CN104578044A - Method for determining unit action coefficient based on subsynchronous oscillation analysis - Google Patents

Abstract

A method for determining a unit action coefficient based on subsynchronous oscillation analysis is used for a multi-direct-current sending end system, and comprises the steps that the conversion current bus voltage of the direct current K corresponding to the maximum value in action coefficients of all direct currents on an ith generating set is reduced by 1%; the change rates of the voltages of other direct current conversion current buses are obtained, and multi-direct-current interaction factors are determined according to the change rates; the equivalent capacity for the multiple direct currents to be equivalent to one direct current K is determined according to the direct current interaction factors; the comprehensive action coefficient of all the direct currents on the ith generating set is worked out through the obtained equivalent capacity. The interaction factors of the multiple direct currents are used for enabling the multiple direct currents to be equivalent to be one direct current, then the comprehensive action coefficient of the multiple direct currents on the generating set is obtained with the single-loop direct current unit action coefficient method, the reliability is high, and the level of analyzing subsynchronous oscillation risks of the multi-direct-current system is increased.

Description

A kind of method of the determination unit function coefficient based on sub-synchronous oscillation analysis

Technical field

The invention belongs to generating set failure analysis techniques field, especially a kind of method of the determination unit function coefficient based on sub-synchronous oscillation analysis.

Background technology

Containing in the electrical network of direct current transportation, sub-synchronous oscillation phenomenon may be produced when fired power generating unit and direct current transportation converting plant close together, for its mechanism of production, electrician circle generally believes, due to the quick control of direct current transportation, may make with the subsynchronous hunting of frequency of shaft system of unit subsynchronous oscillation frequency complementary is negative damping feature in electrical network, and the subsynchronous oscillation of shaft system of unit therefore may be made to occur wild effect.For the sub-synchronous oscillation problem that direct current transportation causes, analytical method main at present comprises unit function coefficient method, it is a kind of quantitative screening implement that IEC919-3 standard provides, initial data required for unit function coefficient method is little, does not need to consider the characteristic of DC power transmission control system and the axle system parameter of generating set.The power of system short-circuit level to HVDC (high-voltage directcurrent, high voltage direct current transmission) system and electrical network coupling is adopted to assess, thus the damping capacity that reflection electric power system is intrinsic.Therefore for DC transmission system, unit function coefficient method is a kind of simple, effective sub-synchronous oscillation quantitative screening method, important role in the planning and design of direct current transportation.

Unit function coefficient method reflects the coupling between unit and single time direct current, but in the electrical network of reality, especially large-scale Energy Base, multiple-circuit line is often adopted to send scheme, between multiple-circuit line, electrical distance is near, all there is coupling between generating set and multiple-circuit line, the negative electrical effect of each bar direct current is all returned and is had an impact to shaft system of unit torsional oscillation.If do not consider that multiple-circuit line interacts, only assess according to the function coefficient between unit and single time direct current, be then difficult to the sub-synchronous oscillation risk effectively reflecting unit.

Summary of the invention

An object of the present invention is to provide a kind of method of the determination unit function coefficient based on sub-synchronous oscillation analysis, of the prior art for adopting multiple-circuit line to send the problem that in scheme, sub-synchronous oscillation risk cannot detect or testing result reliability is low to solve.

In some illustrative embodiment, the method of the described determination unit function coefficient based on sub-synchronous oscillation analysis, for many direct currents sending, comprising: each bar direct current is reduced by 1% to the change of current busbar voltage of direct current k corresponding to maximum in the function coefficient of i-th generating set; Obtain the rate of change of the voltage of other DC converter bus, and determine many direct currents interaction factor according to this rate of change; According to many direct currents interaction factor, determine that many direct currents are equivalent to the equivalent capacity of a direct current k; Described each bar direct current is calculated to the comprehensive function coefficient of i-th generating set with the described equivalent volumeter obtained; Wherein, 1≤i≤m, 1≤k≤n, m and n is respectively the sequence number of generating set and the sequence number of direct current.

Compared with prior art, illustrative embodiment of the present invention comprises following advantage:

The present invention is by analyzing the impact each other of the direct current in many direct currents sending, and adopt many direct currents interaction factor many direct currents to be equivalent to a direct current determination equivalent capacity further, many DC converter buses are obtained to the function coefficient of generating set again by single time direct current unit function coefficient method, reliability is strong, and adopt the method in real process, greatly reduce the risk of sub-synchronous oscillation.

Accompanying drawing explanation

Accompanying drawing described herein is used to provide a further understanding of the present invention, and form a application's part, schematic description and description of the present invention, for explaining the present invention, does not form inappropriate limitation of the present invention.In the accompanying drawings:

Fig. 1 is the flow chart according to illustrative embodiment of the present invention.

Embodiment

In the following detailed description, a large amount of specific detail is proposed, so that provide thorough understanding of the present invention.But, person of skill in the art will appreciate that, also can implement the present invention even without these specific detail.In other cases, do not describe well-known method, process, assembly and circuit in detail, in order to avoid affect the understanding of the present invention.

Illustrative embodiment for a better understanding of the present invention, is briefly described the main thought in illustrative embodiment of the present invention below.

The object of the invention is to provide a kind of MIIF based on depression of order Jacobian matrix to improve computational methods for the deficiencies in the prior art, be characterized in changing the existing operating condition of system, directly can calculate MIIF by system load flow distribution, in itself MIIF is explained, and there is higher accuracy.With calculate the method for MIIF based on nodal impedance matrix compared with, the method compensate for the defect that accurately cannot calculate MIIF when system equipment active reactive characteristic changing.The method makes improvement in original computational methods based on depression of order Jacobian matrix simultaneously, further increases efficiency and the accuracy of calculating.

As shown in Figure 1, disclose a kind of method of the determination unit function coefficient based on sub-synchronous oscillation analysis, for many direct currents sending, comprising:

S11, each bar direct current is reduced by 1% to the change of current busbar voltage of direct current k corresponding to maximum in the function coefficient of i-th generating set;

S12, obtain the rate of change of the voltage of other DC converter bus, and determine many direct currents interaction factor according to this rate of change;

S13, according to many direct currents interaction factor, determine that many direct currents are equivalent to the equivalent capacity of a direct current k;

S14, calculate described each bar direct current to the comprehensive function coefficient of i-th generating set with the described equivalent volumeter obtained;

Wherein, 1≤i≤m, 1≤k≤n, m and n is respectively the sequence number of generating set and the sequence number of direct current.

The present invention is by analyzing the impact each other of the direct current in many direct currents sending, and adopt many direct currents interaction factor many direct currents to be equivalent to a direct current determination equivalent capacity further, many DC converter buses are obtained to the function coefficient of generating set again by single time direct current unit function coefficient method, reliability is strong, and adopt the method in real process, greatly reduce the risk of sub-synchronous oscillation.

In some illustrative embodiment, described according to many direct currents interaction factor, determine that many direct currents are equivalent to the equivalent capacity of a direct current k, specifically comprise:

Described equivalent D.C. capacity S is gone out according to following formulae discovery _eq:

$S_{\mathrm{eq}}=P_{\mathrm{dk},\mathrm{eq}}=P_{\mathrm{dk}}+\underset{j=1,j\≠k}{\overset{n}{\mathrm{\Σ}}}{\mathrm{MIIF}}_{\mathrm{jk}}*P_{\mathrm{dj}};$

Wherein, P _{dk, eq}for the equivalent power of described many DC converter buses, P _dkfor the rated power of DC converter bus k, P _djfor the rated power of DC converter bus j, 1≤j≤n and j ≠ k, MIIF _jkfor described many direct currents interaction factor.

In some illustrative embodiment, describedly calculate described each bar direct current to the comprehensive function coefficient of i-th generating set with the described equivalent volumeter obtained, specifically comprise:

The comprehensive function coefficient UIF of described each bar direct current to described i-th generating set is gone out according to following formulae discovery _i':

${\mathrm{UIF}}_i^{,}=\frac{S_{\mathrm{eq}}}{S_i}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2;$

Wherein, S _ibe the rated capacity of i-th generating set, SC _ifor the three-phase shortcircuit capacity on the DC transmission system converting plant ac bus of the effect of the contribution and alternating current filter that do not calculate i-th generating set, SC _tOTfor calculating the contribution of i-th generating set and the three-phase shortcircuit capacity do not calculated on the DC transmission system converting plant ac bus of the effect of alternating current filter.

In some illustrative embodiment, described by each bar direct current to the function coefficient of i-th generating set in the change of current busbar voltage of direct current k corresponding to maximum reduced before 1%, also comprise:

Calculate the function coefficient of jth bar direct current for described i-th unit; The multiple described function coefficient obtained is compared, determines the function coefficient that numerical value is maximum and the direct current k corresponding with this function coefficient.

In some illustrative embodiment, described in calculate the function coefficient of jth bar direct current for described i-th unit, specifically comprise:

Calculate according to single time direct current unit function coefficient formula:

${\mathrm{UIF}}_{i,j}=\frac{S_{\mathrm{HVDC},j}}{S_j}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2;$

Wherein, UIF _i,jfor jth bar direct current is to the function coefficient of i-th generating set, S _{hVDC, j}for the rated capacity of the change of current bus of jth bar direct current.

In some illustrative embodiment, the rate of change of the voltage of other DC converter bus of described acquisition, and determine many direct currents interaction factor according to this rate of change, specifically comprise:

Described many direct currents interaction factor MIIF is determined according to following formula _jk;

${\mathrm{MIIF}}_{\mathrm{jk}}=\frac{\mathrm{\Δ}{U}_j}{\mathrm{\Δ}{U}_k};$

Wherein, MIIF _jkfor the voltage change ratio △ U of DC converter bus j _jwith the change in voltage △ U of DC converter bus k _kratio.

Below such scheme is specifically described:

Unit function coefficient method is a kind of analytical method put forward for the subsynchronous oscillation of electrical power system problem relevant with DC transmission system.When there are some unfavorable factors between turbo generator set and DC transmission system, sub-synchronous oscillation instability may be there is.These unfavorable factors comprise: Steam Turbine and direct current transportation converting plant are apart from very near; Steam Turbine with exchange bulk power grid and contact weakness; Unit rated capacity is relative with direct current rated capacity close.IEC919-3 standard provides a kind of quantitative screening implement, is used for characterizing generating set and the interactional power of DC transmission system, i.e. unit function coefficient method.The function coefficient of i-th unit can be expressed as:

${\mathrm{UIF}}_i=\frac{S_{\mathrm{HVDC}}}{S_i}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2---(3-1)$

In formula: UIF _iit is the function coefficient of i-th generating set; S _hVDCfor the rated power of DC transmission system; S _iit is the rated capacity of i-th generator; SC _ifor the three-phase shortcircuit capacity on DC transmission system converting plant ac bus, do not comprise the contribution of i-th generator when calculating this capacity of short circuit, do not comprise the effect of alternating current filter yet; SC _tOTfor the three-phase shortcircuit capacity on direct current transportation converting plant ac bus, comprise the contribution of i-th generator when calculating this capacity of short circuit, do not comprise the effect of alternating current filter.

Unit function coefficient UIF is that EPRI recommends, for may be excited the method for the generating set producing sub-synchronous oscillation in check system by DC transmission system.When assessing a certain DC transmission system and may causing in AC system which generating set generation sub-synchronous oscillation, the UIF coefficient first adopting unit function coefficient method to calculate all large turbine-generator set in AC system near converting plant has important references and is worth; Analyzed by UIF and can filter out which generating set there is the danger and must doing that sub-synchronous oscillation occurs further study in great detail, for valuable information such as other unit then need not make further research from the numerous generating set of AC system.

In actual electrical network, especially large-scale Energy Base, often adopt multiple-circuit line to send scheme, between multiple-circuit line, electrical distance is near, all there is coupling between generating set and multiple-circuit line, the negative electrical effect of each bar direct current is all returned and is had an impact to shaft system of unit torsional oscillation.If do not consider that multiple-circuit line interacts, only calculate the function coefficient between unit and single time direct current, be then difficult to effectively reflect that therefore the sub-synchronous oscillation risk of unit needs to revise unit function coefficient.

In ac and dc systems, receiving end AC system rack power is the deciding factor of the stability of a system, in theoretical research and engineer applied, usual employing short circuit ratio (SCR, shown in following formula 5-1) concept assess relative strong or weak relation, the maximum transmitted power of direct current, overvoltage level between AC system with direct current system and possible harmonic frequency.

$\mathrm{SCR}=\frac{S_{\mathrm{ac}}}{P_{\mathrm{dN}}}---(5-1)$

Wherein, S _acfor the capacity of short circuit of DC converter bus, P _dNfor the specified transmission capacity of direct current.

But, along with the extensive use of HVDC Transmission Technology, there is the grid structure that multiple current conversion station electrical distance is close in electrical network, i.e. multi-infeed HVDC system (Multi-infeed DC, MIDC).Large owing to influencing each other between each direct current system, for assessment of single time direct current system SCR index crash.Scholars proposes interactional evaluation index between the many direct current systems of multiple consideration for above-mentioned situation, the definition of the wherein famous i.e. multi-infeed HVDC short circuit ratio (Multi-infeed Short Circuit Ratio, MISCR) of CIGRE DC operation group proposition in 2008.This index is not popularized in an all-round way at present, is still carrying out further investigation further and is improving.

SCR concept is for single time direct current system, or the multiple-circuit line system that distance, coupling are little.For general multi-infeed HVDC system, because each Inverter Station electrical distance is close, coupled characteristic is obvious, still adopts SCR can there is relatively large deviation to assess ac and dc systems.For two direct current systems of feed-in areal, the common factor in the two similar two region of coupled relation, therefore, need definition energy to the index of influence degree between the different direct current system of quantificational description, i.e. many feed-ins correlation factor (Multi-Infeed Interaction Factor, MIIF), this factor is the evolution of the key determining MISCR definition, its experience one section longer.Within 2008, CIGRE working group has formally issued MISCR definition, shown in 5-2.This index causes extensive concern in the industry, and has been introduced into action oriented research work

${\mathrm{MISCR}}_i=\frac{S_{\mathrm{aci}}}{P_{\mathrm{di}}+\underset{j=1,j\≠i}{\overset{n}{\mathrm{\Σ}}}{\mathrm{MIIF}}_{\mathrm{ji}}*P_{\mathrm{dj}}}=\frac{S_{\mathrm{aci}}}{P_{\mathrm{di}}+\underset{j=1,j\≠i}{\overset{n}{\mathrm{\Σ}}}\frac{\mathrm{\Δ}{U}_j}{\mathrm{\Δ}{U}_i}*P_{\mathrm{dj}}}---(5-2)$

In formula: MISCR _ifor the many feed-ins short circuit ratio corresponding to i-th time direct current; U _iand U _jbe respectively i-th time and jth and return rated voltage on DC converter bus; P _diand P _djbe respectively the rated power that i-th time and jth return direct current.In formula, MIIF is specifically defined as: when change of current bus i drop into symmetrical three-phase reactor make the voltage drop on this bus be 1% just time, the ratio of direct current j and direct current i change of current busbar voltage rate of change, obvious 0≤MIIF _ji≤ 1.Here there are three kinds of situations:

(1) MIIF is worked as _ji=1, two direct current system change of current buses overlap, and electrical distance is 0, can think that two direct currents are merged into a direct current system and run;

(2) 0<MIIF is worked as _ji<1, MIIF _jilarger, electrical distance is less, and the voltage influence of change of current bus i voltage fluctuation to change of current bus j is larger, otherwise, MIIF _jiless, then electrical distance is larger, and the impact of change of current bus i voltage fluctuation on the voltage of change of current bus j is less;

(3) MIIF is worked as _ji=0, two direct current system change of current buses, without electrical link, namely when studying ac and dc systems relation, can think single direct current feedthrough system.

From above to the summary of the sub-synchronous oscillation mechanism that direct current transportation causes, the axle system disturbance of unit will cause the perturbation of AC system voltage, namely cause the perturbation of each DC converter busbar voltage, the angle so causing different change of current busbar voltage to change from disturbance considers that the coupling between multiple-circuit line then has certain reasonability.Therefore can refer to the analytical method of many direct current systems short circuit ratio, introduce many feed-ins correlation factor concept, multiple-circuit line transmission capacity is equivalent to the equivalent rated capacity of conversion to a certain time direct current, calculate the function coefficient of this time direct current and unit according to equivalent rated capacity, the comprehensive function of each direct current to unit can be reflected.In order to the accuracy of this equivalence, using with the nearest DC converter bus of unit electrical distance as equivalent point, the principle of selection is that the function coefficient (UIF) of this direct current and unit is maximum.

The concrete calculation procedure of this modification method is following (do not do the variable stated here, its definition is with identical above):

(1) the dependent interaction coefficient between single time direct current and unit is calculated according to conventional method, as shown in the formula:

${\mathrm{UIF}}_{i,j}=\frac{S_{\mathrm{HVDC},j}}{S_i}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2---(5-3)$

Wherein UIF _i,jfor jth bar direct current is to the function coefficient of i-th unit, S _{hVDC, j}for the rated capacity of jth bar direct current;

(2) choose the direct current k that wherein unit function coefficient is maximum, calculate by many feed-ins factor the equivalent rated capacity that many direct currents are scaled to this DC converter bus.

A) pass through to drop into inductive reactive power compensation device on DC converter bus k, make busbar voltage reduce by 1%, calculate many feed-ins factor according to other DC converter busbar voltage rates of change;

${\mathrm{MIIF}}_{\mathrm{jk}}=\frac{\mathrm{\&Delta;}{U}_j}{\mathrm{\&Delta;}{U}_k}---(5-4)$

B) equivalent D.C. capacity S is calculated _eq(i.e. power P _{dk, eq}) as shown in the formula:

$S_{\mathrm{eq}}=P_{\mathrm{dk},\mathrm{eq}}=P_{\mathrm{dk}}+\underset{j=1,j\&NotEqual;k}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{MIIF}}_{\mathrm{jk}}*P_{\mathrm{dj}}---(5-5)$

(3) by equivalent direct current power, unit function coefficient is revised, as shown in the formula:

${\mathrm{UIF}}_i^{,}=\frac{S_{\mathrm{eq}}}{S_i}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2---(5-6)$

The explanation of above embodiment just understands method of the present invention and core concept thereof for helping; Meanwhile, for one of ordinary skill in the art, according to thought of the present invention, all will change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention.

Claims (6)

1., based on a method for the determination unit function coefficient of sub-synchronous oscillation analysis, it is characterized in that, for many direct currents sending, comprising:

Each bar direct current is reduced by 1% to the change of current busbar voltage of direct current k corresponding to maximum in the function coefficient of i-th generating set;

Obtain the rate of change of the voltage of other DC converter bus, and determine many direct currents interaction factor according to this rate of change;

According to many direct currents interaction factor, determine that many direct currents are equivalent to the equivalent capacity of a direct current k;

Described each bar direct current is calculated to the comprehensive function coefficient of i-th generating set with the described equivalent volumeter obtained;

Wherein, 1≤i≤m, 1≤k≤n, m and n is respectively the sequence number of generating set and the sequence number of direct current.

2. method according to claim 1, is characterized in that, described according to many direct currents interaction factor, determines that many direct currents are equivalent to the equivalent capacity of a direct current k, specifically comprises:

Described equivalent D.C. capacity S is gone out according to following formulae discovery _eq:

$S_{\mathrm{eq}}=P_{\mathrm{dk},\mathrm{eq}}=P_{\mathrm{dk}}+\underset{j=1,j\&NotEqual;k}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{MIIF}}_{\mathrm{jk}}*P_{\mathrm{dj}};$

Wherein, P _{dk, eq}for the equivalent power of described many DC converter buses, P _dkfor the rated power of DC converter bus k, P _djfor the rated power of DC converter bus j, 1≤j≤n and j ≠ k, MIIF _jkfor described many direct currents interaction factor.

3. method according to claim 2, is characterized in that, describedly calculates described each bar direct current to the comprehensive function coefficient of i-th generating set with the described equivalent volumeter obtained, and specifically comprises:

The comprehensive function coefficient UIF of described each bar direct current to described i-th generating set is gone out according to following formulae discovery _i':

${{\mathrm{UIF}}_i}^{,}=\frac{S_{\mathrm{eq}}}{S_i}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2;$

Wherein, S _ibe the rated capacity of i-th generating set, SC _ifor the three-phase shortcircuit capacity on the DC transmission system converting plant ac bus of the effect of the contribution and alternating current filter that do not calculate i-th generating set, SC _tOTfor calculating the contribution of i-th generating set and the three-phase shortcircuit capacity do not calculated on the DC transmission system converting plant ac bus of the effect of alternating current filter.

4. the method according to any one of claim 1-3, is characterized in that, described by each bar direct current to the function coefficient of i-th generating set in the change of current busbar voltage of direct current k corresponding to maximum reduced before 1%, also comprise:

Calculate the function coefficient of jth bar direct current for described i-th unit;

The multiple described function coefficient obtained is compared, determines the function coefficient that numerical value is maximum and the direct current k corresponding with this function coefficient.

5. method according to claim 4, is characterized in that, described in calculate the function coefficient of jth bar direct current for described i-th unit, specifically comprise:

Calculate according to single time direct current unit function coefficient formula:

${\mathrm{UIF}}_{i,j}=\frac{S_{\mathrm{HVDC},j}}{S_i}{(1-\frac{{\mathrm{SC}}_i}{{\mathrm{SC}}_{\mathrm{TOT}}})}^2;$

Wherein, UIF _i,jfor jth bar direct current is to the function coefficient of i-th generating set, S _{hVDC, j}for the rated capacity of the change of current bus of jth bar direct current.

6. the method according to any one of claim 1-3, is characterized in that, the rate of change of the voltage of other DC converter bus of described acquisition, and determines many direct currents interaction factor according to this rate of change, specifically comprises:

Described many direct currents interaction factor MIIF is determined according to following formula _jk;

${\mathrm{MIIF}}_{\mathrm{jk}}=\frac{{\mathrm{\&Delta;U}}_j}{\mathrm{\&Delta;}{U}_k};$

Wherein, MIIF _jkfor the voltage change ratio Δ U of DC converter bus j _jwith the change in voltage Δ U of DC converter bus k _kratio.