“The UPS power supply has many working processes and a long time. It is often necessary to use multiple oscilloscopes and high-voltage differential probes to test at the same time, and it is relatively troublesome to record data. Today, I recommend a new test method for you, “fool-style” operation, saving test time 80%!

“

Abstract: The UPS power supply has many working processes and a long time. It is often necessary to use multiple oscilloscopes and high-voltage differential probes to test at the same time. It is also relatively troublesome to record data. 80% time savings!

1. Introduction

During R&D and testing, have you ever had such a bad experience: you want to view more than four signal waveforms at a time, but currently the oscilloscope generally only has four channels at most; headaches when wiring is not isolated between measurement channels, and when mixed wiring is not careful, Burning out the probe or oscilloscope; limited by storage, it is necessary to start, stop, save, and finally open and view one by one during the test; and so on. Now there is a machine that can completely solve such troubles and let you enjoy the smooth testing process. The following is an extremely smooth UPS power test record.

2. Wiring

The main electrical parameters specified in YD/T 1095-2018 are divided into two categories: power and response. In order to protect the jobs of the PA power analyzer group next door, we will not test the power parameters here. This time, we mainly look at the UPS response time. The tested single-phase UPS depends on its working process. In addition to the input and output voltage and current, it also needs to see the voltage and current of the internal battery, so the wiring in my brain is as follows:

A total of six waveform signals need to be measured, and the oscilloscope is powerless. The other protagonist of this test, ZDL6000, is launched in time, which supports up to 16 channels of measurement. Find three current clamps and three voltage probes. Find the corresponding positions of the clamps and probes and connect them at will. Just make sure that there is no short circuit between the test points. Live wire neutral, positive and negative, or common ground or something. You have to be careful when using an oscilloscope. The channel isolation of the ZDL6000 can be so capricious!

3. Test

The test of the response time of the UPS is mainly the switch-in and switch-out of the input (grid) and output (load) ends in the power-on state. Since the ZDL6000 has a recording space at the level of hard disk capacity, there is no need to repeatedly set triggers, start captures, and name and save captured data for each item during testing. After setting the ZDL6000 to open the hard disk recording, you can start the test. The whole process is like a camera that keeps on filming without stopping, without the director calling to stop, all performances are completely recorded, and if you are not satisfied with yourself, you can come back at any time, and stop when you are finished. So the test is completed by pressing the switch, which is very convenient and not smooth.

4. Analysis of results

The most anticipated test results have come out. Click the playback below to see what you will find.

The first is the whole picture of the test data:

From top to bottom are the voltage and current of the input terminal, the battery voltage and current, and the voltage and current of the load terminal. The whole process lasted 60 minutes, and the part that did not change for a long time was that the editor was busy with other things.

Positioned to the front of the waveform, it can be seen from the power-on and output time that the boot time takes 3.4 seconds. At this time, the UPS works in bypass mode, and the output voltage is consistent with the input voltage waveform.

After starting for a period of time, when the load is connected in bypass mode, the voltage of the measurement point only drops briefly, and then returns to normal immediately. This should be caused by the voltage division of the loop impedance under the instantaneous high current. From the load current waveform, we can also see that the load first starts the auxiliary power supply with full-bridge rectification, and then starts the main power supply with power factor correction.

Next is the most critical parameter: the switching time from bypass mode to inverter mode, which is required by the standard to be less than 10ms. If the time is too slow, there is a chance that working appliances will shut down and the UPS will not make sense. From the analysis of the measured waveform in the figure below, the tested UPS meets the standard requirements, and the voltage rises faster, but the output waveform is really quasi-square wave as written in the user manual, which should be the lowest-end model. Parameters such as harmonic content are not extravagant. If you want to see the spectral distribution, you can turn on the machine math operation or the spectrum analysis function of FFT.

The square wave output during inverter leads to a very jittery current spike, which is very detrimental to the working electrical appliances and the surrounding electromagnetic environment. The most direct experience is that the current noise is particularly large, and the greater the load, the greater the noise. If measured with a sound pressure meter, it should exceed the YD/T 1095-2018 standard.

When the load is switched in the inverter mode, the voltage fluctuation is larger than when the working mode is switched, and the stabilization time is longer. This UPS control part needs to be improved. The load cut-in waveform is as follows:

It can be seen from the figure that the slow voltage rise time may cause the voltage of the connected appliances to be too low and shut down. Therefore, when using this UPS, do not increase the load in the inverter mode, otherwise it will not be guaranteed.

So how long does it take to switch from inverter mode to bypass mode? Similarly, closing the input switch of the grid simulates power restoration, and we can see the following waveforms:

The UPS results in 11 seconds before switching back to bypass mode, which is quite slow in terms of operating time. It is not ruled out that the manufacturer deliberately designed this to avoid the influence of the instability of the power grid in the initial stage of power supply recovery. Although this has no additional impact on the load, does it meet the standard requirements?

Because the UPS was not fully charged before the test, the actual discharge time could not be tested. Finally, the power grid could only be cut off to open the load and let it work until the output was terminated. I don’t know how long the battery can last, but the large-capacity recording function of the ZDL6000 has saved me a lot of trouble. I just need to press the switch and put it aside and wait until the end. I don’t have to worry about the storage space and important data. The predicament of having to work overtime and retest again. The end discharge waveform is as follows:

It can be seen that at the end of the discharge time, as the battery voltage decreases, the duty cycle of the square wave becomes larger and larger, until the battery voltage is too low and the output is turned off.

Attentive readers may slap me with the first waveform overview: Isn’t the last waveform of the battery terminating discharge? ! Indeed, in order to avoid making mistakes in the middle and re-testing after the fact, after completing a test process, the editor repeated it again to ensure that there are enough materials to complete this article. This also shows once again the advantages of ZDL6000’s large-capacity storage: you can collect massive data through multiple tests first, and then perform data analysis later.

5. Postscript

Tested with ZDL6000, the deepest experience is that the isolation of multiple channels makes people worry-free, and the large storage makes people labor-saving. So the whole process is worry-free and labor-saving. In the test occasions where ultra-high bandwidth and ultra-high sampling rate are not pursued, ZDL6000 is the best choice, and it can also provide higher precision and more channels! With it, the original complicated testing process is simplified and focused on the most important data analysis, which greatly improves the work efficiency.