| 摘要 |
An electric motor has first, second and third stator windings supplied by a source of alternating voltage having three phases A, B and C, respectively. A separate thyristor switch assembly couples each stator winding to an alternating voltage phase when said switch means is rendered conductive by a trigger signal. When the speed of the motor is above a first predefined level, the thyristor switch assemblies are triggered, in response to the polarity of the voltage between phases A and B being opposed to the polarity of back emf voltage induced across the third winding, to apply current through said first and second stator windings. However, when the speed of the motor is below the first predefined level, the thyristor switch assemblies are triggered, in response to the polarity of the voltage between phases B and C being opposed to the polarity of back emf voltage induced across the third winding, to apply current through said second and third stator windings. Subsequently when the speed of the motor further decreases below a second predefined level, current is applied through said second and third stator windings during every cycle of the voltage between phases B and C.
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