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How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry

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

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

1. Why does the LED industry 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 large. The lower the power factor, the heavier the load on 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, overload of power equipment, unstable power grid, and harmonic pollution.

In everyone’s impression, “the power factor is determined by the phase difference between the voltage and the current, and its physical meaning refers to the cosine value of the phase angle difference between the voltage and the current”. As shown below.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 1 Current-voltage phase angle relationship

Note:

The above relationship only applies to “in a sine wave circuit”, 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 an LED lamp circuit.

Because LED is a semiconductor diode, it needs DC power supply. If it is powered by mains, there must be a rectifier, usually a diode rectifier bridge. In order to get the smoothest possible DC to avoid ripple and flicker, it is usually necessary to add a large electrolytic capacitor. The LED behind can be approximated as a resistor, so the whole circuit is shown in Figure 2.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 2 Equivalent circuit of LED lamp

The various voltage and current waveforms are shown in the figure below, which is the input AC voltage, the charging and discharging waveform of the rectifier diode in the LED circuit, and the input current waveform. Because the current waveform is not a sine wave. So the whole system is a nonlinear system.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 3 Various voltage and current waveforms

Usually, the waveform of electrical equipment is close to a sine wave, and there are not many harmonics. In most cases, the fundamental current ≈ total current, and the input current distortion coefficient λ≈1, ≈, so it can be equivalent to the power factor.

In a non-sinusoidal power supply circuit, the power factor has no clear physical meaning, so in the non-sinusoidal power supply circuit of the LED industry, the fundamental power factor is the focus.

Second, how to test the fundamental power factor?

Recommended Test Equipment 1——PA5000H Power Analyzer

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
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 primary problem. The PA5000H power analyzer has 0.05% power measurement accuracy, 5MHz bandwidth and rich 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 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. 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.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 5 Rich electrical parameter display

2. Dual PLL source frequency multiplication technology

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

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 6 Dual PLL source setup

3.500th harmonic measurement

The PA5000H power analyzer has a bandwidth of up to 5MHz and a sampling rate of up to 2MS/s. It can measure up to 500 harmonics, and has a variety of combined display methods to display the harmonic content at the same time. In order to facilitate users to conduct more detailed analysis, we A function that can check the value of any harmonic is also designed. Through this function, the user can check the value of each harmonic.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 7 Harmonic test of power analyzer

Recommended test equipment 2 – PA310 power meter

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
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 conforms to the international standard for harmonic measurement IEC61000-4-7:2002. According to the fundamental frequency, the voltage and current can be measured to a maximum of 50 Sub-harmonic, whether it is total harmonic distortion (THD), or fundamental wave component, fundamental wave power factor, harmonic content of each order, phase difference, content rate, etc. can be directly measured.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 9 Harmonic Test

Power measurement accuracy as high as 0.1%, minimum measurement current as low as 50µA, capable of measuring power consumption as low as 0.01W

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 temperature steady change of the shunt resistance can be maintained, the temperature drift can be reduced, and the power measurement of 0.1% can be guaranteed from small current to large current measurement. precision. Moreover, in the 5mA range, the PA310 can perform measurements at a resolution of up to 0.01W, conforming to the tests of international standards (IEC62301, ENERGY STAR, SPECpower).

The standard PAM host computer software can monitor and analyze the measurement data in real time, and can be uploaded to the PC through the standard rich communication interfaces USB, RS-232, GPIB and Ethernet interfaces.

How to Solve the Difficulties of Fundamental Power Factor Testing in the LED Industry
Figure 10 PC test analysis

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