CN110994983A - Improved BUCK converter and control method thereof - Google Patents

Improved BUCK converter and control method thereof Download PDF

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Publication number
CN110994983A
CN110994983A CN202010004036.2A CN202010004036A CN110994983A CN 110994983 A CN110994983 A CN 110994983A CN 202010004036 A CN202010004036 A CN 202010004036A CN 110994983 A CN110994983 A CN 110994983A
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China
Prior art keywords
power switch
switch tube
inductor
power
diode
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CN202010004036.2A
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Inventor
郭键
李明
周丽
陈蕾
唐恒亮
杨玺
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Beijing Wuzi University
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Beijing Wuzi University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The present invention provides an improved BUCK converter and a control method thereof, the improved BUCK converter including: the first power switch tube and the second power switch tube are connected with a power supply, the first power switch tube is connected with the second inductor in series, the first capacitor is connected with the first power switch tube in parallel, the second power switch tube is connected with the first inductor in series, the first inductor is connected with the second inductor in series, the primary side of the transformer is connected with the first diode, the first power switch tube and the first inductor, the secondary side of the transformer is connected with the third diode and grounded, the third diode is connected with the power supply, the second inductor is connected with a load in series, and the second end of the load is grounded. The method controls a BUCK converter. The embodiment of the invention provides an improved BUCK converter and a control method thereof, which improve the reliability of a circuit.

Description

Improved BUCK converter and control method thereof
Technical Field
The invention relates to the technical field of power electronics, in particular to an improved BUCK converter and a control method thereof.
Background
The improved BUCK converter has the advantages of simple structure, light weight, high efficiency and the like, is a circuit with wide application, and can be directly used in places needing direct voltage reduction due to the excellent voltage transformation function.
The improved BUCK converter can realize voltage reduction, but a high-frequency switch used by the converter is often in a hard-switching working state, namely a working state in which the voltage and the current are not zero, and according to UI, the switch generates power loss in the hard-switching working state, while in the high-frequency state, the power loss is larger, harsh noise is generated, and a plurality of problems of high switching loss, large voltage and current stress and the like exist.
Disclosure of Invention
In view of the problems in the prior art, embodiments of the present invention provide an improved BUCK converter and a control method thereof, which can at least partially solve the problems in the prior art.
In one aspect, the present invention provides an improved BUCK converter, including a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode, and a third diode, wherein:
the drain electrodes of the first power switch tube and the second power switch tube are respectively connected with the positive electrode of a power supply, the source electrode of the first power switch tube is connected with the first end of the second inductor, the first capacitor is respectively connected with the two ends of the first power switch tube, the source electrode of the second power switch tube is connected with the first end of the first inductor, and the second end of the first inductor is connected with the first end of the second inductor;
the negative electrode of the first diode is connected with the source electrode of the second power switch tube and the first end of the first inductor respectively, the positive electrode of the first diode is connected with the primary side first end of the transformer, the primary side second end of the transformer is connected with the source electrode of the first power switch tube and the second end of the first inductor respectively, the secondary side first end of the transformer is grounded, the secondary side second end of the transformer is connected with the positive electrode of the third diode, and the negative electrode of the third diode is connected with the positive electrode of the power supply;
the second end of the second inductor is connected with the first end of the load, the second end of the load is grounded, the cathode of the second diode is connected with the first end of the second inductor, and the anode of the second diode is grounded.
Wherein the first inductance is smaller than the second inductance.
The driving pulse widths of the first power switch tube and the second power switch tube are the same.
Wherein the second power switch tube is closed before the first power switch tube is closed.
Wherein the second power switch tube is disconnected before the first power switch tube is disconnected.
Wherein a clamping voltage of a secondary side of the transformer is equal to a voltage of the power supply.
The load circuit further comprises a second capacitor, wherein the first end of the second capacitor is respectively connected with the second end of the second inductor and the first end of the load, and the second end of the second capacitor is grounded.
The first power switch tube and the second power switch tube are metal-oxide semiconductor field effect transistors or insulated gate bipolar transistors.
In another aspect, the present invention provides a method for controlling an improved BUCK converter according to any of the above embodiments, including:
closing the second power switch tube and keeping the first power switch tube disconnected, so that the current of the power supply supplies power to the load through the second power switch tube, the first inductor and the second inductor;
after the first preset time, closing the first power switch tube, so that the current of the power supply is converged through the first branch circuit and the second branch circuit and flows through the second inductor to supply power to the load; the first branch circuit comprises the second power switch tube and the first inductor which are connected in series, and the second branch circuit comprises the first power switch;
and the second power switch tube is disconnected, so that the energy stored by the first inductor returns to the power supply through the secondary side of the transformer and the third diode, and the first power switch tube is disconnected after a second preset time, so that the power supply stops supplying power to the load.
Wherein the first preset time and the second preset time are both greater than time tdWherein:
td＝t+t'
t＝L1ID2/Vin
Figure BDA0002354558020000021
wherein L is1An inductance of the first inductance, VinIs the voltage of the power supply, ID2The current of the second diode at the conduction time of the second power switch tube, C1Is the capacitance of the first capacitor.
The improved BUCK converter comprises a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode, wherein the drains of the first power switch tube and the second power switch tube are respectively connected with the positive electrode of a power supply, the source of the first power switch tube is connected with the first end of the second inductor, the first capacitor is respectively connected with two ends of the first power switch tube, the source of the second power switch tube is connected with the first end of the first inductor, the second end of the first inductor is connected with the first end of the second inductor, the negative electrode of the first diode is respectively connected with the source of the second power switch tube and the first end of the first inductor, the positive electrode of the first diode is connected with the first end of the primary side of the transformer, the second end of the transformer is respectively connected with the source of the first power switch tube and the second end of the first inductor, the first end of the secondary side of the transformer is grounded, the second end of the secondary side of the transformer is connected with the anode of the third diode, the cathode of the third diode is connected with the anode of the power supply, the second end of the second inductor is connected with the first end of the load, the second end of the load is grounded, the cathode of the second diode is connected with the first end of the second inductor, and the anode of the second diode is grounded, so that zero-voltage conduction and turn-off of the first power switch tube are realized, zero-current conduction and zero-voltage turn-off of the second power switch tube are realized, the switching loss of the power switch tube is reduced, and the reliability of the circuit is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts. In the drawings:
fig. 1 is a schematic diagram of an improved BUCK converter according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of simulated waveforms of a driving signal, a voltage and a current of a second power switch according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of simulated waveforms of a driving signal, a voltage and a current of a first power switch according to an embodiment of the present invention.
Fig. 4 is a flowchart illustrating a control method of the improved BUCK converter according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
In order to facilitate understanding of the technical solutions provided in the present application, the following briefly describes the research background of the technical solutions in the present application. The soft switching technology can be divided into an active soft switching technology and a passive soft switching technology according to the existence of an auxiliary switching tube; for example, according to the technical development process, there are several types such as a quasi-resonant circuit, a zero-switch PWM circuit, and a zero-conversion PWM circuit. The resonant voltage peak value of the traditional quasi-resonant circuit is large, the requirement on devices is improved, and the auxiliary switch is often introduced into the latter two circuits and is an active soft switching circuit, so that the soft switching of a main circuit can be well realized. However, only when the auxiliary switch is in soft switching operation, the full soft switching operation can be realized, the control becomes relatively complex, and in comparison, the resonant circuit of the zero-conversion PWM circuit is not in the main loop, and the influence of the main loop is small. The improved BUCK converter provided by the embodiment of the invention adopts the active switch circuits of the auxiliary switch and the main switch, soft switching is realized on the main switch and the auxiliary switch, and the voltage and current stress of the auxiliary switch and the main switch is reduced.
Fig. 1 is a schematic structural diagram of an improved BUCK converter provided by an embodiment of the present invention, and as shown in fig. 1, the structure of the improved BUCK converter provided by the embodiment of the present invention includes a first power switch tube 1, a second power switch tube 2, a first capacitor 3, a first inductor 4, a second inductor 5, a transformer 6, a first diode 7, a second diode 8, and a third diode 9, where:
the drain electrodes of the first power switch tube 1 and the second power switch tube 2 are respectively connected with the positive electrode of a power supply, the source electrode of the first power switch tube 1 is connected with the first end of the second inductor 5, the first capacitor 3 is respectively connected with the two ends of the first power switch tube 1, the source electrode of the second power switch tube 2 is connected with the first end of the first inductor 4, and the second end of the first inductor 4 is connected with the first end of the second inductor 5;
the cathode of the first diode 7 is connected with the source of the second power switch tube 2 and the first end of the first inductor 4, the anode of the first diode 7 is connected with the first primary end a of the transformer 6, the second primary end b of the transformer 6 is connected with the source of the first power switch tube 1 and the second end of the first inductor 4, the first secondary end d of the transformer 6 is grounded, the second secondary end c of the transformer 6 is connected with the anode of the third diode 9, and the cathode of the third diode 9 is connected with the anode of the power supply;
the second end of the second inductor 5 is connected to the first end of the load 10, the second end of the load 10 is grounded, the cathode of the second diode 8 is connected to the first end of the second inductor 5, and the anode of the second diode 8 is grounded.
The operation principle of the improved BUCK converter provided by the embodiment of the invention is explained below.
When the circuit works in a stable state, the current in the first inductor 4 is zero, the second power switch tube 2 is closed after the power Vin is switched on, the first power switch tube 1 is in an off state, and at the moment, the current in the power Vin flows through the second power switch tube 2, the first inductor 4 and the second inductor 5 to supply power to the load 10. After a first preset time, when the voltage at a position a in fig. 1 is close to the voltage of the power source Vin, the first power switch tube 1 is closed, at this time, the first power switch tube 1 and the second power switch tube 2 are both closed, the current of the power source Vin is divided into two branches, the first branch passes through the second power switch tube 2 and the first inductor 4, the second branch passes through the first power switch tube 1, and the currents of the two branches join at a position a in fig. 1 and then flow through the second inductor 5 to supply power to the load 10. In the process of closing the power switch, when the second power switch tube 2 is closed, since the current of the first inductor 4 is zero, the conduction current in the process of closing the second power switch tube 2 is approximately zero, and the second power switch tube 2 can be regarded as zero current conduction; when the first power switch tube 1 is closed, since the voltage at a in fig. 1 is approximately equal to the voltage of the power source Vin, the voltage between the source and the drain of the first power switch tube 1 is approximately zero when the first power switch tube 1 is closed, and the first power switch tube 1 can be regarded as zero voltage conduction. The first preset time is set according to actual needs, and the embodiment of the invention is not limited.
When the power source Vin is required to stop supplying power to the load 10, the second power switch tube 2 is disconnected, the current of the second power switch tube 2 is transferred to the first power switch tube 1, the current of the first inductor 4 returns to the first inductor 4 after passing through the primary side (coil a/b) of the transformer 6 and the first diode 7, and the energy stored in the first inductor 4 returns to the power source Vin through the secondary side (coil c/d) of the transformer 6 and the third diode 9. When current flows through the secondary side (coil c/d) of the transformer 6, the clamping voltage at the two ends of the transformer is equal to the voltage of the power Vin, and the transformation ratio of the transformer 6 is designed so that the voltage at the two ends of the primary side of the transformer 6 is a small fixed value, for example 3V, compared with the voltage of the power Vin when current flows through the primary side of the transformer 6. Assuming that the first diode 7 is an ideal device, when the second power switch 2 is turned off, the first diode 7 is immediately turned on, the drain voltage of the second power switch 2 is approximately clamped at the voltage of the power Vin, and the second power switch 2 can be regarded as being turned off at zero voltage. After the second preset time, the first power switch tube 1 is turned off, and due to the existence of the first capacitor 3, the voltage between the drain and the source of the first power switch tube 1 is approximately zero in the turn-off process of the first power switch tube 1, and the first power switch tube 1 may be regarded as being turned off at zero voltage. After the first power switch tube 1 is turned off, the power source Vin charges the first capacitor 3, and the current is supplied to the load 10 through the first capacitor 3 and the second inductor 5. When the charging of the capacitor first capacitor 3 is finished, the second diode 8 is turned on, and the current charges the load 10 through the second diode 8 and the second inductor 5, wherein the second preset time is set according to actual needs, which is not limited in the embodiment of the present invention.
The transformer 6 is used for transferring the energy in the first inductor 4 to the power Vin when the second power switch tube 2 is turned off, and the voltage of the power Vin is stable, so that the primary side (coil a/b) of the transformer 6 can have a programmable voltage. The transformation ratio of the transformer 6 is determined according to the voltage that the primary side of the transformer 6 is expected to clamp during the energy transfer and the voltage of the secondary side. When the primary side clamping voltage of the transformer 6 is high, the energy transfer process in the first inductor 4 is fast, the phase shift between the first power switch tube 1 and the second power switch tube 2 is small, but the voltage of the second power switch tube 2 is high in the turn-off process, and the turn-off loss is large; the primary side clamping voltage of the transformer 6 is low, so that the phase shift between the first power switch tube 1 and the second power switch tube 2 which are driven in the first inductor 4 in the energy transfer process is relatively slow, the voltage of the second power switch tube 2 in the turn-off process is relatively low, and the turn-off loss is relatively low. Due to the transformer 6, a wide selection range of inductance values of the first inductor 4 is possible.
According to the working principle of the improved BUCK converter provided by the embodiment of the invention, the working process of the second inductor 5 in the switching-on and switching-off processes of the power Vin is completely the same as that of the inductor in the existing improved BUCK converter, the same power is output, and the current is not increased. The first inductor 4 returns its stored energy to the power source Vin through the transformer 6 only when the second power switch tube 2 is turned off, but because the inductance of the first inductor 4 is small, the energy returned to the power source Vin brings negligible stress to the second power switch tube 2. After the first capacitor 3 is charged, the energy is stored in the first inductor 4 during the discharging process, and the energy is supplied to the load 10 through the first inductor 4 to the second inductor 5, so that the energy on the first capacitor 3 is not lost. In summary, in the improved BUCK converter provided by the embodiment of the invention, the first power switch tube 1 and the second power switch tube 2 realize zero-current and zero-voltage switching, so that the switching loss is reduced. The improved BUCK converter provided by the embodiment of the invention does not increase the current and voltage stress of the power switch tube, realizes soft switching, reduces the switching loss of the power switch tube and improves the reliability of a circuit.
The improved BUCK converter provided by the embodiment of the invention comprises a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode, wherein the drain electrodes of the first power switch tube and the second power switch tube are respectively connected with the positive electrode of a power supply, the source electrode of the first power switch tube is connected with the first end of the second inductor, the first capacitor is respectively connected with two ends of the first power switch tube, the source electrode of the second power switch tube is connected with the first end of the first inductor, the second end of the first inductor is connected with the first end of the second inductor, the negative electrode of the first diode is respectively connected with the source electrode of the second power switch tube and the first end of the first inductor, the positive electrode of the first diode is connected with the first end of the primary side of the transformer, the second end of the primary side of the transformer is respectively connected with the source electrode of the first power switch tube and the second end of the first inductor, the first end of the secondary side of the transformer is grounded, the second end of the secondary side of the transformer is connected with the anode of the third diode, the cathode of the third diode is connected with the anode of the power supply, the second end of the second inductor is connected with the first end of the load, the second end of the load is grounded, the cathode of the second diode is connected with the first end of the second inductor, and the anode of the second diode is grounded, so that zero-voltage conduction and turn-off of the first power switch tube are realized, zero-current conduction and zero-voltage turn-off of the second power switch tube are realized, the switching loss of the power switch tube is reduced, and the reliability of the circuit is improved.
On the basis of the above embodiments, further, the first inductor 4 is smaller than the second inductor 5, the first inductor 4 may be set to be in the order of uH, for example, 10uH, and the second inductor 5 may be set to be several tens uH to several hundreds uH, for example, 66 uH.
In addition to the above embodiments, the driving pulse widths of the first power switch tube 1 and the second power switch tube 2 are the same.
On the basis of the above embodiments, further, the second power switch tube 2 is closed before the first power switch tube 1 is closed, that is, the second power switch tube 2 is closed first, and after the first preset time, the first power switch tube 1 is closed, so that the second power switch tube 2 is turned on at zero current, and the first power switch tube 1 is turned on at zero voltage.
On the basis of the above embodiments, further, the second power switch tube 2 is turned off before the first power switch tube 1 is turned off, that is, the second power switch tube 2 is turned off first, and after the second preset time, the first power switch tube 1 is turned off, so that the second power switch tube 2 is turned off at zero voltage, and the first power switch tube 1 is turned off at zero voltage.
On the basis of the above embodiments, further, the clamping voltage of the secondary side of the transformer 6 is equal to the voltage of the power source Vin.
On the basis of the above embodiments, further, the improved BUCK converter provided by the embodiment of the invention further includes a second capacitor 10, a first end of the second capacitor 10 is connected to the second end of the second inductor 5 and the first end of the load 10, respectively, and a second end of the second capacitor 10 is grounded.
In addition to the above embodiments, the first power switch tube 1 is a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) or an Insulated Gate Bipolar Transistor (IGBT), and the second power switch tube 2 is a MOSFET or an IGBT.
The improved BUCK converter provided by the embodiment of the invention can be divided into 7 modes in one switching period, and the operation process of the improved BUCK converter is analyzed as follows, assuming that each electronic device in fig. 1 is an ideal device.
Mode 1 (t)0～t1): at t0Before the moment, the first power switch tube 1 and the second power switch tube 2 are disconnected, and the currents of the first power switch tube 1 and the second power switch tube 2 are 0. The improved BUCK converter works in a current continuous mode, the second inductor 5 freewheels through the second diode 8, and the voltage of the point A in the circuit is 0. The current of the first inductor 4 is reduced to 0, the current of the primary side and the secondary side of the transformer 6 is 0, and the voltage at the two ends of the first capacitor 3 is equal to the voltage of the power Vin. At t0At the moment, the second power switch tube 2 is closed, and due to the existence of the first inductor 4, the conduction current of the second power switch tube 2 cannot change suddenly, and the second power switch tube 2 is conducted at zero current. After the second power switch tube 2 is turned on, the current of the first inductor 4 is linearly increased under the action of the power source Vin, meanwhile, the current of the second diode 8 is linearly decreased, the second diode 8 is turned off for zero current, and the current is turned off until t1The current of the second diode 8 at the time becomes 0. Let t0At the moment the current of the second diode 8 is ID2The time when the current conducted from the second power switch tube 2 to the second diode 8 is zero is t, where t is L1ID2/VinWherein L is1Is the inductance of the first inductance 4, VinIs the voltage of the power source Vin.
Mode 2 (t)1～t2)：t1At the moment the current of the second diode 8 becomes zero, the second diode 8 is turned off for zero current. The first inductor 4 and the first capacitor 3 start to work in resonance, the current in the first inductor 4 increases, the second inductor 4 starts to work in resonanceThe voltage across a capacitor 3 drops, the voltage at point A in the circuit gradually rises, t2At the moment, the voltage drop across the first capacitor 3 is zero, and the voltage at the point a in the circuit rises to the voltage of the power Vin. The time for the voltage between the two ends of the first capacitor 3 to drop to 0 is tc，
Figure BDA0002354558020000081
Wherein L is1Is the inductance of the first inductance 4, C1Is the capacitance of the first capacitance 3.
Mode 3 (t)2～t3)：t2At the moment, the voltage drop at two ends of the first capacitor 3 is 0, the power source Vin outputs energy through the second power switch tube 2, the first inductor 4 and the second inductor 5, and the first power switch tube 1 is switched on at any moment and is conducted at zero voltage.
Mode 4 (t)3～t4)：t3The first power switch tube 1 is closed at the moment and is conducted at zero voltage. At this time, the first power switch tube 1 and the second power switch tube 2 are both turned on, and the power source Vin outputs energy backwards through the first power switch tube 1 and the second power switch tube 2. The current of the first power switch tube 1 gradually increases, and the current of the second power switch tube 2 gradually decreases.
Mode 5 (t)4～t5)：t4At this time, the second power switch 2 is turned off and the first diode 9 is turned on. Assuming that the original secondary side turn ratio of the transformer 6 is 10, the secondary side clamp is positioned at the input power end, and the voltage of the power Vin is 48V, the primary side voltage of the transformer 6 is 4.8V, the energy of the first inductor 4 is output to the power Vin through the transformer 6, and theoretically, the energy in the first inductor 4 is lossless. Since the primary voltage of the transformer 6 is small relative to the input voltage, the turn-off process of the second power switch tube 2 can be considered as zero-voltage turn-off. The current of the second power switch tube 2 is transferred to the first power switch tube 1. To t5At this moment, the current of the first inductor 4 is zero. Assuming that the current of the first inductor 4 is I when the second power switch tube 2 is turned offL1The primary voltage of the transformer 6 is VOriginal source. The time taken from the disconnection of the second power switch tube 2 to the zero current of the first inductor 4 is tL，
Figure BDA0002354558020000091
Wherein L is1Is the inductance of the first inductance 4.
Modal 6 (t)5～t6): at t5After the moment, the first power switch tube 1 is turned off, and since the two ends of the first capacitor 3 cannot suddenly change, the first power switch tube 1 is turned off at zero voltage, and the voltage at the two ends of the first capacitor 3 gradually rises.
Mode 7 (t)6～t7)：t6At the moment the voltage across the first capacitor 3 equals the voltage of the supply Vin, the second diode 8 is freewheeling on. t is t7At the moment, the second power switch tube 2 is conducted, and the next switching period cycle is started.
Fig. 2 is a schematic diagram of simulated waveforms of a driving signal, a voltage, and a current of a second power switch tube according to an embodiment of the present invention, and fig. 3 is a schematic diagram of simulated waveforms of a driving signal, a voltage, and a current of a first power switch tube according to an embodiment of the present invention, as shown in fig. 2 and fig. 3, a zero-voltage switch is implemented in the first power switch tube 1, and a zero-current on and a zero-voltage off are implemented in the second power switch tube 2. The simulation waveforms in fig. 2 and 3 are that when the voltage of the power Vin is 96V, the inductance L of the first inductor 4 is12uH, inductance L of the second inductance 5266uH, the turns ratio of the transformer 6 is 10, and the capacitance C of the second capacitor 112The resistance of the load 10 is 5 ohms, the switching frequency is 25KHz, the driving phase difference between the first power switch tube 1 and the second power switch tube 2 is 4us, and the waveform obtained by simulation is carried out under the condition that the duty ratio is 60%.
The improved BUCK converter provided by the embodiment of the invention has the advantages of simple circuit structure, convenience in driving, small number of used devices, small voltage stress and current stress of the first power switching tube and the second power switching tube, contribution to saving cost, capability of realizing soft switching of the power switching tubes in a large load range and a large duty ratio and improvement on the working efficiency of a system.
Fig. 4 is a schematic flow chart of a control method of an improved BUCK converter according to an embodiment of the present invention, and as shown in fig. 4, a control method of an improved BUCK converter according to any of the embodiments of the present invention includes:
s401, closing a second power switch tube and keeping a first power switch tube disconnected, so that current of a power supply supplies power to a load through the second power switch tube, a first inductor and a second inductor;
specifically, after the power supply is switched on, the second power switch tube is closed and the first power switch tube is kept open, and at the moment, the current in the power supply flows through the second power switch tube, the first inductor and the second inductor to supply power to the load. When the second power switch tube is closed, because the current in the first inductor is zero, the conduction current in the closing process of the second power switch tube is approximately zero, and the second power switch tube can be regarded as zero current conduction.
S402, after a first preset time, closing the first power switch tube, enabling the current of the power supply to flow through the second inductor to supply power to the load after the current of the power supply is converged through the first branch circuit and the second branch circuit; the first branch circuit comprises the second power switch tube and the first inductor which are connected in series, and the second branch circuit comprises the first power switch;
specifically, after the second power switch tube is closed for a first preset time, the voltage at the input end of the second inductor is approximately equal to the voltage of the power supply, the first power switch tube is closed, at this time, the first power switch tube and the second power switch tube are both closed, the current of the power supply is divided into two branches, the first branch comprises the second power switch tube and the first inductor which are connected in series, and the second branch comprises the first power switch. And after the current of the power supply flows through the first branch circuit and the second branch circuit respectively, the current is converged at the input end of the second inductor and then supplies power to the load through the second inductor. When the first power switch tube is closed, since the voltage at the input end of the second inductor is approximately equal to the voltage of the power supply, the voltage between the source and the drain of the first power switch tube is approximately zero when the first power switch tube is closed, and the first power switch tube can be regarded as zero-voltage conduction. The first preset time is set according to actual needs, and the embodiment of the invention is not limited.
And S403, disconnecting the second power switch tube, enabling the energy stored in the first inductor to return to the power supply through a secondary side of the transformer and a third diode, and disconnecting the first power switch tube after a second preset time to enable the power supply to stop supplying power to the load.
Specifically, when the power supply stops supplying power to the load, the second power switching tube is disconnected, the current of the second power switching tube is transferred to the first power switching tube, the current of the first inductor returns to the first inductor after passing through the primary side of the transformer and the first diode, and the energy stored in the first inductor returns to the power supply through the secondary side of the transformer and the third diode. And after the second power switch tube is disconnected for a second preset time, the first power switch tube is disconnected, so that the power supply stops supplying power to the load. When the second power switch tube is switched off, the first diode is immediately switched on, the drain voltage of the second power switch tube is approximately clamped at the voltage of a power supply, and the second power switch tube can be regarded as being switched off at zero voltage. When the first power switch tube is turned off, due to the existence of the first capacitor, the voltage between the drain and the source of the first power switch tube is approximately zero in the turn-off process of the first power switch tube, and the first power switch tube can be regarded as being turned off at zero voltage.
The improved control method of the BUCK converter provided by the embodiment of the invention can close the second power switch tube and keep the first power switch tube disconnected, so that the current of the power supply supplies power to the load through the second power switch tube, the first inductor and the second inductor, after the first preset time, the first power switch tube is closed, the current of the power supply is converged through the first branch circuit and the second branch circuit and then flows through the second inductor to supply power to the load, the second power switch tube is disconnected, the energy stored in the first inductor returns to the power supply through the secondary side of the transformer and the third diode, the first power switch tube is disconnected after the second preset time, the power supply stops supplying power to the load, the zero-voltage conduction and disconnection of the first power switch tube are realized, and the zero-current conduction and zero-voltage disconnection of the second power switch tube are realized, so that the switching loss of the power switch tubes is reduced, the reliability of the circuit is improved.
On the basis of the foregoing embodiments, further, both the first preset time and the second preset time are greater than time tdWherein:
td＝t+t'
t＝L1ID2/Vin
Figure BDA0002354558020000111
wherein L is1An inductance of the first inductance, VinIs the voltage of the power supply, ID2The current of the second diode at the conduction time of the second power switch tube, C1Is the capacitance of the first capacitor.
Specifically, in order to obtain the best possible soft switching effect of the power switching tube, the first preset time is greater than the time tdThe second preset time is also greater than the time tdThat is, the time that the driving pulse of the first power switch tube lags behind the driving pulse of the second power switch tube is more than the time td. Wherein, tdT + t'. t is the time when the current from the second power switch tube to the second diode is zero, and t is L1ID2/VinWherein L is1An inductance of the first inductance, VinIs the voltage of the power supply, ID2The current of the second diode at the moment when the second power switch tube is conducted is obtained. After the current in the second diode becomes zero, the first inductor and the first capacitor start to work in resonance, the current in the first inductor increases, the voltage at two ends of the first capacitor decreases, the time for the voltage at the point A to gradually rise to the power voltage in figure 1 is t',
Figure BDA0002354558020000112
wherein L is1An inductance of the first inductance, C1Is the capacitance of the first capacitor. Wherein the inductance of the first inductor can be set to 10uH, and the inductance of the first capacitorThe capacitance can be set in the order of 10nF, tdThe driving pulse period of the first power switch tube or the second power switch tube can be one tenth to one fifth.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
In the description herein, reference to the description of the terms "one embodiment," "a particular embodiment," "some embodiments," "for example," "an example," "a particular example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. An improved BUCK converter, comprising a first power switch, a second power switch, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode, and a third diode, wherein:
the drain electrodes of the first power switch tube and the second power switch tube are respectively connected with the positive electrode of a power supply, the source electrode of the first power switch tube is connected with the first end of the second inductor, the first capacitor is respectively connected with the two ends of the first power switch tube, the source electrode of the second power switch tube is connected with the first end of the first inductor, and the second end of the first inductor is connected with the first end of the second inductor;
the negative electrode of the first diode is connected with the source electrode of the second power switch tube and the first end of the first inductor respectively, the positive electrode of the first diode is connected with the primary side first end of the transformer, the primary side second end of the transformer is connected with the source electrode of the first power switch tube and the second end of the first inductor respectively, the secondary side first end of the transformer is grounded, the secondary side second end of the transformer is connected with the positive electrode of the third diode, and the negative electrode of the third diode is connected with the positive electrode of the power supply;
the second end of the second inductor is connected with the first end of the load, the second end of the load is grounded, the cathode of the second diode is connected with the first end of the second inductor, and the anode of the second diode is grounded.
2. The improved BUCK converter as recited in claim 1, wherein the first inductance is less than the second inductance.
3. The improved BUCK converter according to claim 1, wherein the drive pulse widths of the first and second power switching transistors are the same.
4. The improved BUCK converter according to claim 1, wherein the second power switch is closed before the first power switch is closed.
5. The improved BUCK converter according to claim 1, wherein the second power switch is turned off before the first power switch is turned off.
6. The improved BUCK converter as recited in claim 1, wherein a clamping voltage of a secondary side of the transformer is equal to a voltage of the power supply.
7. The improved BUCK converter as recited in claim 1, further comprising a second capacitor, wherein a first end of the second capacitor is connected to a second end of the second inductor and a first end of the load, respectively, and a second end of the second capacitor is connected to ground.
8. The improved BUCK converter as recited in any one of claims 1 to 7, wherein the first power switch and the second power switch are metal-oxide semiconductor field effect transistors or insulated gate bipolar transistors.
9. A control method using the improved BUCK converter of any of claims 1 to 8, comprising:
closing the second power switch tube and keeping the first power switch tube disconnected, so that the current of the power supply supplies power to the load through the second power switch tube, the first inductor and the second inductor;
after the first preset time, closing the first power switch tube, so that the current of the power supply is converged through the first branch circuit and the second branch circuit and flows through the second inductor to supply power to the load; the first branch circuit comprises the second power switch tube and the first inductor which are connected in series, and the second branch circuit comprises the first power switch;
and the second power switch tube is disconnected, so that the energy stored by the first inductor returns to the power supply through the secondary side of the transformer and the third diode, and the first power switch tube is disconnected after a second preset time, so that the power supply stops supplying power to the load.
10. The method of claim 9, wherein the first predetermined time and the second predetermined time are both greater than time tdWherein:
td＝t+t'
t＝L1ID2/Vin
Figure FDA0002354558010000021
wherein L is1An inductance of the first inductance, VinIs the voltage of the power supply, ID2The current of the second diode at the conduction time of the second power switch tube, C1Is the capacitance of the first capacitor.
CN202010004036.2A 2020-01-03 2020-01-03 Improved BUCK converter and control method thereof Withdrawn CN110994983A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022022228A1 (en) * 2020-07-31 2022-02-03 中兴通讯股份有限公司 Non-isolated soft switch circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022022228A1 (en) * 2020-07-31 2022-02-03 中兴通讯股份有限公司 Non-isolated soft switch circuit

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