Abstract: Introduced the phase shifting bridge stagnates the rear axle of car to realize the zero potential switch’s difficulty, as well as appears in the last few years several solutions, selective analysis their principle of work, compared with theirs good and bad points.
Key word: Zero potential entire bridge converter; In advance bridge arm; Lag bridge arm; Resonant network
Introduction
The entire bridge converter (Full-bridge Converter) usually applies in the power is bigger than 400W in the switching power supply, specially applies in the high efficiency correspondence power source is quite widespread. But, under the hard switch condition’s entire bridge converter can bring the very big switching loss, does not favor the turn-on frequency and the power source transfer efficiency enhancement. In view of the hard switching loss major problem, some people proposed the phase shifting control method. May realize switching valve’s zero potential clear and the shutdown through the phase shifting control, thus improved switching valve’s clear and the shutdown condition greatly, like this then may raise switch’s frequency, reduces power source’s volume, raises power source’s transfer efficiency.
1 outline
Phase shifting entire bridge converter as shown in Figure 1. Must realize switching valve’s zero potential clear, must have switching valve’s junction capacitance which the enough energy uses for to screen out is going to clear (or the exterior additional electric capacity) on electric charge; And switching valve’s junction capacitance which must shut off for the identical bridge arm (or the exterior additional electric capacity) charges; At the same time, considers transformer’s primary side winding’s parasitic capacity, but must screen out on the transformer primary side winding parasitic capacity’s electric charge.
Figure 1 traditional zero potential switch’s phase shifting entire bridge electric circuit
Because the bridge arm has the output current participation in advance in the switching process, therefore, very easy to realize ZVS. But lags the bridge arm in the switching process, the transformer primary side is the short circuit, this time the entire converter is divided into two parts, a part is the primary side electric current changes the circulation direction gradually, its circulation way provides by the contravariant bridge; Another part is the load current provides the after flow return route by the rectification bridge. The load side and the transformer primary side has not related. This time uses for to realize the ZVS energy is only the resonant inductance (leakage inductance and additional resonance inductance) the energy. But the resonant inductance is very small, therefore, lags the bridge arm switching valve to realize the zero potential clear to be quite difficult.
2 non-analysis situs constitutive property change solution
May know from the above analysis, lags bridge arm’s switch motion to occur in the backflow process to the energy transmission process transformed stage, because the output inductance electric current cannot feed back the primary side, enables the lag bridge arm’s switching valve shunt capacitance only to depend upon the transformer primary side the resonant inductance to carry on the charging and discharging, but in the resonant inductance saves the energy is small, causes the lag bridge arm switching valve to realize the zero potential clear becomes very much very difficult, specially in low load time is more obvious. Must realize lag bridge arm’s ZVS, must satisfy LrI22>ClagVin2 CtrVin2, must satisfy it to increase resonant inductance Lr and increase electric current I2. Thus, has two kind of non-analysis situs constitutive property change method [1] to be possible to solve the lag bridge arm switching valve zero potential to clear the difficult question: Increases the exciting current and increases the resonant inductance. But, will increase the exciting current to increase transformer’s loss, will increase the resonant inductance to cause the vice-side dutyfactor loss. For easier to realize the lag bridge arm’s switching valve zero potential clear, achieves both does not increase the clear to lose, and the reduced dutyfactor loses the goal, some new topology was proposed recently.
Figure 2
3 lag bridge arm antiresonance network zero potential switch phase shifting entire bridge converter
In order to overcome the lag bridge arm to realize the zero potential switch difficult question, simultaneously will not cause enlargement which the dutyfactor loss and the clear will lose, literature [2] proposed one kind in the lag bridge arm parallel resonance inductance and two resonant switch’s topology, as shown in Figure 2. Switch’s control policy as shown in Figure 3. This analysis situs has 6 work modalities in a half cycle.
At the same time modality 1S1 and S2 the breakover, the filter inductance electric current linearity increases.
Modality 2S1 shuts off, the primary side electric current extracts S3 on shunt capacitance C3 the electric charge, simultaneously to the S1 shunt capacitance charge, finished in the charging and discharging, D3 breakover. Because the output circuit inductance is very big, therefore, winds through in the filter inductance the electric current to be possible to regard as is a constant current.
Modality 3 after the D3 breakover, may the zero potential clear S3. This time, the transformer primary side voltage becomes zero, the vice-side voltage also simultaneously becomes zero, at the same time 4 rectification diodes the breakover, maintains the output filter inductance electric current.
Figure 3
The modality 4 shut off S2, the use saves on the leakage inductance the energy extracts on C4 the electric charge, and to the C2 charge, when the leakage inductance is very small, saves the energy is insufficient in the leakage inductance to extract on C4 the electric charge, when and for the C2 charge, the D4 not breakover, then S4 cannot realize the zero potential clear. In order to cause S4 to realize the zero potential clear, before shutting off S2 to clear Sa to establish the resonance current first.
Modality 5, when the resonance current establishes is big enough, simultaneously shuts off S2 and Sa, like this has on the resonant inductance and the leakage inductance energy provides the energy which together the charging and discharging need, causes S4 to realize the zero potential clear.
Figure 4
Modality 6, when the D4 breakover, may clear S4 under the zero potential condition, the output current feeds back to the primary side winds through S3 and S4. In resonant inductance energy after S4 and Db back coupling to power source.
The second half cycle active status is the same with the first half cycle.
This electric circuit’s merit is:
1) lags the bridge arm to be able to realize the zero potential clear shutdown successfully;
2) switch’s clear loses is quite low;
3) the dutyfactor loses damages is quite small.
In this electric circuit, the resonant inductance’s design is quite important, if the resonant inductance chooses oversized, easy to cause the nonessential clear loss, if is too small, cannot cause the lag bridge arm to realize the zero potential shutdown. The resonant switch’s turn-on time must choose reasonably, can, in realizes under the condition which the lag bridge arm’s zero potential shuts off not to cause excessively loses.
The above electric circuit’s major object is quite small in the load, realizes in advance bridge arm’s zero potential to shut off is quite difficult; In the electric circuit increased two resonant switches, causes the electric circuit cost to increase; The control circuit is quite complex; Acceptor’s switch is the hard switch shuts off, will have the extra loss; Two acceptors are and the identical bridge arm two switching valves are parallel, cause the electric circuit damping shake aggravating.
Figure 5
4 one kind of new antiresonance network zero potential switch phase shifting entire bridge converter
In literature [3] also proposed one antiresonance network’s method, is separately parallel the resonant network with two bridge arm’s under tubes, as shown in Figure 4. This must adjust the control method, its control policy as shown in Figure 5. S2 and the S4 turn-on time is DT/2, but S1 and the S3 turn-on time for (1-D) T/2, the dutyfactor adjustment does not need the phase shifting, so long as adjusts S2 and the S4 driving signal width may realize. Because S1 and the S3 clear is in the energy transmission process, on its shunt capacitance’s electric charge can before they clear the electric current which comes by the primary side leakage inductance electric current and the vice-side coupling to pull out, they can realize the zero potential clear, but S2 and S4 are in trade the class stage, saves the electric current is insufficient on the leakage inductance to cause S4 or the S2 shunt capacitance’s loss of voltage arrives at zero, such need with the aid of acceptor. Before S2 (S4) the breakover, opens resonant switch Sa1 (Sa2), in resonant inductance establishment resonance current, when S1 (S3) shuts off, may participate in the bridge arm shunt capacitance’s charging and discharging. In the such electric circuit’s 4 switching valves may realize the zero potential clear completely. In this electric circuit, the resonant leg and the main switch tube is parallel, may realize willfully the wide load zero potential switch. Because may reduce the leakage inductance, thus reduced the dutyfactor loss. Active auxiliary circuit type’s increase, causes to choose the most appropriate electric circuit and to enable the design to meet the requirements possibly to become.
Figure 6 and Figure 7
5 one kind of brand-new PWM-ZVS-FB converters
The above electric circuit has a common shortcoming, namely when underloading realizes the zero potential switch to be quite difficult, and increased two resonant switches, causes the control circuit becomes very complex. In literature [4] proposed one kind of brand-new PWM 瞆 VS 睩 the B converter, as shown in Figure 6, converter each profile as shown in Figure 7. The left bridge arm is the lag bridge arm, the right bridge arm is in advance the bridge arm. The left bridge arm and left side two electric capacities (two electric capacities are very big, may regard as is two potential sources), transformer T1 constitutes -and-a-half a bridge topology; About the bridge arm and transformer T2 constitutes an entire bridge topology, the left bridge arm high and low switch’s breakover time is a half cycle (dead time ignores). Through adjusts the right bridge arm and the left bridge arm clear and the shutdown signal phase, realizes the voltage adjustment. Its lag bridge arm zero potential switch mainly realizes through transformer T1 and the transformer T2 exciting current. For the reduced dutyfactor’s loss, obtains two transformer’s leakage inductances is quite small, on transformer T1 exciting current profile as shown in Figure 8, therefore, the transformer T1 exciting current will increase will not cause the dutyfactor loss, but transformer T2 exciting current profile as shown in Figure 9, it will increase will cause the switch breakover loss to increase. In order to reduce the dutyfactor to lose, avoids causing the excessively many clear losses, obtains the transformer T1 exciting current is quite big, obtains the transformer T2 exciting current and two transformer’s leakage inductance is quite small. Because the output voltage is equal to transformer T1 and the transformer T2 sum of vice-side voltage value, when two transformer vice-side voltages and become the zero hour, on the switch S1 voltage has screened out a part, after primary side vice-side clamp, on the S1 voltage is not Vin, but is lower than Vin, causes to realize the lag bridge arm switching valve’s zero potential clear to be easier. The analysis may see by the ideal oscillogram chart 7, because two transformers simultaneously transmit the energy, this electric circuit’s output voltage’s ripple is also very small, like this outputs the filter inductance to be possible to design very much slightly, thus reduced the designed cost and converter’s volume.
This topology in has not increased in any switching valve’s situation, the success realizes the zero potential switch, moreover as a result of the transformer T1 existence, causes the zero potential switch to be possible in the underloading time can realize. Simultaneously enables the output the performance to be improved.
6 conclusions
The traditional phase shifting bridge usually uses in the high efficiency in the switching power supply, its lag bridge arm switching valve realizes the zero potential clear to restrict its application with difficulty, to improve the lag bridge arm’s clear condition well, realizes the zero potential clear truly, many technologies and the analysis situs were proposed. This article through converter’s characteristic and the existence question carries on the analysis to traditional phase shifting PWM 瞆 VS 睩 the B, and to appeared recently realizes the entire bridge zero potential switch’s solution to carry on the detailed analysis, compared with theirs good and bad points. These methods and the analysis situs greatly improved the lag bridge arm’s clear condition, not only specially the final that method has realized the zero potential switch, but also improved the output filter condition, is worth us conducting more thorough research.
