CN104218563B - The distribution network failure arc extinguishing method that a kind of neutral point is grounded through Multilevel Inverters - Google Patents

The distribution network failure arc extinguishing method that a kind of neutral point is grounded through Multilevel Inverters Download PDF

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CN104218563B
CN104218563B CN201410500176.3A CN201410500176A CN104218563B CN 104218563 B CN104218563 B CN 104218563B CN 201410500176 A CN201410500176 A CN 201410500176A CN 104218563 B CN104218563 B CN 104218563B
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CN104218563A (en
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郭谋发
陈静洁
张伟骏
高伟
洪翠
杨耿杰
缪希仁
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Shanghai Honglida Information Technology Co., Ltd.
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Fuzhou University
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

The present invention relates to the distribution network failure arc extinguishing method that a kind of neutral point is grounded through Multilevel Inverters.Using Cascade H bridge type Multilevel Inverters, it is connected directly between by reactor at the neutral point of power distribution network；Singlephase earth fault initial time occurs in power distribution network, the compensation electric current of injection needed for comprehensive computing generation, Multilevel Inverters are then put into rapidly, and compensation electric current is produced using current follow-up control algorithm and PWM policy control Multilevel InvertersAnd power network neutral point is injected, to compensate trouble point ground connection total current, and it is 0 to force faulted phase voltage permanent, and instantaneity earth fault will be eliminated voluntarily, solves the technical barrier of existing failure extinguishing arc technology extinguishing arc effect difference.

Description

The distribution network failure arc extinguishing method that a kind of neutral point is grounded through Multilevel Inverters
Technical field
The present invention relates to a kind of distribution network ground fault arc extinction technical field.
Background technology
Power distribution network broad covered area, go deep into user terminal, be complicated, the method for operation is changeable, random fault is frequent, wherein about 70% distribution network failure is instantaneity earth fault.With the continuous extension and extension of power distribution network, trouble point earth current increases Greatly, instantaneity earth fault extinguishing arc ability, ground arc will be difficult to self-extinguish, easily form unstable discontinuous combustion and show As resulting intermittent arcing ground over-voltage amplitude is higher, up to 2.5~3.5 times of even more highs of phase voltage, effect Time is grown, and damaging effect is big, can cause multiple failure under certain condition, triggers large-area power-cuts, jeopardizes power grid security, influences Social stability.
To limit earth-fault current, China's power distribution network typically uses neutral non-effective grounding mode, now ground connection electricity Stream is smaller.It is generally believed that when earth current is less than 5A, most of arc energy is extinguished naturally, and earth current is right closer to 0 Arc extinction is more favourable.
All kinds of extinguishing arc technologies common at present, including automatic turn-adjusting arc-extinguishing winding, air gap adjustable arc-extinction winding, direct current Arc-suppression coil with magnetic bias, three-phase five-column arc-suppression coil, adjustable capacitive-based arc-suppression coil, high short-circuit impedance formula transformer type arc blowout wire Arc extinguishing method that circle, arc extinction cabinet and arc suppression coil are used cooperatively with earth fault transfer device etc., belongs to passive extinguishing arc skill Art.Passive extinguishing arc technology can only compensate the idle residual flow in trouble point, it is impossible to compensate watt current harmonic electric current, extinguishing arc effect has Limit.
Then, on the basis of passive extinguishing arc, active extinguishing arc technology has been engendered, residual flow compensation device such as Sweden, Master-slave mode secondary side adjusts sense zero residual flow arc suppression coil, flexible ground failure extinguishing arc technology, is suitable for line construction dynamic change Active extinguishing arc technology etc..The residual flow compensation device of Sweden is that power distribution network zero sequence admittance is equal to event after controlling failure by Injection Current Zero sequence admittance before barrier, it make use of the zero sequence admittance before failure, it is impossible to the change of reflection distribution net work structure in real time.Master-slave mode is secondary Zero residual flow arc suppression coil of sense is adjusted in side, and when system generation singlephase earth fault occurs, startup separator route selection program selects failure first Circuit, then entered using the system direct-to-ground capacitance under the zero-sequence current of faulty line, normal condition, faulty line capacitance size etc. Row failure total current is estimated, harmonic component in earth current and active component are compensated, and realizes zero residual flow, and currently for For resonant earthed system, its route selection technology is less perfect, situations such as also choosing in the presence of wrong choosing, leakage, if ground path choosing is wrong, after The direction that continuous work is all towards mistake moves on.Flexible ground failure extinguishing arc technology be it is a kind of based on STATCOM zero Sequence voltage Flexible Control and false voltage arc extinguishing method, this method is using the fixed arc suppression coil of gear and having for two/tri- level Source inventer is used cooperatively, and injects zero-sequence current to power distribution network, realizes extinguishing arc, but distribution net work earthing fault electric current is complicated, may Cause the switching tube frequency of two/tri- level active inverters high, loss is greatly.It is suitable for the active extinguishing arc of line construction dynamic change Technology injects any two primary current, and measure zero sequence at bus to power distribution network respectively when detecting that singlephase earth fault occurs Voltage, grounding resistance is calculated using Injection Current twice and residual voltage, when the calculated value of grounding resistance is less than the ground connection adjusted During the border of resistance, using electric current extinguishing arc algorithm, otherwise, using voltage extinguishing arc algorithm；The technology will first calculate grounding resistance Size, reselection use electric current extinguishing arc algorithm or voltage extinguishing arc algorithm, control complex.
The content of the invention
It is an object of the invention to provide the distribution network failure arc extinguishing method that a kind of neutral point is grounded through Multilevel Inverters, solution The technical barrier of certainly existing failure extinguishing arc technology extinguishing arc effect difference.
To achieve the above object, the technical scheme is that：The distribution that a kind of neutral point is grounded through Multilevel Inverters Net failure arc extinguishing method, comprises the following steps：
Step S01：Using Multilevel Inverters, it is connected directly between by reactor at the neutral point of power distribution network；
Step S02：By analyzing distribution feelings of the compensation electric current in whole distribution network injected to power network neutral point Condition, it is known that no matter metallic earthing failure or resistance eutral grounding failure occur for power distribution network, the active component in injecting compensating electric current All it is identical with reactive component value, it is unrelated with fault ground resistance；
Step S03：When detecting power distribution network and being in the situation of normal operation, every certain time interval, using based on The equivalent direct-to-ground capacitance C of power distribution network is calculated in the checking for grounded current principle of Injection Signal∑With power distribution network leak resistance r over the ground∑, And preserved；
Step S04：When detecting that singlephase earth fault occurs for power distribution network, failure judgement phase, the zero sequence of neutral point is measured Voltage, each harmonic voltage in residual voltage is obtained using fast Fourier algorithm, obtain the harmonic wave point of earth-fault current Amount, and the equivalent direct-to-ground capacitance C of the power distribution network preserved according to system before failure∑With power distribution network leak resistance r over the ground∑, it is comprehensive The compensation electric current of injection needed for computing generation
Step S05：To integrate the compensation electric current of computing generationFor instruction current, Multilevel Inverters are put into, using electric current Tracking control algorithm and PWM policy control Multilevel Inverters produce compensation electric currentAnd power network neutral point is injected, to mend Trouble point ground connection total current is repaid, and it is 0 to force faulted phase voltage permanent, instantaneity earth fault will be eliminated voluntarily；
Step S06：After certain time-delay, whether failure judgement disappears, if failure vanishes, is judged as transient fault, distribution Network recovery normal operation；Otherwise, it is judged as permanent fault, starts line selection apparatus and carry out earth fault line selection protection.
In embodiments of the present invention, the Multilevel Inverters are Cascade H bridge type Multilevel Inverters.
In embodiments of the present invention, in the step S02, the fundametal compoment expression formula compensated in electric current isWhereinFor failure phase electromotive force of source, C∑=Ca+Cb+Cc, 1/r∑=1/ra+1/rb+1/rc, ω =2 π f, Ca、Cb、CcThe respectively equivalent direct-to-ground capacitance of power distribution network A, B, C tri-, ra、rb、rcRespectively power distribution network A, B, C tri- is relative Ground leak resistance.
In embodiments of the present invention, the checking for grounded current principle based on Injection Signal is in the step S03：Every one Fixed time interval, using Multilevel Inverters to injecting zero-sequence current at neutral pointMeasure neutral point voltage simultaneouslyChange Become injection zero-sequence current intoMeasurement zero sequence voltage on neutral point obtains againPass throughWithCalculate To the equivalent direct-to-ground capacitance C of power distribution network∑With power distribution network leak resistance r over the ground∑, its expression formula is as follows,
In embodiments of the present invention, in the step S04, when singlephase earth fault occurs for power distribution network, using quick Fu In leaf algorithm obtain residual voltageIn each harmonic voltage it is as follows：
Wherein,For the phasor of the n-th harmonic voltage of neutral point voltage, the harmonic component in earth-fault current is complete Harmonic current of the portion from power network, harmonic currentExpression formula is：
Further according to the equivalent direct-to-ground capacitance of power distribution network and power distribution network the leak resistance value over the ground of preservation, needed for comprehensive computing generation Injecting compensating electric currentExpression formula is：
For failure phase electromotive force of source.
In embodiments of the present invention, in the step S05, using current follow-up control algorithm and PWM policy control Multilevel Inverters produce and injecting compensating electric currentBasic functional principle be：It is right when singlephase earth fault occurs for power distribution network Answer neutral point of electric network that a zero sequence voltage on neutral point occursThe voltageWith the controllable voltage at Multilevel Inverters both ends Collective effect is on the reactor of connection, then in the presence of following mathematical relationship：
L is the inductance of the reactor,
Current follow-up control algorithm uses PI control algolithms, its can control withOut of phase, different amplitudes PWM produces the pwm signal for controlling each power device using carrier phase modulation strategy, and final realize produces any needs Zero sequence compensation electric current.
In embodiments of the present invention, in the step S06, the method whether failure judgement disappears is to gradually decrease injection Electric current is to 0, the situation that detects the change of Zero Sequence Voltage Versus Injection Current and change, if change and the Injection Current of residual voltage Change it is directly proportional, show trouble point extinguishing arc, be judged as transient fault；Otherwise, it is judged as permanent fault.
Compared to prior art, the invention has the advantages that：
1st, the present invention uses the circuit topological structure of Cascade H bridge type Multilevel Inverters, inverse compared to two/tri- level actives Become for the topological structure of device, without exporting transformer, power capacity is big, and devices switch frequency is low, loss is small, is easy to module Change, the harmonic content of output waveform is lower when level number is higher.
2nd, by analyzing distribution situation of the compensation electric current in whole distribution network injected to power network neutral point, it is known that No matter metallic earthing failure or resistance eutral grounding failure occur for power distribution network, the active component in injecting compensating electric current and idle point Value is unrelated with ground fault resistance.
3rd, in failure extinguishing arc technical elements, the checking for grounded current principle proposed by the present invention based on Injection Signal with it is quick The circuital method of fourier algorithm combination calculating ground fault, can not only measure capacitor current for earthing, moreover it is possible to failure The active component harmony wave component of electric current carries out accurate measurement, and it is 0 to force faulted phase voltage permanent, and arc blowout wire need not be adjusted by having Circle, clear principle, the advantages that being easily achieved, having a wide range of application.
Brief description of the drawings
Fig. 1 is that the distribution network failure arc extinguishing method schematic diagram that neutral point is grounded through Multilevel Inverters (is occurred single-phase with C phases Exemplified by earth fault).
Fig. 2 is the failure extinguishing arc overall control block diagram that neutral point is grounded through Multilevel Inverters.
Fig. 3 is the flow chart of the present invention.
Fig. 4 is the electric current that trouble point before and after singlephase earth fault occurs for the power distribution network that neutral point is grounded through Multilevel Inverters Oscillogram.
Embodiment
Below in conjunction with the accompanying drawings, technical scheme is specifically described.
The distribution network failure arc extinguishing method that a kind of neutral point of the present invention is grounded through Multilevel Inverters, comprises the following steps：
Step S01：Using Multilevel Inverters, it is connected directly between by reactor at the neutral point of power distribution network；
Step S02：By analyzing distribution feelings of the compensation electric current in whole distribution network injected to power network neutral point Condition, it is known that no matter metallic earthing failure or resistance eutral grounding failure occur for power distribution network, the active component in injecting compensating electric current All it is identical with reactive component value, it is unrelated with fault ground resistance；
Step S03：When detecting power distribution network and being in the situation of normal operation, every certain time interval, using based on The equivalent direct-to-ground capacitance C of power distribution network is calculated in the checking for grounded current principle of Injection Signal∑With power distribution network leak resistance r over the ground∑, And preserved；
Step S04：When detecting that singlephase earth fault occurs for power distribution network, failure judgement phase, the zero sequence of neutral point is measured Voltage, each harmonic voltage in residual voltage is obtained using fast Fourier algorithm, obtain the harmonic wave point of earth-fault current Amount, and the equivalent direct-to-ground capacitance C of the power distribution network preserved according to system before failure∑With power distribution network leak resistance r over the ground∑, it is comprehensive The compensation electric current of injection needed for computing generation
Step S05：To integrate the compensation electric current of computing generationFor instruction current, Multilevel Inverters are put into, using electric current Tracking control algorithm and PWM policy control Multilevel Inverters produce compensation electric currentAnd power network neutral point is injected, to mend Trouble point ground connection total current is repaid, and it is 0 to force faulted phase voltage permanent, instantaneity earth fault will be eliminated voluntarily；
Step S06：After certain time-delay, whether failure judgement disappears, if failure vanishes, is judged as transient fault, distribution Network recovery normal operation；Otherwise, it is judged as permanent fault, starts line selection apparatus and carry out earth fault line selection protection.
In the specific embodiment of the invention, the Multilevel Inverters are Cascade H bridge type Multilevel Inverters, in step S03 When leak resistance carries out numerical value preservation over the ground, system uses storehouse first in first out for the equivalent direct-to-ground capacitance of the power distribution network and power distribution network Principle.
Fig. 1 is the distribution network failure arc extinguishing method schematic diagram that the neutral point of the present invention is grounded through Multilevel Inverters,Respectively power distribution network three-phase mains voltage,For neutral point displacement voltage, ra、rb、rcRespectively power distribution network A, B, the relatively leak resistances of C tri-, Ca、Cb、CcRespectively three equivalent direct-to-ground capacitance, RdFor earth fault transition resistance, K is single Phase high-voltage switch gear.
When switching K disconnections, power network neutral point is earth-free, and (R during metallicity singlephase earth fault occurs for C phasesd=0), Then C phase-to-ground voltages vanishing, and the rise of the voltage-to-ground of other two-phases isTimes, i.e.,：
So residual voltage is：
It is assumed that Ca=Cb=Cc=C0、ra=rb=rc=r0, then the zero-sequence current that trouble point is flowed in non-faulting phase is：
The earth-fault current so flowed back to from earth point is：
Wherein, C∑And r∑For the equivalent direct-to-ground capacitance of power distribution network and power distribution network leak resistance over the ground, C∑=Ca+Cb+Cc=3C0, 1/rΣ=1/ra+1/rb+1/rc=3/r0.Now, if Injection Current value is and earth-fault current is equal in magnitude, direction Opposite electric current：
So when switch K closures, input Multilevel Inverters are to neutral point injecting compensating electric current, due to metallic earthing phase Mutually it is shorted when in failure, compensation electric current will all flow to trouble point, therefore can compensate for the ground connection total current of trouble point, make residual flow It is zero.
When switching K disconnections, power network neutral point is earth-free, and (R during resistance eutral grounding failure occurs for C phasesd≠ 0), neutral point Voltage be subjected to displacement forThen the electric current of each phase voltage and each phase flow direction trouble point is：
It can be seen from KCL laws, earth-fault current is：
Now, closure switch K, Multilevel Inverters are put into neutral point injecting compensating electric currentElectric current is compensated by only one Part flows through trouble point, the distribution situation of lower surface analysis compensation electric current in the entire network.
Due to compensating the injection of electric current, neutral point voltage will change and cause the zero-sequence current of each phase all to become Change.If neutral point voltage knots modification isThen：
The zero-sequence current knots modification of each phase flow direction trouble point is：
The earth-fault current knots modification of trouble point is：
It can be seen from KCL laws, the distribution situation of compensation electric current in the entire network is：
If the earth-fault current after order compensationFor 0, then：
WillSubstitute into compensation electric currentArranged in expression formula：
Due toThereforeThen：
Herein,Not consider the compensation electric current obtained in the case of harmonic wave, thereforeThe actual fundamental wave point for compensation electric current Amount.Contrast the active and reactive component and resistance eutral grounding direct fault location compensation electric current of metallicity fault ground injecting compensating electric current Active and reactive component understands that the active component in system injecting compensating electric current and reactive component value are identicals, with fault ground Resistance is unrelated.
By the fundametal compoment of compensation electric currentExpression formula know, compensate the fundametal compoment of electric currentNeed to be according to failure phase power supply Leak resistance is calculated over the ground for the equivalent direct-to-ground capacitance of electromotive force, power distribution network and power distribution network.When single-phase fault occurs for power distribution network, Failure phase electromotive force of source is mutually tried to achieve by failure judgement；In power distribution network normal operation, using the ground connection based on Injection Signal Current detecting principle tries to achieve the equivalent direct-to-ground capacitance of power distribution network and power distribution network leak resistance over the ground.
Checking for grounded current principle based on Injection Signal is specific as follows：
Under system normal operation, every certain time interval (such as 2s), closure switch K, Cascade H bridge type is utilized Multilevel Inverters are to injecting zero-sequence current at neutral pointThe residual voltage for now measuring neutral point obtainsBetween the two Relation is expressed as follows with formula：
Changing the zero-sequence current injected isNow the residual voltage of neutral point will change, measured ThenWithBetween relationship it is as follows：
Above-mentioned two formula is subtracted each other and arranged：
Wherein,For known quantity,It is measurable to learn, therefore the equivalent right of power distribution network is obtained by above formula Ground electric capacity C∑With power distribution network leak resistance r over the ground∑For：
The C that will be detected∑And r∑Preserved, can computing generation benefit in the case of singlephase earth fault occurs for power distribution network The earth-fault current fundametal compoment repaid.
When the harmonic component in fault ground electric current is larger, it is considered as compensating harmonic component.Because system is By the way of neutral point is grounded through Multilevel Inverters, it all is from the absence of the harmonic component of arc suppression coil, therefore system Power network.When singlephase earth fault occurs for power distribution network, residual voltage is obtained using fast Fourier algorithmIn each harmonic Voltage is as follows：
Wherein,For the phasor of the n-th harmonic voltage of neutral point voltage.Harmonic component in earth-fault current is complete Harmonic current of the portion from power network, harmonic currentExpression formula is：
Injecting compensating electric current needed for comprehensive computing generationExpression formula is：
In the harmonic component of earth current, 5 subharmonic contents are maximum, therefore predominantly detect 5 order harmonic components and mended Repay, harmonic component is limited in certain limit, both ensured the accuracy of compensation electric current calculated, reduced operand again.
To integrate the compensation electric current of computing generationAs instruction current, Multilevel Inverters are then put into rapidly, are used PI control algolithms and carrier phase modulation strategy control Multilevel Inverters produce simultaneously injecting compensating electric currentThe course of work General principle is：When singlephase earth fault occurs for power distribution network, a zero sequence voltage on neutral point occurs in corresponding neutral point of electric networkThe voltageWith the controllable voltage at Multilevel Inverters both endsCollective effect then exists as follows on the reactor of connection Mathematical relationship：
L is the inductance of the reactor,
PI control algolithms can control withOut of phase, different amplitudesThe transmission function G of pi regulatorr(s) For：
Wherein, KpFor proportionality coefficient；KiFor integral coefficient.Produced again using carrier phase modulation strategy and control each power The pwm signal of device, realizes the compensation electric current needed for producing, and the basic thought of its modulation strategy is：In LxIt is individual using cascaded H-bridges as In the Multilevel Inverters of unit, using common modulating wave (cycle is 2 π), by the phase of the triangular carrier of each cascaded H-bridges unit Mutually stagger 2 π/(L positionxKc)(KcFor carrier wave ratio), utilize the ripple in the waveform generating mode and multiple technology in SPWM technologies Shape overlaying structure produces related targets waveform.
After putting into Multilevel Inverters progress extinguishing arc, it is delayed (such as 10s) by certain time, carries out earth fault judgement, If trouble point extinguishing arc, failure extinguishing arc, then change the compensation electric current of injection, residual voltage proportional can also change, and two The mathematic(al) representation of person is：
For the changing value of residual voltage,
So the compensation electric current of injection is reduced to zero, if the proportional change of residual voltage, shows that trouble point has disappeared Arc, it is judged as transient fault；Otherwise, it is judged as permanent fault, carries out earth fault line selection protection.
Fig. 2 is the failure extinguishing arc overall control block diagram that neutral point is grounded through Multilevel Inverters, the electricity of Multilevel Inverters Road topology is represented with the current transformer of a dashed box and a unit.The overall control block diagram of system includes three parts：Electric current Tracking control technology, PWM strategy and voltage balance control.System uses PI control algolithms in current follow-up control so that Compensation electric current being capable of the real-time change that must track its instruction current caused by Multilevel Inverters；PWM strategy uses carrier wave Phase shift modulated strategy, it is a kind of switch modulation strategy suitable for high-power converter, and it, which is produced, controls each power device Pwm signal, it is final to realize the zero sequence compensation electric current for producing and needing；Because each concatenation unit DC bus capacitor is separate , the influence of the difference such as its component parameters, inverter bridge loss, pulse delay, it can all cause the imbalance of DC capacitor voltage, Therefore need to increase a voltage balance control in master-plan, control mode is controlled using PI, including balance control and equal Value control.
Fig. 3 is the flow chart of the present invention.Monitor power distribution network three-phase voltage and residual voltage in real time first；When residual voltage is big In 10% phase voltage, earth fault is judged, compare three-phase voltage size, judge voltage most low phase for failure phase.Work as distribution When singlephase earth fault occurs for net, it is grounded using Cascade H bridge type Multilevel Inverters to power distribution network Injection Current, compensation trouble point Total current, and it is 0 to force faulted phase voltage permanent；After certain time-delay (such as 10s), Injection Current is reduced to zero, if neutral point The proportional reduction of voltage, then illustrate trouble point extinguishing arc, distribution network restoration normal operation；Otherwise it is judged as permanent earth event Barrier, start wire selecting protection device.
In order to verify the feasible of power distribution network arc extinguishing method that neutral point described in the invention is grounded through Multilevel Inverters Property, simulation analysis have been carried out to the power distribution network shown in Fig. 1 using PSCAD/EMTDC and MATLAB softwares.Table 1 is distribution network line The parameter setting of parameter and Cascade H bridge type Multilevel Inverters.
Table 1
For different faults resistance, power distribution network the simulation results are as shown in table 2.After generation singlephase earth fault, pass through The zero sequence compensation electric current of injection is controlled, earth-fault current can be limited and level off to 0, reliably extinguish electric arc.
Table 2
Fig. 4 is in the power distribution network that neutral point is grounded through Multilevel Inverters, and in t=0.1s, single-phase connect occurs for system Earth fault (ground fault resistance is 100 Ω), in order to compare the earth-fault current size before and after injection zero sequence compensation electric current, this Input Cascade H bridge type Multilevel Inverters are specially postponed in place's emulation, i.e., at the t=0.2s moment, the zero-sequence current of injecting compensating, this After can be observed fault residual current be greatly lowered even close to 0, compensation effect is preferable.
The specific embodiment of the present invention is the foregoing is only, is not intended to limit the invention, all essences in the present invention God any modification, equivalent substitution and improvements done etc., should be included in the scope of the protection with principle.

Claims (5)

  1. A kind of 1. distribution network failure arc extinguishing method that neutral point is grounded through Multilevel Inverters, it is characterised in that：Including following step Suddenly：
    Step S01：Using Multilevel Inverters, it is connected directly between by reactor at the neutral point of power distribution network；
    Step S02：, can by analyzing distribution situation of the compensation electric current in whole distribution network injected to power network neutral point Know no matter metallic earthing failure or resistance eutral grounding failure occur for power distribution network, active component in injecting compensating electric current and idle Component value is all identical, unrelated with fault ground resistance；
    Step S03：When detection power distribution network is in the situation of normal operation, every certain time interval, using based on injection The equivalent direct-to-ground capacitance C of power distribution network is calculated in the checking for grounded current principle of signal∑With power distribution network leak resistance r over the ground∑, go forward side by side Row preserves；
    Step S04：When detecting that singlephase earth fault occurs for power distribution network, failure judgement phase, the residual voltage of neutral point is measured, The each harmonic voltage in residual voltage is obtained using fast Fourier algorithm, obtains the harmonic component of earth-fault current, and The equivalent direct-to-ground capacitance C of the power distribution network preserved according to system before failureΣWith power distribution network leak resistance r over the ground∑, comprehensive computing life Into the compensation electric current of required injection
    Step S05：To integrate the compensation electric current of computing generationFor instruction current, Multilevel Inverters are put into, using current tracking Control algolithm and PWM policy control Multilevel Inverters produce compensation electric currentAnd power network neutral point is injected, to compensate event Barrier point ground connection total current, and it is 0 to force faulted phase voltage permanent, instantaneity earth fault will be eliminated voluntarily；
    Step S06：After certain time-delay, whether failure judgement disappears, if failure vanishes, is judged as transient fault, and power distribution network is extensive Multiple normal operation；Otherwise, it is judged as permanent fault, starts line selection apparatus and carry out earth fault line selection protection；
    The checking for grounded current principle based on Injection Signal is in the step S03：It is how electric every certain time interval, utilization Flat current transformer is to injecting zero-sequence current at neutral pointMeasure neutral point voltage simultaneouslyChanging the zero-sequence current injected is Measurement zero sequence voltage on neutral point obtains againPass throughWithThe equivalent direct-to-ground capacitance of power distribution network is calculated C∑With power distribution network leak resistance r over the ground∑, its expression formula is as follows,
    <mrow> <msub> <mi>C</mi> <mi>&amp;Sigma;</mi> </msub> <mo>=</mo> <mfrac> <mn>1</mn> <mi>&amp;omega;</mi> </mfrac> <mo>&amp;CenterDot;</mo> <mi>Im</mi> <mo>&amp;lsqb;</mo> <mfrac> <mrow> <msub> <mover> <mi>I</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mi>i</mi> <mn>2</mn> </mrow> </msub> <mo>-</mo> <msub> <mover> <mi>I</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mi>i</mi> <mn>1</mn> </mrow> </msub> </mrow> <mrow> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mn>0</mn> <mi>i</mi> <mn>2</mn> </mrow> </msub> <mo>-</mo> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mn>0</mn> <mi>i</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> <mo>&amp;rsqb;</mo> </mrow>
    <mrow> <mfrac> <mn>1</mn> <msub> <mi>r</mi> <mi>&amp;Sigma;</mi> </msub> </mfrac> <mo>=</mo> <mi>Re</mi> <mo>&amp;lsqb;</mo> <mfrac> <mrow> <msub> <mover> <mi>I</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mi>i</mi> <mn>2</mn> </mrow> </msub> <mo>-</mo> <msub> <mover> <mi>I</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mi>i</mi> <mn>1</mn> </mrow> </msub> </mrow> <mrow> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mn>0</mn> <mi>i</mi> <mn>2</mn> </mrow> </msub> <mo>-</mo> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mn>0</mn> <mi>i</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> <mo>&amp;rsqb;</mo> <mo>;</mo> </mrow>
    Wherein, ω is the π f of angular frequency and ω=2；
    In the step S04, when singlephase earth fault occurs for power distribution network, residual voltage is obtained using fast Fourier algorithm In each harmonic voltage it is as follows：
    <mrow> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mn>0</mn> </msub> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>&amp;infin;</mi> </munderover> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mn>0</mn> <mi>n</mi> </mrow> </msub> </mrow>
    Wherein,For the phasor of the n-th harmonic voltage of neutral point voltage, the harmonic component in earth-fault current all is from The harmonic current of power network, harmonic currentExpression formula is：
    <mrow> <msub> <mover> <mi>I</mi> <mo>&amp;CenterDot;</mo> </mover> <mi>h</mi> </msub> <mo>=</mo> <msub> <mi>j&amp;omega;C</mi> <mi>&amp;Sigma;</mi> </msub> <mo>&amp;CenterDot;</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> <mi>&amp;infin;</mi> </munderover> <mi>n</mi> <mo>&amp;CenterDot;</mo> <msub> <mover> <mi>U</mi> <mo>&amp;CenterDot;</mo> </mover> <mrow> <mn>0</mn> <mi>n</mi> </mrow> </msub> <mo>,</mo> </mrow>
    Further according to the equivalent direct-to-ground capacitance of power distribution network and power distribution network the leak resistance value over the ground of preservation, injected needed for comprehensive computing generation Compensate electric currentExpression formula is：
    For failure phase electromotive force of source.
  2. 2. the distribution network failure arc extinguishing method that a kind of neutral point according to claim 1 is grounded through Multilevel Inverters, its It is characterised by：The Multilevel Inverters are Cascade H bridge type Multilevel Inverters.
  3. 3. the distribution network failure arc extinguishing method that a kind of neutral point according to claim 1 is grounded through Multilevel Inverters, its It is characterised by：In the step S02, the fundametal compoment expression formula compensated in electric current isWherein For failure phase electromotive force of source, CΣ0=Ca+Cb+Cc, 1/rΣ0=1/ra+1/rb+1/rc, Ca、Cb、CcRespectively power distribution network A, B, C Three equivalent direct-to-ground capacitance, ra、rb、rcRespectively power distribution network A, B, C tri- relatively leak resistances.
  4. 4. the distribution network failure arc extinguishing method that a kind of neutral point according to claim 1 is grounded through Multilevel Inverters, its It is characterised by：In the step S05, produced using current follow-up control algorithm and PWM policy control Multilevel Inverters And injecting compensating electric currentBasic functional principle be：When singlephase earth fault occurs for power distribution network, corresponding neutral point of electric network can go out An existing zero sequence voltage on neutral pointThe voltageWith the controllable voltage at Multilevel Inverters both endsCollective effect is in connection On reactor, then in the presence of following mathematical relationship：
    L is the inductance of the reactor,
    Current follow-up control algorithm uses PI control algolithms, its can control withOut of phase, different amplitudesPWM is adjusted System produces the pwm signal for controlling each power device using carrier phase modulation strategy, and final realize produces the zero of any needs Sequence compensates electric current.
  5. 5. the distribution network failure arc extinguishing method that a kind of neutral point according to claim 1 is grounded through Multilevel Inverters, its It is characterised by：In the step S06, the method whether failure judgement disappears is to gradually decrease Injection Current to 0, detects zero sequence The situation that voltage changes with the change of Injection Current, if the change of residual voltage is directly proportional to the change of Injection Current, table Bright trouble point extinguishing arc, is judged as transient fault；Otherwise, it is judged as permanent fault.
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