The Power of Apparent vs Real Power: Understanding the Importance of Power Factor Correction

As I stood in front of the heat gun and LED strip, I couldn't help but think that they seemed like two very different devices. The heat gun, which draws current exactly in phase with our mains voltage and its shape also almost looks like it is sinusoidal, seems to be a perfect example of how real power should work. On the other hand, the terrible LED strip, which draws current abruptly and only for a short amount of time, seems to be a prime example of how apparent power can be much higher than real power.

Apparent power, also known as vector sum or complex power, is the total amount of electric power that flows through a circuit at any given moment. It's measured in units of volt-amperes (VA) and represents the product of the voltage and current in a circuit. In contrast, real power, which is the actual amount of electrical energy used by a device to perform work, is measured in units of watts (W) and represents the amount of power that is actually delivered to the load.

The problem with apparent power is that it can be much higher than real power, especially for devices that draw current at high frequencies. In the case of the LED strip, its abrupt drawing of current creates a lot of reactive power, which is easily noticeable through the low power factor. However, there is no phase shift between the voltage and current in this circuit, so how does it create such reactive power?

The answer lies in the frequency components of the current waveform. Most importantly, there is the 50Hz fundamental frequency, which is our mains voltage frequency and does not feature a phase shift. But then there are also 150Hz, 250Hz, 350Hz and so on, parts which are called third, fifth, seventh and so on current harmonics and they do kind of feature a phase shift that creates the reactive power.

The presence of these harmonics is what causes the LED strip to create such high levels of reactive power. To fix this problem, we need to convert this small current pulse into an even sinusoidal one. This can be achieved through the use of an active Power Factor Correction (PFC) circuit.

An active PFC is essentially a glorified boost converter. It takes in a varying input voltage and produces a constant higher DC voltage that the power supply can then use. By doing so, it eliminates the problem of current pulsing near the peak of the mains voltage. When having a look at our practical example, the MOSFETs switching pattern looks something like with a bigger duty cycle at low input voltages and a smaller duty cycle at higher input voltage which corresponds with the theory.

Using an active PFC is not only effective in reducing reactive power but also makes the device safer to use. When working with all the mains voltage showing in this video, it can be dangerous and you should only do that if you are a professional. I plugged the circuit into mains voltage and was very happy to find out that nothing exploded.

The next step is to open up the power supply that came with the horrible current draw. After removing its full bridge rectifier, I simply connected the output of the PFC to the input of the power supply and by once again plugging in mains voltage, nothing blew up and the power supply seems to work correctly as well. This time though, the input current does follow the mains voltage shape a lot more when drawing more current on the output.

The new power supply now has a much higher power factor, which means that it is using less reactive power. The difference can be seen quite clearly in this chart there which now brings us to the question of how such an active PFC pulls this off? In a nutshell, it does so by increasing the changing mains input voltage into a constant higher DC voltage that the power supply then uses.

Creating such a stable boosted DC voltage from a varying input voltage is not that easy because you need to monitor the input and output voltage as well as the flowing current and then turn on or off the boost converter's MOSFET switch accordingly so that always the right amount of energy gets transferred to the output. This is where the active PFC comes into play, making it a pretty awesome device.

Considering that there are already regulations in place that limit the created current harmonics from appliances, they will sooner or later become mandatory. So if you are shopping for a new beefy power supply, maybe next time consider getting one with a built-in PFC.

I hope you enjoyed this video and learned something new. As always don't forget to like, share, subscribe and hit the notification bell. Stay creative and I will see you next time.

WEBVTTKind: captionsLanguage: enThis heat gun here is pure perfection whilethis LED strip is straight up garbage!Wait what?The reason why I am saying this, is becausewhen looking at the current consumption ofthose two loads we can see a a remarkabledifference.First off the heat gun, which draws currentexactly in phase with our mains voltage andits shape also almost looks like it aka sinusoidal,lovely.But next we got the terrible LED strip whichdraws current abruptly and only for a shortamount of time near the peak of our mainsvoltage.OK, so what is the problem here? I mean bothdevices seem to work perfectly fine.Well, the problem is that the LED strip withits AC to DC power supply draws a lot of apparentpower from the power grid because of the weirdcurrent waveform; while the real power itactually requires to do its job of lightingup LEDs is rather small in comparison.That is a huge problem because nowadays wegot tons of AC to DC power supplies in ourhomes and if they would all perform this badthen our power grid will have to face somebig challenges in the future.But it doesn't have to be this way and thatis why such Power Factor Correction circuitsor PFC for short do exist.And in this video I will show you what theycan do, how we can make them and why theyare super important for our electrical future.Let's get startedThis video is sponsored by Mouser Electronicswho not only offer a huge selection of electronicscomponents but also development boards. AndI am not talking about microcontroller boardsor similar, even though they also have them.No, I am talking about development boardsbuild around the newest ICs and technologies;which also includes functional PFCs that youwill see later. If you are curious for morethen head over to Mouser Electronics or checkthe link in the video description.Now let's start off with a popular analogywhich is the foam to drink ratio.You see, the liquid alone represents our realpower aka the power that actually gets usedto light things up, heat things up or forexample charge your phones battery.But as you can see that is not all in ourglass which in total represents our apparentpower and that is the power your energy provideractually has to deal with in its grid so thatyou can get your desired real power.No, we still got the foam which is our reactivepower and truth be told completely uselessbecause it only oscillates between the energyprovider and hooked up load.Due to it more current flows through the gridthan what we actually need for the real powerdemand and as you might know; for a biggercurrent flow we need thicker wires, so thatthings do not get terrible inefficient andhot and that of course costs lots of money.So keeping the reactive power close to zerois our goal here meaning that apparent powershould equal the real power.And in the heat gun example we started withwe can actually see such a behaviour thatreal power equals apparent power meaning itis definitely possible which brings us tothe question how such reactive power comesto be?The most popular examples for that are simplya motor and a capacitive power supply thatyou can sometimes find in LED lights.Both of them create quite a bit of reactivepower in comparison to their real power andthe root of all evil for that is like I teasedat the beginning their current flow.The power supply ones leads in comparisonto the mains voltage and the one from themotor lags in comparison.The reason for that are of course the electricalproperties of the capacitor for the powersupply and the inductance for the motor coils.But feel free to watch my previous videosabout those topics here so that I can keepthe rest of this video short and sweet.Because in a nutshell such phase shifts docreate reactive power.And the simple fix here is to add inductanceto the capacitance and vice versa capacitanceto the inductance to get rid of the phaseshift and thus reduce the reactive power andget a power factor of almost one.By the way the Power Factor is simply thereal power divided by the apparent power andthus one means real power equals apparentpower which is what we are after.Now like I said; one solution is adding capacitanceor inductance to the power grid to decreasethe phase shift and that is actually the firsttype of a power factor correction circuitand it is called a passive one.Of course, there is also an active one thatI already presented to you at the start.And to understand why we need it, let's goback to the current draw of a common powersupply I found in my shelf.As you can see the more DC current I drawfrom its output, the bigger the current pulseon the input near the peak of the mains voltagegets.And by doing my usual measurements next, wecan see that this current draw creates kindof a lot of reactive power which is easilynoticeable through the low power factor.But there is no phase shift, so how does thatwork?Well, the problem here is that this currentwaveform can be depicted as a sum of lotsof current waveforms with different frequencies.Most importantly of course is the 50Hz fundamentalfrequency which is our mains voltage frequencyand it obviously does not feature a phaseshift.But then there are also 150Hz, 250Hz, 350Hzand so on parts which are called third, fifth,seventh and so on current harmonics and theydo kind of feature a phase shift that createsthe reactive power.By using my oscilloscope we can actually seehow much they matter in comparison to thefundamental 50Hz frequency and let's justsay that they are pretty dominant on the screenhere.So what we can do to fix this problem is basicallyconvert this small current pulse to an evensinusoidal one.And like I said before a circuit that cando that is an active PFC for which I lookedfor on Mouser Electronics.And I found a promising looking IC that onlyrequires a few external components to function.But before creating a whole PCB for it whichrequires lots of time, I firstly wanted todo some initial tests with a similar IC, forwhich Mouser luckily offered a developmentboard.After powering its low voltage side with mylab bench power supply, I next prepared aproper mains voltage wire for it and thisbreak might be a good opportunity to statethat working with all the mains voltage showin in this video can be dangerous and youshould only do that if you are a professional.OK, with that out of the way I plugged thecircuit into mains voltage and was very happyto find out that nothing exploded.On its output I measured a voltage of around400V DC which means the circuit works correctly.And before I start explaining here why thishigh voltage and how it is made and whatnot;let's rather keep it practical and crack openthe power supply that came with the horriblecurrent draw.After removing its full bridge rectifier,I simply connected the output of the PFC tothe input of the power supply and by onceagain plugging in mains voltage, nothing blewup and the power supply seems to work correctlyas well.This time though the input current does followthe mains voltage shape a lot more when drawingmore current on the output.That not only means that the current harmonicsare mostly gone, but also that the reactivepower of the system decreased while the powerfactor increased, awesome.I think you can see the difference with andwithout a PFC pretty clearly in this charthere which now brings us to the question howsuch an active PFC pulls this off?Well, in a nutshell it does so by increasingthe changing mains input voltage into a constanthigher DC voltage that the power supply thenuses; because yes, an active PFC is basicallyjust a glorified boost converter.You see the problem of normal AC to DC powersupplies is that they only draw current nearthe voltage peak of the mains voltage becausethat is when the utilized capacitors voltagedrops beneath the input voltage and thus canget charged up again.But by supplying a constant boosted voltagethis problem basically disappears.Of course creating such a stable boosted DCvoltage from a varying input voltage is notthat easy because you need to monitor theinput and output voltage as well as the flowingcurrent and then turn on or off the boostconverters MOSFET switch accordingly so thatalways the right amount of energy gets transferredto the output.When having a look at our practical examplethan the MOSFETs switching pattern looks somethinglike with a bigger duty cycle at low inputvoltages and a smaller duty cycle at higherinput voltage which corresponds with the theory.So all in all such active PFCs are prettyawesome.And considering that there are already regulationsin place that limit the created current harmonicsfrom appliances, they will sooner or laterbecome mandatory.So if you are shopping for a new beefy powersupply, maybe next time consider getting onewith a built in PFC.With that being said I hope you enjoyed thisvideo and learned something new.As always don't forget to like, share, subscribeand hit the notification bell.Stay creative and I will see you next time.