The LED will go out of a strict route, that is to say, the five-watt lamp is like a child less than one meter two, no need to buy a ticket, no requirement, 5W or more must require a power factor of >0.7. In addition to the small MR16 spotlights, which are 3 watts, most of the LED luminaires are more than 5 watts. So this rule just caught the neck of the LED.
Active power refers to the actual output power, while apparent power refers to the product of the input voltage rms value and the input current rms value. This is completely equivalent to Cosφ in a sine wave system, so there is no problem. But in a nonlinear system, what is active power and what is apparent power is worth exploring. Because in a nonlinear system, the current waveform has many high-order harmonics, it is a big problem to take what it is as its apparent power. There are various practices now.
The rectified voltage and current waveforms are not sinusoidal, and although the voltage waveform before rectification is a sine wave, the current waveform is not a sine wave. So the whole system is a nonlinear system. The original power factor is defined for the linear system, and the input and output voltage and current are required to be sinusoidal at the same frequency. Otherwise, Cosφ cannot be used. However, in a non-sinusoidal system, since the voltage and current waveforms are not sinusoidal, there is no phase angle to say. Therefore, the power factor in a nonlinear system must be redefined.
1. Multiply the effective value of the voltage by the effective value of the current as the apparent power. Many digital power factor meters now use the product of voltage rms and current rms as apparent power. However, the definition of power must be the product of the voltage rms value of the same frequency sine wave and the current rms value. The product of the rms current of the current harmonic and the rms value of the fundamental voltage cannot be considered as power, because its frequency is not the same, so it is meaningless. So using this method to define apparent power is problematic. Unfortunately, many digital meters are now measured this way.
2. Use the cosine of the fundamental current phase as the power factor, or use the cosine of the zero-crossing phase of the current waveform as the power factor, or multiply the fundamental rms value of the current and the sinusoidal voltage rms as its apparent power. . Some instruments are measured like this. It can be seen from the waveform diagram of this current that the higher harmonics of this waveform are very rich, and the fundamental wave is very small. If the fundamental current is used to multiply the fundamental voltage, then the obtained power is compared with the active power. Very small, so its power factor will be very high and may even be greater than 1. This is the case, for example, in some pointer power factor meters.
3. In the case of non-linear loads, the biggest problem is the harmonic current, because although the harmonic current cannot form apparent power with the fundamental voltage, the square of the harmonic current multiplied by the line resistance causes heat loss. Moreover, this harmonic current cannot be compensated by a simple capacitor or inductor. So what really needs to be limited is the harmonic current value. Rather than the so-called "power factor."
In fact, this issue has been controversial in academia, so both the US master's thesis and the Swedish doctoral thesis are still studying this issue. For example, Stefan Svensson of Sweden pointed out in his doctoral thesis that in the case of nonlinearity, seven different definitions have been proposed for the power factor. The same nonlinear system can be obtained under different definitions. A completely different power factor value. And no matter which definition it is, it does not meet the original intention of proposing the power factor in the linear system. E.g. In linear systems, inductive or capacitive loads can be compensated for with pure or pure inductance. This is obviously ineffective in nonlinear systems. So these defined power factors completely lose the meaning of the original power factor.
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