Speed Control systems for cranes and heavy duty material handling purposes are well established systems using AC to AC phase controlled thyristor pairs in each phase to control the stator voltages. The controller includes all the usual functions for crane control, such as joystick handling, limit switch logic with slow down, stop and automatic brake applications where plugging under heavy loads are available with closed loop speed control that helps to improve the crane component life and handling capabilities.
Slip-ring motor torque is controllable at any speed by varying the external rotor resistance. A rotor control algorithm insures minimal stator current taking in consideration the line voltages and required torque. This controller is like a modern car. The control system ensures cruise control (speed regulator) and the automatic gearbox (optimized for rotor characteristics). All these functions are realized via the integrated drive controller.
The Integrated drive controller (IDC) performs stator and rotor control functions, because the available motor torque is proportional to each speed and square to the stator voltages. To get the right speed at certain loads the stator voltage is being varied from 0-30% and then to 100%. One of the major advantages on the MP250 is that you don’t need a tacho meter or any other encoder for speed control. The actual speed information comes from the Rotor Voltage Frequency Estimation (RVFE). This means that by taking the line frequency as reference the fundamental component of the rotor frequency will give the slip of the motor from which the digital motor speed is determined.
Two professional engineering companies were contracted in the certification of the MP250 drive, ensuring that the drive conforms to all safety standards, even with minimum protection. The drive was certified as complying with all regulations and safety standards. (Proof available on request)
Advantages Of Variable Speed Drives
Starting Torque Up To 200%
Energy Saving Control
Over Voltage Protection
Under Voltage Protection
Proper Overload Protection
Trip Fault History(Advantage For Fault Finding)
Smooth Start Up(No Mechanical Stresses)