CN113949255A - Passive clamping circuit suitable for switching tube series type auxiliary power supply - Google Patents

Abstract

The invention discloses a passive clamping circuit suitable for a switching tube series type auxiliary power supply, belongs to the technical field of power electronics and switching power supplies, and aims to solve the problem that the existing auxiliary link for balancing the voltage of a series switching tube is applied to a switching tube series type forward and flyback converter, and the circuit structure is complex. The invention comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Switch tube S₁And S₂Respectively by C₁And C₂Clamping; the method specifically comprises the following steps: when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage equalization.

Description

Passive clamping circuit suitable for switching tube series type auxiliary power supply

Technical Field

The invention relates to a passive clamping circuit, and belongs to the technical field of power electronics and switching power supplies.

Background

With the continuous and deep research of domestic and foreign researchers in the field of power electronic technology, the dc power supply technology has been developed from the traditional linear power supply to the high-frequency switching power supply. At present, research on high-frequency switching power supplies and related technologies thereof has been well developed, and switching power supplies of various power levels have been widely used in various fields of industry and civilian use. With the development of national economy, various electric equipment is more and more in variety, the input voltage grades of power supplies of the electric equipment are different, and various high-voltage input occasions are gradually increased. For example, 1000V dc bus in future ships and drones will become the mainstream; in an urban rail transit system, a power supply grid of a vehicle generally has two systems of 750V direct current and 1500V direct current, wherein the maximum power supply voltage of the power supply grid can reach more than 1800V direct current; in a high-speed railway electrical system, the voltage of an input direct-current bus of various electrical equipment on a vehicle can be up to 2000-4000V; in mining production, the direct-current bus voltage of the high-voltage high-power coal cutter frequency converter can reach 2000-3000V, even higher; in modern energy internet, the medium-voltage interconnection bus voltage of a flexible direct-current power distribution network can reach 10000V. The limitation of factors such as the voltage grade of a power device and the like is always a difficult point in the design process of a high-voltage converter how to effectively reduce the voltage stress of various devices.

The mode of connecting a plurality of switching tubes in series is the most direct method for reducing the voltage stress of the switching device of the high-voltage converter. The key of the application of the plurality of switching tubes in series is to ensure the voltage balance of each switching tube at the switching state transition moment and after the switching tube enters a stable working state, namely, the dynamic voltage balance and the static voltage balance. The static balance of the voltage of each series-connected switching tube can be realized by connecting a resistor with a larger resistance value in parallel with each switching tube, but the dynamic voltage balance is generally not easy to realize. In general, two basic ways of power end control and driving end control can be adopted to realize the dynamic voltage equalization of each series switch tube. The power end control is generally implemented by adding buffer circuits or clamping circuits and other auxiliary links at two ends of each series-connected switching tube to absorb the overvoltage at the moment of switching on and switching off each switching tube. The driving end control is usually adopted to realize the synchronization of the on and off of each series switching tube, and common methods include synchronous control, master-slave control and the like. If the voltage-sharing implementation method is classified according to whether active devices are adopted or not, various existing voltage-sharing implementation methods of the series switch tube can be divided into a passive method and an active method. The typical passive voltage-sharing method is to add passive buffer circuits at two ends of each switching tube, which increases the loss of the circuit and limits the switching frequency of each switching tube.

When the auxiliary link for ensuring the voltage balance of the series switching tube is applied to the switching tube series forward and flyback converters, the forward converter needs to be added with the magnetic reset link of the transformer, and the flyback converter needs to be added with the leakage inductance energy absorption circuit of the transformer, so that the circuit structure becomes very complicated.

Disclosure of Invention

The passive clamping circuit is suitable for the switching tube series auxiliary power supply, and can omit a magnetic reset link when the passive clamping circuit is applied to a forward converter; when the passive clamping circuit is applied to the flyback converter, the flyback converter can omit a transformer leakage inductance energy absorption circuit, and the circuit structure is simplified.

The invention relates to a passive clamping circuit suitable for a switching tube series auxiliary power supply, which adopts two switching tubes S₁、S₂Series connected converters of forward typeA flyback or flyback converter;

the passive clamping circuit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

switch tube S₁And S₂Respectively by C₁And C₂Clamping; the method specifically comprises the following steps:

when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage ofAnd (4) equalizing.

Further, the device also comprises a diode D_LDiode D_LAnode of (2) is connected with a coupling inductor L₁And a diode D_L1Of a common node, diode D_LThe cathode of the converter is connected with the primary side of the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

Furthermore, coupling inductor L of clamping circuit in flyback converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

in the formula: l is_pPrimary winding inductance, L, of transformer for flyback converter_lkTransformer equivalent leakage inductance, V, of flyback converter_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iFor the converter input-side voltage, D is the switching tube S in each switching cycle₁And S₂The duty cycle of (c).

Further, coupling inductance L of clamping circuit in forward converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

L_mfor positive exciting transformer T_FIs equivalent toMagnetic inductance, V_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iFor the converter input-side voltage, D is the switching tube S in each switching cycle₁And S₂The duty cycle of (c).

Further, the winding also comprises a flyback winding L_fAnd a diode D_fFlyback winding L_fAnd a diode D_fA series branch connected in parallel with the output side of the converter, a flyback winding L_fAnd a coupling inductor L₁、L₂Wound together on the same core, coupled with an inductor L₁、L₂The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

Furthermore, coupling inductor L of clamping circuit in flyback converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

in the formula: l is_pPrimary winding inductance, L, of transformer for flyback converter_lkTransformer equivalent leakage inductance, V, of flyback converter_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iIs the converter input side voltage, V_oFor the converter output side voltage, n_fFor coupling an inductance L₁Winding turns and flyback winding L thereof_fThe ratio of the number of winding turns of (c),

d is a switching tube S in each switching period₁And S₂The duty cycle of (c).

Further, coupling inductance L of clamping circuit in forward converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

L_mfor positive exciting transformer T_FEquivalent excitation inductance of, V_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iIs the converter input side voltage, V_oFor the converter output side voltage, n_fFor coupling an inductance L₁Winding turns and flyback winding L thereof_fThe ratio of the number of winding turns of (c),

d is a switching tube S in each switching period₁And S₂The duty cycle of (c).

The invention also provides a technical scheme that: the passive clamping circuit is suitable for a switching tube series type auxiliary power supply, the switching tube series type auxiliary power supply adopts a converter with 2K switching tubes connected in series, and the converter is a forward converter or a flyback converter; the passive clamping circuit comprises K clamping units and a diode D_L；

2K series-connected switch tubes in the converter are divided into K pairs, every two adjacent switch tubes are 1 pair, each pair of series-connected switch tubes is provided with 1 clamping unit, and each clamping unit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

the coupling inductors of the K clamping units are wound on the same magnetic core together;

diode D_LAnode of the anode is connected with the coupling inductor L in the topmost clamping unit₁And a diode D_L1Of a common node, diode D_LThe cathode of the converter is connected with the primary side of the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

The invention also provides a technical scheme that: the passive clamping circuit is suitable for a switching tube series type auxiliary power supply, the switching tube series type auxiliary power supply adopts a converter with 2K switching tubes connected in series, and the converter is a forward converter or a flyback converter; the passive clamping circuit comprises K clamping units and a flyback winding L_fAnd a diode D_f；

2K series-connected switch tubes in the converter are divided into K pairs, every two adjacent switch tubes are 1 pair, each pair of series-connected switch tubes is provided with 1 clamping unit, and each clamping unit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

the coupling inductors of the K clamping units are wound on the same magnetic core together;

flyback winding L_fAnd a diode D_fA series branch connected in parallel with the output side of the converter, a flyback winding L_fCoupling inductor L with K clamping units₁、L₂Wound together on the same core, coupled with an inductor L₁、L₂The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

The invention has the beneficial effects that: the invention relates to a passive clamping circuit suitable for switching tube series flyback and forward auxiliary power converters, which is used in the occasions of high-voltage input and medium and small power. The passive clamping circuit consists of a clamping capacitor, a coupling inductor and a diode, and has the advantages of simple structure and high reliability. In the operation process of the related converter, the adoption of the passive clamping circuit can effectively ensure the voltage balance of each series switch tube. In addition, when the passive clamping circuit is applied to a flyback converter, the passive clamping circuit can also complete the absorption of the leakage inductance energy of the transformer and feed the absorbed energy back to the input side or the output side of the converter, so that the flyback converter does not need to adopt various traditional transformer leakage inductance energy absorption circuits; when the passive clamping circuit is applied to the forward converter, the magnetic reset of the transformer can be completed by the passive clamping circuit, and the absorbed transformer excitation inductance energy is fed back to the input side or the output side of the converter, so that the forward converter does not need to adopt various traditional transformer magnetic reset links. The structure of the switch tube series flyback and forward auxiliary power supply converter is greatly simplified.

Drawings

Fig. 1 is a schematic diagram of a passive clamp circuit for a switching tube series type auxiliary power supply according to the present invention, in which two switches are connected in series with a flyback converter, and a clamp circuit with a first structure;

fig. 2 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, in which two switches are connected in series to a flyback converter, and a clamp circuit with a second structure;

FIG. 3 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, in which two switches are connected in series with a forward converter, and the clamp circuit has a first structure;

FIG. 4 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, in which two switches are connected in series with a forward converter, and a clamp circuit of a second structure;

fig. 5(a) - (d) are equivalent circuits of stages of a two-switch-tube series flyback converter using the passive clamp circuit shown in fig. 1;

fig. 6 (a) - (d) are equivalent circuits of stages of a two-switch-tube series flyback converter using the passive clamp circuit shown in fig. 2;

fig. 7 (a) to (c) are equivalent circuits of stages of a two-switch-transistor series forward converter using the passive clamp circuit shown in fig. 3;

fig. 8 (a) to (c) are equivalent circuits of stages of a two-switch-transistor series forward converter using the passive clamp circuit shown in fig. 4;

fig. 9 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, a four-switch series flyback converter, a first structure clamp circuit;

fig. 10 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, a four-switch series flyback converter, and a clamp circuit with a second structure;

fig. 11 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, a four-switch series forward converter, a first clamp structure; (ii) a

Fig. 12 is a schematic diagram of a passive clamp circuit for a switching tube series auxiliary power supply according to the present invention, a four-switch series forward converter, and a second clamp circuit;

Detailed Description

In the medium and small power occasions, the auxiliary power supply generally adopts a flyback or forward topological structure. The flyback converter comprises a flyback transformer T_fFlyback transformer T_fEquivalent leakage inductance L of_lkDC input voltage V_iDC output voltage V_oAnd an output rectifier diode D_oAnd an output filter capacitor C_o，L_pAnd L_sRespectively, a flyback transformer T_fPrimary winding, secondary winding and output filter capacitor C_oA load with two ends connected in parallel, and the voltage at two ends of the load is DC output voltage V_o。

The forward converter comprises a forward transformer T_FDC input voltage V_iDC output voltage V_oAnd an output rectifier diode D_o1Freewheel diode D_o2An output filter inductor L_oAnd an output filter capacitor C_o，L_mFor positive exciting transformer T_FEquivalent excitation inductance, output filter capacitance C_oTwo ends are connected in parallelThe voltage at two ends of the load is DC output voltage V_o。

The first embodiment is as follows: the present embodiment will be described below with reference to fig. 1 to 4, and the passive clamp circuit applied to the switching tube series type auxiliary power supply in the present embodiment is a two-switching tube series type flyback and forward (fig. 1 and 2 are flyback and fig. 3 and 4 are forward) auxiliary power supply converter (here, a two-switching tube series type converter is mainly used as an example for description). S₁And S₂There are 2 Power switch tubes (typically Power MOSFET switch tubes) connected in series.

The proposed passive clamp circuit has 2 basic structures according to the different energy feedback directions. Wherein: passive clamp (configuration 1) as shown in fig. 1 and 3, this passive clamp feeds back the absorbed energy to the input side of the converter during each switching cycle; passive clamp (configuration 2) as shown in fig. 2 and 4 feeds the absorbed energy back to the output side of the converter during each switching cycle. The passive clamping circuit with 2 structures mainly comprises a clamping capacitor (C)₁＝C₂) Coupled inductor (L)₁＝L₂) And a diode (D)₁、D₂、D_L1、D_L2) And (4) forming. On the basis, a diode D is added in the structure 1_LThe passive clamping circuit is used for feeding the energy absorbed by the passive clamping circuit back to the input side of the converter; in the structure 2, a flyback winding L is added on the coupling inductor_fAnd connected to diode D_fFor feeding back the energy absorbed by the passive clamp to the output side of the converter.

The second embodiment is as follows: the present embodiment will be described below with reference to fig. 1 and 2, and the present embodiment further describes an embodiment, which analyzes the operation of a two-switch-transistor series flyback converter using a passive clamp circuit. For ease of analysis, the following assumptions: the flyback converter operates in a Discontinuous Current Mode (DCM); all devices in the circuit are ideal devices; clamping capacitor C₁、C₂And an output filter capacitor C_oThe capacitance value of (a) is large enough, and the voltage is considered as a constant voltage source during analysis.

FIG. 1 shows a passive clamp circuit with a diode D_LWill couple the inductance L₁、L₂The energy absorbed during each switching cycle is fed back to the input side of the converter. FIG. 2 shows a passive clamp circuit with flyback winding L_fAnd a diode D_fThe formed series branch circuit couples the inductor L₁、L₂The energy absorbed during each switching cycle is fed back to the output side of the converter. The clamping circuit of the flyback converter of the embodiment not only realizes the voltage clamping function of the series switching tube, but also realizes the energy recovery function, and a separate energy absorption circuit is not required to be added, so that the whole circuit structure is simplified.

The passive clamp circuit of FIG. 1 includes a clamp capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

switch tube S₁And S₂Respectively by C₁And C₂Clamping; in particular toComprises the following steps:

when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage equalization.

Further, a diode D_LAnode of (2) is connected with a coupling inductor L₁And a diode D_L1Of a common node, diode D_LThe cathode of the converter is connected with the primary side of the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

C of clamp circuit₂The anode is connected with a primary winding of a transformer and a diode D_LCathode of the capacitor is connected with a direct current input voltage V_iAnd the primary side of the transformer.

The working process of the passive clamp circuit shown in fig. 1 is as follows:

in 1 switching period, the two-switch-tube series flyback converter shown in fig. 1 has the following 4 main operation stages, and the equivalent circuit of each stage is shown in fig. 5.

Working phase 1 (t)_f0～t_f1)：t_f0At any moment, switch tube S₁And S₂And conducting. At this stage, the input voltage V_iTo flyback transformer T_fPrimary side inductance L of_pCharging, the inductor current rises from zero, and the output current of the converter is only output by the output filter capacitor C_oAnd (4) discharging and providing. In the clamping circuit, a clamping capacitor C₁By S₁、S₂And D_L1To L₁Discharge, C₂By S₁、S₂And D_L2To L₂Discharging and the coupled inductor current rises from zero. To t_f1Moment, end of this phase, L₁、L₂And L_pUp to a maximum value within 1 switching cycle.

Working phase 2 (t)_f1～t_f2)：t_f1At any moment, switch tube S₁And S₂And (6) turning off. t is t_f1After the moment, the flyback transformer T_fPrimary side inductance L of_pEnergy transfer to secondary inductor L_sAnd through an output rectifier diode D_oTo the load. In this process, L_pIs clamped at nV_o(in the figure, the positive and negative polarities are up-negative-down-positive, and n is a flyback transformer T_fThe ratio of primary and secondary winding turns of (1), where n²＝L_p/L_s) Leakage inductance L_lkEnergy clamped capacitor C₁、C₂Absorption (clamping capacitor voltage V)_C1＝V_C2>V_i/2+nV_o/2). In the clamping circuit, D₁、D₂、D_LAnd D_L2On, D_L1At this time, L₁And L₂In series and through D_L、D₁And D₂Energy is fed back to the input side of the converter. To t_f2Moment, leakage inductance L_lkThe current of (2) is reduced to zero and the phase ends.

Working phase 3 (t)_f2～t_f4)：t_f2After time, L_sContinuing to transfer energy to the load, L₁And L₂And continuously feeding back energy to the input side of the converter. To t_f3Time of day, L₁And L₂Is reduced to zero, to t_f4Time of day, L_sThe current of (2) is reduced to zero and the phase ends. In this stage, the sequence of the reduction of the inductor current to zero does not need to be strictly fixed.

Working phase 4 (t)_f4～t_f5): to t_f4After the moment, the primary and secondary side currents of the transformer are kept to be zero, and the output current of the converter is only output by an output filter capacitor C_oAnd (4) discharging and providing. To t_f5Time of day, switchPipe S₁And S₂And conducting again, and enabling the converter to enter the work of the next switching period.

The passive clamp circuit of fig. 2 includes a clamp capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

switch tube S₁And S₂Respectively by C₁And C₂Clamping; the method specifically comprises the following steps:

when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage equalization.

Further, a flyback winding L is included_fAnd a diode D_fFlyback winding L_fAnd a diode D_fA series branch connected in parallel with the output side of the converter, a flyback winding L_fAnd a coupling inductor L₁、L₂Wound together on the same core, coupled with an inductor L₁、L₂The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

Diode D of series branch in clamping circuit_fCathode connected rectifier diode D_oFlyback winding L with cathode and series branch_fEnd connection output filter capacitor C_oAnd a loaded negative terminal.

The operation of the passive clamp circuit shown in fig. 2:

in 1 switching period, the two-switch-tube series flyback converter shown in fig. 2 has the following 4 main operation stages, and the equivalent circuit of each stage is shown in fig. 6.

Working phase 1 (t)_f0～t_f1)：t_f0At any moment, switch tube S₁And S₂And conducting. At this stage, the input voltage V_iTo flyback transformer T_fPrimary side inductance L of_pCharging, the inductor current rises from zero, and the output current of the converter is only output by the output filter capacitor C_oAnd (4) discharging and providing. In the clamping circuit, a clamping capacitor C₁By S₁、S₂And D_L1To L₁Discharge, C₂By S₁、S₂And D_L2To L₂Discharging and the coupled inductor current rises from zero. To t_f1Moment, end of this phase, L₁、L₂And L_pUp to a maximum value within 1 switching cycle.

Working phase 2 (t)_f1～t_f2)：t_f1At any moment, switch tube S₁And S₂And (6) turning off. t is t_f1After the moment, the flyback transformer T_fPrimary side inductance L of_pEnergy transfer to secondary inductor L_sAnd through an output rectifier diode D_oTo the load. In this process, L_pIs clamped at nV_o(in the figure, the positive and negative polarities are up-negative-down-positive, and n is a flyback transformer T_fThe ratio of primary and secondary winding turns of (1), where n²＝L_p/L_s) Leakage inductance L_lkEnergy clamped capacitor C₁、C₂Absorption (clamping capacitor voltage V)_C1＝V_C2>V_i/2+nV_o/2). In the clamping circuit, D₁、D₂And D_fOn, D_L1And D_L2When the inductor is cut off, the energy of the coupled inductor is transferred to the flyback winding L of the coupled inductor_fUpper, L₁And L₂The current becomes zero, L_fEnergy of (D) through_fTo the load. To t_f2Moment, leakage inductance L_lkThe current of (2) is reduced to zero and the phase ends.

Working phase 3 (t)_f2～t_f4)：t_f2After time, L_sAnd L_fEnergy continues to be delivered to the load. To t_f3Time of day, L_fIs reduced to zero, to t_f4Time of day, L_sThe current of (2) is reduced to zero and the phase ends. In this stage, the sequence of the reduction of the inductor current to zero does not need to be strictly fixed.

Working phase 4 (t)_f4～t_f5): to t_f4After the moment, the primary and secondary side currents of the transformer are kept to be zero, and the output current of the converter is only output by an output filter capacitor C_oAnd (4) discharging and providing. To t_f5At any moment, switch tube S₁And S₂And conducting again, and enabling the converter to enter the work of the next switching period.

In the working process of the passive clamping circuit (structure 1), 2 equivalent inductors L of the coupling inductor₁And L₂The coupling effect of (A) occurs in the working stage 1-3; in the working process of the passive clamping circuit (structure 2), 2 equivalent inductors L of the coupling inductor₁And L₂By coupling ofOccurs in working phase 1. In the process, if the clamping capacitor C₁And C₂Are different, they will pass through the coupling inductance (L)₁And L₂) Energy mutual transmission is realized: when C is present₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling inductance to C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling inductance to C₁And (5) transferring. Thus, during operation of the converter, the clamping capacitance C is ensured during each switching cycle due to the presence of the coupling inductance₁And C₂Voltage equalization. At the switch tube S₁And S₂During the operation of the switch, the maximum voltage is respectively C₁And C₂The clamping, therefore, adoption of the proposed passive clamping circuit (structure 1 or structure 2) realizes voltage equalization of each series-connected switching tube of the switching tube series-connected flyback converter.

In the operation of the passive clamp (structure 1 and structure 2), the clamp capacitor C₁And C₂Should be large enough to ensure C₁And C₂The voltage is approximately constant during the charging and discharging of each switching cycle.

Coupling inductor L of clamping circuit (structure 1 and structure 2) in flyback converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

to ensure that the coupling inductance current can be reduced to zero during the switching tube is turned off;

in the formula: v_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂A voltage across the terminals D is the switching tube S in each switching cycle₁And S₂Duty ratio of (D ═ t)_f1-t_f0) and/T, T is a switching period.

For the passive clamp (structure 2), to ensure that the energy of the coupling inductor can be transferred to the flyback winding L after the switching tube is turned off_fAbove, further guarantees are required:

wherein n is_fFor coupling an inductance L₁Winding turns and flyback winding L thereof_fThe ratio of the number of winding turns of (c),

the third concrete implementation mode: the present embodiment will be described below with reference to fig. 3 and 4, and the present embodiment further describes an embodiment in which the operation of a two-switch-transistor series forward converter using the proposed passive clamp circuit is analyzed. For ease of analysis, the following assumptions: the forward converter operates in a Continuous Current Mode (CCM) of an output filter inductor; all devices in the circuit are ideal devices; clamping capacitor C₁、C₂And an output filter capacitor C_oThe capacitance value of (a) is large enough, and the voltage is considered as a constant voltage source during analysis.

FIG. 3 shows a passive clamp circuit with a diode D_LWill couple the inductance L₁、L₂The energy absorbed in each switching cycle is fed back to the input side of the forward converter. FIG. 4 shows a passive clamp circuit with flyback winding L_fAnd a diode D_fThe formed series branch circuit couples the inductor L₁、L₂The energy absorbed in each switching cycle is fed back to the output side of the forward converter. The clamping circuit of the forward converter of the embodiment not only realizes the clamping function of the series switching tube, but also completely absorbs the excitation inductance energy of the transformer during the turn-off period of the switching tube, thereby realizing the magnetic reset function of the forward converter, so that a separate magnetic reset circuit is not required to be added, and the whole circuit structure is simplified.

Passive clamp circuit clamping capacitor C as shown in fig. 3₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

switch tube S₁And S₂Respectively by C₁And C₂Clamping; the method specifically comprises the following steps:

when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage equalization.

Further, two polesPipe D_LAnode of (2) is connected with a coupling inductor L₁And a diode D_L1Of a common node, diode D_LThe cathode of the converter is connected with the primary side of the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

C of clamp circuit₂The anode is connected with a synonym terminal of a primary winding of the transformer and a diode D_LCathode of the capacitor is connected with a direct current input voltage V_iThe positive pole of the transformer and the same name end of the primary winding.

The operation of the passive clamp circuit shown in fig. 3:

in 1 switching cycle, the two-switch tube series forward converter shown in fig. 3 has the following 3 main operation stages, and the equivalent circuit of each stage is shown in fig. 7.

Working phase 1 (t)_F0～t_F1)：t_F0At any moment, switch tube S₁And S₂And conducting. At this stage, the rectifier diode D is output_o1Conducting, freewheeling diode D_o2Cut-off, input voltage V_iBy means of a forward transformer T_FExciting inductance L of transformer for supplying power to load_mCurrent and output filter inductance L_oThe current rises linearly. In the clamping circuit, a clamping capacitor C₁By S₁、S₂And D_L1To L₁Discharge, C₂By S₁、S₂And D_L2To L₂Discharging and the coupled inductor current rises from zero. To t_F1Moment, end of this phase, L₁、L₂、L_mAnd L_oUp to a maximum value within 1 switching cycle.

Working phase 2 (t)_F1～t_F3)：t_F1At any moment, switch tube S₁And S₂And (6) turning off. t is t_F1After the moment, the output rectifier diode D_o1Cut-off, freewheeling diode D_o2Conducting and outputting filter inductor L_oBy D_o2Freewheels and provides energy to the load. In the process, the magnet is excitedMagnetic inductance L_mEnergy direction clamping capacitor C₁、C₂And (4) releasing. In the clamping circuit, D₁、D₂、D_LAnd D_L2On, D_L1At this time, L₁And L₂In series and through D_L、D₁And D₂Energy is fed back to the input side of the converter. To t_F2Time of day, L₁And L₂Is reduced to zero, to t_F3Moment, excitation inductance L_mThe current of (2) is reduced to zero and the phase ends. In this stage, the sequence of the reduction of the inductor current to zero does not need to be strictly fixed.

Working phase 3 (t)_F3～t_F4): to t_F3After the moment, the primary and secondary side currents of the transformer are kept to be zero, and the output filter inductance L_oEnergy continues to be provided to the load. To t_F4At any moment, switch tube S₁And S₂And conducting again, and enabling the converter to enter the work of the next switching period.

The passive clamp circuit of fig. 4 includes a clamp capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

switch tube S₁And S₂Respectively by C₁And C₂Clamping; the method specifically comprises the following steps:

when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage equalization.

Further, a flyback winding L is included_fAnd a diode D_fFlyback winding L_fAnd a diode D_fA series branch connected in parallel with the output side of the converter, a flyback winding L_fAnd a coupling inductor L₁、L₂Wound together on the same core, coupled with an inductor L₁、L₂The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

Diode D of series branch in clamping circuit_fCathode connection output filter inductor L_oAnd an output filter capacitor C_oCommon node, flyback winding L of series branch_fEnd connection output filter capacitor C_oAnd a loaded negative terminal.

The operation of the passive clamp circuit shown in fig. 4:

in 1 switching period, the two-switch tube series forward converter shown in fig. 4 has the following 3 main operation stages, and the equivalent circuit of each stage is shown in fig. 8.

Work byStage 1 (t)_F0～t_F1)：t_F0At any moment, switch tube S₁And S₂And conducting. At this stage, the rectifier diode D is output_o1Conducting, freewheeling diode D_o2Cut-off, input voltage V_iBy means of a forward transformer T_FExciting inductance L of transformer for supplying power to load_mCurrent and output filter inductance L_oThe current rises linearly. In the clamping circuit, a clamping capacitor C₁By S₁、S₂And D_L1To L₁Discharge, C₂By S₁、S₂And D_L2To L₂Discharging and the coupled inductor current rises from zero. To t_F1Moment, end of this phase, L₁、L₂、L_mAnd L_oUp to a maximum value within 1 switching cycle.

Working phase 2 (t)_F1～t_F3)：t_F1At any moment, switch tube S₁And S₂And (6) turning off. t is t_F1After the moment, the output rectifier diode D_o1Cut-off, freewheeling diode D_o2Conducting and outputting filter inductor L_oBy D_o2Freewheels and provides energy to the load. In this process, the magnetizing inductance L_mEnergy direction clamping capacitor C₁、C₂And (4) releasing. In the clamping circuit, D₁、D₂And D_fOn, D_L1And D_L2When the inductor is cut off, the energy of the coupled inductor is transferred to the flyback winding L of the coupled inductor_fUpper, L₁And L₂The current becomes zero, L_fEnergy of (D) through_fTo the load. To t_F2Time of day, L_fIs reduced to zero, to t_F3Moment, excitation inductance L_mThe current of (2) is reduced to zero and the phase ends. In this stage, the sequence of the reduction of the inductor current to zero does not need to be strictly fixed.

Working phase 3 (t)_F3～t_F4): to t_F3After the moment, the primary and secondary side currents of the transformer are kept to be zero, and the output filter inductance L_oEnergy continues to be provided to the load. To t_F4At any moment, switch tube S₁And S₂And conducting again, and enabling the converter to enter the work of the next switching period.

In the working process of the passive clamping circuit (structure 1), 2 equivalent inductors L of the coupling inductor₁And L₂The coupling takes place in working phases 1 and 2; in the working process of the passive clamping circuit (structure 2), 2 equivalent inductors L of the coupling inductor₁And L₂Occurs in operating phase 1. In the process, if the clamping capacitor C₁And C₂Are different, they will pass through the coupling inductance (L)₁And L₂) Energy mutual transmission is realized: when C is present₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling inductance to C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling inductance to C₁And (5) transferring. Thus, during operation of the converter, the clamping capacitance C is ensured during each switching cycle due to the presence of the coupling inductance₁And C₂Voltage equalization. At the switch tube S₁And S₂During the operation of the switch, the maximum voltage is respectively C₁And C₂The clamping circuit (structure 1 or structure 2) realizes the voltage equalization of each series-connected switch tube of the switch tube series-connected forward converter.

In the operation of the passive clamp (structure 1 and structure 2), the clamp capacitor C₁And C₂Should be large enough to ensure C₁And C₂The voltage is approximately constant during the charging and discharging of each switching cycle.

Coupling inductor L of clamping circuit in forward converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

in the formula: l is_mFor positive exciting transformer T_FEquivalent excitation inductance of, V_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iIs the converter input side voltage, V_oFor the converter output side voltage, n_fFor coupling an inductance L₁Winding turns and flyback winding L thereof_fThe ratio of the number of winding turns of (c),

d is a switching tube S in each switching period₁And S₂The duty cycle of (c).

Condition 1 is to ensure that the excitation inductance energy of the forward transformer is completely absorbed during the turn-off period of the switching tube, that is, the forward transformer realizes magnetic reset, and condition 1 applies to both structure 1 and structure 2.

Condition 2 is to ensure that the coupled inductor current in the passive clamp (applicable to configuration 1) can be reduced to zero during the switching off of the switching tube.

Condition 3 is to ensure that the energy of the coupled inductor in the passive clamp (applicable to configuration 2) can be transferred to the flyback winding Lf after the switching transistor is turned off.

The fourth concrete implementation mode: the following describes the present embodiment with reference to fig. 9 and 10, which is an extension of the two-switch-tube series flyback converter of the second embodiment, where the switch-tube series auxiliary power supply adopts a converter with 2K switch tubes connected in series, and when K is 2, the converter is a four-switch series flyback converter, and the passive clamp circuit of fig. 9 feeds back the absorbed energy to the input side of the converter in each switching period; FIG. 10 passive clamp circuit feeds the absorbed energy back to the output side of the converter during each switching cycle; the clamp circuit mainly comprises a clamp capacitor (C)₁＝C₂＝C₃＝C₄) Coupled inductor (L)₁＝L₂＝L₃＝L₄) And a diode (D)₁、D₂、D₃、D₄、D_L1、D_L2、D_L3、D_L4) And (4) forming.

On the basis, a diode D is added in the figure 9 (structure 1)_LThe passive clamping circuit is used for feeding the energy absorbed by the passive clamping circuit back to the input side of the converter; the method specifically comprises the following steps:

the passive clamping circuit comprises 4 clamping units and a diode D_L；

4 series switch tubes in the converter are divided into 2 pairs, two adjacent switch tubes are 1 pair, each pair of series switch tubes is provided with 1 clamping unit, and a switch tube S₁、S₂The clamping unit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Switch tube S₃、S₄The clamping unit comprises a clamping capacitor C₃、C₄(ii) a Diode D₃、D₄、D_L3And D_L4(ii) a And a coupling inductor L₃、L₄(ii) a Coupling inductor L₁、L₂、L₃、L₄The winding turns are the same, and the winding turns are wound on the same magnetic core together;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a); coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1); coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

clamping capacitor C₄Two, twoPolar tube D₄Diode D₃A clamp capacitor C₃Clamping capacitors C connected in series in the series branch₄The positive terminal is connected with the switch tube S simultaneously₄And diode D_L3The clamping capacitor C of the series branch₃The negative end is connected with a switch tube S₃Source and diode D_L4Anode of (2), diode D₄Cathode and diode D₃Anode of the switch tube S₃Drain electrode of (1) and switching tube S₄A source electrode of (a); coupling inductor L₄And a diode D_L4Series connection, coupling inductance L of the series branch₄One end of the clamping capacitor C is connected₄The negative electrode of (1); coupling inductor L₃And a diode D_L3Series connection, coupling inductance L of the series branch₃One end of the clamping capacitor C is connected₃The positive electrode of (1);

diode D_LAnode of (2) is connected with a coupling inductor L₃And a diode D_L3Of a common node, diode D_LThe cathode of the transformer is connected with the primary side of the transformer in the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂、L₃、L₄The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

In fig. 10 (structure 2), a flyback winding L is added to the coupling inductor_fAnd connected to diode D_fFor feeding back the energy absorbed by the passive clamp to the output side of the converter.

4 series switch tubes in the converter are divided into 2 pairs, two adjacent switch tubes are 1 pair, each pair of series switch tubes is provided with 1 clamping unit, and a switch tube S₁、S₂The clamping unit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Switch tube S₃、S₄The clamping unit comprises a clamping capacitor C₃、C₄(ii) a Diode D₃、D₄、D_L3And D_L4(ii) a And a coupling inductor L₃、L₄(ii) a Coupling inductor L₁、L₂、L₃、L₄The winding turns are the same, and the winding turns are wound on the same magnetic core together;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a); coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1); coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

clamping capacitor C₄Diode D₄Diode D₃A clamp capacitor C₃Clamping capacitors C connected in series in the series branch₄The positive terminal is connected with the switch tube S simultaneously₄And diode D_L3The clamping capacitor C of the series branch₃The negative end is connected with a switch tube S₃Source and diode D_L4Anode of (2), diode D₄Cathode and diode D₃Anode of the switch tube S₃Drain electrode of (1) and switching tube S₄A source electrode of (a); coupling inductor L₄And a diode D_L4Series connection, coupling inductance L of the series branch₄One end of the clamping capacitor C is connected₄The negative electrode of (1); coupling inductor L₃And a diode D_L3Series connection, coupling inductance L of the series branch₃One end of the clamping capacitor C is connected₃The positive electrode of (1);

flyback winding L_fAnd a diode D_fSeries connected in parallel with the output side of the converter, and flybackWinding L_fAnd a coupling inductor L₁、L₂、L₃、L₄Wound together on the same core, coupled with an inductor L₁、L₂、L₃、L₄The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

The working principle is the same as that of the second embodiment.

The fifth concrete implementation mode: the following describes the present embodiment with reference to fig. 11 and 12, which is an extension of the two-switch-transistor series forward converter of the third embodiment, where a switch-transistor series auxiliary power supply is a converter with 2K switch transistors connected in series, and when K is 2, the converter is a four-switch series forward converter, and the passive clamp circuit of fig. 11 feeds back the absorbed energy to the input side of the converter in each switching period, and the structure of the clamp circuit is the same as that of fig. 9; fig. 12 passive clamp circuit feeds absorbed energy back to the output side of the converter in each switching cycle, the clamp circuit being the same as fig. 10; the clamp circuit mainly comprises a clamp capacitor (C)₁＝C₂＝C₃＝C₄) Coupled inductor (L)₁＝L₂＝L₃＝L₄) And a diode (D)₁、D₂、D₃、D₄、D_L1、D_L2、D_L3、D_L4) And (4) forming. On the basis, a diode D is added in the figure 11 (structure 1)_LThe passive clamping circuit is used for feeding the energy absorbed by the passive clamping circuit back to the input side of the converter; in fig. 12 (structure 2), a flyback winding L is added to the coupling inductor_fAnd connected to diode D_fFor feeding back the energy absorbed by the passive clamp to the output side of the converter. The working principle is the same as that of the third embodiment.

Claims (9)

1. The passive clamping circuit is suitable for a switching tube series auxiliary power supply, and the switching tube series auxiliary power supply adopts two switching tubes S₁、S₂The converter is a forward converter or a flyback converter;

wherein the passive clamp circuit comprises a clamp capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

switch tube S₁And S₂Respectively by C₁And C₂Clamping; the method specifically comprises the following steps:

when clamping capacitor C₁And C₂When a voltage difference occurs, the voltage difference is transmitted through the coupling inductor L₁、L₂Realize mutual energy transmission when C₁Is higher than C₂At a voltage of C, energy is given by C₁By coupling an inductance L₁、L₂To C₂Transferring; when C is present₂Is higher than C₁At a voltage of C, energy is given by C₂By coupling an inductance L₁、L₂To C₁Is transferred to clamp the capacitor C₁And C₂Are equal to each other, thereby ensuring that the switch tube S is switched₁And S₂Voltage equalization.

2. The passive clamp circuit for a switch tube series auxiliary power supply according to claim 1, further comprising a diode D_LDiode D_LAnode of (2) is connected with a coupling inductor L₁And a diode D_L1Of a common node, diode D_LThe cathode of the converter is connected with the primary side of the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

3. The passive clamp circuit for the switch tube series auxiliary power supply as claimed in claim 2, wherein the coupling inductor L of the clamp circuit in the flyback converter is₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

in the formula: l is_pPrimary winding inductance, L, of transformer for flyback converter_lkTransformer equivalent leakage inductance, V, of flyback converter_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iFor the converter input-side voltage, D is the switching tube S in each switching cycle₁And S₂The duty cycle of (c).

4. The passive clamp circuit for the switch tube series auxiliary power supply as claimed in claim 2, wherein the coupling inductance L of the clamp circuit in the forward converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

L_mfor positive exciting transformer T_FEquivalent excitation inductance of, V_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iFor the converter input-side voltage, D is the switching tube S in each switching cycle₁And S₂The duty cycle of (c).

5. The passive clamp circuit suitable for the switching tube series auxiliary power supply as claimed in claim 1, further comprising a flyback winding L_fAnd a diode D_fFlyback winding L_fAnd a diode D_fA series branch connected in parallel with the output side of the converter, a flyback winding L_fAnd a coupling inductor L₁、L₂Wound together on the same core, coupled with an inductor L₁、L₂The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

6. The passive clamp circuit for the switch tube series auxiliary power supply as claimed in claim 5, wherein the coupling inductor L of the clamp circuit in the flyback converter is L₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

in the formula: l is_pPrimary winding inductance, L, of transformer for flyback converter_lkTransformer equivalent leakage inductance, V, of flyback converter_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iIs the converter input side voltage, V_oFor the converter output side voltage, n_fFor coupling an inductance L₁Winding turns and flyback winding L thereof_fThe ratio of the number of winding turns of (c),

d is a switching tube S in each switching period₁And S₂The duty cycle of (c).

7. The passive clamp circuit for a switch tube series auxiliary power supply as claimed in claim 5, wherein the coupling inductance L of the clamp circuit in the forward converter₁、L₂The equivalent inductance value is:

simultaneously, the conditions are met:

L_mfor positive exciting transformer T_FEquivalent excitation inductance of, V_C1Is a clamping capacitor C₁A voltage across, and V_C1＝V_C2，V_C2Is a clamping capacitor C₂Voltage across, V_iIs the converter input side voltage, V_oFor the converter output side voltage, n_fFor coupling an inductance L₁Winding turns and flyback winding L thereof_fThe ratio of the number of winding turns of (c),

d is a switching tube S in each switching period₁And S₂The duty cycle of (c).

8. The passive clamping circuit is suitable for a switching tube series type auxiliary power supply, the switching tube series type auxiliary power supply adopts a converter with 2K switching tubes connected in series, and the converter is a forward converter or a flyback converter; wherein the passive clamping circuit comprises K clamping units and a diode D_L；

2K series-connected switch tubes in the converter are divided into K pairs, every two adjacent switch tubes are 1 pair, each pair of series-connected switch tubes is provided with 1 clamping unit, and each clamping unit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

the coupling inductors of the K clamping units are wound on the same magnetic core together;

diode D_LOf (2) an anodeConnecting the coupling inductor L in the topmost clamping unit₁And a diode D_L1Of a common node, diode D_LThe cathode of the converter is connected with the primary side of the converter; switch tube S₁And S₂When turned off, the inductor L is coupled₁、L₂The energy absorbed in each switching cycle passes through diode D_LFed back to the input side of the converter.

9. The passive clamping circuit is suitable for a switching tube series type auxiliary power supply, the switching tube series type auxiliary power supply adopts a converter with 2K switching tubes connected in series, and the converter is a forward converter or a flyback converter; the passive clamping circuit is characterized by comprising K clamping units and a flyback winding L_fAnd a diode D_f；

2K series-connected switch tubes in the converter are divided into K pairs, every two adjacent switch tubes are 1 pair, each pair of series-connected switch tubes is provided with 1 clamping unit, and each clamping unit comprises a clamping capacitor C₁、C₂(ii) a Diode D₁、D₂、D_L1And D_L2(ii) a And a coupling inductor L₁、L₂(ii) a Coupling inductor L₁、L₂The number of turns of the winding is the same;

clamping capacitor C₂Diode D₂Diode D₁A clamp capacitor C₁Clamping capacitors C connected in series in the series branch₂The positive terminal is connected with the switch tube S simultaneously₂And diode D_L1The clamping capacitor C of the series branch₁The negative end is connected with a switch tube S₁Source and diode D_L2Anode of (2), diode D₂Cathode and diode D₁Anode of the switch tube S₁Drain electrode of (1) and switching tube S₂A source electrode of (a);

coupling inductor L₂And a diode D_L2Series connection, coupling inductance L of the series branch₂One end of the clamping capacitor C is connected₂The negative electrode of (1);

coupling inductor L₁And a diode D_L1Series connection, coupling inductance L of the series branch₁One end of the clamping capacitor C is connected₁The positive electrode of (1);

the coupling inductors of the K clamping units are wound on the same magnetic core together;

flyback winding L_fAnd a diode D_fA series branch connected in parallel with the output side of the converter, a flyback winding L_fCoupling inductor L with K clamping units₁、L₂Wound together on the same core, coupled with an inductor L₁、L₂The energy absorbed in each switching cycle passes through the flyback winding L_fAnd a diode D_fThe formed series branch is fed back to the output side of the converter.

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