Importance

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Abstract

The invention relates to a method and a circuit for regulating the speed of a commutator series-wound motor, especially a universal motor (10), which is supplied with a current from an a.c. voltage source (22) by means of a semiconductor switching element (18) mounted in series with an armature winding (12) and a field winding (14, 16) and controlled by a control unit (28) according to a nominal speed value. The control unit (28) receives, as input signals, signals corresponding to the total voltage drop (Umot) when the motor (10) is supplied with a current, and a substitute signal for the intensity of the motor current (I), corresponding to the voltage drop (Ua, Ufa) on the armature (12) alone or on the armature (12) and on a part (14) of the field winding (14, 16). The input signals of the control unit (28) are compared with motor-typical characteristic lines of the voltages on the excitation field (14) and/or on the armature, stored in the control unit, and control signals for the semiconductor switching element are formed from the deviations.

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First Claim