Asymmetric half-bridge LLC bidirectional DC-DC conversion circuit

Abstract

The invention provides an asymmetric half-bridge LLC bidirectional DC-DC conversion circuit which solves the problems that an existing conversion circuit is high in energy consumption and low in efficiency, meanwhile, the cost is high due to the fact that no elements are used, a primary side of the conversion circuit is an asymmetric half bridge, the asymmetric half bridge comprises a resonance network and a bidirectional switch, the bidirectional switch is composed of two MOS tubes with source electrodes connected oppositely, and the two MOS tubes are connected in series. The resonant network is connected between the transformer and the input cathode, the bidirectional switch is respectively connected in series with bridge arms connected with the transformer and the input cathode, and the secondary side of the conversion circuit is a bridge circuit. In the improved circuit, the asymmetric half-bridge is used for the primary side, and various bridge circuits can be selected for the secondary side, so that not only is the circuit structure simplified, but also the working efficiency of the conversion circuit is improved due to the fact that the complete synchronous rectification technology is realized by the secondary side.

Description

Technical Field

[0001] The present invention relates to the field of DC-DC conversion circuits, and particularly to an asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit. Background Art

[0002] In the era of the rise of new energy, battery charging and energy storage technologies are getting closer and closer to our daily lives. Charging and energy storage are necessarily related to charge and discharge technologies. At present, many charge and discharge facilities are applied in the market, but most of them are AC-DC and DC-AC conversions, that is, the combination of chargers and inverters. There are also some applications of bidirectional DC-DC circuit topologies, but they are all simple combinations of some traditional topologies. For example, small-power DC-DC usually uses topologies such as flyback-flyback, push-pull-push-pull, etc., and larger-power ones also use topologies such as full-bridge-full-bridge, full-bridge-push-pull, etc. These topologies have a common drawback: low efficiency and large switching losses.

[0003] The comparative document CN105207486B discloses a bidirectional resonant DC converter and its control method, including a low-voltage side power supply, a high-voltage side power supply, a first switch tube on the low-voltage side, a second switch tube on the low-voltage side, a third switch tube on the low-voltage side, a fourth switch tube on the low-voltage side, a transformer, a first switch tube on the high-voltage side, a second switch tube on the high-voltage side, a third switch tube on the high-voltage side, a fourth switch tube on the high-voltage side, a first resonant inductor, a second resonant inductor, a resonant capacitor, a first capacitor, and a second capacitor, where the transformer includes a first winding and a second winding. This circuit has high energy consumption at the switch tubes and low conversion efficiency. At the same time, when working in the forward and reverse directions, there are components that do not work, resulting in low component utilization rate and increased cost.

[0004] Therefore, the present invention proposes an asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit, which changes the forward primary side from a symmetrical half-bridge to an asymmetrical half-bridge and changes the secondary side to a bridge circuit to solve the problems of high energy consumption and low efficiency of the above-mentioned resonant circuit, and at the same time, the problem of high cost due to non-utilization. The present invention simplifies the circuit structure and increases the energy transfer efficiency per conversion cycle by changing the connection mode of the primary side and the secondary side to an asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit. Summary of the Invention

[0005] To solve the defects of high energy consumption and low component utilization rate in the existing bidirectional resonant circuit, an asymmetric half-bridge LLC bidirectional DC-DC conversion circuit is proposed. The primary side of the conversion circuit is an asymmetric half-bridge, which includes a resonant network and a bidirectional switch. The resonant network is connected between the transformer and the input negative terminal, and the bidirectional switch is respectively connected in series on the bridge arms connected to the positive output. The secondary side of the conversion circuit is a bridge circuit. Since the connection positions at both ends of the primary resonant circuit are in an asymmetric state, that is, the primary side uses the asymmetric half-bridge circuit method, the working energy consumption of the conversion circuit is reduced, and the response efficiency when the conversion circuit operates in the reverse direction can be increased.

[0006] Preferably, the primary circuit is provided with MOS transistor Q1 and MOS transistor Q2. The drain of MOS transistor Q2 is connected to the source of MOS transistor Q1, and the intersection point A of the primary winding and MOS transistors Q1 and Q2. The drain of MOS transistor Q1 is connected to the drain of MOS transistor Q5 of the upper bidirectional switch above, and the input power supply Vdc1+.

[0007] Preferably, the resonant network is provided with a resonant inductor Lr. One end of the resonant inductor Lr is connected to the connection intersection point B of the upper and lower bidirectional switches and the primary side, and the other end is connected with a resonant capacitor Cr. The other end of the resonant capacitor Cr is connected to the source of MOS transistor Q2 and the negative pole of capacitor C1, and is connected to the input power supply Vdc1-.

[0008] Preferably, the primary side of the conversion circuit is provided with 2 bidirectional switches. By using bidirectional switches to replace the diodes in the general bidirectional resonant circuit, the switches in the conversion circuit only play a role during full-bridge synchronous rectification when operating in the reverse direction, avoiding the risk that the body diodes parasitic in the diodes or unidirectional switches will clamp the primary side voltage of the transformer at certain specific stages of resonance, causing a short-circuit risk of the primary side of the transformer and affecting normal resonance or resulting in abnormal output voltage.

[0009] Preferably, the bidirectional switch is composed of two MOS transistors or IGBTs with their sources connected. In the bidirectional switch in the asymmetric half-bridge circuit, the MOS transistor or IGBT is equivalent to a voltage-type control switch. The sources of the two MOS transistors or IGBTs in the bidirectional switch are connected, and the drains are respectively connected to the circuit part to play a bidirectional control role; The bidirectional switch of the upper half circuit of the primary asymmetric half-bridge is composed of MOS transistors Q5 and Q6. The drain of MOS transistor Q5 is connected to the input power supply Vdc1+ and the drain of MOS transistor Q1 and the positive pole of capacitor C1. The drain of MOS transistor Q6 is connected to the wire between the inductor Lr and the primary winding. Using the bidirectional switch Q5+Q6 can avoid the clamping of the primary winding voltage during forward operation, resulting in abnormal resonance; The bidirectional switch of the lower half circuit of the primary-side asymmetric half-bridge consists of MOS transistors Q7 and Q8. The drain of MOS transistor Q7 is connected to the wire between the inductor Lr and the primary winding. The drain of MOS transistor Q8 is connected to the input power supply Vdc1-, the source of MOS transistor Q2, one end of the resonant capacitor Cr, and the negative electrode of capacitor C1. The use of the bidirectional switch Q7+Q8 can prevent the voltage of the primary winding from being clamped during forward operation, resulting in abnormal resonance.

[0010] Preferably, the gates of the primary-side bidirectional switches Q5 and Q6 are connected, and the gates of the bidirectional switches Q7 and Q8 are connected. The gates of the two field-effect transistors are connected and driven by the same signal, making the structure simpler.

[0011] Preferably, the secondary-side bridge circuit of the conversion circuit is a full-bridge circuit or a half-bridge circuit. The half-bridge circuit can be an asymmetric half-bridge circuit or a symmetric half-bridge circuit. According to the selected circuit, the working mode of the conversion circuit will change accordingly, making the asymmetric conversion circuit more flexible and capable of meeting diverse design requirements under different circuit conditions.

[0012] Preferably, the secondary-side bridge circuit of the conversion circuit includes MOS transistors Q3 and Q4. The drain of MOS transistor Q3 is connected to the positive electrode of capacitor C2, the source of MOS transistor Q3 is connected to the drain of MOS transistor Q4, and the source of MOS transistor Q4 is connected to the negative electrode of capacitor C2. The positive electrode of capacitor C2 is connected to the output power supply Vd2+, and the negative electrode is connected to the output power supply Vd2-.

[0013] Preferably, when the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit operates in the forward direction, the primary-side Lr, Cr, and the primary winding of the transformer form an LLC resonant network. The secondary side consists of MOS transistors Q3, Q4, and the full-bridge synchronous rectifier circuits formed by Q9+Q10 and Q11+Q12. At this time, the two bidirectional switches formed by Q5+Q6 and Q7+Q8 on the primary side basically do not participate in the operation, and Lr1 and Cr1 only play a simple role in suppressing spikes.

[0014] Preferably, when the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit operates in the reverse direction, the primary and secondary sides become the new primary side. The new primary side Lr1, Cr1, and the new primary winding of the transformer form an LLC resonant network. The original primary side becomes the new secondary side, and the new secondary side consists of MOS transistors Q1, Q2, and the full-bridge synchronous rectifier circuits formed by Q5+Q6 and Q7+Q8. Lr and Cr only play a simple role in suppressing spikes.

[0015] Preferably, a full-bridge synchronous rectification circuit is provided on the secondary side of the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit. The full-bridge synchronous rectification circuit includes MOS transistor Q3. The drain of MOS transistor Q3 is connected to the drain of MOS transistor Q9. The source of Q3 is connected to the drain of Q4. The sources of MOS transistors Q9 and Q10 are connected. The source of Q4 is connected to the drain of MOS transistor Q12. The drains of MOS transistors Q10 and Q11 are connected. The sources of MOS transistors Q11 and Q12 are connected. The midpoint A1 where Q3 and Q4 are connected is connected to one end of the secondary winding of the transformer. The other end of the secondary winding of the transformer is connected to the intersection point B1 of Q10 and Q11.

[0016] Preferably, a full-bridge synchronous rectification circuit operating in reverse is provided on the primary side of the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit. The full-bridge synchronous rectification circuit includes MOS transistor Q1. The drain of MOS transistor Q1 is connected to the drain of MOS transistor Q5. MOS transistor Q5 and the sources of MOS transistors Q6 are connected. The source of Q1 is connected to the drain of Q2. The source of Q2 is connected to the drain of MOS transistor Q8. MOS transistors Q7 and the sources of MOS transistors Q8 are connected. The drains of MOS transistors Q6 and Q7 are connected. The midpoint A where Q1 and Q2 are connected is connected to one end of the secondary winding. The other end of the secondary winding is connected to the intersection point B of Q6 and Q7.

[0017] The beneficial effects brought by the technical solution provided by the present invention are as follows: In the improved circuit, the asymmetric half-bridge is used for the primary side, and various bridge circuits can be selected for the secondary side. To simplify the circuit structure, the components that do not function in the original circuit have been removed. The secondary side adopts synchronous rectification control technology, which can directly achieve complete synchronous rectification. In addition, the number of resonant capacitors is reduced from two to one, and the resonant voltage of the resonant capacitor is increased to four times the input voltage. With the same device parameters and magnetic component sizes, the energy that can be transferred per cycle is greatly improved. This improvement not only simplifies the circuit structure but also improves the working efficiency of the conversion circuit due to the implementation of complete synchronous rectification technology on the secondary side. The control of this bidirectional power conversion is the same during forward and reverse operations, which can simplify the control circuit and improve the product reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a topological diagram of the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit in the first embodiment of the present invention, where both the primary and secondary sides are asymmetric half-bridges.

[0019] Figure 2 is a topological diagram after transformation in the first embodiment of the present invention.

[0020] Figure 3 is a topological diagram of the bidirectional conversion DC / DC circuit in the second embodiment of the present invention, where the secondary side adopts a symmetric half-bridge.

[0021] Figure 4 This is the topology diagram of the bidirectional conversion DC / DC circuit with a full-bridge LLC on the secondary side in the third embodiment of the present invention. Specific embodiments

[0022] The embodiment of the present application proposes an asymmetric half-bridge LLC bidirectional DC-DC conversion circuit, which solves the problems of high energy consumption and low efficiency in the resonant circuit in the prior art, and at the same time does not utilize the high cost, etc., achieving the beneficial effects of simplifying the circuit structure and increasing the energy transfer efficiency of each conversion cycle.

[0023] Figure 1 This is the topology diagram of the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit in this embodiment. The primary side of the conversion circuit is an asymmetric half-bridge, and the asymmetric half-bridge includes a resonant network and a bidirectional switch. The resonant network is connected between the negative poles of the transformer input. The bidirectional switches are respectively connected in series on the bridge arms connected to the positive output. The secondary side of the conversion circuit is a bridge circuit; The bidirectional switch is composed of two MOS transistors or IGBTs with their sources connected. The bidirectional switch on the upper half circuit of the primary side asymmetric half-bridge is composed of MOS transistors Q5 and Q6. The drain of MOS transistor Q5 is connected to the input power supply Vdc1+ and the drain of MOS transistor Q1 and the positive pole of capacitor C1. The drain of MOS transistor Q6 is connected to the wire between the inductance Lr and the primary winding. The bidirectional switch on the lower half circuit of the primary side asymmetric half-bridge is composed of MOS transistors Q7 and Q8. The drain of MOS transistor Q7 is connected to the wire between the inductance Lr and the primary winding. The drain of the MOS transistor Q8 is connected to the input power supply Vdc1-, the source of the MOS transistor Q2, one end of the harmonic capacitance Cr and the negative pole of the capacitor C1.

[0024] The resonant network is provided with a resonant inductance Lr. One end of the resonant inductance Lr is connected to the upper and lower bidirectional switches and the intersection point B of the primary side connection. The other end is connected with a resonant capacitance Cr. The other end of the resonant capacitance Cr is connected to the drain of the MOS transistor Q2 and the negative pole of the capacitor C1, and is connected to the input power supply Vdc1-. The source of the MOS transistor Q2 is connected to the drain of the MOS transistor Q1, and the intersection point A of the primary winding and the MOS transistors Q1 and Q2. The source of the MOS transistor Q1 is connected to the source of the MOS transistor Q5 of the upper bidirectional switch and the input power supply Vdc1+.

[0025] The secondary side bridge circuit includes MOS transistors, and the positive and negative poles of the MOS transistors are respectively connected to the positive and negative poles of the capacitor C2. The positive pole of the capacitor C2 is connected to the output power supply Vd2+, and the negative pole is connected to the output power supply Vd2-.

[0026] When the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit works in the forward direction, the primary side Lr, Cr and the primary winding of the transformer form an LLC resonant network, and the secondary side is composed of MOS transistors Q3, Q4 and Q9+Q10 and Q11+Q12 to form a full-bridge synchronous rectification circuit; When the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit operates in the reverse direction, the original primary and secondary sides become the new primary side. The new primary side Lr1, Cr1 and the new primary winding of the transformer form an LLC resonant network. The original primary side becomes the new secondary side, and the new secondary side consists of MOS transistors Q1, Q2, and Q5+Q6 and Q7+Q8 to form a full-bridge synchronous rectification circuit. At this time, the drive signals of MOS transistor Q1, MOS transistor Q3, bidirectional switch MOS transistor Q7 and MOS transistor Q8 are synchronized; the drive signals of MOS transistor Q2, MOS transistor Q4, bidirectional switch MOS transistor Q5 and MOS transistor Q6 are synchronized.

[0027] When the circuit operates in the forward direction, the first resonant frequency fr: The second resonant frequency fm: To ensure operation in the soft-switching state, the switching frequency fs: fm < fs < fr.

[0028] Its working principle is that on the left, Q1, the primary winding of T1, Lr, Cr, and Q2 form an asymmetric half-bridge standard resonant network on the primary side. On the right, it consists of the secondary winding of T1, and Q3, Q4, Q9+Q10, and Q11+Q12 form a full-bridge synchronous rectification. When energy is transferred from the left to the right, Q1 is turned on, and energy flows from the input power supply Vdc1+ → Q1 → the primary side of T1 → Lr → Cr → the input power supply Vdc1-. The primary inductance, leakage inductance of T1, and Lr and Cr form a resonance. When the upper ends of the two windings of the transformer T1 are the same-named terminals and the voltage of the secondary winding is greater than the voltage across the capacitor C2 at the load end, Q3, Q11+Q12 are synchronized with the drive signal of Q1, and full-bridge synchronous rectification can be achieved. Energy flows from the secondary winding of the transformer → Q3 → the load output terminal Vdc2+ → the load → Vdc- → Q11+Q12 → the secondary winding of the transformer, forming a closed-loop energy transfer. The primary side resonates according to the working principle of the standard asymmetric half-bridge LLC.

[0029] The first stage: Q1 is turned on and Q2 is turned off. In this stage, Q1 conducts, allowing current to flow through the primary winding of T1. At the same time, Q2 is in the off state, blocking the current from flowing through the secondary winding of T1. When Q1 is turned on, the resonant current Ir begins to increase. At the same time, the voltage of the resonant capacitor Cr also begins to rise. The voltage directions of Cr, Lr, and Lm are consistent with the current direction. When the voltage of Cr reaches the primary input voltage, the resonant current Ir reaches the maximum value and begins to decrease. At this time, the induced voltages of Lr and Lm become zero and begin to reverse. Lr and Lm begin to release energy, while Cr continues to store energy and the voltage continues to rise.

[0030] At this stage, the primary voltage of the transformer is clamped by the secondary voltage. This means that the voltage of the secondary winding is restricted within a specific range, which is determined by the turn ratio of the primary winding to the secondary winding of the transformer, the average output voltage Vo, and the duty cycle D of the secondary winding at the corresponding moment. In this stage, the voltage drop of the synchronous tube is ignored.

[0031] At this stage, through the interaction of components in the resonant circuit, such as Cr, Lr, and Lm, the system realizes the transfer and storage of energy. This stage is the starting stage of the operation of the energy transfer system, and energy transfer and regulation will continue in subsequent stages.

[0032] Second stage: Q1 conducts, allowing current to flow through the primary winding of T1. At the same time, Q2 is in the off state, blocking the current from flowing through the secondary winding of T1; as time goes by, the resonant current Ir continues to decrease. Lr and Lm start to release energy, and the voltage of Cr continues to rise. The induced voltage of Lm is opposite to the direction of the primary voltage clamped by the secondary voltage nVo. When the maximum voltage of the secondary winding is less than the output voltage Vo, the current of the secondary synchronous rectifier tube drops to zero, and Q3, Q11 + Q12 are turned off simultaneously, that is, zero-current turn-off occurs, and the secondary side of the transformer no longer clamps the primary voltage. After the clamping of the secondary voltage is released, Lr and Lm participate in resonance simultaneously. The resonant current Ir continues to decrease.

[0033] At this stage, since the voltage of Cr is close to twice the input voltage, the reverse voltage applied to Lr and Lm is about one times the input voltage. The voltage of Lm is about Uin·Lm / (Lr + Lm), where Uin is the input voltage. At this time, if the bidirectional switch Q5 + Q6 is replaced by a diode or a switching tube, the voltage of Lm will be clamped by the forward conduction voltage drop of the diode or the conduction voltage drop of the switching tube, that is, the primary side of the transformer is short-circuited, destroying the resonance condition. In contrast, when using the bidirectional switch Q5 + Q6, the voltage of Lm will not be clamped and can resonate normally. When the resonant current is small, Q1 can be turned off. Using the bidirectional switch Q5 + Q6 can maintain the normal resonance of the system without destroying the resonance condition, which helps to reduce losses and ensure the normal operation of the system.

[0034] The third stage: Q1 and Q2 are turned off. The turn-off of Q1 causes the current in the resonant inductor not to change abruptly but to continue decreasing. The turn-off of Q2 causes its body diode to conduct. Due to the turn-off of Q1, Lr and Lm start to release energy. The resonant current Ir continues to decrease, and the voltage across Cr continues to rise. As time goes by, the primary voltage Vp of the transformer gradually approaches the induced voltage of Lm. This voltage is approximately Uin·Lm / (Lr + Lm), where Uin is the input voltage. When the value of Uin·Lm / (Lr + Lm) is greater than the output voltage Vo, Q4 and the bidirectional switch Q9+Q10 conduct simultaneously. The conduction of these switches causes the secondary current to start increasing.

[0035] In the third stage, the operating state of the system changes. Both Q1 and Q2 are in the off state, the resonant current continues to decrease, and the primary voltage of the transformer gradually approaches the induced voltage of Lm. When the primary voltage exceeds the output voltage, the corresponding switches (such as Q4 and the bidirectional switch Q9+Q10) will conduct, causing the secondary current to start increasing.

[0036] The fourth stage: Q1 is turned off and Q2 is turned on. Since the body diode of Q2 conducts, it turns on at zero voltage. Due to the turn-off of Q1, Lr and Lm continue to release energy. The resonant current Ir continues to decrease, and the voltage across Cr continues to rise. As time goes by, the resonant current Ir gradually decreases to zero. In this stage, the voltage across Cr reaches the maximum value, approaching twice the input voltage. When the resonant current Ir decreases to zero, the voltages across Lr and Lm are also zero. The voltage across Cr reaches the maximum value, while Lr and Lm are in the state of energy release.

[0037] In the fourth stage, Q1 is turned off and Q2 is turned on, the resonant current continues to decrease, the voltage across Cr gradually reaches the maximum value, and the voltages across Lr and Lm are zero. This stage marks that the resonant current Ir decreases to zero, the voltage of Cr reaches the maximum value, and Lr and Lm are in the state of energy release.

[0038] The fifth stage: Q1 is turned off and Q2 is turned on. Due to the turn-off of Q1 and the turn-on of Q2, the resonant current Ir starts to reverse and gradually increases. This is because the resonant inductor Lr and the mutual inductance inductor Lm release energy, causing the direction of the resonant current to change. The sum of the voltages across Lr and Lm is equal to the voltage of Cr and is close to twice the input voltage. Since the primary circuit of the transformer is clamped at nVo / D, where n is the turns ratio of the primary winding to the secondary winding of the transformer, Vo is the average output voltage, and D is the duty cycle of the secondary winding at the corresponding moment, Lm does not participate in the resonance. After subtracting the primary voltage nVo / D clamped by the secondary side from the voltage of Cr, the remaining voltage is all applied to the resonant inductor Lr. Due to the reverse and gradual increase of the resonant current Ir, both the primary resonant current and the secondary current increase rapidly. When the voltage of Cr decreases to zero, the resonant current Ir reaches its maximum value. Then, the resonant current starts to decrease, and the voltage of Cr starts to charge in the reverse direction.

[0039] In the fifth stage, Q1 is turned off, Q2 is turned on, the resonant current reverses and gradually increases, and the voltage of Cr, after subtracting the primary voltage clamped by the secondary side, is all applied to the resonant inductor Lr, resulting in a rapid increase in the primary resonant current and the secondary current. When the voltage of Cr decreases to zero, the resonant current reaches its maximum value and then starts to decrease, and the voltage of Cr starts to charge in the reverse direction.

[0040] The sixth stage: Q1 is turned off and Q2 is turned on. Due to the turn-off of Q1 and the turn-on of Q2, the resonant current Ir continues to decrease. Lr and Lm continue to release energy, and the reverse voltage of Cr continues to rise. Due to the continuous increase in the reverse voltage of Cr, the induced voltages across Lr and Lm also continue to increase. This causes the primary voltage of the transformer to be clamped at nVo / D by the secondary induced voltage, where n is the turns ratio of the primary winding to the secondary winding of the transformer, Vo is the average output voltage, and D is the duty cycle of the secondary winding at the corresponding moment. As the reverse voltage of Cr increases, the induced voltages across Lr and Lm also increase. This causes the primary exciting voltage of the transformer to start to decrease. When the maximum voltage across the winding between pins 4 and 5 of the secondary side is less than the output voltage Vo, the current of the secondary synchronous rectifier tube drops to zero, Q3 is turned off (zero-current turn-off), and the secondary side of the transformer no longer clamps the primary voltage.

[0041] In the sixth stage, both Lr and Lm participate in resonance, and the resonance current Ir continues to decrease. Since the reverse voltage of Cr is close to negative twice the input voltage, the reverse voltage applied to Lr and Lm is approximately the input voltage. The voltages on Lr and Lm are respectively in the ratio of the series inductance values. The voltage of Lm is approximately Uin·Lm / (Lr + Lm). If the bidirectional switches Q7+Q8 are replaced with diodes or switching transistors, the voltage of Lm will be clamped by the parasitic diodes of these diodes or switching transistors to the forward conduction voltage drop of the diodes. This is equivalent to short-circuiting the primary side of the transformer, destroying the resonance condition. The voltage of Lm approaches zero, and the original resonance current Ir does not change suddenly but decreases slowly in a linear manner. When Q1 is turned off, the loss will increase significantly and have an adverse effect on the switching ability and loss of the subsequent Q2. If the bidirectional switches Q7+Q8 are used, the voltage of Lm will not be clamped and resonance can proceed normally. When the resonance current is small, Q2 is turned off.

[0042] Seventh stage: Q1 is turned off and Q2 is turned off. Since both Q1 and Q2 are turned off, the direction of the resonance current Ir remains unchanged and continues to decrease. Lr and Lm continue to release energy, and the reverse voltage of Cr continues to increase. Since Q2 is turned off, the current of the resonance inductor does not change suddenly. In this case, the body diode of Q1 conducts, allowing the resonance current to pass through. The primary voltage Vp of the transformer gradually approaches the induced voltage of Lm, which is approximately Uin·Lm / (Lr + Lm). This is because the reverse voltage of Cr is continuously increasing, and the reverse voltages applied to Lr and Lm are also increasing. When the value of Uin·Lm / (Lr + Lm) is greater than the output voltage Vo, Q3 and Q11+Q12 conduct simultaneously. The specific conduction sequence may depend on the control strategy of synchronous rectification, and the body diode may conduct first. The specific control strategy will not be described here. After Q3 and Q11+Q12 conduct, the secondary current begins to increase, so the energy transfer system begins to output energy to the load.

[0043] Eighth stage: Q2 is turned off and Q1 is turned on. When Q1 is turned on, it is turned on at zero voltage, that is, it is turned on at the moment when the current passes through zero. Since Q2 is turned off and Q1 is turned on, the direction of the resonance current Ir remains unchanged and continues to decrease. Lr and Lm continue to release energy, and the reverse voltage of Cr continues to increase. As the resonance current Ir continues to decrease, it finally decreases to zero. This means that the voltages across Lr and Lm will also approach zero. As the resonance current Ir decreases, the reverse voltage of Cr continues to increase until it reaches the maximum value. The maximum value is close to negative twice the input voltage. When the resonance current Ir decreases to zero, the voltages across Lr and Lm will also approach zero. This is because the energy in the energy transfer system has been completely released and there is no current flowing through the inductor components.

[0044] The ninth stage: Q1 conducts and Q2 turns off. The resonant current Ir turns positive and starts to gradually increase, which is the same as the first stage, and the cycle starts to repeat.

[0045] In a second aspect, Figure 2 This is the circuit topology diagram for changing the position of the resonant inductor Lr from between the resonant capacitor Cr and point B to between point A and the primary side of the transformer T1 in the embodiment of the present invention. Its principle is still: on the left, Q1, the primary winding of T1, Lr, Cr, and Q2 form an asymmetric half-bridge standard resonant network on the primary side. On the right, the secondary winding of T1, and Q3, Q4, Q9+Q10, and Q11+Q12 form a full-bridge synchronous rectifier. When energy is transferred from the left to the right, Q1 is turned on, and the energy flows from the input power supply Vdc1+→Q1→the primary side of T1→Lr→Cr→the input power supply Vdc1-. The primary inductance, leakage inductance of T1, and Lr and Cr form a resonance. When the upper ends of the two windings of the transformer T1 are of the same name and the voltage of the secondary winding is greater than the voltage across the load capacitor C2, Q3, Q11+Q12 are synchronized with the driving signal of Q1, and full-bridge synchronous rectification can be achieved. The energy flows from the secondary winding of the transformer→Q3→the load output terminal Vdc2+→the load→Vdc-→Q11+Q12→the secondary winding of the transformer, forming a closed-loop energy transfer. The primary side operates in resonance according to the standard asymmetric half-bridge LLC working principle.

[0046] In a third aspect, Figure 3 This is the topology diagram of the second embodiment of the present invention. Among them, the primary side of the circuit uses an asymmetric half-bridge LLC, and the secondary side uses a symmetric half-bridge LLC.

[0047] On the left, Q1, the primary winding of T1, Lr, Cr, and Q2 form an asymmetric half-bridge standard resonant network on the primary side. On the right, the secondary winding of T1, and Q3, Q4, Q9, and Q10 form a symmetric half-bridge synchronous rectifier. When energy is transferred from the left to the right, Q1 is turned on, and the energy flows from the input power supply Vdc1+→Q1→the primary side of T1→Lr→Cr→the input power supply Vdc1-. The primary inductance, leakage inductance of T1, and Lr and Cr form a resonance. When the upper ends of the two windings of the transformer T1 are of the same name and the voltage of the secondary winding is greater than the voltage across the load capacitor C2, Q3, Q10 are synchronized with the driving signal of Q1, and half-bridge synchronous rectification can be achieved. The energy flows from the secondary winding of the transformer→Q3→the load output terminal Vdc2+→the load→Vdc-→Q10→the secondary winding of the transformer, forming a closed-loop energy transfer. The primary side operates in resonance according to the standard asymmetric half-bridge LLC working principle.

[0048] In a fourth aspect, Figure 4 This is the topology of the third embodiment of the present invention. Among them, the primary side of the circuit uses an asymmetric half-bridge LLC, and the secondary side uses a full-bridge LLC.

[0049] On the left side, the primary windings of Q1 and T1, Lr, Cr, and Q2 form an asymmetric half-bridge standard resonant network on the primary side. On the right side, the secondary winding of T1, together with Q3, Q4, Q9, and Q10, forms a full-bridge synchronous rectifier. When energy is transferred from the left side to the right side, Q1 is turned on, and the energy flows from the input power supply Vdc1+ → Q1 → the primary side of T1 → Lr → Cr → the input power supply Vdc1-. The primary inductance and leakage inductance of T1, together with Lr and Cr, form a resonance. When the upper ends of the two windings of the transformer T1 are of the same name and the voltage of the secondary winding is greater than the voltage across the capacitor C2 at the load end, Q3 and Q10 are synchronized with the driving signal of Q1, and full-bridge synchronous rectification can be achieved. The energy flows from the secondary winding of the transformer → Q3 → the load output terminal Vdc2+ → the load → Vdc- → Q10 → the secondary winding of the transformer, forming a closed-loop energy transfer. The primary side resonates according to the working principle of the standard asymmetric half-bridge LLC.

[0050] Obviously, the "first", "second", or "third", etc. in the embodiments described in the present invention are used to distinguish different objects, rather than to describe a specific order, and there is no prior or posterior priority. Moreover, they are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. Asymmetric half-bridge LLC bidirectional DC-DC conversion circuit, characterized in that The conversion circuit is a bidirectional power conversion circuit, the primary side of which is an asymmetrical half-bridge. The asymmetrical half-bridge includes a resonant network and a bidirectional switch. The resonant network is connected between the transformer and the input negative terminal. The bidirectional switch is respectively connected in series on the bridge arms connected to the transformer and the input positive and negative terminals. The secondary side of the conversion circuit is a bridge circuit.

2. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1, wherein The primary side circuit is provided with MOS transistor Q1 and MOS transistor Q2. The source of MOS transistor Q2 is connected to the drain of MOS transistor Q1, and the intersection point A of the primary side inductor Lm and MOS transistors Q1 and Q2. The source of MOS transistor Q1 is connected to the source of MOS transistor Q5 of the upper bidirectional switch above, and the input power supply Vdc1+.

3. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1, wherein The resonant network is provided with a resonant inductor Lr. One end of the resonant inductor Lr is connected to the connection intersection point B of the upper and lower bidirectional switches and the primary side, and the other end is connected with a resonant capacitor Cr. The other end of the resonant capacitor Cr is connected to the source of MOS transistor Q2 and the negative electrode of capacitor C1, and is connected to the input power supply Vdc1-.

4. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1, wherein There are 2 bidirectional switches on the primary side of the conversion circuit.

5. The asymmetric half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1 or 4, characterized in that, The bidirectional switch is composed of two MOS transistors or IGBTs with their sources connected; The bidirectional switch of the upper half circuit of the primary side asymmetrical half-bridge is composed of MOS transistors Q5 and Q6. The drain of MOS transistor Q5 is connected to the input power supply Vdc1+ and the drain of MOS transistor Q1 and the positive electrode of capacitor C1. The drain of MOS transistor Q6 is connected to the wire between the inductor Lr and the primary side winding. The bidirectional switch of the lower half circuit of the primary side asymmetrical half-bridge is composed of MOS transistors Q7 and Q8. The drain of MOS transistor Q7 is connected to the wire between the inductor Lr and the primary side winding. The drain of MOS transistor Q8 is connected to the input power supply Vdc1- and the source of MOS transistor Q2, and is connected to one end of the harmonic conversion capacitor Cr and the negative electrode of capacitor C1.

6. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 5, wherein The gates of the primary side bidirectional switches Q5 and Q6 are connected, and the gates of the bidirectional switches Q7 and Q8 are connected.

7. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1, wherein The secondary side bridge circuit of the conversion circuit is a full-bridge circuit or a half-bridge circuit. Among them, the half-bridge circuit adopts a symmetrical half-bridge or an asymmetrical half-bridge circuit.

8. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1 or 6, characterized in that, The secondary side bridge circuit of the conversion circuit includes MOS transistor Q3 and MOS transistor Q4. The drain of MOS transistor Q3 is connected to the positive electrode of capacitor C2. The source of MOS transistor Q3 is connected to the drain of MOS transistor Q4. The source of MOS transistor Q4 is connected to the negative electrode of capacitor C2. The positive electrode of capacitor C2 is connected to the output power supply Vd2+, and the negative electrode is connected to the output power supply Vd2-.

9. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1, wherein The secondary side of the asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit is provided with a full-bridge synchronous rectification circuit. The full-bridge synchronous rectification circuit includes MOS transistor Q3. The drain of MOS transistor Q3 is connected to the drain of MOS transistor Q9. The source of Q3 is connected to the drain of Q4. MOS transistor Q9 is connected to the source of MOS transistor Q10. The source of Q4 is connected to the drain of MOS transistor Q12. The drain of MOS transistor Q10 is connected to the drain of MOS transistor Q11. MOS transistor Q11 is connected to the source of MOS transistor Q12. The midpoint A1 where Q3 and Q4 are connected is connected to one end of the secondary side winding of the transformer. The other end of the secondary side winding of the transformer is connected to the intersection point B1 of Q10 and Q11.

10. The asymmetrical half-bridge LLC bidirectional DC-DC conversion circuit according to claim 1, wherein, The primary side of the asymmetric half-bridge LLC bidirectional DC-DC conversion circuit is provided with a full-bridge synchronous rectification circuit operating in the reverse direction. The full-bridge synchronous rectification circuit includes MOS transistor Q1. The drain of MOS transistor Q1 is connected to the drain of MOS transistor Q5. MOS transistor Q5 is connected to the source of MOS transistor Q6. The source of Q1 is connected to the drain of Q2. The source of Q2 is connected to the drain of MOS transistor Q8. MOS transistor Q7 is connected to the source of MOS transistor Q8. MOS transistor Q6 is connected to the drain of MOS transistor Q7. The midpoint A where Q1 and Q2 are connected is connected to one end of the secondary inductor, and the other end of the secondary inductor is connected to the intersection point B of Q6 and Q7.

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