CN105099253A - Pulse-width modulation method for maximum boost pressure and minimum switching frequency of Z-source inverter - Google Patents

Abstract

The invention discloses a pulse-width modulation method for maximum boost pressure and minimum switching frequency of a Z-source inverter. According to the method, direct-current side voltage of an inverter bridge in a switching period Ts is an instantaneous maximum value of the voltage of a three-phase alternating-current output line by adjusting through time of a one-phase bridge arm, so that the equivalent switching frequency of a power semiconductor device in the inverter bridge can be reduced into 1/3fs. According to the pulse-width modulation method, middle direct-current side voltage of the Z-source inverter is controlled to be the instantaneous maximum value of the voltage of an envelope line, namely a three-phase line, of alternating-current output phase voltage, so that the voltage stress and the equivalent switching frequency of the power semiconductor device in a high-gain application occasion are effectively reduced; and reduction of the cost of the power semiconductor device in a converter and improvement of the electric energy conversion efficiency are facilitated. In addition, according to the modulation method disclosed by the invention, the direct-current side inductive current and the capacitor voltage of the Z-source inverter comprise low-frequency ripples of a six-time fundamental frequency. The novel modulation method is also relatively suitable for 400-800Hz intermediate-frequency alternating-current power supply systems, such as airborne power supply systems and ship power supply systems.

Description

The maximum boosting of Z-source inverter and minimal switching frequency pulse duration modulation method

[technical field]

The invention belongs to new forms of energy photovoltaic, fuel cell distributed power field, be specifically related to the maximum boosting of a kind of Z-source inverter and minimal switching frequency pulse duration modulation method.

[background technology]

New forms of energy photovoltaic generation, fuel cell-powered drive system of electric automobile have broad application prospects.But their obvious features are that DC power supply voltage is low, voltage wide range changes, and falls obviously.Therefore, electronic power convertor regulation voltage amplitude and frequency must be adopted to obtain alternating current needed for relatively high electrical network or power consumption equipment.Traditional three-phase voltage source inverter output AC voltage peak value is less than the half of input DC power voltage, therefore, can only realize step-down DC-AC power conversion.When adopt sinusoidal pulse width modulation (SPWM) add third-harmonic zero-sequence voltage or space vector modulation (SVM) improve voltage transmission than time, the maximum ac phase voltage of acquisition is about 0.57 times of direct current power source voltage.Above-mentioned power supply characteristic proposes urgently strict requirement to electronic power convertor: wide region buck regulating power, low cost, high-gain, high efficiency etc.Therefore, the DC-AC inverter topology of high efficiency, high-gain and control method thereof become the focus of domestic scholars research.

Z-source inverter (as shown in Figure 1), introduces the impedance network that inductance is connected with electric capacity Z-type between DC power supply and inverter bridge, utilizes the straight-through realization boosting regulatory function of upper and lower switching device in brachium pontis.Compared to conventional voltage source inventer, Z-source inverter has following obvious advantage, realizes buck regulatory function; As single stage power converter, reduce switching device quantity, improve energy conversion efficiency; Allow the upper and lower switching device of brachium pontis to lead directly to, improve system reliability; Eliminate the dead band of inverter, reduce harmonic wave of output voltage, improve the quality of power supply.Therefore, at wide input DC-AC power conversion occasion Z-source inverter, there is obvious efficiency, cost and reliability advantage.

Due to the circuit structure of Z-source inverter uniqueness, document [1] " PengFangzheng " Z-sourceinverter "; IEEETransactionsonIndustryApplications; vol.39; no.2; pp.504-510, Mar2003 give a kind of typical pulse-widths modulator approach while proposition circuit topology.There is the low shortcoming of direct voltage utilance in typical pulse-widths modulator approach.Existing document [2] " MiaosenShen; JinWang; FangZhengPeng " ConstantboostcontroloftheZ-sourceinvertertominimizecurre ntrippleandvoltagestress "; IEEETransactionsonIndustryApplications, vol.42, no.3; pp.770-778; May2006 proposes the wide modulator approach of Z-source inverter maximum constant boosting rectifier control, improves direct voltage utilance, reduces switching device voltage stress simultaneously.One, Z-source inverter intermediate dc side switch periods (T _s) interior average voltage is constant and for exporting the maximum of phase voltage.Existing document [3] " ZhengPeng; MiaosenShen; ZhaomingQian, " MaximumboostcontroloftheZ-sourceinverter ", IEEETransactionsonPowerElectronics; vol.20; no.4, pp.833-838, July2005 propose maximum boosting pulse duration modulation method; all nought state of Z-source inverter all for the straight-through time, one, intermediate dc side switch periods (T _s) interior average voltage is equivalent to three-phase and exports the envelope of phase voltage.In addition, Z-source inverter direct-passing mode has single-phase bridge arm direct pass and three-phase brachium pontis straight-through two kinds of methods [4] " PohChiangLoh; D.MahindaVilathgamuwa; YueSenLai, " Pulse-WidthModulationofZ-SourceInverters ", IEEETransactionsonPowerElectronics; vol.20; no.6, pp.1346-1355, November2005 simultaneously.Above-mentioned pulse duration modulation method all can adopt document [4] two kinds of different bridge arm direct pass modes.When Z-source inverter adopts maximum constant boosting rectifier control, during single-phase bridge arm direct pass, in inverter bridge, the minimal switching frequency of power device is f _s(f _s=1/T _s), front end diode D ₁switching frequency be 6f _s.When Z-source inverter adopts maximum boosting rectifier control, during single-phase bridge arm direct pass, in inverter bridge, power device equivalent switching frequency is 2/3f _s, diode D ₁switching frequency 4f _s.

[summary of the invention]

The object of the invention is to exist for the existing control method of Z-source inverter reduce switching frequency further to improve the space of energy conversion efficiency, propose a kind of maximum boosting of Z-source inverter and the minimal switching frequency pulse duration modulation method that obtain maximum voltage gain and minimal switching frequency in theory, chien shih switch periods T during by regulating a phase brachium pontis straight-through _sinterior inverter bridge DC voltage is the instantaneous maximum of three-phase alternating current output line voltage, thus the equivalent switching frequency of power semiconductor device in inverter bridge can be reduced to 1/3f _s(f _s=1/T _s).

To achieve these goals, the present invention is achieved by the following technical solutions:

A kind of maximum boosting of Z-source inverter and minimal switching frequency pulse duration modulation method, chien shih switch periods T when regulating a phase brachium pontis straight-through _sinterior inverter bridge DC voltage is the instantaneous maximum of three-phase alternating current output line voltage, and concrete modulator approach comprises the following steps:

1) under given ac output voltage amplitude, according to formula (1) calculating voltage gain:

$G=\frac{{\hat{v}}_{ac}}{V_{dc}/2}=\frac{2{\hat{v}}_{ac}}{V_{dc}}---\left(1\right)$

Wherein, represent to exchange and export phase voltage peak value, V _dcdirect current power source voltage, G represents voltage gain, and it is defined as the ratio exchanging and export phase voltage peak value and 1/2 times of direct current power source voltage;

2) according to space voltage vector definition, ac output voltage is divided into six sectors, calculates in each sector according to formula (2), in arbitrary cycle, the straight-through duty ratio d of single-phase brachium pontis _sT:

$d_{ST}\left(\mathrm{\ω}t\right)=1-\frac{\sqrt{3}\mathrm{\π}G\·cos(\mathrm{\θ}-\frac{\mathrm{\π}}{6})}{6\sqrt{3}G-2\mathrm{\π}}---\left(2\right)$

Wherein: θ=ω t% (π/3), ω=2 π f _line, f _linefor exporting three-phase voltage fundamental frequency;

3) according to the on off state of six power devices in tables listing design inverter bridge:

0°≤θ≤60°

60°≤θ≤120°

120°≤θ≤180°

180°≤θ≤240°

240°≤θ≤300°

300°≤θ≤360°

A phase

S ap＝1；S an＝0

S apS an＝PWM

S ap＝0；S an＝1

S ap＝0；S an＝1

S apS an＝PWM

S ap＝1；S an＝0

B phase

S bpS bn＝PWM

S bp＝1；S bn＝0

S bp＝1；S bn＝0

S bpS bn＝PWM

S bp＝0；S bn＝1

S bp＝0；S bn＝1

C phase

S cp＝0；S cn＝1

S cp＝0；S cn＝1

S cpS cn＝PWM

S cp＝1；S cn＝0

S cp＝1；S cn＝0

S cpS cn＝PWM

4) according to the conducting duty ratio d of formula (3) evaluation work in the upper and lower switching tube of PWM one phase brachium pontis _sip(ω t) and d _sin(ω t):

$\left\{\begin{array}{c}{d}_{Sip}\left(\mathrm{\ω}t\right)=\frac{v_{mid}\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}{v_{\max }\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sin}\left(\mathrm{\ω}t\right)=\[1-d_{Sip}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(3\right)$

Wherein: in arbitrary sector, v _min(ω t) exports phase voltage minimum value; v _max(ω t) is phase voltage maximum, v _mid(ω t) is phase voltage median; I represents a phase a of output voltage median, b or c;

5) after determining each power device on off state of Z-source inverter and duty ratio, generate PWM drive singal by digitial controller, control main circuit.

The present invention further improves and is:

Described step 4) in, a switch periods T _sin, in inverter bridge, the power semiconductor device on off state of two brachium pontis maintains static work, and the power semiconductor device of another brachium pontis adopts pulse-width modulation PWM to take into account inverter bridge DC voltage and exports the adjustment of phase voltage; In inverter bridge, the equivalent switching frequency of power semiconductor device is reduced to 1/3f _s, wherein, f _s=1/T _s;

The on off state of the first sector is: v _max=v _a, v _mid=v _b, v _min=v _c, S _apand S _cnall the time open-minded, S _anand S _cpall the time turn off, the upper and lower switching tube S of B phase brachium pontis _bpand S _bnadopt PWM, its conducting duty ratio d _sbp, d _sbn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sbp}\left(\mathrm{\ω}t\right)=\frac{v_b\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}{v_a\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sbn}\left(\mathrm{\ω}t\right)=\[1-d_{Sbp}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(4\right)$

The on off state of the second sector is: v _max=v _b, v _mid=v _a, v _min=v _c, S _bpand S _cnall the time open-minded, S _bnand S _cpall the time turn off, the upper and lower switching tube S of A phase brachium pontis _apand S _anadopt PWM, its conducting duty ratio d _sap, d _san(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sap}\left(\mathrm{\ω}t\right)=\frac{v_a\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}{v_b\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{San}\left(\mathrm{\ω}t\right)=\[1-d_{Sap}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(5\right)$

The on off state of the 3rd sector is: export three-phase voltage v _max=v _b, v _mid=v _c, v _min=v _a, S _bpand S _anall the time open-minded, S _bnand S _apall the time turn off, the upper and lower switching tube S of C phase brachium pontis _cpand S _cnadopt PWM and on off state is complementary, its conducting duty ratio d _scp, d _scn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Scp}\left(\mathrm{\ω}t\right)=\frac{v_c\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}{v_b\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Scn}\left(\mathrm{\ω}t\right)=\[1-d_{Scp}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(6\right)$

The on off state of the 4th sector is: export three-phase voltage v _max=v _c, v _mid=v _b, v _min=v _a, S _cpand S _anall the time open-minded, S _cnand S _apall the time turn off, the upper and lower switching tube S of B phase brachium pontis _bpand S _bnadopt PWM and on off state is complementary, its conducting duty ratio d _sbp, d _sbn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sbp}\left(\mathrm{\ω}t\right)=\frac{v_b\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}{v_c\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sbn}\left(\mathrm{\ω}t\right)=\[1-d_{Sbp}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(7\right)$

The on off state of the 5th sector is: export three-phase voltage v _max=v _c, v _mid=v _a, v _min=v _b, S _cpand S _bnall the time open-minded, S _cnand S _bpall the time turn off, the upper and lower switching tube S of A phase brachium pontis _apand S _anadopt PWM and on off state is complementary, its conducting duty ratio d _sap, d _san(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sap}\left(\mathrm{\ω}t\right)=\frac{v_a\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}{v_c\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{San}\left(\mathrm{\ω}t\right)=\[1-d_{Sap}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(8\right)$

The on off state of the 6th sector is: export three-phase voltage v _max=v _a, v _mid=v _c, v _min=v _b, S _apand S _bnall the time open-minded, S _anand S _bpall the time turn off, the upper and lower switching tube S of C phase brachium pontis _cpand S _cnadopt PWM and on off state is complementary, its conducting duty ratio d _scp, d _scn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Scp}\left(\mathrm{\ω}t\right)=\frac{v_c\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}{v_a\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Scn}\left(\mathrm{\ω}t\right)=\[1-d_{Sap}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(9\right).$

Compared with prior art, the present invention has following beneficial effect:

The present invention is by by Z-source inverter intermediate dc side voltage control being the interchange output envelope of phase voltage and the instantaneous maximum of three-phase line voltage, obtain direct voltage utilance maximum in theory and voltage gain, efficiently reduce voltage stress and the equivalent switching frequency of power semiconductor device under high-gain application scenario, contribute to reducing the cost of power semiconductor device in current transformer and improve energy conversion efficiency.In addition, the modulator approach that the present invention proposes, Z-source inverter DC side inductive current and capacitance voltage comprise the low-frequency ripple of six times of fundamental frequencies.This new type of modulation method is more suitable for being applied to 400-800Hz midfrequent AC power-supply system, as airborne and marine power generation system equally.

[accompanying drawing explanation]

Fig. 1 is the structural representation of Z-source inverter;

Fig. 2 is the structural representation of three-phase voltage source inverter;

Fig. 3 is the schematic diagram that three phase inverter bridge exports phase voltage and minimum direct current side voltage;

Fig. 4 is diode assistance for lifting pressure inverter direct-flow side equivalent circuit diagram, and wherein, (a) is equivalent circuit diagram during pass-through state, and (b) is equivalent circuit diagram during non-pass-through state;

Fig. 5 is that Z-source inverter adopts different modulation voltage gain comparison diagram, and wherein, (a) is voltage gain and straight-through time relationship, and (b) is voltage gain and inverse cascade equivalent modulation degree relation;

Fig. 6 is that Z-source inverter adopts graph of a relation between different modulation power semiconductor device voltage stress and voltage gain;

Fig. 7 is for adopting new type of modulation method Z-source inverter time-domain simulation results figure, wherein, a () is drive singal, b () is for exporting phase voltage and spectrum analysis, c () is phase voltage after filtering, d () is output line electric current, (e) is capacitance voltage for intermediate dc side voltage, (f);

Fig. 8 is that Z-source inverter adopts distinct pulse widths modulator approach efficiency comparison figure.

[embodiment]

Below in conjunction with accompanying drawing, the present invention will be further described in detail.

Key idea of the present invention is in an output voltage 60 ° of sectors, by regulating the mean value of the straight-through time controling inverter bridge DC voltage of a phase brachium pontis to be the envelope that current transformer three-phase exports phase voltage, i.e. and the instantaneous maximum of line voltage.A switch periods T _sin, in inverter bridge, the power semiconductor device on off state of two brachium pontis maintains static work, and the power semiconductor device of another brachium pontis adopts pulse-width modulation (PWM) to take into account inverter bridge DC voltage and exports the adjustment of phase voltage.Therefore, the equivalent switching frequency of power semiconductor device in inverter bridge can be reduced to 1/3f _s(f _s=1/T _s), the switching frequency of front end diode is reduced to 2f _s, contribute to the energy conversion efficiency reducing power semiconductor device cost and improve current transformer.In addition, the pulse duration modulation method that the present invention proposes, Z-source inverter DC side inductive current and capacitance voltage comprise the low-frequency ripple of six times of fundamental frequencies.For reducing the adverse effect of low-frequency ripple, it is more suitable for being applied to 400-800Hz midfrequent AC power-supply system, as airborne and marine power generation system equally.The invention discloses the pulse duration modulation method of the maximum boosting of a kind of Z-source inverter and minimal switching frequency.The method has simplicity of design, and reliability is high, is easier to the advantages such as practical application.

As shown in Figure 2, Fig. 2 gives traditional three-phase voltage source inverter main circuit.Inverter exports side joint three-phase balancing load, assuming that three-phase output voltage is symmetrical, the expression formula of its output voltage and power is as follows:

$\left\{\begin{array}{c}{v}_a\left(\mathrm{\ω}t\right)={\hat{v}}_{ac}\·cos\left(\mathrm{\ω}t\right)\\ v_b\left(\mathrm{\ω}t\right)={\hat{v}}_{ac}\·\cos (\mathrm{\ω}t-\frac{2}{3}\mathrm{\π})\\ v_c\left(\mathrm{\ω}t\right)={\hat{v}}_{ac}\·\cos (\mathrm{\ω}t+\frac{2}{3}\mathrm{\π})\end{array}\right.---\left(1\right)$

Wherein: with be respectively the peak value of phase voltage and phase current. it is the power-factor of load.ω＝2πf _line。Fig. 3 provides three phase inverter bridge and exports phase voltage and minimum direct current side voltage.When three-phase voltage source inverter adopts sinusoidal pulse width modulation (SPWM) strategy based on triangular carrier, the minimum value of inverter bridge DC voltage is the twice exporting phase voltage peak value as shown on the solid line in figure 3.Three-phase output voltage fundamental frequency f _linefor 50Hz.When adopt SPWM add 3 subharmonic inject or space vector modulation (SVM) improves direct voltage utilance time, DC voltage minimum value is as shown in Fig. 3 chain lines.In addition, also having another kind of possible DC voltage to choose is exactly the instantaneous maximum of three-phase line voltage and the envelope of three-phase output phase voltage, and as shown in dotted line waveform time dependent in figure, its expression formula is:

$V_{dc\_link}\left(\mathrm{\ω}t\right)=\sqrt{3}\·{\hat{v}}_{ac}\·cos(\mathrm{\θ}-\frac{\mathrm{\π}}{6})---\left(3\right)$

Wherein: θ=ω t% (π/3)

If a switch periods T _sin, the mean value of the DC voltage of inverter bridge may be controlled to six pulse wave dotted lines shown in (3) formula or Fig. 3, then exchange on the brachium pontis exporting phase voltage maximum and manage conducting all the time, conducting is all the time managed under exchanging the brachium pontis exporting phase voltage minimum value, the upper and lower switching device of another phase brachium pontis works in pulse-width modulation (PWM) pattern, and in inverter bridge, the operating state of power semiconductor device is as shown in table 1.For the first sector, inverter bridge DC side switch periods T _sthe mean value of interior voltage is line voltage (v _a-v _c).Therefore, S _apand S _cnall the time conducting, S _bpand S _bnwork in pulse-width modulation (PWM) pattern and export phase voltage v to generate _b.In arbitrary sector, have and only have one to work in pulse width modulation mode mutually and upper and lower brachium pontis power device on off state is complementary, its conducting duty ratio d _sip, d _sinexpression formula is respectively Ru shown in (4).In inverter bridge, the equivalent switching frequency of all power semiconductor devices can be reduced to 1/3f _s(f _s=1/T _s).

$\left\{\begin{array}{c}{d}_{Sip}\left(\mathrm{\ω}t\right)=\frac{v_i\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}{v_{\max }\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}\\ d_{Sin}\left(\mathrm{\ω}t\right)=1-d_{Sip}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(4\right)$

Wherein: in arbitrary sector, v _min(ω t) exports phase voltage minimum value; v _max(ω t) exports phase voltage maximum; I is phase brachium pontis a phase, b phase or the c phase adopting pulse-width modulation.

Table 1 inverter bridge power semiconductor device on off state

0°≤θ≤60°

60°≤θ≤120°

120°≤θ≤180°

180°≤θ≤240°

240°≤θ≤300°

300°≤θ≤360°

A phase

S ap＝1；S an＝0

S apS an＝PWM

S ap＝0；S an＝1

S ap＝0；S an＝1

S apS an＝PWM

S ap＝1；S an＝0

B phase

S bpS bn＝PWM

S bp＝1；S bn＝0

S bp＝1；S bn＝0

S bpS bn＝PWM

S bp＝0；S bn＝1

S bp＝0；S bn＝1

C phase

S cp＝0；S cn＝1

S cp＝0；S cn＝1

S cpS cn＝PWM

S cp＝1；S cn＝0

S cp＝1；S cn＝0

S cpS cn＝PWM

The voltage gain of Z-source inverter is defined as the ratio exchanging and export phase voltage peak value and 1/2 times of direct current power source voltage.

$G=\frac{{\hat{v}}_{ac}}{V_{dc}/2}=\frac{2{\hat{v}}_{ac}}{V_{dc}}---\left(5\right)$

Z-source inverter mode of operation can be divided into two kinds, as shown in Figure 4.When converter bridge switching parts device leads directly to, diode D ₁by, two electric capacity to induction charging, v _i=0, inverter bridge exports Zero voltage vector.When converter bridge switching parts device non-straight-through time, diode D ₁conducting, input power and two electric capacity differential concatenations are powered to inverter bridge DC side, v _i=2V _c-Vin, inverter bridge exports active voltage vector.Therefore, in a switch periods, the average voltage of intermediate DC link is:

$\stackrel{\‾}{v_i}=\frac{1}{T_s}\·({\∫}_0^{d_{ST}\·T_s}0\mathrm{dt}+{\∫}_{d_{ST}\·T_s}^{T_s}(2V_C-V_{in}\left)dt\right)=(1-d_{ST})\·(2V_C-V_{in})---\left(6\right)$

The pulse duration modulation method that existing document [1] [2] propose, when given ac output voltage, during stable state, straight-through time d _sTconstant, therefore Z-source inverter intermediate dc side voltage v _iat a switch periods (T _s) in be also constant, be respectively or the pulse duration modulation method that existing document [3] proposes, all zero vectors are all for the straight-through time.When given ac output voltage, during stable state, straight-through time d _sTchange in time.In order to reduce voltage stress and the on-off times of power semiconductor device in inverter bridge further, single bridge arm direct pass time controling can be regulated in inverter bridge at a switch periods T _sinterior v _imean value meet (3) formula.To simplify the analysis, assuming that electric capacity C ₁and C ₂enough large, capacitance voltage approximately constant during stable state.In conjunction with (3) and (6) formula, at a switch periods T _sin, the mean value of inverter bridge DC voltage can by regulating straight-through time d _sTaccurately control.

$(1-d_{ST}(\mathrm{\ω}t\left)\right)\·(2V_C-V_{in})=\sqrt{3}\·{\hat{v}}_{ac}\·cos(\mathrm{\θ}-\frac{\mathrm{\π}}{6})---\left(7\right)$

Wherein: θ=ω t% (π/3)

During stable state, capacitance voltage V _crelevant with the mean value that inverter bridge leads directly to the time, can be expressed as:

$V_{C1}=V_{C2}=V_C=\frac{(1-d_{avg})V_{in}}{1-2d_{avg}}---\left(8\right)$

The mean value of boosting duty ratio can pass through d in (6) formula _sTto quadrature in 60 ° of sectors acquisition.

$d_{avg}=\frac{3}{\mathrm{\π}}\·{\∫}_0^{\mathrm{\π}/3}(1-\frac{V_{dc\_link}\left(\mathrm{\ω}t\right)}{2V_C-V_{in}})\·d\mathrm{\ω}t=1-\frac{3\sqrt{3}}{\mathrm{\π}}\·\frac{{\hat{v}}_{ac}}{2V_C-V_{in}}---\left(9\right)$

In conjunction with (7) (8) and (9), during stable state, the expression formula of capacitance voltage and straight-through time is:

$V_C=\frac{3\sqrt{3}G}{2\mathrm{\π}}\·V_{dc}---\left(10\right)$

$d_{ST}\left(\mathrm{\ω}t\right)=1-\frac{\sqrt{3}\mathrm{\π}G\·cos(\mathrm{\ω}t-\frac{\mathrm{\π}}{6})}{6\sqrt{3}G-2\mathrm{\π}}---\left(11\right)$

Adopt introducing in a phase brachium pontis of pulse-width modulation straight-through at Z-source inverter after, upper and lower brachium pontis power device conducting duty ratio d in (4) formula _sip, d _sinbe rewritten as:

$\left\{\begin{array}{c}{d}_{Sip}\left(\mathrm{\ω}t\right)=\frac{v_i\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}{v_{\max }\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sin}\left(\mathrm{\ω}t\right)=\[1-d_{Sip}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(12\right)$

Wherein: in arbitrary sector, v _min(ω t) exports phase voltage minimum value; v _max(ω t) exports phase voltage maximum; I is phase brachium pontis a phase, b phase or the c phase adopting pulse-width modulation.

Time under Z-source inverter works in boost mode, the duty ratio demand fulfillment of power semiconductor device S: d _sT>=0, therefore, adopt above-mentioned pulse duration modulation method, should 1.27 be greater than by the known voltage gain G of (11) formula.

In electronic power convertor, the key parameter that power semiconductor device is chosen is voltage stress V _s: the maximum blocking voltage born when device turns off; Average current stress I _s: the average current flowing through device in a switch periods.According to the operation principle of Z-source inverter, the identical voltage stress that in inverter bridge, power semiconductor device and front end diode bear, the i.e. maximum of intermediate dc side voltage, non-straight-through time be 2V _c-V _in.Table 2 lists the voltage stress of the new type of modulation method power semiconductor device that Z-source inverter adopts existing pulse duration modulation method and the present invention to propose.

Z-source inverter power semiconductor device voltage stress under table 2 different modulation

The switching frequency that table 3 lists the novel pulse duration modulation method power semiconductor device that Z-source inverter adopts and the present invention proposes compares.

Under table 3 different modulating strategy, Z-source inverter power semiconductor device switching frequency compares

Fig. 5 gives Z-source inverter and adopts existing pulse duration modulation method and this patent to propose pulse duration modulation method, voltage gain and straight-through duty ratio, relation between inverse cascade equivalent modulation degree.Fig. 6 provides Z-source inverter and adopts distinct pulse widths modulator approach, relation between power semiconductor device voltage stress and voltage gain.Under identical voltage gain, new type of modulation method and existing maximum boosting pulse duration modulation method have minimum device voltage stress, reduce switching frequency simultaneously, contribute to reducing switching loss.

In order to verify above-mentioned new type of modulation method and theory analysis, The present invention gives a design example.Main circuit parameter is as follows: V _dc=400V, P _o=2.5kW, V _aN=220V, L ₁=L ₂=2mH, C ₁=C ₂=500uF, R _load=60-300 Ω, T _s=100us.Fig. 7 provides when three-phase alternating current output phase voltage peak value command voltage is 311V, the pulse duration modulation method that Z-source inverter adopts the present invention to propose, the simulation waveform of drive singal, the forward and backward ac output voltage of filtering, output current, intermediate dc side voltage and intermediate capacitance voltage.Calculate according to (8) and (10) and obtain capacitance voltage V _c=514.6V, voltage gain G=1.56.

Simulation result shown in Fig. 7 and theoretical value basically identical.Adopt the pulse duration modulation method that the present invention proposes, Z-source inverter obtains maximum voltage gain and minimum device voltage stress and switching frequency.

In the distributed power supply system of new energy, efficiency evaluates an important indicator of electronic power convertor.The reduction of high efficiency meaning to radiator demand.The loss of electronic power convertor mainly comprises power semiconductor device loss, passive component loss and controller, drive circuit loss etc., wherein the loss of power semiconductor device accounts for main part, and this is also the main object of patent specification loss analysis.For power semiconductor device, the loss of IGBT, except on-state loss, also comprises turn-on consumption and turn-off power loss.The loss of power diode mainly comprises reverse recovery loss and on-state loss, and turn-on consumption is relatively very little, negligible.The switching loss model representation of power semiconductor device is:

$E_{sw(on,off)}=(\mathrm{\α}+\mathrm{\β}\·i_{sw}+\mathrm{\γ}\·i_{sw}^2)\frac{V_{sw}}{V_{ref}}---\left(13\right)$

P _sw＝f _sw·(E _swon+E _swoff)(14)

Wherein: V _swblocking voltage, i _swit is switching current; α, beta, gamma is that switching device is in given junction temperature with reference to direct voltage V _refunder open or the device parameters of turn-off power loss, the mode of fitting of a polynomial can be adopted, the curve in colligator event data handbook and parameter, calculate and obtain.

In booster circuit and inverter bridge, the on-state loss of power semiconductor device can calculate respectively by following formula and obtain.

$P_{con\_dc}=\frac{1}{T_s}\underset{t_t}{\overset{t_2}{\∫}}{v}_{con}\·i_{con}dt---\left(15\right)$

$P_{con\_inv}=\frac{1}{2\mathrm{\π}}\underset{{\mathrm{\λ}}_1}{\overset{{\mathrm{\λ}}_2}{\∫}}{d}_{con}\·v_{on}\·i_{con}{\mathrm{d\θ}}_r---\left(16\right)$

Wherein: v _con=v _th+ ri _conon-state voltage drop, V _thit is turn-on threshold voltage; R is on state resistance; i _conon state current, d _conit is ON time.

Shown in (13) and (14), the switching loss of power semiconductor device and switching frequency (f _sw), switching current (i _sw), blocking voltage (V _sw) relevant.Adopt the Z-source inverter of new type of modulation method, switching frequency and voltage stress can be reduced, thus contribute to reducing switching loss, raise the efficiency.

In order to determine the above-mentioned novel pulse duration modulation method of quantitative analysis to the degree of improved efficiency.Infineon power semiconductor device IGBTIGW25N120 and DIODEIDP18E120 is adopted to build 2.5kWZ source inventer experiment test platform.Design example parameter is as follows: V _dc=4000V, P _o=2500W, V _ac=311V, voltage gain G=1.56.Switch periods T _s=100us.By adjustment load resistance, under measuring different output power, Z-source inverter adopts the efficiency curve of various pulse duration modulation method.

Fig. 8 gives and adopts distinct pulse widths modulator approach, the efficiency curve of Z-source inverter.Due to the pulse duration modulation method adopting the present invention to propose, Z-source inverter reduces the switching frequency with front end power semiconductor device in inverter bridge, thus obviously reduces switching loss.This modulator approach being also Z-source inverter adopts the present invention to propose shows obvious high efficiency advantage.In addition, the pulse duration modulation method that the present invention proposes reduces voltage stress and the heating of power semiconductor device, contributes to the demand reducing silicon (Si) power semiconductor device.The pulse duration modulation method that Z-source inverter adopts the present invention to propose is more suitable for high-gain DC-AC power conversion occasion.

The invention discloses the pulse duration modulation method of the maximum boosting rectifier control of a kind of Z-source inverter and minimal switching frequency, comprise a switch periods (T _s) interior intermediate dc side average voltage controls as the three-phase alternating current output envelope of phase voltage and the instantaneous maximum of line voltage, thus the equivalent switching frequency of power semiconductor device in inverter bridge can be reduced to 1/3f _s(f _s=1/T _s).The present invention further reduces the switching loss of Z-source inverter power device, improves the energy conversion efficiency of current transformer.In addition, adopt the modulator approach that the present invention proposes, inverter direct-flow side inductive current and capacitance voltage comprise the low-frequency ripple of six times of fundamental frequencies.Z-source inverter adopts this modulator approach to be applicable to being applied to the airborne and boats and ships distributed power-supply system of 400-800Hz intermediate frequency equally.

Above content is only and technological thought of the present invention is described; protection scope of the present invention can not be limited with this; every technological thought proposed according to the present invention, any change that technical scheme basis is done, within the protection range all falling into claims of the present invention.

Claims (2)

1. the maximum boosting of Z-source inverter and a minimal switching frequency pulse duration modulation method, is characterized in that, chien shih switch periods T when regulating a phase brachium pontis straight-through _sinterior inverter bridge DC voltage is the instantaneous maximum of three-phase alternating current output line voltage, and concrete modulator approach comprises the following steps:

1) under given ac output voltage amplitude, according to formula (1) calculating voltage gain:

$G=\frac{{\hat{v}}_{ac}}{V_{dc}/2}=\frac{2{\hat{v}}_{ac}}{V_{dc}}---\left(1\right)$

Wherein, represent to exchange and export phase voltage peak value, V _dcdirect current power source voltage, G represents voltage gain, and it is defined as the ratio exchanging and export phase voltage peak value and 1/2 times of direct current power source voltage;

2) according to space voltage vector definition, ac output voltage is divided into six sectors, calculates in each sector according to formula (2), in arbitrary cycle, the straight-through duty ratio d of single-phase brachium pontis _sT:

$d_{ST}\left(\mathrm{\ω}t\right)=1-\frac{\sqrt{3}\mathrm{\π}G\·cos(\mathrm{\θ}-\frac{\mathrm{\π}}{6})}{6\sqrt{3}G-2\mathrm{\π}}---\left(2\right)$

Wherein: θ=ω t% (π/3), ω=2 π f _line, f _linefor exporting three-phase voltage fundamental frequency;

3) according to the on off state of six power devices in tables listing design inverter bridge:

0°≤θ≤60° 60°≤θ≤120° 120°≤θ≤180° 180°≤θ≤240° 240°≤θ≤300° 300°≤θ≤360° A phase S _ap＝1；S _an＝0 S _ap S _an＝PWM S _ap＝0；S _an＝1 S _ap＝0；S _an＝1 S _ap S _an＝PWM S _ap＝1；S _an＝0 B phase S _bp S _bn＝PWM S _bp＝1；S _bn＝0 S _bp＝1；S _bn＝0 S _bp S _bn＝PWM S _bp＝0；S _bn＝1 S _bp＝0；S _bn＝1 C phase S _cp＝0；S _cn＝1 S _cp＝0；S _cn＝1 S _cp S _cn＝PWM S _cp＝1；S _cn＝0 S _cp＝1；S _cn＝0 S _cp S _cn＝PWM

4) according to the conducting duty ratio d of formula (3) evaluation work in the upper and lower switching tube of PWM one phase brachium pontis _sip(ω t) and d _sin(ω t):

$\left\{\begin{array}{c}{d}_{Sip}\left(\mathrm{\ω}t\right)=\frac{v_{mid}\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}{v_{\max }\left(\mathrm{\ω}t\right)-v_{min}\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sin}\left(\mathrm{\ω}t\right)=\[1-d_{Sip}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(3\right)$

Wherein: in arbitrary sector, v _min(ω t) exports phase voltage minimum value; v _max(ω t) is phase voltage maximum, v _mid(ω t) is phase voltage median; I represents a phase a of output voltage median, b or c;

5) after determining each power device on off state of Z-source inverter and duty ratio, generate PWM drive singal by digitial controller, control main circuit.

2. the maximum boosting of Z-source inverter according to claim 1 and minimal switching frequency pulse duration modulation method, is characterized in that, described step 4) in: a switch periods T _sin, in inverter bridge, the power semiconductor device on off state of two brachium pontis maintains static work, and the power semiconductor device of another brachium pontis adopts pulse-width modulation PWM to take into account inverter bridge DC voltage and exports the adjustment of phase voltage; In inverter bridge, the equivalent switching frequency of power semiconductor device is reduced to 1/3f _s, wherein, f _s=1/T _s;

The on off state of the first sector is: v _max=v _a, v _mid=v _b, v _min=v _c, S _apand S _cnall the time open-minded, S _anand S _cpall the time turn off, the upper and lower switching tube S of B phase brachium pontis _bpand S _bnadopt PWM, its conducting duty ratio d _sbp, d _sbn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sbp}\left(\mathrm{\ω}t\right)=\frac{v_b\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}{v_a\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sbn}\left(\mathrm{\ω}t\right)=\[1-d_{Sbp}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(4\right)$

The on off state of the second sector is: v _max=v _b, v _mid=v _a, v _min=v _c, S _bpand S _cnall the time open-minded, S _bnand S _cpall the time turn off, the upper and lower switching tube S of A phase brachium pontis _apand S _anadopt PWM, its conducting duty ratio d _sap, d _san(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sap}\left(\mathrm{\ω}t\right)=\frac{v_a\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}{v_b\left(\mathrm{\ω}t\right)-v_c\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{San}\left(\mathrm{\ω}t\right)=\[1-d_{Sap}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(5\right)$

The on off state of the 3rd sector is: export three-phase voltage v _max=v _b, v _mid=v _c, v _min=v _a, S _bpand S _anall the time open-minded, S _bnand S _apall the time turn off, the upper and lower switching tube S of C phase brachium pontis _cpand S _cnadopt PWM and on off state is complementary, its conducting duty ratio d _scp, d _scn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Scp}\left(\mathrm{\ω}t\right)=\frac{v_c\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}{v_b\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Scn}\left(\mathrm{\ω}t\right)=\[1-d_{Scp}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t))+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(6\right)$

The on off state of the 4th sector is: export three-phase voltage v _max=v _c, v _mid=v _b, v _min=v _a, S _cpand S _anall the time open-minded, S _cnand S _apall the time turn off, the upper and lower switching tube S of B phase brachium pontis _bpand S _bnadopt PWM and on off state is complementary, its conducting duty ratio d _sbp, d _sbn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sbp}\left(\mathrm{\ω}t\right)=\frac{v_b\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}{v_c\left(\mathrm{\ω}t\right)-v_a\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Sbn}\left(\mathrm{\ω}t\right)=\[1-d_{Sbp}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(7\right)$

The on off state of the 5th sector is: export three-phase voltage v _max=v _c, v _mid=v _a, v _min=v _b, S _cpand S _bnall the time open-minded, S _cnand S _bpall the time turn off, the upper and lower switching tube S of A phase brachium pontis _apand S _anadopt PWM and on off state is complementary, its conducting duty ratio d _sap, d _san(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Sap}\left(\mathrm{\ω}t\right)=\frac{v_a\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}{v_c\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{San}\left(\mathrm{\ω}t\right)=\[1-d_{Sap}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(8\right)$

The on off state of the 6th sector is: export three-phase voltage v _max=v _a, v _mid=v _c, v _min=v _b, S _apand S _bnall the time open-minded, S _anand S _bpall the time turn off, the upper and lower switching tube S of C phase brachium pontis _cpand S _cnadopt PWM and on off state is complementary, its conducting duty ratio d _scp, d _scn(3) formula of substitution calculates and obtains:

$\left\{\begin{array}{c}{d}_{Scp}\left(\mathrm{\ω}t\right)=\frac{v_c\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}{v_a\left(\mathrm{\ω}t\right)-v_b\left(\mathrm{\ω}t\right)}\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\\ d_{Scn}\left(\mathrm{\ω}t\right)=\[1-d_{Sap}\left(\mathrm{\ω}t\right)\]\·(1-d_{ST}(\mathrm{\ω}t\left)\right)+d_{ST}\left(\mathrm{\ω}t\right)\end{array}\right.---\left(9\right).$