CN113113905A - Power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control - Google Patents

Power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control Download PDF

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CN113113905A
CN113113905A CN202110303372.1A CN202110303372A CN113113905A CN 113113905 A CN113113905 A CN 113113905A CN 202110303372 A CN202110303372 A CN 202110303372A CN 113113905 A CN113113905 A CN 113113905A
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distribution network
power distribution
fault
phase
current
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喻锟
喻泉
曾祥君
曾举鹏
李佳政
李理
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Changsha University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/08—Limitation or suppression of earth fault currents, e.g. Petersen coil

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Abstract

The invention discloses a power distribution network arc extinction method based on parametrical double-end measurement and closed-loop control, which comprises the following steps: injecting a non-power frequency and non-power frequency integral multiple zero sequence current to the neutral point of the power distribution network by the injection transformer of the flexible grounding device
Figure RE-DDA0003070527300000011
Zero sequence voltage for measuring return of no-load secondary side of voltage transformer in arc suppression coil
Figure RE-DDA0003070527300000012
Measuring and calculating three-phase-to-ground leakage conductance sigma g and ground capacitance sigma C of the power distribution network in real time to further obtain an injection current reference value
Figure RE-DDA0003070527300000013
After the single-phase earth fault and the fault phase are judged, the reference value of the injected current is compared
Figure RE-DDA0003070527300000014
And actual injection value

Description

Power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control
Technical Field
The invention relates to a power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control, which is suitable for solving the problems that fault current is difficult to compensate completely and the arc extinction effect is poor after a single-phase earth fault occurs in a power distribution network.
Background
The power distribution network has complex lines and extends into a user terminal, random faults are easy to occur, wherein about 70% of faults are single-phase earth faults, and the safe and stable operation of the power distribution network is seriously influenced. With the increase of the cable line occupation ratio of the power distribution network and the large investment of nonlinear power electronic equipment, the value of the earth fault current gradually increases, and the amplitude of the active component can reach 13A. If the fault is not timely removed or the fault current is suppressed, the fault may be developed into arc grounding, so that the fault is spread, fire burning and operation accidents are caused, and personal and property safety is seriously threatened. Therefore, it is important to realize reliable arc extinction of the single-phase earth fault.
At present, the distribution network in China widely adopts non-effective grounding modes such as grounding of a neutral point through an arc suppression coil and ungrounded neutral point to limit grounding fault current. The traditional passive arc suppression technology represented by a neutral point connection arc suppression coil of a power distribution network is difficult to compensate all currents of a ground fault, because the technology can only compensate reactive components of the currents of the ground fault and cannot compensate active components (about 2% -8%) and harmonic components (about 5%); and the arc suppression coil has large volume, difficult adjustment, complex operation and easy generation of resonance overvoltage, and the arc suppression effect of the technology is very limited.
Therefore, Huazhong science and technology university has researched and developed the controllable arc suppression coil of magnetic flux and transformer load, controls arc suppression coil equivalent inductance value through regulation and control power electronic component conduction angle, and then control its inductive current, but it has adopted multiunit IGBT to connect in parallel, leads to its cost high, and the economic nature is relatively poor and receives the system harmonic easily and influences.
The Shanghai university of traffic has proposed the arc suppression coil of transferring the circle of constant damping rate for the damping rate keeps invariable when the arc suppression coil carries the transfer circle, and inserts damping resistance at the arc suppression coil secondary side, prevents that the system from taking place the resonance. Although the two methods can realize flexible and adjustable inductance value of the arc suppression coil, the method only improves the arc suppression coil, still can compensate capacitive reactive component in fault current in principle, has no effect on active component and harmonic component, and still has limited arc suppression effect.
The Swedish Neutral company of Swedish develops a GFN ground fault comprehensive protection technology and a device, and a fault line zero-sequence admittance is used as an entry point, and current is injected into a Neutral point of a power distribution network after a fault, so that the fault feeder zero-sequence admittance returns to a normal value. The method has high requirement on the ground parameter measurement precision and strict control requirement on the device, and the equipment is expensive and difficult to popularize and apply.
In summary, a power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control is urgently needed at home and abroad.
Disclosure of Invention
The invention provides a power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control, and aims to solve the problems that fault current is difficult to compensate completely and the arc extinction effect is poor after a single-phase earth fault occurs in a power distribution network.
The technical scheme for solving the technical problems comprises the following steps:
1) zero-sequence current with fixed amplitude and phase angle and with non-power frequency and integer multiple of non-power frequency injected into transformer through flexible grounding device
Figure BDA0002987171200000021
2) Zero sequence voltage returned by no-load secondary side of voltage transformer in arc suppression coil
Figure BDA0002987171200000022
3) Measuring and calculating three-phase-to-ground leakage conductance sigma g and ground capacitance sigma C of the power distribution network in real time to obtain an injection current reference value
Figure BDA0002987171200000023
4) Judging the occurrence of single-phase earth faults and fault phases of the power distribution network;
5) comparing the reference value of the injected current with the actual injected value, correcting the difference value of the reference value and the actual injected value by a proportional resonant controller to obtain a PWM (pulse-width modulation) signal, comparing the PWM signal with a triangular carrier to obtain the pulse drive of an inverter IGBT (insulated gate bipolar transistor), and controlling the on-off of the IGBT to generate a target current;
6) the target current is injected into a neutral point of the power distribution network through an injection transformer of the flexible grounding device after being filtered, the voltage of a fault phase is restrained from being zero, and fault arc extinction is achieved.
The invention has the beneficial effects that: but through two voltage transformer accurate measurement distribution network to ground parameter, and measurement process safety, measuring result are fast, can realize real-time supervision and do not influence the distribution network normal operating, and the proportion resonance closed-loop control that combines again can realize the quick reliable arc extinction of single-phase earth fault, is applicable to different transition resistance fault conditions, has the characteristics that the precision is high, safe, simple and convenient.
Drawings
Fig. 1 is a schematic diagram of active arc extinction of a single-phase earth fault of a power distribution network.
Fig. 2 is a zero sequence equivalent circuit diagram of a distribution network parameter part.
Fig. 3 is an equivalent circuit diagram of a power distribution network.
Fig. 4 is a simplified equivalent circuit diagram of a power distribution network.
Fig. 5 is a block diagram of the closed loop control of the system.
FIG. 6 is a diagram of the open loop Bode of the system before correction.
FIG. 7 is kRAnd taking the corrected system open loop Bode diagram of the PR controller at different values.
FIG. 8 is a diagram of the open loop Bode of the system corrected by the PR controller.
FIG. 9 is R f50 omega fault point electricityCurrent and three-phase voltage waveforms.
FIG. 10 is RfAnd (3) a fault point current and three-phase voltage oscillogram when the voltage is 800 omega.
FIG. 11 bit Rf2000 omega fault point current and three-phase voltage oscillogram.
Detailed Description
In order to make the technical scheme and the implemented functions of the present invention clearer, the present invention is further described below with reference to the accompanying drawings and embodiments.
As shown in figure 1 of the drawings, in which,
Figure BDA0002987171200000031
is an alternating current power supply; is a direct current voltage; cdcAnd RdcRespectively a direct current side capacitor and a resistor; is the voltage across the inverter; l is0Is a filter inductor; l isPIs an arc suppression coil; rhIs an arc suppression coil damping resistor; p denotes the injection transformer of the flexible earthing device, with transformation ratio k1The zero-sequence current source is used for injecting zero-sequence current with specific amplitude and phase to a neutral point of the power distribution network through the PWM active inverter; q represents an internal voltage transformer of the arc suppression coil with a transformation ratio of k2The device is used for monitoring the voltage at two ends of the arc suppression coil in real time; is the neutral point voltage; the method comprises the following steps of (1) representing n-phase power supply electromotive force of a power distribution network (n ═ A, B and C represent phase sequences); m represents a bus; x represents the total number of outgoing lines on the bus (only the leakage conductance and the capacitance to ground of the line 1 are shown in the figure, and the rest lines are omitted); gmnN represents the relative leakage conductance of line m (m ═ 1,2, x); cmnRepresents the n-phase capacitance of line m to ground; rfIs single-phase earth fault transition resistance.
Assuming that a single-phase earth fault occurs in the C phase of the power distribution network line 1, the injected current at the neutral point of the power distribution network can be expressed as follows according to kirchhoff's current law:
Figure BDA0002987171200000041
in the formula: y isnIndicating the relative admittance of the distribution network n,
Figure BDA0002987171200000042
Ymn＝gmn+jωCmn(ii) a Omega is the power frequency angular frequency.
Three-phase power supply of the distribution network is symmetrical, the unbalance degree of the distribution network is generally lower than 2% in normal operation, the distribution network can be approximately regarded as three-phase balance, and
Figure BDA0002987171200000043
will be provided with
Figure BDA0002987171200000044
Substituting, equation (1) can be transformed into:
Figure BDA0002987171200000045
to realize fault arc extinction, the voltage of fault phase needs to be suppressed
Figure BDA0002987171200000046
Let distribution network three-phase ground admittance ∑ Y ═ YA+YB+YCWhen Σ Y is substituted into Σ g + j ω Σ C, the reference value of the injection current at this time can be expressed as:
Figure BDA0002987171200000047
in the formula: sigma g and sigma C are leakage conductance and capacitance to ground of the power distribution network.
As can be seen from equation (3), the reference value of the injected current is independent of the ground fault transition resistance, and is only dependent on the power supply voltage of the fault phase of the distribution network, the arc suppression coil and its damping resistance, and the ground parameter of the distribution network. The voltage of the fault phase power supply, the inductance value of the arc suppression coil and the damping resistance value of the arc suppression coil are known quantities, so that accurate calculation of ground parameters of the power distribution network is a key influencing reliable arc suppression of the single-phase earth fault of the power distribution network.
The equivalent circuit of the part for measuring the parameters in the simplified diagram 1 is shown in FIG. 2. As can be seen from FIG. 2, when the power distribution network is switched toNeutral point injected zero sequence current
Figure BDA0002987171200000051
Zero sequence voltage monitored by no-load secondary side of voltage transformer in arc suppression coil in real time
Figure BDA0002987171200000052
Reduced to the value on the primary side of
Figure BDA0002987171200000053
Namely, it is
Figure BDA0002987171200000054
It is easy to know the current flowing through the arc suppression coil
Figure BDA0002987171200000055
Comprises the following steps:
Figure BDA0002987171200000056
wherein, ω is1The angular frequency is non-power frequency and non-power frequency integral multiple.
Therefore, the three relative admittance of the power distribution network is as follows:
Figure BDA0002987171200000057
is provided with
Figure BDA0002987171200000058
The three relative ground admittances of the distribution network can be deformed into:
Figure BDA0002987171200000059
namely:
Figure BDA00029871712000000510
therefore, the expressions of the leakage conductance and the capacitance to ground of the three phases of the distribution network can be obtained as follows:
Figure BDA00029871712000000511
Figure BDA0002987171200000061
on the basis of obtaining an accurate measurement value of the ground parameters, the closed-loop control method based on the Proportional Resonant (PR) controller is further provided by combining the requirement on a control system when the single-phase ground fault occurs, and the disturbance condition of a fault line is considered. The method reduces the sensitivity of the control system to parameters and reduces the influence of the large change range of the resistance value of the transition resistor on the system; meanwhile, the rapidity of the control system can be improved, so that the fault current can be suppressed in time, and the reliable arc extinction of the fault can be ensured.
The equivalent circuit diagram of the distribution network provided with the flexible grounding device is shown in figure 3. For the convenience of analysis, the parameters of the power distribution network side are equivalent to the flexible grounding device side, and then: l isPs＝LP/k1 2，Rhs＝Rh/k1 2， Cs＝k1 2∑C，gs＝k1 2∑g，Rfs＝Rf/k1 2. Will be provided with
Figure BDA0002987171200000064
The disturbance is regarded as the disturbance of the control system, and all the resistors, inductors and capacitors in the graph 3 are equivalent to admittance y1The equivalent circuit diagram is shown in fig. 4. Wherein: y is1＝L0+[Cs//gs//(LPs+Rhs)//Rfs]。
The closed loop control block diagram of the system available from fig. 4 is shown in fig. 5. And taking the neutral point injection current as a control target, wherein:
Figure BDA0002987171200000067
for the reference value of the injected current, for the purpose of fault extinction, the value thereof should be equal to equation (3);
Figure BDA0002987171200000068
is the actual value of the injected current; gPRIs the PR controller transfer function; ginvIs the inverter transfer function; g1Is a transfer function between the neutral voltage and the injected current. The expressions are respectively as follows:
Figure BDA0002987171200000065
Ginv＝Kinv (11)
Figure BDA0002987171200000066
in the formula: m1＝RfLPsCs；M2＝RfCsRhs+RfgsLPs；M3＝RfgsRhs+Rf+1；N1＝L0RfCsLPs；
N2＝L0Rf(CsRhs+gsLPs)+L0LPs；
N3＝L0Rhs+gsRhsL0Rf+L0Rf+LPsRf；
N4＝RhsRf。
In the above formula: k is a radical ofPAnd kRProportional coefficient and resonance coefficient of PR controller; omegacIs the system cutoff frequency; omega0Is the system resonant frequency; kinvTo allow for a stable dc side voltage and a sufficiently high switching frequency,the proportional link obtained by the equivalent inverter takes the value of 10; the system parameter settings are shown in table 1.
The open-loop transfer function of the original system before correction is obtained according to the data in the table 1 as follows:
Gc＝Ginv·G1 (13)
the Bode diagram is shown in FIG. 6. After the damping resistance of the arc suppression coil is considered, the calculation precision of the injection current is improved, but the system transfer function G is increased at the same time1The order of (2) increases the control difficulty. As can be seen from FIG. 6, the open loop cut-off frequency of the original system before correction is 2 × 104rad/s, gain at fundamental frequency of 2.67, phase angle margin of 91.9 °; and a stable and reliable control system has a phase angle margin of about 45 degrees. The phase angle margin of the original system is too high, the gain at the fundamental frequency is low, the steady-state error of the system is large, the control requirement of the flexible grounding device is not met, and the correction is needed.
The open loop transfer function of the system after correction by the PR controller is:
Gs＝GPR·Gc (14)
proportionality coefficient k of PR controllerPCan be determined according to the formula:
Figure BDA0002987171200000071
from equation (15), the scaling factor k for the PR controller can be calculatedP＝0.1。
Determining a scaling factor kPThe resonance coefficient k can then be determined according to the Laus criterionRThe value range of (a). Shown in FIG. 7 as kP＝0.1，kRAnd respectively taking open-loop Bode diagrams of the system of 0.3, 3, 30 and 300. As can be seen from the figure, kRWhen 4 different values are taken respectively, the system is in a stable state. k is a radical ofRThe larger the gain of the frequency band in the system, and the larger the phase angle margin with kRIncrease and decrease of (1), taking k into accountR＝3。
When k isP＝0.1，kRAt 3, the open loop Bode plot of the system is shown in fig. 8. Known as the channel PThe open loop cut-off frequency of the corrected system of the R controller is 4.25 multiplied by 104rad/s, the phase angle margin is 46.1 degrees, and the gain at fundamental frequency is 30.56, so that the control requirement of the flexible grounding device is met.
In order to verify the feasibility of the invention, a 10kV power distribution network as shown in FIG. 1 is built by utilizing PSIM, 3 bus outgoing lines are set, and in the embodiment, the basic simulation parameters are shown in Table 1.
The ground parameter measurement method for the power distribution network is used for measuring and calculating the ground parameter of the power distribution network, the damping resistance of the arc suppression coil is fixed to be 10 omega, a characteristic frequency current signal with the amplitude of 10A and the phase angle of 0 degrees is injected to a neutral point of the power distribution network through an injection transformer of the flexible grounding device, a returned voltage signal under the characteristic frequency is measured from a no-load secondary side of a voltage transformer in the arc suppression coil, the ground parameter of the power distribution network can be measured by combining the formula (8) and the formula (9), and the measurement results are shown in the table 2, so that the measurement errors are all lower than 0.5%.
From the data in table 3, in the following simulation, the injection current reference value was calculated by selecting the ground parameter measurement result with f being 75 Hz. And setting a fault occurrence position as a C phase of the line 1 in the simulation model, wherein the fault occurrence time is 0.04s, and the flexible grounding device is thrown in at 0.08s, and the simulation time is 0.25 s. Fig. 9 to 11 show waveforms of a single-phase ground fault with a transition resistance of 50 Ω, 800 Ω, and 2000 Ω, respectively, and a fault point current and a three-phase voltage, respectively, and table 3 shows simulation results. It can be seen that the system stably operates before 0.04s, after a 0.04s fault occurs, the fault point current is obviously increased, the fault phase voltage is reduced, and the non-fault phase voltage is increased. After the flexible grounding device is thrown in 0.08s, the fault point current and the fault phase voltage are obviously reduced and approach to zero after about 0.06s, so that the method has high response speed; under different transitional resistance conditions, the fault current can be suppressed to be below 0.6A, the fault phase voltage can be suppressed to be below 32V, the suppression rate is up to 99.69%, and the arc extinction effect is obvious.
TABLE 1 System parameters
Figure BDA0002987171200000091
TABLE 2 measurement results of parameters under different characteristic frequencies
Figure BDA0002987171200000092
TABLE 3 simulation results
Figure BDA0002987171200000093

Claims (5)

1. The utility model provides a distribution network arc extinction method based on to ground parameter bi-polar measurement and closed-loop control, is applied to solving the problem that fault current is difficult to whole compensation, arc extinction effect is not good after the single-phase earth fault takes place in the distribution network, includes following step:
1) injection of specific frequency omega through injection transformer of flexible grounding device1Zero sequence current with lower fixed amplitude and phase angle
Figure RE-FDA0003070527270000011
2) Zero sequence voltage returned by no-load secondary side of voltage transformer in arc suppression coil
Figure RE-FDA0003070527270000012
3) Measuring and calculating three-phase-to-ground leakage conductance sigma g and ground capacitance sigma C of the power distribution network in real time to obtain an injection current reference value
Figure RE-FDA0003070527270000013
4) Judging the occurrence of single-phase earth faults and fault phases of the power distribution network;
5) comparing injected current reference values
Figure RE-FDA0003070527270000014
And actual injection value
Figure RE-FDA0003070527270000015
Correcting the difference value of the two signals by a proportional resonant controller to obtain a PWM (pulse-width modulation) signal, comparing the PWM signal with a triangular carrier to obtain inverter IGBT pulse drive, and controlling the on-off of the IGBT to generate a target current;
6) the target current is injected into a neutral point of the power distribution network through an injection transformer of the flexible grounding device after being filtered, the voltage of a fault phase is restrained from being zero, and fault arc extinction is achieved.
2. The power distribution network arc extinction method based on parameter double-end measurement and closed-loop control according to claim 1, characterized in that the injected zero sequence current in step 1) is zero sequence current
Figure RE-FDA0003070527270000016
Frequency omega thereof1Is non-power frequency and integer multiple of non-power frequency.
3. The power distribution network arc extinction method based on the double-end measurement of the parameters and the closed-loop control according to the claim 1, wherein the calculation formulas of the three-phase earth-to-ground leakage conductance Σ g and the earth-to-ground capacitance Σ C in the step 3) are respectively:
Figure RE-FDA0003070527270000017
and
Figure RE-FDA0003070527270000018
wherein
Figure RE-FDA0003070527270000021
LPIs an arc suppression coil inductance value; rhIs an arc suppression coil damping resistor; k is a radical of2The transformation ratio of a voltage transformer in the arc suppression coil is shown.
4. Method for extinguishing arcs in power distribution networks based on double-ended measurement of parameters and closed-loop control according to claim 1, characterized in that the injected current in step 3) is referenced toValue of
Figure RE-FDA0003070527270000022
The calculation formula of (2) is as follows:
Figure RE-FDA0003070527270000023
wherein
Figure RE-FDA0003070527270000024
The voltage is the C-phase power supply voltage of the power distribution network; omega is the power frequency angular frequency.
5. The power distribution network arc extinction method based on double-ended measurement of the parameters and closed-loop control according to claim 1, wherein the injected target current in the step 6) is power frequency.
CN202110303372.1A 2021-03-22 2021-03-22 Power distribution network arc extinction method based on ground parameter double-end measurement and closed-loop control Pending CN113113905A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114094562A (en) * 2021-11-29 2022-02-25 福州大学 Flexible arc extinction exiting method for single-phase earth fault of power distribution network
CN114123183A (en) * 2021-11-24 2022-03-01 山东大学 Flexible grounding system applied to ungrounded system of power distribution network and control method thereof

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114123183A (en) * 2021-11-24 2022-03-01 山东大学 Flexible grounding system applied to ungrounded system of power distribution network and control method thereof
CN114123183B (en) * 2021-11-24 2024-04-19 山东大学 Flexible grounding system applied to power distribution network ungrounded system and control method thereof
CN114094562A (en) * 2021-11-29 2022-02-25 福州大学 Flexible arc extinction exiting method for single-phase earth fault of power distribution network
CN114094562B (en) * 2021-11-29 2024-03-22 福州大学 Flexible arc extinction and exit method for single-phase earth fault of power distribution network

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