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功率因数校正电路的稳定性测试
2017-05-04
Abstract:
Power factor correction has become an increasingly necessary feature in new power supply designs. In a power factor correction circuit there are two feedback control loops. One loop operates by using the input voltage as a reference to control the input current. This loop is fast and makes the input current instantaneously proportional to input voltage as it would be with a resistive load. A second loop, which is much slower, controls the constant of proportionality to make the average current correct to keep the output voltage of the power factor correction circuit constant. Testing the slow loop for stability is easy with the proper equipment, but testing the faster loop is much more difficult. The operating point of the faster loop is dynamically changing from near zero to the peak value of the input current. This paper discusses the techniques necessary to measure the stability of each of these loops and specifies necessary equipment and procedures to perform these tests.
功率因数校正已经成为新的电源设计越来越必要的特征。在功率因数校正电路中有两个反馈控制环路。一个环路利用输入电压作为参考来控制输入电流。这个环路速度快而且对于电阻负载使输入电流和输入电压瞬间均衡。对于第二个环路，它速度较慢，控制比例常数使平均电流精确到保持功率校正电路的输出电压恒定。测试慢环路的稳定性是简单的，只需要使用适当的设备，但是测试快速环路是很困难的。快速环路的工作点是动态变换的，从接近0到输入电流的峰值。本文讨论了需要测量各回路的稳定性的技术和指定要执行这些测试所需的设备和程序。
Introduction
介绍
What is power factor correction, and why is it necessary?
什么是功率校正因数
Most switching power supplies operate from a 50 or 60 Hertz AC line with a capacitive input filter, as shown in Figure 1. This type of filter draws current from the line only when the line voltage exceeds the filter capacitor voltage, and the filter capacitor is charged to near the peak level of the input line voltage as shown in Figure 2. This means that the input current only flows for a short period near the peak of the input voltage waveform, causing the current to flow as a series of short, narrow pulses rather that the smooth, sinusoidal current that would result from a resistive load.
大多数开关电源工作在50-60HZ带有一个电容性输入滤波器的交流线路上，如图1所示。这种类型的滤波器只有当线电压超于滤波器电容电压而且滤波器电容被充电到附近线电压的峰值水平时才从线上拉动电流，如图2所示。这意味着在短时间内在输入电压波形峰值附近只有输入电流流动，导致电流一系列的不足，窄脉冲，正弦电流，一起将作用在一个电阻线负载上
The root-mean-square (rms) value of this series of current pulses is much higher than the average value. The output power is approximately proportional to the average value of the current, but the rms value determines line losses, fuse ratings, and similar power quality related issues. Improving the power factor brings three benefits:
这一系列电流脉冲的均方根高于平均值。输出功率与电流平均值近似成正比，但是均方根值决定线路损耗，熔断器定额，和类似的电能质量相关问题。提高功率因数所带来的三个好处：
1. Power distribution costs for the electric company are reduced, making the power company much happier. A side benefit is to reduce the tendency of the current peaks to "flatten" the tops of the input voltage sinusoidal waveform as shown in Figure 3.
1.减少电力公司的供电成本，使电力公司更快乐。另一个好处是减少电流峰值扁平化的趋势，输入电压正弦波形顶部如图3所示。
2. More power can be drawn from a line of a given current rating, allowing more powerful equipment to be connected without having to re-wire a building, saving time and money.
2.更多的功率可以从给定的额定电流线路中得到，允许更大功率的设备接入而无需再建，节约时间和金钱。
3. Various governmental and quasi-governmental agencies are passing laws requiring improved power factors on certain types of equipment, especially those which draw a lot of power. These laws make it illegal to sell certain types of equipment without testing and certification of a minimum power factor. To continue to sell medium-to high power supplies in the future, power supply manufacturers will have to deal with power factor correction.
3.各种政府和准政府机构正在通过有关要求提高某些特定设备功率因数的法律，特别是那些大功率的。这些法律使得那些没有测试和最小功率因数认真的设备出售成为了非法行为。如要继续出售中等到高功率电源，电源供应商将不得不处理功率因数校正的问题。
Although the first reason is nice and the second reason saves money, it is the third reason that has given all the impetus to power factor correction development.
虽然第一个原因是好的，第二个原因可以节约金钱，但是第三个原因是功率因数校正发展的所有动力。
How Does PFC Work?
功率因数校正如何工作
The goal of power factor correction is to make input current look like input voltage on a moment by-moment basis, the same as it would with a resistive load. Figure 4 shows line voltage and line current with and without power factor correction. There are two ways of correcting power factor, passive and active.
功率因数校正的目的是使输入电流在时刻的基础上看上去与输入电压相似，就像带有一个电阻负载一样。图4显示了线电压和线电流在没有功率因数校正的情况。功率因数校正有两种方式，有源和无源。
The passive approach uses filters to eliminate harmonic currents and phase-shifting inductors or capacitors to bring the current into phase with the voltage. The passive approach is large, heavy, and expensive, and therefore is not popular with equipment manufacturers.
无源的方式是使用滤波器消除谐振电流和相移电感器或者电容器所带来的电流与电压的相位。无源方法规模较大，笨重，而且贵，因此不受设备制造商的欢迎。
Active power factor correction uses switching regulator technology to draw current from the power line proportional to input voltage. This is accomplished with a fast feedback loop that uses input voltage as a reference to control input current. The output of a power factor correction circuit is usually a fixed DC voltage. A second, slow feedback loop senses the value of the output voltage and uses this voltage to change the constant of proportionality between input voltage and input current so that the average current is right for the load drawn from the output of the circuit. This loop keeps the output voltage constant. This means that in general there is a multiplier in the reference for the fast loop. The Unitrode UC3854 also has a divider whose function is to keep the voltage error amplifier operating point constant with changing input voltage.
有源功率因数校正采用开关电源技术从电源线输入与输入电压成比例的电流。这是一个快速的反馈回路，采用输入电压作为控制输入电流的参考。一个功率因数校正电路的输出通常是一个固定的直流电压。第二，慢速的反馈回路取样输出电压值，然后用这个电压来改变输入电压和输入电流之间的比例常数，这样从电路的输出中可以得到正确的负载平均电流。这个环路保持输出电压的恒定，这也意味着通常在快速回路中有一个参考乘法器。Unitrode UC3854也有除法器的功能，保持与不断变化的输入电压恒定的电压误差放大器的工作点。
Variety of Topologies
各式拓扑结构
Any topology of switching regulator can be used, since the only requirement is to close a fast current loop around the input current and make it look like input voltage. The most popular topology seems to be the boost converter, since the input current flows through an inductor and is relative smooth and easy to control and also easy to measure with a resistor in the power return. Another popular approach, especially at lower power levels, is the flyback, converter. This approach allows isolation and output voltage amplitude scaling as part of the power factor correction process. Figure 5 shows three possible topologies.
任何开关调节器的拓扑结构都可以使用，因为唯一的要求就是在输入电流附近关闭快速电流环路使它看上去接近输入电压。常用的拓扑结构是boost变换器，因为输入电流流过电感器而且相对顺利和容易控制，也容易在电源回路中测量。另一种常用的拓扑结构，特别是在低功率中，反激式变换器是常见的选择。这种方法运行隔离而且输出电压幅值的缩放作为功率因数校正过程的一部分。图5所示3种可能的拓扑结构。
Variety of IC Vendors
Because of the popularity of power factor correction, a number of companies now manufacture power factor correction integrated circuits. These include:
由于功率因数校正的普及，许多公司现在生产功率因数校正集成电路
Cherry Semiconductor Corp.
IXYS Corp.
Linear Technology Corp.
Micro Linear Corp.
Motorola, Inc. (Tempe, AZ)
Unitrode Corp.
The Unitrode UC3854 family is typical and will be used for the examples in this paper. This chip uses boost topology. Figure 6 is from the Unitrode data sheet and shows the UC3854 connected in a typical 250-watt power factor corrected pre-regulator.
Unitrode UC3854 系列是本文中用到的典型例子
Current Loop
Figure 7 shows the UC3854 pre-regulator circuit re-drawn to emphasize the loops and signal paths. The current loop in a Unitrode UC3854 regulates the voltage across the 0.25-ohm current sense resistor in exactly the same manner as a conventional voltage-mode converter. There is an error amplifier to compare the actual current level to a reference (which happens to be dynamic, i.e., changing with time), and then the error amplifier output (pin 3) is compared to fixed amplitude ramp (pin 14) to generate a pulse width modulated waveform to drive the power transistor (pin 16). Unfortunately, the power section inverts the signal at DC, requiring a noninverting op-amp in this particular chip design. Non-inverting op-amps do not have the flexibility of inverting op-amps since the gain can never fall below one. The reference comes from the circuit that multiplies the output error voltage by the absolute value of the instantaneous line voltage. The reference takes the form of a current that is injected into the non-inverting input of the current error amplifier (pin 5). The bandwidth of this particular loop needs to be quite high, since the objective is to accurately follow a rectified 100 or 120 Hertz sine wave with minimal amplitude or phase distortion.
图7是UC3854预调节器电路重绘以强调回路和信号路径。Unitrode UC3854里的电流环调节0.25-ohm电流取样电阻两端电压恰好是同样的方法作为一个传统的电压型变换器。有一个误差放大器对于参考来比较实际电流水平（这恰好也是动态的），而且误差放大器的输出（引脚3）对比固定的放大斜率（引脚14）来产生一个脉冲快读调制波形来驱动功率晶体管（引脚16）。不幸的是，电源部分在直流转化信号，这个特殊的芯片设计需要一个同相运算放大器。非反相运算放大器不具有反相运算放大器的灵活性因为增益的不足。参考来自电路，瞬间线电压的放大器的输出误差电压绝对值。参考以电流注入到非反相的电流误差放大器的形式输入（引脚5）。这种特殊的环路带宽的需求很高，既然目的是要准确地跟踪一个整流100或120赫兹的正弦波的振幅或相位失真最小
Voltage Loop
电压环
The voltage loop is necessary to accommodate changing line and load conditions. It needs to be a slow loop with approximately a 10-Hertz bandwidth. The bandwidth of this loop is critical, since too slow a loop with result in large output voltage transients with changing line and load conditions, and too fast a loop will interfere with and distort the fast current loop and change the input current wave shape so that it is no longer sinusoidal and does not match the input voltage wave shape.
对于电压环来说适应不断变化的线路和负载条件是必要的。它需要一个约10HZ带宽的慢回路。这个环路的带宽是至关重要的，因为速度太慢，与不断变化的线路和负载条件下，结果是大规模的输出电压瞬变。太快循环的干扰和扭曲的快速电流回路和改变输入电流波形，它不再是正弦而且不匹配输入电压波形。
With the UC3854, Unitrode has chosen to limit the low-frequency gain of the voltage error amplifier to a relatively low value. This would normally make the output voltage regulation quite poor, but Unitrode has built in an open loop compensation circuit (the X2 circuit between pin 8 of the chip and input C of the multiplier-divider), which senses the average value of the input voltage and uses this signal to change the gain of the multiplier stage. From a first-order standpoint the operating point of the voltage error amplifier (the voltage on pin 7) does not have to change. This allows the voltage error amplifier to maintain reasonable output voltage regulation in spite of its low gain.
采用UC3854，Unitrode选择限制电压误差放大器的低频增益至一个较低的值。这通常会使输出电压调节相当差，但Unitrode已建成一个开环补偿电路（X2电路之间的引脚8的乘法器-除法器的芯片和输入C），其中检测的输入电压的平均值和使用这个信号来改变倍增器级的增益。在一阶立场上，操作点的电压误差放大器（引脚7上的电压）没有改变。这允许电压误差放大器保持在合理输出的电压调节，尽管增益会比较低。
Testing the Voltage Loop
测试电压回路
The voltage loop in a power factor correction circuit is the loop that keeps the output of the circuit at a constant voltage. In boost topology converters operating from 120 or 240 volts AC, this voltage is usually 400 volts DC The principle of feedback loop measurements is to:
在功率因数校正电路中的电压环是保持在一个恒定电压电路的输出回路。升压转换器拓扑操作是120或240伏交流电，这个电压通常是400伏直流电压。反馈回路的测量原理是：
1. Find a place in the loop where the signal is confined to a single path and where the source is a low impedance and the load is a high impedance. In the voltage loop of the UC3854, this is the point where the output voltage connects to the 499K resistor at the top of the resistive voltage divider string that connects to Vsense, pin 11 of the UC3854.
找到回路中的一个地方，信号是仅限于一个单一的路径，其中源是低阻抗负载是高阻抗。在UC3854电压环中，在电阻分压器串顶部连接到Vsense这个点，输出电压连接到499K电阻器，UC3854的引脚11。
2. Place an injection resistor in series with the loop at this point. The resistor value should be much, much smaller than the input impedance of the circuit. In the case of the voltage loop of a UC3854, 1000 ohms is an appropriate value, since it is much, much smaller than 499K.
在这个点安置一个注入电阻与环路串联。这个电阻值应当比电路的输入阻抗小很多。在UC3854电压环路情况下，1000欧是一个适当的值，因为比499k小得多。
3. Connect a floating sinusoidal oscillator across the injection resistor, turning the resistor into a floating, sinusoidal error voltage in series with the loop. This oscillator is normally the output of the frequency response analyzer used to perform the test. Use an injection transformer to block the 400 volt common mode voltage.
穿过注入电阻连接一个浮动的正弦振荡器，将电阻设为浮动，正弦误差电压与环路串联。该振荡器通常用于测试频率响应分析仪的输出。使用一个注入变压器来抑制400伏的共模电压。
4. Connect a frequency selective voltmeter (normally the inputs of the frequency response analyzer) from each side of the injection resistor to ground. The voltmeter should read voltage at the frequency of the injection oscillator, rejecting all other frequencies and noise. Use a capacitor to block the DC voltage or use 10:1 oscilloscope probes to avoid exceeding the normal mode signal range of the voltmeter (instrument inputs).
在每一个注入电阻接地边连接一个频率选择性伏特计（通常的频率响应分析仪的输入）。电压表应在注射振荡器的频率读取电压，拒绝所有其他的频率和噪声。使用电容器来隔离的直流电压或使用10:1示波器探头来避免超过电压表的正常模式的信号范围（仪器输入）。
5. Sweep the injection oscillator across the frequency band of interest, typically 0.1 to 1000 Hz. Measure the amplitude and phase relative to the oscillator of the voltage to ground from each side of the injection point at each frequency.
扫描注射振荡器所关注的频率波段，通常是0.1到1000赫兹。测量振幅和相位相对于电压振荡器对地电压，在每个频率注入点的每一侧。
6. Divide the input voltage (the point where the 1000 ohm injection resistor connects to the 499K resistor at the top of the divider string) by the output voltage (the 400 volt bus), and plot the ratio of these two voltages as a function of frequency for both amplitude and phase. This produces a Bode plot of the open loop gain versus frequency of the feedback loop.
将输入电压（在分压器的顶部1000欧姆的注入电阻连接到注射499K电阻的点）的输出电压（400伏总线），这两个电压的比值作为振幅和相位频率函数。这将产生一个确定的开环增益与反馈回路的频率图。
All of the above functions are performed automatically with measurement systems such as the Venable Industries Model 350 Frequency Response Analysis System. The voltage loop should be tailored by adjusting the value of the compensation components around the voltage error amplifier (the 0.047 µF capacitor and 240K resistor) connected between pins 7 and 11 of a UC3854. A good value of loop crossover frequency is 10 Hz and a good value of phase margin is 60°. This is fast enough to maintain reasonable transient response, yet slow enough to not distort the current regulating loop significantly. Distortion of the current regulating loop causes reduced power factor and increased harmonic content in the input current.
以上所有功能能够通过进行自动测量系统进行，如在Venable Industries 的350型号的频率响应分析系统。电压回路应通过在电压误差放大器附近（the 0.047 µF capacitor and 240K resistor)connected between pins 7 and 11 of a UC3854）调整补偿元件来调整适应。一个好的环路分频值是10HZ，良好的相位裕度是60°。这个快速的足够维持合理的瞬态响应，慢速的不足以明显扭曲电流调节环。电流调节环的扭曲导致功率因数降低和输入电流谐波含量增加。
Testing the Current Loop
电流环测试
The current loop is more difficult to test than the voltage loop because it is dynamic, i.e., it changes from essentially zero current to the peak value of current 100 or 120 times a second. If conventional measuring techniques are used, the result is an average of all the transfer functions from very low current to very high current. Loop stability may appear satisfactory, but the current loop may still oscillate near zero current or near the peak current even though the average of all the Bode plots shows a stable condition.
电流环比试验电压环更难是因为它是动态的，即它从本质上1秒内100次到120次零电流到电流峰值的变化。如果使用的是传统的测量技术，其结果是一个所有的传递函数的从非常低的电流到非常高的电流的平均值。环路的稳定性可能会出现令人满意的情况，但目前仍可能接近零电流回路振荡或接近峰值电流时，即使所有的Bode图显示一个平均的稳定状态。
In order to accurately test the current loop, the operating point must be "frozen" by using DC power supplies to simulate the correct bias conditions for an instantaneous point in time and then measuring the stability of the current loop at that point. This test must be done at least at low current and high current. It is a good idea to test the stability at a medium current also to assure that the extremes have been bracketed.
为了准确测试电流回路，操作点必须是在时间上的瞬时点通过使用直流电源模拟正确偏置条件 “冻结”，在该点测量电流环的稳定性。这个测试必须至少在低电流和高电流完成。这是一个好主意，在中间的电流也确保极端相等的稳定性试验。
"Freezing" the operating point of the UC3854, means that you have to:
“冻结”的操作点的UC3854，意味着你必须：
1. Connect a variable DC power supply to the input to the power factor correction circuit (across the output of the main bridge rectifier). The input of the circuit is of course not connected to the AC line. The supply has to be able to put out as much voltage and current as the peak of the line voltage. Leave the sense divider (the 620Kresistor into Iac, pin 6 of the UC3854) in place.
连接一个可变的直流电源的功率因数校正电路的输入（在主整流桥输出）。该电路的输入是当然没有连接到AC线。电源已经能够把尽可能多发出的电压和电流，如同线电压的峰值。（620k电阻为IAC，UC3854引脚6）
2. Connect an 18-volt DC source to power the UC3854 (from pin 15 to pin 1). This supply may not be necessary if the bias winding across the main energy storage inductor is still sufficient to power the chip at low input voltage.
连接一个18伏直流电源供电UC3854（从引脚15和引脚1）。这种电源可能不是必要的如果偏压线圈穿过主储能器电感仍足以在低电压对芯片功能。
3. Connect pin 7 of the UC3854 to pin 11. This will fix the output of the voltage error amplifier (input A of the multiplier-divider) at 7.5 volts. It is not necessary to disconnect the compensation components already connected to these pins.
连接UC3854引脚7到引脚11。这将解决输出电压误差放大器（乘数的分频器输入）在7.5伏特。这是没有必要的连接如果已经连接到这些引脚的补偿元件。
4. Connect a 0-10 volt DC variable power supply to pin 8, the Vrms terminal of the UC3854. It is not necessary to disconnect the components connected to this terminal except it may be necessary to add a small pre-load to the power supply if it has no ability to sink current. The purpose of this supply is to adjust the gain of the multiplier-divider circuit to adjust the circuit output current for the proper value given the input voltage. Once set, this voltage will not change between low line and high line. The current feedback loop should track the input voltage and supply the correct current proportional to voltage.
连接一个0-10伏特直流可变电源到引脚8，UC3854的输出电压终端。没有必要的去断开连接到这个终端的部件除非可能必须加入一个小的预负载到电源，如果没有能力吸收电流。这种电源的目的是调整乘法器和除法器的增益来调整电路输出电流为给定的输入电压提供适当的值。一旦设置，电压讲不会在低压线路和高压线路之间变化。电流反馈回路应跟踪输入电压，并提供正确的与电压成比例的电流。
5. Connect a load across the output of the power factor correction circuit. This load can take the form of a 400-volt shunt regulator or a resistive load connected to a 400-volt power supply. The resistive load should draw 1.4 times the normal output current to allow for testing at the peak value of the output. Similarly, the shunt regulator must be rated for 1.4 times the maximum DC output current of the circuit.
连接在功率因数校正电路的输出负载。此负载可以采取一个400伏并联稳压器或电阻性负载连接到一个400伏的电源形式。负载电阻应1.4倍的正常输出电流允许测试在输出峰值。同样，分流调节器必须是额定的1.4倍的最大直流输出电流的电路。
All other connections to the circuit can remain. As before, you have to measure the loop. The steps to do this are:
所有其他连接到电路可以保持。之前，你必须测量回路。要做到这一点的步骤：
1. Find a place in the loop where the signal is confined to a single path and where the source is a low impedance and the load is a high impedance. In the current loop of the UC3854, this is the point where the 0.025-ohm current sense resistor connects to the 4K resistor that connects to MULT OUT, pin 5 of the UC3854.
找到回路中的一个点，信号是只限于一个单一的路径，其中源是低阻抗而负载是高阻抗。在UC3854的电流环路中，这个点是0.025欧姆电流检测电阻连接到连着MULT OUT 的4K电阻的点，UC3854引脚5.
2. Place an injection resistor in series with the loop at this point. The resistor value should be much, much smaller than the input impedance of the circuit. In the case of the current loop of a UC3854, 100 ohms is an appropriate value and is much, much smaller than 4000 ohms.
在这个点放置一个注入阻抗与环路串联。电阻值应该小于电路的输入阻抗。在UC3854电流环的情况下，100欧很合适，远小于4000欧。
3. Connect a floating sinusoidal oscillator across the 100-ohm injection resistor, turning the resistor into a floating, sinusoidal error voltage in series with the loop. In this case the voltage at the injection point is just a few volts and there are no special precautions for connecting there except that the source must be floating. Use of an injection transformer such as the Venable Industries Model 200-002 will satisfy the floating requirement and also minimize the capacitive coupling to ground.
连接一个浮动的正弦振荡器穿过100欧的注入电阻，将电阻转换为浮动的，正弦的误差电压与环路串联。在这种情况下，电压在注入点只有几伏而且对于连接没有特别的防范措施除非电源必须要浮动。使用例如Venable Industries Model 200-002注入变压器可以满足要求，同时还可以减少对地电容耦合。
4. Connect a frequency selective voltmeter (again, the inputs of the frequency response analyzer) from each side of the 100-ohm injection resistor to ground. A point near pin 1 of the UC3854 is the best place to pick up ground. The voltmeters should read voltage at the frequency of the injection oscillator, rejecting all other frequencies and noise. Again, the voltages are low and no special precautions are required to protect the equipment except that ground should really be at or near building ground, not a floating signal merely called "ground". This is normally not a problem when the circuit is powered from a conventional DC power supply.
对于100欧姆注入电阻的每一边连接一个频率选择电压表到地。UC3854引脚1附近是好的接地点。电压表应该在注入振荡器的频率读取电压，拒绝其他频率和噪声。再次，在低电压时，不需要特别的预防措施来保护设备除非地面确实需要或者接近建筑地面，不是一个浮动信号仅仅就称为“地面”。这通常不是问题，当传统直流电源供电时。
5. Sweep the injection oscillator across the frequency band of interest, typically 100 Hz to just under the circuit switching frequency. Measure the amplitude and phase relative to the oscillator of the voltage to ground from each side of the injection point at each frequency.
扫描注入振荡器所关注的频率波段，通常为100赫兹到刚低于电路的开关频率。测量振幅和相位相对于电压振荡器对地电压，在每个频率注入点的每一侧。
6. Divide the input voltage (the point where the 100 ohm injection resistor connects to the 4K resistor going into MULT OUT) by the output voltage (the point where the 100 ohm injection resistor connects to the 0.25 ohm current sense resistor), and plot the ratio of these two voltages as a function of frequency for both amplitude and phase. This produces a Bode plot of the open loop gain versus frequency of the current loop. This loop needs to have a bandwidth of several kilohertz, the higher the better, and phase margin of at least 60°. The gain of this loop can be tailored by changing the compensation components (the 62pF and 620pF capacitors and the 24K resistor) connected between pins 3 and 4 of the UC3854. A complete frequency response analysis workstation such as the Venable Industries Model 350 system will aid greatly in the proper selection of these components.
通过输出电压（100欧姆注入电阻连接4K电阻加入MULT OUT）分离输入电压（100欧姆注入电阻连接0.25欧姆电流检测电阻），然后作为两个电压的幅值与相位作为频率的函数的比值图。这产生一个开环增益对应电流环路频率的伯德图。这个环需要几千HZ的带宽，越高越好而且相位裕度至少60°。环路增益可以通过改变连接在UC3854引脚3和4之间的补偿元件来调整，完整的频响分析仪工作站例如Venable Industries Model 350 system有助于这些组件的合理选择。
Summary
总结
In this paper, it was demonstrated that power factor correction has become an increasingly necessary feature in new power supply designs. It was pointed out that a power factor correction circuit has two feedback control loops. One loop operates by using the input voltage as a reference to control the input current. This loop is fast and makes the input current instantaneously proportional to input voltage as it would be with a resistive load. This loop is normally dynamic, constantly changing operating point as the line voltage changes. By fixing or "freezing" the operating point, a family of Bode plots can be run at various operating points to verify circuit operation across the entire operating range. Techniques for fixing the operating point and also making the measurement were discussed.
本文中，已经表明功率因数校正已经成为新的电源设计所需要注意的越来越必要的特征。同时指出了功率因数校正电路具有两个反馈控制环路。一个环路利用输入电压作为参考电压运行来控制出入电流，这个环路是快速的而且会使输入电流与输入电压瞬时成比例。就如电阻负载一样。这种回路通常是动态的，不断变化的工作点为线电压的变化、通过固定或者冻结工作点，一系列伯德图可以运行在不同的操作点在整个操作范围验证电路的操作。固定操作点的技术和测量同样进行了讨论。
Techniques were demonstrated for testing the stability of the second, much slower loop that controls the constant of proportionality between input voltage and input current. This loop keeps the output voltage of the power factor correction circuit constant. It is not necessary to "freeze" the operating point of this loop since the bandwidth is much lower than the variation rate of the faster loop. The variations of the faster loop are averaged out. Even though the faster loop forms a gain block that is inside the slow loop, an "averaged" transfer function of the faster loop is sufficient for loop gain measurements and stability analysis.
对于第二个较慢的回路，控制输入电压和输入电流的比例常数的技术已经被证实演示测试稳定性。这个回路保持功率因数校正电路的输出电压恒定。这是没有必要的“冻结”的环路工作点因为带宽比快速环路的变化率要低得多。快速环路变化速率达到平衡。尽管快速环以增益块形式在慢回路，但是一个“平均”的传递函数的快速循环足以应对环路增益测量和稳定性分析。
Step-by-step instructions for "freezing" the current loop and for testing both the voltage loop and the current loop for the Unitrode UC3854 power factor correction chip were presented. The principles are the same for all chips and the author welcomes questions or comments about other approaches to power factor correction.
一步一步说明“冻结”的电流环和电压环和电流的测试为Unitrode UC3854芯片提出了功率因数校正回路，原理是相同的。所有芯片和作者欢迎提问或对功率因数校正方法进行修正。
2017-02-11
