Power factor corrector for UPS on-line. Part 6

    Part 1
    Part 2
    Part 3
    Part 4.1
    Part 4.2
    Part 5


    Hello again! ..
    Unfortunately my article was delayed, because an urgent work project arose, as well as interesting difficulties arose in the implementation of the power factor corrector ( hereinafter CCM ). And they were caused by the following - in our production we use a “custom-made” microcircuit to control the KKM, which Austria makes for us under our tasks, especially in 1941, and accordingly we will not meet it on sale. Therefore, the task arose to remake this module for an accessible elementary base and my choice fell on the PWM controller chip - L6561 .
    Why exactly her? Banal accessibility, or rather found it in "Chip and Dip", read datasheet - I liked it. I ordered immediately 50 pcs. cheaper and in my amateur projects I already have several 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 have they to do with it ), why I killed a dozen keys and how to avoid this. 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 with the charger , because they are essentially one module and they must 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 was not “retrained” for longfirst to the welding machine, and then to the power supply for the "goat" . Those who work in production will understand what kind of animal it is and how much it consumes for our warming)))

    And now to our sheep ...

    Why do we even need this KKM?

    The main trouble with the “classic” rectifier with storage capacitors (this is the thing that turns 220V AC into + 308V DC), which works from a sinusoidal current, is that this capacitor is charged (takes energy from the network) only when the voltage applied to him is greater than on himself.

    In a human language, faint of heart and with scientific degrees do not read
    As we know, an electric current completely refuses to go if there is no potential difference. The direction of the current flow will also depend on the sign of this difference! If you freaked out and decided to try 2V to charge your mobile, where the Li-ion battery is rated at 3.7V, then nothing will work. Because the current will give the source that has greater potential, and the one with lower potential will receive energy.
    Everything is as in life! You weigh 60 kg, and the guy on the street who came up to ask you to call 120 kg is understandable that he will give out his puzzles, and you will receive them. So here - a battery with its 60 kg 2V will not be able to give current to the battery with 120 kg3.7B. With a capacitor in the same way, if it has + 310V and you attach + 200V to it, then it will refuse to receive current and will not be charged.

    It is also worth noting that, based on the “rule” described above, the time allocated to the capacitor for charging will be very small. In our country, the current changes according to a sinusoidal law, which means that the required voltage will be only at the peaks of the sinusoid! But the capacitor needs to work, so he gets nervous and tries to charge. 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 for the device to work until the next peak.

    A little about these "peaks":

    Figure 1 - Peaks in which the capacitor charges

    As we see a piece of the period in which the EMF takes a sufficient value for the charge (figuratively 280-310V) is about 10% of the total period in the AC network. It turns out that instead of constantly taking energy smoothly from the network, we tear it out only in small episodes, thereby we “overload” the network. With a power of 1 kW and inductive load, the current at the time of such "peaks" can calmly reach values ​​of 60-80A .

    Therefore, our task is to ensure uniform energy extraction 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 your KKM?

    A power corrector is a common step-up voltage converter, most often it is single-ended. Because Since we use PWM modulation, then at the moment of the public 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 surges.

    Circuitry of our KKM

    Then I decided not to change my principles and also relied on the datasheet of my chosen controller - L6561 . STMicroelectronics engineers have already done everything for me, but more specifically, he has already developed the ideal circuitry for his product.
    Yes, I can recalculate 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? Fortunately , I’ve been able to prove to myself that this stage has long passed)) Here I recall a bearded anecdote about the area of ​​red balls, they say the mathematician uses the formula, and the engineer takes out a table with the area of ​​red balls .... So in this case.

    I advise you to immediately pay attention to the fact that the circuit in the datasheet is designed for 120 watts, which means we should follow itadapt to our 3 kW and exorbitant work voltage.

    Now a little documentation for the one described above:
    Datashit on L6561

    If we look at page 6, we will see several schemes, we are interested in the scheme with the signature Wide-range Mains , which from Basurmans means "to work in a wide range of supply voltage" . It was this “mode” that I had in mind when speaking of transcendental stresses. The device is considered universal, that is, it can operate from any standard network (for example, in 110V states) with a voltage range of 85 - 265V.

    This solution allows us to provide our UPS with a voltage stabilizer function!For many, this range will seem redundant and then they can perform 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 generally devoid of cash registers, and 10% use it only with the calculation of deviations of no more than 15%. This undoubtedly allows you to slightly reduce the cost and dimensions, but if you have not forgotten, then we make a device that is obliged to compete with the APC!

    Therefore, for myself, I decided to choose the most correct option and make an unkillable tank that can even be pulled out at the cottage, where there is a 100V welder or pump in the well in the network:

    Figure 2 - Standard circuitry solution offered by ST

    Adapting standard circuitry to our needs

    a) When I look at this circuit from LH, the first thing that comes to mind is to add a common-mode interference filter! And it’s right, because at high power, they will begin to "drive crazy" electronics. For currents of 15 A and more, it will have a more complicated appearance than many are accustomed to seeing it in the same computer PSUs, where only 500-600 watts. Therefore, this revision will be a separate item.

    b) We see the capacitor C1, we can take a tricky formula and calculate the necessary capacity, and I advise those who want to delve into it, remembering 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 with respect to power growth. That is, taking into account 1 μF per 100 W, we get that for 3000 W we need 30 μF. This capacitance is easily assembled from 7 film capacitors of 4.7 microfarads 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 transistor, because the current consumed from the network will be calculated as follows:

    Figure 3 - Calculation of the rated current for KKM

    We got 41.83A . Now we honestly recognize that to keep the transistor die temperature in the region of 20-25 of C, we have not mastered. We can better master it, but it will be expensive for such power. After 750 kW cost of freon cooling or liquid oxygen is blurred, but it is far from it))) So we need to find a transistor that can give 45-50A at 55-60 for S.

    Given that the circuit is the inductance, I prefer IGBT transistor, for the most tenacious. The limiting current must be chosen to search first about 100A, because is the current at 25 to C, the temperature increases limiting current switching transistor is reduced.

    A bit about Cree FET
    On January 9, I received a parcel from the United States from my friend with a bunch of different transistors for testing, this miracle is called CREE FET . I will not say that this is a new mega technology, in fact, silicon carbide-based transistors were made back in the 80s, they just brought to mind why only now. I, as the original material scientist and composer, are generally sensitive to this industry, therefore I was very interested in this product, the more it was declared 1200V at tens and hundreds of amperes. In Russia, I could not buy them, 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 dearest fireworks!
    8 keys fucked so that I was upset for a long time ... Actually, 1200V is a theoretical figure for the technology, the claimed 65A turned out to be just a pulsed current, although the nominal was clearly written in the documentation. Apparently there was a "nominal pulse current" well, or whatever else the Chinese are coming up with. In general, it’s still bullshit, but there is one BUT!
    When I still did on CMF10120D corrector 300 W, it turned out that he was on the same radiator and the scheme had a temperature of 32 about C against the 43 in the IGBT, and this is very important!
    Conclusion on CREE: the technology is damp, but it is promising and it definitely should be.

    As a result, after looking through the catalogs from the exhibitions I visited (a convenient thing, by the way, ala parametric search), I selected two keys, they became IRG7PH50 and IRGPS60B120 . Both at 1200V, both at 100 + A, but opening the datasheet, the first key dropped out immediately - it is able to switch the current 100A only at a frequency of 1 kHz, this is disastrous for our task. The second key is 120A and a frequency of 40 kHz, which is quite suitable. Look at the datasheet at the link below and look for a graph with the dependence of current on temperature:

    Datasheet on the IRGPS60B120

    Figure 4.1 - Graph with the dependence of the maximum current on the switching frequency for the IRG7PH50, leave it on the chastotnik

    Figure 4.2 - Graph with the operating current at a given temperature for IRGPS60B120

    Then we observe the sacred figures, which show us that at 125 of C and the transistor and diode currents safely overpower a little more than 60A, and we can implement the conversion at a frequency of 25 kHz without any problems and limitations.

    d) Diode D1, we need to choose a diode with an operating voltage of at least 600V and a rated current for our load, that is 45A. I decided to use the diodes that were at my fingertips (I recently purchased them for the development of a welder under the “oblique bridge”) - this is VS-60EPF12 . As can be seen from the markings, it is at 60A and 1200V. I put everything with a margin, because This prototype is being made for myself and it’s so calmer for me.
    In fact, you can put a diode at 50-60A and 600V, but there is no price between the 600 and 1200V version.

    d) Capacitor C5, here everything is as in the case with C1 - it is enough to increase the face value from the datasheet in proportion to the power. Only it is worth considering that if you plan to have a powerful inductive load or dynamic with fast increases in power (ala concert amplifier at 2 kW), then it is better not to save on this point.
    In my version I will supply 10 electrolytes of 330 microfarads and 450V each , 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.

    f) R6 - it is a current shunt, it will save us from crooked hands and random errors, it also protects the circuit from short circuit and overload. The piece is useful unambiguously, but if we act as engineers from ST, then at currents of 40A we get an ordinary boiler. There are 2 options: 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 a given circuit node. How to calculate the current transformer I cited in the previous article, it is important to remember that the protection will work when the voltage on leg 4 rises to 2.5V (in reality, to 2.34V) .
    Knowing this voltage and current of the circuit, using the formulas from part 5, you can easily calculate the current transformer.

    g) And the last point is the power throttle. About him a little lower.

    Power reactor and its calculation

    If someone carefully read my articles and has a great memory, then he should recall article 2 and photograph No. 5 , on it are visible 3 elements of windings that we use. Once again I will show:

    Figure 5 - Frames and core for power winding products

    In this module we will again use our favorite toroidal rings made of atomized iron, but this time not only one, but 10 at once! What do you want? 3 kW is not Chinese crafts to you ...

    We have the initial data:
    1) Current - 45A + 30-40% of 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, the respected Starichok51 saves us time and considers the CaclPFC program .

    I think the calculation showed everyone how serious this design will be)) 4 rings, yes a radiator, a diode bridge, yes IGBT - horror!
    Winding rules can be deducted in the article “Part 2”. The secondary winding on the rings is wound in quantity - 1 turn.

    The result of the throttle:

    1) as you see, the number of rings is already 10 pieces! It is expensive, each ring cost about 140r, but what we get in return in the following paragraphs
    2) Operating temperature 60-70 about C - this is perfect, because many lay an operating temperature of 125 to S. In his own production of 85 onWith a mortgage. Why this is done - for a quiet sleep, I calmly leave home for a week and I know that nothing will break out from me, nothing icy will burn out. I think the price for it in 1500r is not so deadly, is it?
    3) I set the current density to minus 4 A / mm 2 , this will affect both heat and insulation and, accordingly, reliability.
    4) As you can see from 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 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 allow the good to save money, but will grow more current amplitude, and most importantly the temperature rises to no less than 135 of the S. I think this is a good solution for a welding inverter with 60% duty cycle, but not for UPS, which operates around the clock, and certainly 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 in 3A (the computer power supply mentioned above) and for currents 20A, you can compare the circuit from Google on the ATX with the following:

    Figure 7 - Schematic diagram of the common mode filter

    Several features:

    1) C29 is capacitor for filtering electromagnetic interference, is marked "X1" . Its nominal value should be in the range of 0.001 - 0.5 mF.

    2) The inductor is wound on the core E42 / 21/20 .

    3) Two chokes on the rings DR7 and DR9 are wound on any core from a spray gun and with a diameter of more than 20 mm. I wound all the same D46 from material -52 until it was filled in 2 layers. There is practically no noise in the network even at rated power, but this is actually even in my understanding is excessive.

    4) Capacitors C28 and C31 at 0.047 uF and 1 kV and they must be installed in class “Y2”.

    According to the calculation of the inductance of the chokes:

    1) The inductance of the common-mode inductor should be 3.2-3.5 mH

    2) The inductance for differential chokes is calculated by the formula:

    Figure 8 - Calculation of the inductance of differential chokes without magnetic coupling


    Using the competent and professional developments of ST engineers, I managed to produce, if not perfect, then just a great, active power factor corrector with parameters better than any Schneider. The only thing you should definitely remember is how much do 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 adjusting the source data, so that everyone having decided on the parameters for their tasks already calculated and made a module. I hope I was able to show this and in the next article I will demonstrate the joint work of the KKM and the charger from part number 5.

    PS I will try to publish a new article as soon as possible)))

    Also popular now: