基于CCM的单相Boost PFC电路的设计与仿真 下载本文

基于CCM的单相Boost PFC电路的设计与仿真

摘要

近年来,为了避免“电网污染”,如何抑制谐波电流、提高功率因数成了备受关注的问题,而有源功率因数校正技术正是行之有效的方法。尤其是在单相Boost型电路中得到了广泛的应用。它是在桥式整流器与负载接一个DC-DC变换器,应用控制电路的电压电流双环反馈,使电网输入电流波形趋于正弦化且相位保持与输入电压相同,从而大幅降低THD,使得PF接近于1。交流输入电压通过全桥后,得到全波整流电压,再经过MOS管的开关控制使输入电流自动跟随输入电压基准的正弦化脉动,并获得稳定的升压输出,给负载提供直流电压源。

本文先简要介绍了功率因数校正技术的现状与发展,着重讨论了有源功率因数校正的原理、拓扑结构、控制方式等内容,然后对控制器UC3854进行了简单的构造分析,最后设计出基于UC3854芯片CCM工作模式的Boost PFC电路。

关键词:有源功率因数校正,Boost变换器,电流连续模式,平均电流控制,UC3854

ABSTRACT

In recent years, in order to avoid \improve the power factor has become a concern, and active power factor correction technology is an effective method. Especially in single-phase Boost-type circuit has been widely used. It is in the bridge rectifier and the load connected to a DC-DC converter, the application of the control circuit voltage and current double loop feedback, so that the grid input current waveform tends to be sinusoidal and phase to maintain the same with the input voltage, thereby significantly reducing the THD, making PF close In 1. AC input voltage through the full bridge, the full-wave rectifier voltage, and then through the MOS tube switch control so that the input current automatically follows the input voltage reference sinusoidal pulsation, and obtain a stable boost output to the load to provide DC voltage source.

In this paper, the present situation and development of power factor correction technology are briefly introduced. The principle, topology and control mode of active power factor correction are discussed emphatically. Then, the simple structure analysis of controller UC3854 is carried out. Finally, Chip CCM operating mode Boost PFC circuit.

Keywords: Active Power Factor Correction, Boost converter, Current Continuous Mode, Average current control, UC3854

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目录

1 绪论 ....................................................................................................................................................... 1 1.1 功率因数校正的背景意义 ............................................................................................................ 1 1.2 功率因数校正的发展概述 ............................................................................................................ 1 1.3功率因数校正的实现方法分类 ..................................................................................................... 2 1.3.1按PFC电路使用的元器件分类 ................................................................................................. 2 1.3.2 按供电方式分类 ......................................................................................................................... 2 1.3.3 按PFC电路的级联方式分类 .................................................................................................... 2 1.3.4 按PFC电路的电路拓扑结构分类 ............................................................................................ 2 1.4 本文所做的主要工作 .................................................................................................................... 2 2 功率因数校正原理 ............................................................................................................................... 4 2.1 功率因数 ........................................................................................................................................ 4 2.1.1 功率因数的定义 ......................................................................................................................... 4 2.1.2 功率因数与总谐波失真系数(THD)的关系 ......................................................................... 4 2.1.3功率因数校正的任务 .................................................................................................................. 4 2.1.4电源电流波形失真原因简析 ...................................................................................................... 5 2.2 有源功率因数校正的基本原理 .................................................................................................... 5 2.3 有源功率因数校正的拓扑结构 .................................................................................................... 6 2.4 有源功率因数校正的工作模式及控制方式 ................................................................................ 7 2.4.1电流断续模式(Discontinuous Current Mode,DCM) ............................................................. 8 2.4.2电流临界模式(Boundary Conduction Mode,BCM) .............................................................. 8 2.4.3电流连续模式(Continuous Current Mode,CCM) .................................................................. 9 3 PFC主电路主要元器件的参数设计 .................................................................................................. 13 3.1本PFC电路的设计指标 .............................................................................................................. 13 3.2 Boost变换器的工作原理 ............................................................................................................. 13 3.3主电路元器件的参数设计 ........................................................................................................... 15 3.1.1开关频率的选择 ........................................................................................................................ 15 3.1.2升压电感的选择 ........................................................................................................................ 15

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3.1.3输出电容的选择 ........................................................................................................................ 16 3.1.4开关管和二极管的选择 ............................................................................................................ 16 4 基于UC3854控制电路的设计 ......................................................................................................... 17 4.1 UC3854控制器概述 .................................................................................................................... 17 4.2 UC3854控制器的内部结构和功能特点 .................................................................................... 17 4.2.1 UC3854控制器的内部结构 ..................................................................................................... 17 4.2.2 UC3854控制器的功能特点 ..................................................................................................... 18 4.3 UC3854控制电路各参数设计 .................................................................................................... 19 4.3.1 电流感测电阻的选择 ............................................................................................................... 19 4.3.2 峰值电流限制 ........................................................................................................................... 20 4.3.3 前馈电压信号 ........................................................................................................................... 20 4.3.4 乘法器的设定 ........................................................................................................................... 20 4.3.5 乘法器的输入电流 ................................................................................................................... 21 4.3.6 乘法器的输出电流 ................................................................................................................... 21 4.3.7 振荡器的频率 ........................................................................................................................... 21 4.3.8 电流误差放大器的补偿 ........................................................................................................... 22 4.3.9 电压误差放大器的补偿 ........................................................................................................... 22 4.3.10 前馈电压滤波电容 ................................................................................................................. 23 4.4 UC3854的仿真电路及仿真波形展示 ..................................................................................... 23 总结 ......................................................................................................................................................... 28 致谢 ......................................................................................................................................................... 29 参考文献 ................................................................................................................................................. 30

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1 绪论

1.1 功率因数校正的背景意义

世界工业化进程的加快,使得市面上用电设备的样式越来越多、它们的容量也越来越大。但是这些电器设备大都不是纯阻性负载,而是具有非线性特性的阻抗负载。因为如此,电网端输电进入这些设备后,输入电流往往会滞后电网电压,从而产生一个相位角。这样就导致了电网所供应的电能并不完全能被用电设备给利用,除去转化为有用功的部分电能,其余都以磁能的形式储存在储能元器件中而不能被释放。这就使得电网电能的利用率大幅下降。这种现象的普遍存在直接致使了电网的电能质量下跌。另外一些电力电子装置的大面积应用也使得大量谐波电流出现在电网输入端,引起输入电流畸变以造成“电网污染”。然而大量建设发电站并不能很好的解决“电网污染”所造成的供电紧张问题,从成本和环保等方面来说也并不符合当下的“低碳”、“绿色”和“环保”等主题。因此,为了抑制高次谐波污染,提高电能质量,设法提高有关电气产品的功率因数就变得重要。

1.2 功率因数校正的发展概述

最初的PFC概念是针对线性负载而言的,这时候就不用考虑谐波失真情况,它要求输入设备的电压与电流为同频率同相位的正弦波即可。但是对于多数为感性负载的电气设备,此方式所得到的PF显得差强人意。因此为了提升PF,通常在这种感性负载两端并联电容,起移相作用,此方法被称作PF并联补偿。但是该法对于输入电流波形严重失真的状况不作为,这就迫使人们探求新的PFC方案。

后来,在早期的开关电源中,无源功率因数校正(PPFC)开始崭露头角。它是在直流源端或桥式整流器后添加一个LC网络,应用电感电流不能突变的特性,来增加二极管的导通角,使得输入电流失真有了较大的改善。但是该方法有其明显的劣势,即能达到的PF并不理想,而且体积庞大、成本高。后来被更为先进的,由二极管、电容、小电感等无源器件构成的PPFC电路拓扑所取代。

随着对PFC效果的追求越来越高,使得输入总谐波失真(THD)达到足够低,有源功率因数校正技术(APFC)渐渐发展了起来。20世纪80年代初,飞利浦公司开发的单

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