Improvement of the speed controller of three-phase asynchronous motors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors
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The scheme of the powerful part of the regulator is shown in the figure. It replaces nodes A1-A3 of the original. The windings of a three-phase motor M1 must be connected in a star, as shown in the diagram. Connecting them with a "triangle" in this case is unacceptable. The shaper of the three-phase pulse sequence on the DD1-DD3 microcircuits and the power supply unit, including the +300 V voltage rectifier, remain the same. However, windings III-V of transformer T1 are no longer needed.
When the transistor VT4 is open, the current flows through the circuit: +300 V source, motor winding, drain-source section. After the transistor closes, the current continues to flow, falling, through the winding and the opened diode VD1. The remaining two switches (on transistors VT5 and VT6) work in a similar way, but with a phase shift of a third of the period.
The main requirement for transistors VT1-VT3 is high (at least 50) and approximately the same current transfer coefficient. The KT315A transistors indicated in the diagram can be replaced by any of the KT315, KT312, KT3102 series that meet this requirement.
Instead of KP707V transistors, KP707G, KP707D or other field transistors with an n-channel, a permissible drain-source voltage of at least 350 V and a cut-off voltage of not more than 8 V are suitable. W - even more.
Long-term operation of a three-phase motor at speeds below the nominal is not recommended. This can lead to overheating and engine failure.
Author: A. Dubrovsky, Novopolotsk, Belarus
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