CN105978314A - An Active Clamp Circuit for Suppressing Bridge Arm Voltage Spikes of Single-stage Bridge PFC Converter - Google Patents

Abstract

An active clamping circuit that suppresses the voltage spike of the bridge arm of a single-stage bridge PFC converter, in order to solve the impact current of the clamp switch tube during the zero-crossing stage of the input current of the existing active clamping circuit, or the existing voltage spike suppression circuit The problem of large energy consumption and complex circuit structure. It includes an existing active clamping circuit, a current-limiting inductance L _c and a diode D _c ; the current-limiting inductance L _c and the diode D _c are connected in parallel and connected in series to the full circuit of the existing active clamping circuit and a single-stage bridge PFC converter between the bridge arms. The invention is used for suppressing the peak voltage of the bridge arm of the single-stage bridge type PFC converter.

Description

An Active Clamp Circuit for Suppressing Bridge Arm Voltage Spikes of Single-stage Bridge PFC Converter

technical field

The invention relates to an active clamping circuit, in particular to an active clamping circuit for suppressing a bridge arm voltage peak of a single-stage bridge type PFC converter.

Background technique

Due to the leakage inductance of the transformer in the single-stage bridge PFC converter, when the converter is switched from the straight-through state of the bridge arm to the conduction state of the opposite arm, voltage spikes (ie, bridge arm voltage spikes) will be generated at both ends of the bridge arm. If no suppression measures are taken, the voltage stress of the switching device will be greatly increased, which will affect the normal operation of the converter.

Among the existing bridge arm voltage peak snubber circuits, the RCD snubber circuit is the most simple and reliable, but it consumes more energy than the lossless snubber circuit; the LCD passive non-destructive snubber circuit and the auxiliary flyback converter absorbing methods are more complex in structure and cumbersome in design ; In contrast, although the active clamp snubber circuit uses active devices, its principle is simple, easy to implement, and there is no additional loss.

Although the existing active clamping circuit can absorb the voltage spike of the bridge arm of the single-stage bridge PFC converter under certain conditions, it is found that the following problems still exist during use: In the stage, a large inrush current will be generated on the clamp switch tube, so that the clamp switch tube will be damaged. Therefore, none of the aforementioned methods can well solve the problem of the bridge arm voltage spike of the single-stage bridge PFC converter.

Contents of the invention

The purpose of the present invention is to solve the problems of large energy consumption and complex circuit structure of the existing active clamping circuit in the clamping switch tube surge current during the input current zero-crossing phase of the existing active clamping circuit and the existing voltage spike suppression circuit. Active clamping circuit for bridge arm voltage spikes in stage bridge PFC converter.

An active clamping circuit for suppressing a bridge arm voltage spike of a single-stage bridge PFC converter of the present invention includes an existing active clamping circuit, a current-limiting inductance L _c and a diode D _c ;

The current-limiting inductance L _c and the diode D _c are connected in parallel and connected in series between the existing active clamp circuit and the full bridge arm of the single-stage bridge PFC converter.

The existing active clamping circuit includes a clamping switch S _c and a clamping capacitor C _c ;

The source of the clamping switch S _c is connected to one end of the input inductance L _in , one end of the current-limiting inductance L _c , and the cathode of the diode D _c in the PFC converter at the same time, and the other end of the current-limiting inductance L _c is connected to the cathode of the diode D _c The anode is connected to the drain of the switching tube S ₁ and the switching tube S ₃ of the full-bridge arm;

The drain of the clamping switch S _c is connected to one end of the clamping capacitor C _c , and the other end of the clamping capacitor C _c is connected to the sources of the switching tubes S ₂ and S ₄ of the full bridge arms.

The beneficial effect of the present invention is that, on the basis of the existing active clamping circuit, the non-energy-consuming device current-limiting inductance L _c and the diode D _c are added, which can solve the problem that the existing active clamping circuit is applied to a single-stage bridge. When suppressing the voltage spike of the bridge arm of the PFC converter, the problem of the inrush current of the clamp switch tube during the zero-crossing phase of the input current, or the problem that the existing voltage spike suppression circuit consumes a lot of energy and has a complicated circuit structure. The whole scheme is simple in principle, easy to realize, and has no extra loss, so it is a suitable and feasible method.

Description of drawings

Fig. 1 is a structure diagram of a single-stage bridge PFC converter with an additional existing active clamping circuit;

Fig. 2 is the equivalent circuit diagram of the bridge arm voltage peak generated when the opposite arm conduction state is not applied with the voltage peak absorbing circuit;

Figure 3 is the voltage u _AB waveform between A and B when no voltage peak absorption circuit is applied;

Fig. 4 is the working sequence diagram of the single-stage bridge PFC converter in the specific embodiment;

5 is a structural diagram of a single-stage bridge PFC converter with an active clamp circuit attached to this specific embodiment;

Fig. 6 is the voltage u _AB waveform between A and B when the active clamping circuit of the present embodiment works;

Fig. 7 is the equivalent circuit when the opposite arm is turned on during the zero-crossing stage of the input current when the existing active clamp circuit is working;

Fig. 8 shows the waveforms of the clamp capacitor current i _Sc , bridge arm voltage u _MN and S _c switching signals during the zero-crossing stage of the input current when the existing active clamp circuit is working;

FIG. 9 shows the waveforms of clamp capacitor current i _Sc , bridge arm voltage u _MN , and S _c switching signals during the zero-crossing stage of the input current when the active clamp circuit of this specific embodiment is working.

detailed description

This embodiment is described in conjunction with Fig. 1 to Fig. 9. The active clamping circuit described in this embodiment is used to suppress the voltage peak of the bridge arm of the single-stage bridge PFC converter and solve the problem of clamping the switch during the zero-crossing stage of the input current. Tube inrush current problem, the specific principles and implementation methods are as follows:

1. Bridge arm voltage spikes

If no bridge arm voltage peak absorbing circuit is added, the schematic diagram of the single-stage bridge PFC converter with the existing active clamp circuit shown in Figure 1, when the converter switches from the bridge arm through state to the opposite arm conduction state, because the input side inductor current i _L is relatively large, and the current i _p on the leakage inductance L _1k is equal to the excitation current, which is much smaller than i _L , which will cause a resonance voltage peak between the bridge arms. If the input inductance is equivalent to the current source i _L , the equivalent junction capacitance of two switched-off switch tubes in parallel is C _s , the equivalent anti-parallel diode is D _s , and the secondary side of the transformer is equivalent to the voltage of the primary side of the transformer source nU _o , the equivalent circuit of the conduction state of the opposite arm shown in Figure 2 can be obtained. According to the equivalent circuit of the resonance process, the expression of the bridge arm voltage can be obtained as follows:

As shown in Figure 3, the waveform of the voltage u _AB between A and B without the bridge arm voltage peak absorption circuit has a large voltage peak, so the bridge arm voltage u _MN also has a large voltage peak.

It can be seen from formula 1 that the amplitude of the bridge arm voltage peak is related to the transformer leakage inductance L _1k , the switch junction capacitance C _s , the input inductor current i _L and the output voltage U _o .

2. The active clamping circuit of this embodiment absorbs the bridge arm voltage spike:

Taking the stage t ₀ -t ₆ in FIG. 4 as an example to illustrate the suppression effect of the active clamp circuit in this embodiment on the bridge arm voltage spike.

As shown in FIG. 5 , the active clamping circuit of this embodiment adds a current-limiting inductance L _c and a diode D _c on the basis of the existing active clamping circuit;

The existing active clamping circuit includes a clamping switch tube S _c and a clamping capacitor C _c ;

One end of the clamping capacitor C _c is connected to the drain of the clamping switch S _c , and the other end of the clamping capacitor C _c is connected to the sources of the full-bridge arm switch S ₂ and the switch S ₄ in the PFC converter at the same time ; The source of the clamping switch S _c is connected to one end of the input inductance L _in , one end of the current-limiting inductance L _c , and the cathode of the diode D _c in the PFC converter; the other end of the current-limiting inductance L _c is connected to the diode D _c The anode of the PFC converter is connected to the anode, and then simultaneously connected to the drains of the full-bridge arm switch tube S ₁ and the switch tube S ₃ in the PFC converter.

When the bridge arm is straight-through (t ₀ -t ₃ ), the bridge arm voltage u _MN is 0, the clamp switch S _c is turned off, and does not participate in the work of the PFC converter.

When the opposite arm is turned on but the clamp switch S _c is still in the off state (t ₃ -t ₄ ), the transformer leakage inductance L _1k and the switch tube equivalent junction capacitance C _s start to resonate, resulting in a voltage spike, when the voltage spike When it is higher than the clamp capacitor voltage uc, the diode D _c and the anti-parallel diode of the clamp switch S _c will conduct, because the capacitance of the clamp capacitor _{C c is} larger than the equivalent junction capacitance C _s , so the voltage The spike can be absorbed by the clamp capacitor _Cc without generating a voltage spike.

When the opposite arm is turned on and the clamp switch S _c is in the open state (t ₄ -t _{5 )} , if the bridge arm voltage u _MN is higher than the clamp capacitor voltage uc , then u _MN will pass through the diode D _c and the clamp switch The tube S _c is clamped to uc _. If the bridge arm voltage u _MN is lower than the clamp capacitor voltage _uc , u _MN will release energy to the PFC converter through the clamp switch S _c and the current-limiting inductor L _c , so that The clamp capacitor voltage u _c and nU _o remain equal, and there is still no voltage spike between the bridge arms.

The t ₅ -t ₆ stage is similar to the t ₃ -t ₄ stage and will not be described again.

As shown in Figure 6, the waveform of the voltage u _AB between A and B when the active clamp circuit of this embodiment is in operation, compared with Figure 3, it can be seen that u _AB has no voltage spikes, so there is no voltage spike in the bridge arm voltage u _MN , the active clamp circuit of this embodiment can absorb bridge arm voltage spikes.

3. The active clamping circuit of this embodiment solves the problem of the inrush current of the clamping switch tube during the zero-crossing phase of the input current:

In the existing active clamping circuit, the input current zero-crossing stage, as shown in Figure 7, is the equivalent circuit in this case. After the arm is turned on, the input inductor current i _L charges the equivalent junction capacitance C _s , the voltage across C _s gradually increases, but because the inductor current i _L will decrease with the charging process, when the inductor current drops to 0, the voltage u _MN across the equivalent junction capacitance C _s is far from reaching the clamping capacitance When the voltage u _c (u _c =nU _o ) is even 0, the diodes D ₁ and D ₂ on the secondary side of the transformer are cut off and cannot transfer energy to the secondary side; after that, the clamp switch S _c is turned on to replace the input inductance L _in to form a PFC The converter provides energy. At the moment when the clamp switch S _c is turned on, there is a large voltage difference Δu between the clamp capacitor voltage _uc and the bridge arm voltage u _MN , the expression can be expressed by formula 2, where the dead zone time T _z1 =t ₄ -t ₃ =t ₁₀ -t ₉ .

Δu＝nU _o -(i _L T _z1 /C _s ) Formula 2

However, the loop equivalent resistance R _eq1 is very small, therefore, there will be a huge inrush current on the clamp switch S _c , and the peak value i _ic of the inrush current can be approximately expressed by formula 3:

Figure 8 is the current ic _s in the clamp switch S _c at the zero-crossing stage of the input current, the voltage u _MN (bridge arm voltage) at both ends of C _s and the switching signal waveform of the clamp switch S _c , in the clamp switch S Before _c is turned on, u _MN has not yet reached nU _o ; at the moment S _c is turned on, there is a huge inrush current on the clamp switch S _c . If no suppression measures are taken, the clamping switch S _c is easily damaged due to overcurrent despite the short duration of the inrush current.

In the active clamping circuit of this embodiment, when the clamping switch S _c is turned on in the zero-crossing stage of the input current, when the clamping capacitor C _c releases energy to the subsequent circuit, due to the existence of the current-limiting inductance L _c , The current on the inductor L _c cannot change abruptly, so the clamping switch S _c will not have a large inrush current with a peak value. When the improved active clamping circuit works, the current waveform on the clamping switch tube is shown as i _Sc in Figure 9, compared with Figure 8, it can be seen that there is no _inrush current on the clamping switch tube Sc, the active clamping switch tube of this embodiment The clamping circuit can solve the problem of inrush current on the clamping switch S _c during the zero-crossing phase of the input current.

Claims (2)

1. the active clamping circuir suppressing single-grade bridge type pfc converter bridge arm voltage spike, it is characterised in that include existing There are active clamping circuir, current-limiting inductance L_cWith diode D_c；

Current-limiting inductance L_cWith diode D_cIt is connected in parallel, concatenation to existing active clamping circuir and single-grade bridge type pfc converter complete Between bridge brachium pontis.

A kind of active clamping circuir suppressing single-grade bridge type pfc converter bridge arm voltage spike the most according to claim 1, It is characterized in that, described existing active clamping circuir includes clamp switch pipe S_cWith clamping capacitance C_c；

Clamp switch pipe S_cSource electrode simultaneously and pfc converter inputs inductance L_inOne end, current-limiting inductance L_cOne end, two poles Pipe D_cNegative electrode be connected, current-limiting inductance L_cThe other end, diode D_cAnode simultaneously and the switching tube S of full-bridge brachium pontis₁, open Close pipe S₃Drain electrode connect；

Clamp switch pipe S_cDrain electrode and clamping capacitance C_cOne end connect, clamping capacitance C_cThe other end simultaneously with full-bridge brachium pontis Switching tube S₂, switching tube S₄Source electrode connect.