Modularization multi-level converter DC side pulsation of current suppressing methodTechnical field
The invention belongs to multilevel power electronic converter technical fields, are related to a kind of modularization multi-level converter(MMC) DC side pulsation of current suppressing method.
Background technique
Relative to two traditional level and three-level converter, MMC is with high-efficient, output AC voltage harmonic wave is small, highThe features such as spending modularization, is more suitable for high voltage, powerful application, has obtained extensively in fields such as D.C. high voltage transmissionsUsing.
Carrier wave stacking pulsewidth modulation (PD-PWM) method is a kind of relatively common MMC modulator approach.Its way is to pass throughN frequency, the identical triangular carrier of phase and amplitude " stacking " are got up and compared with modulating wave, to obtain the touching of switching deviceSend out pulse.Generally, the phase of the triangular carrier of each phase upper and lower bridge arm is set as opposite.If the upper and lower bridge arm of each phase is givenFixed sinusoidal modulation wave is symmetrical about x-axis, then the sum of submodule number that each phase is put at any time is all n.Ignore bridgePressure drop in arm impedance, thus the sum of the submodule voltage of each phase investment is equal to DC side busbar voltage.
When normal operation, flowing through can be containing biggish two harmonic, to increase inverter in the electric current of MMC bridge armLoss.In order to reduce the loss of MMC, design controller is generally also needed to inhibit the circulation of bridge arm.Currently, two times of common inhibitionThe strategy of frequency circulation is, by extracting two frequency multiplication circulation, then by circulation controller, and the voltage compensation signal referred to,In the sinusoidal modulation wave for the upper and lower bridge arm that the reference voltage thermal compensation signal is added separately to each phase, inhibit two frequencys multiplication to realizeThe purpose of circulation.However, two frequency multiplication circulation are repressed simultaneously, another adverse effect is but brought.Due to upper and lower bridge armIt all joined the voltage compensation component of same two frequency multiplication in sinusoidal modulation wave, so that the reference modulating wave of upper and lower bridge arm no longer closesIt is symmetrical in x-axis.At this point, using PD-PWM modulation algorithm, the submodule number that each phase is put at any time no longer it is constant notBecome.As the voltage compensation component y of two frequencys multiplicationj2When > 0, the submodule number of each phase element investment is n or n-1；When two frequencys multiplicationVoltage compensation component yj2When < 0, the submodule number of each phase element investment is n or n+1.If the voltage of each submodule capacitorEqual to Vdc/ n, wherein VdcIt is DC bus-bar voltage, as a result leads to the sum of voltage of submodule of each phase element investment and direct currentThe sum of side bus voltage is inconsistent, to generate pulse voltage on bridge arm inductance, the amplitude of the voltage is equal to 1 submodule electricityThe voltage of appearance.And then high-frequency current is generated on bridge arm.The phase of pulse voltage on three-phase bridge arm inductance is arbitrary, cannotGuarantee that being added at each moment is all zero, therefore the high-frequency current generated on three-phase bridge arm cannot cancel out each other, and then flow into straightIt flows on side bus, causes the dither of direct current bus bar stream.
Summary of the invention
Goal of the invention of the invention is in view of the above problems, proposing a kind of modularization multi-level converter (MMC) DC sidePulsation of current suppressing method by the way that the carrier wave of each bridge arm of A, B, C three-phase is divided into two groups, and is moved in each carrier cycleThe phase of dynamic 2nd group of carrier wave, can make the sum of the pulse voltage being applied on three-phase bridge arm inductance is zero, the high-frequency current of generationIt will not flow on DC bus, to inhibit the high frequency current ripple on DC bus.
In order to achieve the above object, the technical solution adopted by the present invention is that: a kind of modularization multi-level converter (MMC) is straightSide pulsation of current suppressing method is flowed, the MMC system uses PD-PWM modulator approach, and joined and inhibit two frequency multiplication circulation of bridge armControl algolithm.Specifically includes the following steps: redundancy submodule is not considered, if the submodule number of A, B, C three-phase bridge arm isN, bridge arm and the isoceles triangle variable number of lower bridge arm are all n in each phase and to be divided into the two groups: 1st group include n-1 carrier wave,Wherein upper and lower bridge arm carrier wave is denoted as W respectivelyju_1~Wju_n-1And Wjl_1~Wjl_n-1(j=a, b, c respectively represent A, B, C three-phase),It being evenly distributed in the range of [- 1,1] from top to bottom, frequency and phase are all identical, and amplitude is identical and is equal to 2/ (n-1), andAnd the carrier phase of bridge arm and lower bridge arm is opposite in j phase；2nd group includes 1 carrier wave, wherein upper and lower bridge arm carrier wave is denoted as respectivelyWju_nAnd Wjl_n, amplitude range is [- 1,1], and frequency is identical with the 1st group, and phase is calculated by control algolithm, and bridge in j phaseThe carrier phase of arm and lower bridge arm is opposite.Correspondingly, bridge arm in each phase and the modulating wave of lower bridge arm are all divided into two parts:1 part is given power frequency sinusoidal reference ripple, wherein the power frequency sinusoidal reference ripple respectively-y that upper and lower bridge arm is givenjAnd yj, pointDo not compare with the 1st group of carrier wave of upper and lower bridge arm, obtaining modulation level number is respectively nju_1And njl_1；Part 2 is by circulationThe two frequency multiplication sinusoidal reference ripple y that controller obtainsj2, compare respectively with the 2nd group of carrier wave of upper and lower bridge arm, obtain modulation level numberMesh is respectively nju_2And njl_2.Bridge arm and lower bridge arm are respectively n through the number of levels that ovennodulation obtains in j phasejuAnd njl.Wherein,nju=nju_1+nju_2, njl=njl_1+njl_2.Then pass through traditional pressure strategy, it is each finally to generate driving j phase upper and lower bridge armThe pwm pulse of a submodule, so that the upper and lower bridge arm of j phase puts into n respectivelyju、njlA submodule.
As an improvement of the present invention, the phase of the 2nd group of carrier wave of the above-mentioned each bridge arm of A, B, C three-phase is calculated by controlMethod obtains, specifically includes the following steps:
(1) in each carrier cycle, A, B, C three-phase compensation voltages of sampling ring stream controller output are denoted as respectivelyya2、yb2And yc2；
(2) width for calculating the high-frequency pulse voltage being applied on three-phase bridge arm inductance, is denoted as θ respectivelya、θbAnd θc, thenCalculate their absolute value | θa|、|θb| and | θc|；
(3) right | θa|、|θb| and | θc| sequence obtains corresponding serial number and is denoted as K respectivelyθa、KθbAnd Kθc, serial number value rangeIt is 0,1,2.Wherein, | θa|、|θb| and | θc| middle the maximum corresponds to serial number and is equal to 0；|θa|、|θb| and | θc| middle reckling,Corresponding serial number is equal to 2；Otherwise, it corresponds to serial number and is equal to 1.
(4) position angle of corresponding 2nd group of carrier wave when calculating A, B, C three-phase sequence serial number is respectively 0,1,2, and according to(3) K obtained inθa、KθbAnd Kθc2nd group of carrier wave of each phase upper and lower bridge arm is moved respectively to corresponding phase.
As an improvement of the present invention, it in above-mentioned step (2), in each the triangular carrier cycle, is applied to eachPulse voltage on the bridge arm inductance of phase has 2, and distance difference is π.The width θ of each pulse voltagea、θbAnd θcCalculatingFormula are as follows: θj=yj2·π。yj2θ when > 0a> 0, yj2θ when < 0a<0。
As an improvement of the present invention, in above-mentioned steps (4), the corresponding 2nd group of load of each for A, B, C three-phase serial numberThe position of wave is defined in 1 carrier cycle, the negative peak point of the initial point of carrier cycle to triangular carrier (or positive peakPoint) horizontal distance be θ respectivelyas、θbs、θcs, circular are as follows:
For A phase,
Kθa=0, θas=π
For B phase,
Kθb=0, θbs=π
For C phase,
Kθc=0, θcs=π
The utility model has the advantages that
MMC DC side pulsation of current suppressing method of the invention, does not need to do hardware circuit any change, has followingAdvantage:
1, the pulsation of current being able to suppress on DC bus, practical value are high:
Carrier wave stacking pulsewidth modulation (PD-PWM) method is one of current most widely used MMC modulator approach.However, working asAfter control system joined two frequency multiplication circulation algorithms, pulse voltage can be applied on bridge arm inductance, and then to DC busUpper injection high-frequency current, so that the DC bus current characteristic of MMC is deteriorated.This method has found the problem, and proposes correspondingControl algolithm.This method passes through mobile carrier phase and improves MMC to inhibit the high-frequency current for flowing to DC busPerformance, have biggish practical value.
2, control is simple, should be readily appreciated that and implements:
By analysis, the width θ for the pulse voltage being applied on three-phase bridge arm inductance in a carrier cycle is founda、θbAnd θcAlgebraical sum is zero, but the phase of pulse is random.Therefore, the present invention proposes, by the phase of mobile carrier wave, thusSo that the sum of the pulse voltage on three-phase bridge arm inductance is equal to zero at any time.Such as Fig. 1, carrier wave is divided into two groups, the 1st groupCompare with sinusoidal modulation wave, therefore the sum of the level number of each phase upper and lower bridge arm is fixed；2nd group of only one carrier wave, widthIt is worth output reference voltage of the range in [- 1,1] and two frequency multiplication circulation controllers to compare, in a carrier cycle, each phase is producedRaw 2 pulse voltages, distance difference is π, and the position of pulse and the position of carrier wave are related.Therefore by moving three-phase bridge arm respectivelyThe 2nd group of carrier wave phase, just can control the position of the pulse voltage on three-phase bridge arm inductance.
Detailed description of the invention
Fig. 1 is three-phase MMC and submodule topology diagram；
Fig. 2 is the schematic diagram of this method specific implementation；
Fig. 3 is modulation knot when two frequency multiplication circulation controllers output compensation reference wave is greater than zero in method proposed by the present inventionFruit schematic diagram；
Fig. 4 is modulation knot when two frequency multiplication circulation controllers output compensation reference wave is less than zero in method proposed by the present inventionFruit schematic diagram；
Fig. 5 is the phase shift of the 2nd group of carrier wave and bridge arm inductive drop pulse of three-phase bridge arm in method proposed by the present inventionDynamic schematic diagram.
Specific embodiment
Further explanation is done to the present invention with reference to the accompanying drawing.
The present invention is suitable for three-phase MMC DC side pulsation of current suppressing method, and wherein MMC topological structure is as shown in Figure 1, threeTotally 6 bridge arms, each bridge arm are made of phase MMC n submodule unit (Cell) and series inductance.uals、ubls、uclsRespectivelyA, the sum of upper and lower bridge arm inductive drop of B, C three-phase.Submodule unit is half-bridge topology, is also possible to full-bridge, clamper Shuangzi moduleDeng other topologys.
As shown in Fig. 2, a kind of MMC DC side pulsation of current suppressing method, is laminated pulsewidth modulation (PD-PWM) using carrier waveMethod, and joined the control algolithm for inhibiting two frequency multiplication circulation of bridge arm.Do not consider redundancy submodule, if A, B, C three-phase bridge armSubmodule number is n, and bridge arm and the isoceles triangle variable number of lower bridge arm are all n and are divided into the two groups: 1st group in each phaseIncluding n-1 carrier wave, wherein upper and lower bridge arm carrier wave is denoted as W respectivelyju_1~Wju_n-1And Wjl_1~Wjl_n-1, uniformly divide from top to bottomFor cloth in the range of [- 1,1], frequency and phase are all identical, and amplitude is identical and is equal to 2/ (n-1), and in j phase bridge arm and underThe carrier phase of bridge arm is opposite；2nd group includes 1 carrier wave, wherein upper and lower bridge arm carrier wave is denoted as W respectivelyju_nAnd Wjl_n, amplitude modelEnclosing is [- 1,1], and frequency is identical with the 1st group, and phase is calculated by control algolithm, and in j phase bridge arm and lower bridge arm carrier waveOpposite in phase.Correspondingly, bridge arm in each phase and the modulating wave of lower bridge arm are all divided into two parts: part 1 is given workFrequency sinusoidal reference ripple, wherein the power frequency sinusoidal reference ripple respectively-y that upper and lower bridge arm is givenjAnd yj, respectively with upper and lower bridge arm1st group of carrier wave compares, and obtaining modulation level number is respectively nju_1And njl_1；Part 2 is two times obtained by circulation controllerFrequency sinusoidal reference ripple yj2, compare respectively with the 2nd group of carrier wave of upper and lower bridge arm, obtaining modulation level number is respectively nju_2Withnjl_2.Bridge arm and lower bridge arm are respectively n through the number of levels that ovennodulation obtains in j phasejuAnd njl.Wherein, nju=nju_1+nju_2,njl=njl_1+njl_2.Then pass through traditional pressure strategy, finally generate the PWM of driving each submodule of j phase upper and lower bridge armPulse, so that the upper and lower bridge arm of j phase puts into n respectivelyju、njlA submodule.
A method of the pulsation of current of MMC DC side being inhibited by the phase of mobile the 2nd group of carrier wave of bridge arm, wherein each bridgeThe phase of the 2nd group of carrier wave of arm is obtained by control algolithm, specifically includes the following steps:
(1) in each carrier cycle, A, B, C three-phase compensation voltages of sampling ring stream controller output are denoted as respectivelyya2、yb2And yc2.Here ya2、yb2And yc2All refer to per unit value.It should be noted that since PD-PWM is a kind of high frequency modulationMethod processed, setting carrier frequency is much higher than frequency of modulated wave, therefore, in a carrier cycle, it is believed that ya2、yb2And yc2It is constant.
(2) width for calculating the high-frequency pulse voltage being applied on three-phase bridge arm inductance, is denoted as θ respectivelya、θbAnd θc, and countCalculate corresponding absolute value | θa|、|θb| and | θc|；；
(3) right | θa|、|θb| and | θc| sequence obtains corresponding serial number and is denoted as K respectivelyθa、KθbAnd Kθc, serial number value rangeIt is 0,1,2.Wherein, | θa|、|θb| and | θc| middle the maximum corresponds to serial number and is equal to 0；|θa|、|θb| and | θc| middle reckling,Corresponding serial number is equal to 2；Otherwise, it corresponds to serial number and is equal to 1.
(4) position angle of corresponding 2nd group of carrier wave when calculating A, B, C three-phase sequence serial number is respectively 0,1,2, and according to(3) K obtained inθa、KθbAnd Kθc2nd group of carrier wave of each phase upper and lower bridge arm is moved respectively to corresponding phase.
Wherein, in step (2), in each the triangular carrier cycle, the pulse being applied in the bridge arm reactance of each phase is electric2 are pressed with, distance difference is π.The width θ of each pulse voltagea、θbAnd θcCalculation formula are as follows: θj=yj2·π。yj2When > 0θa> 0, yj2θ when < 0a<0。
In step (4), the position of the corresponding 2nd group of carrier wave of each for A, B, C three-phase serial number is defined on 1 triangleIn carrier cycle, the horizontal distance of the negative peak point (or positive peak point) of the initial point of carrier cycle to triangular carrier is respectivelyθas、θbs、θcs.For the 2nd group of carrier wave of the upper and lower bridge arm of j phase, phase is opposite.Therefore, if θjs=π, at this time j phaseThe initial point of upper bridge arm carrier cycle is just on positive peak point, and the initial point of j phase lower bridge arm carrier cycle is just in negative peakPoint on.The initial point of practical each carrier cycle is to change.θas、θbs、θcsValue be all according to Kθa、KθbAnd KθcAnd with πOn the basis of obtain, circular are as follows:
For A phase,
Kθa=0, θas=π
For B phase,
Kθb=0, θbs=π
For C phase,
Kθc=0, θcs=π
It is as shown in Figure 3 and Figure 4 respectively yj2> 0 and yj2J phase modulation result schematic diagram when < 0.Illustrate by taking Fig. 3 as an example, at thisIt invents in the control method proposed, the 1st group of carrier wave includes n-1 carrier wave, is modulated to given sine wave, upper and lower bridge arm warpModulating obtained number of levels is respectively nju_1And njl_1, since the sinusoidal reference ripple of upper and lower bridge arm is reverse phase, carrier wave is alsoReverse phase, thus the sum of the result modulated is constant, nju_1+njl_1=n-1；2nd group is only had 1 carrier wave, to two frequency multiplication circulationThe output reference wave of controller is modulated, and the modulated obtained number of levels of upper and lower bridge arm is respectively nju_2And njl_2, modulationAs a result non-constant, nju_2+njl_2=1 or 2.If the capacitance voltage of each submodule is equal to Vdc/ n, wherein VdcIt is DC bus electricityPressure, then, ujsm=VdcOr (n+1) Vdc/ n, wherein ujsmIt is the sum of the submodule voltage of the upper and lower bridge arm investment of j phase.As a result,ujls=0 or-Vdc/ n, wherein ujlsIt is the voltage on the upper and lower bridge arm inductance of j phase.To be generated on the upper and lower bridge arm inductance of j phaseHigh frequency voltage pulse.In each carrier cycle, each phase generates 2 voltage pulses through ovennodulation.It can be seen that generationVoltage pulse includes 4 attributes: amplitude, symbol, width and position.The amplitude of the voltage pulse is the electricity of a sub- module capacitancePressure, it is positive and negative and two frequency multiplication circulation controllers to export the positive and negative related of reference wave, width and two frequency multiplication circulation controllersThe size for exporting reference wave is related, and position is related with the position of the 2nd group of triangular carrier, and 2 electricity in each carrier cyclePressing pulse distance difference is π.For three-phase MMC, easy analysis obtains θa+θb+θc=0.It therefore theoretically can be in each carrier waveBy the phase of mobile 2nd group of carrier wave in period, so that the impulse summation of three-phase is offset, any time three-phase bridge arm inductance is realizedOn the sum of voltage pulse be equal to zero.
Fig. 5 gives a kind of situation that carrier phase is mobile.A, the pulse width size relation of B, C three-phase is | θb|>|θa|>|θc|, therefore Kθa=1, Kθb=0, Kθc=2.It is remained stationary on the basis of the triangular carrier of B phase, θbs=π.By the carrier wave of A phaseBe moved to the left π-(| θb|-|θa|)/2, by the carrier wave of C phase move right to π+(| θb|-|θc|)/2.At this point, three-phase bridge arm electricityPulse voltage in sense is cancelled out each other, and the sum of inductive drop of three-phase bridge arm is equal to zero in whole cycle.Then the height generatedThe sum of frequency electric current is also equal to zero, may not flow on DC bus, to inhibit the high frequency current ripple on DC bus.
The foregoing is merely better embodiment of the invention, protection scope of the present invention is not with above embodimentLimit, as long as those of ordinary skill in the art's equivalent modification or variation made by disclosure according to the present invention, should all be included in powerIn the protection scope recorded in sharp claim.