PFM半桥LLC谐振变换器研究

发布时间：2018-08-23 08:57

【摘要】：近年来,具有电能变换功能的开关电源已经广泛应用于航空航天、电子通讯以及新能源等领域。作为高频开关电源不可或缺的环节,DC/DC变换器种类众多且具有重大研究意义。在软开关技术出现之前,DC/DC变换器在工作时会伴有各种开关损耗,致使其使用时间变短,限制了自身的高频化发展。半桥LLC谐振变换器因其工作频率高、抗干扰性能强而备受青睐,成为人们的研究热点。半桥LLC谐振变换器常常采用脉宽调制技术和脉冲频率调制技术来达到输出电压稳定的目的。PWM控制方式在输入电压范围较宽时,容易丢失控制信号,进而引发占空比缺失,变换器的工作效率随之下降。因此本文将采用控制效果优良的PFM控制方式,采用该控制方式的谐振变换器具有电路结构简单、系统响应速度快,工作效率高等优点。本文主要工作内容如下:⑴分析了和软开关技术结合的5种DC/DC变换器的工作原理,并对比它们的优缺点选用了本文要设计的半桥LLC谐振变换器;分析该变换器的工作原理,构建变换器等效电路,推导输出电压和工作频率的关系式,确定其工作频域。⑵给出了半桥LLC谐振变换器的各项设计指标,然后对主电路部分进行设计,包括变压器、谐振网络、主开关管等等。在设计谐振网络时,选取适当的电感归一化量K值和品质因数Q值,根据相关的公式求出各谐振元件的具体参数。⑶对比分析了几种常见的控制方式,选择了控制效果优良的PFM控制方式,然后介绍了控制芯片UC3863的特点和引脚功能;之后在对芯片的外围电路进行一定的分析,对其外接的电容电阻参数进行计算;最后设计了功率驱动电路和光耦反馈电路。⑷采用Saber软件对所设计的变换器进行仿真分析,分别对开关管、谐振网络和副边二极管以及整体电路系统进行了仿真分析。从仿真的结果可知本次设计的变换器实现了软开关功能,且其输出电压纹波小,验证了理论分析的正确性。
[Abstract]:In recent years, switching power supply with power conversion function has been widely used in aerospace, electronic communication and new energy fields. As an indispensable link of high frequency switching power supply, DC / DC converter is of great significance. Before the emergence of soft switching technology, DC / DC converters will be accompanied by various switching losses in operation, resulting in shorter service time, which limits the development of their own high frequency. Half-bridge LLC resonant converter is very popular because of its high frequency and strong anti-jamming performance. Half bridge LLC resonant converter often uses pulse width modulation technology and pulse frequency modulation technology to achieve the purpose of output voltage stability. When the input voltage range is wide, the control signal is easily lost, and then the duty cycle is missing. The efficiency of the converter decreases accordingly. Therefore, the PFM control mode with good control effect will be adopted in this paper. The resonant converter with this control mode has the advantages of simple circuit structure, fast system response speed and high working efficiency. The main work of this paper is as follows: 1 analyzes the working principles of five kinds of DC/DC converters combined with soft switching technology, and compares their advantages and disadvantages with the half-bridge LLC resonant converter designed in this paper, and analyzes the working principle of the converter. The equivalent circuit of the converter is constructed, the relation between the output voltage and the working frequency is deduced, and the design indexes of the half-bridge LLC resonant converter are given in the working frequency domain .2. Then the main circuit is designed, including the transformer. Resonant networks, main switches, etc. In the design of resonant network, appropriate inductance normalized value K value and quality factor Q value are selected. According to the relevant formula, the specific parameters of each resonant element are calculated, and several common control methods are compared and analyzed. The PFM control mode with good control effect is selected, then the characteristics and pin functions of the control chip UC3863 are introduced, and then the peripheral circuit of the chip is analyzed, and the external capacitance resistance parameters are calculated. Finally, the power drive circuit and optocoupler feedback circuit .4 are designed to simulate and analyze the converter with Saber software, and the switching tube, resonant network, auxiliary diode and the whole circuit system are simulated and analyzed respectively. The simulation results show that the designed converter realizes the soft-switching function, and its output voltage ripple is small, which verifies the correctness of the theoretical analysis.
【学位授予单位】：北方民族大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46

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