CN102739071A - Method for controlling direct current capacitor voltage of modular multi-level converter based on circulating current decoupling - Google Patents

Abstract

The invention discloses a method for controlling the direct current capacitor voltage of a modular multi-level converter based on circulating current decoupling. The method is characterized by comprising the following steps of: controlling the total direct current generatrix voltage by using active current which is absorbed from a power grid by the modular multi-level converter; balancing three-phase direct current voltage by using direct current components in circulating current; controlling balance of the direct current generatrixes of upper and lower bridge arms of each phase by using decoupling fundamental wave components in the circulating current; and finely adjusting the output voltage of each module along the current direction of the bridge arms, so the direct current capacitor voltage of each module in the bridge arms is balanced. The control method has the advantages that balanced control over the direct current generatrix voltage of the upper and lower bridge arms can be well realized; by using voltage control rings in other three layers, the direct current voltage of each module can be well balanced and stabilized to be in a given value range; and the method is accurate and reliable, and provides a good reference value for engineering application.

Description

Modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero

Technical field

The present invention relates to modular multilevel topological structure (MMC) mesohigh electric energy quality controller and high voltage direct current transmission research fields such as (HVDC), the particularly balanced control of DC bus-bar voltage between the modular multilevel brachium pontis.

Background technology

Along with social progress and industrial development, there are two big characteristics in modern power systems: electrical power trans mission/distribution system is huge, and idle and nonlinear load capacity increases.At first, modern society is also more and more to the demand of electric power, and in order to satisfy user's demand growing to electric power, it is more and more huger that electric power system becomes, and coverage is also more and more wide.This brings challenges for the stability of electric power system.Simultaneously, different electric power systems often need be interconnected at together, and strengthening the reliability of whole electric power system, but there is nonsynchronous problem in different electric power when interconnected.Secondly, the load of modern power systems also has new characteristics: power electronic equipment has superior performance, is adopted in a large number according to consumption industry by industrial or agricultural.Yet power electronic equipment can inject idle harmonic to electrical network as nonlinear load, and along with the increase of nonlinear load capacity, its influence to distribution system is also increasing, and it is dangerous that system is existed, unstable hidden danger [1].The mesohigh electrical power trans mission/distribution system is carried out the compensation of idle harmonic, can effectively improve the stability [2] [3] of electric power system.Interconnected between the different electric power systems through HVDC transmission system (HVDC), can the asynchronous problem of resolution system, also can stop fault between system, to spread, be the feasible method that improves the stability of a system and reliability.

Modular multilevel current transformer (MMC) just obtains scholar's extensive studies and engineer's strong interest after proposing.The modular multilevel current transformer has plurality of advantages: [4] such as modularized design, low switching frequency, low-power consumption, high-quality spectral characteristics.These advantages are given the manufacturing of modular multilevel current transformer, install, and safeguard and have brought huge convenience, also make it need not net side transformer and directly hang the mesohigh electrical network.The modular multilevel current transformer has been applied to HVDC transmission system and mesohigh quality of power supply control system now, becomes to improve transmission & distribution electric system stability and efficient method in reliability [5]-[9].

In the application of high voltage direct current transmission, mesohigh static reacance generator, mesohigh harmonic compensation device and mesohigh frequency conversion speed-adjusting system; An a lot of copped wave units in series constitute a brachium pontis together, and six brachium pontis are connected into the double star structure through the connection reactor becomes 3-phase power converter.The DC side of each the copped wave unit in each brachium pontis need be incorporated electrolytic capacitor into, need not add independently direct voltage source.The expert has carried out big quantity research to the modular multilevel current transformer both at home and abroad at present, has proposed some control methods.

Yet; In practical application, the loss of each copped wave unit is different, and the time-delay of the switching signal that control circuit produces is also different; It is asymmetric to add in the dynamic process of load changing the current waveform positive-negative half-cycle, all can cause between the brachium pontis or module between dc voltage unbalanced.If do not correct in real time, the module dc voltage that has is increasingly high in addition, and module is operated in the state that exceeds the quata, and causes working life to shorten even direct demolition; The module dc voltage that has is more and more lower, and module is operated in the volume state of owing, and can not bring into play due effect.Therefore, each module dc capacitor voltage control problem becomes the emphasis problem that the modular multilevel transformer is used, and also is difficult point problem [7].

To the DC bus-bar voltage control problem of modular multilevel current transformer, existing now multiple solution: like the module row collimation method, brachium pontis energy preestimating method, circulation collocation method, [10]-[17] such as negative-sequence current equalization.These methods all are to propose to a certain concrete application, do not have versatility and systematicness, and some shortcoming and defect of self are also all arranged simultaneously.Do not see better controlled strategy as yet to the modular multilevel current transformer.For this reason, also need carry out systematic research to the dc capacitor voltage control problem of modular multilevel current transformer.

Below provide the pertinent literature of retrieval

[1] He Xiangning, Chen Alian. the theory of multi-level converter and application technology. Beijing: the .2006 of China Machine Press

[2] Li Yongdong, Xiao Xi, Gao Yue etc. big capacity multi-level converter---principle, control, application. Beijing: the .2005 of Science Press

[3] Wang Zhaoan, Yang Jun, Liu Jinjun. harmonic wave suppresses and reactive power compensation [M]. Beijing: China Machine Press, 2004.

[4]Hirofumi?Akagi.“Classification,Terminology,and?Application?of?the?Modular?Multilevel?Cascade?Converter(MMCC),”IEEE?Trans.Power?Electron.,vol.26,no.11,pp.3119-31305,Jul.2011.

[5]Saeedifard,M.,Iravani,R.“Dynamic?Performance?of?a?Modular?Multileve?Back-to-Back?HVDC?System,”IEEE?Trans.Power?Delivery.,vol.25,no.4,pp.2903-2912,Jul.2010.

[6]Hirofumi?Akagi.“New?Trends?in?Medium-Voltage?Power?Converters?and?Motor?Drives,”Industrial?Electronics(ISIE),2011?IEEE?International?Symposium.pp.5-14,2011.

[7]H.Mohammadi?P.,M.Tavakoli?Bina.“A?Transformerless?Medium-Voltage?STATCOM?Topology?Based?on?Extended?Modular?Multilevel?Converters,”IEEE?Trans.Power?Electron.,vol.26,no.5,pp.1534–1545,Jul.2011.

[8]Xiaofeng?Yang,Jianghong?Li,Wenbao?Fang,et?al.“Research?on?Modular?Multilevel?Converter?Based?STATCOM,”Industrial?Electronics?and?Applications(ICIEA),2011?6th?IEEE?Conference,pp.2569-2574.2011.

[9]B.Gemmell,J.Dorn,D.Retzmann,and?D.Soerangr,“Prospects?of?multilevel?VSC?technologies?for?power?transmission,”in?Proc.Rec.IEEETDCE,Chicago,IL,2008,pp.1–16.

[10]Qing?rui?Tu,Zheng?Xu.“Impact?of?Sampling?Frequency?on?Harmonic?Distortion?for?Modular?Multilevel?Converter,”IEEE?Trans.Power?Delivery.,vol.26,no.1,pp.298–306,Ju1.2011.

[11]Chun?Gao,Jianguo?Jiang,Xingwu?Yang,“A?Novel?Topology?and?Control?Strategy?of?Modular?Multilevel?Converter(MMC),”Electrical?and?Control?Engineering(ICECE),2011International?Conference,pp.967-971,sept.2011.

[12]D.Soto-Sanchez,T.C.Gree.“Control?of?a?modular?multilevel?converter-based?HVDC?transmission?system,”Power?Electronics?and?Application(EPE?2011),Proceedings?of?the2011-14th?European?Conference,pp.1-10.Aug./Sept.2011.

[13]Makoto?Hagiwara,Ryo?Maeda,Hirofumi?Akagi.“Control?and?Analysis?of?the?Modular?Multilevel?Cascade?Converter?Based?on?Double-Star?Chopper-Cells(MMCC-DSCC),”IEEE?Trans.Power?Electron.,vol.26,no.6,pp.1649–1658,Ju1.2011.

[14]Lanhua?Zhang,Guangzhu?Wang.“Voltage?Balancing?Control?of?a?Novel?Modular?Multilevel?Converter,”Electric?Utility?Deregulation?and?Restructuring?and?Power?Technologies(DRPT),2011?4th?International?Conference,pp.109-114,Conf.2011.

[15]Makoto?Hagiwara,Hirofumi?Akagi.“Control?and?Experiment?of?Pulsewidth-Modulated?Modular?Multilevel?Converters,”IEEE?Trans.Power?Electron.,vol.24,no.7,pp.1737–1746,Jul.2009.

[16] Zhao Xin, Zhao Chengyong, Li Guangkai. adopt the modularization multi-level converter capacitance voltage Balance Control [J] of phase-shifting carrier wave technology. Proceedings of the CSEE, the 31st volume, the 21st phase, 48-55,2011.

[17] Guo Jie, Jiang Daozhuo, Zhou Yuebin. the modularization multi-level converter control method that alternating current-direct current side electric current is controlled respectively. Automation of Electric Systems, the 35th volume, the 7th phase, 42-47,2011.

Summary of the invention

The objective of the invention is to propose a kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero.Total be exactly the DC bus-bar voltage that the active current of specifically utilizing the modular multilevel current transformer to absorb from electrical network is controlled; Make dc-voltage balance between the three-phase with the flip-flop in the circulation; With the balance of two brachium pontis dc buss about the every phase of first-harmonic Composition Control of the decoupling zero in the circulation, realize the equilibrium of dc capacitor voltage between inner each module of brachium pontis at last along the output voltage of each module of brachium pontis sense of current fine setting.Emphasis of the present invention is at circulation decoupling zero portion control section.

In order to achieve the above object, the present invention adopts following technical scheme:

A kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero; The total DC bus-bar voltage of active current control that utilizes the modular multilevel current transformer to absorb from electrical network; Make dc-voltage balance between the three-phase with the flip-flop in the circulation; With the balance of two brachium pontis dc buss about the every phase of first-harmonic Composition Control of the decoupling zero in the circulation, realize the equilibrium of dc capacitor voltage between inner each module of brachium pontis at last along the output voltage of each module of brachium pontis sense of current fine setting.

In order to achieve the above object, the present invention can also adopt following technical scheme:

A kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero may further comprise the steps:

Step 1, the DC bus-bar voltage control that three-phase is total

Step 1.1, all copped wave unit dc voltage v of many level current transformers of detection moduleization three-phase _Api, v _Ani, v _Bpi, v _Bni, v _Cpi, v _CniI=1 wherein, 2 ... N, N are natural number; Obtain A go up mutually the brachium pontis dc voltage with Obtain A successively with the method and descend brachium pontis and B, C two total dc voltage of each brachium pontis mutually mutually $v_{c,\mathrm{Na}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Ani}},$ $v_{c,\mathrm{Pb}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Bpi}},$ $v_{c,\mathrm{Nb}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Bni}},$ $v_{c,\mathrm{Pc}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Cpi}},$ $v_{c,\mathrm{Nc}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Cni}},$ Obtain each phase total dc voltage v of two brachium pontis up and down _{Ph, a}=v _{C, pa}+ v _{C, na}, v _{Ph, b}=v _{C, pb}+ v _{C, nb}, v _{Ph, c}=v _{C, pc}+ v _{C, nc}And three-phase average voltage Obtain the average dc voltage of module of each brachium pontis at last $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pa}}}=v_{c,\mathrm{Pa}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Na}}}=v_{c,\mathrm{Na}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pb}}}=v_{c,\mathrm{Pb}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Nb}}}=v_{c,\mathrm{Nb}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pc}}}=v_{c,\mathrm{Pc}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Nc}}}=v_{c,\mathrm{Nc}}/N.$

Step 1.2; Three-phase dc busbar voltage mean value and dc voltage set-point are sent into the single channel subtracter carry out computing; Operation result is sent into the single channel proportional and integral controller and is adjusted, and its output valve is injected into as additional amount as the active current component of modular multilevel current transformer and AC network exchange and controls the active power that whole modular multilevel current transformer absorbs from electrical network on the current inner loop d axle based on dq decoupling zero control.

Step 2, the instruction of DC component in the synthetic circulation

Step 2.1 is utilized step 1.1 detection limit And v _{Ph, a}, v _{Ph, b}, v _{Ph, c}It is poor to do, and sends into three single channel pi regulators and generates

Step 2.2, on go on foot that computing generates instruction as DC component in the circulation.

Step 3, the instruction of alternating current component in the synthetic circulation

Step 3.1 detects three phase network voltage v _{S, a}, v _{S, b}, v _{S, c}

Step 3.2 is carried out the transform operation that the three phase static coordinate is tied to two cordic phase rotators system with three phase network voltage, the numerical value of d axle after the conversion is sent into the single channel low pass filter carry out filtering, and the output of filter is designated as V _PdThen with detected B, C two phase line voltage switches; Carry out the three phase static coordinate again and be tied to the transform operation that two cordic phase rotators are; D axle and q axis values are sent into two single channel low pass filters respectively and are carried out filtering after the computing, and the numerical value of d axle and q axle is designated as V respectively after the filtering _NdAnd V _NqTransformation matrix in this step is:

$T_{\mathrm{abc}-\mathrm{dq}}=\frac{2}{3}\left[\begin{array}{ccc}\sin \left(\mathrm{\ωt}\right)& \sin (\mathrm{\ωt}-2\mathrm{\π}/3)& \sin (\mathrm{\ωt}+2\mathrm{\π}/3)\\ \cos \left(\mathrm{\ωt}\right)& \cos (\mathrm{\ωt}-2\mathrm{\π}/3)& \cos (\mathrm{\ωt}+2\mathrm{\π}/3)\end{array}\right]$

Step 3.3 is with the V of step 3.2 generation _Pd, V _NdAnd V _NqFor people's following relationship formula, generate the perception and the capacitive reference direction of each phase voltage on line side:

v _s,a,1＝V _pd?cosωt+V _nd?cosωt+V _nq?sinωt

v _s,a,-1＝-V _pd?cosωt-V _nd?cosωt-V _nq?sinωt

$v_{s,b,1}=\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}-\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,b,-1}=-\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}+\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,c,1}=-\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}-\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,c,-1}=\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}+\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

Step 3.4 is with the v of step 3.3 generation _{S, b ,-1}And v _{S, c, 1}For people's following relationship formula-v _{S, a}=A (a) v _{S, b ,-1}+ B (a) v _{S, c, 1}Coefficient according to equality the right and left sin ω t and cos ω t equates respectively, asks for coefficient A (a) and B (a); Similarly, foundation-v _{S, b}=A (b) v _{S, c ,-1}+ B (b) v _{S, a, 1}Ask for A (b), B (b), foundation-v _{S, c}=A (c) v _{S, a ,-1}+ B (c) v _{S, b, 1}Ask for A (c), B (c);

Step 3.5 is with the numerical value v of step 1.1 _{C, pa}And v _{C, na}, v _{C, pb}And v _{C, nb}, v _{C, pc}And v _{C, nc}Send into three single channel subtracters respectively, three single channel pi regulators are sent in the output of subtracter again, and the output valve of three pi regulators is defined as respectively: c _a, c _bAnd c _c

Step 3.6, with step 3.3,3.4,3.5 variablees that generate are for people's following relationship formula:

$i_{\mathrm{ac},a}^{*}=c_a\·v_{s,a}+c_b\·B\left(b\right)\·v_{s,a,1}+c_c\·A\left(c\right)\·v_{s,a,-1}$

$i_{\mathrm{ac},b}^{*}=c_a\·A\left(a\right)\·v_{s,b,-1}+c_b\·v_{s,b}+c_c\·B\left(c\right)\·v_{s,b,1}$

$i_{\mathrm{ac},c}^{*}=c_a\·B\left(a\right)\·v_{s,c,1}+c_b\·A\left(b\right)\·v_{s,c,-1}+c_c\·v_{s,c}$

Obtain the interchange circulation instruction of three-phase decoupling zero.

Step 4, the equilibrium control of DC bus-bar voltage between inner each copped wave unit of brachium pontis.

Step 4.1, the actual current i of six brachium pontis of detection _{P, a}, i _{N, a}, i _{P, b}, i _{N, b}, i _{P, c}, i _{N, c}, A is gone up mutually the average dc voltage of brachium pontis copped wave module Go up the dc voltage v of first module of brachium pontis mutually with A _Ap1Send into the single channel subtracter, proportional controller is sent in the output of single channel subtracter, the output valve of adjuster and the current i of last brachium pontis _{P, a}Multiply each other, obtain the amount trimmed that A goes up first module alternating voltage of brachium pontis mutually

In like manner, A is descended mutually the average dc voltage of brachium pontis copped wave module

Descend the dc voltage v of first module of brachium pontis mutually with A _An1Send into the single channel subtracter, proportional controller is sent in the output of single channel subtracter, the inverse value-i of the output valve of adjuster and following brachium pontis electric current _{N, a}Multiply each other, obtain the amount trimmed that A descends first module alternating voltage of brachium pontis mutually

Continue to use same thinking, obtain the alternating voltage amount trimmed of B, first module of C phase upper and lower bridge arm

Step 4.2 is obtained A respectively and is gone up brachium pontis second mutually and instruct

A to descend brachium pontis second to instruct

B to go up brachium pontis second mutually to N module trim voltage mutually to N module trim voltage to instruct B to descend brachium pontis second to instruct

C to go up brachium pontis second mutually to N module trim voltage mutually to N module trim voltage to instruct

C to descend brachium pontis second to N Ge module trim voltage Zhi Linged

mutually to N module trim voltage

Step 5, the instruction of copped wave module alternating voltage PWM modulating wave generates

Step 5.1; The current loop control system of modular multilevel current transformer output current carries out the closed loop tracking Control to instruction current and output current; Its output through the dc loop-current instruction that obtains three-phase output order voltage pwm modulating wave

and modular multilevel current transformer loop current ring control system after the dq inverse transformation and generate step 2.2 and 3.5 with exchange circulation and instruct and add and instruct as total circulation; And total circulation instruction current and actual loop current carried out the closed loop tracking Control, obtain command voltage PWM modulating wave

and

of three-phase control circulation

Step 5.2; Go up A mutually the fine setting instruction

of first H bridge module of brachium pontis PWM modulating wave and press relational expression

computing, obtain the PWM modulating wave that A goes up first module of brachium pontis mutually with

and that step 5.1 generates; Descend A mutually the fine setting instruction

of first H bridge module of brachium pontis PWM modulating wave to press relational expression

computing, obtain the PWM modulating wave that A descends first module of brachium pontis mutually with

and

that step 5.1 generates; By that analogy, the final PWM modulating wave that obtains in the A phase upper and lower bridge arm residue module and

B mutually in the upper and lower bridge arm the final PWM modulating wave of residue module and

C remain final PWM modulating wave

and of module mutually in the upper and lower bridge arm

Step 5.3 is compared with the triangular carrier of phase shift successively with the modulating wave of every each module of phase, generates the switching signal of each module.

The present invention is characterised in that four control rings in the above-mentioned steps, and wherein step 1 is first control ring, and purpose is to control whole modular multilevel current transformer and absorbs meritorious size from electrical network, to offset the power loss of whole current transformer.Step 2 realizes the balance of three alternate DC bus-bar voltages through regulating the needed dc loop-current of the many level current transformers of generation moduleization automatically.Step 3 purpose is to generate the interchange circulation instruction of mutual decoupling zero, redistribute every mutually in active power between the upper and lower bridge arm, make each equilibrium of direct voltage between two brachium pontis up and down mutually.Step 4 purpose is to finely tune the command voltage of each module in each brachium pontis; Reconfigure the active power that each module absorbs; Make the active power of this module actual absorption just can offset the loss of this module self, make the virtual voltage of each module DC side equal rated value.

With respect to prior art, the present invention has following beneficial effect: provide among the present invention based on balance control method between the modular multilevel current transformer upper and lower bridge arm of circulation decoupling zero, and each intermodule balance control method.For the feasibility of authentication control method, the inventor has built capacity in the laboratory be 5kVA, and each brachium pontis is by the small test model machine of two copped wave module series connection.Can find out that from experimental waveform this control method can realize each mutually up and down equilibrium control of DC bus-bar voltage between two brachium pontis well.The voltage control loop that cooperates other three levels again, the dc voltage of each module have been realized balanced well and have been stabilized in set-point.This control strategy all has performance preferably under the various operating modes even under the grid failure state.Experimental result has all proved between the three-phase and the equilibrium of alternate module is controlled, and this method is correct, reliable, for practical applications provides good reference value.

Description of drawings

Fig. 1 is modular multilevel current transformer main circuit structure figure;

Fig. 2 is a modular multilevel current transformer dc capacitor voltage control system block diagram; Fig. 2 (a) is total DC bus-bar voltage control; Fig. 2 (b) is balanced control between the three-phase, k=a, b, c; Fig. 2 (c) is the up and down DC bus-bar voltage control between two brachium pontis of every phase, k-1=c wherein, a, b; K=a, b, c; K+1=b, c, a; Fig. 2 (d) is DC bus-bar voltage control between inner each module of each brachium pontis, k=a wherein, b, c; J=1,2 ... N.

Fig. 3 is a modular multilevel current transformer current control system block diagram; Fig. 3 (a) is the output current control based on dq; Fig. 3 (b) is the circulation control based on proportional controller, k=a, b, c; The total AC side output voltage instruction of each module is: $v_{p,\mathrm{Kj}}^{*}=\frac{E}{2N}-\frac{v_k^{*}}{N}-\frac{v_{z,k}^{*}}{2N}+\mathrm{\Δ}{v}_{p,\mathrm{Kj}}^{*};$ $v_{n,\mathrm{Kj}}^{*}=\frac{E}{2N}-\frac{v_k^{*}}{N}-\frac{v_{z,k}^{*}}{2N}+\mathrm{\Δ}{v}_{n,\mathrm{Kj}}^{*}.$

Fig. 4 is PWM modulation effect figure.The waveform of four passages is followed successively by, and CH1:A goes up the total AC side voltage of brachium pontis mutually; CH2: go up the brachium pontis electric current; CH3: following brachium pontis electric current; CH4: total output current.

Fig. 5 is the experimental verification figure of total DC voltage control.The waveform of four passages is followed successively by, CH1:A phase line voltage; CH2:A phase output current; CH3:A goes up the total output voltage of brachium pontis mutually; CH4:A goes up first module dc voltage of brachium pontis mutually.

Fig. 6 is the experimental verification figure of the balanced control of three-phase.The waveform of four passages is followed successively by, CH1:A phase line voltage; CH2:A goes up first module dc voltage of brachium pontis mutually; CH3:B goes up first module dc voltage of brachium pontis mutually; CH4:C goes up first module dc voltage of brachium pontis mutually.

Fig. 7 is the experimental verification figure of balanced control between every inner mutually two brachium pontis up and down.The waveform of four passages is followed successively by, CH1:A phase line voltage; CH2:A phase output current; CH3:A goes up first module dc voltage of brachium pontis mutually; CH4:A descends first module dc voltage of brachium pontis mutually.

Fig. 8 is the experimental verification figure of balanced control between inner each module of brachium pontis.The waveform of four passages is followed successively by, CH1:A phase line voltage; CH2:A phase output current; CH3:A goes up first module dc voltage of brachium pontis mutually; CH4:A goes up second module dc voltage of brachium pontis mutually.

Fig. 9 compensates the experimental verification figure of symmetrical reactive load for the modular multilevel current transformer.The waveform of four passages is followed successively by, CH1:A phase line voltage; CH2:A phase current on line side; CH3:A phase output current; CH4:A goes up first module dc voltage of brachium pontis mutually.

Figure 10 is the experimental verification figure of modular multilevel current transformer compensation asymmetrical non linearity load.Figure 10 (a) is the asymmetric line voltage of three-phase; Figure 10 (b) is a three-phase nonlinear load electric current; Figure 10 (c) is the three-phase output current; Figure 10 (d) is line voltage and dc capacitor voltage.

Embodiment

With reference to Fig. 1, the many level current transformers of link blockization between three-phase power supply system and the threephase load.The main circuit structure of mixed multi-level current transformer is connected the reactor series connection respectively by six brachium pontis with six, constitute double star then and connect.Each brachium pontis has two copped wave modules to be composed in series, and the module DC side parallel has electrolytic capacitor, and switching device adopts large power all-controlled devices such as IGBT or GTO.Connect the switching frequency that the reactor parameters of choice depends primarily on the H bridge module.

The serial module structure number does not have the upper limit in each brachium pontis, and value is decided by the electric power system electric pressure.In order to narrate conveniently, among the present invention, be that example is elaborated with two module series connection.The electrical network three-phase voltage is designated as u _s, that is: u _Sa, u _Sb, u _ScThe power supply three-phase current is designated as i _s, that is: i _Sa, i _Sb, i _Sc12 unit dc voltages of series connection copped wave module are designated as v respectively _Ap1, v _Ap2, v _An1, v _An2, v _Bp1, v _Bp2, v _Bn1, v _Bn2, v _Cp1, v _Cp2, v _Cn1, v _Cn2The three-phase offset current of many level of cascaded H bridge combining inverter output is designated as i _c, that is: i _Ca, i _Cb, i _CcThe threephase load electric current is designated as i _L, that is: i _Ka, i _Lb, i _Lc

With reference to Fig. 2, the modular multilevel current transformer DC bus-bar voltage control method among the present invention comprises four control rings; Wherein step 1 is first control ring; Be total AC/DC energy exchange, step 2 is second control ring, and step 3 is the 3rd control ring; Step 4 is the 4th control ring, and concrete steps are following:

Step 1, the DC bus-bar voltage control that three-phase is total

Step 1.1, all copped wave unit dc voltage v of many level current transformers of detection moduleization three-phase _Api, v _Ani, v _Bpi, v _Bni, v _Cpi, v _CniI=1 wherein, 2 ... N, N are natural number; Obtain A go up mutually the brachium pontis dc voltage with

Obtain A successively with the method and descend brachium pontis and B, C two total dc voltage of each brachium pontis mutually mutually $v_{c,\mathrm{Na}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Ani}},$ $v_{c,\mathrm{Pb}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Bpi}},$ $v_{c,\mathrm{Nb}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Bni}},$ $v_{c,\mathrm{Pc}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Cpi}},$ $v_{c,\mathrm{Nc}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Cni}},$ Obtain each phase total dc voltage v of two brachium pontis up and down _{Ph, a}=v _{C, pa}+ v _{C, na}, v _{Ph, b}=v _{C, pb}+ v _{C, nb}, v _{Ph, c}=v _{C, pc}+ v _{C, nc}And three-phase average voltage

Obtain the average dc voltage of module of each brachium pontis at last $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pa}}}=v_{c,\mathrm{Pa}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Na}}}=v_{c,\mathrm{Na}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pb}}}=v_{c,\mathrm{Pb}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Nb}}}=v_{c,\mathrm{Nb}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pc}}}=v_{c,\mathrm{Pc}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Nc}}}=v_{c,\mathrm{Nc}}/N.$

Step 1.2; Three-phase dc busbar voltage mean value

and dc voltage set-point

are sent into the single channel subtracter carry out computing; Operation result is sent into the single channel proportional and integral controller and is adjusted, and its output valve is injected into as additional amount as the active current component of modular multilevel current transformer and AC network exchange and controls the active power that whole modular multilevel current transformer absorbs from electrical network on the current inner loop d axle based on dq decoupling zero control.

Step 2, the instruction of DC component in the synthetic circulation

Step 2.1 is utilized step 1.1 detection limit

Respectively with v _{Ph, a}, v _{Ph, b}, v _{Ph, c}It is poor to do, and sends into three single channel pi regulators and generates respectively

Step 2.2, on go on foot

that computing generates instruction as DC component in the circulation.

Step 3, the instruction of alternating current component in the synthetic circulation

Step 3.1 detects three phase network voltage v _{S, a}, v _{S, b}, v _{S, c}

Step 3.2 is carried out the transform operation that the three phase static coordinate is tied to two cordic phase rotators system with three phase network voltage, the numerical value of d axle after the conversion is sent into the single channel low pass filter carry out filtering, and the output of filter is designated as V _PdThen with detected B, C two phase line voltage switches; Carry out the three phase static coordinate again and be tied to the transform operation that two cordic phase rotators are; D axle and q axis values are sent into two single channel low pass filters respectively and are carried out filtering after the computing, and the numerical value of d axle and q axle is designated as V respectively after the filtering _NdAnd V _NqTransformation matrix in this step is:

$T_{\mathrm{abc}-\mathrm{dq}}=\frac{2}{3}\left[\begin{array}{ccc}\sin \left(\mathrm{\ωt}\right)& \sin (\mathrm{\ωt}-2\mathrm{\π}/3)& \sin (\mathrm{\ωt}+2\mathrm{\π}/3)\\ \cos \left(\mathrm{\ωt}\right)& \cos (\mathrm{\ωt}-2\mathrm{\π}/3)& \cos (\mathrm{\ωt}+2\mathrm{\π}/3)\end{array}\right]$

Step 3.3 is with the V of step 3.2 generation _Pd, V _NdAnd V _NqFor people's following relationship formula, generate the perception and the capacitive reference direction of each phase voltage on line side:

v _s,a,1＝V _pd?cosωt+V _nd?cosωt+V _nq?sinωt

v _s,a,-1=-V _pd?cosωt-V _nd?cosωt-V _nq?sinωt

$v_{s,b,1}=\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}-\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,b,-1}=-\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}+\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,c,1}=-\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}-\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,c,-1}=\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}+\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

Step 3.4 is with the v of step 3.3 generation _{S, b ,-1}And v _{S, c, 1}For people's following relationship formula

-v _{S, a}=A (a) v _{S, b ,-1}+ B (a) v _{S, c, 1}Coefficient according to equality the right and left sin ω t and cos ω t equates respectively, asks for coefficient A (a) and B (a); Similarly, foundation-v _{S, b}=A (b) v _{S, c ,-1}+ B (b) v _{S, a, 1}Ask for A (b), B (b), foundation-v _{S, c}=A (c) v _{S, a ,-1}+ B (c) v _{S, b, 1}Ask for A (c), B (c);

Step 3.5 is with the numerical value v of step 1.1 _{C, pa}And v _{C, na}, v _{C, pb}And v _{C, nb}, v _{C, pc}And v _{C, nc}Send into three single channel subtracters respectively, three single channel pi regulators are sent in the output of subtracter again, and the output valve of three pi regulators is defined as respectively: c _a, c _bAnd c _c

Step 3.6, with step 3.3,3.4,3.5 variablees that generate are for people's following relationship formula:

$i_{\mathrm{ac},a}^{*}=c_a\·v_{s,a}+c_b\·B\left(b\right)\·v_{s,a,1}+c_c\·A\left(c\right)\·v_{s,a,-1}$

$i_{\mathrm{ac},b}^{*}=c_a\·A\left(a\right)\·v_{s,b,-1}+c_b\·v_{s,b}+c_c\·B\left(c\right)\·v_{s,b,1}$

$i_{\mathrm{ac},c}^{*}=c_a\·B\left(a\right)\·v_{s,c,1}+c_b\·A\left(b\right)\·v_{s,c,-1}+c_c\·v_{s,c}$

Obtain the interchange circulation instruction of three-phase decoupling zero.

Step 4, the equilibrium control of DC bus-bar voltage between inner each copped wave unit of brachium pontis.

Step 4.1, the actual current i of six brachium pontis of detection _{P, a}, i _{N, a}, i _{P, b}, i _{N, b}, i _{P, c}, i _{N, c}, A is gone up mutually the average dc voltage of brachium pontis copped wave module

Go up the dc voltage v of first module of brachium pontis mutually with A _Ap1Send into the single channel subtracter, proportional controller is sent in the output of single channel subtracter, the output valve of proportional controller and the current i of last brachium pontis _{P, a}Multiply each other, obtain the amount trimmed that A goes up first module alternating voltage of brachium pontis mutually

In like manner, A is descended mutually the average dc voltage of brachium pontis copped wave module

Descend the dc voltage v of first module of brachium pontis mutually with A _An1Send into the single channel subtracter, proportional controller is sent in the output of single channel subtracter, the inverse value-i of the output valve of proportional controller and following brachium pontis electric current _{N, a}Multiply each other, obtain the amount trimmed that A descends first module alternating voltage of brachium pontis mutually Continue to use same thinking, obtain the alternating voltage amount trimmed of B, first module of C phase upper and lower bridge arm

Step 4.2 is obtained A respectively and is gone up brachium pontis second mutually and instruct

A to descend brachium pontis second to instruct

B to go up brachium pontis second mutually to N module trim voltage mutually to N module trim voltage to instruct B to descend brachium pontis second to instruct

C to go up brachium pontis second mutually to N module trim voltage mutually to N module trim voltage to instruct

C to descend brachium pontis second to N Ge module trim voltage Zhi Linged

mutually to N module trim voltage

Step 5, the instruction of copped wave module alternating voltage PWM modulating wave generates.

Step 5.1; The current loop control system of modular multilevel current transformer output current carries out the closed loop tracking Control to instruction current and output current; Its output through the dc loop-current instruction that obtains three-phase output order voltage pwm modulating wave and

modular multilevel current transformer loop current ring control system after the dq inverse transformation and generate step 2.2 and 3.5 with exchange circulation and instruct and add and instruct as total circulation; And total circulation instruction current and actual loop current carried out the closed loop tracking Control, obtain command voltage PWM modulating wave

and

of three-phase control circulation

Step 5.2; Go up A mutually the fine setting instruction

of first H bridge module of brachium pontis PWM modulating wave and press relational expression

computing, obtain the PWM modulating wave that A goes up first module of brachium pontis mutually with

and

that step 5.1 generates; Descend A mutually the fine setting instruction of first H bridge module of brachium pontis PWM modulating wave to press relational expression

computing, obtain the PWM modulating wave that A descends first module of brachium pontis mutually with and

that step 5.1 generates.By that analogy, the final PWM modulating wave

that obtains in the A phase upper and lower bridge arm residue module and B mutually in the upper and lower bridge arm the final PWM modulating wave

of residue module and

C remain final PWM modulating wave

and

of module mutually in the upper and lower bridge arm

Step 5.3 is compared with the triangular carrier of phase shift successively with the modulating wave of every each module of phase, generates the switching signal of each module.

Step 1 is first control ring, and it is meritorious from the electrical network absorption that purpose is to control whole modular multilevel current transformer, to offset the loss that whole combining inverter produces.Step 2 is through calculating the DC component instruction of synthesizing in the circulation, the balance of regulating DC bus-bar voltage between the three-phase.Step 3 realizes the balance of DC bus-bar voltage between each phase upper and lower bridge arm through the instruction of the alternating current component in the circulation that calculates synthetic mutual decoupling zero.Step 4 is through the output voltage instruction of inner each module of fine setting brachium pontis; Redistribute the active power that each module absorbs; Make the active power of this module actual absorption just can offset the loss of this module self, thereby make the stable operation under specified command voltage value of each module.The output voltage instruction that synthetic each module of step 5 is final is used for the PWM modulation.

For the feasibility of authentication control method, the inventor has built capacity in the laboratory be 5kVA, and each brachium pontis is by the small test model machine of two copped wave module series connection.Fig. 4,5,6,7,8,9,10 has provided the experimental waveform that adopts control method among the present invention; Be respectively the PWM modulation effect, total dc voltage, balanced control between the three-phase; The balanced control of DC bus-bar voltage between every inner mutually two brachium pontis up and down; The balanced control of DC bus-bar voltage between inner each module of each brachium pontis, the compensation effect during the compensation three phase symmetry load, the compensation effect of compensation three-phase nonlinear load under the electric network fault situation.Can find out that from experimental waveform this control method can realize each mutually up and down equilibrium control of DC bus-bar voltage between two brachium pontis well.The voltage control loop that cooperates other three levels again, the dc voltage of each module have been realized balanced well and have been stabilized in set-point.This control strategy all has performance preferably under the various operating modes even under the grid failure state.

Claims (6)

1. modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero; It is characterized in that; The total DC bus-bar voltage of active current control that utilizes the modular multilevel current transformer to absorb from electrical network; Make dc-voltage balance between the three-phase with the flip-flop in the circulation; With the balance of two brachium pontis dc buss about the every phase of first-harmonic Composition Control of the decoupling zero in the circulation, realize the equilibrium of dc capacitor voltage between inner each module of brachium pontis at last along the output voltage of each module of brachium pontis sense of current fine setting.

2. the modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero is characterized in that, may further comprise the steps:

Step 1, the DC bus-bar voltage control that three-phase is total

Step 1.1, all copped wave unit dc voltage v of many level current transformers of detection moduleization three-phase _Api, v _Ani, v _Bpi, v _Bni, v _Cpi, v _CniI=1 wherein, 2 ... N, N are natural number; Obtain A go up mutually the brachium pontis dc voltage with

A descends brachium pontis and B, C two total dc voltage of each brachium pontis mutually mutually $v_{c,\mathrm{Pb}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Bpi}},$ $v_{c,\mathrm{Nb}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Bni}},$ $v_{c,\mathrm{Pc}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Cpi}},$ $v_{c,\mathrm{Nc}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{v}_{\mathrm{Cni}},$ Obtain each phase total dc voltage v of two brachium pontis up and down _{Ph, a}=v _{C, pa}+ v _{C, na}, v _{Ph, b}=v _{C, pb}+ v _{C, nb}, v _{Ph, c}=v _{C, pc}+ v _{C, nc}And three-phase average voltage

Obtain the average dc voltage of module of each brachium pontis at last $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pa}}}=v_{c,\mathrm{Pa}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Na}}}=v_{c,\mathrm{Na}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pb}}}=v_{c,\mathrm{Pb}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Nb}}}=v_{c,\mathrm{Nb}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Pc}}}=v_{c,\mathrm{Pc}}/N,$ $\stackrel{\‾}{V_{\mathrm{Cel},\mathrm{Nc}}}=v_{c,\mathrm{Nc}}/N;$

Step 1.2; Three-phase dc busbar voltage mean value

and dc voltage set-point

are sent into the single channel subtracter carry out computing; Operation result is sent into the single channel proportional and integral controller and is adjusted, and its output valve is injected into as additional amount as the active current component

of modular multilevel current transformer and AC network exchange and controls the active power that whole modular multilevel current transformer absorbs from electrical network on the current inner loop d axle based on dq decoupling zero control.

3. a kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero according to claim 2 is characterized in that said control method is further comprising the steps of:

Step 2, the instruction of DC component in the synthetic circulation

Step 2.1 is utilized step 1.1 detection limit

Respectively with v _{Ph, a}, v _{Ph, b}, v _{Ph, c}It is poor to do, and sends into three single channel pi regulators and generates respectively

Step 2.2, on go on foot

that computing generates instruction as DC component in the circulation.

4. a kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero according to claim 3 is characterized in that said control method is further comprising the steps of:

Step 3, the instruction of alternating current component in the synthetic circulation

Step 3.1 detects three phase network voltage v _{S, a}, v _{S, b}, v _{S, c}

Step 3.2 is carried out the transform operation that the three phase static coordinate is tied to two cordic phase rotators system with three phase network voltage, the numerical value of d axle after the conversion is sent into the single channel low pass filter carry out filtering, and the output of filter is designated as V _PdThen with detected B, C two phase line voltage switches; Carry out the three phase static coordinate again and be tied to the transform operation that two cordic phase rotators are; D axle and q axis values are sent into two single channel low pass filters respectively and are carried out filtering after the computing, and the numerical value of d axle and q axle is designated as V respectively after the filtering _NdAnd V _NqTransformation matrix in this step is:

$T_{\mathrm{abc}-\mathrm{dq}}=\frac{2}{3}\left[\begin{array}{ccc}\sin \left(\mathrm{\ωt}\right)& \sin (\mathrm{\ωt}-2\mathrm{\π}/3)& \sin (\mathrm{\ωt}+2\mathrm{\π}/3)\\ \cos \left(\mathrm{\ωt}\right)& \cos (\mathrm{\ωt}-2\mathrm{\π}/3)& \cos (\mathrm{\ωt}+2\mathrm{\π}/3)\end{array}\right]$

Step 3.3 is with the V of step 3.2 generation _Pd, V _NdAnd V _NqFor people's following relationship formula, generate the perception and the capacitive reference direction of each phase voltage on line side:

v _s，a,1＝V _pd?cosωt+V _nd?cosωt+V _nq?sinωt

v _s，a,-1＝-V _pd?cosωt-V _nd?cosωt-V _nq?sinωt

$v_{s,b,1}=\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}-\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,b,-1}=-\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}+\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}+1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,c,1}=-\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}-\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}+\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

$v_{s,c,-1}=\frac{\sqrt{3}}{2}{V}_{\mathrm{pd}}\sin \mathrm{\ωt}+\frac{1}{2}{V}_{\mathrm{pd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nd}}\cos \mathrm{\ωt}-\frac{\sqrt{3}-1}{2}{V}_{\mathrm{nq}}\sin \mathrm{\ωt}$

Step 3.4 is with the v of step 3.3 generation _{S, b ,-1}And v _{S, c, 1}For people's following relationship formula-v _{S, a}=A (a) v _{S, b ,-1}+ B (a) v _{S, c, 1}Coefficient according to equality the right and left sin ω t and cos ω t equates respectively, asks for coefficient A (a) and B (a); Similarly, foundation-v _{S, b}=A (b) v _{S, c ,-1}+ B (b) v _{S, a, 1}Ask for A (b), B (b), foundation-v _{S, c}=A (c) v _{S, a ,-1}+ B (c) v _{S, b, 1}Ask for A (c), B (c);

Step 3.5 is with the numerical value v of step 1.1 _{C, pa}And v _{C, na}, v _{C, pb}And v _{C, nb}, v _{C, pc}And v _{C, nc}Send into three single channel subtracters respectively, three single channel pi regulators are sent in the output of subtracter again, and the output valve of three pi regulators is defined as respectively: c _a, c _bAnd c _c

Step 3.6, with step 3.3,3.4,3.5 variablees that generate are for people's following relationship formula:

$i_{\mathrm{ac},a}^{*}=c_a\·v_{s,a}+c_b\·B\left(b\right)\·v_{s,a,1}+c_c\·A\left(c\right)\·v_{s,a,-1}$

$i_{\mathrm{ac},b}^{*}=c_a\·A\left(a\right)\·v_{s,b,-1}+c_b\·v_{s,b}+c_c\·B\left(c\right)\·v_{s,b,1}$

$i_{\mathrm{ac},c}^{*}=c_a\·B\left(a\right)\·v_{s,c,1}+c_b\·A\left(b\right)\·v_{s,c,-1}+c_c\·v_{s,c}$

Obtain the interchange circulation instruction of three-phase decoupling zero.

5. a kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero according to claim 4 is characterized in that said control method is further comprising the steps of:

Step 4, the equilibrium control of DC bus-bar voltage between inner each copped wave unit of brachium pontis

Step 4.1, the actual current i of six brachium pontis of detection _{P, a}, i _{N, a}, i _{P, b}, i _{N, b}, i _{P, c}, i _{N, c}, A is gone up mutually the average dc voltage of brachium pontis copped wave module

Go up the dc voltage v of first module of brachium pontis mutually with A _Ap1Send into the single channel subtracter, proportional controller is sent in the output of single channel subtracter, the output valve of proportional controller and the current i of last brachium pontis _{P, a}Multiply each other, obtain the amount trimmed that A goes up first module alternating voltage of brachium pontis mutually

A is descended mutually the average dc voltage of brachium pontis copped wave module

Descend the dc voltage v of first module of brachium pontis mutually with A _An1Send into the single channel subtracter, proportional controller is sent in the output of single channel subtracter, the inverse value-i of the output valve of proportional controller and following brachium pontis electric current _{N, a}Multiply each other, obtain the amount trimmed that A descends first module alternating voltage of brachium pontis mutually

Along using the same method, obtain the alternating voltage amount trimmed of B, first module of C phase upper and lower bridge arm

Step 4.2, obtain respectively A go up mutually brachium pontis second to N module trim voltage instruct A descend mutually brachium pontis second to N module trim voltage instruct

B go up mutually brachium pontis second to N module trim voltage instruct

B descend mutually brachium pontis second to N module trim voltage instruct

C go up mutually brachium pontis second to N module trim voltage instruct C mutually the brachium pontis of Xiaing second to N Ge module trim voltage Zhi Linged

6. a kind of modular multilevel current transformer dc capacitor voltage control method based on the circulation decoupling zero according to claim 5 is characterized in that said control method is further comprising the steps of:

Step 5, the instruction of copped wave module alternating voltage PWM modulating wave generates

Step 5.1; The current loop control system of modular multilevel current transformer output current carries out the closed loop tracking Control to instruction current and output current; Its output through the dc loop-current instruction that obtains three-phase output order voltage pwm modulating wave

and

modular multilevel current transformer loop current ring control system after the dq inverse transformation and generate step 2.2 and 3.5 with exchange circulation and instruct and add and instruct as total circulation; And total circulation instruction current and actual loop current carried out the closed loop tracking Control, obtain command voltage PWM modulating wave

and

of three-phase control circulation

Step 5.2; Go up A mutually the fine setting instruction of first H bridge module of brachium pontis PWM modulating wave and press relational expression

computing, obtain the PWM modulating wave that A goes up first module of brachium pontis mutually with

and

that step 5.1 generates; Descend A mutually the fine setting instruction

of first H bridge module of brachium pontis PWM modulating wave to press relational expression

computing, obtain the PWM modulating wave that A descends first module of brachium pontis mutually with

and that step 5.1 generates; By that analogy, the final PWM modulating wave that obtains in the A phase upper and lower bridge arm residue module and

B mutually in the upper and lower bridge arm the final PWM modulating wave

of residue module and

C remain final PWM modulating wave

and

of module mutually in the upper and lower bridge arm

Step 5.3 is compared with the triangular carrier of phase shift successively with the modulating wave of every each module of phase, generates the switching signal of each module.

Images