Regulator-stabilizer of the frequency of rotation of the collector motor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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In many household electrical appliances and power tools equipped with commutator motors, it is not possible to adjust the motor shaft speed and torque. This makes such devices inconvenient to use, forcing them to perform many operations in a far from optimal mode. These shortcomings are eliminated by the proposed regulator-stabilizer of the speed, designed to control the DC motor UV-705 (400 V, 10 A). The regulator can be used with other collector motors.

Using the regulator described below, the frequency and torque can be changed and maintained in the range from zero to the maximum developed by the engine. The reduced torque mode is useful, for example, to limit the tension of the wire in a winder or to prevent breakage of the cutting tool if it jams in the material being processed. The device implements a proportional-integrating (PI) controller algorithm.

The scheme of the device is shown in fig. 1. The electric motor M1 is powered by a controlled rectifier of trinistors VS1, VS2 and diodes VD3, VD4. DC power is also favorable for AC collector motors. They even develop more torque in this mode than the nominal one. Resistor R10, shunting the motor, ensures that with short-term breaks in the circuit characteristic of the collector-brush assembly of the motor, the current through the switched-on trinistor remains greater than the turn-off current.

(click to enlarge)

The pulses that open the trinistors are formed by a node consisting of a generator based on transistors VT3, VT4, connected according to the analogue circuit of a unijunction transistor, a power amplifier based on a VT5 transistor and a pulse transformer T1.

The zero detector on transistors VT1, VT2 at the beginning of each half-cycle of the mains voltage discharges the capacitor C1, after which the capacitor is charged by the current flowing through the resistors R6, R19 and the diode VD10 and proportional to the output voltage of the op-amp DA1. The greater the charging current, the faster the voltage across the capacitor C1 reaches the threshold of operation of the analog of the unijunction transistor. At this moment, a pulse with a duration of approximately 200 μs is formed, which opens one of the trinistors VS1, VS2, the voltage at the anode of which in this half-cycle is positive relative to the cathode.

As the experiment showed, a pulse of such duration is sufficient to open any of the tested trinistors. By shortening the pulse, it was possible to reduce the power consumed by the control device to 1,6 W (taking into account the power dissipated by the resistor R1).

From the tachogenerator G1 mechanically connected to the engine M1, a voltage proportional to the shaft speed enters the stabilization system. Op-amp DA1 serves as an element for comparing this voltage with that coming from the engine of the variable resistor R12 - the speed controller. Capacitor C4 eliminates the short-term inclusion of full engine speed at the moment the mains voltage is applied.

Thanks to the feedback through the R20C5 circuit, the op-amp DA1 not only amplifies the error signal, but also acts as a proportional-integrating filter for the speed stabilization system. The variable resistor R19 regulates the torque. The more resistance is introduced, the less torque.

Most of the parts of the regulator-stabilizer are placed on a board made of one-sided fiberglass 1,5 mm thick (Fig. 2). Fixed resistors - MLT, oxide capacitors - K50-6, capacitors C1 and C5 - KM-4, KM-5 or other ceramic ones. The pulse transformer T1 is wound on a K16x10x4 2000NM ferrite ring. Two windings of 50 turns of wire PEV-2 0,35 are isolated from each other and from the magnetic circuit by segments of a PVC tube according to the method described in D. Priymak's article "Winding a pulse transformer" ("Radio", 1988, No. 9, p. 60) . Instead of a home-made one, you can install a ready-made transformer MIT-4vm.

(click to enlarge)

A small-sized DC electric motor DPM-20-3.01 is used as a tachogenerator, you can use DPM-25-NZ-03 or DP-1-26TsR-2M (the latter after the removal of the centrifugal regulator). Other small-sized collector motors with permanent magnet stators are also suitable, for example, from electromechanical toys and portable tape recorders. The mechanical connection of the shafts of the tachogenerator G1 and the electric motor M1 must be rigid and without play, otherwise the stabilization system may lose stability and undamped oscillations in the speed of rotation will occur.

When choosing a tachogenerator, it should be borne in mind that it is electrically connected to the network, and mechanically - to the shaft and housing of the M1 electric motor, accessible to the operator, and sometimes grounded. The latter will ensure electrical safety, but in the event of a breakdown of the insulation of the tachogenerator, it will lead to the failure of the regulator. If the quality of the insulation of the tachogenerator winding from its shaft and housing is in doubt, it is better to abandon the transformerless power supply of the regulator-stabilizer by applying an alternating voltage of 1 ... 12 V to the VD15 bridge from a small power step-down transformer.

By adjusting the regulator, primarily by selecting resistors R11 and R13, they ensure that setting the variable resistor R12 engine to the upper position according to the diagram leads to a complete stop of the M1 electric motor. The specified maximum speed (engine R12 in the lower position) is achieved by selecting the resistor R16.

If, with a sharp translation of the engine of the variable resistor R12 from one position to another, the rotational speed of the motor shaft M1 reaches a new steady value too slowly or this process is accompanied by fluctuations in the rotational speed, it is necessary to select the values ​​​​of the resistor R20 and capacitor C5. For convenience, the printed circuit board (Fig. 2) provides additional pads for the specified capacitor, which allows you to "recruit" it from two smaller capacitance.

Author: V.Voinkov, Severodvinsk, Arkhangelsk region.

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