高功率因数DCM Buck PFC变换器的研究

发布时间：2018-05-09 19:53

本文选题：功率因数校正 + 降压变换器　；参考：《南京理工大学》2017年硕士论文

【摘要】：经过几十年的高速发展,电力电子技术越来越成熟,应用也越来越广泛,例如电力系统、工业生产、航空航天和日常生活等领域都可以发现有电力电子器件的应用,而电力电子器件比如二极管、Mos管、IGBT等都是非线性元件,它们的大量使用带来了日益严峻的谐波污染问题,不仅严重破坏电网的供电质量,还会影响其他用电设备的正常工作。为了保证电网的供电质量,提高电网运行可靠性,保护用电设备免受谐波污染,国际上制定了许多谐波标准来限制用电设备使用时产生的谐波含量,目前应用较为广泛的谐波标准是IEC61000-3-2。本文首先阐述了一些基本概念,引入功率因数校正技术并简要分析各种方法的优劣后,选定DCM Buck PFC变换器作为研究对象,分析了占空比恒定的正弦电流控制下变换器的工作原理,详细介绍了电感电流断续时它的三种工作模态,列出了开关管通断状态对应的电感电流上升和下降斜率,推导出电感电流的峰值包络线表达式,作出了三个模态的电流流通路径以及电感、开关管、二极管和电容的电流波形,推导出输入电流、占空比、输入功率因数的表达式。对输入电流进行傅里叶展开后发现,正弦电流控制下DCM Buck PFC变换器输入功率因数不高的原因是输入电流中含有大量的奇次谐波,尤其是3次谐波含量最高且都与基波相位相差180°,由此引入了在输入电流的非死区内加入与基波相位相同的3次谐波的最优三次谐波电流控制方法。为了在整个设计输入区间内使得输入功率因数都取得最大值,必须求得最优的三次谐波电流与输入电压的关系式,进而求得实现这一目的必须满足的占空比表达式,并对其进行简化实现,得到最终的简化控制电路。文中对正弦电流控制和最优三次谐波电流控制下,变换器的输入电流及其谐波、输入功率因数、临界电感值、电感电流有效值及峰值、输出电压纹波和占空比等典型指标作了详细对比。对比结果显示,采用最优三次谐波电流控制的优点有:(1)减小了输入电流的峰值,且大幅降低了三次谐波的含量,THD显著减少;(2)PF值在整个设计输入区间内均有所提高,尤其是低输入电压下PF值提高的幅度更高;(3)除了 90VAC输入电压下的临界电感值近似相等外,其它输入电压下均比正弦电流控制对应的临界电感值大,电感电流的峰值包络线的最大值及电感电流有效值在整个设计输入区间内均有所减小;(4)输出电压纹波更小。针对本文提出的正弦电流控制和最优三次谐波电流控制方法设计了一款120W的实验样机并经过了实验测试,验证了所提方法有效性,达到了预期效果。
[Abstract]:After decades of rapid development, power electronics technology has become more and more mature and widely used. For example, power systems, industrial production, aerospace and daily life can all be found to have applications of power electronic devices. The power electronic devices such as diode mos transistor IGBT and so on are nonlinear elements. Their extensive use has brought more and more serious harmonic pollution problems which not only seriously damage the power supply quality of the power grid but also affect the normal operation of other power equipment. In order to ensure the quality of power supply, improve the reliability of the power network, and protect the power equipment from harmonic pollution, many harmonic standards have been established in the world to limit the harmonic content in the use of power equipment. At present, the widely used harmonic standard is IEC 61000-3-2. This paper introduces some basic concepts, introduces power factor correction (PFC) technology and briefly analyzes the advantages and disadvantages of various methods, and selects DCM Buck PFC converter as the research object. This paper analyzes the working principle of the converter under sinusoidal current control with constant duty cycle, introduces in detail the three working modes of the converter when the inductance current is intermittent, and lists the rising and falling slope of the inductor current corresponding to the on-off state of the switch tube. The expression of peak envelope of inductance current is derived, the current flow path of three modes and the current waveforms of inductor, switch tube, diode and capacitor are derived, and the expressions of input current, duty cycle and input power factor are derived. After Fourier expansion of input current, it is found that the input power factor of DCM Buck PFC converter under sinusoidal current control is due to the large number of odd-order harmonics in the input current. Especially, the third harmonic has the highest content and is 180 掳different from the fundamental phase, so an optimal third harmonic current control method is introduced, in which the third harmonic with the same fundamental phase is added in the non-dead region of the input current. In order to obtain the maximum input power factor in the whole design input range, the optimal relationship between the third harmonic current and the input voltage must be obtained, and the duty cycle expression which must be satisfied for this purpose is obtained. Finally, the simplified control circuit is obtained. For sinusoidal current control and optimal third harmonic current control, the input current and its harmonics, the input power factor, the critical inductance, the effective value and the peak value of inductance current are discussed in this paper. The typical indexes such as output voltage ripple and duty cycle are compared in detail. The comparison results show that the optimal third harmonic current control has the advantages of reducing the peak value of input current, and greatly reducing the content of third harmonic. THD significantly reduces the value of THD and increases the PF value in the whole design input range. In particular, the increase of PF value at low input voltage is higher than that of critical inductance under sinusoidal current control, except that the critical inductance at 90VAC input voltage is approximately equal, and the other input voltages are larger than those corresponding to sinusoidal current control. The maximum value of the peak envelope of the inductance current and the effective value of the inductance current decrease the output voltage ripple even less in the whole design input range. Aiming at the sinusoidal current control and the optimal third-harmonic current control method proposed in this paper, an experimental prototype of 120W is designed and tested, the validity of the proposed method is verified and the expected effect is achieved.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46

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