Research On Phase-shift Controlled High-output-voltage DC-DC Converter

In practical applications,the traditional PSFB(phase shift full bridge)converter is widely used because it's easy to achieve SS(soft switching)technique.Besides,this topology also has a simple structure and good EMI characteristics.However,the limited SS range,the duty cycle loss,the voltage spike in secondary diode and other drawbacks is holding this traditional topology back for wider use.Moreover,since the traditional voltage-controlled PSFB converter is an isolated buck converter,the turn ratio of the transformer will be large if you need it to output high voltage.To achieve that,the parasitic parameters like leakage inductance and the parastic capacitors will increase noticeably,which makes the earlier mentioned drawbacks to be more significant and makes this topology hard to be applied in high output voltage applications,such as Power Processing Unit.Therefore,it's meaningful to improve the traditional topology so it can be used in high voltage output applications.Considering the practical need in high voltage output applications and the characteristics of the converters which are now applied in this field,this paper brought up four different types of high output voltage converters.The specific research contents are as follows:The first part brought up a high output voltage converter with resonance clamping circuits to improve the characteristics of the traditional voltage controlled PSFB converter.The main improvement of the brought-up topology is that it can achieve ZVS(zero-voltage-switching)in a wide range by reducing the voltage stress in the output diode.To fully research this new topology,the paper analyzed the current ripple of the output filter inductor.Also,the paper produces the ZVS conditions for main power switching devices,the characteristics of the secondary rectifier bridge's voltage stress and the corresponding parameters of the topology.Concerning the problem in the traditional CD(current-driven)PSFB converter,which is that the lagging-leg switches can't achieve ZVS,the second part of the paper brought up a high output voltage converter.This converter is a combination of the LLC resonance converter and the CD-PSFB converter.And it adopted the strategy to share the lagging leg switches to make sure all switches can achieve ZVS in a wide load range without using any auxiliary circuits.To meet the need of high output voltage,the outputs on the secondary side is connected in series to reduce the voltage stress in output diodes.In this paper,the author analyzed this converter's working principles and gives out the DC gain of the converter,the design of the duty-ratio in DCM,the soft-switching conditions,the integrated magnetic structure of the transformer and also the corresponding topology's parameters.For the demand of wide voltage output range,a primary-and secondary-side PS ZVZCS(zero-voltage and zero-current-switching)FB converter is proposed in the third part of this paper.To reduce the voltage stress in the power devices at the secondary-side and make sure power switches can achieve ZVZCS in the full load range,this proposed converter has a structure which shares leading-leg switches and connectes the secondary side output in series.The total output voltage is controlled by adopting the primary and secondary-side sequential PS control strategy.This strategy makes sure the total output voltage is fluently adjustable in a wide output voltage range.The working principle of the converter under different PS control modes is analyzed,and the SS conditions is gived out,and the corresponding DC gains as well as the related topology parameters are illustrated.In the last part,the paper delivers a interleaved integrated magnetic CD-PSFB converter to solve the problem in the conventional CD-PSFB topology.And the interleaved strategy is used to reduce the current stress in switches and the current ripple in filters.Besides,to solve the problems in the CD-PSFB converter,which is that it can't achieve ZVS in the lagging-leg switches,the paper proposes an auxiliary circuit connected at the two phase's middle point of the lagging-legs.Moreover,a new integrated magnetic structure which integrates the primary inductor into the power transformer is used to promote the transformer's efficiency and power density of the converter.The working principle of the converter is analyzed.The inner characteristics of the converter,such as the DC gain,DCM operation of AC inductor,input ripple current and the soft-switching conditions are analyzed.Except that,the design process of the topology's parameter is also given,along with the experimental verification and analysis.