LED lamp mainly focuses on “energy saving and environmental protection”, so the power factor test will be carried out before the LED lamp leaves the factory. But the input current of LED driving power supply is non sine wave, so it is necessary to test the fundamental power factor, so how to do this test correctly? This article takes you to find out.
1、 Why should LED industry test fundamental power factor?
The general definition of power factor is the ratio of active power to apparent power. The low power factor indicates the high reactive power of the circuit. The lower the power factor is, the heavier the load of power supply equipment is, and the more unstable the power grid is. For high-power lamps, if the power factor is low, it may cause: large equipment loss, overload of power equipment, power grid instability, harmonic pollution and other problems.
In our impression, “power factor is determined by the phase difference between voltage and current, and its physical meaning refers to the cosine value of the phase angle difference between voltage and current”. As shown in the figure below.
The above relationship is only applicable to “sine wave circuit”, and if in non sine wave circuit, power factor is related to total harmonic distortion and fundamental power factor, such as in LED lamp circuit.
Because LED is a semiconductor diode, it needs DC power supply. If it is powered by commercial power, there must be a rectifier, usually a diode rectifier bridge. In order to get as smooth DC as possible and avoid ripple flicker, it is usually necessary to add a large electrolytic capacitor. The LED behind can be approximately a resistor, so the whole circuit is shown in Figure 2.
Figure 2 equivalent circuit of LED lamp
Figure 3 various voltage and current waveforms
2、 How to test the fundamental power factor?
Recommended test equipment 1 — pa5000h power analyzer
The LED industry pays more attention to the voltage, current, power, harmonic and power factor of the power supply. How to accurately measure these parameters is the first problem to be solved. Pa5000h power analyzer has 0.05% power measurement accuracy, 5MHz bandwidth and rich harmonic measurement functions, which can be widely used in the research and development and testing of LED power supply.
1. Abundant electrical parameter measurement
How to improve the power factor has always been a difficult problem in the LED industry. To improve the power factor, it is necessary to accurately measure various electrical parameters of the power supply at the same time. Pa5000h power analyzer can not only directly measure the fundamental power factor (Pf1) for non sinusoidal system, but also display the voltage and current waveforms in real time. Rich electrical parameter display items can let users analyze various performance indicators of the power supply, It can help users improve the power factor and provide strong data support for the design.
Figure 5 abundant electrical parameter display
2. Double PLL source frequency doubling technology
By introducing dual PLL hardware circuit, pa5000h power analyzer can synchronize the sampling frequency with the signal frequency, ensure that the sampling data is an integral multiple of the signal period, eliminate the spectrum leakage, and obtain the prepared harmonic measurement results.
Figure 6 dual PLL source setup
3.500 harmonic measurement
The bandwidth of pa5000h power analyzer is up to 5MHz, the sampling rate is up to 2ms / s, and it can measure up to 500th harmonic. There are many combined display modes, which can display the content of each harmonic at the same time. In order to facilitate users to carry out more detailed analysis, we also designed a function to view the value of any harmonic. Through this function, users can view the value of each harmonic.
Figure 7 harmonic test of power analyzer
Recommended test equipment 2 — pa310 power meter
4. Direct measurement of fundamental power factor
Pa300 series power meter adopts pure hardware analog filter and phase-locked loop technology. The harmonic measurement function fully conforms to the international standard iec61000-4-7:2002 for harmonic measurement. According to the fundamental frequency, the voltage and current can respectively measure the maximum 50th harmonic, whether it is the total harmonic distortion (THD), or the fundamental component, fundamental power factor, harmonic content, phase difference of each order The content can be measured directly.
Figure 9 harmonic test
The power measurement accuracy is as high as 0.1%, the minimum measurement current is as low as 50 μ a, and the power consumption as low as 0.01W can be measured
The basic measurement accuracy of the power meter can be as high as 0.1%. Due to the application of the double shunt technology, the steady temperature change of the shunt resistance can be maintained, the temperature drift can be reduced, and the power measurement accuracy of 0.1% can be guaranteed from small current to large current measurement. Moreover, in 5mA range, pa310 can perform the measurement at the highest resolution of 0.01W, which meets the international standards (iec62301, energy star, specpower).
The standard PAM upper computer software can monitor and analyze the measurement data in real time, and can be uploaded to the PC through the standard communication interfaces of USB, RS-232, GPIB and Ethernet.
Figure 10 test and analysis of upper computer