交流电流过负载时，加在该负载上的交流电压与通过该负载的交流电流产生相位差，人们便从中引出功率因数这一概念。人们生产、生活用电来自电网，电网提供频率为50Hz或60Hz的交流电。作为交流电的负载有电阻、电感、电容三种类型：

1、当交流电通过纯电阻负载时，加在该电阻上的交流电压与通过该电阻的交流电流是同相位的，即它们之间的相位夹角ф= 0°，同时在电阻负载上消耗有功功率，电网要供出能量。

2、当交流电通过纯电感负载时，其上的交流电压的相位超前交流电流相位90°，它们之间的夹角ф= 90°，在电感负载上产生无功功率，电网供给的电能在电感中变为磁场能短暂储存后又回馈到电网变为电能，如此周期性循环，结果电网并不供出能量，故谓“无功功率”，但产生“无功功率”的“无功电流”还是实际存在的。

3、当交流电通过纯电容负载时，亦类似于此，只不过其上的交流电压的相位滞后交流电流相位90°，它们之间的夹角ф= - 90°。

这里，定义相位角度超前为正，相位角度滞后为负。实际负载是电阻、电感的感抗、电容的容抗三种类型的复物，复合后统称“阻抗”，写成数学式即是：阻抗Z= R+j （ XL – XC、。其中R为电阻，XL为感抗，XC为容抗。如果（ XL– XC、> 0， 称为“感性负载”；反之，如果（ XL – XC、< 0称为“容性负载”。

交流电通过感性负载时，交流电压的相位超前交流电流相位（0°<ф<90°）；交流电通过容性负载时，交流电压的相位滞后交流电流相位（-90°<ф< 0°）；电工学定义该角度ф为功率因数角，功率因数角ф的余弦值即Cosф叫做功率因数。对于电阻性负载，其电压与电流的位相差为0°，因此，电路的功率因数为1最大（Cos 0°=1、；而纯电感电路，电压与电流的位相差为90°，并且是电压超前电流；在纯电容电路中，电压与电流的位相差则为- 90°，即电流超前电压。在后两种电路中，功率因数都为零（Cos 90°= 0、。对于一般性负载的电路，功率因数就介于0与1之间。由数学式阻抗Z= R+ j （ XL – XC），如果XL = XC，则Z= R，即阻抗Z变成了一个纯电阻，功率因数便等于1。

这就是说，感性负载和容性负载可以互相补偿，一个电路里的感性元件的感抗值正好等于容性元件的容抗值则可以完全补偿，功率因数补偿的办法就源于此。交流电通过阻抗负载时，产生的总功率S称“视在功率”，视在功率S包括有功功率P和无功功率Q两个分量。其中有功功率P = S*Cosф，无功功率Q = S*Sinф。只有当功率因数Cosф值等于最大值1即ф= 0°时，无功分量Q才等于零，有功功率P等于视在功率 S的值。但负载的实际工作能力只与有功功率相关。

** 功率因数与****LED照明**

本文主要叙述了功率因数、功率因数补偿的概念，由LED灯具容性负载特点，论证在LED照明灯具内无需增加功率因数补偿电路的结论。

** 功率因数偏低的害处**

（1） 供电设备的带负载能力被打了折扣，即降低了带负载能力。如某设备能供出100KVA的视在功率，若功率因数为0.7，则只能供出70KW的有功功率了；若功率因数为0.9，则能供出90KW的有功功率，可见提高功率因数很有意义。

（2） 输电线路由于无功电流存在，增加了输电线路损耗。例如功率因数为0.7，要供出70KW的有功功率，则需要供出100KVA的视在功率，输电线路的电流增大，线路损耗必然增大。

** 功率因数补偿方法**

供电部门供的电能是以“视在功率”来计算的，但是收电费却是以“有功功率”来计算的，用户的“电度表”实为“有功功率表”，两者之间有一个“功率因数”折扣，所以功率因数是供电部门非常在意的一个数据。用户如果没有达到理想的功率因数，相对地就是在消耗供电部门的资源。目前就国内而言功率因数规定是必须介于电感性的0.9～1之间。

**可采取以下方式进行功率因数补偿：**

（1） 半集中、集中补偿法，要求用电企业的各个配电房必须安装功率因数自控装置，实时检测功率因数大小，自动投入或切除补偿电力电容器的个数，用于电动机运行补偿（因企业主要用电负荷是电动机、，做到局部用电网络功率因数达标。这个办法从上世纪七十年代末、八十年代初便已强制实施，至今少说已有二十多年。还有各个供电所也安装功率因数自控装置，对其下辖供电区域进一步补偿。

（2） 分散补偿法，要求每个用电器具设计时便采用先进技术，满足功率因数达标，这样不论何时何地用电均能保证功率因数达标。但这样做会增加成本、增加电器体积，而有的电器对体积大小限制很严格，加大了设计难度。

电光源照明灯具与功率因数补偿的回顾电光源是由白炽灯泡开始的，白炽灯泡是纯电阻负载，没有功率因数补偿的问题。上世纪50年代后，日光灯迅速普及成了主要的照明灯具，镇流器用的是硅钢片电感，可靠性高，寿命长，至今仍有少量采用的，大多数没有什么功率因数补偿措施，可能是受到成本因素的影响，抑或人们对功率因数补偿不甚了解，节能意识不强。也有加接适当容量的电容器作功率因数补偿的，多用在30W、40W大瓦数日光灯上，20W以下很少用。上世纪90年代后，人们的环保、节能意识增强，开发出三基色萤光粉节能灯，其光功效更高。电子镇流器也随后问世，配上三基色萤光粉灯管，节能效果更加显著。国内外一些集成电路厂商推出了带有源功率因数补偿的灯用芯片，用于电子镇流器，性能优秀，但增加了成本和电子镇流器体积，老百姓还不能接受它的价格，大约只用在高端灯具产品上。大量的普及型电子镇流器包括用于节能灯的都没有加什么功率因数补偿措施，这在市面流行的节能灯、日光灯上随处可见。也就是说以往的灯具基本上没有什么功率因数补偿措施，但大家都在用。

LED耗电更省，灯具功率比起节能灯还要小。LED照明当然更为进步，对环境保护、节能减排更为适宜。LED灯具是否加功率因数补偿，笔者的看法是：

（1） 据专家分析，LED为容性负载。电网的感性负载甚多，例如电动机、变压器等等。往往需要接入容性负载进行补偿，功率因数自控装置就是作此用途的。LED为容性负载，恰恰补偿了电网因感性负载多导致功率因数低的问题，正是用得其所。源于这种认识，笔者认为LED照明灯具原则上无需加功率因数补偿措施。

（2） 室内照明用的单盏LED灯具均是小功率的，功率不会超过30W。灯具功率小对电网的影响也小，笔者认为这类灯具完全可以免去功率因数补偿措施，加了反而不好，反而会失去LED灯具是容性负载能够补偿电网因感性负载多导致功率因数低的功能。这些小功率灯具多是小体积紧凑型的，内部空间十分有限，例如MR16、PAR30、PAR38灯杯，电源PCB板增大后放不下，就是好心想加功率因数补偿措施也加不进。还有加了功率因数补偿后会带来效率下降的副作用，或云得不偿失。再则成本增加影响销售。何况供电部门已采取了应对措施对电网功率因数进行补偿，灯具厂家大可不必再去画蛇添足。

（3） 功率100W以上的可以考虑加功率因数补偿措施，功率大的负载对电网的影响也大，例如一百瓦到数百瓦的LED路灯。路灯属于公益事业，成本略增加一点无大碍，电源PCB板增大一点也有位置可放。加功率因数补偿措施可以帮助供电部门减轻一些调节负担，防止容性负载过大产生过度补偿。

The concept of power factor is derived from the phase difference between the ac voltage applied to the load and the ac current applied to the load as it flows through the load. People produce and live electricity from the power grid, which provides alternating current with a frequency of 50Hz or 60Hz. There are three types of load as alternating current: resistance, inductance and capacitance:

1, when an alternating current by purely resistive load, and the resistance of the ac voltage, and through the resistance of the alternating current is in phase, the phase Angle between them ф = 0 °, active power consumption on the resistance load at the same time, the grid for the energy.

2, when an alternating current by pure inductance load of the ac voltage phase advance of alternating current phase 90 °, the Angle between them ф = 90 °, the reactive power in the inductance load, the power supply of electricity in inductance into a magnetic field can short storage and then back to the grid into electricity, so cycle, the power grid is not for the energy, the so called "reactive power", but "reactive power" of "reactive current" still exist.

3, when an alternating current by pure capacitance load, also like this, but its the ac voltage on the phase lag phase alternating current to 90 °, the ф = - 90 ° Angle between them.

Here, the phase Angle lead is defined as positive, and the phase Angle lag is defined as negative. The actual load is a complex of three types: resistance, inductive reactance of inductance and capacitive reactance of capacitance, which are collectively referred to as "impedance" after compound. Written in mathematical formula, it is: impedance Z= R+j (XL -- XC). Where R is resistance, XL is inductive reactance and XC is capacitive reactance. If (XL - XC, > 0, called "perceptual load"; Conversely, if (XL - XC, < 0 is called "capacitive load".

Alternating current (ac) by inductive load, the voltage phase advance of alternating current phase (0 ° < ф < 90 °); Alternating current (ac) by capacitive load, the ac voltage phase lag of the alternating current phase (- 90 ° ф < 0 °); Electrotechnics defines this Angle as the power factor Angle, and the cosine of the power factor Angle is called the power factor. For resistive load, the voltage and current of the phase difference of 0 °, therefore, the power factor of the circuit is 1 the largest (Cos 0 ° = 1, And pure inductance circuit, voltage and current of the phase difference of 90 °, leading current and voltage; In pure capacitance, voltage and current of the phase difference is - 90 °, the current voltage in advance. In the two circuits, the power factor is zero (90 ° = 0, Cos. For circuits of general load, the power factor is between 0 and 1. From the mathematical expression impedance Z= R+ j (XL -- XC), if XL = XC, Z= R, that is, impedance Z becomes a pure resistance, the power factor is equal to 1.

That is to say, the inductive load and the capacitive load can compensate each other, and the inductive element in a circuit whose inductive reactance value is exactly equal to the capacitive element's reactance value can be fully compensated. This is the source of power factor compensation. When the alternating current passes through the impedance load, the total power S generated is called "apparent power", and the apparent power S includes active power P and reactive power Q. Where, active power P = S*Cos, reactive power Q = S*Sin. Only when the power factor Cos ф value is equal to the maximum 1 ф = 0 °, namely reactive component Q is equal to zero, the value of the active power P is equal to the apparent power S. However, the actual working capacity of the load is only related to the active power.

Power factor with LED lighting

This paper mainly describes the concepts of power factor and power factor compensation. Based on the capacitive load characteristics of LED lamps, it is proved that there is no need to add power factor compensation circuit in LED lamps.

The harm of low power factor

(1) the load capacity of the power supply equipment is reduced, that is, the load capacity is reduced. If a device can provide 100KVA of apparent power, if the power factor is 0.7, it can only provide 70KW of active power; If the power factor is 0.9, the active power of 90KW can be provided, so it is significant to improve the power factor.

(2) transmission line loss is increased due to the existence of reactive current. For example, if the power factor is 0.7, the apparent power of 100KVA should be provided if the active power of 70KW is to be provided. As the current of the transmission line increases, the line loss will inevitably increase.

Power factor compensation method

The electric energy provided by the power supply department is calculated as "apparent power", but the electricity charge is calculated as "active power". The "watt-hour meter" of the user is actually "active power meter", and there is a "power factor" discount between the two, so the power factor is a data that the power supply department CARES about very much. If the user does not reach the ideal power factor, it will consume the resources of the power supply department. At present, the power factor must be between 0.9 ~ 1 of the inductance.

Power factor compensation can be carried out in the following ways:

(1) a focused, concentrated compensation method, requests each transformer room electricity companies to install power factor control devices, real-time detection of power factor size, automatic or removal of the number of power capacitor compensation, used in motor running compensation (for enterprise, is the main power load motor, do local power network power factor. It has been enforced since the late 1970s and early 1980s and has been in place for at least two decades now. There are also power factor automatic control devices installed in each power supply station to further compensate the power supply area under its jurisdiction.

(2) decentralized compensation method, requires that each electrical appliance design will use advanced technology, to meet the power factor standard, so that no matter when and where electricity can ensure that the power factor standard. But this will increase the cost, increase the volume of electrical appliances, and some electrical appliances on the size of the volume restrictions are very strict, increasing the difficulty of design.

Review of electric light source lighting fixture and power factor compensation electric light source started from incandescent bulb. After the 1950 s, fluorescent lamp rapidly became the main lighting lamps and lanterns, is silicon steel sheet inductance ballasts, high reliability, long life, there are still a few USES, most has no power factor compensation measures, may be affected by the cost factor, or people not understanding of power factor compensation, energy saving awareness is not strong. Also add add add the capacitor of appropriate capacity to make power factor compensation, multi-purpose on fluorescent lamp of 30W, 40W big wattage, 20W the following is used rarely. Since the 1990s, people's awareness of environmental protection and energy saving has been enhanced, and tri-color fluorescent powder energy saving lamp has been developed, with higher light efficiency. Electronic ballast also came out later, with three - color fluorescent powder lamp, more significant energy - saving effect. Some integrated circuit manufacturers at home and abroad launched a lamp with source power factor compensation chip, for electronic ballast, excellent performance, but increased the cost and volume of electronic ballast, people can not accept its price, about only in high-end lamps and lanterns products. A large number of popular electronic ballasts, including those used for energy-saving lamps, have not been added with any power factor compensation measures, which can be seen everywhere in the popular energy-saving lamps and fluorescent lamps on the market. That is to say former lamps and lanterns basically does not have what power factor compensation measure, but everybody is using.

Leds consume less power and are less powerful than energy-saving lamps. Of course, LED lighting is more progressive and more suitable for environmental protection, energy conservation and emission reduction. Whether power factor compensation is added to LED lamps or not, the author's opinion is as follows:

(1) according to expert analysis, LED is capacitive load. The inductive load of power network is very much, for example motor, transformer and so on. Often need to be connected to the capacitive load compensation, power factor automatic control device is for this purpose. LED is a capacitive load, which exactly compensates for the low power factor caused by multiple inductive loads in the power grid. From this understanding, the author believes that LED lighting without power factor compensation measures in principle.

(2) all single LED lamps for indoor lighting are low-power, and the power will not exceed 30W. Small power of lamps has a small impact on the power grid. The author believes that such lamps can be completely exempted from power factor compensation measures. It is not good to add LED lamps, but they will lose the function that capacitive load can compensate the power factor of the power grid due to multiple inductive loads. These small power lamps and lanterns are mostly compact in small size, and the internal space is very limited, such as MR16, PAR30, PAR38 lamp cup, power PCB board increased after not put, is a good idea to add power factor compensation measures are not added. There will be a power factor compensation after the efficiency decline side effects, or cloud outweighs the benefits. Moreover, the increase in costs affects sales. Besides, the power supply department has taken measures to compensate the power factor of the power grid.

(3) if the power is more than 100W, additional power factor compensation measures can be considered. High-power load has a great impact on the power grid, such as 100W to 100W LED street lamps. Street lamps belong to public welfare undertakings, so a slight increase in cost is not harmful. If the power PCB board is increased a little, there will be a place to put it. The additional power factor compensation measures can help the power supply department to reduce some of the regulatory burden and prevent the capacitive load from excessive compensation.