CN105978388A - Single-phase voltage boosting-reducing type photovoltaic inverter capable of inhibiting current leakage and control method thereof - Google Patents

Abstract

The invention discloses a single-phase voltage boosting-reducing type photovoltaic inverter capable of inhibiting leakage current and a control method thereof. The inverter consists of six switch tubes, two diodes, one DC inductor, two filtering inductors with identical inductance values and a filtering capacitor. The single-phase voltage boosting-reducing type photovoltaic inverter has functions of boosting voltage and reducing voltage and has a wide input voltage range; the four power switches of the bridge arms of the inverter are in a power frequency state and only two power switches are working at a high frequency; the switch loss is small, a dead area does not need to be set for driving pulse, and circuit reliability is high. The single-phase voltage boosting-reducing type photovoltaic inverter capable of inhibiting leakage current and the control method thereof enable voltage on two ends of a parasite capacitor to ground of the photovoltaic system does not contain high frequency components, and enable current leakage to be effectively inhibited.

Description

One can suppress leakage current single-phase buck-boost type photovoltaic DC-to-AC converter and control method thereof

Technical field

The invention belongs to electric and electronic technical field, be specifically related to one and can suppress leakage current single-phase buck-boost type Photovoltaic DC-to-AC converter and control method thereof, it is adaptable in single-phase inversion application scenario.

Background technology

The energy is the material base that the mankind depend on for existence and development, the finiteness of fossil energy and substantial amounts of exploitation Utilization causes energy starved problem day by day serious, also result in going from bad to worse of environmental problem simultaneously.The sun Can be as presently most cleaning, most one of regenerative resource having the prospect of large-scale developing and utilizing, its photovoltaic profit With by common concern all over the world.And solar energy power generating is the main development of solar energy photovoltaic utilization Trend, will obtain developing the most rapidly in future.

In photovoltaic generating system, the efficiency of DC-to-AC converter and safety will directly affect the property of whole system Energy and practicality.According to the transformer configuration situation in inverter, existing inverter can be divided into band work Frequency power transformer type inverter, band high frequency transformer type inverter and inverter without transformer.Band power frequency transformation The inverter of device or band high frequency transformer all can play and boost and the effect of isolation, but band Industrial Frequency Transformer type There is the problems such as volume and weight is big, price is high in inverter；Although band high frequency transformer type inverter volume and Weight greatly reduces, but structure is complicated, and whole efficiency reduces.And inverter without transformer has structure letter List, volume are little, low cost, efficiency advantages of higher, have therefore obtained more attention.

In Transformer-free photovoltaic parallel in system, owing to losing the electrical isolation of transformator, photovoltaic cell Parasitic capacitance (generally 50-150nF/kWp), photovoltaic combining inverter and the earth between array and the earth Between will form loop, bring leakage problem.Leakage current not only can cause EMI problem, the most also can Reduce grid-connected current quality, and the personal safety of the personnel of giving brings potential safety hazard, therefore, at transless In type combining inverter, leakage problem must have been resolved.

In inverter without transformer, some inverter topologies have been had to solve common-mode voltage persistent problem, But there is other problems, such as circuit structure is complicated, does not have stepping functions, opening of high-frequency work simultaneously Close more, the problems such as switching loss is big.One proposed by the invention can suppress leakage current single-phase buck-boost type The problem that photovoltaic DC-to-AC converter and control method thereof solve above-mentioned existence.

Summary of the invention

Instant invention overcomes shortcoming of the prior art, it is provided that one can suppress leakage current single-phase buck-boost type light Volt inverter and control method thereof, it is constant that this inverter enables to common-mode voltage, effectively suppresses leakage current, And simple in construction, there is stepping functions simultaneously.

In order to solve the technical problem of above-mentioned existence, present invention employs following technical scheme:

One can suppress leakage current single-phase buck-boost type photovoltaic DC-to-AC converter, and this inverter includes six power switch Filter inductance that pipe, two power diodes, DC inductance, two inductance value are identical and a filtered electrical Hold composition；Dc bus "+" end be connected with the anode of the 5th power switch pipe, the "-" of dc bus End is connected with the negative electrode of the 6th power switch pipe；The negative electrode of one end of DC inductance and the 5th power switch pipe and The negative electrode of the second power diode is connected, the other end of DC inductance and the anode of the 6th power switch pipe and the The anode of one power diode is connected；The negative electrode of the first power diode respectively with the sun of the first power switch pipe The anode of pole and the 3rd power switch pipe connects；The anode of the second power diode respectively with the second power switch The negative electrode of pipe and the negative electrode of the 4th power switch pipe connect；Filter capacitor "+" hold and open with the first power respectively The anode closing the negative electrode of pipe and the second power switch pipe connects, the "-" end of filter capacitor respectively with the 3rd power The negative electrode of switching tube and the anode of the 4th power switch pipe connect；One end of first filter inductance and filter capacitor "+" end connects, the other end of the first filter inductance and electrical network "+" hold and be connected；Second filter inductance One end connect with the "-" end of filter capacitor, the "-" end of the other end of the second filter inductance and electrical network is even Connect.

Described a kind of control method suppressing leakage current single-phase buck-boost type photovoltaic DC-to-AC converter, the method Comprise the following specific steps that:

(1) first, given sinusoidal modulation wave is taken absolute value, obtain full sinusoidal wave X, then will just String all-wave X obtains actual modulated ripple r (t) through the mathematical conversion of X/ (1+X), finally, by modulating wave R (t) and carrier wave obtain switch logic signals R by after comparator₅、R₆, in order to drive the 5th respectively Power switch pipe and the 6th power switch pipe；

(2) with two complementary power frequency square waves respectively as the first power switch pipe, the 4th power switch The driving pulse of pipe and the second power switch pipe, the driving pulse of the 3rd power switch pipe；

In grid-connected current positive half period, the first power switch pipe and the 4th power switch pipe are constantly on, the Merit two rate switching tube and the 3rd power switch pipe turn off always, the 5th power switch pipe and the 6th power switch pipe PWM is used to control its on or off；When the 5th power switch pipe and the 6th power switch pipe turn off, The circulation path of grid-connected current is: anode → the first power diode → the first power of the first power diode Switching tube → the first filter inductance → electrical network → the second filter inductance → the 4th power switch pipe → the second power two The anode of pole pipe → DC inductance → the first power diode；When the 5th power switch pipe and the 6th power switch During pipe conducting, the circulation path of grid-connected current is: filter capacitor "+" end the → the first filter inductance → electrical network "-" end → the filter capacitor of the → the second filter inductance → filter capacitor "+" end；

In grid-connected current negative half-cycle, the first power switch pipe and the 4th power switch pipe turn off always, the Two power switch pipes and the 3rd power switch pipe are constantly on, the 5th power switch pipe and the 6th power switch pipe PWM is used to control its on or off；When the 5th power switch pipe and the 6th power switch pipe turn off, The circulation path of grid-connected current is: anode → the first power diode of the first power diode → the 3rd power Switching tube → the second filter inductance → electrical network → the first filter inductance → the second power switch pipe → the second power two The anode of pole pipe → DC inductance → the first power diode；When the 5th power switch pipe and the 6th power switch During pipe conducting, the circulation path of grid-connected current is: the "-" end → the second filter inductance → electrical network of filter capacitor → the first filter inductance → filter capacitor "+" the "-" end of end → filter capacitor.

Owing to using technique scheme, the invention has the beneficial effects as follows:

(1) the inverter power switch tube driving pulse of the present invention is without arranging dead band, and circuit reliability is high；

(2) inverter of the present invention has stepping functions, and DC voltage has wider input voltage range；

(3) four power switch pipes on the inverter leg of the present invention are all in power frequency duty, only 5th power switch pipe and the 6th power switch pipe are operated in high frequency state, and switching loss is little；

(4) control method of the present invention uses convention carrier to modulate, switching signal generative circuit simple in construction, Photovoltaic battery panel parasitic capacitance both end voltage over the ground can be made without high fdrequency component, ensure that system is altogether simultaneously Mode voltage is constant, makes leakage current be effectively suppressed.

Accompanying drawing explanation

Fig. 1 is that the one of the present invention can suppress leakage current single-phase buck-boost type photovoltaic DC-to-AC converter topological structure；

Fig. 2 is the single-phase buck-boost type photovoltaic DC-to-AC converter modulation implementation schematic diagram of the present invention；

Fig. 3 is the single-phase buck-boost type photovoltaic DC-to-AC converter on-off control drive waveforms of the present invention；

Fig. 4 is current waveform and the grid-connected current of the single-phase buck-boost type photovoltaic DC-to-AC converter DC inductance of the present invention Simulation waveform；

Fig. 5 is the common-mode voltage simulation waveform figure of the single-phase buck-boost type photovoltaic DC-to-AC converter of the present invention；

Fig. 6 is the leakage current simulation waveform figure of the single-phase buck-boost type photovoltaic DC-to-AC converter of the present invention.

Detailed description of the invention

In order to more specifically describe the present invention, below in conjunction with the accompanying drawings and the detailed description of the invention skill to the present invention Art scheme is described in detail.

One can suppress leakage current single-phase buck-boost type photovoltaic DC-to-AC converter, and its topological structure is as it is shown in figure 1, be somebody's turn to do Inverter includes that six power switch pipes, two power diodes, a DC inductance, two inductance value are identical Filter inductance and filter capacitor composition；Dc bus "+" hold and the 5th power switch tube S₅Sun The most connected, the "-" end of dc bus and the 6th power switch tube S₆Negative electrode be connected；DC inductance L_DC's One end and the 5th power switch tube S₅Negative electrode and the second power diode S₂Negative electrode be connected, DC inductance L_DC The other end and the 6th power switch tube S₆Anode and the first power diode S₁Anode be connected；First merit Rate diode VD₁Negative electrode respectively with the first power switch tube S₁Anode and the 3rd power switch tube S₃Anode Connect；Second power diode VD₂Anode respectively with the second power switch tube S₂Negative electrode and the 4th power open Close pipe S₄Negative electrode connect；Filter capacitor C₁"+" end respectively with the first power switch tube S₁Negative electrode and Two power switch tube S₂Anode connect, filter capacitor C₁"-" end respectively with the 3rd power switch tube S₃ Negative electrode and the 4th power switch tube S₄Anode connect；First filter inductance L₁One end and filter capacitor C₁ "+" end connect, the first filter inductance L₁The other end and electrical network "+" end is connected；Second filtered electrical Sense L₂One end and filter capacitor C₁"-" end connect, the second filter inductance L₂The "-" of the other end and electrical network End connects.

Inverter proposed by the invention is analyzed, is referred to the analysis side of buck-boost changer Formula, does hypothesis below: in (1) circuit, all elements are all ideal component the most to simplify the analysis；(2) by In switching frequency much larger than fundamental frequency, thus in several switch periods it is believed that inductive current meansigma methods and Capacitance voltage meansigma methods is constant；(3) inverter works in steady statue.Now, inductive current and electric capacity electricity The variable quantity being pressed in a switch periods is approximately zero.The 5th power switch pipe and the 6th power switch pipe is made to open Time logical, the ratio of inductive energy storage time and switch periods is dutycycle d, then this inverter exists following relation:

When 0～dT, the 5th power switch tube S₅With the 6th power switch tube S₆Open-minded:

$L_{dc}\frac{{\mathrm{di}}_{L_{dc}}}{dt}=U_{dc}---\left(1\right)$

$2L_1\frac{{\mathrm{di}}_1}{dt}=U_{C1}-U_g---\left(2\right)$

When dT～T, the 5th power switch tube S₅With the 6th power switch tube S₆Turn off:

$L_{dc}\frac{{\mathrm{di}}_{L_{dc}}}{dt}=-U_{C_1}---\left(3\right)$

$2L_1\frac{{\mathrm{di}}_{L_1}}{dt}=U_{C_1}-U_g---\left(4\right)$

WhereinFor DC inductance L_DCElectric current,For flowing through the first filter inductance L₁Electric current, U_dcDefeated for direct current Enter voltage,For filter capacitor C₁Both end voltage.

DC inductance L can be flow through within 0～dT time period by formula (1) and formula (2)_DCCurrent change quantity For:

${\mathrm{\Δ}}_1{I}_{L_{dc}}=\frac{1}{L_{dc}}{\∫}_0^{dT}{U}_{dc}dt=\frac{U_{dc}}{L_{dc}}dT---\left(5\right)$

Flow through the first filter inductance L₁Current change quantity be:

${\mathrm{\Δ}}_2{I}_{L_2}=\frac{1}{2L_1}{\∫}_0^{dT}(U_{C_1}-U_g)dt=\frac{U_{C_1}-U_g}{2L_1}dT---\left(6\right)$

DC inductance L can be flow through in dT～T time section by formula (3) and formula (4)_DCCurrent change quantity For:

${\mathrm{\Δ}}_2{I}_{L_{dc}}=\frac{1}{L_{dc}}{\∫}_{dT}^T(-U_{C_1})dt=-\frac{U_{C_1}}{L_{dc}}(1-d)T---\left(7\right)$

Flow through the first filter inductance L₁Current transformation amount be:

${\mathrm{\Δ}}_2{I}_{L_2}=\frac{1}{2L_1}{\∫}_{dT}^T(U_{C_1}-U_g)dt=\frac{U_{C_1}-U_g}{2L_1}(1-d)T---\left(8\right)$

Due to inductive current L_DCVariable quantity a switch periods is zero, so having:

${\mathrm{\Δ}}_1{I}_{L_{dc}}+{\mathrm{\Δ}}_2{I}_{L_{dc}}=0---\left(9\right)$

${\mathrm{\Δ}}_1{I}_{L_1}+{\mathrm{\Δ}}_2{I}_{L_1}=0---\left(10\right)$

Wushu (5) and formula (7) substitute into formula (9) formula, wushu (6) and formula (8) and substitute into formula (10) formula :

$U_{C_1}=U_g---\left(11\right)$

Contravarianter voltage gain is:

$M=\frac{U_g}{U_{dc}}=\frac{d}{1-d}---\left(12\right)$

If the 5th power switch tube S₅With the 6th power switch tube S₆Dutycycle in t is d (t), then export Voltage and input voltage meet following relation

$\frac{\left|U_g\right|}{U_{dc}}=\frac{d\left(t\right)}{1-d\left(t\right)}---\left(13\right)$

If line voltage is U_g=u_mSin (ω t), then:

$\frac{\left|U_g\right|}{U_{dc}}=\frac{d\left(t\right)}{1-d\left(t\right)}=\frac{u_m\left|sin\left(\mathrm{\ω}t\right)\right|}{U_{dc}}---\left(14\right)$

The 5th power switch tube S can be obtained by formula (14)₅With the 6th power switch tube S₆Dutycycle expression formula is:

$d\left(t\right)=\frac{\left|U_g\right|}{U_{dc}+\left|U_g\right|}=\frac{M\left|sin\left(\mathrm{\ω}t\right)\right|}{1+M\left|\sin \left(\mathrm{\ω}t\right)\right|}---\left(15\right)$

Wherein

First power switch tube S₁With the 4th power switch tube S₄Identical power frequency square-wave pulse is used to drive, the Two power switch tube S₂With the 3rd power switch tube S₃Use and the first power switch tube S₁With the 4th power switch Pipe S₄Complementary power frequency square-wave pulse drives, the 5th power switch tube S₅With the 6th power switch tube S₆Use PWM controls, and its modulation scheme is as follows:

Modulation wave signalWhereinu_mFor line voltage peak value, U_dcFor directly Stream voltage, ω is electrical network first-harmonic angular frequency；With r (t) as modulating wave, high frequency triangle wave is carrier wave, modulates institute The PWM waveform needed, it is achieved to the 5th power switch pipe and the control of the 6th power switch pipe, as M ＞ 1, The inverter of the present invention is boosting output；As M ＜ 1, the inverter of the present invention is reduced output voltage.

As in figure 2 it is shown, the realization of this inverter control method comprises the following specific steps that:

(1) first, given sinusoidal modulation wave is taken absolute value, obtain full sinusoidal wave X, then sine is complete Ripple X obtains actual modulated ripple r (t) through the mathematical conversion of X/ (1+X), finally, by modulating wave r (t) and load Ripple obtains switch logic signals R by after comparator₅、R₆, in order to drive the 5th power switch pipe respectively S₅With the 6th power switch tube S₆；

(2) with two complementary power frequency square waves respectively as the first power switch pipe_S1, the 4th power opens Close pipe S₄Driving pulse and the second power switch tube S₂, the 3rd power switch tube S₃Driving pulse；

Fig. 3 show each switch drive pulse waveform obtained after using above-mentioned implementation.

In the photovoltaic combining inverter of the present invention is operated in grid-connected current positive half period, the first power switch pipe S₁With the 4th power switch tube S₄Constantly on, the second power switch tube S₂With the 3rd power switch tube S₃Always Turn off, when the 5th power switch tube S₅With the 6th power switch tube S₆During shutoff,I.e. photovoltaic system parasitic capacitance C_pvBoth end voltage isNow common-mode voltage U_cm=U_dc/ 2, when the 5th power switch tube S₅With the 6th merit Rate switching tube S₆Turn on constantly,I.e. photovoltaic system parasitic capacitance C_pvTwo ends Voltage isNow common-mode voltage U_cm=U_dc/2。

In the photovoltaic combining inverter of the present invention is operated in grid-connected current negative half-cycle, the second power switch pipe S₂With the 3rd power switch tube S₃Constantly on, the first power switch tube S₁With the 4th power switch tube S₄Always Turn off, when the 5th power switch tube S₅With the 6th power switch tube S₆During shutoff,I.e. photovoltaic system parasitic capacitance C_pvBoth end voltage isNow common-mode voltage U_cm=U_dc/ 2, when the 5th power switch tube S₅With the 6th merit Rate switching tube S₆During conducting,I.e. photovoltaic system parasitic capacitance C_pvTwo ends electricity Pressure isNow common-mode voltage U_cm=U_dc/2。

Table 1 lists the on off state of 4 mode of operations and corresponding C_pvBoth end voltage and common-mode voltage. Wherein U_m、With the amplitude that ω is respectively line voltage, phase and frequency, ON representation switch turns on, OFF Representation switch turns off.

Common-mode voltage synopsis under table 1 different working modes

As shown in Table 1, common-mode voltage is constant, parasitic capacitance C_pvBoth end voltage does not contains high fdrequency component, owing to being System leakage current isAccording to above-mentioned analysis, this topology can effectively reduce leakage current.

Fig. 5 show photovoltaic DC-to-AC converter DC inductance electric current and the grid-connected current analogous diagram of the present invention, can see Go out DC inductance electric current and be rendered as full sinusoidal wave pulses, but grid-connected current still keeps preferable sine.

Fig. 6 show photovoltaic DC-to-AC converter parasitic capacitance both end voltage and the common mode current simulations figure of the present invention, can To find out that common-mode voltage is constant, demonstrating the analysis of table 1, leakage current is the least.

Claims (3)

1. one kind can be suppressed leakage current single-phase buck-boost type photovoltaic DC-to-AC converter, it is characterised in that: this inverter bag Include six power switch pipes, two power diodes, DC inductance, filtered electrical that two inductance value are identical Sense and a filter capacitor composition；Dc bus "+" end be connected, directly with the anode of the 5th power switch pipe The "-" end of stream bus and the negative electrode of the 6th power switch pipe are connected；One end of DC inductance is opened with the 5th power The negative electrode of the negative electrode and the second power diode that close pipe is connected, the other end of DC inductance and the 6th power switch The anode of pipe and the anode of the first power diode are connected；The negative electrode of the first power diode respectively with the first merit The anode of rate switching tube and the anode of the 3rd power switch pipe connect；The anode of the second power diode respectively with The negative electrode of the second power switch pipe and the negative electrode of the 4th power switch pipe connect；Filter capacitor "+" end is respectively Being connected with the negative electrode of the first power switch pipe and the anode of the second power switch pipe, the "-" end of filter capacitor divides It is not connected with the negative electrode of the 3rd power switch pipe and the anode of the 4th power switch pipe；The one of first filter inductance End and filter capacitor "+" end connects, the other end of the first filter inductance and electrical network "+" hold and be connected； One end of second filter inductance connects with the "-" end of filter capacitor, the other end of the second filter inductance and electrical network "-" end connect.

A kind of control suppressing leakage current single-phase buck-boost type photovoltaic DC-to-AC converter Method, it is characterised in that: the method content comprises the following specific steps that:

(1) first, given sinusoidal modulation wave is taken absolute value, obtain full sinusoidal wave X, then sine is complete Ripple X obtains actual modulated ripple r (t) through the mathematical conversion of X/ (1+X), finally, by modulating wave r (t) Switch logic signals R is obtained by after comparator with carrier wave₅、R₆, in order to drive the 5th power respectively Switching tube and the 6th power switch pipe；

(2) with two complementary power frequency square waves respectively as the first power switch pipe, the 4th power switch The driving pulse of pipe and the second power switch pipe, the driving pulse of the 3rd power switch pipe；

In grid-connected current positive half period, the first power switch pipe and the 4th power switch pipe are constantly on, the Merit two rate switching tube and the 3rd power switch pipe turn off always, the 5th power switch pipe and the 6th power switch pipe PWM is used to control its on or off；When the 5th power switch pipe and the 6th power switch pipe turn off, The circulation path of grid-connected current is: anode → the first power diode → the first power of the first power diode Switching tube → the first filter inductance → electrical network → the second filter inductance → the 4th power switch pipe → the second power two The anode of pole pipe → DC inductance → the first power diode；When the 5th power switch pipe and the 6th power switch During pipe conducting, the circulation path of grid-connected current is: filter capacitor "+" end the → the first filter inductance → electrical network "-" end → the filter capacitor of the → the second filter inductance → filter capacitor "+" end；

In grid-connected current negative half-cycle, the first power switch pipe and the 4th power switch pipe turn off always, the Two power switch pipes and the 3rd power switch pipe are constantly on, the 5th power switch pipe and the 6th power switch pipe PWM is used to control its on or off；When the 5th power switch pipe and the 6th power switch pipe turn off, The circulation path of grid-connected current is: anode → the first power diode of the first power diode → the 3rd power Switching tube → the second filter inductance → electrical network → the first filter inductance → the second power switch pipe → the second power two The anode of pole pipe → DC inductance → the first power diode；When the 5th power switch pipe and the 6th power switch During pipe conducting, the circulation path of grid-connected current is: the "-" end → the second filter inductance → electrical network of filter capacitor → the first filter inductance → filter capacitor "+" the "-" end of end → filter capacitor.

One the most according to claim 1 can suppress leakage current single-phase buck-boost type photovoltaic DC-to-AC converter, its Being characterised by, the first power switch pipe and the 4th power switch pipe use identical power frequency square-wave pulse to drive, Second power switch pipe and the 3rd power switch pipe use mutual with the first power switch pipe and the 4th power switch pipe The power frequency square-wave pulse mended drives, and the 5th power switch pipe and the 6th power switch pipe use PWM to control, its Modulation scheme is as follows:

Modulation wave signalWhereinu_mFor line voltage peak value, U_dcFor directly Stream voltage, ω is electrical network first-harmonic angular frequency；With r (t) as modulating wave, high frequency triangle wave is carrier wave, modulates institute The PWM waveform needed, it is achieved to the 5th power switch pipe and the control of the 6th power switch pipe, as M ＞ 1, The inverter of the present invention is boosting output；As M ＜ 1, the inverter of the present invention is reduced output voltage.