Control system and method for AC motor driven cyclic load

A method of controlling an AC motor driven cyclic load in which the AC motor has a rotor driven by a rotating magnetic field, comprising:

• controlling the cycle speed of the cyclic load by adjusting the frequency of the electric power supplied to the motor in order to maintain a difference between the speed of rotation of the magnetic field and the speed of rotation of the rotor, the controlling step further comprising:
• generating a transducer signal which is a function of the cycle speed of the cyclic load;
• generating a tachometer signal which is a function of the speed of rotation of the motor's rotor;
• generating an outside set point signal representative of a desired set point cycle speed of the cyclic load;
• generating a control signal adapted to maintain the cycle speed of the load at the set point cycle speed by comparing the difference in the transducer signal and tachometer signal to the outside set point signal;
• and
• using the control signal to adjust the frequency of the electric power supplied to the motor;
• storing rotational kinetic energy provided by the motor and load on a rotating mass having a relatively large moment of inertia during portions of a cycle of the cyclic load when there is excess energy;
• and
• returning the stored rotational kinetic energy to drive the cyclic load during portions of a cycle of the cyclic load when there is an energy demand by the cyclic load.

A control system for an AC motor driven cyclic load, the AC motor having a rotor driven by a magnetic field, the cyclic load having subcycle speed and loading oscillations, the system comprising:

• a flywheel, rotatably connectable between the motor and the load, for receiving and storing rotational kinetic energy from the motor and the load during portions of a cycle of the cyclic load when there is excess energy and for delivering rotational kinetic energy to drive the load during portions of a cycle when there is energy demand by the cyclic load, the flywheel having a sufficiently large moment of inertia to control subcycle speed variations of the cyclic load;
• transducer means for generating a transducer signal which is a function of the cycle speed of the cyclic load;
• tachometer means for generating a tachometer signal which is a function of the speed of rotation of the motor's rotor;
• outside set point means for generating an outside set point signal representative of a desired set point cycle speed of the cyclic load;
• speed controller means for receiving and comparing the transducer signal and the outside set point signal and generating a speed set point signal representative of an adjustment in the cycle speed needed to achieve the set point cycle speed of the cyclic load;
• frequency controller means for receiving and comparing the tachometer signal and the speed set point signal and generating the control signal representative of the power supply frequency necessary to create the difference between the speed of rotation of the motor's magnetic field and the speed of rotation of the motor's rotor, and thereby the motor output torque, needed to achieve the set point cycle speed of the cyclic load;
• and
• variable frequency power supply means, having a power input connectable to an AC power source and a power output connectable to the AC motor, for receiving and processing the control signal to adjust the frequency of the power supplied to the AC motor and thereby achieve the set point cycle speed of the cyclic load.

A control system for an AC motor driven cyclic load, the AC motor having a rotor driven by a magnetic field, the cyclic load having subcycle speed and loading oscillations, the system comprising:

• a flywheel, rotatably connectable between the motor and the load, for receiving and storing rotational kinetic energy from the motor and the load during portions of a cycle of the cyclic load when there is excess energy and for delivering rotational kinetic energy to drive the load during portions of a cycle when there is energy demand by the cyclic load, the flywheel having a sufficiently large moment of inertia to control subcycle speed variations of the cyclic load;
• transducer means for generating a transducer signal which is a function of the cycle speed of the cyclic load;
• tachometer means for generating a tachometer signal which is a function of the speed of rotation of the motor's rotor;
• outside set point means for generating an outside set point signal representative of a desired set point cycle speed of the cyclic load;
• speed controller means for receiving and comparing the transducer signal and the outside set point signal and generating a speed control signal representative of the adjustment in the output torque of the AC motor needed to achieve the set point cycle speed of the cyclic load;
• slip set point means for generating a slip set point signal representative of a desired set point difference between the speed of rotation of the motor's magnetic field and the speed of rotation of the motor's rotor;
• frequency controller means for receiving and comparing the tachometer signal and the slip set point signal and generating the control signal representative of the adjustment in the power supply frequency output to the motor needed to achieve the desired set point difference between the speed of rotation of the magnetic field and the speed of rotation of the rotor;
• and
• variable frequency power supply means, having a power input connectable to an AC power source and a power output connectable to the AC motor, for receiving and processing the control signal to adjust the frequency of the power supplied to the AC motor and for receiving the speed control signal and varying the voltage output per unit of frequency to the AC motor in order to adjust the output torque of the motor and thereby the cycle speed of the cyclic load.