Regulators of rotation of AC motors. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Regulators of rotation of AC motors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

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AC motor speed controllers are often described in the literature. But not all of them are designed for universal purposes and universal engines. In some cases, an AC motor, designed for a voltage of 220 V and relatively high rotational speeds (without a gearbox), is tried to be used to reduce its speed. It will still rotate at high speeds. Sometimes it is necessary that such an AC motor work at low speeds (such a mode is, for example, in some electric drills). In addition, in practice there are electric motors without an excitation winding, with an excitation winding that is structurally connected in series with the main stator winding, or with an excitation winding that can be connected to a break in the control circuit. For the cases described, different rotation controllers are needed.

The main difference between simple thyristor-triac controllers is the nature of the passage of electric current. Full-wave AC motor speed controllers are useful for permanent loads where the maximum motor speed needs to be limited slightly. A diagram of such a device is shown in Fig.1.

Depending on the resistance of the variable resistor R1, the current is limited through the KN102V dinistor, which controls the triac VS1. In fact, this is a dimmer circuit - a device that changes the current through the load. In this circuit, not only AC motors are used as a load, but also another active load, such as incandescent lamps. Load power should not exceed 600 W. The triac must be installed on the heat sink.

Variable resistor R1 type SP5-30-1-15G or similar. Resistor R2 type MLT-2. All non-polar capacitors of types K73-3, K73-9, MBM or similar, designed for an operating voltage of at least 300 V. Deviation in the ratings of resistors and capacitors can reach 20%. Triac KU208G can be replaced by KU208V, TS122-10, TS122-25, T820KV.

Attention! When operating the device, it is necessary to observe safety measures, since its elements are under voltage of the lighting network. The variable resistor adjustment knob must be isolated from its body and engine. Compliance with the phases in this circuit is optional.

In the circuit shown in Figure 2, the thyristor is phase controlled to supply a pulsating voltage to the motor winding.

Thyristor VS1 opens at the moments of a single half-cycle of alternating voltage (the second half-cycle is cut off by the diode VD1). Moreover, with a smooth increase in the voltage at the anode VD1, the residual induced voltage on the motor winding turns out to be larger in amplitude than when the engine of the variable resistor R2 is abruptly moved to the upper (according to the circuit) position. Due to this residual induced voltage, the AC motor is somewhat inert in changing speed at low speeds.

Any diode VD1, designed for a reverse voltage of at least 500 V. The parameters of the resistors and the requirements for them are similar to the previous description. Thyristor VS1 can be replaced by K201L-KU201N, KU202L-KU202N and similar electrical characteristics.

The scheme shown in Fig. 3 is similar in principle to the previous one. The bridge rectifier on diodes VD1-VD4 generates a pulsating signal, and the thyristor is a phase-controlled switch. An important difference from the previous scheme is that this device provides a smooth change in the engine rotation parameters at low speeds.

The parameters of the elements and the safety requirements are the same as in the previous descriptions. Rectifier diodes VD1-VD4 are powerful, D233B, D234B, D247B.

Author: A.P. Kashkarov

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