Direct-current transmission end power grid short-circuit ratio value calculation method and system
阅读说明：本技术 一种直流送端电网短路比取值计算方法和系统 (Direct-current transmission end power grid short-circuit ratio value calculation method and system ) 是由 潘尔生 刘建琴 安之 王智冬 戚庆茹 齐芳 周明 李庚银 张天舒 陆明璇 宋新甫 于 2019-11-21 设计创作，主要内容包括：本发明涉及一种直流送端电网短路比取值计算方法和系统,其包括以下步骤：根据直流实际运行要求确定直流送端电网的最大传输功率；根据所述最大传输功率以及预先确定的直流送端电网短路比与最大传输功率的关系,得到直流送端电网的最小短路比；其中,所述直流送端电网短路比与最大传输功率的关系为根据预先确定的直流送端电网整流站定电流控制运行特性以及直流送端电网电网的短路比的计算公式计算得到。本发明基于直流最大传输功率确定送端短路比的最小取值,解决了直流送端电网与受端电网控制方式不同,导致电网短路比取值不同的问题,可以广泛应用于直流送端电网短路比计算领域。(The invention relates to a method and a system for calculating a short-circuit ratio value of a direct-current transmission end power grid, which comprise the following steps: determining the maximum transmission power of a direct current transmitting end power grid according to the actual direct current operation requirement; obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power; the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power is calculated according to a predetermined constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and a calculation formula of the short-circuit ratio of the direct-current transmission end power grid. The method and the device determine the minimum value of the sending-end short-circuit ratio based on the DC maximum transmission power, solve the problem that the control modes of a DC sending-end power grid and a receiving-end power grid are different, so that the values of the power grid short-circuit ratio are different, and can be widely applied to the field of calculation of the DC sending-end power grid short-circuit ratio.)
1. A direct current sending end power grid short circuit ratio value calculation method is characterized by comprising the following steps:
determining the maximum transmission power of a direct current transmitting end power grid according to the actual direct current operation requirement;
obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power;
the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power is calculated according to a predetermined constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and a calculation formula of the short-circuit ratio of the direct-current transmission end power grid.
2. The method for calculating the short-circuit ratio of the direct-current transmission-end power grid as claimed in claim 1, wherein: the short circuit ratio of the direct current sending end power grid comprises single direct current sendingAnd multiple direct current output working conditions, wherein the short circuit ratio I of the direct current transmission end power grid of single direct current outputSCRThe calculation formula of (2) is as follows:
in the formula, SCIndicating short-circuit capacity, P, of AC bus of converter stationdcNRepresents the rated power of direct current;
short-circuit ratio ME of multi-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, MIIFmnFor multiple feed-in of interacting factors, SnFor short-circuit capacity, Q, of AC buses of converter stationstnFor capacity of reactive compensation at the converter station, PdnN is the rated value of the dc transmission power, and is the number of dc transmissions.
3. The method for calculating the short-circuit ratio of the direct-current transmission-end power grid as claimed in claim 1, wherein: the method for determining the constant current control operation characteristic of the direct current transmission end power grid rectifying station comprises the following steps:
firstly, establishing a direct current sending end power grid model with single direct current sending and multiple direct current sending according to a single feed-in alternating current-direct current system model;
secondly, determining a constant current control operation characteristic expression of the rectifier station based on the established single-direct-current-output and multi-direct-current-output power grid models:
Pd＝CU2(cos2α-cos(2α+2μ))，
Qd＝CU2(2μ+sin2α-sin(2α+2μ))，
Id＝KU(cosα-cos(α+μ))，
Qc＝BcU2，
Pd-Pac＝0，
Qd-Qac-Qc＝0，
in the formula, PdAnd QdThe active power and the reactive power of the alternating current side of the direct current converter station are represented; i isdRepresents a direct current; u shapedRepresents a direct voltage; pacAnd QacRepresenting ac active and reactive power; u and delta respectively represent the amplitude and the phase angle of the alternating current bus voltage at the sending end; b iscThe equivalent susceptance of the alternating current filter and the reactive compensation capacitor is represented; qcRepresenting a reactive compensation capacity; z and theta represent the equivalent impedance magnitude and phase of the alternating current system; e represents the amplitude of the equivalent electromotive force of the alternating current system; k and C are two constants related to the rectifier side converter transformer parameter and the direct current system reference value respectively; u shapeiRepresenting the voltage of a current converting bus at the receiving end, gamma representing the extinction angle of the inverter station at the receiving end, α representing a trigger delay angle, mu representing a phase conversion angle and XdIs the impedance of the direct current transmission line.
4. The method for calculating the short-circuit ratio of the direct-current transmission-end power grid as claimed in claim 1, wherein: the method for calculating the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power according to the predetermined calculation formula of the constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and the short-circuit ratio of the direct-current transmission end power grid comprises the following steps:
according to the rectificationThe station constant current controls the operation characteristic, and the active power P of the AC side of the DC transmitting end power grid converter station with single DC output is made under different transmitting end short circuit ratiosdFollowing DC current IdA profile of change;
making a commutation angle mu following the direct current I under different sending end short-circuit ratiosdA profile of change;
according to the short-circuit ratio of different sending ends, the active power P of the alternating current side of the direct current sending end power grid converter station is sent out by single direct currentdFollowing DC current IdCurve of variation and commutation angle mu with DC current IdFitting a relation between the short-circuit ratio of the single-DC-output DC transmitting end power grid and the maximum transmission power by using a variable curve;
calculating the maximum transmission power of each single direct current in the direct current sending end power grid with multiple direct currents sent out according to the relational expression of the short-circuit ratio and the maximum transmission power;
calculating the maximum transmission power of the multi-DC-sent DC sending end power grid according to the maximum transmission power of each single DC in the multi-DC-sent sending end power grid;
changing the short-circuit ratio of the multi-DC-output DC transmitting end power grid, and making the active power P on the AC side of the multi-DC-output transmitting end power grid converter station under different multi-DC-output short-circuit ratiosdFollowing DC current IdA profile of change;
according to active power P on the AC side of the transmitting-end power grid converter station with multiple DC outputs under different multiple DC output short circuit ratiosdFollowing DC current IdFitting the maximum transmission power Z of the multi-DC-output DC transmission end power grid by the changed curvemaxAnd short circuit ratio.
5. The method for calculating the short-circuit ratio of the direct-current transmission-end power grid as claimed in claim 4, wherein: the relation between the single-direct-current-output direct-current sending end power grid short-circuit ratio and the maximum transmission power is as follows:
Pdm1＝-0.0049ISCR 2+0.0653ISCR+0.9812，
in the formula, Pdm1Indicating DC power transmissionLimit of (1), ISCRIs the short circuit ratio of the sending end system.
6. The method for calculating the short-circuit ratio of the direct-current transmission-end power grid as claimed in claim 4, wherein: when the maximum transmission power of the direct current sending end power grids sent by the multiple direct currents is calculated according to the maximum transmission power of each direct current in the sending end power grids sent by the multiple direct currents, the adopted objective function is as follows:
in the formula, ZmaxRepresenting the maximum transmission power of a plurality of direct currents, N representing the number of direct current transmissions, PiThe power transmission limit of the ith direct current;
the constraint condition is that when the maximum transmission power is reached, each alternating current power flow channel is not out of limit.
7. The method for calculating the short-circuit ratio of the direct-current transmission-end power grid as claimed in claim 4, wherein: maximum transmission power Z of multi-DC-output DC transmitting end power gridmaxAnd the short circuit ratio is as follows:
in the formula, MESCRiThe transmission short-circuit ratio for each direct current.
8. A direct current send end electric wire netting short circuit ratio value calculation system which characterized in that: it includes:
the maximum transmission power determining module is used for determining the maximum transmission power of the direct current transmitting end power grid according to the actual direct current operation requirement;
the minimum short-circuit ratio determining module is used for obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power; the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power is calculated according to a predetermined constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and a calculation formula of the short-circuit ratio of the direct-current transmission end power grid.
9. The system for calculating the short-circuit ratio of the direct-current transmission-side power grid according to claim 8, wherein: the short-circuit ratio calculation formula of the direct-current sending end power grid determined by the minimum short-circuit ratio determination module comprises two working conditions of single direct-current sending and multiple direct-current sending, wherein the short-circuit ratio I of the direct-current sending end power grid with single direct-current sendingSCRThe calculation formula of (2) is as follows:
in the formula, SCIndicating short-circuit capacity, P, of AC bus of converter stationdcNRepresents the rated power of direct current;
short-circuit ratio ME of multi-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, MIIFmnFor multiple feed-in of interacting factors, SnFor short-circuit capacity, Q, of AC buses of converter stationstnFor capacity of reactive compensation at the converter station, PdnN is the rated value of the dc transmission power, and is the number of dc transmissions.
10. The system for calculating the short-circuit ratio of the direct-current transmission-side power grid according to claim 8, wherein: the minimum short circuit ratio determination module includes:
the minimum short-circuit ratio calculation module is used for obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power;
the short-circuit ratio and direct-current transmission limit determining module is used for calculating the relation between the direct-current transmission end power grid short-circuit ratio and the maximum transmission power according to the predetermined constant current control operation characteristics of the direct-current transmission end power grid rectifying station and the calculation formula of the short-circuit ratio of the direct-current transmission end power grid;
the short circuit ratio and direct current transmission limit determining module comprises:
the active power change curve drawing module is used for drawing active power P on the alternating current side of the direct current transmission end power grid direct current converter station under different transmission end short circuit ratios according to the constant current control operation characteristics of the rectifier stationdFollowing DC current IdA profile of change;
a module for drawing the change curve of phase change angle [ mu ] with DC current I under different sending end short circuit ratiosdA profile of change;
the single direct current short-circuit ratio and maximum direct current transmission power relation fitting module is used for fitting a relation between the short-circuit ratio of the single direct current sending-end power grid and the maximum transmission power;
the single direct current maximum direct current transmission power calculation module is used for calculating the maximum transmission power of each single direct current in the direct current sending end power grid with multiple direct current sending-out according to the determined short circuit ratio and the maximum transmission power relation;
the transmission end power grid maximum direct current transmission power calculation module is used for calculating the maximum transmission power of the multiple direct current-sent direct current transmission end power grids according to the maximum transmission power of each single direct current in the multiple direct current-sent transmission end power grids;
an active power change curve drawing module for drawing active power P on the AC side of the DC transmitting end power grid converter station with multiple DC outputs under the condition of different multiple-output short circuit ratiosdFollowing DC current IdA profile of change;
a fitting module for relation between the multiple direct current short-circuit ratio and the maximum direct current transmission power, which is used for transmitting active power P at the alternating current side of the power grid converter station of the direct current transmitting end according to the multiple direct currentsdFollowing DC current IdFitting the maximum transmission power Z of the multi-DC-output DC transmission end power grid by the changed curvemaxAnd a DC short circuit ratio.
Technical Field
The invention belongs to the field of power systems, mainly aims at evaluating the safety quality of the power system, and particularly relates to a method and a system for calculating a short-circuit ratio of a direct-current transmission end power grid.
Background
With the gradual shift of the gravity center of future energy development in China to the west and the north, long-distance and high-capacity extra/ultrahigh voltage direct current transmission plays an increasingly important role in the cross-regional power internet in China. Most of energy bases for subsequent planning and development in China are located in geographical remote areas such as the west, the north and the like, the alternating current power grid is relatively weak, and the characteristics of multi-loop direct current output, high new energy occupation ratio and the like are faced, so that the power grid has complex operation characteristics and the characteristics of a direct current weak transmission end power grid with low power grid reliability.
At present, the index of short-circuit ratio, which can represent the quality of the power grid structure of the AC/DC parallel system, is obtained through research in China. CIGRE (international large grid conference) takes the ratio of the short-circuit capacity of the ac system to the rated dc power as the short-circuit ratio. And the traditional method for determining the short-circuit ratio of the receiving-end power grid is derived by adopting a mathematical formula, and curves of the relation between the direct-current power and the direct-current power under different short-circuit ratios are made, so that the short-circuit ratio is more than 3, namely a strong power grid, 2 to 3 are weak systems, and less than 2 is an extremely weak system.
The short-circuit ratio can be used for reflecting the strength of an alternating current system relative to a direct current system and the voltage support condition at a converter bus, but 3 problems still exist: the existing short-circuit ratio value determination method is only based on a receiving-end power grid, a constant current control is adopted on a direct-current transmission general rectifying side, and a constant voltage control is adopted on an inverting side, so that the short-circuit ratio value of a transmitting-end power grid is greatly different from that of the receiving-end power grid; secondly, the existing determination method for the short circuit ratio value is only for the single feed condition, and the multi-feed short circuit ratio value can not be determined by the existing method; and thirdly, the short-circuit ratio index only aims at the AC/DC power transmission channel, and the influence of other sections of the AC system on the value is not considered.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a method and a system for calculating a short-circuit ratio of a dc transmitting-side power grid, which fully consider the problem of different values of the short-circuit ratio of the power grid due to different control modes of the dc transmitting-side power grid and the receiving-side power grid, and also cover two situations of single dc sending and multiple dc sending, so that the short-circuit ratio value calculation result is more accurate.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a direct current transmission end power grid short circuit ratio value calculation method, which comprises the following steps:
determining the maximum transmission power of a direct current transmitting end power grid according to the actual direct current operation requirement;
obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power;
the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power is calculated according to a predetermined constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and a calculation formula of the short-circuit ratio of the direct-current transmission end power grid.
Furthermore, the short-circuit ratio of the direct-current sending end power grid comprises two working conditions of single direct-current sending and multiple direct-current sending, wherein the short-circuit ratio I of the direct-current sending end power grid with single direct-current sendingSCRThe calculation formula of (2) is as follows:
in the formula, SCIndicating short-circuit capacity, P, of AC bus of converter stationdcNRepresents the rated power of direct current;
short-circuit ratio ME of multi-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, MIIFmnFor multiple feed-in of interacting factors, SnFor short-circuit capacity, Q, of AC buses of converter stationstnFor capacity of reactive compensation at the converter station, PdnN is the rated value of the dc transmission power, and is the number of dc transmissions.
Further, the method for determining the constant current control operation characteristic of the direct current transmission end power grid rectifying station comprises the following steps:
firstly, establishing a direct current sending end power grid model with single direct current sending and multiple direct current sending according to a single feed-in alternating current-direct current system model;
secondly, determining a constant current control operation characteristic expression of the rectifier station based on the established single-direct-current-output and multi-direct-current-output power grid models:
Pd＝CU2(cos2α-cos(2α+2μ))，
Qd＝CU2(2μ+sin2α-sin(2α+2μ))，
Id＝KU(cosα-cos(α+μ))，
Qc＝BcU2，
Pd-Pac＝0，
Qd-Qac-Qc＝0，
in the formula, PdAnd QdThe active power and the reactive power of the alternating current side of the direct current converter station are represented; i isdRepresents a direct current; u shapedRepresents a direct voltage; pacAnd QacRepresenting ac active and reactive power; u and delta respectively represent the amplitude and the phase angle of the alternating current bus voltage at the sending end; b iscThe equivalent susceptance of the alternating current filter and the reactive compensation capacitor is represented; qcRepresenting a reactive compensation capacity; z and theta represent the equivalent impedance magnitude and phase of the alternating current system; e represents the amplitude of the equivalent electromotive force of the alternating current system; k and C are two constants related to the rectifier side converter transformer parameter and the direct current system reference value respectively; u shapeiRepresenting the voltage of a current converting bus at the receiving end, gamma representing the extinction angle of the inverter station at the receiving end, α representing a trigger delay angle, mu representing a phase conversion angle and XdIs the impedance of the direct current transmission line.
Further, according to a predetermined calculation formula of the constant current control operation characteristic of the direct current sending end power grid rectifying station and the short-circuit ratio of the direct current sending end power grid, the method for calculating the relation between the short-circuit ratio of the direct current sending end power grid and the maximum transmission power comprises the following steps:
according to the constant current control operation characteristic of the rectifier station, the active power P of the AC side of the DC transmitting end power grid converter station at single DC output under different transmitting end short circuit ratios is madedFollowing DC current IdA profile of change;
making a commutation angle mu following the direct current I under different sending end short-circuit ratiosdA profile of change;
according to the short-circuit ratio of different sending ends, the active power P of the alternating current side of the direct current sending end power grid converter station is sent out by single direct currentdFollowing DC current IdCurve of variation and commutation angle mu with DC current IdFitting a relation between the short-circuit ratio of the single-DC-output DC transmitting end power grid and the maximum transmission power by using a variable curve;
calculating the maximum transmission power of each single direct current in the direct current sending end power grid with multiple direct currents sent out according to the relational expression of the short-circuit ratio and the maximum transmission power;
calculating the maximum transmission power of the multi-DC-sent DC sending end power grid according to the maximum transmission power of each single DC in the multi-DC-sent sending end power grid;
changing the short-circuit ratio of the multi-DC-output DC transmitting end power grid, and making the active power P on the AC side of the multi-DC-output transmitting end power grid converter station under different multi-DC-output short-circuit ratiosdFollowing DC current IdA profile of change;
according to active power P on the AC side of the transmitting-end power grid converter station with multiple DC outputs under different multiple DC output short circuit ratiosdFollowing DC current IdFitting the maximum transmission power Z of the multi-DC-output DC transmission end power grid by the changed curvemaxAnd short circuit ratio.
Further, the relationship between the single-dc-output dc-sending-end grid short-circuit ratio and the maximum transmission power is as follows:
Pdm1＝-0.0049ISCR 2+0.0653ISCR+0.9812，
in the formula, Pdm1Denotes the limit of the DC power transmission, ISCRIs the short circuit ratio of the sending end system.
Further, in the step 2.5), when the maximum transmission power of the multiple dc-sent dc-sending end power grids is calculated according to the maximum transmission power of each dc in the multiple dc-sent sending end power grids, an objective function is adopted as:
in the formula, ZmaxRepresenting the maximum transmission power of a plurality of direct currents, N representing the number of direct current transmissions, PiThe power transmission limit of the ith direct current;
the constraint condition is that when the maximum transmission power is reached, each alternating current power flow channel is not out of limit.
Further, the maximum transmission power Z of the multi-DC-output DC transmitting end power gridmaxAnd the short circuit ratio is as follows:
in the formula, MESCRiThe transmission short-circuit ratio for each direct current.
The second aspect of the present invention provides a dc transmission side power grid short-circuit ratio value calculation system, which includes:
the maximum transmission power determining module is used for determining the maximum transmission power of the direct current transmitting end power grid according to the actual direct current operation requirement;
the minimum short-circuit ratio determining module is used for obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power; the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power is calculated according to a predetermined constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and a calculation formula of the short-circuit ratio of the direct-current transmission end power grid. Further, the short-circuit ratio calculation formula of the direct-current sending end power grid determined by the minimum short-circuit ratio determination module comprises two working conditions of single direct-current sending and multiple direct-current sending, wherein the short-circuit ratio I of the direct-current sending end power grid sent by the single direct current sendingSCRThe calculation formula of (2) is as follows:
in the formula, SCIndicating short-circuit capacity, P, of AC bus of converter stationdcNRepresents the rated power of direct current;
short-circuit ratio ME of multi-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, MIIFmnFor multiple feed-in of interacting factors, SnFor short-circuit capacity, Q, of AC buses of converter stationstnFor capacity of reactive compensation at the converter station, PdnN is the rated value of the dc transmission power, and is the number of dc transmissions.
Further, the minimum short circuit ratio determination module includes:
the minimum short-circuit ratio calculation module is used for obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power;
the short-circuit ratio and direct-current transmission limit determining module is used for calculating the relation between the direct-current transmission end power grid short-circuit ratio and the maximum transmission power according to the predetermined constant current control operation characteristics of the direct-current transmission end power grid rectifying station and the calculation formula of the short-circuit ratio of the direct-current transmission end power grid;
the short circuit ratio and direct current transmission limit determining module comprises:
the active power change curve drawing module is used for drawing active power P on the alternating current side of the direct current transmission end power grid direct current converter station under different transmission end short circuit ratios according to the constant current control operation characteristics of the rectifier stationdFollowing DC current IdA profile of change;
a module for drawing the change curve of phase change angle [ mu ] with DC current I under different sending end short circuit ratiosdA profile of change;
the single direct current short-circuit ratio and maximum direct current transmission power relation fitting module is used for fitting a relation between the short-circuit ratio of the single direct current sending-end power grid and the maximum transmission power;
the single direct current maximum direct current transmission power calculation module is used for calculating the maximum transmission power of each single direct current in the direct current sending end power grid with multiple direct current sending-out according to the determined short circuit ratio and the maximum transmission power relation;
the transmission end power grid maximum direct current transmission power calculation module is used for calculating the maximum transmission power of the multiple direct current-sent direct current transmission end power grids according to the maximum transmission power of each single direct current in the multiple direct current-sent transmission end power grids;
an active power change curve drawing module for drawing active power P on the AC side of the DC transmitting end power grid converter station with multiple DC outputs under the condition of different multiple-output short circuit ratiosdFollowing DC current IdA profile of change;
a fitting module for relation between the multiple direct current short-circuit ratio and the maximum direct current transmission power, which is used for transmitting active power P at the alternating current side of the power grid converter station of the direct current transmitting end according to the multiple direct currentsdFollowing DC current IdFitting the maximum transmission power Z of the multi-DC-output DC transmission end power grid by the changed curvemaxAnd a DC short circuit ratio.
Due to the adoption of the technical scheme, the invention has the following advantages: the invention has the beneficial effects that: 1) the invention determines the minimum value of the sending end short-circuit ratio based on the DC maximum transmission power, and solves the problem that the values of the power grid short-circuit ratio are different due to different control modes of a DC sending end power grid and a DC receiving end power grid. 2) The method and the device determine the minimum value of the short-circuit ratio of the sending end based on the maximum direct-current transmission power, can evaluate a specific direct-current sending end power grid, and guide the power grid planning. Therefore, the method can be widely applied to the field of evaluation of the safety quality of the power system.
Drawings
FIG. 1 is a flow chart of a short-circuit ratio calculation method for a direct-current transmission end power grid according to the present invention;
FIG. 2 is a single DC-out send-side grid model of the present invention;
fig. 3 is a dc-side grid model with multiple dc outputs according to the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and examples.
As shown in fig. 1, the method for calculating the short-circuit ratio of the dc transmission side power grid provided by the present invention includes the following steps:
1) and establishing a direct current transmission end power grid model, and determining a rectifier station operation characteristic expression according to the direct current transmission end power grid model. Specifically, the method comprises the following steps:
1.1) building a direct current sending end power grid model with single direct current sending and multiple direct current sending by using a traditional single-feed alternating current-direct current system model for reference.
As shown in fig. 2 and 3, respectively, for the established single dc output andthe direct current sending end power grid model with multiple direct current sending is taken as an example of a direct current sending end power grid model with single direct current sending, wherein E ∠ 0 DEG is equivalent potential of an alternating current system, | Z | ∠ theta is equivalent impedance of the alternating current system, and P is equivalent impedance of the alternating current systemacAnd QacActive power and reactive power of an alternating current system are respectively; pdAnd QdRespectively the active power and the reactive power of the network side of the direct current converter transformer; xTFor equivalent reactance of converter transformer, U ∠ delta for AC bus voltage of converter station, BcThe equivalent admittance of the alternating current filter and the reactive compensation capacitor; u shapedAnd IdRespectively direct voltage and direct current; and tau is the transformation ratio of the converter transformer.
1.2) establishing a constant current control operation characteristic expression of the rectifier station based on the established single-direct-current-output and multi-direct-current-output power grid models.
The rectification side adopts constant current control, and the inverter side converter bus voltage can be ensured to be a rated value by assuming that an alternating current system connected with the inverter side is strong enough, and the established rectifier station constant current control operation characteristic expression is as follows:
Pd＝CU2(cos2α-cos(2α+2μ)) (1)
Qd＝CU2(2μ+sin2α-sin(2α+2μ)) (2)
Id＝KU(cosα-cos(α+μ)) (3)
Qc＝BcU2(7)
Pd-Pac＝0 (8)
Qd-Qac-Qc＝0 (9)
in the formula, PdAnd QdThe active power and the reactive power of the alternating current side of the direct current converter station are represented; i isdRepresents a direct current; u shapedRepresents a direct voltage; pacAnd QacRepresenting ac active and reactive power; u and delta respectively represent the amplitude and the phase angle of the alternating current bus voltage at the sending end; b iscThe equivalent susceptance of the alternating current filter and the reactive compensation capacitor is represented; qcRepresenting a reactive compensation capacity; z and theta represent the equivalent impedance magnitude and phase of the alternating current system; e represents the amplitude of the equivalent electromotive force of the alternating current system; k and C are two constants related to the rectifier side converter transformer parameter and the direct current system reference value respectively; u shapeiRepresenting the voltage of a current converting bus at the receiving end, gamma representing the extinction angle of the inverter station at the receiving end, α representing a trigger delay angle, mu representing a phase conversion angle and XdIs the impedance of the direct current transmission line.
2) And determining a mathematical expression of the short-circuit ratio value of the direct-current transmitting-end power grid according to the existing receiving-end power grid short-circuit ratio value calculation formula.
The short circuit ratio of the direct current sending end power grid comprises two working conditions of single direct current sending and multiple direct current sending, and can be obtained according to a receiving end power grid short circuit ratio value calculation formula:
short-circuit ratio I of single-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, SCIndicating short-circuit capacity, P, of AC bus of converter stationdcNIndicating the dc rated power.
Short-circuit ratio ME of multi-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, MIIFmnThe multi-feed interaction factor is mainly used for measuring the voltage interaction strength among any 2 converter stations in the multi-feed system, and can be quantitatively described as the influence of voltage drop of the converter bus on other converter buses. SnFor short-circuit capacity, Q, of AC buses of converter stationstnFor capacity of reactive compensation at the converter station, PdnN is the rated value of the dc transmission power, and is the number of dc transmissions.
3) And calculating to obtain the relation between the short-circuit ratio and the maximum transmission power according to the constant current control operation characteristic of the rectifier station determined in the step 1) and the calculation formula of the short-circuit ratio of the direct-current transmission end power grid determined in the step 2).
Specifically, the method comprises the following steps:
3.1) making the active power P of the AC side of the DC transmitting end power grid converter station with single DC transmission under different transmitting end short circuit ratio values according to the operating characteristics of the rectifier station in the step 1)dFollowing DC current IdThe curve of the change. According to the invention, the curve is analyzed, and the conclusion is drawn that for the power grid at the sending end, the rated operation point of the rectifying side is always at the rising edge of the power curve.
3.2) making the phase change angle mu following the direct current I under different sending end short circuit ratiosdThe curve of the change. By analyzing the curve, the invention finds that the commutation angle mu is always in constant current control when reaching 30 degrees, and the operating point when reaching 30 degrees is at the right side of the rated operating point. That is, in the constant current control mode, the limit of the dc power transmission cannot be reached until the control mode is switched once (the constant current control is converted into the constant minimum firing angle control).
3.3) fitting the relation between the short-circuit ratio of the direct current sending end power grid and the maximum transmission power which are sent out by single direct current according to the change curves obtained in the step 3.1) and the step 3.2) as follows:
Pdm1＝-0.0049ISCR 2+0.0653ISCR+0.9812 (13)
in the formula, Pdm1Denotes the limit of the DC power transmission, ISCRIs the short circuit ratio of the sending end system.
3.4) calculating the maximum transmission power of each single direct current in the direct current sending end power grid with multiple direct current sending according to the relation between the short-circuit ratio and the maximum transmission power determined in the step 3.3).
And 3.5) calculating the maximum transmission power of the multi-DC-sent DC sending end power grid according to the maximum transmission power of each single DC in the multi-DC-sent sending end power grid.
Under the condition of considering the interaction factors of multiple direct current outputs and the constraint condition that an alternating current power flow channel is not out of limit, the maximum transmission power P of each direct currentiThe objective function is
In the formula, ZmaxRepresenting the maximum transmission power of the multi-DC-output DC transmitting end power grid, N representing the number of DC transmissions, PiThe power transmission limit of the ith direct current.
3.6) changing the short-circuit ratio of the DC transmitting end power grid with multiple DC outputs, and making the active power P on the AC side of the DC transmitting end power grid converter station with multiple DC outputs under the condition of different multiple-output short-circuit ratiosdFollowing DC current IdThe curve of the change.
3.7) maximum transmission power Z by multiple outgoing direct currentsmaxAnd the change relation of the multi-sending short circuit ratio is fitted to obtain ZmaxAnd MESCRThe relationship of (1):
in the formula, MESCRiThe transmission short-circuit ratio for each direct current.
4) And (3) obtaining the minimum short-circuit ratio of the direct current sending end power grid according to the direct current actual operation requirement (usually, the direct current is limited to have 10% power boost capacity) and the relationship between the short-circuit ratio obtained in the step 3) and the limit transmission power.
The invention also provides a direct current sending end power grid short circuit ratio value calculation system, which comprises:
the maximum transmission power determining module is used for determining the maximum transmission power of the direct current transmitting end power grid according to the actual direct current operation requirement;
the minimum short-circuit ratio determining module is used for obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power; the relation between the short-circuit ratio of the direct-current transmission end power grid and the maximum transmission power is calculated according to a predetermined constant-current control operation characteristic of the direct-current transmission end power grid rectifying station and a calculation formula of the short-circuit ratio of the direct-current transmission end power grid.
Further, the short-circuit ratio calculation formula of the direct-current sending end power grid determined by the minimum short-circuit ratio determination module comprises two working conditions of single direct-current sending and multiple direct-current sending, wherein the short-circuit ratio I of the direct-current sending end power grid sent by the single direct current sendingSCRThe calculation formula of (2) is as follows:
in the formula, SCIndicating short-circuit capacity, P, of AC bus of converter stationdcNRepresents the rated power of direct current;
short-circuit ratio ME of multi-DC-output DC sending end power gridSCRThe calculation formula of (2) is as follows:
in the formula, MIIFmnFor multiple feed-in of interacting factors, SnFor short-circuit capacity, Q, of AC buses of converter stationstnFor capacity of reactive compensation at the converter station, PdnN is the rated value of the dc transmission power, and is the number of dc transmissions.
Further, the minimum short circuit ratio determination module includes: the minimum short-circuit ratio calculation module is used for obtaining the minimum short-circuit ratio of the direct-current transmission end power grid according to the maximum transmission power and the relationship between the predetermined direct-current transmission end power grid short-circuit ratio and the maximum transmission power; and the short-circuit ratio and direct-current transmission limit determining module is used for calculating the relation between the direct-current transmission end power grid short-circuit ratio and the maximum transmission power according to the predetermined constant current control operation characteristics of the direct-current transmission end power grid rectifying station and the calculation formula of the short-circuit ratio of the direct-current transmission end power grid.
Further, the short circuit ratio and dc transmission limit determining module includes: the active power change curve drawing module is used for drawing active power P on the alternating current side of the direct current transmission end power grid direct current converter station under different transmission end short circuit ratios according to the constant current control operation characteristics of the rectifier stationdFollowing DC current IdA profile of change; a module for drawing the change curve of phase change angle [ mu ] with DC current I under different sending end short circuit ratiosdA profile of change; the single direct current short-circuit ratio and maximum direct current transmission power relation fitting module is used for fitting a relation between the short-circuit ratio of the single direct current sending-end power grid and the maximum transmission power; the single direct current maximum direct current transmission power calculation module is used for calculating the maximum transmission power of each single direct current in the direct current sending end power grid with multiple direct current sending-out according to the determined short circuit ratio and the maximum transmission power relation; the transmission end power grid maximum direct current transmission power calculation module is used for calculating the maximum transmission power of the multiple direct current-sent direct current transmission end power grids according to the maximum transmission power of each single direct current in the multiple direct current-sent transmission end power grids; an active power change curve drawing module for drawing active power P on the AC side of the DC transmitting end power grid converter station with multiple DC outputs under the condition of different multiple-output short circuit ratiosdFollowing DC current IdA profile of change; a fitting module for relation between the multiple direct current short-circuit ratio and the maximum direct current transmission power, which is used for transmitting active power P at the alternating current side of the power grid converter station of the direct current transmitting end according to the multiple direct currentsdFollowing DC current IdFitting the maximum transmission power Z of the multi-DC-output DC transmission end power grid by the changed curvemaxAnd a DC short circuit ratio.
The following describes the embodiments in detail with reference to an example.
1) As shown in fig. 2, a model of the interaction of the ac-dc system is constructed, wherein the ac system is represented by equivalent impedance obtained by thevenin's theorem of equivalence, and the effect of changing the strength of the transmitting end system can be achieved without changing the phase angle by changing the mode of the impedance;
2) parameter values in the model are determined. For convenience of calculation, the following calculations all use per unit values. By using the conventional converter transformer value ST＝1.15PdN，XCWhen τ is equal to 1, 0.18, it can be calculated as:
and taking another equivalent impedance angle theta of the alternating current system as 90 degrees, operating the rectifying station in a rated state, taking the rated trigger angle of the rectifying station as 15 degrees, switching the control mode when the minimum trigger angle reaches 5 degrees, and converting the constant current control into the constant minimum trigger angle control.
For more convenient change of the short-circuit ratio of the sending-end system, the formula of the short-circuit ratio can be changed into:
when the voltage and the power both take per unit values of 1, the formula of the short-circuit ratio is as follows:
3) according to the formula (1) and the formula (2), the direct current power transmission limit at different short circuit ratios is calculated.
And calculating to obtain the following data in the case of single-stream output: when the short circuit ratio is 0.7, the maximum transmission power is 1; in the case of multi-dc transmission, the maximum transmission power can reach 1.194 when the short-circuit ratio is 5.
4) In order to ensure that the emergency power boosting capacity is 1.1 times in the actual operation of direct current, namely the maximum transmission power of the direct current is required to be at least 1.1 times of a rated value, through analysis, the short-circuit ratio of a sending end system which sends the direct current out can not be less than 1.6.
Similarly, the value of the system short circuit ratio of the multiple direct current outputs can also be calculated. It should be noted that the multiple-output dc short-circuit ratio needs to consider the interaction between multiple dc, i.e. the interaction factor, and for the convenience of calculation, the interaction factor can be expressed by the ratio of the equivalent node impedances.
It is worth mentioning that the short circuit ratio value calculation method is not limited to a simple system, and can be expanded to any actual power grid. Therefore, the above steps are only used for illustrating the technical method of the present invention, and not for limiting the present invention, and any modifications or partial replacements without departing from the spirit and scope of the present invention shall be covered by the claims of the present invention.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.