FORWARD CONVERTER WITH SECONDARY LCD CONNECTED IN PARALLEL TO REALIZE FORWARD AND BACKWARD ENERGY TRANSMISSION

Abstract

The present disclosure provides a forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission, comprising a forward converter main circuit and an energy transfer and transmission circuit. The forward converter main circuit includes a high-frequency transformer T, a switching tube S, a diode D1, a diode D2, an inductance L1, and a capacitor C1. The energy transfer and transmission circuit includes a diode D3, a capacitor C2 and an inductance L2.

Claims

1. A forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission, comprising: a forward converter main circuit (1); and an energy transfer and transmission circuit (2) connected to the forward converter main circuit (1); wherein, the forward converter main circuit (1) includes: a high-frequency transformer T; a switching tube S; a diode D1; a diode D2; an inductance L1; and a capacitor C1; and wherein, the same-named end of the primary side of the high-frequency transformer T is the positive voltage input end IN+ of the forward converter main circuit (1), which is connected to the positive output end of the external power supply, and the different-named end of the primary side of the high-frequency transformer T is connected to the drain of the switching tube S; the source of the switching tube S is the negative voltage input end IN− of the forward converter main circuit (1), which is connected to the negative output end of the external power supply; the gate of the switching tube S is connected to the output end of the external controller; the same-named end of the secondary side of the high-frequency transformer T is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the cathode of the diode D2 and one end of the inductance L1; the other end of the inductance L1 is connected to one end of the capacitor C1 and is the positive voltage output end OUT+ of forward converter main circuit (1); the different-named end of the secondary side of the high-frequency transformer T is connected to the anode of the diode D2 and the other end of the capacitor C1 and is the negative voltage output end OUT− of the forward converter main circuit (1); the negative voltage output end OUT− of the forward converter main circuit (1) is grounded; wherein, the energy transfer and transmission circuit (2) includes: a diode D3; a capacitor C2; and an inductance L2; and wherein, the anode of the diode D3 is connected to the anode of the diode D2, the cathode of the diode D3 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the anode of the diode D1, one end of the inductance L2 is connected to the cathode of the diode D3, the other end of the inductance L2 is connected to the positive voltage output end OUT+ of forward converter main circuit (1).

2. The forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission as in claim 1, wherein the diodes D1 and D2 are fast recovery diodes.

3. The forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission as in claim 1, wherein the switching tube S is a fully-controlled power semiconductor device.

4. The forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission as in claim 1, wherein the capacitor C2 of the forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission is selected according to the first selection step; wherein the steps of the first selection step include: step 101, selecting the capacitance C.sub.2 of the capacitor C2 of energy storage; step 102, combining the input voltage V.sub.i of the converter and turns ratio n of transformer to calculate the withstand voltage V.sub.C2,Ton of the capacitor C2 of energy storage; step 103, selecting the capacitor of energy storage with a capacitance C.sub.2 and a withstand voltage greater than V.sub.C2,Ton.

5. The forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission as in claim 4, wherein the inductance L2 of the forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission is selected according to the second selection step; wherein the steps of the second selection step include: step 201, determining the value range of the inductance L.sub.2 of the inductance L2; step 202, determining the current of the inductance L2; step 203, selecting the inductance according to the steps 201 and 202.

6. The forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission as in claim 4, wherein the diode D3 of the forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission are selected according to the third selection step; wherein the steps of the third selection step include: step 301, calculating the maximum current I.sub.D3,max flowing through the diode D3; step 302, calculating the withstand voltage V.sub.D3,max of the diode D3; step 303, selecting the diode according to the steps 301 and 302.

7. The forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission as in claim 5, wherein the diode D3 of the forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission are selected according to the third selection step; wherein the steps of the third selection step include: step 301, calculating the maximum current I.sub.D3,max flowing through the diode D3; step 302, calculating the withstand voltage V.sub.D3,max of the diode D3; step 303, selecting the diode according to the steps 301 and 302.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a circuit schematic diagram of the forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission of the present disclosure.

[0027] In the drawings:

[0028] 1: forward converter main circuit; 2: energy transfer and transmission circuit.

DETAILED DESCRIPTION

[0029] As shown in FIG. 1, in one embodiment, the present disclosure provides a forward converter with secondary LCD connected in parallel to realize forward and backward energy transmission, comprising a forward converter main circuit 1; and an energy transfer and transmission circuit 2 connected to the forward converter main circuit 1; wherein, the forward converter main circuit 1 includes a high-frequency transformer T, a switching tube S, a diode D1, a diode D2, an inductance L1 and a capacitor C1; the same-named end of the primary side of the high-frequency transformer T is the positive voltage input end IN+ of the forward converter main circuit 1, which is connected to the positive output end of the external power supply, and the different-named end of the primary side of the high-frequency transformer T is connected to the drain of the switching tube S; the source of the switching tube S is the negative voltage input end IN− of the forward converter main circuit 1, which is connected to the negative output end of the external power supply; the gate of the switching tube S is connected to the output end of the external controller; the same-named end of the secondary side of the high-frequency transformer T is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the cathode of the diode D2 and one end of the inductance L1; the other end of the inductance L1 is connected to one end of the capacitor C1 and is the positive voltage output end OUT+ of forward converter main circuit 1; the different-named end of the secondary side of the high-frequency transformer T is connected to the anode of the diode D2 and the other end of the capacitor C1 and is the negative voltage output end OUT− of the forward converter main circuit 1; the negative voltage output end OUT− of the forward converter main circuit 1 is grounded; the energy transfer and transmission circuit 2 includes a diode D3, a capacitor C2 and an inductance L2; the anode of the diode D3 is connected to the anode of the diode D2, the cathode of the diode D3 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the anode of the diode D1, one end of the inductance L2 is connected to the cathode of the diode D3, the other end of the inductance L2 is connected to the positive voltage output end OUT+ of forward converter main circuit 1.

[0030] specifically, the load RL is connected between the positive voltage output end OUT+ and the negative voltage output end OUT− of the forward converter main circuit 1. In the forward converter main circuit 1, both the inductance L1 and the capacitor C1 are used for filtering.

[0031] In one embodiment, the diode D1 is a rectifier diode, and the diode D2 is a fast recovery diode. The diode D2 is used for freewheeling.

[0032] In one embodiment, the switching tube S is an NMOS switching tube.

[0033] The working principle of this embodiment is:

[0034] Before analyzing the working principle of this embodiment, it is assumed that the forward inductance L1 works in CCM, the auxiliary inductance L2 and the transformer secondary inductance Lw2 work in DCM. The working principle of this embodiment is analyzed in the present disclosure, which is divided into the off period and the on period of the switching tube. In order to facilitate the introduction of the principle, the convention is as follows: for C2, the voltage is assumed to be a forward voltage when the left voltage of C2 is negative and the right voltage of C2 is positive, the voltage is assumed to be a reverse voltage when the left voltage of C2 is positive and the right voltage of C2 is negative; for the secondary winding w2, the current is assumed to be a forward current when the current of w2 is from bottom to top, the current is assumed to be a reverse current when the current of w2 is from top to bottom.

[0035] 1. The working principle during the off period of the switching tube S

[0036] It is assumed that before the switching tube is switched off, the reverse voltage of C2 is risen to the maximum value, the current of inductance L1, L2 and Lw2 is risen to the maximum value. D1 is switched on, while D2 and D3 are switched off.

[0037] Stage 1: the switching tube is switched off at low voltage

[0038] In the process of the switching tube passing from the conduction to the shutdown, the parasitic capacitance of the switching tube is charged by the excitation current and secondary reflected current, the primary voltage and secondary voltage of the transformer is decreased. Once the secondary voltage is decreased to be equal to the reverse voltage of C2, this stage is over. At this stage, the voltage borne by the switching tube is Vi-nVC2 (Vi is input voltage, VC2 is the maximum reverse voltage of C2, n is the transformer ratio), so the voltage borne by the switching tube is much smaller than Vi, and the switching tube is switched off at low voltage (under certain parameters, zero voltage shutdown can also be achieved). At this stage, D1 is kept on, while D2 and D3 are switched off.

[0039] Stage 2: the reverse energy storage of capacitor C2 is released

[0040] After the secondary voltage is decreased to be equal to the reverse voltage of C2, D3 is switched on, the inductance L2 begins to be freewheeled, the reverse energy storage of capacitor C2 begins to be released. At this time, D1 is kept on, and the reverse energy storage of C2 is released through two loops: one is that the reverse energy storage of C2 is released through D1, L1, RL, and D3, which makes the diode D1 not switch off immediately, while D2 is still kept off; the other is that the reverse energy storage of C2 is released through W2 and D3. The capacitor C2 is discharged until the reverse voltage is dropped to zero, the primary voltage and the secondary voltage of the transformer is also decreased to zero at the same time, D3 is kept on, the reverse energy storage of C2 is released completely, and this stage is over. At this stage, after the reverse energy storage of C2 being dropped to zero, D1 and D2 are commutated naturally. Therefore, D1 is switched off at zero voltage and zero current, while D2 is switched on at zero voltage and zero current.

[0041] Stage 3: the forward energy of capacitor C2 is stored (continuous flow is provided by L1 and L2 at the same time)

[0042] After the reverse voltage of the capacitor C2 being dropped to zero, D3 is kept on, continuous flow continues to be provided by L2, the capacitor C2 is charged forward by the reverse current of secondary winding of the transformer, the forward voltage of C2 begins to be increased from zero. At this stage, D2 is switched on, continuous flow provided by L1 is stopped when the current of inductance L1 is dropped to zero, this stage is over.

[0043] Stage 4: the forward energy of capacitor C2 is stored (continuous flow is only provided by L2)

[0044] After the current of inductance L1 being dropped to zero, D3 is remained on, and the inductance L2 is freewheeled through D3 and the current of inductance L2 is decreased linearly. The reverse current of the secondary winding of the transformer continues to be decreased and the capacitor C2 continues to be charged. Until the next switch-on period comes, the current of L2 is dropped to the minimum value, at this time, the reverse current of the secondary winding is also drops to the minimum value, the forward voltage of C2 is reached the maximum value, and this stage is over.

[0045] 2. The working principle during the on period of the switching tube S

[0046] Stage 1: the forward energy storage of capacitor C2 is released

[0047] After the switching tube is switched on, the input voltage Vi is applied to across the primary winding of the transformer, and the voltage coupled to the secondary winding w2 is positive at the top and negative at the bottom, D1 is switched on, and the forward excitation energy is transferred to the load through the two branches. One is that the forward excitation energy is transferred to the load through D1 and L1, the current of L1 is risen linearly; the other is that the forward excitation energy is transferred to the load through C2 and L2, the current of L2 is risen linearly. At this stage, the excitation energy storage of C2 is released from the maximum value, and the forward voltage of C2 is gradually decreased until the forward voltage of capacitor C2 is dropped to zero, and this stage is over.

[0048] Stage 2: the reverse energy of capacitor C2 is stored

[0049] After the forward voltage of capacitor C2 being dropped to zero, D1 is remained on and the current of L1 continues to be risen linearly. C2 begins to be charged in reverse from zero, and the current of L2 continues to be risen. In order to transmit the high power by the branch of L2 (which could reduce the loss of diode), the current of L2 has been being risen during the on-period. When the switching tube is switched off, the currents of L1 and L2 are reached the maximum value, and the voltage across C2 is reached the maximum value in reverse direction, preparing for the switch-off at low voltage. This stage is over.

[0050] In this embodiment, the capacitor C2 is selected according to the first selection step; the steps of the first selection step include:

[0051] step 101, selecting the capacitance £ of the capacitor C2 of energy storage according to the following formula:

[00001]$\frac{4{\left(1-d\right)}^2{n}^2}{L_m{\pi }^2{f}^2}\le C_2\le \frac{{n^2\left(1-d\right)}^2}{L_m{f^2\left(\arcsin \lambda \right)}^2};$

[0052] step 102, calculating the withstand voltage V.sub.C2,Ton of the capacitor C2 of energy storage according to the following formula:

[00002]$V_{\mathrm{C2},\mathrm{Ton}}=\frac{V_i\mathrm{dT}\sin \left(w\left(1-d\right)T\right)}{\sqrt{L_m{C}_2}.Math.\left[1-\cos \left(w\left(1-d\right)T\right)\right]};$

[0053] In the above formulas, the V.sub.i is the input voltage of the forward converter main circuit 1, the d is the duty ratio of the switching tube S, the n is the turns ratio of the primary winding and the secondary winding of the high-frequency transformer T, L.sub.m is the excitation inductance of the primary winding of the high-frequency transformer T, f is the operating frequency of the forward converter main circuit 1, λ is generally takes 0.8≤λ≤1.

[0054] step 103, selecting the capacitor of energy storage with a capacitance C.sub.2 and a withstand voltage greater than V.sub.C2,Ton.

[0055] In this embodiment, the inductance L2 is selected according to the second selection step; wherein the steps of the second selection step include:

[0056] step 201, determining the value range of the inductance L.sub.2 of the inductance L2 according to the following formula:

L.sub.2=min(L.sub.2,min1,L.sub.2,min2)

[0057] In the above formula, the minimum value L.sub.2,min1 and L.sub.2,min1 of inductance L2 is calculated according to the following formulas:

[00003]$L_{2,\min 1}={\frac{1}{C_2}\left[\frac{V_o\left(1-d\right)T}{\left(V_{C2,\mathrm{Ton}}+\frac{V_i-{\mathrm{nV}}_o}{n}\right)\sin \left(\frac{dT}{\sqrt{L_2{C}_2}}\right)}\right]}^2{L}_{2,\min 2}={\frac{1}{C_2}\left[\frac{dT}{\arccos \left[\frac{V_i-{\mathrm{nV}}_o}{\left(n{V}_{C2,\mathrm{Ton}}+V_i-{\mathrm{nV}}_o\right)}\right]}\right]}^2$

[0058] The V.sub.o is the output voltage of the forward converter main circuit 1;

[0059] step 202, determining the maximum current of the inductance L2 according to the following formula:

[00004]$I_{\mathrm{L2},\min }=\frac{\sqrt{\frac{C_2}{L_2}}.Math.\left(V_{\mathrm{C2},\mathrm{Ton}}+\frac{V_i-{\mathrm{nV}}_o}{n}\right).Math.\sin \left(\frac{dT}{\sqrt{L_2{C}_2}}\right)-\frac{V_o}{L_2}\left(1-d\right)T}{1-\cos \left(\frac{dT}{\sqrt{L_2{C}_2}}\right)};$

[0060] step 203, selecting the inductance according to the steps 201 and 202.

[0061] In this embodiment, the diode D3 is selected according to the third selection step; the steps of the third selection step include:

[0062] step 301, calculating the maximum current I.sub.D3,max flowing through the diode D3 according to the following formula:

[00005]$I_{D3,\max }=I_{L1,\max }+I_{L2,\max }=\frac{V_{i,\max }-{\mathrm{nV}}_o}{n{L}_1}dT+\frac{V_{\circ }}{L_2}\left(1-d\right)T+\frac{\sqrt{\frac{C_2}{L_2}}.Math.\left(V_{\mathrm{C2},\mathrm{Ton}}+\frac{V_{i,\max }-n{V}_o}{n}\right).Math.\sin \left(\frac{dT}{\sqrt{L_2{C}_2}}\right)-\frac{V_o}{L_2}\left(1-d\right)T}{1-\cos \left(\frac{dT}{\sqrt{L_2{C}_2}}\right)}$

[0063] step 302, calculating the withstand voltage V.sub.D3,max of the diode D3 according to the following formula:

[00006]$V_{D3,\max }=V_{C2,\mathrm{Ton}}+\frac{V_i}{n}=\frac{V_{i,\max }\mathrm{dT}\sin \left(w\left(1-d\right)T\right)}{\sqrt{L_m{C}_2}.Math.\left[1-\cos \left(w\left(1-d\right)T\right)\right]}+\frac{V_{i,\max }}{n}$

[0064] I.sub.L1,max is the maximum current flowing through the primary winding of the high-frequency transformer T, I.sub.L2 is the current flowing through the inductance L2;

[0065] step 303, selecting the diode according to the steps 301 and 302;

[0066] It should be understood that the above description is merely to illustrate the feasibility of the technical solution of the present disclosure, and the principles and corresponding formulas of one of the listed working modes are not the only and limited descriptions, and are only used for reference.

[0067] It should be particularly noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, not to limit them. For those skilled in the art, the technical solutions described in the above embodiments may be modified, or some of the technologies features are equivalently replaced; and all these modifications and replacements should fall within the scope of protection of the appended claims of the present disclosure.