LLC谐振变换器的轻载性能优化研究

发布时间：2018-11-11 20:03

【摘要】：LLC谐振变换拓扑具有软开关、效率高、功率密度高、EMI较低、可使用磁集成技术等优点。在千瓦功率等级的应用中,LLC谐振变换器的最大效率值可以达到97%。因此在中功率DC-DC变换中得到广泛的应用。在工业电源应用中,功率变换器的负载状态具有多变性。对于通信基站的燃料电池备用电源,它的输入电压波动较大,负载范围也较宽,因此对功率变换器的宽负载特性提出了较高的要求。传统的LLC谐振变换器在轻载下会有增益失真等问题,传统的解决方法是增加假负载,但是这样又会带来额外的损耗,增加成本。本文针对近年来颇受研究者关注的LLC谐振变换器的轻载增益失真以及轻载效率问题进行了研究。首先,本文从拓扑分析的角度,提出传统的稳态分析模型不适合用于对轻载状态的分析。因为寄生电容的存在,改变了轻载状态下谐振电路的谐振工作过程。在全负载范围的分析中,不能忽略电路中寄生电容的影响。在考虑寄生电容的前提下,本文利用基波分析法建立了LLC谐振变换器的稳态模型,分析了其轻载工作过程和直流电压增益。并建立了LLC谐振变换器在轻载时的损耗模型,用来有针对性地提高变换器的效率。其次,通过分析LLC的谐振参数对于变换器增益特性以及变换器效率的影响,本文设计了轻载增益失真和效率问题的解决方法。改进了LLC谐振参数的设计方法,以几个关键参数为变量,以满足增益需求、满足软开关条件、对效率的影响尽量小等作为边界条件,得到可以避免轻载增益失真的LLC谐振参数。优化了变换器的控制策略,轻载时加入改进了的间歇控制模式,提高变换器在轻载时的转换效率。最后,本文依托燃料电池功率转换系统的DC-DC功率变换模块的具体应用,对改进后的方法进行了SABER仿真和实验验证。设计了一台满载输出功率为5kW的全桥LLC谐振变换器样机,对优化方法进行了验证。实验结果证明,采用的优化方法可以避免轻载时的增益失真问题,并能有效提高轻载时的效率。
[Abstract]:LLC resonant topology has the advantages of soft switching, high efficiency, high power density, low EMI and magnetic integration technology. In the application of kilowatt power level, the maximum efficiency of LLC resonant converter can reach 97. So it is widely used in medium power DC-DC transform. In the application of industrial power supply, the load state of power converter is variable. For the fuel cell reserve power supply of the communication base station, its input voltage fluctuates greatly and the load range is also wide, so the wide load characteristic of the power converter is required. The traditional LLC resonant converter will have gain distortion under light load. The traditional solution is to increase the false load, but this will bring extra loss and increase the cost. In this paper, the light load gain distortion and light load efficiency of LLC resonant converters which have attracted much attention in recent years are studied. Firstly, from the point of view of topological analysis, this paper proposes that the traditional steady-state analysis model is not suitable for the analysis of light load state. Because of the existence of parasitic capacitance, the resonant process of resonant circuit under light load is changed. In the analysis of full load range, the influence of parasitic capacitance in the circuit can not be ignored. On the premise of considering parasitic capacitance, the steady state model of LLC resonant converter is established by using fundamental wave analysis method, and its light-load operation process and DC voltage gain are analyzed. The loss model of LLC resonant converter under light load is established to improve the efficiency of the converter. Secondly, by analyzing the influence of resonant parameters of LLC on gain characteristics and efficiency of converter, a method to solve the problem of gain distortion and efficiency under light load is designed in this paper. This paper improves the design method of LLC resonant parameters, takes several key parameters as variables to satisfy the gain requirements, meet the soft switching conditions, and minimize the influence on efficiency as the boundary conditions, to obtain the LLC resonant parameters which can avoid light load gain distortion. The control strategy of the converter is optimized, the improved intermittent control mode is added to the light load control mode, and the conversion efficiency of the converter under light load is improved. Finally, based on the specific application of the DC-DC power conversion module of the fuel cell power conversion system, the improved method is simulated by SABER and verified by experiments. A full-bridge LLC resonant converter with full load output power of 5kW is designed and the optimization method is verified. The experimental results show that the proposed optimization method can avoid the gain distortion and improve the efficiency of light load effectively.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46

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