A buffer circuit for BUCK converter

Abstract

The present invention provides a buffer circuit for a buck converter (BUCK) converter, comprising a power transistor VT1, diodes D1, D2, VD1, resistors R1, R2, R3, Ro, capacitors C1, C2, C3, Co, inductors Lm, L1, an input voltage Uin, and an output voltage Uout. The buck converter of the present invention incorporates a buffer circuit on the power transistor and freewheeling diode. This buffer circuit significantly suppresses voltage and current spikes during power device switching, reduces turn-on and turn-off losses, and improves the buck converter's conversion efficiency. The buck converter eliminates the need for an auxiliary switch buffer circuit, resulting in high converter efficiency. Furthermore, the buck converter also eliminates the need for an auxiliary switch drive circuit, simplifying the control circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of buffer circuits, and in particular to a buffer circuit for a BUCK converter. Background Art

[0002] With the continuous improvement of my country's manufacturing industry and the implementation of the national "casting to welding" policy, the total amount of steel cut, as a major raw material, is increasing. This places higher demands on cutting efficiency, cutting quality, environmental friendliness, and product cost. The demand for high-performance, reliable, high-power plasma cutting power supplies is becoming increasingly urgent. The cutting power supply is the core of the air plasma cutting machine. Plasma cutting power supplies utilize modern power electronics and automatic control theories to achieve efficient power conversion and control, tailored to the plasma arc load characteristics and cutting process requirements. Chopper-type plasma cutting power supplies offer the advantages of simple structure, high switching frequency, excellent control characteristics, and high reliability. However, chopper-type plasma cutting power supplies still use an industrial frequency transformer to step down the voltage, which is bulky, heavy, and inefficient. Inverter technology, coupled with high-power power electronic switches and high-frequency transformers, can replace the industrial frequency transformer. This significantly reduces the weight, volume, and material requirements of the transformer and reactor, thereby improving efficiency. Plasma cutting power supplies above 20kW typically utilize dual-buck converters in parallel to increase output power. Dual-buck converters offer advantages such as simple control circuitry, high switching frequency, excellent control characteristics, and high reliability, making them an ideal choice for high-power air plasma cutting power supplies. However, chopper-type cutting power supplies require hard-on or hard-off switching of the power tubes, which not only reduces the efficiency of the cutting power supply but also causes voltage and current spikes, impacting the stability and service life of the cutting power supply.

[0003] Soft switching technology can be divided into active soft switching technology and passive soft switching technology according to whether there is an auxiliary switch tube. Passive soft switching technology can be divided into: 1) Full resonant converter, which is divided into series resonant converter and parallel resonant converter according to the resonance mode of the resonant element; 2) Quasi-resonant converter, multi-resonant converter, the resonant element participates in a certain stage of energy conversion, not the whole process, and this type of converter uses frequency modulation method; 3) Passive lossy buffer and low-loss buffer technology, this type of technology has energy-consuming resistors; 4) Passive lossless buffer technology, which uses all passive components and has no energy-consuming resistors in the resonant link. The circuit structure is simple and theoretically does not consume energy. The energy generated by the switching transient is fed back to the power supply end or the load end, thereby achieving losslessness. LC resonance mainly circulates energy and cannot use resonance to achieve zero current turn-on and zero voltage turn-off of the power tube.

[0004] Buck converters use inductors and capacitors to shape the switching trajectory of switches, achieving soft switching. The earliest approach employed lossy snubber circuits. From an energy perspective, this transfers switching losses to the snubber circuit, dissipating them and improving the switching conditions of the switch. However, this does not improve converter efficiency and may even reduce it. Summary of the Invention

[0005] (1) Technical problems solved

[0006] To address the drawback of the aforementioned buck converter, which utilizes a lossy snubber circuit that affects converter efficiency, the present invention provides a snubber circuit for the buck converter. The buck converter incorporates snubber circuits on the power transistor VT1 and the freewheeling diode VD1. The snubber circuits significantly suppress voltage and current spikes during power device switching, reducing turn-on and turn-off losses and improving the buck converter's conversion efficiency. The buck converter eliminates the need for an auxiliary switch snubber circuit, resulting in high converter efficiency and a simple control circuit.

[0007] (2) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] A buffer circuit for a BUCK converter, comprising a power tube VT1, diodes D1, D2, VD1, resistors R1, R2, R3, Ro, capacitors C1, C2, C3, Co, inductors Lm, L1, an input voltage Uin, and an output voltage Uout; the positive electrode of the input voltage Uin is connected to the resistor R1 and the collector of the power tube VT1, the other end of the resistor R1 is connected to one end of the capacitor C1 and the cathode of the diode D1, the other end of the capacitor C1 and the anode of the diode D1 are connected to the negative electrode of the input voltage Uin, the emitter of the power tube VT1 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the negative electrode of the input voltage Uin; the input voltage Uin is connected to the positive electrode of the resistor R1 and the collector of the power tube VT1, the other end of the resistor R1 is connected to one end of the capacitor C1 and the cathode of the diode D1, the other end of the capacitor C1 and the anode of the diode D1 are connected to the negative electrode of the input voltage Uin, the emitter of the power tube VT1 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the negative electrode of the input voltage Uin; The negative pole of in is connected to one end of resistor R3 and the anode of diode VD1. The other end of resistor R2 is connected to one end of capacitor C3. The other end of capacitor C3 is connected to the anode of diode D2, the cathode of diode VD1, and one end of inductor L1. The cathode of diode D2 is connected to one end of resistor R2. The other end of resistor R2 is connected to the other end of inductor L1, the emitter of power tube VT1, and one end of inductor Lm. The other end of inductor Lm is connected to one end of resistor Ro and capacitor Co respectively. One end of resistor Ro and capacitor Co is the positive pole of output voltage Uout. The other end of resistor Ro and capacitor Co is connected to the anode of diode VD1. The other end of resistor Ro and capacitor Co is the negative pole of output voltage Uout.

[0010] According to an embodiment of the present invention, the power tube VT1 is an IGBT.

[0011] According to an embodiment of the present invention, the IGBT model is CM200DY-12NF, with a rated voltage of 600V and a rated current of 200A.

[0012] According to an embodiment of the present invention, the diode VD1 is a fast recovery diode BYW29-200.

[0013] According to an embodiment of the present invention, the diode D1 is an ultrafast recovery diode MUR3060PT.

[0014] According to an embodiment of the present invention, the diode D2 is an ultrafast recovery diode MUR3060PT.

[0015] According to an embodiment of the present invention, the capacitor C1 is a double-sided metallized polypropylene film capacitor.

[0016] According to an embodiment of the present invention, the capacitor C2 is a double-sided metallized polypropylene film capacitor.

[0017] According to an embodiment of the present invention, the capacitor C3 is a double-sided metallized polypropylene film capacitor.

[0018] According to an embodiment of the present invention, the capacitor Co is an aluminum electrolytic capacitor with a capacity of 250uF and a withstand voltage of 400V.

[0019] (3) Beneficial effects

[0020] The present invention has the following beneficial effects: a buffer circuit for a buck converter, in which a buffer circuit is added to a power tube and a freewheeling diode. The buffer circuit greatly suppresses voltage and current spikes during the switching process of the power device, reduces turn-on and turn-off losses of the power device, and improves the conversion efficiency of the buck converter. Compared with an active buffer circuit, no auxiliary switch tube buffer circuit is required, resulting in high converter efficiency, no auxiliary switch tube drive circuit is required, and the control circuit is simple. In a lossy buffer circuit, as the power of the power supply increases, the switching loss increases, and the loss of the buffer circuit also increases accordingly. The buffer circuit of the present invention can reduce the loss of the buffer circuit and improve the efficiency of the buck converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 these drawings without paying any creative work.

[0022] Figure 1This is a schematic diagram of the buffer circuit of the present invention.

[0023] Description of reference numerals:

[0024] Resistors R1, R2, R3, Ro, capacitors Co, C1, C2, C3, diodes D1, D2, VD1, power tube VT1, inductors Lm, L1, input voltage Uin, output voltage Uout. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] Combine Figure 1 A buffer circuit for a BUCK converter includes a power tube VT1, diodes D1, D2, VD1, resistors R1, R2, R3, Ro, capacitors C1, C2, C3, Co, inductors Lm, L1, an input voltage Uin, and an output voltage Uout; the positive electrode of the input voltage Uin is connected to the resistor R1 and the collector of the power tube VT1, the other end of the resistor R1 is connected to one end of the capacitor C1 and the cathode of the diode D1, the other end of the capacitor C1 and the anode of the diode D1 are connected to the negative electrode of the input voltage Uin, the emitter of the power tube VT1 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the negative electrode of the input voltage Uin; the input voltage Uin The negative electrode is connected to one end of the resistor R3 and the anode of the diode VD1. The other end of the resistor R2 is connected to one end of the capacitor C3. The other end of the capacitor C3 is connected to the anode of the diode D2, the cathode of the diode VD1, and one end of the inductor L1. The cathode of the diode D2 is connected to one end of the resistor R2. The other end of the resistor R2 is connected to the other end of the inductor L1, the emitter of the power tube VT1, and one end of the inductor Lm. The other end of the inductor Lm is connected to one end of the resistor Ro and the capacitor Co respectively. One end of the resistor Ro and the capacitor Co is the positive electrode of the output voltage Uout. The other end of the resistor Ro and the capacitor Co is connected to the anode of the diode VD1. The other end of the resistor Ro and the capacitor Co is the negative electrode of the output voltage Uout.

[0027] Power transistor VT1 is an IGBT (CM200DY-12NF) with a rated voltage of 600V and a rated current of 200A. Diode VD1 is a BYW29-200 fast recovery diode. Diode D1 is a MUR3060PT ultra-fast recovery diode. Diode D2 is a MUR3060PT ultra-fast recovery diode. Capacitor C1 is a double-sided metallized polypropylene film capacitor. Capacitor C2 is a double-sided metallized polypropylene film capacitor. Capacitor C3 is a double-sided metallized polypropylene film capacitor. Capacitor Co is a 250uF aluminum electrolytic capacitor with a withstand voltage of 400V.

[0028] Capacitor C1 not only suppresses surge voltages caused by the DC bus's parasitic inductance but also clamps power transistor VT1 through R1, C1, and D1, suppressing oscillations during VT1's shutdown. Capacitor C2 reduces shutdown losses during VT1's shutdown process while also suppressing EMI noise. The parallel connection of capacitor C2 limits and improves the rate of voltage rise between the collector and emitter of VT1, enabling the power transistor to achieve near-zero voltage shutdown. To suppress voltage oscillations during the shutdown of freewheeling diode VD1, resistor R3 and capacitor C3 are connected in series across freewheeling diode VD1. To suppress reverse recovery during the shutdown of freewheeling diode VD1, auxiliary inductor L1 is installed between freewheeling diode VD1 and the positive terminal of input voltage Uin. To prevent the freewheeling diode VD1 from being delayed due to the series connection of auxiliary inductor L1, resistor R2 and diode D2 are connected in series across auxiliary inductor L1. Resistor R2 and diode D2 provide a freewheeling circuit for inductor Lm at the moment VT1 shuts down. When the freewheeling diode VD1 is turned off, the resistor R2 and the diode D2 provide a freewheeling loop for the current in the auxiliary inductor L1 .

[0029] During specific operation, the non-inductive absorption capacitor C1 on the input side of the power tube VT1 suppresses the surge voltage impact of the DC bus parasitic inductance on the one hand, and on the other hand performs RCD clamping on the power tube VT1 to suppress the oscillation phenomenon when the IGBT is turned off; during the shutdown process of the power tube VT1, the voltage between the collector and emitter of the power tube VT1 will quickly rise to the output voltage level, and the large du / dt will also cause large turn-off losses and generate EMI noise. The limitation and improvement of the voltage rise rate between the collector and emitter can be achieved by connecting a capacitor C2 in parallel. Capacitor C2 is a buffer capacitor that allows the power tube to achieve approximately zero voltage shutdown. Increasing the value of capacitor C2 can greatly reduce the turn-off loss, but too large a capacitance will cause a large current spike when the power tube is turned on, and the turn-on oscillation will be aggravated. The buffer capacitor C2 is the key to achieving low loss in the buffer circuit. Capacitor C3 and resistor R3 are mainly used to suppress the voltage oscillation when the freewheeling diode VD1 is turned off; the auxiliary inductor L1 is mainly used to suppress the reverse recovery when the freewheeling diode VD1 is turned off, but it limits the current growth rate when the freewheeling diode VD1 is turned on; the buffer absorption network R2 and D2 connected in parallel at both ends of the inductor L1 can avoid the problem caused by the freewheeling diode being unable to freewheel in time due to the auxiliary inductor connected in series with the freewheeling diode, and provide freewheeling for the inductor Lm at the moment the power tube VT1 is turned off, and at the same time provide a freewheeling loop for the current in L1 when the freewheeling diode VD1 is turned off.

[0030] In summary, the embodiments of the present invention provide a snubber circuit for a buck converter. The buck converter incorporates snubber circuits on the power transistor VT1 and the freewheeling diode VD1. These snubber circuits significantly suppress voltage and current spikes during power device switching, reducing turn-on and turn-off losses, and improving the buck converter's conversion efficiency. Compared to active snubber circuits, these circuits eliminate the need for auxiliary switch snubber circuits, resulting in higher converter efficiency and a simpler control circuit. In lossy snubber circuits, switching losses increase as power increases, leading to increased snubber circuit losses. The snubber circuit of the present invention reduces snubber circuit losses and improves buck converter efficiency.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A buffer circuit for a BUCK converter, characterized in that: It includes a power tube VT1, diodes D1, D2, VD1, resistors R1, R2, R3, Ro, capacitors C1, C2, C3, Co, inductors Lm, L1, input voltage Uin, and output voltage Uout; the positive electrode of the input voltage Uin is connected to the resistor R1 and the collector of the power tube VT1, the other end of the resistor R1 is connected to one end of the capacitor C1 and the cathode of the diode D1, the other end of the capacitor C1 and the anode of the diode D1 are connected to the negative electrode of the input voltage Uin, the emitter of the power tube VT1 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the negative electrode of the input voltage Uin; the negative .... 3 and the anode of the diode VD1, the other end of the resistor R3 is connected to one end of the capacitor C3, the other end of the capacitor C3 is connected to the anode of the diode D2, the cathode of the diode VD1, and one end of the inductor L1, the cathode of the diode D2 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the other end of the inductor L1, the emitter of the power tube VT1, and one end of the inductor Lm, the other end of the inductor Lm is connected to the resistor Ro and one end of the capacitor Co respectively, one end of the resistor Ro and the capacitor Co is the positive electrode of the output voltage Uout, the other end of the resistor Ro and the capacitor Co is connected to the anode of the diode VD1, and the other end of the resistor Ro and the capacitor Co is the negative electrode of the output voltage Uout; The diode VD1 is a fast recovery diode BYW29-200; the diode D1 is an ultra-fast recovery diode MUR3060PT; the diode D2 is an ultra-fast recovery diode MUR3060PT; the capacitor C1 is a double-sided metallized polypropylene film capacitor; the capacitor C2 is a double-sided metallized polypropylene film capacitor; the capacitor C3 is a double-sided metallized polypropylene film capacitor.

2. A buffer circuit for a BUCK converter according to claim 1, characterized in that: The power tube VT1 is an IGBT.

3. The buffer circuit for a BUCK converter according to claim 2, wherein: The capacitor Co is an aluminum electrolytic capacitor with a capacity of 250uF and a withstand voltage of 400V.

4. The buffer circuit for a BUCK converter according to claim 3, wherein: The IGBT model is CM200DY-12NF, with a rated voltage of 600V and a rated current of 200A.

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