CN103490659B - Based on the quasi sine flat-top modulating wave PWM overmodulation method optimized - Google Patents

Abstract

The present invention relates to a kind of quasi sine flat-top modulating wave PWM overmodulation method based on optimizing, it is characterized in that: first build a quasi sine flat-topped wave as modulating wave, and triangular carrier is modulated, then adopt three-phase PWM Overmodulation Method to carry out ovennodulation.The present invention adopts triangular carrier to sample and generates three-phase PWM, and comparatively SPWM is high by 19% for the maximum output line voltage fundamental voltage amplitude in linear zone, significantly improves direct voltage utilance.

Description

Based on the quasi sine flat-top modulating wave PWM overmodulation method optimized

Technical field

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

Background technology

PWM overmodulation technique refers to that 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 current research is SVPWM(SpaceVectorPWM Using dSPACE of SVPWM) overmodulation technique.

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

Vector space is divided into 6 sectors by 6 fundamental space voltage vectors by 1, linear zone: SVPWM, as shown in Figure 1.Basic vector label take abc as sequence, and 1 to represent brachium pontis in this phase open-minded, 0 represent this phase under brachium pontis open-minded.Uref represents output reference voltage vector, and θ is Vector Rotation angle.

In each switch periods Ts, two fundamental space voltage vector Ux, Ux ± 1 comprised with sector, place are gone to approach Uref to be output with the linear combination of zero vector U7, U8, namely

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

In formula, Ts=T1+T2+2T0, T1 are the action time of Ux, and T2 is the action time of Ux ± 1, and T0 is the action time of zero vector U7, U8. ud is DC bus-bar voltage.According to each principle only switching an on off state, to two fundamental space voltage vectors that each sector comprises, determine that the vector containing 1 " 1 " in vector label is Ux, the vector containing 2 " 1 " is Ux ± 1.Application sine show that each sector space voltage vector action time T1, T2 are as shown in table 1.

Table 1 each sector basic vector action time

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

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

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

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

Actual output region vector locus between the regular hexagon border that fundamental space voltage vector is formed and inscribed circle, as shown in Figure 2.In figure, heavy line part is the track of real space vector in each sector, and a part for this track is regular hexagon border, and another part is the circular arc and the compensating basin that connect these two ends, border.The PWM algorithm key step in ovennodulation I district is: 1, table look-up according to modulation degree M 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 regular hexagon border.All the other algorithm steps are consistent with linear zone.

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

PWM algorithm mainly contains to table look-up determines the maintenance angle α corresponding with modulation degree M _hthe i.e. time of staying of output region vector on regular hexagon summit and the vector contraction etc. of non-stacking area, all the other algorithm steps are consistent with linear zone.When M be 1 namely keep angle α _hreach time, PWM exports square wave.

The shortcoming of existing SVPWM overmodulation technology is that algorithm is complicated, is mainly manifested in following several respects:

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

2, no matter ovennodulation I district or IIth district, its algorithm also will determine offset angle α by table look-up (according to M value) _r(for ovennodulation I district) or maintenance angle α _h(for ovennodulation II district), dividing each sector accordingly is again two subintervals, is suitable for different PWM algorithm respectively again;

3, algorithm needs to determine space vector place sector number;

4, algorithm relates to division arithmetic.

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

PWM algorithm should make every effort to simple, 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 object of this invention is to provide a kind of quasi sine flat-top modulating wave PWM overmodulation method based on optimizing; Adopt triangular carrier sampling to generate three-phase PWM, comparatively SPWM is high by 19% for the maximum output line voltage fundamental voltage amplitude in linear zone, significantly improves direct voltage utilance; In overmodulation, then the method expanding modulating wave flat-top width is adopted to continue to increase contained first-harmonic, until square wave exports; For keeping the linear relationship between first-harmonic and modulation degree M, wide for the flat-top numerical relation with M is tabulated, in advance by acquisition analog value of tabling look-up; There is the advantage 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 overmodulation method based on optimizing, it is characterized in that: first build a quasi sine flat-topped wave as modulating wave, and triangular carrier is modulated, then adopt 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 modulating wave flat-top is high; be that two waists are wide.

In an embodiment of the present invention, described to carry out modulation to triangular carrier be adopt asymmetric regular 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 pulse width time and intermittent time; for carrier cycle; for carrier wave ratio; ω=2 π f is modulating wave angular frequency; for 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 be achieved by the real-time calculating of DSP device that described employing three-phase PWM Overmodulation Method carries out ovennodulation, comprises the following steps:

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

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

S03: arrange timer T1 for increase and decrease Counts pattern, its period register T1PR value is set to carrier cycle time value T _c1/2nd; Enable timer T1 underflow and cycle interruption, namely there is twice interruption at each carrier cycle in setting program, and program is made up 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;

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 export 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, then PWM is in linear zone, makes α=0.658, and makes calculate modulation wave height as 1.19≤M≤4/ π, be overmodulation, then according to 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, first calculates current sampling point sequence number k value, namely often occurs once to interrupt adding 1 to k value, 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}angle is in which kind of range of waveforms of 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 that sampling location is in the sinusoidal waveform portion of modulating wave, then press formula respectively $t_{\mathrm{on}}=\frac{T_C}{4}(1+\frac{M_h}{\sin \mathrm{\&alpha;}}\sin {\mathrm{\&omega;t}}_{i=a,b,c})$ With $t_{\mathrm{off}}=\frac{T_C}{4}(1-\frac{M_h}{\sin \mathrm{\&alpha;}}\sin {\mathrm{\&omega;t}}_{i=a,b,c})$ In calculating a, b, c phase, brachium pontis and lower brachium pontis are at every half carrier cycle the service time of interior (lower same); As α < ω t _{i=a, b, c}during < π-α, show that sampling location is in the positive flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a, b, c phase; As π+α < ω t _{i=a, b, c}during <2 π-α, show that sampling location is in the negative flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a, b, c phase, and then draw the comparison value corresponding with this time pulsewidth, and by this comparison value respectively stored 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, linear zone PWM maximum output line voltage fundamental voltage amplitude is higher than SVPWM technology by 3.2%, and direct voltage utilance improves further.

2, PWM real time algorithm is simple.Show: (1) linear zone or overmodulation all adopt same pwm pulse computing formula, this formula containing division arithmetic, does not have the steps necessary comprising discriminant space vector place sector number in SVPWM algorithm yet; (2) when linear zone (0≤M≤1.19) and overmodulation ( ) algorithm difference be only that his-and-hers watches levy two parameters-flat-top height M of modulating wave _hwith the different operating of α angle (representing flat-top wide); Keep in linear zone α angle constant, change M _h, overmodulation keeps M _h=1 is constant, reduces α until square wave exports, and adopt look-up table to keep linear output character therebetween, algorithm is simple and clear, without the need to overmodulation being divided two subregions as SVPWM, is suitable for algorithms of different respectively.

3, because PWM algorithm is simple, corresponding software programming is easy to realize, and program structure is comparatively simple, is conducive to improving calculating real-time and computational accuracy.

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

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 5,7,11,13 subharmonic is with α angle change curve.

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

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

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

Fig. 9 b is that 1/sin α of the present invention is with 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 and SPWM of the present invention.

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

Figure 13 to Figure 16 is DSP interrupt subroutine flow schematic diagram.

Embodiment

Basic thought of the present invention constructs a kind of new type of modulation ripple containing larger fundametal compoment, and make contained harmonic component little as far as possible.This modulating wave as shown in Figure 3, this modulating wave U _rto be pruned gained waveform behind top by sine wave, 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, triangular carrier amplitude is 1.

From Fourier analysis, fundametal compoment contained by the modulating wave described by (2) formula reduces and increases along with the increase of flat-top width and α angle.When α → 0, modulating wave develops into square wave, and its fundamental voltage amplitude reaches maximum therefore expand flat-top width to be conducive to improving fundametal compoment, but on the other hand, contained harmonic component also has fluctuations with the increase (namely α angle reduces) of flat-top width.Therefore resolving the contradiction increased between both first-harmonic and harmonic effects is the key obtaining 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 voltage fundamental amplitude.

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

Fig. 4, Fig. 5 sets forth and work as M _hfirst-harmonic U when=1 ₁harmonic wave to 53 is added up with influential low-order harmonic distortion factor UTHD, ITHD() with α angle change curve.Fig. 6 is that 5,7,11,13 subharmonic are with α angle change curve.

Shown by Fig. 4 ~ 6, along with the reduction of α or the increase of flat-top width, must association harmonic effects, this is the cost increasing fundametal compoment.But objectively there is preferentially space, an optimum point can be sought betwixt, namely in the process promoting 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 gives that modulating wave contains under the value of α=0.658, wherein maximum harmonic value only 0.0337.Comprehensive all situations, the modulating wave under the value of α=0.658 can be considered best.Except optimum point α=0.658, be not difficult to find out by Fig. 4, Fig. 5, the modulating wave in the span of 0.6≤α≤0.8 has lower total harmonic distortion and higher fundametal compoment.

The each harmonic component of table 2 and harmonic distortion angle value

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

$M=\frac{2U_1}{\sqrt{3}{U}_{\mathrm{dc}}}---\left(5\right);$

(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 _hduring by 0 → 1 change, corresponding M value is 0 → 1.19, therefore has the first-harmonic value of the PWM in this region is with M _hlinear change.

Adopt asymmetric regular sampling method to calculate PWM, 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 pulse width time and intermittent time; for carrier cycle; for carrier wave ratio; ω=2 π f is modulating wave angular frequency; M _hfor modulation wave height; T is carrier wave summit or the lowest point sampling instant.To in formula (namely ) item can in advance evaluation as constant process.

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

As modulating wave height M _hwhen=1, enter overmodulation.Now keep M _h=1 is constant, and continue to promote PWM fundamental voltage amplitude by reducing α, when α → 0, PWM becomes square wave and exports, and modulating wave change 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 is stored in DSP.PWM calculation procedure is tabled look-up according to M and is determined α and 1/sin α value, and substitution formula (6), (7) calculate.

In sum, the essence of PWM ovennodulation new technology algorithm is the flat-top height M to modulating wave _hwith the different operating of α angle (representing flat-top wide) two characteristic parameters.The algorithm realization of corresponding three-phase PWM overmodulation technique is as follows:

Adopt dsp software to realize quasi sine flat-top modulating wave three-phase PWM wave voltage to export.Three-phase inversion main circuit as shown in Figure 10.The control pole of each brachium pontis switch I GBT is connected to PWM1 ~ PWM6 six pins of DSP device respectively by drive circuit.By comparand register CMPR1, CMPR2, the CMPR3 in the task manager EVA of DSP respectively control a phase, b phase, c phase brachium pontis PWM export.Arrange timer T1 for increase and decrease Counts pattern, its period register T1PR value is set to 1/2nd of carrier cycle time value TC; Enable timer T1 underflow and cycle interruption, namely there is twice interruption at each carrier cycle in setting program.Program is made up 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, then PWM is in linear zone, makes α=0.658, and makes calculate modulation wave height as 1.19≤M≤4/ π, be overmodulation, then according to 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, first calculate a phase modulating wave angle corresponding to current sampling point sequence number k value (often occurring once to interrupt adding 1 to k value) ( for carrier wave ratio), then differentiate angle is in which kind of range of waveforms of modulating wave, as 0≤ω t≤α, or π-α≤ω t≤π+α, or during 2 π-α≤ω t≤2 π, show that sampling location is in the sinusoidal waveform portion of modulating wave, then press formula respectively with in calculating a phase, brachium pontis and lower brachium pontis are at every half carrier cycle the service time of interior (lower same); As α < ω t< π-α, show that sampling location is in the positive flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a phase; As π+α < ω t<2 π-α, show that sampling location is in the negative flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a phase, and then draw the comparison value corresponding with this time pulsewidth, and by this value stored in comparand register CMPR1.The PWM wave method of calculating b phase, c phase is consistent with a, and namely first calculate b phase, c phase modulating wave angle that current sampling point sequence number k value is corresponding, its value is larger than a phase modulating wave angle ω t respectively with then by brachium pontis service time t in above-mentioned calculating a phase _onwith lower brachium pontis service time t _offsame procedure show that b phase, c phase are at every half carrier cycle the interior comparison value corresponding to PWM time pulsewidth, and by comparison value respectively stored in comparand register CMPR2 and CMPR3.

Concrete, in interruption subroutine, first calculate current sampling point sequence number k value, namely often occur once to interrupt adding 1 to k value, 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}angle is in which kind of range of waveforms of 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 that sampling location is in the sinusoidal waveform portion of modulating wave, then press formula respectively with in calculating a, b, c phase, brachium pontis and lower brachium pontis are at every half carrier cycle the service time of interior (lower same); As α < ω t _{i=a, b, c}during < π-α, show that sampling location is in the positive flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a, b, c phase; As π+α < ω t _{i=a, b, c}during <2 π-α, show that sampling location is in the negative flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a, b, c phase, and then draw the comparison value corresponding with this time pulsewidth, and by this comparison value respectively stored in comparand register CMPR1, CMPR2, CMPR3.

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 export 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 the dsp system main program flow schematic diagram according to the inventive method design, and Figure 13 ~ Figure 16 is DSP interrupt subroutine flow schematic diagram.

As previously mentioned, quasi sine flat-top modulating wave contains larger fundametal compoment, and the maximum output line voltage fundamental voltage amplitude of PWM is significantly improved, but also needs the ITHD value situation of change investigating full voltage range on the other hand, to assess the harmonic effects of this technology.The correlation curve of the ITHD value of the three-phase PWM line voltage that the quasi sine flat-top modulating wave that Figure 11 shows optimization generates and SPWM line voltage.The two ITHD value contrast is about is boundary with M=0.55, and as modulation degree M>0.55, the ITHD value little (excellent) of quasi sine flat-top modulating wave PWM is in SPWM; As 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 has half share in the ITHD index of M ∈ [0,1.19] full voltage range.

Above-listed preferred embodiment; the object, technical solutions and advantages of the present invention are further described; be 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 amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (5)

1. the quasi sine flat-top modulating wave PWM overmodulation method based on optimization, it is characterized in that: first build a quasi sine flat-topped wave as modulating wave, and triangular carrier is modulated, then adopt 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 modulating wave flat-top is high; be that two waists are wide;

It is be achieved by the real-time calculating of DSP device that described employing three-phase PWM Overmodulation Method carries out ovennodulation, comprises the following steps:

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

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

S03: arrange timer T1 for increase and decrease Counts pattern, its period register T1PR value is set to carrier cycle time value T _c1/2nd; Enable timer T1 underflow and cycle interruption, namely there is twice interruption at each carrier cycle in setting program, and program is made up 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;

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 export PWM voltage wave, voltage U between 3 _ab, U _bc, U _cabe three-phase PWM line voltage;

The concrete account form of described main program is as follows: when 0≤M≤1.19, then PWM is in linear zone, makes α=0.658, and makes calculate modulation wave height as 1.19≤M≤4/ π, be overmodulation, then according to M value table look-up determine α and and will assignment, to Um, keeps modulation wave height M _h=1 is constant; Wherein, U _mfor the intermediate variable in main program calculating, and

2. the quasi sine flat-top modulating wave PWM overmodulation method based on optimizing according to claim 1, is characterized in that: described to carry out modulation to triangular carrier be adopt asymmetric regular sampling method to calculate PWM, and computing formula is as follows:

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

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

In formula, t _onwith t _offbe respectively half carrier cycle interior pulse width time and intermittent time; for carrier cycle; for carrier wave ratio; ω=2 π f is modulating wave angular frequency; for 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 overmodulation method based on optimizing according to claim 1, it is characterized in that: the concrete account form of described interruption subroutine is as follows: in interruption subroutine, first current sampling point sequence number k value is calculated, namely often occur once to interrupt adding 1 to k value, 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}angle is in which kind of range of waveforms of 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 that sampling location is in the sinusoidal waveform portion of modulating wave, then press formula respectively with in calculating a, b, c phase, brachium pontis and lower brachium pontis are at every half carrier cycle interior service time; As α < ω t _{i=a, b, c}during < π-α, show that sampling location is in the positive flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a, b, c phase; As π+α < ω t _{i=a, b, c}during < 2 π-α, show that sampling location is in the negative flat-topped wave part of modulating wave, then press formula respectively with calculate brachium pontis and lower brachium pontis service time in a, b, c phase, and then draw the comparison value corresponding with this time pulsewidth, and by this comparison value respectively stored in comparand register CMPR1, CMPR2, CMPR3.

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

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