CN113036730B - Control method of power distribution network single-phase earth fault flexible arc extinction device - Google Patents
Control method of power distribution network single-phase earth fault flexible arc extinction device Download PDFInfo
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- 230000001276 controlling effect Effects 0.000 claims description 10
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- 238000010586 diagram Methods 0.000 description 17
- 230000000694 effects Effects 0.000 description 11
- 230000000087 stabilizing effect Effects 0.000 description 9
- 238000004088 simulation Methods 0.000 description 8
- 238000010891 electric arc Methods 0.000 description 2
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
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Abstract
本发明提出一种配电网单相接地故障柔性消弧装置的控制方法，其特征在于：柔性消弧装置的直流侧电源采用电容，通过接地故障补偿电流和直流侧电容稳压电流在对地支路和相间支路的协同控制，实现柔性消弧装置的直流侧电容电压稳定以及接地故障电流的全补偿。其不仅能实现接地故障电流的全补偿，而且省去了直流侧供电电源，节约了装置投入成本以及减小了设备体积，为配电网柔性消弧装置的推广应用和经济运行提供有力保障。
The invention provides a control method for a flexible arc suppression device for single-phase grounding faults in a distribution network, which is characterized in that: the DC side power supply of the flexible arc suppression device adopts a capacitor, and the ground fault compensation current and the DC side capacitor regulated current are used in the ground support. The coordinated control of the circuit and the phase-to-phase branch realizes the stability of the DC side capacitor voltage of the flexible arc suppression device and the full compensation of the ground fault current. It can not only realize full compensation of ground fault current, but also save the DC side power supply, save the investment cost of the device and reduce the size of the equipment, and provide a strong guarantee for the popularization, application and economic operation of the flexible arc suppression device in the distribution network.
Description
Technical Field
The invention belongs to the technical field of arc extinction of single-phase ground faults of power grids, and particularly relates to a control method of a flexible arc extinction device for single-phase ground faults of a power distribution network.
Background
As the size of the distribution network increases, the ground fault current increases. In addition, in recent years, nonlinear elements such as renewable energy sources, distributed power sources, flexible/direct-current power grids, variable-frequency loads and the like are widely applied, and the cabling degree of urban distribution lines is gradually improved, so that the harmonic current content and the active current content of the ground fault current are remarkably increased. So that the ground fault electric arc can not be extinguished by itself, fire and interphase short circuit fault are caused, intermittent electric arc ground fault is easy to occur, arc light overvoltage is generated, and the breakdown damage of power grid equipment is caused. The existing arc suppression devices are most widely applied to arc suppression coils, but only can compensate the reactive component of the earth fault current, and cannot compensate the harmonic component and the active component in the earth fault current, so that the flexible arc suppression devices for compensating the harmonic component and the active component of the earth fault current by using an active inverter appear.
At present, the topological structure of the existing flexible arc extinguishing device mainly comprises: master-slave mode, neutral point insertion type and split-phase mode. The master-slave flexible arc suppression device takes an arc suppression coil as a master arc suppression device to compensate the reactive component of the earth fault current, takes a single-phase inverter as a slave arc suppression device to compensate the harmonic wave and the active component of the earth fault current, and the slave arc suppression device is connected in parallel with two ends of the arc suppression coil through a step-up transformer. The neutral point connection type flexible arc extinction device is connected to a power distribution network through a single-phase inverter via a step-up transformer and a Z-shaped transformer and used as an arc extinction device to compensate earth fault current. The split-phase flexible arc extinguishing device is directly hung on a distribution bus or a circuit by a three-phase cascade H-bridge converter, and a three-phase common point is directly grounded or grounded through a switch.
The existing flexible arc extinguishing device has the main problems that: in the aspect of a topological structure, the master-slave topological structure needs the matching of an inverter and an arc suppression coil, the output level is low, and the switching frequency is high; when the neutral point connection type structure is in normal operation of a power distribution network, the neutral point voltage is low, and direct current side source taking is difficult; the voltage resistance of each phase current transformer of the split-phase structure needs to be line voltage, and the number of power electronic devices is large. In the aspect of taking a source from the direct current side, if the above topology structure needs to provide an independent direct current source for the direct current side of the inverter to realize the full compensation of the ground fault current, the direct current side is supplied with power in a mode of a step-down transformer and a rectifier, the number of input elements is large, the control is complex, the device cost is high, and the device size is large. The direct-current side voltage stabilization control strategy of the flexible arc extinction device topological structure in the absence of a direct-current source is not found in the prior art.
Disclosure of Invention
In view of the above, in order to make up for the gaps and the defects of the prior art, the present invention aims to provide a method for controlling a single-phase ground fault flexible arc extinction device of a power distribution network, and to provide five topology structures of the flexible arc extinction device, which are divided into a single-phase access type, a two-phase access type, a three-phase access type, a neutral point access type, and the like according to different ways of accessing a power grid, and to provide a flexible arc extinction method and a direct-current side voltage stabilization control method suitable for the five topology structures of the flexible arc extinction device. A direct-current side power supply of the flexible arc suppression device selects a capacitor, and the direct-current side capacitor voltage stabilization and the full compensation of the ground fault current of the flexible arc suppression device are realized through the cooperative control of the ground fault compensation current and the direct-current side capacitor voltage stabilization current on the ground branch and the interphase branch. The topology and the control method of the flexible arc extinction device not only can realize the full compensation of the grounding fault current, but also saves a power supply at a direct current side, saves the input cost of the device and reduces the volume of equipment, and provides powerful guarantee for the popularization and the application and the economic operation of the flexible arc extinction device of the power distribution network.
The invention specifically adopts the following technical scheme:
a control method of a power distribution network single-phase earth fault flexible arc extinction device is characterized by comprising the following steps: a direct-current side power supply of the flexible arc suppression device adopts a capacitor, and the direct-current side capacitor voltage stabilization and the full compensation of the ground fault current of the flexible arc suppression device are realized through the cooperative control of the ground fault compensation current and the direct-current side capacitor voltage stabilization current on the ground branch and the interphase branch.
And further, a single-phase access type flexible arc extinguishing device or a two-phase access type flexible arc extinguishing device or a three-phase access type flexible arc extinguishing device or a neutral point access type flexible arc extinguishing device is used for accessing the power grid.
Furthermore, the topology of the single-phase access type flexible arc suppression device adopts a single-phase H-bridge converter, one end of the converter is connected with a phase line on the low-voltage side of a distribution line or a step-up transformer, and the other end of the converter is connected with the ground; the single-phase H-bridge converter is one of a two-level single-phase half bridge, a three-level single-phase half bridge, a multi-level single-phase half bridge and a single-phase cascading H bridge;
the topology of the two-phase access type flexible arc suppression device adopts the grounding of a common point of a two-phase H-bridge converter through an arc suppression coil or the grounding of a common point of a two-phase H-bridge converter through a single-phase H-bridge converter; one end of the two-phase converter is connected with a phase line of a low-voltage side of the distribution line or the step-up transformer, the other end of the two-phase converter is connected with a common point, and the two-phase H-bridge converter is directly connected with any two phases of the distribution line or connected with any two phases of the distribution line through the step-up transformer; the two-phase H-bridge converter consists of two single-phase H-bridge converters;
the topology of the three-phase access type flexible arc extinction device adopts a four-bridge-arm H-bridge converter, wherein three bridge arms are three-phase H-bridge converters, a grounding bridge arm is a single-phase H-bridge converter, the three-phase H-bridge converters are directly connected in an articulated mode or connected to three phases of a distribution line through a boosting transformer, and a common point of the three-phase H-bridge converters is grounded through the single-phase H-bridge converter, namely the grounding bridge arm; the three-phase H-bridge converter is one of a two-level three-phase half bridge, a three-level three-phase half bridge, a multi-level three-phase half bridge or a three-phase cascading H bridge;
the topology of the neutral point access type flexible arc extinguishing device adopts a single-phase H-bridge converter to access a power distribution network through a Z-shaped transformer.
Further, when the single-phase access type flexible arc suppression device is accessed to a power grid, the following control method is specifically adopted:
when the single-phase flexible arc extinction device normally operates, the single-phase flexible arc extinction device is controlled to absorb active power from a grid connection point for stable control of capacitance voltage of a direct current side of the single-phase flexible arc extinction device;
when an earth fault occurs and the direct current side capacitor voltage is in a set value interval, controlling the single-phase flexible arc suppression device to output earth fault full compensation current; when the earth fault occurs and the voltage of the direct current side capacitor is not in the set value interval, the single-phase flexible arc extinction device is controlled to enable the output current of the single-phase flexible arc extinction device to be equal to the sum of the reactive component of the earth fault compensation current and the voltage stabilization current of the direct current side capacitor.
Further, when a two-phase access type flexible arc suppression device is used for accessing a power grid and a structure that a common point of a two-phase H-bridge converter is grounded through an arc suppression coil is adopted, the following control method is specifically adopted:
when the direct-current-side converter normally operates, the H-bridge converter of the two-phase bridge arm is controlled to absorb active power from the line voltage of the grid-connected point to charge the direct-current-side capacitor;
when the phase converter is in ground fault, the total injection current synthesized by the two-phase H-bridge converter is controlled to be the full compensation current of the ground fault all the time, the injection current of each phase is formed by superposing three parts of the compensation current of the ground fault, the voltage stabilization current at the direct current side of the phase converter and the voltage stabilization current negative value at the direct current side of the other phase converter, and the voltage stabilization current only circulates among phases and does not pass through a ground branch; the earth fault compensation current reference value is calculated by the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the local phase voltage stabilization current reference value and the local phase voltage absorb active power to stabilize the direct current side capacitance voltage; the arc suppression coil of the grounding branch is set to be in a full compensation state.
Further, when a two-phase access type flexible arc suppression device is used for accessing a power grid and a structure that a common point of a two-phase H-bridge converter is grounded through a single-phase H-bridge converter is adopted, the following control method is specifically adopted:
when the grounding bridge arm normally operates, the H-bridge converter of the grounding bridge arm is controlled to absorb active power from the common point of the two-phase bridge arm to charge the direct-current side capacitor;
when the phase converter is in ground fault, the total injection current synthesized by the two-phase H-bridge converter is controlled to be the full compensation current of the ground fault all the time, the injection current of each phase is formed by superposing three parts of the compensation current of the ground fault, the voltage stabilization current at the direct current side of the phase converter and the voltage stabilization current negative value at the direct current side of the other phase converter, and the voltage stabilization current only circulates among phases and does not pass through a ground branch; the earth fault compensation current reference value is calculated by the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the local phase voltage stabilization current reference value and the local phase voltage absorb active power to stabilize the direct current side capacitance voltage; the H-bridge converter injection current of the grounding branch circuit is the grounding fault full compensation current, and meanwhile, the common point voltage is regulated and controlled, so that the active power is absorbed from the common point, and the voltage stability of the direct current side capacitor is kept.
Further, when a three-phase access type flexible arc suppression device is used for accessing a power grid, the following control method is specifically adopted:
when the bridge is in normal operation, the H-bridge converter of the three-phase bridge arm is controlled to absorb active power from the three-phase voltage of the grid-connected point to charge the capacitor at the direct current side; after the direct-current side capacitors of the three-phase bridge arm converter are charged, two phases of the three-phase bridge arm converter are withdrawn, one phase is reserved, and the H-bridge converter of the grounding bridge arm absorbs active power from the common point of the three-phase bridge arm and the reserved one phase to charge the direct-current side capacitors;
when the three-phase H-bridge converter is in ground fault, the total injected current synthesized by the three-phase H-bridge converter is controlled to be the full compensating current of the ground fault all the time, the injected current of each phase is formed by superposing three parts of the ground fault compensating current, the voltage stabilizing current at the direct current side of the current transformer of the phase and one-half negative value of the voltage stabilizing current at the direct current side of the current transformer of the other two phases, and the voltage stabilizing current only circulates among phases and does not pass through a ground branch. The earth fault compensation current reference value is obtained by calculating the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the direct current side capacitance voltage is stabilized; the H-bridge converter injection current of the grounding branch circuit is the grounding fault full compensation current, and meanwhile, the common point voltage is regulated and controlled, so that the active power is absorbed from the common point, and the voltage stability of the direct current side capacitor is kept.
Further, when the neutral point access type flexible arc extinguishing device is used for accessing a power grid, the following control method is specifically adopted:
when the transformer normally operates, one phase of the Z-type transformer is switched in through the split-phase switch to charge a direct-current side capacitor of the H-bridge transformer;
when the three phases of the Z-type transformer are all put into operation during the earth fault, and when the capacitance voltage at the direct current side is in a set value interval, the single-phase H-bridge converter is controlled to output earth fault full compensation current; and when the voltage of the direct-current side capacitor is not in the set value interval, controlling the single-phase H-bridge converter to output the sum of the reactive component of the ground fault compensation current and the voltage stabilization current of the direct-current side capacitor.
Compared with the prior art, the invention and the optimized scheme thereof have the following beneficial effects:
1. the single-phase access type flexible arc extinguishing device, the neutral point access type flexible arc extinguishing device and the control scheme successfully solve the problem that the active component of the ground fault compensation current is inconsistent with the active current of the direct-current side capacitor voltage stabilization when the single-branch flexible arc extinguishing device without an independent direct-current source is used for ground fault current compensation through time-sharing switching of ground fault current active component compensation control and direct-current side capacitor voltage stabilization control. Although the direct-current side capacitor voltage stabilization and the earth fault current active component full compensation can not be carried out simultaneously by adopting the time-sharing control method, the topological structure has the advantages of fewer used elements, low equipment investment cost, no need of an independent direct-current power supply, smaller proportion of the active component of the earth fault current under the common condition and capability of being popularized and applied to a power distribution system with smaller active component of the earth fault current.
2. The two-phase access type flexible arc extinction device and the control scheme successfully solve the problem of direct current side source taking of the flexible arc extinction device through distribution of ground fault compensation current and direct current side capacitance voltage stabilization current among all phases, do not need an independent direct current power supply, save equipment such as a step-down transformer and a rectifier, reduce the manufacturing cost of the equipment and reduce the volume of the equipment. Compared with the single-phase access type flexible arc extinguishing device provided by the invention, the single-phase access type flexible arc extinguishing device needs more elements, can ensure the stability of the direct-current side capacitance voltage while fully compensating the grounding fault current, has wider application range, and can be popularized and applied to all power distribution systems.
3. The three-phase access type flexible arc extinguishing device and the control scheme are similar to the two-phase access type flexible arc extinguishing device. Through the distribution of the earth fault compensation current and the direct current side capacitance voltage stabilization current among all phases, the direct current side source taking problem of the flexible arc extinction device is successfully solved, an independent direct current power supply is not needed, equipment such as a step-down transformer and a rectifier is omitted, the manufacturing cost of the equipment is reduced, and the equipment volume is reduced. Although the three-phase access type flexible arc extinguishing device needs more elements compared with the two-phase access type flexible arc extinguishing device provided by the invention, the three-phase access type flexible arc extinguishing device can integrate functions of reactive compensation, harmonic suppression and the like, and the integrated equipment overall cost and volume are effectively improved compared with the combination of a plurality of independent equipment, so that the integrated cost is low, and the three-phase access type flexible arc extinguishing device can be popularized and applied to all power distribution systems with the requirements of reactive compensation, harmonic suppression, flexible arc extinguishing and the like.
Drawings
The invention is described in further detail below with reference to the following figures and detailed description:
FIG. 1 is a schematic diagram of a power distribution network and a single-phase access type flexible arc suppression device topology structure according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a topology structure of a power distribution network and a two-phase access type flexible arc suppression device according to an embodiment of the invention;
FIG. 3 is a schematic diagram of a power distribution network and a three-phase access type flexible arc suppression device topology structure according to an embodiment of the invention;
FIG. 4 is a schematic diagram of a topological structure of a power distribution network and a neutral point access type flexible arc suppression device according to an embodiment of the invention;
FIG. 5 is a control block diagram of a single-phase access type flexible arc suppression device according to an embodiment of the invention;
fig. 6 is a schematic diagram illustrating the flow of a voltage stabilizing current and a ground fault compensation current of a capacitor on the dc side of the two-phase access type flexible arc suppression device according to the embodiment of the present invention;
fig. 7 is a schematic diagram illustrating the flow of a stabilizing current and a compensating current of a ground fault of a capacitor on the dc side of a three-phase access type flexible arc extinguishing device according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a simulation model of a simulation example according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of a single-phase access type flexible arc suppression device ground fault current compensation effect and a direct current side capacitance voltage stabilization effect of a simulation example according to an embodiment of the present invention;
fig. 10 is a schematic diagram of a ground fault current compensation effect and a dc-side capacitance voltage stabilization effect of the single-phase and two-phase access type flexible arc extinguishing device in the simulation example of the embodiment of the present invention;
fig. 11 is a schematic diagram of a single three-phase access type flexible arc suppression device ground fault current compensation effect and a direct current side capacitance voltage stabilization effect of a simulation example according to an embodiment of the present invention;
fig. 12 is a schematic diagram of the basic structure and principle of the embodiment of the invention.
Detailed Description
In order to make the features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail as follows:
as shown in fig. 12, the present embodiment provides a topology structure and a control method of a single-phase ground fault flexible arc suppression device for a power distribution network. A direct-current side power supply of the flexible arc suppression device selects a capacitor, and the direct-current side capacitor voltage stabilization and the full compensation of the ground fault current of the flexible arc suppression device are realized through the cooperative control of the ground fault compensation current and the direct-current side capacitor voltage stabilization current on the ground branch and the interphase branch.
Meanwhile, the topological structures of the five flexible arc suppression devices are divided into a single-phase access type, a two-phase access type, a three-phase access type and a neutral point access type according to different modes of accessing a power grid.
In the embodiment, the single-phase access type flexible arc extinguishing device. The topology adopts a single-phase H-bridge converter. The converter is connected with the phase line of the low-voltage side of the distribution line or the step-up transformer at one end, and is connected with the ground at the other end, and the schematic diagram is shown in fig. 1. The single-phase H-bridge converter can be a high-voltage grade single-phase converter and can be directly hung on a bus or a line with 6kV, 10kV, 35kV or 66kV voltage grade. The single-phase H-bridge converter can be a low-voltage grade single-phase converter and is hung on a 6kV, 10kV, 35kV or 66kV voltage grade bus or line through a step-up transformer.
A fault current compensation and direct-current side capacitance voltage stabilization control method for a single-phase access type flexible arc suppression device. When the single-phase flexible arc extinction device normally operates, the single-phase flexible arc extinction device is controlled to absorb active power from a grid connection point for stable control of capacitance voltage of a direct current side of the single-phase flexible arc extinction device; when an earth fault occurs and the direct current side capacitor voltage is in a set value interval, controlling the single-phase flexible arc suppression device to output earth fault full compensation current; when the earth fault occurs and the voltage of the direct current side capacitor is not in the set value interval, the single-phase flexible arc extinction device is controlled to enable the output current of the single-phase flexible arc extinction device to be equal to the sum of the reactive component of the earth fault compensation current and the voltage stabilization current of the direct current side capacitor.
Two-phase access type flexible arc extinguishing device. The topology adopts the common point of the two-phase H-bridge converter to be grounded through an arc suppression coil (2 PCHB + ASC for short) or the common point of the two-phase H-bridge converter to be grounded through a single-phase H-bridge converter (2 PCHB + CHB for short). One end of the two-phase converter is connected to the phase line of the low-voltage side of the distribution line or the step-up transformer, and the other end is connected to the common point, and the two-phase H-bridge converter is directly connected to or connected to any two phases of the distribution line through the step-up transformer, and the schematic diagram is shown in fig. 2. The two-phase H-bridge converter can be a high-voltage grade two-phase converter and can be directly hung on a bus or a line with the voltage grade of 6kV, 10kV, 35kV or 66 kV. The two-phase H-bridge converter can be a low-voltage grade two-phase converter and is hung on a 6kV, 10kV, 35kV or 66kV voltage grade bus or line through a step-up transformer.
A fault current compensation and direct-current side capacitance voltage stabilization control method for a two-phase access type flexible arc suppression device. And when the grounding bridge arm with the 2PCHB + CHB structure normally operates, the H-bridge converter of the two-phase bridge arm is controlled to absorb active power from the line voltage of the grid-connected point to charge the capacitor at the direct current side, and the H-bridge converter of the grounding bridge arm with the 2PCHB + CHB structure absorbs active power from the common point of the two-phase bridge arm to charge the capacitor at the direct current side. When the grounding fault occurs, for the topological structure of 2PCHB + ASC, the total injection current synthesized by the two-phase H-bridge converter is controlled to be the grounding fault full compensation current all the time, and each phase injection current is formed by superposing three parts, namely the grounding fault compensation current, the direct-current side voltage stabilization current of the phase converter and the direct-current side voltage stabilization current negative value of the other phase converter, wherein the voltage stabilization current only circulates at the phase positions and does not pass through a grounding branch circuit. The earth fault compensation current reference value is calculated by the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the local phase voltage stabilization current reference value and the local phase voltage absorb active power to stabilize the direct current side capacitance voltage; the arc suppression coil of the grounding branch is set to be in a full compensation state. For a 2PCHB + CHB topological structure, the control method of the two-phase H-bridge converter is the same as that of the 2PCHB + ASC structure, the current injected by the H-bridge converter of the grounding branch is the grounding fault full compensation current, and the voltage of the common point is regulated and controlled simultaneously, so that the active power is absorbed from the common point, and the voltage stability of the capacitor at the direct current side is kept.
Three-phase access type flexible arc extinguishing device. The topology adopts a four-bridge-arm H-bridge converter, wherein three bridge arms are three-phase H-bridge converters, a grounding bridge arm is a single-phase H-bridge converter, the three-phase H-bridge converter is directly connected with three phases of a distribution line in a hanging mode, and a common point of the three-phase H-bridge converter is grounded through the single-phase H-bridge converter, namely the grounding bridge arm. The three-phase inverter is connected to the phase line of the low-voltage side of the distribution line or the step-up transformer at one end and is connected to the common point at another end, and the schematic diagram is shown in fig. 3. The three-phase H-bridge converter can be a high-voltage grade three-phase converter and can be directly hung on a bus or a line with 6kV, 10kV, 35kV or 66kV voltage grade. The three-phase H-bridge converter can be a low-voltage grade three-phase converter and is connected to a 6kV, 10kV, 35kV or 66kV voltage grade bus or line in a hanging mode through a step-up transformer.
A fault current compensation and direct-current side capacitance voltage stabilization control method of a three-phase access type flexible arc suppression device. When the bridge is in normal operation, the H-bridge converter of the three-phase bridge arm is controlled to absorb active power from the three-phase voltage of the grid-connected point to charge the capacitor at the direct current side; and after the direct-current side capacitors of the three-phase bridge arm converter are charged, two phases of the three-phase bridge arm converter are withdrawn, one phase is reserved, and the H-bridge converter of the grounding bridge arm absorbs active power from the common point of the three-phase bridge arm and the reserved one phase to charge the direct-current side capacitors. When the three-phase H-bridge converter is in ground fault, the total injected current synthesized by the three-phase H-bridge converter is controlled to be the full compensating current of the ground fault all the time, the injected current of each phase is formed by superposing three parts of the ground fault compensating current, the voltage stabilizing current at the direct current side of the current transformer of the phase and one-half negative value of the voltage stabilizing current at the direct current side of the current transformer of the other two phases, and the voltage stabilizing current only circulates among phases and does not pass through a ground branch. The earth fault compensation current reference value is obtained by calculating the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the direct current side capacitance voltage is stabilized; the H-bridge converter injection current of the grounding branch circuit is the grounding fault full compensation current, and meanwhile, the common point voltage is regulated and controlled, so that the active power is absorbed from the common point, and the voltage stability of the direct current side capacitor is kept.
The neutral point is connected into the flexible arc extinguishing device. The topology adopts a single-phase H-bridge converter to be connected to a power distribution network through a Z-type transformer, and the schematic diagram is shown in FIG. 4.
A fault current compensation and direct-current side capacitance voltage stabilization control method of a neutral point contact-in type flexible arc suppression device. When the transformer normally operates, one phase of the Z-type transformer is switched in through the split-phase switch to charge a direct-current side capacitor of the H-bridge transformer; when the three phases of the Z-type transformer are all put into operation during the earth fault, and when the capacitance voltage at the direct current side is in a set value interval, the single-phase H-bridge converter is controlled to output earth fault full compensation current; and when the voltage of the direct-current side capacitor is not in the set value interval, controlling the single-phase H-bridge converter to output the sum of the reactive component of the ground fault compensation current and the voltage stabilization current of the direct-current side capacitor.
The technical solution of the present embodiment is explained in detail from the principle perspective as follows:
1. principle of single-phase access type flexible arc extinguishing device
1.1 Single-phase access type earth fault current compensation principle
According to KCL
In the formula (I), the compound is shown in the specification,
and
system A, B and C respectively are current to ground,
and
respectively, a ground fault current and a current transformer injection current.
If the injection current is controlled
Then the fault point current according to equation (1)
Is suppressed to zero.
Converting the formula (1) into a voltage form to obtain
In the formula
And
for each phase of the power supply voltage,
is neutral point voltage, RfTo ground transition resistance, YA、YB、YCFor each phase admittance, Y is given a three-phase symmetry with respect to the earth parameterA＝YB＝YC＝Y0。
As can be seen from equation (2), if the total compensation current for the ground fault is taken as
Then the ground fault current will be completely cancelled to zero.
1.1 DC side capacitance voltage stabilization control principle
Given value of H-bridge converter injection current is fully compensated by earth fault
And DC side capacitor regulated current
The converter consists of two parts, because the earth fault full compensation current and the direct current side capacitor voltage stabilization current both pass through the single-phase H-bridge converter, the compensation effect of the earth fault current is influenced when the direct current side capacitor voltage stabilization is carried out, the residual current is increased, the residual current is mainly the active component of the current injected by the converter, but the value of the component is generally smaller. Therefore, the invention provides a time-sharing switching method for compensating the active component of the earth fault current and stably controlling the direct-current side capacitor voltage. When the earth fault current is fully compensated, the active component, the reactive component and the harmonic component of the earth fault current are compensated, and the direct-current side capacitor voltage stabilization control is quitted; and simultaneously detecting the capacitor voltage, and when the capacitor voltage is lower than or higher than a set threshold interval, quitting the compensation of the active component of the earth fault current and inputting the capacitor voltage stabilization at the direct current side. The control block diagram is shown in fig. 5.
2. Principle of two-phase access type flexible arc extinguishing device
2.1 two-phase injection type earth fault current compensation principle
Assuming that the A phase has ground fault, the two-phase converter is connected with the BC two phases, and the full compensation current of the ground fault is
Total injection current of phase B of
The current phase is obtained by accumulating the earth fault compensation current of the current phase, the stabilized current of the current phase and the stabilized current negative value of the connected other phase (namely, the C phase). Total injection current of C phase
The difference value is obtained by the total compensation current of the system earth fault and the total injection current of the B phase, namely
FIG. 6 is a schematic view of the topology current flow of the two-phase access type flexible arc-extinguishing device, and KCL is written on the COM point sequence of FIG. 6
The formula (4) can be substituted for the formula (5),
therefore, the current flowing through the grounding branch is always the grounding fault full compensation current.
2.2 two-phase injection type DC side capacitance voltage-stabilizing principle
Controlling the total injection current of the B phase as the compensation current of the local phase earth fault
This phase voltage-stabilizing current
And the connected other phase (namely C phase) regulated current
Superposition of three parts of negative value, in which the given value of the B-phase compensation current is taken
Then
According to the formulas (4) and (6), the total injection current of the C phase is obtained
The formula (7) can be converted from the formula (2)
The current in the grounding branch is always the full compensating current for the grounding fault and the sum of the injected two-phase currents, i.e.
The voltage stabilizing current of the direct current side capacitor only flows between the injected two phases and does not pass through the grounding branch.
3. Three-phase access type flexible arc extinguishing device principle
3.1 three-phase injection type earth fault current compensation principle
If the A phase has a ground fault, the full compensation current of the ground fault is
Calculating reference current value by taking any two phases of the three phases, and if taking AC two phases, the reference value of the A-phase compensation current is
Total injection current of
The C-phase compensation current reference value is
Total injection current of
And the total injection current reference value of the phase B is obtained by calculating the difference value of the system ground fault full compensation current and the total injection current of the phase A and the phase C.
3.2 three-phase injection type DC side capacitance voltage stabilization principle
Controlling the total injection current of the A phase and the C phase as the superposition of four parts of the negative value of one half of the ground fault compensation current of the phase, the stabilized current of the phase and the stabilized current of the other two phases, so that the total injection current of the A phase and the C phase is respectively
And the total injection current of the B phase is obtained by solving the difference between the total compensation current of the system ground fault and the total injection current of the A phase and the C phase. The compensation current and the stabilized current of the phase (B phase) can be calculated according to the formula (2), the formula (9) and the formula (10)
The flow conditions of the direct-current side capacitor regulated current and the ground fault compensation current are shown in figure 7.
4. Principle of neutral point connection type flexible arc extinguishing device
The principle of the neutral point connection type flexible arc extinguishing device is the same as that of a single-phase connection type flexible arc extinguishing device, so that the description is omitted.
In order to make the technical solution of the present invention better understood by those skilled in the art, the present invention is further described below with reference to a simulation example.
And (3) building a power distribution network simulation model containing 6 feeders as shown in figure 8 by using PSCAD software. The distribution line adopts a Bergeron model. For the distribution network shown in fig. 2, the ground fault point is set at node 1, the a-phase ground fault is set, and the simulation results are shown in fig. 9 to 11.
As can be seen from fig. 9, although the compensation of the ground fault current and the dc-side capacitive voltage stabilization cannot be performed simultaneously in the single-phase access type flexible arc extinguishing apparatus, the residual current of the ground fault is small by the time-sharing control.
As can be seen from fig. 10, the ground fault current compensation and the dc-side capacitance voltage stabilization of the two-phase access type flexible arc suppression device can be performed simultaneously, and the compensation effect and the voltage stabilization effect are good.
As can be seen from fig. 11, the ground fault current compensation and the dc-side capacitance voltage stabilization of the three-phase access type flexible arc suppression device can be performed simultaneously, and the compensation effect and the voltage stabilization effect are better.
The embodiment provides five topological structures of flexible arc suppression devices, which are divided into a single-phase access type, a two-phase access type, a three-phase access type, a neutral point access type and the like according to different modes of accessing a power grid, and provides a flexible arc suppression method and a direct-current side voltage stabilization control method suitable for the five topological structures of the flexible arc suppression devices. A direct-current side power supply of the flexible arc suppression device selects a capacitor, and the direct-current side capacitor voltage stabilization and the full compensation of the ground fault current of the flexible arc suppression device are realized through the cooperative control of the ground fault compensation current and the direct-current side capacitor voltage stabilization current on the ground branch and the interphase branch. The topology and the control method of the flexible arc extinction device not only can realize the full compensation of the grounding fault current, but also saves a power supply at a direct current side, saves the input cost of the device and reduces the volume of equipment, and provides powerful guarantee for the popularization and the application and the economic operation of the flexible arc extinction device of the power distribution network.
The present invention is not limited to the above preferred embodiments, and any other control method for the single-phase ground fault flexible arc-extinguishing device of the distribution network in various forms can be obtained according to the teaching of the present invention.
Claims (6)
1. A control method of a power distribution network single-phase earth fault flexible arc extinction device is characterized by comprising the following steps: the direct-current side power supply of the flexible arc suppression device adopts a capacitor, and the direct-current side capacitor voltage stabilization and the full compensation of the ground fault current of the flexible arc suppression device are realized through the cooperative control of the ground fault compensation current and the direct-current side capacitor voltage stabilization current on the ground branch and the interphase branch;
a single-phase access type flexible arc extinguishing device or a two-phase access type flexible arc extinguishing device or a three-phase access type flexible arc extinguishing device or a neutral point access type flexible arc extinguishing device is adopted to be accessed into the power grid;
the topology of the single-phase access type flexible arc extinguishing device adopts a single-phase H-bridge converter, one end of the converter is connected with a phase line on the low-voltage side of a distribution line or a step-up transformer, and the other end of the converter is connected with the ground; the single-phase H-bridge converter is one of a two-level single-phase half bridge, a three-level single-phase half bridge, a multi-level single-phase half bridge and a single-phase cascading H bridge;
the topology of the two-phase access type flexible arc suppression device adopts the grounding of a common point of a two-phase H-bridge converter through an arc suppression coil or the grounding of a common point of a two-phase H-bridge converter through a single-phase H-bridge converter; one end of the two-phase converter is connected with a phase line of a low-voltage side of the distribution line or the step-up transformer, the other end of the two-phase converter is connected with a common point, and the two-phase H-bridge converter is directly connected with any two phases of the distribution line or connected with any two phases of the distribution line through the step-up transformer; the two-phase H-bridge converter consists of two single-phase H-bridge converters;
the topology of the three-phase access type flexible arc extinction device adopts a four-bridge-arm H-bridge converter, wherein three bridge arms are three-phase H-bridge converters, a grounding bridge arm is a single-phase H-bridge converter, the three-phase H-bridge converters are directly connected in an articulated mode or connected to three phases of a distribution line through a boosting transformer, and a common point of the three-phase H-bridge converters is grounded through the single-phase H-bridge converter, namely the grounding bridge arm; the three-phase H-bridge converter is one of a two-level three-phase half bridge, a three-level three-phase half bridge, a multi-level three-phase half bridge or a three-phase cascading H bridge;
the topology of the neutral point access type flexible arc extinguishing device adopts a single-phase H-bridge converter to access a power distribution network through a Z-shaped transformer.
2. The control method of the flexible arc suppression device for the single-phase ground fault of the power distribution network according to claim 1, characterized in that: when the single-phase access type flexible arc suppression device is used for accessing a power grid, the following control method is specifically adopted:
when the single-phase flexible arc extinction device normally operates, the single-phase flexible arc extinction device is controlled to absorb active power from a grid connection point for stable control of capacitance voltage of a direct current side of the single-phase flexible arc extinction device;
when an earth fault occurs and the direct current side capacitor voltage is in a set value interval, controlling the single-phase flexible arc suppression device to output earth fault full compensation current; when the earth fault occurs and the voltage of the direct current side capacitor is not in the set value interval, the single-phase flexible arc extinction device is controlled to enable the output current of the single-phase flexible arc extinction device to be equal to the sum of the reactive component of the earth fault compensation current and the voltage stabilization current of the direct current side capacitor.
3. The control method of the flexible arc suppression device for the single-phase ground fault of the power distribution network according to claim 1, characterized in that: when a two-phase access type flexible arc suppression device is used for accessing a power grid and a structure that a common point of a two-phase H-bridge converter is grounded through an arc suppression coil is adopted, the following control method is specifically adopted:
when the direct-current-side converter normally operates, the H-bridge converter of the two-phase bridge arm is controlled to absorb active power from the line voltage of the grid-connected point to charge the direct-current-side capacitor;
when the phase converter is in ground fault, the total injection current synthesized by the two-phase H-bridge converter is controlled to be the full compensation current of the ground fault all the time, the injection current of each phase is formed by superposing three parts of the compensation current of the ground fault, the voltage stabilization current at the direct current side of the phase converter and the voltage stabilization current negative value at the direct current side of the other phase converter, and the voltage stabilization current only circulates among phases and does not pass through a ground branch; the earth fault compensation current reference value is calculated by the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the local phase voltage stabilization current reference value and the local phase voltage absorb active power to stabilize the direct current side capacitance voltage; the arc suppression coil of the grounding branch is set to be in a full compensation state.
4. The control method of the flexible arc suppression device for the single-phase ground fault of the power distribution network according to claim 1, characterized in that: when a two-phase access type flexible arc suppression device is used for accessing a power grid and a structure that a common point of a two-phase H-bridge converter is grounded through a single-phase H-bridge converter is adopted, the following control method is specifically adopted:
when the grounding bridge arm normally operates, the H-bridge converter of the grounding bridge arm is controlled to absorb active power from the common point of the two-phase bridge arm to charge the direct-current side capacitor;
when the phase converter is in ground fault, the total injection current synthesized by the two-phase H-bridge converter is controlled to be the full compensation current of the ground fault all the time, the injection current of each phase is formed by superposing three parts of the compensation current of the ground fault, the voltage stabilization current at the direct current side of the phase converter and the voltage stabilization current negative value at the direct current side of the other phase converter, and the voltage stabilization current only circulates among phases and does not pass through a ground branch; the earth fault compensation current reference value is calculated by the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the local phase voltage stabilization current reference value and the local phase voltage absorb active power to stabilize the direct current side capacitance voltage; the H-bridge converter injection current of the grounding branch circuit is the grounding fault full compensation current, and meanwhile, the common point voltage is regulated and controlled, so that the active power is absorbed from the common point, and the voltage stability of the direct current side capacitor is kept.
5. The control method of the flexible arc suppression device for the single-phase ground fault of the power distribution network according to claim 1, characterized in that: when a three-phase access type flexible arc suppression device is used for accessing a power grid, the following control method is specifically adopted:
when the bridge is in normal operation, the H-bridge converter of the three-phase bridge arm is controlled to absorb active power from the three-phase voltage of the grid-connected point to charge the capacitor at the direct current side; after the direct-current side capacitors of the three-phase bridge arm converter are charged, two phases of the three-phase bridge arm converter are withdrawn, one phase is reserved, and the H-bridge converter of the grounding bridge arm absorbs active power from the common point of the three-phase bridge arm and the reserved one phase to charge the direct-current side capacitors;
when the ground fault occurs, the total injection current synthesized by the three-phase H-bridge converter is controlled to be the full compensation current of the ground fault all the time, the injection current of each phase is formed by superposing three parts, namely the ground fault compensation current, the voltage stabilization current at the direct current side of the current transformer of the phase and one-half negative value of the voltage stabilization current at the direct current side of the current transformer of the other two phases, and the voltage stabilization current only circulates among phases and does not pass through a ground branch;
the earth fault compensation current reference value is obtained by calculating the product of the local phase voltage and the local phase-to-earth admittance, and the local phase voltage stabilization current reference value and the local phase voltage have the same phase, so that the direct current side capacitance voltage is stabilized; the H-bridge converter injection current of the grounding branch circuit is the grounding fault full compensation current, and meanwhile, the common point voltage is regulated and controlled, so that the active power is absorbed from the common point, and the voltage stability of the direct current side capacitor is kept.
6. The control method of the flexible arc suppression device for the single-phase ground fault of the power distribution network according to claim 1, characterized in that: when the neutral point access type flexible arc suppression device is used for accessing a power grid, the following control method is specifically adopted:
when the transformer normally operates, one phase of the Z-type transformer is switched in through the split-phase switch to charge a direct-current side capacitor of the H-bridge transformer;
when the three phases of the Z-type transformer are all put into operation during the earth fault, and when the capacitance voltage at the direct current side is in a set value interval, the single-phase H-bridge converter is controlled to output earth fault full compensation current; and when the voltage of the direct-current side capacitor is not in the set value interval, controlling the single-phase H-bridge converter to output the sum of the reactive component of the ground fault compensation current and the voltage stabilization current of the direct-current side capacitor.
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