A PROCESS AND DEVICE FOR CHANGING THE ACTUAL ROTATION SPEED OF A MULTI-PHASE NON-SYNCHRONOUS MOTOR AND A SUITABLE MOTOR SYSTEM FOR APPLYING THE PROCESS

摘要

The frequence of the stator current is variable and is changed at a predetermined frequency variation rate. The resultant rms value of the stator current is compared with the power supply current. If it is greater the frequency is kept constant. If this does not correspond to the rated rotation speed the process is terminated; otherwise the frequency variation starts again as soon as the rms value drops below the power supply current. An a.c. mains supply can run, accelerate or brake the motor via a rectifier and an a.c./d.c. converter, and in the event of a power failure the stator current is diverted to a load resistor. The rotation speed may be varied continuously or in ''waves'' and a measure of the ''torsional stiffness of the drive'' may be given by the shape and size of the ''waves''. On changeover between star and delta connection, the frequency range may be extended in order to keep the torque substantially constant. To implement the process a motor system may be set up from multi-phase non-synchronous motors of the same torque mutually tuned with root 3 or root 2 as the quotient of the operating voltage/operating frequency characteristics.