method and device for adjusting the speed of a multi-phase asynchronmotors is, and the implementation of the procedure suitable motorensystem.

摘要

PCT No. PCT/CH89/00188 Sec. 371 Date Aug. 30, 1990 Sec. 102(e) Date Aug. 30, 1990 PCT Filed Oct. 30, 1989 PCT Pub. No. WO90/05407 PCT Pub. Date May 17, 1990.The stator current has a variable frequency which is changed by using a predetermined frequency change rate. The resulting effective value of the stator current is compared with the current control variable. If it is greater the frequency is now kept constant. If this corresponds to the setpoint speed the process terminates, if not, the frequency change will start again as soon as the effective value gets smaller than the current control variable. An a.c. voltage mains may operate, accelerate or brake the motor via a rectifier and an inverter, in cases of voltage failure the stator current is switched through to a load resistor. The variation of the speed may follow a steady or a garland-shaped course, from the from and dimension of a festoon element a measure for the "torsional rigidity" may be obtained. By means of shifting between star connection and delta connection the frequency range may be expanded in order to keep the torque essentially the same. For performing the process a motor system may be used comprising several motors having the same torque and harmonized with each other by using 2ROOT 3 or 2ROOT 2 as quotient for the characteristic operating voltage/operating frequency values.