Views:1 Author:Site Editor Publish Time: 2018-04-03 Origin:Site
Power factor compensation: in the fifties of the last century, an improved method was proposed to improve the power supply efficiency caused by the different phases of voltage and current of AC appliances with inductive load (due to the voltage added by the current lag of the inductive load, Because of the different phase of voltage and current, the burden of power supply line becomes heavier and the efficiency of power supply line decreases, which requires that a capacitor should be connected on the inductive appliance to adjust the voltage and current phase characteristics of the appliance. For example: the 40W fluorescent lamp required to be used at that time must be connected in parallel with a 4.75 μ F capacitor). With capacitors connected to inductive loads, the characteristics of current leading voltage on capacitors are used to compensate the characteristics of hysteresis voltage on inductors to make the overall characteristics close to resistance. Thus, the method of improving inefficiency is called power factor compensation (the power factor of alternating current can be expressed by the cosine function value cos φ of the phase angle of power supply voltage and load current).
Since the 1980s, a large number of switching power supplies with high efficiency have been used in electrical appliances. Since the switching power supply is rectified with a large capacity of filter capacitance, the load characteristics of the appliance are capacitive. . The minimum voltage on the filter capacitor is far from zero, which is not much different from its maximum (ripple peak). . The rectifier diode is turned off due to reverse bias. In other words, the diode will only turn on in the vicinity of its peak value during each half cycle of the AC line voltage.