| 摘要 |
A motor control circuit for an a.c. motor which is energized via power switches by a direct voltage obtained from an alternating voltage mains via rectifiers and a smoothing capacitor. A frequency reference signal is applied to a circuit which controls the power switches via a first amplifier with output signal limitation in series with an integrator, whose output provides feedback to the input of the first amplifier. A negative current-feedback loop with a motor current detector, whose output signal is compared with the reference signal in a comparator, acts at a point between the amplifier and the integrator in order to close the negative feedback loop when the motor current exceeds a predetermined value. A negative voltage-feedback loop with a detector for the direct voltage obtained from the a.c. mains, the output signal of said detector being compared with a reference signal, also acts at the point between the amplifier and integrator in order to close said negative voltage-feedback loop when said direct voltage exceeds a predetermined value.
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