Determn of variable for joltless connection of inverter to induction motor not using speed sensors

摘要

A procedure is given for evaluating a quantity derived from a measured variable at the terminals of an induction motor, for the pull-in operation used in the smooth connection of an inverter to the sensor-free motor spinning at an unknown speed. At the motor terminals the rotating frequency of a voltage phasor is found, which rotates on the basis of an as-yet-undecayed rotor flux, a residual flux resulting from the remanence or a voltage pulse superimposed separately on the motor, and then from this frequency, an estimate for the rotor frequency is derived to be used as the pull-in variable.