CN105808958A - Direct-current short-circuit calculation and analysis method considering actual control and protection properties - Google Patents

Abstract

The invention provides a direct-current short-circuit calculation and analysis method considering actual control and protection properties. The method comprises the steps of determining change stages of a direct-current system towards an injected short-circuit current on an alternating-current side within a time period from an occurrence moment of an alternating-current three-phase short-circuit fault to a removal moment of the fault; obtaining end time of each change stage; calculating a rise rate of the injected short-circuit current; and constructing a calculation model of the injected short-circuit current. Compared with the prior art, the direct-current short-circuit calculation and analysis method considering the actual control and protection properties, provided by the invention, considers an electromagnetic transient process of the direct-current system after occurrence of the three-phase short-circuit fault on the alternating-current side and can be suitable for calculating alternating-current-side three-phase short-circuit currents in various actual ultra high-voltage direct-current transmission projects.

Description

Consider that the direct-current short circuit calculation and analysis methods of characteristic is protected in reality control

Technical field

The present invention relates to technical field of ultrahigh voltage direct current, be specifically related to a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control.

Background technology

International Electrotechnical Commission IEC60909 and American National Standards Institute (ANSI) (AmericanNationalStandardsInstitute, ANSI) have ignored AC system in calculation of short-circuit current standard to be short-circuited the straight-flow system contribution to short circuit current after fault, existing domestic and international short-circuit current calculation program PSS/E, BPA etc. also have ignored the straight-flow system contribution to short circuit current when calculating.But, along with DC transmission system is at the development construction of China, the electrical network feature that the many feed-ins of direct current, direct current transmission capacity accounting increase is progressively notable, if still can ignore the straight-flow system contribution to short circuit current becomes a problem demanding prompt solution.In electric power system fault, although the chance that three phase short circuit fault occurs is less, but its situation is more serious, and is the basis of research other types short trouble, it is therefore desirable to give enough attention.

During for AC generation three phase short circuit fault, DC transmission system contributes mechanism and the computational methods of short circuit current, rarely has research both at home and abroad at present, and correlational study work mostly is the alternating current-direct current combined hybrid system fault simulation analysis based on electromagnetic transients program.These work can be subdivided into several aspect: (1) sets up the dynamic model of Traditional DC inverter, is integrated into by DC converter during the time-domain-simulation of AC system calculates, but and is not concerned with the calculating of short circuit current；(2) set up based on the DC transmission system mathematical model of switch function and asymmetric order components, and simulation analysis when carrying out alternating current-direct current combined hybrid system generation AC fault, but it is left out the transient characterisitics after fault.

More than study the steady-state characteristic all only focusing on straight-flow system after a period of time occurs fault, the less research of electro-magnetic transient characteristic in the short time after fault is occurred.

Summary of the invention

In order to meet the needs of prior art, the invention provides a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control.

The technical scheme is that

Described method includes:

Determine that straight-flow system injects the changes phase of short circuit current i (t) to AC within AC three-phase short trouble generation moment to the time period of Failure elimination；Described changes phase includes first stage, second stage, phase III and fourth stage；

The end time T of described second stage, phase III, fourth stage is obtained respectively by emulating described AC three-phase short trouble₁、T₂、T₃, clearing time of fault T₄, and within the described first stage maximum I of described injection short circuit current i (t)_dmax；

According to described end time T₁、T₂、T₃With the maximum I injecting short circuit current_dmax, calculate the climbing speed K of described injection short circuit current i (t) within the described first stage；

According to described end time T₁、T₂、T₃, inject short circuit current maximum I_dmaxWith the computation model that climbing speed K builds described injection short circuit current i (t).

The preferred embodiment that the present invention further provides is:

Described first stage and second stage are the linearly ascent stage of described injection short circuit current i (t)；

The described phase III is the exponentially decling phase of described injection short circuit current i (t)；

Described fourth stage is the linearly decline stage of described injection short circuit current i (t).

The preferred embodiment that the present invention further provides is: the computing formula of the climbing speed K of described injection short circuit current i (t) is:

$K=\frac{I_{dmax}-B_r{I}_{Ndc}/n}{T_1}---\left(1\right)$

Wherein, B_rFor the sum of converter bridge, I_NdcDC current during for stable operation, n is converter power transformer no-load voltage ratio.

The preferred embodiment that the present invention further provides is: the expression formula of the computation model of described injection short circuit current i (t) is:

$i\left(t\right)=\left\{\begin{array}{cc}\frac{B_r{I}_{Ndc}}{n}+K\&times;t& 0<t<T_1\\ I_{d\max }{e}^{-\frac{t-T_1}{L_T/R_T}}& T_1\&le;t<T_2\\ I_{d\max }{e}^{-\frac{T_2-T_1}{L_T/R_T}}\&times;\left(\frac{T_3-t}{T_3-T_2}\right)& T_2\&le;t<T_3\\ 0& T_3\&le;t<T_4\end{array}\right.---\left(2\right)$

Wherein, B_rFor the sum of converter bridge, I_NdcDC current during for stable operation, L_TFor converter power transformer leakage reactance inductance, R_TFor converter power transformer copper loss resistance, n is converter power transformer no-load voltage ratio.

Compared with immediate prior art, the invention has the beneficial effects as follows:

1, a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control provided by the invention, consider the electromagnetic transient of straight-flow system after AC generation three phase short circuit fault, it is possible to the AC Three-phase Short-circuit Current suitable in various actual extra-high voltage direct-current transmission engineerings is calculated；

2, a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control provided by the invention, the process that calculates is simple, convenient to be used, it is possible to provides basis for the work such as lectotype selection, protection seting, is conducive to improving AC/DC Power System failure analysis methods.

Accompanying drawing explanation

Fig. 1: a kind of direct-current short circuit calculation and analysis methods flow chart considering that characteristic is protected in actual control in the embodiment of the present invention；

Fig. 2: the equivalent circuit diagram of inverter and converter power transformer in the embodiment of the present invention；

Fig. 3: DC current and converter power transformer secondary a phase current waveform schematic diagram during three-phase alternating current short trouble in the embodiment of the present invention；

Wherein, 1: the first converter valve；2: the second converter valve；3: the three converter valve: 4: the four converter valve；5: the five converter valve；6: the six converter valve；7: first stage and second stage；8: the phase III；9: fourth stage；10: the stage repeatedly.

Detailed description of the invention

For making the purpose of the embodiment of the present invention, technical scheme and advantage clearly, below in conjunction with the accompanying drawing in the embodiment of the present invention, technical scheme in the embodiment of the present invention is illustrated clearly and completely, obviously, described embodiment is a part of embodiment of the present invention, rather than whole embodiments.Based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art obtain under not making creative work premise, broadly fall into the scope of protection of the invention.

Separately below in conjunction with accompanying drawing, a kind of direct-current short circuit calculation and analysis methods considering actual control guarantor's characteristic that the embodiment of the present invention is provided illustrates.

Fig. 1 is a kind of direct-current short circuit calculation and analysis methods flow chart considering that characteristic is protected in actual control in the embodiment of the present invention, as shown in the figure, in the present embodiment, the direct-current short circuit calculation and analysis methods of the actual control guarantor's characteristic of this consideration considers the change procedure of actual DC electro-magnetic transient, and it concretely comprises the following steps:

Step S101: determine that straight-flow system injects the changes phase of short circuit current i (t) to AC within AC three-phase short trouble generation moment to the time period of Failure elimination.

In the present embodiment, changes phase includes first stage, second stage, phase III and fourth stage.Wherein:

First stage and second stage are inject the linearly ascent stage of short circuit current i (t), phase III, fourth stage was inject the linearly decline stage of short circuit current i (t) in order to inject the exponentially decling phase of short circuit current i (t).

Fig. 2 is the equivalent circuit diagram of inverter and converter power transformer in the embodiment of the present invention, as it can be seen, DC transmission system inverter side is comparatively sensitive to AC fault, fault in ac transmission system frequently can lead to inverter side generation commutation failure.Also just because of this characteristic of inverter side, existing research is often thought and is formed short circuit path thus having isolated ac and dc systems by converter valve generation commutation failure after inverter side fault in ac transmission system.But, the short circuit path of converter valve is not along with the generation of fault is formed immediately.Owing to the control system of actual DC engineering being integrated with commutation failure forecast function, fall monitoring inverter side alternating voltage or angle of flow α after imbalance, can be reduced, the triggering signal making converter valve arrives in advance, and DC current rises the fastest stage after this stage fault just, the induced voltage that in inductance, curent change produces is that converter valve provides commutation voltage so that it is can be triggered when triggering signal and arriving and enter commutation process.In order to after studying inverter side fault in ac transmission system, straight-flow system contributes the mechanism of short circuit current, it is necessary for the transient process of straight-flow system generation commutation failure after fault is analyzed.Suppose in the present embodiment that AC three-phase short trouble occurs moment the 3rd converter valve 3 and the 4th converter valve 4 to turn on, then each changes phase that straight-flow system injects short circuit current i (t) to AC is:

1, the first stage

When in the present embodiment, fault occurs, converter power transformer secondary current is:

$\left\{\begin{array}{c}{i}_a=i_d\\ i_b=-i_d\\ i_c=0\end{array}\right.---\left(1\right)$

2, second stage

After in the present embodiment, fault occurs, AC voltage drops to zero, and commutation failure prediction work opens effect, and the 5th converter valve 5 triggers signal and arrives in advance, and this up-to-date style (1) is still set up, due to DC current i_dRise, then exist:

$\left\{\begin{array}{c}{u}_b-u_n=L\frac{{\mathrm{di}}_b}{dt}<0\\ u_c-u_n=0\end{array}\right.---\left(2\right)$

The voltage that 5th converter valve 5 is born is:

u_v5=u_c-u_b> 0 (3)

Due in inductance curent change and the induced voltage that produces is that the 5th converter valve provides commutation voltage, it is made to trigger the commutation process of entrance and the 3rd converter valve 3 after signal arrives, now the 3rd converter valve the 3, the 4th converter valve 4 and the 5th converter valve 5 simultaneously turn on, and converter power transformer secondary current is:

$\left\{\begin{array}{c}{i}_a=i_d\\ i_b+i_c=-i_d\\ {\mathrm{di}}_b={\mathrm{di}}_c\end{array}\right.---\left(4\right)$

3, the phase III

In the present embodiment similar with second stage, the triggering signal of the 6th converter valve 6 also arrives in advance, now the 6th converter valve 6 bears forward voltage, making to trigger the 6th converter valve 6 after signal arrives and enter commutation course, now the 3rd converter valve the 3, the 4th converter valve the 4, the 5th converter valve 5 and the 6th converter valve 6 simultaneously turn on.3rd converter valve 3 and the 6th converter valve 6 simultaneously turn on rear U_d=0, the 4th converter valve 4 place branch road is shorted, but owing to there is inductance composition on the 4th converter valve 4 place branch road, in inductance, electric current can not suddenly change, and now there is following relation:

$\left\{\begin{array}{c}{L}_T\frac{{\mathrm{di}}_{v4}}{dt}+R_T{i}_{v4}=0\\ i_{v6}=i_d-i_{v4}\end{array}\right.---\left(5\right)$

Solved by formula (5):

$i_{v4}=I_{v40}{e}^{-(R_T/L_T)t}---\left(6\right)$

Wherein, I_v40It is the 6th converter valve 6 i when turning on_v4Instantaneous value.Through type (6) can go to top, although inverter side commutation failure causes that a certain brachium pontis forms short circuit path after three phase short circuit fault, but the DC component still suffering from a decay injects AC system.

4, fourth stage

DC current i after fault generation in the present embodiment_dReduce under the adjustment effect of rectification side Given current controller again after rising rapidly, if i_dDecrease speed compares i_v4The rate of decay fast, then work as i_dDrop to and i_v4After equal, i_v6Dropping to zero makes the 6th converter valve 6 turn off, and the 3rd converter valve the 3, the 4th converter valve 4 and the 5th converter valve 5 simultaneously turn on individual, shown in converter power transformer secondary current such as formula (4), now meet following relation:

$\left\{\begin{array}{c}{i}_{v4}=i_d\\ i_{v6}=0\end{array}\right.---\left(7\right)$

Fig. 3 is DC current and converter power transformer secondary a phase current waveform schematic diagram during three-phase alternating current short trouble in the embodiment of the present invention, as it can be seen, solid line is DC current i_d, dotted line is a phase current i_a.Above-mentioned analysis according to each changes phase that straight-flow system is injected to AC short circuit current i (t), can obtain, AC three-phase short trouble occur after straight-flow system be injected into the short circuit current of AC first in first stage and second stage 7 along with DC current i_dRise and rise, then decay according to damping time constant in the phase III 8, facing to DC current i in fourth stage 9_dDrop to zero, wherein there is a DC current i in fourth stage_dStage 10 repeatedly.

According to formula (1)～(7), with variable each shown in Fig. 3, it may be determined that defective device straight-flow system is injected the A of AC and to the expression formula of short circuit current is:

$i_A\left(t\right)=\left\{\begin{array}{cc}\frac{B_r{i}_d\left(t\right)}{n}& 0<t<T_1\\ \frac{B_r{i}_d\left(T_1\right)}{n}{e}^{-\frac{t-T_1}{L_T/R_T}}& T_1\&le;t<T_2\\ \frac{B_r{i}_d\left(t\right)}{n}& T_2\&le;t<T_3\\ 0& T_3\&le;t<T_4\end{array}\right.---\left(8\right)$

Wherein, 0～T₁For time first stage, T₁～T₂For second stage time, T₂～T₃For time phase III, T₄For clearing time of fault.

Step S102: obtain the end time T of second stage, phase III, fourth stage by emulating AC three-phase short trouble respectively₁、T₂、T₃, clearing time of fault T₄, and within the first stage, inject the maximum I of short circuit current i (t)_dmax。

The nonlinear elements such as the existence PI control due to straight-flow system, and the impact of long distance transmission line distribution capacity, circuit traveling wave, it is impossible to obtain accurately end time T₁、T₂、T₃With DC current i_dAnalytical expression, it is therefore desirable to end time T₁、T₂、T₃With DC current i_dInfluence factor be analyzed, so that it is determined that end time T₁、T₂、T₃、T₄With DC current i_d。

(1) when three phase short circuit fault occurs:

By commutation failure forecast function, after three phase short circuit fault occurs, inverter side angle of flow α reduces rapidly, the time that when therefore although fault occurs, valve group has turned within this cycle different (each valve group each cycle turns on 120 °), but after fault occurs, next one triggering signal all arrives rapidly, next makes the triggering time of arrival (toa) of bridgc arm short also be determined by commutation failure forecast function.Therefore, T₁Value is determined by the parameter of commutation failure forecast function, to same system T₁Value is basically unchanged.

(2) after three phase short circuit fault occurs:

Starting stage after three phase short circuit fault, inverter side DC voltage drops to zero, inverter side controls system and loses the control ability to DC current, and due to high voltage DC engineering transmission distance often more than 1000 kilometers, now rectification side not yet detects that fault occurs, the current instruction value of rectification side Given current controller not yet changes, therefore starting stage i after fault_dChange mainly determined by line parameter circuit value, to same system, i_dThe climbing speed of starting stage is constant after a failure, and then it compares I_NdcThe variation delta I of (DC current during stable operation)_dT () (DC current variable quantity) is also constant.

(3) after three phase short circuit fault is transferred to rectification side:

After fault is delivered to rectification side, rectification side DC voltage declines, after it drops to the activation threshold value of VDCOL link, and the I of rectification side Given current controller_ord(current instruction value) begins to decline with the decline of DC voltage, until reducing to I_omin(minimum current command value).Considering that DC control system responds quick feature, after VDCOL action, DC current declines rapidly, and this decline process can be approximated to be linearly, and T₂、T₃In succession arriving also with the triggering of VDCOL link, its concrete value is by the voltage threshold of VDCOL link, minimum current command value, and the gain coefficient of Given current controller, proportionality coefficient determine.Thus can be approximately considered for same system T₂、T₃Also essentially identical, and T₂To T₃Between i_dIt is approximately and linearly declines.

By above-mentioned analysis it was determined that for same straight-flow system: when controlling parameter and determining, after fault, straight-flow system injects each time point T of AC short circuit current₁、T₂、T₃Can be approximately considered and remain unchanged；Fault starting stage DC current i_dVariable quantity be also held essentially constant, therefore fault starting stage DC current i_dMainly there is its initial value to determine, namely determined by direct current transmission power.

Step S103: according to end time T₁、T₂、T₃With the maximum I injecting short circuit current_dmax, calculate the climbing speed K injecting short circuit current i (t) within the first stage.

The computing formula of the climbing speed K injecting short circuit current i (t) in the present embodiment is:

$K=\frac{I_{dmax}-B_r{I}_{Ndc}/n}{T_1}---\left(9\right)$

Wherein, B_rFor the sum of converter bridge, I_NdcDC current during for stable operation.

Owing to, in Practical Project, DC transmission system often adopts team design, the line parameter circuit value of DC transmission system and control parameter etc. are in operation and often no longer change.Therefore in practical application, K, T₁、T₂、T₃Value can determine according to the detailed model fault simulation of real system: emulated by three phase short circuit fault under typical condition, obtain the maximum I of straight-flow system contribution short circuit current under this transmission power_dmax, and each material time point T after fault₁、T₂、T₃Representative value, and according to formula (9) release K value.K, the T obtained accordingly₁、T₂、T₃Value can be used for the three phase short circuit fault under other operating mode and calculates.Certainly, these parameters also can obtain in the design phase through emulation and provide as systematic parameter.

Step S104: according to end time T₁、T₂、T₃, inject short circuit current maximum I_dmaxThe computation model injecting short circuit current i (t) is built with climbing speed K.

In the present embodiment fault occur after first stage and second stage in DC current linearly rise according to climbing speed k is approximate.All identical for different transmission powers this climbing speed k, and the line parameter circuit value that given by real system of the value of climbing speed k and control systematic parameter and determine, therefore first stage and second stage straight-flow system are injected AC short circuit current and can also be:

$i_A\left(t\right)=\frac{B_r(I_{Ndc}+k\&times;t)}{n}=\frac{B_r{I}_{Ndc}}{n}+K\&times;t---\left(10\right)$

Wherein,

Inject the maximum I of short circuit current_dmaxComputing formula be:

$I_{d\max }=\frac{B_r{I}_{Ndc}}{n}+K\&times;T_1---\left(11\right)$

In phase III, straight-flow system injection AC short circuit current can also be:

$i_A\left(t\right)=I_{dmax}{e}^{-\frac{t-T_1}{L_T/R_T}}---\left(12\right)$

In fourth stage, straight-flow system injection AC short circuit current can also be:

$i_A\left(t\right)=I_{dmax}{e}^{-\frac{T_2-T_1}{L_T/R_T}}\&times;\left(\frac{T_3-t}{T_3-T_2}\right)---\left(13\right)$

By above-mentioned analysis, it may be determined that the present invention injects the expression formula of the computation model of short circuit current i (t) and is:

$i\left(t\right)=\left\{\begin{array}{cc}\frac{B_r{I}_{Ndc}}{n}+K\&times;t& 0<t<T_1\\ I_{d\max }{e}^{-\frac{t-T_1}{L_T/R_T}}& T_1\&le;t<T_2\\ I_{d\max }{e}^{-\frac{T_2-T_1}{L_T/R_T}}\&times;\left(\frac{T_3-t}{T_3-T_2}\right)& T_2\&le;t<T_3\\ 0& T_3\&le;t<T_4\end{array}\right.---\left(14\right)$

Wherein, B_rFor the sum of converter bridge, I_NdcDC current during for stable operation, L_TFor converter power transformer leakage reactance inductance, R_TFor converter power transformer copper loss resistance, n is converter power transformer no-load voltage ratio.

One of ordinary skill in the art will appreciate that all or part of flow process realizing in above-described embodiment method, can be by the hardware that computer program carrys out instruction relevant to complete, described program can be stored in a computer read/write memory medium, this program is upon execution, it may include such as the flow process of the embodiment of above-mentioned each side method.Wherein, described storage medium can be magnetic disc, CD, read-only store-memory body (Read-Only, ROM) or random store-memory body (RandomAccessMemory, RAM) etc..

A kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control in the embodiment of the present invention, consider the electromagnetic transient of straight-flow system after AC generation three phase short circuit fault, it is possible to the AC Three-phase Short-circuit Current suitable in various actual extra-high voltage direct-current transmission engineerings is calculated.

Obviously, the present invention can be carried out various change and modification without deviating from the spirit and scope of the present invention by those skilled in the art.So, if these amendments of the present invention and modification belong within the scope of the claims in the present invention and equivalent technologies thereof, then the present invention is also intended to comprise these change and modification.

Claims (4)

1. one kind considers that the direct-current short circuit calculation and analysis methods of characteristic is protected in actual control, it is characterised in that described method includes:

Determine that straight-flow system injects the changes phase of short circuit current i (t) to AC within AC three-phase short trouble generation moment to the time period of Failure elimination；Described changes phase includes first stage, second stage, phase III and fourth stage；

The end time T of described second stage, phase III, fourth stage is obtained respectively by emulating described AC three-phase short trouble₁、T₂、T₃, clearing time of fault T₄, and within the described first stage maximum I of described injection short circuit current i (t)_dmax；

According to described end time T₁、T₂、T₃With the maximum I injecting short circuit current_dmax, calculate the climbing speed K of described injection short circuit current i (t) within the described first stage；

According to described end time T₁、T₂、T₃, inject short circuit current maximum I_dmaxWith the computation model that climbing speed K builds described injection short circuit current i (t).

2. a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control as claimed in claim 1, it is characterised in that

Described first stage and second stage are the linearly ascent stage of described injection short circuit current i (t)；

The described phase III is the exponentially decling phase of described injection short circuit current i (t)；

Described fourth stage is the linearly decline stage of described injection short circuit current i (t).

3. a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control as claimed in claim 1, it is characterised in that the computing formula of the climbing speed K of described injection short circuit current i (t) is:

$K=\frac{I_{dmax}-B_r{I}_{Ndc}/n}{T_1}---\left(1\right)$

Wherein, B_rFor the sum of converter bridge, I_NdcDC current during for stable operation, n is converter power transformer no-load voltage ratio.

4. a kind of direct-current short circuit calculation and analysis methods considering that characteristic is protected in actual control as claimed in claim 1, it is characterised in that the expression formula of the computation model of described injection short circuit current i (t) is:

$i\left(t\right)=\left\{\begin{array}{cc}\frac{B_r{I}_{Ndc}}{n}+K\&times;t& 0<t<T_1\\ I_{dmax}{e}^{-\frac{t-T_1}{L_T/R_T}}& T_1\&le;t<T_2\\ I_{d\max }{e}^{-\frac{T_2-T_1}{L_T/R_T}}\&times;\left(\frac{T_3-t}{T_3-T_2}\right)& T_2\&le;t<T_3\\ 0& T_3\&le;t<T_4\end{array}\right.---\left(2\right)$

Wherein, B_rFor the sum of converter bridge, I_NdcDC current during for stable operation, L_TFor converter power transformer leakage reactance inductance, R_TFor converter power transformer copper loss resistance, n is converter power transformer no-load voltage ratio.