CN111371316A - Zero-input ripple high-gain direct current converter based on coupling inductor - Google Patents

Abstract

The invention relates to a zero-input ripple high-gain direct current converter based on a coupled inductor. It includes a DC input power supply, a switch tube, a coupled inductor, a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a first inductor, a second inductor, and a first diode. A capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor and a load. The invention combines the coupling inductance ratio boosting, the capacitor diode boosting network and the capacitor clamping together to form a zero-input ripple high-gain DC converter, which has the advantages of high voltage gain, small zero-input ripple and high conversion efficiency, and is very suitable for For high boost ratio DC voltage conversion applications.

Description

A Zero Input Ripple High Gain DC Converter Based on Coupled Inductors

technical field

The invention relates to the technical field of power electronics, in particular to a zero-input ripple high-gain DC converter based on a coupled inductor.

Background technique

In the renewable energy power generation system, due to the low output DC voltage of many renewable energy sources, in order to supply power to the grid-connected inverter at the later stage, a high-gain DC converter needs to be used to convert the low-voltage DC power into suitable for grid-connected power. Therefore, high-efficiency and high-gain DC converters are indispensable.

At present, on the basis of traditional DC converters, the ways to improve the gain of the converters usually include: cascading converters, adding switched capacitors, using coupled inductors, and so on. Cascading converters can effectively improve the voltage gain, but there are disadvantages such as complex topology and control methods, and the loop design is relatively difficult; the boost gain of the switched capacitor circuit is limited, in order to obtain a higher boost gain, it is necessary to use more A switched capacitor unit increases the circuit complexity and cost; in applications that do not require electrical isolation, since the voltage gain can be increased by setting the coupled inductor turns ratio, it is easy to achieve high gain conversion. Boost-gain DC-DC converters have received extensive attention.

For new energy sources such as photovoltaics and fuel cells, the input current ripple of the DC converter not only affects its power generation efficiency, but also affects the service life of photovoltaic panels and fuel cells. Therefore, the low input current ripple and high gain DC converter topology become a research hotspot.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a zero-input ripple high-gain DC converter based on a coupled inductor, which combines the coupled inductor transformation ratio boost, capacitor diode boost network and capacitor clamp to form a zero-input ripple high-gain DC converter , has the advantages of high voltage gain, zero input ripple and high conversion efficiency, and is very suitable for high boost ratio DC voltage conversion applications.

In order to achieve the above purpose, the technical scheme of the present invention is: a zero-input ripple high-gain DC converter based on a coupled inductor, comprising a DC input power supply, a switch tube, a coupled inductor, a first diode, a second diode, The third diode, the fourth diode, the fifth diode, the first inductor, the second inductor, the first capacitor, the second capacitor, the third capacitor, the fourth capacitor, the fifth capacitor and the load; DC input The positive pole of the power supply is connected to one end of the first inductor and one end of the first capacitor through the second inductor, and the negative pole of the DC input voltage is connected to the source of the switch tube, one end of the third capacitor, one end of the fifth capacitor, and one end of the load. The other end of the first inductor is connected to the anode of the first diode and the anode of the second diode, the other end of the first capacitor is connected to the cathode of the first diode, one end of the second capacitor, and the primary winding of the coupled inductor The first end of the second capacitor is connected to the cathode of the fifth diode, the other end of the fifth capacitor, and the other end of the load, and the cathode of the second diode is connected to the second end of the primary winding of the coupled inductor. terminal, the first terminal of the secondary winding of the coupled inductor, the drain of the switch tube, and the anode of the third diode; the second terminal of the secondary winding of the coupled inductor is connected to the anode of the fifth diode and the anode of the third diode through the fourth capacitor The cathodes of the four diodes are connected, the cathode of the third diode is connected to the anode of the fourth diode, and the other end of the third capacitor is connected.

In an embodiment of the present invention, the zero-input ripple high-gain DC converter is composed of a coupled-inductor ratio boost, a capacitor-diode boost network, and a capacitor clamp, and has the advantages of high voltage gain and small input current ripple. and high conversion efficiency.

In an embodiment of the present invention, the zero input ripple high gain DC converter utilizes the clamping action of the first capacitor and the second capacitor to make the voltage across the second inductor close to zero, thereby achieving zero input current ripple.

其中，n为耦合电感副边与原边的匝数比，D为开关管工作占空比。In an embodiment of the present invention, the voltage gain of the zero-input ripple high-gain DC-DC converter is

Among them, n is the turns ratio between the secondary side and the primary side of the coupled inductor, and D is the duty cycle of the switch.

In an embodiment of the present invention, the working mode of the zero-input ripple high-gain DC-DC converter is as follows:

(1) Mode 1 (t ₀ -t ₁ ): at time t ₀ , the switch S is turned on, the second diode VD ₂ and the fifth diode VD _o are turned on, and the first diode VD ₁ , The third diode VD ₃ and the fourth diode VD ₄ are turned off; the DC input power supply Vin is connected _in series with the second inductor L _a , the first capacitor C ₁ , and the second capacitor C ₂ to provide energy to the load side; DC The input power V _in charges the first inductor L ₁ through the second diode VD ₂ and the switch S, and the inductor current i _L1 rises linearly; the DC input power V _in passes through the second inductor L _a and the first capacitor C ₁ in series The switch tube _S charges the leakage inductance Lk of the primary winding of the coupled inductor, the current i _p of the primary winding of the coupled inductor increases linearly and rapidly, and the excitation current i _Lm decreases; the secondary winding of the coupled inductor and the fourth capacitor C ₄ are connected in series through the switch tube S , The fifth diode VD _o transmits energy to the load side, and when the current i _VDo of the fifth diode VD _o decreases to 0 at time t ₁ , this mode ends;

(2) Mode 2 (t ₁ -t ₂ ): the switch S continues to be turned on, the second diode VD ₂ and the fourth diode VD ₄ are turned on, the first diode VD ₁ , the third and second diodes The pole tube VD ₃ and the fifth diode VD _o are turned off; the DC input power supply V _in is connected in series with the second inductance L _a and the first capacitor C ₁ to charge the excitation inductance L _m of the primary winding of the coupled inductance through the switch tube S, The excitation current i _Lm rises linearly; the DC input power V _in continues to charge the first inductor L ₁ through the second diode VD ₂ and the switch S, and the inductor current i _L1 rises linearly; the secondary winding of the coupled inductor and the third capacitor C ₃ The fourth capacitor C ₄ is charged in series through the switch tube S and the fourth diode VD ₄ ; the fifth capacitor C _o discharges and supplies the load R energy to the second capacitor C ₂ , and at time t ₂ , the switch tube S is turned off , the modal ends;

(3) Mode 3 (t ₂ -t ₃ ): At time t ₂ , the switch S is turned off, the first diode VD ₁ , the third diode VD ₃ , and the fourth diode VD ₄ are turned on, The second diode VD ₂ and the fifth diode VD _o are turned off; the first inductor L ₁ discharges to the first capacitor C ₁ through the first diode VD ₁ , and the inductor current i _L1 decreases; the primary winding of the coupled inductor The energy of the leakage inductance L _k is absorbed by the third capacitor C ₃ through the third diode VD ₃ , and the primary current i _p begins to decrease; the secondary winding of the coupled inductor passes through the third diode VD ₃ and the fourth diode VD _4. Continue to charge the fourth capacitor C ₄ ; the fifth capacitor C _o provides energy to the load R, and at time t ₃ , the fourth diode VD ₄ is turned off, and this mode ends;

(4) Mode 4 (t ₃ -t ₄ ): the switch S continues to be turned off, the first diode VD ₁ , the third diode VD ₃ , and the fifth diode VD _o are turned on, and the second diode VD 1 is turned on. The pole tube VD ₂ and the fourth diode VD ₄ are turned off; the DC input power supply V _in is connected in series with the second inductor L _a , the first capacitor C ₁ , and the second capacitor C ₂ to provide energy to the load side; the first inductor L ₁ Continue to discharge to the first capacitor C ₁ through the first diode VD ₁ ; the excitation inductance _Lm of the primary winding of the coupled inductor transfers energy to the load side through the secondary winding of the coupled inductor, the excitation current i _Lm decreases, and the primary current i _p continues to decrease; the secondary winding of the coupled inductor is connected in series with the third capacitor C ₃ and the fourth capacitor C ₄ to transfer energy to the load side through the fifth diode VD _o , and at time t ₄ , the energy flows through the third diode VD When the current i _VD3 of ₃ is 0, this mode ends;

(5) Mode 5 (t ₄ -t ₅ ): the switch S continues to be turned off, the first diode VD ₁ and the fifth diode VD _o are turned on, the second diode VD ₂ , the third and second diodes The pole tube VD ₃ and the fourth diode VD ₄ are turned off; the DC input power supply V _in is connected in series with the second inductor L _a , the first capacitor C ₁ , and the second capacitor C ₂ to provide energy to the load side; the first inductor L ₁ continues to discharge, and the inductor current i _L1 decreases; the primary winding and secondary winding of the coupled inductor are connected in series with the fourth capacitor C ₄ through the fifth diode VD _o to charge the second capacitor C ₂ , and the primary current i _p is related to the excitation The current i _Lm continues to decrease. When the switch tube S is turned on at time t ₅ , this mode ends and the next switching cycle begins.

Compared with the prior art, the present invention has the following beneficial effects: the present invention is based on a zero-input ripple high-gain DC converter based on a coupled inductor, which combines a coupled inductor transformation ratio boost, a capacitor diode boost network and a capacitor clamp to form It has the advantages of high voltage gain, zero input ripple and high conversion efficiency, and is very suitable for high boost ratio DC voltage conversion applications.

Description of drawings

FIG. 1 is a zero input ripple high gain DC converter of the present invention.

FIG. 2 is the equivalent circuit of each mode of the zero-input ripple high-gain DC converter of the present invention.

FIG. 3 is the main working waveform of the zero input ripple high gain DC converter of the present invention.

FIG. 4 is the main current simulation waveform of the zero-input ripple high-gain DC converter of the present invention.

FIG. 5 is the main voltage simulation waveform of the zero-input ripple high-gain DC converter of the present invention.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings.

The present invention provides a zero-input ripple high-gain DC converter based on a coupled inductor, comprising a DC input power supply, a switch tube, a coupled inductor, a first diode, a second diode, a third diode, a fourth diode, and a fourth diode. A diode, a fifth diode, a first inductor, a second inductor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor and a load; One end of the first inductor and one end of the first capacitor are connected, the negative electrode of the DC input voltage is connected to the source of the switch tube, one end of the third capacitor, one end of the fifth capacitor, and one end of the load, and the other end of the first inductor is connected to the first The anode of one diode and the anode of the second diode are connected, the other end of the first capacitor is connected to the cathode of the first diode, one end of the second capacitor, and the first end of the primary winding of the coupled inductor, the second The other end of the capacitor is connected to the cathode of the fifth diode, the other end of the fifth capacitor, and the other end of the load, and the cathode of the second diode is connected to the second end of the primary winding of the coupled inductor and the secondary winding of the coupled inductor. The first end, the drain of the switch tube, and the anode of the third diode are connected, and the second end of the secondary winding of the coupled inductor is connected to the anode of the fifth diode and the cathode of the fourth diode through the fourth capacitor, The cathode of the third diode is connected to the anode of the fourth diode and the other end of the third capacitor.

The following is a specific implementation process of the present invention.

As shown in FIG. 1 , a zero-input ripple high-gain DC converter based on a coupled inductor of the present invention includes a DC input power supply, a switch tube, a coupled inductor, a first diode, a second diode, and a third diode. tube, the fourth diode, the fifth diode, the first inductor, the second inductor, the first capacitor, the second capacitor, the third capacitor, the fourth capacitor, the fifth capacitor and the load; the present invention transforms the coupling inductor into The ratio boost, capacitor diode boost network and capacitor clamp are combined to form a zero input ripple high gain DC converter, which has the advantages of high voltage gain, small input current ripple and high conversion efficiency.

即

从而实现了零输入电流纹波。本发明的高增益直流变换器的电压增益为

其中，n为耦合电感副边与原边的匝数比，D为开关管工作占空比。In the zero-input ripple high-gain DC converter based on the coupled inductor of the present invention, when the capacitor is selected to be large enough, the clamping effect of the capacitors C ₁ and C ₂ is used to make the voltage across the inductor L _a

which is

This achieves zero input current ripple. The voltage gain of the high-gain DC converter of the present invention is

Among them, n is the turns ratio between the secondary side and the primary side of the coupled inductor, and D is the duty cycle of the switch.

The working principle of a zero-input ripple high-gain DC converter based on coupled inductors of the present invention is as follows:

To simplify the analysis, the following assumptions are made:

1) Capacitors C ₁ , C ₂ , C ₃ , C ₄ , and C _o are large enough, and the voltage ripple across the capacitors is negligible;

2) Switches and diodes are ideal devices;

3) The excitation inductance is much larger than the leakage inductance, that is, L _m ＞＞ L _k

In order to facilitate the principle analysis, the coupled inductance formed by the primary winding L ₂ and the secondary winding L ₃ in Fig. 1 is equivalent to an excitation inductance L _m and an ideal transformer (the number of turns on the primary and secondary sides are N _p and N _s respectively) The primary side is connected in parallel and in series with the leakage inductance L _k of the coupled inductor. The zero-input ripple high-gain DC converter based on the coupled inductor of the present invention has five operating modes in one switching cycle. The equivalent circuit of each mode is shown in FIG.

1) Mode 1 (t ₀ -t ₁ ): At time t ₀ , the switch S is turned on, the diodes VD ₂ and VD _o are turned on, and the diodes VD ₁ , VD ₃ , and VD ₄ are turned off. The modal equivalent circuit is as follows: Figure 2(a). The input power V _in is connected in series with the input inductor L _a , capacitors C ₁ and C ₂ to provide energy to the load side; the input power V _in charges the inductor L ₁ through the diode VD ₂ and the switch S, and the inductor current i _L1 rises linearly; The input power V _in is connected in series with the input inductor L _a and the capacitor C ₁ to charge the coupled inductor leakage inductance L _k through the switch S, the primary current i _p increases linearly and rapidly, and the excitation current i _Lm decreases; the secondary winding and the capacitor C ₄ In series, energy is transferred to the load side through the switch tube S and the diode VD _o . When the diode _VDo current i _VDo decreases to 0 at time _t1 , this mode ends.

2) Mode 2 (t ₁ -t ₂ ): the switch S continues to conduct, the diodes VD ₂ and VD ₄ are conducted, and the diodes VD ₁ , VD ₃ and VD _o are turned off, and the modal equivalent circuit is shown in Figure 2 ( b) shown. The input power V _in is connected in series with the input inductance L _a and the capacitor C ₁ to charge the primary excitation inductance L _m of the coupled inductor through the switch S, and the excitation current i _Lm rises linearly; the input power V _in passes through the diode VD ₂ and the switch S Continue to charge the inductor L ₁ , and the inductor current i _L1 rises linearly; the secondary winding of the coupled inductor and the capacitor C ₃ are connected in series to charge the capacitor C ₄ through the switch S and the diode VD ₄ ; the output capacitor C _o discharges the capacitor C ₂ and provides a load R energy. When the switch S is turned off at time _t2 , this mode ends.

3) Mode 3 (t ₂ -t ₃ ): at t ₂ , the switch S is turned off, the diodes VD ₁ , VD ₃ , and VD ₄ are turned on, and the diodes VD ₂ and VD _o are turned off. The modal equivalent circuit is shown in the figure 2(c). The inductor L ₁ discharges to the capacitor C ₁ through the diode VD ₁ , and the inductor current i _L1 decreases; the coupling inductor leakage inductance L _k energy is absorbed by the clamping capacitor C ₃ through the diode VD ₃ , and the primary current i _p begins to decrease; the coupling inductor The secondary winding continues to charge the capacitor C ₄ through the diodes VD ₃ and VD ₄ ; the output capacitor C _o provides energy to the load R. When _t3 time, diode _VD4 is turned off, this mode ends.

4) Mode 4 (t ₃ -t ₄ ): the switch S continues to be turned off, the diodes VD ₁ , VD ₃ and VD _o are turned on, and the diodes VD ₂ and VD ₄ are turned off. The modal equivalent circuit is shown in Figure 2 ( d) shown. The input power V _in is connected in series with the input inductor L _a , capacitors C ₁ , and C ₂ to provide energy to the load side; the inductor L ₁ continues to discharge to the capacitor C ₁ through the diode VD ₁ ; the primary excitation inductance L _m of the coupled inductor passes through the secondary side The winding transfers energy to the load side, the excitation current i _Lm decreases, and the primary current i _p continues to decrease; the secondary side of the coupled inductor is connected in series with capacitors C ₃ and C ₄ to transfer energy to the load side through the diode VD _o . This mode ends when the current i _VD3 flowing through the diode _VD3 is 0 at time t4 _.

5) Mode 5 (t ₄ -t ₅ ): the switch S continues to be turned off, the diodes VD ₁ and VD _o are turned on, and the diodes VD ₂ , VD ₃ and VD ₄ are turned off, and the modal equivalent circuit is shown in Figure 2 ( e) shown. The input power V _in is connected in series with the input inductor L _a , capacitors C ₁ , and C ₂ to provide energy to the load side; the inductor L ₁ continues to discharge, and the inductor current i _L1 decreases; the primary and secondary windings of the coupled inductor and the capacitor C ₄ In series, the capacitor C ₂ is charged through the diode VD _o , and the primary current i _p and the excitation current i _Lm continue to decrease. When the switch tube S is turned _on at time t5, this mode ends and the next switching cycle begins.

Characteristic Analysis

(1) Voltage gain

From the volt-second balance of the inductances L _a , L ₁ , and L _m , the expressions of the capacitor voltage and the output voltage can be obtained as:

then the voltage gain

D为开关管工作占空比。where V _in is the input voltage, V _o is the output voltage,

D is the duty cycle of the switch tube.

(2) Zero input current characteristics

For the inductor L _a , the voltage across it is:

When the values of capacitors C ₁ and C ₂ are large enough and the voltage ripple of each capacitor is ignored, there are:

V _in +v _C1 +v _C2 -v _o ≈V _in +V _C1 +V _C2 -V _o =0

Therefore, the voltage across the inductor L _a is:

It can be seen that as long as the capacitance of the selected capacitor is large enough to make the voltage ripple across the inductor L _a sufficiently small, even a small input inductor L _a can well achieve zero input current ripple.

In order to verify the feasibility of the circuit, the proposed circuit is simulated. The simulation parameters are: input voltage V _in =36V, V ₀ =380V, inductance La =30uH, L _{1 =} 350uH, L _m =297uH, coupled inductance turns ratio n=1, capacitance C ₁ =C ₂ =C ₃ =C ₄ =22uF, C _o =22uF, R=1444Ω, duty cycle D=0.4669.

几乎相等，仿真结果与理论分析一致。Figure 4 and Figure 5 are the main simulation waveforms. It can be seen that the current of the input inductor La is almost _a straight line, and its ripple is close to zero. The simulation value of the output voltage is V ₀ =378.76V, and its gain is 10.52, which is the same as the theoretical value. Calculated

are almost equal, and the simulation results are consistent with the theoretical analysis.

The above are the preferred embodiments of the present invention, all changes made according to the technical solutions of the present invention, when the resulting functional effects do not exceed the scope of the technical solutions of the present invention, belong to the protection scope of the present invention.

Claims (5)

1. A zero-input ripple high-gain direct current converter based on a coupling inductor is characterized by comprising a direct current input power supply, a switch tube, the coupling inductor, a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a first inductor, a second inductor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor and a load; the positive pole of the direct current input power supply is connected with one end of a first inductor and one end of a first capacitor through a second inductor, the negative pole of the direct current input voltage is connected with the source electrode of a switching tube, one end of a third capacitor, one end of a fifth capacitor and one end of a load, the other end of the first inductor is connected with the anode of a first diode and the anode of a second diode, the other end of the first capacitor is connected with the cathode of a first diode, one end of a second capacitor and the first end of a primary winding of a coupling inductor, the other end of the second capacitor is connected with the cathode of a fifth diode, the other end of the fifth capacitor and the other end of the load, the cathode of the second diode is connected with the second end of the primary winding of the coupling inductor, the first end of a secondary winding of the coupling inductor, the drain electrode of the switching tube and the anode of the third diode, and the second end of the secondary winding of the coupling inductor is connected with the, The cathode of the fourth diode is connected, and the cathode of the third diode is connected with the anode of the fourth diode and the other end of the third capacitor.

2. The zero-input ripple high-gain direct current converter based on the coupled inductor according to claim 1, wherein the zero-input ripple high-gain direct current converter is formed by combining a coupled inductor ratio boost, a capacitor diode boost network and a capacitor clamp together to realize high voltage gain and zero input current ripple.

3. The zero-input ripple high-gain direct current converter based on the coupled inductor according to claim 1, wherein the zero-input ripple high-gain direct current converter utilizes clamping effects of the first capacitor and the second capacitor to enable a voltage across the second inductor to approach zero, so that a zero-input current ripple is realized.

4. The zero-input ripple high-gain DC converter based on the coupled inductor as claimed in claim 1, wherein the voltage gain of the zero-input ripple high-gain DC converter is as follows

Wherein n is the turn ratio of the secondary side and the primary side of the coupling inductor, and D is the working duty ratio of the switching tube.

5. The zero-input ripple high-gain direct current converter based on the coupled inductor according to claim 1, wherein the zero-input ripple high-gain direct current converter operates as follows:

(1) mode 1 (t)₀-t₁)：t₀At the moment, the switch tube S is conducted and the second diode VD₂The fifth diode VD_oConducting, the first diode VD₁A third diode VD₃And the fourthDiode VD₄Cutting off; DC input power supply V_inAnd a second inductor L_aA first capacitor C₁A second capacitor C₂Are connected in series to provide energy for a load side; DC input power supply V_inThrough a second diode VD₂And a switching tube S for the first inductor L₁Charging, inductor current i_L1Linearly increasing; DC input power supply V_inAnd a second inductor L_aA first capacitor C₁The leakage inductance L of the primary winding of the coupling inductor is connected in series through a switching tube S_kCharging, coupling of inductor primary winding current i_pLinear rapid increase, exciting current i_LmDecrease; coupling the secondary winding of the inductor with a fourth capacitor C₄Is connected in series through a switching tube S and a fifth diode VD_oTransferring energy to the load side when t₁At time instant, the fifth diode VD_oCurrent i_VDoWhen the value is reduced to 0, the mode is ended;

(2) mode 2 (t)₁-t₂): the switch tube S is continuously conducted, and the second diode VD₂And a fourth diode VD₄Conducting, the first diode VD₁A third diode VD₃The fifth diode VD_oCutting off; DC input power supply V_inAnd a second inductor L_aA first capacitor C₁Are connected in series and supply the primary winding excitation inductance L of the coupling inductance through the switching tube S_mCharging, exciting current i_LmLinearly increasing; DC input power supply V_inThrough a second diode VD₂And a switching tube S for the first inductor L₁Charging is continued with inductor current i_L1Linearly increasing; coupling inductor secondary winding and third capacitor C₃Is connected in series through a switching tube S and a fourth diode VD₄To a fourth capacitor C₄Charging; fifth capacitor C_oTo a second capacitance C₂Discharging and supplying energy to load R when t₂At the moment, the switching tube S is turned off, and the mode is ended;

(3) mode 3 (t)₂-t₃)：t₂At the moment, the switch tube S is turned off and the first diode VD₁A third diode VD₃And a fourth diode VD₄Conducting, the second diode VD₂The fifth diode VD_oCutting off; first inductance L₁Through a first diode VD₁To the first capacitor C₁Discharge, inductor current i_L1Decrease; coupled inductor primary winding leakage inductance L_kEnergy passes through a third diode VD₃Is covered by a third capacitor C₃Absorbing, primary side current i_pBegin to decrease; the secondary winding of the coupling inductor passes through a third diode VD₃And a fourth diode VD₄Continue to supply the fourth capacitor C₄Charging; fifth capacitor C_oProviding energy to a load R when t₃Time of day, the fourth diode VD₄Turning off, and ending the mode;

(4) mode 4 (t)₃-t₄): the switch tube S is continuously turned off, and the first diode VD₁A third diode VD₃The fifth diode VD_oConducting, the second diode VD₂And a fourth diode VD₄Cutting off; DC input power supply V_inAnd a second inductor L_aA first capacitor C₁A second capacitor C₂Are connected in series to provide energy for a load side; first inductance L₁Through a first diode VD₁To the first capacitor C₁Continuing discharging; coupled inductor primary winding excitation inductor L_mEnergy is transferred to a load side through a secondary winding of a coupling inductor, and an exciting current i_LmDecrease of primary side current i_pContinuing to decrease; coupling the secondary winding of the inductor with a third capacitor C₃A fourth capacitor C₄Series connection fifth diode VD_oTransferring energy to the load side when t₄At the moment, flows through the third diode VD₃Current i of_VD3At 0, this mode ends;

(5) mode 5 (t)₄-t₅): the switch tube S is continuously turned off, and the first diode VD₁The fifth diode VD_oConducting, the second diode VD₂A third diode VD₃And a fourth diode VD₄Cutting off; DC input power supply V_inAnd a second inductor L_aA first capacitor C₁A second capacitor C₂Are connected in series to provide energy for a load side; first inductance L₁Continue discharging, inductanceCurrent i_L1Decrease; coupling inductance primary winding, secondary winding and fourth capacitor C₄Series connection fifth diode VD_oTo a second capacitance C₂Charging, primary side current i_pWith excitation current i_LmContinues to decrease when t₅At that moment, when the switching tube S is turned on, this mode ends and the next switching cycle begins.

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