a ring-opening scheme or not according to the relationship between the simulation ring-opening cost and the estimated ring-opening cost of the electromagnetic ring network; specifically, if the simulation ring-opening cost is less than or equal to the estimated ring-opening cost of the electromagnetic ring network, a debugged target ring-opening scheme is adopted as a ring-opening scheme, a flexible direct-current back-to-back system with a simulation active power value is additionally arranged at a ring-opening point, and the electromagnetic ring network is opened; and if the simulation ring-opening cost is larger than the estimated ring-opening cost of the electromagnetic ring network, abandoning to adopt the debugged target ring-opening scheme as the ring-opening scheme, and reselecting the existing other ring-opening schemes to open the ring of the electromagnetic ring network.
In order to more clearly describe the design method of the ring-opening scheme of the electromagnetic ring network provided in the above embodiment, referring to fig. 3-5, in the local power grid shown in fig. 3, the grid structure of the electromagnetic ring network existing on the outgoing channel of the sending-end power grid 5 is taken as an example to verify the ring-opening effect of the ring-opening method of the electromagnetic ring network provided in the embodiment of the present invention.
In the local power grid shown in fig. 3, A, B, C, E, F, G, H, I, J, K are each power plant in the local power grid, D is a converter station, c, D, e, f, g, h, i, j, k, l are each substation in the local power grid, a and b are each 500kV substations, and m and n are each 220kV substations; wherein, a 500kV first outgoing channel 1 formed by a-A and a 500kV second outgoing channel 2 formed by a-B are high-voltage lines of an outgoing channel of a sending-end power grid 5, a 220kV first outgoing channel 3 formed by m-n and a 220kV second outgoing channel 4 formed by m-n are low-voltage lines of the outgoing channel of the sending-end power grid 5, and the high-voltage lines and the low-voltage lines form an electromagnetic ring network of the outgoing channel of the sending-end power grid 5.
In the local power grid shown in fig. 3, the 500kV first outgoing channel 1 and the 500kV second outgoing channel 2 are in the same forest area, and in a forest fire season, the 500kV first outgoing channel 1 and the 500kV second outgoing channel 2 are easy to trip simultaneously, which causes the sending-end power grid 5 of the local power grid to operate in an isolated grid; if the operation of an electromagnetic ring network in a local power grid needs to be kept, the active power value of the sending section of the sending end power grid needs to be reduced, so that the situation that the 220kV first outgoing channel 3 and the 220kV second outgoing channel 4 are overloaded after the 500kV first outgoing channel 1 and the 500kV second outgoing channel 2 trip is avoided.
However, in order to ensure that the active power output by the outgoing channel of the sending-end power grid 5 can meet the use requirement of the main grid 6 and the isolated network operation frequency of the sending-end power grid 5 is stable, the electromagnetic looped network of the outgoing channel of the sending-end power grid 5 needs to be looped, the looping-off point should be at the 220kV first outgoing channel 3 formed by m-n and the 220kV second outgoing channel 4 formed by m-n, and referring to fig. 4, a virtual looping-off scheme is constructed in which a set of flexible direct-current back-to-back systems 7 is additionally arranged in the m transformer substation.
When the loop of the power transmission end grid 5 is released through the virtual loop-releasing scheme, a rated frequency value when the isolated network operation frequency of the power transmission end grid 5 is stable, namely a stable rated frequency value f, is determined firstlyWIs 50Hz, the maximum is not more than 50.5 Hz; transient nominal frequency value fZIs 51Hz, and the maximum value does not exceed 51.5 Hz.
When the sending-end power grid operates in a small-large operation mode of the power system, the total active power value P of the sending-end power grid unit for generating powerG2500MW, active power value P of outgoing channel of transmission end power gridLThe steady-state frequency deviation value delta f allowed by isolated network operation of the power grid at the transmitting end is 900MWWThe frequency modulation difference-adjusting coefficient R of the power grid unit at the sending end is 0.1, the inertia time constant M of the power grid unit at the sending end is 10, and the time constant T of the first-order lag link is 0.5.
According to the method for determining the critical active power value of the flexible direct current back-to-back system provided by the embodiment of the invention, the values of the parameters are substituted to determine that:
first steady-state critical active power value of flexible direct current back-to-back system
Transient active power value delta P of power generation of transmission end power grid unit is 0.18PG；
First transient critical active power value P of flexible direct current back-to-back systemVSC1-Z＝PL-ΔPZ＝450MW；
First critical active power value of flexible direct current back-to-back system
PVSC1＝Max(PVSC1-W，PVSC1-Z)＝450MW；
fZ1When the frequency is 51.5Hz,fZ2when the frequency is equal to 51Hz,
cutting amount of high-cycle cutting machine
Second steady-state critical active power value of flexible direct current back-to-back system
Second transient critical active power value of flexible direct current back-to-back system
PVSC2-Z＝PL-ΔPZ-ΔPC＝200MW；
Second critical active power value of flexible direct current back-to-back system
PVSC2＝Max(PVSC2-W，PVSC2-Z)＝200MW；
Critical active power value P of flexible direct current back-to-back systemVSC＝Min(PVSC1，PVSC2)＝200MW。
According to the determined critical active power value 200MW of the flexible direct current back-to-back system, the ring-opening cost required by additionally arranging the flexible direct current back-to-back system can be calculated to be 2.4 million yuan, and when a conventional ring-opening scheme is adopted, the estimated ring-opening cost of the electromagnetic ring network is 3 million yuan; the loop-opening cost of the virtual loop-opening scheme provided by the embodiment is less than the estimated loop-opening cost of the electromagnetic looped network, and the virtual loop-opening scheme provided by the embodiment can be determined as a target loop-opening scheme.
In order to check that the isolated network operation frequency of the transmission-end power grid shown in fig. 3 can be kept stable when the flexible direct-current back-to-back system has the minimum critical active power value of 200MW, a simulation model of the flexible direct-current back-to-back system is additionally arranged at an electromagnetic ring network ring-opening point is constructed in power system analysis software PSD-BPA, and simulation analysis of all tripping operations of a 500kV first outgoing channel 1 and a 500kV second outgoing channel 2 is performed; setting a critical active power value 200MW of the flexible direct current back-to-back system as an active power simulation parameter of the flexible direct current back-to-back system; setting that the flexible direct current back-to-back system does not send active power when in normal operation; when the high-frequency cutting machine is adopted for safety control assistance, if the transient frequency reaches the transient rated frequency value fZAnd arranging a high-frequency cutting machine to cut off 250MW units in the generator set of the transmission-end power grid.
The result of simulation analysis after the flexible direct-current back-to-back system is added at the ring-opening point of the electromagnetic ring network is shown in fig. 5, after the flexible direct-current back-to-back system opens the electromagnetic ring network, the flexible direct-current back-to-back system provides quick active power regulation for the power grid at the sending end, so that the maximum transient frequency value after the power grid at the sending end operates in an isolated network mode is not more than 51.5Hz, and the maximum steady frequency value is not more than 50.43Hz, and the operation requirement of stable frequency of the power grid in the isolated network mode can be met.
In the foregoing description of embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (9)
1. A design method of an electromagnetic ring network loop-opening scheme is provided, wherein the electromagnetic ring network is positioned in an outgoing channel of a sending-end power grid, and the design method of the electromagnetic ring network loop-opening scheme is characterized by comprising the following steps:
step 1, acquiring a ring-opening point of the electromagnetic looped network, and additionally arranging a flexible direct-current back-to-back system for ring opening at the ring-opening point to construct a virtual ring-opening scheme;
step 2, the electromagnetic looped network is looped off through the virtual looping-off scheme, and a critical active power value of the flexible direct current back-to-back system is obtained under the condition that the isolated network operation frequency of a power grid at a sending end is stable; the acquisition method comprises the following steps:
step 201, determining a rated frequency value when the isolated network operation frequency of a power grid at a sending end is stable, wherein the rated frequency value comprises a stable rated frequency value fWAnd a transient nominal frequency value fZ；
Step 202, obtaining a first steady state critical active power value P of the flexible direct current back-to-back systemVSC1-W；
Step 203, obtaining a first transient critical active power value P of the flexible direct current back-to-back systemVSC1-Z；
Step 204, setting a first steady critical active power value P of the flexible direct current back-to-back systemVSC1-WAnd a first transient critical active power value P of the flexible direct current back-to-back systemVSC1-ZComparing, and taking the larger value as the critical active power value of the flexible direct current back-to-back system; wherein,
critical active power value of the flexible direct current back-to-back system is Max (P)VSC1-W，PVSC1-Z)；
Step 3, determining the loop-opening cost for additionally arranging the flexible direct current back-to-back system according to the critical active power value of the flexible direct current back-to-back system;
and 4, determining whether the virtual ring-opening scheme is adopted as a target ring-opening scheme or not according to the relationship between the ring-opening cost and the estimated ring-opening cost of the electromagnetic ring network.
2. The method according to claim 1, wherein in step 202, the first steady-state critical active power value P is determinedVSC1-WThe method comprises the following steps:
wherein, PLFor the value of the active power of the outgoing channel of the transmitting-end network, PGTotal active power value for generating power of sending-end power grid unitR is the single frequency modulation difference adjustment coefficient of the power grid unit at the sending end, delta fWAnd (4) a steady-state frequency deviation value allowed for isolated grid operation of the power grid at the sending end.
3. The method for designing an electromagnetic ring network loopback scheme as claimed in claim 1, wherein in step 203, the first transient critical active power value P is determinedVSC1-ZThe method comprises the following steps:
obtaining the active power value P of the outgoing channel of the sending end power gridL，
Obtaining the transient state operation frequency of the isolated grid of the power grid at the sending end equal to the transient state rated frequency value fZTransient active power value delta P of power generation of sending-end power grid unitZ；
According to the active power value P of the outgoing channel of the sending-end power gridLAnd the transient active power value delta P generated by the sending end power grid unitZObtaining the first transient critical active power value PVSC1-Z(ii) a Wherein, PVSC1-Z＝PL-ΔPZ。
4. The method according to claim 3, wherein the transient active power value Δ P generated by the sending-end grid unit is a transient active power value Δ PZThe method comprises the following steps:
establishing a relation function between a frequency variable delta f of a transmission-end power grid after correction through a first-order lag link and an active power variable delta P generated by a transmission-end power grid unit:
in the formula,
the value range of active power variable delta P generated by the sending-end power grid unit is 0-PG；
Wherein, PGFor sending end electric network machineThe method comprises the following steps that (1) the total active power value of group power generation, R is a single frequency modulation difference adjustment coefficient of a sending end power grid unit, M is an inertia time constant of the sending end power grid unit, T is a first-order lag link time constant, and T is a time variable;
when the frequency variable delta f of the sending-end power grid after being corrected through a first-order lag link is equal to the transient rated frequency value fZThen, the active power variable Δ P generated by the sending-end power grid unit obtained through the relation function is the transient active power value Δ P generated by the sending-end power grid unitZ。
5. The design method of the electromagnetic ring network solution according to claim 1,
in step 204, the obtained critical active power value of the flexible direct current back-to-back system is a first critical active power value PVSC1，PVSC1＝Max(PVSC1-W，PVSC1-Z)；
In step 2, the method for obtaining the critical active power value of the flexible direct current back-to-back system further includes:
step 205, obtaining a second steady-state critical active power value P of the flexible direct-current back-to-back system after the high-frequency generator tripping is used by the sending-end power gridVSC2-M；
Step 206, obtaining a second transient critical active power value P of the flexible direct current back-to-back system after the high cycle generator is used by the sending-end power gridVSC2-Z；
Step 207, setting a second steady critical active power value P of the flexible direct current back-to-back systemVSC2-WAnd a second transient critical active power value P of the flexible direct current back-to-back systemVSC2-ZComparing the two power values, and taking the larger value as a second critical active power value P of the flexible direct current back-to-back systemVSC2，PVSC2＝Max(PVSC2-W，PVSC2-Z)；
Step 208, determine the first critical active power value PVSC1And said second critical active power value PVSC2Comparing, and taking the smaller value as the flexible direct current back-to-backCritical active power value of the system, and critical active power value of the flexible direct current back-to-back system being Min (P)VSC1，PVSC2)。
6. The design method of the electromagnetic ring network solution according to claim 5,
in step 205, the second steady-state critical active power value PVSC2-WThe method comprises the following steps:
wherein, PLFor the value of the active power of the outgoing channel of the transmitting-end network, PGThe total active power value for generating power of the power grid unit at the sending end, R is the single frequency modulation difference adjustment coefficient of the power grid unit at the sending end, and delta fwAllowable steady-state frequency deviation value delta P for isolated network operation of power grid at transmission endCThe cutting amount of the high-circumference cutting machine.
7. The method according to claim 5, wherein in step 206, the second transient critical active power value P is determinedVSC2-ZThe method comprises the following steps:
obtaining the active power value P of the outgoing channel of the sending end power gridL，
Obtaining the transient state operation frequency of the isolated grid of the power grid at the sending end equal to the transient state rated frequency value fZTransient active power value delta P of power generation of sending-end power grid unitZ，
Obtain high circumference cutter's cutter volume delta PC，
According to the active power value P of the outgoing channel of the sending-end power gridLAnd the transient active power value delta P generated by the sending end power grid unitZAnd the cutting amount delta P of the high-circumference cutting machineCObtaining the second transient critical active power value PVSC2-Z(ii) a Wherein, PVSC2-Z＝PL-ΔPZ-ΔPC。
8. The method for designing an electromagnetic ring network solution according to any one of claims 1 to 7, wherein when the condition for determining the target solution is that the solution cost is less than or equal to the estimated solution cost of the electromagnetic ring network, the method for designing an electromagnetic ring network solution further includes:
step 5, constructing a simulation model according to the target loop-opening scheme, and setting a critical active power value of the flexible direct current back-to-back system as an active power simulation parameter of the flexible direct current back-to-back system;
step 6, carrying out simulation analysis on the simulation model so as to verify whether the flexible direct-current back-to-back system can stabilize the isolated network operation frequency of the power grid at the sending end according to the target ring-opening scheme;
and determining whether the target ring-opening scheme is adopted as a ring-opening scheme or not according to the stability of the isolated network operation frequency of the power grid at the sending end.
9. The design method of the electromagnetic ring network solution according to claim 8,
determining the target ring-opening scheme according to the stability of the isolated network operation frequency of the power transmission end power grid to ensure that the isolated network operation frequency of the power transmission end power grid is stable, and adopting the target ring-opening scheme as a ring-opening scheme;
when it is determined that the target ring-opening scheme fails to stabilize the isolated network operation frequency of the transmission-end power grid according to the stability of the isolated network operation frequency of the transmission-end power grid, the ring-opening method of the electromagnetic ring network further comprises the following steps:
step 7, debugging active power simulation parameters of the flexible direct current back-to-back system until the flexible direct current back-to-back system enables the isolated network operation frequency of the power grid at the sending end to be stable in the simulation model, and obtaining a simulation active power value of the flexible direct current back-to-back system;
step 8, determining the simulation loop-opening cost for additionally arranging the flexible direct current back-to-back system according to the simulation active power value of the flexible direct current back-to-back system;
and 9, determining whether the debugged target ring-opening scheme is adopted as the ring-opening scheme or not according to the relationship between the simulation ring-opening cost and the estimated ring-opening cost of the electromagnetic ring network.
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