CN114156906B - Multifunctional compensation method for asymmetric power distribution network - Google Patents
Multifunctional compensation method for asymmetric power distribution network Download PDFInfo
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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
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
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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
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- Engineering & Computer Science (AREA)
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- Supply And Distribution Of Alternating Current (AREA)
Abstract
The invention relates to a multifunctional compensation method of an asymmetric power distribution network, which takes a four-bridge arm cascade H-bridge converter without an independent direct current source as a multifunctional converter and takes sequencing control as a control strategy of the multifunctional converter, and comprises a reactive power compensation current target value calculation method, a three-phase relative ground parameter asymmetric compensation current calculation method, a three-phase bridge arm converter ground fault compensation current calculation method, an inter-phase control method of direct current side capacitor regulated current, a ground bridge arm converter ground fault compensation current calculation method and a direct current side capacitor regulated voltage calculation method thereof. The method has the advantages of high equipment utilization rate, low realization cost, comprehensive compensation effect and better fault suppression performance.
Description
Technical Field
The invention belongs to the field of power distribution networks, and particularly relates to a multifunctional compensation method for an asymmetric power distribution network.
Background
The flexible arc extinction and reactive compensation converters of the single-phase earth fault of the power distribution network have single functions, the flexible arc extinction converters only play a role in the fault period, the utilization rate is low, and the economy of equipment is poor.
At present, the existing topological structure with the functions of flexible arc extinction and reactive compensation mainly comprises the following components: the neutral point of the three-phase cascade H-bridge converter is directly grounded or grounded through a switch, and the neutral point of the three-phase cascade H-bridge converter is grounded through an arc suppression coil. However, when the neutral point of the three-phase cascade H-bridge converter is directly grounded or grounded through a switch, the voltage of the non-fault phase is close to the line voltage and the voltage of the fault phase is close to zero during the low-resistance ground fault, so that the withstand voltage of each phase of converter needs not to be lower than the line voltage and more power electronic elements should be input. In addition, at this time, the voltage at both ends of the fault phase converter is close to zero, active power cannot be absorbed from the grid-connected point to maintain the voltage stability of the capacitor at the direct current side, the operation must be stopped, reactive compensation and fault suppression can only be multiplexed in a time-sharing manner, and cannot be performed simultaneously. The control object of the ground fault current compensation of the neutral point of the three-phase cascade H-bridge converter through the arc suppression coil grounding type is complex in calculation, the grounding transition resistance needs to be obtained first, however, the grounding transition resistance can be changed all the time when the arc is grounded, and the calculation is difficult. In addition, the dynamic response speed of the arc suppression coil is low, the initial arc suppression effect of the grounding fault is affected, the three-phase cascade H-bridge converter is matched with the arc suppression coil, and the control is complex.
Disclosure of Invention
The invention aims to provide a multifunctional compensation method for an asymmetric power distribution network, which has the advantages of high equipment utilization rate, low realization cost, comprehensive compensation effect and better fault suppression performance.
In order to achieve the above purpose, the invention adopts the following technical scheme: a multifunctional compensation method for an asymmetric power distribution network uses a four-bridge arm cascade H-bridge converter without an independent direct current source as a multifunctional converter and uses sequencing control as a control strategy of the multifunctional converter, and the multifunctional compensation method comprises a reactive power compensation current target value calculation method, a three-phase relative ground parameter asymmetric compensation current calculation method, a three-phase bridge arm converter ground fault compensation current calculation method, an inter-phase control method for direct current side capacitance regulated current, a ground bridge arm converter ground fault compensation current calculation method and a direct current side capacitance regulated voltage calculation method, and reactive power compensation, ground fault compensation and asymmetric current compensation are realized.
Further, the multifunctional converter comprises a three-phase bridge arm adopting a three-phase H-bridge converter, the three-phase bridge arm is connected in a star shape, and a grounding bridge arm adopting the single-phase H-bridge converter is additionally arranged between a star connection point and the ground.
Further, the three-phase H-bridge converter comprises a three-phase cascade H-bridge and a connecting inductor, wherein the three-phase cascade H-bridge comprises 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 cascade H-bridge; the single-phase H-bridge converter comprises a single-phase H-bridge and a connecting inductor, wherein the single-phase H-bridge comprises a two-level single-phase half-bridge, a three-level single-phase half-bridge, a multi-level single-phase half-bridge or a single-phase cascade H-bridge; and the direct current sides of the three-phase H-bridge converter and the single-phase H-bridge converter are not provided with independent direct current sources.
Further, the reactive compensation current target value calculating method comprises the following steps: according to the instantaneous power theory, a given reactive power target value is converted and calculated into a q-axis target current value through abc-dq, a d-axis target current value is set to be zero, and then the d-axis target current value and the q-axis target current value are reversely converted into a reference target value for three-phase reactive compensation current calculation through dq-abc.
Further, the three-phase-to-earth parameter asymmetry compensation current calculation method comprises the following steps: and controlling the zero sequence voltage of the system to be zero, measuring the output current of the grounding bridge arm of the multifunctional converter at the moment, and taking the output current as a reference target value of asymmetric current calculation.
Further, the method for calculating the ground fault compensation current of the three-phase bridge arm converter comprises the following steps: the sum of the ground fault compensation currents of the three-phase bridge arm is always the ground fault full compensation current, namely the product of the negative value of the fault phase power supply voltage and the admittance of the system to the ground, the fault phase compensation current is the product of the negative value of the fault phase power supply voltage and the local relative admittance and the number 2, and the non-fault phase compensation current is the product of the local phase power supply voltage and the local relative admittance.
Further, the interphase control method of the capacitor regulated current at the direct current side of the three-phase bridge arm converter comprises the following steps: the regulated current at the direct current side of the three-phase bridge arm converter only flows at the interphase, and does not pass through the ground branch, namely the sum of the three-phase regulated current is always kept to be zero; and the total regulated current of each phase is obtained by the difference value of half of the regulated current of the current phase and the regulated current of other two phases.
Further, the method for calculating the ground fault compensation current of the grounding bridge arm converter comprises the following steps: the ground fault compensation current of the ground bridge arm is the ground fault full compensation current, namely the product of the negative value of the power supply voltage of the fault phase and the admittance of the system to the ground.
Further, the calculation method of the direct-current side capacitor regulated voltage of the grounding bridge arm converter comprises the following steps: the output current of the grounding bridge arm is always the full compensation current of the grounding fault, and the direct current side voltage stabilization of the grounding bridge arm converter adopts a mode of regulating and controlling the common point voltage of the three-phase bridge arm.
Compared with the prior art, the invention has the following beneficial effects:
1. the multifunctional converter topology structure with the four-bridge arm H-bridge converter provided by the invention enables one set of converter to have single-phase grounding fault suppression, asymmetric current compensation and reactive compensation functions, improves the utilization rate of equipment, and has fewer elements required to be input and better economy of the equipment because the bearing voltage of each phase of cascaded H-bridge converter is the phase voltage. In addition, the invention has the advantages of high dynamic response speed, no independent power supply at the direct current side, capability of inhibiting the arc ground fault, capability of realizing the full compensation of the ground fault current and the like.
2. The method for calculating the ground fault compensation current of the three-phase converter not only ensures the full compensation of the ground fault current, but also distributes the capacitor regulated current of the direct current side of the converter to each phase more uniformly, and has better cooperative performance of fault suppression and capacitor voltage stable control of the direct current side and lower control complexity.
3. According to the interphase control method for the direct-current side capacitor regulated current of the converter, the regulated current only flows in the interphase without passing through the grounding loop, the regulated current and the grounding fault compensation current are decoupled, the influence of the regulated current on fault suppression is avoided, and the fault suppression performance of the multifunctional converter is better.
Drawings
Fig. 1 is a schematic diagram of a topology structure of a multifunctional converter in a method according to an embodiment of the present invention;
fig. 2 is a control strategy of the multifunctional converter in the method according to the embodiment of the present invention;
fig. 3 is an effect diagram of multi-objective control of the multi-functional converter in the method according to the embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
As shown in fig. 1 and 2, the embodiment provides a multifunctional compensation method for an asymmetric power distribution network, and the method uses a four-bridge arm cascade H-bridge converter without an independent direct current source as a multifunctional converter, so that a set of converters has the functions of single-phase grounding fault suppression, asymmetric current compensation and reactive power compensation. The method takes the sequence control as a control strategy of the multifunctional converter, and comprises a reactive power compensation current target value calculation method, a three-phase relative ground parameter asymmetric compensation current calculation method, a three-phase bridge arm converter grounding fault compensation current calculation method, an inter-phase control method of direct-current side capacitor regulated current of the three-phase bridge arm converter grounding fault compensation current calculation method, a grounding bridge arm converter grounding fault compensation current calculation method and a direct-current side capacitor regulated voltage calculation method of the grounding bridge arm converter grounding fault compensation current calculation method, so that reactive power compensation, grounding fault compensation and asymmetric current compensation are realized. According to the method for calculating the ground fault compensation current of the three-phase bridge arm converter and the method for controlling the phase-to-phase of the direct-current side capacitor regulated current, which are suitable for the multifunctional converter, the direct-current side capacitor regulated current of the converter is distributed to each phase more uniformly, the regulated current is ensured not to pass through a ground loop and to circulate only between the phases, and the effective coordination of fault suppression and direct-current side capacitor voltage stable control is realized.
In this embodiment, the multifunctional converter includes a three-phase bridge arm adopting a three-phase H-bridge converter, the three-phase bridge arm is connected in a star shape, and a grounding bridge arm adopting a single-phase H-bridge converter is additionally arranged between the star connection point and the ground. The three-phase bridge arm is used for reactive power compensation, the grounding bridge arm provides a circulation loop for single-phase grounding fault current and asymmetric compensation current, and the grounding fault current compensation and the asymmetric current compensation are realized. The three-phase H-bridge converter comprises a three-phase cascade H-bridge and a connecting inductor, wherein the three-phase cascade H-bridge comprises 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 cascade H-bridge; the single-phase H-bridge converter comprises a single-phase H-bridge and a connecting inductor, wherein the single-phase H-bridge comprises a two-level single-phase half-bridge, a three-level single-phase half-bridge, a multi-level single-phase half-bridge or a single-phase cascade H-bridge. And the direct current sides of the three-phase H-bridge converter and the single-phase H-bridge converter are not provided with independent direct current sources.
The reactive compensation current target value calculating method specifically comprises the following steps: according to the instantaneous power theory, a given reactive power target value is converted and calculated into a q-axis target current value through abc-dq, a d-axis target current value is set to be zero, and then the d-axis target current value and the q-axis target current value are reversely converted into a reference target value for three-phase reactive compensation current calculation through dq-abc.
The three-phase-to-earth parameter asymmetric compensation current calculation method specifically comprises the following steps: and controlling the zero sequence voltage of the system to be zero, measuring the output current of the grounding bridge arm of the multifunctional converter at the moment, and taking the output current as a reference target value of asymmetric current calculation.
The method for calculating the ground fault compensation current of the three-phase bridge arm converter specifically comprises the following steps: the sum of the ground fault compensation currents of the three-phase bridge arm is always the ground fault full compensation current, namely the product of the negative value of the fault phase power supply voltage and the admittance of the system to the ground, the fault phase compensation current is the product of the negative value of the fault phase power supply voltage and the local relative admittance and the number 2, and the non-fault phase compensation current is the product of the local phase power supply voltage and the local relative admittance.
The interphase control method of the direct-current side capacitor regulated current of the three-phase bridge arm converter specifically comprises the following steps: the regulated current at the direct current side of the three-phase bridge arm converter only flows at the interphase, and does not pass through the ground branch, namely the sum of the three-phase regulated current is always kept to be zero. And the total regulated current of each phase is obtained by the difference value of half of the regulated current of the current phase and the regulated current of other two phases.
The grounding bridge arm converter grounding fault compensation current calculation method specifically comprises the following steps: the ground fault compensation current of the ground bridge arm is the ground fault full compensation current, namely the product of the negative value of the power supply voltage of the fault phase and the admittance of the system to the ground.
The calculation method of the direct-current side capacitor regulated voltage of the grounding bridge arm converter specifically comprises the following steps: the output current of the grounding bridge arm is always the full compensation current of the grounding fault, and the direct current side voltage stabilization of the grounding bridge arm converter adopts a mode of regulating and controlling the common point voltage of the three-phase bridge arm.
The following describes in detail the relevant principles involved in the implementation of the method:
1. reactive power compensation principle
The instantaneous power is known to be according to the instantaneous power theory
And also has
Wherein T is a park transformation, u a 、u b And u c Three-phase voltages of grid connection points of the multifunctional converters, u d 、u q The voltages of grid-connected points are respectively converted into voltages of d axis and q axis, E is the amplitude of phase power supply voltage, omega is the angular frequency of the system, i d And i q The current transformer is respectively injected with currents which are converted to d-axis and q-axis.
Substituting and sorting the parameters of T into (2)
The reference current values of d-axis and q-axis at reactive compensation can be obtained from the formulas (1) and (3) as
Wherein P is * And Q * The target values of active power compensation and reactive power compensation which are respectively issued by the power dispatching department are respectively obtained, and the multifunctional converter only performs reactive power compensation, so that the target value of active power compensation is set to be zero.
The reference current value shown in the formula (4) can be obtained as the reference current value of the three-phase reactive compensation after the dq-abc inverse transformation
The reactive power compensation can be realized by controlling each phase-change current transformer to output the compensation current.
2. Ground fault suppression
Assuming that the phase A has single-phase ground fault and the three phases are symmetrical relative to the ground parameters, the leakage resistance to the ground is r 0 The capacitance to ground is C 0 According to kirchhoff's law and substituting the ground parameter and voltage, the method is finished
To make the fault point current zero, i.e. I f ＝(U 0 +E a )/R f Zero, E a Can be approximated to a constant value, U 0 ＝-E a Substituting the current into the current (6) to obtain the control target of the total fault current compensation of the grounding bridge arm converter
3. DC side voltage stabilization control
The dc side voltage of the converter is maintained by absorbing active power from the grid-connected point, and is mainly related to the current flowing through the converter, the voltage across the converter and the included angle between the current and the voltage across the converter. The ground fault does not affect the normal operation of the multifunctional converter in the reactive compensation mode, only the voltage of a common point and the voltage of a parallel point are changed, and the voltages at two ends of a three-phase bridge arm (namely the difference value between the voltage of the parallel point and the voltage of the common point) of the multifunctional converter are always kept close to the phase power supply voltage. The invention provides a novel method for distributing ground fault compensation current in a three-phase converter, which specifically comprises the following expression
The zero sequence current of the three-phase current transformer is full compensation current, and the compensation current of each phase is the product of the voltages at two ends of the phase-change current transformer and the parameters to the ground. The damping rate of the distribution line is generally smaller, so that the included angle between the compensation current of each phase and the voltage at two ends of the phase change current transformer is close to 90 degrees, the compensation current distributed by the fault phase and the non-fault phase is two thirds and one third of the total compensation current respectively, and the active power required to be absorbed by each phase of the current transformer is smaller and is easier to realize.
The sum of the three-phase output currents (zero-sequence current) must be the total compensation current of the ground fault, so the regulated current of the three-phase converter should flow only among the three phases, i.e. the sum of the three-phase regulated currents is zero, the regulated current of the direct current side of each phase is
In which I idc (i=a, B, C) is the regulated current of each phase itself generated in fig. 2.
The output current of the grounding bridge arm converter must be always kept as the full compensation current of the grounding fault, if the voltage stabilizing current of the direct current side is superposed, the grounding fault current compensation is affected, therefore, the voltage of the two ends of the grounding bridge arm converter can be regulated to stabilize the capacitor voltage of the direct current side, one end of the grounding bridge arm converter is directly grounded, the other end of the grounding bridge arm converter is connected with the common point of the three-phase converter, and the voltage stabilizing control of the direct current side of the grounding bridge arm converter can be realized only by regulating the voltage of the common point, and the generation mode of the voltage stabilizing voltage is shown in fig. 2.
4. DC side voltage stabilization control
According to kirchhoff's law and substituting the ground parameter and voltage, the method is finished
In the formula (10), if the current injected into the converter is three-phase-to-earth parameter unbalanced current I Z ＝I 0bd ＝E A ·Y A +E B ·Y B +E C ·Y C The zero sequence voltage of the system is suppressed to zero; and if the zero sequence voltage of the control system is zero, the current injected into the converter is three-phase-to-earth parameter unbalanced current. Therefore, the three-phase-to-earth parameter unbalanced current can be calculated by measuring the current injected by the converter with zero sequence voltage of the control system. The control strategy of the multifunctional converter is shown in fig. 2.
In order to enable a person skilled in the art to better understand the technical solution of the present invention, the present invention is further described below with reference to a simulation example.
And building a power distribution network simulation model containing 6 feeder lines by using PSCAD software. The distribution line adopts a Bergeron model. For the distribution network shown in fig. 1, a phase a ground fault is set, and the asymmetry of the system to the ground parameter is 2.8%. The grounding bridge arm and the three-phase bridge arm of the multifunctional converter are respectively put into the moment 0.24s and the moment 0.3s to compensate reactive power and asymmetric current, a grounding fault with the transition resistance of 10Ω is arranged at a bus at the moment 0.4s, the grounding fault compensation current is output at the moment 0.5s, the given compensation capacity of reactive power compensation is 1.0Mvar, and the multifunctional converter is controlled to output comprehensive compensation current for asymmetric current compensation, reactive power compensation, grounding fault suppression and direct current side capacitance voltage stabilization according to a split-phase control strategy, wherein the compensation effect is shown in figure 3.
As can be seen from fig. 3, the multifunctional converter can perform reactive compensation, asymmetric current compensation and ground fault suppression simultaneously, and can ensure the stability of the capacitor voltage at the dc side of the converter.
The invention provides a multifunctional compensation method of an asymmetric power distribution network, which uses a four-bridge arm cascade H-bridge converter as a multifunctional converter, wherein three-phase bridge arms are connected in a star shape and used for reactive power compensation, and a grounding bridge arm formed by a single-phase cascade H-bridge converter is additionally arranged between a star-shaped connection point and the ground, so that a circulation loop is provided for single-phase grounding fault current, and the grounding fault current compensation is realized. The invention ensures that a set of current transformer has the functions of single-phase grounding fault suppression, asymmetric current compensation and reactive compensation, improves the utilization rate of equipment and enhances the economical efficiency of the equipment. The invention provides a three-phase converter grounding fault compensation current calculation method and an interphase control method of a converter direct-current side capacitor regulated current, which are suitable for a multifunctional converter, wherein the converter direct-current side capacitor regulated current is more uniformly distributed to each phase, the regulated current is ensured not to pass through a grounding loop and only flows between the interphase, and the effective coordination of fault suppression and direct-current side capacitor voltage stable control is realized. The direct current side of the converter does not need to be additionally provided with an independent power supply, so that elements are saved, the equipment cost is reduced, and conditions are provided for popularization and application of the multifunctional converter.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.
Claims (3)
1. The multifunctional compensation method for the asymmetric power distribution network is characterized in that a four-bridge arm cascade H-bridge converter without an independent direct current source is used as a multifunctional converter, and sequencing control is used as a control strategy of the multifunctional converter, and the multifunctional compensation method comprises a reactive power compensation current target value calculation method, a three-phase relative ground parameter asymmetric compensation current calculation method, a three-phase bridge arm converter ground fault compensation current calculation method, an inter-phase control method for direct current side capacitance regulated current of the three-phase bridge arm converter, a ground bridge arm converter ground fault compensation current calculation method and a direct current side capacitance regulated voltage calculation method of the ground bridge arm converter ground fault compensation current calculation method are used for realizing reactive power compensation, ground fault compensation and asymmetric current compensation;
the reactive compensation current target value calculating method comprises the following steps: according to the instantaneous power theory, a given reactive power target value is converted and calculated into a q-axis target current value through abc-dq, a d-axis target current value is set to be zero, and then the d-axis target current value and the q-axis target current value are reversely converted into a reference target value calculated by three-phase reactive compensation current through dq-abc;
the three-phase-to-earth parameter asymmetric compensation current calculation method comprises the following steps: the zero sequence voltage of the system is controlled to be zero, the output current of a grounding bridge arm of the multifunctional converter at the moment is measured, and the output current is used as a reference target value for calculating asymmetric current;
the method for calculating the ground fault compensation current of the three-phase bridge arm converter comprises the following steps: the sum of the ground fault compensation currents of the three-phase bridge arm is always the ground fault full compensation current, namely the product of the negative value of the fault phase power supply voltage and the admittance of the system to the ground, the fault phase compensation current is the product of the negative value of the fault phase power supply voltage, the local relative admittance and the number 2, and the non-fault phase compensation current is the product of the local phase power supply voltage and the local relative admittance;
the interphase control method of the capacitor regulated current at the direct current side of the three-phase bridge arm converter comprises the following steps: the regulated current at the direct current side of the three-phase bridge arm converter only flows at the interphase, and does not pass through the ground branch, namely the sum of the three-phase regulated current is always kept to be zero; the total voltage-stabilizing current of each phase is obtained by the difference value of half of the voltage-stabilizing current of the current phase and the voltage-stabilizing current of other two phases;
the calculation method of the grounding fault compensation current of the grounding bridge arm converter comprises the following steps: the ground fault compensation current of the ground bridge arm is the ground fault full compensation current, namely the product of the negative value of the power supply voltage of the fault phase and the admittance of the system to the ground;
the calculation method of the direct-current side capacitor regulated voltage of the grounding bridge arm converter comprises the following steps: the output current of the grounding bridge arm is always the full compensation current of the grounding fault, and the direct current side voltage stabilization of the grounding bridge arm converter adopts a mode of regulating and controlling the common point voltage of the three-phase bridge arm.
2. The multifunctional compensation method of an asymmetric power distribution network according to claim 1, wherein the multifunctional converter comprises a three-phase bridge arm adopting a three-phase H-bridge converter, the three-phase bridge arm is connected in a star shape, and a grounding bridge arm adopting a single-phase H-bridge converter is additionally arranged between a star connection point and the ground.
3. The multifunctional compensation method of an asymmetric power distribution network according to claim 2, wherein the three-phase H-bridge converter comprises a three-phase cascaded H-bridge and a connecting inductor, and the three-phase cascaded H-bridge comprises 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 cascaded H-bridge; the single-phase H-bridge converter comprises a single-phase H-bridge and a connecting inductor, wherein the single-phase H-bridge comprises a two-level single-phase half-bridge, a three-level single-phase half-bridge, a multi-level single-phase half-bridge or a single-phase cascade H-bridge; and the direct current sides of the three-phase H-bridge converter and the single-phase H-bridge converter are not provided with independent direct current sources.
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