宽输入高增益隔离型DC-DC变换器的研究

【作者】 陈申；

【导师】 吕征宇；

【作者基本信息】 浙江大学 ， 电力电子与电力传动， 2012， 硕士

【摘要】 隔离升压型DC-DC变换器是一类可以将低压直流母线变换成高压直流母线并实现电气隔离的变换器的统称,比较常见的有正激变换器、反激变换器和隔离型Boost变换器等三种基本变换器及它们的衍生拓扑。隔离升压型DC-DC变换器已经在储能系统以及航天电源系统等领域取得广泛应用。并且就目前电力电子领域的发展形势来看,隔离升压DC-DC功率变换将成为新能源发电以及新能源汽车等领域的关键技术之一。概括起来,新一代隔离升压型DC-DC变换器的特点可以表述为：宽输入、高增益和高效率。LLC谐振变换器不需要辅助电路就可以实现原边开关管的零电压开关和副边整流管的零电流开关,具有结构简单和高效率功率变换的优点,近年来已在工业界得到广泛应用,典型应用是前端DC-DC功率变换器。LLC谐振变换器的宽范围输入适应性好、全负载范围内实现软开关以及高效率功率变换等特点,很好地符合新一代隔离升压型DC-DC变换器的要求,因此本文以升压型LLC谐振变换器作为研究对象,首先提出了一种改进型的LLC谐振变换器参数设计方法,然后提出了基于LLC谐振变换器的两种宽输入高增益隔离升压型DC-DC功率变换的解决方案,它们分别是单级型和级联型功率变换。LLC谐振变换器的设计主要是三个谐振元件的设计。传统的设计方法是建立在变换器的增益函数的基础上。目前描绘LLC谐振变换器的增益函数的方法主要有三种：基波等效法(Fundamental Harmonic Approximation, FHA)、仿真分析法和时域分析法。传统的LLC谐振变换器参数设计方法的问题在于过分依赖经验而且没有固定的范式。针对这一缺点,本文提出了一种改进的LLC谐振变换器设计方法——基于“电流角”模型的LLC谐振变换器设计方法。电流角的大小直接决定了换流过程中MOSFET寄生电容充放电所需电荷的供给量。电流角越大,供给量越大,越容易实现软开关,但是多余供给量会造成额外的损耗,造成效率下降。因此,该设计方法将电流角作为优化设计变量,通过控制电流角来优化变换器效率。针对高增益隔离升压型DC-DC功率变换,本文提出了两种解决方案：单级型和级联型。单级型就是在输入和输出之间只有一个DC-DC拓扑,该拓扑同时满足宽输入和高增益隔离升压的高效率功率变换需求。而级联型则是采用Boost级联直流变压器的结构,其中直流变压器的作用是抬升功率变换电平以使得Boost变换器落在理想的工作区域。本文分别制作了实验样机来验证两种解决方案的可行性。隔离型DC-DC变换器的输出倍压技术主要有整流倍压技术和谐振倍压技术。理论上,任何变压器双向磁化的隔离型DC-DC变换器均可以采用输出倍压技术,对于变压器输出为电流型的拓扑可以采用整流倍压技术,而对于变压器输出为电压型的拓扑则需要采用谐振倍压技术。本文设计了一台实验样机以验证谐振倍压技术在变压器输出为电压型的应用的可行性。最后,本文就各部分的研究内容和成果做了总结,并提出了进一步改进与研究的方向。更多还原

【Abstract】 The isolated step-up DC-DC converter is a kind of converter which can convert low voltage DC bus into high voltage DC bus and realize electrical isolation. The common topologies are forward converter, flyback converter, isolated Boost converter and their variations. The isolated step-up DC-DC converter has been widely used in fields such as energy storage system and aeronautical power supply system. And according to the developing tendency of power electronics, the isolated step-up DC-DC converter will become one of the key technology in fields like new energy generation and new energy vehicle. In conclusion, the characteristics of the new generation isolated step-up DC-DC converter is wide input, high step-up gain and high efficiency.LLC resonant converter can achieve zero-voltage switching (ZVS) for primary side switches and zero-current switching for secondary side rectifiers without auxiliary circuit, so it features simple structure and high efficiency. And it is widely used in front-end DC-DC converter in recent years. LLC resonant converter has avdantages over other topologies, such as wide input adaption, full load range soft switching and high efficiency power conversion, and it satisfies the requirements of the new generation isolated step-up DC-DC converter. This paper takes objective of LLC resonant converter, firstly proposes a improved design methodology and then presents two kinds of power conversion solutions based on it, which are single stage and cascaded stage power conversion.The design of LLC resonant converter is mainly the design of three resonant components. Traditional design is based on the gain curve, therefore the key point is drawing out the gain curve. There are three methods to realize it, which are fundamental harmonic approximation, simulation analysis and time domain analysis. The disadvantages of traditional design method is that it is excessively depended on experience and has no normal form. According to this, this paper proposes a improved design methodology based on the current angle. The size of the current angle directly determines the charging and discharging precess of MOSFET parasitic capacitor during commutation. The larger the current angle, the easier the realization of soft switching. Howerver, the excess energy makes additional power loss which degrades the converter efficiency. For this reason, the proposed method optimizes the current angle for efficiency optimisation.According to high step-up isolated DC-DC power conversion, this paper presents two practical solutions, which are single stage and cascaded stage. The single stage means that there is only one DC-DC topology between the input and output. And the cascaded stage is a two stage power conversion, that is Boost+DC-DC transformer. The effect of the DC-DC transformer is to boost the DC voltage bus so that the Boost converter can work in satisfactory region. Two prototypes are made to verify the two power solutions respectively.The output voltage doubling technology of isolated DC-DC converter has two kinds, which are the rectified doubling and the resonant doubling. Theoretically, any isolated DC-DC converter with two-way magnetization can adopt output voltage doubling. The topology of current form can adopt rectified doubling and the voltage form can adopt resonant doubling. A prototype is made to verify the feasibility of resonant doubling in the voltage form topology.Finally, this paper makes a conclusion of each part and presents further research direction.更多还原