LED lights are mainly “energy saving and environmental protection”, so LED lights will be tested for power factor before they leave the factory. However, the input current of the LED drive power supply is non-sine wave, so it is necessary to test the fundamental wave power factor, so how to carry out this test correctly? This article takes you to find out.

1. Why does the LED industry need to test the fundamental power factor?

The general definition of power factor is the ratio of active power to apparent power. The low power factor indicates that the reactive power of the circuit is high. The lower the power factor, the heavier the load of the power supply equipment, and the more unstable the power grid. For high-power lamps, if the power factor is low, it may cause problems such as large equipment loss, power equipment overload, grid instability, and harmonic pollution.

In everyone’s 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 below. Figure 1 Current and voltage phase angle relationship

Note: The above relationship only applies to “sine wave circuits”, and if in a non-sine wave circuit, the power factor is related to the total harmonic distortion and the fundamental power factor, such as in the LED light circuit.

Because LED is a semiconductor diode, it needs DC power supply. If it is powered by city power, there must be a rectifier, usually a diode rectifier bridge. In order to get the smoothest DC possible to avoid ripple flicker, a large electrolytic capacitor is usually needed. The latter LED can be approximated as a resistor, so the entire circuit is shown in Figure 2. Figure 2 Equivalent circuit of LED lamp

The various voltage and current waveforms are shown in the figure below, where Is the input AC voltage, Is the charge and discharge waveform of the rectifier diode in the LED circuit, Is the input current waveform. Because the current waveform is not a sine wave. So the whole system is a non-linear system. Figure 3 Various voltage and current waveforms

Generally, the waveform of electrical equipment is relatively close to sine wave, and there are not many harmonics. In most cases, the fundamental current is ≈Total current , The input current distortion coefficient λ≈1,  ,so Can be equated to power factor.

In the non-sinusoidal power supply circuit, the power factor has no clear physical meaning. Therefore, the fundamental wave power factor will be concerned in the non-sinusoidal power supply circuit of the LED industry. .

2. How to test the fundamental wave power factor?

Recommended test equipment 1-PA5000H power analyzer Figure 4 PA5000H

The LED industry pays more attention to the voltage, current, power, harmonics and power factor of the power supply. How to accurately measure these parameters is the first problem to be solved. The PA5000H power analyzer has a power measurement accuracy of 0.05%, a bandwidth of 5MHz and a wealth of harmonics. The wave measurement function can be widely used in the development and testing of LED power supplies.

1. Abundant electrical parameter measurement

How to improve the power factor has always been a problem in the LED industry. To improve the power factor, various electrical parameters of the power supply must be accurately measured at the same time. The PA5000H power analyzer can not only directly measure the fundamental power factor (PF1) for non-sinusoidal systems, but also Real-time Display of voltage and current waveforms, rich electrical parameter Display items allow users to analyze various performance indicators of the power supply, and can help users improve power factor design and provide strong data support. Figure 5 Rich electrical parameter display

2. Double PLL source frequency multiplication technology

PA5000H power analyzer introduces dual PLL hardware circuits to synchronize the sampling frequency and signal frequency, ensuring that the sampling data is exactly an integer multiple of the signal period, eliminating spectrum leakage, and obtaining prepared harmonic measurement results. Figure 6 Dual PLL source settings

3. 500th harmonic measurement

The PA5000H power analyzer has a bandwidth of up to 5MHz, a sampling rate of up to 2MS/s, and can measure up to 500 harmonics. There are multiple combined display methods that can simultaneously display the content of each harmonic. In order to facilitate users to perform more detailed analysis, we A function to view the value of any harmonic is also designed. Through this function, the user can view the value of each harmonic. Figure 7 Harmonic test of power analyzer

Recommended test equipment 2-PA310 power meter Figure 8 PA310

4. Direct measurement of fundamental power factor

The PA300 series power meter adopts pure hardware analog filter and phase-locked loop technology. The harmonic measurement function fully complies with the international standard IEC61000-4-7:2002 for harmonic measurement. According to the fundamental frequency, voltage and current can be measured up to 50%. Sub-harmonics, whether it is the total harmonic distortion (THD), or the fundamental wave component, fundamental wave power factor, harmonic content of each order, phase difference, content rate, etc. can be directly measured. Figure 9 Harmonic test

The power measurement accuracy is as high as 0.1%, the minimum measurement current is as low as 50µA, 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 dual shunt technology, the temperature of the shunt resistor can be maintained at a steady state change, the temperature drift can be reduced, and the power measurement of 0.1% can be guaranteed from small current to large current measurement. Accuracy. Moreover, in the 5mA range, PA310 can perform measurement at a resolution of up to 0.01W, which conforms to international standards (IEC62301, Energy Star, SPECpower).

The standard PAM host computer software can monitor and analyze the measurement data in real time, and it can be uploaded to the PC through the standard rich communication interface USB, RS-232, GPIB and Ethernet interface. Figure 10 The upper computer test analysis