【作者】 秦伟；

【导师】 吴新科；

【作者基本信息】 浙江大学 ， 电气工程， 2019， 博士

【摘要】 电能从电网到信息系统中的各种芯片负载和设备,需要完成从高压到低压的转换。而从较高的直流母线给信息系统中各种低压的数字和模拟负载供电,业界广泛采用可靠、灵活、可扩展性强的中间母线供电架构。这一架构包含两级功率变换,前级的中间母线变换器将48V或者24V变换成12V左右的中间电压母线并实现电气隔离,后级的负载点变换器将中间电压母线变换成负载所需要的电压。在该架构中,提高前级母线变换器的效率和功率密度对实现应用系统中相关设备的轻量化、小型化十分关键。本文以中间母线变换架构中的母线变换器为研究对象,针对适用于小功率DC/DC应用的高频单管全谐振软开关拓扑及其控制策略进行了深入研究和探讨,主要包含以下内容:针对现有隔离型谐振软开关拓扑方案复杂的问题,首先揭示了现有电压源输入型软开关谐振腔的内在限制,由此提出了电流源输入型和电流源输出型单管全谐振单元以突破这一限制。在此基础上推演出系列单管电流源型全谐振正激电路拓扑族。所提出的单管谐振正激拓扑能实现零电压零电流全软开关(Zero-Voltage and Zero-Current Switching,ZVZCS)特性,且占空比和工作频率固定,能始终工作在最佳工作点,为小功率应用场合提供了高效的单管谐振拓扑方案。此外,本文还提出单管全谐振单元的组合和扩展方法,进而推演出一族能够实现开关管零电压开通和零电流关断的全谐振软开关拓扑,该族拓扑能够适应不同功率和电压等级的中间母线供电架构的应用需求。文中详细分析了所提出的新型全谐振单元的电气特性和参数设计方法,并通过仿真和实验证明了所提出全谐振单元的可行性和有效性。基本的单管谐振正激电路具有结构简易性和ZVZCS全软开关特性,但是其利用开关管结电容电压实现变压器磁复位的方式带来了开关管电压应力过高的问题,因而较适合低压输入应用场合,对于输入电压较高的场合,电路需要采用耐压较高的器件。针对这一问题,本文研究了利用变压器箝位绕组和箝位二极管对开关管两端电压进行箝位的无源箝位方法,并提出了适合降压应用场合的电流源输入型副边箝位谐振正激电路。该拓扑通过输出电压对开关管两端的电压进行箝位,开关管电压应力小,且保持了基本单管全谐振正激电路的ZVZCS软开关特性,高频工作时能够取得较高的转换效率。对单管谐振正激电路采用无源箝位的方法可以优化器件的应力,但其占空比受限于0.5,导致效率的提升有限,并且漏感与结电容的振荡弱化了箝位效果。为了进一步提高单管谐振电路的效率性能,消除高频振荡,降低尖峰电压应力,本文提出了电流源输入型有源箝位谐振正激电路,该拓扑利用一个辅助开关管和箝位电容对开关管两端的电压进行箝位,相较于无源箝位谐振正激变换器而言电路的ZVZCS性能更优且箝位电路的损耗更小。同时电路可以实现大于0.5的占空比,电流有效值小,有利于提高满载效率。另一方面,利用箝位电容电压随控制参数灵活变化的特性,本文进一步地提出一种变导通时间控制策略,通过在不同负载下改变电路的导通时间,该策略巧妙地解决了轻载时全谐振DC/DC变换器中变压器磁芯损耗比重太大的问题,大幅提高了轻载效率。最后通过实验证明了所提出的功率变换方法能有效提高电路全负载范围的效率性能。单管谐振正激电路原边或者副边开关管的电压应力不能被很好地箝位,因而其启动过程不仅存在传统谐振电路面临的谐振腔电流应力问题,还存在开关管的电压应力问题,这一额外的电压应力问题限制了传统软启动方法的应用。针对单管谐振正激电路的启动,本文提出了一种利用开关器件恒流工作区的软启动方法,在实现输出电压缓慢建立的同时,减小了启动过程中谐振腔的电流过冲以及开关管的电压过冲。并且,该软启动方法还能推广应用至双端谐振拓扑的启动中。更多还原

【Abstract】 The integrated circuit(IC)chips and other equipment iin information and communication technology(ICT)systems require low voltage power from the high voltage grid.And to power various low-voltage digital and analog loads from high-voltage DC bus,the intermediate bus architecture(IBA)is widely used due to its high reliability,high flexibility and good extendibility.The IBA is a two-stage architecture.The first stage is an isolated dc/dc bus converter,which has voltage specifications of 48V/12V(4:1)and 24V/12V(2:1).The second stage is the point of load(PoL)converter which has regulating ability.In this architecture,high power density and high efficiency bus converter is very crucial to reduce weight and volume of relevant equipment.This dissertation targets at improving the power density and efficiency of bus converter in IBA,and focuses on high frequency single-switch Zero-Voltage and Zero-Current-Switching(ZVZCS)resonant topologies and their control schemes.Firstly,the intrinsic limit of existing voltage feed soft-switching resonant tank that leads to the complex structure of available isolated resonant topologies is revealed.Based on this,current-feed and current-sink single-switch ZVZCS resonant cells are proposed,from which current-feed and current-sink single-switch ZVZCS resonant forward topologies can be directly obtained.The proposed single-switch resonant forward topologies can realize ZVZCS,and they can always operate at this optimal ZVZCS point with switches operating at fixed frequency and fixed duty cycle,therefore,the work presented here makes high-efficiency single-switch resonant topology become available for low-power applications.Besides,more compound resonant cells can be constructed from the basic single-switch ZVZCS resonant cells,and a family of ZVZCS resonant topologies for IBA applications with various power and voltage levels is derived.The electrical characteristics and design considerations of the proposed ZVZCS resonant cells are analyzed in detail,and simulation and experimental results are provided to verify their high frequency and low loss features.The basic single-switch resonant forward converters are simple and have good ZVZCS features,but they utilize the drain-source voltage of switch to reset the transformer and this introduces high voltage stress issues.Therefore,they are more suitable for low voltage applications,and for high voltage applications,switches with high voltage rating must be adopted.To alleviate the voltage stress issue,the passive clamping technique using transformer clamping winding and clamping diode is adopted,and a current-feed single-switch resonant forward converter with secondary diode-clamping is proposed which is suitable for step-down applications.The proposed converter makes use of the output voltage to clamp the switch voltage stress,and maintains the ZVZCS features of the basic single-switch resonant forward converter,thus it can achieve high efficiency at high frequency.Applying the passive clamping technique to the basic single-switch resonant converter can reduce the switch voltage stress,but with this method the switch duty cycle is limited to 0.5 and thus the efficiency improvement is limited.Besides,the resonance between leakage inductance and parasitic capacitance weakens the clamping effect.In order to further improve the efficiency of single-switch resonant topologies and eliminate the high frequency ringing in passive clamping solution,a current-feed active-clamp resonant forward converter is proposed,which utilize an auxiliary switch and a clamping capacitor to clamp the switch voltage stress.This converter has better ZVZCS feature and less clamping loss than the passive clamping solution.Meanwhile,this converter can achieve duty cycle larger than 0.5 which can reduce the RMS current and improve the efficiency at heavy load.What’s more,by usage of the unique flexibility of the clamping capacitor,a load adaptive ON-time control that can significantly reduce core loss at light load is proposed,and this scheme greatly improves the light-load efficiency.Finally,experimental results verify that the proposed converter can effectively improve the whole-load-range efficiency.Because of the single-switch structure,the voltage stress of the primary or secondary switches of single-switch resonant converters is not well clamped.Therefore,not only the current stress issue in resonant tank which is common in traditional resonant converters but also voltage stress issue of switches exist in the start-up process of the proposed single-switch resonant topologies.In order to realize soft start-up of this kind of converters,a method using the constant current region of MOSFETs is proposed,which can slowly establish the output voltage and at the same time reduce the stress issues aforementioned.Besides,this soft start-up method can be extended to the start-up of double-ended resonant converters.更多还原