CN103490659A - PWM overmodulation method based on optimized quasi sine flat modulating wave - Google Patents

Abstract

The invention relates to a PWM overmodulation method based on an optimized quasi sine flat modulating wave. The method is characterized in that firstly, one quasi sine flat wave is established to serve as the modulating wave, a triangular carrier wave is modulated, and then a three-phase PWM overmodulation algorithm is adopted for overmodulation. According to the method, three-phase PWM is generated by adopting the triangular carrier wave, the largest output linear voltage fundamental wave amplitude value of the three-phase PWM in a linear area is 19% higher than that of SPWM, and therefore the direct-current voltage use ratio is remarkably improved.

Description

Quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing

Technical field

The present invention relates to a kind of quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing.

Background technology

The PWM overmodulation technique refers to that the DC bus-bar voltage utilance maximizes, and its maximum output reaches a kind of PWM technology of square wave pattern.The more PWM overmodulation technique of research is the SVPWM(SpaceVectorPWM Using dSPACE of SVPWM at present) overmodulation technique.

The modulation range of whole SVPWM is divided into linear zone and overmodulation, and corresponding PWM algorithm is described below.

1, linear zone: SVPWM is divided into 6 sectors by 6 fundamental space voltage vectors by vector space, as shown in Figure 1.The basic vector label be take abc as order, and 1 to represent that this goes up brachium pontis mutually open-minded, and 0 represents that this descends brachium pontis open-minded mutually.Uref represents the output reference voltage vector, and θ is the Vector Rotation angle.

In each switch periods Ts, Uref to be exported is removed to approach with the linear combination of zero vector U7, U8 in two fundamental space voltage vector Ux that comprise with the sector, place, Ux ± 1,

U _refT _s=U _xT ₁+U _x±1T ₂+U ₇T ₀+U ₈T ₀ （1）

Ts=T1+T2+2T0 in formula, the action time that T1 is Ux, the action time that T2 is Ux ± 1, the action time that T0 is zero vector U7, U8.

ud is DC bus-bar voltage.According to only switch the principle of an on off state at every turn, two fundamental space voltage vectors that each sector is comprised, determine that the vector that contains 1 " 1 " in the vector label is Ux, and the vector that contains 2 " 1 " is Ux ± 1.The application sine show that each sector space voltage vector T1 action time, T2 are as shown in table 1.

Each sector basic vector of table 1 action time

Annotate: $W=\sqrt{3}{U}_{\mathrm{ref}}/U_d.$

When exporting reference vector Uref in linear zone, its vector end rotational trajectory is in the inscribed circle of regular hexagon shown in Fig. 1 zone, $\left|U_{\mathrm{ref}}\right|\≤U_d/\sqrt{3};$ Modulation degree $M=\frac{\mathrm{\π}{U}_{\mathrm{ref}}}{2U_d}\≤0.907.$

2, overmodulation: as modulation degree M > 0.907 the time, SVPWM enters overmodulation.According to the excursion of modulation degree M, again overmodulation is divided into to two subareas.

(1) ovennodulation I district (0.907≤M<0.952)

Between regular hexagon border and inscribed circle that actual output region vector locus forms at the fundamental space voltage vector, as shown in Figure 2.In figure, heavy line partly is the track of real space vector in each sector, and the part of this track is the regular hexagon border, and another part is compensating basin for the circular arc that connects these two ends, border.The PWM algorithm key step in ovennodulation I district is: 1, according to modulation degree M, table look-up and determine offset angle α _r; 2, the output region vector outside compensating basin shrinks in proportion, and vector end rotational trajectory is dropped on the regular hexagon border.All the other algorithm steps are consistent with linear zone.

(2) ovennodulation II district (0.952≤M≤1)

The PWM algorithm mainly contains to table look-up determines the maintenance angle α corresponding with modulation degree M _hbe the output region vector in the time of staying on regular hexagon summit and the vector contraction of non-stacking area etc., all the other algorithm steps are consistent with linear zone.When M 1 keeps angle α _hreach

the time, PWM exports square wave.

The shortcoming of existing SVPWM overmodulation technique is the algorithm complexity, is mainly manifested in following several respects:

1, overmodulation is divided into to the different Liang Ge of algorithm district, i.e. HeⅡ district, ovennodulation I district.Therefore, before calculating PWM, should differentiate between which kind of overmodulation according to modulation degree M value, and then select different PWM algorithms;

2, no matter ovennodulation I district or II district, its algorithm also will be determined offset angle α by table look-up (according to the M value) _r(for ovennodulation I district) or maintenance angle α _h(for ovennodulation II district), divide each Wei Liangge subinterval, sector accordingly again, is suitable for respectively again different PWM algorithms;

3, algorithm need to be determined space vector place sector number;

4, algorithm relates to division arithmetic.

It is rather complicated that above-mentioned algorithm content forms the SVPWM overmodulation technique.When adopting the DSP device to be achieved, the programming difficulty of its PWM calculation procedure strengthens, and the program structure complexity need take more processor resource and CPU running time, unfavorable to computing time performance and operational precision.

The PWM algorithm should be made every effort to simply, and this is an important indicator of its quality of assessment.For this reason, the present invention separately wards off thinking, proposes a kind of PWM ovennodulation new technology based on " the new modulating wave of quasi sine flat-top ".

Summary of the invention

In view of this, the purpose of this invention is to provide a kind of quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing; Adopt the triangular carrier sampling to generate three-phase PWM, the maximum output line voltage fundamental voltage amplitude in linear zone is high by 19% than SPWM, has significantly promoted the direct voltage utilance; At overmodulation, adopt the method that enlarges the modulating wave flat-top width to continue to increase contained first-harmonic, until square wave output; For keeping the linear relationship between first-harmonic and modulation degree M, flat-top is wide and numerical relation M is tabulated in advance, obtains analog value by tabling look-up; Have advantages of that algorithm is simple, THD is low.

The present invention adopts following scheme to realize: a kind of quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing, it is characterized in that: at first build a quasi sine flat-topped wave as modulating wave, and triangular carrier is modulated, then adopt the three-phase PWM Overmodulation Method to carry out ovennodulation, the waveform mathematical description of described quasi sine flat-topped wave is as follows:

$U_r=\left\{\begin{array}{cc}\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 0\&le;\mathrm{\&omega;t}\&le;\mathrm{\&alpha;}\\ M_h& \mathrm{\&alpha;}<\mathrm{\&omega;t}<\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& \mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;\mathrm{\&pi;}+\mathrm{\&alpha;}\\ -M_h& \mathrm{\&pi;}+\mathrm{\&alpha;}<\mathrm{\&omega;t}<2\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 2\mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;2\mathrm{\&pi;}\end{array}\right.;$

0≤M in formula _h≤ 1 is that the modulating wave flat-top is high;

be that two waists are wide.

In an embodiment of the present invention, described triangular carrier is modulated is to adopt the nonsymmetrical rule sampling method to calculate PWM, and computing formula is as follows:

$t_{\mathrm{on}}=\left\{\begin{array}{cc}\frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\mathrm{si}\mathrm{n\&omega;t})& 0\&le;\mathrm{\&omega;t}\&le;\mathrm{\&alpha;}\\ \frac{T_C}{4}(1+M_h)& \mathrm{\&alpha;}<\mathrm{\&omega;t}<\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \mathrm{\&omega;t})& \mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;\mathrm{\&pi;}+\mathrm{\&alpha;}\\ \frac{T_C}{4}(1-M_h)& \mathrm{\&pi;}+\mathrm{\&alpha;}<\mathrm{\&omega;t}<2\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \mathrm{\&omega;t})& 2\mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;2\mathrm{\&pi;}\end{array}\right.;$

$t_{\mathrm{off}}=\frac{T_C}{2}-t_{\mathrm{on}};$

In formula, t _onwith t _offbe respectively half carrier cycle interior pulsewidth time and intermittent time;

for carrier cycle; for carrier wave ratio; ω=2 π f are the modulating wave angular frequency;

for the modulating wave flat-top is high,

for modulation degree, U ₁for line voltage fundamental amplitude, U _dcfor DC bus-bar voltage; T is carrier wave summit or the lowest point sampling instant.

In an embodiment of the present invention, it is that real-time calculating by the DSP device is achieved that described employing three-phase PWM Overmodulation Method carries out ovennodulation, comprises the following steps:

S01: the control utmost point of the IGBT switch of each phase brachium pontis of three-phase inverting circuit is connected to respectively to the PWM output pin of a DSP device by one drive circuit;

S02: comparand register CMPR1, the CMPR2 in the task manager EVA of DSP, CMPR3 control respectively the PWM output of a phase, b phase, c phase brachium pontis;

S03: timer T1 is set for increase and decrease counting mode of operation, its period register T1PR value is made as carrier cycle time value T _c1/2nd; Enable timer T1 underflow and cycle interruption, twice interruption occurs at each carrier cycle in setting program, and program consists of main program and interruption subroutine; Main program mainly calculates carrier wave ratio N and current modulation degree M value, and then differentiates its scope; When an interrupt occurs, program proceeds in interruption subroutine and carries out PWM and calculate in real time;

The S04:DSP device according to the IGBT switch of each phase brachium pontis of the Numerical Control in CMPR1, CMPR2, CMPR3 at each carrier cycle T _cinterior opens and the turn-off time, makes a, b, c point output PWM voltage wave, voltage U between 3 _ab, U _bc, U _cabe three-phase PWM line voltage.

In an embodiment of the present invention, the concrete account form of described main program is as follows: when 0≤M≤1.19, PWM, in linear zone, makes α=0.658, and makes calculate the modulation wave height

when 1.19≤M≤4/ π, be overmodulation, according to the M value table look-up determine α and

and will

assignment, to Um, keeps modulation wave height M _h=1 is constant.

In an embodiment of the present invention, the concrete account form of described interruption subroutine is as follows: in interruption subroutine, at first calculate current sampling point sequence number k value, i.e. every generation is once interrupted the k value is added to 1, then calculates corresponding a, b, c phase modulating wave angle ω t _{i=a, b, c}, for a phase modulating wave angle,

for b phase modulating wave angle,

for c phase modulating wave angle,

for carrier wave ratio, then differentiate ω t _{i=a, b, c}which kind of range of waveforms of angle in modulating wave, as 0≤ω t _{i=a, b, c}≤ α, or π-α≤ω t _{i=a, b, c}≤ π+α, or 2 π-α≤ω t _{i=a, b, c}during≤2 π, show the sinusoidal wave part of sampling location in modulating wave, press respectively formula $t_{\mathrm{on}}=\frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin {\mathrm{\&omega;t}}_{i=a,b,c})$ With $t_{\mathrm{off}}=\frac{T_C}{4}(1-\frac{M_h}{\sin \mathrm{\&alpha;}}\sin {\mathrm{\&omega;t}}_{i=a,b,c})$ Calculate a, b, c and go up mutually brachium pontis and lower brachium pontis at every half carrier cycle

the service time of interior (lower same); As α<ω t _{i=a, b, c}during<π-α, show the positive flat-topped wave part of sampling location in modulating wave, press respectively formula

with

calculate a, b, c and go up mutually brachium pontis and lower brachium pontis service time; As π+α<ω t _{i=a, b, c}during<2 π-α, show the negative flat-topped wave part of sampling location in modulating wave, press respectively formula

with

calculate a, b, c and go up mutually brachium pontis and lower brachium pontis service time, and then draw the comparison value corresponding with this time pulsewidth, and this comparison value is deposited in respectively in comparand register CMPR1, CMPR2, CMPR3.

In an embodiment of the present invention, described 0.6≤α≤0.8.

In an embodiment of the present invention, described α=0.658.

Compared with prior art, the present invention has the following advantages:

1, the maximum output line voltage fundamental voltage amplitude of linear zone PWM is higher by 3.2% than SVPWM technology, and the direct voltage utilance further improves.

2, the PWM real time algorithm is simple.Show: (1) linear zone or overmodulation all adopt same pwm pulse computing formula, and this formula does not contain division arithmetic, also there is no in the SVPWM algorithm steps necessary that comprises discriminant space vector place sector number; When (2) linear zone (0≤M≤1.19) is with overmodulation (

) the algorithm difference only be that his-and-hers watches levy two high M of parameter-flat-top of modulating wave _hdifferent operating with α angle (representing that flat-top is wide); At linear zone, keep the α angle constant, change M _h, overmodulation keeps M _h=1 is constant, dwindles α until square wave output adopts look-up table to keep linear output character therebetween, and algorithm is simple and clear, without as SVPWM, overmodulation being divided to two subregions, is suitable for respectively algorithms of different.

3, because the PWM algorithm is simple, the corresponding software programming is easy to realization, and program structure is simpler, is conducive to improve calculating real-time and computational accuracy.

For making purpose of the present invention, technical scheme and advantage clearer, below will, by specific embodiment and relevant drawings, the present invention be described in further detail.

The accompanying drawing explanation

Fig. 1 is space vector of voltage figure in prior art.

Fig. 2 is ovennodulation I district reference voltage vector trajectory diagram in prior art.

Fig. 3 is quasi sine flat-top modulation waveform figure of the present invention.

Fig. 4 is that UTHD of the present invention and fundamental voltage component are with α angle change curve.

Fig. 5 is that ITHD of the present invention is with α angle change curve.

Fig. 6 is that the present invention's 5,7,11,13 subharmonic are with α angle change curve.

Fig. 7 is that linear zone modulating wave of the present invention changes schematic diagram.

Fig. 8 is that overmodulation modulating wave of the present invention changes schematic diagram.

Fig. 9 a is that α of the present invention angle is with the M change curve.

Fig. 9 b is that 1/sin α of the present invention is with the M change curve.

Figure 10 is three-phase inverting circuit schematic diagram of the present invention.

Figure 11 is the ITHD contrast of quasi sine flat-top modulating wave PWM of the present invention and SPWM.

Figure 12 is the dsp system main program flow schematic diagram according to the inventive method design.

Figure 13 is DSP interruption subroutine schematic flow sheet to Figure 16.

Embodiment

Basic thought of the present invention is to construct a kind of new type of modulation ripple that contains larger fundametal compoment, and makes contained harmonic component as far as possible little.This modulating wave as shown in Figure 3, this modulating wave U _rby the sine wave gained waveform behind top of pruning, mid portion is flat-topped wave, and two waists are sinusoidal wave; Its mathematical description is as follows:

$U_r=\left\{\begin{array}{cc}\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 0\&le;\mathrm{\&omega;t}\&le;\mathrm{\&alpha;}\\ M_h& \mathrm{\&alpha;}<\mathrm{\&omega;t}<\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& \mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;\mathrm{\&pi;}+\mathrm{\&alpha;}\\ -M_h& \mathrm{\&pi;}+\mathrm{\&alpha;}<\mathrm{\&omega;t}<2\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 2\mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;2\mathrm{\&pi;}\end{array}\right.---\left(2\right);$

0≤M in formula (2) _h≤ 1 is that flat-top is high;

be that two waists are wide, the triangular carrier amplitude is 1.

From Fourier analysis, the contained fundametal compoment of the described modulating wave of (2) formula is along with the increase of flat-top width is that the α angle reduces and increases.When α → 0, modulating wave develops into square wave, and its fundamental voltage amplitude reaches maximum

therefore enlarging flat-top width is conducive to improve fundametal compoment, yet on the other hand, contained harmonic component also has fluctuations with the increase (being that the α angle reduces) of flat-top width.Therefore resolve that to increase the two contradiction of first-harmonic and harmonic effects be to obtain the key of best modulating wave.Harmonic effects can be weighed by total harmonic distortion, is defined as follows:

The voltage harmonic distortion factor $\mathrm{UTHD}=\sqrt{\underset{k=\mathrm{5,7,11,13},...}{\mathrm{\&Sigma;}{U}_k^2}}/U_1---\left(3\right);$

The current harmonics distortion factor $\mathrm{ITHD}=\sqrt{\underset{k=\mathrm{5,7,11,13},...}{\mathrm{\&Sigma;}}{\left(\frac{U_k}{k}\right)}^2}/U_1---\left(4\right);$

(3), U in (4) formula _kfor k voltage harmonic amplitude, U ₁for the voltage fundamental amplitude.

Because the modulating wave shown in Fig. 3 does not contain even-order harmonic, and do not contain three times and the multiple subharmonic in line voltage, so (3), (4) formula harmonic number k only consider the odd harmonics of non-three times times yet.

Fig. 4, Fig. 5 have provided respectively and have worked as M _hthe first-harmonic U of=1 o'clock ₁with influential low-order harmonic distortion factor UTHD, ITHD(accumulative total harmonic wave to 53) with α angle change curve.Fig. 6 is that 5,7,11,13 subharmonic are with α angle change curve.

By Fig. 4～6, shown, along with reducing or the increase of flat-top width of α, must the association harmonic effects, this is the cost that increases fundametal compoment.Yet objectively exist preferentially space, can seek betwixt an optimum point, in the process that promotes fundametal compoment, seek harmonic effects relatively minimum.Be not difficult to find out, when α=0.658, ITHD has a minimum, and corresponding fundamental voltage amplitude reaches 1.19, and UTHD also obtains minimum near this point.The influential low-order harmonic amplitudes such as 5,7,11,13 that table 2 has provided that modulating wave contains under α=0.658 value, wherein maximum harmonic value only 0.0337.Comprehensive all situations, it is best that the modulating wave under α=0.658 value can be considered.Except optimum point α=0.658, by Fig. 4, Fig. 5, to be not difficult to find out, the modulating wave in 0.6≤α≤0.8 span has lower total harmonic distortion and higher fundametal compoment.

Each harmonic component of table 2 and total harmonic distortion value

Preferably, the best modulating wave of below determining with α=0.658, carry out follow-up analytic explanation, after having determined best modulating wave, triangular carrier modulated.Definition modulation degree M is:

$M=\frac{2{\mathrm{<figure-callout\; id="1"\; label="U"\; filenames="130924143009.png,130924143012.png"\; state="\{\{state\}\}">U</figure-callout>}}_1}{\sqrt{3}{U}_{\mathrm{dc}}}---\left(5\right);$

(5) in formula, U ₁for line voltage fundamental amplitude, U _dcfor DC bus-bar voltage.According to the excursion of modulation degree M, PWM divides two modulator zones.

Linear zone (0≤M≤1.19);

As shown in Figure 7, keep α=0.658 constant, as modulating wave height M _hwhile changing by 0 → 1, corresponding M value is 0 → 1.19, therefore has

the first-harmonic value of PWM in this zone is with M _hlinear change.

Adopt the nonsymmetrical rule sampling method to calculate PWM, the pulse computing formula is as follows:

$U_r=\left\{\begin{array}{cc}\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 0\&le;\mathrm{\&omega;t}\&le;\mathrm{\&alpha;}\\ M_h& \mathrm{\&alpha;}<\mathrm{\&omega;t}<\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& \mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;\mathrm{\&pi;}+\mathrm{\&alpha;}\\ -M_h& \mathrm{\&pi;}+\mathrm{\&alpha;}<\mathrm{\&omega;t}<2\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 2\mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;2\mathrm{\&pi;}\end{array}\right.---\left(6\right);$

$t_{\mathrm{off}}=\frac{T_C}{2}-t_{\mathrm{on}}---\left(7\right);$

In formula (6), (7), t _onwith t _offbe respectively half carrier cycle

interior pulsewidth time and intermittent time;

for carrier cycle;

for carrier wave ratio; ω=2 π f are the modulating wave angular frequency; M _hfor the modulation wave height; T is carrier wave summit or the lowest point sampling instant.To in formula

(

) item in advance evaluation as constant, process.

Overmodulation ( $1.19\&le;M\&le;\frac{4}{\mathrm{\&pi;}}$ ）；

As modulating wave height M _h, enter overmodulation at=1 o'clock.Now keep M _h=1 is constant, by reducing α, continue to promote the PWM fundamental voltage amplitude, and when α → 0, PWM becomes square wave output, and modulating wave changes as shown in Figure 8.For continuity fundametal compoment U ₁and the linear relationship between modulation degree M, must calculate the relation curve of α and 1/sin α and M as shown in Figure 9, and tabulation deposits in DSP.The PWM calculation procedure is tabled look-up and is determined α and 1/sin α value according to M, and substitution formula (6), (7) are calculated.

In sum, the essence of PWM ovennodulation new technology algorithm is the high M of flat-top to modulating wave _hdifferent operating with two characteristic parameters in α angle (representing that flat-top is wide).The algorithm of corresponding three-phase PWM overmodulation technique is achieved as follows:

Adopt dsp software to realize the output of quasi sine flat-top modulating wave three-phase PWM wave voltage.The three-phase inversion main circuit as shown in figure 10.The control utmost point of each brachium pontis switch I GBT is connected to respectively six pins of PWM1～PWM6 of DSP device by drive circuit.Comparand register CMPR1, CMPR2 in the task manager EVA of DSP, CMPR3 control respectively the PWM output of a phase, b phase, c phase brachium pontis.Timer T1 is set for increase and decrease counting mode of operation, its period register T1PR value is made as 1/2nd of carrier cycle time value TC; Enable timer T1 underflow and cycle interruption, twice interruption occurs at each carrier cycle in setting program.Program consists of main program and interruption subroutine.Main program mainly calculates carrier wave ratio N and current modulation degree M value, and then differentiates its scope.When 0≤M≤1.19, PWM, in linear zone, makes α=0.658, and makes

calculate the modulation wave height

when 1.19≤M≤4/ π, be overmodulation, according to the M value table look-up determine α and

and will

assignment is to U _m, keep modulation wave height M _h=1 is constant.When an interrupt occurs, program proceeds in interrupt service subroutine and carries out PWM and calculate in real time.In interrupt service subroutine, at first calculate a phase modulating wave angle corresponding to current sampling point sequence number k value (every generation is once interrupted the k value is added to 1)

(

for carrier wave ratio), then differentiate which kind of range of waveforms of angle in modulating wave, as 0≤ω t≤α, or π-α≤ω t≤π+α, during or 2 π-α≤ω t≤2 π, show the sinusoidal wave part of sampling location in modulating wave, presses respectively formula

with

calculate a and go up mutually brachium pontis and lower brachium pontis at every half carrier cycle

the service time of interior (lower same); When α<ω t<π-α, show the positive flat-topped wave part of sampling location in modulating wave, press respectively formula

with

calculate a and go up mutually brachium pontis and lower brachium pontis service time; When π+α<ω t<2 π-α, show the negative flat-topped wave part of sampling location in modulating wave, press respectively formula

with

calculate a and go up mutually brachium pontis and lower brachium pontis service time, and then draw the comparison value corresponding with this time pulsewidth, and this value is deposited in comparand register CMPR1.The PWM wave method that calculates b phase, c phase is consistent with a, first calculates b phase corresponding to current sampling point sequence number k value, c phase modulating wave angle, and its value is larger than a phase modulating wave angle ω t respectively

with

then go up mutually brachium pontis service time t by above-mentioned calculating a _onwith lower brachium pontis service time t _offsame procedure show that b phase, c are at every half carrier cycle

the interior corresponding comparison value of PWM time pulsewidth, and comparison value is deposited in respectively in comparand register CMPR2 and CMPR3.

Concrete, in interruption subroutine, at first calculate current sampling point sequence number k value, i.e. every generation is once interrupted the k value is added to 1, then calculates corresponding a, b, c phase modulating wave angle ω t _{i=a, b, c}, for a phase modulating wave angle,

for b phase modulating wave angle,

for c phase modulating wave angle,

for carrier wave ratio, then differentiate ω t _{i=a, b, c}which kind of range of waveforms of angle in modulating wave, as 0≤ω t _{i=a, b, c}≤ α, or π-α≤ω t _{i=a, b, c}≤ π+α, or 2 π-α≤ω t _{i=a, b, c}during≤2 π, show the sinusoidal wave part of sampling location in modulating wave, press respectively formula

with

calculate a, b, c and go up mutually brachium pontis and lower brachium pontis at every half carrier cycle

the service time of interior (lower same); As α<ω t _{i=a, b, c}during<π-α, show the positive flat-topped wave part of sampling location in modulating wave, press respectively formula with

calculate a, b, c and go up mutually brachium pontis and lower brachium pontis service time; As π+α<ω t _{i=a, b, c}during<2 π-α, show the negative flat-topped wave part of sampling location in modulating wave, press respectively formula

with

calculate a, b, c and go up mutually brachium pontis and lower brachium pontis service time, and then draw the comparison value corresponding with this time pulsewidth, and this comparison value is deposited in respectively in comparand register CMPR1, CMPR2, CMPR3.

The DSP device according to the IGBT switch of each phase brachium pontis of the Numerical Control Figure 10 in CMPR1, CMPR2, CMPR3 at each carrier cycle T _cinterior opens and the turn-off time, makes a, b, c point output PWM voltage wave, voltage U between 3 _ab, U _bc, U _cabe three-phase PWM line voltage.Refer to Figure 12～Figure 16, Figure 12 is that Figure 13～Figure 16 is DSP interruption subroutine schematic flow sheet according to the dsp system main program flow schematic diagram of the inventive method design.

As previously mentioned, quasi sine flat-top modulating wave contains larger fundametal compoment, makes the maximum output line voltage fundamental voltage amplitude of PWM be significantly improved, yet also needs on the other hand to investigate the ITHD value situation of change of full voltage range, to assess the harmonic effects of this technology.Figure 11 shows the correlation curve of the ITHD value of three-phase PWM line voltage that the quasi sine flat-top modulating wave of optimization generates and SPWM line voltage.The contrast of the two ITHD value approximately be take M=0.55 as boundary, as modulation degree M > 0.55 the time, the ITHD value little (excellent) of quasi sine flat-top modulating wave PWM is in SPWM; When M<0.55, its ITHD value increases to some extent than SPWM, but maximum recruitment is no more than 2.2%.As can be seen here, the two ITHD index at M ∈ [0,1.19] full voltage range has half share.

Above-listed preferred embodiment; the purpose, technical solutions and advantages of the present invention are further described; institute is understood that; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention; within the spirit and principles in the present invention all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (7)

1. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing, it is characterized in that: at first build a quasi sine flat-topped wave as modulating wave, and triangular carrier is modulated, then adopt the three-phase PWM Overmodulation Method to carry out ovennodulation, the waveform mathematical description of described quasi sine flat-topped wave is as follows:

$U_r=\left\{\begin{array}{cc}\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 0\&le;\mathrm{\&omega;t}\&le;\mathrm{\&alpha;}\\ M_h& \mathrm{\&alpha;}<\mathrm{\&omega;t}<\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& \mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;\mathrm{\&pi;}+\mathrm{\&alpha;}\\ -M_h& \mathrm{\&pi;}+\mathrm{\&alpha;}<\mathrm{\&omega;t}<2\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{M_h}{\sin \mathrm{\&alpha;}}\sin \left(\mathrm{\&omega;t}\right)& 2\mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;2\mathrm{\&pi;}\end{array}\right.;$

0≤M in formula _h≤ 1 is that the modulating wave flat-top is high;

be that two waists are wide.

2. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing according to claim 1, it is characterized in that: described triangular carrier modulate is to adopt nonsymmetrical rule sampling method calculating PWM, and computing formula is as follows:

$t_{\mathrm{on}}=\left\{\begin{array}{cc}\frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\mathrm{si}\mathrm{n\&omega;t})& 0\&le;\mathrm{\&omega;t}\&le;\mathrm{\&alpha;}\\ \frac{T_C}{4}(1+M_h)& \mathrm{\&alpha;}<\mathrm{\&omega;t}<\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \mathrm{\&omega;t})& \mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;\mathrm{\&pi;}+\mathrm{\&alpha;}\\ \frac{T_C}{4}(1-M_h)& \mathrm{\&pi;}+\mathrm{\&alpha;}<\mathrm{\&omega;t}<2\mathrm{\&pi;}-\mathrm{\&alpha;}\\ \frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin \mathrm{\&omega;t})& 2\mathrm{\&pi;}-\mathrm{\&alpha;}\&le;\mathrm{\&omega;t}\&le;2\mathrm{\&pi;}\end{array}\right.;$

$t_{\mathrm{off}}=\frac{T_C}{2}-t_{\mathrm{on}};$

In formula, t _onwith t _offbe respectively half carrier cycle

interior pulsewidth time and intermittent time;

for carrier cycle;

for carrier wave ratio; ω=2 π f are the modulating wave angular frequency;

for the modulating wave flat-top is high, for modulation degree, U ₁for line voltage fundamental amplitude, U _dcfor DC bus-bar voltage; T is carrier wave summit or the lowest point sampling instant.

3. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing according to claim 1 is characterized in that: it is that real-time calculating by the DSP device is achieved that described employing three-phase PWM Overmodulation Method carries out ovennodulation, comprises the following steps:

S01: the control utmost point of the IGBT switch of each phase brachium pontis of three-phase inverting circuit is connected to respectively to the PWM output pin of a DSP device by one drive circuit;

S02: comparand register CMPR1, the CMPR2 in the task manager EVA of DSP, CMPR3 control respectively the PWM output of a phase, b phase, c phase brachium pontis;

S03: timer T1 is set for increase and decrease counting mode of operation, its period register T1PR value is made as carrier cycle time value T _c1/2nd; Enable timer T1 underflow and cycle interruption, twice interruption occurs at each carrier cycle in setting program, and program consists of main program and interruption subroutine; Main program mainly calculates carrier wave ratio N and current modulation degree M value, and then differentiates its scope; When an interrupt occurs, program proceeds in interruption subroutine and carries out PWM and calculate in real time;

The S04:DSP device according to the IGBT switch of each phase brachium pontis of the Numerical Control in CMPR1, CMPR2, CMPR3 at each carrier cycle T _cinterior opens and the turn-off time, makes a, b, c point output PWM voltage wave, voltage U between 3 _ab, U _bc, U _cabe three-phase PWM line voltage.

4. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing according to claim 3, it is characterized in that: the concrete account form of described main program is as follows: when 0≤M≤1.19, PWM, in linear zone, makes α=0.658, and makes

calculate the modulation wave height

when 1.19≤M≤4/ π, be overmodulation, according to the M value table look-up determine α and

and will

assignment, to Um, keeps modulation wave height M _h=1 is constant.

5. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing according to claim 3, it is characterized in that: the concrete account form of described interruption subroutine is as follows: in interruption subroutine, at first calculate current sampling point sequence number k value, be that every generation is once interrupted the k value is added to 1, then calculate corresponding a, b, c phase modulating wave angle ω t _{i=a, b, c}, for a phase modulating wave angle,

for b phase modulating wave angle,

for c phase modulating wave angle, for carrier wave ratio, then differentiate ω t _{i=a, b, c}which kind of range of waveforms of angle in modulating wave, as 0≤ω t _{i=a, b, c}≤ α, or π-α≤ω t _{i=a, b, c}≤ π+α, or 2 π-α≤ω t _{i=a, b, c}during≤2 π, show the sinusoidal wave part of sampling location in modulating wave, press respectively formula $t_{\mathrm{on}}=\frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin {\mathrm{\&omega;t}}_{i=a,b,c})$ With $t_{\mathrm{off}}=\frac{T_C}{4}(1-\frac{M_h}{\sin \mathrm{\&alpha;}}\sin {\mathrm{\&omega;t}}_{i=a,b,c})$ Calculate a, b, c and go up mutually brachium pontis and lower brachium pontis at every half carrier cycle

the service time of interior (lower same); As α<ω t _{i=a, b, c}during<π-α, show the positive flat-topped wave part of sampling location in modulating wave, press respectively formula

with calculate a, b, c and go up mutually brachium pontis and lower brachium pontis service time; As π+α<ω t _{i=a, b, c}during<2 π-α, show the negative flat-topped wave part of sampling location in modulating wave, press respectively formula

with

calculate a, b, c and go up mutually brachium pontis and lower brachium pontis service time, and then draw the comparison value corresponding with this time pulsewidth, and this comparison value is deposited in respectively in comparand register CMPR1, CMPR2, CMPR3.

6. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing according to claim 1, is characterized in that: described 0.6≤α≤0.8.

7. the quasi sine flat-top modulating wave PWM ovennodulation method based on optimizing according to claim 1, is characterized in that: described α=0.658.

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