Three-phase inverter, 36 volts. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters

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In industry, especially when working in rooms with a high hazard category, power tools are usually powered by three-phase mains 36 V 400 Hz or 42 V 200 Hz. The proposed inverter will allow you to use such a power tool in places where there is only a single-phase network 36 V 50 Hz.

It provides a protective shutdown of the device in case of overcurrent. The inverter circuit is shown in fig. 4.52. Its output voltage is 3x42 V, frequency is 200 Hz.

(click to enlarge)

Load power - no more than 400 watts. Efficiency at maximum output power - not less than 90%. The alternating voltage of a single-phase network is supplied to the bridge rectifier VD2 ... VD5. The rectified voltage of 42 V is fed by the inverter itself, made according to the well-known "Larionov scheme" on transistors VT2 ... VT10 with protective diodes VD6 ... VD11. Delta- or star-connected loads can be connected via an isolating transformer or without it.

Elements DD1.,1 and DD1.2 form a master oscillator, and microcircuits DD2 ... DD4, together with elements DD1.3 ... DD1.5, are a pulse distributor that controls power switches. Microcircuits are fed through a voltage regulator, consisting of a resistor R1, a zener diode VD1 and a transistor VT1.

To protect the inverter from overload, a trinistor VS1 connected in parallel to the zener diode is used.

Its control electrode receives a part of the voltage proportional to the load current, which drops across the resistor R2. If it exceeds the trinistor opening threshold, the latter will "close" the zener diode and the supply voltage of the microcircuits will decrease almost to zero.

The master oscillator and the pulse distributor will stop working, and all power switches will be closed. The activation of the protection is signaled by the extinguished LED HL1. To restart the inverter, you must press the button SB1.

Setting up the device should begin with setting the protection threshold. To do this, by setting the slider of the trimmer resistor R3 to the extreme left (according to the diagram) position, break the circuit at point A. Then apply a voltage of 3 V to the extreme terminals of the resistor R1,2 from an external source (plus - to the right terminal according to the diagram), corresponding to the voltage drop across the resistor R2 when a current of 12 A flows through it.

Slowly rotating the engine of the resistor R3, the protection is activated. After that, the external voltage source is turned off and the circuit at point A is restored.

Finally, use the trim resistor R5 to set the frequency of the inverter output voltage to 200 Hz. The pulse repetition rate at the output of element D1.2 should be six times greater - 1200 Hz. Transistors VT1, VT3, VT4, VT6, VT7, VT9, VT10 must be equipped with heat sinks with an area of ​​100 ... 200 cm2. It should be borne in mind that various instances of the KU101A trinistor open at a voltage on the control electrode from 0,25 to 10 V, so not all of them will be able to work in the proposed device.

For more reliable operation of the device, it is recommended to increase the resistance of resistors R4, R12, R17 to 2 kOhm.

Author: Semyan A.P.

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