CN115347785A - A High Efficiency Photovoltaic Converter Without Input Filter - Google Patents

Abstract

The application belongs to the field of photovoltaic power generation, and discloses a high-efficiency photovoltaic converter without an input filter. The photovoltaic converter includes a switch tube, three diodes, two auxiliary inductors, a three-winding transformer and five capacitors. It can completely eliminate the switching frequency ripple of the input current, no input filter capacitor is required, and the reliability is improved; it has a strong boost capability, allowing the voltage of the solar cell to vary in a wide range; the number of power tubes is small and the voltage stress is low, and it can be used The low withstand voltage device reduces the cost and loss, and improves the conversion efficiency; the volume of the auxiliary inductor is small, and the power density is high; the input and output share the same ground, so the electromagnetic interference is small, and the sampling circuit structure is simple.

Description

A High Efficiency Photovoltaic Converter Without Input Filter

technical field

The invention belongs to the field of photovoltaic power generation, and in particular relates to a high-efficiency photovoltaic converter without an input filter.

Background technique

The output voltage of solar cells is low and has a wide range of variation. Therefore, distributed photovoltaic power generation systems usually use a DC converter with a high gain as the photovoltaic interface, and then can be integrated into the public grid through a traditional voltage source grid-connected inverter. The input current of the traditional Boost converter is continuous, the number of components is small, and the structure is simple, so it is widely used in various boosting occasions. However, the voltage stress of the power tube is equal to the output voltage, the on-state loss and switching loss are large, and the voltage gain generally does not exceed 5, which makes it difficult to achieve voltage matching between solar cells and the grid. The Flyback-boost converter can greatly increase the boost multiple by changing the turn ratio of the transformer to meet the voltage gain requirements of the photovoltaic interface, and has a lower power tube voltage stress. However, the leakage inductance energy of its transformer is difficult to recover, resulting in higher voltage spikes and lower conversion efficiency. In addition, the input current of this converter has severe pulsation. In order to avoid affecting the power generation efficiency of solar cells due to excessive input current ripple, a large-capacity filter capacitor needs to be connected in parallel on the input side, but the system size and cost will increase and reliability will decrease. Capacitor series-connected two-phase interleaved parallel Boost converter can double the voltage gain of the traditional Boost, reduce the voltage stress of the power tube to half of the output voltage, and reduce the input current ripple. Doubling the frequency reduces the required input capacitance. However, these good characteristics will all be lost when the duty cycle is less than 0.5. Therefore, in the case of photovoltaic power generation where the input voltage varies in a wide range, the use of capacitor series-connected two-phase interleaved parallel Boost converters as photovoltaic converters cannot really reduce the input capacitance.

Contents of the invention

In view of this, the purpose of the present invention is to provide a high-efficiency photovoltaic converter without an input filter, the high-efficiency photovoltaic converter can eliminate the switching frequency ripple of the input current, thereby completely removing the filter capacitor on the input side, and has a boost It has the advantages of strong voltage capability, small number of switching tubes, low voltage stress and cost, high conversion efficiency and reliability, etc.

In order to achieve the above object, the technical scheme proposed by the present invention is as follows:

A high-efficiency photovoltaic converter without an input filter, including a first capacitor C ₁ , a second capacitor C ₂ , a third capacitor C ₃ , a fourth capacitor C ₄ , a fifth capacitor C _o , a three-winding transformer, a first Auxiliary inductance L _s1 , second auxiliary inductance L _s2 , switch tube S, first diode D ₁ , second diode D ₂ , third diode D ₃ , the three-winding transformer includes a first winding N _1. The second winding N ₂ and the third winding N ₃ , the number of turns of the second winding N ₂ and the third winding N ₃ are the same, the first auxiliary inductance L _s1 and the second auxiliary inductance L _s2 The current flows bidirectionally; the second end of the _first winding N1 is connected to the drain of the switching tube S, the anode of the _first diode D1, the cathode of the _second capacitor C2, the The cathode of the fourth capacitor _C4 is connected; the cathode of the _first diode D1 is connected to the first end of the second winding _N2 and the anode of the first capacitor _C1 ; the second winding N The second end of ₂ is connected to one end of the first auxiliary inductance L _s1 , and the other end of the first auxiliary inductance L _s1 is connected to the anode of the second capacitor C ₂ and the anode of the second diode D ₂ anode connection; the cathode of the _second diode D2 is connected to the anode of the _third capacitor C3 and the first end of the _third winding N3 _; the second end of the third winding N3 is connected to One end of the second auxiliary inductance L _s2 is connected, and the other end of the second auxiliary inductance L _s2 is connected to the anode of the third diode _D3 and the anode of the fourth capacitor _C4 ; the first The cathode of the _three diodes D3 is connected to the positive pole of the fifth capacitor C _o ; the source of the switching tube S is connected to the negative pole of the first capacitor _C1 , the negative pole of the _third capacitor C3, and the negative pole of the third capacitor C3. The negative pole of the fifth capacitor C _o is connected; the first end of the _first winding N1 is connected to the positive pole of the power supply U _in ; the source of the switching tube S is connected to the negative pole of the power supply U _in ; the fifth capacitor The positive pole of C _o is connected to one end of the load; the negative pole of the fifth capacitor C _o is connected to the other end of the load.

Further, in the three-winding transformer,

The value range of the turn ratio n of the second winding _N2 and the _first winding N1:

In the formula, G is the voltage gain of the photovoltaic converter, and δ% is the ratio of the peak-to-peak value of the excitation inductance current of the three-winding transformer to the maximum average current; usually δ% is 20%-30%.

The excitation inductance L _m of the three-winding transformer needs to satisfy:

In the formula, U _in is the input voltage, U _o is the output voltage, f _s is the switching frequency, P _o,max is the maximum output power.

Further, the inductances of the first auxiliary inductance L _s1 and the second auxiliary inductance L _s2 are equal, which is: L _s1 =L _s2 =2n(1-n)L _m .

Further, the ideal voltage gain is (1+2D)/(1-D), where D is the duty cycle of the drive signal of the switching tube S;

Further, the voltage stresses of the switch tube S, the first diode D ₁ , the second diode D ₂ and the third diode D ₃ are all (2U _in +U _o ) /3.

Further, the working process of the photovoltaic converter in each switching cycle includes the following two modes:

(1) Mode 1[t ₀ -t ₁ ]:

At time t ₀ , the switch tube S is turned on, the first diode D ₁ , the second diode D ₂ , and the third diode D ₃ are all turned off due to the reverse voltage, and all the inductors are subjected to the forward voltage. The excitation inductance current i _Lm of the three-winding transformer increases linearly, the first auxiliary inductance current i _Ls1 and the second auxiliary inductance current i _Ls2 first decrease linearly in the reverse direction to 0 and then increase linearly in the forward direction, and at time t ₁ , modal 1 ends;

(2) Mode 2[t ₁ -t ₂ ]:

At time _t1 , the switch tube S is turned off, the _first diode D1, the _second diode D2, and the third diode _D3 are all forward-conducting, all inductors are subjected to reverse voltage, and the three The excitation inductance current i _Lm of the winding transformer decreases linearly, the first auxiliary inductance current i _Ls1 and the second auxiliary inductance current i _Ls2 both decrease linearly in the forward direction to 0 and then increase linearly in the reverse direction. At time t ₂ , the modal 2 end;

Wherein, all the inductances include the excitation inductance of the three-winding transformer, the first auxiliary inductance L _s1 and the second auxiliary inductance L _s2 .

Compared with the prior art, the high-efficiency photovoltaic converter without input filter proposed by the present invention has the following technical effects:

1) Completely eliminate the switching frequency ripple of the input current, so no input filter capacitor is required, which improves reliability, reduces volume and cost;

2) It has a strong boosting capability, and the voltage gain is 13 when the duty cycle is equal to 0.8.

3) There is only one switch tube and three diodes, and the voltage stress of all power tubes is low, which is (2U _in + U _o )/3, and devices with low withstand voltage can be used, reducing system cost and loss.

4) The volume of the inductor is small.

Description of drawings

Fig. 1 is the schematic diagram of the circuit structure of the high-efficiency photovoltaic converter without input filter provided by the present invention;

Fig. 2 is the working modal equivalent diagram of the high-efficiency photovoltaic converter without input filter shown in Fig. 1 in one switching cycle;

Fig. 3 is the main waveform diagram in one switching cycle of the high-efficiency photovoltaic converter without input filter shown in Fig. 1;

Fig. 4 is the average current equivalent circuit schematic diagram of the high-efficiency photovoltaic converter without input filter shown in Fig. 1;

FIG. 5 is a steady-state simulation waveform diagram of the high-efficiency photovoltaic converter without an input filter shown in FIG. 1 .

Fig. 6 is the control block diagram of the high-efficiency photovoltaic converter without input filter provided by the present invention;

FIG. 7 is a dynamic simulation waveform diagram of the high-efficiency photovoltaic converter without an input filter shown in FIG. 1 .

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

The present invention provides a high-efficiency photovoltaic converter without an input filter, and the circuit structure is shown in FIG. 1 . It includes a first capacitor C ₁ , a second capacitor C ₂ , a third capacitor C ₃ , a fourth capacitor C ₄ , a fifth capacitor C _o , a three-winding transformer, a first auxiliary inductor L _s1 , a second auxiliary inductor L _s2 , Switching tube S; the three-winding transformer includes a first winding N ₁ , a second winding N ₂ and a third winding N ₃ ; the first winding N ₁ is the primary winding of the three-winding transformer; the first winding N ₁ The second end is connected to the drain of the switch tube S, the anode of the _first diode D1, the cathode of the _second capacitor C2, and the cathode of the fourth capacitor _C4 ; the cathode of the _first diode D1 is connected to the second The first end of the winding _N2 is connected to the positive pole of the first capacitor _C1 ; the second end of the second winding _N2 is connected to one end of the first auxiliary inductance L _s1 , and the other end of the first auxiliary inductance L _s1 is connected to the second capacitor The positive pole of _C2 is connected to the anode of the _second diode D2 _; the cathode of the second diode D2 is connected to the positive pole of the _third capacitor C3 and the first end of the _third winding N3; the _third winding N3 The second terminal of the second auxiliary inductance L _s2 is connected to one end of the second auxiliary inductance L _s2 , and the other end of the second auxiliary inductance L s2 is connected to the anode of the third diode _D3 and the anode of the fourth capacitor _C4 ; the third diode D The cathode of ₃ is connected to the positive pole of the fifth capacitor C _o ; the source of the switch tube S is connected to the negative pole of the first capacitor _C1 , the negative pole of the _third capacitor C3, and the negative pole of the fifth capacitor C _o ; the _first winding N1 The first end of the first terminal is connected to the positive pole of the power supply U _in ; the source of the switch tube S is connected to the negative pole of the power supply U _in ; the positive pole of the fifth capacitor C _o is connected to one end of the output side load; the negative pole of the fifth capacitor C _o is connected to the output Connect the other end of the side load.

The working process of the high-efficiency photovoltaic converter without input filter shown in FIG. 1 will be described below.

In order to simplify the analysis, the following assumptions are made: the first capacitor C ₁ , the second capacitor C ₂ , the third capacitor C ₃ , the fourth capacitor C ₄ , the fifth capacitor C _o , the first auxiliary inductance L _s1 , the second auxiliary inductance L _s2 , switch tube S, first diode D ₁ , second diode D ₂ , and third diode D ₃ are all ideal devices; the first capacitor C ₁ , the second capacitor C ₂ , and the third capacitor C _3. The fourth capacitor C ₄ and the fifth capacitor C _o are large enough to ignore the voltage ripple; the negative terminal of the input power supply U _in is a zero potential reference point. The working process of the high-efficiency photovoltaic converter without input filter shown in Figure 1 can be divided into two modes in one switching cycle. The equivalent circuit of each mode is shown in Fig. 2. Its main waveform in a switching cycle is shown in Figure 3.

Mode 1[t ₀ , t ₁ ] (the equivalent circuit is shown in Figure 2(a))

At time t ₀ , the switch tube S is turned on, the first diode D ₁ , the second diode D ₂ , and the third diode D ₃ are all turned off due to back pressure, and all inductors (including the first auxiliary inductor The current i _Ls1 , the second auxiliary inductance current i _Ls2 and the excitation inductance of the three-winding transformer) all bear the forward voltage, the excitation inductance current i _Lm of the three-winding transformer increases linearly, the first auxiliary inductance current i _Ls1 , the second auxiliary inductance The current i _Ls2 first decreases linearly in the reverse direction to 0 and then increases linearly in the forward direction, and its expression is as follows:

Among them, U _in is the input voltage, U _C1 , U _C2 , U _C3 , and U _C4 are the terminal voltages of the first capacitor C ₁ , the second capacitor C ₂ , the third capacitor C ₃ , and the fourth capacitor C ₄ respectively, and n is Turn ratios of the second winding N ₂ , the third winding N ₃ and the first winding N ₁ (n=N ₂ /N ₁ =N ₃ /N ₁ ).

Mode 2[t ₁ , t ₂ ] (the equivalent circuit is shown in Figure 2(b))

At time _t1 , the switch tube S is turned off, the _first diode D1, the _second diode D2, and the third diode _D3 are all forward-conducting, all inductors are subjected to reverse voltage, and the excitation inductor current i _Lm decreases linearly, the first auxiliary inductor current i _Ls1 and the second auxiliary inductor current i _Ls2 both decrease linearly in the forward direction to 0 and then increase linearly in the reverse direction. The expressions are as follows:

At time t ₂ , both the first auxiliary inductor current i _Ls1 and the second auxiliary inductor current i _Ls2 increase linearly in reverse to reach a maximum value. At this point, mode 2 ends and enters the next switching cycle.

Based on the above working principles, the steady-state characteristics of the high-efficiency photovoltaic converter without input filter of the present invention will be analyzed below.

According to the volt-second balance of the exciting inductance and the auxiliary inductance, it can be obtained:

Wherein, D is the duty ratio of the driving signal of the switching tube S.

In addition, it can be seen from Figure 2(b) (equivalent circuit diagram of mode 2):

Among them, U _o is the output voltage.

According to formula (7) and formula (8), the ideal voltage gain G of the high-efficiency photovoltaic converter without input filter of the present invention can be obtained as:

The voltage stress of the first capacitor U _C1 , the second capacitor U _C2 , the third capacitor U _C3 and the fourth capacitor U _C4 is:

The voltage stress of the switch tube S, the first diode D ₁ , the second diode D ₂ , and the third diode D ₃ is:

Among them, U _S is the terminal voltage of the switch tube S.

After entering the steady state, the average current of the first capacitor C ₁ , the second capacitor C ₂ , the third capacitor C ₃ , the fourth capacitor C ₄ , and the fifth capacitor C _o is zero, so the equivalent circuit of the average current can be obtained The schematic diagram can be obtained from Figure 4:

Among them, I _Ls1 is the average current value of the first auxiliary inductance L _s1 , I _Ls2 is the average current value of the second auxiliary inductance L _s2 , I _D1 is the average current value of the _first diode D1, and I _D2 is the second _The average current value of diode D2, I _D3 is the average current value of the third diode _D3 , I _o is the average value of the output current, I _in is the average value of the input current, I _S is the value of the switch tube S The average current value, I _Lm is the average current value of the exciting inductance L _m .

In order to eliminate the switching frequency ripple of the input current of the photovoltaic converter proposed in the present invention, the following conditions must be met:

L _s1 =L _s2 =2n(1-n)L _m (13)

This condition is proved below.

Let L _s1 = L _s2 = L _s , then when the photovoltaic converter of the present invention works in mode 1 and mode 2, respectively:

Wherein, i _Ls (t)=i _Ls1 (t)=i _Ls2 (t). ΔI _Ls is the current ripple, its value is equal to the current ripple of the first auxiliary inductance L _s1 and also equal to the current ripple of the second auxiliary inductance L _s2 , ΔI _Lm is the current ripple of the exciting inductance L _m .

in,

When L _s1 ＝L _s2 ＝2n(1-n)L _m , then:

It can be seen that the expression of the input current i _in does not contain the time variable t at this time, so it is a constant, which shows that the condition shown in formula (13) is satisfied, that is, the switching frequency ripple of the input current can be completely eliminated.

Next, the parameter design method of the photovoltaic converter proposed by the present invention is given.

The excitation inductance L _m of the three-winding transformer needs to meet:

Among them, δ% is the ratio of the peak-to-peak value of the exciting inductor current of the three-winding transformer to its maximum average current, usually 20%-30%, P _o,max is the maximum output power, and f _s is the switching frequency.

The first auxiliary inductor L _s1 and the second auxiliary inductor L _s2 both work in the current bidirectional conduction mode in the full load range, so there are:

From formula (15) and formula (18), we can get:

From formula (17) and formula (19), we can get:

Simplifying the formula (20), the value range of the turn ratio n of the three-winding transformer can be obtained:

The smaller n is, the smaller L _s is, and the volumes of the first auxiliary inductor L _s1 and the second auxiliary inductor L _s2 are smaller, but the current ripple rate increases, and the copper loss and iron loss of the inductor increase. Therefore, the value of the turns ratio n needs to be weighed.

Substituting the turns ratio n into formula (17), the value range of the exciting inductance L _m can be obtained. In order to reduce the volume, weight and cost of the transformer, and improve the rapidity of the system, the value of the excitation inductance L _m is usually slightly larger than its lower limit.

Substituting the exciting inductance L _m and the turn ratio n into formula (15), L _s can be obtained.

The design method of the photovoltaic converter proposed in the present invention will be described below with reference to specific examples.

The design indexes of the converter proposed in the present invention are: switching frequency f _s =100kHz, input power terminal voltage U _in =56V, output voltage U _o =400V, maximum output power P _o,max =250W, δ% =30%.

Under this index, the voltage gain of the proposed converter is: G=400/56=7.14.

Substituting δ%=30% and G=7.14 into formula (22), it can be obtained: n<0.63. Here, n=0.1 is selected.

Substituting n=0.1 into formula (17), it can be obtained: L _m >273 μH, and L _m =300 μH actually.

L _m =300 μH and n=0.1 are substituted into formula (15), and it can be obtained: L _s =54 μH.

Next, the Saber simulation software is used to simulate and verify the working principle, steady-state characteristics and correctness of the design method of the converter proposed in the present invention.

The specific technical indicators and circuit parameters are as follows: switching frequency f _s =100kHz, input power terminal voltage U _in =56V, output voltage U _o =400V, maximum output power P _o,max =250W, second capacitor C ₂ , fourth capacitor C ₄ : C ₂ =C ₄ =47μF, the first capacitor C ₁ , the third capacitor C ₃ , the fifth capacitor C _o : C ₁ =C ₃ =C _o =4.7μF, the excitation inductance L _m =300μH, the first Auxiliary inductance L _s1 , second auxiliary inductance L _s2 : L _s1 =L _s2 =L _s =54 μH. At this point, the voltage gain G = 7.14, from formula (9) can get the theoretical duty cycle D ≈ 0.672. The steady-state simulation waveform is shown in Figure 5.

Fig. 5(a) shows the simulation waveforms of the PWM driving signal _ugs of the switching tube S, the input current i _in , the exciting inductor current i _Lm , the first auxiliary inductor current i _Ls1 , and the second auxiliary inductor current i _Ls2 . It can be seen that the switching frequency ripple of the input current i _in is almost zero, and the ratio of the peak-to-peak value of the excitation inductor current i _Lm to its maximum average current is less than 30%; unanimous.

FIG. 5( b ) shows the simulation waveforms of the switch tube S, the first diode D ₁ , the second diode D ₂ , and the third diode D ₃ . It can be seen that the voltage stress of the switch tube S is 172V, and the voltage stress of the first diode D ₁ , the second diode D ₂ , and the third diode D ₃ are all 171V, which are basically consistent with the theoretical values.

FIG. 5( c ) shows the simulation waveforms of the first capacitor C ₁ , the second capacitor C ₂ , the third capacitor C ₃ , and the fourth capacitor C ₄ . It can be seen that the voltage stresses of the first capacitor C ₁ , the second capacitor C ₂ , the third capacitor C ₃ , and the fourth capacitor C ₄ are respectively 171V, 115V, 286V, and 230V, which are basically consistent with the theoretical values.

The converter proposed in the present invention adopts double closed-loop control of input voltage and input current, and its structure is shown in FIG. 6 . It can be seen that it compares the input voltage sampling value u _in,f with the preset input voltage reference value u _in,ref to obtain the first error signal u _e1 ; u _e1 passes through the voltage controller G _uo (s) and unit After processing to the limiting link Lim1, the input current reference value i _in,ref is obtained; the input current sampling value i _in,f is compared with i _in,ref to obtain the second error signal u _e2 ; u _e2 passes through the current controller G in turn _iin (s) and the one-way limiting link _Lim2 process to obtain the adjustment signal ur; _ur intersects with the unipolar triangular carrier uc to generate the PWM driving signal _ugs of the switch _tube S. During dynamic simulation, a variable resistor is used in series with the power supply U _in =112V to simulate a solar cell. When the simulation reaches 100ms, the variable resistor is switched from 10Ω to 50Ω instantaneously to simulate a sudden change in light. Its dynamic adjustment process is shown in Figure 7. It can be seen that before the light mutation, the input voltage of the proposed converter is stable at 56V, and the input current has no switching frequency ripple; Still no switching frequency ripple.

The high-efficiency photovoltaic converter without an input filter provided by the present invention has the following advantages: (1) the ideal voltage gain is (1+2D)/(1-D), and the boosting capability is strong; (2) the number of power devices is small, The structure is simple; (3) the input current switching frequency ripple is eliminated, and the parallel electrolytic capacitor is no longer needed on the input side; (4) there is only one switching tube, and the voltage stress is low, which is (2U _in +U _o )/3, which can Choose devices with low rated voltage and low cost; (5) The input and output share the same ground, and the structure of the sampling circuit is simple.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is a relationship between these entities or operations. There is no such actual relationship or order between them. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention, rather than limiting it. It should be pointed out that those skilled in the art can make some improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims (7)

1. A high-efficiency photovoltaic converter without an input filter is characterized by comprising a first capacitor C ₁ A second capacitor C ₂ A third capacitorC ₃ A fourth capacitor C ₄ A fifth capacitor C _o Three-winding transformer, first auxiliary inductor L _s1 A second auxiliary inductor L _s2 A switch tube S and a first diode D ₁ A second diode D ₂ A third diode D ₃ The three-winding transformer comprises a first winding N ₁ A second winding N ₂ And a third winding N ₃ Said second winding N ₂ And said third winding N ₃ Has the same number of turns, and the first auxiliary inductor L _s1 A second auxiliary inductor L _s2 The current of the power supply is bidirectionally circulated;

the first winding N ₁ With the drain of the switching tube S and the first diode D ₁ And the second capacitor C ₂ Negative pole of (1), the fourth capacitor C ₄ The negative electrode of (1) is connected;

the first diode D ₁ And the second winding N ₂ First terminal of, said first capacitor C ₁ The positive electrode of (1) is connected;

the second winding N ₂ And the second terminal of the first auxiliary inductor L _s1 Is connected to the first auxiliary inductance L _s1 And the other end of the second capacitor C ₂ The anode of the second diode D ₂ The anode of (2) is connected;

the second diode D ₂ And the third capacitor C ₃ Positive pole of (2), the third winding N ₃ Is connected;

the third winding N ₃ And the second terminal of the second auxiliary inductor L _s2 Is connected to the second auxiliary inductance L _s2 And the other end of the third diode D ₃ Anode of, the fourth capacitance C ₄ The positive electrode of (1) is connected;

the third diode D ₃ And the fifth capacitor C _o The positive electrode of (2) is connected;

the source electrode of the switch tube S and the first capacitor C ₁ Negative pole of (2), the third capacitance C ₃ Negative pole of (1), the fifth capacitor C _o Negative pole ofConnecting;

the first winding N ₁ First terminal and power supply U _in The positive electrodes of the two electrodes are connected;

source electrode of switch tube S and power supply U _in The negative electrodes are connected;

the fifth capacitor C _o The positive electrode of (2) is connected with one end of a load;

the fifth capacitor C _o Is connected to the other end of the load.

2. A high efficiency photovoltaic converter according to claim 1 wherein in said three winding transformer, the second winding N is ₂ And said first winding N ₁ The value range of the turn ratio n is as follows:

in the formula, G is the voltage gain of the photovoltaic converter, and delta% is the ratio of the peak value of the exciting inductance current of the three-winding transformer to the maximum average current of the three-winding transformer;

excitation inductance L of the three-winding transformer _m The requirements are as follows:

in the formula of U _in For input voltage, U _o To output voltage, f _s To the switching frequency, P _o,max Is the maximum output power.

3. A high efficiency photovoltaic converter as claimed in claim 2 wherein δ% is from 20% to 30%.

4. The high efficiency photovoltaic converter of claim 1, wherein the first auxiliary inductance L _s1 And the second auxiliary inductor L _s2 The inductance values are equal and are as follows: l is _s1 ＝L _s2 ＝2n(1-n)L _m 。

5. The high efficiency photovoltaic converter of claim 1 wherein the ideal voltage gain is (1 + 2d)/(1-D), where D is the duty cycle of the switching tube S drive signal;

6. a high efficiency photovoltaic converter according to claim 1, wherein said switching tube S, said first diode D ₁ The second diode D ₂ And the third diode D ₃ All voltage stresses of (2U) _in +U _o )/3。

7. The photovoltaic converter according to claim 1, wherein the operation of the photovoltaic converter in each switching cycle includes the following two modes:

(1) 2[ 2 ], [ t ] ₀ -t ₁ ]：

At t ₀ At all times, the switch tube S and the first diode D are turned on ₁ A second diode D ₂ A third diode D ₃ All are turned off by bearing back voltage, all inductors bear forward voltage, and exciting inductance current i of the three-winding transformer _Lm Linearly increasing, first auxiliary inductor current i _Ls1 A second auxiliary inductor current i _Ls2 Are all linearly decreased from reverse to 0 and then linearly increased from forward to t ₁ At that time, modality 1 ends;

(2) Modal 2[ t ] ₁ -t ₂ ]：

At t ₁ At all times, the switch tube S and the first diode D are turned off ₁ A second diode D ₂ A third diode D ₃ All the inductors are conducted in the forward direction, all the inductors bear reverse voltage, and the exciting inductance current i of the three-winding transformer _Lm Linearly decreasing, first auxiliary inductor current i _Ls1 A second auxiliary inductor current i _Ls2 All decrease to 0 in forward linearity and increase in reverse linearity to t ₂ At that time, modality 2 ends;

wherein the inductors comprise an excitation inductor of a three-winding transformer and the first auxiliary inductor L _s1 And the second auxiliary inductor L _s2 。

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