CN114094564A - Active arc suppression method and system for single-phase grounding fault in distribution network considering line voltage drop - Google Patents

Abstract

The invention discloses an active arc suppression method and system for a single-phase grounding fault of a distribution network that takes into account the line voltage drop. For ground fault, the fault phase is selected by the amplitude and phase relationship of the three-phase bus voltage after the fault, and the fault line is selected by the direction of the zero-sequence current of each outgoing line; the active arc suppression device is used to inject current into the distribution network; The neutral point voltage before and after the source arc suppression device is put into operation, the injection current of the active arc suppression device, the three-phase current and zero-sequence current of the fault outlet, and the fault distance is calculated; based on the fault distance, the control of the neutral point voltage of the distribution network is updated. target to suppress the fault point voltage to zero. The invention can reduce the influence of the line voltage drop between the fault phase bus and the fault point on the arc suppression effect, and can reliably suppress the arc under different load sizes, transition resistances and fault distances.

Description

Active arc suppression method and system for single-phase grounding fault in distribution network considering line voltage drop

technical field

The invention relates to the technical field of arc suppression for single-phase grounding faults in distribution networks, in particular to an active arc suppression method and system for single-phase grounding faults in distribution networks that take into account line voltage drop.

Background technique

The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

The structure of the distribution network is complex, and the single-phase grounding fault occurs frequently, which poses a great threat to the safety of electrical equipment and personal safety.

Traditionally, after the single-phase grounding fault occurs in the distribution network, the three-phase line voltage of the distribution network is still symmetrical, and it is generally allowed to continue running with power for 1-2 hours. However, for arc faults, during the intermittent arc grounding period, a huge arc overvoltage will be caused, which may lead to the breakdown of the non-faulty phase insulation, and the single-phase grounding fault will be transformed into a phase-to-phase short-circuit fault, which increases the harm of the fault. With the expansion of the distribution network and the wide application of power electronic equipment, the harmonic components and active components in the fault current of the distribution network are getting larger and larger, and the inductive current generated by the arc suppression coil can only compensate for the reactive power in the fault current. The flaws of the fundamental component are gradually exposed. Therefore, in order to achieve reliable arc suppression for instantaneous faults in the distribution network, it is necessary to propose an arc suppression method that can compensate for the harmonic components and active components in the fault current.

In order to achieve reliable suppression of fault arcs, in recent years, scholars have proposed many new arc suppression methods. According to different control objectives, they can be mainly divided into the following two categories: one is to inject compensation current through an external arc suppression device. The other is the voltage-type arc suppression method that realizes arc suppression by controlling the fault voltage to zero, such as the "arc suppression cabinet" that reduces the fault voltage by directly grounding the fault phase and the active The arc suppression device controls the active voltage type arc suppression of the neutral point voltage, etc.

The prior art proposes a current-type arc suppression method that uses an external arc suppression device to inject compensation current. The injected current is in the opposite direction to the fault current. Due to the flexible control characteristics of power electronic devices, this method can reduce the reactive power in the fault current. The wave component, active component and harmonic component are fully compensated to achieve precise arc suppression. However, this method needs to use the system ground parameters to calculate the reference value of the injected current, especially in the process of calculating the harmonic components, and the inaccuracy of the ground parameter measurement will cause certain errors in the calculation results, thus making the elimination of Arc effect is weakened.

The prior art proposes a method of using an "arc suppression cabinet" to directly ground the faulty phase bus to control the voltage of the faulty phase to zero, so that the fault arc cannot be reignited after the natural zero-crossing point, thereby extinguishing the fault arc. The method is simple in principle, easy to implement, does not require complex calculations, and can not only suppress the reactive fundamental component in the fault current, but also effectively suppress the active component and harmonic components. However, this method is based on ignoring the line voltage drop between the faulty phase bus and the fault point. This method actually controls the faulty phase busbar voltage to zero instead of controlling the fault point voltage to zero. When a single-phase ground fault occurs at the end of the line when the transition resistance is low, there will still be a large fault current.

The prior art proposes a method of controlling the neutral point voltage through an active arc suppression device such as an inverter. After a fault, the faulty phase is selected, and the active arc suppression device is used to control the neutral point voltage of the distribution network to be the faulty phase. The opposite number of the power supply voltage, so as to control the fault phase voltage to zero, and then extinguish the arc. The control objective of this method is simple and clear, and there is no need to calculate the capacitance to ground parameter. However, this method also ignores the line voltage drop between the faulty bus and the fault point, and the line end fault will also remain under heavy load and low transition resistance. A large fault current exists.

It can be seen that the existing single-phase grounding arc suppression scheme of the distribution network does not take into account the influence of the line voltage drop, and is a reliable scheme that can control the voltage at the fault point to zero and can accurately suppress each component of the fault arc.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention proposes an active arc suppression method and system for a single-phase grounding fault in a distribution network that takes into account the line voltage drop. And, it can avoid the influence of the line voltage drop between the fault phase bus and the fault point on the arc suppression effect; the control target is less affected by the measurement accuracy of the ground parameters; it can be used under different load sizes, transition resistances and fault distances. Can achieve better arc suppression effect.

In some embodiments, the following technical solutions are adopted:

An active arc suppression method for a single-phase grounding fault in a distribution network that takes into account the line voltage drop, comprising:

Obtain the operating voltage and current data of the distribution network to determine whether a single-phase ground fault occurs;

If a single-phase ground fault occurs, use the amplitude and phase relationship of the three-phase busbar voltage after the fault to select the faulty phase, and use the direction of the zero-sequence current of each outgoing line to select the faulty line;

The active arc suppression device is used to inject current into the distribution network, and the initial control target of the neutral point voltage of the distribution network is set as the opposite number of the power supply voltage of the faulty phase;

Based on the neutral point voltage before and after the active arc suppression device is put into operation, the injection current of the active arc suppression device, the three-phase current of the fault outlet and the zero sequence current, the fault distance is calculated; based on the fault distance, taking into account the line voltage drop, update the configuration The control target of the grid neutral point voltage to suppress the fault point voltage to zero.

In other embodiments, the following technical solutions are adopted:

An active arc suppression system for a single-phase grounding fault of a distribution network that takes into account the line voltage drop, comprising:

The fault judgment module is used to obtain the operating voltage and current data of the distribution network to judge whether a single-phase ground fault occurs;

The fault phase selection and line selection module is used to select the faulty phase by using the amplitude and phase relationship of the three-phase busbar voltage after the fault when a single-phase grounding fault occurs, and select the faulty line by the direction of the zero-sequence current of each outgoing line;

The active arc suppression module is used to inject current into the distribution network by using the active arc suppression device, and set the initial control target of the neutral point voltage of the distribution network to be the opposite number of the power supply voltage of the faulty phase; The neutral point voltage, the injection current of the active arc suppression device, the three-phase current of the fault outlet and the zero sequence current are used to calculate the fault distance; based on the fault distance, taking into account the line voltage drop, update the control target of the neutral point voltage of the distribution network , to suppress the fault point voltage to zero.

In other embodiments, the following technical solutions are adopted:

A terminal device, which includes a processor and a memory, the processor is used to implement each instruction; the memory is used to store a plurality of instructions, the instructions are suitable for being loaded by the processor and executing the above-mentioned power distribution network list considering line voltage drop. Phase-to-ground fault active arc suppression system method.

Compared with the prior art, the beneficial effects of the present invention are:

(1) According to the calculated fault distance, the present invention sets the control target of the neutral point voltage of the distribution network as the sum of the inverse number of the power supply voltage of the fault phase and the line voltage drop, suppresses the fault point voltage to zero, and can reduce the faulty phase busbar and the line voltage drop. The influence of the line voltage drop between the fault points on the arc suppression effect can be reliably suppressed under different load sizes, transition resistances and fault distances.

(2) In addition to suppressing the reactive fundamental wave component in the fault arc, the present invention can also suppress/compensate the active power component and the harmonic component in the fault current.

(3) The present invention firstly controls the neutral point voltage to the initial reference value -E _A by controlling the arc suppression device with the single-phase inverter as the core, and calculates the fault distance between the fault point and the bus, so as to reduce the line voltage drop. Calculate; by calculating the fault distance to compensate the influence of the line voltage drop, the influence of the line voltage drop between the fault point and the busbar on the arc suppression effect can be reduced; among them, the measurement results of the ground parameters only appear indirectly in During the calculation of the fault distance, even if there is a certain error in the calculation of the fault distance, most of the line voltage drops can be compensated, so that the arc suppression effect can still be improved over the existing methods.

(4) The present invention adopts the double closed-loop control strategy based on the series connection of PI and PR links, on the basis of using the PI link to set the phase angle margin and bandwidth of the control system, and improves the fundamental frequency of the control system through the series-connected PR links with fixed parameters Therefore, on the basis of ensuring the stability of the control system and the ability to resist high-frequency interference, it can reduce the steady-state error and improve its steady-state performance.

(5) In the active arc suppression device of the present invention, the inverter adopts the capacitor current feedback inner loop and the neutral point voltage feedback closed-loop double closed-loop control strategy, which can adapt to the change of the load and restrain the connection of the output terminal of the inverter to a certain extent. Resonant spikes caused by LC filters.

(6) The phase selection method of the present invention is to analyze the zero-sequence voltage trace after the fault, and directly use the electrical quantity characteristics after the fault to select the faulty phase. The method is relatively simple and can also eliminate parameter asymmetry and transition resistance. It does not need to inject current into the distribution network, the time required for phase selection is short, and no additional equipment costs are required.

Other features and advantages of additional aspects of the invention will be set forth in part from the description that follows, and in part will become apparent from the description below, or will be learned by practice of the present aspects.

Description of drawings

FIG. 1 is a flow chart of a method for active arc suppression of a single-phase ground fault taking into account the line voltage drop according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of phase selection for a single-phase ground fault according to an embodiment of the present invention;

3 is a schematic diagram of a single-phase grounding zero-potential point trajectory according to an embodiment of the present invention;

4 is a schematic diagram of active arc suppression of a distribution network according to an embodiment of the present invention;

5 is a schematic diagram of an average current calculation according to an embodiment of the present invention;

FIG. 6 is an active arc suppression fault current simulation waveform diagram considering line voltage drop according to an embodiment of the present invention;

7 is a block diagram of a double closed-loop control of an inverter based on a series connection of a PI and a PR controller according to an embodiment of the present invention;

FIG. 8 is an outer-loop closed-loop transfer function of an embodiment of the present invention.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

Example 1

Referring to the flowchart shown in FIG. 1 , this embodiment provides an active arc suppression method for a single-phase grounding fault in a distribution network that takes into account the line voltage drop, including the following steps:

Step 1: Measure the neutral point voltage, the three-phase bus voltage, the three-phase current of each outgoing line and the zero-sequence current in real time, calculate the amplitude and phase of the collected electrical quantity by the fast Fourier transform, and the neutral point voltage amplitude exceeds the three-phase current A single-phase-to-earth fault in the distribution network is considered to occur at 15% of the power supply voltage amplitude.

三相母线电压

各出线三相电流

以及零序电流

的幅值、相位数据进行保存，基于三相母线电压的幅值、相位关系选出故障相，基于各出线零序电流的方向选出故障线路。Step 2: After judging that a single-phase grounding fault occurs in the distribution network, the neutral point voltage collected after the fault occurs

Three-phase bus voltage

Three-phase current of each outlet

and zero sequence current

The amplitude and phase data are saved, and the faulty phase is selected based on the amplitude and phase relationship of the three-phase bus voltage, and the faulty line is selected based on the direction of the zero-sequence current of each outgoing line.

Among them, the phase with the largest lag phase in the three-phase voltage is selected as the fault phase, and the phase selection principle is as follows:

Taking the A-phase-to-ground fault in the distribution network where the neutral point is not grounded as shown in Figure 2 as an example, the expression of the neutral point voltage after the fault can be calculated by Kirchhoff's current law, specifically:

为中性点电压，

为A相电源电压，C_X(X＝A,B,C)为三相对地电容，R₀为相对地泄露电阻，R_f为过渡电阻，

为配电网不对称度，

为配电网原本的阻尼率，

为R_f造成的附加阻尼率。in,

is the neutral point voltage,

is the A-phase power supply voltage, C _{X (X=A, B, C)} is the three-phase-to-ground capacitance, R ₀ is the relative-to-ground leakage resistance, R _f is the transition resistance,

is the distribution network asymmetry,

is the original damping rate of the distribution network,

is the additional damping rate due to R _f .

为电压正方向参考轴，可以得到零电位点的轨迹如图3所示。图中，圆弧O₁和O₂分别是配电网三相对地参数对称时的零电位点随着过渡电阻增大时的变化轨迹以及系统参数不对称造成的零电位点轨迹偏移，而圆弧O则是考虑系统参数不对称时零电位点的变化轨迹。由图3可以看出，在A相接地的情况下，随着过渡电阻的增大，A相电压大小有可能会超过B相电压，不再是电压最小相，而C相电压则始终是三相电压中最大的，因此，可以选择三相电压中滞后最大相的那一相为故障相，此方法不受过渡电阻大小以及配电网参数不对称的影响。According to this expression, with the neutral point as the origin,

As the reference axis in the positive direction of the voltage, the trajectory of the zero potential point can be obtained as shown in Figure 3. In the figure, the arcs O ₁ and O ₂ are the trajectories of the zero-potential point when the three-phase-to-ground parameters of the distribution network are symmetrical with the increase of the transition resistance and the trajectory of the zero-potential point caused by the asymmetry of the system parameters, while The arc O is the change trajectory of the zero potential point when the system parameters are asymmetrical. It can be seen from Figure 3 that in the case of phase A being grounded, with the increase of the transition resistance, the voltage of phase A may exceed the voltage of phase B, and it is no longer the phase with the minimum voltage, while the voltage of phase C is always The largest of the three-phase voltages, therefore, the phase with the largest lag in the three-phase voltages can be selected as the faulty phase. This method is not affected by the size of the transition resistance and the asymmetry of the distribution network parameters.

Considering that the present invention uses the active arc suppression device to replace the traditional arc suppression coil for arc suppression, therefore, when the fault has just occurred and the active arc suppression device has not been put into use, the distribution network is in a state where the neutral point is not grounded. At this time, the zero-sequence current direction of the non-fault outgoing line in the distribution network is from the bus to the line, while the zero-sequence current of the fault outgoing line flows from the line to the bus. Therefore, the outgoing lines with different zero-sequence current directions can be selected as the fault outgoing line.

Step 3: Put the active arc suppression device into use, and set the initial reference value of the neutral point voltage of the distribution network to the opposite number of the power supply voltage of the faulty phase, specifically:

为有源消弧装置输出电压控制目标值，

为A相电源电压；in,

is the output voltage control target value of the active arc suppression device,

is the A-phase power supply voltage;

As shown in Figure 4, the active arc suppression device is mainly composed of a DC side power supply, a single-phase inverter, an LC filter and a step-down transformer T. The active arc suppression device is used to control the neutral point voltage to the fault phase power supply voltage After the opposite number of , the bus voltage of the faulty phase is zero.

有源消弧装置注入电流

故障出线三相电流

以及零序电流

并根据其与步骤2中保存的数据对故障距离进行计算，故障距离的计算公式，具体为：Step 4: After the active arc suppression device is put into operation, after a certain delay, measure the neutral point voltage at this time

Active arc suppression device injection current

Three-phase current of fault outgoing line

and zero sequence current

And calculate the fault distance according to it and the data saved in step 2. The calculation formula of the fault distance is as follows:

Taking the single-phase grounding fault in the distribution network shown in Figure 4 as an example, the calculation principle of the fault distance l _Z in step 4 is introduced:

Before the active arc suppression device is put into operation, the relationship between the positive, negative and zero-sequence voltages and currents at the fault point can be obtained according to the boundary conditions of the fault point when the single-phase grounding of the distribution network is carried out, specifically:

为故障点电压；

分别为故障点的正、负、零序电压；

分别为故障点的正、负、零序电流。in,

is the fault point voltage;

are the positive, negative and zero-sequence voltages of the fault point, respectively;

are the positive, negative and zero sequence currents at the fault point, respectively.

The relationship between the positive, negative and zero-sequence voltages at the fault point and the positive, negative and zero-sequence voltages of the faulty phase bus can be expressed as:

是故障A相母线的正、负、零序电压；Z_(1,2,0)是故障出线单位长度的正、负、零序阻抗，一般来说，Z₁＝Z₂；

为故障出线A相正、负、零序电流。in,

is the positive, negative and zero-sequence voltage of the faulty A-phase bus; Z _(1,2,0) is the positive, negative and zero-sequence impedance per unit length of the fault outlet line, generally speaking, Z ₁ =Z ₂ ;

It is the positive, negative and zero sequence current of phase A of the fault outgoing line.

According to the above formula, the relationship between the neutral point voltage and the fault point voltage after the fault can be obtained, specifically:

Similarly, after the active arc suppression device is put into operation, the neutral point voltage is controlled to be the opposite number of the power supply voltage of the faulty phase. After a delay of 20ms, the measured electrical quantities are basically stable at this time. Similar to the derivation process of the relationship between the neutral point voltage and the fault point voltage before the above-mentioned active arc suppression device is put into operation, it can be obtained that the relationship is specifically:

By combining the relationship between the neutral point voltage and the fault point voltage before and after the active arc suppression device is put into operation, the fault distance l _Z can be calculated, specifically:

是逆变器向中性点的注入电流测量值，Y_∑是配电网的对地导纳参数。in,

is the measured value of the injected current of the inverter to the neutral point, and Y _∑ is the ground admittance parameter of the distribution network.

It should be noted that, because there may be branch loads in the outgoing lines of the distribution network or inaccurate measurement of the ground admittance parameters of the distribution network, it will have a certain degree of influence on the calculation results of the fault distance, so that the fault distance obtained by this method will be affected. There is a slight error between the calculated result and the actual distance, but considering that the actual effect of this result is to reduce the influence of the line voltage drop between the fault point and the bus on the arc suppression effect, rather than to use the fault line to find the actual fault point, Therefore, even if there is a slight error in the calculation result of the fault distance, the influence of the line voltage drop between the line fault point and the bus can be greatly reduced, and the arc suppression effect can be enhanced. Therefore, there is a slight error in the fault distance calculation result. acceptable.

Step 5: According to the fault distance calculated in Step 4, set the neutral point voltage control target of the distribution network to a new reference value that takes into account the line voltage drop, that is, the sum of the inverse number of the fault phase power supply voltage and the line voltage drop. The voltage suppression at the fault point is zero, and the reference value of the neutral point voltage considering the line voltage drop is as follows:

和

分别是经计算获得的故障出线母线和故障点之间线路的故障相电流平均值与零序电流平均值，Z₁和Z₀分别是故障出线单位长度的正序阻抗和零序阻抗。in,

and

are the average value of the fault phase current and the zero-sequence current of the line between the fault outlet bus and the fault point, respectively, and Z ₁ and Z ₀ are the positive-sequence impedance and zero-sequence impedance per unit length of the fault outlet, respectively.

与零序电流平均值

的获取原理为：Among them, the average value of the fault phase current of the line between the fault outgoing busbar and the fault point

and zero sequence current average

The acquisition principle is:

和零序电流

受到相间电容电流以及对地电容电流的影响会沿着出线不断发生变化，当故障点距离母线较远时，故障相电流和零序电流会出现较为明显的变化，此时故障出线的相电流与零序电流首端测量值与母线和故障点之间的平均值之间会存在较大的出入。以图5所示的配电网发生A相接地故障为例，对故障相电流平均值

和零序电流平均值

的计算方法进行介绍。fault phase current

and zero sequence current

Affected by the interphase capacitance current and the ground capacitance current, it will continuously change along the outgoing line. When the fault point is far away from the bus, the fault phase current and zero sequence current will change significantly. At this time, the phase current of the fault outgoing line is different from There will be a large discrepancy between the measured value of the zero sequence current head end and the average value between the bus and the fault point. Taking the A-phase grounding fault in the distribution network shown in Figure 5 as an example, the average value of the faulted phase current is calculated as follows:

and zero sequence current average

The calculation method is introduced.

In Figure 5, C _(1,2,0) is the positive, negative and zero-sequence capacitance per unit length of the fault outlet line of the distribution network, and C _m is the phase-to-phase capacitance of the fault outlet line, and its specific value is:

The phase-to-phase capacitive current flowing through the A-phase unit length line in the fault outgoing line is:

Considering that the voltage of the faulted phase is generally low after a single-phase grounding fault, the capacitance current relative to the fault is small, and the influence on the change of the faulted phase current along the outgoing line is relatively small, so the measured value of the A-phase current at the head end of the faulted outgoing line can be used to correlate with the fault. The average value of the fault phase current is calculated from the average value of the phase-to-phase capacitive current flowing in phase A between the point and the bus, specifically:

为故障出线A相电流在线路首端的测量值。in,

It is the measured value of the A-phase current of the fault outgoing line at the head end of the line.

The average value of the zero-sequence current between the fault point and the busbar is approximately replaced by the zero-sequence current flowing through the fault point and the midpoint of the busbar.

为故障出线首端零序电流的测量值，可以根据其进行计算得到零序电流平均值

具体为：in,

It is the measured value of the zero-sequence current at the head end of the fault outgoing line, which can be calculated to obtain the average value of the zero-sequence current.

Specifically:

与故障点电压

的关系式可知，如果将配电网中性点电压控制为新的电压参考值

则其前半部分

可以补偿故障点与母线之间的线路压降对消弧效果的影响，将故障点电压控制为零，从而在不同负荷大小、过渡电阻以及故障位置的情况下都能够达到较为良好的消弧效果。According to the neutral point voltage in step 4

and fault point voltage

It can be seen from the relationship of

then its first half

It can compensate the influence of the line voltage drop between the fault point and the busbar on the arc suppression effect, and control the voltage at the fault point to zero, so that a relatively good arc suppression effect can be achieved under different load sizes, transition resistances and fault locations. .

Use MATLAB/Simulink to build a simulation model of active arc suppression of medium voltage distribution network, and simulate and verify the proposed arc suppression method:

1) Build the model

The simulation model is shown in Figure 4. In the model, the reference voltage level of the distribution network is 10.5kV, and the distribution system adopts a 110/10kV transformer with a transformer capacity of 40MW; the lengths of the four outgoing lines L ₁ , L ₂ , L ₃ , and L ₄ are 8km, 10km, 10km, and 12km respectively. ;The load of each outgoing line adopts delta connection, and the load size is P= _4.299MW , QL= _0.165Mvar , QC=0; each outgoing line adopts cable standard parameters: positive sequence resistance is 0.27Ω/km, positive sequence inductance is 0.255 mH/km, the positive-sequence capacitance is 0.339uF/km, the zero-sequence resistance is 2.7Ω/km, the zero-sequence inductance is 1.019mH/km, and the zero-sequence capacitance is 0.28uF/km.

2) Set the _A -phase grounding faults at 1km, 5km, and 10km from the bus bar respectively, and set the transition resistance to 10Ω, 100Ω, and 1000Ω respectively; use over-compensated arc suppression coils to suppress arcs and control the neutral point. The active arc suppression method in which the voltage is the opposite number of the power supply voltage of the fault phase, and the active arc suppression method considering the line voltage drop are used to deal with the fault point arc, and the active arc suppression method considering the line voltage drop proposed by the present invention is used. The arc suppression effect is compared with the two existing arc suppression methods. Table 1-Table 3 shows the maximum value of fault current when a fault occurs at each position and the arc is not extinguished under different transition resistances and the maximum value of residual current at the fault point using three methods:

Table 1 Residual current of three arc suppression methods at fault at 1km

Table 2 Residual current of three arc suppression methods at fault at 5km

Table 3 Residual current of three arc suppression methods at fault at 10km

From the simulation results in Table 1-3, it can be seen that without arc suppression, the residual current at the fault point is around 80-90A, 50-60A, and 5-10A under the conditions of 10Ω, 100Ω, and 1000Ω transition resistance, respectively; When the arc coil is used for arc suppression, most of the residual current at the fault point is above 5A. In the case of 10Ω transition resistance, the residual current at the fault is above 10A, which will make the fault arc continue to burn, and with the increase of harmonic components and active components. The residual current generated by the arc suppression method using the arc suppression coil will be larger, and the arc suppression effect is not ideal; the method of controlling the neutral point voltage to be the opposite number of the fault phase power supply voltage, in the case of a large transition resistance The fault current can be limited to less than 5A. With the decrease of transition resistance and the increase of fault distance, the fault residual current will increase accordingly. When the fault point is far away from the busbar, it may even cause the fault residual current. The current is larger than that when the arc suppression coil is used for arc suppression. When a 10Ω transition resistance fault occurs at 10km, the residual current at the fault point will even exceed 40A; and the active arc suppression method proposed by the present invention considering the line voltage drop can When a single-phase-to-ground fault with different transition resistance occurs at each location of the distribution network, the fault current can be reliably limited to less than 5A, which is not affected by the fault location, and the larger the transition resistance, the smaller the residual fault current, eliminating the The arc effect is ideal.

As shown in Figure 6, when the A-phase grounding fault with different transition resistances occurs at 10km, the arc-extinguishing fault is carried out by the active arc-extinguishing method for the single-phase grounding fault of the distribution network that takes into account the line voltage drop proposed by the present invention The current simulation waveform diagram is taken as an example to analyze the arc-extinguishing effect of the active arc-extinguishing method proposed by the present invention in detail. Among them, the dashed line is the fault current when the 10Ω transition resistance is grounded, the dotted line is the fault current when the 100Ω transition resistance is grounded, and the solid line is the fault current when the 1000Ω transition resistance is grounded. After the fault, select the fault phase and line, control the neutral point voltage to the opposite number of the fault phase power supply voltage at 0.06s, and calculate the fault distance after a delay of 20ms, and set the neutral point at 0.08s. The voltage reference is adjusted to a new reference that takes into account the line voltage drop. It can be seen from the fault current simulation waveform in Figure 6 that after the reference value is applied, the fault residual current can attenuate to below 5A after about 30ms, the residual current at the final fault point is stabilized below 2A, and the total arc extinguishing time is within 80ms. The arc suppression effect achieved is ideal.

As an optional implementation manner, for the inverter of the active arc suppression device, the inverter double closed-loop control strategy based on the series connection of the PI and the PR controller is used for control.

Figure 7 is a control block diagram of the dual closed-loop control strategy provided in this embodiment, which mainly includes a capacitive current feedback inner loop and a neutral point voltage feedback closed loop, which can adapt to changes in the load and restrain the output of the inverter to a certain extent. Resonant spikes caused by the connected LC filter. In the figure, the feedback value of the neutral point voltage is compared with the reference voltage, and the reference value of the inner loop current is generated after the outer loop regulator _Gv formed by the PI and PR controller in series; In contrast, the modulation wave of the inverter is generated through the adjustment of the inner loop PI controller G _I ; thus, the output voltage is generated on the equivalent load of the distribution network through the inverter and the LC filter. Among them, G _inv is the equivalent transfer function of the inverter, which is generally a constant, equal to the ratio of the DC side voltage of the inverter to the carrier voltage; L ₀ and C ₀ are the filter inductor and filter capacitor, respectively, whose resonant frequency is far Below the switching frequency; _{Req and Ceq are} the equivalent resistance and equivalent capacitance of the distribution network on the low voltage side of the transformer.

In the control strategy provided in this embodiment, the inner loop controller G _i is regulated by PI, and the outer loop controller G _v is regulated by a series connection of PI and PR controllers. The transfer functions of the outer loop PI controller and PR controller are:

Among them, K _{p_PI} and K _i are the proportional coefficient and integral coefficient of the outer loop PI controller, respectively; K _{p_PR} and K _r are the proportional coefficient and resonance coefficient of the outer loop PR controller, respectively, w ₀ is the fundamental frequency of the distribution network, ; The PI controller is used to provide appropriate bandwidth and phase angle margin for the outer-loop open-loop transfer function, and the PR controller is used to improve the fundamental frequency gain of the open-loop transfer function. The value of K _{p_PR} is fixed to 1, and the value of K _r is 100. Limit the influence of the PR controller to the outer-loop open-loop transfer function in the low frequency band, to prevent its proportional coefficient from being too large, which leads to an excessively large system bandwidth, which causes the high-frequency gain of the system to be too high, which reduces the system’s ability to resist high-frequency interference and prevents The phase lag generated in the mid-frequency band reduces the phase margin of the system to ensure the stability of the system.

Taking the data in the above simulation model as an example, the parameters of the double closed-loop control based on the series connection of PI and PR controllers are set. The distribution network is equivalent to the low voltage side of the transformer, and the parameters of the LC filter are selected as L ₀ =2uH, C ₀ =100uF, the DC side voltage is 400V, G _inv =400, and the switching frequency is set to 100kHz. By setting the proportional coefficient of the inner loop PI controller to 0.0051, the integral coefficient to 314.66, the cutoff frequency of the inner loop to 1/10 of the switching frequency, and the phase angle margin to 45°, the outer loop PI controller is set to The proportional coefficient is set to 1.198, the integral coefficient is set to 33789, the outer loop bandwidth is set to about 1/3 of the inner loop bandwidth, the phase angle margin is about 60°, and the fixed parameters K _{p_PR} is 1, K _r is 100 The PR controller connected in series can increase the fundamental frequency gain of the outer loop by 40dB, greatly reducing the steady-state error of the control system. The Bode diagram of the closed-loop transfer function of the outer loop before and after adjustment is shown in Figure 8. It can be seen that the amplitude and phase control errors of the control system at the fundamental frequency can be made close to 0 by connecting the PI and PR controllers in series. , the control effect is good.

Embodiment 2

In one or more embodiments, a single-phase-to-ground fault active arc suppression system for a distribution network considering line voltage drop is disclosed, including:

The fault judgment module is used to obtain the operating voltage and current data of the distribution network to judge whether a single-phase ground fault occurs;

The fault phase selection and line selection module is used to select the faulty phase by using the amplitude and phase relationship of the three-phase busbar voltage after the fault when a single-phase grounding fault occurs, and select the faulty line by the direction of the zero-sequence current of each outgoing line;

The active arc suppression module is used to inject current into the distribution network by using the active arc suppression device, and set the initial control target of the neutral point voltage of the distribution network to be the opposite number of the power supply voltage of the faulty phase; The neutral point voltage, the injection current of the active arc suppression device, the three-phase current of the fault outlet and the zero sequence current are used to calculate the fault distance; based on the fault distance, taking into account the line voltage drop, update the control target of the neutral point voltage of the distribution network , to suppress the fault point voltage to zero.

It should be noted that the specific implementation manners of the above modules have been described in detail in the first embodiment, and will not be described in detail here.

Embodiment 3

In one or more embodiments, a terminal device is disclosed, including a server, the server including a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor executing the During the program, the method for active arc suppression of the single-phase grounding fault of the distribution network in consideration of the line voltage drop in the first embodiment is implemented. For brevity, details are not repeated here.

It should be understood that, in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate array FPGA or other programmable logic devices , discrete gate or transistor logic devices, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

The memory may include read-only memory and random access memory and provide instructions and data to the processor, and a portion of the memory may also include non-volatile random access memory. For example, the memory may also store device type information.

In the implementation process, each step of the above-mentioned method can be completed by a hardware integrated logic circuit in a processor or an instruction in the form of software.

Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to pay creative work. Various modifications or deformations that can be made are still within the protection scope of the present invention.

Claims (10)

1. An active arc extinction method for a single-phase earth fault of a power distribution network considering line voltage drop is characterized by comprising the following steps:

acquiring running voltage and current data of the power distribution network, and judging whether a single-phase earth fault occurs or not;

if single-phase earth faults occur, selecting fault phases by using the amplitude and phase relation of three-phase bus voltage after the faults, and selecting fault lines by using the direction of zero-sequence current of each outgoing line;

injecting current into the power distribution network by using an active arc suppression device, and setting an initial control target of the neutral point voltage of the power distribution network as the opposite number of the fault phase power supply voltage;

calculating a fault distance based on neutral point voltages before and after the active arc suppression device is put into operation, the injected current of the active arc suppression device, the three-phase current of a fault outgoing line and the zero-sequence current; and on the basis of the fault distance, calculating line voltage drop, and updating a control target of the neutral point voltage of the power distribution network so as to suppress the fault point voltage to zero.

2. The active arc extinction method for the single-phase earth fault of the power distribution network considering the line voltage drop, according to claim 1, is characterized in that operating voltage and current data of the power distribution network are obtained, whether the single-phase earth fault occurs or not is judged, and the method specifically comprises the following steps:

acquiring neutral point voltage, three-phase bus voltage, three-phase current of each outgoing line and zero-sequence current data; and when the voltage amplitude of the neutral point exceeds the set value of the voltage amplitude of the three-phase power supply, the single-phase earth fault is considered to occur in the power distribution network.

3. The active arc extinction method for the single-phase ground fault of the power distribution network considering the line voltage drop, according to claim 1, is characterized in that a fault phase is selected by using the amplitude and phase relation of three-phase bus voltage after the fault, and specifically comprises the following steps: the phase with the largest lag among the three-phase voltages is selected as the failed phase.

4. The active arc extinction method for the single-phase earth fault of the power distribution network considering the line voltage drop, according to claim 1, is characterized in that a fault line is selected by utilizing the direction of zero sequence current of each outgoing line, and specifically comprises the following steps:

the zero sequence current direction of the non-fault outgoing line in the power distribution network flows from the bus to the line, and the zero sequence current of the fault outgoing line flows from the line to the bus.

5. The active arc suppression method for the single-phase earth fault of the power distribution network considering the line voltage drop as claimed in claim 1, wherein the active arc suppression device comprises: the direct current side power supply, the inverter, the LC filter and the step-down transformer T are connected in sequence; after the neutral point voltage is controlled to be the opposite number of the fault phase power supply voltage by the active arc suppression device, the fault phase bus voltage is zero.

6. The active arc extinction method for the single-phase ground fault of the power distribution network considering the line voltage drop, as claimed in claim 5, wherein the inverter adopts a double closed-loop control strategy, specifically including:

comparing the feedback value of the neutral point voltage with a reference voltage, and generating a reference value of an inner loop current after passing through an outer loop regulator formed by connecting a PI controller and a PR controller in series;

and comparing the feedback value of the capacitance current with the reference value of the inner loop current, and regulating by an inner loop PI controller to generate a modulation wave of the inverter.

7. The active arc extinction method for the single-phase earth fault of the power distribution network considering the line voltage drop, as claimed in claim 1, is characterized in that the fault distance is calculated based on neutral point voltage before and after the active arc extinction device is put into operation, the active arc extinction device injection current, the fault outgoing line three-phase current and the zero sequence current, and specifically includes:

wherein l_ZIn order to be the distance of the fault,

is a measure of the current injected into the neutral point by the inverter, Y_∑Is the admittance to ground parameter of the distribution network;

and

three-phase current measured values of the head ends of fault outgoing lines before and after the active arc suppression device is put into operation respectively,

and

before and after the active arc-extinguishing device is put into operationA zero sequence current measured value at the head end of the outgoing line,

and

respectively are the neutral point voltage measured values before and after the active arc-extinguishing device is put into operation,

is a phase A power supply voltage, Z_(1,2,0)Is the positive, negative and zero sequence impedance of the fault outgoing line in unit length.

8. The active arc extinction method for the single-phase earth fault of the power distribution network considering the line voltage drop is characterized in that based on the fault distance, the line voltage drop is considered, and the control target for updating the neutral point voltage of the power distribution network is as follows: the sum of the opposite of the faulted phase supply voltage and the line drop.

9. The utility model provides a take into account active arc extinguishing system of single-phase earth fault of distribution network of line voltage drop which characterized in that includes:

the fault judgment module is used for acquiring the operating voltage and current data of the power distribution network and judging whether a single-phase earth fault occurs or not;

the fault phase selection and line selection module is used for selecting a fault phase by using the amplitude and phase relation of three-phase bus voltage after fault when a single-phase earth fault occurs, and selecting a fault line by using the direction of zero-sequence current of each outgoing line;

the active arc suppression module is used for injecting current into the power distribution network by using the active arc suppression device and setting the initial control target of the neutral point voltage of the power distribution network as the opposite number of the fault phase power supply voltage; calculating a fault distance based on neutral point voltages before and after the active arc suppression device is put into operation, the injected current of the active arc suppression device, the three-phase current of a fault outgoing line and the zero-sequence current; and on the basis of the fault distance, calculating line voltage drop, and updating a control target of the neutral point voltage of the power distribution network so as to suppress the fault point voltage to zero.

10. A terminal device comprising a processor and a memory, the processor being arranged to implement instructions; the memory is configured to store a plurality of instructions, wherein the instructions are adapted to be loaded by the processor and to perform the method of any of claims 1-7 for a single-phase ground fault active arc suppression system for a power distribution network that accounts for line drops.

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