CN103199729A - Modularization multi-level converter submodule grouping stair wave modulation method - Google Patents

Abstract

The invention provides a modularization multi-level converter submodule grouping stair wave modulation method. The method comprises the steps of dividing submodules in a commutation chain into N submodule groups, rounding reference voltages of the submodule groups to obtain rounded reference stair wave voltages Vstair_wave, distributing trigger pulses to submodules inside the submodule groups, and carrying out voltage-sharing among the submodule groups. According to the modularization multi-level converter submodule grouping step wave modulation method, the submodules are divided into the N submodule groups, each submodule group is taken as a controllable voltage source, stair wave modulation is adopted in the submodule groups, the N submodule groups adopt rounding correction, and therefore a purpose similar to carrier phase-shifting is achieved; and due to the fact that voltage stability control is carried out among the submodule groups by means of a proper voltage-sharing control method, difficulty of the stair wave modulation is reduced, and requirements of the modulation algorithm and the voltage-sharing control algorithm for software and hardware are greatly reduced.

Description

A kind of modular multilevel current transformer submodule grouping staircase waveform modulator approach

Technical field

The invention belongs to electric and electronic technical field, be specifically related to a kind of modular multilevel current transformer submodule grouping staircase waveform modulator approach.

Background technology

Traditional adopt the mode of phase control rectifier based on the DC transmission system of thyristor, three-phase alternating current is become the direct currents of six pulsation or 12 pulsation, but this DC transmission system need absorb a large amount of reactive powers, is especially exchanging under the side failure condition.DC transmission system (VSC-HVDC) based on voltage source converter is equivalent to a controllable voltage source, can four quadrant running, realize exchanging the meritorious idle independent regulation of side, and this is significant to constituting direct current network.Because the modular multilevel current transformer adopts modularized design, comprise a big electric capacity in each submodule voltage is carried out clamper, its electric pressure and capacity can be expanded by the series connection of submodule, and therefore this current transformer is a kind of rising current transformer.But when this current transformer is applied to the occasion of high-voltage large-capacity, need the submodule number of series connection very many, this makes the distribution of trigger impulse become difficult, it is difficult that the realization of electrical secondary system also becomes, or even infeasible, therefore, when the modular multilevel current transformer is applied to the occasion of high-voltage large-capacity, be necessary to rethink numerous submodules is divided into groups to control, to reduce the difficulty that trigger impulse distributes, also make electrical secondary system be more prone to realize.

Summary of the invention

In order to overcome above-mentioned the deficiencies in the prior art, the invention provides a kind of modular multilevel current transformer submodule grouping staircase waveform modulator approach, submodule is divided into N submodule group, each submodule group is considered as a controllable voltage source, adopt the staircase waveform modulation in the submodule group, N submodule group adopts and rounds correction, can reach the purpose that is similar to phase-shifting carrier wave, adopt appropriate Pressure and Control mode to carry out voltage stabilizing control between the submodule group, simplify the complexity of staircase waveform modulation, greatly reduced modulation algorithm and Pressure and Control algorithm to the requirement of software and hardware.

In order to realize the foregoing invention purpose, the present invention takes following technical scheme:

A kind of modular multilevel current transformer submodule grouping staircase waveform modulator approach is provided, said method comprising the steps of:

Step 1: the submodule in the change of current chain is divided into N submodule group;

Step 2: the reference voltage of submodule group is rounded the reference staircase voltage V after obtaining rounding _{Stair_wave}

Step 3: distribute trigger impulse to the submodule of submodule group inside;

Step 4: all press between the submodule group.

In the described step 1, the submodule group is controllable voltage source, and the control signal of controllable voltage source is the reference voltage V of submodule group _Ref

In the described step 2, the reference staircase voltage V after rounding _{Stair_wave}Be expressed as

$V_{\mathrm{stair}\_\mathrm{wave}}=\mathrm{floor}(\frac{V_{\mathrm{ref}}}{V_{\mathrm{sm}}}+{\mathrm{\δ}}_k)---\left(1\right)$

Wherein, V _RefBe the reference voltage of submodule group, V _SmBe the average voltage of submodule group, the floor function is the bracket function of negative infinity, δ _kBe the correction that rounds of submodule group, δ _k=(2k-1)/2N+m _k, k=1 wherein, 2 ... N; m _kBe integer, and

The submodule group round correction δ _kMean value be 0.5, that is:

Described step 3 may further comprise the steps:

Step 3-1: judge that the brachium pontis sense of current is positive direction or negative direction;

Step 3-2: submodule F.F. row is dropped into or excision according to the brachium pontis sense of current.

Step 3-3: judge the submodule number dropped into and the submodule number that needs to drop into whether consistent, if inconsistent, then need to excise or drop into the submodule of the submodule difference number of the submodule that dropped into and needs input, make the two unanimity again.

Among the described step 3-2, if the brachium pontis sense of current is positive direction, then the brachium pontis electric current charges to the electric capacity of the submodule that dropped into, and submodule is dropped into or the excision process is:

A) if need to drop into submodule, then find out and do not drop into the lower submodule of voltage in the submodule, with its input;

B) if need the excision submodule, then find out and do not drop into the higher submodule of voltage in the submodule, with its excision.

In the process that the brachium pontis electric current charges to the electric capacity of the submodule that dropped into, if the higher submodule of capacitance voltage is than the high u of the voltage that does not drop into the submodule that capacitance voltage is lower in the submodule in the submodule that has dropped into, the then higher submodule excision of capacitance voltage in the submodule that will drop into will not drop into the submodule that capacitance voltage is lower in the submodule simultaneously and will drop into.

Among the described step 3-2, if the brachium pontis sense of current is negative direction, then the brachium pontis electric current discharges to the electric capacity of the submodule that dropped into, and submodule is dropped into or the excision process is:

A) if need to drop into submodule, then find out and do not drop into the higher submodule of voltage in the submodule, with its input;

B) if need the excision submodule, then find out and do not drop into the lower submodule of voltage in the submodule, with its excision.

In the process that the brachium pontis electric current discharges to the electric capacity of the submodule that dropped into, if the submodule that voltage is lower in the submodule that has dropped into is than the low u of the capacitance voltage that does not drop into the higher submodule of voltage in the submodule, the submodule excision that then capacitance voltage is lower in the submodule that will drop into will not drop into the higher submodule input of capacitance voltage in the submodule simultaneously.

In the described step 4, all press according to following Pressure and Control mode between the submodule group:

Mode 1:N submodule group round correction δ _kBetween N submodule group, recycle, unbalanced with the voltage of eliminating the submodule group that causes owing to the difference that rounds correction;

Mode 2: to the average voltage V of submodule group _SmSort, when the modular multilevel current transformer is operated in inverter mode, the submodule group rounded correction δ _kCompose successively from big to small and give voltage submodule group from small to large, make the low submodule group charging of capacitor averaging voltage more; When the modular multilevel current transformer is operated in rectification state, the submodule group rounded correction δ _kCompose successively from big to small and give voltage submodule group from big to small, the submodule group discharge that capacitor averaging voltage is high is more;

Mode 3: according to the average voltage V of submodule group _SmDifference with change of current chain average voltage, stack DC component or alternating current component in the voltage modulated ripple of submodule group, the submodule group that average voltage is higher is discharged, the submodule group that average voltage is lower is charged, so that submodule group electric voltage equalization.

Compared with prior art, beneficial effect of the present invention is:

1, the submodule group is considered as independently controllable voltage source, the inner staircase waveform that adopts of submodule group is modulated, and the coupling between the submodule group reduces greatly, therefore greatly reduces modulation algorithm and control algolithm to the requirement of software and hardware;

2, adopt the different corrections that rounds between the submodule group, can reach the purpose that is similar to phase-shifting carrier wave, the harmonic wave of submodule group is cancelled out each other, thereby the voltage waveform that makes the output of change of current chain is more close to sine wave;

3, adopt appropriate Pressure and Control mode between the submodule, the voltage between the submodule group is kept in balance, thereby can guarantee that current transformer can normally move.

Description of drawings

Fig. 1 is modular multilevel current transformer submodule grouping staircase waveform modulator approach schematic diagram;

Fig. 2 is modularization multi-level converter structure chart in the modular multilevel current transformer submodule grouping staircase waveform modulator approach.

Embodiment

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

A kind of modular multilevel current transformer submodule grouping staircase waveform modulator approach is provided, said method comprising the steps of:

Step 1: the submodule in the change of current chain is divided into N submodule group;

Step 2: the reference voltage of submodule group is rounded the reference staircase voltage V after obtaining rounding _{Stair_wave}

Step 3: distribute trigger impulse to the submodule of submodule group inside;

Step 4: all press between the submodule group.

In the described step 1, the submodule group is controllable voltage source, and the control signal of controllable voltage source is the reference voltage V of submodule group _Ref

In the described step 2, the reference staircase voltage after rounding _{Vstair_wave}Be expressed as

$V_{\mathrm{stair}\_\mathrm{wave}}=\mathrm{floor}(\frac{V_{\mathrm{ref}}}{V_{\mathrm{sm}}}+{\mathrm{\δ}}_k)---\left(1\right)$

Wherein, V _RefBe the reference voltage of submodule group, V _SmBe the average voltage of submodule group, the floor function is the bracket function of negative infinity, δ _kBe the correction that rounds of submodule group, δ _k=(2k-1)/2N+m _k, k=1 wherein, 2 ... N; m _kBe integer, and

The submodule group round correction δ _kMean value be 0.5, that is:

Described step 3 may further comprise the steps:

Step 3-1: judge that the brachium pontis sense of current is positive direction or negative direction;

Step 3-2: submodule F.F. row is dropped into or excision according to the brachium pontis sense of current.

Step 3-3: judge the submodule number dropped into and the submodule number that needs to drop into whether consistent, if inconsistent, then need to excise or drop into the submodule of the submodule difference number of the submodule that dropped into and needs input, make the two unanimity again.

Among the described step 3-2, if the brachium pontis sense of current is positive direction, then the brachium pontis electric current charges to the electric capacity of the submodule that dropped into, and submodule is dropped into or the excision process is:

A) if need to drop into submodule, then find out and do not drop into the lower submodule of voltage in the submodule, with its input;

B) if need the excision submodule, then find out and do not drop into the higher submodule of voltage in the submodule, with its excision.

In the process that the brachium pontis electric current charges to the electric capacity of the submodule that dropped into, if the higher submodule of capacitance voltage is than the high u of the voltage that does not drop into the submodule that capacitance voltage is lower in the submodule in the submodule that has dropped into, the then higher submodule excision of capacitance voltage in the submodule that will drop into will not drop into the submodule that capacitance voltage is low in the submodule simultaneously and will drop into.

Among the described step 3-2, if the brachium pontis sense of current is negative direction, then the brachium pontis electric current discharges to the electric capacity of the submodule that dropped into, and submodule is dropped into or the excision process is:

A) if need to drop into submodule, then find out and do not drop into the higher submodule of voltage in the submodule, with its input;

B) if need the excision submodule, then find out and do not drop into the lower submodule of voltage in the submodule, with its excision.

In the process that the brachium pontis electric current discharges to the electric capacity of the submodule that dropped into, if the submodule that voltage is lower in the submodule that has dropped into is than the low u of the capacitance voltage that does not drop into the higher submodule of voltage in the submodule, the submodule excision that then capacitance voltage is lower in the submodule that will drop into will not drop into the higher submodule input of capacitance voltage in the submodule simultaneously.

In the described step 4, all press according to following Pressure and Control mode between the submodule group:

Mode 1:N submodule group round correction δ _kBetween N submodule group, recycle, unbalanced with the voltage of eliminating the submodule group that causes owing to the difference that rounds correction;

Mode 2: to the average voltage V of submodule group _SmSort, when the modular multilevel current transformer is operated in inverter mode, the submodule group rounded correction δ _kCompose successively from big to small and give voltage submodule group from small to large, make the low submodule group charging of capacitor averaging voltage more; When the modular multilevel current transformer is operated in rectification state, the submodule group rounded correction δ _kCompose successively from big to small and give voltage submodule group from big to small, the submodule group discharge that capacitor averaging voltage is high is more;

Mode 3: according to the average voltage V of submodule group _SmDifference with change of current chain average voltage, stack DC component or alternating current component in the voltage modulated ripple of submodule group, the submodule group that average voltage is higher is discharged, the submodule group that average voltage is lower is charged, so that submodule group electric voltage equalization.

Should be noted that at last: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit, although with reference to above-described embodiment the present invention is had been described in detail, those of ordinary skill in the field are to be understood that: still can make amendment or be equal to replacement the specific embodiment of the present invention, and do not break away from any modification of spirit and scope of the invention or be equal to replacement, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (9)

1. modular multilevel current transformer submodule grouping staircase waveform modulator approach is characterized in that: said method comprising the steps of:

Step 1: the submodule in the change of current chain is divided into N submodule group;

Step 2: the reference voltage of submodule group is rounded the reference staircase voltage V after obtaining rounding _{Stair_wave}

Step 3: distribute trigger impulse to the submodule of submodule group inside;

Step 4: all press between the submodule group.

2. modular multilevel current transformer submodule according to claim 1 grouping staircase waveform modulator approach, it is characterized in that: in the described step 1, the submodule group is controllable voltage source, the control signal of controllable voltage source is the reference voltage V of submodule group _Ref

3. modular multilevel current transformer submodule according to claim 1 grouping staircase waveform modulator approach is characterized in that: in the described step 2, and the reference staircase voltage V after rounding _{Stair_wave}Be expressed as

$V_{\mathrm{stair}\_\mathrm{wave}}=\mathrm{floor}(\frac{V_{\mathrm{ref}}}{V_{\mathrm{sm}}}+{\mathrm{\δ}}_k)---\left(1\right)$

Wherein, V _RefBe the reference voltage of submodule group, V _SmBe the average voltage of submodule group, the floor function is the bracket function of negative infinity, δ _kBe the correction that rounds of submodule group, δ _k=(2k-1)/2N+m _k, k=1 wherein, 2 ... N; m _kBe integer, and

The submodule group round correction δ _kMean value be 0.5, that is:

4. modular multilevel current transformer submodule according to claim 1 grouping staircase waveform modulator approach, it is characterized in that: described step 3 may further comprise the steps:

Step 3-1: judge that the brachium pontis sense of current is positive direction or negative direction;

Step 3-2: submodule F.F. row is dropped into or excision according to the brachium pontis sense of current;

Step 3-3: judge the submodule number dropped into and the submodule number that needs to drop into whether consistent, if inconsistent, then need to excise or drop into the submodule of the submodule difference number of the submodule that dropped into and needs input, make the two unanimity again.

5. modular multilevel current transformer submodule according to claim 4 grouping staircase waveform modulator approach, it is characterized in that: among the described step 3-2, if the brachium pontis sense of current is positive direction, then the brachium pontis electric current charges to the electric capacity of the submodule that dropped into, and submodule is dropped into or the excision process is:

A) if need to drop into submodule, then find out and do not drop into the lower submodule of voltage in the submodule, with its input;

B) if need the excision submodule, then find out and do not drop into the higher submodule of voltage in the submodule, with its excision.

6. modular multilevel current transformer submodule according to claim 5 grouping staircase waveform modulator approach, it is characterized in that: in the process that the brachium pontis electric current charges to the electric capacity of the submodule that dropped into, if the higher submodule of capacitance voltage is than the high u of the voltage that does not drop into the submodule that capacitance voltage is lower in the submodule in the submodule that has dropped into, the then higher submodule excision of capacitance voltage in the submodule that will drop into will not drop into the submodule that capacitance voltage is lower in the submodule simultaneously and will drop into.

7. modular multilevel current transformer submodule according to claim 4 grouping staircase waveform modulator approach, it is characterized in that: among the described step 3-2, if the brachium pontis sense of current is negative direction, then the brachium pontis electric current discharges to the electric capacity of the submodule that dropped into, and submodule is dropped into or the excision process is:

A) if need to drop into submodule, then find out and do not drop into the higher submodule of voltage in the submodule, with its input;

B) if need the excision submodule, then find out and do not drop into the lower submodule of voltage in the submodule, with its excision.

8. modular multilevel current transformer submodule according to claim 7 grouping staircase waveform modulator approach, it is characterized in that: in the process that the brachium pontis electric current discharges to the electric capacity of the submodule that dropped into, if the submodule that voltage is lower in the submodule that has dropped into is than the low u of the capacitance voltage that does not drop into the higher submodule of voltage in the submodule, the submodule excision that then capacitance voltage is lower in the submodule that will drop into will not drop into the higher submodule input of capacitance voltage in the submodule simultaneously.

9. modular multilevel current transformer submodule according to claim 1 grouping staircase waveform modulator approach is characterized in that: in the described step 4, all press according to following Pressure and Control mode between the submodule group:

Mode 1:N submodule group round correction δ _kBetween N submodule group, recycle, unbalanced with the voltage of eliminating the submodule group that causes owing to the difference that rounds correction;

Mode 2: to the average voltage V of submodule group _SmSort, when the modular multilevel current transformer is operated in inverter mode, the submodule group rounded correction δ _kCompose successively from big to small and give voltage submodule group from small to large, make the low submodule group charging of capacitor averaging voltage more; When the modular multilevel current transformer is operated in rectification state, the submodule group rounded correction δ _kCompose successively from big to small and give voltage submodule group from big to small, the submodule group discharge that capacitor averaging voltage is high is more;

Mode 3: according to the average voltage V of submodule group _SmDifference with change of current chain average voltage, stack DC component or alternating current component in the voltage modulated ripple of submodule group, the submodule group that average voltage is higher is discharged, the submodule group that average voltage is lower is charged, so that submodule group electric voltage equalization.

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