Method and apparatus for suppressing torsional vibration in an electric motor speed control system

An electric motor control apparatus to be used in a motor speed control system having a mechanism for transmitting a drive torque from an electric motor to a load through a drive shaft of low rigidity disposed at a load side of the electric motor, and a control apparatus for controlling a torque of the electric motor in accordance with a torque command signal T.sub.RFA obtained by amplifying the deviation signal between a motor average speed N.sub.MAVG and a speed command N.sub.REF in a speed controller having a proportional gain;

• said apparatus comprising:
• motor acceleration torque control means having a proportional gain and an integrator, for computing a torque command compensating signal T.sub.RFL from a deviation signal between the torque command signal T.sub.RFA outputted from said speed control means and a signal which is prepared by multiplying a signal made by substantially differentiating said motor average speed N.sub.MAVG by a mechanical time constant .tau..sub.M of the electric motor;
• and
• motor torque control means for controlling the torque of the electric motor in accordance with a torque command T.sub.RFM formed by the addition of the torque command signal T.sub.RFA outputted from said speed control means and the torque command compensating signal T.sub.RFL outputted from said motor acceleration torque control means.

A method for suppressing torsional vibration in an electric motor speed control system including a mechanism for transmitting a rotational torque from an electric motor to a machine through a drive shaft of low torsional rigidity disposed at a load side of the electric motor, and a control apparatus for controlling a torque of the electric motor in accordance with a torque command signal T.sub.RFA obtained by amplifying the deviation signal between a motor average speed N.sub.MAVG and a speed command N.sub.REF by a speed controller having a proportional gain;

• said method comprising the steps of:
• feeding back to said torque command signal T.sub.RFA a signal which is prepared by multiplying a signal made by substantially differentiating said motor average speed N.sub.MAVG by the mechanical time constant .tau..sub.M, as a feedback signal T.sub.MAFB of a motor acceleration torque;
• obtaining a torque compensating signal T.sub.RFL by amplifying a deviation signal between said torque command signal T.sub.RFA and said feedback signal T.sub.MAFB whose high frequency signals are eliminated by a proportional integration arithmetic unit and a filter having a quadratic lag element at the output side;
• preparing a torque control signal T.sub.RFM by adding the torque compensating signal T.sub.RFL ;
• and
• controlling a torque of said electric motor in accordance with said torque control signal T.sub.RFM, thereby canceling a motor load torque by said torque compensating signal T.sub.RFL which is computed and outputted so that said torque command signal T.sub.RFA outputted from said speed controller may accord with said motor acceleration feedback signal T.sub.MAFB.

An electric motor control apparatus to be used in a motor speed control system including a mechanism for transmitting a rotational torque from an electric motor to a machine through a drive shaft of low rigidity disposed at a load side of the electric motor, and a control apparatus for controlling a torque of the electric motor in accordance with a torque command signal T.sub.RFA obtained by amplifying the deviation signal between a motor average speed N.sub.MAVG and a speed command N.sub.REF by a speed controller having a proportional gain;

• said apparatus comprising:
• motor acceleration torque control means having a proportional gain, an integrator and a filter having a quadratic lag element, for computing a torque command compensating signal T.sub.RFL from a deviation signal between the torque command signal T.sub.RFA outputted from said speed control means, and a signal which is prepared by multiplying a signal made by substantially differentiating said motor average speed N.sub.MAVG by a mechanical time constant .tau..sub.M of the electric motor;
• and
• motor torque control means for controlling the torque of the electric motor in accordance with a torque command T.sub.RFM formed by the addition of the torque command signal T.sub.RFA outputted from said speed control means and the torque command compensating signal T.sub.RFL outputted from said motor acceleration torque control means.