CN113595130A - Method and system for online evaluation of dynamic power controllability of direct-current power transmission system - Google Patents
Method and system for online evaluation of dynamic power controllability of direct-current power transmission system Download PDFInfo
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Abstract
The invention provides an online evaluation method for the dynamic power controllability of a direct current transmission system, which is used for collecting the voltage of a converter bus, direct current and a turn-off angle of an inverter station of the direct current transmission system in real time; comparing whether the direct current and the turn-off angle are out of limit or not, and further evaluating the allowable range of active power and reactive power of the direct current transmission system under the direct current constraint and the turn-off angle constraint according to the real-time collected current conversion bus voltage; finally, according to the current conversion bus voltage acquired in real time, the controllable capability of the dynamic power of the direct current transmission system under the direct current constraint and the turn-off angle constraint is evaluated; the method can accurately quantify the relation of each electric quantity of the inverter station, comprehensively considers the safety constraint of the direct current transmission system and the running state of the power grid, accurately and visually evaluates the dynamic power controllable capability of the direct current transmission system, has simple data processing and easy realization, is convenient for constructing the direct current transmission system dynamic power controllable capability online evaluation system with low hardware cost, and has stronger economical efficiency and practicability.
Description
Technical Field
The invention relates to the technical field of power system protection and control, in particular to a method and a system for online evaluation of dynamic power controllability of a direct-current power transmission system.
Background
With the accelerated energy system propulsion of China, the energy system is converted to be saving and efficient, the energy structure is converted to be green and low-carbon, and renewable energy sources such as wind power, solar energy and the like are rapidly developed. Because the energy center and the load center in China are in a reverse distribution pattern, the direct current transmission technology is suitable for large-capacity and long-distance energy transmission and is convenient for new energy grid connection. The direct-current power grid can realize asynchronous interconnection of a plurality of alternating-current systems, the new energy consumption level is improved, and the method is more reliable, flexible and economical. The current source type high voltage direct current transmission technology (LCC-HVDC) based on the power grid commutation becomes an important technical means for power transmission by virtue of the advantages of high voltage, large capacity and good economical efficiency.
By 2020, LCC-HVDC engineering in China reaches 32 projects. China has built the largest worldwide scale alternating current-direct current hybrid power grid with the highest voltage level, and all large-area power grids are interconnected through ultra-high voltage alternating current-direct current transmission lines.
With the continuous improvement of direct current transmission capacity, on one hand, the mutual coupling of alternating current and direct current and the interaction influence of a transmitting end and a receiving end are more serious, the influence of disturbance impact caused by a direct current system on an alternating current power grid is not ignored, and the safe operation risk of multiple direct current output and feeding power grids is continuously increased; on the other hand, the direct-current transmission system has high power electronic device action speed and strong controllability, thereby providing possibility for the rapid optimization control of the power grid and providing new available resources for the emergency coordination control of the system. Therefore, it is urgent to evaluate the power controllability of the dc transmission system, and further provide theoretical support for the dc transmission system to participate in the fast optimization and the emergency coordination control of the power grid.
The method is only suitable for evaluating the power characteristics of the direct current transmission system during normal operation. In addition, the existing method does not consider the power coupling characteristic and the coupling action of an alternating current-direct current power grid, and neglects the influence of the active power and reactive power coupling characteristic on the power adjustable range.
Therefore, how to comprehensively consider the safety constraint of the direct current transmission system and the operation state of the power grid, accurately quantize the relationship of each electric quantity of the inverter station, and accurately and intuitively evaluate the dynamic power controllable capability of the direct current transmission system becomes a problem which needs to be solved by the technical personnel in the field.
Disclosure of Invention
Aiming at the defects in the prior art, the invention needs to solve the problems that: how to comprehensively consider the safety constraint of the direct current transmission system and the running state of a power grid, accurately quantize the relation of each electric quantity of the inverter station, and accurately and intuitively evaluate the dynamic power controllability of the direct current transmission system.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for online evaluation of dynamic power controllability of a direct current transmission system comprises the following steps:
s101, collecting the voltage, the direct current and the turn-off angle of a converter bus of an inverter station of a direct current transmission system in real time;
s102, calculating the adjustable ranges of active power and reactive power of the direct-current transmission system under direct-current constraint and turn-off angle constraint according to the collected current conversion bus voltage;
and S103, evaluating the dynamic power controllability of the direct current transmission system according to the adjustable ranges of the active power and the reactive power of the direct current transmission system.
In the above method for online evaluation of dynamic power controllability of dc power transmission system, as a preferred scheme, in step S102, the active power P of the dc power transmission systemdThe adjustable range of (c) is calculated as follows:
Pdl≤Pd≤Pdu；
in the formula, PdlAnd PduThe minimum allowable value and the maximum allowable value of the active power which meet the direct current constraint and the turn-off angle constraint under any reactive power exchange quantity are respectively determined by the following formula:
in the formula, QacThe reactive power of the direct current transmission system; gamma is a turn-off angle of the inversion station; gamma raynIs a rated off angle; gamma raylimTo avoid commutation lossCritical shutdown angle of failure; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
In the above method for online evaluation of dynamic power controllability of dc power transmission system, as a preferred scheme, in step S102, the reactive power Q of the dc power transmission systemacThe adjustable range of (c) is calculated as follows:
Qdl≤Qac≤Qdu；
in the formula, QdlAnd QduThe minimum allowable value and the maximum allowable value of the reactive power which meet the direct current constraint and the turn-off angle constraint under any active power are determined by the following formula:
in the formula, PdActive power of the direct current transmission system; gamma is a turn-off angle of the inversion station; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
In the above method for online evaluation of dynamic power controllability of a dc power transmission system, as a preferred scheme, the power coupling function Γ (P) of the dc power transmission systemd,Qac) Is determined by the following formula:
the coefficient K satisfies:
in the formula, the coefficients m, n, p and q are respectively:
in the formula, gamma is a turn-off angle of the inverter station; u shapeacThe effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system is obtained; b iscThe equivalent susceptance of a reactive power compensation device in the station is obtained; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
In the above online evaluation method for the dynamic power controllability of the dc power transmission system, as a preferred scheme, in step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: forward maximum active adjustable quantity delta P in normal operationupAnd negative maximum active adjustable quantity delta PdownThe method comprises the following steps:
in the formula, Pd0Calculating the real-time value of active power P according to the collected electric quantity of the inverter station during normal operationdminAnd PdmaxRespectively calculating the minimum allowable value and the maximum allowable value of the active power of the inverter station under the condition that the direct current does not exceed the limit during normal operation according to the following formula:
in the formula, gamma0The switching-off angle of the inverter station during normal operation; u shapeac.0The effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system during normal operation is obtained; i isd.0For the direct current transmission in normal operationThe direct current value of the electric system inverter station; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
In the above online evaluation method for the dynamic power controllability of the dc power transmission system, as a preferred scheme, in step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: maximum forward reactive adjustable quantity delta Q in normal operationupAnd negative maximum reactive adjustable quantity delta QdownThe method comprises the following steps:
in the formula, Qac0For real-time values of reactive exchange capacity, Q, during normal operationacminAnd QacmaxRespectively calculating the minimum allowable value and the maximum allowable value of the reactive power of the inverter station under the condition that the direct current does not exceed the limit during normal operation according to the following formulas:
in the formula, coefficient Ai、Bi、CiRespectively as follows:
in the formula, BcFor reactive compensation in inverter stationEquivalent susceptance; gamma ray0The switching-off angle of the inverter station during normal operation; u shapeac.0The effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system during normal operation is obtained; i isd.0The direct current value of the direct current transmission system inverter station in normal operation is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
In the above online evaluation method for the dynamic power controllability of the dc power transmission system, as a preferred scheme, in step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: the maximum active adjustable quantity in the power grid fault comprises the positive maximum active adjustable quantity delta P under the condition of avoiding the commutation failure of the direct current inversion stationup.fAnd negative maximum active adjustable quantity delta Pdown.fThe method comprises the following steps:
in the formula, Pd.fReal-time active power P in case of grid faultsmin.fAnd Pmax.fThe minimum allowable value and the maximum allowable value of the active power of the inverter station under the conditions that the direct current is not out of limit and the commutation failure is avoided when the power grid fails are respectively calculated by the following formula:
in the formula, gammafFor the failure of the gridThe instantaneous turn-off angle of the inverter station; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
In the above online evaluation method for the dynamic power controllability of the dc power transmission system, as a preferred scheme, in step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: the maximum reactive adjustable quantity in the power grid fault comprises a forward maximum reactive adjustable quantity delta Q under the condition of avoiding commutation failureup.fAnd negative maximum reactive adjustable quantity delta Qdown.fThe method comprises the following steps:
in the formula, Qac.fIs real-time reactive exchange quantity, Q, in the case of a power grid faultmin.fAnd Qmax.fThe minimum allowable value and the maximum allowable value of the reactive power of the inverter station under the conditions that the direct current is not out of limit and the commutation failure is avoided during the power grid fault are respectively calculated by the following formula:
in which isNumber Ai、Bi、CiRespectively as follows:
in the formula, BcThe equivalent susceptance of a reactive power compensation device in the inverter station is obtained; gamma rayfThe instantaneous turn-off angle of the inverter station when the power grid fails; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
In the above online evaluation method for the dynamic power controllability of the dc power transmission system, as a preferred scheme, in step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: maximum adjustable quantity delta P of active power under condition that inverter station does not absorb reactive power during grid faultmvpThe method comprises the following steps:
ΔPmvp＝Pd.mvf-Pd.f；
in the formula, Pd.fReal-time active power when the power grid fails; pd.mvfWhen the power grid fails, the direct current does not exceed the limit, the phase commutation failure is avoided, and the inverter station does not absorb the maximum active allowable value under the reactive condition, and the maximum active allowable value is obtained when the reactive power switching quantity is equal to 0; are calculated by the following formulas, respectively:
in the formula, gammafThe instantaneous turn-off angle of the inverter station when the power grid fails; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; pi is the circumference ratio; pdActive power of the direct current transmission system; qacThe reactive power of the direct current transmission system; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
In addition, the invention also correspondingly provides an online evaluation system for the dynamic power controllability of the direct current transmission system, and for this purpose, the invention adopts the following technical scheme:
the utility model provides a controllable ability on-line evaluation system of DC transmission system dynamic power, includes memory, treater and a plurality of online monitoring device who installs in inverter station current conversion busbar department, wherein:
the online monitoring device is used for acquiring the voltage, the direct current and the turn-off angle of a converter bus of the direct current transmission system inverter station in real time;
the memory is used for storing the application program and the data generated by the application program;
the processor is used for running the application program stored in the memory to realize the online evaluation method for the dynamic power controllable capability of the direct current power transmission system.
Compared with the prior art, the invention has the beneficial effects that:
1. the method for evaluating the controllable capacity of the dynamic power of the direct current transmission system on line realizes the evaluation of the adjustable ranges of the active power and the reactive power of the direct current transmission system on the basis of comparing and judging whether the direct current and the turn-off angle are out of limit or not according to the voltage of a converter bus, the direct current and the turn-off angle of an inverter station of the direct current transmission system which are acquired in real time.
2. The method for online evaluating the dynamic power controllability of the direct current transmission system calculates the real-time values of active power and reactive power according to the collected electric quantity of the inverter station, and further calculates the maximum positive and negative active and reactive adjustable quantities; compared with the prior art, the method can be used for determining the maximum adjustable quantity of the maximum power during normal operation and power grid faults and the maximum adjustable quantity of the active power under the condition that the inverter station does not absorb reactive power during power grid faults.
3. The method for online evaluating the dynamic power controllability of the DC transmission system has the advantages of clear implementation mode, low requirements on the precision and the function of an online monitoring device, simple data processing, easy realization, convenient construction of the dynamic power controllability online evaluation system of the DC transmission system with low hardware cost and strong economical efficiency and practicability, and can be realized by only acquiring the converter bus voltage, the DC current and the turn-off angle of an inverter station of the DC transmission system and utilizing the existing monitoring equipment of the DC transmission system.
Drawings
For purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made in detail to the present invention as illustrated in the accompanying drawings, in which:
fig. 1 is a schematic diagram of an exemplary LCC-HVDC direct current transmission system.
Fig. 2 is a schematic flow chart of the method for online evaluation of dynamic power controllability of the direct current transmission system.
Fig. 3 is a diagram illustrating a result of evaluating power controllability of the dc power transmission system in normal operation in the embodiment.
Fig. 4 is a diagram illustrating a result of evaluating power controllability of a dc power transmission system in case of a power grid fault in the embodiment.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the method for online evaluating the dynamic power controllability of a dc power transmission system of the present invention includes the following steps:
s101, collecting the voltage, the direct current and the turn-off angle of a converter bus of an inverter station of a direct current transmission system in real time;
s102, calculating the adjustable ranges of active power and reactive power of the direct-current transmission system under direct-current constraint and turn-off angle constraint according to the collected current conversion bus voltage;
and S103, evaluating the dynamic power controllability of the direct current transmission system according to the adjustable ranges of the active power and the reactive power of the direct current transmission system.
The method for online evaluating the dynamic power controllability of the direct current transmission system judges whether the direct current and the turn-off angle are out of limit or not by acquiring the voltage of a converter bus, the direct current and the turn-off angle of an inverter station of the direct current transmission system in real time, and further evaluates the adjustable range of active power and reactive power of the direct current transmission system and the dynamic power controllability of the direct current transmission system under the direct current constraint and the turn-off angle constraint according to the voltage of the converter bus acquired in real time. The method can accurately quantify the relation of each electric quantity of the inverter station, comprehensively consider the safety constraint of the direct current transmission system and the running state of the power grid, and accurately and intuitively evaluate the dynamic power controllable capability of the direct current transmission system.
In specific implementation, in step S102, the active power P of the dc transmission systemdThe adjustable range of (c) is calculated as follows:
Pdl≤Pd≤Pdu；
in the formula, PdlAnd PduThe minimum allowable value and the maximum allowable value of the active power which meet the direct current constraint and the turn-off angle constraint under any reactive power exchange quantity are respectively determined by the following formula:
in the formula, QacThe reactive power of the direct current transmission system; gamma is a turn-off angle of the inversion station; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
In specific implementation, in step S102, the reactive power of the dc power transmission systemRate QacThe adjustable range of (c) is calculated as follows:
Qdl≤Qac≤Qdu；
in the formula, QdlAnd QduThe minimum allowable value and the maximum allowable value of the reactive power which meet the direct current constraint and the turn-off angle constraint under any active power are determined by the following formula:
when the method is implemented, the power coupling function gamma (P) of the direct current transmission systemd,Qac) Is determined by the following formula:
the coefficient K satisfies:
K2＝p2U2 ac-0.5p2U2 accos2γ+0.25qPd；
in the formula, the coefficients m, n, p and q are respectively:
in the formula, gamma is a turn-off angle of the inverter station; u shapeacThe effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system is obtained; b iscThe equivalent susceptance of a reactive power compensation device in the station is obtained; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
In specific implementation, in step S103, the evaluating parameters for evaluating the dynamic power controllability of the dc power transmission system may include:
forward maximum active adjustable quantity delta P in normal operationupAnd negative maximum active adjustable quantity delta Pdown；
Maximum forward reactive adjustable quantity delta Q in normal operationupAnd negative maximum reactive adjustable quantity delta Qdown；
The maximum active adjustable quantity in the power grid fault comprises the positive maximum active adjustable quantity delta P under the condition of avoiding the commutation failure of the direct current inversion stationup.fAnd negative maximum active adjustable quantity delta Pdown.f；
The maximum reactive adjustable quantity in the power grid fault comprises a forward maximum reactive adjustable quantity delta Q under the condition of avoiding commutation failureup.fAnd negative maximum reactive adjustable quantity delta Qdown.f；
And the maximum adjustable quantity delta P of the active power under the condition that the inversion station does not absorb the reactive power when the power grid failsmvp(ii) a And the like.
In specific implementation, the maximum positive active adjustable quantity delta P in normal operationupAnd negative maximum active adjustable quantity delta PdownThe method comprises the following steps:
in the formula, Pd0Calculating the real-time value of active power P according to the collected electric quantity of the inverter station during normal operationdminAnd PdmaxRespectively calculating the minimum allowable value and the maximum allowable value of the active power of the inverter station under the condition that the direct current does not exceed the limit during normal operation according to the following formula:
in the formula, gamma0For normal transportationThe turn-off angle of the inverter station during running; u shapeac.0The effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system during normal operation is obtained; i isd.0The direct current value of the direct current transmission system inverter station in normal operation is obtained; i isdminA direct current minimum limit value for avoiding overvoltage generated on inductive elements such as a converter transformer, a smoothing reactor and the like due to the interruption of direct current; i isdmaxThe direct current maximum limit value for ensuring the safety of the converter valve and a cooling system thereof.
In specific implementation, the maximum forward reactive adjustable quantity delta Q in normal operationupAnd negative maximum reactive adjustable quantity delta QdownThe method comprises the following steps:
in the formula, Qac0For real-time values of reactive exchange capacity, Q, during normal operationacminAnd QacmaxRespectively calculating the minimum allowable value and the maximum allowable value of the reactive power of the inverter station under the condition that the direct current does not exceed the limit during normal operation according to the following formulas:
in the formula, coefficient Ai、Bi、CiRespectively as follows:
in the formula, BcThe equivalent susceptance of the reactive power compensation device in the inverter station is obtained.
In specific implementation, the maximum active adjustable quantity in power grid fault comprises the maximum forward active adjustable quantity delta P under the condition of avoiding the commutation failure of the direct-current inverter stationup.fAnd negative maximum active adjustable quantity delta Pdown.fThe method comprises the following steps:
in the formula, Pd.fReal-time active power P in case of grid faultsmin.fAnd Pmax.fThe minimum allowable value and the maximum allowable value of the active power of the inverter station under the conditions that the direct current is not out of limit and the commutation failure is avoided when the power grid fails are respectively calculated by the following formula:
in the formula, gammafThe instantaneous turn-off angle of the inverter station when the power grid fails; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained.
In specific implementation, the maximum reactive power adjustable quantity during the power grid fault comprises the forward maximum reactive power adjustable quantity delta Q under the condition of avoiding commutation failureup.fAnd negative maximum reactive adjustable quantity delta Qdown.fThe method comprises the following steps:
in the formula, Qac.fIs real-time reactive exchange quantity, Q, in the case of a power grid faultmin.fAnd Qmax.fThe minimum allowable value and the maximum allowable value of the reactive power of the inverter station under the conditions that the direct current is not out of limit and the commutation failure is avoided during the power grid fault are respectively calculated by the following formula:
in the formula, coefficient Ai、Bi、CiRespectively as follows:
in specific implementation, when the power grid fails, the inverter station does not absorb the maximum adjustable quantity delta P of the active power under the reactive power conditionmvpThe method comprises the following steps:
ΔPmvp＝Pd.mvf-Pd.f；
in the formula, Pd.fReal-time active power when the power grid fails; pd.mvfWhen the power grid fails, the direct current does not exceed the limit, the phase commutation failure is avoided, and the inverter station does not absorb the maximum active allowable value under the reactive condition, and the maximum active allowable value is obtained when the reactive power switching quantity is equal to 0; are calculated by the following formulas, respectively:
the invention also provides an online evaluation system for the dynamic power controllability of the direct current transmission system, which comprises a memory, a processor and a plurality of online monitoring devices arranged at a converter bus of the inverter station, wherein the online monitoring devices comprise:
the online monitoring device is used for acquiring the voltage, the direct current and the turn-off angle of a converter bus of the direct current transmission system inverter station in real time;
the memory is used for storing the application program and the data generated by the application program;
the processor is used for running the application program stored in the memory to realize the online evaluation method for the dynamic power controllable capability of the direct current power transmission system.
The processor can adopt a DSP (digital signal processor), the hardware cost is low, and the computing power can meet the actual use requirement.
Example (b):
to verify the effectiveness of the method of the present invention, analytical calculations were performed using the CIGRE HVDC standard test model shown in FIG. 1 as an example. The rated voltage of LCC-HVDC monopole is 500kV, and the reference capacity is 1000 MW. And in normal operation, the voltage of the converter bus is 230kV, and the direct current is 2 kA. The method takes normal operation of the inverter station and short-circuit faults at the alternating-current bus as scenes to verify the on-line evaluation effect of the power controllability of the direct-current transmission system.
The method provided by the invention comprises the following steps: the method disclosed by the invention is adopted to evaluate the power controllable capability under normal operation and power grid fault, wherein the maximum limit value of the direct current is 1.1pu, and the minimum limit value I of the direct current isdmin0.1 pu.
The conventional power calculation method comprises the following steps: and respectively calculating the active power and the reactive power exchange quantity of the inverter station based on a quasi-steady state equation of the direct current transmission system.
Fig. 3 and 4 show power evaluation results during normal operation and grid fault, respectively. In fig. 3 and 4, the abscissa represents the active power of the inverter station, and the ordinate represents the active power of the inverter station.
P corresponding to point A in FIG. 3d0And Qac0The active power and the reactive power of the inverter station are obtained by adopting a conventional power calculation method during normal operation. FIG. 3 is a gray shaded area representing the adjustable ranges of the active power and the reactive power of the DC transmission system under the DC current constraint and the turn-off angle constraint calculated by the method of the present invention, and the maximum forward active adjustable quantity Δ P during normal operationupAnd negative maximum active adjustable quantity delta Pdown90MVA and 876MVA respectively, and forward maximum reactive power adjustable quantity delta Q in normal operationupAnd negative maximum reactive adjustable quantity delta Qdown512Mvar and 76Mvar, respectively.
P corresponding to point B in FIG. 4d.fAnd Qac.fThe active power and the reactive power of the inverter station are obtained by adopting a conventional power calculation method when the power grid fails. The hatched area of the oblique line in fig. 4 is the adjustable range of the active power and the reactive power of the dc power transmission system under the direct current constraint and the turn-off angle constraint calculated by the method of the present invention, and the maximum active adjustable quantity during the power grid fault includes the maximum forward active adjustable quantity Δ P under the condition of avoiding the commutation failure of the dc inverter stationup.fAnd negative maximum active adjustable quantity delta Pdown.f66MVA and 684MVA respectively, and the maximum reactive power adjustable quantity in the case of power grid fault comprises a forward maximum reactive power adjustable quantity delta Q under the condition of avoiding commutation failureup.fAnd negative maximum reactive adjustable quantity delta Qdown.f446Mvar and 65Mvar, respectively.
From experimental data, the existing method is only suitable for calculating the active power and reactive power values of the inverter station under a certain voltage and current, and lacks an evaluation method of the power adjustable range and the dynamic power controllable capability of the direct-current transmission system; the method for evaluating the controllable dynamic power capacity of the direct-current transmission system on line can calculate the adjustable range of the active power and the reactive power of the direct-current transmission system, is used for calculating the maximum adjustable power of the direct-current transmission system during normal operation and power grid failure, and realizes accurate and visual evaluation of the controllable dynamic power capacity of the direct-current transmission system.
In summary, the method for online evaluating the dynamic power controllability of the direct current transmission system can evaluate the adjustable ranges of the active power and the reactive power of the direct current transmission system on the basis of comparing and judging whether the direct current and the turn-off angle are out of limit or not according to the voltage of a converter bus, the direct current and the turn-off angle of an inverter station of the direct current transmission system which are acquired in real time; on the other hand, the method for online evaluating the dynamic power controllability of the direct current transmission system can calculate the maximum positive and negative active and reactive adjustable quantities according to the real-time values of the active power and the reactive power obtained by the collected electric quantity of the inverter station, and further calculate the maximum positive and negative active and reactive adjustable quantities; the method has the advantages of clear implementation mode, low requirements on the precision and the function of the on-line monitoring device, acquisition of the converter bus voltage, the direct current and the turn-off angle of the inverter station of the direct current transmission system, realization by using the existing monitoring equipment of the direct current transmission system, simple data processing, easy realization, convenient construction of the on-line evaluation system with the controllable dynamic power capability of the direct current transmission system with low hardware cost, and strong economy and practicability.
Finally, it is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that, while the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A method for online evaluation of dynamic power controllability of a direct current transmission system is characterized by comprising the following steps:
s101, collecting the voltage, the direct current and the turn-off angle of a converter bus of an inverter station of a direct current transmission system in real time;
s102, calculating the adjustable ranges of active power and reactive power of the direct-current transmission system under direct-current constraint and turn-off angle constraint according to the collected current conversion bus voltage;
and S103, evaluating the dynamic power controllability of the direct current transmission system according to the adjustable ranges of the active power and the reactive power of the direct current transmission system.
2. The method according to claim 1, wherein in step S102, the active power P of the dc power transmission system is estimateddThe adjustable range of (c) is calculated as follows:
Pdl≤Pd≤Pdu；
in the formula, PdlAnd PduThe minimum allowable value and the maximum allowable value of the active power which meet the direct current constraint and the turn-off angle constraint under any reactive power exchange quantity are respectively determined by the following formula:
in the formula, QacThe reactive power of the direct current transmission system; gamma is a turn-off angle of the inversion station; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
3. The method for online evaluation of dynamic power controllability of direct current transmission system according to claim 1, wherein in step S102, the reactive power Q of the direct current transmission systemacThe adjustable range of (c) is calculated as follows:
Qdl≤Qac≤Qdu；
in the formula, QdlAnd QduThe minimum allowable value and the maximum allowable value of the reactive power which meet the direct current constraint and the turn-off angle constraint under any active power are determined by the following formula:
in the formula, PdActive power of the direct current transmission system; gamma is a turn-off angle of the inversion station; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
4. The on-line assessment method for dynamic power controllability of DC power transmission system according to claim 2 or 3, characterized in that the power coupling function Γ (P) of said DC power transmission systemd,Qac) Is determined by the following formula:
the coefficient K satisfies:
in the formula, the coefficients m, n, p and q are respectively:
in the formula, gamma is a turn-off angle of the inverter station; u shapeacThe effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system is obtained; b iscThe equivalent susceptance of a reactive power compensation device in the station is obtained; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
5. The direct current transmission system dynamic power controllability online assessment method according to claim 1, characterized in thatIn step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: forward maximum active adjustable quantity delta P in normal operationupAnd negative maximum active adjustable quantity delta PdownThe method comprises the following steps:
in the formula, Pd0Calculating the real-time value of active power P according to the collected electric quantity of the inverter station during normal operationdminAnd PdmaxRespectively calculating the minimum allowable value and the maximum allowable value of the active power of the inverter station under the condition that the direct current does not exceed the limit during normal operation according to the following formula:
in the formula, gamma0The switching-off angle of the inverter station during normal operation; u shapeac.0The effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system during normal operation is obtained; i isd.0The direct current value of the direct current transmission system inverter station in normal operation is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
6. The dc power transmission system dynamic power controllability online of claim 1The evaluation method is characterized in that in step S103, the evaluation parameters for evaluating the dynamic power controllability of the dc power transmission system include: maximum forward reactive adjustable quantity delta Q in normal operationupAnd negative maximum reactive adjustable quantity delta QdownThe method comprises the following steps:
in the formula, Qac0For real-time values of reactive exchange capacity, Q, during normal operationacminAnd QacmaxRespectively calculating the minimum allowable value and the maximum allowable value of the reactive power of the inverter station under the condition that the direct current does not exceed the limit during normal operation according to the following formulas:
in the formula, coefficient Ai、Bi、CiRespectively as follows:
in the formula, BcThe equivalent susceptance of a reactive power compensation device in the inverter station is obtained; gamma ray0The switching-off angle of the inverter station during normal operation; u shapeac.0The effective value of the grid side line voltage of a converter transformer of the inverter station of the direct current transmission system during normal operation is obtained; i isd.0The direct current value of the direct current transmission system inverter station in normal operation is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
7. The method according to claim 1, wherein in step S103, the evaluating parameters for evaluating the dynamic power controllability of the dc power transmission system include: the maximum active adjustable quantity in the power grid fault comprises the positive maximum active adjustable quantity delta P under the condition of avoiding the commutation failure of the direct current inversion stationup.fAnd negative maximum active adjustable quantity delta Pdown.fThe method comprises the following steps:
in the formula, Pd.fReal-time active power P in case of grid faultsmin.fAnd Pmax.fThe minimum allowable value and the maximum allowable value of the active power of the inverter station under the conditions that the direct current is not out of limit and the commutation failure is avoided when the power grid fails are respectively calculated by the following formula:
in the formula, gammafThe instantaneous turn-off angle of the inverter station when the power grid fails; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
8. The method according to claim 1, wherein in step S103, the evaluating parameters for evaluating the dynamic power controllability of the dc power transmission system include: the maximum reactive adjustable quantity in the power grid fault comprises a forward maximum reactive adjustable quantity delta Q under the condition of avoiding commutation failureup.fAnd negative maximum reactive adjustable quantity delta Qdown.fThe method comprises the following steps:
in the formula, Qac.fIs real-time reactive exchange quantity, Q, in the case of a power grid faultmin.fAnd Qmax.fThe minimum allowable value and the maximum allowable value of the reactive power of the inverter station under the conditions that the direct current is not out of limit and the commutation failure is avoided during the power grid fault are respectively calculated by the following formula:
in the formula, coefficient Ai、Bi、CiRespectively as follows:
in the formula, BcThe equivalent susceptance of a reactive power compensation device in the inverter station is obtained; gamma rayfThe instantaneous turn-off angle of the inverter station when the power grid fails; gamma raynIs a rated off angle; gamma raylimCritical turn-off angle to avoid commutation failure; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained; i isdminIs the minimum limit value of the direct current; i isdmaxIs the maximum limit value of the direct current; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; and pi is the circumferential ratio.
9. The method according to claim 1, wherein in step S103, the evaluating parameters for evaluating the dynamic power controllability of the dc power transmission system include: maximum adjustable quantity delta P of active power under condition that inverter station does not absorb reactive power during grid faultmvpThe method comprises the following steps:
ΔPmvp＝Pd.mvf-Pd.f；
in the formula, Pd.fReal-time active power when the power grid fails; pd.mvfWhen the power grid fails, the direct current does not exceed the limit, the phase commutation failure is avoided, and the inverter station does not absorb the maximum active allowable value under the reactive condition, and the maximum active allowable value is obtained when the reactive power switching quantity is equal to 0; are calculated by the following formulas, respectively:
in the formula, gammafThe instantaneous turn-off angle of the inverter station when the power grid fails; u shapeac.fThe effective value of the network side line voltage of the inverter station converter transformer is the effective value of the network side line voltage when the power grid fails; i isd.fThe value of the direct current transmission system inverter station when the power grid fails is obtained; k is the transformation ratio of the converter transformer; n is the number of 6 pulse current converters in each pole of the inverter station; xrIs a commutation reactance; pi is the circumference ratio; pdActive power of the direct current transmission system; qacThe reactive power of the direct current transmission system; gamma (P)d,Qac) Is the power coupling function of the dc transmission system.
10. The utility model provides a controllable ability on-line evaluation system of DC transmission system dynamic power which characterized in that, includes memory, treater and a plurality of online monitoring device who installs in inverter station current conversion busbar department, wherein:
the online monitoring device is used for acquiring the voltage, the direct current and the turn-off angle of a converter bus of the direct current transmission system inverter station in real time;
the memory is used for storing the application program and the data generated by the application program;
the processor is used for running an application program stored in the memory to realize the on-line evaluation method for the dynamic power controllability of the direct current power transmission system according to any one of claims 1 to 9.
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