[introduction]Power factor is corrective (PFC) is one of functions that the client seeks when choosing power source, because it is right,the integral efficiency of equipment is having tremendous effect. Article archives introduced power factor corrective (the basic fact of PFC) and principle and the code that govern this function. It still discussed common cause and the issue that should avoid to obtain PFC.

Brief introduction

Power factor is corrective (PFC) is one of functions that the client seeks when choosing power source, because it is right,the integral efficiency of equipment is having tremendous effect. Article archives introduced power factor corrective (the basic fact of PFC) and principle and the code that govern this function. It still discussed common cause and the issue that should avoid to obtain PFC.

What is power factor

Power factor (Pf) definition is power of have rendered great service (P) and inspect in power (of S) than, or the Yu Xian that expresses the phase angle between electric current and voltage (the sterling bowstring wave to electric current and voltage) with voltage weaveform (see a picture 1) . Power factor can be in 0 to 1 between change, and can be perceptual (lag, point to on) or allow a gender (lead, point to below) . To reduce inductive lag, till Pf is equal to,add capacitor 1. When electric current and voltage weaveform are inphase, power factor is ° of 1 (cos (0) = 1) . Making power factor is equal to the whole purpose of 1 is to make circuit looks pure resistor (inspect power of have rendered great service is equal to in power) .

Power of have rendered great service (made of baked clay) produce actual result; This is energy transmission part (for example report arrives the rotate speed of electric machinery) . Having result power is generation magnetic field (loss power) the power that needs in order to finish real work place, inspect the general power that in power company of power be regardinged as provides among them, if pursue,1 is shown. This general power is through advocate the electric power that power source provides, in order to produce a power of needed have rendered great service.

The reason with low efficiency

Switch mode power source (a problem of SMPS) is them the power factor that does not use any forms is corrective, and input capacitor CIN (if the graph is shown 4 times) be close to VPEAK or VIN in VIN only to be more than capacitor voltage VCIN. If frequency of use input voltage designs CIN, criterion electric current can be close to input weaveform more it seems that (depend on laden) ; However, on masterstroke any tiny interrupt can bring about whole system to produce negative reaction. That is to say, when designing SMPS, the maintenance of CIN the frequency that time designs so that be more than VIN, such, if VIN appears burr, miss a few cycle, CIN will have enough energy memory to be its load power supply in order to continue.

Graph 3 express VCIN(t) (if pursue,4 medium circuit are shown) academic result, load is very light, CIN discharge is very accordingly little. As the addition of laden impedance, the VCIN(t) between follow-up peak value will have more pressing to fall, but hold very small percentage only at total VIN relatively (for example, the input is 120V, may appear of 3-5 bend over pressure fall. The place before be like is narrated, be more than its when VIN only when memory voltage, CIN just can charge, this means blame PFC circuit to be able to be in only one fraction charges for CIN inside whole and periodic time.

90 degrees hind (graph 4) , the half-period of bridge falls to capacitor voltage (CIN) is the following; It undertakes slanting reversely to bridge buy, restrain electric current to flow into capacitor (through VIN) . The aiguille of input electric current that notices inductance has how old. All circuit in supplying chain (the diode in wall wiring, bridge, breaker) must can bear the weight of so tremendous peak value electric current. Inside these short time, CIN must fill report, because this is met from the pulse of big electric current inside short time of the derive in VIN. It is OK to have a kind of method average this aiguille, such odd time that it can use cycle will accumulate energy, it is substantially come through making diligent rate factor corrective flowing and tremendous peak value electric current.

Follow for more close together ground VIN and do not produce pulse of these tall extent electric current, CIN must charge inside whole cycle, is among them one fraction not just. Current nonlinear load makes us know when to need big surge electricity impossible, the surge that holds capacitor inside whole cycle accordingly is constant it is beneficial, and allow use smaller CIN. This kind of method calls power factor corrective.

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