CN204408212U - Flyback transformer leakage inductance energy absorption feedback circuit - Google Patents

Abstract

A flyback transformer leakage inductance energy absorption feedback circuit, the leakage inductance energy absorption and feedback circuit are integrated together, only composed of a clamping tube S _c and a clamping capacitor C _c , the structure is simple and reliable. The control method is that the clamp tube is turned on for T _c after the flyback supervisor is turned off, and T _c is half of the resonance period of the leakage inductance and the clamp capacitor, which is much shorter than the shut-off time of the supervisor. The leakage inductance energy absorbed by the clamp capacitor is released to the main power circuit through the resonance of the clamp capacitor and the leakage inductance, which effectively reduces the turn-off voltage peak of the flyback circuit supervisor and improves the efficiency of the flyback converter. At the same time, due to the non-complementary conduction of the clamp tube and the main tube, the conduction time of the clamp tube is much smaller than the off time of the main tube, so the absorption and feedback circuit does not affect the switching process of the main tube, and is suitable for flyback circuits in any working mode. The circuit reliability and efficiency of the miniature photovoltaic grid-connected inverter adopting the scheme of the utility model are greatly improved.

Description

Flyback Transformer Leakage Inductance Energy Absorption Feedback Circuit

technical field

The utility model relates to an absorption and feedback circuit of leakage inductance energy of a flyback transformer in the field of photovoltaic grid-connected power generation and a control method thereof.

Background technique

The micro grid-connected photovoltaic inverter improves the power generation efficiency of the system under the conditions of photovoltaic module power mismatch and shadow, and at the same time has the advantages of safety and module-level monitoring. It has been obtained in the household photovoltaic grid-connected system application of photovoltaics.

Micro grid-connected photovoltaic inverters are generally installed on the bracket under the module, or directly on the frame of the module. Maintenance is extremely troublesome, so it needs to have the same lifespan and reliability as the module. In addition, since the micro-inverter operates outdoors, the ambient temperature can reach up to 65°C. For reliability reasons, it usually dissipates heat naturally. Therefore, the micro-inverter needs to have very high efficiency to operate reliably in an environment of 65°C.

Due to the simple structure, the flyback converter works reliably, and the input and output are electrically isolated. It has been widely used in current miniature photovoltaic grid-connected inverters. In particular, the flyback converter in the critical discontinuous operation mode has been favored by various micro-inverter manufacturers because it can realize the ZVS soft switching of the switching tube.

At present, the efficiency of micro photovoltaic grid-connected inverters using flyback circuits in critical discontinuous working mode can generally reach 95%, which is 1-2 percentage points lower than that of traditional string inverters. One of the main reasons why the efficiency of the current flyback solution is difficult to improve is the large loss of the leakage inductance of the flyback transformer. The leakage inductance of the flyback transformer generally accounts for 1%-2% of the excitation inductance. If the energy of the leakage inductance is not processed, It will be dissipated in the form of heat, and a high turn-off voltage peak will be generated on the flyback main switch tube, which increases the voltage stress of the switch tube and seriously affects the reliable operation of the micro-inverter.

Therefore, the leakage inductance energy absorption and feedback circuit of the flyback transformer is extremely necessary, it absorbs and releases the leakage inductance energy into the main power circuit, eliminates the turn-off voltage peak of the flyback main switching tube, and thus can effectively Improve the efficiency and reliability of current micro photovoltaic grid-connected inverters. At present, the existing schemes include passive RCD absorption and dissipation schemes, passive LCD absorption feedback schemes, traditional active clamping schemes, passive clamping + active absorption schemes, etc. Among them, the passive RCD absorption and dissipation scheme can only absorb and dissipate the absorbed leakage inductance energy, reduce the voltage stress of the main switch tube, and cannot feed back the leakage inductance energy, and cannot improve efficiency; the structure of the active LCD absorption and feedback scheme is relatively Complicated and difficult to implement. The traditional active clamping scheme is due to the complementary conduction of the supervisor and the clamping tube, the clamping tube will affect the working state of the supervisor, and the flyback circuit cannot work in the discontinuous and critical discontinuous mode, so it cannot be applied to the critical discontinuous mode widely used at present. In the continued flyback scheme; in the passive clamp + active snubber scheme, the active snubber circuit is generally composed of a buck or flyback circuit, the topology and control method are very complicated, and the efficiency of the buck and flyback circuit is not high during feedback , poor absorption.

Contents of the invention

The utility model aims to solve the above-mentioned problems of the prior art, and provides the most general, simple, reliable and efficient flyback transformer leakage inductance energy absorption and feedback circuit and its control method so far.

The utility model is suitable for flyback circuits in continuous, discontinuous, and critical discontinuous operating modes, and solves the problems of the existing critical discontinuous operating mode flyback transformer leakage inductance energy absorption and feedback circuit and its control are too complicated, and improves Improve the reliability and efficiency of the flyback circuit.

The technical scheme adopted by the utility model to solve the above-mentioned technical problems is: the leakage inductance energy absorption of the flyback transformer and the feedback circuit are integrated, and only consist of a clamping tube and a clamping capacitor. The non-complementary conduction control of the clamp tube and the main tube makes this absorption and feedback scheme suitable for discontinuous and critical discontinuous (quasi-resonant) operating mode flyback circuits.

A flyback transformer leakage inductance energy absorbing and feedback circuit is characterized in that the absorbing and feedback circuits are integrated and only consist of a clamping tube and a clamping capacitor. The source of the clamping tube is connected to the drain of the flyback supervisor, and the drain of the clamping tube is connected to the clamping capacitor. The clamp tube provides a channel for absorbing and releasing leakage inductance energy, and the clamp capacitor is a medium for temporarily storing leakage inductance energy.

Said flyback transformer leakage inductance energy absorption and feedback circuit clamping tube can use N-channel MOSFET or P-channel MOSFET.

The utility model also provides a control method of the absorption and feedback circuit, which is characterized in that the clamping tube and the main tube are non-complementary conduction. The clamp tube is only turned on for a short time _Tc after the supervisor is turned off, which is much shorter than the shut-off time of the supervisor. During this time, the leakage inductance energy absorbed by the clamp capacitor is released to the input capacitor and output capacitor through the resonance of the clamp capacitor and the leakage inductance.

The conduction time of the clamp tube can be obtained by the following formula:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}$

Among them, L _k is the inductance value of the leakage inductance, and C _c is the capacitance value of the clamping capacitor.

In the control method described in the utility model, the clamping tube absorbs and releases the leakage inductance energy to the main power circuit in a short time T _c after the supervisor is turned off, and then the clamping tube is turned off without interfering with intermittent and critical off The resonance process of the magnetizing inductor and the junction capacitance after the magnetizing inductor current of the continuous mode flyback converter is reset to zero. Therefore, the flyback transformer leakage inductance energy absorption and feedback circuit machine control method provided by the utility model is suitable for flyback circuits in various working modes.

The flyback transformer leakage inductance energy absorption feedback circuit and control method of the utility model have the following technical advantages:

1. The absorption and feedback circuit are integrated, simple and reliable

2. The switch of the clamp tube does not affect the work of the supervisor, and is suitable for intermittent, critical intermittent, and continuous working mode flyback circuits

3. Leakage inductance energy is reliably absorbed by the clamp capacitor, which eliminates the voltage spike of the main power tube of the flyback circuit and improves the reliability of the flyback circuit

4. The leakage inductance energy absorbed by the clamp capacitor can be completely released to the main power circuit, which improves the efficiency of the flyback circuit

Description of drawings

The utility model will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1a, Fig. 1b and Fig. 1c are the schematic diagrams of the miniature photovoltaic grid-connected inverter applying the leakage inductance energy absorption and feedback circuit of the flyback converter of the present invention.

Fig. 1a is the first embodiment of the utility model

Fig. 1b is the second embodiment of the present utility model

Fig. 1c is the third embodiment of the present utility model

Fig. 2 is a block diagram of generation of driving signals of the clamping tube of the absorbing feedback circuit of the present invention.

Fig. 3 is a switching cycle, the waveform diagram of the flyback circuit supervisor, the drive signal of the clamp tube, the leakage inductance current and the voltage of the clamp capacitor.

Detailed ways

The utility model will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the utility model should not be limited thereby.

Fig. 1a is the first embodiment of the utility model, and the circuit 100 in the figure is the leakage inductance energy absorption and feedback circuit proposed by the utility model, which is composed of an N-channel MOSFET clamping tube _Sc and a clamping capacitor _Cc . The source of the clamping tube is connected to the drain of the supervisor S _m of the flyback circuit, the drain of the clamping tube is connected to the positive pole of the clamping capacitor C _c , and the negative pole of the clamping capacitor C _c is connected to the ground of the input terminal of the flyback circuit.

Fig. 1b is the second embodiment of the utility model, in which the circuit 101 is the leakage inductance energy absorption and feedback circuit proposed by the utility model, which is composed of an N-channel MOSFET clamping tube _Sc and a clamping capacitor _Cc . The source of the clamping tube is connected to the drain of the supervisor S _m of the flyback circuit, the drain of the clamping tube is connected to the positive pole of the clamping capacitor C _c , the negative pole of the clamping capacitor C _c is connected to the PV+ of the input terminal of the flyback circuit, Compared with the first embodiment, this way reduces the withstand voltage of the clamping capacitor C _c .

Fig. 1c is the third embodiment of the utility model, in which the circuit 102 is the leakage inductance energy absorption and feedback circuit proposed by the utility model, which is composed of a P-channel MOSFET clamping tube _Sc and a clamping capacitor _Cc . The source of the clamping tube is connected to the ground of the input terminal of the flyback circuit, the drain of the clamping tube is connected to the negative pole of the clamping capacitor C _c , and the positive pole of the clamping capacitor C _c is connected to the drain of the supervisor S _m of the flyback circuit. Compared with the first and second embodiments, this method simplifies the drive of the clamp tube

Fig. 2 illustrates the control method of leakage inductance energy absorption and feedback circuit clamping tube proposed by the utility model.

After the supervisor of the flyback circuit is turned off, the clamping tube S _c is turned on for a period of time T _c , and the turn-on time T _c is much shorter than the shut-off time of the supervisor. During this period, the clamp capacitor completes the absorption and release of leakage inductance energy through the clamp tube _Sc , and releases all the recovered leakage inductance energy to the main power circuit. The control method can be conveniently realized through an analog circuit or a digital circuit.

Figure 3 shows the driving signals of the main tube and the clamp tube, as well as the leakage inductance current and the voltage waveform of the clamp capacitor. The principle of leakage inductance energy feedback is the resonance between the clamp capacitor and the leakage inductance. The conduction time T _c of the clamp tube is half a resonance cycle. At this time, the leakage inductance energy just resonates to zero, and the leakage inductance absorbed by the clamp capacitor All energy is released into the main power circuit.

The above descriptions are only preferred embodiments of the utility model, and are not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present utility model shall be included within the scope of claims of the present utility model.

Claims (3)

1. flyback transformer leakage inductance energy absorption feedback circuit, is characterized in that: absorb and feedback circuit integrated, be only made up of a clamper tube and a clamp capacitor; Clamper tube source electrode is connected with flyback supervisor drain electrode, and clamper tube drain electrode is connected with clamp capacitor, the passage that clamper tube provides leakage inductance energy to absorb and discharge, and clamp capacitor is then the medium that leakage inductance energy temporarily stores.

2. flyback transformer leakage inductance energy absorption feedback circuit as claimed in claim 1, is characterized in that: described clamper tube adopts N-channel MOS FET, or P channel mosfet.

3. the control method of flyback transformer leakage inductance energy absorption feedback circuit as claimed in claim 1, is characterized in that: described clamper tube and the conducting of supervisor's incomplementarity; Clamper tube is only had no progeny in supervisor pass ON time T _c, T _cmuch smaller than the turn-off time of supervisor; The ON time T of clamper tube _ccomputing formula be:

Wherein L _kfor leakage inductance inductance value, C _cfor clamp capacitor capacitance.