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MICROCONTROLLER CONTROLLED STABILIZER
Scheme, device operation modes
The stabilizer works on the principle of stepwise voltage correction by switching the taps of the T2 autotransformer winding using triac keys Q1 ... Q6 under the control of a microcontroller ( MK ), which monitors the voltage level in the network. After turning on the QF1 machine, the mains voltage is supplied to the transformer T1 and the microcontroller starts to work according to the specified program.
The backlight of the display lights up and after 3 seconds the message “PREPARATION FOR WORK” appears on the display ( Fig. 2 ). The next 7 seconds, the microprocessor analyzes the network voltage, and if it is within 120 ... 270V , depending on the measurement results, one of the triacs VS1 ... VS6 opens , thereby connecting one of the six taps of the autotransformer .
The load is connected to the fifth (bottom from the diagram) branch of the autotransformer through the circuit breaker QF1 , which serves to limit the power consumption. At the same time, two “internal” voltmeters induce the mains voltage in the upper line of the LCD display, and the load voltage in the lower line ( Fig. 3 ).
If the voltage is lower than 120V or higher than 270V , the load is de-energized. At this moment, the current line voltage is induced on the display in the upper line, and the message “SECURITY MODE” flashes in the lower line ( Fig. 4 ).
As soon as the voltage enters the range of 120 ... 270V , the load will be connected again.
In the event of a power failure and subsequent appearance, the microprocessor automatically reboots and after 10 seconds reconnects the load.
Galvanic isolation of triacs with MK is carried out by optocouplers U1 ... U6 . In the process of regulation, the opening pulse is removed from the switched-on triac and fed to another triac at the moment the sinusoid passes through “0” , thereby eliminating “current surges” in the windings and triacs. This is achieved due to the fact that for 1 period of a sinusoid the microcontroller measures the state of the amplitude of the mains voltage 100 times! The oscillogram of this process is shown in Fig. 5 .
For the correct operation of the circuit, it is necessary that the anodes of the triacs and the wires from the “internal voltmeters” be connected to the phase wire.
Construction and details
The stabilizer controller ( Fig. 6 ) is assembled on a 10x12cm printed circuit board from one-sided foil fiberglass 1.5 mm thick ( Fig. 7 ). and developed a printed circuit board with two transformers TPG 2-12 on the board.
Alternatively, the HL1 ... HL8 LEDs can be mounted on the side of the printed conductors, so that when installing the printed circuit board in the case, they are inserted into the holes with a diameter of 5 mm drilled in the front panel of the device.
In this case, the controller is installed (with a seal on the front panel) on racks of the corresponding height, screwed to the front panel of the stabilizer case with screws in place.
The value of the current-limiting resistor R22 must be selected so that the current flowing through the LEDs of triac optocouplers U1.1 ... U6.1 is within 8 ... 10 mA . In the diode bridge VD1 ... VD4 , Schottky diodes 11DQ10 are used , due to the small voltage drop on them. Trimmer resistors R2, R10 wire multi-turn SP5-2 or SP5-3 . It is advisable to use type C2-23 (metal- dielectric ) constant resistors R1, R5 ... R9 with a dissipation power of at least that indicated in the circuit. The rest can be of any type. Electrolytic capacitors C1, C2, C4, C5, C8, C9 can be any, with the capacitance indicated in the diagram and the voltage not lower than indicated for them. Capacitors C3, C6, C7 - any film or ceramic. Capacitors C10 ... C15 - film for a voltage of at least 630V .
Imported triac optocouplers MOC3052 (U1 ... U7) are selected because they do not contain built-in controllers for voltage transition through zero. This is not necessary because synchronization of turning off one powerful triac and turning on another is carried out programmatically.
Powerful triacs VS1 ... VS6 - BTA 40-600 . All triacs VS1 ... VS6 are installed on one heat sink, with a cooling surface area of at least 800 cm 2 , preferably using thermal paste to ensure reliable heat dissipation. The stabilizer chip ( DA1 ) KR1158EN5A (B) must be installed on a heat sink of at least 80 cm 2 .
The transformer T1 is home-made, designed for an overall power of 8 W , having a cross-sectional area of the magnetic circuit of 2.3 cm 2 . Its network winding I is designed for a maximum emergency voltage of 380 V , it contains 8669 turns of PEV-2 wire with a diameter of 0.1 mm . The winding II contains 585 turns of wire PEV-2 with a diameter of 0.25 mm . At a rated voltage of 220 V, the output winding voltage should be 13.5 V at a load current of 250 mA .
Device setup is as follows. A reference voltmeter (digital tester) is connected to the network. Controller circuit and is connected to the network. Trimmer resistors R2 and R10 alternately adjust both internal stabilizer voltmeters to the readings of the reference voltmeter. To calm the soul with the help of LATR, you can make sure that the LEDs HL2 ... HL7 are sequentially switched when thresholds of 120, 137, 157, 179, 205, 235 and 270 V are crossed.
This completes the setup of the device.
Ways of switching taps
There are two ways to switch the T2 autotransformer taps.
Switching taps “inlet” (
Triac switches stand up to the autotransformer, switching the taps so that the load always removed from one tap ( No. 5 from the bottom according to the diagram) is in the required output voltage range 205 ... 235V .
Advantages: when winding an autotransformer, it is not necessary to take into account an overvoltage coefficient of up to 380 V (380/220 = 1.7) , which affects both the dimensions of the core and the amount of copper required for winding. and it is possible to use low-voltage triacs BTA40-600 , since triacs when exceeding 270V simply disconnect the autotransformer from the network.
Disadvantages: the current flowing through the triacs and the primary winding of the autotransformer is limited to 25A , and as a result, the output winding current is 14.5A .
Conclusions: the “input” switching option allows you to remove 3 kW of useful power from the triac BTA40-600 . There is a saving on copper, core and triacs.
If you are satisfied with the power of the stabilizer 3kW , then this scheme is for you! In my estimation, it has more advantages than disadvantages!
Mains voltage is connected to branch No. 2 . Triac switches stand after the autotransformer, connecting to the load the tap on which the voltage is within the necessary limits of 205 ... 235V .
Advantages: this connection option allows you to “remove” 5.5 kW of useful power from the BTA 40-600 triac , which is almost 2 times more than the “input” switching option.
Disadvantages: the disadvantage is the need for triacs designed for an operating voltage of at least 800 V (in the three top taps of the autotransformer), and a 1.7- fold increased number of turns of the autotransformer winding.
Conclusions: to eliminate the above drawbacks, it will be necessary to introduce an additional powerful 80A triac key (TC142-80-8) directly in front of the autotransformer, which will turn off the primary winding (tap No. 2 from the bottom according to the diagram) when the mains voltage exceeds 120 .. .270V . In analog versions, this will lead to a significant complication of the controller circuit, therefore, an input-based switching circuit is preferable. In the microcontroller version, this can be realized by adding several lines in the microcontroller program!
The use of cheap triac BTA41
In the “input” switching option , the power in the load will be 1.2 kW . All triacs can be BTA41-600 . At the output of the autotransformer (before the load), it is necessary to put the QF2 machine at 6A , and use the machine at 10A as QF1 .
In the “output” switching option , the power in the load will be 2.2 kW . To do this, in the three upper branches according to the scheme, it is necessary to use BTA41-800 triacs.
This is necessary because the voltage in these branches with an emergency voltage in the network of 380V will exceed, or will be close to 600V . The rest (lower) may be BTA41-600 . At the output of the autotransformer (before the load), it is necessary to put the QF2 machine at 10A , and use the machine at 20A as QF1 .
It was tested that a maximum current of up to 13A can flow through the BTA41 triac. When this value is exceeded, the terminals of the triacs begin to fade as fuses, since their cross section is 0.6 mm 2 ( 0.6 x 1 mm ). It is optimal to limit the current through triacs at 10A .
Godin A. High-voltage line voltage stabilizer with load power up to 6 kW - Radio amateur, No. 7/2005 , p. 36-40 .
On all issues related to the described device, you can get advice by sending a request to the author's email address indicated at the beginning of the article.
Author: Godin Alexey Valerievich, Moscow
PS Material is protected.
Publication date 09/22/2006