Converter for powering a two-phase asynchronous electric motor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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In various household and industrial devices, not only three-, but also two-phase asynchronous motors are used. To obtain the AC voltage necessary for their operation, shifted in phase by 90 ° relative to the network, the simplest capacitor phase-shifting circuits are usually used. However, this is not always the best solution, especially when the motor speed needs to be controlled.
Fig. 1
We propose to use a converter similar to that described in [L] to power a two-phase electric motor. Only two of the three nodes A2 are left in it, to the outputs of which the motor windings are connected in accordance with Fig. 1. The maximum motor power is 500W. Node A1 of the two-phase converter is assembled according to the scheme shown in fig. 2. It generates pulse sequences shifted by a quarter of their period.
Fig. 2
The oscillation frequency of the master oscillator on the DA1 timer is regulated by a variable resistor R1.1 in the range of 32...832 Hz. The pulse sequences required to control two nodes A2 are formed using triggers of the DD1, DD3 microcircuits and logic elements of the DD2, DD4 microcircuits at the outputs B1, H1, B2, H2. The pauses between the pulses that open the "upper" and "lower" keys of these nodes, which are necessary to prevent the "through" current from flowing through them, are formed due to the delay in switching the triggers of the DD3 microcircuit relative to the triggers of the DD1 microcircuit created by inverting the element DD2.1 of the driving pulses supplied to the triggers. generator.
In the original version of the converter [L], the effective value of the voltage applied to the motor windings varied depending on the frequency by changing the duration of this pause. In the case under consideration, the pause remains unchanged, but additional modulation of control pulses is applied with relatively high-frequency pulses of variable duty cycle. This makes it possible to change the effective value of the voltage applied to the motor windings over a wider range.
The modulating pulse generator is made on the DA2 chip. Their frequency remains equal to 3,5 kHz, and the relative duration is adjusted from 2 to 98° of the repetition period by a variable resistor R1.2, paired with a resistor R1.1 that changes the speed. These pulses are fed to one of the inputs of each element of the DD4 chip and the DD2.2 element, creating high-frequency "inserts" of the zero level of adjustable duty cycle in the output signals of the converter.
Thus, at rated or increased speed, almost full voltage is supplied to the motor, and as the frequency decreases, it decreases. When setting up the converter, it is advisable to check the current consumed by the motor with an ammeter and make sure that even at the lowest frequency it does not exceed the nominal value for this motor. The same method of voltage regulation can be applied in a three-phase converter [L], which will expand the range of regulation of the shaft speed of the motor fed from it. For this, node A1 (see Fig. 2 in [L]) must be modified according to the scheme shown in Fig. . 3.
Fig. 3
Part of this node, assembled on the chips DD2-DD4 and DD6, remains the same. Microcircuits DD1 and DD5 (K561LA7), consisting of 2I-NOT elements, are replaced by K561LA9 with ZI-NOT elements. The master oscillator circuit on the DA1 timer is slightly changed and another generator is added on the DA2 timer.
Literature
- Kalashnik V., Cheremisinova N. Single-phase to three-phase voltage converter. - Radio, 2009, No. 3, p. 31-34.
Author: V. Kalashnik, N. Cheremisinova, V. Chernikov, Voronezh; Publication: radioradar.net
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