CN105449693A - A hierarchical control method for a direct ac-ac type railway traction power regulator - Google Patents

Abstract

The invention discloses a hierarchical control method for a direct ac-ac type railway traction power regulator. In light of Hierarchical control, problems of divergence of capacitor voltages between chain link sets due to direct use of the RTPC for compensation of a V/v voltage transformer traction power supply system are solved through circulation control in a creative way. The control method is divided into three hierarchies: system-level control, control between the chain link sets and control inside the chain links, wherein the system-level control maintains the total energy of a device to be stable and the control between the chain link sets controls and adjusts imbalance active power between the chain links so as to avoid divergence of capacitor voltages between the chain link sets of the regulator. The control inside the chain links controls and maintains the capacitor voltage balance of power modules inside the chain link sets. The control method brought forward by the invention has relatively high universality, and can improve the performance of controlling the RTPC high speed railway compensation system and has good practical value.

Description

A kind of hierarchical control method of direct ac-ac type railway traction power adjuster

Technical field

The present invention relates to a kind of power quality controlling field of railroad traction system, particularly a kind of hierarchical control method of direct ac-ac type railway traction power adjuster.

Background technology

High-speed electric railway is integrated as contemporary new and high technology, there is the advantages such as capacity is large, energy consumption is low, it is little to pollute, safety and comfort, being the Transportation Model of sustainability and environment friendly, is one of important symbol of National Innovation Capacity, overall national strength and modernization of the country degree.But, high-speed electric railway is due to the supply power mode of its uniqueness and locomotive load characteristic, bring the power quality problems such as negative phase-sequence, harmonic wave, voltage fluctuation and flicker to electric power system, reduce the power supply quality of electric power system, the contiguous power network safety operation of impact.In recent years, further developing and growing along with high-speed railway electric power system, the negative phase-sequence brought thus and the power quality problem such as idle are more and more serious, must take effective control measures, realize that railway traction power supply system is high-quality, safety and economic power supply.

In order to administer the negative phase-sequence of railway power system, the power quality problem such as idle, multiple power quality compensation scheme is had to be suggested and to apply both at home and abroad.Document is had to adopt Scott (SCOTT) transformer, impedance matching transformer isoequilibrium transformer device structure to reduce negative-sequence current balanced three-phase current.On traditional electric locomotive circuit, because its power factor is lower, have document to adopt and passive filter be installed, passive part easily and electric network impedance produce series parallel resonance.There is document to adopt TCR type Static Var Compensator (staticvarcompensator, SVC) to carry out dynamic compensation to the idle of traction substation, but produce harmonic current.Have document to propose silent oscillation dynamic reactive compensator based on magnet controlled reactor, no-harmonic wave pollution, but dynamic compensation ability is limited.In order to the harmonic current suppressing electric locomotive and Static Var Compensator to produce, have document to adopt hybrid active filter to carry out dynamic compensation to harmonic current, passive and actively to mix, complex structure, reliability is not high.Document is had to propose to adopt full-control type Static Synchronous generator (StaticsynchronousCompensator, STATCOM) to the idle harmonious ripple dynamic compensation of trailer system, but STATCOM is mounted in three-phase high-voltage side, complex structure, power device is many, cost intensive.Consider the design feature of railway power system, Japanese scholars proposes railway power regulator (railwaytractionpowerconditioner, RTPC), back-to-back 2 power converters are utilized to be arranged on two supply arms of electric power system, both can combine carry out gaining merit, idle and harmonic controling, can realize negative phase-sequence and Reactive-current General Compensation.Because railway locomotive load is principal characteristic load, capacity is large, so the capacity requirement of compensation arrangement is also large.In order to improve power compensating device capacity, proposed to adopt multiple module paralleling form to form a kind of railway power regulator of multiplex by scholar, the AC of single each current transformer of the unit of power model back-to-back (H bridge) divides winding parallel by the secondary of step-down transformer with split winding, DC bus capacitor is separate, realizes multiplex by phase-shifting carrier wave.This kind of structure needs two step-down transformer with split windings, and capacity is suitable with compensation capacity, thus causes the cost of device high, the large heaviness of volume.

The topological structure of traditional railway power governor as shown in Figure 1.Because railway locomotive load is principal characteristic load, capacity is large, so the capacity requirement of compensation arrangement is also large.In order to improve power compensating device capacity, by the railway power regulator adopting multiple module paralleling form to form a kind of multiplex, single power model unit is made up of two back-to-back H bridge current transformers, and centre is linked together by DC bus capacitor.The AC of two H bridge current transformers of each power model unit divides winding parallel, the then former limit of transformer with split winding and being connected of traction power supply arm by the secondary of transformer with split winding.Two, the left and right H bridge current transformer of RTPC controls respectively, and realizes multiplex by phase-shifting carrier wave.

Summary of the invention

Technical problem to be solved by this invention is, not enough for prior art, provides a kind of hierarchical control method of direct ac-ac type railway traction power adjuster.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of hierarchical control method of direct ac-ac type railway traction power adjuster, be applicable to the high-speed railway bucking-out system of the many level block of dual star topology full-bridge, described high-speed railway bucking-out system comprises MMC formula rail traction power governor, MMC formula rail traction power governor comprises four limits, and four limits connect into quadrangle; Each limit comprises a H bridge chain and a filter inductance be connected with this H bridge chain; H bridge chain comprises the H-bridge unit of multiple series connection; Four intersection points of quadrangle are divided into two groups by diagonal, and two groups of intersection points are respectively connected with a traction power supply arm respectively; It is characterized in that, the method comprises the following steps:

1) current i of four H bridge chains is detected ₁, i ₂, i ₃, i ₄, calculate the biphase current i that high-speed railway bucking-out system exports _ca, i _cbwith loop current i _z;

2) detect the DC voltage of all H-bridge unit of high-speed railway bucking-out system, wherein the capacitance voltage of y power model of an xth chain link is u _cxy, try to achieve rail traction power governor all H-bridge unit voltage summation u _c ^Σ, by u _c ^Σwith given reference value u _refdifference send into PI controller, PI controller, export the amplitude Δ I being active current _dc, by Δ I _dcthe a phase of RTPC and b phase DC voltage conditioning signal is obtained, the negative sequence compensation current-order i that a phase is tried to achieve with detection respectively with b phase DC voltage conditioning signal after being multiplied by the synchronizing signal of two supply arms _ca ^*, i _cb ^*superposition, obtains the combination current instruction i of RTPC _ar, i _br; Two-phase output current inner ring adopts PR to control, and controller exports the overall modulation signal m obtaining two groups of chain links _a, m _b;

3) rational circulation voltage instruction u is tried to achieve according to constraints _zref, then try to achieve the circulation instruction i that need inject _zref, wherein constraints is as follows:

Wherein, $\{\begin{array}{c}{u}_{c14}^{\Σ}=u_{c1}^{\Σ}+u_{c4}^{\Σ}\\ u_{c23}^{\Σ}=u_{c2}^{\Σ}+u_{c3}^{\Σ}\end{array};$ be respectively the voltage of four H bridge chains;

4) by difference the corrected signal i injecting circulation is obtained after sending into P controller _zref2, by i _zref2with i _zrefcomprehensive circulation instruction i is obtained after superposition _zr; By comprehensive circulation instruction i _zrwith detection ring flow valuve i _zsubtract each other, the value after subtracting each other adopts PI link to regulate the rear output-Δ u of process _zwith Δ u _z, general-Δ u _zwith Δ u _zrespectively with circulation control command u _zrefbe added, obtain chain link 1,4 and chain link 2,3 liang group chain link circulation control voltage reference u _z1ref, u _z2ref: $\{\begin{array}{c}{u}_{z1ref}={\mathrm{\Δu}}_z+u_{zref}\\ u_{z2ref}=-{\mathrm{\Δu}}_z+u_{zref}\end{array};$ By u _z1ref, u _z2refrespectively divided by two link set voltages obtain modulation signal m between link set _z1, m _z2;

5) the capacitance voltage mean value u of chain link 1,4 and chain link 2,3 is asked for _cav14, u _cav23;

6) output of comprehensive each layer control, obtains the modulation signal m sending into an xth chain link y power model _xy;

7) modulation signal is sent into phase-shift PWM unit and obtain switching drive signal, switching drive signal drives the power switch pipe of corresponding H-bridge unit, makes it to export the electric current and voltage expected.

I _ca, i _cb, i _zcomputing formula as follows:

$\{\begin{array}{c}{i}_{cb}=(i_1+i_3+i_2+i_4)/2\\ i_{ca}=(i_2-i_1+i_3-i_4)/2\end{array};$

$i_z=\frac{i_4+i_3-i_2-i_1}{4}.$

U _c ^Σcomputing formula as follows:

$\left\{\begin{array}{cc}\begin{array}{c}{u}_{cx}^{\Σ}=\Σu_{cxy}\\ u_c^{\Σ}=\Σ\Σu_{cxy}\end{array}& x=1,2,3,4;y=1,\mathrm{2...}Y;\end{array}\right.$

Wherein, Y is the H-bridge unit quantity of each chain link.

U _cav14, u _cav23computing formula be:

$\{\begin{array}{c}{u}_{cav14}=(u_{c1}^{\Σ}+u_{c4}^{\Σ})/2Y\\ u_{cav23}=(u_{c2}^{\Σ}+u_{c3}^{\Σ})/2Y\end{array}.$

Modulation signal m _xycomputing formula be:

$\left\{\begin{array}{c}{m}_{1y}=m_b-m_a+m_{z1}+{\mathrm{\Δm}}_{1y}\\ m_{2y}=m_b+m_a-m_{z2}+{\mathrm{\Δm}}_{2y}\\ m_{3y}=m_b+m_a+m_{z2}+{\mathrm{\Δm}}_{3y}\\ m_{4y}=m_b-m_a-m_{z1}+{\mathrm{\Δm}}_{4y}\end{array}\right..$

Compared with prior art, the beneficial effect that the present invention has is: each limit of quadrangle of the present invention is a H bridge chain, does not need step-down transformer directly can be connected with traction power supply arm; Centre does not need DC link, can realize two-way changing and the flowing of power, can compensate the idle of two traction power supply arms and harmonic wave simultaneously.Control method proposed by the invention has stronger versatility, and can improve the control performance for RTPC high-speed railway bucking-out system, has good practical value.

Accompanying drawing explanation

Fig. 1 is the topology diagram of traditional railway power governor;

Fig. 2 is the topology diagram of direct ac-ac type railway power compensator;

Fig. 3 (a)-Fig. 3 (d) is the control block diagram of direct ac-ac type railway power compensator of the present invention;

In Fig. 2,1 is the direct railway power compensator of MMC formula; 2 is H bridge chain; 3 is filter inductance.

Embodiment

The topological structure of the direct railway electric energy quality compensator of MMC formula as shown in Figure 2.The direct railway power compensator 1 of MMC formula is made up of four limits; Each limit is made up of a H bridge chain 2 and a filter inductance 3; H bridge chain 2 is connected by multiple H-bridge unit to be formed; Four intersection points of quadrangle are divided into two groups by diagonal, and two groups of intersection points are connected with two traction power supply arms respectively by cable.This device forms a single-phase AC-AC converter of quadrangle by adopting many level cascade converter, does not need step-down transformer directly can be connected with traction power supply arm.Do not need DC link simultaneously, directly can realize two-way changing and the flowing of power, the idle of traction power supply arm locomotive load generation can be compensated simultaneously.Therefore device is by adopting many level cascaded transformation technology, saves two step-down transformers, substantially reduces volume and the cost of device.

Conveniently analyze, first define current i ₁the H bridge chain flow through is first H bridge chain, other the like.The traction power supply arm simultaneously defining the right is a phase supply arm, and the traction power supply arm on the left side is b phase supply arm.Can see from structure chart, for a phase supply arm power supply, first H bridge chain is connected with the 3rd H bridge chain, and second H bridge chain is connected with the 4th H bridge chain, and so latter two H bridge chain group is in parallel; For b phase supply arm power supply, first H bridge chain is connected with second H bridge chain, and the 3rd H bridge chain is connected with the 4th H bridge chain, and so latter two H bridge chain group is in parallel.This kind of device has following basic characteristics and quantitative relation:

$\left\{\begin{array}{c}{i}_{cb}=-i_1+i_2=i_3-i_4\\ i_{ca}=i_1+i_3=i_2+i_4\\ i_1=i_4,i_2=i_3\end{array}\right.$

Then have:

$\left\{\begin{array}{c}{i}_1=i_4=(i_{ca}-i_{cb})/2\\ i_2=i_3=(i_{ca}+i_{cb})/2\end{array}\right.$

Meanwhile, suppose that first H bridge chain AC output voltage is u ₁, other the like.Then have according to the circuit structure in figure:

$\left\{\begin{array}{c}L\frac{{\mathrm{di}}_1}{dt}+u_1+L\frac{{\mathrm{di}}_4}{dt}+u_4=u_a-u_b\\ L\frac{{\mathrm{di}}_2}{dt}+u_2+L\frac{{\mathrm{di}}_3}{dt}+u_3=u_b+u_a\end{array}\right.$

Wherein L represents the inductance value of single filter inductance, u _aand u _bbe the voltage of two traction power supply arms.According to the output characteristic of this kind of structure, there is u ₁=u ₄, u ₂=u ₃.Then can release:

$\left\{\begin{array}{c}{u}_1=u_4=\frac{u_a-u_b}{2}-L\frac{{\mathrm{di}}_1}{dt}\\ u_2=u_3=\frac{u_b+u_a}{2}-L\frac{{\mathrm{di}}_2}{dt}\end{array}\right.$

Suppose the voltage u of two traction power supply arms _aand u _bas follows:

$\left\{\begin{array}{c}{u}_a=U_{a}sin(\mathrm{\ω}t+{\mathrm{\θ}}_a)\\ u_b=U_{b}sin(\mathrm{\ω}t+{\mathrm{\θ}}_b)\end{array}\right.$

Wherein U _a, U _b, θ _aand θ _bbe respectively amplitude and the phase angle of the voltage of two traction power supply arms.Suppose that the two-phase input current of the direct railway electric energy quality compensator of MMC formula is simultaneously:

$\left\{\begin{array}{c}{i}_{ca}=I_{Pa}sin(\mathrm{\ω}t+{\mathrm{\θ}}_a)+I_{Qa}sin(\mathrm{\ω}t+{\mathrm{\θ}}_a+\mathrm{\π}/2)\\ i_{cb}=I_{Pb}\sin (\mathrm{\ω}t+{\mathrm{\θ}}_b)+I_{Qb}\sin (\mathrm{\ω}t+{\mathrm{\θ}}_b+\mathrm{\π}/2)\end{array}\right.$

Wherein I _pa, I _pb, I _qaand I _qbbe respectively the amplitude of the meritorious of two traction power supply arm input currents and idle component.Simultaneously according to the negative sequence compensation principle of tractive power supply system, adjuster carries out meritorious transfer, if ignore the loss of power device, input and output meritorious equal, is I _pa=-I _pa=I _p.Then have:

P _Sa＝u _a*i _ca＝UI _P[1-cos2(ωt+θ _a)]/2+UI _Qa[-cos(2ωt+2θ _a+π/2)]/2

P _Sb＝u _b*i _cb＝-UI _P[1-cos2(ωt+θ _b)]/2+UI _Qb[-cos(2ωt+2θ _b+π/2)]/2

Thus can in the hope of total instantaneous power be:

P _S＝UI _Pcos2(ωt+θ _b)/2-UI _Pcos2(ωt+θ _a)/2

-UI _Qacos(2ωt+2θ _a+π/2)/2-UI _Qbcos(2ωt+2θ _b+π/2)/2

Can see, total instantaneous power of compensator AC is secondary wave kinetic power, and flip-flop is cancelled out each other, then the H-bridge unit DC voltage of compensator exists secondary voltage ripple.Suppose that DC voltage is u _drepresent DC component, δ and represent amplitude and the phase angle of secondary wave component.The instantaneous gross power of DC bus capacitor is then had to be:

Wherein, N represents the sum of DC voltage, and N=4m, m represent the H-bridge unit number of each chain.Due to the structural particularity of this kind of single-phase AC-AC converter of quadrangle, can produce secondary ripple wave voltage at DC voltage, secondary ripple wave is determined by instantaneous power.Simultaneously known, the size of DC voltage secondary ripple wave is relevant with DC voltage, electric capacity and mains frequency.

Fig. 3 (a)-Fig. 3 (d) is the control block diagram of the direct railway power compensator of MMC formula of the present invention.This control method is applicable to the novel high speed railway bucking-out system of the many level block of dual star topology full-bridge, take hierarchical control as main thought, creative control with circulation solves the problem of dispersing causing capacitance voltage between link set when RTPC is directly used in and compensates V/v transformer tractive power supply system.Control method is divided into three layers: control between system-level control (Fig. 3 (b)), link set to control (Fig. 3 (d)) in (Fig. 3 (c)), link set, unbalanced active power between regulating and controlling chain link between stable, the link set of wherein system-level control holdout device gross energy, this can be avoided the capacitor voltage balance controlling to maintain link set internal power module in the dispersing of capacitance voltage between adjuster link set, link set.Control method proposed by the invention has stronger versatility, and can improve the control performance for RTPC high-speed railway bucking-out system, has good practical value.Here the control method of total system is studied by the method for four bridge arm current detecting compensator.Concrete rate-determining steps is as follows:

1) current i of four H bridge chains is detected ₁, i ₂, i ₃, i ₄, calculate the biphase current i that the direct railway power compensator of MMC formula exports _ca, i _cbwith loop current i _z, as follows:

$\left\{\begin{array}{c}{i}_{cb}=(i_1+i_3+i_2+i_4)/2\\ i_{ca}=(i_2-i_1+i_3-i_4)/2\end{array}\right.$

$i_z=\frac{i_4+i_3-i_2-i_1}{4}$

2) detect the DC voltage of all H-bridge unit of MMC formula direct railway power compensator, wherein the capacitance voltage of y power model of an xth chain link is u _cxy, try to achieve RTPC module voltage summation u _c ^Σ, as follows:

$\left\{\begin{array}{cc}\begin{array}{c}{u}_{cx}^{\Σ}=\Σu_{cxy}\\ u_c^{\Σ}=\Σ\Σu_{cxy}\end{array}& x=1,2,3,4;y=1,\mathrm{2...}Y;\end{array}\right.$

Y is the H-bridge unit quantity of each chain link; By u _c ^Σwith given with reference to u _refdifference send into PI controller, controller exports the amplitude Δ I being active current _dc, obtain a phase of DSBC-RTPC and b phase DC voltage conditioning signal after being multiplied by the synchronizing signal of two supply arms, and the negative sequence compensation current-order i tried to achieve with detection _ca ^*, i _cb ^*superposition, obtains the combination current instruction i of RTPC _ar, i _br; Two-phase output current inner ring adopts PR to control, and controller exports the overall modulation signal m obtaining two chain groups _a, m _b;

3) in order to realize the voltage balancing control between two chain groups, an inner circulation is injected in RTPC inside; Rational circulation voltage instruction u is tried to achieve according to constraints _zref, after try to achieve the circulation instruction i that need inject _zref, wherein constraints is as follows:

$u_{zref}{i}_{zref}=\frac{U_s{I}_Q}{4}sin({\mathrm{\θ}}_a-{\mathrm{\θ}}_b)$

U _a, u _brepresent the voltage of a, b two-phase traction power supply arm; I _lim-, I _lim+the limit value of converter output current;

4) try to achieve link set 1 voltage sum with the capacitance voltage sum of link set 2 as follows:

$\left\{\begin{array}{c}{u}_{c14}^{\Σ}=u_{c1}^{\Σ}+u_{c4}^{\Σ}\\ u_{c23}^{\Σ}=u_{c2}^{\Σ}+u_{c3}^{\Σ}\end{array}\right.$

By its difference the corrected signal i injecting circulation is obtained after sending into P controller _zref2, by itself and i _zrefcomprehensive circulation instruction i is obtained after superposition _zr; By comprehensive circulation instruction i _zrwith detection ring flow valuve i _zsubtract each other, adopt PI link to realize regulating the rear output-Δ u of process _zwith Δ u _z, with circulation control command u _zrefaddition can obtain chain link 1,4 and chain link 2,3 liang group chain link circulation control voltage reference u _z1ref, u _z2ref, have

$\left\{\begin{array}{c}{u}_{z1ref}={\mathrm{\Δu}}_z+u_{zref}\\ u_{z2ref}=-{\mathrm{\Δu}}_z+u_{zref}\end{array}\right.$

By u _z1ref, u _z2refsentence link set voltage respectively with after modulation signal m between link set _z1, m _z2;

5) two groups of chain link capacitance voltage mean value u are asked for _cav14, u _cav23, have:

$\left\{\begin{array}{c}{u}_{cav14}=(u_{c1}^{\Σ}+u_{c4}^{\Σ})/2Y\\ u_{cav23}=(u_{c2}^{\Σ}+u_{c3}^{\Σ})/2Y\end{array}\right.$

The capacitor voltage balance of link set internal power module is realized, by each power model capacitance voltage u by phase-shifting carrier wave modulation _cxypoor with corresponding mean value, error is multiplied by this chain link current i after P controller _xobtain voltage balancing control signal delta m in link set _xy;

6) output of comprehensive each layer control, can send into the modulation signal m of an xth chain link y power model _xyfor:

$\left\{\begin{array}{c}{m}_{1y}=m_b-m_a+m_{z1}+{\mathrm{\Δm}}_{1y}\\ m_{2y}=m_b+m_a-m_{z2}+{\mathrm{\Δm}}_{2y}\\ m_{3y}=m_b+m_a+m_{z2}+{\mathrm{\Δm}}_{3y}\\ m_{4y}=m_b-m_a-m_{z1}+{\mathrm{\Δm}}_{4y}\end{array}\right.$

7) modulation signal is sent into phase-shift PWM unit and obtain switching drive signal, switching drive signal drives the power switch pipe of corresponding H-bridge unit to make it to export the electric current and voltage expected.

Claims (5)

1. the hierarchical control method of a direct ac-ac type railway traction power adjuster, be applicable to the high-speed railway bucking-out system of the many level block of dual star topology full-bridge, described high-speed railway bucking-out system comprises MMC formula rail traction power governor, MMC formula rail traction power governor comprises four limits, and four limits connect into quadrangle; Each limit comprises a H bridge chain and a filter inductance be connected with this H bridge chain; H bridge chain comprises the H-bridge unit of multiple series connection; Four intersection points of quadrangle are divided into two groups by diagonal, and two groups of intersection points are respectively connected with a traction power supply arm respectively; It is characterized in that, the method comprises the following steps:

1) current i of four H bridge chains is detected ₁, i ₂, i ₃, i ₄, calculate the biphase current i that high-speed railway bucking-out system exports _ca, i _cbwith loop current i _z;

2) detect the DC voltage of all H-bridge unit of high-speed railway bucking-out system, wherein the capacitance voltage of y power model of an xth chain link is u _cxy, try to achieve rail traction power governor all H-bridge unit voltage summation u _c ^Σ, by u _c ^Σwith given reference value u _refdifference send into PI controller, PI controller, export the amplitude Δ I being active current _dc, by Δ I _dcthe a phase of RTPC and b phase DC voltage conditioning signal is obtained, the negative sequence compensation current-order i that a phase is tried to achieve with detection respectively with b phase DC voltage conditioning signal after being multiplied by the synchronizing signal of two supply arms _ca ^*, i _cb ^*superposition, obtains the combination current instruction i of RTPC _ar, i _br; Two-phase output current inner ring adopts PR to control, and obtains the overall modulation signal m of two groups of chain links _a, m _b;

3) rational circulation voltage instruction u is tried to achieve according to constraints _zref, then try to achieve the circulation instruction i that need inject _zref, wherein constraints is as follows:

Wherein, $\left\{\begin{array}{c}{u}_{c14}^{\mathrm{\Σ}}=u_{c1}^{\mathrm{\Σ}}+u_{c4}^{\mathrm{\Σ}}\\ u_{c23}^{\mathrm{\Σ}}=u_{c2}^{\mathrm{\Σ}}+u_{c3}^{\mathrm{\Σ}}\end{array}\right.;$ be respectively the voltage of four H bridge chains;

4) by difference the corrected signal i injecting circulation is obtained after sending into P controller _zref2, by i _zref2with i _zrefcomprehensive circulation instruction i is obtained after superposition _zr; By comprehensive circulation instruction i _zrwith detection ring flow valuve i _zsubtract each other, the value after subtracting each other adopts PI link to regulate the rear output-Δ u of process _zwith Δ u _z, general-Δ u _zwith Δ u _zrespectively with circulation control command u _zrefbe added, obtain chain link 1,4 and chain link 2,3 liang group chain link circulation control voltage reference u _z1ref, u _z2ref: $\left\{\begin{array}{c}{u}_{z1ref}={\mathrm{\Δu}}_z+u_{zref}\\ u_{z2ref}=-{\mathrm{\Δu}}_z+u_{zref}\end{array}\right.;$ By u _z1ref, u _z2refrespectively divided by two link set voltages obtain modulation signal m between link set _z1, m _z2;

5) the capacitance voltage mean value u of chain link 1,4 and chain link 2,3 is asked for _cav14, u _cav23;

6) output of comprehensive each layer control, obtains the modulation signal m sending into an xth chain link y power model _xy;

7) modulation signal is sent into phase-shift PWM unit and obtain switching drive signal, switching drive signal drives the power switch pipe of corresponding H-bridge unit, makes it to export the electric current and voltage expected.

2. method according to claim 1, is characterized in that, i _ca, i _cb, i _zcomputing formula as follows:

$\left\{\begin{array}{c}{i}_{cb}=(i_1+i_3+i_2+i_4)/2\\ i_{ca}=(i_2-i_1+i_3-i_4)/2\end{array}\right.;$

$i_z=\frac{i_4+i_3-i_2-i_1}{4}.$

3. method according to claim 2, is characterized in that, u _c ^Σcomputing formula as follows:

$\left\{\begin{array}{c}{u}_{cx}^{\mathrm{\Σ}}={\mathrm{\Σu}}_{cxy}\\ u_c^{\mathrm{\Σ}}={\mathrm{\Σ\Σu}}_{cxy}\end{array}\right.,x=1,2,3,4;y=1,2...Y;$

Wherein, Y is the H-bridge unit quantity of each chain link.

4. method according to claim 3, is characterized in that, u _cav14, u _cav23computing formula be:

$\left\{\begin{array}{c}{u}_{cav14}=(u_{c1}^{\mathrm{\Σ}}+u_{c4}^{\mathrm{\Σ}})/2Y\\ u_{cav23}=\left(u_{c2}^{\mathrm{\Σ}}+u_{c3}^{\mathrm{\Σ}}\right)/2Y\end{array}\right..$

5. method according to claim 4, is characterized in that, modulation signal m _xycomputing formula be:

$\left\{\begin{array}{c}{m}_{1y}=m_b-m_a+m_{z1}+{\mathrm{\Δm}}_{1y}\\ m_{2y}=m_b+m_a-m_{z2}+{\mathrm{\Δm}}_{2y}\\ m_{3y}=m_b+m_a+m_{z2}+{\mathrm{\Δm}}_{3y}\\ m_{4y}=m_b-m_a-m_{z1}+{\mathrm{\Δm}}_{4y}\end{array}\right..$