CN104617576B - Multi-DC-feed (multi-direct current-feed) AC (alternate current) grid fault calculating method taking DC control characteristics into consideration - Google Patents

Abstract

The invention discloses a multi-DC-feed AC grid fault calculating method taking DC control characteristics into consideration. The multi-DC-feed AC grid fault calculating method comprises the following steps of inputting system parameters, DC control strategies and fault parameters of an MODC (multi-outfeed direct current) system; forming an AC system sequence network chart through the system parameters and the fault parameters of an AC grid, establishing an AC constraint equation, and establishing a DC constraint equation between the DC voltage and the DC current of a DC side through the DC control characteristics; setting initial values for all variables; establishing converter switch function models SI and SU of every DC subsystem; according to the AC constraint equation, the DC constraint equation and voltage and current switch functions, solving the transient state parameters of the AC side and the DC side of the MODC system; performing iterative computation, and when variable errors meet computational requirements, outputting the computation results of the transient state parameters of the AC side and the DC side of the MODC system. The multi-DC-feed AC grid fault calculating method taking the DC control characteristics into consideration is high in computation speed, accuracy and adaptability and has high engineering practical value in the aspect of setting and cooperation of fault computation and relay protection of multi-DC-outfeed AC grids.

Description

Consider that many direct currents of DC control characteristic feed out AC network fault calculation methods for transmission

Technical field

The present invention relates to the research field of electric power system fault computational methods, consider DC control characteristic particularly to a kind of Many direct currents feed out AC network fault calculation methods for transmission.

Background technology

Direct current transportation has many advantages, such as compared with ac transmission in terms of distance, large capacity transmission, is widely used in electric power Resourceful west area conveys in the transmission system of electric energy to the coastal region in east China.With the continuous expansion of need for electricity, The west area AC network a plurality of DC transmission system of extraction enriching from electric power resource forms many direct currents and feeds out power transmission system To realize.After rather eastern DC transmission engineering, second DC transmission engineering in Ningxia is rather to the east of the extra-high straightening in Zhejiang Stream power transmission engineering plan is built up and is put into operation for 2016, and when the time comes, Ningxia power feeds out alternating current containing multiple-circuit line system by becoming more Net.It is the basis of its relay protection setting cooperation that the accident analysis of electrical network calculates, and has had relatively for traditional pure AC network For ripe fault calculation methods for transmission, and in the alternating current-direct current Power network fault calculation containing straight-flow system, then generally by straight-flow system Equivalent is constant-current source or constant power load model.Because the control characteristic of straight-flow system rectification side during AC network fault is with fault bar The change of part and have larger difference, if not considering the control characteristic of straight-flow system during fault, will necessarily be to calculation of fault result Cause certain error.For modc (multi-outfeed direct current system, modc), one Aspect respectively feeds out and there is close interaction relationship between direct current subsystem；On the other hand, because direct current feeds out general power Proportion larger, the impact to fault current for straight-flow system control characteristic that sending end electric network fault the is caused change then even more can not Ignore.But at present effective computational methods are also lacked for the AC network calculation of fault that system containing multiple-circuit line feeds out, and Although detailed electromagnetical transient emulation method is capable of the fault transient process of Detailed simulation modc network, and in system containing multiple-circuit line In the case of system, electromagnetic transient simulation model is more complicated, simulation calculation take extremely long it is difficult to be applied to computation rate is had higher The occasion requiring is it is therefore necessary to propose a kind of new method improving computation rate on the basis of ensureing computational accuracy.

Content of the invention

Present invention is primarily targeted at filling up the blank of this research field, overcoming shortcoming and the deficiency of prior art, carrying Go out a kind of consideration DC control characteristic feeds out AC network fault calculation methods for transmission containing many direct currents.

In order to achieve the above object, the present invention employs the following technical solutions:

A kind of many direct currents considering DC control characteristic feed out AC network fault calculation methods for transmission, comprise the steps:

(1) systematic parameter of input modc system, DC control strategy and its control parameter；

(2) AC system sequence diagrams are formed by ac grid system parameter and fault parameter, set up exchange constraint equation, by The control strategy of straight-flow system and control parameter form the direct current constraint equation between DC side DC voltage and DC current；

(3) make k=0, initial value is put to whole variables；

(4) make i=1, according to known 1st time change of current busbar voltageTry to achieve its power frequency line voltage WithAgain by DC component i of power frequency line voltage, DC current_[1]d0And straight-flow system rectification side Trigger Angle α_[1], build Vertical voltage x current switch function model, obtains the switch function of voltage, electric currentWith

(5) by exchange side bus voltageWith voltage switch functionTry to achieve straight-flow system DC voltage

(6) according to direct current constraint equation and DC voltageTry to achieve DC current

(7) by DC side DC currentWith current switch functionTry to achieve straight-flow system to be injected into by inverter The equal currents of AC system

(8) i=2,3 ... ..., according to the method for the 1st time step (4) shown in change of current bus～(7), calculate remaining respectively and change Stream bus and its connected straight-flow system are injected into the equal currents of AC system by inverter

(9) according to exchange constraint equation and alternating currentTry to achieve change of current busbar voltage

(10) calculate respectivelyWithError, when maximum error is unsatisfactory for requiring, make k=k+1, repeat step (4) process of～(10)；When maximum error satisfaction requires, export the knot as calculation of fault for the variate-value of+1 computing of kth Really.

Preferably, in step (2), according to the structure and parameter of modc system, and fault parameter forms and is applied to fault Calculate AC system sequence diagrams and exchange constraint equation, the control strategy according to straight-flow system and control parameter formation unidirectional current Stream is with the direct current constraint equation of DC voltage change；Exchange constraint equation and direct current constraint equation specify that AC voltage, electricity Functional relationship and between DC voltage, electric current between stream；Described exchange constraint equation is as follows:

$\left\{\begin{array}{c}{\stackrel{\·}{u}}_{f0\left(n\right)}^{+}=\left\{\begin{array}{c}\underset{i}{\mathrm{\σ}}(z_{\left[i\right]1}^{+}{\stackrel{.}{i}}_{\left[i\right]1}^{+}+y_{\left[i\right]s1}^{+}{\stackrel{.}{e}}_{\left[i\right]s});n=1\\ \underset{i}{\mathrm{\σ}}{z}_{\left[i\right]\left(n\right)}^{+}{\stackrel{.}{i}}_{\left[i\right]\left(n\right)}^{+};n\&notequal;1\end{array}\right.\\ {\stackrel{\·}{u}}_{f0\left(n\right)}^{-}=\underset{i}{\mathrm{\σ}}{z}_{\left[i\right]\left(n\right)}^{-}{\stackrel{.}{i}}_{\left[i\right]\left(n\right)}^{-}\end{array}\right.---\left(1\right)$

In formula (1),N equivalent positive sequence, negative sequence voltage source being respectively in fault sequence diagrams, For obtained according to AC system network structure and failure boundary condition during faultAC network sequence resistance during independent role It is anti-,For electromotive force of sourceAC network power frequency positive sequence admittance during independent role, n=1,2,3 ....

Further, formed the compound sequence network of short circuit after fault by fault type and transition resistance, further according to compound sequence Positive sequence, negative phase-sequence and the residual voltage of trouble point obtained by net:

$\left\{\begin{array}{c}{\stackrel{.}{u}}_{\left(n\right)}^{+}={\stackrel{.}{u}}_{f0\left(n\right)}^{+}-z_{\mathrm{\σ}\left(n\right)}^{+}{\stackrel{.}{i}}_{\left(n\right)}^{+}\\ {\stackrel{.}{u}}_{\left(n\right)}^{-}={\stackrel{.}{u}}_{f0\left(n\right)}^{-}-z_{\mathrm{\σ}\left(n\right)}^{-}{\stackrel{.}{i}}_{\left(n\right)}^{-}\\ {\stackrel{.}{u}}_{\left(n\right)}^0=z_{\mathrm{\σ}\left(n\right)}^0{\stackrel{.}{i}}_{\left(n\right)}^0\end{array}\right.---\left(2\right)$

In formula (2),WithIt is respectively n positive sequence, negative phase-sequence and the residual voltage of fault point； WithIt is respectively n positive sequence, negative phase-sequence and the zero sequence total impedance of compound sequence network,WithIt is respectively compound sequence N positive sequence of net, negative phase-sequence and zero-sequence current, the relation between three depends on the structure of compound sequence network.

Further, can be tried to achieve often by n positive sequence of the nodal method of analysis and fault point voltage, negative phase-sequence, zero sequence phasor Return change of current bus voltage:

$\left\{\begin{array}{c}{\stackrel{.}{u}}_{\left[i\right]\left(n\right)}^{+}=f_{\left[i\right]\left(n\right)+}\left({\stackrel{.}{u}}_{\left(n\right)}^{+}\right)\\ {\stackrel{.}{u}}_{\left[i\right]\left(n\right)}^{-}=f_{\left[i\right]\left(n\right)-}\left({\stackrel{.}{u}}_{\left(n\right)}^{-}\right)\\ {\stackrel{.}{u}}_{\left[i\right]\left(n\right)}^0=f_{\left[i\right]\left(n\right)0}\left({\stackrel{.}{u}}_{\left(n\right)}^0\right)\end{array}\right.---\left(3\right)$

In formula (3),WithBe expressed as n positive sequence of i-th time change of current busbar voltage, negative phase-sequence, Zero sequence phasor, f_[i](n)+、f_[i](n)-And f_[i](n)0Respectively represent n positive sequence of i-th time change of current busbar voltage, negative phase-sequence, zero sequence phasor and The functional relationship of n corresponding sequence phasor of fault point voltage.

Further, positive and negative for change of current bus, residual voltage can be converted to a, b, c tri- by the definition according to Park Transformation Phase voltage:

$\left\{\begin{array}{c}{\stackrel{.}{u}}_{\left[i\right]}^{+}=\underset{n}{\mathrm{\σ}}{\stackrel{.}{u}}_{\left[i\right]\left(n\right)}^{+}\\ {\stackrel{.}{u}}_{\left[i\right]}^{-}=\underset{n}{\mathrm{\σ}}{\stackrel{.}{u}}_{\left[i\right]\left(n\right)}^{-}\\ {\stackrel{.}{u}}_{\left[i\right]}^0=\underset{n}{\mathrm{\σ}}{\stackrel{.}{u}}_{\left[i\right]\left(n\right)}^0\end{array}\right.---\left(4\right)$

${\stackrel{.}{u}}_{\left[i\right]}=\left[\begin{array}{c}{\stackrel{.}{u}}_{\left[i\right]a}\\ {\stackrel{.}{u}}_{\left[i\right]b}\\ {\stackrel{.}{u}}_{\left[i\right]c}\end{array}\right]=\left[\begin{array}{ccc}1& 1& 1\\ a^2& a& 1\\ a& a^2& 1\end{array}\right]\left[\begin{array}{c}{\stackrel{.}{u}}_{\left[i\right]}^{+}\\ {\stackrel{.}{u}}_{\left[i\right]}^{-}\\ {\stackrel{.}{u}}_{\left[i\right]}^0\end{array}\right]---\left(5\right)$

In formula (5),For i-th change of current busbar voltage,It is respectively its a, b, c phase voltage, bag Containing fundamental wave and each harmonic component, a=e^j2π/3.

Further, direct current constraint side can be tried to achieve by the control strategy and control parameter of each direct current subsystem controller Journey:

$\left\{\begin{array}{c}{i}_{\left[i\right]d0}=f_{\left[i\right]d0}\left(u_{\left[i\right]d0}\right)\\ i_{\left[i\right]d\left(n\right)}=u_{\left[i\right]d\left(n\right)}/z_{\left[i\right]d\left(n\right)}\end{array}\right.---\left(6\right)$

In formula (6), i_[i]d0、u_[i]d0And f_[i]d0Represent DC current DC component, the direct current of i-th time straight-flow system respectively Voltage DC component, the control characteristic of controller；i_[i]d(n)、u_[i]d(n)And z_[i]d(n)Represent n unidirectional current of straight-flow system respectively Stream, DC voltage, harmonic impedance.

Preferably, in step (3), k is enumerator, represents interative computation number of times, when calculation error is unsatisfactory for requiring, K value adds 1；Variable containing subscript " (k) " represents the value of kth time computing, is Compact representations, in variable symbol, omits subscript “(k)”.

Preferably, in step (4), change of current busbar voltageComprise the information of a, b, c three-phase voltage, by phase voltage phase Subtract and can get line voltage, extract power frequency componentWithAgain by power frequency line voltage, DC current straight Flow component i_[1]d0And straight-flow system rectification side Trigger Angle α_[1], calculate the skew of synchronizing voltage phase placeConverter valve turn on delay angle θ_mn, actual Trigger Angle α_mnWith actual angle of overlap μ_mn.

IfWithRepresent α component and the β component of commutation voltage respectively, calculated by following formula:

$\left[\begin{array}{c}{\stackrel{.}{u}}_{\mathrm{\α}}\\ {\stackrel{.}{u}}_{\mathrm{\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -1/2& -1/2\\ 0& \sqrt{3}/2& -\sqrt{3}/2\end{array}\right]\left[\begin{array}{c}{\stackrel{.}{u}}_{\mathrm{ca}1}\\ {\stackrel{.}{u}}_{\mathrm{ab}1}\\ {\stackrel{.}{u}}_{\mathrm{bc}1}\end{array}\right]---\left(7\right)$

The phase place of DC control system synchronizing voltage can be tried to achieve using the α component of commutation voltage and β component

IfPhase angle bePhase angle bePhase angle beCan be counted by formula (9) Calculate the phase offset of synchronizing voltage

In formula (9),For the phase offset of ca phase and synchronizing voltage,Inclined with the phase place of synchronizing voltage for ab phase Move,Phase offset for bc phase and synchronizing voltage；

Turn on delay angle θ_mnComputing formula be:

In formula (10), mn=ab, bc, ca, wherein a, b, c represent the phase in three-phase respectively；

Actual Trigger Angle α_mnComputing formula be:

In formula (10) and (11), all angles are with delayed for just, being negative in advance；

Angle of overlap μ during the biphase commutation of mn_mnComputing formula be:

${\mathrm{\μ}}_{\mathrm{mn}}={\cos }^{-1}(\cos {\mathrm{\α}}_{\mathrm{mn}}-2x_r{i}_{\mathrm{dc}0}/{\stackrel{.}{u}}_{\mathrm{mn}1})-{\mathrm{\α}}_{\mathrm{mn}}---\left(12\right)$

In formula (12), x_rCommutating reactance for straight-flow system converting plant；

According to θ_mn、α_mnAnd μ_mnMake three-phase voltage current switching waveform, utilized in Fu by this three-phase voltage current waveform Leaf-size class number derives each order component of voltage x current switch function:

$\left\{\begin{array}{c}{\stackrel{.}{s}}_{\mathrm{uak}}=\frac{1}{t}{\&integral;}_0^t{s}_{\mathrm{ua}}{e}^{-\mathrm{jk\ω\τ}}\mathrm{d\τ}\\ {\stackrel{.}{s}}_{\mathrm{ubk}}=\frac{1}{t}{\&integral;}_0^t{s}_{\mathrm{ub}}{e}^{-\mathrm{jk\ω\τ}}\mathrm{d\τ}\\ {\stackrel{.}{s}}_{\mathrm{uck}}=\frac{1}{t}{\&integral;}_0^t{s}_{\mathrm{uc}}{e}^{-\mathrm{jk\ω\τ}}\mathrm{d\τ}\end{array}\right.---\left(13\right)$

$\left\{\begin{array}{c}{\stackrel{.}{s}}_{\mathrm{iak}}=\frac{1}{t}{\&integral;}_0^t{s}_{\mathrm{ia}}{e}^{-\mathrm{jk\ω\τ}}\mathrm{d\τ}\\ {\stackrel{.}{s}}_{\mathrm{ibk}}=\frac{1}{t}{\&integral;}_0^t{s}_{\mathrm{ib}}{e}^{-\mathrm{jk\ω\τ}}\mathrm{d\τ}\\ {\stackrel{.}{s}}_{\mathrm{ick}}=\frac{1}{t}{\&integral;}_0^t{s}_{\mathrm{ic}}{e}^{-\mathrm{jk\ω\τ}}\mathrm{d\τ}\end{array}\right.---\left(14\right)$

In formula (13) and (14),Be respectively three-phase voltage switch function k order component, k=0, 1,2,3 ..., t are 2 π；

Set up the order components of voltage x current switch functionWith

${\stackrel{.}{s}}_{i(n-m)}^{\&plusminus;}=\frac{1}{3}\left[\begin{array}{ccc}1& a& a^2\\ 1& a^2& a\end{array}\right]\left[\begin{array}{c}{\stackrel{.}{s}}_{\mathrm{ia}(n-m)}\\ {\stackrel{.}{s}}_{\mathrm{ib}(n-m)}\\ {\stackrel{.}{s}}_{\mathrm{ic}(n-m)}\end{array}\right]---\left(15\right)$

${\stackrel{.}{s}}_{u(m-n)}^{\&plusminus;}=\left[\begin{array}{ccc}{\stackrel{.}{s}}_{\mathrm{ua}(m-n)}& {\stackrel{.}{s}}_{\mathrm{ub}(m-n)}& {\stackrel{.}{s}}_{\mathrm{uc}(m-n)}\end{array}\right]\left[\begin{array}{cc}1& 1\\ a^2& a\\ a& a^2\end{array}\right]---\left(16\right)$

In formula (15) and (16),The m-n phasor for three-phase voltage switch function；For its positive and negative sequence component；The n-m phasor for three-phase current switch function；For its positive and negative sequence component；M=0,1,2,3 ....

Preferably, the relation of DC voltage in step (5), is tried to achieve by exchange change of current busbar voltage and voltage switch function Formula is:

${\stackrel{.}{u}}_{\left[1\right]d\left(m\right)}=\underset{n}{\mathrm{\σ}}\left[\begin{array}{cc}{\stackrel{.}{s}}_{\left[1\right]u(m-n)}^{+}& {\stackrel{.}{s}}_{\left[1\right]u(m-n)}^{-}\end{array}\right]\left[\begin{array}{c}{\stackrel{.}{u}}_{\left[1\right]\left(n\right)}^{+}\\ {\stackrel{.}{u}}_{\left[1\right]\left(n\right)}^{-}\end{array}\right]---\left(17\right)$

In formula (17),The m phasor for DC voltage；

In step (6), byTry to achieve m phasor of DC side electric current by formula (6)

In step (7), by the relational expression that DC current and current switch function try to achieve alternating current it is:

${\stackrel{.}{i}}_{\left[1\right]\left(n\right)}^{\&plusminus;}=\underset{m}{\mathrm{\σ}}{\stackrel{.}{s}}_{\left[1\right]i(n-m)}^{\&plusminus;}{\stackrel{.}{i}}_{\left[1\right]d\left(m\right)}---\left(18\right)$

In step (8), according to the method for the 1st time step (4) shown in change of current bus～(7), calculate remaining change of current respectively Bus and its alternating current of connected straight-flow system equivalent injection inverter

In step (9), according to exchange constraint equation and alternating currentTry to achieve change of current busbar voltage

Preferably, in step (10), by comparing the change of current busbar voltage fundamental frequency of kth time and+1 AC network of kth The error of component amplitude, and ask for max value of error, when maximum error meets calculating and requires, the knot of output+1 calculating of kth Really；When maximum error is unsatisfactory for calculating and requires, replace, with the result of+1 calculating of kth, the variate-value that kth time calculates, under carrying out Iterative calculation once.

The present invention compared with prior art, has the advantage that and beneficial effect:

1st, the object of study of the present invention is to feed out AC network containing multiple-circuit line system more, has filled up system containing multiple-circuit line The blank feeding out AC network calculation of fault aspect research of system, are the whole of the stable operation of modc system and its relay protection more Determine cooperation to lay a good foundation.

2nd, the present invention be can be analyzed to by modc system is carried out with positive and negative, zero sequence decomposition, the calculation of fault of modc system Positive and negative, three separate networks of zero sequence solve, and are conducive to improving computation rate.

3rd, the present invention considers DC control characteristic, and straight-flow system Practical Calculation parameter becomes with the difference of fault parameter Change, the fault transient feature being calculated by this method more conforms to practical situation, accuracy in computation is high.

4th, calculating speed of the present invention is fast, accuracy is high, is feeding out AC network calculation of fault containing multiple-circuit line system more And its setting value order aspect of relay protection has very strong engineering practical value.

Brief description

Fig. 1 is the flow chart of the present invention；

Fig. 2 is modc system equivalent circuit diagram of the present invention；

Fig. 3 (a)-Fig. 3 (c) is positive and negative, zero sequence diagrams after the modc system failure of the present invention；

Fig. 4 is 3 times direct current modc system model figures in the present embodiment；

Fig. 5 is the compound sequence network figure of single-phase earthing in the present embodiment；

Fig. 6 is cigre standard straight-flow system control characteristic curve in the present embodiment.

Specific embodiment

With reference to embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention do not limit In this.

Embodiment

As shown in figure 1, a kind of many direct currents considering DC control characteristic of the present invention feed out AC network fault calculation methods for transmission, Comprise the steps:

(1) systematic parameter, DC control strategy and its control parameter of modc system are inputted；

(2) AC system sequence diagrams are formed by ac grid system parameter and fault parameter, set up exchange constraint equation, by The control strategy of straight-flow system and control parameter form the direct current constraint equation between DC side DC voltage and DC current；

(3) make k=0, initial value is put to whole variables；

(4) make i=1, according to known 1st time change of current busbar voltageTry to achieve its power frequency line voltage WithAgain by the DC component of power frequency line voltage, DC currentAnd straight-flow system rectification side Trigger Angle α_[1], set up Voltage x current switch function model, obtains the switch function of voltage, electric currentWith

(5) by exchange side bus voltageWith voltage switch functionTry to achieve straight-flow system DC voltage

(6) according to direct current constraint equation and DC voltageTry to achieve DC current

(7) by DC side DC currentWith current switch functionTry to achieve straight-flow system to be injected into by inverter The equal currents of AC system

(8) i=2,3 ... ..., according to the method for the 1st time step (4) shown in change of current bus～(7), calculate remaining respectively and change Stream bus and its connected straight-flow system are injected into the equal currents of AC system by inverter

(9) according to exchange constraint equation and alternating currentTry to achieve change of current busbar voltage

(10) calculate respectivelyWithError, when maximum error is unsatisfactory for requiring, make k=k+1, repeat step (4) process of～(10)；When maximum error satisfaction requires, export the knot as calculation of fault for the variate-value of+1 computing of kth Really.

Fig. 2 is modc system equivalent circuit diagram, and in figure is designated as " [i] " parameter under containing represents the i-th change of current bus and its phase The even parameter corresponding to straight-flow system, similarly hereinafter.In Fig. 2, dc_[i]Represent i-th time DC transmission system,z_[i]s、z_[i]cRespectively For AC system equivalence electrical source voltage, system impedance, filtering and reactive power compensator impedance,For change of current busbar voltage, It is injected into the equal currents of AC system, z for straight-flow system by inverter_[ij]For i-th connection and between j-th strip change of current bus Winding thread impedance, equivalent circuit diagram as shown in Figure 2 can try to achieve AC system equivalent positive and negative, the zero sequence when f point breaks down Net figure, respectively as shown in Fig. 3 (a), Fig. 3 (b), Fig. 3 (c),Represent the change of current become zero sequence impedance, in figure contain above be designated as "+,-, 0 " parameter represent its corresponding positive sequence, negative phase-sequence, zero-sequence component, similarly hereinafter.

In the present embodiment, direct current constraint equation embodies the functional relationship between DC current and DC voltage, and direct current Voltage is related to change of current busbar voltage and switch function, that is, related to fault parameter, and therefore in the present invention, straight-flow system is actual Calculating parameter is as the difference of fault parameter and changes, rather than straight-flow system is considered as constant-current source or constant power load model mould Type, the fault transient feature being calculated by this method more conforms to practical situation.

The present embodiment is established based on pscad/emtdc and three feeds out AC network containing three times direct currents, AC-DC parameter with Gigre standard DC test system is reference, and the transient state parameter in the case of calculating various faults difference transition resistance is to verify this The correctness of the carried computational methods of literary composition, modc model is as shown in Figure 4.

In the diagram, the parameter of modc AC is:Unit kv；z_[1]s= z_[2]s=z_[3]s=4.78+j47.41, z_[1]c=z_[2]c=z_[3]c=4.28-j189.95, z_[12]=z_[13]=z_[23]=25, unit ω；AC system short-circuit ratio scr is 2.5.Three times straight-flow system operational factor is all consistent with control parameter, the parameter of DC side For: DC rated voltage 500kv, DC rated current 2ka, rectification side Trigger Angle α₀For 19.95 °.

The calculating of the present embodiment taking fundamental component as a example, the computational methods class of secondary and above harmonic component and fundamental component Seemingly, trouble point is arranged at the change of current one mother.

Obtain the original of system impedance, reactive power compensator and interconnection according to the sequence diagrams shown in Fig. 3 (a)-Fig. 3 (c) Positive and negative, Zero sequence parameter, current source is opened a way, voltage source short circuit, enters to carry out abbreviation to network, obtain exchange from the point of view of fault Positive sequence total impedance after electric network faultNegative phase-sequence total impedanceWith zero sequence total impedanceIts value is respectively 8.38+j21.53, 8.37+j21.93,5.19+j9.32.

According to superposition theorem, obtained by formula (1)WithFault sequence during effect The equivalent positive sequence total voltage of net figureObtain in the same mannerDuring effect, the equivalent negative phase-sequence of fault sequence diagrams is always electric PressureWith iterative processRenewal and change, but its functional relationship is to be determined by sequence diagrams , do not change with the renewal of equal currents.

After obtaining above parameter, the species according to fault forms the compound sequence network of short circuit, and, it is combined taking single-phase earthing as a example Sequence net as shown in figure 5, in Figure 5, r_fFor transition resistance, single-phase earthing compound sequence network is in series by positive and negative zero sequence, its negative phase-sequence, Zero-sequence current is all equal with forward-order current, and sequence diagrams as shown in Figure 5 and formula (2) can obtain the positive sequence voltage of trouble point Negative sequence voltageResidual voltageObtain the positive and negative residual voltage of every change of current bus, using formula (4) again by formula (3) (5) positive and negative residual voltage is converted to abc three-phase voltage.Line to line fault, line to line fault ground connection and three-phase shortcircuit computational methods Similar with single-phase earthing, difference is the structure slightly difference of its compound sequence network.

The control characteristic curve of cigre standard DC test model is as shown in fig. 6, its control strategy is: whole when one, normal Stream side Given current controller, inverter side determines γ₀Control, system operation is in o point；2nd, when alternating voltage declines very little, rectification side exists Given current controller effect is lower to be reduced α rapidly, as long as α is also not reaching to its upper limit α_minSo that it may so that electric current returns to adjusts Value, operating point is still in o point；3rd, alternating voltage decline is less, but α has reached its upper limit α_minWhen, rectification side is limited in determines α_minControl On yeast production line, the control of inverter side current deviation functions to, and inverter side is still to determine γ₀Control, but γ now₀Setting valve Also include controlling, by current deviation, the γ producing₀The increment at angle, operates inOn curve；4th, when voltage declines more, rectification Side is still to determine α_minControl, inverter side vdcol controls input, operates on ef curve；5th, when voltage declines a lot, rectification side is still For determining α_minControl, inverter side enters minimum current and limits and controls, and so that electric current is maintained at and determines current curve i_dOn=0.45, run ?On curve.Direct current constraint equation (perunit value) can be obtained by control characteristic:

$i_d=\left\{\begin{array}{c}-7.79u_d+8.8\cos {\mathrm{\&gamma;}}_0,0.8529<u_d\&le;1\\ 0.892u_d+\mathrm{0.089,0.4045}<u_d\&le;0.8529\\ \mathrm{0.45,0}<u_d\&le;0.4045\end{array}\right.---\left(19\right)$

In formula (19), γ₀Represent that straight-flow system inverter side closes the angle of rupture, be 15 ° during stable state, with DC current under failure condition Change, its expression formula is γ₀=133.65-118.65i_d.

Arranging whole variable initial values is steady-state operation value, and that is, change of current busbar voltage is DC voltage is u_d=1.0, DC current is i_d=1.0.

Progressively calculated according to step (4)～step (10), step-up error is that the relative of result of calculation is missed twice in front and back Difference is less than 0.001, calculates the result of calculation of this computational methods through successive ignition.

Example one: setting single-phase earthing, line to line fault, line to line fault ground connection and three-phase shortcircuit, take fault resistance equal For 30 ω, the positive sequence of stable state change of current bus, negative phase-sequence and residual voltage, this algorithm result of calculation and pscad/ after calculating fault The simulation result of emtdc simulation software is as shown in table 1.

Table 1 transition resistance is the result of calculation of different faults in the case of 30 ω

Example two: setting single-line to ground fault, take fault resistance to be respectively 10 ω, 30 ω, 50 ω and 100 ω, meter The positive sequence of stable state change of current bus, negative phase-sequence and residual voltage, this algorithm result of calculation and pscad/emtdc simulation software after calculation fault Simulation result as shown in table 2.

Result of calculation in the case of table 2 singlephase earth fault difference transition resistance

Knowable to upper Tables 1 and 2, this algorithm transition resistances different with same fault under the same transition resistance of different faults Under result of calculation and the equal very little of error between phantom simulation value, thus illustrate that this computational methods accuracy in computation is high, energy It is applied to various short troubles, and calculating speed is fast, is that a kind of stronger many direct currents of practicality feed out AC network calculation of fault Method.

Above-described embodiment is the present invention preferably embodiment, but embodiments of the present invention are not subject to above-described embodiment Limit, other any spirit without departing from the present invention and the change made under principle, modification, replacement, combine, simplify, All should be equivalent substitute mode, be included within protection scope of the present invention.

Claims (10)

1. under a kind of many direct currents considering DC control characteristic feed out AC network fault calculation methods for transmission it is characterised in that including State step:

(1) systematic parameter of input modc system, DC control strategy and its control parameter；

(2) AC system sequence diagrams are formed by ac grid system parameter and fault parameter, set up exchange constraint equation, by direct current The control strategy of system and control parameter form the direct current constraint equation between DC side DC voltage and DC current；

(3) make k=0, initial value is put to whole variables；

(4) make i=1, according to known 1st time change of current busbar voltageTry to achieve its power frequency line voltage WithAgain by DC component i of power frequency line voltage, DC current_[1]d0And straight-flow system rectification side Trigger Angle α_[1], set up electricity Current voltage switch function model, obtains the switch function of voltage, electric currentWith

(5) by the 1st time change of current busbar voltageWith voltage switch functionTry to achieve straight-flow system DC voltage

(6) according to direct current constraint equation and DC voltageTry to achieve DC current

(7) by DC side DC currentWith current switch functionTry to achieve straight-flow system and exchange is injected into by inverter The equal currents of system

(8) i=2,3 ... ..., according to the method for the 1st time step (4) shown in change of current bus～(7), calculate remaining change of current respectively female Line and its connected straight-flow system are injected into the equal currents of AC system by inverter

(9) according to exchange constraint equation and alternating currentTry to achieve change of current busbar voltage

(10) calculate respectivelyWithError, when maximum error is unsatisfactory for requiring, make k=k+1, repeat step (4)～ (10) process；When maximum error satisfaction requires, export the result as calculation of fault for the variate-value of+1 computing of kth.

2. the many direct currents considering DC control characteristic according to claim 1 feed out AC network fault calculation methods for transmission, its It is characterised by, in step (2), according to the structure and parameter of modc system, and fault parameter forms and is applied to calculation of fault AC system sequence diagrams with exchange constraint equation, the control strategy according to straight-flow system and control parameter form DC current with straight The direct current constraint equation of stream change in voltage；Exchange constraint equation and direct current constraint equation specify that between AC voltage, electric current and Functional relationship between DC voltage, electric current；Described exchange constraint equation is as follows:

$\left\{\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{f0\left(n\right)}^{+}=\left\{\begin{array}{cc}\underset{i}{\mathrm{\&sigma;}}\left(z_{\&lsqb;i\&rsqb;1}^{+}{\stackrel{\&centerdot;}{i}}_{\&lsqb;i\&rsqb;1}^{+}+y_{\&lsqb;i\&rsqb;s1}^{+}{\stackrel{\&centerdot;}{e}}_{\&lsqb;i\&rsqb;s}\right);& n=1\\ \underset{i}{\mathrm{\&sigma;}}{z}_{\&lsqb;i\&rsqb;\left(n\right)}^{+}{\stackrel{\&centerdot;}{i}}_{\&lsqb;i\&rsqb;\left(n\right)}^{+};& n\&notequal;1\end{array}\right.\\ {\stackrel{\&centerdot;}{u}}_{f0\left(n\right)}^{-}=\underset{i}{\mathrm{\&sigma;}}{z}_{\&lsqb;i\&rsqb;\left(n\right)}^{-}{\stackrel{\&centerdot;}{i}}_{\&lsqb;i\&rsqb;\left(n\right)}^{-}\end{array}\right.---\left(1\right)$

In formula (1),N equivalent positive sequence, negative sequence voltage source being respectively in fault sequence diagrams,For fault When obtained according to AC system network structure and failure boundary conditionAC network sequence impedance during independent role, For electromotive force of sourceAC network power frequency positive sequence admittance during independent role, n=1,2,3 ....

3. the many direct currents considering DC control characteristic according to claim 2 feed out AC network fault calculation methods for transmission, its It is characterised by, formed the compound sequence network of short circuit after fault by fault type and transition resistance, obtain fault further according to compound sequence network The positive sequence of point, negative phase-sequence and residual voltage:

$\left\{\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\left(n\right)}^{+}={\stackrel{\&centerdot;}{u}}_{f0\left(n\right)}^{+}-z_{\mathrm{\&sigma;}\left(n\right)}^{+}{\stackrel{\&centerdot;}{i}}_{\left(n\right)}^{+}\\ {\stackrel{\&centerdot;}{u}}_{\left(n\right)}^{-}={\stackrel{\&centerdot;}{u}}_{f0\left(n\right)}^{-}-z_{\mathrm{\&sigma;}\left(n\right)}^{-}{\stackrel{\&centerdot;}{i}}_{\left(n\right)}^{-}\\ {\stackrel{\&centerdot;}{u}}_{\left(n\right)}^0=z_{\mathrm{\&sigma;}\left(n\right)}^0{\stackrel{\&centerdot;}{i}}_{\left(n\right)}^0\end{array}\right.---\left(2\right)$

In formula (2),WithIt is respectively n positive sequence, negative phase-sequence and the residual voltage of fault point； WithIt is respectively n positive sequence, negative phase-sequence and the zero sequence total impedance of compound sequence network,WithIt is respectively n time of compound sequence network Positive sequence, negative phase-sequence and zero-sequence current, the relation between three depends on the structure of compound sequence network.

4. the many direct currents considering DC control characteristic according to claim 2 feed out AC network fault calculation methods for transmission, its It is characterised by, every time change of current bus can be tried to achieve by n positive sequence of the nodal method of analysis and fault point voltage, negative phase-sequence, zero sequence phasor Voltage:

$\left\{\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;\left(n\right)}^{+}=f_{\&lsqb;i\&rsqb;\left(n\right)+}\left({\stackrel{\&centerdot;}{u}}_{\left(n\right)}^{+}\right)\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;\left(n\right)}^{-}=f_{\&lsqb;i\&rsqb;\left(n\right)-}\left({\stackrel{\&centerdot;}{u}}_{\left(n\right)}^{-}\right)\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;\left(n\right)}^0=f_{\&lsqb;i\&rsqb;\left(n\right)0}\left({\stackrel{\&centerdot;}{u}}_{\left(n\right)}^0\right)\end{array}\right.---\left(3\right)$

In formula (3),WithIt is expressed as n positive sequence of i-th time change of current busbar voltage, negative phase-sequence, zero sequence phase Amount, f_[i](n)+、f_[i](n)-And f_[i](n)0Represent n positive sequence of i-th go back to change of current busbar voltage, negative phase-sequence, zero sequence phasor and trouble point respectively The functional relationship of n corresponding sequence phasor of voltage.

5. the many direct currents considering DC control characteristic according to claim 2 feed out AC network fault calculation methods for transmission, its It is characterised by, according to the definition of Park Transformation, positive and negative for change of current bus, residual voltage can be converted to a, b, c three-phase voltage:

$\left\{\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}^{+}=\underset{n}{\&sigma;}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;\left(n\right)}^{+}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}^{-}=\underset{n}{\&sigma;}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;\left(n\right)}^{-}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}^0=\underset{n}{\&sigma;}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;\left(n\right)}^0\end{array}\right.---\left(4\right)$

${\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}=\left[\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;a}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;b}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;c}\end{array}\right]=\left[\begin{array}{ccc}1& 1& 1\\ a^2& a& 1\\ a& a^2& 1\end{array}\right]\left[\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}^{+}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}^{-}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;i\&rsqb;}^0\end{array}\right]---\left(5\right)$

In formula (5),For i-th time change of current busbar voltage,It is respectively its a, b, c phase voltage, comprise base Ripple and each harmonic component, a=e^j2π/3.

6. the many direct currents considering DC control characteristic according to claim 2 feed out AC network fault calculation methods for transmission, its It is characterised by, direct current constraint equation can be tried to achieve by the control strategy of each direct current subsystem controller and control parameter:

$\left\{\begin{array}{c}{i}_{\&lsqb;i\&rsqb;d0}=f_{\&lsqb;i\&rsqb;d0}\left(u_{\&lsqb;i\&rsqb;d0}\right)\\ i_{\&lsqb;i\&rsqb;d\left(n\right)}=u_{\&lsqb;i\&rsqb;d\left(n\right)}/z_{\&lsqb;i\&rsqb;d\left(n\right)}\end{array}\right.---\left(6\right)$

In formula (6), i_[i]d0、u_[i]d0And f_[i]d0Represent DC current DC component, the DC voltage of i-th time straight-flow system respectively DC component, the control characteristic of controller；i_[i]d(n)、u_[i]d(n)And z_[i]d(n)Respectively represent straight-flow system n DC current, DC voltage, harmonic impedance.

7. the many direct currents considering DC control characteristic according to claim 1 feed out AC network fault calculation methods for transmission, its It is characterised by, in step (3), k is enumerator, represents interative computation number of times, when calculation error is unsatisfactory for requiring, k value adds 1；Variable containing subscript " (k) " represents the value of kth time computing, is Compact representations, in variable symbol, omits subscript " (k) ".

8. the many direct currents considering DC control characteristic according to claim 1 feed out AC network fault calculation methods for transmission, its It is characterised by, in step (4), change of current busbar voltageComprise the information of a, b, c three-phase voltage, subtracted each other and can be obtained by phase voltage To line voltage, extract power frequency componentWithAgain by the DC component of power frequency line voltage, DC current i_[1]d0And straight-flow system rectification side Trigger Angle α_[1], calculate the skew of synchronizing voltage phase placeThe change of current Valve turn on delay angle θ_mn, actual Trigger Angle α_mnWith actual angle of overlap μ_mn；

IfWithRepresent α component and the β component of commutation voltage respectively, calculated by following formula:

$\left[\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\mathrm{\&alpha;}}\\ {\stackrel{\&centerdot;}{u}}_{\mathrm{\&beta;}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -1/2& -1/2\\ 0& \sqrt{3}/2& -\sqrt{3}/2\end{array}\right]\left[\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{ca1}\\ {\stackrel{\&centerdot;}{u}}_{ab1}\\ {\stackrel{\&centerdot;}{u}}_{bc1}\end{array}\right]---\left(7\right)$

The phase place of DC control system synchronizing voltage can be tried to achieve using the α component of commutation voltage and β component

IfPhase angle bePhase angle bePhase angle beSynchronization can be calculated by formula (9) The phase offset of voltage

In formula (9),For the phase offset of ca phase and synchronizing voltage,For the phase offset of ab phase and synchronizing voltage,Phase offset for bc phase and synchronizing voltage；

Turn on delay angle θ_mnComputing formula be:

In formula (10), mn=ab, bc, ca, wherein a, b, c represent the phase in three-phase respectively；

Actual Trigger Angle α_mnComputing formula be:

In formula (10) and (11), all angles are with delayed for just, being negative in advance；

Angle of overlap μ during mn biphase commutation_mnComputing formula be:

${\mathrm{\&mu;}}_{mn}={\cos }^{-1}({\mathrm{cos\&alpha;}}_{mn}-2x_r{i}_{dc0}/{\stackrel{\&centerdot;}{u}}_{mn1})-{\mathrm{\&alpha;}}_{mn}---\left(12\right)$

In formula (12), x_rCommutating reactance for straight-flow system converting plant；i_dc0Represent the DC component of DC side electric current；

According to θ_mn、α_mnAnd μ_mnMake three-phase voltage current switching waveform, Fourier's level is utilized by this three-phase voltage current waveform Several each order components deriving voltage x current switch function:

$\left\{\begin{array}{c}{\stackrel{\&centerdot;}{s}}_{uak}=\frac{1}{t}{\&integral;}_0^t{s}_{ua}{e}^{-jk\mathrm{\&omega;}\mathrm{\&tau;}}d\mathrm{\&tau;}\\ {\stackrel{\&centerdot;}{s}}_{ubk}=\frac{1}{t}{\&integral;}_0^t{s}_{ub}{e}^{-jk\mathrm{\&omega;}\mathrm{\&tau;}}d\mathrm{\&tau;}\\ {\stackrel{\&centerdot;}{s}}_{uck}=\frac{1}{t}{\&integral;}_0^t{s}_{uc}{e}^{-jk\mathrm{\&omega;}\mathrm{\&tau;}}d\mathrm{\&tau;}\end{array}\right.---\left(13\right)$

$\left\{\begin{array}{c}{\stackrel{\&centerdot;}{s}}_{iak}=\frac{1}{t}{\&integral;}_0^t{s}_{ia}{e}^{-jk\mathrm{\&omega;}\mathrm{\&tau;}}d\mathrm{\&tau;}\\ {\stackrel{\&centerdot;}{s}}_{ibk}=\frac{1}{t}{\&integral;}_0^t{s}_{ib}{e}^{-jk\mathrm{\&omega;}\mathrm{\&tau;}}d\mathrm{\&tau;}\\ {\stackrel{\&centerdot;}{s}}_{ick}=\frac{1}{t}{\&integral;}_0^t{s}_{ic}{e}^{-jk\mathrm{\&omega;}\mathrm{\&tau;}}d\mathrm{\&tau;}\end{array}\right.---\left(14\right)$

In formula (13) and (14),Be respectively three-phase voltage switch function k order component, k=0,1,2, 3 ..., t are 2 π；

Set up the order components of voltage x current switch functionWith

${\stackrel{\&centerdot;}{s}}_{i(n-m)}^{\&plusminus;}=\frac{1}{3}\left[\begin{array}{ccc}1& a& a^2\\ 1& a^2& a\end{array}\right]\left[\begin{array}{c}{\stackrel{\&centerdot;}{s}}_{ia(n-m)}\\ {\stackrel{\&centerdot;}{s}}_{ib(n-m)}\\ {\stackrel{\&centerdot;}{s}}_{ic(n-m)}\end{array}\right]---\left(15\right)$

${\stackrel{\&centerdot;}{s}}_{u(m-n)}^{\&plusminus;}=\left[\begin{array}{ccc}{\stackrel{\&centerdot;}{s}}_{ua(m-n)}& {\stackrel{\&centerdot;}{s}}_{ub(m-n)}& {\stackrel{\&centerdot;}{s}}_{uc(m-n)}\end{array}\right]\left[\begin{array}{cc}1& 1\\ a^2& a\\ a& a^2\end{array}\right]---\left(16\right)$

In formula (15) and (16),The m-n phasor for three-phase voltage switch function； For its positive and negative sequence component；The n-m phasor for three-phase current switch function；For it Positive and negative sequence component；M=0,1,2,3 ....

9. the many direct currents considering DC control characteristic according to claim 1 feed out AC network fault calculation methods for transmission, its It is characterised by, in step (5), by the relational expression that the 1st time change of current busbar voltage and voltage switch function try to achieve DC voltage be:

${\stackrel{\&centerdot;}{u}}_{\&lsqb;1\&rsqb;d\left(m\right)}=\underset{n}{\&sigma;}\left[\begin{array}{cc}{\stackrel{\&centerdot;}{s}}_{\&lsqb;1\&rsqb;u(m-n)}^{+}& {\stackrel{\&centerdot;}{s}}_{\&lsqb;1\&rsqb;u(m-n)}^{-}\end{array}\right]\left[\begin{array}{c}{\stackrel{\&centerdot;}{u}}_{\&lsqb;1\&rsqb;\left(n\right)}^{+}\\ {\stackrel{\&centerdot;}{u}}_{\&lsqb;1\&rsqb;\left(n\right)}^{-}\end{array}\right]---\left(17\right)$

In formula (17),The m phasor for DC voltage；

In step (6), byTry to achieve m phasor of DC side electric current by formula (6)

In step (7), by the relational expression that DC current and current switch function try to achieve alternating current it is:

${\stackrel{\&centerdot;}{i}}_{\&lsqb;1\&rsqb;\left(n\right)}^{\&plusminus;}=\underset{m}{\&sigma;}{\stackrel{\&centerdot;}{s}}_{\&lsqb;1\&rsqb;i(n-m)}^{\&plusminus;}{\stackrel{\&centerdot;}{i}}_{\&lsqb;1\&rsqb;d\left(m\right)}---\left(18\right)$

In step (8), according to the method for the 1st time step (4) shown in change of current bus～(7), calculate remaining change of current bus respectively And its alternating current of connected straight-flow system equivalent injection inverter

In step (9), according to exchange constraint equation and alternating currentTry to achieve change of current busbar voltage

10. the many direct currents considering DC control characteristic according to claim 1 feed out AC network fault calculation methods for transmission, its It is characterised by, in step (10), by comparing the change of current busbar voltage fundamental component width of kth time and+1 AC network of kth The error of value, and asks for max value of error, when maximum error meets calculating and requires, the result of output+1 calculating of kth；When When big error is unsatisfactory for calculating and requires, replace, with the result of+1 calculating of kth, the variate-value that kth time calculates, carry out next time Iterative calculation.