??????? 交流電流過負載時，加在該負載上的交流電壓與通過該負載的交流電流產生相位差，人們便從中引出功率因數這一概念。人們生產、生活用電來自電網，電網提供頻率為50Hz或60Hz的交流電。作為交流電的負載有電阻、電感、電容三種類型：

1、當交流電通過純電阻負載時，加在該電阻上的交流電壓與通過該電阻的交流電流是同相位的，即它們之間的相位夾角ф= 0°，同時在電阻負載上消耗有功功率，電網要供出能量。

2、當交流電通過純電感負載時，其上的交流電壓的相位超前交流電流相位90°，它們之間的夾角ф= 90°，在電感負載上產生無功功率，電網供給的電能在電感中變為磁場能短暫儲存后又回饋到電網變為電能，如此周期性循環，結果電網并不供出能量，故謂“無功功率”，但產生“無功功率”的“無功電流”還是實際存在的。

3、當交流電通過純電容負載時，亦類似于此，只不過其上的交流電壓的相位滯后交流電流相位90°，它們之間的夾角ф= - 90°。

這里，定義相位角度超前為正，相位角度滯后為負。實際負載是電阻、電感的感抗、電容的容抗三種類型的復物，復合后統稱“阻抗”，寫成數學式即是：阻抗Z= R+j （ XL – XC、。其中R為電阻，XL為感抗，XC為容抗。如果（ XL– XC、> 0， 稱為“感性負載”；反之，如果（ XL – XC、< 0稱為“容性負載”。

交流電通過感性負載時，交流電壓的相位超前交流電流相位（0°<ф<90°）；交流電通過容性負載時，交流電壓的相位滯后交流電流相位（-90°<ф< 0°）；電工學定義該角度ф為功率因數角，功率因數角ф的余弦值即Cosф叫做功率因數。對于電阻性負載，其電壓與電流的位相差為0°，因此，電路的功率因數為1最大（Cos 0°=1、；而純電感電路，電壓與電流的位相差為90°，并且是電壓超前電流；在純電容電路中，電壓與電流的位相差則為- 90°，即電流超前電壓。在后兩種電路中，功率因數都為零（Cos 90°= 0、。對于一般性負載的電路，功率因數就介于0與1之間。由數學式阻抗Z= R+ j （ XL – XC），如果XL = XC，則Z= R，即阻抗Z變成了一個純電阻，功率因數便等于1。

這就是說，感性負載和容性負載可以互相補償，一個電路里的感性元件的感抗值正好等于容性元件的容抗值則可以完全補償，功率因數補償的辦法就源于此。交流電通過阻抗負載時，產生的總功率S稱“視在功率”，視在功率S包括有功功率P和無功功率Q兩個分量。其中有功功率P = S*Cosф，無功功率Q = S*Sinф。只有當功率因數Cosф值等于最大值1即ф= 0°時，無功分量Q才等于零，有功功率P等于視在功率 S的值。但負載的實際工作能力只與有功功率相關。

** 功率因數與****LED照明**

本文主要敘述了功率因數、功率因數補償的概念，由LED燈具容性負載特點，論證在LED照明燈具內無需增加功率因數補償電路的結論。

** 功率因數偏低的害處**

?。?） 供電設備的帶負載能力被打了折扣，即降低了帶負載能力。如某設備能供出100KVA的視在功率，若功率因數為0.7，則只能供出70KW的有功功率了；若功率因數為0.9，則能供出90KW的有功功率，可見提高功率因數很有意義。

?。?） 輸電線路由于無功電流存在，增加了輸電線路損耗。例如功率因數為0.7，要供出70KW的有功功率，則需要供出100KVA的視在功率，輸電線路的電流增大，線路損耗必然增大。

** 功率因數補償方法**

供電部門供的電能是以“視在功率”來計算的，但是收電費卻是以“有功功率”來計算的，用戶的“電度表”實為“有功功率表”，兩者之間有一個“功率因數”折扣，所以功率因數是供電部門非常在意的一個數據。用戶如果沒有達到理想的功率因數，相對地就是在消耗供電部門的資源。目前就國內而言功率因數規定是必須介于電感性的0.9～1之間。

**可采取以下方式進行功率因數補償：**

?。?） 半集中、集中補償法，要求用電企業的各個配電房必須安裝功率因數自控裝置，實時檢測功率因數大小，自動投入或切除補償電力電容器的個數，用于電動機運行補償（因企業主要用電負荷是電動機、，做到局部用電網絡功率因數達標。這個辦法從上世紀七十年代末、八十年代初便已強制實施，至今少說已有二十多年。還有各個供電所也安裝功率因數自控裝置，對其下轄供電區域進一步補償。

?。?） 分散補償法，要求每個用電器具設計時便采用先進技術，滿足功率因數達標，這樣不論何時何地用電均能保證功率因數達標。但這樣做會增加成本、增加電器體積，而有的電器對體積大小限制很嚴格，加大了設計難度。

電光源照明燈具與功率因數補償的回顧電光源是由白熾燈泡開始的，白熾燈泡是純電阻負載，沒有功率因數補償的問題。上世紀50年代后，日光燈迅速普及成了主要的照明燈具，鎮流器用的是硅鋼片電感，可靠性高，壽命長，至今仍有少量采用的，大多數沒有什么功率因數補償措施，可能是受到成本因素的影響，抑或人們對功率因數補償不甚了解，節能意識不強。也有加接適當容量的電容器作功率因數補償的，多用在30W、40W大瓦數日光燈上，20W以下很少用。上世紀90年代后，人們的環保、節能意識增強，開發出三基色螢光粉節能燈，其光功效更高。電子鎮流器也隨后問世，配上三基色螢光粉燈管，節能效果更加顯著。國內外一些集成電路廠商推出了帶有源功率因數補償的燈用芯片，用于電子鎮流器，性能優秀，但增加了成本和電子鎮流器體積，老百姓還不能接受它的價格，大約只用在高端燈具產品上。大量的普及型電子鎮流器包括用于節能燈的都沒有加什么功率因數補償措施，這在市面流行的節能燈、日光燈上隨處可見。也就是說以往的燈具基本上沒有什么功率因數補償措施，但大家都在用。

LED耗電更省，燈具功率比起節能燈還要小。LED照明當然更為進步，對環境保護、節能減排更為適宜。LED燈具是否加功率因數補償，筆者的看法是：

?。?） 據專家分析，LED為容性負載。電網的感性負載甚多，例如電動機、變壓器等等。往往需要接入容性負載進行補償，功率因數自控裝置就是作此用途的。LED為容性負載，恰恰補償了電網因感性負載多導致功率因數低的問題，正是用得其所。源于這種認識，筆者認為LED照明燈具原則上無需加功率因數補償措施。

?。?） 室內照明用的單盞LED燈具均是小功率的，功率不會超過30W。燈具功率小對電網的影響也小，筆者認為這類燈具完全可以免去功率因數補償措施，加了反而不好，反而會失去LED燈具是容性負載能夠補償電網因感性負載多導致功率因數低的功能。這些小功率燈具多是小體積緊湊型的，內部空間十分有限，例如MR16、PAR30、PAR38燈杯，電源PCB板增大后放不下，就是好心想加功率因數補償措施也加不進。還有加了功率因數補償后會帶來效率下降的副作用，或云得不償失。再則成本增加影響銷售。何況供電部門已采取了應對措施對電網功率因數進行補償，燈具廠家大可不必再去畫蛇添足。

?。?） 功率100W以上的可以考慮加功率因數補償措施，功率大的負載對電網的影響也大，例如一百瓦到數百瓦的LED路燈。路燈屬于公益事業，成本略增加一點無大礙，電源PCB板增大一點也有位置可放。加功率因數補償措施可以幫助供電部門減輕一些調節負擔，防止容性負載過大產生過度補償。

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.