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能源管理

被动和主动的功率因素纠正器有什么区别？

2015年12月10日,

Current draw by different types of load-generating waveforms needs to be regulated in order to achieve power factor unity and comply with industrial standards.

玛丽亚·格拉（Maria Guerra）

本文是能源管理系列：What’s the Difference Between Watts, RMS, and More?

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Every day, the amount of electronic devices using switched-mode power supplies increases. As a result, power-factor correction has become a very significant issue, leading to the creation of regulatory standards. Thanks to those standards, design/application engineers are using the latest technologies in passive and active components and controller integrated circuits (ICs) to create a wide range of power-factor correctors.

功率因数

1. Power-factor triangle relates the real power, the reactive power, and the apparent power. (Courtesy of Vector Group)

让我们从谈论权力因数（PF）的概念开始。假设完美的线性负载具有理想的正弦波功率，电源系统的功率因数是真实功率（KW）与明显功率（KVA）（KVA）之间的比率（KVA）（KVA）（KVA）（Fig. 1).

它也可以定义为代表电流波形和电压波形之间的相角的余弦。功率因数的值范围为0到1。当电流和电压相位时，功率因数为1。

2.所示的是具有统一功率因数的理想正弦波。（由Vicor提供）

当载荷由线性（电流和电压不变）组成时，通常会发生理想的正弦波。这种类型的功率因数通常与工业设备相关，例如电动机（电动机（Fig. 2).

如今，找到在非鼻腔波形中绘制电流的功率因数非常普遍（Fig. 3）在具有非线性载荷的电子设备中。这样的电子设备使用功率转换来更好地控制或节省能源。这种电源转换是通过使用开关模式电源来实现的，该电源通常在PC，视听设备，荧光灯，调光器，复印机，电池充电器等中找到。

3. Here we see non-sinusoidal waveforms with a severe distortion of the current wave. (Courtesy of Electrical Engineering Stack Exchange)

图3表明电流和电压完全处于相位，即使电流波的严重失真。应用“相角余弦”将导致错误的结论，即该电源的功率因数为1.0。在这种情况下，应根据功率线基本频率的谐波系列分析功率因数。考虑到总谐波扭曲（THD）的绝对值，可以定义非线性负载的功率因数，如在Fig. 4.

4.该图表描述了功率因数与总谐波扭曲（THD）之间的关系。

不等于统一的功率因数可能会导致谐波失真。这种失真可能会干扰其他设备从同一来源供电。看着Fig. 4，我们可以说，要达到1.0的功率因数，THD值应为零。谐波失真会导致严重的问题，例如网络内的电缆和其他设备的损坏以及过热和火灾风险，高压和循环电流，设备故障和组件故障等等。

功率因子校正器

功率因子校正（PFC）用于避免输入电流谐波，从而最大程度地减少对从同一源供电的其他设备的干扰。在欧洲和日本，电气设备必须遵守标准IEC61000-3-2。该标准适用于具有超过75 W（D类设备）的输入功率的大多数电器。它还指定了线路频率谐波的最大幅度，包括39^Thharmonic.

There are no standards in the United States for limiting the harmonic current emissions emitted by electric equipment like there is in Europe (IEC6100-3-2). However, an initiative called 80 PLUS is trying to integrate more efficient power supply units, especially for desktop computers, servers, and laptops.

80 PLUS certifies to more than 80% energy efficiency at 20%, 50%, and 100% of the rated load. To meet the 80 PLUS certification, PSUs require a PFC of 0.9 or greater at 100% load. This means PSUs that waste 20% or less electric energy (as heat at the specified load levels) will lead to reduced electricity consumption and lower bills. Rebates are sometimes given to manufacturers who use 80 PLUS certified PSUs.

功率因子校正器的类型

5.单个PI滤波器是一个被动的电源校正器。（由维基百科提供）

使用两种类型的功率因子校正器来减少谐波失真：被动PFC和主动PFC。

As the name implies, a passive PFC uses passive components to correct poor power factors (e.g., inductors and capacitors). Passive PFC corrects the power factor to 0.7-0.85. Here are the most common types of passive PFCs:

1.电容器输入过滤器：也称为π过滤器,删除不必要的联邦quencies from a signal. The filter reduces the harmonic content of a current waveform by making sure that the cut-off frequency of the filter is just above the fundamental frequency. As a result, the optimum attenuation of harmonics can be achieved (Fig. 5).

2. Valley-fill PFC:该功率因子校正器可用于低功率应用中，其中可以耐受直流输出的高效波纹电压。它经常用于电子镇流器应用中。该电路包含两个电容器和三个二极管。这两个电容器在线峰值上以峰值线电压的一半为单位充电。当线电压降至单个电容器电压以下时，桥梁整流器二极管会反向偏置，这不允许电流流动。然后进行谷填充的二极管进行操作，并且电容器并行连接以供电。图6shows a conventional valley-filled circuit.

6.山谷填充是一个被动的电源校正器。（由P. Parto和K. Smedley提供，加利福尼亚大学）

被动技术通常使用简单的线路频率LC滤波器来扩展电流传导角并减少二极管电容器整流器的输入电流的THD。由于其简单性，被动LC滤波器是一种高效率和低成本的PFC解决方案，可以在低功率范围内符合IEC 61000-3-2类D规格。然而，在较高的功率水平下，由于存在较重，较大的滤镜感应器，因此被动组件的大小和重量成为问题。被动技术具有一定的优势，例如简单性，可靠性和坚固性，对噪声和冲浪的不敏感性，没有产生高频电磁界面（EMI），也没有高频切换损失。

Active PFCs use active electronics circuits, which contain devices like MOSFETs, BJTs, and IGBTs. There is a wide range of topologies for active PFCs, and electronic/power supply designers are able to create circuits with different modes of operations and different challenges as technology evolves. Here are two basic types of active PFCs:

1. Boost:This popular implementation, which also is called a step-up converter, is a power converter with an output dc voltage greater than its input dc voltage. This class of switching-mode power supply (SMPS) contains at least two semiconductor switches and at least one energy-storage element. Filters are normally added to the output of the converter to reduce output voltage ripple. Because power must be conserved, the output current is lower than the input current.

Almost all boost PFCs utilize a standard controller chip for the purposes of ease of design, reduced circuit complexity, and cost savings (Fig. 7).

7. A boost circuit is an active power-factor corrector. (Courtesy of L. Rossetto, G. Spiazzi, P. Tenti, University of Padova)

当关闭开关时，电感器输出连接到地面，并将电压（VI）放置在其上。电感器电流以等于VI/L的速率增加。但是，当开关打开时，电感器上的电压变化，等于VL-VIN。电感器中流动的电流以等于（VL-VI）/L的速率。

8.降压设计是一个主动的功率因子校正器。（由无线电电子设备提供）

The filter inductor on the input side is the main advantage of boost PFCs because it allows low-distorted input currents that prevent the reduction of the power factor value. A disadvantage to this approach is that the output voltage is always greater than the peak input voltage. In addition, there is a lack of current limitation during overload and short-circuit conditions, due to the direct connection between line and load.

2. Buck:该电压降压转换器和当前的升级转换器在电感器中存储能量的主体运行。有一个可以打开或封闭的开关元件（功率MOSFET或IGBT）（Fig. 8).

当开关处于ON位置（即状态下的MOSFET）时，电流向负载和能量的刷新存储在电感器（L）和电容器（C）中，并且没有电流流过二极管是反向偏置的。当开关处于OFF位置时，存储在（L）中的能量将释放回电路，电流通过负载和二极管流动。在某个时候，当负载电压开始下降时，存储在C中的电荷成为电流的主要来源，直到开关再次打开为止。

降压转换器可能非常有效（集成电路的95％或更高）。