CN108539767B - Novel voltage feedforward control method for static var generator and static var generator - Google Patents

Novel voltage feedforward control method for static var generator and static var generator Download PDF

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CN108539767B
CN108539767B CN201810412193.XA CN201810412193A CN108539767B CN 108539767 B CN108539767 B CN 108539767B CN 201810412193 A CN201810412193 A CN 201810412193A CN 108539767 B CN108539767 B CN 108539767B
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current
sequence voltage
static var
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CN108539767A (en
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瞿李锋
孙建军
习楠
李尚盛
查晓明
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Wuhan Keliyuan Electric Co ltd
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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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • Y02E40/10—Flexible AC transmission systems [FACTS]
    • 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
    • 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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Abstract

The invention discloses a new voltage feedforward control method for a static var generator and the static var generator, wherein the new voltage feedforward control method for the static var generator comprises the following steps: the static var generator acquires the current negative sequence voltage when the power grid is unbalanced; determining the current zero sequence voltage of the static var generator according to the current negative sequence voltage and a preset corresponding relation, wherein the preset corresponding relation is the corresponding relation between the negative sequence voltage and the zero sequence voltage, so as to realize voltage feedforward control of the static var generator; and superposing the current zero-sequence voltage to the three-phase unbalanced voltage to carry out the feedforward control of the three-phase voltage reconstruction so as to realize the voltage feedforward control of the static var generator. The invention solves the technical problems that when the voltage drop of a single phase, two phases or three phases of the power grid is asymmetric, the direct voltage between the three phases of the star-shaped chain type static var generator is stable and has the capability of continuously outputting reactive current, and the response speed of the asymmetric fault of the power grid is accelerated.

Description

Novel voltage feedforward control method for static var generator and static var generator
Technical Field
The invention relates to the field of power electronics, in particular to a novel voltage feedforward control method for a static var generator and the static var generator.
Background
When the power grid is unbalanced and falls, the negative sequence voltage on the power grid side can enable the output side of the SVG to generate negative sequence current, and the positive sequence reactive current, the negative sequence current and the power grid voltage output by the chained SVG (Static Var Generator) interact with each other to enable active power absorbed among three phases to be unbalanced, so that three-phase direct voltage is unequal and three-phase direct voltage is unstable.
At present, when the power grid is in an unbalanced drop fault, a control strategy capable of maintaining the stability of the interphase direct voltage of the chained SVG has a control strategy of injecting negative sequence current.
The control strategy of injecting negative sequence current adjusts the amplitude and the phase of the negative sequence current by analyzing the fluctuation quantity of active power among three phases caused by the interaction of the negative sequence current and the voltage of a grid-connected point, and adjusts and balances the active power among the three phases by injecting the negative sequence current, but the control limits the proportion of three-phase current under the unbalanced working condition, the output capacity of the positive sequence current is sacrificed under the condition of high unbalance degree of a power grid, and the complete compensation of the load unbalanced current is difficult to realize.
The above is only for the purpose of assisting understanding of the technical aspects of the present invention, and does not represent an admission that the above is prior art.
Disclosure of Invention
The invention mainly aims to provide a new voltage feedforward control method for a static var generator, and aims to solve the technical problems of controlling direct voltage balance among three phases of a star-connected static var generator and accelerating the response speed of asymmetrical faults of a power grid when the voltage of the power grid drops in a single phase or two phases.
In order to achieve the above object, the present invention provides a new voltage feedforward control method for a static var generator, which includes:
the static var generator acquires the current negative sequence voltage when the power grid is unbalanced;
determining the current zero-sequence voltage according to the current negative-sequence voltage and a preset corresponding relation, wherein the preset corresponding relation is the corresponding relation between the negative-sequence voltage and the zero-sequence voltage;
and superposing the current zero-sequence voltage to the three-phase unbalanced voltage to carry out the feedforward control of the three-phase voltage reconstruction so as to realize the voltage feedforward control of the static var generator.
Preferably, before determining the current zero-sequence voltage according to the current negative-sequence voltage and the preset corresponding relationship, the new method for voltage feedforward control of the static var generator further includes:
acquiring positive sequence voltage and negative sequence voltage of instantaneous voltage of a power grid when an asymmetric fault occurs and output current of a static var generator;
respectively calculating the three-phase average active power according to the positive sequence voltage, the negative sequence voltage and the output current of the static var generator;
acquiring three-phase power fluctuation quantity of negative sequence voltage according to the three-phase average active power;
and determining the corresponding relation between the negative sequence voltage and the zero sequence voltage according to the three-phase power fluctuation quantity of the negative sequence voltage.
Preferably, the three-phase average active power is respectively calculated according to the positive sequence voltage, the negative sequence voltage and the output current of the static var generator by using the following formulas:
Figure BDA0001646565720000021
Figure BDA0001646565720000022
Figure BDA0001646565720000023
Figure BDA0001646565720000024
wherein, Ua、Ub、UcRespectively three-phase grid voltage; i.e. ia、ib、icThree-phase output currents of the static var generator are respectively: wherein U isp、UnEffective values, theta, of positive and negative sequence voltages, respectivelynIs the negative sequence voltage initial phase; i ispOutputting positive sequence reactive current effective value for static var generator, α is positive sequence reactive current phase, pi/2 or-pi/2, PkIs the three-phase average active power;
three-phase average active power P in formula (1)a、PbAnd PcPower P generated by positive sequence voltage and positive sequence reactive current action of the first part respectivelyapp、Pbpp、PcppAnd the power P generated by the action of the negative sequence voltage and the positive sequence reactive current of the second partanp、Pbnp、PcnpForming; wherein the first part of the three-phase power quantity is calculated to be equal, i.e. Papp＝Pbpp＝PcppSecond part three-phase power quantity Panp、Pbnp、PcnpNot equal; the second term is the amount of power fluctuation between three phases.
Preferably, the determining the corresponding relationship between the negative sequence voltage and the zero sequence voltage according to the three-phase power fluctuation amount specifically includes:
assuming that zero-sequence voltage is injected into three-phase voltage, Uz is an effective value of the zero-sequence voltage, and theta z is an initial phase of the zero-sequence voltage, wherein the expression of the zero-sequence voltage is as follows:
Figure BDA0001646565720000031
then, the three-phase power amount generated by the zero-sequence voltage output by the static var generator and the positive-sequence reactive current is not equal, and the three-phase power fluctuation amount caused by the zero-sequence voltage is:
Figure BDA0001646565720000032
and the three-phase power fluctuation quantity caused by the action of the negative sequence voltage and the positive sequence reactive current is equal to the three-phase power fluctuation quantity caused by the action of the zero sequence voltage and the positive sequence reactive current, and the zero sequence voltage can be obtained by a negative sequence voltage expression.
Preferably, the new static var generator voltage feedforward control method further comprises the following steps:
acquiring three-phase average direct-current voltage and three-phase feedback direct-current voltage at the direct-current side of the static var generator;
synthesizing zero-sequence voltage according to the obtained three-phase average direct current voltage and the three-phase feedback direct current voltage;
and directly superposing the zero sequence voltage into the modulation wave.
Preferably, the synthesizing of the zero sequence voltage according to the obtained three-phase average dc voltage and the three-phase feedback dc voltage specifically includes:
the three-phase average direct current voltage is differed from the three-phase feedback direct current voltage, and proportional integral control is carried out on the differencing result to obtain the power fluctuation amount of each phase;
and calculating zero sequence voltage according to the power fluctuation amount of each phase.
Preferably, the new static var generator voltage feedforward control method further comprises the following steps:
acquiring reactive current and three-phase feedback current which are required to be compensated by a load and collected by a static var generator;
and adding reactive current and total direct-voltage control active current according to the working mode of the static var generator to obtain command current, and performing proportional control on the difference between the command current and three-phase feedback current to superpose the command current and the three-phase feedback current on a modulation wave.
Preferably, the feed-forward control of adding the negative sequence voltage structure zero sequence voltage of the static var generator into the three-phase unbalanced voltage when the power grid is unbalanced specifically comprises
And transforming the voltage of the power grid in a reverse dq manner, filtering the voltage by a low-pass filter to obtain a negative sequence voltage, and constructing a zero sequence voltage Uz by the detected negative sequence voltage according to a preset relation. And inverting and superposing the zero sequence voltage to the three-phase unbalanced voltage and multiplying the three-phase unbalanced voltage by a feedforward coefficient to be used as a part of a modulation wave. .
In addition, to achieve the above object, the present invention further provides a static var generator, wherein the static var generator voltage feedforward control device includes: a memory, a processor and a computer program stored on the memory and executable on the processor, the computer program, when executed by the processor, implementing the steps of the method as described above.
The novel voltage feedforward control method for the static var generator provided by the embodiment of the invention has the advantages that the current negative sequence voltage when the power grid is unbalanced is decomposed, the current negative sequence voltage is utilized to synthesize the current zero sequence voltage, and the synthesized current zero sequence voltage is superposed to the three-phase unbalanced voltage to carry out the feedforward control of the three-phase voltage reconstruction, so that the voltage feedforward control of the static var generator is realized, the three-phase direct voltage of the static var generator is balanced and stable when the power grid is unbalanced, the reactive current is output, the asymmetric fault response speed of the power grid is accelerated, and the non-stop operation of the static var generator can be guaranteed.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of a static var generator;
FIG. 2 is a schematic diagram of a first process of an embodiment of the novel SVG voltage feedforward control method of the present invention;
FIG. 3 is a second flow chart of an embodiment of the novel SVG voltage feedforward control method of the present invention;
fig. 4 is a third flow diagram of an embodiment of the novel method for voltage feedforward control of a static var generator according to the present invention.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Referring to fig. 1, a first embodiment of the new method for voltage feedforward control of a svg according to the present invention provides a new method for voltage feedforward control of a svg. In this embodiment, the static var generator is a star-shaped chain type static var generator. The star-shaped chain type static var generator is based on a multi-level structure of an H-bridge power unit module.
Referring to fig. 2, the new static var generator voltage feedforward control method includes:
s100, the static var generator obtains the current negative sequence voltage when the power grid is unbalanced.
The static reactive generator is characterized in that a self-commutation bridge circuit is directly connected to a power grid in parallel through a reactor, the phase and amplitude of output voltage at the alternating current side of the bridge circuit are adjusted, or the current at the alternating current side of the bridge circuit is directly controlled, so that the circuit absorbs or emits reactive power meeting requirements, and the purpose of dynamic reactive compensation is achieved.
In S100, when the three-phase voltage of the power grid is unbalanced, sampling the three-phase voltage of the power grid, and obtaining the corresponding current negative sequence voltage after dq conversion and low-pass filtering processing.
S200, determining the current zero sequence voltage according to the current negative sequence voltage and a preset corresponding relation, wherein the preset corresponding relation is the corresponding relation between the negative sequence voltage and the zero sequence voltage.
The preset corresponding relation is obtained in advance through an experimental mode. By presetting the corresponding relation, the zero sequence voltage can be obtained by calculating the negative sequence voltage.
And S300, superposing the current zero-sequence voltage to the three-phase unbalanced voltage to perform feedforward control of three-phase voltage reconstruction so as to realize voltage feedforward control of the static var generator.
It is easy to understand that the obtained current zero sequence voltage is inverted, that is, the positive and negative attributes of the current zero sequence voltage are inverted and then are superposed on the three-phase unbalanced voltage to perform the feedforward control of the three-phase voltage reconstruction. At the moment, when the power grid is unbalanced, the three-phase power fluctuation amount caused by the negative sequence voltage can be offset by the three-phase power fluctuation amount generated by the reverse zero sequence voltage. Thereby achieving the purpose of balancing three-phase voltage.
The novel voltage feedforward control method for the static var generator provided by the embodiment of the invention has the advantages that the negative sequence voltage when the power grid is unbalanced is decomposed, the current negative sequence voltage is utilized to synthesize the current zero sequence voltage, and the synthesized current zero sequence voltage is superposed on the modulation wave of the static var generator, so that the balanced control on the unbalance of the power grid is realized, the three-phase direct voltage of the static var generator is balanced and stable when the power grid is unbalanced, the response speed of the asymmetric fault of the power grid is accelerated, and the reactive current is output and runs without stopping.
Referring to fig. 3 and 4, further, before determining the current zero-sequence voltage according to the current negative-sequence voltage and the preset corresponding relationship, the new static var generator voltage feedforward control method further includes:
s210, acquiring a positive sequence voltage and a negative sequence voltage of the instantaneous voltage of the power grid when the asymmetric fault occurs and the output current of the static var generator.
It should be noted that the asymmetric grid fault refers to a local voltage asymmetry of a grid system caused by a short circuit or an open circuit of one phase in the grid. In this embodiment, the static var generator is arranged to sample the three-phase voltage when the power grid fails and the output current of the static var generator respectively, so as to obtain the required positive sequence voltage, negative sequence voltage and current parameters.
And S220, respectively calculating the three-phase average active power according to the positive sequence voltage, the negative sequence voltage and the output current of the static var generator.
In this embodiment, the three-phase average active power is calculated by a correlation formula.
Specifically, according to the positive sequence voltage, the negative sequence voltage and the output current of the static var generator, the following formulas are adopted to respectively calculate the three-phase average active power:
Figure BDA0001646565720000061
Figure BDA0001646565720000062
Figure BDA0001646565720000063
wherein, Ua、Ub、UcRespectively three-phase grid voltage; i.e. ia、ib、icThree-phase output currents of the static var generator are respectively: wherein U isp、UnEffective values of positive and negative sequence voltages, θnIs the negative sequence voltage initial phase; i ispOutputting positive sequence reactive current effective value for static var generator, α is positive sequence reactive current phase position pi/2 or-pi/2, PkIs the three-phase average active power.
It should be noted that the formula (1) includes three groups of voltage calculation formulas, which are calculation formulas of a, b, and c three-phase voltages, respectively.
In the formula (2), the formula is a calculation formula including output currents of three groups of static var generators, and the calculation formula is the active output currents of the a, b and c three-phase static var generators.
The three-phase average active power can be calculated by the formulas (1), (2) and (3). The expressions of Pa, Pb and Pc of the three-phase average active power are obtained by calculation as follows:
Figure BDA0001646565720000071
and S230, acquiring the three-phase power fluctuation quantity of the negative sequence voltage according to the three-phase average active power.
Specifically, the formula (4) is used for generating three-phase power P by the action of the first partial positive sequence voltage and the positive sequence reactive currentapp、Pbpp、PcppAnd the power P generated by the action of the negative sequence voltage and the positive sequence reactive current of the second partanp、Pbnp、PcnpAnd (4) forming. Wherein the first part of the three-phase power quantity is calculated to be equal, i.e. Papp＝Pbpp＝PcppSecond part of three-phase power Panp、Pbnp、PcnpNot equal. Second part Panp、Pbnp、PcnpNamely the power fluctuation amount between three phases.
And S240, determining the corresponding relation between the negative sequence voltage and the zero sequence voltage according to the three-phase power fluctuation quantity of the negative sequence voltage.
The three-phase power fluctuation quantity of the zero-sequence voltage is respectively equal to the three-phase power fluctuation quantity of the negative-sequence voltage, the corresponding zero-sequence voltage can be obtained from the negative-sequence voltage when the power grid is unbalanced, the zero-sequence voltage is inverted and superposed into the three-phase unbalanced voltage, and the three-phase power fluctuation quantity caused by the negative-sequence voltage when the power grid is unbalanced can be offset by the three-phase power fluctuation quantity generated by the reverse zero-sequence voltage.
In an embodiment, assuming that an effective value of the injected zero-sequence voltage is Uz, and θ z is an initial phase of the zero-sequence voltage, expressions of three-phase zero-sequence voltages Uza, Uzb, and Uzc are respectively:
Figure BDA0001646565720000072
the three-phase power quantity generated by the zero-sequence voltage output by the SVG and the positive-sequence reactive current is unequal, and the three-phase power fluctuation quantity caused by the zero-sequence voltage is respectively as follows:
Figure BDA0001646565720000081
let Panp＝Pazp、Pbnp＝Pbzp、Pcnp＝PczpAnd obtaining the corresponding relation between the negative sequence voltage and the zero sequence voltage.
Further, the new static var generator voltage feedforward control method further comprises the following steps:
s400, three-phase average direct current voltage and three-phase feedback direct current voltage on the direct current side of the static var generator are obtained.
Referring to fig. 2, in the static var generator, a direct current voltage (capacitor voltage) is also present in the H-bridge power cell module. Due to the unbalance of the three-phase power grid, the voltage of the power grid is unbalanced, so that the three-phase absorbed active power is unequal, the direct current voltage of each phase is unequal, and the three-phase direct current of the static var generator is unbalanced. In order to improve the reactive compensation control capability and stability of the static var generator, zero sequence voltage is obtained through two parameters of three-phase average direct current voltage and three-phase feedback direct current voltage, and the zero sequence voltage is superposed to modulation waves of the static var generator so as to compensate the direct current voltage in the static var generator and realize the balance of the three-phase direct current voltage of the static var generator.
And S500, synthesizing zero sequence voltage according to the obtained three-phase average direct current voltage and the three-phase feedback direct current voltage.
The three-phase average direct current voltage is obtained by sampling the three-phase direct current voltage, summing the three-phase direct current voltage, and calculating an average value of the three-phase direct current voltage, wherein the three-phase feedback direct current voltage is the sampled three-phase direct current voltage.
In this embodiment, the three-phase average dc voltage is respectively subtracted from the three-phase feedback dc voltage, and the difference result is subjected to proportional-integral control to obtain the power fluctuation amount of each phase. It should be noted that, in the existing static var generator dc voltage balance control, the adjustment of each phase of power fluctuation amount can be realized only by adjusting two parameters, namely, the three-phase average dc voltage and the three-phase feedback dc voltage. And calculating to obtain zero sequence voltage according to the power fluctuation amount of each phase.
And S600, directly superposing the zero sequence voltage to the modulation wave.
Further, the new static var generator voltage feedforward control method further comprises the following steps:
and S700, acquiring reactive current and three-phase feedback current which are required to be compensated by the load and collected by the static var generator.
The three-phase feedback current is a three-phase current value output by the static var generator to the three-phase grid system.
And S800, adding the reactive current and the total direct-voltage control active current according to the working mode of the static var generator to form an instruction current, and adding the instruction current and the three-phase feedback current to a modulation wave through proportional control.
Therefore, reactive compensation of the static var generator to the three-phase power grid is realized, and the basic function of the static var generator is realized.
Based on the new method for voltage feedforward control of the static var generator, the invention also provides the static var generator, the processor and the computer program which is stored on the memory and can run on the processor, and the computer program realizes the steps of the new method for voltage feedforward control of the static var generator when being executed by the processor.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or system. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or system that comprises the element.
The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims (6)

1. A new voltage feedforward control method for a static var generator is characterized by comprising the following steps:
the static var generator acquires the current negative sequence voltage when the power grid is unbalanced;
determining the current zero-sequence voltage according to the current negative-sequence voltage and a preset corresponding relation, wherein the preset corresponding relation is the corresponding relation between the negative-sequence voltage and the zero-sequence voltage;
superposing the current zero-sequence voltage to the three-phase unbalanced voltage to carry out feedforward control of three-phase voltage reconstruction so as to realize voltage feedforward control of the static var generator;
before determining the current zero-sequence voltage according to the current negative-sequence voltage and the preset corresponding relation, the new voltage feedforward control method for the static var generator further comprises the following steps:
acquiring positive sequence voltage and negative sequence voltage of instantaneous voltage of a power grid when an asymmetric fault occurs and output current of a static var generator;
respectively calculating the three-phase average active power according to the positive sequence voltage, the negative sequence voltage and the output current of the static var generator;
acquiring three-phase power fluctuation quantity of negative sequence voltage according to the three-phase average active power;
determining the corresponding relation between the negative sequence voltage and the zero sequence voltage according to the three-phase power fluctuation quantity of the negative sequence voltage;
and respectively calculating the three-phase average active power by adopting the following formulas according to the positive sequence voltage, the negative sequence voltage and the output current of the static var generator:
Figure FDA0002394160790000011
Figure FDA0002394160790000012
Figure FDA0002394160790000013
Figure FDA0002394160790000021
wherein, Ua、Ub、UcRespectively three-phase grid voltage; i.e. ia、ib、icThree-phase output currents of the static var generator are respectively: wherein U isp、UnEffective values, theta, of positive and negative sequence voltages, respectivelynIs the negative sequence voltage initial phase; i ispOutputting positive sequence reactive current effective value for static var generator, α is positive sequence reactive current phase, pi/2 or-pi/2, PkIs the three-phase average active power;
three-phase average active power P in formula (1)a、PbAnd PcPower P generated by positive sequence voltage and positive sequence reactive current action of the first part respectivelyapp、Pbpp、PcppAnd the power P generated by the action of the negative sequence voltage and the positive sequence reactive current of the second partanp、Pbnp、PcnpForming; wherein the first part of the three-phase power quantity is calculated to be equal, i.e. Papp＝Pbpp＝PcppSecond part three-phase power quantity Panp、Pbnp、PcnpNot equal; the second term is the three-phase power fluctuation amount;
the determining the corresponding relation between the negative sequence voltage and the zero sequence voltage according to the three-phase power fluctuation quantity specifically comprises the following steps:
assuming that zero-sequence voltage is injected into three-phase voltage, Uz is an effective value of the zero-sequence voltage, and theta z is an initial phase of the zero-sequence voltage, wherein the expression of the zero-sequence voltage is as follows:
Figure FDA0002394160790000022
then, the three-phase power amount generated by the zero-sequence voltage output by the static var generator and the positive-sequence reactive current is not equal, and the three-phase power fluctuation amount caused by the zero-sequence voltage is:
Figure FDA0002394160790000023
and the three-phase power fluctuation quantity caused by the action of the negative sequence voltage and the positive sequence reactive current is equal to the three-phase power fluctuation quantity caused by the action of the zero sequence voltage and the positive sequence reactive current, and the zero sequence voltage can be obtained by a negative sequence voltage expression.
2. A new method for voltage feedforward control of a static var generator according to claim 1, characterized in that the new method for voltage feedforward control of a static var generator further comprises:
acquiring three-phase average direct-current voltage and three-phase feedback direct-current voltage at the direct-current side of the static var generator;
synthesizing zero-sequence voltage according to the obtained three-phase average direct current voltage and the three-phase feedback direct current voltage;
and directly superposing the zero sequence voltage into the modulation wave.
3. A new method for voltage feedforward control of a static var generator according to claim 2, wherein the step of synthesizing a zero-sequence voltage according to the obtained three-phase average dc voltage and the three-phase feedback dc voltage includes:
the three-phase average direct current voltage is differed from the three-phase feedback direct current voltage, and proportional integral control is carried out on the differencing result to obtain the power fluctuation amount of each phase;
and calculating zero sequence voltage according to the power fluctuation amount of each phase.
4. A new method for voltage feedforward control of a static var generator according to claim 1, characterized in that the new method for voltage feedforward control of a static var generator further comprises:
acquiring reactive current and three-phase feedback current which are required to be compensated by a load and collected by a static var generator;
and adding reactive current and total direct-voltage control active current according to the working mode of the static var generator to obtain command current, and performing proportional control on the difference between the command current and three-phase feedback current to superpose the command current and the three-phase feedback current on a modulation wave.
5. The new static var generator voltage feedforward control method according to claim 1, wherein the feedforward control of adding the negative sequence voltage of the static var generator when the power grid is unbalanced into the three-phase unbalanced voltage is obtained, specifically comprising:
the method comprises the steps of converting the voltage of a power grid in a reverse dq mode, obtaining negative sequence voltage after filtering processing of a low-pass filter, constructing zero sequence voltage Uz according to a preset relation by the detected negative sequence voltage, and multiplying the zero sequence voltage by a feedforward coefficient to be used as a part of a modulation wave by inverting and overlapping the zero sequence voltage into three-phase unbalanced voltage.
6. A static var generator, characterized in that said static var generator voltage feedforward control means comprise: memory, processor and computer program stored on the memory and executable on the processor, which computer program, when executed by the processor, carries out the steps of the method according to any one of claims 1 to 5.
CN201810412193.XA 2018-04-28 2018-04-28 Novel voltage feedforward control method for static var generator and static var generator Active CN108539767B (en)

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