CN106357140A - In-phase disposition type SPWM (synchronized pulse-width modulation) pulse distribution method applied to cascaded multilevel inverters - Google Patents

Abstract

The invention discloses an in-phase disposition type SPWM (synchronized pulse-width modulation) pulse distribution method applied to cascaded multilevel inverters. Trigger pulses are switched in every 1/4 output period, power balance between cascaded modules can be realized through three times of switching, and the line voltage THD (total harmonic distortion) is not changed basically. Compared with an existing scheme, the method consumes shorter time and is equally applicable to the condition of low modulation rate. The scheme feasibility is verified through simulation and experiments.

Description

A kind of homophase cascade type spwm pulse distribution being applied to cascaded multilevel inverter Method

Technical field

The present invention relates to cascaded multilevel inverter technical field, more particularly, to one kind to be applied to cascade connection multi-level inverse Become the homophase cascade type spwm pulse allocating method of device.

Background technology

Cascaded multilevel inverter is widely used in high-power drive system, and multi-electrical level inverter can be divided into two poles Pipe wrench bit-type, striding capacitance type, and three kinds of cascade connection type.It is little that multi-electrical level inverter has switching voltage stress；Output level number is many； Switching frequency can be reduced；Dv/dt is little, the advantages of can reduce output filter.Wherein cascaded inverter has and is easy to modularity With the feature of phase voltage redundancy, however it is necessary that independent current source is powered so that it is highly suitable in photovoltaic generating system, modularity Many level (mmc) inherit the advantage of h bridge cascade structure, in application of special occasions such as flexible DC power transmissions (mmc-hvdc) relatively Many.

In multi-electrical level inverter, got over because its output line voltage percent harmonic distortion is low with phase shift amplitude carrier layered manner Carry out more concerns.However, because gang mould module units at different levels are separate, homophase layered manner has its inherent shortcoming, i.e. inversion There is the unbalanced problem of power in device each cascade module when transmitting active power.For solving this problem, Wang Xuehua etc. employs A kind of ipd of cycle pulse controls it is achieved that inverter cell power at different levels balances, and demonstrates ipd by theoretical derivation Method is more excellent relative to the line voltage waveform that other move stacking (cd) method output of width carrier wave.Dan Qingxiao etc. is superfluous according to phase voltage switch combination Remaining feature, determines power supply and the working condition of switch by random distribution method, equal with the working opportunity that ensures each module. Therefore, cycle pulse ipd method generally requires after the longer working time, and each unit utilization rate just can tend to equal, realizes The power-balance of each module, and the method is for the occasion effect on driving birds is not good needing frequent start-stop.Hongyan wang etc. proposes The frequency passing through increase other positions carrier wave when modulation ratio is relatively low equalizes the operating frequency of each switching device, but modulation ratio When too low, some switches cannot obtain pulse signal, leads to part h bridge unit Non voltage output, even if increasing carrier frequency This defect cannot be changed, there is limitation in this way.

Therefore, prior art existing defects, need to improve.

Content of the invention

The technical problem to be solved is to provide one kind to be applied to cascade connection multi-level for the deficiencies in the prior art The homophase cascade type spwm pulse allocating method of inverter.

Technical scheme is as follows:

A kind of homophase cascade type spwm pulse allocating method being applied to cascaded multilevel inverter, every 1/4 output cycle Rotation is carried out to trigger pulse, just can reach power-balance between each cascade module it is ensured that line voltage thd base through 3 rotations This is constant.

The inventive method is not only shorter than existing program in time, and equally applicable to the situation of low modulation ratio.This Invention is by having emulated with experimental verification the feasibility of scheme.

Brief description

Fig. 1 cascades h bridge inverter for m level；

Fig. 2 is ipd modulation principle figure；(a) ipd modulation waveform and the relation of carrier wave, the output electricity of (b) a phase difference h bridge Pressure；

Fig. 3 is a phase h bridge unit output voltage during low modulation ratio；

Fig. 4 is cascade h bridge unit pulse sequence；The h bridge unit pulse sequence of (a) tradition ipd, the h bridge of (b) new ipd Unit pulse sequence,

Fig. 5 is ipd and cps method harmonic wave of output voltage, (a) ω_cPlace's phase voltage harmonic content, (b) ω_cPlace's line voltage harmonic wave Content；

Fig. 6 is new ipd method h bridge unit output voltage；

Fig. 7 is traditional and new ipd method output phase voltage and line voltage waveform；

Fig. 8 is line voltage v_abFft analysis；

Fig. 9 is m_aIpd simulation result when=0.6, (a) tradition ipd method h bridge unit output voltage waveforms, (b) new ipd Method h bridge unit output voltage waveforms, (c) new ipd method output a phase phase voltage and line voltage；

Figure 10 is output phase voltage and line voltage waveform；

Figure 11 is a phase h bridge unit output voltage.

Specific embodiment

Below in conjunction with specific embodiment, the present invention is described in detail.

Homophase stacking control methods (being contrasted with the effect of embodiment 2) of embodiment 1 cascaded multilevel inverter

For m level series connection h bridge inverter, as shown in figure 1, often mutually there being n h bridge cascade, independently supplied by direct voltage source e Electricity.Its phase voltage can be expressed as

v_xn=v_hx1+v_hx2+v_hx3+…+v_hxn(0)

X=a, b, c in formula；X=a, b, c.v_xnRepresent phase voltage, v_hxnRepresent n-th h bridge unit of x phase.Due to each h Bridge can export tri- kinds of level of 0, ± e so that phase voltage is very flexible to the selection of level.

In general, the inverter of m level needs (m-1) individual triangular wave, for 7 electrical level inverters, needs 6 triangles to carry Ripple.Taking a phase as a example, shown in its modulation principle such as Fig. 2 (a), Fig. 2 (a) is the pass of ipd sinusoidal modulation wave and triangular carrier waveform System, 6 carrier phases of in figure are consistent, are layered on top of each other up and down, v_cr1And v_cr1-It is respectively used to produce h_a1Open on two brachium pontis in left and right Close s_a11、s_a31, lower switch s_a21、s_a41Control pulse respectively with corresponding on switch complementation.In conjunction with Fig. 2 (b), work as v_ma>v_cr1, s_a11Conducting, s_a31Turn off, h_a1Output forward voltage；Work as v_ma<v_cr1-Then contrary；In the same manner, remaining 4 carrier wave is respectively used to produce h_a2, h_a3On control pulse to inductive switch.So, h bridge output voltage waveforms are consistent with corresponding pulse sequence, according to modulation Principle, 3 h bridge output voltage v of a phase_hanThe waveform of (n=1,2,3), such as shown in Fig. 2 (b).The frequency of in figure output voltage and when Length directly reflects corresponding switching frequency and conducting duration, and modulation ratio m_aWhen difference will affect its switching frequency and switch Long.Equally, by+120 ° of modulating wave phase shift, -120 ° can be obtained by the control wave that b phase and c are relative to inductive switch.

Can be seen that in 0～π cycle by Fig. 2 (b), v_ha1, v_ha23 pulse voltages of output, and v_ha3Only output one, half In the individual cycle, the pulse voltage duration sum of three is also unequal.So that inverter different concatenation unit in a cycle Conduction loss unequal.

In order to better illustrate this problem, the present invention to be defined with two alternate h bridges using ON time and frequency The power imbalances degree of unit, in 0～π half period, defines power imbalances degree function

$s(\mathrm{\&alpha;},\mathrm{\&beta;})=|1-\frac{t_{hp\mathrm{\&alpha;}}}{t_{hp\mathrm{\&beta;}}}|x+|1-\frac{f_{hp\mathrm{\&alpha;}}}{f_{hp\mathrm{\&beta;}}}|(y+z)---\left(1\right)$

Formula (1) is divided into two parts, and the left side is the power imbalances part being determined by ON time difference, and the right is by switching The power imbalances part that frequency difference determines, two parts sum is 1.h_pα, h_pβRepresent two h bridge units of homophase, t_hpα, t_hpβ, f_hpα, f_hpβRepresent p (p=a, b, c) phase jackshaft h respectively_pα, h_pβThe average on-time of switching tube and frequency, x represents in h bridge The weight coefficient of switching tube conduction loss, y and z represents the weight coefficient turning on and off loss respectively.If only considering, conducting is damaged Consumption, makes x=1, y=z=0, formula (1) is reduced to

$s_m(\mathrm{\&alpha;},\mathrm{\&beta;})=|1-\frac{t_{hp\mathrm{\&alpha;}}}{t_{hp\mathrm{\&beta;}}}|---\left(2\right)$

Formula (2) illustrates, ideally the power imbalances degree of h bridge unit can be determined by the average on-time of switching tube.

In addition, the output defining h bridge unit in 0～π half period is p_hpαIt is assumed that phase voltage and phase current homophase Position, can obtain

$p_{hp\mathrm{\&alpha;}}=u*i_p=\sqrt{\frac{e^2*2t_{hp\mathrm{\&alpha;}}}{0.5t}}*i_p---\left(3\right)$

In formula, u represents h bridge unit output voltage virtual value, i_pRepresent phase voltage virtual value, t represents the output cycle.Formula (3) it is also denoted as

$p_{hp\mathrm{\&alpha;}}=\frac{1}{3}{u}_p*i_p---\left(4\right)$

U in formula (4)_pRepresent phase voltage virtual value, if t_hpα=t_hpβ, s (α, β)=0 is obtained by formula (2), represents, p_hpα= p_hpβ.

Consider a kind of extreme case, when modulation ratio m_aWhen relatively low, a certain h bridge Non voltage output can be made.Research shows, when 0.33<m_a< 0.66, modulating wave v_maWith v_cr1, v_cr1-Non-intersect it is impossible to produce bridge h_a1Breaker in middle pipe trigger pulse, thus v_ha1No Voltage output, as shown in Figure 3.

Bridge h in whole cycle_a1Switching tube be not turned on, no conduction loss produce, now, s_m(1,2)=1, s_m(1,3)= 1,0 < s_m(2,3) < 1, illustrate bridge h_a1With h_a2, h_a1With h_a3Power imbalances degree very high, and h_a2With h_a3Power imbalances degree phase To relatively low.Work as m_a< 0.33, h_a2Switching tube be also no longer turned on, now, s_m(1,3)=1, s_m(2,3)=1, so modulation ratio m_a Uncertainty can be brought to the change of power imbalances degree, increase the difficulty of power equalization.

The new homophase cascade type spwm pulse distribution strategy of embodiment 2 present invention

Fig. 4 show traditional ipd and new ipd apply in 7 electrical level inverter wherein one mutually cascade h bridge is corresponding opens Close pulse sequence.In figure, s_pxSwitching pulse signal set on expression x-th h bridge of p (p=a, b, c) phase, waveform symmetry, it Positive and negative do not have practical significance, is intended merely to be consistent with now corresponding h bridge output voltage polarity.s_pxComprise 4 switches Pulse signal.The pulse collection distributing to first h bridge of this phase is defined as s_p1, then s_p1=[s_p11s_p12s_p13 s_p14], in set, the subscript of each element is corresponding with the subscript of switching tube each in Fig. 1, represents the pulse signal to inductive switch, with this Analogize, second h bridge pulse collection is s_p2=[s_p21s_p22s_p23s_p24], the 3rd h bridge pulse collection is defined as s_p3= [s_p31s_p32s_p33s_p34].

As Fig. 4 (a) show the switching pulse sequential that traditional ipd controls lower 7 electrical level inverter h bridges.In figure shows, is used for Produce v_hx1, v_hx2, v_hx3Switching pulse signal be s respectively_p1, s_p2, s_p3, wherein shadow region indicates intensive pulsed beams, carries Bob is higher, and the pulsed beams in shadow region are closeer, and hollow area represents corresponding switching tube constant conduction.Except s_p1Outward, s_p2, s_p3Often Half period all can experienced three stages, such as in 0～π half period, s in shadow region_p2=[1/0,0,0,1/0], hollow section S in domain_p2=[1,0,0,0], 0 expression does not produce pulse of setting out, and switches off, 1 indicates lasting trigger pulse, and switch is led Logical, 1/0 expression switching pulse s_p21, s_p23Discontinuously but synchronous, frequently conducting turns off switch, due to waveform symmetry, the later half cycle with First half cycle hatched area is equal, and hollow parts are also equal, and switching tube average on-time and average frequency of switching are described Equal.But s_p1, s_p2, s_p3Shade or the hollow area tending to are simultaneously unequal, and average switch frequency in each h bridge in traditional ipd method is described The peaceful duration that is both turned on of rate is unequal, so switch power loss cannot equalize, the output of each h bridge is also unequal.

H bridge pulse signal sequential under new ipd shown in Fig. 4 (b).In in figure 0～1/4 cycle, pulse signal is kept Consistent with traditional ipd pulse, the corresponding switching pulse signal of each h bridge is s_p1, s_p2, s_p3, as the first row of table 1, now, h bridge Switching pulse sequence is s_p1, s_p2, s_p3；Then, after 1/4 cycle, pulse signals sequential carries out rotation, that is, at 1/4～1/2 week In phase, the corresponding switching pulse signal of each h bridge is s_p2, s_p3, s_p1, as the second row of table 1；In the same manner, within 1/2～3/4 cycle, Corresponding pulse signal is s_p3, s_p1, s_p2, corresponding table 1 the third line；In last a quarter cycle, the corresponding switching pulse of h bridge Signal is consistent with traditional ipd pulse, that is, 3/4 cycle complete one cycle, so circulation.Because each h bridge switch pulse signal is every The rotation of a quarter cycle is once so that the average on-time of switching tube and average frequency of switching are essentially equal.

Table 1 pulse distribution order

Fig. 4 (b) and table 1 all show, the every 1/4 cycle rotation of each h bridge switch pipe pulse signal once, seven level cascade unsteady flows Device completes a rotation through 3/4 cycle each h bridge pulse signal, then definable minimum rotational cycle t_m=3/4t, cycle t_mIt is interior, Pulse signal set s_p1, s_p2, s_p3Mean allocation action time, so the average on-time of each h bridge switch pipe and averagely opening Close frequency equal.Assume pulse signal s in 1/4 cycle_pxThe conduction loss producing and switching loss sum are e (s_px), then One t_mInside have

$\left\{\begin{array}{c}{e}_{hx1}=e\left(s_{p1}\right)+e\left(s_{p2}\right)+e\left(s_{p3}\right)\\ e_{hx2}=e\left(s_{p2}\right)+e\left(s_{p3}\right)+e\left(s_{p1}\right)\\ e_{hx3}=e\left(s_{p3}\right)+e\left(s_{p1}\right)+e\left(s_{p2}\right)\end{array}\right.---\left(5\right)$

Obviously, e in formula (5)_hx1=e_hx2=e_hx3, show in a minimum rotational cycle t_mInterior, three cascade h of every phase The switching tube of bridge achieves power attenuation equilibrium, and each h bridge output will be equal.

The line voltage frequency analyses of the new homophase cascade type spwm pulse distribution policy control of embodiment 3

New ipd-spwm pulse distribution strategy changes the sequential of each h bridge unit output voltage, and exports phase voltage etc. In the superposition of the h bridge unit output voltage of homophase cascade, but h bridge output voltage sequential is otherwise varied with traditional ipd, in order to beg for Whether affect inverter output voltage characteristic by new ipd pulse distribution strategy, the present invention taking seven level h bridges as a example, by implementing Ipd specificity analysises in example 1, know that h bridge output voltage waveforms are consistent with corresponding pulse sequence, 2 split GUAN-pulse in conjunction with the embodiments The analysis rushing sequential can sum up the output voltage rule of new ipd, and table 2 show the new ipd method after pulse rotation Lower h bridge output voltage sequence.

Table 2 output voltage order

The output voltage v of any phase under new ipd_xnewCan be expressed as

v_xnew=v_hx1new+v_hx2new+v_hx3new(6)

In formula, x represents a, any one phase, v in b, c_hx1new, v_hx1new, v_hx1newIt is respectively the defeated of the lower three h bridges of new ipd Go out voltage, because new ipd output voltage is only the sequential rotation of traditional ipd output voltage, therefore, each when inscribe three bridges Output voltage sum does not change.Therefore, the output phase voltage of multi-electrical level inverter and line voltage and tradition under new ipd Completely the same during ipd, have no effect on output voltage characteristic.

Below frequency analyses are carried out to new ipd method inverter output voltage, be compared with cps method simultaneously.Ipd and Cps modulation method be essentially unipolarity modulation method, according to the feature of spwm modulation method, the output voltage of inverter should have as follows Three kinds of harmonic contents

(1) modulate the integral multiple subharmonic of angular frequency；

(2) the integral multiple subharmonic of triangular carrier angular frequency；

(3) centered on triangular carrier angular frequency integral multiple subharmonic, to modulate the sideband harmonic wave as beat frequency for the angular frequency；

For m electrical level inverter, every phase n h bridge cascade, through bilateral Fourier transformation, obtain meeting above-mentioned harmonic wave spy The line voltage formula (7) of point,

$\begin{array}{c}{u}_{an}\left(t\right)=a_{00}/2+\underset{n=1}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\&lsqb;a_{0n}\cos \left({\mathrm{n\&omega;}}_{0}t\right)+b_{0n}\sin \left({\mathrm{n\&omega;}}_{0}t\right)\&rsqb;+\\ \underset{m=1}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\&lsqb;a_{mn}\cos \left({\mathrm{n\&omega;}}_{0}t+{\mathrm{n\&omega;}}_{c}t\right)+b_{mn}\sin \left({\mathrm{n\&omega;}}_{0}t+{\mathrm{n\&omega;}}_{c}t\right)\&rsqb;\end{array}---\left(7\right)$

ω in formula₀, ω_cFor sinusoidal modulation wave and triangular carrier angular frequency, m, n are integer, a₀₀For DC component, a_mn, b_mn For carrier wave integral multiple subharmonic and neighbouring sideband harmonic constant.

Define voltage transfer ratio r, if the benchmark harmonic voltage of single h bridge is

u_r(t)=ru_insin(ω₀t) (8)

According to document (Wu Zhizhuo, Li Sheng, etc. improved homophase cascade type spwm controls cascaded multilevel inverter [j]. Power Electronic Technique, 2014,10:22-25.) relevant conclusion, then can get phase voltage u of ipd method output_{ipd_an}(t) and line Voltage u_{ipd_ab}T the expression formula of () is respectively

$\begin{array}{c}{u}_{ipd\_an}\left(t\right)={\mathrm{nru}}_{in}\sin \left({\mathrm{\&omega;}}_{0}t\right)+\underset{m=1}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\left\{b_{p1}\left(m,n\right)\&centerdot;\sin \&lsqb;\left(2m-1\right){\mathrm{\&omega;}}_{c}t+2{\mathrm{n\&omega;}}_{0}t\&rsqb;\right\}\\ +\underset{m=1}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\left\{c_{p1}\left(m,n\right)\&centerdot;\sin \&lsqb;2{\mathrm{m\&omega;}}_{c}t+\left(2n-1\right){\mathrm{\&omega;}}_{0}t\&rsqb;\right\}\end{array}---\left(9\right)$

In formula,

A=4u_in(-1)^kj_2k+1·[3r(2m-1)π]/[π²(2m-1)], b=(2n-2k-1)^-1, c=(2n+2k+1)^-1,

c_p1(m, n)=[u_in/(πm)]j_2n-1(6rm π), j is Bessel function.

$\begin{array}{c}{u}_{ipd\_ab}\left(t\right)=\sqrt{3}{\mathrm{nru}}_{in}\sin \left({\mathrm{\&omega;}}_{0}t+\mathrm{\&pi;}/6\right)+\underset{m=1}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\left\{b_{11}\left(m,n\right)\sin \&lsqb;\left(2m-1\right){\mathrm{\&omega;}}_{c}t+2{\mathrm{n\&omega;}}_{0}t-2n\mathrm{\&pi;}/3\&rsqb;\right\}\\ +\underset{m=1}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\mathrm{\&sigma;}}}\left\{c_{11}\left(m,n\right)\sin \&lsqb;2{\mathrm{m\&omega;}}_{c}t+\left(2n-1\right){\mathrm{\&omega;}}_{0}t-\left(2n-1\right)\mathrm{\&pi;}/3\&rsqb;\right\}\end{array}---\left(10\right)$

B in formula₁₁(m, n)=2sin (2n π/3) b_p1(m, n), c₁₁(m, n)=2sin [(2n-1) π/3] c_p1(m,n).

Output phase voltage and the line voltage of cps modulation method can be obtained with similar method

$u_{cps\_an}\left(t\right)={\mathrm{nru}}_{in}sin\left({\mathrm{\&omega;}}_{0}t\right)+\underset{m=1}{\overset{\mathrm{\&infin;}}{\&sigma;}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\&sigma;}}\{b_{p2}(m,n)\&centerdot;sin\&lsqb;6{\mathrm{m\&omega;}}_{cc}t+(2n-1){\mathrm{\&omega;}}_{0}t\&rsqb;\}---\left(11\right)$

$u_{cps\_ab}\left(t\right)={\mathrm{nru}}_{in}sin\left({\mathrm{\&omega;}}_{0}t\right)+\underset{m=1}{\overset{\mathrm{\&infin;}}{\&sigma;}}\underset{n=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\&sigma;}}\{b_{12}(m,n)\&centerdot;sin\&lsqb;6{\mathrm{m\&omega;}}_{cc}t+(2n-1)({\mathrm{\&omega;}}_{0}t-\mathrm{\&pi;}/3)\&rsqb;\}---\left(12\right)$

B in formula (11)_p2(m, n)=2u_inj_(2n-1)(m π nr)/(π m),

B in formula (12)₁₂(m, n)=2sin [(2n-1) π/3] b_p2(m,n).

When taking m=1, the main energetic of two kinds of modulator approach output harmonic waves concentrates on ω_cNear.Document (Wu Zhizhuo, Lee Victory, etc. improved homophase cascade type spwm controls cascaded multilevel inverter [j]. Power Electronic Technique, 2014,10:22- 25.), give the spectrum analyses of cps and cd modulation method, now cascading h bridge inverter with 7 level is taking 5 electrical level inverters as a example Example, provides ipd and cps modulation method in carrier frequency ω_cNeighbouring harmonic content.

$\left\{\begin{array}{c}{h}_{pd\_an}=\frac{\sqrt{\underset{n=1}{\overset{10}{\&sigma;}}{b}_{p1}^2(1,n)}}{3{\mathrm{ru}}_{in}},h_{pd\_ab}=\frac{\sqrt{\underset{n=1}{\overset{10}{\&sigma;}}{b}_{11}^2(1,n)}}{3\sqrt{3}{\mathrm{ru}}_{in}}\\ h_{cps\_an}=\frac{\underset{n=1}{\overset{10}{\&sigma;}}{b}_{p2}^2(1,n)}{3{\mathrm{ru}}_{in}},h_{cps\_ab}=\frac{\underset{n=1}{\overset{10}{\&sigma;}}{b}_{12}^2(1,n)}{3\sqrt{3}{\mathrm{ru}}_{in}}\end{array}\right.---\left(13\right)$

Calculate the harmonic wave of output voltage curve of ipd and cps modulation method in conjunction with formula (13).

In Fig. 5 (a), two harmonic curves essentially coincide it can be determined that the phase voltage of two kinds of modulator approaches is in ω_cThe harmonic wave at place Content is essentially identical, and in Fig. 5 (b), the harmonic curve of ipd modulation method is significantly lower than cps method, illustrates ipd modulation method Line voltage waveform quality is higher than cps.

The emulation of embodiment 4 the inventive method and test

For feasibility and the reliability of proof theory analysis, by matlab/simulink emulation platform to 7 level levels Connection h bridge inverter carries out simulation analysis.Design capacity 2mva, inverter exports fundamental wave line voltage 2300v, inverter output frequency 50hz, every phase load 200 ω, frequency of modulated wave 50hz, carrier frequency 5khz, modulation ratio is respectively set to 0.99 and 0.6.Set up Phantom, when modulation ratio is 0.99, obtains the voltage simulation waveform of new ipd method output.Contrast Fig. 6 and Fig. 4 (b), card Clear switching pulse sequential is consistent with h bridge output voltage sequential, illustrates the correctness of theory analysis, and in Fig. 7, new ipd method is defeated Go out phase voltage identical with traditional ipd method with line voltage simulation waveform, also demonstrate defeated with regard to new ipd method in embodiment 3 analysis Going out voltage does not affect to export phase voltage, the conclusion of line voltage waveform quality.

V in Fig. 8_abThd only have 10.78%, under equivalent environment, not using pulse signal shift process measurement thd Essentially identical it can be seen that, new ipd-spwm pulse distribution strategy, inherit traditional ipd method low line voltage thd excellent Point, demonstrates theory analysis.

Changing modulation ratio is 0.6, and the traditional ipd method of contrast and new ipd FAXIA cascade h bridge unit output voltage.Due to adjusting System ratio is relatively low, v in Fig. 9 (a)_hx1Non voltage output, according to formula (2), obtains s_m(1,2)=1, s_m(1,3)=1, power imbalances degree pole Height, then according to formula (5), e (s_p1)=0, that is, the switch of this first h bridge of phase do not produce loss, Fig. 9 (b) is made using new ipd method Obtain v_hx1There is voltage output, through 0.15s, i.e. minimum rotational cycle t_m, s can be made_m(1,2)=s_m(1,3)=s_m(2,3)=0, H bridge unit output is of substantially equal, due to occurring signal rotation, average frequency of switching and time equal, according to formula (1) also There is s (1,2)=s (1,3)=s (2,3)=0, power imbalances eliminate；Another aspect e_hx1=e_hx2=e_hx3, represent the 3 of homophase Individual h bridge unit switch pipe loss is equal, reaches power equalization.Fig. 9 (c) neutral voltage v_abThd meet equal to 17.43% pre- Phase.

In order to verify the correctness based on new homophase cascade type spwm pulse distribution strategy, the present invention sets up 7 level levels Connection h bridge experimental prototype.The power supply of h bridge unit is provided by the s-350-24 of nova electric corporation, is 24v.Control chip is adopted With the tms320f2812 of ti company, oscillograph adopts tectronix dpo3014, and power analyzer adopts yokogawa Wt310, switching frequency 5khz, load resistance 200 ω.Figure 10 is output phase voltage and line voltage waveform, and Figure 11 is a phase h bridge list First output voltage.Experimental waveform is basically identical with Digital Simulation waveform.Due to there occurs pulse signal rotation, switch between each h bridge Power attenuation reach balance, and the output of h bridge is also equal.Because the power attenuation of switch is difficult to measure, here hard Rate analyser tests output voltage and the power of each h bridge unit, and each h bridge unit output voltage virtual value is about 18v, Output is about 3w, and correctness and the feasibility of institute of the present invention extracting method are described.

It should be appreciated that for those of ordinary skills, can be improved according to the above description or be converted, And all these modifications and variations all should belong to the protection domain of claims of the present invention.

Claims (1)

1. a kind of homophase cascade type spwm pulse allocating method being applied to cascaded multilevel inverter is it is characterised in that every 1/4 The output cycle carries out rotation to trigger pulse, just can reach power-balance between each cascade module through 3 rotations.