CN101969206A - Evaluation method for judging influence of grid structure on alternating current/direct current (AC/DC) system - Google Patents

Abstract

The invention relates to the field of alternating current/direct current (AC/DC) power system planning and running control, in particular to an evaluation method for judging the influence of changes of an AC grid structure on a DC system short circuit ratio and effective short circuit ratio. On the basis of definition of the AC/DC system short circuit ratio and the effective short circuit ratio, a calculation formula of an AC/DC parallel/series connection short circuit ratio is acquired, an indicator concept of a parallel AC channel for the contribution rate of the short circuit ratio and an effective short circuit ratio and a security domain thereof are provided, a principle computing method and a practical computing method are provided, and the indicator and the method are further popularized to the general AC/DC system and a multi-infeed DC system. In the invention, a theoretical system for evaluating the influence of changes of the AC grid structure on the DC system short circuit ratio and the effective short circuit ratio is established, can be used for controlling AC/DC power system planning and running, and overcomes the defect of lack of guidance target in the conventional method.

Description

A kind of appraisal procedure of judging grid structure to the ac and dc systems influence

Technical field

The present invention relates to AC and DC power system planning and operation control field, be specifically related to a kind of appraisal procedure of judging the variation of interchange rack to direct current system short circuit ratio and effective short circuit ratio influence degree.

Background technology

In ac and dc systems is analyzed, the deciding factor of restriction direct current system ability to transmit electricity be connect the intensity of AC system, in theory research and engineering are used, adopt usually short circuit ratio and effectively the notion of short circuit ratio assess relative strong or weak relation between AC system and the direct current system.Along with direct current inserts the complicated of the variation of electrical network form and electric network composition, the possibility that the relative strong or weak relation of ac and dc systems that exists active reasons such as passive reason such as barrier for some reason or maintenance to cause the grid structure variation to cause changes significantly, particularly in alternating current-direct current parallel/hybrid system, the switching of parallel connection alternating current circuit directly influences the grid structure and the alternating current-direct current strong or weak relation changes in contrast of whole system, therefore need introduce a kind of appraisal procedure or index and judge that grid structure changes and the electric component throwing is moved back short circuit ratio and effective short circuit ratio influence degree in planning and designing and operational mode arrangement.

The present invention propose a kind of be used to assess exchange rack and change index and method direct current system short circuit ratio and effectively short circuit ratio influence, the theoretical foundation of this index and method and derivation gained formula are based on following background technology:

According to direct current system short circuit ratio and the effectively definition of short circuit ratio, be the voltage rating U of current conversion station ac bus if get the reference voltage U of AC system _N, reference power is got specified direct current power P _DNThereby short circuit ratio and effective short circuit ratio can be expressed as:

$\left\{\begin{array}{c}\mathrm{SCR}=\frac{S_{\mathrm{SC}}}{P_{\mathrm{dN}}}=\frac{{U_N}^2}{P_{\mathrm{dN}}}\×\frac{1}{\left|Z\right|}=\frac{1}{\left|Z\right|/Z_B}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}\\ \mathrm{ESCR}=\frac{S_{\mathrm{SC}}-Q_C}{P_{\mathrm{dN}}}=\frac{{U_N}^2}{P_{\mathrm{dN}}}\×(\frac{1}{\left|Z\right|}-B)=\frac{1}{\left|Z\right|/Z_B}-\frac{B}{1/Z_B}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}-B_{\mathrm{pu}}\end{array}\right.$

In the formula, S _SCBe system's change of current busbar short-circuit capacity, Q _CExert oneself for filter and the idle of capacitor reactive compensation equipment, Z is the system equivalent impedance, and B is the equivalent susceptance of filter and capacitor reactive compensation equipment, Z _BBe the impedance reference value under reference power and the reference voltage, Z _PuBe system equivalent impedance per unit value, B _PuBe filter and the equivalent susceptance per unit value of capacitor reactive compensation.

Do not consider coupled relation between the direct current system for eliminating traditional short circuit ratio in many feed-ins direct current system is used, CIGRE working group introduces and has defined the notion of many feed-ins short circuit ratio MISCR (Multi-infeed Short Circuit Ratio):

$\mathrm{MIS}{\mathrm{CR}}_i=\frac{S_{\mathrm{aci}}}{P_{\mathrm{di}}+\underset{j=i,j\≠i}{\overset{n}{\mathrm{\Σ}}}{\mathrm{MIIF}}_{\mathrm{ji}}*P_{\mathrm{dj}}}$

$=\frac{S_{\mathrm{aci}}}{P_{\mathrm{di}}+\underset{j=i,j\≠i}{\overset{n}{\mathrm{\Σ}}}\frac{{\mathrm{\ΔU}}_j}{{\mathrm{\ΔU}}_i}{P}_{\mathrm{dj}}}$

Many feed-ins ac and dc systems is carried out multiport Dai Weinan equivalence in the change of current bus bar side of each time direct current, and the port of reservation only has the DC converter bus, and system's mark is changed, and by deriving, following formula can also be expressed as form:

${\mathrm{MISCR}}_i=\frac{1}{\left|Z_{\mathrm{eqii}}\right|P_{\mathrm{di}}+\underset{j=i,j\≠i}{\overset{n}{\mathrm{\Σ}}}\left|Z_{\mathrm{eqij}}\right|P_{\mathrm{dj}}}$

In the formula, MISCR _iBe that i returns the pairing many feed-ins short circuit ratio of direct current; U _iBe that i returns the rated voltage on the change of current bus; Z _EqiiFor i in the equivalent impedance matrix returns the pairing self-impedance of change of current bus; Z _EqijFor returning change of current bus and j, i in the equivalent impedance matrix returns mutual impedance between the change of current bus; P _DiBe the rated power that i returns direct current; P _DjBe the rated power that j returns direct current.

Summary of the invention

The objective of the invention is to, provide a cover to reflect and exchange evaluation index and the method for rack variation direct current system short circuit ratio and effective short circuit ratio influence degree, the definition of this evaluation index is direct, the concentrated expression ac and dc systems influences each other substantive characteristics, is applicable to instruct design of alternating current-direct current Electric Power Network Planning and operational mode arrangement.

(1) short circuit ratio of alternating current-direct current parallel/hybrid system and effectively short circuit ratio computational methods

According to direct current system short circuit ratio (SCR) and the effectively definition of short circuit ratio (ESCR), be the voltage rating U of current conversion station ac bus if get the reference voltage U of AC system _N, reference power P _DNGet specified direct current power P _d, short circuit ratio and effective short circuit ratio can be expressed as:

$\left\{\begin{array}{c}\mathrm{SCR}=\frac{S_{\mathrm{SC}}}{P_{\mathrm{dN}}}=\frac{{U_N}^2}{P_{\mathrm{dN}}}\×\frac{1}{\left|Z\right|}=\frac{1}{\left|Z\right|/Z_B}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}\\ \mathrm{ESCR}=\frac{S_{\mathrm{SC}}-Q_C}{P_{\mathrm{dN}}}=\frac{{U_N}^2}{P_{\mathrm{dN}}}\×(\frac{1}{\left|Z\right|}-B)=\frac{1}{\left|Z\right|/Z_B}-\frac{B}{1/Z_B}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}-B_{\mathrm{pu}}\end{array}---\left(1\right)\right.$

In the formula, S _SCBe system's change of current busbar short-circuit capacity, Q _CExert oneself for filter and the idle of capacitor reactive compensation equipment, Z is the system equivalent impedance, and B is the equivalent susceptance of filter and capacitor reactive compensation equipment, Z _BBe the impedance reference value under reference power and the reference voltage, Z _PuBe system equivalent impedance per unit value, B _PuBe filter and the equivalent susceptance per unit value of capacitor reactive compensation.

Because the AC system send receiving end to have alternating current interconnection, so the capacity of short circuit at inversion end change of current bus place is not only relevant with the receiving-end system grid structure, also closely related with the intensity of sending and alternating current circuit in parallel, as shown in Figure 1.

$Z_I=\frac{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}---\left(2\right)$

In the formula, Z _Inverter, Z _RectiferAnd Z _ParallelBe respectively receiving-end system equivalent impedance per unit value, sending equivalent impedance per unit value, and communication channel equivalent impedance per unit value in parallel.

Simultaneous formula (1) can get the AC system short-circuit with (2):

${\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}=\frac{1}{\left|\frac{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}\right|}---\left(3\right)$

$=\left|\frac{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}\right|$

Formula (3) can further be written as following form:

${\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}=|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}|---\left(4\right)$

Can obtain the effective short circuit ratio computing formula of AC system equally is:

${\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}-B_{\mathrm{pu}}=\left|\frac{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}}\right|-B_{\mathrm{pu}}---\left(5\right)$

Formula (5) also can be expressed as:

${\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}=|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}|-B_{\mathrm{pu}}---\left(6\right)$

According to formula (4) and (6) as can be known: be connected comparatively closely if send receiving-end system to pass through communication channel in parallel, and sending end is strong system, and communication channel equivalent impedance then in parallel is to the SCR of direct current receiving end _AC-DCAnd ESCR _AC-DCThe size influence is bigger; Connect comparatively weakly if send receiving-end system to pass through communication channel in parallel, and sending end electrical network weakness is then to the SCR of direct current receiving end _AC-DCAnd ESCR _AC-DCThe size influence is less relatively.

(2) communication channel in parallel is to short circuit ratio and the effectively definition of short circuit ratio contribution rate index

For communication channel in parallel being described to short circuit ratio and effective short circuit ratio influence degree, introduce the notion of " communication channel in parallel is to short circuit ratio and effective short circuit ratio contribution rate " and assess such problem, adopt CR respectively _SCRAnd CR _ESCRDescribe.Its concrete form is as follows:

${\mathrm{CR}}_{\mathrm{SCR}}=\left|\frac{\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}}{\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}}\right|=\frac{1}{|1+\frac{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}}|}---\left(7\right)$

${\mathrm{CR}}_{\mathrm{ESCR}}=\frac{\left|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}\right|}{|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}|-B_{\mathrm{pu}}}---\left(8\right)$

$=\frac{1}{|1+\frac{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}}|-B_{\mathrm{pu}}\×|Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}|}$

In formula (7) and (8), CR _SCRScope be 0＜CR _SCR＜1; CR _ESCRScope be 0＜CR _ESCR＜1.Parallel port and sending equivalent impedance are big more, CR _SCRAnd CR _ESCRMore little, more little to direct-current short circuit ratio and effective short circuit ratio influence; Meanwhile, receiving-end system is weak more, CR _SCRAnd CR _ESCRBig more, communication channel in parallel is also big more to direct-current short circuit ratio and effective short circuit ratio influence with sending intensity.

(3) CR _SCRAnd CR _ESCRThe index practical calculation method

In practical computational analysis, adopt the computational methods of equivalent impedance comparatively loaded down with trivial details, the formula that needs usually to adopt similar conventional short circuit ratio to calculate is described, and therefore can obtain and formula (7) and (8) form of equal value:

${\mathrm{CR}}_{\mathrm{SCR}}=1-\frac{{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}^{\′}}{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}=1-\frac{\frac{{S_{\mathrm{SC}}}^{\′}}{P_d}}{\frac{S_{\mathrm{SC}}}{P_d}}=1-\frac{{S_{\mathrm{SC}}}^{\′}}{S_{\mathrm{SC}}}=\frac{S_{\mathrm{SC}}-{S_{\mathrm{SC}}}^{\′}}{S_{\mathrm{SC}}}---\left(9\right)$

${\mathrm{CR}}_{\mathrm{ESCR}}=1-\frac{{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}^{\′}}{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}=1-\frac{\frac{{S_{\mathrm{SC}}}^{\′}-Q_C}{P_d}}{\frac{S_{\mathrm{SC}}-Q_C}{P_d}}=1-\frac{{S_{\mathrm{SC}}}^{\′}-Q_C}{S_{\mathrm{SC}}-Q_C}=\frac{S_{\mathrm{SC}}-{S_{\mathrm{SC}}}^{\′}}{S_{\mathrm{SC}}-Q_C}---\left(10\right)$

In the formula, SCR _AC-DC' and ESCR _AC-DC' be respectively disconnect communication channel in parallel or give, direct current system short circuit ratio and effective short circuit ratio size under circuit or the element situation arbitrarily in the receiving end AC system, SCR _AC-DCAnd ESCR _AC-DCBe respectively short circuit ratio and effective short circuit ratio under the normal condition; S _SC' for disconnect communication channel in parallel or give, change of current bus place system short circuit capacity size under circuit or the element situation arbitrarily in the receiving end AC system, S _SCBe the change of current bus place system short circuit capacity size under the normal condition.

(4) CR _SCRAnd CR _ESCRSecurity domain

It has been generally acknowledged that the direct current system short circuit ratio less than 3 or effectively short circuit ratio less than 2, the ac and dc systems maintenance level is relatively poor, in planning and designing and operational mode arrangement, avoided, particularly when short circuit ratio less than 2 or effectively short circuit ratio less than 1.5～1.7, ac and dc systems will be difficult to operation, so ac and dc systems is to having critical short circuit ratio CSCR and critical effective short circuit ratio CESCR; In actual applications, this value does not have unified value, therefore within the specific limits as required or engine request get final product for respectively critical short circuit ratio CSCR and estimated value of critical effective short circuit ratio CESCR.Therefore, according to formula (9) and (10), can solve CR _SCRAnd CR _ESCRIndex is recommended security domain, is:

${{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}^{\&prime;}=(1-{\mathrm{CR}}_{\mathrm{SCR}})\&times;{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}<\mathrm{CSCR}---\left(11\right)$

Find the solution and to get CR _SCRIndex is recommended security domain:

$\left\{\begin{array}{c}{\mathrm{CR}}_{\mathrm{SCR}}<{\mathrm{CCR}}_{\mathrm{SCR}}\\ {\mathrm{CCR}}_{\mathrm{SCR}}=\frac{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}-\mathrm{CSCR}}{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}\end{array}\right.---\left(12\right)$

In the formula (12), CCR _SCRBe CR _SCRCritical value.

In like manner, can solve CR _ESCRIndex is recommended security domain, is:

$\left\{\begin{array}{c}{\mathrm{CR}}_{\mathrm{ESCR}}<{\mathrm{CCR}}_{\mathrm{ESCR}}\\ {\mathrm{CCR}}_{\mathrm{ESCR}}=\frac{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}-\mathrm{CESCR}}{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}\end{array}\right.---\left(13\right)$

In the formula (13), CCR _ESCRBe CR _ESCRCritical value.

Therefore, formula (12) and (13) show: work as CR _SCROr CR _ESCRWhen surpassing the represented critical value of computing formula, illustrate that promptly this AC system communication channel is excessive to the short circuit ratio influence, there is certain hidden danger in power network safety operation.

(5) CR _SCRAnd CR _ESCRIndex and security domain notion thereof are applied to general ac and dc systems

CR _SCRAnd CR _ESCRNotion only be not applicable to the AC system, this notion and method also can be applied to general ac and dc systems or many feed-ins direct current system, are used to assess any rack variation or element throwing and move back direct current system short circuit ratio and the effectively influence of short circuit ratio variation.For example change to short circuit ratio with effectively during the short circuit ratio influence degree, at first calculate short circuit ratio and effective short circuit ratio before and after the receiving end AC system bar line disconnection, adopt formula (9) and (10) can calculate CR then at the receiving-end system rack of the pure dc online of assessment _SCRAnd CR _ESCRSize; Utilize formula (12) and (13) to calculate short circuit ratio and effective short circuit ratio security domain, i.e. the critical value CCR of this ac and dc systems of description _SCRAnd CCR _ESCRCheck CR _SCRAnd CR _ESCRWhether surpass CCR _SCRAnd CCR _ESCR, if greater than critical value, then this circuit is paid attention in planning and designing and operational mode arrangement to short circuit ratio with effectively the short circuit ratio influence is excessive, if less than critical value, then this circuit to short circuit ratio and effectively short circuit ratio influence relative less.

For many feed-ins direct current system,, adopt the influence degree of same thought assessment grid structure variation to MISCR according to the definition of CIGRE to many feed-ins short circuit ratio MISCR.In calculating, real system can adopt CR _MISCRDescribe circuit or element and throw the influence degree of moving back MISCR.

${\mathrm{CR}}_{\mathrm{MISCR}}=1-\frac{{\mathrm{MISCR}}_i^{\&prime;}}{{\mathrm{MISCR}}_i}$

$=1-\frac{\left|Z_{\mathrm{eqii}}\right|P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left|Z_{\mathrm{eqij}}\right|P_{\mathrm{dj}}}{\left|{Z_{\mathrm{eqii}}}^{\&prime;}\right|P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left|{Z_{\mathrm{eqij}}}^{\&prime;}\right|P_{\mathrm{dj}}}---\left(14\right)$

$=\frac{\left(\right|{Z_{\mathrm{eqii}}}^{\&prime;}|-|Z_{\mathrm{eqii}}\left|\right)P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left(\right|{Z_{\mathrm{eqij}}}^{\&prime;}|-|Z_{\mathrm{eqij}}\left|\right)P_{\mathrm{dj}}}{\left|{Z_{\mathrm{eqii}}}^{\&prime;}\right|P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left|{Z_{\mathrm{eqij}}}^{\&prime;}\right|P_{\mathrm{dj}}}$

In the formula, MISCR _iBe that i returns the pairing many feed-ins short circuit ratio of direct current; U _iBe that i returns the rated voltage on the change of current bus; Z _EqiiFor i in the equivalent impedance matrix returns the pairing self-impedance of change of current bus; Z _EqijFor returning change of current bus and j, i in the equivalent impedance matrix returns mutual impedance between the change of current bus; P _DiBe the rated power that i returns direct current; P _DjBe the rated power that j returns direct current.MISCR ', Z in the formula _Eqii', Z _Eqij' be that circuit or element are thrown the calculated value of stepping back correspondence.

The invention has the beneficial effects as follows:

The present invention proposes assessment interchange rack variation or any electric component and throw index notion and the security domain thereof that moves back direct current system short circuit ratio and effective short circuit ratio influence degree, provided theoretical calculation method and practical calculation method.This method is applicable to alternating current-direct current parallel/hybrid system and general ac and dc systems or many feed-ins direct current system, can be used for fields such as alternating current-direct current Electric Power Network Planning and operational mode arrangement, has solved the defective of this field shortage guidance target.

Description of drawings

For content of the present invention more is expressly understood, and be convenient to the description of embodiment, provide description of drawings related to the present invention below:

Accompanying drawing 1 has provided valve systems such as AC, Z among the figure _Inverter, Z _RectiferAnd Z _ParallelBe respectively receiving-end system equivalent impedance per unit value, sending equivalent impedance per unit value, and communication channel equivalent impedance per unit value in parallel.

Accompanying drawing 2 has provided an AC system-computed example, send, receiving end alternating current circuit electric pressure is 500kV, and the DC transmission system electric pressure is 3000MW for ± 500kV, specified transmitted power.

Accompanying drawing 3 is flow charts of the appraisal procedure of carrying.

Embodiment

The invention provides a kind of interchange rack that can reflect and change evaluation index and the method to direct current system short circuit ratio and effective short circuit ratio influence degree, the definition of this evaluation index is direct, the concentrated expression ac and dc systems influences each other substantive characteristics.Be a preferred exemplifying embodiment of the present invention below, the technical scheme that the present invention realizes be described further below in conjunction with accompanying drawing of the present invention.

Fig. 2 has provided the example of an AC system, quantizes explanation communication channel in parallel to sending receiving end short circuit ratio influence degree as object.

Table 1 has provided communication channel in parallel and has cut-off that direct current send under the situation, the result of calculation of receiving end short circuit ratio size, with this influence degree of communication channel in parallel to short circuit ratio is described.

Table 1 alternating current circuit in parallel switching is to short circuit ratio and effectively short circuit ratio influence

In this example, for leave certain nargin to system, get critical short circuit ratio CSCR=2.5, therefore critical effective short circuit ratio CESCR=1.7 calculates direct current system inversion side CCR under the normal mode according to formula (12) and (13) _SCRAnd CCR _ESCR

${\mathrm{CCR}}_{\mathrm{SCR}}=\frac{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}-\mathrm{CSCR}}{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}=\frac{3.24-2.5}{3.24}=0.228$

${\mathrm{CCR}}_{\mathrm{ESCR}}=\frac{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}-\mathrm{CESCR}}{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}=\frac{2.64-1.7}{2.64}=0.356$

According to table 1 result of calculation, relatively can get:

(1) after 1 time 500kV circuit of parallel port all hinders disconnection for some reason

(CR _SCR＝0.205)＜(CCR _SCR＝0.228)

(CR _ESCR＝0.251)＜(CCR _ESCR＝0.356)

(2) after 2 times 500kV circuits of parallel port all hinder disconnection for some reason

(CR _SCR＝0.550)＞(CCR _SCR＝0.228)

(CR _ESCR＝0.675)＞(CCR _ESCR＝0.356)

Result of calculation shows: after 1 time 500kV circuit of parallel port hindered disconnection for some reason, the short circuit ratio of receiving-end system and effective short circuit ratio fall were less, less than critical value, sent receiving end short circuit ratio and effective short circuit ratio still in proper range; After 2 times 500kV circuits of parallel port all hinder disconnection for some reason, the short circuit ratio of receiving-end system and effective short circuit ratio fall are excessive, surpassed critical value, than too high with effective short circuit ratio influence degree, there is comparatively serious safe operation hidden danger in system to communication channel in parallel to the receiving-end system system short-circuit.Stability simulation calculates and shows, if disconnect 1 go back to alternating current circuit in parallel, system can keep stable operation; If disconnect 2 go back tos alternating current circuits in parallel, that receiving-end system will lose will be stable, can't normally move, and simulation result is consistent with the appraisal procedure conclusion that adopts the present invention's proposition.

Claims (3)

1. judge that exchanging rack changes the appraisal procedure of direct current system short circuit ratio with effective short circuit ratio influence degree, is characterized in that this method may further comprise the steps for one kind:

(1) short circuit ratio of alternating current-direct current parallel/hybrid system and effectively short circuit ratio computational methods

According to direct current system short circuit ratio SCR and the effectively definition of short circuit ratio ESCR, be the voltage rating U of current conversion station ac bus if get the reference voltage U of AC system _N, reference power P _DNGet specified direct current power P _d, short circuit ratio and effective short circuit ratio can be expressed as:

$\left\{\begin{array}{c}\mathrm{SCR}=\frac{S_{\mathrm{SC}}}{P_{\mathrm{dN}}}=\frac{{U_N}^2}{P_{\mathrm{dN}}}\&times;\frac{1}{\left|Z\right|}=\frac{1}{\left|Z\right|/Z_B}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}\\ \mathrm{ESCR}=\frac{S_{\mathrm{SC}}-Q_C}{P_{\mathrm{dN}}}=\frac{{U_N}^2}{P_{\mathrm{dN}}}\&times;(\frac{1}{\left|Z\right|}-B)=\frac{1}{\left|Z\right|/Z_B}-\frac{B}{1/Z_B}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}-B_{\mathrm{pu}}\end{array}---\left(1\right)\right.$

In the formula, S _SCBe system's change of current busbar short-circuit capacity, Q _CExert oneself for filter and the idle of capacitor reactive compensation equipment, Z is the system equivalent impedance, and B is the equivalent susceptance of filter and capacitor reactive compensation, Z _BBe the impedance reference value under reference power and the reference voltage, Z _PuBe system equivalent impedance per unit value, B _PuBe filter and the equivalent susceptance per unit value of capacitor reactive compensation;

Because the AC system send receiving end to have alternating current interconnection, so the capacity of short circuit at inversion end change of current bus place is not only relevant with the receiving-end system grid structure, also closely related with the intensity of sending and alternating current circuit in parallel:

$Z_I=\frac{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}---\left(2\right)$

In the formula, Z _Inverter, Z _RectiferAnd Z _ParallelBe respectively receiving-end system equivalent impedance per unit value, sending equivalent impedance per unit value, and communication channel equivalent impedance per unit value in parallel;

Simultaneous formula (1) can get the AC system short-circuit with (2):

${\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}=\frac{1}{\left|\frac{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}\right|}---\left(3\right)$

$=\left|\frac{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}\right|$

Formula (3) can further be written as following form:

${\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}=|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}|---\left(4\right)$

Can obtain the effective short circuit ratio computing formula of AC system equally is:

${\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}=\frac{1}{\left|Z_{\mathrm{pu}}\right|}-B_{\mathrm{pu}}=\left|\frac{Z_{\mathrm{inverter}}+Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}(Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}})}\right|-B_{\mathrm{pu}}---\left(5\right)$

Formula (5) also can be expressed as:

${\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}=|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}|-B_{\mathrm{pu}}---\left(6\right)$

According to formula (4) and (6) as can be known: be connected comparatively closely if send receiving-end system to pass through communication channel in parallel, and sending end is strong system, and communication channel equivalent impedance then in parallel is to the SCR of direct current receiving end _AC-DCAnd ESCR _AC-DCThe size influence is bigger; Connect comparatively weakly if send receiving-end system to pass through communication channel in parallel, and sending end electrical network weakness is then to the SCR of direct current receiving end _AC-DCAnd ESCR _AC-DCThe size influence is less relatively;

(2) communication channel in parallel is to short circuit ratio and the effectively definition of short circuit ratio contribution rate index

For communication channel in parallel being described to short circuit ratio and effective short circuit ratio influence degree, introduce the notion of " communication channel in parallel is to short circuit ratio and effective short circuit ratio contribution rate " and assess such problem, adopt CR respectively _SCRAnd CR _ESCRDescribe.Its concrete form is as follows:

${\mathrm{CR}}_{\mathrm{SCR}}=\left|\frac{\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}}{\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}}\right|=\frac{1}{|1+\frac{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}}|}---\left(7\right)$

${\mathrm{CR}}_{\mathrm{ESCR}}=\frac{\left|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}\right|}{|\frac{1}{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}+\frac{1}{Z_{\mathrm{inverter}}}|-B_{\mathrm{pu}}}---\left(8\right)$

$=\frac{1}{|1+\frac{Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}}{Z_{\mathrm{inverter}}}|-B_{\mathrm{pu}}\&times;|Z_{\mathrm{rectifier}}+Z_{\mathrm{parallel}}|}$

In formula (7) and (8), CR _SCRScope be 0＜CR _SCR＜1; CR _ESCRScope be 0＜CR _ESCR＜1, parallel port and sending equivalent impedance are big more, CR _SCRAnd CR _ESCRMore little, more little to direct-current short circuit ratio and effective short circuit ratio influence; Meanwhile, receiving-end system is weak more, CR _SCRAnd CR _ESCRBig more, communication channel in parallel is also big more to direct-current short circuit ratio and effective short circuit ratio influence with sending intensity;

(3) CR _SCRAnd CR _ESCRThe index practical calculation method

In practical computational analysis, adopt the computational methods of equivalent impedance comparatively loaded down with trivial details, the formula that needs usually to adopt similar conventional short circuit ratio to calculate is described, and therefore can obtain and formula (7) and (8) form of equal value:

${\mathrm{CR}}_{\mathrm{SCR}}=1-\frac{{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}^{\&prime;}}{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}=1-\frac{\frac{{S_{\mathrm{SC}}}^{\&prime;}}{P_d}}{\frac{S_{\mathrm{SC}}}{P_d}}=1-\frac{{S_{\mathrm{SC}}}^{\&prime;}}{S_{\mathrm{SC}}}=\frac{S_{\mathrm{SC}}-{S_{\mathrm{SC}}}^{\&prime;}}{S_{\mathrm{SC}}}---\left(9\right)$

${\mathrm{CR}}_{\mathrm{ESCR}}=1-\frac{{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}^{\&prime;}}{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}=1-\frac{\frac{{S_{\mathrm{SC}}}^{\&prime;}-Q_C}{P_d}}{\frac{S_{\mathrm{SC}}-Q_C}{P_d}}=1-\frac{{S_{\mathrm{SC}}}^{\&prime;}-Q_C}{S_{\mathrm{SC}}-Q_C}=\frac{S_{\mathrm{SC}}-{S_{\mathrm{SC}}}^{\&prime;}}{S_{\mathrm{SC}}-Q_C}---\left(10\right)$

In the formula, SCR _AC-DC' and ESCR _AC-DC' be respectively disconnect communication channel in parallel or give, direct current system short circuit ratio and effective short circuit ratio size under circuit or the element situation arbitrarily in the receiving end AC system, SCR _AC-DCAnd ESCR _AC-DCBe respectively short circuit ratio and effective short circuit ratio under the normal condition; S _SC' for disconnect communication channel in parallel or give, change of current bus place system short circuit capacity size under circuit or the element situation arbitrarily in the receiving end AC system, S _SCBe the change of current bus place system short circuit capacity size under the normal condition;

(4) CR _SCRAnd CR _ESCRSecurity domain

It has been generally acknowledged that the direct current system short circuit ratio less than 3 or effectively short circuit ratio less than 2, the ac and dc systems maintenance level is relatively poor, in planning and designing and operational mode arrangement, avoided, particularly when short circuit ratio less than 2 or effectively short circuit ratio less than 1.5～1.7, ac and dc systems will be difficult to operation, so ac and dc systems is to having critical short circuit ratio CSCR and critical effective short circuit ratio CESCR; In actual applications, this value does not have unified value, therefore within the specific limits as required or engine request get final product for respectively critical short circuit ratio CSCR and estimated value of critical effective short circuit ratio CESCR, therefore, according to formula (9) and (10), can solve CR _SCRAnd CR _ESCRIndex is recommended security domain, is:

SCR _AC-DC′＝(1-CR _SCR)×SCR _AC-DC＜CSCR (11)

Find the solution and to get CR _SCRIndex is recommended security domain:

$\left\{\begin{array}{c}{\mathrm{CR}}_{\mathrm{SCR}}<{\mathrm{CCR}}_{\mathrm{SCR}}\\ {\mathrm{CCR}}_{\mathrm{SCR}}=\frac{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}-\mathrm{CSCR}}{{\mathrm{SCR}}_{\mathrm{AC}-\mathrm{DC}}}\end{array}\right.---\left(12\right)$

In the formula (12), CCR _SCRBe CR _SCRCritical value;

In like manner, can solve CR _ESCRIndex is recommended security domain, is:

$\left\{\begin{array}{c}{\mathrm{CR}}_{\mathrm{ESCR}}<{\mathrm{CCR}}_{\mathrm{ESCR}}\\ {\mathrm{CCR}}_{\mathrm{ESCR}}=\frac{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}-\mathrm{CESCR}}{{\mathrm{ESCR}}_{\mathrm{AC}-\mathrm{DC}}}\end{array}\right.---\left(13\right)$

In the formula (13), CCR _ESCRBe CR _ESCRCritical value;

Therefore, formula (12) and (13) show: work as CR _SCROr CR _ESCRWhen surpassing the represented critical value of computing formula, illustrate that promptly this AC system communication channel is excessive to the short circuit ratio influence, there is certain hidden danger in power network safety operation.

2. appraisal procedure as claimed in claim 1 is characterized in that the CR with this method _SCRAnd CR _ESCRIndex and security domain notion thereof are applied to general ac and dc systems, CR _SCRAnd CR _ESCRNotion only be not applicable to the AC system, this notion and method also can be applied to general ac and dc systems or many feed-ins direct current system, are used to assess any rack variation or element throwing and move back direct current system short circuit ratio and the effectively influence of short circuit ratio variation.

3. appraisal procedure as claimed in claim 2, it is characterized in that this method is when the general ac and dc systems rack of assessment changes short circuit ratio and effective short circuit ratio influence degree, at first calculate short circuit ratio and effective short circuit ratio of sending end or receiving end AC system bar line disconnection front and back, adopt formula (9) and (10) can calculate CR then _SCRAnd CR _ESCRSize; Utilize formula (12) and (13) to calculate short circuit ratio and effective short circuit ratio security domain, i.e. the critical value CCR of this ac and dc systems of description _SCRAnd CCR _ESCRCheck CR _SCRAnd CR _ESCRWhether surpass CCR _SCRAnd CCR _ESCR, if greater than critical value, then this circuit is paid attention in planning and designing and operational mode arrangement to short circuit ratio with effectively the short circuit ratio influence is excessive, if less than critical value, then this circuit to short circuit ratio and effectively short circuit ratio influence relative less;

For many feed-ins direct current system,, adopt the influence degree of same thought assessment grid structure variation to MISCR according to the definition of CIGRE to many feed-ins short circuit ratio MISCR.In calculating, real system can adopt CR _MISCRDescribe circuit or element and throw the influence degree of moving back MISCR;

${\mathrm{CR}}_{\mathrm{MISCR}}=1-\frac{{\mathrm{MISCR}}_i^{\&prime;}}{{\mathrm{MISCR}}_i}$

$=1-\frac{\left|Z_{\mathrm{eqii}}\right|P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left|Z_{\mathrm{eqij}}\right|P_{\mathrm{dj}}}{\left|{Z_{\mathrm{eqii}}}^{\&prime;}\right|P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left|{Z_{\mathrm{eqij}}}^{\&prime;}\right|P_{\mathrm{dj}}}---\left(14\right)$

$=\frac{\left(\right|{Z_{\mathrm{eqii}}}^{\&prime;}|-|Z_{\mathrm{eqii}}\left|\right)P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left(\right|{Z_{\mathrm{eqij}}}^{\&prime;}|-|Z_{\mathrm{eqij}}\left|\right)P_{\mathrm{dj}}}{\left|{Z_{\mathrm{eqii}}}^{\&prime;}\right|P_{\mathrm{di}}+\underset{j=i,j\&NotEqual;i}{\overset{n}{\mathrm{\&Sigma;}}}\left|{Z_{\mathrm{eqij}}}^{\&prime;}\right|P_{\mathrm{dj}}}$

In the formula, MISCR _iBe that i returns the pairing many feed-ins short circuit ratio of direct current; U _iBe that i returns the rated voltage on the change of current bus; Z _EqiiFor i in the equivalent impedance matrix returns the pairing self-impedance of change of current bus; Z _EqijFor returning change of current bus and j, i in the equivalent impedance matrix returns mutual impedance between the change of current bus; P _DiBe the rated power that i returns direct current; P _DjBe the rated power that j returns direct current.MISCR ', Z in the formula _Eqii', Z _Eqij' be that circuit or element are thrown the calculated value of stepping back correspondence.

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