PFC (Power Factor Correction) is translated as "Power Factor Correction", the name "reactive power compensation" is also found. With regard to switching power supplies (only PSUs of this type are currently used in computer system units), this term means the presence in the power supply of a corresponding set of circuitry elements, which is also commonly called "PFC". These devices are designed to reduce the reactive power consumed by the power supply.
Actually, the factor or power factor is the ratio of active power (the power consumed by the power supply irrevocably) to the total, i.e. to the vector sum of active and reactive powers. In fact, the power factor (not to be confused with efficiency!) Is the ratio of useful and received power, and the closer it is to unity, the better.
PFC comes in two varieties - passive and active.
When operating, a switching power supply without any additional PFC consumes power from the mains in short pulses, approximately coinciding with the peaks of the sinusoid of the mains voltage.
The simplest and therefore the most common is the so-called passive PFC, which is a conventional choke of a relatively large inductance, connected to the network in series with the power supply.
Passive PFC somewhat smoothes the current pulses, stretching them in time - however, to seriously affect the power factor, a high inductance choke is required, the dimensions of which do not allow it to be installed inside a computer power supply. The typical power factor of a PSU with passive PFC is only around 0.75.
Active PFC is another switching power supply, moreover, increasing the voltage.
The shape of the current consumed by a power supply with an active PFC differs very little from the consumption of a conventional resistive load - the resulting power factor of such a power supply without a PFC block can reach 0.95 ... 0.98 when operating at full load. True, as the load decreases, the power factor decreases, at a minimum dropping to about 0.7 ... 0.75 - that is, to the level of blocks with passive PFC. However, it should be noted that the peak current consumption of units with active PFC is still noticeably lower even at low power than for all other units.
In addition to the fact that the active PFC provides close to ideal power factor, unlike the passive one, it improves the operation of the power supply - it additionally stabilizes the input voltage of the main stabilizer of the block - the block becomes noticeably less sensitive to reduced mains voltage, also when using an active PFC blocks with universal power supply 110 ... 230V are quite easy to develop, which do not require manual switching of the mains voltage. (Such PSUs have a specific feature - their operation in conjunction with cheap UPSs that issue a stepped signal when running on batteries can lead to computer failures, so manufacturers recommend using Smart class UPSs in such cases, which always output a sinusoidal signal.)
Also, the use of active PFC improves the response of the power supply during short-term (fractions of a second) mains voltage dips - at such moments, the unit operates due to the energy of the high-voltage rectifier capacitors, the efficiency of which is more than doubled. Another advantage of using active PFC is the lower level of high-frequency interference on the output lines.
For example, the voltage on 1 leg of the FAN7530 depends on the divider assembled on R10 and R11, and, accordingly, on the capacitor C9.
What is PFC and why is it needed
Electronic devices
PFC( abbreviation for Power Factor Correction)- translated as "Power factor correction", the name "reactive power compensation" is also found.
Actually, the factor or power factor is the ratio of active power (the power consumed by the power supply irrevocably) to the total, i.e. to the vector sum of active and reactive powers. In fact, the power factor (not to be confused with efficiency!) Is the ratio of useful and received power, and the closer it is to unity, the better.
PFC comes in two varieties - passive and active.
When operating, a switching power supply without any additional PFC consumes power from the mains in short pulses, approximately coinciding with the peaks of the sinusoid of the mains voltage.
The simplest and therefore the most common is the so-called passive PFC, which is a conventional choke of relatively large inductance, connected to the network in series with the power supply.
Passive PFC somewhat smoothes the current pulses, stretching them over time - however, for a serious impact on the power factor, a high inductance choke is required, the dimensions of which do not allow it to be installed inside the power supply (computer or in a TV set, there is no difference). The typical power factor of a PSU with passive PFC is only around 0.75.
Active PFC is another switching power supply, moreover, increasing the voltage.
Very often it is also called "swapping" or "prekondey"
As you can see, the shape of the current consumed by the power supply with active PFC, differs very little from the consumption of a conventional resistive load - the resulting power factor of such a unit can reach 0.95 ... 0.98 when operating at full load.
True, as the load decreases, the power factor decreases, at a minimum dropping to approximately 0.7 ... 0.75 - that is, to the level of blocks with passive PFC. However, it should be noted that the peak current consumption of units with active PFC still, even at low power, they turn out to be noticeably less than all other blocks.
Besides that active PFC provides a close to ideal power factor, so, unlike passive, it improves the operation of the power supply - it additionally stabilizes the input voltage of the main stabilizer of the unit - the unit becomes noticeably less sensitive to low mains voltage, and when using active PFC, blocks with universal power supply 110...230V, not requiring manual switching of mains voltage.
Such PSUs have a specific feature - their operation in conjunction with cheap UPSs that issue a stepped signal when running on batteries can lead to computer malfunctions, so manufacturers recommend using Smart class UPSs in such cases, which always output a sinusoidal signal.
Also use of active PFC improves the response of the power supply during short-term (fractions of a second) mains voltage dips - at such moments, the unit operates due to the energy of the capacitors of the high-voltage rectifier, the efficiency of which is more than doubled. Another benefit of using active PFC is lower level of high frequency interference on the output lines, i.e. such power supplies are recommended for use in a PC with peripherals designed to work with analog audio / video material.
And now some theory
The usual, classic, 220V AC voltage rectification circuit consists of a diode bridge and a smoothing capacitor. The problem is that the capacitor charge current is of a pulsed nature (duration of the order of 3mS) and, as a result, a very large current.
For example, for a PSU with a load of 200W, the average current from a 220V network will be 1A, and the pulse current will be 4 times more. If there are many such power supplies and (or) are they more powerful? ... then the currents will be simply crazy - the wiring, sockets will not withstand, and you will have to pay more for electricity, because the quality of the current consumption is very much taken into account.
For example, in large plants there are special capacitor units for "cosine" compensation. In modern computer technology, they faced the same problems, but no one will install multi-storey structures, and they went the other way - they put a special element in the power supplies to reduce the "pulse" of the consumed current - PFC.
The different types are separated by colors:
- red - regular PSU without PFC,
- yellow - alas, "an ordinary PSU with passive PFC",
- green - PSU with passive PFC of sufficient inductance.
The model shows the processes when the power supply is turned on and a short-term dip through 250mS. The large voltage spike with a passive PFC is due to too much energy being stored in the inductor when the smoothing capacitor is charged. To combat this effect, the PSU is gradually turned on - first, a resistor is connected in series with the inductor to limit the starting current, then it is shorted.
For a PSU without PFC or with a decorative passive PFC, this role is played by a special thermistor with positive resistance, i.e. its resistance increases greatly when heated. With a high current, such an element heats up very quickly and the current decreases, then it cools down due to a decrease in current and has no effect on the circuit. Thus, the thermistor performs its limiting functions only at very high starting currents.
For passive PFCs, the turn-on current pulse is not so large and the thermistor often does not fulfill its limiting function. In normal, large passive PFCs, in addition to the thermistor, a special circuit is also installed, but in "traditional", decorative ones, this is not the case.
And according to the charts. Decorative passive PFC gives a voltage surge, which can lead to a breakdown of the PSU power circuit, the average voltage is somewhat less than the case without_PFC, and during a short-term power outage, the voltage drops by a larger amount than without_PFC. On the face of a clear deterioration in dynamic properties. Normal passive PFC also has its own characteristics. If we do not take into account the initial surge, which must necessarily be compensated by the switching sequence, then we can say the following:
The output voltage has decreased. This is correct, because it is not equal to the peak input, as for the first two types of power supply, but to the "acting" one. The difference between the peak and the current is equal to the root of two.
The output voltage ripple is much less, because part of the smoothing functions goes to the throttle.
- The voltage dip in the event of a momentary power failure is also smaller for the same reason.
- After a failure, a surge follows. This is a very significant drawback and is the main reason why passive PFCs are not common. This surge occurs for the same reason that it occurs when turned on, but for the case of initial switching on, a special circuit can correct something, but it is much more difficult to do this in work.
- With a short-term loss of input voltage, the output does not change as sharply as in other PSU options. This is very valuable, because. the PSU control circuit works out a slow change in voltage very successfully and there will be no interference at the output of the PSU.
For other variants of the power supply unit, with such dips, interference will certainly occur at the outputs of the power supply unit, which may affect the reliability of operation. How common are brief power outages? According to statistics, 90% of all non-standard situations with a 220V network occur just in such a case. The main source of occurrence is switching in the power system and connecting powerful consumers.
The figure shows the effectiveness of PFC in reducing current pulses:
For a PSU without PFC, the current reaches 7.5A, passive PFC reduces it by 1.5 times, and normal PFC reduces current much more.
Converter technology
Introduction
In recent decades, the amount of electronics used in homes, offices and factories has increased dramatically, and most devices use switching power supplies. Such sources generate harmonic and non-linear current distortions that adversely affect the wiring of the electrical network and electrical appliances connected to it. This influence is expressed not only in various interference affecting the operation of sensitive devices, but also in overheating of the neutral line. When currents flow in loads with significant harmonic components that are out of phase with the voltage, the current in the neutral wire (which, with a symmetrical load, is practically zero) can increase to a critical value.
The International Electrotechnical Commission (IEC) and the European Organization for Electrotechnical Standards (CENELEC) have adopted the IEC555 and EN60555 standards, which set limits on the harmonic content in the input current of secondary power supplies, fluorescent lamp electronic loads, DC motor drivers and similar devices.
One of the effective ways to solve this problem is to use PFC (Power Factor Correction) power factor correctors. In practice, this means that a special PFC circuit must be included in the input circuit of almost any electronic device with pulse converters, which ensures the reduction or complete suppression of current harmonics.
Power factor correction
A typical switching power supply consists of a mains rectifier, a smoothing capacitor, and a voltage converter. Such a source consumes power only at those moments when the voltage supplied from the rectifier to the smoothing capacitor is higher than the voltage on it (capacitor), which occurs for about a quarter of a period. The rest of the time, the source does not consume power from the network, since the load is powered by a capacitor. This leads to the fact that the power is taken by the load only at the voltage peak, the consumed current has the form of a short pulse and contains a set of harmonic components (see Fig. 1).
A secondary power supply with power factor correction consumes current with low harmonic distortion, draws power from the network more evenly, and has a crest factor (the ratio of the peak value of the current to its RMS value) lower than that of an uncorrected source. Power factor correction reduces the RMS current drawn, allowing more devices to be connected to the same power outlet without overcurrent (see Figure 2).
Power factor
Power factor (PF) - a parameter that characterizes the distortion created by the load (in our case, the secondary power supply) in the AC network. There are two types of distortion - harmonic and non-linear. Harmonic distortion is caused by a reactive load and is a phase shift between current and voltage. Nonlinear distortions are introduced into the network by "nonlinear" loads. These distortions are expressed in the deviation of the current or voltage waveform from a sinusoid. When harmonic distortion the power factor is the cosine of the phase difference between current and voltage or the ratio of active power to the apparent power consumed from the network. For non-linear distortion the power factor is equal to the proportion of the power of the first harmonic component of the current in the total power consumed by the device. It can be considered an indicator of how evenly the device consumes power from the mains.
In general power factor is the product of the cosine of the angle of the phase difference between voltage and current and the cosine of the angle between the fundamental vector and the total current vector. The reasoning given below leads to this definition. The effective current flowing in an active load has the form:
I 2 eff \u003d I 2 0 + I 2 1 eff + SI 2 neff,
where I 2 neff is the constant component (in the case of a sinusoidal voltage it is equal to zero), I 2 1eff is the fundamental harmonic, and under the sum sign are the lower harmonics. When working on a reactive load, a reactive component appears in this expression, and it takes the form:
I 2 eff \u003d I 2 0 + (I 2 1 eff (P) + I 2 1 eff (Q)) + SI 2 n eff. Active power is the average value of the power allocated to the active load over the period.
It can be represented as a product of the effective voltage and the active component of the current P \u003d U eff H I 1eff (P) . Physically, this is the energy released in the form of heat per unit time on the active resistance. Reactive power is understood as the product of the effective voltage and the reactive component of the current: Q \u003d U eff H I 1eff (Q) . The physical meaning is the energy that is pumped twice per period from the generator to the load and twice - from the load to the generator. The full power is the product of the operating voltage and the total operating current: S \u003d U eff H I eff (total). On the complex plane, it can be represented as the sum of the vectors P and Q, from which the dependence I 2 \u003d I 1eff (total) cos j is visible, where j is the angle between the vectors P and Q, which also characterizes the phase difference between current and voltage in the circuit.
Based on the above, we derive the definition for the power factor:
PF=P/S=(I 1eff cos j)/(I eff(gen)).
It is worth noting that the ratio (I 1eff) / (I eff (general)) is the cosine of the angle between the vectors corresponding to the effective value of the total current and the effective value of its first harmonic. If this angle is denoted by q, then the expression for the power factor becomes: PF=cos j × cos q. The task of power factor correction is to bring the angle of the phase difference j between voltage and current to zero, as well as the angle q of harmonic distortion of the consumed current (or, in other words, to bring the shape of the current curve as close as possible to a sinusoid and to compensate for the phase shift as much as possible).
Power factor is expressed as a decimal fraction, the value of which lies between 0 and 1. Its ideal value is one (for comparison, a typical switching power supply without correction has a power factor value of about 0.65), 0.95 is a good value; 0.9 - satisfactory; 0.8 - unsatisfactory. Applying power factor correction can increase the device's power factor from 0.65 to 0.95. Values in the range of 0.97 ... 0.99 are also quite real. In the ideal case, when the power factor is equal to unity, the device draws a sinusoidal current from the network with zero phase shift relative to the voltage (which corresponds to a fully resistive load with a linear current-voltage characteristic).
Passive power factor correction
The passive correction method is most often used in low-cost low-power devices (where there are no strict requirements for the intensity of the lower harmonics of the current). Passive correction makes it possible to achieve a power factor of about 0.9. This is convenient when the power supply has already been designed, it remains only to create a suitable filter and include it in the input circuit.
Passive power factor correction consists in filtering the consumed current using a bandpass LC filter. This method has several limitations. An LC filter can only be effective as a power factor corrector if voltage, frequency, and load vary within a narrow range.. Since the filter must operate in the low frequency region (50/60 Hz), its components are large in size, weight and low quality factor(which is not always acceptable). Firstly, the number of components in the passive approach is much less and, therefore, the time between failures is greater, and secondly, with passive correction, less electromagnetic and contact interference is created than with active correction.
Active power factor correction
An active power factor corrector must satisfy three conditions:
1) The form of the consumed current should be as close to sinusoidal as possible and - "in phase" with the voltage. The instantaneous value of the current consumed from the source must be proportional to the instantaneous voltage of the network.
2) The power taken from the source must remain constant even if the mains voltage changes. This means that when the mains voltage decreases, the load current must be increased, and vice versa.
3) The voltage at the output of the PFC-corrector should not depend on the magnitude of the load. When the voltage on the load decreases, the current through it must increase, and vice versa.
There are several schemes with which you can implement active power factor correction. The most popular at present is the “boost converter circuit”. This scheme satisfies all the requirements for modern power supplies. Firstly, it allows you to work in networks with different values of the supply voltage (from 85 to 270 V) without restrictions and any additional adjustments. Secondly, it is less susceptible to deviations in the electrical parameters of the network (power surges or short-term power outages). Another advantage of this scheme is the simpler implementation of surge protection. A simplified diagram of the “boost converter” is shown in fig. 3.
Principle of operation
The standard power factor corrector is a Pulse Width Modulated (PWM) AD/DC converter. The modulator controls a powerful (usually MOSFET) switch, which converts a constant or rectified mains voltage into a sequence of pulses, after rectification of which a constant voltage is obtained at the output.
Timing diagrams of corrector operation are shown in fig. 4. When the MOSFET switch is on, the current in the inductor increases linearly - while the diode is locked, and capacitor C2 is discharged to the load. Then, when the transistor turns off, the voltage across the inductor "opens" the diode and the energy stored in the inductor charges the capacitor C2 (and simultaneously powers the load). In the above circuit (unlike the source without correction), the capacitor C1 has a small capacitance and serves to filter high-frequency noise. The conversion frequency is 50...100 kHz. In the simplest case, the circuit operates with a constant duty cycle. There are ways to increase the efficiency of correction by dynamically changing the duty cycle (matching the cycle with the voltage envelope from the mains rectifier).
The "boost converter" circuit can operate in three modes: continuous , discrete and the so-called critical conduction mode". AT discrete mode during each period, the inductor current has time to "fall" to zero and after a while starts to increase again, and in continuous- the current, not having time to reach zero, again begins to increase. Mode critical conductivity less frequently used than the previous two. It is more difficult to implement. Its meaning is that the MOSFET opens at the moment when the inductor current reaches zero. When operating in this mode, it is easier to adjust the output voltage.
The choice of mode depends on the required output power of the power supply. In devices with a power of more than 400 W, continuous mode is used, and in low-power ones, discrete mode. Active power factor correction allows reaching values of 0.97...0.99 with THD (Total Harmonic Distortion) within 0.04...0.08.
It's no secret that one of the main building blocks of a computer is power unit. When buying, we pay attention to various characteristics: the maximum power of the unit, the characteristics of the cooling system and the noise level. But not everyone is wondering what is PFC?
So, let's see what PFC gives
With regard to switching power supplies (only PSUs of this type are currently used in computer system units), this term means the presence of an appropriate set of circuitry elements in the power supply.
Power Factor Correction- translated as "Power factor correction", the name "reactive power compensation" is also found.
Actually, the factor or power factor is the ratio of active power (the power consumed by the power supply irrevocably) to the total, i.e. to the vector sum of active and reactive powers. In fact, the power factor (not to be confused with efficiency!) Is the ratio of useful and received power, and the closer it is to unity, the better.
PFC comes in two varieties - passive and active.
When operating, a switching power supply without any additional PFC consumes power from the mains in short pulses, approximately coinciding with the peaks of the sinusoid of the mains voltage.
The simplest and therefore the most common is the so-called passive PFC, which is a conventional choke of relatively large inductance, connected to the network in series with the power supply.
Passive PFC somewhat smoothes the current pulses, stretching them in time - however, to seriously affect the power factor, a high inductance choke is required, the dimensions of which do not allow it to be installed inside a computer power supply. The typical power factor of a PSU with passive PFC is only about 0.75.
Active PFC is another switching power supply, moreover, increasing the voltage.
As you can see, the shape of the current consumed by the power supply with active PFC, differs very little from the consumption of a conventional resistive load - the resulting power factor of such a unit can reach 0.95 ... 0.98 when operating at full load.
True, as the load decreases, the power factor decreases, at a minimum dropping to approximately 0.7 ... 0.75 - that is, to the level of blocks with passive PFC. However, it should be noted that the peak current consumption of units with active PFC still, even at low power, they turn out to be noticeably less than all other blocks.
Besides that active PFC ensures close to ideal power factor, so, unlike the passive one, it improves the operation of the power supply - it additionally stabilizes the input voltage of the main stabilizer of the block - the block becomes noticeably less sensitive to low mains voltage, also when using active PFC, blocks with universal power supply 110 are quite easy to develop ... 230V, not requiring manual switching of mains voltage.
Such PSUs have a specific feature - their operation in conjunction with cheap UPSs that issue a stepped signal when running on batteries can cause computer crashes, so manufacturers recommend using in such cases Smart UPS, which always outputs a sinusoidal signal.
Also use of active PFC improves the response of the power supply during short-term (fractions of a second) mains voltage dips - at such moments, the unit operates due to the energy of the capacitors of the high-voltage rectifier, the efficiency of which is more than doubled. Another benefit of using active PFC is lower level of high frequency interference on the output lines, i.e. such power supplies are recommended for use in a PC with peripherals designed to work with analog audio / video material.
And now some theory
The usual, classic, 220V AC voltage rectification circuit consists of a diode bridge and a smoothing capacitor. The problem is that the capacitor charge current is of a pulsed nature (duration of the order of 3mS) and, as a result, a very large current.
For example, for a PSU with a load of 200W, the average current from a 220V network will be 1A, and the pulse current will be 4 times more. If there are many such power supplies and (or) are they more powerful? ... then the currents will be simply crazy - the wiring, sockets will not withstand, and you will have to pay more for electricity, because the quality of the current consumption is very much taken into account.
For example, in large plants there are special capacitor units for "cosine" compensation. In modern computer technology, they faced the same problems, but no one will install multi-storey structures, and they went the other way - they put a special element in the power supplies to reduce the "pulse" of the consumed current - PFC.
The different types are separated by colors:
- red - regular PSU without PFC,
- yellow - alas, "an ordinary PSU with passive PFC",
- green - PSU with passive PFC of sufficient inductance.
The model shows the processes when the power supply is turned on and a short-term dip through 250mS. The large voltage spike with a passive PFC is due to too much energy being stored in the inductor when the smoothing capacitor is charged. To combat this effect, the PSU is gradually turned on - first, a resistor is connected in series with the inductor to limit the starting current, then it is shorted.
For a PSU without PFC or with a decorative passive PFC, this role is played by a special thermistor with positive resistance, i.e. its resistance increases greatly when heated. With a high current, such an element heats up very quickly and the current decreases, then it cools down due to a decrease in current and has no effect on the circuit. Thus, the thermistor performs its limiting functions only at very high starting currents.
For passive PFCs, the turn-on current pulse is not so large and the thermistor often does not fulfill its limiting function. In normal, large passive PFCs, in addition to the thermistor, a special circuit is also installed, but in "traditional", decorative ones, this is not the case.
And according to the charts. Decorative passive PFC gives a voltage surge, which can lead to a breakdown of the PSU power circuit, the average voltage is somewhat less than the case without_PFC, and during a short-term power outage, the voltage drops by a larger amount than without_PFC. On the face of a clear deterioration in dynamic properties. Normal passive PFC also has its own characteristics. If we do not take into account the initial surge, which must necessarily be compensated by the switching sequence, then we can say the following:
The output voltage has decreased. This is correct, because it is not equal to the peak input, as for the first two types of power supply, but to the "acting" one. The difference between the peak and the current is equal to the root of two.
The output voltage ripple is much less, because part of the smoothing functions goes to the throttle.
- The voltage dip in the event of a momentary power failure is also smaller for the same reason.
- After a failure, a surge follows. This is a very significant drawback and is the main reason why passive PFCs are not common. This surge occurs for the same reason that it occurs when turned on, but for the case of initial switching on, a special circuit can correct something, but it is much more difficult to do this in work.
- With a short-term loss of input voltage, the output does not change as sharply as in other PSU options. This is very valuable, because. the PSU control circuit works out a slow change in voltage very successfully and there will be no interference at the output of the PSU.
For other variants of the power supply unit, with such dips, interference will certainly occur at the outputs of the power supply unit, which may affect the reliability of operation. How common are brief power outages? According to statistics, 90% of all non-standard situations with a 220V network occur just in such a case. The main source of occurrence is switching in the power system and connecting powerful consumers.
The figure shows the effectiveness of PFC in reducing current pulses:
For a PSU without PFC, the current reaches 7.5A, passive PFC reduces it by 1.5 times, and normal PFC reduces current much more.
Hello again!..Unfortunately, my article was delayed, because. an urgent work project arose, and there were also interesting difficulties when implementing the power factor corrector ( further KKM). And they were caused by the following - in our production, to control the KKM, we use a “custom” microcircuit, which Austria, especially in 1941, friendly, especially in 1941, produces for our tasks and, accordingly, cannot be found on sale. Therefore, the task arose to remake this module for an accessible elementary base, and my choice fell on a PWM controller chip - L6561.
Why is she? Banal accessibility, or rather found it in "Chip & Dip", I read the datasheet - I liked it. I ordered 50 pieces at once, because. cheaper and in my amateur projects I already have a few tasks for her.
Now about the main thing:
in this article I will tell you how almost from scratch I recalled the design of single-cycle converters ( it would seem what are they doing here), why he killed a dozen keys and how you can avoid it. This part will tell the theory and what happens if you neglect it. The practical implementation will be released in the next part, as I promised along with charger, because they are essentially one module and they need to be tested together.
Looking ahead, I’ll say that for the next part I have already prepared a couple of dozen photos and videos, where my memory is not for long "retrained" first to the welding machine, and then to the power supply for "goat". Those who work in production will understand what kind of animal it is and how much it consumes to keep us warm)))
And now to our sheep...
Why do we need this KKM at all?
The main thing misfortune The “classic” rectifier with a storage capacitor (this is the thing that turns 220V AC into + 308V DC), which operates from a sinusoidal current, is that this very capacitor is charged (takes energy from the network) only at the moments when the voltage is applied more to him than to himself.
In human language, faint of heart and with scientific degrees, do not read
As we know, the electric current completely refuses to go if there is no potential difference. The direction of current flow will also depend on the sign of this difference! If you freaked out and decided to try to charge your mobile with a voltage of 2V, where the Li-ion battery is designed for 3.7V, then nothing will come of it. Because the current will be given by the source that has a higher potential, and the one with the lower potential will receive energy.
Everything is like in life! You weigh 60 kg, and the guy on the street who came up to ask you to call is 120 kg - it's clear that he will distribute pizdyuly, and you will receive them. So here - a battery with its 60 kg 2V will not be able to give current to a battery with 120 kg 3.7V. With a capacitor in the same way, if it has + 310V and you apply + 200V to it, then it will refuse to receive current and will not charge.
It is also worth noting that, based on the “rule” described above, the time allotted for the capacitor to charge will be very small. In our case, the current changes according to a sinusoidal law, which means the required voltage will be only at the peaks of the sinusoid! But the capacitor needs to work, so it gets nervous and tries to recharge. He knows the laws of physics, unlike some, and “understands” that time is short and therefore begins to consume just a huge current at these very moments when the voltage is at its peak. After all, it should be enough to operate the device until the next peak.
A little about these "peaks":
Figure 1 - Peaks in which the capacitor is charged
As we can see, the piece of the period in which the EMF takes on a sufficient value for the charge (figuratively 280-310V) is about 10% of the full period in the AC network. It turns out that instead of constantly taking energy smoothly from the network, we pull it out only in small episodes, thereby we “overload” the network. With a power of 1 kW and an inductive load, the current at the time of such “peaks” can calmly reach values of 60-80A.
Therefore, our task is to ensure a uniform selection of energy from the network so as not to overload the network! It is KKM that will allow us to implement this task in practice.
Who is this KKM of yours?
Power corrector- This is a conventional step-up voltage converter, most often it is single-ended. Because we use PWM modulation, then at the time of the open key, the voltage across the capacitor is constant. If we stabilize the output voltage, then the current taken from the network is proportional to the input voltage, that is, it changes smoothly according to a sinusoidal law without the previously described consumption peaks and jumps.Circuitry of our KKM
Then I decided not to change my principles and also relied on the datasheet of the controller I chose - L6561. Company engineers STMicroelectronics have already done everything for me, and more specifically, they have already developed the ideal circuitry for their product.Yes, I can count everything from scratch and spend a day or two on this business, that is, all my own and so rare weekends, but I ask why? To prove to myself that I can, this stage, fortunately, has long been passed)) Here I recall a bearded anecdote about the area of red balls, they say a mathematician applies a formula, and an engineer takes out a table with the area of red balls .... So it is in this case.
I advise you to immediately pay attention to the fact that the circuit in the datasheet is designed for 120 W, which means we should follow it adapt to our 3 kW and extreme operating stresses.
Now some documentation for the above:
Datasheet on L6561
If we look at page 6, we will see several diagrams, we are interested in a diagram with a signature Wide Range Mains, which means from Basurman "for operation in a wide range of supply voltage" . It was this “mode” that I had in mind when speaking of extreme stresses. The device is considered universal, that is, it can operate from any standard network (for example, in the states 110V) with a voltage range of 85 - 265V.
This solution allows us to provide our UPS with the function of a voltage stabilizer! For many, this range will seem redundant and then they can make this module taking into account the supply voltage of 220V + - 15%. This is considered the norm and 90% of devices in the price category up to 40 thousand rubles are completely devoid of cash registers, and 10% use it only with the calculation of deviations of no more than 15%. This undoubtedly allows you to somewhat reduce the cost and dimensions, but if you have not forgotten, then we are making a device that must compete with ARS!
Therefore, for myself, I decided to choose the most correct option and make an indestructible tank that can be pulled out even in the country, where there is a 100V welding machine or a pump in the well: 
Figure 2 - Standard circuit solution offered by ST
Adaptation of standard circuitry to our tasks
a) When I look at this scheme from LH, the first thing that comes to mind is you need to add a common mode filter! And rightly so, because at high power, they will begin to "crazy" electronics. For currents of 15 A or more, it will have a more complicated look than many are used to seeing in the same computer PSUs, where there are only 500-600 watts. Therefore, this revision will be a separate item.B) We see capacitor C1, you can take a tricky formula and calculate the required capacitance, and I advise those who want to delve into it to do it, remembering electrical engineering 2 courses from any polytechnic in one. But I will not do this, because. according to my own observations from old calculations, I remember that up to 10 kW this capacity grows almost linearly relative to the increase in power. That is, taking into account 1 uF per 100 W, we get that for 3000 W we need 30 uF. This container is easily collected from 7 film capacitors of 4.7 uF and 400V each. Even a little with a margin, because The capacitance of a capacitor is highly dependent on the applied voltage.
C) We need a serious power transistor, because. the current consumed from the network will be calculated as follows: 
Figure 3 - Calculation of the rated current for PFC
We got 41.83A. Now we honestly admit that we will not be able to keep the temperature of the transistor crystal in the region of 20-25 ° C. Rather, we can overpower it, but it will be expensive for such power. After 750 kW, the cost of cooling with freon or liquid oxygen is eroded, but so far this is far from it))) Therefore, we need to find a transistor that can give 45-50A at a temperature of 55-60 o C.
Given that there is inductance in the circuit, then I prefer IGBT transistor, for the most tenacious. The limiting current must be chosen for the search, first about 100A, because this is the current at 25 ° C, with increasing temperature, the limiting switched current of the transistor decreases.
A little about Cree FET
I literally received on January 9 a parcel from the States from my friend with a bunch of different transistors for a test, this miracle is called - CREE FET. I won’t say that this is a new mega technology, in fact, silicon carbide-based transistors were made back in the 80s, they just brought it to mind why only now. I, as the original materials scientist and composite engineer, am generally scrupulous about this industry, so I was very interested in this product, especially since 1200V was declared at tens and hundreds of amperes. I couldn’t buy them in Russia, so I turned to my former classmate and he kindly sent me a bunch of samples and a test board with forward.
I can say one thing - it was my most expensive fireworks!
8 keys flickered so that I was upset for a long time ... In fact, 1200V is a theoretical figure for the technology, the declared 65A turned out to be only a pulsed current, although the nominal one was clearly written in the documentation. Apparently there was a "rated impulse current" well, or whatever else the Chinese come up with. In general, it's still bullshit, but there is one BUT!
When I did it all CMF10120D corrector for 300 W, it turned out that on the same radiator and circuit it had a temperature of 32 ° C versus 43 for IGBT, and this is very significant!
Conclusion on CREE: the technology is raw, but it is promising and it definitely SHOULD be.
As a result, after looking through the catalogs from the exhibitions I visited (a handy thing, by the way, ala parametric search), I chose two keys, they became - IRG7PH50 and IRGPS60B120. Both are at 1200V, both are at 100+A, but upon opening the datasheet, the first key was eliminated immediately - it is able to switch a current of 100A only at a frequency of 1 kHz, which is disastrous for our task. The second key is 120A and a frequency of 40 kHz, which is quite suitable. See the datasheet at the link below and look for a graph with the dependence of current on temperature:
Figure 4.1 - Graph with the dependence of the maximum current on the switching frequency for the IRG7PH50, let's leave it to the frequency converter
Figure 4.2 - Graph with operating current at a given temperature for IRGPS60B120
Here we observe the cherished figures that show us that at 125 ° C both the transistor and the diode can easily handle currents slightly more than 60A, while we can implement the conversion at a frequency of 25 kHz without any problems and restrictions.
D) Diode D1, we need to choose a diode with an operating voltage of at least 600V and a current rated for our load, that is 45A. I decided to use those diodes that I had at hand (not long ago I bought them to develop a welder under the "oblique bridge") this is - VS-60EPF12. As can be seen from the marking, it is 60A and 1200V. I put everything with a margin, because. this prototype is made for myself and I feel so much calmer.
You can actually put a 50-60A and 600V diode, but there is no price between the 600 and 1200V version.
E) Capacitor C5, everything is the same as in the case of C1 - it is enough to increase the value from the datasheet in proportion to the power. It is only worth considering that if you are planning a powerful inductive load or a dynamic one with rapid power increases (like a 2 kW concert amp), then it is better not to save on this item.
I will put in my version 10 electrolytes at 330 uF and 450V, if you plan to power a couple of computers, routers and other trifles, then you can limit yourself to 4 electrolytes of 330 microfarads and 450V.
E) R6 - it is also a current shunt, it will save us from crooked hands and accidental errors, it also protects the circuit from short circuits and overload. The thing is definitely useful, but if we act like engineers from ST, then at currents of 40A we will get an ordinary boiler. There are 2 options here: a current transformer or a factory shunt with a drop of 75mV + op amp ala LM358.
The first option is simpler and provides galvanic isolation of this circuit node. How to calculate the current transformer I gave in a previous article, it is important to remember that the protection will work when the voltage on leg 4 rises to 2.5V (in reality, up to 2.34V).
Knowing this circuit voltage and current, using the formulas from parts 5 you can easily count the current transformer.
G) And the last point is the power choke. About him a little lower.
Power choke and its calculation
If someone carefully read my articles and he has an excellent memory, then he should remember article 2 and photo no. 5, it shows 3 hank elements that we use. I'll show you again:
Figure 5 - Frames and core for power winding products
In this module, we will again use our favorite pulverized iron toroidal rings, only this time not one, but 10 at once! And how did you want? 3 kW is not Chinese crafts for you ...
We have initial data:
1) Current - 45A + 30-40% for the amplitude in the inductor, total 58.5A
2) Output voltage 390-400V
3) input voltage 85-265V AC
4) Core - material -52, D46
5) Clearance - distributed
Figure 6 - And again, dear Starichok51 saves us time and considers it a program CaclPFC
I think the calculation showed everyone how serious it would be)) 4 rings, yes a radiator, a diode bridge, and IGBT - horror!
Winding rules can be read in the article "Part 2". The secondary winding on the rings is wound in the amount - 1 turn.
Throttle summary:
1) as you can see, the number of rings is already 10 pieces! This is expensive, each ring costs about 140 rubles, but what will we get in return in the following paragraphs
2) the operating temperature is 60-70 ° C - this is absolutely ideal, because many lay the operating temperature at 125 ° C. We lay 85 ° C in our production. Why this was done - for a restful sleep, I calmly leave home for a week and I know that nothing will flare up, everything icy will not burn out. I think the price for this at 1500r is not so deadly, is it?
3) I set the current density to a meager 4 A / mm 2, this will affect both heat and insulation and, accordingly, reliability.
4) As you can see, according to the calculation, the capacitance after the inductor is recommended to be almost 3000 microfarads, so my choice with 10 electrolytes of 330 microfarads fits perfectly here. The capacitance of capacitor C1 turned out to be 15 microfarads, we have a double margin - you can reduce it to 4 film conders, you can leave 7 pieces and it will be better.
Important! The number of rings in the main inductor can be reduced to 4-5, simultaneously increasing the current density to 7-8 A / mm 2. This will save a lot of money, but the current amplitude will increase somewhat, and most importantly, the temperature will rise to at least 135 ° C. I think this is a good solution for a welding inverter with a duty cycle of 60%, but not for a UPS that works around the clock and probably in a rather limited space .
What can I say - we have a growing monster)))
Common mode filter
To understand how the circuits for this filter differ for currents of 3A (the computer PSU mentioned above) and for currents of 20A, you can compare the schematic from Google on ATX with the following:
Figure 7 - Schematic diagram of the common mode filter
A few features:
1) C29 is a capacitor for filtering electromagnetic interference, it is marked "X1". Its value should be in the range of 0.001 - 0.5 mF.
2) The throttle is wound on on the core E42/21/20.
3) Two chokes on rings DR7 and DR9 are wound on any core from a spray and with a diameter of more than 20 mm. I wound on all the same D46 from -52 material before filling in 2 layers. There is practically no noise in the network even at rated power, but this is actually redundant even in my understanding.
4) Capacitors C28 and C31 of 0.047 uF and 1 kV and they must be set to class Y2.
According to the calculation of the inductance of the chokes:
1) Common mode inductance should be 3.2-3.5mH
2) Inductance for differential chokes is calculated by the formula: 
Figure 8 - Calculation of the inductance of differential chokes without magnetic coupling
Epilogue
Using the competent and professional developments of ST engineers, I managed to produce, at minimal cost, if not perfect, then simply excellent active power factor correction with better parameters than any Schneider. The only thing you should definitely remember is how much you need it? And based on this, adjust the parameters for yourself.My goal in this article was just to show the calculation process with the possibility of correcting the initial data, so that everyone, having decided on the parameters for their tasks, would already calculate and manufacture the module. I hope I managed to show this and in the next article I will demonstrate the joint operation of the KKM and the charger from part No. 5.
