CN104158427A - Single-phase non-transformer isolation-type Z-source photovoltaic grid-connected inverter and modulation method - Google Patents

Abstract

The invention discloses a single-phase non-transformer isolation-type Z-source photovoltaic grid-connected inverter and a modulation method and relates to the technical field of a photovoltaic grid-connected inverter. The invention aims to solve the problems that when a conventional Z-source inverter is applied to a photovoltaic grid-connected system, grid connection efficiency is low and a large common mode current is generated. The single-phase non-transformer isolation-type Z-source photovoltaic grid-connected inverter comprises a No.1 fast recovery diode D1, a No.2 fast recovery diode D2, a No.1 electrolytic capacitor CZ1, a No.2 electrolytic capacitor CZ2, a No.3 electrolytic capacitor CPV, a No.1 switching tube S1, a No.2 switching tube S2, a No.3 switching tube S3, a No.4 switching tube S4, a No.5 switching tube S5, a third inductance LZ1 and a fourth inductance LZ2; a network voltage modulates the single-phase non-transformer isolation-type Z-source photovoltaic grid-connected inverter to have three switching modes in both positive and negative half periods. The single-phase non-transformer isolation-type Z-source photovoltaic grid-connected inverter and the modulation method can be used in the photovoltaic grid-connected system.

Description

Single-phase transless isolated form Z source photovoltaic combining inverter and modulator approach

Technical field

The present invention relates to single-phase transless isolated form Z source photovoltaic combining inverter.Belong to photovoltaic combining inverter technical field.

Background technology

Z-source inverter is applied in photovoltaic parallel in system, can realize by the structure that is similar to single stage type system and complete the function of boosting with inversion two-stage system simultaneously, to adapt to the large feature of photovoltaic cell change in voltage scope.At present, both at home and abroad experts and scholars to traditional and various modified model Z-source inverters the application in photovoltaic parallel in system carried out a large amount of research, promoted the service behaviour of traditional Z source inventer, but their common shortcoming is in the grid-connected application of reality, all to need to utilize extra transformer as the electrical isolation device between photovoltaic system and electrical network, can make like this cost, volume, weight and the loss of system increase, make the Efficiency Decreasing of system, thereby make the advantage of Z-source inverter not perform to ultimate attainment.But not isolation type grid-connected inverter is not used isolating transformer, simplification system also has that cost is low, efficiency advantages of higher, contributes to promote the development of parallel network power generation technology.So research non-isolation type Z source photovoltaic combining inverter, both can utilize Z-source inverter compared with the advantage of conventional inverter, can bring into play to a certain extent again the advantage of non-isolation type combining inverter.

In non-isolation type combining inverter, exist the influential stray element of common mode current, i.e. series resistance between stray capacitance, inverter and electrical network earth point between stray capacitance between photovoltaic array and ground, inverter output mid point and ground.These stray elements form common mode resonance circuit together with filter element, electric network impedance, and the voltage at the stray capacitance two ends in resonant circuit between photovoltaic array and ground can change because of inverter switching device action, encourages thus common mode resonance circuit to produce common mode current.And the appearance of common mode current can increase system loss, causes conducted interference and radiated interference, increase grid-connected current harmonic wave, affect Electromagnetic Compatibility and safety issue.

The common-mode voltage that traditional Z source photovoltaic combining inverter has high frequency to change, therefore produced thus very large common mode current, this topological structure is not suitable for non-isolation type photovoltaic grid-connected inverting system.

Summary of the invention

The present invention is applied in photovoltaic parallel in system in order to solve traditional Z-source inverter, and grid connection efficiency is low and produce the large problem of common mode current.Single-phase transless isolated form Z source photovoltaic combining inverter and modulator approach are now provided.

Single-phase transless isolated form Z source photovoltaic combining inverter, it comprises photovoltaic array module U _pV, the first inductance L _ac1, the second inductance L _ac2with electrical network u _g, it also comprises fast recovery diode D No. one ₁, No. two fast recovery diode D ₂, an electrochemical capacitor C _z1, No. two electrochemical capacitor C _z2, No. three electrochemical capacitor C _pV, a switching tube S ₁, No. two switching tube S ₂, No. three switching tube S ₃, No. four switching tube S ₄, No. five switching tube S ₅, the 3rd inductance L _z1with the 4th inductance L _z2,

Described photovoltaic array module U _pVcathode output end connect fast recovery diode D No. one simultaneously ₁anode and No. three electrochemical capacitor C _pVpositive pole, a fast recovery diode D ₁negative electrode connect electrochemical capacitor C No. one simultaneously _z1positive pole and the 3rd inductance L _z1one end, the 3rd inductance L _z1the other end connect electrochemical capacitor C No. two simultaneously _z2positive pole and No. five switching tube S ₅collector electrode, No. five switching tube S ₅emitter connect switching tube S No. one simultaneously ₁collector electrode and No. three switching tube S ₃collector electrode, a switching tube S ₁emitter connect switching tube S No. two simultaneously ₂collector electrode and the first inductance L _ac1one end, No. three switching tube S ₃emitter connect switching tube S No. four simultaneously ₄collector electrode and the second inductance L _ac2one end, the first inductance L _ac1the other end connect electrical network u _gone end, electrical network u _gthe other end connect the second inductance L _ac2the other end,

An electrochemical capacitor C _z1negative pole connect the 4th inductance L simultaneously _z2one end, No. two switching tube S ₂emitter and No. four switching tube S ₄emitter, the 4th inductance L _z2the other end connect electrochemical capacitor C No. two simultaneously _z2negative pole and No. two fast recovery diode D ₂anode, No. two fast recovery diode D ₂negative electrode connect electrochemical capacitor C No. three simultaneously _pVnegative pole and photovoltaic array module U _pVcathode output end.

The modulator approach that adopts single-phase transless isolated form Z source photovoltaic combining inverter to realize, this modulator approach is:

The described single-phase transless isolated form Z source photovoltaic combining inverter of line voltage modulation all has three kinds of switching modes in positive and negative half period,

When line voltage is positive half period, control inverter periodic duty is at effective status, pass-through state, nought state, pass-through state and effective status, and the control signal of described effective status is S _1,2,3,4,5={ 1001 1}, the control signal of nought state is S _1,2,3,4,5={ 1010 0}, the control signal of pass-through state is S _1,2,3,4,5={ 1011 1};

When line voltage is negative half-cycle, control inverter periodic duty is at effective status, pass-through state, nought state, pass-through state and effective status, and the control signal of described effective status is S _1,2,3,4,5={ 0110 1}, the control signal of nought state is S _1,2,3,4,5={ 1010 0}, the control signal of pass-through state is S _1,2,3,4,5={ 1110 1}.

Beneficial effect of the present invention is: five switching tubes of the present invention all can produce 3 kinds of switching modes in line voltage is positive and negative half period, the commutation circuit of 3 kinds of switching modes is in effective status, nought state and pass-through state and each half cycle has two switching tubes respectively in permanent conducting or permanent off state, on off state reduces, the switching loss of system reduces, and grid connection efficiency is high.When effective status and nought state, an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2charging, the 3rd inductance L _z1with the 4th inductance L _z2release energy, inductive current i _l1and i _l2decline;

When pass-through state, an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2electric discharge, the 3rd inductance L _z1with the 4th inductance L _z2from an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2obtain energy, in inverter commutation course, pass-through state, between traditional nought state and effective status, and only has switching tube S No. one ₁with No. three switching tube S ₃, there is not switching tube S No. two in traditional nought state of afterflow conducting ₂with No. four switching tube S ₄the nought state of afterflow conducting, it is constant that common mode capacitance voltage keeps; Under pass-through state, a fast recovery diode D ₁, No. two fast recovery diode D ₂can blocking light photovoltaic array and Z-source inverter, common mode capacitance voltage discharge off path.Therefore, this inverter topology common mode current is very little.

In order to verify the practicality of the inventive method, adopt the New single-phase transless isolated form Z source photovoltaic combining inverter topological structure proposing, designed the experimental prototype of a rated power 1kW.Line voltage 220VAC, power frequency 50Hz, switching frequency is 10kHz.

Accompanying drawing explanation

Fig. 1 is the principle schematic of the single-phase transless isolated form Z source photovoltaic combining inverter described in embodiment one,

Fig. 2 is the single-phase non-isolated Z-source inverter positive half period PWM modulation strategy principle schematic described in embodiment two, and Reference numeral 1 represents pass-through state, T _srepresent switch periods, T represents the straight-through time,

Fig. 3 is the single-phase non-isolated Z-source inverter negative half-cycle PWM modulation strategy principle schematic described in embodiment two, and Reference numeral 1 represents pass-through state,

Fig. 4 is the current direction of line voltage of the present invention nought state while being positive half period,

Fig. 5 is the current direction of line voltage of the present invention pass-through state while being positive half period,

Fig. 6 is the current direction of line voltage of the present invention effective status while being positive half period,

Fig. 7 is the current direction of line voltage of the present invention nought state while being negative half-cycle,

Fig. 8 is the current direction of line voltage of the present invention pass-through state while being negative half-cycle,

Fig. 9 is the current direction of line voltage of the present invention effective status while being negative half-cycle,

Figure 10 is grid-connected current of the present invention and grid voltage waveform figure, and Reference numeral 2 represents grid-connected current waveform, and Reference numeral 3 represents grid voltage waveform,

Figure 11 is the equivalent electric circuit of the non-pass-through state of single-phase non-isolated Z source photovoltaic combining inverter,

Figure 12 is the equivalent electric circuit of single-phase non-isolated Z source photovoltaic combining inverter pass-through state.

Embodiment

Embodiment one: with reference to Fig. 1, illustrate present embodiment, the single-phase transless isolated form Z source photovoltaic combining inverter described in present embodiment, it comprises photovoltaic array module U _pV, the first inductance L _ac1, the second inductance L _ac2with electrical network u _g, it also comprises fast recovery diode D No. one ₁, No. two fast recovery diode D ₂, an electrochemical capacitor C _z1, No. two electrochemical capacitor C _z2, No. three electrochemical capacitor C _pV, a switching tube S ₁, No. two switching tube S ₂, No. three switching tube S ₃, No. four switching tube S ₄, No. five switching tube S ₅, the 3rd inductance L _z1with the 4th inductance L _z2,

Described photovoltaic array module U _pVcathode output end connect fast recovery diode D No. one simultaneously ₁anode and No. three electrochemical capacitor C _pVpositive pole, a fast recovery diode D ₁negative electrode connect electrochemical capacitor C No. one simultaneously _z1positive pole and the 3rd inductance L _z1one end, the 3rd inductance L _z1the other end connect electrochemical capacitor C No. two simultaneously _z2positive pole and No. five switching tube S ₅collector electrode, No. five switching tube S ₅emitter connect switching tube S No. one simultaneously ₁collector electrode and No. three switching tube S ₃collector electrode, a switching tube S ₁emitter connect switching tube S No. two simultaneously ₂collector electrode and the first inductance L _ac1one end, No. three switching tube S ₃emitter connect switching tube S No. four simultaneously ₄collector electrode and the second inductance L _ac2one end, the first inductance L _ac1the other end connect electrical network u _gone end, electrical network u _gthe other end connect the second inductance L _ac2the other end,

An electrochemical capacitor C _z1negative pole connect the 4th inductance L simultaneously _z2one end, No. two switching tube S ₂emitter and No. four switching tube S ₄emitter, the 4th inductance L _z2the other end connect electrochemical capacitor C No. two simultaneously _z2negative pole and No. two fast recovery diode D ₂anode, No. two fast recovery diode D ₂negative electrode connect electrochemical capacitor C No. three simultaneously _pVnegative pole and photovoltaic array module U _pVcathode output end.

Embodiment two: with reference to Fig. 2 and Fig. 3, illustrate present embodiment, the modulator approach that adopts the single-phase transless isolated form Z source photovoltaic combining inverter described in embodiment one to realize, this modulator approach is:

When line voltage is positive half period, control inverter periodic duty is at effective status, pass-through state, nought state, pass-through state and effective status, and the control signal of described effective status is S _1,2,3,4,5={ 1001 1}, the control signal of nought state is S _1,2,3,4,5={ 1010 0}, the control signal of pass-through state is S _1,2,3,4,5={ 1011 1};

When line voltage is negative half-cycle, control inverter periodic duty is at effective status, pass-through state, nought state, pass-through state and effective status, and the control signal of described effective status is S _1,2,3,4,5={ 0110 1}, the control signal of nought state is S _1,2,3,4,5={ 1010 0}, the control signal of pass-through state is S _1,2,3,4,5={ 1110 1}.

The modulator approach of present embodiment, to convert in nought state the pass-through state that increases T`/2 between effective status to, at effective status, be transformed into the pass-through state that has also increased T`/2 between nought state, this pass-through state, between traditional nought state and effective status, fast recovery diode D1 and No. two fast recovery diode D2 can blocking light photovoltaic array and Z-source inverters, make common mode capacitance voltage discharge off path, therefore, make the common mode current of inverter topology very little.

Embodiment three: illustrate present embodiment with reference to Fig. 4, Fig. 5 and Fig. 6, the difference of the modulator approach that the single-phase transless isolated form Z of the employing source photovoltaic combining inverter described in present embodiment and embodiment two is realized is, when line voltage is positive half period, No. three switching tube S ₃the on off state sinusoidal reference signal that is M by modulation ratio and the signal that produces of carried-based PWM control, No. four switching tube S ₄on off state with No. three switching tube S ₃on the basis of complementary conducting, increased the straight-through time, No. five switching tube S ₅on off state and No. four switching tube S ₄synchronously.

In present embodiment, the scope that modulation ratio is M is 0<M≤1.

In present embodiment, when line voltage is positive half period at nought state S _1,2,3,4,5={ 1010 0}, a described fast recovery diode D ₁, No. two fast recovery diode D ₂with a switching tube S ₁conducting, No. two switching tube S ₂, No. four switching tube S ₄with No. five switching tube S ₅turn-off, wherein, No. three diode S ₃anti-paralleled diode conducting, an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2charging, the 3rd inductance L _z1with the 4th inductance L _z2release energy, inductive current i _l1and i _l2decline; As shown in Figure 4,

When line voltage is positive half period at pass-through state S _1,2,3,4,5={ 1011 1}, a described switching tube S ₁, No. three switching tube S ₃, No. four switching tube S ₄with No. five switching tube S ₅conducting, a fast recovery diode D ₁, No. two fast recovery diode D ₂with No. two switching tube S ₂turn-off, wherein, No. three switching tube S ₃anti-paralleled diode conducting, an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2electric discharge, the 3rd inductance L _z1with the 4th inductance L _z2from an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2obtain energy, as shown in Figure 5,

When line voltage is positive half period at effective status S _1,2,3,4,5={ 1001 1}, a described fast recovery diode D ₁, No. two fast recovery diode D ₂, a switching tube S ₁, No. four switching tube S ₄with No. five switching tube S ₅conducting, No. two switching tube S ₂with No. three switching tube S ₃turn-off an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2charging, the 3rd inductance L _z1with the 4th inductance L _z2release energy, inductive current i _l1and i _l2decline; As shown in Figure 6.

Embodiment four: illustrate present embodiment with reference to Fig. 7, Fig. 8 and Fig. 9, the difference of the modulator approach that the single-phase transless isolated form Z of the employing source photovoltaic combining inverter described in present embodiment and embodiment two is realized is, when line voltage is negative half-cycle, a switching tube S ₁the on off state sinusoidal reference signal that is M by modulation ratio and the signal that produces of carried-based PWM control, No. two switching tube S ₂on off state with a switching tube S ₁on the basis of complementary conducting, increased the straight-through time, No. five switching tube S ₅on off state and No. two switching tube S ₂synchronously.

When line voltage is negative half-cycle at nought state S _1,2,3,4,5={ 1010 0}, a described fast recovery diode D ₁, No. two fast recovery diode D ₂with No. three switching tube S ₃conducting, No. two switching tube S ₂, No. four switching tube S ₄with No. five switching tube S ₅turn-off, wherein, a switching tube S ₁antiparallel diode current flow, an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2charging, the 3rd inductance L _z1with the 4th inductance L _z2release energy, inductive current i _l1and i _l2decline; As shown in Figure 7,

When line voltage is negative half-cycle at pass-through state S _1,2,3,4,5={ 1110 1}, a described switching tube S ₁, No. two switching tube S ₂, No. three switching tube S ₃with No. five switching tube S ₅conducting, a fast recovery diode D ₁, No. two fast recovery diode D ₂with No. four switching tube S ₄turn-off, wherein, a diode S ₁antiparallel diode current flow, an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2electric discharge, the 3rd inductance L _z1with the 4th inductance L _z2from an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2obtain energy, as shown in Figure 8,

When line voltage is negative half-cycle at effective status S _1,2,3,4,5={ 0110 1}, a described fast recovery diode D ₁, No. two fast recovery diode D ₂, No. two switching tube S ₂, No. three switching tube S ₃with No. five switching tube S ₅conducting, a switching tube S ₁with No. four switching tube S ₄turn-off an electrochemical capacitor C _z1with No. two electrochemical capacitor C _z2charging, the 3rd inductance L _z1with the 4th inductance L _z2release energy, inductive current i _l1and i _l2decline; As shown in Figure 9.

In the present invention, line voltage is modulated single-phase transless isolated form Z source photovoltaic combining inverter, all has three kinds of switching modes in line voltage positive and negative half period, when pass-through state, and Z source capacitor discharge, Z source inductance obtains energy from Z source electric capacity.A fast recovery diode D ₁, No. two fast recovery diode D ₂can blocking light photovoltaic array and Z-source inverter, common mode capacitance voltage discharge off path.

Figure 10 is grid-connected current and grid voltage waveform, and both frequencies equate, phase place is basically identical, meet grid-connected requirement.The common-mode voltage waveform demonstration producing, when effective status and nought state, it is constant that common-mode voltage maintains.

In the present invention, the principle Analysis method of single-phase non-isolated Z-source inverter and traditional Z source inventer are similar, first suppose that Z source network is symmetrical network, an electrochemical capacitor C _z1, No. two electrochemical capacitor C _z2with the 3rd inductance L _z1with the 4th inductance L _z2meet:

$\left\{\begin{array}{c}{L}_{Z1}=L_{Z2}=L\\ C_{Z1}=C_{Z2}=C\end{array}\right.---\left(1\right)$

According to symmetry and the principle of equal effects, have

$\left\{\begin{array}{c}{U}_{L1}=U_{L2}=U_L\\ U_{C1}=U_{C2}=U_C\end{array}\right.---\left(2\right)$

According at a switch periods T _swhether interior inverter bridge is operated in direct mode operation, and single-phase non-isolated Z-source inverter is the same with traditional Z source inventer, also has two kinds of operating states: pass-through state and non-pass-through state.Under pass-through state, between Z source energy storage network internal inductance capacitance, carry out energy exchange, avoided the instantaneous variation of voltage or electric current, this in effective protection device for power switching also for inverter provides unique buck characteristic.

(1) non-pass-through state is according to non-pass-through state circuit equivalent Figure 11), a fast recovery diode D now ₁, No. two fast recovery diode D ₂forward conduction, Z source network energy storage inductor is by load discharge, and inverter bridge can be equivalent to a controlled current source i _i.Suppose at a switch periods T _sin, the time that inverter bridge is operated in non-pass-through state is T ₁, have

$\left\{\begin{array}{c}{U}_{\mathrm{FB}}=U_C-U_L=2U_C-U_{\mathrm{PV}}\\ U_d=U_{\mathrm{PV}}=U_L+U_C\end{array}\right.---\left(3\right)$

Wherein, U _pVfor photovoltaic array module; U _dbe a fast recovery diode D ₁negative electrode and No. two fast recovery diode D ₂voltage between anode; U _fBfor inverter bridge busbar voltage.

(2) pass-through state is according to pass-through state circuit equivalent Figure 12), diode D now ₁and D ₂bear back-pressure and turn-off, inverter bridge short circuit.At a switch periods T _sin, inverter bridge pass-through state operating time and non-pass-through state operating time are complementary, and the operating time of establishing pass-through state is T (T=T _s-T ₁), have

$\left\{\begin{array}{c}{U}_L=U_C\\ U_{\mathrm{FB}}=0\\ U_d=2U_C>U_{\mathrm{PV}}\end{array}\right.---\left(4\right)$

Under stable condition, from the weber balance principle of DC inductance, in a switch periods, the average voltage at energy storage inductor two ends, Z source must be zero, by formula (3) and formula (4), is obtained

U _CT+(U _PV-U _C)T ₁＝0 (5)

Arrange to such an extent that Z source capacitance voltage is

$U_C=\frac{T_1}{T_1-T}{U}_{\mathrm{PV}}---\left(6\right)$

In like manner known, inverter bridge DC side average voltage is

$U_{\mathrm{FB}}=\frac{T_1}{T_1-T}{U}_{\mathrm{PV}}=U_C---\left(7\right)$

Under non-pass-through state, inverter bridge bus crest voltage to the gain B of input voltage is

$B=\frac{{\hat{U}}_{\mathrm{FB}}}{U_{\mathrm{PV}}}=\frac{T_S}{T_1-T}=\frac{1}{1-2d_0}\&GreaterEqual;1---\left(8\right)$

Wherein, for inverter bridge bus crest voltage; d ₀for straight-through duty ratio, d ₀=T '/T _s.

The Sine Modulated factor M of inverter is

$M=\frac{{\hat{u}}_{\mathrm{ab}}}{{\hat{U}}_{\mathrm{FB}}}---\left(9\right)$

Wherein, for exchanging output sinusoidal voltage first-harmonic peak value.

Therefore, whole single-phase non-isolated Z-source inverter output voltage is

${\hat{u}}_{\mathrm{ab}}={\hat{U}}_{\mathrm{FB}}M=\frac{T_S}{T_1-T}{U}_{\mathrm{PV}}M={\mathrm{BMU}}_{\mathrm{PV}}---\left(10\right)$

From formula (10), when non-isolation type Z-source inverter is applied to photovoltaic parallel in system, its AC voltage is clamped down on by electrical network, therefore by modulating the grid-connected of DC side input voltage that straight-through duty ratio and the Sine Modulated factor can realize arbitrary size.Than traditional electrical potential source type inverter, single-phase non-isolated Z-source inverter, not needing, under the prerequisite of extra intergrade translation circuit, to have expanded the transformation range of system, has improved the combination property of system.

Claims (4)

1. single-phase transless isolated form Z source photovoltaic combining inverter, it comprises photovoltaic array module U _pV, the first inductance L _ac1, the second inductance L _ac2with electrical network u _g, it is characterized in that, it also comprises fast recovery diode D No. one ₁, No. two fast recovery diode D ₂, an electrochemical capacitor C _z1, No. two electrochemical capacitor C _z2, No. three electrochemical capacitor C _pV, a switching tube S ₁, No. two switching tube S ₂, No. three switching tube S ₃, No. four switching tube S ₄, No. five switching tube S ₅, the 3rd inductance L _z1with the 4th inductance L _z2,

Described photovoltaic array module U _pVcathode output end connect fast recovery diode D No. one simultaneously ₁anode and No. three electrochemical capacitor C _pVpositive pole, a fast recovery diode D ₁negative electrode connect electrochemical capacitor C No. one simultaneously _z1positive pole and the 3rd inductance L _z1one end, the 3rd inductance L _z1the other end connect electrochemical capacitor C No. two simultaneously _z2positive pole and No. five switching tube S ₅collector electrode, No. five switching tube S ₅emitter connect switching tube S No. one simultaneously ₁collector electrode and No. three switching tube S ₃collector electrode, a switching tube S ₁emitter connect switching tube S No. two simultaneously ₂collector electrode and the first inductance L _ac1one end, No. three switching tube S ₃emitter connect switching tube S No. four simultaneously ₄collector electrode and the second inductance L _ac2one end, the first inductance L _ac1the other end connect electrical network u _gone end, electrical network u _gthe other end connect the second inductance L _ac2the other end,

An electrochemical capacitor C _z1negative pole connect the 4th inductance L simultaneously _z2one end, No. two switching tube S ₂emitter and No. four switching tube S ₄emitter, the 4th inductance L _z2the other end connect electrochemical capacitor C No. two simultaneously _z2negative pole and No. two fast recovery diode D ₂anode, No. two fast recovery diode D ₂negative electrode connect electrochemical capacitor C No. three simultaneously _pVnegative pole and photovoltaic array module U _pVcathode output end.

2. the modulator approach that adopts single-phase transless isolated form Z claimed in claim 1 source photovoltaic combining inverter to realize, is characterized in that, this modulator approach is:

The described single-phase transless isolated form Z source photovoltaic combining inverter of line voltage modulation all has three kinds of switching modes in positive and negative half period,

When line voltage is positive half period, control inverter periodic duty is at effective status, pass-through state, nought state, pass-through state and effective status, and the control signal of described effective status is S _1,2,3,4,5={ 1001 1}, the control signal of nought state is S _1,2,3,4,5={ 1010 0}, the control signal of pass-through state is S _1,2,3,4,5={ 1011 1};

When line voltage is negative half-cycle, control inverter periodic duty is at effective status, pass-through state, nought state, pass-through state and effective status, and the control signal of described effective status is S _1,2,3,4,5={ 0110 1}, the control signal of nought state is S _1,2,3,4,5={ 1010 0}, the control signal of pass-through state is S _1,2,3,4,5={ 1110 1}.

3. the modulator approach that the single-phase transless isolated form Z of employing according to claim 2 source photovoltaic combining inverter is realized, is characterized in that, when line voltage is positive half period, and No. three switching tube S ₃the on off state sinusoidal reference signal that is M by modulation ratio and the signal that produces of carried-based PWM control, No. four switching tube S ₄on off state with No. three switching tube S ₃on the basis of complementary conducting, increased the straight-through time, No. five switching tube S ₅on off state and No. four switching tube S ₄synchronously.

4. the modulator approach that the single-phase transless isolated form Z of employing according to claim 2 source photovoltaic combining inverter is realized, is characterized in that, when line voltage is negative half-cycle, and a switching tube S ₁the on off state sinusoidal reference signal that is M by modulation ratio and the signal that produces of carried-based PWM control, No. two switching tube S ₂on off state with a switching tube S ₁on the basis of complementary conducting, increased the straight-through time, No. five switching tube S ₅on off state and No. two switching tube S ₂synchronously.