Motor control arrangement

A motor control circuit for an a.c. motor energized from a source of direct voltage via power switches comprising, a direct voltage source including a rectifier for rectifying an a.c. supply voltage and a smoothing circuit, a frequency control circuit comprising a frequency reference signal input connected to an input of a first amplifier having means for limiting the output signal, means connecting an output of said first amplifier to an input of an integrator, an output of said integrator supplying a frequency control signal to a circuit which controls the power switches and further providing feedback to the input of the first amplifier, a negative current-feedback loop comprising first means for generating a motor current signal which is a measure of the current flowing in the motor and a first comparator for comparing said motor current signal with a reference signal, means connecting an output of said first comparator to the input of the integrator so that the negative current-feedback loop is closed via the first comparator and the integrator when the motor current exceeds a predetermined value, a negative-voltage feedback loop comprising second means for generating a voltage signal which is a measure of the voltage across the direct voltage source and a second comparator for comparing said voltage signal with a reference signal, and means connecting an output of said second comparator to the integrator so that the negative voltage-feedback loop is closed via the second comparator and the integrator when the voltage of the direct voltage source exceeds a predetermined value.