Isolated three-level soft-switching buck-boost converter

Abstract

This application discloses an isolated three-level soft-switching buck-boost converter, belonging to the field of power converter technology. It includes a primary-side conversion module, an isolated conversion module, a first secondary-side conversion module, and a second secondary-side conversion module. The second secondary-side conversion module includes: a first switch, the first terminal of which is connected to the first terminal of the output voltage; the second terminal of which is connected to the first terminal of a second switch and the first terminal of a first inductor; the second terminal of the first inductor is connected to the first output terminal of the first secondary-side conversion module; and the second terminal of the second switch is connected to the second terminal of the output voltage and the second output terminal of the first secondary-side conversion module. The first and second switches are complementary in conduction. When the current of the first inductor drops to the minimum negative current required for soft switching, the first switch is turned off. This application achieves zero-voltage turn-on across all modes and load ranges, minimizes the effective value of the inductor current, and balances multiple objectives such as high frequency, miniaturization, and high efficiency.

Description

Technical Field

[0001] This application relates to the field of power converter technology, and in particular to an isolated three-level soft-switching buck-boost converter. Background Technology

[0002] As data centers evolve towards high-voltage direct current (HVDC) power supply architectures, server power supplies are facing multiple challenges, including high voltage, high power, high efficiency, and high power density. Traditional hard-switching converters, due to their large switching losses, struggle to balance high frequency and high efficiency, severely hindering the miniaturization of power supplies.

[0003] While zero-voltage soft-switching technology can effectively eliminate switching losses and improve frequency and power density, achieving reliable zero-voltage turn-on (ZVS) across all operating conditions, including high-voltage input and a wide load range, is extremely challenging. Existing topologies and control methods are limited by issues such as ZVS failure under light loads, reactive circulating current, and wide frequency variation ranges, resulting in suboptimal efficiency and performance. Summary of the Invention

[0004] This application aims to provide an isolated three-level soft-switching buck-boost converter, which achieves zero-voltage turn-on across the entire input, output, and load range at a constant switching frequency. By actively shaping the current waveform, it minimizes the effective value of the inductor current, thus achieving multiple goals such as high frequency, miniaturization, and high efficiency, thereby meeting the stringent requirements of next-generation data centers for extreme efficiency and power density.

[0005] To achieve the above objectives, the technical solution of this application is as follows: An isolated three-level soft-switching buck-boost converter includes, The primary-side conversion module receives the input voltage, divides and transforms the input voltage, and converts the DC energy into a first square wave voltage and outputs it. An isolation transformation module receives the first square wave voltage output by the primary-side transformation module, and outputs a high-frequency voltage after electrical isolation and transformation. The first secondary-side conversion module receives the high-frequency voltage output by the isolation conversion module, performs high-frequency pulse conversion, and outputs a second square wave voltage. The second secondary-side conversion module receives the second square wave voltage output from the first secondary-side conversion module, rectifies and modulates it to obtain the third square wave voltage, and outputs a stable output voltage after filtering. The second secondary-side conversion module includes: a first switch, a first terminal of the first switch connected to a first terminal of the output voltage, a second terminal of the first switch connected to a first terminal of a second switch and a first terminal of a first inductor, a second terminal of the first inductor connected to a first output terminal of the first secondary-side conversion module, and a second terminal of the second switch connected to a second terminal of the output voltage and a second output terminal of the first secondary-side conversion module.

[0006] Optionally, the first switch and the second switch are complementary in conducting to modulate the first inductor current into a quadrilateral waveform. When the first inductor current drops to the minimum negative current required for soft switching, the first switch is turned off.

[0007] Optionally, both the first switch and the second switch include a body diode and a corresponding parasitic capacitance, with the first terminal of the first switch and the second terminal of the second switch being the drain and the second terminal of the first switch and the second switch being the source.

[0008] Optionally, the primary-side transformation module includes: A first capacitor, with its first terminal connected to the first terminal of the input voltage; its second terminal connected to the first terminal of a second capacitor; the second terminal of the second capacitor connected to the second terminal of the input voltage; a third switch, with its first terminal connected to the first terminal of the first capacitor; the second terminal of the third switch connected to the first terminal of a fourth switch; the second terminal of the fourth switch connected to the first terminal of a fifth switch; the second terminal of the fifth switch connected to the first terminal of a sixth switch; and the second terminal of the sixth switch connected to the second terminal of the second capacitor; a first diode, with its first terminal connected to the second terminal of the third switch and the first terminal of the fourth switch; the second terminal of the first diode connected to the first terminal of the second diode and the midpoint between the first and second capacitors; and the second terminal of the second diode connected to the second terminal of the fifth switch and the first terminal of the sixth switch; wherein the first terminals of the first and second diodes are cathodes, and the second terminals of the first and second diodes are anodes. The third, fourth, fifth, and sixth switches each include a body diode and a corresponding parasitic capacitance. The first terminal of the third, fourth, fifth, and sixth switches is the drain, and the second terminal of the third, fourth, fifth, and sixth switches is the source.

[0009] Optionally, the third switch and the sixth switch have the same duty cycle and are 180° out of phase; the fourth switch and the fifth switch are turned on during the positive half-cycle and the negative half-cycle, respectively.

[0010] Optionally, the first capacitor and the second capacitor are voltage divider capacitors.

[0011] Optionally, the isolation conversion module includes: a second inductor, the first end of which is connected to the midpoint of the connection between the second end of the fourth switch and the first end of the fifth switch, the second end of which is connected to the first end of the primary winding of the transformer, the second end of which is connected to the midpoint of the connection between the first capacitor and the second capacitor, the first end of the secondary winding of the transformer being connected to the first input terminal of the second secondary conversion module, and the second end of which is connected to the second input terminal of the second secondary conversion module.

[0012] Optionally, the first secondary-side conversion module includes: an eighth switch, the first end of which is connected to the first end of a ninth switch, the second end of which is connected to the first end of a tenth switch and the first end of the transformer secondary winding, the second end of the tenth switch being connected to the second end of an eleventh switch, and the second end of the ninth switch being connected to the first end of the eleventh switch and the second end of the transformer secondary winding; the first end of the ninth switch is the first output end of the first secondary-side conversion module, and the second end of the eleventh switch is the second output end of the first secondary-side conversion module; The eighth, ninth, tenth, and eleventh switches each include a body diode and a corresponding parasitic capacitance; the first terminal of the eighth, ninth, tenth, and eleventh switches is the drain, and the second terminal of the eighth, ninth, tenth, and eleventh switches is the source.

[0013] Optionally, the primary-side conversion module can be any one of a diode-type midpoint clamping three-level circuit structure, a flying capacitor-type midpoint clamping three-level circuit structure, or an active midpoint clamping three-level circuit structure.

[0014] Optionally, the first secondary-side conversion module can be any of a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a half-wave rectifier circuit structure.

[0015] The isolated three-level soft-switching buck-boost converter proposed in this application, by adding the first and second switches, possesses buck-boost characteristics, increasing additional control degrees of freedom and enabling optimized control. By adjusting the phase difference between the first and second switches and the primary-side switch, the waveform of the secondary-side inductor current is modulated, resulting in smaller ripple in the secondary-side inductor current and improved switching frequency and power density. Simultaneously, by adjusting the turn-off time of the first switch, zero-voltage turn-on of all switches is achieved across the entire input, output, and load range at a constant switching frequency.

[0016] To make the above-mentioned features and advantages of the application more apparent and understandable, specific embodiments are provided below, and detailed descriptions are given in conjunction with the accompanying drawings. Attached Figure Description

[0017] Figure 1This is a block diagram of the isolated three-level soft-switching buck-boost converter proposed in this application.

[0018] Figure 2 This is a circuit diagram of a specific embodiment of an isolated three-level soft-switching buck-boost converter.

[0019] Figure 3 This is a schematic diagram of the first operating mode of an isolated three-level soft-switching buck-boost converter.

[0020] Figure 4 This is a schematic diagram of the second operating mode of an isolated three-level soft-switching buck-boost converter.

[0021] Figure 5 This is a schematic diagram of the third operating mode of an isolated three-level soft-switching buck-boost converter.

[0022] Figure 6 This is a schematic diagram of the fourth operating mode of an isolated three-level soft-switching buck-boost converter.

[0023] Figure 7 This is a schematic diagram of the fifth operating mode of an isolated three-level soft-switching buck-boost converter.

[0024] Figure 8 This is a schematic diagram of the sixth operating mode of an isolated three-level soft-switching buck-boost converter.

[0025] Figure 9 This is a schematic diagram of the seventh operating mode of an isolated three-level soft-switching buck-boost converter.

[0026] Figure 10 This is a schematic diagram of the eighth operating mode of an isolated three-level soft-switching buck-boost converter.

[0027] Figure 11 This is a schematic diagram of the ninth operating mode of an isolated three-level soft-switching buck-boost converter.

[0028] Figure 12 The simulation waveforms of the isolated three-level soft-switching buck-boost converter at rated output power are shown below. Figure 12 Figure (a) shows the simulated waveform of the voltage at point AB under rated output power. Figure 12 Figure (b) shows the simulated waveform of the primary current at rated output power. Figure 12 Figure (c) shows the simulation waveform of the output voltage of the first secondary-side converter module at rated output power. Figure 12 Figure (d) shows the simulated waveform of the secondary inductor current under rated output power.

[0029] In the accompanying drawings, similar reference numerals refer to the same elements. Detailed Implementation

[0030] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0031] In one embodiment, see Figure 1 This application provides an isolated three-level soft-switching buck-boost converter, comprising: Primary-side conversion module 11, the primary-side conversion module 11 receives input voltage V in For input voltage V in The voltage is divided and converted to convert DC energy into a first square wave voltage and then output. The isolation transformation module 12 receives the first square wave voltage output by the primary-side transformation module 11, and outputs a high-frequency voltage after electrical isolation and transformation. The first secondary-side conversion module 13 receives the high-frequency voltage output by the isolation conversion module 12, performs high-frequency pulse conversion, and outputs a second square wave voltage. The second secondary-side conversion module 14 receives the second square wave voltage output from the first secondary-side conversion module 13, rectifies and modulates it to obtain a third square wave voltage, and outputs a stable output voltage after filtering. V o .

[0032] As an example, the second secondary-side transformation module 14 includes: an inductor L c ,switch Q R1 ,switch Q R2 ,switch Q R1 The first terminal is connected to the output voltage. V o The first end, switch Q R1 The second end is connected to a switch Q R2 First terminal and inductor L c The first end, inductor L c The second end is connected to the first output end of the first secondary side conversion module 13, and the switch is activated. QR2 The second terminal is connected to the output voltage. V o The second end and the second output end of the first secondary side transformation module 13.

[0033] As an example, a switch Q R1 ,switch Q R2 Each includes a body diode and its corresponding parasitic capacitance.

[0034] As an example, a switch Q R1 ,switch Q R2 The first terminal is the drain, and the switch... Q R1 ,switch Q R2 The second end is the source pole.

[0035] As an example, the output voltage V o The first terminal is the positive terminal, and the output voltage is... V o The second end is the negative electrode.

[0036] As an example, inductor L c This is a filter inductor. The current flows through the inductor. L c The secondary inductor current is i Lc .

[0037] As an example, a switch Q R1 With switch Q R2 Complementary conduction, transferring the secondary inductor current i Lc Modulated into a quadrilateral waveform, when the secondary inductor current... i Lc Descending to − I ZVS Immediately turn off the switch. Q R1 .in, I ZVS To enable the isolated three-level soft-switching buck-boost converter to achieve the minimum current for soft switching.

[0038] As an example, please continue reading Figure 2 In this specific embodiment, the primary-side conversion module 11 adopts a midpoint clamped three-level circuit structure, and the first secondary-side conversion module 13 adopts a full-bridge rectifier circuit structure.

[0039] As an example, the primary-side transformation module 11 includes: a capacitor C in1 ,capacitance C in2 ,switch Q 1. Switch Q 2. Switch Q 3. Switch Q 4. Diode D c1 ,diode D c2 The capacitor C in1 The first terminal is connected to the input voltage. V in The first terminal, capacitor C in1 The second end is connected to a capacitor C in2 The first terminal, capacitor C in2 The second terminal is connected to the input voltage. V in The second end. Capacitor. C in1 With capacitor C in2 The midpoint is point B. The switch... Q The first terminal of 1 is connected to a capacitor. C in1 The first end, switch Q The second end of 1 is connected to a switch. Q The first end of 2, the switch Q The second end of 2 is connected to a switch. Q The first terminal of 3, the switch Q The second end of 3 is connected to a switch. Q 4, the first terminal, the switch Q The second end of 4 is connected to a capacitor. C in2 The second end; diode D c1 The first end is connected to the switch Q The second terminal of 1 is connected to the switch. Q 2. The first terminal, diode D c1 The second end is connected to a diode. D c2 First terminal and capacitor C in1 With capacitor C in2 Midpoint B, diode D c2 The second end is connected to a switch Q The second terminal of 3 is connected to the switch. QThe first terminal of 4. Switch Q 2. Second terminal and switch Q 3. The midpoint of the first connection is point A.

[0040] As an example, the capacitor C in1 and capacitor C in2 It is a voltage divider capacitor.

[0041] As an example, the input voltage V in The first terminal is the positive terminal, and the input voltage is... V in The second end is the negative electrode.

[0042] As an example, diode D c1 ,diode D c2 The first end is the cathode, diode D c1 ,diode D c2 The second end is the anode.

[0043] As an example, diode D c1 ,diode D c2 It is a clamping diode.

[0044] As an example, a switch Q 1. Switch Q4 is controlled by pulse width modulation (PWM). Q Switch 1 has the same duty cycle as switch Q4 but is 180° out of phase; Q 2 and switch Q 3. The switch conducts during both the positive and negative half-cycles. Q 2 and switch Q 3 are in a complementary conduction state.

[0045] As an example, a switch Q 1. Switch Q 2. Switch Q 3. Switch Q Each of the four includes a body diode and a corresponding parasitic capacitance, which converts DC energy into a first square wave voltage and outputs it.

[0046] As an example, a switch Q 1. Switch Q 2. Switch Q 3. Switch Q The first terminal of 4 is the drain, and the switch... Q 1. Switch Q 2. Switch Q3. Switch Q The second end of 4 is the source.

[0047] As an example, please continue reading Figure 2 The isolation conversion module 12 includes: a transformer. T r ,inductance L k The inductor L k The first end is connected to the switch Q 2. Second terminal and switch Q 3. The connection point A of the first end, inductor L k The second end is connected to the transformer T r The first end of the primary winding, transformer T r A capacitor is connected to the second end of the primary winding. C in1 With capacitor C in2 The connection midpoint B, transformer T r The first end of the secondary winding is connected to the first input end of the second secondary winding conversion module 14, and the transformer... T r The second end of the secondary winding is connected to the second input end of the second secondary winding conversion module 14.

[0048] As an example, inductor L k This is leakage inductance. Current flows through the inductor. L k The primary current is i p .

[0049] As an example, please continue reading Figure 2 The first secondary-side conversion module 13 includes: a switch Q 5. Switch Q 6. Switch Q 7. Switch Q 8, the switch Q The first end of 5 is connected to a switch. Q The first end of 6, switch Q The second end of 5 is connected to a switch. Q 7's first terminal and transformer T r The first end of the secondary winding, switch Q The second end of 7 is connected to a switch. Q The second end of 8, switch Q The second end of 6 is connected to a switch. Q 8's first terminal and transformerT r The second end of the secondary winding; switch Q The first terminal of 6 is the first output terminal of the first secondary-side conversion module 13, and the switch... Q The second end of 8 is the second output end of the first secondary side transformation module 13.

[0050] As an example, a switch Q 5. Switch Q 6. Switch Q 7. Switch Q 8 form a synchronous rectifier to obtain the second square wave voltage.

[0051] As an example, a switch Q 5. Switch Q 6. Switch Q 7. Switch Q Each of the 8 includes a body diode and its corresponding parasitic capacitance.

[0052] As an example, a switch Q 5. Switch Q 6. Switch Q 7. Switch Q The first terminal of 8 is the drain, and the switch... Q 5. Switch Q 6. Switch Q 7. Switch Q The second end of 8 is the source.

[0053] As an example, please continue reading Figure 2 The isolated three-level soft-switching buck-boost converter also includes: capacitors. Q f ,capacitance C f The first end is connected to the switch Q R1 First terminal and output voltage V o The first terminal, capacitor C f The second end is connected to a switch Q R2 The second terminal and output voltage V o The second end.

[0054] As an example, capacitor C f This is a filter capacitor.

[0055] As an example, the primary-side conversion module 11 may include: a diode-type midpoint clamping three-level circuit structure, a flying capacitor-type midpoint clamping three-level circuit structure, or an active midpoint clamping three-level circuit structure, etc., and is not limited to the cases proposed in this application.

[0056] As an example, the first secondary-side conversion module 13 may include a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a half-wave rectifier circuit structure, etc., and is not limited to the cases proposed in this application.

[0057] The following will continue to combine Figure 2 This paper describes the working principle of this application.

[0058] By configuring the primary-side transformation module 11 as a three-level circuit structure, the switch... Q 1 and switch Q4 are controlled by pulse width modulation. Q Switch 1 has the same duty cycle as switch Q4 but is 180° out of phase. Q 2 and switch Q 3. The switch conducts during both the positive and negative half-cycles. Q 2 and switch Q 3. In a complementary conduction state, the isolated three-level soft-switching buck-boost converter operates identically in both the positive and negative half-cycles. When only the switch... Q 2 or switch Q 3. When conducting, the clamping diode D c1 , D c2 Synergistic effect, switching Q 1- Q 2- Q The potential clamping at the midpoint A of the 3-Q4 bridge arm is at the input voltage. V in This reduces the voltage oscillation at the midpoint of the bridge arm by half, thereby outputting a stable three-level voltage. This effectively suppresses voltage oscillation at the midpoint of the bridge arm, significantly reduces the voltage stress on the power switch under high input voltage conditions, improves the efficiency and reliability of the isolated three-level soft-switching buck-boost converter, and realizes the three-level operating mode of the primary-side conversion module 11.

[0059] Furthermore, set a switch. Q R1 With switch Q R2 This enables the isolated three-level soft-switching buck-boost converter to have buck-boost characteristics. This is achieved by setting the switch... Q R1 With switch Q R2 Complementary conduction, precise control of primary-side switch and switching Q R1 and switch Q R2 Adjust the switch according to the activation time. Q R1 and switch Q R2The phase difference with the primary-side switch modulates the primary-side current. i p With secondary inductor current i Lc Waveform, minimizing secondary inductor current i Lc The pulsation and RMS value are adjusted to improve switching frequency and power density. Simultaneously, this is combined with adjustments to the switching... Q R1 At the turn-off time, all switches can be turned on at zero voltage across the entire input, output, and load range at a constant switching frequency.

[0060] The following will continue to combine Figures 3 to 11 This paper describes the operation of the isolated three-level soft-switching buck-boost converter proposed in this application. Figures 3 to 11 for Figure 2 The diagram shows the operating modes of an isolated three-level soft-switching buck-boost converter, where the primary current... i p Path and secondary inductor current i Lc The paths are highlighted in red.

[0061] Please see Figure 3 , Figure 3 This is a schematic diagram of the first operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 1, t During the 2] time period, the isolated three-level soft-switching buck-boost converter is in the first operating mode, and the switch... Q 1. Switch Q 2. Switch Q 5. Switch Q 8 and switches Q R2 Simultaneously, the circuit is activated. At this time, the voltage at point AB is... V in / 2, the amplitude of the output voltage of the first secondary-side conversion module 13 is V in / 2 N ,in N For transformer T r Turns ratio, switch Q R1 and switch Q R2 The midpoint potential is 0. At this time, the voltage applied to the inductor is 0. L c The voltage across the two ends is V in / 2 N Secondary inductor current i Lc Linear increase, primary side currenti p This is the value of the secondary current referred back to the primary side.

[0062] Please see Figure 4 , Figure 4 This is a schematic diagram of the second operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 2, t During the time interval [3], the isolated three-level soft-switching buck-boost converter is in the second operating mode. t At time 2, turn off the switch. Q R2 Secondary inductor current i Lc Give the switch Q R2 The output capacitor is charged, supplying power to the switch. Q R1 The output capacitor discharges. At this time, the switch... Q R1 and switch Q R2 The midpoint potential rises. t At time 3, switch Q R1 and switch Q R2 Midpoint potential rises to V o ,switch Q R1 The parasitic diode naturally conducts, at which point the switch is turned on. Q R1 This enables the switching on and off mechanism. Q R1 Zero-voltage turn-on.

[0063] Please see Figure 5 , Figure 5 This is a schematic diagram of the third operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 3, t During the 4] time period, the isolated three-level soft-switching buck-boost converter is in the third operating mode. t At time 3, switch Q R1 When turned on, the inductor L c The voltage across the two ends is V in / 2 N−V o ,when V in / 2 N > V o At that time, the secondary inductor currenti Lc Linear increase; when V in / 2 N < V o At that time, the secondary inductor current i Lc Linear decrease.

[0064] Please see Figure 6 , Figure 6 This is a schematic diagram of the fourth operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 4, t During the time interval [5], the isolated three-level soft-switching buck-boost converter is in the fourth operating mode. t At time 4, turn off the switch. Q 1. Primary current i p Give the switch Q The output capacitor of 1 supplies power to the switch. Q 3 and switch Q The output capacitor of 4 discharges. Note that the switch... Q 3 and switch Q The output capacitor of 4 is connected in series with the switch. Q The output capacitors of 1 are connected in parallel. Therefore, when the switch... Q The voltage across the output capacitor of 1 is charged to V in When / 2, the potential at point A is V in / 2, Switch Q 3 and switch Q 4. Output capacitor voltage divider, switch Q 3 and switch Q The potentials across the output capacitor of 4 are respectively V in / 4. For the secondary side of an isolated three-level soft-switching buck-boost converter, in this operating mode, the secondary inductor current... i Lc Simultaneously give the switch Q 6 and switch Q The output capacitor of module 7 discharges, and the output voltage of the first secondary-side converter module 13... V rect decline.

[0065] Please see Figure 7 , Figure 7 This is a schematic diagram of the fifth operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 5, tDuring the time period of 6], the isolated three-level soft-switching buck-boost converter is in the fifth operating mode. t At time 5, the potential at point A drops to V in / 2, the voltage at point AB is 0, clamping diode D c1 Natural conduction clamps the potential at point A. Due to the transformer... T r The leakage inductance is usually much smaller than the secondary inductance. L c The output voltage of the first secondary-side conversion module 13 V rect Approximately 0, applied to the inductor L c The voltage across the two ends is − V o Secondary inductor current i Lc Linear decrease, primary current i p Secondary inductor current i Lc The current value is converted to the original transformer.

[0066] Please see Figure 8 , Figure 8 This is a schematic diagram of the sixth operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 6, t During the time period of 7], the isolated three-level soft-switching buck-boost converter is in the sixth operating mode. t At time 6, the secondary inductor current i Lc Descending to I ZVS / N Because at this time the output voltage of the first secondary-side conversion module 13 is... V rect Approximately 0, therefore, in t 6-hour switch on Q 6 and switch Q 7 can approximately achieve zero-voltage turn-on of the switch of the first secondary-side conversion module 13. Afterwards, the output voltage of the first secondary-side conversion module 13... V rect The value is 0. At this point, since the voltage at point AB is also clamped to 0, the leakage inductance... L k The voltage across the terminals is 0, and the primary current is... i p It remains unchanged.

[0067] Please see Figure 9 , Figure 9This is a schematic diagram of the seventh operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [ t 7, t During the time period [8], the isolated three-level soft-switching buck-boost converter is in the seventh operating mode. t At time 7, the secondary inductor current i Lc Descending to − I ZVS Turn off the switch Q R1 Secondary inductor current i Lc switch Q R1 The output capacitor is charged, supplying power to the switch. Q R2 The output capacitor discharges, and the switch... Q R1 and switch Q R2 The midpoint voltage drops. When the switch... Q R1 and switch Q R2 When the midpoint voltage drops to 0, the switch Q R2 The parasitic diode naturally conducts, at which point the switch is turned on. Q R2 This allows all switches to be turned on at zero voltage.

[0068] Please see Figure 10 , Figure 10 This is a schematic diagram of the eighth operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 8, t During the time period [9], the isolated three-level soft-switching buck-boost converter is in the eighth operating mode. t At 8 o'clock, turn on the switch. Q R2 At this time, the inductor L c The voltage across the terminals is also 0, and the secondary inductor current... i Lc Maintain at - I ZVS constant.

[0069] Please see Figure 11 , Figure 11 This is a schematic diagram of the ninth operating mode of the isolated three-level soft-switching buck-boost converter proposed in this application. [In [ t 9, t 10 During the specified time, the isolated three-level soft-switching buck-boost converter is in its ninth operating mode.t At 9 o'clock, turn off the switch. Q 2. Switch Q 5 and switches Q 8. Primary current supplies to the switch Q The output capacitor of 2 is charged to power the switch. Q 3 and switch Q 4. Output capacitor discharge: For the secondary side of an isolated three-level soft-switching buck-boost converter, in this operating mode, the secondary inductor current... i Lc Simultaneously give the switch Q 5 and switches Q The output capacitor of module 8 is charged, and the output voltage of the first secondary-side converter module 13 is increased. V rect Ascend. Note that the switch should be turned on at this time. Q 3 and switch Q The output capacitor of 4 is connected in series with the switch. Q The output capacitors of unit 2 are connected in parallel. During this process, the clamping diode... D c1 Always maintain clamp position. Therefore, when the switch... Q The voltage across the output capacitor of 2 is charged to... V in When the voltage drops to 2, the potential at point A decreases to 0. (Switch) Q 3 and switch Q The diode at position 4 will conduct naturally, and then the switch will be turned on. Q 3 and switch Q 4. It can achieve zero-voltage switching of all switches.

[0070] Furthermore, t 10 After a certain time, the isolated three-level soft-switching buck-boost converter enters the negative half-cycle, and its operation is the same as that of the positive half-cycle, which will not be described in detail here.

[0071] As an example, all switches of the isolated three-level soft-switching buck-boost converter can achieve zero-voltage switching in all operating modes and load ranges.

[0072] In a specific embodiment of this application, to further illustrate the superiority of the control method proposed by the present invention, a simulation example of the present invention is given below.

[0073] Based on the parameters of the 60 kW isolated three-level soft-switching buck-boost converter with rated output power given in Table 1, a simulation circuit was built using Saber simulation software. Figure 12 Simulation waveforms of an isolated three-level soft-switching buck-boost converter at rated output power are presented. Figure 12Figure (a) shows the voltage V at points AB of an isolated three-level soft-switching buck-boost converter. AB Simulation waveform at rated output power. Figure 12 Figure (b) shows the primary current of an isolated three-level soft-switching buck-boost converter. i p Simulation waveform at rated output power. Figure 12 Figure (c) shows the output voltage of the first secondary-side converter module 13 of the isolated three-level soft-switching buck-boost converter. V rect Simulation waveform at rated output power. Figure 12 Figure (d) shows the secondary inductor current of an isolated three-level soft-switching buck-boost converter. i Lc The simulation waveform at rated output power, with time t being 40 microseconds ( μ As can be seen from the s / division, all switches can achieve zero-voltage turn-on and the secondary inductor current is... i Lc The pulsation is relatively small.

[0074] Table 1. Main Parameters of Isolated Three-Level Soft-Switching Buck-Boost Converter

[0075] The isolated three-level soft-switching buck-boost converter proposed in this application, by adding a switch... Q R1 and switch Q R2 The isolated three-level soft-switching buck-boost converter features buck-boost characteristics, increasing control flexibility and enabling optimized control. This can be achieved by adjusting the switches. Q R1 and switch Q R2 The phase difference with the primary-side switch modulates the secondary-side inductor current. i Lc The waveform causes the secondary inductor current to... i Lc The reduced pulsation allows for increased switching frequency and power density. Simultaneously, this is combined with adjustments to the switching... Q R1 At the turn-off time, all switches can be turned on at zero voltage across the entire input, output, and load range at a constant switching frequency.

[0076] Although this application has been disclosed above with reference to embodiments, it is not intended to limit this application. Anyone skilled in the art may make some modifications and refinements without departing from the spirit and scope of this application. Therefore, the scope of protection of this application shall be determined by the appended claims.

Claims

1. An isolated three-level soft-switching buck-boost converter, characterized in that, include, The primary-side conversion module receives the input voltage, divides and transforms the input voltage, and converts the DC energy into a first square wave voltage and outputs it. An isolation transformation module receives the first square wave voltage output by the primary-side transformation module, and outputs a high-frequency voltage after electrical isolation and transformation. The first secondary-side conversion module receives the high-frequency voltage output by the isolation conversion module, performs high-frequency pulse conversion, and outputs a second square wave voltage. The second secondary-side conversion module receives the second square wave voltage output from the first secondary-side conversion module, rectifies and modulates it to obtain the third square wave voltage, and outputs a stable output voltage after filtering. The second secondary-side conversion module includes: a first switch, a first terminal of the first switch connected to a first terminal of the output voltage, a second terminal of the first switch connected to a first terminal of a second switch and a first terminal of a first inductor, a second terminal of the first inductor connected to a first output terminal of the first secondary-side conversion module, and a second terminal of the second switch connected to a second terminal of the output voltage and a second output terminal of the first secondary-side conversion module.

2. The isolated three-level soft-switching buck-boost converter as described in claim 1, characterized in that, The first switch and the second switch are complementary and conduct, modulating the first inductor current into a quadrilateral waveform. When the first inductor current drops to the minimum negative current to achieve soft switching, the first switch is turned off.

3. The isolated three-level soft-switching buck-boost converter as described in claim 2, characterized in that, Both the first switch and the second switch include a body diode and a corresponding parasitic capacitance. The first terminal of the first switch and the second switch is the drain, and the second terminal of the first switch and the second switch is the source.

4. The isolated three-level soft-switching buck-boost converter as described in claim 2, characterized in that, The original-edge transformation module includes: A first capacitor, with its first terminal connected to the first terminal of the input voltage; its second terminal connected to the first terminal of a second capacitor; the second terminal of the second capacitor connected to the second terminal of the input voltage; a third switch, with its first terminal connected to the first terminal of the first capacitor; the second terminal of the third switch connected to the first terminal of a fourth switch; the second terminal of the fourth switch connected to the first terminal of a fifth switch; the second terminal of the fifth switch connected to the first terminal of a sixth switch; and the second terminal of the sixth switch connected to the second terminal of the second capacitor; a first diode, with its first terminal connected to the second terminal of the third switch and the first terminal of the fourth switch; the second terminal of the first diode connected to the first terminal of the second diode and the midpoint between the first and second capacitors; and the second terminal of the second diode connected to the second terminal of the fifth switch and the first terminal of the sixth switch; wherein the first terminals of the first and second diodes are cathodes, and the second terminals of the first and second diodes are anodes. The third, fourth, fifth, and sixth switches each include a body diode and a corresponding parasitic capacitance. The first terminal of the third, fourth, fifth, and sixth switches is the drain, and the second terminal of the third, fourth, fifth, and sixth switches is the source.

5. The isolated three-level soft-switching buck-boost converter as described in claim 4, characterized in that, The third switch and the sixth switch have the same duty cycle and are 180° out of phase; the fourth switch and the fifth switch are turned on during the positive half-cycle and the negative half-cycle, respectively.

6. The isolated three-level soft-switching buck-boost converter as described in claim 4, characterized in that, The first capacitor and the second capacitor are voltage divider capacitors.

7. The isolated three-level soft-switching buck-boost converter as described in claim 4, characterized in that, The isolation conversion module includes: a second inductor, the first end of which is connected to the midpoint of the connection between the second end of the fourth switch and the first end of the fifth switch, the second end of which is connected to the first end of the primary winding of the transformer, the second end of which is connected to the midpoint of the connection between the first capacitor and the second capacitor, the first end of the secondary winding of the transformer being connected to the first input terminal of the second secondary conversion module, and the second end of the secondary winding of the transformer being connected to the second input terminal of the second secondary conversion module.

8. The isolated three-level soft-switching buck-boost converter as described in claim 7, characterized in that, The first secondary-side conversion module includes: an eighth switch, the first end of which is connected to the first end of a ninth switch, the second end of which is connected to the first end of a tenth switch and the first end of the transformer secondary winding, the second end of the tenth switch being connected to the second end of an eleventh switch, and the second end of the ninth switch being connected to the first end of the eleventh switch and the second end of the transformer secondary winding; the first end of the ninth switch is the first output end of the first secondary-side conversion module, and the second end of the eleventh switch is the second output end of the first secondary-side conversion module; The eighth, ninth, tenth, and eleventh switches each include a body diode and a corresponding parasitic capacitance; the first terminal of the eighth, ninth, tenth, and eleventh switches is the drain, and the second terminal of the eighth, ninth, tenth, and eleventh switches is the source.

9. The isolated three-level soft-switching buck-boost converter as described in claim 1, characterized in that, The primary-side conversion module can be any of the following: a diode-type midpoint clamping three-level circuit structure, a flying capacitor-type midpoint clamping three-level circuit structure, or an active midpoint clamping three-level circuit structure.

10. The isolated three-level soft-switching buck-boost converter as described in claim 1, characterized in that, The first secondary-side conversion module can be any of a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a half-wave rectifier circuit structure.

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