CN104267288A - HVDC commutation failure fault diagnosis method based on valve voltages or valve currents - Google Patents

Abstract

The invention discloses an HVDC commutation failure fault diagnosis method based on valve voltages or valve currents. The method comprises the following steps that a commutation failure mechanism and commutation failure influence factors are analyzed; commutation failure process analysis is carried out, and a commutation failure criterion is determined; an HVDC model contravariant side equivalent circuit is built, and a commutation failure critical inductance value is determined; whether the diagnosis result is accurate or not is verified through simulation. According to the fast commutation failure diagnosis method based on the converter valve voltages or the valve currents, the theoretical analysis and stimulation result proves the accuracy and effectiveness of the method, no blind diagnosis area exists, and the method is simple in theory and easy to implement, and has certain project application value.

Description

Based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current

Technical field

The present invention relates to a kind of HVDC commutation failure method for diagnosing faults based on threshold voltage or valve electric current.

Background technology

HVDC relies on the advantages such as transmission capacity is large, high, the asynchronous contact ability of power adjustments rapid flexible, reliability is strong, plays more and more important effect in recent years in long-distance and large-capacity power transmission and large regions Power System Interconnection ^[1-3].Commutation failure is one of modal peculiar fault of HVDC system, the consequences such as DC voltage is fallen, DC current is uprushed, the reduction of direct current transmission power can be caused, if control measure timely and effectively cannot be taked, also can cause follow-up commutation failure, or even direct current locking, and then threaten the safe and stable operation of whole ac and dc systems ^[4-5].

The quick and precisely diagnosis of commutation failure is the prerequisite taking effective control measure.Document [6] thinks to only have when extinguish angle is less than intrinsic limit extinguish angle, and valve current continuity, threshold voltage are when being zero continuously, just commutation failure can occur, but this viewpoint is too conservative, in principle, commutation failure can be judged as when meeting any one in three conditions; Document [7] has been derived the computing formula causing the minimum voltage needed for commutation failure to land under symmetrical and asymmetric fault in detail, but this critical value is under the infinitely-great prerequisite of supposition AC system, metastable state equation based on transverter draws, have ignored in derivation between age at failure that voltage waveform distortion is on the impact of commutation failure, accuracy is poor; Document [8] is analyzed commutation process in conjunction with angle of overlap, has drawn the quantitative relationship of commutation voltage time and area and commutation failure, but its supposition commutation voltage is sine value, and between age at failure, DC current and Trigger Angle are definite value; Document [9] is pointed out by the wavelet analysis to DC current and change of current busbar voltage, not only can the generation of efficient diagnosis commutation failure, the fault type causing commutation failure can also be distinguished, but its threshold value and the setting of criterion are relevant to the structure and parameter of system, method comparison is complicated, and Project Realization difficulty is large.

Wherein, list of references is:

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[2] Wu Ping, Lin Weifang, Sun Huadong, etc. Multi-infeed HVDC transmission system commutation failure mechanism and characteristic [J]. electric power network technique, 2012,36 (5): 269-273.

Wu?Ping，Lin?Weifang，Sun?Huadong，et?al.Research?and?electromechanical?transient?simulation?on?mechanism?of?commutation?failure?in?multi-infeed?HVDC?power?transmission?system[J].Power?System?Technology，2012，36(5)：269-273(in?Chinese).

[3] Shao Yao, Tang Yong, Guo Xiaojiang, waits .2015 extra-high voltage to plan the commutation failure analysis [J] of electrical network North China and East China Multi-infeed HVDC transmission system. electric power network technique, 2011,35 (10): 9-15.

Shao?Yao，Tang?Yong，Guo?Xiaojiang，et?al.Analysis?on?commutation?failures?in?multi-infeed?HVDC?transmission?systems?in?North?China?and?East?China?power?grids?planned?for?UHV?power?grids?in2015[J].Power?System?Technology，2011，35(10)：9-15(in?Chinese).

[4] Shao Yao, Tang Yong. adopt many feed-ins interaction factor to judge the method [J] of commutation failure of high voltage direct current system. Proceedings of the CSEE, 2012,32 (4): 108-114.

Shao?Yao，Tang?Yong.A?commutation?failure?detection?method?for?HVDC?systems?based?on?muti-infeed?interaction?factors[J].Proceedings?of?the?CSEE，2012，32(4)：108-114(in?Chinese).

[5]Changchun?Z，Zheng?X.Study?on?commutation?failure?of?multi-infeed?HVDC?system[C]//Proceedings?of?International?Conference?on?Power?System?Technology.Kunming：IEEE/PES，2002：2462-2466.

[6] He Chaorong, Li Xingyuan, golden Xiao Ming, etc. the simulation analysis [J] of Commutation Failure Criteria for HVDC Transmission Systems. electric power network technique, 2007,31 (1): 20-23.

He?Chaorong，Li?Xingyuan，Jin?Xiaoming，et?al.Simulation?analysis?on?commutation?failure?criteria?for?HVDC?transmission?systems[J].Power?System?Technology，2007，31(1)：20-23(in?Chinese).

[7]Thio?C?V，Davies?J?B，Kent?K?L.Commutation?failures?in?HVDC?transmission?system[J].IEEE?Trans?on?Power?Delivery，1996，11(2)：946-957.

[8] Wang Gang, Li Zhikeng, Huang Min, waits the fault close angle Influencing Mechanism [J] of .HVDC transmission system commutation failure. Automation of Electric Systems, 2010,34 (4): 49-54.

Wang?Gang，Li?Zhikeng，Huang?Min，et?al.Influence?of?initial?fault?voltage?angle?on?commutation?failure?identification?in?a?HVDC?system[J].Automation?of?Electric?Power?System，2010，34(4)：49-54(in?Chinese).

[9] Lin Lingxue, Zhang Yao, Zhong Qing, etc. based on the HVDC commutation failure fault diagnosis [J] of wavelet energy statistics method. Automation of Electric Systems, 2007,31 (23): 61-63.

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Summary of the invention

The present invention is in order to solve the problem, propose a kind of HVDC commutation failure method for diagnosing faults based on threshold voltage or valve electric current, this method analyzes mechanism and the process of commutation failure, from the essential characteristic of commutation failure, and carried out detailed simulation analysis based on the HVDC model that MATLAB provides, the accuracy of simulation results show the method and validity.

To achieve these goals, the present invention adopts following technical scheme:

Based on a HVDC commutation failure method for diagnosing faults for threshold voltage or valve electric current, comprise the following steps:

(1) commutation failure mechanism and commutation failure influence factor is analyzed;

(2) carry out commutation failure process analysis procedure analysis, determine commutation failure criterion;

(3) set up HVDC model inverter side equivalent electrical circuit, determine commutation failure threshold inductance value;

(4) whether simulating, verifying diagnostic result is correct.

In described step (1), after commutation failure refers to that two brachium pontis of transverter terminate commutation, the valve just having exited conducting is between reverse voltage action period, if forward blocking ability fails to recover, or commutation process is failed to carry out complete always, then threshold voltage be changed to positive to time, all switched phase by the original predetermined valve exiting conducting by the valve of commutation.

In described step (1), commutation failure can cause the valve that should turn off to continue conducting, should the valve breakdown of conducting, makes transverter form dc-side short-circuit when next valve is opened, thus causes falling of DC voltage and uprushing of DC current; The probability of inverter generation commutation failure is greater than rectifier, and rectifier only just commutation failure can occur when trigger circuit fault.

In described step (1), the extinguish angle of inverter is less than the intrinsic limit extinguish angle γ of converter valve _mintime can there is commutation failure, wherein γ _minthat in Thyristor, Carrier recombination switch sets up P-N junction restraining barrier to recover the forward voltage blocking ability necessary time, its size and thyristor relating to parameters, and increase along with the increase of the voltage put on thyristor, electric current, corresponding electrical angle gets 7 ~ 10 °.

In described step (1), the factor of commutation failure comprises: receiving end fault in ac transmission system, control system pulse are abnormal, gating advance angle β or extinguish angle γ setting value is too small, converter valve short circuit and DC current increase, for Multi-infeed HVDC transmission system, also comprise the electrical couplings relation between Inverter Station.

In described step (2), commutation failure invariably accompanies the constant conduction of some valve, each valve only conducting 120 ° under normal circumstances, and the duration is at least a cycle, show as that corresponding threshold voltage is continuously zero, valve continuing current flow non-zero keep higher magnitude, for 1.5-2.5 rated current doubly, it can be used as the essential characteristic of commutation failure, simultaneously owing to being easy to measure threshold voltage and valve electric current, therefore propose threshold voltage to be continuously zero or valve continuing current flow non-zero as the new criterion of commutation failure, namely threshold voltage is continuously the time t of zero _uor the time t of valve continuing current flow non-zero _iwhen meeting following relation, judge to there occurs commutation failure:

Wherein, f is AC system fundamental frequency.

In described step (3), when HVDC inverter side change of current bus breaks down, the computing formula causing the minimum voltage needed for commutation failure to fall is:

$\mathrm{\ΔU}=1-\frac{I_d^{\′}}{I_d}\frac{X_{\mathrm{cpu}}}{X_{\mathrm{cpu}}+\cos {\mathrm{\γ}}_0-\cos \mathrm{\γ}}$

Wherein, I _dand I _d' represent DC current during rated direct current and Voltage Drop, X respectively _cpufor the equivalent commutating reactance that perunit value represents, γ ₀inverter extinguish angle setting valve when representing intrinsic limit extinguish angle respectively with γ and normally run.

In described step (3), set up HVDC model inverter side equivalent electrical circuit, change of current busbar voltage is replaced with minimum voltage and falls value, calculating threshold inductance value is:

$\frac{1-0.96(1-\mathrm{\ΔU})}{X_{\mathrm{eq}}}+\frac{0.96(1-\mathrm{\ΔU})}{X_{\mathrm{ceq}}}=\frac{0.96(1-\mathrm{\ΔU})}{X_f}$

Wherein, X _eqrepresent receiving end AC system equivalent reactance, X _ceqrepresent the capacitive reactance of the reactive-load compensator of change of current bus parallel connection, X _ffor the fault reactance of three-phase ground fault.

In described step (4), use MATLAB to carry out the emulation of inverter side change of current bus three-phase fault, inverter side change of current bus single-phase fault, verify.

Beneficial effect of the present invention is:

Commutation failure fault is the most common failure of D.C. high voltage transmission, and risk factor is many, failure effect is serious (one pole or bi-pole protection block), therefore accurately judges that whether the generation of this fault is the important research content of high-voltage dc transmission electrical domain always.This invention, by analyzing the mechanism of inverter generation commutation failure fault, extracts the phenomena typical after this fault " threshold voltage be continuously zero, valve continuing current flow non-zero ", and then proposes the new criterion of commutation failure fault diagnosis.This invention has good reference value to the control and scheduling co-design improving DC engineering, and has following technological merit:

(1) this invention proposes based on the essential characteristic of commutation failure, not by factors such as electrical couplings relations between fault type, commutation voltage wave form distortion, many feed-ins Inverter Station, and the impact of extinguish angle calculation deviation and the non-definite value of intrinsic limit extinguish angle, there is not diagnosis blind area, can not judge by accident, have higher accuracy;

(2) Diagnostic Time of this invention is 20ms, is less than 40ms-80ms actuation time of general quick protection, easily realizes coordinating with the effective of protective device;

(3) this inventive principle is simple, only need carry out the comparison in time scale to threshold voltage or valve electric current, and threshold voltage and valve electric current directly can be obtained by measurement, and therefore the present invention is easy to realize, and has higher engineer applied to be worth.

Accompanying drawing explanation

Fig. 1 is 6 pulsation inverter key wiring diagrams of the present invention;

Fig. 2 is Commutation Failure oscillogram of the present invention;

Fig. 3 is HVDC inverter side equivalent circuit diagram of the present invention;

Fig. 4 is extinguish angle oscillogram of the present invention;

Fig. 5 is DC voltage of the present invention, dc current waveform figure;

Fig. 6 is threshold voltage oscillogram of the present invention;

Fig. 7 is valve current waveform figure of the present invention;

Fig. 8 is DC voltage of the present invention, dc current waveform figure;

Fig. 9 is emulation threshold voltage oscillogram of the present invention;

Figure 10 is emulation valve current waveform figure of the present invention;

Figure 11 is inverter side change of current busbar voltage oscillogram of the present invention;

Figure 12 is DC voltage of the present invention, dc current waveform figure;

Figure 13 is threshold voltage oscillogram of the present invention;

Figure 14 is valve current waveform figure of the present invention.

Embodiment:

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

1 commutation failure mechanism

1.1 commutation failure

After commutation failure refers to that two brachium pontis of transverter terminate commutation, the valve just having exited conducting is between reverse voltage action period, if forward blocking ability fails to recover, or commutation process is failed to carry out complete always, then threshold voltage be changed to positive to time, all switched phase by the original predetermined valve exiting conducting by the valve of commutation.The valve that should turn off will be caused like this to continue conducting, should the valve breakdown of conducting, make transverter form dc-side short-circuit when next valve is opened, thus cause falling of DC voltage and uprushing of DC current.The probability of inverter generation commutation failure is far longer than rectifier, and rectifier only just commutation failure can occur when trigger circuit fault.

In other words, the extinguish angle of inverter is less than the intrinsic limit extinguish angle γ of converter valve _mintime just can there is commutation failure, wherein γ _minthat in Thyristor, Carrier recombination switch sets up P-N junction restraining barrier to recover the forward voltage blocking ability necessary time, its size and thyristor relating to parameters, and increase along with the increase of the voltage put on thyristor, electric current, corresponding electrical angle gets about 7 ~ 10 ° usually.

1.2 commutation failure influence factors

Extinguish angle γ is and the electric parameters of converter valve and external circuit condition

Be closely related, itself and gating advance angle β, inverter side DC current I _d, equivalent commutating reactance X _c, inverter side change of current bus line voltage effective value U _lfollowing relation is met with converter power transformer no-load voltage ratio k:

$\mathrm{\γ}=\arccos (\frac{\sqrt{2}k{I}_d{X}_c}{U_L}+\cos \mathrm{\β})---\left(1\right)$

When AC system generation unbalanced fault causes commutation voltage zero crossing reach φ, meet:

$\mathrm{\γ}=\arccos (\frac{\sqrt{2}k{I}_d{X}_c}{U_L}+\cos \mathrm{\β})-\mathrm{\φ}---\left(2\right)$

In conjunction with above-mentioned formula and HVDC practical operating experiences known, make

Become commutation failure because of have receiving end fault in ac transmission system, control system pulse abnormal (as pulse daley, pulse missing, false triggering etc.), gating advance angle β or extinguish angle γ setting value is too small, converter valve short circuit, DC current increase etc., the change of current busbar voltage that wherein receiving end fault in ac transmission system causes declines and zero crossing to offset be the main cause causing commutation failure.In addition, for Multi-infeed HVDC transmission system, the electrical couplings relation between Inverter Station be also the multiple Inverter Station of impact whether simultaneously or the key factor of commutation failure occurs in succession.

2 commutation failure criterions

Commutation failure is the coefficient result of many factors, and there is interaction between each factor, the relation between commutation failure and other factors is drawn under the hypothesis that some factor is constant, the inevitable error easily caused in judgement, and consider that all factors are unpractiaca, therefore only have the criterion by reflection commutation failure essential characteristic, could realize diagnosing fast and accurately.

Although extinguish angle determining method embodies the essence of commutation failure, namely extinguish angle is less than intrinsic limit extinguish angle, also be the most frequently used method of current diagnosis commutation failure, but should be noted the problem of following two aspects: one is that the extinguish angle of converter valve in engineering reality cannot be surveyed, can only be drawn by operational factor indirect calculation such as the DC current of straight-flow system, change of current busbar voltages, therefore cannot the real change of real-time follow-up extinguish angle; Two are intrinsic limit extinguish angles is not definite value, but relevant to the voltage and current of the intrinsic parameter of thyristor and applying.In view of the reason of these two aspects, in some situation, as under commutation failure critical conditions, adopt extinguish angle determining method may cause erroneous judgement.Therefore, the criterion setting up new reflection commutation failure essential characteristic is needed.

2.1 commutation failure process analysis procedure analyses

Fig. 1 is the key wiring diagram of 6 pulsation inverters, wherein, and V ₁~ V ₆for 6 converter valve of conducting successively in the normal order, u _a, u _b, u _cbe respectively the fundamental frequency phase voltage of equivalent AC system, i _a, i _b, i _cbe respectively three-phase alternating current, L _cfor every equal value commutation inductance, be mainly the leakage reactance of converter power transformer, L _dfor the inductance of smoothing reactor.

With V shown in Fig. 2 ₁to V ₃commutation be that example is analyzed, wherein C ₁~ C ₆represent line voltage zero-cross point, i.e. converter valve V ₁~ V ₆triggering zero point, P _ifor the converter valve V of correspondence _itrigger instants.If V ₃trigger instants angle of overlap μ is comparatively large, makes V ₁fail to recover forward voltage blocking ability during reverse voltage, then after threshold voltage zero crossing, V ₁meeting conducting again, makes V ₃switch to V ₁, V ₃turn off in the A moment; When angle of overlap is excessive, even arrive C ₆moment V ₁to V ₃commutation process all failed, with that from V ₃switch to V ₁.Switch after terminating mutually, V ₁and V ₂the conducting of meeting maintenance, if do not take commutation failure control measure, then by the original order each valve of triggering following successively, at V ₄after triggering and conducting, V will be passed through ₁and V ₄form inverter direct-flow side short circuit, cause DC voltage and the instantaneous of direct current transmission power to fall, and the uprushing of DC current.At P ₅moment, V ₅cannot open because bearing reverse voltage, until V ₄success commutation is to V ₆time, dc-side short-circuit just can disappear.If after this no longer there is commutation failure, then HVDC can return to normal operation voluntarily.In this failure process, V ₁the time of constant conduction is a cycle, and be 3 times when normally running, the electrical angle that dc-side short-circuit is corresponding is 120 ° of+μ.

By the restriction of the regulator response such as electric current and extinguish angle time, after inverter direct-flow side short circuit 120 ° usually, direct-current short circuit electric current still can not be controlled completely, and therefore the angle of overlap of inverter still can be very large, make V ₄to V ₆commutation failed equally, dc-side short-circuit will exist.General peak value of short occurs during a cycle after commutation failure, is about the rated current of 2 times.Until about 50ms after dc-side short-circuit, DC current could control at setting valve or zero by the current regulator of rectification side.After this, V ₆or V ₃triggering and conducting, thus remove dc-side short-circuit.

If V ₁to V ₃commutation failure after, V ₂to V ₄commutation failed equally, i.e. twice continuous commutation failure, then V ₁and V ₂by nearly for a continuous conducting cycle, continuous reverse voltage 180 °, the reduction of inverter back electromotive force also can cause the reduction of DC voltage and the increase of DC current.

2.2 commutation failure criterions

As the above analysis, V ₁to V ₃after commutation failure, if V ₄success conducting, then pass through V ₁and V ₄form dc-side short-circuit, usually will continue about about 50ms, V ₁and V ₄conducting will be kept in a long time; If V ₄same commutation failure, considers the response time of all kinds of regulator, then V ₁and V ₂by at least one cycle of continuous conducting.

Therefore, commutation failure invariably accompanies the constant conduction (each valve only conducting 120 ° under normal circumstances) of some valve, and the duration is at least a cycle, show as that corresponding threshold voltage is continuously zero, valve continuing current flow non-zero keep higher magnitude, be about the rated current of 2 times, two other essential characteristic of commutation failure can be it can be used as, simultaneously because the measurement of threshold voltage and valve electric current is very easy, therefore propose threshold voltage to be continuously zero or valve continuing current flow non-zero as the new criterion of commutation failure, namely threshold voltage is continuously the time t of zero _uor the time t of valve continuing current flow non-zero _ican judge to there occurs commutation failure when meeting following relation:

Wherein, f is AC system fundamental frequency.In addition, the method can demonstrate the converter valve that commutation failure occurs intuitively.

3 fault simulation analyses

The determination of 3.1 commutation failure threshold inductance values

The one pole 12 pulsation HVDC model that simulation analysis provides based on MATLAB, its rated voltage is 500kV, and rated current is 2kA, and direct current transmission power is 1000MW.

Fault in ac transmission system mainly comprises symmetric fault and unbalanced fault, and modal fault form is inductive grounding short circuit.During HVDC inverter side change of current bus generation three-phase ground fault, the computing formula causing the minimum voltage needed for commutation failure to fall is:

$\mathrm{\ΔU}=1-\frac{I_d^{\′}}{I_d}\frac{X_{\mathrm{cpu}}}{X_{\mathrm{cpu}}+\cos {\mathrm{\γ}}_0-\cos \mathrm{\γ}}---\left(4\right)$

Wherein, I _dand I _d' represent DC current during rated direct current and Voltage Drop, X respectively _cpufor the equivalent commutating reactance that perunit value represents, γ ₀inverter extinguish angle setting valve when representing intrinsic limit extinguish angle respectively with γ and normally run.X in this model _cpu, γ ₀be respectively 0.24,8 ° and 18 ° with the value of γ, assuming that when DC current is constant before and after Voltage Drop, the Voltage Drop critical value Δ U=14.04% of commutation failure can be caused.

Figure 3 shows that HVDC model inverter side equivalent circuit diagram, wherein X _eqrepresenting receiving end AC system equivalent reactance, is 13.18 Ω; X _ceqrepresenting the capacitive reactance of the reactive-load compensator of change of current bus parallel connection, is 555.6 Ω; X _ffor the fault reactance of three-phase ground fault.Change of current busbar voltage U during normal operation _l=0.96E, then, when change of current busbar voltage falls value Δ U=14.04%, when can calculate inverter side change of current bus three-phase ground fault according to formula (5), cause the critical reactance value X of commutation failure _f=55.92 Ω, corresponding threshold inductance value is 0.18H.DC current I during supposing Voltage Drop when considering and calculate Δ U _d' be ratings, therefore this result of calculation is less than normal than actual threshold inductance value.

$\frac{1-0.96(1-\mathrm{\ΔU})}{X_{\mathrm{eq}}}+\frac{0.96(1-\mathrm{\ΔU})}{X_{\mathrm{ceq}}}=\frac{0.96(1-\mathrm{\ΔU})}{X_f}---\left(5\right)$

3.2 inverter side change of current bus three-phase faults

In order to verify the accuracy of commutation failure method for diagnosing faults under various fault of proposition, choose typical three-phase and single-phase fault herein as analysis example.

First arrange three-phase electricity perception earth fault to inverter side change of current bus, fault initial time is 0.6s, duration 0.05s, and fault inductance gets 0.2H, and slightly larger than calculating gained critical value, simulation time 1.2s, result as shown in Figure 4 to 7.

As shown in Figure 4, inverter side extinguish angle minimum value between age at failure is 6.2 °, according to extinguish angle criterion, then thinks that commutation failure occurs HVDC, and the phenomenon that after there is no commutation failure in Fig. 5, DC voltage drops to zero, DC current is uprushed, contradict with extinguish angle determining method conclusion; Threshold voltage, the valve current waveform of inverter side Y bridge 6 converter valve shown in further analysis chart 6 or Fig. 7 are known, each valve is conducting successively in the normal order, ON time is 120 °, earth fault only causes threshold voltage and valve electric current numerically slightly to fluctuate, do not occur that threshold voltage is continuously zero, valve continuing current flow non-zero keep the situation of higher magnitude, do not meet the commutation failure criterion that formula (3) provides, therefore there is not commutation failure in HVDC, and this conclusion is consistent with the DC voltage in Fig. 5 and current waveform.

Extinguish angle determining method is subject to the impact of extinguish angle calculation deviation and the non-definite value of intrinsic limit extinguish angle, there is certain diagnosis blind area, erroneous judgement can be caused near commutation failure critical conditions, by contrast, according to threshold voltage or valve current waveform diagnosis commutation failure, there is higher accuracy.

By three-phase electricity perception earth fault fault inductance value be decreased to 0.1H, all the other fault parameters and simulation parameter the same, gained simulation result is as shown in Fig. 8 ~ Figure 10.

Fig. 9 shows that the voltage of valve 1 and valve 4 is continuously zero between age at failure, duration about two cycles; The electric current that Figure 10 shows valve 1 and valve 4 continues non-zero and keeps higher magnitude, duration equally about two cycles between age at failure, and the instantaneous maximal value of valve electric current occurs being about the rated current of 2 times by about 20ms after a failure.Threshold voltage or valve current waveform all show valve 1 and valve 4 constant conduction after a failure, and threshold voltage is continuously the time t of zero _uor the time t of valve continuing current flow non-zero _imeet the commutation failure criterion in formula (3), therefore judge that commutation failure occurs HVDC, this also drops to zero with DC voltage in Fig. 8, phenomenon that DC current is uprushed is consistent.

Further to threshold voltage and valve amperometry known, fault occur the moment, V ₂to V ₄commutation just complete, V ₄conducting, its threshold voltage reduces to zero, and valve electric current is increased to DC current by zero, and because inverter side change of current bus three-phase ground fault causes inverter back electromotive force to reduce, therefore DC current is now than large under nominal situation.After 60 ° of electrical angles, V ₃to V ₅success commutation.The increase of DC current and the reduction of inverter side commutation voltage increase angle of overlap, cause V between reverse voltage action period ₄to V ₆commutation process failed, i.e. commutation failure, makes V ₄continuation is kept conducting.Along with V ₅to V ₁successful commutation, pass through V ₁and V ₄form dc-side short-circuit, V ₁and V ₄valve electric current, namely DC current continues to increase compared with the fault starting stage, close to the DC current ratings of 2 times.Subsequently, V ₂cannot open owing to bearing reverse voltage, V ₁to V ₃commutation unsuccessful equally, cause within the time being greater than a cycle afterwards, V ₁and V ₄continue to keep conducting, until fault clearance.In this failure process, V ₁and V ₄simultaneously the time of constant conduction, namely the dc-side short-circuit time is about 2 cycles.

3.3 inverter side change of current bus single-phase faults

Arrange single-phase inductive earth fault to inverter side change of current bus, for A phase, fault initial time is 0.6s, duration 0.05s, and fault inductance value is 0.1H, and simulation time 1.2s, acquired results is as shown in Figure 11 ~ Figure 14.

The change of current of inverter side shown in Figure 11 bus three-phase voltage waveform shows, A phase inductance earth fault result in the distortion of three-phase voltage waveform, and commutation voltage is no longer sinusoidal wave.Figure 13 shows threshold voltage between age at failure and is continuously zero, Figure 14 and shows valve continuing current flow non-zero and keep higher magnitude, t _uor t _imeet commutation failure criterion, can draw the conclusion of commutation failure, the situation of change of DC voltage shown in this with Figure 12, DC current is consistent.

Contrast fault inductance value is 0.1H, when all the other simulation parameters are identical with fault parameter, DC voltage, DC current, threshold voltage and valve current waveform in inverter side change of current bus three-phase fault and single-phase fault two kinds of situations are known, in three-phase fault situation, namely direct current returns to specified running status at 0.8s, and the release time namely after fault clearance only has about 0.15s; And direct current is when 1.2s just close to specified running status in single-phase fault situation, the release time after fault clearance reaches 0.55s.This illustrates that the wave form distortion of change of current busbar voltage is the key factor affecting commutation failure, and the impact ignoring voltage waveform distortion in minimum voltage landing method is irrational.

4 conclusions

(1) the inevitable constant conduction along with some valve of commutation failure, except extinguish angle is less than intrinsic limit extinguish angle, threshold voltage is continuously zero, valve continuing current flow non-zero keep higher magnitude to can be used as the essential characteristic of commutation failure equally.

(2) extinguish angle determining method is subject to the impact of extinguish angle calculation deviation and the non-definite value of intrinsic limit extinguish angle, can cause erroneous judgement in commutation failure critical conditions situation.

(3) method based on converter valve voltage or valve electric current quick diagnosis commutation failure is proposed, the accuracy of theoretical analysis and simulation results show the method and validity, there is not diagnosis blind area, and the method principle is simple, be easy to realize, there is certain engineer applied and be worth.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (9)

1., based on a HVDC commutation failure method for diagnosing faults for threshold voltage or valve electric current, it is characterized in that: comprise the following steps:

(1) commutation failure mechanism and commutation failure influence factor is analyzed;

(2) carry out commutation failure process analysis procedure analysis, determine commutation failure criterion;

(3) set up HVDC model inverter side equivalent electrical circuit, determine commutation failure threshold inductance value;

(4) whether simulating, verifying diagnostic result is correct.

2. as claimed in claim 1 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (1), after commutation failure refers to that two brachium pontis of transverter terminate commutation, the valve just having exited conducting is between reverse voltage action period, if forward blocking ability fails to recover, or commutation process is failed to carry out complete always, then threshold voltage be changed to positive to time, all switched phase by the original predetermined valve exiting conducting by the valve of commutation.

3. as claimed in claim 2 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (1), commutation failure can cause the valve that should turn off to continue conducting, should the valve breakdown of conducting, make transverter form dc-side short-circuit when next valve is opened, thus cause falling of DC voltage and uprushing of DC current; The probability of inverter generation commutation failure is greater than rectifier, and rectifier only just commutation failure can occur when trigger circuit fault.

4., as claimed in claim 3 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (1), the extinguish angle of inverter is less than the intrinsic limit extinguish angle γ of converter valve _mintime can there is commutation failure, wherein γ _minthat in Thyristor, Carrier recombination switch sets up P-N junction restraining barrier to recover the forward voltage blocking ability necessary time, its size and thyristor relating to parameters, and increase along with the increase of the voltage put on thyristor, electric current, corresponding electrical angle gets 7 ~ 10 °.

5. as claimed in claim 1 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (1), the factor of commutation failure comprises: receiving end fault in ac transmission system, control system pulse are abnormal, gating advance angle β or extinguish angle γ setting value is too small, converter valve short circuit and DC current increase, for Multi-infeed HVDC transmission system, also comprise the electrical couplings relation between Inverter Station.

6. as claimed in claim 1 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (2), commutation failure invariably accompanies the constant conduction of some valve, each valve only conducting 120 ° under normal circumstances, and the duration is at least a cycle, show as corresponding threshold voltage and be continuously zero, valve continuing current flow non-zero also keeps higher magnitude, for 1.5-2.5 rated current doubly, it can be used as the essential characteristic of commutation failure, simultaneously owing to being easy to measure threshold voltage and valve electric current, therefore propose threshold voltage to be continuously zero or valve continuing current flow non-zero as the new criterion of commutation failure, namely threshold voltage is continuously the time t of zero _uor the time t of valve continuing current flow non-zero _iwhen meeting following relation, judge to there occurs commutation failure:

Wherein, f is AC system fundamental frequency.

7. as claimed in claim 1 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (3), when HVDC inverter side change of current bus breaks down, the computing formula causing the minimum voltage needed for commutation failure to fall is:

$\mathrm{\ΔU}=1-\frac{I_d^{\′}}{I_d}\frac{X_{\mathrm{cpu}}}{X_{\mathrm{cpu}}+\cos {\mathrm{\γ}}_0-\cos \mathrm{\γ}}$

Wherein, I _dand I _d' represent DC current during rated direct current and Voltage Drop, X respectively _cpufor the equivalent commutating reactance that perunit value represents, γ ₀inverter extinguish angle setting valve when representing intrinsic limit extinguish angle respectively with γ and normally run.

8. as claimed in claim 7 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (3), set up HVDC model inverter side equivalent electrical circuit, change of current busbar voltage is replaced with minimum voltage and falls value, calculating threshold inductance value is:

$\frac{1-0.96(1-\mathrm{\ΔU})}{X_{\mathrm{eq}}}+\frac{0.96(1-\mathrm{\ΔU})}{X_{\mathrm{ceq}}}=\frac{0.96(1-\mathrm{\ΔU})}{X_f}$

Wherein, X _eqrepresent receiving end AC system equivalent reactance, X _ceqrepresent the capacitive reactance of the reactive-load compensator of change of current bus parallel connection, X _ffor the fault reactance of three-phase ground fault.

9. as claimed in claim 1 based on the HVDC commutation failure method for diagnosing faults of threshold voltage or valve electric current, it is characterized in that: in described step (4), use MATLAB to carry out the emulation of inverter side change of current bus three-phase fault, inverter side change of current bus single-phase fault, verify.