84Parameter Description - Motor DataField weakening speedThe field weakening speed determines at which speed the peaktorque limit starts being reduced. It is necessary to reduce the peaktorque limit of the motor since the drive’s ability to force currentinto the motor is limited by the applied voltage as rated speed isreached.If the drive tries to demand more torque than the motor can producegiven the available voltage and actual motor speed, it is possiblethat the breakdown torque of the motor will be exceeded and asa result the motor will appear to stall and run at less than desiredspeed.Generally this phenomenon can be identified as the car reachescontract speed momentarily but then drops to a lower speed or thecar speed stalls at some speed lower than contact speed. Monitorparameter ru.42. If the value is reaching 100% or higher, the votlagelimit is being reached. As a result the peak torque command mustbe further limited in order to maintain control of the motor.The solution is simply to reduce the value of LF.16 to about 60% ofsynchronous speed (720 rpm for a 1200 rpm motor). A setting of45% of synchronous speed should be used as the practical lowerlimit of this parameter.IMUnit: rpmValue range: 0.0...6000 rpmDefault setting: 60.0 rpmInitial adjustment value: approx. 80% of synchronousspeedFor PM motors this parameter is not necessary and thereforeis not visible.PM
