Control method for variable speed electric motor system and control device for variable speed electric motor system

A control method of a variable speed electric motor system comprising an electric device that generates rotational driving force and a transmission device that changes a speed of the rotational driving force generated by the electric device and transmits the changed rotational driving force to an object to be driven, the control method comprising:

• accepting an instruction for a number of rotations of an output shaft;
• calculating a number of rotations of a variable speed electric motor based on the number of rotations of the output shaft;
• determining whether the calculated number of rotations of the variable speed electric motor is in an uncontrollable range;
• and
• performing uncontrollable speed range operation comprising repeatedly and alternately performing a forward direction minimum rotation number instruction that drives the variable speed electric motor at a minimum number of rotations in a forward direction, and a reverse direction minimum rotation number instruction that drives the variable speed electric motor at a minimum number of rotations in a reverse direction, when the calculated number of rotations of the variable speed electric motor is in the uncontrollable range,
• wherein the transmission device comprises:
• a sun gear that rotates about an axis;
• a sun gear shaft that is fixed to the sun gear and extends in an axial direction about the axis;
• a planetary gear that is engaged with the sun gear, revolves about the axis, and rotates about a center line of the planetary gear;
• an internal gear that comprises a plurality of teeth arranged about the axis in an annular shape and is engaged with the planetary gear;
• a planetary gear carrier that comprises a planetary gear carrier shaft extending in the axial direction about the axis and supports the planetary gear to be revolvable about the axis and to be rotatable about the center line of the planetary gear;
• and
• an internal gear carrier that comprises an internal gear carrier shaft extending in the axial direction about the axis and supports the internal gear to be rotatable about the axis,
• wherein among the sun gear shaft, the planetary gear carrier shaft, and the internal gear carrier shaft, one serves as the output shaft connected to the object to be driven, another one serves as a constant speed input shaft, a remaining one serves as a variable speed input shaft, and
• wherein the electric device comprises:
• a constant speed electric motor that comprises a constant speed rotor connected to the constant speed input shaft of the transmission device;
• and
• the variable speed electric motor that comprises a variable speed rotor connected to the variable speed input shaft of the transmission device and controls a number of rotations in the forward direction and the reverse direction, and has the uncontrollable range in which control is not possible in a range between the minimum number of rotations in the forward direction and the minimum number of rotations in the reverse direction.