CN114069686A - Combined loss reduction method for power module of flexible direct current transmission system - Google Patents

Combined loss reduction method for power module of flexible direct current transmission system Download PDF

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CN114069686A
CN114069686A CN202111431654.6A CN202111431654A CN114069686A CN 114069686 A CN114069686 A CN 114069686A CN 202111431654 A CN202111431654 A CN 202111431654A CN 114069686 A CN114069686 A CN 114069686A
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current
frequency
value
bridge arm
parameter
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刘汉军
张军
盛俊毅
赵玲
纪攀
郝翔
汤明杰
齐彦军
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Tbea Xi'an Flexible Power T&d Co ltd
TBEA Xinjiang Sunoasis Co Ltd
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Tbea Xi'an Flexible Power T&d Co ltd
TBEA Xinjiang Sunoasis 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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
    • H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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Abstract

A power module combined loss reduction method for a flexible direct current transmission system comprises the steps of firstly adopting double-frequency circulating current to inject loss reduction, wherein a forward peak value of double-frequency circulating current of bridge arm current corresponds to a forward peak value of a fundamental frequency current component in a rectification mode, a forward peak value of double-frequency circulating current of bridge arm current corresponds to a negative peak value of the fundamental frequency current component in an inversion mode, and the loss of a power module injected by the double-frequency circulating current is relatively small at the moment; secondly, the loss is reduced by adopting a module voltage sorting algorithm of variable g parameters, and the method has two control dimensions, wherein the first control dimension is used for outputting a reference parameter g according to the degree of deviation of the average value of the switching frequency from a target valuebThe reference value of the g parameter is gradually converged in four steps, the second dimension control is the reference parameter g determined in the first control dimension according to the absolute value of the bridge arm currentbThe fluctuation quantity which changes along with the bridge arm current is superposed and is output to a power module sequencing voltage-sharing algorithm as a final g parameter, and the area with larger bridge arm current is subjected toThe switching frequency is properly transferred to a region with smaller bridge arm current, so that the switching loss of the power module is reduced; the method or the system provided by the invention can reduce the switching loss of the power sub-module of the existing flexible direct current converter valve, improve the transmission efficiency of the flexible direct current transmission system and improve the economy.

Description

Combined loss reduction method for power module of flexible direct current transmission system
Technical Field
The invention belongs to the technical field of flexible direct current transmission, and particularly relates to a combined loss reduction method for a power module of a flexible direct current transmission system.
Background
The flexible direct-current transmission system has the characteristics of flexible control, bidirectional flow of tide, reactive support providing, no commutation failure and the like, and has unique technical advantages and is very suitable for the fields of asynchronous power grid interconnection, new energy access, island power supply and the like.
The flexible direct-current transmission system is formed by cascading power modules, a large number of power semiconductor switching devices exist in the flexible direct-current converter valve, when current flows through the power module switching devices and the switching devices are disconnected, loss can be generated, the larger the current flows, the higher the loss is generated, and the transmission efficiency of the flexible direct-current transmission system is severely limited. At present, the common method for reducing the loss of the converter valve power module is to add double-frequency circulating current suppression, and although the method is simple to control, the power module does not work in a lower loss state.
In conclusion, further exploring the low-loss operation of the converter valve power module of the flexible direct current transmission system has important significance, and therefore a new combined loss reduction method for the power module of the flexible direct current transmission system is urgently needed to improve the operation efficiency and the economy of the flexible direct current transmission system.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a combined loss reduction method for a power module of a flexible direct-current transmission system, which adopts a module voltage sequencing algorithm of double-frequency circulating injection and variable g parameters to reduce loss jointly, can reduce the operation loss of the power module of the conventional flexible direct-current converter valve on the premise of constant switching frequency of the power module, improves the transmission efficiency of the flexible direct-current transmission system, and improves the economy.
In order to achieve the purpose, the invention adopts the following technical scheme:
a combined loss reduction method for a power module of a flexible direct current transmission system comprises the following steps:
step one, injecting double frequency circulation to reduce loss;
and step two, further reducing the loss of the power module by adopting a module voltage sorting algorithm with variable g parameters.
The first specific method comprises the following steps:
injecting a double-frequency circulating current into the power module at a certain angle, wherein the bridge arm current consists of a direct-current component of one third of direct-current bus current, a fundamental frequency component of one half of alternating current on the valve side of the converter valve, the double-frequency circulating current component and even harmonic components of four times or more, the loss of the power module is little due to the small content of the even harmonic components of the four times or more, the influence of the even harmonic components of the four times or more on the power module is ignored, and the bridge arm current expression in the rectification operation mode is the same as that in the rectification operation mode
Figure BDA0003380351680000021
The bridge arm current expression under the inversion operation mode is
Figure BDA0003380351680000022
In the above formula, the first and second carbon atoms are,
Figure BDA0003380351680000023
the phase difference between the fundamental frequency current component and the double frequency circulation component;
in the bridge arm current expression in the rectification mode, let
Figure BDA0003380351680000024
The value is taken to satisfy that the positive peak value of the fundamental frequency current component corresponds to the negative peak value of the frequency doubling circulating current component, and the negative peak value of the fundamental frequency current component corresponds to the negative peak value of the frequency doubling circulating current component; in the inversion mode, let
Figure BDA0003380351680000025
The value of the current component of the fundamental frequency is obtained to meet the condition that the positive peak value of the current component of the fundamental frequency corresponds to the positive peak value of the frequency doubling circulating current component, and the negative peak value of the current component of the fundamental frequency corresponds to the positive peak value of the frequency doubling circulating current component;
then scanning and calculating the range of-180 degrees to obtain: the double frequency circulation current content is the same, the effective value of the positive current of the bridge arm current in the rectification mode is the minimum, and the peak value of the negative current of the bridge arm current in the inversion mode is the minimum, so that the double frequency circulation current injection angle is obtained
Figure BDA0003380351680000026
At this time, the power module loss is lower than that under the circulating current suppression.
The double frequency circulation injection method in the first step comprises the following steps:
based on alternating current voltage phase locking, solving the angle of a current inner loop positive sequence dq axis, after phase shifting 180 degrees, using cosine of the angle multiplied by injected double frequency content as a frequency doubling d-axis instruction value, using sine of the angle multiplied by injected double frequency content as a frequency doubling q-axis instruction value, then performing dq transformation on double frequency circulation based on the phase of the alternating current voltage phase-locked loop to serve as a dq-axis feedback value, outputting the instruction value and the feedback value through a PI (proportional-integral) controller, then outputting a modulation wave of the frequency doubling circulation through dq inverse transformation, and additionally controlling the module switching number on the modulation wave synthesized by a fundamental frequency component and a direct current component
1) Phase locking is carried out on three-phase voltage Uabc of the alternating-current power grid to obtain a phase locking angle theta;
2) dq transformation is carried out on the three-phase alternating-current voltage Iabc at the valve side based on the phase locking angle theta to obtain d-axis current IdAnd q-axis current Iq；
3) Solving for IdAnd IqThe new angle theta' is obtained after the phase shift of 180 degrees (pi) and the product of the rest of the chords and the injection content I of the frequency doubling circulation is obtained2refObtaining a d-axis command value I of the double frequency circulation2drefThe sine of the sine is multiplied by the double frequency circulation injection content I2refObtaining a double frequency circulation q-axis instruction value I2qref；
4) Three-phase circulation I of bridge arm current is decomposedcccsCarrying out dq axis transformation based on the 2 theta angle to obtain a double frequency circulation d-axis current I2dAnd q-axis current I2q；
5) Frequency doubling circulation command value I2dref、I2qrefAnd a feedback value I2d、I2qOutputting modulation ratio M through PI link2dAnd M2q；
6) Based on 2 theta angle pair M2dAnd M2qCarrying out dq axis inverse transformation to obtain a double frequency circulation modulation wave V2refWith a direct current component VdcAnd a fundamental frequency component VrefAnd obtaining an integral modulation wave after superposition, obtaining the number of bridge arm conducting modules, and realizing accurate control on the double frequency circulation.
The specific method of the second step is as follows: the loss of the power module is further reduced by adopting a module voltage sorting algorithm with variable g parameters; the g parameter represents a control target value of a difference value between the maximum value and the minimum value of the module voltage in the current state and is used for controlling the switching frequency of the power module and the voltage unbalance of the power module, the g parameter and the switching frequency are in an inverse relation, the higher the switching frequency is, the smaller the g parameter is, the lower the switching frequency is, the larger the g parameter is, and the g parameter directly determines the loss of the power module;
the variable-g-parameter module voltage sequencing algorithm has two control dimensions:
the first control dimension is to output a reference parameter g based on the degree to which the average value of the switching frequency deviates from the target valuebGradually converging the g parameter reference value in four steps;
first gear, target value of switching frequency frefF for representing and switching frequency actual feedback valuefedWhen f denotesref-ffed>Δf1Time reference parameter gbSubtracting sigma from the last state1When f isref-ffed<-Δf1Time reference parameter gbAdding sigma on the basis of the last state1(ii) a Fast convergence of the switching frequency to the deviation range deltaf1Internal;
second gear when fref-ffed>Δf2Time reference parameter gbSubtracting sigma from the last state2When f isref-ffed<-Δf2Time reference parameter gbAdding sigma on the basis of the last state2(ii) a Continue to converge the switching frequency to the deviation range Deltaf2Internal;
third gear when fref-ffed>Δf3Time reference parameter gbSubtracting sigma from the last state3When f isref-ffed<-Δf3Time reference parameter gbAdding sigma on the basis of the last state3(ii) a Further converging the switching frequency to the deviation range deltaf3Internal;
fourth gear when fref-ffed>Δf4Time reference parameter gbSubtracting sigma from the last state4When f isref-ffed<-Δf4Time reference parameter gbAdding sigma on the basis of the last state4When- Δ f4<fref-ffed<Δf4Time reference parameter gbKeeping the original shape; converging the switching frequency to the deviation range Deltaf4Internal;
the fourth gear, the switching frequency deviation range Deltaf1>Δf2>Δf3>Δf4Reference parameter gbVariation σ1>σ2>σ3>σ4；
A second dimension of control based onAccording to the absolute value of the bridge arm current, determining a reference parameter g in a first control dimensionbThe fluctuation quantity delta g changing along with the bridge arm current is superposed and is output to a module voltage sequencing algorithm of the variable g parameter as a final g parameter, and the method specifically comprises the following steps:
firstly, storing bridge arm current data of a cycle in real time, and finding out the maximum absolute value of the bridge arm current; calculating the fluctuation amount, namely multiplying the ratio of the current absolute value of the bridge arm current to the maximum absolute value of the cycle bridge arm current by a coefficient k, wherein delta g is kxiarm ÷ Imax |; superimposing the fluctuation quantity Δ g on a reference parameter g determined in a first control dimensionbThe above is used as the g parameter;
the g parameter is subjected to amplitude limiting processing by adopting a module voltage sequencing algorithm of variable g parameter, and when an upper limit g is triggeredlim1When g is equal to glim1(ii) a When triggering the lower limit glim2When g is equal to glim2(ii) a And inputting the limited g parameters into a power module sequencing voltage-sharing algorithm, outputting the switching state of each power module, and transferring the switching frequency of the area with large bridge arm current to the area with small bridge arm current, so that the switching loss of the power modules is reduced.
Compared with the prior art, the invention has the following beneficial effects:
according to the combined loss reduction method for the power modules of the flexible direct-current power transmission system, the loss reduction is combined by adopting a module voltage sequencing algorithm of double-frequency circulating current injection and variable g parameters, compared with double-frequency circulating current inhibition, the loss of the power modules can be obviously reduced, the running economy of the flexible direct-current power transmission system is greatly improved, and the method has high popularization and application values.
Drawings
FIG. 1 is a converter valve topology of a flexible DC power transmission system in an embodiment of the invention;
fig. 2 is a diagram of a double frequency circulating current injection algorithm of the flexible direct current transmission system in the embodiment of the invention;
fig. 3 is a flow chart of a variable-g parameter algorithm of the flexible direct current transmission system in the embodiment of the invention;
FIG. 4 shows waveforms of effective values of bridge arm currents in a full-angle range of a rectification mode of a flexible direct-current power transmission system according to an embodiment of the invention;
FIG. 5 illustrates bridge arm currents and g-parameter waveforms for a rectification mode range of a flexible DC power transmission system in an embodiment of the present invention;
fig. 6 shows waveforms of effective values of bridge arm currents in an inversion mode full-angle range of the flexible direct-current transmission system in an embodiment of the invention;
fig. 7 illustrates bridge arm currents and g-parameter waveforms in the inversion mode range of the flexible direct current transmission system in an embodiment of the present invention;
in fig. 1, an ac power supply; 2. an alternating current circuit breaker; 3. a converter transformer; 4. a soft start resistance; 5. a soft start resistance circuit breaker; 6. bridge arm inductance; 7. a power sub-module; 8. a half-bridge power sub-module; 9. a full bridge power sub-module.
Detailed Description
In order to make the purpose, technical effect and technical solution of the embodiments of the present invention clearer, the following clearly and completely describes the technical solution of the embodiments of the present invention with reference to the drawings in the embodiments of the present invention; it is to be understood that the described embodiments are only some of the embodiments of the present invention. Other embodiments, which can be derived by one of ordinary skill in the art from the disclosed embodiments without inventive faculty, are intended to be within the scope of the invention.
Referring to fig. 1, in the flexible direct-current transmission system, an alternating-current power supply 1 is connected with a converter valve through an alternating-current circuit breaker 2, a converter transformer 3 and a soft start resistor 4, the soft start resistor 4 is connected with a soft start resistor circuit breaker 5 in parallel, the converter valve comprises six bridge arms, each bridge arm is composed of a bridge arm inductor 6 and a plurality of power sub-modules 7, and each power sub-module 7 is composed of a half-bridge power sub-module 8 and a full-bridge power sub-module 9.
A combined loss reduction method for a power module of a flexible direct current transmission system comprises the following steps on the premise that the switching frequency of the power module is constant:
step one, injecting double frequency circulation to reduce loss;
and step two, the loss of the power module is further reduced by adopting a variable-g parameter algorithm.
The first specific method comprises the following steps:
injecting a double-frequency circulating current into the power module at a certain angle, wherein the bridge arm current consists of a direct-current component of one third of a direct-current bus current, a fundamental frequency component of one half of an alternating-current at the valve side of the converter valve, the double-frequency circulating current component and an even harmonic component of four times or more, and considering that the even harmonic component of four times or more has less content and has less influence on the loss of the power module, and neglecting the influence of the even harmonic component of four times or more on the loss of the power module, the bridge arm current expression in the rectification operation mode is that
Figure BDA0003380351680000071
The bridge arm current expression under the inversion operation mode is
Figure BDA0003380351680000072
In the above formula, the first and second carbon atoms are,
Figure BDA0003380351680000073
the phase difference between the fundamental frequency current component and the double frequency circulation component;
selecting the angle of injected double frequency circulation in the first step:
in the above formula, the first and second carbon atoms are,
Figure BDA0003380351680000074
the phase difference between the fundamental frequency current component and the double frequency circulation component; in the rectification mode, the power supply is switched on,
Figure BDA0003380351680000075
when the peak value of the time base frequency current component is equal to 0, the positive peak value of the frequency doubling circulation component corresponds to the negative peak value of the frequency doubling circulation component, and the negative peak value of the fundamental frequency current component corresponds to the negative peak value of the frequency doubling circulation component; under the condition of an inversion mode, the air conditioner is controlled to be in a closed state,
Figure BDA0003380351680000076
the forward peak value of the time-base frequency current component equal to 0 corresponds to the forward peak value of the frequency-doubled circulating current component,the negative peak of the fundamental current component corresponds to the positive peak of the double frequency circulating current component.
Through the scanning calculation in the range of-180 to 180 degrees, the phase difference of the double frequency circulation is injected
Figure BDA0003380351680000077
When the current is equal to 0, the double-frequency circulating current content is the same, the effective value of the positive current of the bridge arm in the rectification mode is the minimum, the peak value of the negative current of the bridge arm in the inversion mode is the minimum, and the loss of the power module of the converter valve is all at the moment
Figure BDA0003380351680000078
The angle is relatively small and is lower than the power module loss under the circulation suppression, so the frequency doubling circulation injection angle
Figure BDA0003380351680000079
Take 0.
Fig. 2 shows a frequency doubling circulating current injection method of a flexible direct current transmission system:
1) phase locking is carried out on three-phase voltage Uabc of the alternating-current power grid to obtain a phase locking angle theta;
2) dq transformation is carried out on the three-phase alternating-current voltage Iabc at the valve side based on the phase locking angle theta to obtain d-axis current IdAnd q-axis current Iq；
3) Solving for IdAnd IqThe new angle theta' is obtained after the phase shift of 180 degrees (pi) and the product of the rest of the chords and the injection content I of the frequency doubling circulation is obtained2refObtaining a d-axis command value I of the double frequency circulation2drefThe sine of the sine is multiplied by the double frequency circulation injection content I2refObtaining a d-axis command value I of the double frequency circulation2qref；
4) Three-phase circulation I of bridge arm current is decomposedcccsCarrying out dq axis transformation based on the 2 theta angle to obtain a double frequency circulation d-axis current I2dAnd q-axis current I2q；
5) Frequency doubling circulation command value I2dref、I2qrefAnd a feedback value I2d、I2qOutputting modulation ratio M through PI link2dAnd M2q；
6) Base ofAt 2 theta angle pair M2dAnd M2qCarrying out dq axis inverse transformation to obtain a double frequency circulation modulation wave V2refWith a direct current component VdcAnd a fundamental frequency component VrefAnd obtaining an integral modulation wave after superposition, obtaining the number of bridge arm conducting modules, and realizing accurate control on the double frequency circulation.
The injection content of the double frequency circulation is preferably 20-25% of the fundamental frequency component of the bridge arm current.
Referring to fig. 3, the module voltage sequencing algorithm flow of the variation parameter in the second step is as follows:
counting the average switching frequency of a power module in a period of time, and counting the absolute maximum value of the bridge arm current in a period;
step two, adopting four gears to carry out convergence control on the switching frequency, wherein the target value of the switching frequency is frefF for representing and switching frequency actual feedback valuefedIndicates, first gear, when fref-ffed>Δf1When the reference g parameter is reduced by σ based on the previous state1When f isref-ffed<-Δf1Time reference parameter gbAdding sigma on the basis of the last state1(ii) a Second gear when fref-ffed>Δf2Time reference parameter gbSubtracting sigma from the last state2When f isref-ffed<-Δf2Time reference parameter gbAdding sigma on the basis of the last state2(ii) a Third gear when fref-ffed>Δf3When the reference parameter g is reduced by σ from the previous state3When f isref-ffed<-Δf3Time reference parameter gbAdding sigma on the basis of the last state3(ii) a Fourth gear when fref-ffed>Δf4Time reference parameter gbSubtracting sigma from the last state4When f isref-ffed<-Δf4Time reference parameter gbAdding sigma on the basis of the last state4When- Δ f4<fref-ffed<Δf4Time, referenceParameter gbAnd maintained unchanged.
The fourth gear, the switching frequency deviation range Deltaf1>Δf2>Δf3>Δf4Reference g parameter variation σ1>σ2>σ3>σ4(ii) a Wherein, Δ f1Suggesting a switching frequency command value f ref20% to 30%, Δ f2Suggesting a switching frequency command value f ref9% to 12%, Δ f3Suggesting a switching frequency command value fref5% to 6%, Δ f4Suggesting a switching frequency command value f ref1 to 1.5 percent of; reference g parameter variation σ1It is recommended to use 0.5% -0.6%, which has the effect of rapidly converging the switching frequency to the deviation range Deltaf1Internal; sigma2It is recommended to take 0.25% -0.3%, the effect of which is to continue to converge the switching frequency to the deviation range Δ f2Internal; sigma3It is recommended to take 0.1% to 0.1.5%, which further acts to converge the switching frequency to the deviation range Δ f3Internal; sigma4It is recommended to take 0.02% -0.03%, which has the effect of setting the switching frequency at the deviation delta f4Fine adjustment is carried out within the range;
step three, calculating g parameter fluctuation quantity delta g changing along with bridge arm current according to the absolute value of the bridge arm current, wherein the delta g is k x iarm/Imax, the range of the coefficient k is recommended to be 5% -9%, the small coefficient is suitable for light load working conditions, the large coefficient is suitable for heavy load working conditions, and then the fluctuation quantity delta g is superposed on the reference parameter gbThe above is used as the g parameter;
step four, carrying out amplitude limiting processing on the parameter g, and when an upper limit g is triggeredlim1When g is equal to glim1(ii) a When triggering the lower limit glim2When g is equal to glim2(ii) a And inputting the g parameters after amplitude limiting into a power module sequencing and voltage-sharing algorithm, and outputting the switching state of each power module.
Referring to fig. 4 to 6, for the calculation results of converter valve parameters of a certain flexible direct current transmission system, a full-bridge and half-bridge series-parallel structure is adopted, the full-bridge power module accounts for 50% under the condition of no redundancy, and a full-bridge power module with 5% redundancy is additionally configured.
With reference to figure 4 of the drawings,scanning calculation is carried out from the range of-180 degrees to 180 degrees, when the injection content of the double frequency circulation is 25 percent of the fundamental frequency current component, and the phase difference between the double frequency circulation and the fundamental frequency component
Figure BDA0003380351680000091
And when the current of the bridge arm is in the positive direction, the effective value is the largest, and the negative effective value is the smallest.
Referring to fig. 5, the upper limit and the lower limit of the variable-g parameter algorithm are set to be 9.5% and 0.5%, the injection content of the double frequency circulation is 25%, and the phase difference between the double frequency circulation and the fundamental frequency component is set
Figure BDA0003380351680000092
Under the condition that the switching frequency of the power module is 100Hz, the absolute maximum value of the bridge arm current is 4kA, the g parameter reaches the upper limit of 9.5% when the absolute value of the bridge arm current is greater than 2.4kA, and the variable g parameter is greater than the fixed g parameter when the absolute value of the bridge arm current is greater than 1.3kA, which means that the switching times of the bridge arm current absolute value exceeding 1.3kA under the variable g parameter are reduced; when the absolute value of the bridge arm current is less than 1.3kA, the variable g parameter is less than the fixed g parameter, which means that the switching times of the bridge arm current with the absolute value of less than 1.3kA under the variable g parameter are increased.
Referring to fig. 6, scanning calculation is performed from-180 to 180 degrees, when the injection content of the double frequency circulation is 20% of the fundamental frequency current component, and the phase difference between the double frequency circulation and the fundamental frequency component
Figure BDA0003380351680000101
And when the current of the bridge arm is in the positive direction, the effective value is the largest, and the negative effective value is the smallest.
Referring to fig. 7, the injection content of the double frequency circulation is 25%, and the phase difference between the double frequency circulation and the fundamental frequency component
Figure BDA0003380351680000102
Under the condition that the switching frequency of the power module is 100Hz, the absolute maximum value of the bridge arm current is 4kA, the g parameter reaches the upper limit of 9.5% when the absolute value of the bridge arm current is greater than 3.1kA, and the variable g parameter is greater than the fixed g parameter when the absolute value of the bridge arm current is greater than 1.2kA, which means that the switching times of the bridge arm current absolute value exceeding 1.2kA under the variable g parameter are reduced; the absolute value of the bridge arm current is smallAt 1.32A, the variable-g parameter is smaller than the fixed-g parameter, which means that the switching times of the bridge arm current absolute value under the variable-g parameter is less than 1.2kA are increased.
Further, under the system parameters, representative full-load operation working conditions and half-load operation working conditions are selected to verify the loss reduction strategy of the converter valve power module, and the loss of the converter valve power module is shown in the table 1. Under a full-load rectification mode, the injected double-frequency circulating current content is 25%, compared with double-frequency circulating current suppression, the loss of a half-bridge power module under the injection of the double-frequency circulating current is reduced by 185W, the loss is reduced by 2.9%, the loss of a full-bridge power module is reduced by 126W, the loss is reduced by 1.16%, and the loss is reduced by 1.76% as a whole; under the full-load inversion mode, the injected double-frequency circulating current content is 20%, compared with double-frequency circulating current suppression, the half-bridge power module loss under the double-frequency circulating current injection is reduced by 95W, the loss is reduced by 1.53%, the full-bridge power module loss is reduced by 148W, the loss is reduced by 1.44%, and the loss is reduced by 1.47% as a whole.
Further, under a half-load rectification mode, the content of injected double-frequency circulation is 25%, compared with double-frequency circulation inhibition, the loss of a half-bridge power module under double-frequency circulation injection is reduced by 54W, the loss is reduced by 1.94%, the loss of a full-bridge power module is reduced by 74W, the loss is reduced by 1.72%, and the loss is reduced by 1.8% integrally; under the half-load inversion mode, the injected double-frequency circulating current content is 20%, compared with double-frequency circulating current suppression, the half-bridge power module loss is reduced by 58W and 2.19% under the double-frequency circulating current injection, the full-bridge power module loss is reduced by 123W, the loss is reduced by 2.88%, and the loss is reduced by 2.63% integrally.
Further, under a full-load rectification mode, the injection frequency doubling circulating current content is 25%, compared with frequency doubling circulating current inhibition, the half-bridge power module loss is reduced by 288W under the combined strategy of frequency doubling circulating current injection and variable g parameters, the loss is reduced by 4.51%, the loss of the full-bridge power module is reduced by 303W, the loss is reduced by 3.73%, and the loss is reduced by 4.0% as a whole; under a full-load inversion mode, the injected double-frequency circulation content is 20%, compared with double-frequency circulation suppression, the loss of a half-bridge power module under a combined strategy of double-frequency circulation injection and variable g parameters is reduced by 479W, the loss is reduced by 7.70%, the loss of a full-bridge power module is reduced by 521W, the loss is reduced by 5.03%, and the loss is reduced by 5.96% as a whole.
Further, under a half-load rectification mode, the injected double-frequency circulating current content is 25%, compared with double-frequency circulating current suppression, the loss of a half-bridge power module under a combined strategy of double-frequency circulating current injection and variable g parameters is reduced by 409W, the loss is reduced by 14.65%, the loss of a full-bridge power module is reduced by 343W, the loss is reduced by 7.95%, and the loss is reduced by 10.41% integrally; under a half-load inversion mode, the injection frequency doubling circulation content is 20%, compared with frequency doubling circulation inhibition, the half-bridge power module loss under the combined strategy of frequency doubling circulation injection and variable g parameters is reduced by 337W, the loss is reduced by 12.84%, the full-bridge power module loss is reduced by 362W, the loss is reduced by 8.48%, and the loss is reduced by 10.03% as a whole.
Furthermore, by adopting a double-frequency-multiplication and variable-g parameter combined loss reduction strategy, the loss of a converter valve power module can be obviously reduced, the average loss reduction amplitude under the full-load working condition can reach 5%, and the average loss reduction amplitude under the half-load working condition can reach 10%.
TABLE 1
Figure BDA0003380351680000111
Figure BDA0003380351680000121
In summary, the embodiment of the present invention provides a method and a system for joint loss reduction of a power module of a flexible direct current transmission system, which reduce the loss rate of the flexible direct current transmission system and improve the operation efficiency and the economy of the system by a joint algorithm of double frequency circulating current injection and variable g parameters; the operation life of the flexible direct current transmission project is 30-40 years, after the combined loss reduction method is adopted, the economic benefit brought by the whole life cycle is considerable, thousands of yuan of electric energy loss can be saved per GW in the conservative estimation whole life cycle, and the flexible direct current transmission project has high popularization and application values.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can make modifications and equivalents to the embodiments of the present invention without departing from the spirit and scope of the present invention, which is set forth in the claims of the present application.

Claims (5)

1. A combined loss reduction method for a power module of a flexible direct current transmission system is characterized by comprising the following steps:
step one, injecting double frequency circulation to reduce loss;
and step two, further reducing the loss of the power module by adopting a module voltage sorting algorithm with variable g parameters.
2. The combined loss reduction method for the power modules of the flexible direct current transmission system according to claim 1, wherein the step one specific method is as follows:
injecting a double-frequency circulating current into the power module at a certain angle, wherein the bridge arm current consists of a direct-current component of one third of direct-current bus current, a fundamental frequency component of one half of alternating current on the valve side of the converter valve, the double-frequency circulating current component and even harmonic components of four times or more, the loss of the power module is little due to the small content of the even harmonic components of the four times or more, the influence of the even harmonic components of the four times or more on the power module is ignored, and the bridge arm current expression in the rectification operation mode is the same as that in the rectification operation mode
Figure FDA0003380351670000011
The bridge arm current expression under the inversion operation mode is
Figure FDA0003380351670000012
In the above formula, the first and second carbon atoms are,
Figure FDA0003380351670000013
is divided by the fundamental frequency currentPhase difference between the magnitude and the double frequency circulating current component;
in the bridge arm current expression in the rectification mode, let
Figure FDA0003380351670000014
The value is taken to satisfy that the positive peak value of the fundamental frequency current component corresponds to the negative peak value of the frequency doubling circulating current component, and the negative peak value of the fundamental frequency current component corresponds to the negative peak value of the frequency doubling circulating current component; in the inversion mode, let
Figure FDA0003380351670000015
The value of the current component of the fundamental frequency is obtained to meet the condition that the positive peak value of the current component of the fundamental frequency corresponds to the positive peak value of the frequency doubling circulating current component, and the negative peak value of the current component of the fundamental frequency corresponds to the positive peak value of the frequency doubling circulating current component;
then scanning and calculating the range of-180 degrees to obtain: the double frequency circulation current content is the same, the effective value of the positive current of the bridge arm current in the rectification mode is the minimum, and the peak value of the negative current of the bridge arm current in the inversion mode is the minimum, so that the double frequency circulation current injection angle is obtained
Figure FDA0003380351670000016
At this time, the power module loss is lower than that under the circulating current suppression.
3. The combined loss reduction method for the power modules of the flexible direct current transmission system according to claim 1 or 2, wherein in the first step, the double frequency circulating current injection method comprises the following steps:
based on alternating current voltage phase locking, solving the angle of a current inner loop positive sequence dq axis, after phase shifting 180 degrees, using cosine of the angle multiplied by injected double frequency content as a frequency doubling d-axis instruction value, using sine of the angle multiplied by injected double frequency content as a frequency doubling q-axis instruction value, then performing dq transformation on double frequency circulation based on the phase of the alternating current voltage phase-locked loop to serve as a dq-axis feedback value, outputting the instruction value and the feedback value through a PI (proportional-integral) controller, then outputting a modulation wave of the frequency doubling circulation through dq inverse transformation, and additionally controlling the module switching number on the modulation wave synthesized by a fundamental frequency component and a direct current component
1) Phase locking is carried out on three-phase voltage Uabc of the alternating-current power grid to obtain a phase locking angle theta;
2) dq transformation is carried out on the three-phase alternating-current voltage Iabc at the valve side based on the phase locking angle theta to obtain d-axis current IdAnd q-axis current Iq；
3) Solving for IdAnd IqThe new angle theta' is obtained after the phase shift of 180 degrees (pi) and the product of the rest of the chords and the injection content I of the frequency doubling circulation is obtained2refObtaining a d-axis command value I of the double frequency circulation2drefThe sine of the sine is multiplied by the double frequency circulation injection content I2refObtaining a double frequency circulation q-axis instruction value I2qref；
4) Three-phase circulation I of bridge arm current is decomposedcccsCarrying out dq axis transformation based on the 2 theta angle to obtain a double frequency circulation d-axis current I2dAnd q-axis current I2q；
5) Frequency doubling circulation command value I2dref、I2qrefAnd a feedback value I2d、I2qOutputting modulation ratio M through PI link2dAnd M2q；
6) Based on 2 theta angle pair M2dAnd M2qCarrying out dq axis inverse transformation to obtain a double frequency circulation modulation wave V2refWith a direct current component VdcAnd a fundamental frequency component VrefAnd obtaining an integral modulation wave after superposition, obtaining the number of bridge arm conducting modules, and realizing accurate control on the double frequency circulation.
4. The combined loss reduction method for the power modules of the flexible direct current transmission system according to claim 1, wherein the specific method in the second step is as follows: the loss of the power module is further reduced by adopting a module voltage sorting algorithm with variable g parameters; the g parameter represents a control target value of a difference value between the maximum value and the minimum value of the voltage of the current state module and is used for controlling the switching frequency of the power module and the voltage unbalance of the power module, the g parameter and the switching frequency are in an inverse proportion relation, the higher the switching frequency is, the smaller the g parameter is, the lower the switching frequency is, the larger the g parameter is, and the g parameter directly determines the loss of the power module.
5. The combined loss reduction method for the power modules of the flexible direct current transmission system according to claim 4, wherein the variable-g-parameter module voltage sequencing algorithm has two control dimensions:
the first control dimension is to output a reference parameter g based on the degree to which the average value of the switching frequency deviates from the target valuebGradually converging the g parameter reference value in four steps;
first gear, target value of switching frequency frefF for representing and switching frequency actual feedback valuefedWhen f denotesref-ffed>Δf1Time reference parameter gbSubtracting sigma from the last state1When f isref-ffed<-Δf1Time reference parameter gbAdding sigma on the basis of the last state1(ii) a Fast convergence of the switching frequency to the deviation range deltaf1Internal;
second gear when fref-ffed>Δf2Time reference parameter gbSubtracting sigma from the last state2When f isref-ffed<-Δf2Time reference parameter gbAdding sigma on the basis of the last state2(ii) a Continue to converge the switching frequency to the deviation range Deltaf2Internal;
third gear when fref-ffed>Δf3Time reference parameter gbSubtracting sigma from the last state3When f isref-ffed<-Δf3Time reference parameter gbAdding sigma on the basis of the last state3(ii) a Further converging the switching frequency to the deviation range deltaf3Internal;
fourth gear when fref-ffed>Δf4Time reference parameter gbSubtracting sigma from the last state4When f isref-ffed<-Δf4Time reference parameter gbAdding sigma on the basis of the last state4When- Δ f4<fref-ffed<Δf4Time reference parameter gbKeeping the original shape;converging the switching frequency to the deviation range Deltaf4Internal;
the fourth gear, the switching frequency deviation range Deltaf1>Δf2>Δf3>Δf4Reference parameter gbVariation σ1>σ2>σ3>σ4；
And the second dimension control is realized by superposing a fluctuation quantity delta g which changes along with the bridge arm current on a reference parameter gb determined by the first control dimension according to the absolute value of the bridge arm current, and outputting the fluctuation quantity delta g serving as a final g parameter to a module voltage sequencing algorithm of a variable g parameter, wherein the details are as follows:
firstly, storing bridge arm current data of a cycle in real time, and finding out the maximum absolute value of the bridge arm current; calculating the fluctuation amount, namely multiplying the ratio of the current absolute value of the bridge arm current to the maximum absolute value of the cycle bridge arm current by a coefficient k, wherein delta g is kxiarm ÷ Imax |; superimposing the fluctuation quantity Δ g on a reference parameter g determined in a first control dimensionbThe above is used as the g parameter;
the g parameter is subjected to amplitude limiting processing by adopting a module voltage sequencing algorithm of variable g parameter, and when an upper limit g is triggeredlim1When g is equal to glim1(ii) a When triggering the lower limit glim2When g is equal to glim2(ii) a And inputting the limited g parameters into a power module sequencing voltage-sharing algorithm, outputting the switching state of each power module, and transferring the switching frequency of the area with large bridge arm current to the area with small bridge arm current, so that the switching loss of the power modules is reduced.
CN202111431654.6A 2021-11-29 2021-11-29 Combined loss reduction method for power module of flexible direct current transmission system Pending CN114069686A (en)

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