CN103780070B - A kind of MMC redundancy protected method containing cycle optimal control - Google Patents

Abstract

The invention discloses a kind of MMC redundancy protected method containing cycle optimal control in operation and control of electric power system technical field.Comprise: after the submodule of MMC system breaks down, the carrier wave of fault submodule is passed to redundancy submodule; By modulating wave and the carrier wave of the submodule of input, calculate the submodule sum that each brachium pontis of each moment drops into and the redundancy submodule number dropped into; The redundancy submodule number that each brachium pontis drops into is optimized, the redundancy submodule number that after being optimized, each brachium pontis drops into; According to redundancy submodule number and the redundancy submodule number optimizing rear input, the redundancy submodule number of the normal-sub number of modules that adjustment drops into and input.The present invention's situation of dividing adjusts the carrier wave of normal-sub module and redundancy submodule, and cycle optimal control is carried out to carrier wave adjustment, make redundancy submodule and normal-sub module separately between capacitance voltage deviation less, thus again reach stable state fast after ensureing the MMC system failure.

Description

A kind of MMC redundancy protected method containing cycle optimal control

Technical field

The invention belongs to operation and control of electric power system technical field, particularly relate to a kind of MMC redundancy protected method containing cycle optimal control.

Background technology

Along with the fast development of renewable energy power generation technology and power electronic technology, Light HVDC Transmission system (HighVoltageDirectCurrent, HVDC) is economical with it, flexibly and the controlled feature of height become study hotspot.Based on the all-controlling power electronics devices such as IGBT and pulse-width modulation (Pulse-widthModulation, PWM) voltage source converter (VoltageSourceConverter of technology, VSC) new trend of direct current transportation development is become, grid-connected at Large Scale Wind Farm Integration, distributed power generation is grid-connected, island with power, asynchronous AC network are interconnected and the field such as multi-terminal HVDC transmission is widely used.

Voltage source converter mostly is low level converter (2 level or 3 level) traditionally.Because low level converter needs the switch elements in series of hundreds of to form usually, therefore voltage source converter exists that switching frequency is high, level number is low, harmonic wave of output voltage is large, current conversion station floor space is large and the shortcoming such as dynamic voltage balancing is difficult.Modularization multi-level converter (modularmultilevelconverter, MMC) with advantages such as high, the modular structure of its output level number, the two-way flow easily realizing energy and four quadrant runnings, become the high voltage direct current transmission mode having prospect at present, become the focus of research both at home and abroad.

MMC is often made up of upper and lower two brachium pontis, each brachium pontis is by a current-limiting reactor and several submodules (sub-module, SM) be composed in series, submodule is divided into normal-sub module and redundancy submodule according to classification, and the submodule that redundancy submodule only replaces fault after normal-sub module breaks down puts into operation.When the number of redundancy submodule is greater than the number of fault submodule, then after fault, MMC system need not be out of service, but replace fault submodule by redundancy submodule; When the sub-number of redundancy submodule is less than the number of fault submodule, then after fault, converter cannot normally work, need be out of service by converter blocking, and this will cause serious threat to the reliability of whole direct current system.Therefore, MMC system redundancy submodule Preservation tactics is very important part in control strategy.

At present, the guard method that MMC is conventional mainly contains two large classes: voltage approaches modulator approach and carried based PWM method.Wherein, voltage approaches modulator approach uses nearest voltage vector or level is instantaneous approaches modulating wave, it can be roughly divided into space vector width pulse modulation method (spacevectorpulse-widthmodulation again, SVPWM) with nearest Level modulation scheme (nearestlevelmodulation, NLM).Voltage approaches modulator approach is by the switching of capacitance voltage sequence determinant module, and the realization of its redundancy protecting strategy is relatively easy.It is stacked with carrier phase modulator approach (carrierphase-shiftedSPWM that carried based PWM method mainly contains carrier wave, CPS-SPWM), CPS-SPWM method compares generation triggering signal by the carrier wave that each submodule is corresponding with modulating wave, does not carry out electric capacity sequence.

But, still have problems based on the MMC redundancy protected method of carrier phase modulation.After fault occurs, the action that a kind of redundancy protected method is intuitively taked is: bypass fault submodule, drops into the submodule of redundancy, the carrier wave of fault submodule is directly passed to the redundancy submodule of input.In this process, directly the carrier wave of submodule is passed to corresponding submodule, redundancy submodule may be caused when bridge arm current is greater than zero, and the number not dropping into or drop into is too much; When bridge arm current is less than zero, redundancy submodule drops into electric discharge and capacitance voltage natively on the low side is reduced further.Therefore; after fault occurs; based on carrier phase modulation MMC redundancy protected method carrier wave replace after; still need the input number adjusting redundancy submodule to the input number optimized; post-fault system is made to reach on the basis of stable state fast; reduce the fluctuation of bridge arm voltage and direct voltage, reduce alternate circulation.

Summary of the invention

The object of the invention is to; a kind of MMC redundancy protected method containing cycle optimal control under carrier phase modulation is provided; after MMC system jam; the carrier wave of fault submodule is passed to redundancy submodule; number is dropped into according to the redundancy submodule optimized; the carrier wave of the situation of dividing adjustment normal-sub module and redundancy submodule; and cycle optimal control is carried out to carrier wave adjustment; make redundancy submodule and this two classes submodule of normal-sub module separately between capacitance voltage deviation less, thus again reach stable state fast after ensureing the MMC system failure.

To achieve these goals, the technical scheme that the present invention proposes is, a kind of MMC redundancy protected method containing cycle optimal control, is characterized in that described method comprises:

Step 1: after the submodule of modularization multi-level converter MMC system breaks down, the carrier wave of fault submodule is passed to redundancy submodule;

Step 2: by modulating wave and the carrier wave of the submodule of input, calculates the submodule sum that each brachium pontis of each moment drops into and the redundancy submodule number dropped into;

Step 3: be optimized calculating to the redundancy submodule number that each brachium pontis drops into, obtains the theoretical optimization value of the redundancy submodule number that each brachium pontis drops into;

Step 4: the theoretical optimization value of the redundancy submodule number that the redundancy submodule number dropped into according to each brachium pontis and each brachium pontis drop into, adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into.

The submodule that each brachium pontis of described calculating each moment drops into adopts formula $N_p=\underset{i=1}{\overset{N+M}{\mathrm{\Σ}}}\text{\Γ}(M_{\mathrm{odi}}>T_{\mathrm{ci}});$

Wherein, M _odifor the modulating wave of i-th submodule in brachium pontis;

T _cifor the carrier wave of i-th submodule in brachium pontis;

Γ (M _odi>T _ci) be two-valued function, work as M _odi>T _citime, Γ (M _odi>T _ci)=1; Work as M _odi≤ T _citime, Γ (M _odi>T _ci)=0;

N is the N total number of modules that every phase upper and lower bridge arm of modularization multi-level converter MMC drops into;

M is the redundancy submodule number on each brachium pontis.

The redundancy submodule number that each brachium pontis of described calculating each moment drops into adopts formula

$N_{\mathrm{rp}}=\underset{i\∈I}{\mathrm{\Σ}}\mathrm{\Γ}(M_{\mathrm{odi}}>T_{\mathrm{ci}});$

M _odifor the modulating wave of i-th submodule in set I;

T _cifor the carrier wave of i-th submodule in set I;

Γ (M _odi>T _ci) be two-valued function, work as M _odi>T _citime, Γ (M _odi>T _ci)=1; Work as M _odi≤ T _citime, Γ (M _odi>T _ci)=0;

Set I is the U that satisfies condition in brachium pontis _ci(t ₀) <1.05 × U _{pre_max}submodule composition set, i.e. I={i|U _ci(t ₀) <1.05 × U _{pre_max};

U _ci(t ₀) be current time t ₀the capacitance voltage value of i-th submodule;

U _{pre_max}for modularization multi-level converter MMC system adopts the capacitance voltage maximum under precharge Starting mode.

Described step 3 specifically comprises following sub-step:

As bridge arm current I _br>0 and 0<N _pduring≤N-s+1, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=1;

As bridge arm current I _br>0 and N _pduring >N-s+1, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=N _p-N+s;

As bridge arm current I _br<0 and 0<N _pduring≤N-s, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=0;

As bridge arm current I _br<0 and N _pduring >N-1-s, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=N _p-(N-1)+s;

N _pfor the submodule number dropped into;

N is the level number of modularization multi-level converter MMC;

S is the number of the normal-sub module broken down.

Described step 4 is specifically:

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpduring >0, the process that described adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into is:

Sub-step A1: make Num1=Num2=N _rp-N ' _rp;

Sub-step A2: if Num1>0, then become the redundancy submodule of input, and make Num1=Num1-1 by the redundancy submodule of 1 bypass;

Sub-step A3: if Num2>0, then become the redundancy submodule of bypass, and make Num2=Num2-1 by the normal-sub module that 1 is dropped into;

Sub-step A4: judge whether Num1=0 and Num2=0 all sets up, if Num1=0 and Num2=0 sets up, then adjustment process terminates, the redundancy submodule number N by each brachium pontis now obtained drops into " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into; Otherwise, return sub-step A2;

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpduring <0, the process that described adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into is:

Sub-step B1: make Num1=Num2=N _rp-N ' _rp;

Sub-step B2: if Num1<0, then become the redundancy submodule of bypass, and make Num1=Num1+1 by the redundancy submodule that 1 is dropped into;

Sub-step B3: if Num2<0, then become the normal-sub module of input, and make Num2=Num2+1 by the normal-sub module of 1 bypass;

Sub-step B4: judge whether Num1=0 and Num2=0 all sets up, if Num1=0 and Num2=0 sets up, then adjustment process terminates, the redundancy submodule number N by each brachium pontis now obtained drops into " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into; Otherwise, return sub-step B2;

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpwhen=0, do not adjust normal-sub number of modules and the redundancy submodule number of input that each brachium pontis drops into, the redundancy submodule number N directly dropped into now each brachium pontis " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into.

The redundancy submodule number also comprising normal-sub number of modules and the input dropped into each brachium pontis after described step 4 carries out the step of cycle optimization.

The described normal-sub number of modules dropped into each brachium pontis is carried out period modulation and is comprised:

Sub-step C1: make i=1, count (i)=0, num=N _p-N " _rp, V _drefifor the capacitance voltage of fault initial time i-th normal-sub module;

Wherein, N _pfor the submodule sum that each brachium pontis drops into;

N " _rpfor the true optimal value of the redundancy submodule number that each brachium pontis drops into;

Sub-step C2: by carrier wave T _cbpass to all normal-sub modules;

Described carrier wave T _cbfor the normal-sub module making normal-sub module become bypass;

Sub-step C3: judge | V _ci-V _drefi|>=V _εwhether set up, if | V _ci-V _drefi|>=V _ε, then sub-step C4 is performed; Otherwise, perform sub-step C5;

Wherein, V _ciit is the capacitance voltage of i-th normal-sub module;

V _drefibe i-th normal-sub module voltage change reference value;

V _εfor setting threshold;

Sub-step C4: make V _drefi=V _ciand make count (i)=count (i)+1;

Sub-step C5: judge i<N _nwhether set up, if i<N _n, then make i=i+1, return sub-step C2; Otherwise, perform step C6; N _nfor the number of normal-sub modules all on brachium pontis;

Sub-step C6: make j=1,

Sub-step C7: judge whether num>0 sets up, if num>0, then performs sub-step C8; Otherwise, perform sub-step C14;

Sub-step C8: judge whether count (j)=minn sets up, if count (j)=minn, then performs sub-step C9; Otherwise, perform sub-step C11;

Sub-step C9: by carrier wave-T _cbpass to a jth normal-sub module, and make num=num-1;

Described carrier wave-T _cbfor the normal-sub module making normal-sub module become input;

Sub-step C10: judge whether num>0 sets up, if num>0, then performs sub-step C11; Otherwise, perform sub-step C14;

Sub-step C11: judge j<N _nwhether set up, if j<N _n, then sub-step C12 is performed; Otherwise, perform sub-step C13;

Sub-step C12: make j=j+1, returns sub-step C8;

Sub-step C13: make j=1, minn=minn+1, return sub-step C8;

Sub-step C14: terminate.

The described redundancy submodule number dropped into each brachium pontis is carried out period modulation and is comprised:

Sub-step D1: make i=1, count (i)=0, num=N " _rp, V _drefifor the capacitance voltage of fault initial time i-th redundancy submodule;

Wherein, N " _rpfor the true optimal value of the redundancy submodule number that each brachium pontis drops into;

Sub-step D2: by carrier wave T _cbpass to all redundancy submodule;

Described carrier wave T _cbfor the redundancy submodule making redundancy submodule become bypass;

Sub-step D3: judge | V _ci-V _drefi|>=V _εwhether set up, if | V _ci-V _drefi|>=V _ε, then sub-step D4 is performed; Otherwise, perform sub-step D5;

Wherein, V _ciit is the capacitance voltage of i-th redundancy submodule;

V _drefibe i-th redundancy submodule change in voltage reference value;

V _εfor setting threshold;

Sub-step D4: make V _drefi=V _ciand make count (i)=count (i)+1;

Sub-step D5: judge whether i<s sets up, if i<s, then make i=i+1, return sub-step D2; Otherwise, perform step D6; S is the redundancy submodule number that brachium pontis drops into;

Sub-step D6: make j=1,

Sub-step D7: judge whether num>0 sets up, if num>0, then performs sub-step D8; Otherwise, perform sub-step D14;

Sub-step D8: judge whether count (j)=minn sets up, if count (j)=minn, then performs sub-step D9; Otherwise, perform sub-step D11;

Sub-step D9: by carrier wave-T _cbpass to a jth redundancy submodule, and make num=num-1;

Described carrier wave-T _cbfor the redundancy submodule making normal-sub module become input;

Sub-step D10: judge whether num>0 sets up, if num>0, then performs sub-step D11; Otherwise, perform sub-step D14;

Sub-step D11: judge whether j<s sets up, if j<s, then performs sub-step D12; Otherwise, perform sub-step D13;

Sub-step D12: make j=j+1, returns sub-step D8;

Sub-step D13: make j=1, minn=minn+1, return sub-step D8;

Sub-step D14: terminate.

Effect of the present invention is, after fault, the carrier wave of fault submodule is passed to redundancy submodule, keeps the carrier wave of other normal-sub modules constant; Now, the carrier wave after change is not directly passed to each submodule, but drops into number according to the redundancy submodule of each time optimization of brachium pontis, judge whether to need adjustment redundancy submodule to drop into number; Always dropping into according to brachium pontis submodule the carrier wave adjustment that number carries out normal-sub module and redundancy submodule when needing to adjust, when without the need to adjusting, keeping submodule carrier wave constant.In addition, this method also carries out cycle optimal control, the submodule discharge and recharge overlong time or too short avoiding carrier wave to adjust for carrier wave adjustment, causes the capacitance voltage deviation between submodule excessive.

Accompanying drawing explanation

Fig. 1 is the MMC redundancy protected method flow chart containing cycle optimal control provided by the invention;

Fig. 2 is submodule running status figure; Wherein (a) is blocking figure, and (b), for dropping into state diagram, (c) is bypass condition figure;

Fig. 3 is the direct replacement process figure of carrier wave;

Fig. 4 is the carrier wave argument table of definition;

Fig. 5 is the number table of submodule;

Fig. 6 is the carrier wave adjustment flow chart of redundancy protecting;

Fig. 7 is the carrier wave adjustment figure containing cycle optimization;

Fig. 8 is 7 level both-end MMC DC transmission system simulation model structure charts;

Fig. 9 is system emulation parameter list;

Figure 10 is not containing the submodule capacitor voltage oscillogram that the cycle is optimized;

Figure 11 is the submodule capacitor voltage oscillogram containing cycle optimization;

Figure 12 is that redundancy submodule drops into number comparison diagram;

Figure 13 is each electric parameters oscillogram before and after fault.

Embodiment

Below in conjunction with accompanying drawing, preferred embodiment is elaborated.It is emphasized that following explanation is only exemplary, instead of in order to limit the scope of the invention and apply.

Fig. 1 is the MMC redundancy protected method flow chart containing cycle optimal control provided by the invention.As shown in Figure 1, the MMC redundancy protected method containing cycle optimal control provided by the invention comprises:

Step 1: after the submodule of modularization multi-level converter MMC system breaks down, the carrier wave of fault submodule is passed to redundancy submodule.

MMC three-phase upper and lower bridge arm all has multiple submodule and current-limiting inductance to be in series, and for N+1 level MMC system, every phase upper and lower bridge arm has N number of module and puts into operation.By carrier phase angle successively phase shift 2 π/N, form N group carrier wave.

On MMC Controller gain variations, because the energy between ABC three-phase may imbalance make MMC controller need loop current suppression to control, in order to maintain submodule capacitor voltage near rated value, capacitor voltage equalizing is needed to control.For brachium pontis in A phase, M _uairepresent the modulating wave of i-th submodule, mainly contain three part compositions: the fundamental modulation ripple U that brachium pontis is common _uai, corresponding submodule capacitor voltage equalizing controlled quentity controlled variable U _vbaiwith loop current suppression controlled quentity controlled variable U _cira.

M _uai=U _uai+U _vbai+U _cira（1）

Wherein, the fundamental modulation ripple of upper and lower bridge arm is:

$\left\{\begin{array}{c}{U}_{\mathrm{uai}}=\frac{U_{\mathrm{dc}}}{2N}-\frac{U_{\mathrm{ra}}}{N}\\ U_{\mathrm{lai}}=\frac{U_{\mathrm{dc}}}{2N}+\frac{N_{\mathrm{ra}}}{N}\end{array}\right.---\left(2\right)$ In formula (2), U _dcfor direct voltage, U _rafor the A cross streams voltage produced through dq uneoupled control, U _laifor lower brachium pontis fundamental modulation ripple.

The modulating wave corresponding by more each submodule and carrier wave produce trigger impulse, control N number of submodule and drop into or excision, form the staircase waveform of N+1 level.Represent the shutoff of submodule by-pass switch and IGBT, the state of conducting respectively with 0,1, then according to the state of cut-offfing of by-pass switch K and IGBT, the running status of submodule is classified.As K=1, IGBT1=0 and IGBT2=0 time, submodule is in redundancy cold standby state, when brachium pontis has sub-module fault, bypass fault submodule, drop into redundancy submodule; As K=0, submodule is in running status, is divided into locking, input and bypass three kinds of states, as shown in Figure 2 according to the state of IGBT1 and IGBT2.

In the MMC system of a N+1 level band M redundancy submodule, s submodule breaks down, then bypass fault submodule, drops into s redundancy submodule, is recorded by the carrier wave of fault submodule, pass to the redundancy submodule of input, as shown in Figure 3.Therefore by the N number of carrier wave T in Fig. 4 _cpsjthe modulating wave corresponding with each submodule contrasts, and as the formula (1), can count front 3 amounts in the table that Fig. 5 provides.

Step 2: by modulating wave and the carrier wave of the submodule of input, calculates the submodule sum that each brachium pontis of each moment drops into and the redundancy submodule number dropped into.

Before MMC submodule breaks down, the carrier wave of the redundancy submodule do not dropped into is the positive constant being greater than modulating wave assignment, and redundancy submodule bypass avoids the redundancy submodule of precharge to discharge.Have in MMC system submodule break down out of service after, bypass fault submodule also drops into redundancy submodule, is recorded by the carrier wave of fault submodule and passes to redundancy submodule, and the carrier wave of redundancy submodule becomes the triangular wave T through phase shift _cps.Now, by the submodule carrier wave of all inputs and the contrast of corresponding modulating ripple, the total submodule of each brachium pontis of each moment can be counted and drop into number N _pwith the input number N of redundancy submodule _rp.For N+1 level and the MMC system of each brachium pontis band M redundancy submodule, represent the sequence number of i-th submodule and U with i _cifor the capacitance voltage value of correspondence, then N _pand N _rpcan be obtained by formula (3):

$\left\{\begin{array}{c}{N}_p=\underset{i=1}{\overset{N+M}{\mathrm{\&Sigma;}}}\mathrm{\&Gamma;}(M_{\mathrm{odi}}>T_{\mathrm{ci}})\\ N_{\mathrm{rp}}=\underset{i\&Element;I}{\mathrm{\&Sigma;}}\mathrm{\&Gamma;}(M_{\mathrm{odi}}>T_{\mathrm{ci}})\end{array}\right.---\left(3\right)$

In formula (3), M _odifor the modulating wave of i-th submodule in brachium pontis, T _cifor the carrier wave of i-th submodule in brachium pontis.Γ (M _odi>T _ci) be two-valued function, work as M _odi>T _citime, Γ (M _odi>T _ci)=1; Work as M _odi≤ T _citime, Γ (M _odi>T _ci)=0.N is the N total number of modules that every phase upper and lower bridge arm of modularization multi-level converter MMC drops into, and M is the redundancy submodule number on each brachium pontis.Set I is the U that satisfies condition in brachium pontis _ci(t ₀) <1.05 × U _{pre_max}submodule composition set, i.e. I={i|U _ci(t ₀) <1.05 × U _{pre_max}, U _ci(t ₀) be current time t ₀the capacitance voltage value of i-th submodule.U _{pre_max}for modularization multi-level converter MMC system adopts the capacitance voltage maximum under precharge Starting mode, and have

$U_{\mathrm{pre}\_\max }=\sqrt{2}\&times;U_s/(N+M)---\left(4\right)$

In formula (4), U _sfor the effective value of three-phase alternating current line voltage.

When MMC system stable operation, the capacitance voltage of normal-sub module fluctuates near rated value, and rated value calculation expression is such as formula (5):

U _cref=U _dc/ N(5) in formula (5), U _dcfor the direct voltage under stable state.

Due to capacitance voltage rated value U _crefbe at least redundancy submodule capacitance voltage initial value U _{pre_max}1.414 times, and therefore two values of through type (4) and (5) normal-sub module and redundancy submodule can be distinguished.

Step 3: be optimized calculating to the redundancy submodule number that each brachium pontis drops into, is optimized and calculates the theoretical optimization value of the redundancy submodule number that rear each brachium pontis drops into.

The submodule number N that each brachium pontis of MMC system drops into _pbe actually one and approach sinusoidal staircase waveform, the N that therefore can obtain according to step 2 _rpthe theoretical optimization value N ' of the redundancy submodule number dropped into each brachium pontis _rpcompare, determine that redundancy submodule drops into number the need of adjustment.

For more low level MMC system and s normal-sub module break down, the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpdetermined by following manner: as bridge arm current I _br>0 and 0<N _pduring≤N-s+1, the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rp=1, namely drop into 1 redundancy submodule at every turn.As bridge arm current I _br>0 and N _pduring >N-s+1, the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rp=N _p-N+s, namely drops into all N-s normal-sub module, then drops into N _p-N+s redundancy submodule.As bridge arm current I _br<0 and 0<N _pduring≤N-s, preferentially drop into N _pindividual normal-sub module.As bridge arm current I _br<0 and N _pduring >N-s, the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rp=N _p-N+s, namely drops into all N-s normal-sub module, then drops into N _p-N+s redundancy submodule.

The theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpsuch as formula (6):

${N_{\mathrm{rp}}}^{\&prime;}=\left\{\begin{array}{c}1,(I_{\mathrm{br}}>0,0<N_p\&le;N-s+1)\\ N_p-N+s,(I_{\mathrm{br}}>0,N_p>N-s+1)\\ 0,(I_{\mathrm{br}}<0,0<N_p\&le;N-s)\\ N_p-N+s,(I_{\mathrm{br}}<0,N_p>N-s)\end{array}\right.---\left(6\right)$

Fig. 6 is the carrier wave adjustment flow chart of redundancy protecting, by Fig. 6, can realize the optimization of the redundancy submodule number that each brachium pontis drops into.In this process, when bridge arm current is greater than zero, and the input number of redundancy submodule needs adjustment, and the preferential redundancy submodule that drops into is charged.When needs many inputs redundancy submodule, then the carrier wave adjusting the redundancy submodule of bypass makes it become input state; When needs many bypasses redundancy submodule, then the carrier wave adjusting the redundancy submodule of input makes it become bypass condition, and the adjustment of normal-sub module is contrary with the adjustment of redundancy submodule, and it is constant that guarantee brachium pontis submodule always drops into number.When the input number without the need to adjusting redundancy submodule, then keep the carrier wave of all submodules constant.

When bridge arm current is less than zero, and the input number of redundancy submodule needs adjustment, and the preferential normal-sub module that drops into is discharged.When needs many bypasses redundancy submodule, then the carrier wave of adjustment input redundancy submodule makes it become bypass condition; When needs many inputs redundancy submodule, then the carrier wave adjusting bypass redundancy submodule makes it become input state.When the input number of redundancy submodule is without the need to adjustment, then keep the carrier wave of all submodules constant.

Therefore, by the adjustment of carrier wave between normal-sub module and redundancy submodule, can the input of optimizing redundancy submodule, preferentially drop into when redundancy submodule is charged, preferentially exit during electric discharge, ensure that redundancy submodule can charge to rated value rapidly, shortening system reaches the stable time.

Step 4: the theoretical optimization value of the redundancy submodule number that the redundancy submodule number dropped into according to each brachium pontis and each brachium pontis drop into, adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into.

In this step, the theoretical optimization value of the redundancy submodule number of the input according to formula (6), with N _rpcompare, determine whether the input number needing to change redundancy submodule.

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpduring >0, the process that adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into is:

Sub-step A1: make Num1=Num2=N _rp-N ' _rp.

Sub-step A2: if Num1>0, then become the redundancy submodule of input, and make Num1=Num1-1 by the redundancy submodule of 1 bypass.

Sub-step A3: if Num2>0, then become the redundancy submodule of bypass, and make Num2=Num2-1 by the normal-sub module that 1 is dropped into.

Sub-step A4: judge whether Num1=0 and Num2=0 all sets up, if Num1=0 and Num2=0 sets up, then adjustment process terminates, the redundancy submodule number N by each brachium pontis now obtained drops into " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into; Otherwise, return sub-step A2.

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpduring <0, the process that described adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into is:

Sub-step B1: make Num1=Num2=N _rp-N ' _rp.

Sub-step B2: if Num1<0, then become the redundancy submodule of bypass, and make Num1=Num1+1 by the redundancy submodule that 1 is dropped into.

Sub-step B3: if Num2<0, then become the normal-sub module of input, and make Num2=Num2+1 by the normal-sub module of 1 bypass.

Sub-step B4: judge whether Num1=0 and Num2=0 all sets up, if Num1=0 and Num2=0 sets up, then adjustment process terminates, the redundancy submodule number N by each brachium pontis now obtained drops into " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into; Otherwise, return sub-step B2.

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpwhen=0, do not adjust normal-sub number of modules and the redundancy submodule number of input that each brachium pontis drops into, the redundancy submodule number N directly dropped into now each brachium pontis " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into.

Step 5: the redundancy submodule number N dropped into according to each brachium pontis _rpwith the true optimal value N of the redundancy submodule number that each brachium pontis drops into " _rp, adjust the normal-sub number of modules of each brachium pontis input and the redundancy submodule number of input.

According to the running status of normal-sub module, the input number of redundancy submodule is reduced by the input number increasing normal-sub module, or increased the input number of redundancy submodule by the input number reducing normal-sub module, this ensures that there brachium pontis and drop into submodule number N _pconsistent with before adjustment.But in this process, likely certain normal-sub module controlled time is long, causes the capacitance voltage deviation ratio of normal-sub intermodule larger.Or the time of adjustment is shorter, the IGBT of submodule is caused to cut-off frequency excessive.Therefore, the present invention can after step 4, and the redundancy submodule number increasing a normal-sub number of modules dropped into each brachium pontis and input carries out the step of cycle optimization, less to ensure the capacitance voltage deviation between submodule.

Below for normal-sub module, illustrate that the normal-sub number of modules dropped into each brachium pontis carries out the process of cycle optimization, the process that redundancy submodule number carries out cycle optimization is identical with it.

As shown in Figure 7, the step that the normal-sub number of modules dropped into each brachium pontis carries out cycle optimization comprises:

Sub-step C1: make i=1, count (i)=0, num=N _p-N " _rp, V _drefifor the capacitance voltage of fault initial time i-th normal-sub module.Wherein, N _pfor the submodule sum that each brachium pontis drops into, N " _rpfor the true optimal value of the redundancy submodule number that each brachium pontis drops into.

Sub-step C2: by carrier wave T _cbpass to all normal-sub modules.Carrier wave T wherein _cbfor the normal-sub module making normal-sub module become bypass.

Sub-step C3: judge | V _ci-V _drefi|>=V _εwhether set up, if | V _ci-V _drefi|>=V _ε, then sub-step C4 is performed; Otherwise, perform sub-step C5.Wherein, V _cibe the capacitance voltage of i-th normal-sub module, V _drefibe i-th normal-sub module voltage change reference value, V _εfor setting threshold.

Sub-step C4: make V _drefi=V _ciand make count (i)=count (i)+1.

Sub-step C5: judge i<N _nwhether set up, if i<N _n, then make i=i+1, return sub-step C2; Otherwise, perform step C6; N _nfor the number of normal-sub modules all on brachium pontis.

Sub-step C6: make j=1,

Sub-step C7: judge whether num>0 sets up, if num>0, then performs sub-step C8; Otherwise, perform sub-step C14.

Sub-step C8: judge whether count (j)=minn sets up, if count (j)=minn, then performs sub-step C9; Otherwise, perform sub-step C11.

Sub-step C9: by carrier wave-T _cbpass to a jth normal-sub module, and make num=num-1.Wherein carrier wave-T _cbfor the normal-sub module making normal-sub module become input.

Sub-step C10: judge whether num>0 sets up, if num>0, then performs sub-step C11; Otherwise, perform sub-step C14.

Sub-step C11: judge j<N _nwhether set up, if j<N _n, then sub-step C12 is performed; Otherwise, perform sub-step C13.

Sub-step C12: make j=j+1, returns sub-step C8.

Sub-step C13: make j=1, minn=minn+1, return sub-step C8.

Sub-step C14: terminate.

The redundancy submodule number dropped into each brachium pontis is carried out period modulation and is comprised:

Sub-step D1: make i=1, count (i)=0, num=N " _rp, V _drefifor the capacitance voltage of fault initial time i-th redundancy submodule.Wherein, N " _rpfor the true optimal value of the redundancy submodule number that each brachium pontis drops into.

Sub-step D2: by carrier wave T _cbpass to all redundancy submodule.Wherein, carrier wave T _cbfor the redundancy submodule making redundancy submodule become bypass.

Sub-step D3: judge | V _ci-V _drefi|>=V _εwhether set up, if | V _ci-V _drefi|>=V _ε, then sub-step D4 is performed; Otherwise, perform sub-step D5.Wherein, V _cibe the capacitance voltage of i-th redundancy submodule, V _drefibe i-th redundancy submodule change in voltage reference value, V _εfor setting threshold.

Sub-step D4: make V _drefi=V _ciand make count (i)=count (i)+1.

Sub-step D5: judge whether i<s sets up, if i<s, then make i=i+1, return sub-step D2; Otherwise, perform step D6; S is the redundancy submodule number that brachium pontis drops into.

Sub-step D6: make j=1,

Sub-step D7: judge whether num>0 sets up, if num>0, then performs sub-step D8; Otherwise, perform sub-step D14.

Sub-step D8: judge whether count (j)=minn sets up, if count (j)=minn, then performs sub-step D9; Otherwise, perform sub-step D11.

Sub-step D9: by carrier wave-T _cbpass to a jth redundancy submodule, and make num=num-1.Carrier wave-T _cbfor the redundancy submodule making normal-sub module become input.

Sub-step D10: judge whether num>0 sets up, if num>0, then performs sub-step D11; Otherwise, perform sub-step D14.

Sub-step D11: judge whether j<s sets up, if j<s, then performs sub-step D12; Otherwise, perform sub-step D13.

Sub-step D12: make j=j+1, returns sub-step D8.

Sub-step D13: make j=1, minn=minn+1, return sub-step D8.

Sub-step D14: terminate.

The function containing the MMC redundancy protected method of cycle optimal control of just the present invention's proposition below and effect, be described in detail in conjunction with simulation example.

In PSCAD/EMTDC, build 7 level both-end MMC DC transmission system simulation models, as shown in Figure 8, system emulation parameter as shown in Figure 9.

In MMC system, in A phase, brachium pontis SM1 and SM6 breaks down out of service when 1.5s, and redundancy submodule SM7 and SM8 puts into operation.Now, the carrier wave of fault submodule SM1 and SM6 is recorded, passes to SM7 and SM8.

Carrier wave according to submodule compares with corresponding modulating wave, obtain the input number of brachium pontis redundancy submodule, according to formula (6), carrier wave is adjusted, not to carrier wave adjustment employing cycle optimal control, before and after each sub-module fault, capacitance voltage waveform is as Figure 10, and the cycle adjusted owing to not adopting carrier wave is optimized, and causes the excessive cycle that carrier wave adjusts, the voltage fluctuation of capacitor of normal-sub intermodule is comparatively large, makes system there is larger fluctuation.When adopting the cycle optimal control of carrier wave adjustment, system carries out stable state through 0.080s, and capacitance voltage waveform corresponding to submodule is as Figure 11, and between reduction submodule while voltage fluctuation of capacitor, the frequency of cut-offfing of control IGBT can not be too high.

The theoretical optimization value N ' of number is dropped into according to redundancy submodule _rp, by the carrier wave adjustment between normal-sub module and redundancy submodule, carry out the optimization that redundancy submodule drops into number, before and after carrier wave adjustment, redundancy submodule drops into number contrast as shown in figure 12.Redundancy submodule charging is preferentially dropped into when bridge arm current is greater than zero, and at 0<N _ponly drop into 1 redundancy submodule during≤N-s+1, reduce voltage fluctuation; Normal-sub module discharge is preferentially dropped into when bridge arm current is less than zero.

Although for each submodule, carrier wave there occurs sudden change, system brachium pontis electric current I _u, direct voltage U _dc, the active-power P 1 of converting plant and reactive power Q 1 change steady, as shown in figure 13, not obvious to the disturbance of system when carrier wave changes.

The above; fully demonstrating the present invention can by the input number of adjustment carrier wave optimizing redundancy submodule after MMC sub-module fault; effectively can reduce the fluctuation of bridge arm voltage and direct voltage after fault; suppress alternate circulation, overcome the defect based on the lower existing MMC redundancy protecting of carrier phase modulation.In addition, method of the present invention also to carrier wave adjustment carry out cycle optimal control, namely carrier wave adjustment cycle set, avoid carrier wave adjustment cycle long or too short, the deviation of capacitance voltage between submodule can be reduced, and effectively reduce IGBT cut-off frequency.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (6)

1., containing a MMC redundancy protected method for cycle optimal control, it is characterized in that described method comprises:

Step 1: after the submodule of modularization multi-level converter MMC system breaks down, the carrier wave of fault submodule is passed to redundancy submodule;

Step 2: by modulating wave and the carrier wave of the submodule of input, calculates the submodule sum that each brachium pontis of each moment drops into and the redundancy submodule number dropped into;

Step 3: be optimized calculating to the redundancy submodule number that each brachium pontis drops into, obtains the theoretical optimization value of the redundancy submodule number that each brachium pontis drops into;

Step 4: the theoretical optimization value of the redundancy submodule number that the redundancy submodule number dropped into according to each brachium pontis and each brachium pontis drop into, adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into;

The submodule that each brachium pontis of described calculating each moment drops into adopts formula

Wherein, M _odifor the modulating wave of i-th submodule in brachium pontis;

T _cifor the carrier wave of i-th submodule in brachium pontis;

Γ (M _odi>T _ci) be two-valued function, work as M _odi>T _citime, Γ (M _odi>T _ci)=1; Work as M _odi≤ T _citime, Γ (M _odi>T _ci)=0;

N is the N total number of modules that every phase upper and lower bridge arm of modularization multi-level converter MMC drops into;

M is the redundancy submodule number on each brachium pontis;

The redundancy submodule number that each brachium pontis of described calculating each moment drops into adopts formula $N_{rp}=\underset{i\&Element;I}{\&Sigma;}\mathrm{\&Gamma;}(M_{odi}>T_{ci});$

M _odifor the modulating wave of i-th submodule in set I;

T _cifor the carrier wave of i-th submodule in set I;

Γ (M _odi>T _ci) be two-valued function, work as M _odi>T _citime, Γ (M _odi>T _ci)=1; Work as M _odi≤ T _citime, Γ (M _odi>T _ci)=0;

Set I is the U that satisfies condition in brachium pontis _ci(t ₀) <1.05 × U _{pre_max}submodule composition set, i.e. I={i|U _ci(t ₀) <1.05 × U _{pre_max};

U _ci(t ₀) be current time t ₀the capacitance voltage value of i-th submodule;

U _{pre_max}for modularization multi-level converter MMC system adopts the capacitance voltage maximum under precharge Starting mode.

2. method according to claim 1, is characterized in that described step 3 specifically comprises following sub-step:

As bridge arm current I _br>0 and 0<N _pduring≤N-s+1, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=1;

As bridge arm current I _br>0 and N _pduring >N-s+1, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=N _p-N+s;

As bridge arm current I _br<0 and 0<N _pduring≤N-s, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=0;

As bridge arm current I _br<0 and N _pduring >N-1-s, the theoretical optimization value of the redundancy submodule number of input is N ' _rp=N _p-(N-1)+s;

N _pfor the submodule number dropped into;

N is the level number of modularization multi-level converter MMC;

S is the number of the normal-sub module broken down.

3. method according to claim 1, is characterized in that described step 4 specifically:

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpduring >0, the process that described adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into is:

Sub-step A1: make Num1=Num2=N _rp-N ' _rp;

Sub-step A2: if Num1>0, then become the redundancy submodule of input, and make Num1=Num1-1 by the redundancy submodule of 1 bypass;

Sub-step A3: if Num2>0, then become the redundancy submodule of bypass, and make Num2=Num2-1 by the normal-sub module that 1 is dropped into;

Sub-step A4: judge whether Num1=0 and Num2=0 all sets up, if Num1=0 and Num2=0 sets up, then adjustment process terminates, the redundancy submodule number N by each brachium pontis now obtained drops into " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into; Otherwise, return sub-step A2;

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpduring <0, the process that described adjustment obtains the true optimal value of the redundancy submodule number that each brachium pontis drops into is:

Sub-step B1: make Num1=Num2=N _rp-N ' _rp;

Sub-step B2: if Num1<0, then become the redundancy submodule of bypass, and make Num1=Num1+1 by the redundancy submodule that 1 is dropped into;

Sub-step B3: if Num2<0, then become the normal-sub module of input, and make Num2=Num2+1 by the normal-sub module of 1 bypass;

Sub-step B4: judge whether Num1=0 and Num2=0 all sets up, if Num1=0 and Num2=0 sets up, then adjustment process terminates, the redundancy submodule number N by each brachium pontis now obtained drops into " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into; Otherwise, return sub-step B2;

As the redundancy submodule number N that each brachium pontis drops into _rpwith the theoretical optimization value N ' of the redundancy submodule number that each brachium pontis drops into _rpmeet N _rp-N ' _rpwhen=0, do not adjust normal-sub number of modules and the redundancy submodule number of input that each brachium pontis drops into, the redundancy submodule number N directly dropped into now each brachium pontis " _rpas the true optimal value of the redundancy submodule number that each brachium pontis drops into.

4., according to the method in claim 1-3 described in any one claim, the redundancy submodule number that it is characterized in that also comprising after described step 4 normal-sub number of modules and the input dropped into each brachium pontis carries out the step of cycle optimization.

5. method according to claim 4, is characterized in that the described normal-sub number of modules dropped into each brachium pontis is carried out period modulation and comprised:

Sub-step C1: make i=1, count (i)=0, num=N _p-N " _rp, V _drefifor the capacitance voltage of fault initial time i-th normal-sub module;

Wherein, N _pfor the submodule sum that each brachium pontis drops into;

N " _rpfor the true optimal value of the redundancy submodule number that each brachium pontis drops into;

Sub-step C2: by carrier wave T _cbpass to all normal-sub modules;

Described carrier wave T _cbfor the normal-sub module making normal-sub module become bypass;

Sub-step C3: judge | V _ci-V _drefi|>=V _εwhether set up, if | V _ci-V _drefi|>=V _ε, then sub-step C4 is performed; Otherwise, perform sub-step C5;

Wherein, V _ciit is the capacitance voltage of i-th normal-sub module;

V _drefibe i-th normal-sub module voltage change reference value;

V _εfor setting threshold;

Sub-step C4: make V _drefi=V _ciand make count (i)=count (i)+1;

Sub-step C5: judge i<N _nwhether set up, if i<N _n, then make i=i+1, return sub-step C2; Otherwise, perform step C6; N _nfor the number of normal-sub modules all on brachium pontis;

Sub-step C6: make j=1,

Sub-step C7: judge whether num>0 sets up, if num>0, then performs sub-step C8; Otherwise, perform sub-step C14;

Sub-step C8: judge whether count (j)=minn sets up, if count (j)=minn, then performs sub-step C9; Otherwise, perform sub-step C11;

Sub-step C9: by carrier wave-T _cbpass to a jth normal-sub module, and make num=num-1;

Described carrier wave-T _cbfor the normal-sub module making normal-sub module become input;

Sub-step C10: judge whether num>0 sets up, if num>0, then performs sub-step C11; Otherwise, perform sub-step C14;

Sub-step C11: judge j<N _nwhether set up, if j<N _n, then sub-step C12 is performed; Otherwise, perform sub-step C13;

Sub-step C12: make j=j+1, returns sub-step C8;

Sub-step C13: make j=1, minn=minn+1, return sub-step C8;

Sub-step C14: terminate.

6. method according to claim 4, is characterized in that the described redundancy submodule number dropped into each brachium pontis is carried out period modulation and comprised:

Sub-step D1: make i=1, count (i)=0, num=N " _rp, V _drefifor the capacitance voltage of fault initial time i-th redundancy submodule;

Wherein, N " _rpfor the true optimal value of the redundancy submodule number that each brachium pontis drops into;

Sub-step D2: by carrier wave T _cbpass to all redundancy submodule;

Described carrier wave T _cbfor the redundancy submodule making redundancy submodule become bypass;

Sub-step D3: judge | V _ci-V _drefi|>=V _εwhether set up, if | V _ci-V _drefi|>=V _ε, then sub-step D4 is performed; Otherwise, perform sub-step D5;

Wherein, V _ciit is the capacitance voltage of i-th redundancy submodule;

V _drefibe i-th redundancy submodule change in voltage reference value;

V _εfor setting threshold;

Sub-step D4: make V _drefi=V _ciand make count (i)=count (i)+1;

Sub-step D5: judge whether i<s sets up, if i<s, then make i=i+1, return sub-step D2; Otherwise, perform step D6; S is the redundancy submodule number that brachium pontis drops into;

Sub-step D6: make j=1,

Sub-step D7: judge whether num>0 sets up, if num>0, then performs sub-step D8; Otherwise, perform sub-step D14;

Sub-step D8: judge whether count (j)=minn sets up, if count (j)=minn, then performs sub-step D9; Otherwise, perform sub-step D11;

Sub-step D9: by carrier wave-T _cbpass to a jth redundancy submodule, and make num=num-1;

Described carrier wave-T _cbfor the redundancy submodule making normal-sub module become input;

Sub-step D10: judge whether num>0 sets up, if num>0, then performs sub-step D11; Otherwise, perform sub-step D14;

Sub-step D11: judge whether j<s sets up, if j<s, then performs sub-step D12; Otherwise, perform sub-step D13;

Sub-step D12: make j=j+1, returns sub-step D8;

Sub-step D13: make j=1, minn=minn+1, return sub-step D8;

Sub-step D14: terminate.