CN104953876A - Method for minimally modulating on-off times of cascaded h-bridge multilevel inverter - Google Patents

Abstract

The invention discloses a method for minimally modulating the on-off times of a cascaded H-bridge multilevel inverter, and belongs to the field of modulation of cascaded multilevel inverters. A conventional unipolar SPWM causes unnecessary on-off times, and along with the increase of the number of cascaded units, the unnecessary on-off times are overlaid. Aiming at solving the problem, a strategy for minimally modulating the on-off times of a cascaded multilevel inverter is provided, and comprises the following steps: an integrated cascaded structure adopts a carrier phase-shifting modulating way; each single cascaded unit adopts an improved unipolar modulating way, and the on-off state of a switching tube on the chopping arm of each H-bridge unit of the cascaded multilevel inverter; the percent, for occupying the time, of the on-off state of the chipping arm in the modulating period is calculated. Compared with the conventional unipolar SPWM, The strategy has the advantages that the on-off times can be reduced greatly, and the variation of output performance, which is caused by the fact that the on-off times are reduced, is avoided.

Description

H bridge cascaded multilevel inverter on-off times minimizes the method for modulation

Technical field

The present invention relates to the modulation field of cascaded multilevel inverter, refer in particular to a kind of method that H bridge cascaded multilevel inverter on-off times minimizes modulation.

Background technology

Voltage stress on H bridge cascaded multilevel inverter switching device is little, the degree of modularity is high, level number is many, be easy to realize redundancy, be easy to expansion and control, harmonic wave of output voltage characteristic is good, failure tolerant ability is strong, realize the conversion of high-power electric energy with low-voltage power electronic device, can be applicable in the high pressure higher power device such as the energy source regeneration apparatus such as high voltage direct current transmission, STATCOM and Active Power Filter-APF, photovoltaic generation and fuel cell power generation and the driving of high-power high swallow variable-frequency motor.

Modulation technique is the key technology of H bridge cascade multilevel inverter.The modulator approach that H bridge cascade multilevel inverter adopts mainly comprises Staircase wave, particular harmonic eliminates PWM, carrier phase-shifted PWM and many level SVPWMs etc.Wherein phase-shifted SPWM a kind of modulation technique that current cascaded multilevel inverter is generally adopted.Traditional phase-shifted SPWM generally adopts frequency multiplication SPWM modulator approach, and thus each power modules needs 2 PWM generator to produce drive singal, for H bridge cascaded multilevel inverter, must need to occupy a large amount of processor resources.Be incorporated in phase-shifted SPWM by Unipolar SPWM modulation system, more traditional employing frequency multiplication SPWM modulator approach can reduce the PWM generator of half, has saved a large amount of processor resource.

Conventional unipolar SPWM modulation system has the advantages such as switching loss is little, harmonic distortion is low compared with bipolar SPWM modulation system; The PWM generator of half can be reduced compared with multiple-frequency SPWM modulation system, saved processor resource.But conventional unipolar SPWM can bring unnecessary on-off times to the device for power switching on H bridge inverter copped wave arm, and along with H bridge cascaded multilevel inverter progression increase this unnecessary on-off times will be more obvious.

Summary of the invention

The object of the invention is the problem for conventional unipolar SPWM, the power device on H bridge inverter copped wave arm being brought to unnecessary on-off times, propose a kind of method that H bridge cascaded multilevel inverter on-off times minimizes modulation, be intended to the on-off times reducing H cascaded multilevel inverter.

The invention provides a kind of method that H bridge cascaded multilevel inverter on-off times minimizes modulation, in setting H bridge cascade multilevel inverter, the triangle carrier signal excursion of each submodule is identical, and be change between-1 ~ 1, the triangular carrier phase angle difference of adjacent two submodules is 360 °/N, and wherein N is cascade submodule number; Described modulator approach is as follows:

(1) by amplitude be the sinewave modulation signal of-1 to 1 and after zero level compares, obtain square-wave signal, this square-wave signal is followed successively by a road drive singal Vg1 of each submodule pitman arm device for power switching of H bridge cascaded multilevel inverter;

(2) to the square-wave signal logical inversion that step (1) obtains, another road drive singal Vg2 of each submodule pitman arm device for power switching of H bridge cascaded multilevel inverter is obtained;

(3) triangle carrier signal that the sinewave modulation signal in step (1) is corresponding with each submodule of H bridge cascaded multilevel inverter is obtained more afterwards the pwm pulse signal Vg3n ' that a road is associated with each power modules copped wave arm device for power switching;

(4) by the pwm pulse signal logical inversion that step (3) obtains, the pwm pulse signal Vg4n ' that another road is associated with each power modules copped wave arm device for power switching is obtained.

Further: H bridge cascaded multilevel inverter is made up of the direct cascade of multiple H-bridge unit structures, and described single H-bridge unit pitman arm and copped wave arm drive singal are obtained by following steps:

(5) step (1) and step (2) is adopted to obtain drive singal Vgn1 and Vgn2 of single power model pitman arm power device;

(6) step (3) and step (4) obtains two-way pwm signal Vgn3 ' and Vgn4 ', n are the n-th H-bridge unit is adopted;

(7) under passive linear load, fundametal compoment I ₀₁lag behind fundamental voltage U ₀₁, and phase difference formula is:

ω is inverse envelope frequency, L ₀for load inductance, R ₀for load resistance;

(8) within a modulation period, when the Vgn1 signal that step (5) obtains is low level by high level saltus step, load voltage values is zero, and obtain now load current value I by step (7) phase difference formula, and this moment is defined as zero moment, the electric current obtained is initial current I ₀;

(9) on step (8) basis, suppose that the Vgn3 ' signal of the corresponding step (6) when Vgn1 signal is low is for high, now the mode of operation of single power model is by load, diode D _n2and switching tube S _n3form discharge loop 1, loop equation is:

$L\frac{di}{{\mathrm{dt}}_a}+iR=0$

Can obtain:

r is load inductance, and L is load resistance;

(10) on step (9) basis, work as Vgn3 ' signal and become low level from high level, now the mode of operation of single power model is by D _n4, load, electric power generating composition discharge loop 2, loop equation is:

$L\frac{di}{{\mathrm{dt}}_b}+iR+U=0,$ U is supply voltage;

Can obtain:

$C=i_0+\frac{U}{R}$

Wherein, i ₀for the current value exported on a upper discharge loop back loading;

Can obtain:

$i=C*e^{-\frac{R}{L}{t}_b}-\frac{U}{R};$

(11) t in step (9) and step (10) _aand t _bbe the discharge time of discharge loop 1 and discharge loop 2 respectively, adopt the SPWM pulse generation method of asymmetric regular sampling method to be converted to and calculate t discharge time _aand t _b, until calculate by discharge circuit current value i=0 or i<0 that in step (9) or step (10), load exports;

(12) the time t that calculates of step (8) _awith t _bsum just for load is within a modulation period, discharges into zero total time t used after Vgn1 signal step-down _xif a square-wave signal is Vgx, and its duty ratio is:

$D=\frac{Tx/2+tx}{Tx}\&times;100\%$

Tx is the cycle of Vgx;

(13) the square-wave signal Vgx that the pwm signal Vgn3 ' step (6) obtained and step (12) obtain carries out logic and operation, obtains a road drive singal Vgn3 of power device on single power model copped wave arm;

(14) by the square-wave signal Vgx of step (12) to reach 180 °, obtain Vgx ' signal;

(15) the square-wave signal Vgx ' that the pwm signal Vgn4 ' step (6) obtained and step (14) obtain carries out logic and operation, obtains another road drive singal Vgn4 of power device on single power model copped wave arm.

Compared with prior art, such scheme of the present invention, the active power adopting phase-shifted SPWM modulation system that each concatenation unit can be made to bear is equal; Improvement Unipolar SPWM modulation system being incorporated in phase-shifted SPWM comparatively multiple-frequency SPWM can saving resource, and the present invention can reduce on-off times compared with conventional unipolar SPWM under the constant condition of output harmonic wave content.

Accompanying drawing explanation

Fig. 1 is the present invention's single-phase H bridge cascaded multilevel inverter topology diagram;

Fig. 2 is the PWM drive singal that a kind of method that single-phase H bridge inverter adopts H bridge cascaded multilevel inverter on-off times to minimize modulation obtains;

Fig. 3 is that single-phase H bridge inverter adopts a kind of H bridge cascaded multilevel inverter on-off times to minimize the voltage waveform of the method output of modulation;

Fig. 4 is that one-phase five-level inverter adopts a kind of H bridge cascaded multilevel inverter on-off times to minimize each submodule of method PWM drive singal of modulation;

Fig. 5 is that one-phase five-level inverter adopts a kind of H bridge cascaded multilevel inverter on-off times to minimize the method output voltage waveforms of modulation.

Embodiment

Technical scheme in the present invention is understood better in order to make those skilled in the art person, below in conjunction with the accompanying drawing in the embodiment of the present invention, technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.

Embodiment one

With reference to figure 2, it illustrates method that a kind of H bridge cascaded multilevel inverter on-off times provided by the invention minimizes modulation and be applied to the power device drive singal that Cell1 in Fig. 1 obtains, specifically comprise the following steps:

1) single-phase H bridge inverter is set, triangular carrier u _camplitude excursion is between-1 to 1;

2) set modulation wave signal as sinusoidal wave, modulating wave cycle fs is 50Hz, modulation depth m is 0.8;

3) by step 2) in the sinewave modulation signal that obtains compare with zero level, obtain power device S on H bridge inverter pitman arm _a1drive singal Vg1;

4) by step 3) the drive singal Vg1 logical inversion that obtains, obtain power device S on H bridge inverter pitman arm _a2drive singal Vg2;

5) by step 1) triangular carrier u _cwith step 2) sinewave modulation signal compare and obtain pulse signal Vg3 ';

6) by step 5) pulse signal Vg3 logical inversion obtain pulse signal Vg4 ';

7) under passive linear load, fundametal compoment I ₀₁lag behind fundamental voltage U ₀₁, and phase difference formula is:

ω is inverse envelope frequency, L ₀for load inductance, R ₀for load resistance;

8) within a modulation period, when step 3) the Vg1 signal that obtains is when being low level by high level saltus step, load voltage values is zero, and by step 7) phase difference formula obtains now load current value I, and this moment is defined as zero moment, the electric current obtained is initial current I ₀;

9) in step 8) on basis, suppose the corresponding step 5 when Vg1 signal is low) Vg3 ' signal for high, now the mode of operation of single power model is by load, diode D ₂and switching tube S _a3form discharge loop 1, loop equation is:

$L\frac{di}{{\mathrm{dt}}_a}+iR=0$

Can obtain:

r is load inductance, and L is load resistance;

10) in step 9) on basis, work as Vg3 ' signal and become low level from high level, now the mode of operation of single power model is by D ₄, load, electric power generating composition discharge loop 2, loop equation is:

$L\frac{di}{{\mathrm{dt}}_b}+iR+U=0,$ U is supply voltage;

Can obtain:

i ₀for the current value exported on a upper discharge loop back loading;

$i=C*e^{-\frac{R}{L}{t}_b}-\frac{U}{R};$

11) step 9) and step 10) in t _aand t _bbe the discharge time of discharge loop 1 and discharge loop 2 respectively, adopt the SPWM pulse generation method of asymmetric regular sampling method to be converted to and calculate t discharge time _aand t _b, until calculate step 9 by discharge circuit) or step 10) in load export current value i=0 or i<0;

12) step 11) the time t that calculates _awith t _bsum is just for load is within a modulation period, and Vg1 signal step-down back loading discharges into zero total time t used _x, obtain a square-wave signal Vgx, its duty ratio is:

$D=\frac{Tx/2+tx}{Tx}\&times;100\%$

Tx is the cycle (the present embodiment value is 0.02s) of Vgx;

13) by step 5) the drive singal Vg3 ' that obtains and step 12) the square-wave signal Vgx logic and operation that obtains, to obtain in Fig. 1 on Cell1 power device S on copped wave arm _a3drive singal Vg3;

14) by step 12) square-wave signal Vgx to reach 180 °, obtain Vgx ' signal;

15) by step 6) the drive singal Vg4 ' that obtains and step 14) the square-wave signal Vgx ' logic and operation that obtains, to obtain in Fig. 1 on Cell1 power device S on copped wave arm _a4drive singal Vg4;

Embodiment two

With reference to figure 4, it illustrates the method that a kind of H bridge cascaded multilevel inverter on-off times provided by the invention minimizes modulation, when H bridge cascade number is 2, the output voltage waveforms obtained be five level as shown in Figure 5.As shown in Figure 4, the PWM drive singal on each submodule.Modulator approach specifically comprises the following steps:

1) triangle carrier signal u corresponding to two submodules is set _c1and u _c2, its frequency is identical with amplitude, and phase angle differs 180 °;

2) employing is compared with zero level with a kind of identical sinewave modulation signal of embodiment, power device one road drive singal Vgn1 (n=1 on two submodule pitman arms, 2), by another road of power device drive singal Vgn2 (n=1,2) on drive singal Vgn1 logical inversion computing pitman arm;

3) by modulation wave signal and step 1) in corresponding triangular carrier compare respectively and obtain pwm pulse signal Vgn3 ' (n=1,2);

4) by step 2) in pwm pulse signal Vgn3 ' carry out logical inversion computing and obtain pwm pulse signal Vgn4 ' (n=1,2);

5) step 7 in embodiment one is adopted) to step 15) obtain drive singal Vgn3, the Vgn4 (n=1,2) of each power device in two power models.

In sum: improve the on off state of switching tube on each H-bridge unit copped wave arm, calculate under single H bridge minimizes on-off times modulation strategy, on copped wave arm, switching tube on-off times accounts for the percentage of time of a modulation period;

On single H bridge copped wave arm the on-off times of one of them switching tube account for one modulation period percentage of time:

$P=\frac{tx+\frac{Ts}{2}}{Ts}*100\%$

Ts is modulation period.

Therefore within a modulation period, minimize on-off times modulation strategy and greatly reduce compared to the on-off times of conventional unipolar SPWM modulation strategy switching tube.

Those of ordinary skill in the art will appreciate that, embodiment described here is to help reader understanding's implementation method of the present invention, should be understood to that protection scope of the present invention is not limited to so special statement and embodiment.Those of ordinary skill in the art can make various other various concrete distortion and combination of not departing from essence of the present invention according to these technology enlightenment disclosed by the invention, and these distortion and combination are still in protection scope of the present invention.

Claims (2)

1. a H bridge cascaded multilevel inverter on-off times minimizes the method for modulation, it is characterized in that: in setting H bridge cascade multilevel inverter, the triangle carrier signal excursion of each submodule is identical, and be change between-1 ~ 1, the triangular carrier phase angle difference of adjacent two submodules is 360 °/N, and wherein N is cascade submodule number; Described modulator approach is as follows:

(1) by amplitude be the sinewave modulation signal of-1 to 1 and after zero level compares, obtain square-wave signal, this square-wave signal is followed successively by a road drive singal Vg1 of each submodule pitman arm device for power switching of H bridge cascaded multilevel inverter;

(2) to the square-wave signal logical inversion that step (1) obtains, another road drive singal Vg2 of each submodule pitman arm device for power switching of H bridge cascaded multilevel inverter is obtained;

(3) triangle carrier signal that the sinewave modulation signal in step (1) is corresponding with each submodule of H bridge cascaded multilevel inverter is obtained more afterwards the pwm pulse signal Vg3n ' that a road is associated with each power modules copped wave arm device for power switching;

(4) by the pwm pulse signal logical inversion that step (3) obtains, the pwm pulse signal Vg4n ' that another road is associated with each power modules copped wave arm device for power switching is obtained.

2. H bridge cascaded multilevel inverter on-off times according to claim 1 minimizes the method for modulation, it is characterized in that: H bridge cascaded multilevel inverter is made up of the direct cascade of multiple H-bridge unit structures, and described single H-bridge unit pitman arm and copped wave arm drive singal are obtained by following steps:

(5) step (1) and step (2) is adopted to obtain drive singal Vgn1 and Vgn2 of single power model pitman arm power device;

(6) step (3) and step (4) obtains two-way pwm signal Vgn3 ' and Vgn4 ', n are the n-th H-bridge unit is adopted;

(7) under passive linear load, fundametal compoment I ₀₁lag behind fundamental voltage U ₀₁, and phase difference formula is:

ω is inverse envelope frequency, L ₀for load inductance, R ₀for load resistance;

(8) within a modulation period, when the Vgn1 signal that step (5) obtains is low level by high level saltus step, load voltage values is zero, and obtain now load current value I by step (7) phase difference formula, and this moment is defined as zero moment, the electric current obtained is initial current I ₀;

(9) on step (8) basis, suppose that the Vgn3 ' signal of the corresponding step (6) when Vgn1 signal is low is for high, now the mode of operation of single power model is by load, diode D _n2and switching tube S _n3form discharge loop 1, loop equation is:

$L\frac{di}{{\mathrm{dt}}_a}+iR=0$

Can obtain:

r is load inductance, and L is load resistance;

(10) on step (9) basis, work as Vgn3 ' signal and become low level from high level, now the mode of operation of single power model is by D _n4, load, electric power generating composition discharge loop 2, loop equation is:

$L\frac{di}{{\mathrm{dt}}_b}+iR+U=0,$ U is supply voltage;

Can obtain:

$C=i_0+\frac{U}{R}$

Wherein, i ₀for the current value exported on a upper discharge loop back loading;

Can obtain:

$i=C*e^{-\frac{R}{L}{t}_b}-\frac{U}{R};$

(11) t in step (9) and step (10) _aand t _bbe the discharge time of discharge loop 1 and discharge loop 2 respectively, adopt the SPWM pulse generation method of asymmetric regular sampling method to be converted to and calculate t discharge time _aand t _b, until calculate by discharge circuit current value i=0 or i<0 that in step (9) or step (10), load exports;

(12) the time t that calculates of step (8) _awith t _bsum just for load is within a modulation period, discharges into zero total time t used after Vgn1 signal step-down _xif a square-wave signal is Vgx, and its duty ratio is:

$D=\frac{Tx/2+tx}{Tx}\&times;100\%$

Tx is the cycle of Vgx;

(13) the square-wave signal Vgx that the pwm signal Vgn3 ' step (6) obtained and step (12) obtain carries out logic and operation, obtains a road drive singal Vgn3 of power device on single power model copped wave arm;

(14) by the square-wave signal Vgx of step (12) to reach 180 °, obtain Vgx ' signal;

(15) the square-wave signal Vgx ' that the pwm signal Vgn4 ' step (6) obtained and step (14) obtain carries out logic and operation, obtains another road drive singal Vgn4 of power device on single power model copped wave arm.