CN103825478B - Control method based on power frequency fixed switching frequency modular multi-level converter - Google Patents

Abstract

The invention discloses a kind of control method based on power frequency fixed switching frequency modular multi-level converter, by the modulation strategy periodically impulse waveform shifted, so that it is determined that often organize the feature of four impulse waveform parameters, and then the occurrence of impulse waveform parameter is determined with reference to nearest level modulation strategy, and use impulse waveform parameter vector form, impulse waveform parameter is finely adjusted by the principle according to the meritorious equipartition of energy, it is compiled into impulse waveform parameter list, under conditions of ensureing total harmonic distortion, it is achieved module absorbed power autobalance.Modulation ratio is determined by detection line voltage and current actual value, impulse waveform parameter is obtained than tabling look-up according to modulation, and then by corresponding principle and sub module cascade number size, impulse waveform carried out submodule switching signal when periodic shift obtains controlling without capacitance voltage, achieve control based on power frequency fixed switching frequency modular multi-level converter, provide good reference value for engineer applied.

Description

Control method based on power frequency fixed switching frequency modular multi-level converter

Technical field

The present invention relates to modular multilevel topological structure mesohigh electric energy quality controller and D.C. high voltage transmission neck Territory, particularly relates to a kind of control method based on power frequency fixed switching frequency modular multi-level converter.

Background technology

Along with social progress and industrial development, there is two major features in modern power systems: electrical power trans mission/distribution system is huge, power train System voltage and the continuous lifting of power grade.First, the demand of electric power is got more and more, in order to meet user to electricity by modern society The demand that power is growing, power system becomes more and more huger, and coverage is more and more wide.This gives the steady of power system Qualitative bring challenges.Simultaneously as China is vast in territory, but uneven geographical distribution of resources, in order to improve the effect of long term distance transmission of electricity Rate, the application of D.C. high voltage transmission (HVDC, high-voltage direct current) technology is more and more extensive.Secondly, modern The load of power system also has new feature: power electronic equipment has superior performance, by consumption industries such as industrial or agricultural A large amount of employings.But, power electronic equipment, as nonlinear load, can inject idle and harmonic wave to electrical network, along with non-linear negative Carrying the increase of capacity, it is the most increasing on the impact of distribution system, makes system exist dangerous, unstable hidden danger.Centering is high Pressure electrical power trans mission/distribution system carries out reactive-load compensation, can be effectively improved the stability of power system.By height between different electric power systems Pressure DC transmission system (HVDC) interconnection, can solve the asynchronous problem of system, it is also possible to stop fault to spread between the systems, It it is the feasible method improving system stability with reliability.

Modular multi-level converter (MMC, Modular Multilevel Converter) must after proposing Research widely and the strong interest of engineer to scholar.Modular multi-level converter has plurality of advantages: modularity sets Meter, low switching frequency, low-power consumption, high-quality spectral characteristic etc..These advantages are to the manufacture of modular multi-level converter, peace Dress, safeguards and brings huge convenience, also make it directly be linked into mesohigh electrical network without net side transformer.How electric modularity is now Flat current transformer has been applied to HVDC transmission system and mesohigh utility power quality control system, becomes that to improve power transmission and distribution system steady The qualitative effective ways with reliability.

Along with the development of high-power, engineer applied always being wished, modular multi-level converter has higher Efficiency.One method of most effective of which is exactly to reduce the switching frequency of semiconductor switch device.But, in actual applications, The reduction of switching frequency can control to bring extreme difficulties to modulation strategy and capacitor voltage balance.Become for modular multilevel Many modulation strategies that stream device is proposed are the most applicable with capacitor voltage balance control method.Accordingly, it would be desirable to it is a kind of novel It is solid that modulation strategy and corresponding capacitor voltage balance control method make modular multi-level converter operate effectively in Determine under power frequency switching frequency.

For the control method problem under modular multi-level converter low switching frequency, many research work are with achievement It is suggested.A kind of modulation strategy based on fixing power frequency switching frequency, and the uniform distribution that energy is between submodule be by Periodically shift pulse waveform realizes, but the method is not owing to considering problem that each submodule energy loss is different and nothing Method ensures that DC capacitor voltage meansigma methods is constant.As the most perfect, also scholar proposes a kind of fine setting pulse width Control method carry out holding capacitor voltage constant, but this method can increase the harmonic content of output voltage.A class is also had to put down The method of weighing apparatus capacitance voltage is by being ranked up capacitance voltage and being judged whether to enter electric capacity by the polarity of bridge arm current Row discharge and recharge.But to be switching frequency higher and does not fixes for the problem of this kind of method.Author not yet sees for based on work Frequently the good control strategy of fixed switching frequency modular multi-level converter.To this end, also need to based on power frequency switch lock The control strategy problem of rate modular multi-level converter carries out systematic research.

Summary of the invention

For drawbacks described above or deficiency, it is an object of the invention to provide a kind of at power frequency fixed switching frequency lower mold massing The modulation strategy of Multilevel Inverters and corresponding capacitor voltage balance control method.

For reaching object above, the technical solution used in the present invention is:

Comprise the following steps:

1), establishment impulse waveform initial parameter table:

1.1, according to the feature of impulse waveform in a power frequency period, set represent this impulse waveform one group of parameter as (r_k,w_k), wherein, r_kFor impulse waveform center position, w_kIt it is half impulse waveform width；

1.2, the submodule of each for modular multi-level converter brachium pontis is divided into some groups, often containing four submodules in group Block, and the impulse waveform set in every group includes s_k1, s_k2, s_k3, s_k4, its parameter is respectively (r_k,w_k), (-r_k,π-w_k), (-r_k, w_k), (r_k,π-w_k)；

1.3, set modulation ratio m, set modulation is substituted into following relationship than m, obtains set modulation ratio under m Impulse waveform initial parameter r_k'、w_k':

${\mathrm{sw}}_i=\arccos \[\frac{1}{m}-\frac{2}{N\·m}(i-0.5)\]---\left(1\right)$

${r_k}^{\′}=\frac{{\mathrm{sw}}_k+{\mathrm{sw}}_{k+N/4}+\mathrm{\π}}{2}---\left(2\right)$

${w_k}^{\′}=\frac{{\mathrm{sw}}_k+\mathrm{\π}-{\mathrm{sw}}_{k+N/4}}{2}---\left(3\right)$

Wherein i=1,2 ..., (N/2), N is each brachium pontis submodule number, k=1,2 ..., N/4, sw_iFor pulse Waveform initial time value；

1.4, according to formula in step 1.3 (1) (2) (3), order modulation take different values than m, modulated accordingly than lower often Initial parameter (the r of group pulse waveform_k',w_k'), by modulation than m and the corresponding initial parameter modulated than lower every group pulse waveform (r_k',w_k') it is compiled into impulse waveform initial parameter table；

2), impulse waveform initial parameter table fine setting:

2.1, two-dimensional coordinate plane graph is set up, by the initial parameter of group pulse waveform every in impulse waveform initial parameter table (r_k',w_k') be mapped in two-dimensional coordinate plane with the form of vector；

2.2, according to modular multi-level converter cascade submodule number, to impulse waveform initial parameter (r_k',w_k') It is finely adjusted, obtains impulse waveform parameter (r_k,w_k)；

2.3, by impulse waveform parameter (r obtained after step 2.2 is finely tuned_k,w_k), it is compiled into impulse waveform parameter Table；

3) determination of submodule switching signal when, controlling without capacitance voltage:

3.1, the three-phase current i of detection module Multilevel Inverters AC_a,i_b,i_c, by three-phase current i_a,i_b,i_cEnter Row three-phase static coordinate system, to the computing of biphase rotating coordinate system, obtains watt current actual value i after computing_dReal with reactive current Actual value i_q；

3.2, by watt current command value i_d ^*With watt current actual value i_dAnd referenced reactive current value i_q ^*With idle electricity Stream actual value i_qIt is separately input on d axle and the q axle of current inner loop based on dq uneoupled control；3.3, obtain based on dq decoupling control Active voltage command value v of the current inner loop output of system_id ^*With reactive voltage command value v_iq ^*, and according to active voltage command value v_id ^*With reactive voltage command value v_iq ^*Obtain modulating the phase contrast δ than m and line voltage and current transformer ac output voltage；

3.4, according to the modulation generated in step 3.3 than m, by inquiry impulse waveform parameter list obtain this modulation than under Set of pulses waveform parameter (r_k,w_k)；

3.5, phaselocked loop is utilized to detect current time electric network voltage phase θ_PLL, the phase obtained with step 3.3 by it Potential difference δ is added, and obtains current time current transformer output AC voltage phase theta_ph,x；

3.6, according to step 3.4 and step 3.5 gained impulse waveform parameter and current transformer output AC voltage phase theta_ph,x, Obtain the submodule pulse waveform signal before shifting

In formula (4), ph=a, b, c；X=u, l；I=1,2 ..., N, a phase, b phase, c phase is modular multilevel unsteady flow The three-phase of device AC, u is the upper brachium pontis of modular multi-level converter, and l is the lower brachium pontis of modular multi-level converter；

3.7, the pulse waveform signal generated in step 3.6 is carried out periodic shift, when generation controls without capacitance voltage Each submodule switching signal.

When setting up two-dimensional coordinate plane graph in described step 2.1, its x-axis, y-axis coordinate be: x=Lcos (r_k'), y= Lsin(r_k'), wherein, L=sin (w_k')。

In described step 2.2, according to the number of modular multi-level converter cascade submodule, ginseng initial to impulse waveform Number (r_k',w_k') it is finely adjusted and specifically includes:

(1), when modular multi-level converter cascade submodule number is less than or equal to 12, then keep impulse waveform initial Parameter (r_k',w_k') representated by the vertical coordinate of vector constant, abscissa is displaced toPlace, obtains impulse waveform parameter (r_k,w_k)；

(2), when modular multi-level converter cascade submodule number is less than 60 more than 12, two group pulse waveforms ginsengs are selected Number is finely adjusted, and the principle of fine setting is to make the meansigma methods of the abscissa of vector represented by two group pulse waveform parameters beObtain impulse waveform parameter (r_k,w_k)；

(3), when modular multi-level converter cascade submodule number is more than 60, three group pulse waveform parameters are selected to enter Row fine setting, the principle of fine setting is to make the meansigma methods of the abscissa of vector represented by three group pulse waveform parameters be? To impulse waveform parameter (r_k,w_k)。

By three-phase current i in described step 3.1_a,i_b,i_cCarry out the three-phase static coordinate system fortune to biphase rotating coordinate system The transformation matrix calculated is:

$T_{abc-dq}=\frac{2}{3}\left[\begin{array}{ccc}\sin \left(\mathrm{\ω}t\right)& \sin (\mathrm{\ω}t-2\mathrm{\π}/3)& \sin (\mathrm{\ω}t+2\mathrm{\π}/3)\\ \cos \left(\mathrm{\ω}t\right)& \cos (\mathrm{\ω}t-2\mathrm{\π}/3)& \cos (\mathrm{\ω}t+2\mathrm{\π}/3)\end{array}\right]---\left(5\right)$

Wherein, ω is the angular frequency of modular multi-level converter.

Watt current command value i in described step 3.2_d ^*With referenced reactive current value i_q ^*Particularly as follows:

When modular multi-level converter is operated under rectification mode, watt current command value i_d ^*By three-phase dc bus The result that average voltage is exported through single channel subtractor and single channel proportional and integral controller with DC voltage set-point is true Fixed；Referenced reactive current value i_q ^*Determine according to the actual reactive requirement of AC network.

The modulation in described step 3.3 calculating than the phase contrast δ of m and line voltage and current transformer ac output voltage Formula is:

$m=\frac{\sqrt{v_{id}^{*2}+v_{iq}^{*2}}}{\left(\frac{V_{dc,bus}}{2}\right)}---\left(6\right)$

$\mathrm{\δ}={\tan }^{-1}(-\frac{v_{iq}^{*}}{v_{id}^{*}})---\left(7\right).$

The pulse waveform signal generated in step 3.6 is carried out periodic shift by described step 3.7, generates without electric capacity electricity Voltage-controlled processed time each submodule switching signal specifically include:

(1), when modular multi-level converter cascade submodule number is less than or equal to 12, by shared set of pulses waveform Parameter (r_k,w_k) four submodules be divided into a group, in each group, the pulse waveform signal corresponding to the first two submodule is carried out Periodic shift, the pulse waveform signal corresponding to latter two submodule is also carried out same displacement, thus produces corresponding to phase Answer the switching signal that submodule is new；

(2) when modular multi-level converter cascade submodule number is less than 60 more than 12, by two group pulse waveform parameters The meansigma methods of representative vector abscissa isEight submodules be divided into one big group, wherein parameter (r_ka,w_ka) institute Four corresponding submodules are a group, parameter (r_kb,w_kbFour submodules corresponding to) are b group；By a group the first two submodule institute Corresponding pulse waveform signal carries out periodic shift with the pulse waveform signal corresponding to b group the first two submodule；By a, b two The pulse waveform signal that in group, latter two submodule is corresponding shifts；

(3) when modular multi-level converter cascade submodule number is more than 60, by three group pulse waveform parameter institute's generations The meansigma methods of table vector abscissa is12 submodules be divided into one big group, wherein parameter (r_ka,w_ka) institute right Four submodules answered are a group, parameter (r_kb,w_kbFour submodules corresponding to) are b group, parameter (r_kc,w_kcCorresponding to) four Individual submodule is c group；Impulse waveform corresponding to the first two submodule in a group, b group and c group is shifted, latter two submodule Impulse waveform corresponding to block shifts.

Described step 3) after also include capacitor voltage balance control, particularly as follows:

4.1, half power frequency period every to submodule DC capacitor voltage is sampled once, is input to by sampling gained signal Moving average low pass filter obtains capacitance voltage flip-flop after processing；

4.2, each for step 4.1 gained brachium pontis N number of capacitance voltage value is carried out descending sort, and according to ranking results antithetical phrase Module is numbered；

4.3, the submodule capacitor voltage value of numbered i and numbered N+1-i is subtracted each other, obtains difference, wherein i=1, 2 ..., N/2, then, by difference compared with marginal value Δ V, if difference is more than or equal to Δ V, then turn to step 4.4；If difference Less than Δ V, then continue after adding 1 by i value to implement step 4.3；

4.4, at the initial time of each power frequency period, the bridge arm current signal that previous periodic sampling obtains is utilized, to this Current calculation its from LE_iMoment is to LE_N+1-iThe integration in moment, obtains rising edge transfer charge amount Q_L, and, to the previous cycle Bridge arm current calculates it from FE_iMoment is to FE_N+1-iThe integration in moment, obtains trailing edge transfer charge amount Q_F；Wherein, LE_iFor numbering The rising edge time of the submodule switching pulse signal of i, LE_N+1-iRising for the submodule switching pulse signal of numbering N+1-i Along the moment,

FE_iFor the trailing edge moment of the submodule switching pulse signal of numbering i, FE_N+1-iSubmodule for numbering N+1-i is opened Close the trailing edge moment of pulse signal；

4.5, rising edge transfer charge amount Q obtained by step 4.4 is judged_L:

If rising edge transfer charge amount Q_LMore than 0, then exchange the submodule of numbered i and the submodule of numbered N+1-i The rising edge of switching pulse signal, and make i value add 1；Otherwise, the operation that i value is added 1 is carried out；

Judge trailing edge transfer charge amount Q_F:

If trailing edge transfer charge amount Q_FLess than 0, then exchange the submodule of numbered i and the submodule of numbered N+1-i The trailing edge of switching pulse signal, and make i value add 1；

Otherwise carry out the operation that i value is added 1, i with N/2 is compared, if more than N/2, then illustrate that all submodules switch arteries and veins Rush signal all to have determined that；Otherwise, forward step 4.3 to continue to implement above-mentioned steps.

Compared with the prior art, the invention have the benefit that

The invention provides a kind of control method based on power frequency fixed switching frequency modular multi-level converter, pass through The modulation strategy periodically shifted impulse waveform, according to requirement such as direct current and meritorious first-harmonic to modulation strategy under power frequency The balance of component, the symmetry of waveform, so that it is determined that often organize the feature of four impulse waveform parameters, and then adjust with reference to nearest level System strategy determines the occurrence of impulse waveform parameter and is compiled into impulse waveform initial parameter table, and uses impulse waveform parameter to vow Amount form, is finely adjusted impulse waveform parameter list according to the principle of the meritorious equipartition of energy, reduces voltage harmonic further the most abnormal Variability.Further, the present invention determines modulation ratio m by detection line voltage and current actual value, obtains than tabling look-up according to modulation Corresponding impulse waveform parameter, and then by the size of certain principle and sub module cascade number, impulse waveform is carried out periodically Submodule switching signal when displacement obtains controlling without capacitance voltage, it is achieved that to how electric based on power frequency fixed switching frequency modularity The control of flat current transformer, provides good reference value for engineer applied.

Further, sorted by antithetical phrase module capacitance voltage sample and bridge arm current zero passage detection judges whether full Foot give-and-take conditions, if meeting, exchanging rising edge or the trailing edge of corresponding two sub-module switch pulse signals, thus obtaining Whole submodule switching pulse signal.

Accompanying drawing illustrates:

Fig. 1 is modular multi-level converter main circuit topological structure of the present invention；

Fig. 2 is capacitor voltage balance control method flow chart of the present invention；

Fig. 3 is power frequency switching frequency modular multi-level converter system total closed loop control block diagram of the present invention；

Fig. 4 is closed loop capacitor voltage balance control system block diagram of the present invention；

Fig. 5 is two-dimensional coordinate plane graph of the present invention；Wherein, (a) is that a parameter maps two-dimensional coordinate plane graph, and (b) is Multiple parameters map two-dimensional coordinate plane graph；

Fig. 6 is the submodule number of the present invention switching signal displacement policy map less than 12；

Fig. 7 is the submodule number of the present invention switching signal displacement policy map more than 12 less than 60；

Fig. 8 is the submodule number of the present invention switching signal displacement policy map more than 60；

Fig. 9 is the emulation experiment figure of power frequency modulation strategy；

Figure 10 is the l-G simulation test figure of capacitor voltage balance control method；

Figure 11 is the l-G simulation test figure being operated in dynamic response under rectification mode；

Figure 12 is the l-G simulation test figure being operated in dynamic response under inverter mode.

Detailed description of the invention:

Below in conjunction with the accompanying drawings the present invention is described in detail.

With reference to Fig. 1,2,3,4, the control based on power frequency fixed switching frequency modular multi-level converter in the present invention Method, including the modulation strategy periodically shifted impulse waveform and exchange impulse waveform rising edge or the electric capacity of trailing edge Voltage balancing control method.Specifically comprise the following steps that

The invention provides a kind of control method based on power frequency fixed switching frequency modular multi-level converter, including Following steps:

1), establishment impulse waveform initial parameter table:

1.1, according to the feature of impulse waveform in a power frequency period, set represent this impulse waveform one group of parameter as (r_k,w_k), wherein, r_kFor impulse waveform center position, w_kIt it is half impulse waveform width；

1.2, the submodule of each for modular multi-level converter brachium pontis is divided into some groups, often containing four submodules in group Block, and the impulse waveform set in every group includes s_k1, s_k2, s_k3, s_k4, it is often organized parameter and is respectively (r_k,w_k), (-r_k,π-w_k), (- r_k,w_k), (r_k,π-w_k)；

1.3, set modulation ratio m, set modulation is substituted into following relationship than m, obtains set modulation ratio under m Impulse waveform initial parameter r_k'、w_k':

${\mathrm{sw}}_i=\arccos \[\frac{1}{m}-\frac{2}{N\·m}(i-0.5)\]---\left(1\right)$

${r_k}^{\′}=\frac{{\mathrm{sw}}_k+{\mathrm{sw}}_{k+N/4}+\mathrm{\π}}{2}---\left(2\right)$

${w_k}^{\′}=\frac{{\mathrm{sw}}_k+\mathrm{\π}-{\mathrm{sw}}_{k+N/4}}{2}---\left(3\right)$

Wherein i=1,2 ..., (N/2-1), N is each brachium pontis submodule number, k=1,2 ..., N/4, sw_iFor arteries and veins Rush waveform initial time value；

1.4, according to the relational expression in step 1.3, order modulation takes different values than m, is modulated accordingly and often organizes arteries and veins than lower Rush the initial parameter (r of waveform_k',w_k'), by modulation than m and the corresponding initial parameter (r modulated than lower every group pulse waveform_k', w_k') it is compiled into impulse waveform initial parameter table；

2) impulse waveform initial parameter table fine setting:

2.1, set up two-dimensional coordinate plane graph, see Fig. 5, at the beginning of group pulse waveform every in impulse waveform initial parameter table Beginning parameter (r_k',w_k') be mapped in two-dimensional coordinate plane with the form of vector, when setting up two-dimensional coordinate plane graph, its x-axis, y-axis Coordinate is: x=Lcos (r_k'), y=Lsin (r_k'), wherein, L=sin (w_k')。

2.2, according to the number of modular multi-level converter cascade submodule, to impulse waveform initial parameter (r_k',w_k') It is finely adjusted, obtains impulse waveform parameter (r_k,w_k)；

To impulse waveform initial parameter (r_k',w_k') it is finely adjusted and specifically includes:

(1), when modular multi-level converter cascade submodule number is less than or equal to 12, then keep impulse waveform initial Parameter (r_k',w_k') representated by the vertical coordinate of vector constant, force to be displaced to abscissaPlace, obtains impulse waveform Parameter (r_k,w_k)；

(2), when modular multi-level converter cascade submodule number is less than 60 more than 12, two group pulse waveforms ginsengs are selected Number is finely adjusted, and the principle of fine setting is to make the meansigma methods of the abscissa of vector represented by two group pulse waveform parameters beAgain vertical coordinate is finely adjusted in unit circle, makes the total harmonic distortion of current transformer output voltage reduce, obtain Impulse waveform parameter (r_k,w_k)；

(3), when modular multi-level converter cascade submodule number is more than 60, three group pulse waveform parameters are selected to enter Row fine setting, the principle of fine setting is to make the meansigma methods of the abscissa of vector represented by three group pulse waveform parameters be? To impulse waveform parameter (r_k,w_k)。

2.3, by impulse waveform parameter (r obtained after step 2.2 is finely tuned_k,w_k), it is compiled into impulse waveform parameter Table；

3) determination of submodule switching signal when, controlling without capacitance voltage:

3.1, the three-phase current i of detection module Multilevel Inverters AC_a,i_b,i_c, by three-phase current i_a,i_b,i_cEnter Row three-phase static coordinate system, to the computing of biphase rotating coordinate system, obtains watt current actual value i after computing_dReal with reactive current Actual value i_q；

By three-phase current i_a,i_b,i_cCarry out the three-phase static coordinate system transformation matrix to the computing of biphase rotating coordinate system For:

$T_{abc-dq}=\frac{2}{3}\left[\begin{array}{ccc}sin\left(\mathrm{\ω}t\right)& sin(\mathrm{\ω}t-2\mathrm{\π}/3)& sin(\mathrm{\ω}t+2\mathrm{\π}/3)\\ cos\left(\mathrm{\ω}t\right)& cos(\mathrm{\ω}t-2\mathrm{\π}/3)& cos(\mathrm{\ω}t+2\mathrm{\π}/3)\end{array}\right]---\left(5\right)$

Wherein, ω is the angular frequency of modular multi-level converter, and t is the time.

3.2, by watt current command value i_d ^*With watt current actual value i_dAnd referenced reactive current value i_q ^*With idle electricity Stream actual value i_qIt is separately input on d axle and the q axle of current inner loop based on dq uneoupled control；

3.3, active voltage command value v of current inner loop based on dq uneoupled control output is obtained_id ^*Instruct with reactive voltage Value v_iq ^*, and according to active voltage command value v_id ^*With reactive voltage command value v_iq ^*Obtain modulating than m and line voltage and unsteady flow The phase contrast δ of device ac output voltage；

Wherein, merit current instruction value i_d ^*With referenced reactive current value i_q ^*Particularly as follows:

When modular multi-level converter is operated under rectification mode, watt current command value i_d ^*By three-phase dc bus The result that average voltage is exported through single channel subtractor and single channel proportional and integral controller with DC voltage set-point is true Fixed；Referenced reactive current value i_q ^*Determine according to the actual reactive requirement of AC network.

3.4, according to the modulation generated in step 3.3 than m, by inquiry impulse waveform parameter list obtain this modulation than under Set of pulses waveform parameter (r_k,w_k)；The modulation calculating than the phase contrast δ of m and line voltage and current transformer ac output voltage Formula is:

$m=\frac{\sqrt{v_{id}^{*2}+v_{iq}^{*2}}}{\left(\frac{V_{dc,bus}}{2}\right)}---\left(6\right)$

$\mathrm{\δ}={\tan }^{-1}(-\frac{v_{iq}^{*}}{v_{id}^{*}}).---\left(7\right).$

3.5, phaselocked loop is utilized to detect current time electric network voltage phase θ_PLL, the phase obtained with step 3.3 by it Potential difference δ is added, and obtains current time current transformer output AC voltage phase theta_ph,x；

3.6, according to step 3.4 and step 3.5 gained impulse waveform parameter and current transformer output AC voltage phase theta_ph,x, Obtain the submodule pulse waveform signal before shifting

Wherein, ph=a, b, c；X=u, l；I=1,2 ..., N, a phase, b phase, c phase is detection moduleization many level unsteady flow The three-phase of device AC, u is the upper brachium pontis of modular multi-level converter, and l is the lower brachium pontis of modular multi-level converter；

3.7, the pulse waveform signal generated in step 3.6 is carried out periodic shift, when generation controls without capacitance voltage Each submodule switching signal.

See Fig. 6, specifically include:

(1), when modular multi-level converter cascade submodule number is less than or equal to 12, by shared set of pulses waveform Parameter (r_k,w_k) four submodules be divided into a group, in each group, the pulse waveform signal corresponding to the first two submodule enters Line period shifts, and the pulse waveform signal corresponding to latter two submodule is also carried out same displacement, thus produce corresponding to The switching signal that corresponding submodule is new；

(2) when modular multi-level converter cascade submodule number is less than 60 more than 12, Fig. 7 is seen, by two group pulses Representated by waveform parameter, the meansigma methods of vector abscissa isEight submodules be divided into one big group, wherein parameter (r_ka,w_kaFour submodules corresponding to) are a group, parameter (r_kb,w_kbFour submodules corresponding to) are b group；By front for a group two Pulse waveform signal corresponding to individual submodule and the pulse waveform signal corresponding to b group the first two submodule carry out periodically moving Position；Pulse waveform signal corresponding for latter two submodule in a, b two groups is shifted；

(3) when modular multi-level converter cascade submodule number is more than 60, by three group pulse waveform parameter institute's generations The meansigma methods of table vector abscissa is12 submodules be divided into one big group, wherein parameter (r_ka,w_ka) institute right Four submodules answered are a group, parameter (r_kb,w_kbFour submodules corresponding to) are b group, parameter (r_kc,w_kcCorresponding to) four Individual submodule is c group；Impulse waveform corresponding to the first two submodule in a group, b group and c group is shifted, latter two submodule Impulse waveform corresponding to block shifts.

4), capacitor voltage balance controls:

4.1, half power frequency period every to submodule DC capacitor voltage is sampled once, is input to by sampling gained signal Moving average low pass filter obtains capacitance voltage flip-flop after processing；

4.2, each for step 4.1 gained brachium pontis N number of capacitance voltage value is carried out descending sort, and according to ranking results antithetical phrase Module is numbered；

4.3, the submodule capacitor voltage value of numbered i and numbered N+1-i is subtracted each other, obtains difference, wherein i=1, 2 ..., N/2, then, by difference compared with marginal value Δ V, if difference is more than or equal to Δ V, then turn to step 4.4；If difference Less than Δ V, then continue after adding 1 by i value to implement step 4.3；

4.4, see Fig. 6,7, at the initial time of each power frequency period, utilize the bridge arm current that previous periodic sampling obtains Signal, to this Current calculation its from LE_iMoment is to LE_N+1-iThe integration in moment, obtains rising edge transfer charge amount Q_L, and, right The bridge arm current in previous cycle calculates it from FE_iMoment is to FE_N+1-iThe integration in moment, obtains trailing edge transfer charge amount Q_F；Its In, LE_iFor the rising edge time of the submodule switching pulse signal of numbering i, LE_N+1-iSubmodule for numbering N+1-i switchs arteries and veins Rush the rising edge time of signal, FE_iFor the trailing edge moment of the submodule switching pulse signal of numbering i, FE_N+1-iFor numbering N+1- The trailing edge moment of the submodule switching pulse signal of i；

4.5, rising edge transfer charge amount Q obtained by step 4.4 is judged_L:

If rising edge transfer charge amount Q_LMore than 0, then exchange the submodule of numbered i and the submodule of numbered N+1-i The rising edge of switching pulse signal, and make i value add 1；Otherwise, the operation that i value is added 1 is carried out；

Judge trailing edge transfer charge amount Q_F:

If trailing edge transfer charge amount Q_FLess than 0, then exchange the submodule of numbered i and the submodule of numbered N+1-i The trailing edge of switching pulse signal, and make i value add 1；

Otherwise carry out the operation that i value is added 1, i with N/2 is compared, if more than N/2, then illustrate that all submodules switch arteries and veins Rush signal all to have determined that；Otherwise, forward step 4.3 to continue to implement above-mentioned steps.

Seeing Fig. 9,10,11,12 and give the simulation waveform using control method of the present invention, wherein, Fig. 9 is power frequency modulation The simulating, verifying of strategy, five simulation waveform figures are followed successively by from top to bottom: brachium pontis output voltage in A phase；Current transformer output lead electricity Pressure；A cross streams side exports electric current and upper brachium pontis and lower bridge arm current；In A phase first submodule capacitor voltage of brachium pontis and Flip-flop；The output voltage of first submodule of brachium pontis in A phase.

Figure 10 is the checking of capacitor voltage balance control method, and three simulation waveform figures are followed successively by from top to bottom: current transformer AC three-phase phase voltage；AC side of converter three-phase phase current；24 submodule capacitor voltage of brachium pontis in A phase.

Figure 11 is the checking being operated in the dynamic response under rectification mode, and five simulation waveform figures are followed successively by from top to bottom: Watt current command value and actual value and referenced reactive current value and actual value；AC side of converter three-phase phase voltage；Unsteady flow Device AC three-phase phase current；24 submodule capacitor voltage of brachium pontis in A phase；DC side busbar voltage.

Figure 12 is the checking being operated in the dynamic response under inverter mode, and four simulation waveforms are followed successively by from top to bottom: have Merit current instruction value and actual value and referenced reactive current value and actual value；AC side of converter three-phase phase voltage；Current transformer AC three-phase phase current；24 submodule capacitor voltage of brachium pontis in A phase.

From simulation waveform it can be seen that this control method can make modular multi-level converter be operated in power frequency effectively Under fixed switching frequency, and the dynamic characteristic that system work is in different modes also has well performance.

With reference to Fig. 1, constructing modular Multilevel Inverters in simulation software.The main circuit of modular multi-level converter Structure, by respectively with six the linked reactor series connection of six brachium pontis, then constitutes double star and connects.Each brachium pontis has 24 copped waves Block coupled in series forms, and module DC side parallel has electrolysis condenser, and switching device uses the large power all-controlled devices such as IGBT or GTO Part.

In each brachium pontis, serial module structure number does not has the upper limit, value to be decided by electric power system electric pressure.In order to describe conveniently, In the present invention, it is described in detail as a example by 24 block coupled in series.Again because the symmetry of A, B, C three-phase and upper and lower bridge arm Symmetry, the most only needs the situation of brachium pontis in A phase of analyzing.Electrical network three-phase voltage is designated as u_s, it may be assumed that u_sa、u_sb、u_sc；Power supply three Phase current is designated as i_s, it may be assumed that i_sa、i_sb、i_sc；In A phase, brachium pontis series connection 24 unit DC voltages of copped wave module are designated as v respectively_ap1、 v_ap2、v_ap3……v_ap24。

The present invention is given the control method of a kind of modular multi-level converter based on power frequency fixed switching frequency.Need It is noted that the present invention is applicable to the integral multiple that number is 4 of the submodule on each brachium pontis of modular multi-level converter Situation.For the feasibility of authentication control method, it is 100MVA that author has built capacity in simulation software, each brachium pontis by The phantom of 24 copped wave block coupled in series.Modulator approach based on power frequency switching frequency in the present invention and capacitor voltage balance Control method is verified in simulation software, and simulation results show modulation strategy effectively ensures fixing power frequency switch Frequency and several power frequency period self-energy can be divided equally in submodule.Capacitance voltage control strategy realizes the most well simultaneously The balance of submodule capacitor voltage controls in the case of do not affect AC output voltage waveforms.The method is correct, reliable, Good reference value is provided for engineer applied.

Claims (4)

1. a control method based on power frequency fixed switching frequency modular multi-level converter, it is characterised in that include with Lower step:

1), establishment impulse waveform initial parameter table:

1.1, according to the feature of impulse waveform in a power frequency period, the one group of parameter representing this impulse waveform is set as (r_k, w_k), wherein, r_kFor impulse waveform center position, w_kIt it is half impulse waveform width；

1.2, the submodule of each for modular multi-level converter brachium pontis is divided into some groups, often containing four submodules in group, And the impulse waveform set in every group includes s_k1, s_k2, s_k3, s_k4, its parameter is respectively (r_k,w_k), (-r_k,π-w_k), (-r_k,w_k), (r_k,π-w_k)；

1.3, set modulation ratio m, set modulation is substituted into following relationship than m, obtain set modulation than the arteries and veins under m Rush waveform initial parameter r_k'、w_k':

${\mathrm{sw}}_i=arccos\[\frac{1}{m}-\frac{2}{N\·m}(i-0.5)\]---\left(1\right)$

${r_k}^{\′}=\frac{{\mathrm{sw}}_k+{\mathrm{sw}}_{k+N/4}+\mathrm{\π}}{2}---\left(2\right)$

${w_k}^{\′}=\frac{{\mathrm{sw}}_k+\mathrm{\π}-{\mathrm{sw}}_{k+N/4}}{2}---\left(3\right)$

Wherein i=1,2 ..., (N/2), N is each brachium pontis submodule number, k=1,2 ..., N/4, sw_iFor impulse waveform Initial time value；

1.4, according to formula in step 1.3 (1) (2) (3), order modulation takes different values than m, is modulated accordingly and often organizes arteries and veins than lower Rush the initial parameter (r of waveform_k',w_k'), by modulation than m and the corresponding initial parameter (r modulated than lower every group pulse waveform_k', w_k') it is compiled into impulse waveform initial parameter table；

2), impulse waveform initial parameter table fine setting:

2.1, two-dimensional coordinate plane graph is set up, by the initial parameter (r of group pulse waveform every in impulse waveform initial parameter table_k', w_k') be mapped in two-dimensional coordinate plane with the form of vector；

2.2, according to the number of modular multi-level converter cascade submodule, to impulse waveform initial parameter (r_k',w_k') carry out Fine setting, obtains impulse waveform parameter (r_k,w_k)；

2.3, by impulse waveform parameter (r obtained after step 2.2 is finely tuned_k,w_k), it is compiled into impulse waveform parameter list；

3) determination of submodule switching signal when, controlling without capacitance voltage:

3.1, the three-phase current i of detection module Multilevel Inverters AC_a,i_b,i_c, by three-phase current i_a,i_b,i_cCarry out three Phase static coordinate is tied to the computing of biphase rotating coordinate system, obtains watt current actual value i after computing_dWith reactive current actual value i_q；

3.2, by watt current command value i_d ^*With watt current actual value i_dAnd referenced reactive current value i_q ^*Real with reactive current Actual value i_qIt is separately input on d axle and the q axle of current inner loop based on dq uneoupled control；

3.3, active voltage command value v of current inner loop based on dq uneoupled control output is obtained_id ^*With reactive voltage command value v_iq ^*, and according to active voltage command value v_id ^*With reactive voltage command value v_iq ^*Obtain modulating than m and line voltage and current transformer The phase contrast δ of ac output voltage；

3.4, according to the modulation generated in step 3.3 than m, by inquiry impulse waveform parameter list obtain this modulation than under one group Impulse waveform parameter (r_k,w_k)；

3.5, phaselocked loop is utilized to detect current time electric network voltage phase θ_PLL, the phase contrast obtained with step 3.3 by it δ is added, and obtains current time current transformer output AC voltage phase theta_ph,x；

3.6, according to step 3.4 and step 3.5 gained impulse waveform parameter and current transformer output AC voltage phase theta_ph,x, obtain Submodule pulse waveform signal before shifting

In formula (4), ph=a, b, c；X=u, l；I=1,2 ..., N；A phase, b phase, c phase is handed over for modular multi-level converter The three-phase of stream side, u is the upper brachium pontis of modular multi-level converter, and l is the lower brachium pontis of modular multi-level converter；

3.7, the pulse waveform signal generated in step 3.6 is carried out periodic shift, generate each son when controlling without capacitance voltage Module switch signal；

When setting up two-dimensional coordinate plane graph in described step 2.1, its x-axis, y-axis coordinate be: x=Lcos (r_k'), y=Lsin (r_k'), wherein, L=sin (w_k')；

In described step 2.2, according to the number of modular multi-level converter cascade submodule, to impulse waveform initial parameter (r_k',w_k') it is finely adjusted and specifically includes:

(1), when modular multi-level converter cascade submodule number is less than or equal to 12, then impulse waveform initial parameter is kept (r_k',w_k') representated by the vertical coordinate of vector constant, abscissa is displaced toPlace, obtains impulse waveform parameter (r_k, w_k)；

(2), when modular multi-level converter cascade submodule number is less than 60 more than 12, two group pulse waveform parameters are selected to enter Row fine setting, the principle of fine setting is to make the meansigma methods of the abscissa of vector represented by two group pulse waveform parameters be? To impulse waveform parameter (r_k,w_k)；

(3), when modular multi-level converter cascade submodule number is more than 60, three group pulse waveform parameters are selected to carry out micro- Adjusting, the principle of fine setting is to make the meansigma methods of the abscissa of vector represented by three group pulse waveform parameters beObtain arteries and veins Rush waveform parameter (r_k,w_k)；

The pulse waveform signal generated in step 3.6 is carried out periodic shift by described step 3.7, generates without capacitance voltage control Time processed, each submodule switching signal specifically includes:

(1), when modular multi-level converter cascade submodule number is less than or equal to 12, by shared set of pulses waveform parameter (r_k,w_k) four submodules be divided into a group, in each group, the pulse waveform signal corresponding to the first two submodule carries out the cycle Property displacement, the pulse waveform signal corresponding to latter two submodule is also carried out same displacement, thus produces corresponding to corresponding son The switching signal that module is new；

(2) when modular multi-level converter cascade submodule number is less than 60 more than 12, by two group pulse waveform parameter institute's generations The meansigma methods of table vector abscissa isEight submodules be divided into one big group, wherein parameter (r_ka,w_ka) institute right Four submodules answered are a group, parameter (r_kb,w_kbFour submodules corresponding to) are b group；By right for a group the first two submodule institute The pulse waveform signal answered carries out periodic shift with the pulse waveform signal corresponding to b group the first two submodule；By a, b two groups In pulse waveform signal corresponding to latter two submodule shift；

(3) when modular multi-level converter cascade submodule number is more than 60, will vow representated by three group pulse waveform parameters The meansigma methods of amount abscissa is12 submodules be divided into one big group, wherein parameter (r_ka,w_ka) corresponding Four submodules be a group, parameter (r_kb,w_kbFour submodules corresponding to) are b group, parameter (r_kc,w_kcCorresponding to) four Submodule is c group；Impulse waveform corresponding to the first two submodule in a group, b group and c group is shifted, latter two submodule Corresponding impulse waveform shifts；

Described step 3) after also include capacitor voltage balance control, particularly as follows:

4.1, half power frequency period every to submodule DC capacitor voltage is sampled once, is input to sampling gained signal slide Average low pass filter obtains capacitance voltage flip-flop after processing；

4.2, each for step 4.1 gained brachium pontis N number of capacitance voltage value is carried out descending sort, and according to ranking results to submodule It is numbered；

4.3, the submodule capacitor voltage value of numbered i and numbered N+1-i is subtracted each other, obtains difference, wherein i=1, 2 ..., N/2, then, by difference compared with marginal value Δ V, if difference is more than or equal to Δ V, then turn to step 4.4；If difference Less than Δ V, then continue after adding 1 by i value to implement step 4.3；

4.4, at the initial time of each power frequency period, the bridge arm current signal that previous periodic sampling obtains is utilized, to this electric current Calculate it from LE_iMoment is to LE_N+1-iThe integration in moment, obtains rising edge transfer charge amount Q_L, and, the brachium pontis to the previous cycle Current calculation its from FE_iMoment is to FE_N+1-iThe integration in moment, obtains trailing edge transfer charge amount Q_F；Wherein, LE_iFor numbering i The rising edge time of submodule switching pulse signal, LE_N+1-iDuring for the rising edge of the submodule switching pulse signal of numbering N+1-i Carve, FE_iFor the trailing edge moment of the submodule switching pulse signal of numbering i, FE_N+1-iSubmodule for numbering N+1-i switchs arteries and veins Rush the trailing edge moment of signal；

4.5, rising edge transfer charge amount Q obtained by step 4.4 is judged_L:

If rising edge transfer charge amount Q_LMore than 0, then exchange the submodule of numbered i and the submodule switch arteries and veins of numbered N+1-i Rush the rising edge of signal, and make i value add 1；Otherwise, the operation that i value is added 1 is carried out；

Judge trailing edge transfer charge amount Q_F:

If trailing edge transfer charge amount Q_FLess than 0, then exchange the submodule of numbered i and the submodule switch arteries and veins of numbered N+1-i Rush the trailing edge of signal, and make i value add 1；

Otherwise carry out the operation that i value is added 1, i with N/2 is compared, if more than N/2, then illustrating that all submodule switching pulses are believed Number all have determined that；Otherwise, forward step 4.3 to continue to implement above-mentioned steps.

Control method based on power frequency fixed switching frequency modular multi-level converter the most according to claim 1, its It is characterised by, by three-phase current i in described step 3.1_a,i_b,i_cCarry out the three-phase static coordinate system fortune to biphase rotating coordinate system The transformation matrix calculated is:

$T_{abc-dq}=\frac{2}{3}\left[\begin{array}{ccc}sin\left(\mathrm{\ω}t\right)& sin(\mathrm{\ω}t-2\mathrm{\π}/3)& sin(\mathrm{\ω}t+2\mathrm{\π}/3)\\ cos\left(\mathrm{\ω}t\right)& cos(\mathrm{\ω}t-2\mathrm{\π}/3)& cos(\mathrm{\ω}t+2\mathrm{\π}/3)\end{array}\right]---\left(5\right)$

Wherein, ω is the angular frequency of modular multi-level converter.

Control method based on power frequency fixed switching frequency modular multi-level converter the most according to claim 1, its It is characterised by, watt current command value i in described step 3.2_d ^*With referenced reactive current value i_q ^*Particularly as follows:

When modular multi-level converter is operated under rectification mode, watt current command value i_d ^*By three-phase dc busbar voltage The result that meansigma methods is exported through single channel subtractor and single channel proportional and integral controller with DC voltage set-point determines；Nothing Merit current instruction value i_q ^*Determine according to the actual reactive requirement of AC network.

Control method based on power frequency fixed switching frequency modular multi-level converter the most according to claim 1, its It is characterised by, the meter than the phase contrast δ of m and line voltage and current transformer ac output voltage of the modulation in described step 3.3 Calculation formula is:

$m=\frac{\sqrt{v_{id}^{*2}+v_{iq}^{*2}}}{\left(\frac{V_{dc,bus}}{2}\right)}---\left(6\right)$

$\mathrm{\δ}={\tan }^{-1}(-\frac{v_{iq}^{*}}{v_{id}^{*}})---\left(7\right).$