Refinement of the speed controller for three-phase asynchronous motors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors
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In the journal "Radio" No. 4 for 2001, an article by A. Dubrovsky "The speed controller of three-phase asynchronous motors" was published. In the described device, a control unit with the so-called algorithm l is used (the pulse duration is equal to half the period, and the duty cycle is two). At the same time, in order to use the possibility indicated by the author to power motors with a power of more than 300 W from the regulator, it is advisable to use a more efficient control algorithm. The proposed measure will reduce losses in the regulator.
It is known that the harmonic composition of the voltage at the output of the inverter improves somewhat with the control algorithm 5π/6 (the duration of the control pulse is less than the initial one by 1/6 of a half-cycle and is equal to 150 arc degrees) [1, 2]. Such an algorithm is easy to implement by introducing an additional node on two microcircuits into the control device: K155LAZ and K155LI1 (Fig. 1).
His work is illustrated by the diagrams in Fig. 2.
An indispensable condition is that the duty cycle of the clock pulses must necessarily be equal to two.
The node can be used with different three-phase sequencers. Element DD4.4 is connected if the counter is triggered by the edge of the pulse (for the K155IE4 counter, which is triggered by a decline, this element is not needed).
In addition, it should be noted that the mode of operation of an asynchronous motor depends on the ratio of changes in frequency and voltage. The ratio f/U=const ensures the constancy of the torque on the motor shaft, af/√u=const - power constancy. These additional conditions can be met by using a separate isolating transformer and LATR to power the mains rectifier, the movable contact of which is mechanically connected to the engine of a variable resistor that regulates the frequency. It is possible to fulfill the condition of constant torque or power approximately by choosing the appropriate characteristic of the variable resistor (exponential, linear or logarithmic) and additional resistors connected in series or in parallel with the variable resistor.
Literature
- Sandler A. S., Sarbatov R. S. Electric drives with semiconductor control. Frequency converters for controlling asynchronous motors. - M.-L.: Energy, 1966.
- Burkov A. T. Electronic equipment and converters. - M.: Transport, 1999.
Author: S.Kalugin, Moscow
See other articles Section Electric motors.
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