A flexible arc-extinguishing device of inductance series voltage division type

Abstract

The application provides a flexible arc-extinguishing device of inductance series voltage division type, and the topology structure of the flexible arc-extinguishing device is that a single-phase converter is connected in series with an arc-extinguishing coil, one end of which is connected to the ground, and the other end is connected to a power distribution network through a grounding transformer; and the control method of the flexible arc-extinguishing device is that a part of the grounding fault current which cannot be compensated by the arc-extinguishing coil is compensated by the single-phase converter, so that full compensation of the fault current is realized. By applying the technical scheme, the pressure resistance requirement of the converter can be reduced, the manufacturing cost can be saved, and the equipment size can be reduced under the premise of full compensation of the grounding fault current. The flexible voltage arc-extinguishing method can suppress the grounding fault arc without measuring the ground parameter, and has good engineering application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single-phase grounding fault arc extinction of power distribution network, and particularly relates to an inductance series voltage division type flexible arc extinction device. BACKGROUND

[0002] With the rapid development of society in China, the scale of power distribution network gradually increases, and the grounding fault current also increases. In addition, due to the wide application of nonlinear elements and cable lines, the proportion of harmonic components and active components of the grounding fault current significantly increases, and the traditional arc suppression coil cannot compensate for these components, which leads to the grounding fault arc that cannot extinguish itself, and easily aggravates the fault, for example, generates arc overvoltage to cause damage to power grid equipment, or develops into an inter-phase short-circuit fault, or even causes a fire, so the flexible arc extinction device for compensating for the harmonic components and active components of the grounding fault current through an active inverter appears.

[0003] The existing flexible arc extinction device can be divided into master-slave type, neutral point access type and split-phase type according to the topological structure. The master-slave type flexible arc extinction device is generally a parallel type, the arc suppression coil is used as the main arc extinction device to compensate for most of the reactive components of the grounding fault current, and the single-phase inverter is used as the slave arc extinction device to compensate for the harmonic components and active components of the grounding fault current through the boost transformer connected in parallel at both ends of the arc suppression coil. The neutral point access type flexible arc extinction device is connected to the power distribution network through the boost transformer and the Z-type grounding transformer by the single-phase inverter, and can realize full compensation of the grounding fault current. The split-phase type flexible arc extinction device directly connects the three-phase cascaded H-bridge converter to the power distribution bus or line, and the three-phase common point is directly grounded or grounded through a switch, and can realize full compensation of the grounding fault current.

[0004] The main problems of the existing flexible arc extinction device are as follows: the output level of the master-slave type flexible arc extinction device is low, and the switching frequency is high; the DC side of the neutral point access type flexible arc extinction device is difficult to obtain a source; and the voltage withstand requirement of the converter used in the split-phase type flexible arc extinction device is high, and many power electronic devices are used. Moreover, the DC side power supply of the above topological structure adopts an independent DC source, and a step-down transformer and a rectifier are used to supply power to the DC side, so the investment cost is high, and the equipment size is large. SUMMARY

[0005] Therefore, the purpose of the present application is to provide an inductance series voltage division type flexible arc extinction device, which reduces the voltage withstand requirement of the converter, saves the manufacturing cost and reduces the equipment size under the premise of realizing full compensation of the grounding fault current. The flexible voltage arc extinction method can suppress the grounding fault arc without measuring the ground parameters, and has good engineering application value.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: an inductor series voltage divider type flexible arc suppression device, wherein the topology of the flexible arc suppression device is that a single-phase converter and an arc suppression coil are connected in series, one end of which is connected to the ground, and the other end is connected to the distribution network through a grounding transformer; the control method of the flexible arc suppression device is to compensate for the part of the ground fault current that the arc suppression coil cannot compensate for by the single-phase converter, thereby achieving full compensation of the fault current.

[0007] In a preferred embodiment: the DC power supply of the single-phase converter in the flexible arc suppression device is a capacitor. The output voltage of the converter is calculated to be the product of the distribution network damping rate and the fault phase power supply voltage; thereby determining the minimum and maximum values ​​of the DC capacitor voltage setting range of the converter.

[0008] In a preferred embodiment: when using an arc suppression coil with a non-adjustable inductance value, the flexible arc suppression device specifically employs the following control method:

[0009] During normal operation, if the DC side capacitor voltage of the single-phase converter is less than the minimum value of the set range, any two phases are led out from the secondary side of the Z-type grounding transformer and charged to the DC side capacitor of the converter through the rectifier until the DC side capacitor voltage of the converter reaches the maximum value of the set range. Then, the connection between the flexible arc suppression device and the neutral point is disconnected through the single-phase high-voltage switch, so that the distribution network works in the neutral point ungrounded state.

[0010] When a ground fault occurs, the single-phase high-voltage switch is closed. At this time, one end of the converter and the arc suppression coil are connected to the ground, and the other end is connected to the neutral point of the distribution network. Based on the principle of current or voltage arc suppression, the converter is controlled to compensate for the residual reactive, active, and harmonic components in the fault current, thereby achieving full compensation of the fault current.

[0011] In a preferred embodiment: when using an arc suppression coil with adjustable inductance, the flexible arc suppression device specifically employs the following control method:

[0012] During normal operation, if the DC side capacitor voltage of the single-phase converter is less than the minimum value of the set range, any two phases are led out from the secondary side of the Z-type grounding transformer and charged to the DC side capacitor of the converter through the rectifier until the DC side capacitor voltage of the converter reaches the maximum value of the set range. Then, the connection between the flexible arc suppression device and the neutral point is disconnected through the single-phase high-voltage switch, so that the distribution network works in the neutral point ungrounded state.

[0013] During a ground fault, based on the measured capacitance parameters of the distribution network to ground, and following the principle of full compensation of the arc suppression coil, the inductance value of the arc suppression coil is calculated and adjusted. The single-phase high-voltage switch is then closed. At this time, one end of the converter and the arc suppression coil are connected to the ground, and the other end is connected to the neutral point of the distribution network. Based on the principle of current or voltage arc suppression, the converter is controlled to compensate for the residual active and harmonic components and a small portion of reactive components in the fault current, thereby achieving full compensation of the fault current.

[0014] In a preferred embodiment: the flexible arc suppression device is controlled as a current source, and its output current is the ground fault full compensation current injected into the neutral point. Its value is the product of the negative value of the fault phase power supply voltage and the total ground admittance of the distribution network. The output voltage of the single-phase converter in the flexible arc suppression device is the difference between the negative value of the fault phase power supply voltage and the calculated value of the voltage across the arc suppression coil.

[0015] In a preferred embodiment: the flexible arc suppression device is controlled as a voltage source, the output voltage of which is the negative value of the fault phase power supply voltage, and the output voltage of the single-phase converter in the flexible arc suppression device is the difference between the negative value of the fault phase power supply voltage and the measured value of the voltage across the arc suppression coil.

[0016] Compared with existing technologies, this invention has the following advantages: The inductor-series voltage divider type flexible arc suppression device proposed in this invention, through the structure of a single-phase converter and an arc suppression coil connected in series and the control method based on the current and voltage arc suppression principle, can significantly reduce the actual output voltage of the converter while achieving full compensation for ground fault current, i.e., reducing the withstand voltage requirement of the converter, saving manufacturing costs of the flexible arc suppression device, and reducing the size of the equipment. Furthermore, the flexible voltage arc suppression method can suppress ground fault arcs without measuring ground parameters, and has good engineering application value. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the topology and principle of the flexible arc-extinguishing device according to a preferred embodiment of the present invention;

[0018] Figure 2 The circuit diagram for the computational equivalent circuit of the flexible arc-extinguishing device according to a preferred embodiment of the present invention is shown below.

[0019] Figure 3 This is a schematic diagram of a simulation model for a preferred embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of the fault current compensation effect of the flexible arc suppression device in a simulation example of a preferred embodiment of the present invention when the ground fault transition resistance is 100Ω.

[0021] Figure 5 This is a schematic diagram of the fault current compensation effect of the flexible arc suppression device in a simulation example of a preferred embodiment of the present invention when the ground fault transition resistance is 200Ω.

[0022] Figure 6 This is a schematic diagram of the fault current compensation effect of the flexible arc suppression device in a simulation example of a preferred embodiment of the present invention when the ground fault transition resistance is 500Ω. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, 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 pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] like Figure 1 and Figure 2 As shown, this embodiment provides the topology, schematic diagram, and equivalent circuit calculation of an inductor-series voltage divider type flexible arc suppression device. Based on the principle of current or voltage arc suppression, it compensates for the portion of the ground fault current that the arc suppression coil cannot compensate for by a single-phase converter, thereby achieving full compensation of the fault current. The single-phase converter is one of the following: a two-level single-phase half-bridge / full-bridge, a three-level single-phase half-bridge / full-bridge, a multi-level single-phase half-bridge / full-bridge, or a single-phase cascaded H-bridge. Figure 1 Taking the cascaded H-bridge as an example; the arc suppression coil is either an arc suppression coil with a non-adjustable inductance value or an arc suppression coil with an adjustable inductance value; the DC power supply of the single-phase converter uses a capacitor.

[0027] When the distribution network is three-phase symmetrical and the arc suppression coil is operating with full compensation, the expression for the converter output voltage is U. INV =dE f Where d is the distribution network damping ratio, E f Given the faulty phase power supply voltage, the minimum value of the DC-side capacitor voltage setting range for the converter can be determined as dE. m E m Given the voltage amplitude of any one phase of the power supply, the set range of the DC-side capacitor voltage of the single-phase converter is taken as [dE]. m ,kdE m], where k is the capacitor voltage setting coefficient, which is negatively correlated with the capacitor value and positively correlated with the three-phase asymmetry of the distribution network and the detuning degree of the arc suppression coil. Usually, the calculated value of d does not exceed 10%, and the value of k does not exceed 1.5.

[0028] When using an arc suppression coil with non-adjustable inductance, the flexible arc suppression device employs the following control method: During normal operation, if the DC-side capacitor voltage of the single-phase converter is less than the minimum value of the set range, any two phases are drawn from the secondary side of the Z-type grounding transformer and charged through a rectifier to the DC-side capacitor of the converter until the DC-side capacitor voltage reaches the maximum value of the set range. Then, the connection between the flexible arc suppression device and the neutral point is disconnected via a single-phase high-voltage switch, allowing the distribution network to operate in a neutral-point ungrounded state. During a ground fault, the single-phase high-voltage switch is closed. At this time, one end of the converter and the arc suppression coil is connected to the ground, and the other end is connected to the neutral point of the distribution network. Based on the current or voltage arc suppression principle, the converter is controlled to compensate for the residual reactive, active, and harmonic components in the fault current, thereby achieving full compensation of the fault current.

[0029] When using an arc suppression coil with adjustable inductance, the flexible arc suppression device employs the following control method: During normal operation, if the DC-side capacitor voltage of the single-phase converter is less than the minimum value of the set range, any two phases are drawn from the secondary side of the Z-type grounding transformer and charged through a rectifier to the DC-side capacitor of the converter until the DC-side capacitor voltage reaches the maximum value of the set range. Then, the connection between the flexible arc suppression device and the neutral point is disconnected via a single-phase high-voltage switch, allowing the distribution network to operate in a neutral-point ungrounded state. During a ground fault, based on the measured distribution network capacitance parameters, and following the principle of full compensation of the arc suppression coil, the inductance value of the arc suppression coil is calculated and adjusted. The single-phase high-voltage switch is closed. At this time, one end of the converter and the arc suppression coil is connected to the ground, and the other end is connected to the neutral point of the distribution network. Based on the current or voltage arc suppression principle, the converter is controlled to compensate for the residual active and harmonic components and a small portion of reactive components in the fault current, thereby achieving full compensation of the fault current.

[0030] In the two control methods described above, when using a single-phase cascaded H-bridge converter, it is necessary to control the sum of the DC-side capacitor voltages of each H-bridge stage to be within a set range.

[0031] When using the flexible current arc suppression method, the flexible arc suppression device is controlled as a current source, and its output current is the ground fault full compensation current, which is injected into the neutral point. The expression for the full compensation current is I. in =-E f (1 / r ∑ +jωC Σ The output voltage expression of the single-phase converter in the flexible arc suppression device is U. INV =-E f +I in jωL, where rΣ and C ∑ These are the total leakage resistance to ground and capacitance to ground of the distribution network, E, respectively. f L is the power supply voltage of the faulty phase, and L is the inductance value of the arc suppression coil.

[0032] When the flexible voltage arc suppression method is used, the flexible arc suppression device is controlled as a voltage source, and its output voltage is the negative value of the fault phase power supply voltage. The output voltage expression of the single-phase converter in the flexible arc suppression device is U. INV =-E f -U ASC U ASC This represents the measured voltage across the arc suppression coil.

[0033] The technical solution of this embodiment will be described in detail from the perspective of principle as follows:

[0034] 1. Principle of Inductor Series Voltage Divider Type Flexible Arc Extinguishing Device

[0035] 1.1 Flexible Voltage Arc Extinguishing Principle

[0036] like Figure 1 and Figure 2 As shown, taking a single-phase ground fault in phase A as an example, the following equations are given.

[0037]

[0038] In the formula, U f For the faulty phase voltage, U A E is the phase voltage of phase A in the distribution network. A U is the voltage of phase A of the power supply network, U0 is the neutral point voltage, and U INV U is the output voltage of the single-phase converter. ASC This represents the measured voltage across the arc suppression coil.

[0039] According to the principle of flexible voltage arc suppression, if the output voltage of the flexible arc suppression device is controlled to be the negative value of the fault phase power supply voltage, that is, the neutral point voltage U0 = -E A , making U f =0, I f =0, which can effectively suppress the ground fault arc. From equation (1), the expression for the output voltage of the single-phase converter is:

[0040] U INV =-E A -U ASC (2)

[0041] Similarly, when single-phase grounding faults occur in phases B and C, it can be seen from equation (2) that when using the voltage-based arc suppression method, the inductor series voltage divider type flexible arc suppression device can suppress the grounding fault arc without measuring the ground parameters.

[0042] 1.2 Flexible Current Arc Extinguishing Principle

[0043] like Figure 1 and Figure 2 As shown, taking a single-phase ground fault in phase A as an example, the following equations are given.

[0044]

[0045] In the formula, I A0 I B0 I C0 These are the three-phase ground currents of the distribution network, I in I is the output current of the flexible arc suppression device. f For ground fault current, E A E B E C These are the three-phase power supply voltages of the distribution network, U A U B U C These are the three-phase phase voltages of the distribution network, where U0 is the neutral point voltage, and U... INV U is the output voltage of the single-phase converter. ASC The voltage across the arc suppression coil is r. A r B r C These are the three-phase-to-ground leakage resistances of the distribution network, C A C B C C These are the three-phase equivalent capacitances to ground of the distribution network, and L is the inductance of the arc suppression coil.

[0046] According to the principle of flexible current arc suppression, if the output current of the flexible arc suppression device is controlled to be the ground fault full compensation current, the full compensation current is injected into the neutral point, making U f =0,I f =0, which can effectively suppress the ground fault arc. From equation (3), it can be seen that the output current of the flexible arc suppression device is

[0047]

[0048] Let C be an example. A =C B =C C =C0, r A =r B =r C =r0, from U0=-E A have to

[0049]

[0050] In the formula, r ∑ =r0 / 3,C∑ =3C0. From equation (3), the expression for the output voltage of a single-phase converter is also given.

[0051] U INV =-E A +I in jωL (6)

[0052] The same applies to single-phase grounding faults in phases B and C.

[0053] 2. Calculation of output voltage of single-phase converter

[0054] To demonstrate that the inductor-series voltage divider type flexible arc suppression device can significantly reduce the actual output voltage of the converter, i.e., reduce the withstand voltage requirement of the converter, thereby reducing the investment cost of the converter, the following derivation and calculation are performed.

[0055] For arc suppression coils with non-adjustable inductance, the L value is generally calculated based on the overcompensation principle. For arc suppression coils with adjustable inductance, the L value can be calculated and adjusted according to the principle of full compensation of the arc suppression coil during a short-circuit fault. That is to say, the reactive component in the fault current is mainly compensated by the arc suppression coil, and the remaining component is compensated by the single-phase converter. The remaining component is mainly the active component and harmonic component.

[0056] Let the damping rate of the distribution network be d = G. ∑ / (jωC ∑ ), where G ∑ =1 / r ∑ r ∑ and C ∑ These are the system's leakage resistance to ground and capacitance to ground, respectively. Let ωL = 1 / (ωC) ∑ Then, from equations (5) and (6), we can obtain...

[0057]

[0058] Under normal insulation conditions, the damping rate of overhead lines does not exceed 3-5%, and the damping rate of cable lines does not exceed 2-4%. When insulation aging occurs, the damping rate of the distribution network generally does not exceed 10%. As can be seen from equation (7), compared with the method of completely connecting the single-phase converter to the neutral point of the distribution network to achieve arc suppression of single-phase grounding faults in the distribution network, the actual output voltage of the single-phase converter in the inductor series voltage divider type flexible arc suppression device proposed in this invention, i.e., the withstand voltage requirement, can theoretically be reduced to less than 1 / 10, thereby saving manufacturing costs and reducing equipment volume to a great extent.

[0059] 3. Determine the DC-side capacitor voltage setting range of the converter.

[0060] As can be seen from equation (7), the minimum value of the DC-side capacitor voltage setting range of the converter is dE.m E m Let be the voltage amplitude of any one phase of the power supply. From equations (4) and (6), it can be seen that when the three phases of the distribution network are unbalanced, or when the arc suppression coil is operating in an overcompensated state, the output voltage of the single-phase converter will be larger than the result in equation (7). Therefore, the set range of the DC-side capacitor voltage of the single-phase converter can be taken as [dE]. m ,kdE m ], where k is the capacitor voltage setting coefficient, which is negatively correlated with the capacitor value and positively correlated with the three-phase asymmetry of the distribution network and the detuning degree of the arc suppression coil. Usually, the value of k does not exceed 1.5.

[0061] To enable those skilled in the art to better understand the technical solution of this invention, the invention will be further described below with reference to a simulation example.

[0062] Build using Matlab / Simulink, such as Figure 3 The simulation model of the distribution network with 5 feeders shown has a phase-A ground fault set at the fault point. The simulation results are as follows. Figures 4-6 As shown.

[0063] Depend on Figure 4 It can be seen that the inductor series voltage divider type flexible arc suppression device proposed in this invention has a small residual current and a good fault current compensation effect when the ground fault transition resistance is 100Ω.

[0064] Depend on Figure 5 It can be seen that the inductor series voltage divider type flexible arc suppression device proposed in this invention has a small residual current and a good fault current compensation effect when the ground fault transition resistance is 200Ω.

[0065] Depend on Figure 6 It can be seen that the inductor series voltage divider type flexible arc suppression device proposed in this invention has a small residual current and a good fault current compensation effect when the ground fault transition resistance is 500Ω.

[0066] This embodiment verifies the arc suppression effect of the inductor-series voltage divider type flexible arc suppression device under different ground fault transition resistance conditions. It proposes a calculation method for the single-phase converter control target value of the flexible current and voltage arc suppression method suitable for this device structure, and derives and gives the expression for the single-phase converter output voltage. The arc suppression coil compensates for most of the reactive component in the fault current, while the single-phase converter mainly compensates for the active and harmonic components of the fault current. This device, while achieving full compensation for the ground fault current, reduces the converter's withstand voltage requirement, saves manufacturing costs, and reduces equipment size.

[0067] This patent is not limited to the above-described preferred embodiment. Anyone can derive other forms of inductor series voltage divider flexible arc suppression devices under the guidance of this patent. All equivalent changes and modifications made within the scope of this patent application shall fall within the scope of this patent.

Claims

1. An inductor-series voltage divider type flexible arc suppression device, characterized in that: The topology of the flexible arc suppression device is that a single-phase converter and an arc suppression coil are connected in series, with one end connected to the ground and the other end connected to the power distribution network through a grounding transformer; the control method of the flexible arc suppression device is to compensate for the part of the ground fault current that the arc suppression coil cannot compensate for by the single-phase converter, so as to achieve full compensation of the fault current. In the flexible arc suppression device, the DC power supply of the single-phase converter is a capacitor. According to the calculation, the output voltage of the converter is the product of the distribution network damping rate and the fault phase power supply voltage; thus, the minimum and maximum values ​​of the DC-side capacitor voltage setting range of the converter are determined. When using an arc-suppression coil with an adjustable inductance value, the flexible arc-suppression device specifically employs the following control method: During normal operation, if the DC side capacitor voltage of the single-phase converter is less than the minimum value of the set range, any two phases are led out from the secondary side of the Z-type grounding transformer and charged to the DC side capacitor of the converter through the rectifier until the DC side capacitor voltage of the converter reaches the maximum value of the set range. Then, the connection between the flexible arc suppression device and the neutral point is disconnected through the single-phase high-voltage switch, so that the distribution network works in the neutral point ungrounded state. When a ground fault occurs, the single-phase high-voltage switch is closed. At this time, one end of the converter and the arc suppression coil are connected to the ground, and the other end is connected to the neutral point of the distribution network. According to the principle of current or voltage arc suppression, the converter is controlled to compensate for the residual reactive, active and harmonic components in the fault current, thereby achieving full compensation of the fault current. When using an arc-suppression coil with adjustable inductance, the flexible arc-suppression device specifically employs the following control method: During normal operation, if the DC side capacitor voltage of the single-phase converter is less than the minimum value of the set range, any two phases are led out from the secondary side of the Z-type grounding transformer and charged to the DC side capacitor of the converter through the rectifier until the DC side capacitor voltage of the converter reaches the maximum value of the set range. Then, the connection between the flexible arc suppression device and the neutral point is disconnected through the single-phase high-voltage switch, so that the distribution network works in the neutral point ungrounded state. During a ground fault, based on the measured capacitance parameters of the distribution network to ground, and following the principle of full compensation of the arc suppression coil, the inductance value of the arc suppression coil is calculated and adjusted. The single-phase high-voltage switch is then closed. At this time, one end of the converter and the arc suppression coil are connected to the ground, and the other end is connected to the neutral point of the distribution network. Based on the principle of current or voltage arc suppression, the converter is controlled to compensate for the residual active and harmonic components and a small portion of reactive components in the fault current, thereby achieving full compensation of the fault current.

2. The inductor-series voltage divider type flexible arc suppression device according to claim 1, characterized in that: The flexible arc suppression device is controlled as a current source, and its output current is the ground fault full compensation current, which is injected into the neutral point. Its value is the product of the negative value of the fault phase power supply voltage and the total ground admittance of the distribution network. The output voltage of the single-phase converter in the flexible arc suppression device is the difference between the negative value of the fault phase power supply voltage and the calculated value of the voltage across the arc suppression coil.

3. The inductor-series voltage divider type flexible arc suppression device according to claim 1, characterized in that: The flexible arc suppression device is controlled as a voltage source, and its output voltage is the negative value of the fault phase power supply voltage. The output voltage of the single-phase converter in the flexible arc suppression device is the difference between the negative value of the fault phase power supply voltage and the measured value of the voltage across the arc suppression coil.

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