CN103580465A - Simplified modulation algorithm for restraining common-mode voltage of three-phase PWM (pulse-width modulation) converter - Google Patents

Abstract

The invention belongs to the field of power electronics and relates to a simplified modulation algorithm for restraining common-mode voltage of a three-phase PWM (pulse-width modulation) converter. The simplified modulation algorithm is characterized in that a non-zero basis vector instead of a zero vector is utilized for synthesizing a reference voltage vector, then the common-mode voltage is effectively restrained, the modulation algorithm is simplified simultaneously, switching-on and switching-off time of each bridge arm is directly figured out according to a relation between three-phase reference voltage, and the calculation formula is simple. The simplified modulation algorithm is further characterized in that the reason of failure of the modulation algorithm for restraining the common-mode voltage due to dead zone time is analyzed, and the algorithm failure area is eliminated by adjusting time for switching-on and switching-off actions, so that the modulation algorithm for restraining the common-mode voltage has a better effect. With the adoption of the simplified modulation algorithm, the calculation amount is greatly reduced, the influence of the dead zone time on the modulation algorithm for restraining the common-mode voltage is eliminated, so that a common-mode voltage peak is limited to one sixth of DC (direct current) bus voltage, the common-mode current is effectively reduced, and reliable guarantee is provided for safe system operation and personal safety.

Description

A kind of simplification modulation algorithm that suppresses three-phase PWM current transformer common-mode voltage

Technical field

The invention belongs to electric and electronic technical field, relate to a kind of simplification modulation algorithm that suppresses three-phase PWM current transformer common-mode voltage.

Background technology

Three-phase PWM current transformer has energy capable of bidirectional flowing because of it, higher voltage utilization, power factor is the feature such as adjustable and low harmonic pollution continuously, is widely used in the field of power electronics such as power factor compensation, three phase electric machine driving, high-performance rectifier, electric energy feedback, active power filtering.Traditional pulse duration pulse duration (pulse width modulation, PWM) modulation algorithm is the modulation strategy that voltage source converter is conventional, but will be according to the relation judgement sector, reference voltage place of three-phase reference voltage and DC voltage, thereby determine the base vector of synthesized reference voltage, and then calculate base vector action time, strengthened the load of controller.And the common-mode voltage poor-performing of this modulation algorithm, does not consider the impact on common-mode voltage of Dead Time, when common-mode voltage has current path, can produce common mode current, can work the mischief to the systems such as motor and personal safety.

Summary of the invention

The object of the invention is to complicated for conventional P WM modulation algorithm process, computing cycle long, common-mode voltage can on the safe operation of the systems such as motor and personal safety works the mischief and the problems such as impact of Dead Time on common-mode voltage, proposes a kind of simplification PWM modulation algorithm that suppresses three-phase PWM current transformer common-mode voltage.

A simplification modulation algorithm for three-phase PWM current transformer common-mode voltage, is characterized in that, the method comprises the steps:

Step 1: current transformer three-phase reference voltage is v _refa, v _refb, v _refc, with DC bus-bar voltage V _dcfor fiducial value is by its standardization, obtain V _a, V _b, V _c, through type

$\left[\begin{array}{c}{V}_{\mathrm{\α}}\\ V_{\mathrm{\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{V}_a\\ V_b\\ V_c\end{array}\right]$

Can obtain reference voltage vector V _refcomponent V on α, β axle _αand V _β;

Two level current transformers have V ₀～V ₇eight space voltage vectors, wherein V ₀, V ₇for zero vector, be positioned at the initial point of α β coordinate system, V ₁, V ₂, V ₃, V ₄, V ₅, V ₆be six base vectors, six base vectors are on average divided into α β plane 6 sectors of 60 °, are defined as respectively I sector, II sector, III sector, IV sector, V sector, VI sector;

Step 2: for suppressing common-mode voltage, select synthesized reference voltage vector V _refspace voltage vector time, avoid selecting V ₀and V ₇two zero vectors, space voltage vector is selected as follows:

As reference voltage vector V _refwhen I sector, select base vector V ₁, V ₂, V ₃, V ₆carry out V _refsynthetic, V wherein ₃and V ₆equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen II sector, select base vector V ₁, V ₂, V ₃, V ₄carry out V _refsynthetic, V wherein ₁and V ₄equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen III sector, select base vector V ₂, V ₃, V ₄, V ₅carry out V _refsynthetic, V wherein ₂and V ₅equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen IV sector, select base vector V ₃, V ₄, V ₅, V ₆carry out V _refsynthetic, V wherein ₃and V ₆equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen V sector, select base vector V ₁, V ₄, V ₅, V ₆carry out V _refsynthetic, V wherein ₁and V ₄equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen VI sector, select base vector V ₁, V ₂, V ₅, V ₆carry out V _refsynthetic, V wherein ₂and V ₅equal and opposite in direction, opposite direction;

Step 3: carry out sector judgement according to three-phase reference voltage relation, and directly calculate the switch motion moment of each brachium pontis, result is as follows

Wherein, T is switch periods.

The existence of considering Dead Time can cause this modulation algorithm in some area failures, cannot suppress common-mode voltage, needs the switch motion of each brachium pontis in step 3 constantly to revise, and makes up the region that algorithm lost efficacy, and the result after adjustment is as follows:

Wherein, t _dfor Dead Time.

Beneficial effect: modulation algorithm computational process of the present invention is simple, eliminated the region that algorithm that the existence because of Dead Time causes lost efficacy, common-mode voltage peak value can better be suppressed for 1/6 of DC bus-bar voltage, effectively reduce common mode current, thereby provide reliable guarantee for normal operation and the personal safety of system.

Accompanying drawing explanation

Fig. 1. 3-phase power converter system construction drawing;

Fig. 2. the distribution map of space voltage vector on α β plane;

Fig. 3. reference voltage vector V _refin the time of in Ι sector, vector synthesis mode of the present invention;

Fig. 4. base vector V ₁action time in short-term, common-mode voltage peak value figure;

Fig. 5. base vector V ₂action time in short-term, common-mode voltage peak value figure;

Fig. 6. reference voltage vector V _refin the time of in Ι sector, the flow chart of elimination algorithm failed areas method of the present invention;

Fig. 7. common-mode voltage experimental waveform figure of the present invention.

Embodiment

The present invention will be further described with embodiment by reference to the accompanying drawings.

Two level 3-phase power converter system construction drawings as shown in Figure 1, v _an, v _bn, v _cnbe respectively the output voltage of three brachium pontis, V _dcfor DC bus-bar voltage.The on off state function of three brachium pontis of definition is as follows:

In formula, j=a, b, c.

In two level current transformers, S _a, S _b, S _chave 2 ³plant different on off states, form 2 ³individual space voltage vector.With V _dcfor fiducial value is by three-phase reference voltage v _refa, v _refb, v _refcstandardization, obtains V _a, V _b, V _c.If V _α, V _βbe respectively reference voltage vector V _refcomponent after 3-2 conversion on α, β axle, and the distribution of space voltage vector on α β plane is as shown in Figure 2, and voltage vector is V ₀～V ₇.

In 3-phase power converter, common-mode voltage is the potential difference of current transformer outlet side three-phase star load neutral point to reference location, and as shown in Figure 1, common-mode voltage is

$v_{\mathrm{no}}=\frac{v_{\mathrm{ao}}+v_{\mathrm{bo}}+v_{\mathrm{co}}}{3}$

To make common-mode voltage value result corresponding to used time as follows for each base vector of current transformer:

Base vector	v ao	v bo	v co	v no
					000	-V dc/2	-V dc/2	-V dc/2	-V dc/2
100	V dc/2	-V dc/2	-V dc/2	-V dc/6
					110	V dc/2	V dc/2	-V dc/2	V dc/6
010	-V dc/2	V dc/2	-V dc/2	-V dc/6
					011	-V dc/2	V dc/2	V dc/2	V dc/6
001	-V dc/2	-V dc/2	V dc/2	-V dc/6
					101	V dc/2	-V dc/2	V dc/2	V dc/6
111	V dc/2	V dc/2	V dc/2	V dc/2

The reference voltage vector of take is positioned at Ι sector to be analyzed as example, the modulation algorithm of inhibition common-mode voltage of the present invention, and adopting phase difference is two base vector V of 180 ° ₃and V (010) ₆(101) substitute zero vector V ₀and V ₇, reference voltage vector V _refsynthetic base vector be V ₁, V ₂, V ₃, V ₆, as shown in Figure 3.Due to V ₃and V ₆equal and opposite in direction, opposite direction, makes two voltage vector t action time ₃=t ₆, common-mode voltage peak value is now reduced to V _dc/ 6, common-mode voltage is effectively suppressed.Reference voltage vector is synthetic as follows

V _refT＝V ₁t ₁+V ₂t ₂

In formula, T is switch periods.

?

$\left[\begin{array}{c}{t}_1\\ {\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">t</figure-callout>}}_2\end{array}\right]=\sqrt{3}\left|V_{\mathrm{ref}}\right|\left[\begin{array}{c}\sin (\frac{2\mathrm{\&pi;}}{3}-\mathrm{\&theta;})\\ \sin \mathrm{\&theta;}\end{array}\right]T$

If reference voltage vector is projected as n in base vector _k,

n _k＝V _ref·V _k＝|V _ref||V _k|cosθ

Wherein θ is the angle of reference voltage vector and base vector, and k=1,2,3,4,5,6.?

$\left[\begin{array}{c}{n}_1\\ {\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">n</figure-callout>}}_2\end{array}\right]=\left[\begin{array}{c}\frac{2}{3}{V}_{\mathrm{\&alpha;}}\\ \frac{1}{3}{V}_{\mathrm{\&alpha;}}+\frac{\sqrt{3}}{3}{V}_{\mathrm{\&beta;}}\end{array}\right]=\frac{4}{9}\left[\begin{array}{c}{V}_a-\frac{1}{2}{V}_b-\frac{1}{2}{V}_c\\ \frac{1}{2}{V}_a+\frac{1}{2}{V}_b-V_c\end{array}\right]$

By Fig. 2, can be obtained

$\left[\begin{array}{c}{n}_1\\ {\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">n</figure-callout>}}_2\end{array}\right]=\frac{2\left|V_{\mathrm{ref}}\right|}{3}\left[\begin{array}{c}\cos \mathrm{\&theta;}\\ \cos (\frac{2\mathrm{\&pi;}}{3}-\mathrm{\&theta;})\end{array}\right]$

?

$\left[\begin{array}{c}{t}_1\\ {\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">t</figure-callout>}}_2\end{array}\right]=\frac{3}{2}T\left[\begin{array}{cc}2& -1\\ -1& 2\end{array}\right]\left[\begin{array}{c}{n}_1\\ {\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">n</figure-callout>}}_2\end{array}\right]=\left[\begin{array}{c}{V}_a-V_b\\ V_b-V_c\end{array}\right]T$

Due to t ₁, t ₂perseverance is greater than 0, V _a>V _b, V _b>V _c, this conclusion can be used as reference voltage vector at the Rule of judgment of Ι sector.Make base vector V ₃and V ₆action time t ₃, t ₆,

t ₃＝t ₆＝T-t ₁-t ₂＝T(1-V _a+V _c)

Adopt symmetrical seven segmentation modulation, the switch motion of each brachium pontis is constantly

$T_a=\frac{T}{4}-\frac{T}{4}(V_a-V_c)$

$T_b=\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="HDA0000419385630000013.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}+\frac{T}{4}(-V_a+2V_b-V_c)$

$T_c=\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="HDA0000419385630000013.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}+\frac{T}{4}(V_a-V_c)$

In order to avoid, current transformer upper and lower bridge arm is straight-through damages power electronic device, need in control impuls, add Dead Time t _d.And the membership that adds of Dead Time causes each brachium pontis switch motion constantly to change, affect the output voltage of inverter, cause the inefficacy that suppresses common-mode voltage algorithm.Load current reference direction as shown in Figure 1, be take a brachium pontis as example, in Dead Time, and i _aduring >0, brachium pontis output voltage clamper is in low level; i _aduring <0, brachium pontis output voltage clamper is at high level.

With reference voltage vector V _refin Ι sector, be example, as reference voltage vector V _refin the time of near sector conversion, i.e. base vector V ₁or V ₂action time when too short, because of the existence of Dead Time, the switch motion of each brachium pontis changes constantly, affects brachium pontis output voltage, occurs common mode peak voltage, and modulation algorithm was lost efficacy.And brachium pontis output voltage is relevant with load current direction, by judging that the locus of output voltage vector can judge threephase load sense of current.

As base vector V ₁action time too short, i now _a>0, i _b<0, i _c<0, in Dead Time, v _ao=-V _dc/ 2, v _bo=V _dc/ 2, v _co=V _dc/ 2, common-mode voltage peak value figure as shown in Figure 4, as seen from the figure because base vector V ₁action time too short, cause base vector V ₁become zero vector V ₇, common-mode voltage peak value is by V _dc/ 6 become V _dc/ 2, suppress common-mode voltage modulation algorithm and lost efficacy, there is common mode peak voltage.Eliminate common mode peak voltage, need to constantly adjust each brachium pontis switch motion.

As base vector V ₂action time too short, i now _a>0, i _b<0, i _c>0, in Dead Time, v _ao=-V _dc/ 2, v _bo=V _dc/ 2, v _co=-V _dc/ 2, common-mode voltage peak value figure as shown in Figure 5.With base vector V ₁too short situation comparison action time, because each brachium pontis output current direction is different, in Dead Time, brachium pontis output voltage is also different, synthesized reference voltage vector V _refbase vector remain unchanged, common-mode voltage peak value is still V _dc/ 6, there is not common mode peak voltage, do not need each brachium pontis switch motion constantly to adjust.

There is the condition of common mode peak voltage in analysis.As shown in Figure 4, only as base vector V ₁t action time ₁<2t _dtime, Dead Time can cover base vector V ₁action time, now need the switch motion of each brachium pontis constantly to adjust, to eliminate common mode peak voltage, according to weber equilibrium principle, improve the switch motion of each brachium pontis after modulation algorithm and be constantly

${T_a}^{\&prime;}=T_a+\frac{{\mathrm{<figure-callout\; id="2"\; label="t\; d"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">t</figure-callout>}}_d}{2}$

${T_b}^{\&prime;}=T_b-\frac{{\mathrm{<figure-callout\; id="2"\; label="t\; d"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">t</figure-callout>}}_d}{2}$

${T_c}^{\&prime;}=T_c+\frac{{\mathrm{<figure-callout\; id="2"\; label="t\; d"\; filenames="HDA0000419385630000015.png"\; state="\{\{state\}\}">t</figure-callout>}}_d}{2}$

Eliminate the flow chart of common mode peak voltage as shown in Figure 6.

In sum, can draw reference voltage vector V _refdecision condition in other sectors, each brachium pontis switch motion each brachium pontis switch motion constantly and after improvement modulation algorithm constantly.

Fig. 7 has provided common-mode voltage experimental waveform figure of the present invention, and now DC bus-bar voltage is 30V, and common-mode voltage peak value is 5V as seen from the figure, effectively suppresses, for 1/6 of DC bus-bar voltage, to have verified the correctness of modulation algorithm of the present invention.

Claims (2)

1. a simplification modulation algorithm that suppresses three-phase PWM current transformer common-mode voltage, is characterized in that, the method comprises the steps:

Step 1: current transformer three-phase reference voltage is v _refa, v _refb, v _refc, with DC bus-bar voltage V _dcfor fiducial value is by its standardization, obtain V _a, V _b, V _c, through type

$\left[\begin{array}{c}{V}_{\mathrm{\&alpha;}}\\ V_{\mathrm{\&beta;}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{V}_a\\ V_b\\ V_c\end{array}\right]$

Can obtain reference voltage vector V _refcomponent V on α, β axle _αand V _β;

Two level current transformers have V ₀～V ₇eight space voltage vectors, wherein V ₀, V ₇for zero vector, be positioned at the initial point of α β coordinate system, V ₁, V ₂, V ₃, V ₄, V ₅, V ₆be six base vectors, six base vectors are on average divided into α β plane 6 sectors of 60 °, are defined as respectively I sector, II sector, III sector, IV sector, V sector, VI sector;

Step 2: for suppressing common-mode voltage, select synthesized reference voltage vector V _refspace voltage vector time, avoid selecting V ₀and V ₇two zero vectors, space voltage vector is selected as follows:

As reference voltage vector V _refwhen I sector, select base vector V ₁, V ₂, V ₃, V ₆carry out V _refsynthetic, V wherein ₃and V ₆equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen II sector, select base vector V ₁, V ₂, V ₃, V ₄carry out V _refsynthetic, V wherein ₁and V ₄equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen III sector, select base vector V ₂, V ₃, V ₄, V ₅carry out V _refsynthetic, V wherein ₂and V ₅equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen IV sector, select base vector V ₃, V ₄, V ₅, V ₆carry out V _refsynthetic, V wherein ₃and V ₆equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen V sector, select base vector V ₁, V ₄, V ₅, V ₆carry out V _refsynthetic, V wherein ₁and V ₄equal and opposite in direction, opposite direction;

As reference voltage vector V _refwhen VI sector, select base vector V ₁, V ₂, V ₅, V ₆carry out V _refsynthetic, V wherein ₂and V ₅equal and opposite in direction, opposite direction;

Step 3: carry out sector judgement according to three-phase reference voltage relation, and directly calculate the switch motion moment of each brachium pontis, result is as follows:

Wherein, T is switch periods.

2. a kind of simplification modulation algorithm that suppresses three-phase PWM current transformer common-mode voltage according to claim 1, it is characterized in that: the existence of considering Dead Time can cause this modulation algorithm in some area failures, cannot suppress common-mode voltage, need the switch motion of each brachium pontis in step 3 constantly to revise, make up the region that algorithm lost efficacy, the result after adjustment is as follows:

Wherein, t _dfor Dead Time.

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