Rectifier control of induction motor secondary impedance

Claim 1

IN COMBINATION WITH AN ASYCHRONOUS MOTOR HAVING A ROTOR WINDING AND A RECTIFIER FOR RECTIFYING THE VOLTAGE ACROSS SAID ROTOR WINDING, A CONTROL CIRCUIT FOR CONTROLLING THE SPEED OF SAID MOTOR, SAID CONTROL CIRCUIT COMPRISING IN COMBINATION: A RESISTANCE CONECTED ACROSS SAID RECTIFIED VOLTAGE; AND ELECTRONIC SWITCHING MEANS CONNECTED TO SAID RESISTANCE FOR PRODUCING ALTERNATING PERIODS DURING WHICH SAID RESISTANCE IS SHORT-CIRCUITED AND PERIODS DURING WHICH SAID RESISTANCE IS NOT SHORT-CIRCUITED, WHEREBY THERE IS OBTAINED AN EFFECTIVE RESISTANCE WHICH IS A FUNCTION OF THE RATIO OF THE LENGTHS OF THE DIFFERENT PERIODS AND CONSEQUENTLY A ROTOR CURRENT WHICH IS LIKEWISE A FUNCTION OF SAID RATIO, THEREBY TO CONTROL THE SEPEED OF SAID MOTOR, SAID SWITCHING MEANS COMPRISING A FIRST CONTROLLED RECTIFIER CONNECTED IN PARALLEL ACROSS THE RESISTANCE, A SECOND CONTROLLED RECTIFIER CONNECTED IN SERIES WITH THE RESISTANCE, AND MEANS FOR INTERMITTENTLY CHANGING THE STATES OF CONDUCTIVITY OF SAID RECTIFIERS.