CN105024574A - MMC slave module capacitance voltage balance control method suitable for carrier phase shifting modulation - Google Patents

Abstract

The invention provides an MMC slave module capacitance voltage balance control method suitable for carrier phase shifting modulation. According to the invention, pulses in a carrier period are divided into first half period pulses and second half period pulses based on traditional carrier phase shifting modulation so that a ranking rule of pulse duty ratio in half a carrier period can be obtained. Dynamic ranking is performed on all slave module capacitance voltage in each half carrier period. Pulses in the half carrier periods are reallocated according to the magnitude of the capacitance voltage, so that dynamic balance of slave module capacitance voltage is realized. According to the invention, slave module capacitance voltage balance can be realized without changing prior modulation waves and the modulation effect totally equals to that carrier phase shifting modulation. No external loop current is generated at the same time of realizing the slave module capacitance voltage balance, so that output current quality is ensured.

Description

Be applicable to the MMC submodule capacitor voltage balance control method of phase-shifting carrier wave modulation

Technical field

The present invention relates to flexible DC power transmission in electric power system, electric and electronic technical field, particularly, relate to a kind of MMC submodule capacitor voltage balance control method.

Background technology

Modular multilevel converter (modular multilevel converter, MMC) flexible direct-current transmission field is widely used in, it is a kind of converters being applicable to high-power application, extensibility is strong, in submodule, the voltage stress of power switch is little, there is more level number, export the quality of power supply higher.The control of submodule capacitor voltage balance is one of MMC key control technology, and MMC needs to adopt suitable submodule capacitor voltage balance control method that each submodule capacitor voltage is consistent, and avoids submodule capacitor voltage to disperse.

The less MMC of number of modules often adopts phase-shifting carrier wave modulator approach, can obtain higher equivalent switching frequency and less harmonic wave, each submodule operating state relative equilibrium.

The submodule capacitor voltage balance control technology being applicable to this modulator approach at present can be divided into two classes:

1, modulating wave correction

The size of each submodule capacitor voltage and bridge arm current direction in the method sampling brachium pontis, adopt specific algorithm in the modulating wave of each submodule, add certain correction component, realize the capacitor voltage balance of each submodule.The defect of the method is: revise component and make former modulating wave produce distortion, in output voltage, electric current, create imperfect component, have impact on the quality that MMC exports electric energy; On the other hand, the method needs to carry out a large amount of real-time calculating, higher to controller hardware resource requirement.

2, carrier phase correction

The carrier wave of the method adopts unequal phase shifting angle, and sorts to submodule capacitor voltage, and the size according to submodule capacitor voltage distributes the pulse produced by different carrier, realizes submodule capacitor voltage balance.The defect of the method is: the carrier wave of unequal phase shift forms circulation in brachium pontis, in the DC side electric current that this circulation can be embodied in MMC or ac-side current, have impact on MMC output current quality.

Through retrieval, " the modularization multi-level converter capacitor voltage balance of employing phase-shifting carrier wave technology controls " (Proceedings of the CSEE, 31st volume, 21st phase, 2011), controlling to realize capacitor voltage balance in the document, devising the modulating wave of multiple controller to submodule and revising; The distortion that revised modulating wave produces can export and have an impact MMC DC side, AC, makes that current harmonics becomes large, circulation increases; Each submodule needs multiple independent control, and algorithm is comparatively complicated, when MMC submodule number increases, needs to carry out a large amount of real-time calculating, implements tool and acquire a certain degree of difficulty." the modularization multi-level converter capacitor voltage balance adopting phase-shifting carrier wave to modulate controls " (Proceedings of the CSEE, 32nd volume, 9th phase, 2012), the document introduces the additional reference voltages with bridge arm current phase place on submodule reference voltage, be still the object reaching balanced capacitance voltage by revising modulating wave in essence, the distortion that revised modulating wave produces can export and have an impact MMC DC side, AC, make that current harmonics becomes large, circulation increases, this is the intrinsic problem of these class methods." A Control Method for Voltage Balancing in Modular MultilevelConverters " (IEEE transactions on power electronics, vol.29, no.1, 2014), in the phase-shifting carrier wave modulation that the document adopts, each phase-shifting carrier wave angle is not etc., the circulation of a frequency higher than carrier wave is created in brachium pontis, the discharge and recharge of this circulation to electric capacity is utilized to realize the equilibrium of capacitance voltage, the defect of the method is in the direct current that brachium pontis medium-high frequency circulation can be embodied in MMC or alternating current, current harmonics is made to become large, it is the problem that this method is difficult to avoid.

Summary of the invention

For defect of the prior art, the object of this invention is to provide a kind of MMC submodule capacitor voltage balance control method being applicable to phase-shifting carrier wave modulation, the method realizes submodule capacitor voltage balance under the condition not changing original modulating wave, and modulation effect realizes the complete equivalence of modulating with phase-shifting carrier wave; While realizing submodule capacitor voltage balance, do not produce extra circulation, ensure output current quality.

For realizing above object, the invention provides a kind of MMC submodule capacitor voltage balance control method being applicable to phase-shifting carrier wave modulation, the method is on the basis of convention carrier phase shift modulation, pulse in a carrier cycle is split as first half recurrent pulse and rear half recurrent pulse, obtain the sequence rule of the pulse duty factor in half carrier cycle, every half carrier cycle carries out a dynamic order to all submodule capacitor voltage, distribution is re-started according to the pulse in large young pathbreaker half carrier cycle of capacitance voltage, realize the dynamic equilibrium of submodule capacitor voltage,

Described method comprises the steps:

Step 1: the pulse duty factor in half carrier cycle is sorted;

Step 2: carry out sampling and sorting every half sampling period antithetical phrase module capacitance magnitude of voltage;

Step 3: carry out pulse distribution according to bridge arm current direction and submodule capacitor voltage ranking results.

Preferably, in step 1, concrete:

Choose arbitrarily a carrier wave as reference carrier, be designated as C ₁, delayed successively N-1 the carrier wave of phase place is designated as C ₂, C ₃c _n, the pulse produced by N number of carrier wave is designated as P respectively ₁, P ₂p _n; With carrier wave C ₁region between two peak values is defined as one-period interval, carrier wave C ₁the interval being reduced to minimum value by peak value is that front half carrier cycle is interval, carrier wave C ₁the interval being increased to peak value by minimum value is that rear half carrier cycle is interval; Because frequency of modulated wave is far below carrier frequency, can think that modulating wave is approximate constant in one-period interval;

Modulate rule by phase-shifting carrier wave to derive at reference carrier C ₁the sequence rule that each pulse duty factor in front half carrier cycle and in rear half carrier cycle is descending, can be divided into four kinds of situations according to the concrete numerical value of N:

1.N is odd number, for odd number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

$P_{\frac{3N+5}{4}}\≥P_{\frac{3N+1}{4}}\≥P_{\frac{3N+9}{4}}\≥\mathrm{...}\≥P_{\frac{N+3}{2}}=P_{\frac{N+1}{2}}\≥P_1\≥\mathrm{...}\≥P_{\frac{N-1}{4}}\≥P_{\frac{N+7}{4}}\≥P_{\frac{N+3}{4}}$

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

$P_{\frac{N+3}{4}}\≥P_{\frac{N+7}{4}}\≥P_{\frac{N-1}{4}}\≥\mathrm{...}\≥P_{\frac{N+1}{2}}=P_{\frac{N+3}{2}}\≥P_1\≥\mathrm{...}\≥P_{\frac{3N+9}{4}}\≥P_{\frac{3N+1}{4}}\≥P_{\frac{3N+5}{4}};$

2.N is odd number, for even number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

$P_{\frac{3N+3}{4}}\≥P_{\frac{3N+7}{4}}\≥P_{\frac{3N-1}{4}}\≥P_{\frac{3N+11}{4}}\≥\mathrm{...}\≥P_{\frac{N+3}{2}}=P_{\frac{N+1}{2}}\≥P_1\≥\mathrm{...}\≥P_{\frac{N-3}{4}}\≥P_{\frac{N+9}{4}}\≥P_{\frac{N+1}{4}}\≥P_{\frac{N+5}{4}}$

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

$P_{\frac{N+5}{4}}\≥P_{\frac{N+1}{4}}\≥P_{\frac{N+9}{4}}\≥P_{\frac{N-3}{4}}\≥\mathrm{...}\≥P_{\frac{N+1}{2}}=P_{\frac{N+3}{2}}\≥P_1\≥\mathrm{...}\≥P_{\frac{3N+11}{4}}\≥P_{\frac{3N-1}{4}}\≥P_{\frac{3N+7}{4}}\≥P_{\frac{3N+3}{4}};$

3.N is even number, for even number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

$P_{\frac{3N+4}{4}}\≥P_{\frac{3N+8}{4}}\≥P_{\frac{3N}{4}}\≥\mathrm{...}\≥P_{\frac{N+2}{2}}=P_1\≥\mathrm{...}\≥P_{\frac{N}{4}}\≥P_{\frac{N+8}{4}}\≥P_{\frac{N+4}{4}}$

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

$P_{\frac{N+4}{4}}\≥P_{\frac{N}{4}}\≥P_{\frac{N+8}{4}}\≥\mathrm{...}\≥P_{\frac{N+2}{2}}=P_1\≥\mathrm{...}\≥P_{\frac{3N+8}{4}}\≥P_{\frac{3N}{4}}\≥P_{\frac{3N+4}{4}};$

4.N is even number, for odd number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

$P_{\frac{3N+2}{4}}\≥P_{\frac{3N+6}{4}}\≥P_{\frac{3N-2}{4}}=P_{\frac{3N+10}{4}}\≥\mathrm{...}\≥P_{\frac{N+2}{2}}=P_1\≥P_{\frac{N-2}{4}}=P_{\frac{N+10}{4}}\≥\mathrm{...}\≥P_{\frac{N+2}{4}}=P_{\frac{N+6}{4}}$

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

$P_{\frac{N+2}{4}}\≥P_{\frac{N+6}{4}}\≥P_{\frac{N-2}{4}}=P_{\frac{N+10}{4}}\≥\mathrm{...}\≥P_{\frac{N+2}{2}}=P_1\≥P_{\frac{3N-2}{4}}=P_{\frac{3N+10}{4}}\≥P_{\frac{3N+2}{4}}=P_{\frac{3N+6}{4}};$

Once number of modules N, reference carrier C ₁determine, then above ranking results is determined completely, belongs to static ordering.

Preferably, in step 2, concrete:

Respectively at reference carrier C ₁maximum and minimum value place submodule capacitor voltage is sampled, line ordering of going forward side by side.

Preferably, in step 3, concrete:

Sample to bridge arm current, if bridge arm current is charged to submodule module capacitance, then capacitance voltage N number of module is from small to large distributed in duty ratio N number of pulse from big to small successively; If bridge arm current antithetical phrase module capacitance is discharged, then capacitance voltage N number of module is from big to small distributed in duty ratio N number of pulse from big to small successively.

Compared with prior art, the present invention has following beneficial effect:

1) submodule capacitor voltage fast convergence rate, portfolio effect are good;

2) only need carry out a minor sort to submodule capacitor voltage every half carrier cycle, algorithm is simple, is convenient to realize;

3) modulation effect is equivalent to phase-shifting carrier wave modulation completely, and output voltage does not produce any distortion, can not produce extra brachium pontis circulation, exports the quality of power supply better.

Accompanying drawing explanation

By reading the detailed description done non-limiting example with reference to the following drawings, other features, objects and advantages of the present invention will become more obvious:

Fig. 1 is the MMC structural representation of the employing half-bridge structure submodule of one embodiment of the invention;

Fig. 2 is convention carrier phase shift modulation schematic diagram;

Fig. 3 is the half carrier cycle pulse duty factor sequence schematic diagram of one embodiment of the invention;

Fig. 4 is the pulse generate flow chart of one embodiment of the invention;

Fig. 5 is the MMC submodule capacitor voltage balance simulation result figure of one embodiment of the invention.

Embodiment

Below in conjunction with specific embodiment, the present invention is described in detail.Following examples will contribute to those skilled in the art and understand the present invention further, but not limit the present invention in any form.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, some distortion and improvement can also be made.These all belong to protection scope of the present invention.

As shown in Figure 1, for adopting the MMC of half-bridge structure submodule, be illustrated in figure 2 convention carrier phase shift modulation schematic diagram, if have N number of submodule in MMC brachium pontis, then should there is N number of triangular carrier mutually, exporting pulse when modulating wave is larger than carrier wave is 1, and the upper pipe representing half-bridge submodule is opened, lower pipe turns off, and submodule electric capacity is in input state; Exporting pulse when modulating wave is less than carrier wave is 0, and the upper pipe representing half-bridge submodule turns off, lower pipe is open-minded, and submodule electric capacity is in excision state.

The present embodiment provides a kind of MMC submodule capacitor voltage balance control method being applicable to phase-shifting carrier wave modulation, the method adopts MMC structure as shown in Figure 1, its rated power 30MW, there are 20 submodules in brachium pontis, the rated voltage of each module capacitance is 2500V, carrier frequency is 200Hz, DC voltage is 50000V, exchange that side line voltage effective value is 15000V, frequency is 50Hz.Described method is on the basis of convention carrier phase shift modulation, pulse in a carrier cycle is split as first half recurrent pulse and rear half recurrent pulse, as shown in Figure 3, obtain the sequence rule of the pulse duty factor in half carrier cycle, every half carrier cycle carries out a dynamic order to all submodule capacitor voltage, re-start distribution according to the pulse in large young pathbreaker half carrier cycle of capacitance voltage, realize the dynamic equilibrium of submodule capacitor voltage.

As shown in Figure 4, described method specifically comprises the steps:

Step 1, the pulse duty factor in half carrier cycle to be sorted, concrete:

Choose phase shifting angle be the carrier wave of 0 as reference carrier, be designated as C ₁, delayed successively 19 carrier waves of phase place are designated as C ₂, C ₃c ₂₀, the pulse produced by these 20 carrier waves is designated as P respectively ₁, P ₂p ₂₀; Then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

P ₁₆≥P ₁₇＝P ₁₅≥P ₁₈＝P ₁₄≥P ₁₉＝P ₁₃≥P ₂₀＝P ₁₂≥P ₁₁＝P ₁

≥P ₁₀＝P ₂≥P ₉＝P ₃≥P ₈＝P ₄≥P ₅＝P ₇≥P ₆

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

P ₆≥P ₇＝P ₅≥P ₈＝P ₄≥P ₉＝P ₃≥P ₁₀＝P ₂≥P ₁₁＝P ₁

≥P ₂₀＝P ₁₂≥P ₁₉＝P ₁₃≥P ₁₈＝P ₁₄≥P ₁₅＝P ₁₇≥P ₁₆

Step 2: carry out sampling and sorting every half sampling period antithetical phrase module capacitance magnitude of voltage

At carrier wave C ₁maximum and minimum value place respectively capacitance voltage is sampled, line ordering of going forward side by side.

Step 3: carry out pulse distribution according to bridge arm current direction and submodule capacitor voltage ranking results

Bridge arm current is sampled, and distribute according to the sense of current and capacitance voltage ranking results paired pulses, as shown in Figure 4, if bridge arm current is charged to submodule module capacitance, then capacitance voltage 20 modules are from small to large distributed in duty ratio 20 pulses from big to small successively; If bridge arm current antithetical phrase module capacitance is discharged, then capacitance voltage 20 modules are from big to small distributed in duty ratio 20 pulses from big to small successively.Emulate in RTLAB real-time simulation platform, under rated condition in A phase each module voltage of brachium pontis as shown in Figure 5, the program obtains good capacitor voltage balance effect.

Submodule capacitor voltage fast convergence rate of the present invention, portfolio effect are good; Only need carry out a minor sort to submodule capacitor voltage every half carrier cycle, method is simple, is convenient to realize; Modulation effect of the present invention is equivalent to phase-shifting carrier wave modulation completely, and output voltage does not produce any distortion, can not produce extra brachium pontis circulation, exports the quality of power supply better.

Above specific embodiments of the invention are described.It is to be appreciated that the present invention is not limited to above-mentioned particular implementation, those skilled in the art can make various distortion or amendment within the scope of the claims, and this does not affect flesh and blood of the present invention.

Claims (4)

1. one kind is applicable to the MMC submodule capacitor voltage balance control method of phase-shifting carrier wave modulation, it is characterized in that, the method is on the basis of convention carrier phase shift modulation, pulse in a carrier cycle is split as first half recurrent pulse and rear half recurrent pulse, obtain the sequence rule of the pulse duty factor in half carrier cycle, every half carrier cycle carries out a dynamic order to all submodule capacitor voltage, re-start distribution according to the pulse in large young pathbreaker half carrier cycle of capacitance voltage, realize the dynamic equilibrium of submodule capacitor voltage.

2. a kind of MMC submodule capacitor voltage balance control method being applicable to phase-shifting carrier wave modulation according to claim 1, it is characterized in that, described method comprises the steps:

Step S1: the pulse duty factor in half carrier cycle is sorted;

Choose arbitrarily a carrier wave as reference carrier, be designated as C ₁, delayed successively N-1 the carrier wave of phase place is designated as C ₂, C ₃c _n, the pulse produced by N number of carrier wave is designated as P respectively ₁, P ₂p _n; With carrier wave C ₁region between two peak values is defined as one-period interval, carrier wave C ₁the interval being reduced to minimum value by peak value is that front half carrier cycle is interval, carrier wave C ₁the interval being increased to peak value by minimum value is that rear half carrier cycle is interval;

Modulate rule by phase-shifting carrier wave to release: at reference carrier C ₁the sequence rule that each pulse duty factor in front half carrier cycle and in rear half carrier cycle is descending, is divided into four kinds of situations according to the concrete numerical value of N:

1) N is odd number, for odd number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

2) N is odd number, for even number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

3) N is even number, for even number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

4) N is even number, for odd number, then

C ₁the order that in front half carrier cycle, pulse duty factor is descending is:

C ₁the order that in rear half carrier cycle, pulse duty factor is descending is:

Once number of modules N, reference carrier C ₁determine, then above ranking results is determined completely, belongs to static ordering;

Step S2: carry out sampling and sorting every half sampling period antithetical phrase module capacitance magnitude of voltage;

Step S3: carry out pulse distribution according to bridge arm current direction and submodule capacitor voltage value ranking results.

3. a kind of MMC submodule capacitor voltage balance control method being applicable to phase-shifting carrier wave modulation according to claim 2, is characterized in that, in step S2, be specially: respectively at reference carrier C ₁maximum and minimum value place submodule capacitor voltage is sampled, line ordering of going forward side by side.

4. a kind of MMC submodule capacitor voltage balance control method being applicable to phase-shifting carrier wave modulation according to claim 2, it is characterized in that, in step S3, be specially: bridge arm current is sampled, if bridge arm current is charged to submodule electric capacity, then capacitance voltage N number of module is from small to large distributed in duty ratio N number of pulse from big to small successively; If bridge arm current antithetical phrase module capacitance is discharged, then capacitance voltage N number of module is from big to small distributed in duty ratio N number of pulse from big to small successively.