Isolated buck-boost converter

Abstract

The invention discloses an isolation buck-boost converter which comprises an input inductor, a primary side conversion circuit, a transformer and a secondary side rectification circuit, the input inductor is an input inductor L connected with an alternating current input end Ac, the primary side conversion circuit comprises Q-d and Q + c connected with the input inductor L, the other end of Q-d is connected with Q + u, the other end of Q + u is connected with the primary side of the transformer and Q-u, and the secondary side rectification circuit is connected with the secondary side rectification circuit. The other end of the Q-u is connected with the Q + d, the other end of the Q + c is connected with the C +, the other end of the C + is connected with the other end of the primary side of the transformer and the C-, the other end of the C-is connected with the Q-c, the other end of the Q-c is connected with the other end of the Q + d and the other end of the alternating current input Ac, the secondary side circuit comprises a Qlu and a Qru which are connected with the output positive electrode DC +, the other end of the Qlu is connected with the secondary side of the transformer and the Qld, and the other end of the Qru is connected with the other end of the secondary side of the transformer and the Qrd. And the other end of the Qld and the other end of the Qrd are connected to an output negative electrode DC-together. The converter can work in the Buck mode and the Boost mode, the Buck mode is used when the output voltage is low, the Boost mode is used when the output voltage is high, and the input-output proportion is expanded. Input current is modulated according to sine waves to improve the power factor of the power supply. By simplifying single-stage topology control, the circuit is more stable, the converter control is simple, the device utilization rate is high, the efficiency is high, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and in particular to an isolated buck-boost converter. Background Technology

[0002] Typical AC rectifier-isolation converters have an input voltage that is proportional to the output voltage due to the transformer, and therefore cannot operate in a wide range higher than the transformer's input voltage. If a wider range of operation is required, an additional boost converter stage must be added, which results in problems such as complex circuit control, low component utilization, and low efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide an isolated buck-boost converter to solve the problems of complex circuit control, low device utilization, and low efficiency in existing power converters.

[0004] The present invention solves the above problems through the following technical solution: An isolated buck-boost converter includes an input inductor connected to the input, a primary-side conversion circuit, a transformer, and a secondary-side rectifier circuit connected to the output. Input Ac+ is connected to input inductor L. The other end of L is connected to the source (S) of switching transistor Qd and the source (S) of switching transistor Q+c. The drain (D) of switching transistor Qd is connected to the drain (D) of switching transistor Q+u. The source (S) of switching transistor Q+u and the source (S) of switching transistor Qu are connected together to terminal 1 of transformer T. The drain (D) of switching transistor Qu is connected to the drain (D) of switching transistor Q+d. The drain (D) of switching transistor Q+c is connected to capacitor C+. The other end of capacitor C+ is connected to capacitor C- and terminal 2 of transformer T. The other end of capacitor C- is connected to the drain (D) of switching transistor Qc. The source (S) of switching transistor Q+d and the source (S) of switching transistor Qc are connected together to input Ac-. The DC output DC+ is connected to the drain of the switching transistor Qlu and the drain of the switching transistor Qru. The source of the switching transistor Qlu is connected to the drain of the switching transistor Qld and terminal 4 of the transformer T. The source of the switching transistor Qru is connected to the drain of the switching transistor Qrd and terminal 3 of the transformer T. The sources of the switching transistors Qld and Qrd are connected together to the DC output DC-.

[0005] Working principle: A. Single-phase rectification and conversion, such as Figure 1 , Figure 4 As shown, Figure 2 Define the phase of a single-phase sinusoidal AC circuit, and set the output DC reflected voltage Vref to the input AC sinusoidal voltage value at 30°. Examples of current flow are given for operation at 0-30°, 30-150°, 150-180°, and various freewheeling phases; the same applies to 180-360°.

[0006] 1. Using standard single-phase sinusoidal alternating current as input, as shown in the attached diagram. Figure 1All operating modes are listed. When current flows through the body diode of the switching transistor, the switching transistor can be turned on for synchronous control to further reduce losses.

[0007] 2. Replace the switching transistors Qlu, Qru, Qld, and Qrd in the secondary rectifier circuit with diodes Dlu, Dru, Dld, and Drd. The diodes and the body diodes of the switching transistors are aligned in the same direction to perform single-phase diode rectification.

[0008] B. Three-phase rectification and conversion, such as Figure 5 , Figure 6 As shown, Figure 3 To define the phase of a three-phase sinusoidal alternating current, the output DC reflected voltage Vref is set to the absolute value of the sinusoidal voltage at 20° for phase A and the sinusoidal voltage at 0° for phase C. Using a standard three-phase sinusoidal alternating current as input, examples are given of the current flow direction of each phase operating in Buck, Boost, and freewheeling phases from 0° to 20°. The same logic applies to other angles.

[0009] 1. As attached Figure 5 For example, in each operating mode, when current flows through the body diode of the switching transistor, the switching transistor can be turned on for synchronous control to further reduce losses.

[0010] 2. As attached Figure 6 The secondary rectifier switches Qau, Qbu, Qcu, Qad, Qbd, and Qcd are replaced with diodes Dau, Dbu, Dcu, Dad, Dbd, and Dcd. The diodes and the body diodes of the switches are aligned in the same direction to perform diode-based three-phase rectification.

[0011] Figure 1 Yes - the circuit schematic diagram of Embodiment 1 of the present invention; Figure 2 This is a single-phase sinusoidal alternating current waveform diagram of the present invention; Figure 3 This is a three-phase sinusoidal alternating current waveform diagram of the present invention; Figure 4 This is a circuit schematic diagram of Embodiment 2 of the present invention; Figure 5 This is a circuit schematic diagram of Embodiment 3 of the present invention; Figure 6 This is a circuit schematic diagram of Embodiment 4 of the present invention; Figure 7 In Embodiment 1 of this invention, the rectifier is 0-30° and 150-180° in the forward direction, Vref>Vin, and Boost is started. Figure 8 In Embodiment 1 of the present invention, the rectification is positive at 0-30° and 150-180°, Vref>Vin, Boost freewheeling, C+ charging, and the transformer operates in the forward direction; Figure 9During the first embodiment of the present invention, when the rectifier is in the forward direction of 0 - 30° and 150 - 180°, Vref > Vin, Boost operates, C+ discharges, and the transformer operates in the reverse direction; Figure 10 During the first embodiment of the present invention, when the rectifier is in the forward direction of 0 - 30° and 150 - 180°, Vref > Vin, Boost freewheels, C+ charges, and the transformer operates in the forward direction; Figure 11 During the first embodiment of the present invention, when the rectifier is in the forward direction of 0 - 30° and 150 - 180°, Vref > Vin, Boost starts; Figure 12 During the first embodiment of the present invention, when the rectifier is in the forward direction of 0 - 30° and 150 - 180°, Vref > Vin, Boost freewheels, C+ and C- charge, and the transformer operates in the reverse direction; Figure 13 During the first embodiment of the present invention, when the rectifier is in the forward direction of 0 - 30° and 150 - 180°, Vref > Vin, Boost operates, C- discharges, and the transformer operates in the forward direction; Figure 14 During the first embodiment of the present invention, when the rectifier is in the forward direction of 0 - 30° and 150 - 180°, Vref > Vin, Boost freewheels, C+ discharges, C- charges, and the transformer operates in the reverse direction; Figure 15 During the first embodiment of the present invention, when the rectifier is in the forward direction of 150 - 180°, Vref < Vin, Buck starts, C+ charges, and the transformer operates in the forward direction; Figure 16 During the first embodiment of the present invention, when the rectifier is in the forward direction of 150 - 180°, Vref < Vin, Buck freewheels, C+ discharges, C- charges, and the transformer operates in the reverse direction; Figure 17 During the first embodiment of the present invention, when the rectifier is in the forward direction of 150 - 180°, Vref < Vin, Buck operates, C+ and C- charge, and the transformer operates in the reverse direction; Figure 18 During the first embodiment of the present invention, when the rectifier is in the forward direction of 150 - 180°, Vref < Vin, Buck freewheels, C+ charges, and the transformer operates in the forward direction; Figure 19 During the third embodiment of the present invention, when the rectifier is at 0 - 20°, Vref > |Va|, |Vb|, Vc, Boost starts; Figure 20 During the third embodiment of the present invention, when the rectifier is at 0 - 20°, Vref > |Va|, |Vb|, Vc, Boost freewheels, Cc+, Cb-, Ca- charge, and the transformer operates in the forward direction; Figure 21In Embodiment 3 of the present invention, the rectification is 0-20°, Vref>|Va|,|Vb|,Vc, the Boost operates, Cc+, Cb-, and Ca- discharge, and the transformer operates in reverse. Figure 22 In Embodiment 3 of the present invention, the rectification is 0-20°, Vref>|Va|、|Vb|、Vc, the boost current is freewheeling, Cc+、Cb-、Ca- is charged, and the transformer is working in the forward direction; Figure 23 In Embodiment 3 of the present invention, the rectification is 0-20°, |Va|, |Vb|, Vc>Vref, Buck starts, Cc+, Cb-, Ca- are charged, and the transformer works in the forward direction; Figure 24 In Embodiment 3 of the present invention, the rectification is 0-20°, |Va|, |Vb|, Vc>Vref, Buck freewheeling, Cc+, Cb-, Ca- discharging, Cc-, Cb+, Ca+ charging, and the transformer operates in reverse. Figure 25 In Embodiment 3 of the present invention, the rectification is 0-20°, |Va|, |Vb|, Vc>Vref, Buck works, Cc+, Cb-, Ca- are charged, Cc-, Cb+, Ca+ are discharged, and the transformer works in the forward direction; Figure 26 In Embodiment 3 of the present invention, the rectification is 0-20°, |Va|, |Vb|, Vc>Vref, Buck freewheeling, Cc+, Cb-, Ca- discharging, Cc-, Cb+, Ca+ charging, and the transformer operates in reverse. Detailed Implementation

[0012] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0013] In the rectification and conversion of Examples 1 and 2, the input is a sinusoidal single-phase alternating current, as shown in the attached diagram. Figure 2 As shown, the operating state is from 0-180°, and the same applies to 180-360°. The output DC reflected voltage Vref is set to the value of the AC sinusoidal voltage at 30°. In the rectification and conversion of Embodiments 3 and 4, the input is a sinusoidal three-phase AC power, as shown in the attached figure. Figure 3 The diagram illustrates the operating state from 0-20°, with similar examples for other states. The output DC reflected voltage Vref is set to the absolute value of the C-phase AC sinusoidal voltage at 0° and the A-phase AC sinusoidal voltage at 20°. The current waveform is modulated with a sine wave to approximate the input sinusoidal voltage waveform, maximizing the power factor. Examples of current flow are shown in Buck, Boost, and various freewheeling phases.

[0014] Example 1: Combined with appendix Figure 1 As shown, an isolated buck-boost converter includes an input inductor connected to the input, a primary-side conversion circuit, a transformer, and a secondary-side synchronous rectification circuit. The input Ac+ is connected to the input inductor L. The other end of L is connected to the source (S) of Qd and the source (S) of Q+c. The drain (D) of Qd is connected to the drain (D) of Q+u. The source (S) of Q+u and the source (S) of Qu are connected to terminal 1 of transformer T. The drain (D) of Qu is connected to the drain (D) of Q+d. The drain (D) of Q+c is connected to C+. The other end of C+ is connected to C- and terminal 2 of the primary side of transformer T. The other end of C- is connected to the drain (D) of Qc. The source (S) of Q+d and the source (S) of Qc are connected to the input Ac-. The DC output DC+ is connected to the drain (D) of Qlu and the drain (D) of Qru. The source (S) of Qlu is connected to the drain (D) of Qld and terminal 4 of the secondary side of transformer T. The source (S) of Qru is connected to the drain (D) of Qrd and terminal 3 of the secondary side of transformer T. The source (S) of Qld and Qrd are connected together to the DC output DC-.

[0015] Working principle: Here's an example of the current flow direction when the Ac+ input voltage is positive; the reverse is similar.

[0016] A. Rectification forward Boost conversion, the transformer operates in the forward direction.

[0017] 1. Appendix Figure 7 When the rectified positive direction is 0-30° or 150-180°, and the input voltage is less than the set output reflected voltage Vref, the Boost starts, and the input current Ip flows back to the input through Ac+, ​​L, Qd, Q+u, Qu, Q+d, and Ac-.

[0018] 2. Appendix Figure 8 When the rectifier is in the forward direction of 0-30° or 150-180°, and the input voltage is less than the set output reflected voltage Vref, C+ charges, the transformer operates in the forward direction, and the Boost freewheeling current is activated. The input current Ip flows back to the input through Ac+, ​​L, Q+c, C+, the 2-1 winding of T, Qu, Q+d, and Ac-. The secondary current Is flows back to the 4-3 winding of T through the 4-3 winding of T, Qru, DC+, DC-, and Qld.

[0019] 3. Appendix Figure 9 When the rectification is in the forward direction of 0-30° and 150-180°, and the input voltage is less than the set output reflected voltage Vref, C+ discharges, the transformer operates in reverse, and the Boost operates. The input current Ip flows back to the input through Ac+, ​​L, Qd, Q+u, Qu, Q+d, and Ac-. The C+ discharge current Ic+ flows back to C+ through Q+c, Qd, Q+u, and windings 1-2 of T. The secondary current Is flows back to windings 3-4 of T, Qlu, DC+, DC-, and Qrd.

[0020] 4. Appendix Figure 10 When the rectifier is in the forward direction of 0-30° or 150-180°, and the input voltage is less than the set output reflected voltage Vref, C+ charges, the transformer operates in the forward direction, and the Boost freewheeling current is activated. The input current Ip flows back to the input through Ac+, ​​L, Q+c, C+, the 2-1 winding of T, Qu, Q+d, and Ac-. The secondary current Is flows back to the 4-3 winding of T through the 4-3 winding of T, Qru, DC+, DC-, and Qld.

[0021] B. The rectifier performs a forward Boost conversion, while the transformer operates in reverse.

[0022] 1. Appendix Figure 11 When the rectified positive direction is 0-30° or 150-180°, and the input voltage is less than the set output reflected voltage Vref, the Boost starts, and the input current Ip flows back to the input through Ac+, ​​L, Qd, Q+u, Qu, Q+d, and Ac-.

[0023] 2. Appendix Figure 12 The rectification is in the forward direction of 0-30° and 150-180°. When the input voltage is less than the set output reflected voltage Vref, C+ and C- charge, the transformer operates in reverse, and the Boost freewheeling current is activated. The input current Ip flows back to the input through Ac+, ​​L, Qd, Q+u, windings 1-2 of T, C-, Qc, and Ac-. The charging current Ic+ of capacitor C+ flows back to the input through Ac+, ​​L, Q+c, C+, C-, Qc, and Ac-. The secondary current Is flows back to windings 3-4 of T through windings 3-4, Qlu, DC+, DC-, and Qrd.

[0024] 3. Appendix Figure 13 When the rectifier is in the forward direction of 0-30° or 150-180°, and the input voltage is less than the set output reflected voltage Vref, C- discharges, the transformer operates in the forward direction, the Boost operates, and the input current Ip flows back to the input through Ac+, ​​L, Qd, Q+u, Qu, Q+d, and Ac-; the C- discharge current Ic- flows back to C- through the 2-1 winding of T, Qu, Q+d, Qc, and C-; the secondary current Is flows back to the 4-3 winding of T through the 4-3 winding of T, Qru, DC+, DC-, and Qld.

[0025] 4. Appendix Figure 14When the rectifier is in the forward direction (0-30°, 150-180°), and the input voltage is less than the set output reflected voltage Vref, C+ discharges and C- charges, the transformer operates in reverse, and the Boost freewheeling current is activated. The input current Ip flows back to the input through the 1-2 windings of Ac+, ​​L, Qd, Q+u, T, C-, Qc, and Ac-. The discharge current Ic+ of capacitor C+ flows back to C+ through the 1-2 windings of Q+c, Qd, Q+u, and T. The secondary current Is flows back to the 3-4 windings of T through the 3-4 windings of T, Qlu, DC+, DC-, and Qrd.

[0026] C. Rectification in the forward direction (Buck converter) means the transformer operates in the forward direction.

[0027] 1. Appendix Figure 15 When the rectifier is 30-150° forward, and the input voltage is greater than the set output reflected voltage Vref, C+ charges, Buck starts, the transformer operates in the forward direction, and the input current flows back to the input through Ac+, ​​L, Q+c, C+, T's 2-1 winding, Qu, Q+d, and Ac-; the secondary current Is flows back to T's 4-3 winding through T's 4-3 winding, Qru, DC+, DC-, and Qld.

[0028] 2. Appendix Figure 16 When the rectification is in the forward direction of 30-150°, and the input voltage is greater than the set output reflected voltage Vref, C+ discharges, C- charges, Buck freewheels, and the transformer operates in reverse. The input current flows back to the input through the 1-2 windings of Ac+, ​​L, Qd, Q+u, T, C-, Qc, and Ac-. The discharge current Ic+ of capacitor C+ flows back to C+ through the 1-2 windings of Q+c, Qd, Q+u, and T. The secondary current Is flows back to the 3-4 windings of T through the 3-4 windings of T, Qlu, DC+, DC-, and Qrd.

[0029] 3. Appendix Figure 17 When the rectification is 30-150° forward, and the input voltage is greater than the set output reflected voltage Vref, C+ and C- charge, the transformer operates in reverse, and the Buck converter operates. The input current Ip flows back to the input through Ac+, ​​L, Qd, Q+u, windings 1-2 of T, C-, Qc, and Ac-. The charging current Ic+ of capacitor C+ flows back to the input through Ac+, ​​L, Q+c, C+, C-, Qc, and Ac-. The secondary current Is flows back to windings 3-4 of T through windings 3-4, Qlu, DC+, DC-, and Qrd.

[0030] 4. Appendix Figure 18When the rectification is 30-150° forward, and the input voltage is greater than the set output reflected voltage Vref, C+ charges, the transformer operates in the forward direction, and the Buck freewheels. The input current flows back to the input through Ac+, ​​L, Q+c, C+, T's 2-1 winding, Qu, Q+d, and Ac-. The secondary current Is flows back to T's 4-3 winding through T's 4-3 winding, Qru, DC+, DC-, and Qld.

[0031] Example 2: Combined with appendix Figure 4 As shown, an isolated buck-boost converter, reference Figure 1 Replace Qld, Qrd, Qlu, and Qru with diodes Dld, Drd, Dlu, and Dru, with the diodes pointing in the same direction as the switching diodes. The control method is the same as in Example 1.

[0032] Example 3: Combined with appendix Figure 5 As shown, an isolated buck-boost converter includes an input inductor connected to three inputs A, B, and C, a primary-side conversion circuit, a transformer, and a secondary-side three-phase synchronous rectifier circuit.

[0033] Phase A input A is connected to input inductor La. The other end of La is connected to the source (S) of Qa-d and Qa+c. The drain (D) of Qa-d is connected to the drain of Qa+u. The source (S) of Qa+u and Qa-u are connected together to the primary side 1 of transformer Ta. The drain (D) of Qa-u is connected to the drain (D) of Qa+d. The drain (D) of Qa+c is connected to Ca+. The other end of Ca+ is connected to Ca- and the primary side 2 of transformer Ta. The other end of Ca- is connected to the drain (D) of Qa-c. The source (S) of Qa+d and Qa-c are connected together at the midpoint. The B-phase input is connected to the input inductor Lb. The other end of Lb is connected to the source (S) of Qb-d and Qb+c. The drain (D) of Qb-d is connected to the drain of Qb+u. The source (S) of Qb+u and Qb-u are connected together to the primary side 1 of the transformer Tb. The drain (D) of Qb-u is connected to the drain (D) of Qb+d. The drain (D) of Qb+c is connected to Cb+. The other end of Cb+ is connected to Cb- and the primary side 2 of the transformer Tb. The other end of Cb- is connected to the drain (D) of Qb-c. The source (S) of Qb+d and Qb-c are connected together at the midpoint. The C-phase input C is connected to the input inductor Lc. The other end of Lc is connected to the source (S) of Qc-d and Qc+c. The drain (D) of Qc-d is connected to the drain of Qc+u. The source (S) of Qc+u and Qc-u are connected together to the primary side 1 of transformer Tc. The drain (D) of Qc-u is connected to the drain (D) of Qc+d. The drain (D) of Qc+c is connected to Cc+. The other end of Cc+ is connected to Cc- and the primary side 2 of transformer Tc. The other end of Cc- is connected to the drain (D) of Qc-c. The source (S) of Qc+d and Qc-c are connected together at the midpoint. The DC output DC+ is connected to the drain (D) of Qau, the drain (D) of Qbu, and the drain (D) of Qcu. The source (S) of Qau is connected to the drain (D) of Qad, terminal 4 of the secondary side of transformer Ta, and terminal 3 of the secondary side of transformer Tc. The source (S) of Qbu is connected to the drain (D) of Qbd, terminal 4 of the secondary side of transformer Tb, and terminal 3 of the secondary side of transformer Ta. The source (S) of Qcu is connected to the drain (D) of Qcd, terminal 4 of the secondary side of transformer Tc, and terminal 3 of the secondary side of transformer Tb. The source (S) of Qad, Qbd, and Qcd are connected together to the DC output DC-.

[0034] Working principle: A. Set the output DC reflected voltage Vref to the absolute value of the C-phase AC sinusoidal voltage at 0°, perform rectifier boost conversion, and the transformer operates in the forward direction.

[0035] 1. Appendix Figure 19 After rectification to 0-20°, Vref > |Va|, |Vb|, Vc, Boost starts. The current Ia in phase A flows back to phase A through the midpoint, Qa+d, Qa-u, Qa+u, Qa-d, La, and A; the current Ib in phase B flows back to phase B through the midpoint, Qb+d, Qb-u, Qb+u, Qb-d, Lb, and B; the current Ic in phase C flows to the midpoint through C, Lc, Qc-d, Qc+u, Qc-u, and Qc+d.

[0036] 2. Appendix Figure 20 The rectification is 0-20°, Vref>|Va|、|Vb|、Vc, Cc+、Cb-、Ca- is charged, the transformer works in the forward direction, Boost freewheeling, the A-phase current Ia flows back to A phase through the midpoint, Qa-c, Ca-, Ta 2-1 winding, Qa+u, Qa-d, La, A; the B-phase current Ib flows back to B phase through the midpoint, Qb-c, Cb-, Tb 2-1 winding, Qb+u, Qb-d, Lb, B; the C-phase current Ic flows to the midpoint through C, Lc, Qc+c, Cc+, Tc 2-1 winding, Qc-u, Qc+d. The secondary A-phase current Isa flows back to the 4-3 winding of Ta via winding 4-3, Qbu, DC+, DC-, and Qad; the secondary B-phase current Isb flows back to the 4-3 winding of Tb via winding 4-3, Qcu, DC+, DC-, and Qbd; the secondary C-phase current Isc flows back to the 4-3 winding of Tc via winding 4-3, Qau, DC+, DC-, and Qcd.

[0037] 3. Appendix Figure 21Rectification 0-20°, Vref>|Va|、|Vb|、Vc, When Cc+, Cb-, and Ca- discharge, the transformer operates in reverse and Boost mode is activated. The current Ia in phase A flows back to phase A through the midpoint, Qa+d, Qa-u, Qa+u, Qa-d, La, and A. The discharge current Ia- in phase Ca- flows back to phase Ca- through windings 1-2 of Qa-c, Qa+d, Qa-u, and Ta. The current Ib in phase B flows back to phase B through the midpoint, Qb+d, Qb-u, Qb+u, Qb-d, Lb, and B. The discharge current Ib- in phase C- flows back to phase Cb- through windings 1-2 of Qb-c, Qb+d, Qb-u, and Tb. The current Ic in phase C flows to the midpoint through C, Lc, Qc-d, Qc+u, Qc-u, and Qc+d. The discharge current Ic+ in phase C- flows back to phase C- through windings 1-2 of Qc+c, Qc-d, Qc+u, and Tc. The secondary A-phase current Isa flows back to the 3-4 winding of Ta via windings 3-4, Qau, DC+, DC-, and Qbd; the secondary B-phase current Isb flows back to the 3-4 winding of Tb via windings 3-4, Qbu, DC+, DC-, and Qcd; the secondary C-phase current Isc flows back to the 4-3 winding of Tc via windings 3-4, Qcu, DC+, DC-, and Qad.

[0038] 4. Appendix Figure 22 The rectification is 0-20°, Vref>|Va|、|Vb|、Vc, Cc+、Cb-、Ca- is charged, the transformer works in the forward direction, Boost freewheeling, the A-phase current Ia flows back to A phase through the midpoint, Qa-c, Ca-, Ta 2-1 winding, Qa+u, Qa-d, La, A; the B-phase current Ib flows back to B phase through the midpoint, Qb-c, Cb-, Tb 2-1 winding, Qb+u, Qb-d, Lb, B; the C-phase current Ic flows to the midpoint through C, Lc, Qc+c, Cc+, Tc 2-1 winding, Qc-u, Qc+d. The secondary A-phase current Isa flows back to the 4-3 winding of Ta via winding 4-3, Qbu, DC+, DC-, and Qad; the secondary B-phase current Isb flows back to the 4-3 winding of Tb via winding 4-3, Qcu, DC+, DC-, and Qbd; the secondary C-phase current Isc flows back to the 4-3 winding of Tc via winding 4-3, Qau, DC+, DC-, and Qcd.

[0039] B. Set the output DC reflected voltage Vref to the 20° AC sinusoidal voltage value of phase A, rectify and convert the Buck converter, and the transformer will operate in the forward direction.

[0040] 1. Appendix Figure 23The rectification is 0-20°, |Va|, |Vb|, Vc>Vref, Cc+, Cb-, Ca- are charged, the transformer works in the forward direction, Buck starts, the A-phase current Ia flows back to A phase through the midpoint, Qa-c, Ca-, Ta's 2-1 winding, Qa+u, Qa-d, La, and A; the B-phase current Ib flows back to B phase through the midpoint, Qb-c, Cb-, Tb's 2-1 winding, Qb+u, Qb-d, Lb, and B; the C-phase current Ic flows to the midpoint through C, Lc, Qc+c, Cc+, Tc's 2-1 winding, Qc-u, and Qc+d. The secondary A-phase current Isa flows back to the 4-3 winding of Ta via winding 4-3, Qbu, DC+, DC-, and Qad; the secondary B-phase current Isb flows back to the 4-3 winding of Tb via winding 4-3, Qcu, DC+, DC-, and Qbd; the secondary C-phase current Isc flows back to the 4-3 winding of Tc via winding 4-3, Qau, DC+, DC-, and Qcd.

[0041] 2. Appendix Figure 24 Rectification from 0-20°, |Va|, |Vb|, Vc>Vref, Cc+, Cb-, Ca- discharge, Cc-, Cb+, Ca+ charge, transformer reverse operation, Buck freewheeling, A-phase current Ia flows back to A phase through the midpoint, Qa+d, Qa-u, Ta's 1-2 windings, Ca+, Qa+c, La, A, Ca- discharge current Ia- flows back to Ca- through Qa-c, Qa+d, Qa-u, Ta's 1-2 windings; B-phase current Ib flows back through the midpoint, Qb+d, Qb-u, The current flows back to phase B through windings 1-2 of Tb, Cb+, Qb+c, Lb, and B. The discharge current Ib- of Cb- flows back to Cb- through windings 1-2 of Qb-c, Qb+d, Qb-u, and Tb. The current Ic of phase C flows to the midpoint through windings 1-2 of C, Lc, Qc-d, Qc+u, and Tc, Cc-, and Qc-c. The discharge current Ic+ of phase Cc+ flows back to Cc+ through windings 1-2 of Qc+c, Qc-d, Qc+u, and Tc. The secondary A-phase current Isa flows back to the 3-4 winding of Ta via windings 3-4, Qau, DC+, DC-, and Qbd; the secondary B-phase current Isb flows back to the 3-4 winding of Tb via windings 3-4, Qbu, DC+, DC-, and Qcd; the secondary C-phase current Isc flows back to the 3-4 winding of Tc via windings 3-4, Qcu, DC+, DC-, and Qad.

[0042] 3. Appendix Figure 25Rectification from 0-20°, |Va|, |Vb|, Vc>Vref, Cc+, Cb-, Ca- charge, Cc-, Cb+, Ca+ discharge, transformer forward operation, Buck operation, A-phase current Ia flows back to A phase through the midpoint, Qa-c, Ca-, Ta's 2-1 winding, Qa+u, Qa-d, La, A, Ca+ discharge current Ia+ flows back to Ca+ through Ta's 2-1 winding, Qa+u, Qa-d, Qa+c; B-phase current Ib flows through the midpoint, Qb-c, Cb-, T The current in phase B flows back to phase B via the 2-1 winding of phase B, Qb+u, Qb-d, Lb, and B. The discharge current Ib+ in phase C flows back to phase Cb+ via the 2-1 winding of phase Tb, Qb+u, Qb-d, and Qb+c. The current in phase C Ic flows to the midpoint via phase C, Lc, Qc+c, Cc+, the 2-1 winding of phase Tc, Qc-u, and Qc+d. The discharge current Ic- in phase Cc- flows back to phase Cc- via the 2-1 winding of phase Tc, Qc-u, Qc+d, and Qc-c. The secondary A-phase current Isa flows back to the 4-3 winding of Ta via winding 4-3, Qbu, DC+, DC-, and Qad; the secondary B-phase current Isb flows back to the 4-3 winding of Tb via winding 4-3, Qcu, DC+, DC-, and Qbd; the secondary C-phase current Isc flows back to the 4-3 winding of Tc via winding 4-3, Qau, DC+, DC-, and Qcd.

[0043] 4. Appendix Figure 26 Rectification from 0-20°, |Va|, |Vb|, Vc>Vref, Cc+, Cb-, Ca- discharge, Cc-, Cb+, Ca+ charge, transformer reverse operation, Buck freewheeling, A-phase current Ia flows back to A phase through the midpoint, Qa+d, Qa-u, Ta's 1-2 windings, Ca+, Qa+c, La, A, Ca- discharge current Ia- flows back to Ca- through Qa-c, Qa+d, Qa-u, Ta's 1-2 windings; B-phase current Ib flows back through the midpoint, Qb+d, Qb-u, The current flows back to phase B through windings 1-2 of Tb, Cb+, Qb+c, Lb, and B. The discharge current Ib- of Cb- flows back to Cb- through windings 1-2 of Qb-c, Qb+d, Qb-u, and Tb. The current Ic of phase C flows to the midpoint through windings 1-2 of C, Lc, Qc-d, Qc+u, and Tc, Cc-, and Qc-c. The discharge current Ic+ of phase Cc+ flows back to Cc+ through windings 1-2 of Qc+c, Qc-d, Qc+u, and Tc. The secondary A-phase current Isa flows back to the 3-4 winding of Ta via windings 3-4, Qau, DC+, DC-, and Qbd; the secondary B-phase current Isb flows back to the 3-4 winding of Tb via windings 3-4, Qbu, DC+, DC-, and Qcd; the secondary C-phase current Isc flows back to the 3-4 winding of Tc via windings 3-4, Qcu, DC+, DC-, and Qad.

Claims

1. An isolated buck-boost converter, characterized in that, It includes the input inductor, primary-side converter circuit, transformer, and secondary-side rectifier circuit, wherein: Input Ac+ is connected to input inductor L. The other end of L is connected to the source (S) of switching transistor Qd and the source (S) of switching transistor Q+c. The drain (D) of switching transistor Qd is connected to the drain (D) of switching transistor Q+u. The source (S) of switching transistor Q+u and the source (S) of switching transistor Qu are connected together to terminal 1 of transformer T. The drain (D) of switching transistor Qu is connected to the drain (D) of switching transistor Q+d. The drain (D) of switching transistor Q+c is connected to capacitor C+. The other end of capacitor C+ is connected to capacitor C- and terminal 2 of transformer T. The other end of capacitor C- is connected to the drain (D) of switching transistor Qc. The source (S) of switching transistor Q+d and the source (S) of switching transistor Qc are connected together to input Ac-. The DC output DC+ is connected to the drain of the switching transistor Qlu and the drain of the switching transistor Qru. The source of the switching transistor Qlu is connected to the drain of the switching transistor Qld and terminal 4 of the transformer T. The source of the switching transistor Qru is connected to the drain of the switching transistor Qrd and terminal 3 of the transformer T. The sources of the switching transistors Qld and Qrd are connected together to the DC output DC-.

2. In the isolated buck-boost converter according to claim 1, the switching transistors Qlu, Qru, Qld and Qrd in the secondary rectifier circuit are replaced with diodes Dlu, Dru, Dld and Drd, with the diodes and the body diodes of the switching transistors having the same direction, for single-phase diode rectification.

3. The isolated buck-boost converter according to claim 1, characterized in that... Add two identical input inductors, a primary branch, and a transformer. Connect the Ac- terminals together. Connect the three secondary sides of the transformer in a delta configuration and change it to a three-phase rectifier circuit. Input three-phase AC power to the three Ac+ terminals and output DC power.

4. The isolated step-up / step-down converter according to claim 1, wherein the three secondary sides of the transformer are connected in a Y-shape for three-phase rectification.

5. An isolated step-up / step-down converter according to claim 3, wherein the switching transistors Qau, Qbu, Qcu, Qad, Qbd, and Qcd in the three-phase rectifier circuit are replaced with diodes Dau, Dbu, Dcu, Dad, Dbd, and Dcd, with the diodes and the body diodes of the switching transistors having the same direction, performing diode three-phase rectification conversion.

6. An isolated buck-boost converter according to claims 1 and 3, which can operate in both Buck and Boost modes.

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