基于二次侧谐振回路的高增益变换器及阻抗问题研究

Renewable energy sources such as solar arrays and fuel cells usually have low output voltage characteristics. Therefore, high step-up converters have been widely focused on. In traditional isolated step-up converters, the power loss caused by large primary-side current takes a great proportion. Meanwhile, the power loss caused by hard-switching and the high voltage spikes caused by leakage inductance both limit the efficiency and voltage gain in the traditional isolated step-up converters. ①This work will study how to construct resonant loops on the transformer secondary-side by the inductance and basic voltage-multiplier cells. Meanwhile, this work will propose a family of isolated high step-up converters with natural boost function and soft-switching characteristics. By this means, the primary-side circuit structure is simplified and the primary-side power loss can be significantly decreased. ②By the research of device multiplexing technology and topology simplification, this work will also propose a family of multi-phase high step-up converters with interleaved characteristics so to extend power rating and promote power density. ③From the perspectives of optimizing dynamic model and optimizing power loss model, this work will propose the parameter design method and control strategy. ④Because high step-up converters are widely used as the front-stage converter in a cascaded system. In order to avoid the overlap situation between output-impedance of front-stage converter and the input-impedance of load converter, an output-impedance shaping control method based on virtual complex-number impedance is proposed in this work in order to improve the system stability. Finally the research achievements can produce a systematical theory and technology of isolated high step-up converters based on the secondary-side resonant loops, including the derivation of topologies, the optimization method and the related control method. This work can provide solution schemes for the requirements of high gain, high power and high stability.

光伏、燃料电池等新能源设备输出电压偏低，因此高增益变换器得到了广泛研究。传统隔离升压变换器中低压侧大电流引发的损耗较大，硬开关造成的损耗、变压器漏感造成的电压尖峰等问题限制了变换器效率和增益。①本课题将研究如何利用电感与基本倍压单元，在变压器的二次侧合成谐振回路，构造并提出一类具有自然升压、软开关特性的高增益隔离变换器拓扑，从而简化一次侧结构、降低一次侧大电流造成的损耗;②进一步研究器件复用及拓扑简化方法，提出一类具有交错特性的多相高增益变换器，以扩展功率等级、提升功率密度;③提出以优化损耗模型、动态模型为目标的控制策略及参数设计方法;④针对高增益变换器应用于级联系统、作为前级变换器的场景，提出基于虚拟复阻抗的输出阻抗整形方法，彻底避免前后级变换器发生阻抗交叠，提升系统稳定性。研究结果将形成一类高增益隔离拓扑的构造理论、优化方法和控制技术，为高增益、大功率、高稳定性的应用需求提供解决方案。

光伏、燃料电池等新能源设备输出电压偏低，因此高增益变换器得到了广泛研究。传统隔离升压变换器中低压侧大电流引发的损耗较大，硬开关造成的损耗、变压器漏感造成的电压尖峰等问题限制了变换器的效率和增益。本课题围绕这一问题，研究了如何利用电感与基本倍压单元，在变压器的二次侧合成谐振回路，提出了一类具有自然升压、软开关特性的高增益隔离变换器拓扑，从而简化一次侧结构、降低一次侧大电流造成的损耗。根据所提出的变换器拓扑，从器件复用的角度，进一步提出了一种三相DC/DC变换器拓扑。此外，本课题根据传统LLC谐振变换器的特点，根据其对偶结构、提出了一种具有零电流软开关特点的隔离变换器。面向所提出的变换器拓扑，从优化控制模型及损耗模型的角度，研究了相应的控制方法和主电路参数设计方法。此外，面向典型的级联结构应用场景、围绕其中的稳定性问题，提出了一种通用的基于虚拟复阻抗的输出阻抗整形方法。该方法适用于采用电压外环、电流内环控制的DC/DC变换器，可以有效避免前后级变换器发生阻抗交叠，提升系统稳定性。研究结果形成了一类高增益隔离拓扑的构造理论、优化方法和控制技术，为高增益、大功率、高稳定性的应用需求提供了解决方案。