Full-bridge three-level resonant converter

Abstract

The invention discloses a full-bridge three-level resonant converter, which comprises an input power supply, a three-level switching circuit, a resonant circuit, a transformer and an output feedback circuit, the input power supply is connected with the three-level switch circuit; one end of the resonance circuit is connected with a first alternating current terminal of the three-level switch circuit, and the other end of the resonance circuit is connected with a second alternating current terminal of the three-level switch circuit; the resonance circuit is connected with a primary winding of the transformer; the output feedback circuit comprises a first switch tube and a second switch tube, the first switch tube and the second switch tube are connected in series, and the first switch tube and the second switch tube are respectively connected with a secondary winding of the transformer. High-frequency smooth waveforms are generated through the three-level switching circuit and the resonance circuit, boosting or reducing of input voltage is achieved, control is conducted through the output feedback circuit, and the stability and precision of output voltage are guaranteed; an output rectifier diode of the output feedback circuit is changed into a first switching tube and a second switching tube, so that the efficiency can be improved by reducing voltage drop.

Description

Technical Field

[0001] The present invention relates to the technical field of resonant converters, and in particular to a full-bridge three-level resonant converter. Background Art

[0002] Inductor-Inductor-Capacitor (LLC) resonant converter has the advantages of low switching loss and high efficiency because the primary side switch tube can realize (Zero Voltage Switch, ZVS) soft switching and the secondary side rectifier tube can realize (Zero Current Switch, ZCS) soft switching. Therefore, LLC is widely used in DC-DC conversion circuits.

[0003] The LLC resonant converter achieves output voltage control by adjusting the switching frequency and changes the output voltage gain by frequency modulation. When a wide output voltage range is required, the resonant converter operates in a very wide frequency range. Especially when the required output voltage gain is small, the operating frequency will be much greater than the resonant frequency. At this time, the switching loss of the primary switch tube increases and the secondary rectifier tube is lost, resulting in reduced system efficiency. Summary of the invention

[0004] The main purpose of the present invention is to propose a full-bridge three-level resonant converter, aiming to solve the problem of reduced converter efficiency.

[0005] To achieve the above object, the present invention proposes a full-bridge three-level resonant converter, comprising an input power supply, a three-level switching circuit, a resonant circuit, a transformer, and an output feedback circuit;

[0006] The input power supply is connected to the three-level switch circuit;

[0007] One end of the resonant circuit is connected to the first AC terminal of the three-level switch circuit, and the other end of the resonant circuit is connected to the second AC terminal of the three-level switch circuit;

[0008] The resonant circuit is connected to the primary winding of the transformer;

[0009] The output feedback circuit includes a first switch tube and a second switch tube, the first switch tube and the second switch tube are connected in series, and the first switch tube and the second switch tube are respectively connected to the secondary winding of the transformer.

[0010] In one embodiment, the three-level switching circuit also includes a voltage divider circuit, which includes a first capacitor and a second capacitor, the first capacitor and the second capacitor are connected in series, the voltage divider circuit is connected at both ends of the input power supply, and the midpoint of the voltage divider circuit is connected to the clamping midpoint of the three-level switching circuit.

[0011] In one embodiment, the output feedback circuit includes a first inductor, a second inductor, a third capacitor, and an output load;

[0012] One end of the first inductor is connected to the drain of the first switch tube, and the other end of the first inductor is connected to the third capacitor and the output load;

[0013] The third capacitor is connected in parallel with the output load, and one end of the second inductor is connected to the drain of the second switch tube.

[0014] In one embodiment, the resonant circuit includes a third inductor and a fourth capacitor, two ends of the third inductor are respectively connected to the two ends of the primary winding of the transformer, one end of the fourth capacitor is connected to the second AC terminal, and the other end of the fourth capacitor is connected to the third inductor and the opposite end of the primary winding of the transformer.

[0015] In one embodiment, the three-level switching circuit includes a third switching tube, a fifth capacitor, a first diode, a fourth switching tube, a sixth capacitor, and a second diode. The source of the third switching tube, one end of the fifth capacitor, the positive electrode of the first diode, the drain of the fourth switching tube, one end of the sixth capacitor, and the negative electrode of the second diode are connected to the first AC terminal.

[0016] In one embodiment, the three-level switching circuit includes a fifth switching tube, a seventh capacitor, a third diode, a sixth switching tube, an eighth capacitor, and a fourth diode, and the source of the fifth switching tube, one end of the seventh capacitor, the anode of the third diode, the drain of the sixth switching tube, one end of the eighth capacitor, and the cathode of the fourth diode are connected to the second AC terminal.

[0017] In one embodiment, the full-bridge three-level resonant converter further includes a clamping circuit, and the clamping circuit is connected to the voltage divider circuit and the three-level switch circuit.

[0018] In one embodiment, the clamping circuit includes a fifth diode and a sixth diode, and an anode of the fifth diode is connected to a cathode of the sixth diode.

[0019] In one embodiment, a midpoint of the clamping circuit is connected to a midpoint of the voltage divider circuit.

[0020] In one embodiment, the full-bridge three-level resonant converter further includes a ninth capacitor, and the ninth capacitor is connected in parallel with the clamping circuit.

[0021] The present invention generates a high-frequency smooth waveform through a three-level switch circuit and a resonant circuit to achieve boosting or bucking of the input voltage, and controls it through an output feedback circuit to ensure the stability and accuracy of the output voltage. The output rectifier diode of the output feedback circuit is replaced by a first switch tube and a second switch tube to reduce the voltage drop and improve efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0023] Figure 1 It is the module schematic diagram of the full-bridge three-level resonant converter;

[0024] Figure 2 is a circuit diagram of a full-bridge three-level resonant converter;

[0025] Figure 3 It is the main waveform diagram of the full-bridge three-level resonant converter using the control strategy of chopping plus phase shifting;

[0026] Figure 4 is the equivalent circuit of switching mode 0;

[0027] Figure 5 is the equivalent circuit of switching mode 1;

[0028] Figure 6 is the equivalent circuit of switching mode 2;

[0029] Figure 7 is the equivalent circuit of switching mode 3;

[0030] Figure 8 is the equivalent circuit of switching mode 4;

[0031] Fig. 9 is the equivalent circuit of switching mode 5;

[0032] Fig.10 is the equivalent circuit of switching mode 6;

[0033] Fig.11 It is the equivalent circuit of switching mode 7.

[0034] Description of Figure Numbers:

[0035] 1-input power supply, 2-three-level switching circuit, 3-resonant circuit, T1-transformer, 4-output feedback circuit, A-first AC terminal, B-second AC terminal, QS1-first switch tube, QS2-second switch tube, Q1-seventh switch tube, Q4-eighth switch tube, Q5-ninth switch tube, Q8-tenth switch tube, Q2-third switch tube, Q3-fourth switch tube, Q6-fifth switch tube, Q7-sixth switch tube, 5-voltage divider circuit, Cd1-first capacitor, Cd2-second capacitor, Css1-ninth capacitor, Css2-fourteenth capacitor, Lr1-first inductor, Lr2 -second inductor, Lm-third inductor, Cr-fourth capacitor, C2-fifth capacitor, C3-sixth capacitor, C6-seventh capacitor, C7-eighth capacitor, C1-tenth capacitor, C4-eleventh capacitor, C5-twelfth capacitor, C8-thirteenth capacitor, Cf-third capacitor, Vo-voltage source, Lr1-first inductor, Lr2-second inductor, R-output load, D2-first diode, D3-second diode, D6-third diode, Q7-sixth switch tube, D7-fourth diode, 6-clamping circuit, D9-fifth diode, D10-sixth diode, D4-eighth diode.

[0036] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0039] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if the meaning of "and / or" appearing in the full text is to include three parallel schemes, taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0040] like Figure 1 As shown, Figure 1 The module schematic diagram of the full-bridge three-level resonant converter is shown in FIG. 1 . The present invention provides a full-bridge three-level resonant converter, comprising an input power supply 1, a three-level switch circuit 2, a resonant circuit 3, a transformer T1, and an output feedback circuit 4;

[0041] The input power supply 1 is connected to the three-level switch circuit 2;

[0042] One end of the resonant circuit 3 is connected to the first AC terminal A of the three-level switch circuit 2, and the other end of the resonant circuit 3 is connected to the second AC terminal B of the three-level switch circuit 2;

[0043] The resonant circuit 3 is connected to the primary winding of the transformer T1;

[0044] The output feedback circuit 4 includes a first switch tube QS1 and a second switch tube QS2. The first switch tube QS1 and the second switch tube QS2 are connected in series. The first switch tube QS1 and the second switch tube QS2 are respectively connected to the secondary winding of the transformer T1.

[0045] In the embodiment of the present invention, Figure 1 As shown, the three-level switching circuit 2 and the resonant circuit 3 of the full-bridge three-level resonant converter generate a high-frequency smooth waveform to achieve a boost or buck of the input voltage, and are controlled by the output feedback circuit 4 to ensure the stability and accuracy of the output voltage. The output rectifier diode of the output feedback circuit 4 is replaced by the first switch tube QS1 and the second switch tube QS2 to reduce the voltage drop and improve the efficiency.

[0046] The transformer T1 only needs to transmit approximately half of the output current to the output feedback circuit 4, so that the structure of the transformer T1 is simple. The output rectifier uses the first switch tube QS1 and the second switch tube QS2, which reduces the number of output rectifier tubes. In this embodiment, the first switch tube QS1 and the second switch tube QS2 are MOS tubes.

[0047] like Figure 2 As shown, Figure 2 : is a circuit diagram of a full-bridge three-level resonant converter. The three-level switch circuit 2 further includes a seventh switch tube Q1, an eighth switch tube Q4, a ninth switch tube Q5, and a tenth switch tube Q8. The main waveform diagram of the full-bridge three-level resonant converter using the chopping plus phase shift control strategy is as follows: Figure 3 As shown, the seventh switch tube Q1 and the eighth switch tube Q4 are in phase with the third switch tube Q2 and the fourth switch tube Q3 respectively and work synchronously under PWM control. The seventh switch tube Q1 and the eighth switch tube Q4, the third switch tube Q2 and the fourth switch tube Q3 are complementary, and are turned on alternately with each other during operation, and the conduction time differs by 180°. The ninth switch tube Q5 and the fifth switch tube Q6, the sixth switch tube Q7 and the tenth switch tube Q8 are complementary, and are turned on alternately with each other during operation, and the conduction time differs by 180°. The third switch tube Q2 leads the sixth switch tube Q7 and the tenth switch tube Q8 by a certain phase angle and works in phase shift. The third switch tube Q2 also leads the ninth switch tube Q5 and the fifth switch tube Q6 by the same phase angle and works in phase shift. The seventh switch tube Q1 and the eighth switch tube Q4 are defined as chopper tubes, the third switch tube Q2 and the fourth switch tube Q3 are leading tubes, the ninth switch tube Q5 and the fifth switch tube Q6, the sixth switch tube Q7 and the tenth switch tube Q8 are lagging tubes. When the input voltage does not change much, the output voltage can be adjusted by adjusting the duty ratio of the seventh switch tube Q1 and the eighth switch tube Q4. As the input voltage increases, the duty ratio of the seventh switch tube Q1 and the eighth switch tube Q4 decreases to zero. At this time, the third switch tube Q2 and the fourth switch tube Q3 can be phase-shifted relative to the sixth switch tube Q7 and the tenth switch tube Q8, the ninth switch tube Q5 and the fifth switch tube Q6, respectively. By adjusting their phase angles, the output voltage can be adjusted.

[0048] The three-level switch circuit 2 also includes a voltage divider circuit 5, which includes a first capacitor Cd1 and a second capacitor Cd2. The first capacitor Cd1 and the second capacitor Cd2 are connected in series. The voltage divider circuit 5 is connected to both ends of the input power supply 1, and the midpoint of the voltage divider circuit 5 is connected to the clamping midpoint of the three-level switch circuit 2.

[0049] In the three-level switch circuit 2, the clamping action refers to limiting the voltage fluctuation range by some means so that the output voltage is kept within a certain stable range. The midpoint of the voltage divider circuit 5 is usually used to provide a reference voltage or reference potential, which helps to adjust and stabilize the output voltage. By connecting the midpoint of the voltage divider circuit 5 to the clamping midpoint of the three-level switch circuit 2, it can be ensured that the circuit operates at the desired voltage level to avoid damage to the circuit components caused by excessively high or low voltages; the three-level switch circuit 2 is usually used to achieve multi-level voltage output to reduce harmonic distortion of the output waveform. The midpoint of the voltage divider circuit 5 is connected to the clamping midpoint of the three-level switch circuit 2, which can help balance the current between the various levels and ensure that the current distribution of the system is reasonable, thereby improving the efficiency and stability of the circuit; in the three-level switch circuit 2, if the midpoint is correctly connected and clamped, it can reduce transient voltage and current fluctuations caused by improper switch operation, thereby reducing switching losses and other unnecessary energy losses, and improving the overall efficiency of the system.

[0050] Figure 2 : It is a circuit diagram of a full-bridge three-level resonant converter, the three-level switch circuit 2 includes two three-level bridge arms, the two three-level bridge arms include a first capacitor Cd1 and a second capacitor Cd2 as input voltage-dividing capacitors, D9-D12 as freewheeling diodes, a ninth capacitor Css1 and a fourteenth capacitor Css2 as flying capacitors, the secondary side of the transformer T1 is an output feedback circuit 4 of synchronous current-doubling rectification, the resonant circuit 3 includes a resonant inductor calculated to the secondary side: a first inductor Lr1 and a second inductor Lr2 (including the primary leakage inductance of the transformer T1), a third inductor Lm is the excitation inductance of the transformer T1 (that is, the primary inductance of the transformer T1), and a fourth capacitor Cr is a resonant capacitor, which is connected in series in the main circuit and also plays a role of direct current isolation.

[0051] In this embodiment, the working principle of the full-bridge three-level resonant converter is analyzed with the following assumptions:

[0052] 1. All components used are ideal components.

[0053] 2. The fifth capacitor C2, the sixth capacitor C3, the seventh capacitor C6, the eighth capacitor C7, the tenth capacitor C1, the eleventh capacitor C4, the twelfth capacitor C5, and the thirteenth capacitor C8 are all equal.

[0054] 3. The first capacitor Cd1 and the second capacitor Cd2 are large enough and equal, and they evenly divide the input voltage, which is equivalent to two voltage sources of Vin / 2.

[0055] 4. The ninth capacitor Css1 and the fourteenth capacitor Css2 of the flying capacitor are large enough, and their voltages remain basically unchanged, which is Vin / 2.

[0056] 5. The third capacitor Cf of the output filter capacitor is large enough to be approximately equivalent to a voltage source Vo (Vo is the output voltage).

[0057] The output feedback circuit 4 includes a first inductor Lr1, a second inductor Lr2, a third capacitor Cf, and an output load R; one end of the first inductor Lr1 is connected to the drain of the first switch tube QS1, and the other end of the first inductor Lr1 is connected to the third capacitor Cf and the output load R; the third capacitor Cf is connected to the output load R in parallel, and one end of the second inductor Lr2 is connected to the drain of the second switch tube QS2.

[0058] The first inductor Lr1 plays the role of filtering, energy storage and current limiting. During the switching process of the first switch tube QS1, the first inductor Lr1 can prevent current mutations and reduce current fluctuations by hindering current changes, thereby ensuring the stability of current and voltage; the third capacitor Cf can store and release charges, provide smooth voltage output, reduce voltage fluctuations caused by the switching of the first switch tube QS1, and prevent excessive voltage fluctuations in the output load R; the second inductor Lr2 is used to adjust the current waveform, reduce high-frequency noise in the power supply, and improve the efficiency and stability of the circuit; the output load R is usually the final load device (such as a motor, a power module, etc.), which needs to obtain a smooth and stable voltage or current from the circuit. The third capacitor Cf and the first inductor Lr1 ensure that the load end can obtain appropriate current and voltage by smoothing the voltage and reducing current fluctuations, and prevent the load from being affected by unstable voltage.

[0059] The resonant circuit 3 includes a third inductor Lm and a fourth capacitor Cr, wherein two ends of the third inductor Lm are respectively connected to two ends of the primary winding of the transformer T1, one end of the fourth capacitor Cr is connected to the second AC terminal B, and the other end of the fourth capacitor Cr is connected to the third inductor Lm and the opposite end of the primary winding of the transformer T1. The third inductor Lm of the primary side is refracted to the secondary side to reduce loss and lower temperature.

[0060] The three-level switch circuit 2 includes a third switch tube Q2, a fifth capacitor C2, a first diode D2, a fourth switch tube Q3, a sixth capacitor C3, and a second diode D3. The source of the third switch tube Q2, one end of the fifth capacitor C2, the anode of the first diode D2, the drain of the fourth switch tube Q3, one end of the sixth capacitor C3, and the cathode of the second diode D3 are connected to the first AC terminal A. The three-level switch circuit 2 includes a fifth switch tube Q6, a seventh capacitor C6, a third diode D6, a sixth switch tube Q7, an eighth capacitor C7, and a fourth diode D7. The source of the fifth switch tube Q6, one end of the seventh capacitor C6, the anode of the third diode D6, the drain of the sixth switch tube Q7, one end of the eighth capacitor C7, and the cathode of the fourth diode D7 are connected to the second AC terminal B.

[0061] Each three-level bridge arm of the three-level switch circuit 2 can provide three different voltage levels at its output end, usually: +V_dc (positive voltage), 0V (zero voltage) and −V_dc (negative voltage).

[0062] When the two three-level bridge arms work together, they can provide a wider voltage adjustment range, so that the output voltage has three different levels. By adjusting the switching state of the three-level bridge arm, any of these voltage levels can be output; the three-level bridge arm circuit can generate an output waveform that is closer to a sine wave, which can effectively reduce high-frequency harmonic components compared to the two-level bridge arm (the waveform generated is usually a square wave); the output voltage is smoother, which helps to reduce electromagnetic interference and thermal damage to the load (such as motors, transformer T1, etc.), thereby improving the overall efficiency and reliability of the system; through the cooperation of the two three-level bridge arms, the circuit can provide a smoother and more accurate output voltage waveform, which helps to improve the power quality of the system; compared with the traditional two-level circuit, the three-level circuit can usually achieve a lower switching frequency, because each bridge arm will work at a lower switching frequency in each cycle, and through fewer switching operations, the switching loss (especially the hard switching loss) is reduced, thereby improving the efficiency of the system; in a three-phase system, two three-level bridge arms can control the output voltage of two phases respectively, or in more complex applications, multiple three-level bridge arms can work together to achieve more voltage level regulation.

[0063] The full-bridge three-level resonant converter further includes a clamping circuit 6, which is connected to the voltage divider circuit 5 and the three-level switch circuit 2. The clamping circuit 6 includes a fifth diode D9 and a sixth diode D10, and the anode of the fifth diode D9 is connected to the cathode of the sixth diode D10. The midpoint of the clamping circuit 6 is connected to the midpoint of the voltage divider circuit 5.

[0064] By connecting the midpoint of the clamp circuit 6 to the midpoint of the voltage divider circuit 5, the clamp circuit 6 can work when the output signal is too high or too low to limit the maximum and minimum voltages of the signal. This ensures that the subsequent circuit operates within a safe voltage range, thereby protecting the circuit from damage; the midpoint of the voltage divider circuit 5 provides a specific reference voltage, which can be used as a reference level when the clamp circuit 6 is working. By properly designing the voltage divider network, the voltage at its midpoint can be adjusted to an operating area suitable for the clamp circuit 6, providing a stable reference point for subsequent analysis or control; if a voltage signal needs to be adjusted to another required level, by connecting the midpoint of the clamp circuit 6 and the midpoint of the voltage divider circuit 5, level conversion can be performed between the two areas. This is very useful for level adaptation in analog signal processing or digital circuits; appropriate connection and configuration can improve the linearity and reduce distortion during signal transmission, thereby improving the performance of the overall circuit.

[0065] The full-bridge three-level resonant converter also includes a ninth capacitor Css1, which is connected in parallel with the clamping circuit 6. When the ninth capacitor Css1 is connected in parallel with the clamping circuit 6, the ninth capacitor Css1 can help smooth the input signal and reduce high-frequency noise. The clamping circuit 6 itself is used to limit the range of voltage to prevent the voltage from exceeding a certain threshold, while the ninth capacitor Css1 provides additional filtering in the circuit to suppress spikes or instantaneous fluctuations in the signal. Especially when processing AC signals or pulse signals, the capacitor can effectively filter out high-frequency noise. When the ninth capacitor Css1 is connected in parallel in the clamping circuit 6, it can provide an instantaneous charge reserve for the circuit. When the voltage changes suddenly (for example, a spike signal is generated), the ninth capacitor Css1 can quickly release or absorb charge to help stabilize the voltage and prevent excessive voltage fluctuations. For example, the clamping circuit 6 usually "clamps" the voltage within a certain range when the voltage exceeds a predetermined value, and the ninth capacitor Css1 connected in parallel can slow down the speed of voltage change to avoid the impact of instantaneous voltage jumps on the circuit.

[0066] The clamp circuit 6 itself may generate certain interference due to instantaneous voltage changes in some applications, especially in high-speed or pulse circuits. The ninth capacitor Css1 connected in parallel can better stabilize the circuit performance and ensure that the voltage will not fluctuate due to short-term interference, especially when the power supply or load is unstable.

[0067] The clamping circuit 6 and the ninth capacitor Css1 in parallel can work together to reduce noise and electromagnetic interference (EMI) caused by the switching action. The ninth capacitor Css1 helps to maintain voltage stability and reduce interference by absorbing or releasing high-frequency noise signals.

[0068] Sometimes the clamp circuit 6 itself is to protect the circuit from excessive voltage, especially in the case of instantaneous excessive voltage, the clamp circuit 6 will limit the voltage. However, if the excessive voltage is sudden (for example, due to electrical interference or power transient), the parallel capacitor can help the circuit consume the instantaneous electrical energy more quickly and reduce the damage to the circuit.

[0069] The ninth capacitor Css1 can also change the dynamic response characteristics of the clamp circuit 6. For example, the clamp circuit 6 may produce a certain delay or instability when the voltage changes, and the ninth capacitor Css1 connected in parallel can help the clamp circuit 6 respond to the voltage change more quickly and smoothly by providing additional charge reserve, thereby reducing the hysteresis effect of the clamp circuit 6.

[0070] Figure 3 It is the main waveform diagram of the full-bridge three-level resonant converter using the chopping plus phase shift control strategy. It gives the working waveform of half a cycle of the full-bridge three-level resonant converter in the three-level mode, which includes 7 switching modes. The equivalent circuit of each switching mode is shown below.

[0071] 1. Switching mode 0 (before t0), as shown in Figure 4, Figure 4 The equivalent circuit of the switching mode 0 is as follows: before t0, the ninth switch tube Q5, the fifth switch tube Q6, the seventh switch tube Q1 and the third switch tube Q2 are turned on, the voltage VAB between the first AC terminal A and the second AC terminal B is 0, the first switch tube QS1 and the second switch tube QS2 on the secondary side of the transformer T1 are turned off, and the output is disconnected from the primary side. The first inductor Lr1, the second inductor Lr2, the third inductor Lm and the fourth capacitor Cr resonate, and the resonant capacitor current iCr of the fourth capacitor Cr is equal to the current iLm of the third inductor Lm, and iLm at this time is the maximum current Im.

[0072] 2. Switching mode 1 (t0, t1) is shown in Figure 5. Figure 5 : is the equivalent circuit of the switching mode 1. At time t0, the zero-point voltage turns off the ninth switch tube Q5 and the fifth switch tube Q6. The resonant capacitor current iCr charges the twelfth capacitor C5 and the seventh capacitor C6. At the same time, the eighth capacitor C7 and the thirteenth capacitor C8 are discharged through the fourteenth capacitor Css2. The voltage VAB between the first AC terminal A and the second AC terminal B increases positively from zero. The resonant capacitor current iCr remains unchanged in this process and is still the maximum current Im. At time t1, the fourth diode D7 and the seventh diode D8 of the sixth switch tube Q7 and the tenth switch tube Q8 are turned on.

[0073] 3. Switching mode 2 (t1, t2) is shown in Figure 6. Figure 6This is the equivalent circuit of the switching mode 2. At time t1, since the body diodes of the sixth switch tube Q7 and the tenth switch tube Q8 are already turned on, the sixth switch tube Q7 and the tenth switch tube Q8 are turned on at zero voltage. At this time, VAB = input voltage Vin, the resonant capacitor current iCr> the current iLm of the third inductor Lm, the first switch tube QS1 is turned on, the voltage source voltage KVo is applied to the third inductor Lm, the current iLm of the third inductor Lm increases linearly, and the input voltage Vin-voltage source voltage KVo will be applied to the fourth capacitor Cr, so that the resonant capacitor current iCr increases in the form of a sine wave.

[0074] 4. Switching mode 3 (t2, t3) Figure 7 As shown, Figure 7 This is the equivalent circuit of switch mode 3. At time t2, the seventh switch tube Q1 is turned off, the resonant capacitor current iCr charges the tenth capacitor C1, and discharges the eleventh capacitor C4 through the ninth capacitor Css1. Due to the buffering effect of the tenth capacitor C1 and the eleventh capacitor C4, Q1 is turned off at approximately zero voltage. The first switch tube QS1 continues to be turned on, and the voltage source voltage KVo continues to act on the third inductor Lm, so the current iLm of the third inductor Lm continues to increase linearly in the equivalent circuit of switch mode 2.

[0075] 5. Switching mode 4 (t3, t4) Figure 8 As shown, Figure 8 This is the equivalent circuit of switching mode 4. At time t3, the voltage on the tenth capacitor C1 reaches Vin / 2, and the voltage on the eleventh capacitor C4 is zero. The fifth diode D9 is turned on, and Vin / 2-voltage source voltage KVo is added to the fourth capacitor Cr to make it resonate.

[0076] 6. Switching mode 5 (t4, t5) Fig. 9 As shown, Fig. 9 The equivalent circuit of the switching mode 5 is shown in FIG. 1 . Due to the sinusoidal drop of the resonant capacitor current iCr after reaching the maximum value and the linear increase of the current iLm of the third inductor Lm, at time t4, the resonant capacitor current iCr = the current iLm of the third inductor Lm, the first switch tube QS1 will be turned off, and the current iDR1 of the first inductor Lr1 will resonate to zero, thereby avoiding reverse recovery. At this moment, the reverse voltage of the first switch tube QS1 and the second switch tube QS2 is Vo, the secondary side of the transformer T1 is separated from the primary side of the transformer T1, the voltage VLm of the third inductor Lm is no longer limited by the output voltage, and the third inductor Lm re-participates in the resonance. Because the third inductor Lm is relatively large, the resonant capacitor current iCr and the current iLm of the third inductor Lm remain basically unchanged in the equivalent circuit of the switching mode 4 during this period.

[0077] 7. Switching mode 6 (t5, t6), such as Fig.10 As shown, Fig.10 This is the equivalent circuit of switching mode 6. At time t5, the third switch tube Q2 is turned off. While the resonant capacitor current iCr charges the fifth capacitor C2, the ninth capacitor Css1 discharges the sixth capacitor C3. Due to the buffering effect of the fifth capacitor C2 and the sixth capacitor C3, the third switch tube Q2 is turned off at approximately zero voltage. At time t6, the second diode D3 of the fourth switch tube Q3 will be turned on.

[0078] 8. Switching mode 7 (t6, t7), such as Fig.11 As shown, Fig.11 It is the equivalent circuit of switching mode 7. At time t6, the second diode D3 and the eighth diode D4 are turned on. Therefore, the fourth switch tube Q3 and the eighth switch tube Q4 can be turned on with zero voltage at this moment, and VAB=0. Because the third inductor Lm is relatively large, the resonant capacitor current iCr remains basically unchanged, and the maximum current Im still charges the fourth capacitor Cr, and the voltage Vcr of the fourth capacitor Cr will increase in the reverse direction.

[0079] At time t7, zero voltage turns off the sixth switch tube Q7 and the tenth switch tube Q8, and starts another half-cycle of work. Its working condition is similar to the above-mentioned switching mode. Similarly, since the two three-level bridge arms are completely symmetrical, the ninth switch tube Q5 and the tenth switch tube Q8 can also be defined as chopper tubes, the fifth switch tube Q6 and the sixth switch tube Q7 can be defined as leading tubes, and the seventh switch tube Q1, the third switch tube Q2, the fourth switch tube Q3 and the eighth switch tube Q4 can be defined as lagging tubes. The analysis is the same as the above-mentioned switching mode. When the full-bridge three-level resonant converter works in the phase shift state, that is, when the input voltage is large, the chopper tube is turned off, and the full-bridge three-level resonant converter works in the two-level state. Its working process is also the above process. At this time, the full-bridge three-level resonant converter is equivalent to the full-bridge resonant converter, but it also has the advantages of the three-level converter, solving the problem of difficulty in achieving zero voltage switching (ZVS) when light load.

[0080] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A full-bridge three-level resonant converter, characterized in that: It includes an input power supply, a three-level switching circuit, a resonant circuit, a transformer, and an output feedback circuit; The input power supply is connected to the three-level switch circuit; One end of the resonant circuit is connected to the first AC terminal of the three-level switch circuit, and the other end of the resonant circuit is connected to the second AC terminal of the three-level switch circuit; The resonant circuit is connected to the primary winding of the transformer; The output feedback circuit includes a first switch tube and a second switch tube, the first switch tube and the second switch tube are connected in series, and the first switch tube and the second switch tube are respectively connected to the secondary winding of the transformer.

2. The full-bridge three-level resonant converter according to claim 1, characterized in that: The three-level switch circuit also includes a voltage divider circuit, which includes a first capacitor and a second capacitor. The first capacitor and the second capacitor are connected in series. The voltage divider circuit is connected at both ends of the input power supply, and the midpoint of the voltage divider circuit is connected to the clamping midpoint of the three-level switch circuit.

3. The full-bridge three-level resonant converter according to claim 1, characterized in that: The output feedback circuit includes a first inductor, a second inductor, a third capacitor, and an output load; One end of the first inductor is connected to the drain of the first switch tube, and the other end of the first inductor is connected to the third capacitor and the output load; The third capacitor is connected in parallel with the output load, and one end of the second inductor is connected to the drain of the second switch tube.

4. The full-bridge three-level resonant converter according to claim 1, characterized in that: The resonant circuit includes a third inductor and a fourth capacitor, two ends of the third inductor are respectively connected to the two ends of the primary winding of the transformer, one end of the fourth capacitor is connected to the second AC terminal, and the other end of the fourth capacitor is connected to the third inductor and the opposite end of the primary winding of the transformer.

5. The full-bridge three-level resonant converter according to claim 1, characterized in that: The three-level switching circuit includes a third switching tube, a fifth capacitor, a first diode, a fourth switching tube, a sixth capacitor, and a second diode. The source of the third switching tube, one end of the fifth capacitor, the positive electrode of the first diode, the drain of the fourth switching tube, one end of the sixth capacitor, and the negative electrode of the second diode are connected to the first AC terminal.

6. The full-bridge three-level resonant converter according to claim 1, characterized in that: The three-level switching circuit includes a fifth switching tube, a seventh capacitor, a third diode, a sixth switching tube, an eighth capacitor, and a fourth diode. The source of the fifth switching tube, one end of the seventh capacitor, the anode of the third diode, the drain of the sixth switching tube, one end of the eighth capacitor, and the cathode of the fourth diode are connected to the second AC terminal.

7. The full-bridge three-level resonant converter according to claim 2, characterized in that: The full-bridge three-level resonant converter further includes a clamping circuit, and the clamping circuit is connected to the voltage divider circuit and the three-level switch circuit.

8. The full-bridge three-level resonant converter according to claim 7, characterized in that: The clamping circuit includes a fifth diode and a sixth diode, and an anode of the fifth diode is connected to a cathode of the sixth diode.

9. The full-bridge three-level resonant converter according to claim 8, characterized in that: The midpoint of the clamping circuit is connected to the midpoint of the voltage divider circuit.

10. The full-bridge three-level resonant converter according to claim 9, characterized in that: The full-bridge three-level resonant converter further includes a ninth capacitor, and the ninth capacitor is connected in parallel with the clamping circuit.

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